This session provides a platform for transdisciplinary science that addresses the continuum of the river and its catchment to the coastal sea. We invite studies across geographical borders; from the source to the sea including groundwater, and across the freshwater-marine water transition, including estuaries, deltas and marshlands. The session particularly welcomes studies that link environmental and social science, addressing the impacts of climate change and extreme events and impact of human activities on water and sediment quality and quantity, hydromorphology, biodiversity, ecosystem functioning and services of River-Sea continua. Such a systems approach is required to develop solutions for sustainable management of River-Sea social-ecological systems.
We need to fully understand how River-Sea Systems function. How are River-Sea continua changing due to human pressures? What is the impact of processes in the catchment on coastal and marine systems function, and vice versa? How can we discern between human-induced changes or those driven by natural processes from climate-induced variability and extreme events? What will the tipping points of socio-ecologic system states be and what will they look like? How can we better characterise river-sea systems from the latest generation Earth observation to citizen science based observatories. How can we predict short and long term changes in River-Sea-Systems to manage them sustainably? What is the limit to which it is possible to predict the natural and human-influenced evolution of River-Sea-Systems? The increasing demand to jointly enable intensive human use and environmental protection in River-Sea Systems requires holistic and integrative research approaches with the ultimate goal of enhanced system understanding as the knowledge base for sustainable management solutions.
vPICO presentations: Mon, 26 Apr
The Carmel River runs 58 km from the Santa Lucia Mountains through the Carmel Valley eventually entering a lagoon at Carmel River State Beach near Carmel, California, USA. During the dry summer months, the lagoon is closed, with no connection to the coastal ocean. However, during the wet winter months, the river often breaches through the lagoon allowing water to freely flow between the river and Carmel Bay. Sediment transport, in part owing to river discharge and in part owing to ocean forcing (tides and waves), contributes heavily to whether the lagoon is open or closed: when there are low flow conditions, waves and tides can decrease flow rates in the breach, allowing sediment to settle. The sediment budget is expected to be a closed system, owing to the rocky headlands and long-term stability (no yearly regression or transgression) of the shoreline, despite managed attempts to control breach and closure timing. However, it is currently unknown 1) how velocity profiles evolve during breaching, and 2) how much sediment moves during such an event. The hypothesis is that the breach mouth can completely disappear and re-emerge over a single breach-closure cycle, leading to meter-scale daily accretion and erosion rates of berm height if berm elevation is significantly lower than the expected steady-state berm height. Furthermore, it is hypothesized that during active breaching, discharge rates through the breach channel are larger than upstream river discharge rates owing to elevated water levels within the back lagoon. This study uses a RiverSurveyor M9 Acoustic Doppler Profiler to measure outflow discharge and GPS topographic surveys to quantify elevation changes. A velocity profile can be built which will estimate the sediment transport potential within the breach. The information obtained will help identify and better understand the river discharge thresholds which contribute to frequent breaching as well as estimates of morphological evolution during breaching, which are currently unknown, and can assist in determining likelihood of successful managed breaching and closure events.
How to cite: Orescanin, M., McPherson, T., and Jessen, P.: Rapid morphological evolution during beach breaching and closure at a bar-built estuary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-219, https://doi.org/10.5194/egusphere-egu21-219, 2020.
Globally the riverine sediment supply to estuaries is decreasing and the mean sea level is rising, while the effects of these changes on the long-term estuarine morphodynamics have not been fully investigated. An idealized numerical model was used to explore the long-term morphodynamics of a large estuary subject to these changes. In the model, a funnel-shaped channel with fixed banks, constant riverine water and sediment fluxes, a single grain size and a semi-diurnal tide were used. A range of values of changes in the sediment supply (50-90% reduction) and sea level (1-5~mm/yr increase) were considered. Starting from an equilibrium state for an initial sediment supply, the estuary shifts to a new equilibrium for the considered changes on a timescale of millennia. Half of the bed level change occurs within several hundreds of years. A larger decrease in the sediment supply leads to a stronger bed erosion, while the corresponding adjustment time has minor changes in its range for the considered settings. When combined with sea level rise, the erosion is weakened and the adjustment time is shortened. The equilibrium state under sea level rise is characterized by a bed level keeping pace with the sea level and a significant amount of sediment being trapped in the estuary. Additional numerical experiments that use more realistic geometry and forcing of the Yangtze Estuary show that overall erosion of the estuary is expected for centuries.
How to cite: Yuan, B., Sun, J., Lin, B., and Zhang, F.: Effect of decreasing sediment supply and sea level rise on the long-term morphodynamics of a large estuary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1016, https://doi.org/10.5194/egusphere-egu21-1016, 2021.
In recent decades, the invasion of saltmarsh plant Spartina alterniflora (S. alterniflora) over a large part of coastal wetlands in China, including the Yellow River Estuary (YRE) as a regional economic hub and global ecosystem services hotspot, has caused increasing concern because of its serious threats to native ecosystems. During the same period, local authorities have implemented a Water-Sediment Regulation Scheme (WSRS) in the Yellow River for flood mitigation and delta restoration purposes. The altered hydrological regime has resulted in unintended changes to estuarine ecosystem. However, the direct consequence of the WSRS on the expansion of S. alterniflora remains unclear. In this study, quantitative relationship between the inter- and intra-annual expansion patterns of S. alterniflora represented by relevant landscape metrics and indicators that quantify the concurrent variations of river and sediment discharges as the proxy of the WSRS impacts were analysed over the period of Year 2011 to 2018, and the analyses were performed on the YRE as a whole and on five different zones subdivided based on the invasion sequence. The results showed that there was no significant difference in the inter-annual area variation of S. alterniflora between the years with and without WSRS. Compared with the years without WSRS (2016-2017), the intra-annual (monthly) increment of the various landscape metrics (i.e. NP (number of patches), CA (class area), LPI (largest patch index) and AI (aggregation index)) were found to be significantly higher in the initial stage of peak growing season (June-July) than in the mid- and late stages (July-September) in the years with WSRS (2011-2015, 2018) in the subregion located close to the south bank of YRE as the most prominent impact zone. In addition, F (mean flow), Ff (number of high flow pulses), Tf (Julian date of maximum flow) and D (duration of WSRS) were identified as the explanatory variables for the intra-annual vegetation landscape pattern changes, and their relative contributions to resultant changes were also assessed. Our results broaden the understanding of estuarine hydrological disturbance as a potential driver regulating the saltmarsh vegetation, and also have implications for S. alterniflora invasion control at estuaries under changing environment.
How to cite: Shao, D.: Effects of the Water-Sediment Regulation Scheme (WSRS) on the expansion of Spartina alterniflora at the Yellow River Estuary, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1007, https://doi.org/10.5194/egusphere-egu21-1007, 2021.
Fluvial and fluvio-tidal meandering channels are widespread in coastal areas, where they shape the present-day landscapes and build up thick sedimentary successions. Deposits accumulated by these channels host the most surficial aquifers, which are deeply exploited by agricultural and industrial activities. Understanding sedimentary facies distribution within these deposits is crucial to predict groundwater flow and also has relevant implications for aquifer management.
This study focuses on deposits accumulated by a late Holocene meandering river of the Venetian Plain (Northeast Italy). Combining remote sensing and geophysical data, sedimentary cores, and statistical analyses, we characterize the geometry and sedimentology of two adjacent point-bar bodies, with a specific focus on along-bar sediment grain-size distribution.
The study paleochannel is ca. 30 m wide and its planform evolution was reconstructed by analyzing the scroll-bar pattern of the related point bars from satellite images. This channel generated two meander bends, namely B1 and B2, that progressively expanded during their evolution; moreover, bend B1 was affected by a downstream rotation of the bend apex during its final stage of growth.
Geophysical investigations (Frequency Domain Electro-Magnetometer) provided information about the electric conductivity of the studied sedimentary bodies by allowing for the visualization of horizontal 2D maps with averaged conductivity values with a vertical resolution of 1 m. Point-bar bodies are characterized by slightly lower conductivity values (7 to 80 mS/m) than channel-fill deposits (49-147 mS/m), whereas overbank deposits exhibit the highest values (115 to 300 mS/m). In the B1 point-bar, conductivity values reflect the scroll-bar pattern and are lower in the upstream and pool zones, whereas, in the B2 point-bar, the conductivity exhibits almost uniform horizontal values at each depth.
Sedimentary cores reveal that the two point bars consist of well-sorted sands, ranging from fine to very coarse sand, with no heterolithic deposits. Bar deposits cover a basal lag consisting of very coarse sand with shell fragments. Channel-fill deposits are made of fine to very fine sand with muddy intercalations. Overbank deposits consist of massive mud, which is locally organic-rich.
The combination of core analysis and conductivity maps highlights a correlation between conductivity values and sediment textural properties, revealing that finer sediments (i.e., mud in overbank areas) are more conductive than coarser ones (i.e., sand in the point-bar bodies). These observations provide information about the spatial distribution of grain size at different depths, showing the occurrence of different vertical grain-size trends within point-bar deposits. Moreover, statistical analyses reveal that the conductivity values in bar deposits are primarily influenced by the grain-size sorting, and subordinately by grain size and composition.
Our findings provide a link between planform evolution of fluvial bends and grain-size distribution within the related bars, with implications to predict subsurface flow propagation within alluvial sedimentary bodies.
How to cite: Bellizia, E., Boaga, J., Tognin, D., Finotello, A., Cosma, M., Puppin, A., D'Alpaos, A., Cassiani, G., and Ghinassi, M.: Linking sediment properties with conductivity values: an approach to investigate intra point bar grain-size variability in fluvial deposits, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10150, https://doi.org/10.5194/egusphere-egu21-10150, 2021.
Environmental changes in the Volga River delta attract attention of researchers due to increasing anthropogenic pressure on the river catchment, global climate changes, and natural fluctuation cycles of the Caspian Sea level. These changes significantly affect the hydrological regime and erosion-accumulative processes in the Volga delta.
In 2018-2020, the authors conducted series of field hydrological and geochemical studies within the Volga River delta, which covered all major systems of the deltaic water streams. We have determined water discharge, suspended sediment concentration, content of dissolved and suspended chemical elements (ICP-MS/ICP-AES). The results obtained in the study provide a comprehensive view of the current spatial and temporal distribution of the water flow, suspended sediment yield, and geochemical flows along the main branches, numerous channels and rivers during the both high and low water periods, and also allow us to compare them with long-term trends established by previous studies.
We have found that the present distribution of water flow and suspended sediment load within the Volga delta differs from the second half of the XX century. It determines the ongoing restructuring of the water balance, and transformation of the rate of erosion and accumulative processes within the main systems of the deltaic branches. The study allowed delineating the Volga Delta by zones of erosion, transition, and accumulation of suspended matter in different phases of the water regime in relation to the modern basis of erosion, which is the current level of the Caspian Sea.
The distribution of geochemical runoff within the Volga Delta is determined by water and sediment runoff, as well as concentrations of dissolved and suspended forms of chemical elements. The largest geochemical runoff passes through the Bakhtemir and Buzan systems. During the low-water period, the volumes of geochemical runoff of these branches are similar. During the flood period, despite the increasing share of Buzan water runoff, the prevailing fluxes of matter pass through the Bakhtemir system due to higher concentrations of elements and larger solid discharge.
The ratio of dissolved and suspended elements in flows is determined mainly by the properties of chemical elements. According to the percentage ratio of dissolved and suspended forms, we divided elements into 3 groups: 1) migrating mainly in dissolved forms (Na, Ca, Sr, Mg, Mo, U, K, Li, Ba, As, Sb), 2) migrating mainly in suspended forms (Pb, Y, Zr, Ti, Mn, Fe, Al, REE), 3) elements with changeable behavior depending on geochemical and hydrological conditions (Ni, Cd, Zn, Co, Cu, et al.).
The research was supported by RFBR project No. 18-05-80094 and №17-05-41174-RGS.
How to cite: Zavadskaya, M., Zavadskiy, A., and Lychagin, M.: Present distribution and variability of water flow, suspended sediment load, and geochemical runoff in the Volga River delta, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9698, https://doi.org/10.5194/egusphere-egu21-9698, 2021.
Neonicotinoid insecticides (NNs) and the herbicide glyphosate are systemic pesticides widely used in agriculture and urban environments. They are the most used pesticides worldwide. Their extensive use has led to great social concerns regarding their environmental fate and toxicity to non-target organisms and to human health. Consequently, glyphosate is at risk of being banned in the EU and 3 NNs (imidacloprid, clothianidin and thiamethoxam) have recently been permanently banned for outdoor applications. Nevertheless, their use is still permitted in China. Moreover, NNs have been incorporated in the watch list of substances for the EU monitoring program in surface waters (2015/495/EU) due to possible threats to aquatic organisms. Therefore, these compounds are emerging environmental contaminants of concern.
This study investigates the temporal and spatial occurrence of 7 NNs, as well as other insecticides (fipronil, imidaclothiz, cycloxaprid and sulfoxaflor), the herbicide glyphosate and several of their transformation products in the Chinese Bohai Sea and its surrounding rivers. Water samples were collected in the summer and fall of 2018 from 36 rivers and 47 stations in the Bohai Sea. All samples were immediately stored at -20°C until analysis. All samples were extracted by solid-phase extraction (1L water sample was used for the insecticides, whereas 20 mL water sample was used for glyphosate and its main metabolite AMPA (aminomethylphosphonic acid)), eluted with methanol and further enriched by evaporation. For glyphosate and AMPA, the water samples were first derivatized with FMOC-Cl (9-Fluorenylmethoxycarbonyl chloride). All samples were analyzed by HPLC-MS/MS.
The results show that, from the 18 compounds analyzed, 15 were detected in river samples and 12 in seawater samples. Acetamiprid was detected in all river- and seawater samples. Much higher concentrations were observed in the rivers (<LOD – 4487 ng.L-1) as compared to the Bohai Sea (<LOD – 120.5 ng.L-1). AMPA was the compound detected at the highest concentration for both river- (4487 ng.L-1 – Xiaoqinglong River) and seawaters (120.5 ng.L-1), followed by glyphosate (Xiaoqing River = 463.6 ng.L-1; seawater = 27.4 ng.L-1) and then by acetamiprid (Duliujian River = 127.4 ng.L-1; seawater = 1.7 ng.L-1). Except for AMPA, all compounds were found at higher concentrations during the summer season.
In conclusion, the ubiquitous presence of acetamiprid and the high concentrations and detection frequencies of AMPA in the sampled waters suggest a high persistence and stability of these compounds in surface waters. Therefore, these compounds may accumulate in aquatic/marine environments and may pose a risk to aquatic/marine organisms. The Bohai and Laizhou Bays presented the highest contamination status, to where most contaminated rivers were flowing, indicating that riverine discharges are important contributors to the pollution status of the marine environment. The higher detection frequencies and concentrations of the transformation products of imidacloprid, fipronil and glyphosate in the marine environment indicate the rapid degradation of their parent compounds during their “journey” from the contaminated rivers to the Bohai Sea. Since evidence shows that these transformation products have similar or even higher persistence and toxicity to non-target organisms, it is important to further monitor these compounds in the marine environment.
How to cite: Bento, C. P. M., Naumann, T., Wittmann, A., Tang, J., Zhen, X., Liu, L., and Ebinghaus, R.: River-Sea Systems: Spatial and temporal occurrence of Neonicotinoids, Glyphosate and related transformation products in the Chinese Bohai Sea and 36 surrounding Rivers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13296, https://doi.org/10.5194/egusphere-egu21-13296, 2021.
The Don River Delta is densely populated and subjected to the significant anthropogenic impact caused by agriculture, shipping, recreation and fishing activities. One of the major problems in the delta is wind surges, which cause catastrophic consequences due to the sharp water rise (up to 3,2 meter in 2014). Increasing technogenic pressure coupled with the unstable hydrological regime determines great interest of scientists in its study. Research of aquatic systems of the Don River delta carried out by the authors since 2012. Since that, a great data on heavy metals (HM) and polycyclic aromatic hydrocarbons (PAH) content in water, suspended matter and bottom sediments has been received. The data characterize different hydrological conditions including spring flood, summer and winter low water periods, and water surges of 2014 and 2019.
The content of HMs and PAHs in water and suspended matter of the Don delta is usually below the world average. There is a significant seasonal and spatial variability in the concentration of pollutants in suspended matter. In general, the majority of heavy metals are characterized by an increase in contents from the top of the delta to the estuary seaside. Deltaic waters were found polluted Cu with the maximum value in the mouth of the main shipping channel. Increased concentrations of HMs and PAHs are observed near or downstream of settlements and industrial facilities. According to seasonal changes the heavy metals in the Don delta can be divided into 2 groups. The first group includes Fe, Mn and Pb, which maximum concentrations are characteristic of the winter low-water period. The second group includes Cu, Ni, Zn and Mo, with the highest content during floods.
The average concentration of PAHs in the summer-autumn low-water period (300 ng/g) is almost 10 times lower than in the winter low-water period (3000 ng/g). The composition of PAHs in suspended matters is dominated by light compounds: diphenyl-phenanthrene-naphthalene association in the summer-autumn low-water period and phenanthrene-naphthalene-anthracene association during the winter low-water period. Small low-flow channels have a low content of polyarenes.
Surge events significantly affect the spatial distribution of HMs and polyarenes in suspended matter and bottom sediments, mainly due to an increase in flow turbulence. During the surge the content of HMs and PAHs in upper part of the sediments was found decreased, since in suspended matter increased.
This work was carried out with the financial support of the RFBR grant 18-05-80094.
How to cite: Tkachenko, A., Piskareva, V., Koshovsky, T., Gennadiev, A., and Lychagin, M.: Wind surge influence on flows of heavy metals and polycyclic aromatic hydrocarbons in the Don River delta, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14880, https://doi.org/10.5194/egusphere-egu21-14880, 2021.
The Po River delta (northern Italy) is a complex system composed of terrestrial, transitional and coastal-marine ecosystems strongly influenced by different natural and anthropogenic stressors. In this study, we aimed to provide the anthropic impact during the last 200 years through geochemical concentration of heavy metals. In order to reach this objective, trace Metals (TMs: Pb, Zn, Cu, Cr, Cd and Ni), major elements (Al, Fe and Mn) and natural/artiﬁcial radionuclides (210Pb/137Cs) were analysed on the sediment core (EL14-C01) collected in 2014 in the Po River prodelta. We assumed the TMs mean concentrations during the pre-industrial time (before 1850) as the natural background in this area. Sediments deposited after 1850 exhibited a TMs gradual rise compared to the concentrations recorded in the pre-industrial era, in particular Pb, Zn and Cu (PZC). PZC vertical profiles show that the contamination has increased dramatically after the Second World War, during the so called ‘‘Italian Economic Miracle’’ period, exceeding up to 2.5, 2 and 1.5 (Pb>Zn>Cu) times the concentrations of the pre-industrial era. Post-war years saw the birth of the mechanical, chemical, ceramics Italian industries, and the switch from coal to oil and the plastic derivatives it entailed (Romano et al. 2013). The PZC concentrations reached the maximum between 1970s and 1980s, in agreement with anthropogenic atmospheric emissions changes. The distributions of ZPC indicate a sharp contamination decrease from the second half of the 1980s. Probably this reduction was related to the introduction of the Italian Law 319/76 and to the implementation of anti-pollution policies on automotive Pb (unleaded fuels). Recently, the levels of anthropogenic ZPC pollution are similar to the pre-WWII values. During the XXth century, the geochemical analysis show some TMs/Al peaks corresponding to the seven major Po floods with discharges above 8000 m3/s occurred in 1917, 1926, 1928, 1951, 1976, 1994, and 2000.
How to cite: Riminucci, F., Capotondi, L., and Ravaioli, M.: Trace metals accumulation on the Po river prodelta, North Adriatic Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6459, https://doi.org/10.5194/egusphere-egu21-6459, 2021.
Antimony (Sb) radionuclides (e.g., 125Sb half-life of 2.76 y), are fission products of nuclear reactions released to the environment during nuclear power plant (NPP) accidental events and current operating fuel reprocessing. In coastal systems, 125Sb shows high mobility and dispersion in the dissolved phase but its environmental biogeochemical behaviour in continent-ocean transition systems is still not fully understood . Based on the widely accepted hypothesis of similar geochemical behaviour between radioactive and stable isotopes of the same element, this work quantified inherent concentrations of dissolved Sb (Sbd, <0.2 µm mesh size) along the salinity and turbidity gradients of the Gironde Estuary (SW of France) covering contrasting hydrological conditions (i.e., intermediate freshwater discharge and drought) by direct analysis of estuarine and seawater samples with QQQ-ICP-MS (KED mode, iCAP TQ Thermo®). Dissolved Sb trends along the salinity gradient showed a non-conservative (additive) behaviour, ranging between 100-140 ng L-1 in the freshwater endmember (i.e., matching known upstream concentrations ) to max. 440 ng L-1 in mid-salinities during drought conditions, followed by decreasing values towards the marine endmember due to dilution (mixing) with seawater (i.e., ~200 ng L-1). The specific mechanisms behind Sb desorption from the particle phase are unknown, potentially related to the interplay between biogeochemical processes and intra-estuarine residence times of water and suspended particles in macrotidal, hyperturbid estuaries, independent from the salinity gradient . Daily gross Sbd fluxes into the estuary (i.e., 10.4 kg d-1 and 3.4 kg d-1) and net estuarine coastal output (i.e., 27.0 kg d-1 and 11.4 kg d-1) for intermediate and drought conditions were calculated, respectively, following known methods . Sorption experiments using isotopically labelled spikes of stable Sb exposed to water and particles from the Gironde Estuary simulating the salinity and turbidity gradients showed <2% sorption of added Sb in 24h , suggesting that potential liquid releases of 125Sb from a NPP in the central Gironde Estuary may persist in the dissolved fraction. Dispersion scenarios of hypothetical 125Sb discharges are expected to reflect water residence times, resulting in long-term intra-estuarine 125Sb retention during draught (water residence times of 80 days) and highest concentrations of inherent Sb. In contrast, hypothetical 125Sb releases during intermediate conditions (i.e., water residence times of 1-2 months) would result in faster exportation of 125Sb to the coastal ocean, where enhanced dilution might probably limit the exposure levels of coastal organisms to 125Sb but imply a wider dispersion following oceanic currents along the Atlantic coast, possibly reaching the oyster farms north of the estuary mouth. Bio-uptake of Sb radionuclides, related radiotoxicity and potential sorption onto suspended particles (e.g., after longer contact times) or plankton and the resulting reactivity/mobility need further investigation.
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How to cite: Gil-Díaz, T., Schäfer, J., Pougnet, F., and Dutruch, L.: Dispersion scenarios of radioactive antimony in a macro-tidal continent-ocean transition system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14658, https://doi.org/10.5194/egusphere-egu21-14658, 2021.
In oxic waters, ReVII is the stable oxidation state which undergo hydrolysis to the relatively unreactive perrhenate ion, ReVIIO4- . The oceanic dissolved Re exhibits quite conservative behaviour with the concentration of about 40 pM . Despite the frequent utilization of Re for the atmosphere and the ocean past redox state reconstructions, the geochemical behaviour of Re in the modern surface environments such as rivers, estuaries as well as in seawater is not well studied. Understudy is partially arising from the fact that Re has low seawater and riverine concentration of 4 pM and 16.5 pM, respectively[1, 3]. In the Amazon and the Hudson estuaries, in crease of Re concentration at low and middle salinity regions is observed . On the other hand, Re exhibits complete conservative behaviour in Indian river estuaries, i.e. Narmada, Tapi and the Mandovi estuaries in the Arabian Sea and the Hooghly estuary in the Bay of Bengal . Deviation from conservative behaviour in Re can be explained as the interplay of variety of factors including the nature and composition of the particles, Eh-pH conditions, biological productivity and fate of the organic matter. .
Here we present the Re concentration profiles in the freshwater part of the karstic Krka river (Croatia) and its 23 km long estuarine segment, covering a full salinity range (0.1 to 38.6). Analysis of Re was performed by its preconcentration and separation using an anion exchange resin (Dowex 1X8) followed with the ICP-MS quantification using isotope dilution (ID) method. The Krka River spring is characterised by the low Re concentration (~6 pM). A noticeable anthropogenic influence at the point of the wastewater discharge of the Knin town was observed (27 pM). This input probably caused a progressive downstream increase of Re concentration to 12 pM at the freshwater end-member in the winter period (with a high Krka River discharge) and 17 pM in the summer period (low Krka River discharge). In the estuarine segment, a near-conservative behaviour of Re was found, with the "oceanic" concentration of 38 pM in the seawater end-member.
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How to cite: Bura-Nakić, E., Knežević, L., Mandić, J., Cindrić, A.-M., and Omanović, D.: Rhenium distribution and behaviour in the salinity gradient of a highly stratified estuary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4745, https://doi.org/10.5194/egusphere-egu21-4745, 2021.
Inland waters including rivers, lakes, and groundwater are suggested to act as a transport pathway for water and dissolved substances, and play some role in continental biogeochemical cycling (Cole et al., 2007; Battin et al., 2009). Quantifying the physical and chemical connections between land and associated fresh and coastal waters is critical for understanding the dynamics of carbon cycle in aquatic ecosystems. Recently, process-based National Integrated Catchment-based Eco-hydrology (NICE) model (Nakayama and Watanabe, 2004) was developed to couple with various biogeochemical cycle models in biosphere, aquatic ecosystems, and carbon weathering, etc. in global major river basins (NICE-BGC) (Nakayama, 2017; Nakayama and Pelletier, 2018). NICE-BGC also included the feedback between soil organic content and overland carbon fluxes, and succeeded to simulate inter-annual variations of carbon cycle in a terrestrial-aquatic continuum greatly affected by the extreme weather patterns (Nakayama, 2020). To evaluate global changes in the carbon cycle due to anthropogenic factors, such as application of fertilizer and manure, in major rivers including 130 tidal estuaries over an 18-year period (1998-2015), the present study expanded NICE-BGC to estuary in land and ocean margins where it is generally considered to be net heterotrophic ecosystems and show significant supersaturation of CO2 (Frankignoulle et al., 1998; Regnier et al., 2013). The new model used Dirichlet boundary condition at the downstream of global major rivers by using some variables (water temperature, salinity, dissolved oxygen, nutrient, alkalinity, and pH, etc.) in coastal ocean. The simulated result showed that total nitrogen and phosphorus fluxes in overland flow were found to increase with nutrient application. In contrast, total suspended sediment decreased in some regions because the vegetation was able to expand to cover the ground, resulting in less erosion. NICE-BGC simulated the difference in carbon budget in major rivers with and without nutrient application. Generally, CO2 degassing above water decreased and particulate organic carbon (POC) increased in most rivers through variations in carbon budget, reflecting various hydrologic and biogeochemical conditions. The simulated result also showed that the estuarine carbon cycle was sensitive to intense anthropogenic disturbances reflected by nutrient load, seawater temperature, increases in sea level, and ocean acidification. Extension of previous studies only by categorizing MARCATS segment numbers showed that the estimated total CO2 flux from the world’s estuaries was 0.14 Pg C/yr. The simulation generally showed that incorporation of the nutrient cycle into the terrestrial-aquatic-estuarine continuum improved estimates of net land flux and carbon budget in inland waters, thus emphasizing that the effect of estuarine inland water should be explicitly included in the global carbon model to minimize the range of uncertainty.
How to cite: Nakayama, T.: Estimation of carbon cycle changes in river-estuarine continuum by using advanced earth system model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3602, https://doi.org/10.5194/egusphere-egu21-3602, 2021.
Understanding river-sea-systems requires a thorough understanding of processes that span different Earth system compartments. To overcome issues related to the interaction of different scientific disciplines and compartments, such as different measurement and calibration standards, quality control approaches and data formats for specific environmental parameters, joint measurement campaigns have been initiated within the Helmholtz Association’s MOSES (Modular Observation Solutions for Earth Systems) project. Following multiple senor comparison and intercalibration campaigns in 2019, MOSES’ Hydrological Extremes event chain working group initiated joint field campaigns in summer 2020 covering the Elbe river from the Czech-German border to the tidal Elbe and further on into the estuary and the German Bight.
The fundamental objective was to establish scientifically sound and resilient multi-ship applicable sampling procedures and to create reference data for the main environmental parameters for future investigation of extreme events such as flooding and drought and their overall impact on the catchment region and the adjacent estuarine area of a large European fresh water / marine system. The campaign involved four research vessels, four research centers and spanned nearly two months. Measurements included standard hydrological and oceanographic parameters, as well as quantities relevant to the nutrient and carbonate system. Furthermore, selected water quality indicators and atmospheric measurements were performed. In the fresh water section of the Elbe river measurements were taken while drifting with the water mass. In the tidal section of the river sampling was done against the ebb current while in the North Sea a grid covering a large part of the German exclusive economic zone (EEZ) was sampled.
We detected a longitudinal increase of phytoplankton biomass along the 585 km freshwater part of the river towards the tidal system. In contrast, concentrations of dissolved nitrate and phosphate decreased to low values due the uptake by planktonic algae. The concentration of dissolved CO2 decreased caused by increasing photosynthesis while the concentration of methane increased along the river stretch, particularly in the most downstream part when sedimentation of phytoplankton increased the organic load of sediments. The tidal part of the transect showed a strong influence of Hamburg harbor on almost all quantities, while downstream towards the estuary, the effects of the tidal cycle dominated variabilities. In the marine area, elevated chlorophyll concentrations were mainly found near the west coast of Schleswig-Holstein, probably mostly influenced by the Eider river outflow or the adjacent tidal flats. While most of the measured parameters showed an expected behavior relative to their individual compartments, the transfer of quantities between the compartments revealed rather complex and sometimes difficult to understand behaviors and patterns, especially when considering a functional quantitative analysis. The first results of this trans-compartment campaign showed that a quantitative understanding of the fate and dynamics of water constituents across compartments from the spring to the sea needs enhanced scientific collaboration and awareness to finally come to a better integrated understanding of physical, biogeochemical and biological processes from the local to the global scale.
How to cite: Brix, H., Kamjunke, N., Bussmann, I., Achterberg, E., Dietrich, P., Fischer, P., Flöser, G., Geißler, F., Koedel, U., Koschorreck, M., Rewrie, L., and Schütze, C.: Elbe 2020 – investigating a river-sea system from upstream into the North Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8721, https://doi.org/10.5194/egusphere-egu21-8721, 2021.
Overall, estuaries are net CO2 sources to the atmosphere, releasing an estimated 0.25 Pg C yr-1, which could counterbalance the shelf uptake of approximately 0.25 Pg C yr-1. River discharge can influence both, the CO2 flux from estuary to the atmosphere, as well as the magnitude of dissolved inorganic carbon (DIC) exported to coastal waters. In Europe, climate change is expected to cause an increased precipitation in winter and longer periods of drought in summer. The goal of this study is to elucidate the influence of climate-change-induced hydrological changes on an estuarine carbonate system.
The Elbe River is one largest river basins in central Europe, where over 24 million people live in the catchment area. Since 2014, annual Elbe river discharge has been relatively low at 492.95 m3 s-1, compared to the mean river discharge from 2008 to 2018 at 652.95 m3 s-1. 2018 was especially dry, with a discharge of 441 m3 s-1, the lowest annual mean river discharge since 1992. The Elbe estuary has been extensively sampled by the Flussgebietsgemeinschaft (FGG) Elbe (Elbe River Basin Community), qualifying the region as a suitable site to study the natural and anthropogenic impacts on estuarine systems.
Preliminary results of the 1985-2018 FGG dataset indicate a major shift in the carbonate system dynamics in the Elbe estuary. From assessing the behaviour of DIC and other ecosystem parameters along the estuary over time, the region can be separated into three ecosystem states. During the time of high pollution, from 1985 to 1990, the estuary exhibited high levels of DIC. Between 1991 and 1996 is the transitional period. After 1997, the ecosystem parameters appear to be exhibiting similar patterns throughout each year with similar levels and therefore this period can be classified as the current ecosystem state. Since 1997, DIC exhibits a drawdown in spring and summer months in the upper region, coinciding with the increase in dissolved oxygen saturation and pH, which can indicate that this region is net autotrophic. Further downstream, DIC then increases along the estuary, and often peaks in the maximum turbidity zone.
For this study, we apply multiple linear regression to determine the relative importance of ecosystem variables that contribute to annual and monthly DIC variability in the recent ecosystem state. Key ecosystem variables include particulate and dissolved organic carbon, pH, dissolved oxygen and river discharge.
How to cite: Rewrie, L., Voynova, Y., Brix, H., Ollesch, G., and Baschek, B.: Long-term changes in inorganic carbon in the Elbe estuary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7325, https://doi.org/10.5194/egusphere-egu21-7325, 2021.
Surface waters are known to be significant sources of greenhouse gases (CH4 and CO2), but our understanding of large scale patterns is still incomplete. The greenhouse gases in rivers originate both from in-stream processes and interactions with the catchment. For coastal seas, rivers are suspected to be one of the main source of greenhouse gases, while the role of the interjacent tidal flats is still ambiguous. Especially the reaction of the entire system on terrestrial hydrological extremes such as low flow situations are still under consideration. The functional understanding of such events and their impacts on the water chemistry along its transition pathway in the terrestrial and limnic compartment as well as in the coastal marine environment is crucially needed for the evaluation of its relevance in the Earth system. As part of a MOSES campaign (Modular Observation Solutions for Earth Systems) spanning disciplines as well as earth system compartments we investigated the aquatic as well as the atmospheric compartemt in and above the Elbe River from inland waters through the tidal section of the river and the estuary to the North Sea with the goal to explore spatial heterogeneity of CO2 and CH4 concentrations in the water and in ambient air above the water during a low water period in summer 2020.
Overall, dissolved CH4 concentrations ranged over three orders of magnitude. Along the freshwater part of the transect, dissolved CH4 increased and weirs and harbors appeared to be hot spots of elevated CH4 concentrations both for the dissolved and atmospheric phase. We observed a longitudinal gradient of CO2 in the river which was closely linked to primary production. In the estuary and the marine part, dissolved CH4 concentrations of the transect were determined by the variability of temperature and salinity. Correlations with other water parameters revealed the complex regulation of dissolved CH4 concentrations along the freshwater-seawater continuum. For atmospheric CH4 above the North Sea, wind direction and wind speed proved to be crucial. Besides the typical diurnal fluctuations of atmospheric CO2 and CH4, an observed link between dissolved and atmospheric concentrations has to be further clarified.
How to cite: Bussmann, I., Brix, H., Kamjunke, N., Ködel, U., Koschorreck, M., and Schütze, C.: Characteristics of dissolved and atmospheric methane concentrations along a freshwater-seawater transect from the River Elbe into the North Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8270, https://doi.org/10.5194/egusphere-egu21-8270, 2021.
Estuaries are crucial in transforming matter fluxes from land to sea. To better understand and quantify these processes and respective fluxes, it is important to determine the input into an estuary accurately. To allow for such studies in the Elbe estuary in Germany, a state-of-the-art research platform is currently being set-up just upstream of the weir in Geesthacht at the entrance of the estuary. Here, we report on small-scale spatial dynamics of organic matter and associated processes from several cross and longitudinal profiles around the planned location and the implications for the set-up of the aforementioned research platform.
Based on preliminary data obtained in August 2020 during a period of relatively low discharge, we present the following results: (1) In three cross profiles along a 10 km transect of the Elbe upstream of the weir, we observed considerable small-scale gradients regarding currents and various biogeochemical parameters. In comparison to the fairway, water from the riverbanks was depleted in suspended particulate matter, chlorophyll a, dissolved oxygen, and nitrate, and enhanced in ammonium, phosphate and silicate, as well as total alkalinity and dissolved inorganic carbon paralleled by decreasing pH. This suggests that in the summer, organic matter is deposited and remineralised at the riverbanks, resulting in the release of ammonium, phosphate and silicate, and in the removal of nitrate, presumably by denitrification. (2) Along the 10 km transect towards the weir, we observed that concentrations of suspended particulate matter, chlorophyll a, dissolved oxygen, nitrate and pH were decreasing. In contrast, we found that ammonium, phosphate and silicate, total alkalinity and dissolved inorganic carbon increased towards the weir. This suggests an increased sedimentation and subsequent remineralisation due to the reduced flow velocities in front of the weir. (3) An analysis of a 10-year time series from the weir supports this by showing higher ammonium concentrations when discharges were relatively low. The implications of these findings for the set-up of the research platform in this area, as well as for optimising estimates of budgets are discussed. The research platform will contribute to understand further such variations in biogeochemical parameters at the entrance of the Elbe estuary over time.
The research platform is set-up in cooperation with the Helmholtz initiative MOSES (“Modular Observation Solutions for Earth Systems“) and will be incorporated in the Elbe-North Sea Supersite of DANUBIUS-RI (“International Centre for Advanced Studies on River-Sea Systems“). Funding is provided by European Regional Development Funds, the federal state of Schleswig-Holstein, the Helmholtz Association and the Helmholtz-Zentrum Geesthacht. The research platform, planned to be operational in autumn 2021, will also be open for users e.g. to develop and test new methods and technologies. Data will be made available through the “Helmholtz Coastal Data Centre” (HCDC).
How to cite: Bold, S., van Beusekom, J. E. E., Voynova, Y. G., Cysewski, M., Van Dam, B., Stresser, M., Carrasco Alvarez, R., Horstmann, J., Dähnke, K., Sanders, T., Friedrich, J., Pröfrock, D., and Thomas, H.: Small-Scale Gradients in Big River: Implications for a State-of-the-Art Research Platform in the Elbe, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7101, https://doi.org/10.5194/egusphere-egu21-7101, 2021.
How to cite: van Beusekom, J. E. E., Fehling, D., Bold, S., and Sanders, T.: Pelagic oxygen consumption rates in the Elbe estuary: Proxies and spatial patterns., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8699, https://doi.org/10.5194/egusphere-egu21-8699, 2021.
Recent decades have witnessed large scale modifications in the natural flow regime of river systems. What follows are shifts in various instream processes that ultimately govern the air-water fluxes of major greenhouse gases (GHGs) like CH4, CO2, and N2O. However, due to paucity of data, the process dynamics and controls on fluxes of GHGs in tropical rivers are understudied, contributing to uncertainty in their global budget. In this study, an attempt was made to estimate the fluxes of GHGs and thereby decipher the controls on evasive processes in an anthropogenically affected Sabarmati River (catchment ~ 27,674 km2 and channel length ~371 km) located in semi-arid western India. After originating from a relatively pristine region, Sabarmati passes through a major twin city (Ahmedabad-Gandhinagar), where construction of a riverfront resulted in increased residence time of water within the city limits.
To compare and understand changes in in-stream biogeochemical processes as a result of human interventions, sampling was carried out at 50 sites along the Sabarmati river continuum and a parallel running, but not so anthropogenically modified, Mahi River along with their tributaries. Results indicated relatively lower fluxes of GHGs in pristine upstream of Sabarmati and Mahi River continuum with CH4, CO2 and N2O fluxes at 0.99 ± 0.35 mg C m-2 d-1, 4250.99 ± 477.74 mg C m-2 d-1 and 0.055 ± 0.026 mg N m-2 d-1 respectively. The effect of higher residence time of water could be seen in the riverfront with increased CH4 and N2O fluxes at 3.27 ± 1.02 mg C m-2 d-1 and 0.129 ± 0.024 mg N m-2 d-1, respectively. However, the CO2 flux did not show much increase. The fluxes increased significantly post city limits until its mouth in the Arabian Sea with extremely large flux for methane (CH4: 102.84 ± 41.32 mg C m-2 d-1, CO2: 9563.58 ± 1252.43 mg C m-2 d-1, and N2O: 0.16 ± 0.11 mg N m-2 d-1, respectively). Overall, it appeared that even within the anthropogenically stressed river, the nature of flow regime, exerts significant control on cycling of elements leading to differential fluxes. Also, the level of coupling between nitrogen and carbon appeared to change within the course of the river.
How to cite: Sarkar, S., Rathi, A., and Kumar, S.: Greenhouse gas dynamics in an anthropogenically modified tropical river continuum, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9361, https://doi.org/10.5194/egusphere-egu21-9361, 2021.
The Arctic ocean receives 11% of the entire global river discharge via several great Arctic rivers that drain vast catchments underlain with carbon-rich permafrost. Arctic marginal shelf seas are therefore heavily influenced by terrestrial dissolved organic matter (tDOM) supply, influencing coastal biogeochemical processes and food-webs, as well as physio-chemical properties (e.g. stratification or nutrient concentrations).
Whilst carbon and associated macronutrients supplied by tDOM may enhance the nutrient and carbon substrates for lower trophic levels (phytoplankton/zooplankton), promoting increased local and regional productivity, it can also have opposing effects through a series of indirect processes (e.g. increased light absorption limiting light penetration through the water column). Understanding the relative importance and timing of these processes, and how they vary spatially, is necessary to identify how land-ocean interfaces currently operate.
Future climate scenarios indicate increased quantities of riverine tDOM delivered to the near-shore, with increased freshwater runoff and greater terrestrial permafrost thaw and erosion. This is likely to be exacerbated by the disappearance of seasonal sea ice cover and increased coastal erosion rates. We can therefore expect changes in planktonic phenology and productivity, with concomitant changes in bacterial and higher trophic level success. Understanding how these factors interact and may change under future climate scenarios is therefore critical to predict the future impact on shelf sea Arctic ecosystems and the ecosystem services they provide.
In the Changing Arctic Carbon cycle in the cOastal Ocean Near-shore (CACOON) project (UK-Germany collaboration) we are using coupled hydrodynamic-biogeochemical models in the extensive shallow shelf of the Laptev sea to explore the relationship between these factors. The ecosystem model ERSEM has been adapted to explicitly include a tDOM component. This coupled model system allows us to investigate both the role of present day tDOM in an Arctic coastal ecosystem and to project the potential impacts of increased tDOM input in future.
How to cite: Bedington, M., Torres, R., Polimene, L., Wallhead, P., Juhls, B., Palmtag, J., Strauss, J., and Mann, P. J.: Impacts of riverine terrestrial organic matter on the lower trophic levels of an Arctic shelf ecosystem, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12897, https://doi.org/10.5194/egusphere-egu21-12897, 2021.
Possible sea level rise and changes in hydrological regime of rivers are the major threats to estuarine systems. The sensibility of hydrodynamic regime of the Northern Dvina delta and the Onega estuary under various scenarios of climate change has been investigated. Hydrodynamic models HEC-RAS (USA, US Army Corps of Engineers Hydrologic Engineering Center) and STREAM_2D (Russia, authors V.Belikov et.al.) were used for analysis of estuarine flow regime (variations of water levels, discharges and flow velocities throughout tidal cycles). Input runoff changes were simulated for different climate scenarios using ECOMAG model (Russia, author Yu.Motovilov) based on data of global climate models (GSM) of CMIP5 project for the White Sea region.
ECOMAG modelling has demonstrated that the maximum river discharges averaged for 30-year period 2036 – 2065 can reduce for about 20 – 27% for the Onega and 15 – 20% for the Northern Dvina river compared against the historical period 1971 – 2000.Averaged minimum river discharges can reduce for about 33 – 45% for the Onega and 30 – 40% for the Northern Dvina.
The White Sea level rise by 0.27 m in average (with inter-model variation from 0.20 to 0.38 m) can took place by the middle of the XXI century according to input data of GSM models. The 12 scenarios of estuarine hydrodynamic changes were simulated for the both rivers based on combining river runoff changes and sea level elevation.
In general, the expected flow changes are negative for the local industry and population. According to modelling results for ‘high runoff/spring tide’ scenarios the flooding area in the Northern Dvina delta will increase by 13-20% depending on the intensity of sea level rise. In the low water seasons the distance from the river mouth to the upper boundary of the reach, where reverse currents can be observed, will move upstream by 8 - 36 km depending of sea/river conditions due to decrease in minimum river runoff. It may adversely effect on shipping conditions at the city of Arkhangelsk and on brackish water intrusion up-to industrial and communal water intakes.
The reverse currents also will intensify in the Onega estuary (tidal flow velocities increase for 11 – 19%) that leads to the change of the sediment regime and can significantly deteriorate the navigation conditions at the seaport of the Onega town. The problem of the intensification of salt intrusion can arise there as well.
The research was supported by the Russian Foundation for Basic Research (Projects No. 18- 05-60021 in development of the scenarios; No. 19-35-90032 in providing hydrodynamic modelling of the Onega; Project No. 19-35-60032 in providing hydrodynamic modelling of the Northern Dvina).
How to cite: Panchenko, E., Alabyan, A., Krylenko, I., and Lebedeva, S.: Modelling the climate change impact on the largest White Sea estuarine areas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8274, https://doi.org/10.5194/egusphere-egu21-8274, 2021.
Prime Hook National Wildlife Refuge and its adjacent water bodies are important natural features along western Delaware Bay, USA. Historically salt and brackish marsh habitats, portions of the Refuge were diked and managed as freshwater impoundments starting in the early 1980s. Over the past decade, some of these impoundments have reverted to saline conditions, largely due to several storm events (including Hurricane Sandy in 2012) that have caused flooding, erosion, and opened several breaches between the Refuge and Delaware Bay. Because of these significant morphologic changes, the United States Fish and Wildlife Service (USFWS) completed a series of surveys, numerical modeling using Delft3D and coastal engineering analyses to aid in developing restoration alternatives for managing the Refuge and its marshlands. This work will review the results of the strategic planning used to recommend a preferred restoration alternative for managing the Refuge under the new environmental regime aimed at resilience. As a result of this effort, a project for restoring and managing the Refuge was recommended and constructed in 2018. Total cost of the project was $40 million US and was the largest restoration/recovery project authorized to address the impacts of Hurricane Sandy.
The project included two major components: 1) shoreline reconstruction and 2) marsh restoration. The shoreline reconstruction portion of the project included placing approximately 1.2 million cubic meters of sand from an offshore borrow area along the shoreline to reconstruction a 12 m wide dune, 45 m beach berm and 30 m back-bay marsh platform (essentially rebuilding the entire barrier island). In addition, the project included a major marsh restoration effort including dredging 48 km of conveyance channels and “thin layer” disposal of 460,000 cubic meters of sediment to create 2,000 hectares of salt marsh.
Herein will present findings from an analysis using monitoring data and observations to evaluate converting freshwater wetlands to saltwater marshes and the resulting increase in carbon sequestration. As tidal marshes are restored, harmful emissions decline as the project site transforms from a freshwater to a saltwater environment. Therefore, carbon is stored in the soils more readily under tidal marsh conditions. The findings will show the increase in carbon sequestration as a result of the vegetation community response and discuss future projections. Methodologies used for identifying vegetation community response included:
- Salt Marsh Integrity (SMI) and Saltmarsh Habitat & Avian Research Program (SHARP)
- Mid-Atlantic Tidal Rapid Assessment Method (MidTRAM)
- Normalized Difference Vegetation Index (NDVI)
This work will show the importance of incorporating coastal restoration projects and carbon sequestration into policies and management in the coastal zone.
How to cite: Tabar, A., Guiteras, S., and Tabar, J.: Prime Hook National Wildlife Refuge Marsh Restoration & Shoreline Resilience Project – A Carbon Sequestration Case Study in the Coastal Zone , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7944, https://doi.org/10.5194/egusphere-egu21-7944, 2021.
The propagation of tides and riverine floodwater in coastal wetlands is controlled by subtle topographic differences and a thick vegetation canopy. A precise quantification of fluxes of water, sediments and nutrients is crucial to determine the resilience and vulnerability of coastal wetlands to sea level rise. High-resolution numerical models have been used in recent years to simulate fluxes across wetlands. However, these models are based on sparse field data that can lead to unreliable results. Here, we utilize high spatial-resolution, rapid repeat interferometric data from the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) to provide a synoptic measurement of sub-canopy water-level change resulting from tide propagation into wetlands. These data are used to constrain crucial model parameters and improve the performance and realism of simulations of the Wax Lake wetlands in coastal Louisiana (USA). A sensitivity analysis shows that the boundary condition of river discharge should be calibrated first, followed by iterative correction of terrain elevation. The calibration of bed friction becomes important only with the boundary and topography calibrated. With the model parameters calibrated, the overall Nash-Sutcliffe model efficiency for water-level change increases from 0.15 to 0.53 with the RMSE reduced by 26%. More importantly, constraining model simulations with UAVSAR observations drives iterative modifications of the original Digital Terrain Model. In areas with dense wetland grasses, the LiDAR signal is unable to reach the soil surface, but the L-band UAVSAR instrument detects changes in water levels that can be used to infer the true ground elevation. The high spatial resolution and repeat-acquisition frequency (minutes to hours) observations provided by UAVSAR represent a groundbreaking opportunity for a deeper understanding of the complex hydrodynamics of coastal wetlands.
How to cite: Fagherazzi, S., Zhang, X., Jones, C., Oliver-Cabrera, T., and Simard, M.: Using Rapid Repeat SAR Interferometry to improve Hydrodynamic Models of flood propagation in Coastal Wetlands , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12609, https://doi.org/10.5194/egusphere-egu21-12609, 2021.
Predictions of the effects of sea-level rise over the next century on coastal wetlands vary widely due to uncertainties on environmental variables, but also due to simplifications on the simulation methodologies used. Here, we investigate how accretion and migration processes affect wetland response to sea level rise (SLR) using a computational framework that includes all relevant hydrodynamic, sediment transport and vegetation dynamics mechanisms that affect wetland evolution, and it is efficient enough computationally to allow the simulation of long time periods. We apply this framework to different settings typically found in coastal wetlands around the world, comprising different vegetation types, different sediment loads, obstructions to flow and drainage structures, both natural and man-made. We find that the vast majority of wetland settings analysed are unable to cope with high SLR rates and disappear before the end of the century. Our findings are consistent with paleo-records that indicate limits on the accretion capacity of coastal wetlands during periods of high SLR rates.
How to cite: Rodriguez, J., Breda, A., Saco, P., Sandi, S., Saintilan, N., and Riccardi, G.: Physical-biological interactions limit the resilience of coastal wetlands to sea level rise, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14219, https://doi.org/10.5194/egusphere-egu21-14219, 2021.
Coastal salt-marshes are important eco-geomorphic features of coastal landscapes providing valuable ecosystem services, but unfortunately, they are among the most vulnerable ecosystems around the world. Their survival is mainly threatened by sea-level rise, wave erosion and human pressure. Halophytic vegetation distribution and dynamics control salt-marsh erosional and depositional patterns, critically determining marsh survival through complex bio-morphodynamic feedbacks. Although a number of studies have proposed species-classification methods and analyzed halophytic vegetation species distribution, our knowledge of the temporal evolution of species composition remains limited. To fill these gaps and better describe vegetation composition changes in time, we developed a novel classification method which is based on the Random Forest soft classification algorithm, and applied the method to two multi-spectral images of the San Felice marsh in the Venice lagoon (Italy) acquired in 2001 and 2019. The Random Forest soft classification achieves high accuracy (0.60 < R2 < 0.96) in the estimation of the fractional abundance of each species in both images. We also determined the local dominant species, i.e. the species with the highest fractional abundance in each pixel. Our observations on the dominant species in 2001 and 2019 show that: 1) the area dominated by Juncus and Spartina decreased dramatically in such period; 2) the area dominated by Limonium almost maintained constant; 3) a noticeable decrease in the bare-soil area occurred due to the encroachment of Salicornia between 2001 and 2019. We also noticed that the probability distribution of the dominant patch area of each species is consistent with a power-law distribution, with different slopes for different vegetation species at different times. We suggest that vegetation composition changes are related to sea-level rise and to the species-specific inundation tolerance.
How to cite: Yang, Z., Silvestri, S., Marani, M., and D'Alpaos, A.: Analyses on salt-marsh vegetation composition changes in the Venice lagoon in the last twenty years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13624, https://doi.org/10.5194/egusphere-egu21-13624, 2021.
Salt marshes are widespread morphological features in coastal and estuarine tidal landscapes, and are ecologically and economically important as they significantly contribute to coastal primary production, support high biodiversity, and provide a broad range of valuable ecosystem services.
The ability of salt marshes to counteract changes in external forcings depends on the complex dynamic interactions between physical and biological processes acting at different spatial and temporal scales. In particular, the evolution of tidal marshes in the vertical direction results from the balance and feedbacks between organic and inorganic deposition, erosion, and changes in relative sea level. For example, colonization of salt marsh platforms by halophytic vegetation enhances both organic and inorganic deposition due to increased flow resistance, reduced bottom shear stresses, capture of sediment particles by plant stems, and direct biomass accumulation. Moreover, halophytes control soil aeration, which feeds back into vegetation zonation and the related biogeomorphic interactions typically observed in tidal marshes.
In spite of their importance, however, modeling vegetation dynamics in intertidal marshes remains a major challenge both at the theoretical and practical/numerical level. Improving our current understandings of the mechanisms that drive the zonation of halophytic species is of critical importance to enhance projections of salt-marsh response to changes in climate and relative sea level.
Here we present a new bi-dimensional, spatially explicit ecological model aimed to simulate the spatial dynamics of halophytic vegetation in tidal saline wetlands. Vegetation dynamics are treated differently compared to previous models, which employed relatively simple deterministic or probabilistic mechanisms, dictated only by the ability of different species to adapt to different topographic elevations. In our model, in contrast, spatial vegetation dynamics depend not only on the local habitat quality, but also on spatially explicit mechanism of dispersal and competition among multiple, potentially interacting species. The temporal evolution of vegetation biomass at each site depends on death and colonization processes, both local and resulting from dispersal. These processes are modulated for each species by the habitat quality of the considered site. The latter is synthesized only through the local elevation relative to the mean sea level, and is mathematically modeled using a logistic function that represents the theoretical niche of each considered species.
Results indicate that such a relatively simple model, where species have elevation-dependent fitness and otherwise neutral traits, can predict realistic diversity and species-richness patterns. More importantly, the model is also able to effectively reproduce the outcome of classical ecological experiments, in which a species is transplanted to an area outside its optimal (realized) niche. A direct comparison clearly shows how previous models not accounting for dispersal and interspecific competitions are unable to reproduce such dynamics.
How to cite: Finotello, A., Bertuzzo, E., D'Alpaos, A., and Marani, M.: Modelling salt-marsh vegetation dynamics through species dispersal and competition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13174, https://doi.org/10.5194/egusphere-egu21-13174, 2021.
Tidal marshes are vulnerable and dynamic ecosystems with essential roles from protection against marine storms to biodiversity preservation. However, the survival of these environments is threatened by external stressors such as increasing mean sea level, reduction in sediment supply, and erosion. Tidal marshes are formed by deposition over the last centuries to millennia of sediments transported by surface water and biodegradation of organic matter derived from halophytic vegetation. Therefore, the sediment at the surface is characterized by high porosity and their large consolidation potential plays an important role in the future elevation dynamics, which is often not fully recognized.
Here we propose a novel three-dimensional numerical model to simulate the long-term dynamics of tidal marshes. A 3D groundwater flow equation in saturated conditions is implemented to compute the over-pressure dissipation with the aid of the finite element (FE) method, whereas the sediment consolidation is computed according to Terzaghi's theory.
A Lagrangian approach is implemented in the FE numerical model to properly consider the large soil deformation arising from the deposition of highly compressible material. The hydro-geomechanical properties, that depend on the intergranular effective stress, are highly non-linear.
The model takes advantage of a dynamic mesh that simulates the evolution of the landform elevation by means of an accretion/compaction mechanism: the elements deform in time as the soil consolidates and increase in number as the new sediments deposit over the marsh surface. The deposition is treated as input to the consolidation model and can vary in space and time.
The model is applied to simulate the long-term evolution of realistic tidal marshes in terms of accretion and consolidation due to the coupled dynamics of surficial and subsurface processes.
How to cite: Xotta, R., Zoccarato, C., Minderhoud, P. S. J., and Teatini, P.: Embedding compaction processes in long-term evolution modeling of tidal marshes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7740, https://doi.org/10.5194/egusphere-egu21-7740, 2021.
Tidal wetlands are critical intertidal ecosystem which accommodates a large range of flora and fauna species. The intertidal subsurface environment is subjected to continuous groundwater-seawater mixing which results in dynamic solute transport in the aquifer and to the ocean. Salt distribution and transport play a vital role in the wetland ecology and near-shore biogeochemical activities. While many field and simulation studies have been presented to characterize the salt distribution in the intertidal beach aquifer under the influence of tidal inundation, salt distribution in the tidal wetland subsurface system yet requires more investigation. Moreover, the impact of evaporation on porewater salt distribution could be essential in subtropical areas with numerous coastal wetlands as evaporation extracts porewater from the soil surface and leaves salt in the surface and wetland root zone. However, this parameter was commonly ignored by previous studies.
In this study, field monitoring was carried out to map the groundwater level and spatial salt distribution in a subtropical wetland located in Southeastern Queensland, Australia. Two dimensional, variable-density, saturated-unsaturated groundwater flow and solute transport model was used to examine the pore water flow and salt distribution patterns in a cross-shore section of the field site under the influences of the spring-neap tide and evaporation. Field and simulation results consistently showed that salinity is greatly impacted by evaporation and showed different distributions from the saline seawater intrusion patterns displayed by most of the former studies.
How to cite: Liu, Y., Zhang, C., Liu, X., Li, L., Scheuermann, A., and Lockington, D.: Field and numerical study of solute transport under evaporation in a subtropical tidal wetland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9356, https://doi.org/10.5194/egusphere-egu21-9356, 2021.
Along estuaries and coasts, tidal marsh restoration projects are increasingly being executed on formerly embanked agricultural land to regain the ecosystem services provided by tidal wetlands. There are, however, more and more indications that restored tidal marshes do not deliver these ecosystem services to the same extent as natural tidal marshes. In particular, we found that marsh restoration on a compacted agricultural soil (which has a very low porosity and hydraulic conductivity) leads to reduced groundwater fluxes and soil aeration, which may imply decreased soil-water interactions, reduced biogeochemical cycling and impaired vegetation development.
We studied the subsurface hydrology in the restored marsh Lippenbroek (Scheldt estuary, Belgium). To investigate spatial and temporal variation of groundwater fluxes in the restored tidal marsh, we developed a real-time groundwater flux sensor (iFLUX sensor) that enables us to measure both the groundwater flow velocity and flow direction in real-time. With these instruments installed at multiple locations and depths in the marsh soil, we were able to capture the effects of the tidal regime and soil stratigraphy on groundwater flow in high detail.
Furthermore, we set up a 2D vertical model in HYDRUS with a domain representing a creek and marsh cross-section. The model enables variably saturated flow calculations for groundwater flow and solute transport in dual porosity soils. Input parameters for the model were obtained by soil sampling and laboratory measurements of saturated hydraulic conductivity and soil water retention curves. Simulated results are in good agreement with in situ measured groundwater levels in monitoring wells.
With a scenario analysis, we showed that in a scenario in which the compact subsoil is absent, 6 times more water passes through the marsh soil during a spring tide – neap tide cycle compared to the reference scenario in which the compact soil starts at a depth of 60 cm. In the compact layer, which is always saturated, flow rates are so low that this layer is expected not to contribute to nutrient cycling.
We then simulated the effect of (i) creek excavation (by varying the number of creeks in the domain) and (ii) soil amendments (by varying the depth to the compact layer) on groundwater flow in newly restored tidal marshes. We found that increasing the creek density from 1 creek to 2 creeks per 50 m marsh, or changing the depth to the compact layer from 20 cm to 40 cm, both more than doubles the volume of water processed by the marsh soil. As such , our study demonstrates that groundwater modelling is a useful tool in support of designing marsh restoration measures aiming to optimize groundwater fluxes and related ecosystem services.
How to cite: Van Putte, N., Meire, P., Seuntjens, P., Verreydt, G., Joris, I., De Kleyn, T., Cools, J., Maiheu, B., Hambsch, L., and Temmerman, S.: Improving groundwater dynamics in restored tidal marshes: an explorative field and modelling study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12694, https://doi.org/10.5194/egusphere-egu21-12694, 2021.
Groundwater is the main source of drinking water in Slovenia, but nitrate pollution originating from agricultural activities as well as urban sources such as faulty sewage systems is threatening its quality in several areas of the country. One of such is the Krško-brežiško polje alluvial plain in the southeast. The main aim of this study was to assess the water and nitrogen balance for three common land-use types, as well as the whole area. Three field trial sites were set up to monitor water and nitrogen balance. Gaps in data were further evaluated by SWAT model simulations. Results will contribute to the existing knowledge of nitrate pollution pathways in the area, and strengthen understanding of land use and soil type’s influence on the process.
This work was funded by the Slovenian Research Agency project L4-8221 and IAEA TCP-SLO5004.
How to cite: Curk, M., Glavan, M., Pintar, M., and Zupanc, V.: Water and nitrogen balance assessment for Krško polje aquifer case study in Slovenia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4161, https://doi.org/10.5194/egusphere-egu21-4161, 2021.
Abstraction from surface and groundwater bodies alters river flow regimes. The economic and social benefits of abstraction need to be balanced against their consequences for hydrology dependent ecological functions, ecosystem services, cultural values and recreation. However, impacts of an abstraction on flow regimes are often assessed in isolation and so cumulative impacts of many spatially distributed abstractions on the catchment are not understood. While spatially distributed, high-resolution model(s) (e.g. MODFLOW) can be developed to understand the cumulative impacts of abstractions, this is cost prohibitive and the demand for data is high (e.g., system properties, hydroclimatic) to develop such a model at regional scales and, further, such site specific models cannot be transferred to other spatial locations. We have developed a model to estimate cumulative streamflow depletion at given locations of a stream network resulting from both surface and groundwater abstractions. The surface water abstractions directly deplete the nearest river segment with which the abstraction is associated. However, depletion owing to each groundwater take, response times of which can extend to weeks, months or even years following the abstractions, was associated with all river segments which were within a 2 km radius of the groundwater take. The proportion of depletion from each river segment owing to a groundwater take is dependent on distance between well and segment, flow (based on the naturalised 7-day mean annual low flow) and length of the segment within 2 km radius of the well. Two aquifer parameters (transmissivity and storativity) are used for calculating the streamflow depletion. Field tests can be used to measure these parameters but observations are not available for all necessary locations. We used Random Forest statistical techniques to estimate the aquifer parameters at unmeasured locations. Results of the streamflow depletion model are displayed using an interactive application (app). The model can be used to obtain timeseries of cumulative stream depletion at any location in the river network from many spatially distributed abstractions.
How to cite: Rajanayaka, C., Booker, D., and Yang, J.: Estimating cumulative catchment streamflow depletion from abstractions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1803, https://doi.org/10.5194/egusphere-egu21-1803, 2021.
Groundwater fluctuation in coastal aquifers depends on a number of processes which interact with each other in a complex way. In this work, we analyzed the response of the groundwater’s quality and quantity indicators of Troia costal aquifer to several forcing factors. Troia peninsula is underlayed by a multi-layer aquifer consisting of an upper phreatic layer freshwater porous aquifer, a salt water sandy layer with interbeded clay lenses and a deeper semi-confined karst aquifer. This study focuses on the upper aquifer region (10m depth), where influences of oceanic and atmospheric drivers are expected to be strongest. Groundwater data was collected from a borehole located approx. 200m from the shoreline. Hourly records of the piezometric level, conductivity, and temperature data from the hydrological year 2006-2007 were related to data of barometric pressure, rainfall and tides using correlation and singular spectral analytical methods. All variables (precipitation, barometric pressure and tidal cycles) uniquely affect the groundwater’s level and quality with different magnitudes and time scales. Regarding the long-term and larger scales, precipitation seems to be the most influential factor, contributing to 46 % of the variability of the groundwater time series. This percentage of variabillity is due the seasonality of the water cycle, with 29% related to the semi-annual cycle and 17% related to the quarterly cycle. The barometric pressure seems to affect the groundwater in similar scales as the precipitation, however tidal cycles have a much smaller impact. The tidal data was modelled with WxTides software with an interval of 15 minutes. The cyclic patterns of semidiurnal and fortnightly tidal-induced sea level changes can clearly be observed in the records of the groundwater level throughout the entire time series. Tides and groundwater level present a maximum positive correlation coefficient of 0.58 in the month of August, when other forcing factors, such as precipitation, are the lowest. Groundwater level displays a 16-day time lag with the precipitation, a two-day time lag with the barometric pressure and a two-hour time lag with the modelled tides. The correlations and lags found in this study are being used as a basis for ongoing research on the complexity of groundwater level oscillations in littoral zones. The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.
How to cite: Juchem, M., da Conceição Neves, M., and Dill, A.: Processes influencing groundwater in the coastal aquifer of Troia Portugal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13475, https://doi.org/10.5194/egusphere-egu21-13475, 2021.
River-Aquifer Interaction is a natural and complex phenomenon for understanding its physical dynamic processes. These interactions highly vary with time and space and are to be investigated at river reach scale. The present study aims to understand and quantify the spatio-temporal variations of river-aquifer interaction process in Kosi river basin, India. This basin is majorly dominated with agricultural lands and irrigation requirement of the crops are mostly met by groundwater. In order to quantify the river-aquifer exchange flux at reach scale, a physically based sub-surface hydrological model has been carried for the study area. For this purpose, high resolution remotely sensed evapotranspiration data and groundwater recharge (estimated using soil water budget method method) along with other aquifer parameters were utilized for simulating the monthly groundwater levels as well as exchange flux between river and aquifer. The model results showed that simulated groundwater levels were well calibrated and validated with measured groundwater levels. Further, this calibrated groundwater flow model has been used to quantify the river-aquifer exchange flux. Based on the obtained exchange flux values, three different interaction zones were identified from upstream (Kosi barrage) to downstream (confluence point with Ganga river) in the study reach. It is observed that the river mostly loses water to the aquifer (as influent) in Zone I (80km from upstream) and the river mostly gains water from the aquifer (as effluent) in Zone III (40 km above downstream to confluence point). Whereas, the river has a combination of both losing and gaining natures in Zone II (between Zone I and III). From this study, it can be concluded that use of satellite remote sensing inputs (groundwater recharge and evapotranspiration) in the sub-surface hydrological model, facilitated to improve the assessment and understanding river-aquifer interaction process in an alluvial River basin.
How to cite: Laveti, N. V. S., Kartha, S. A., and Dutta, S.: Investigating of River-Aquifer Interactions using Sub-Surface Hydrological Model and Remote Sensing Inputs in an agriculturally Dominated Kosi River Basin, India., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14106, https://doi.org/10.5194/egusphere-egu21-14106, 2021.
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