HS2.2.4

Freshwater salinisation (FS) can be defined as the alteration of the salt concentrations and ion ratios in freshwater ecosystems. As evidence of the economic, environmental and societal impacts of FS mounts, the issue is receiving increasing attention from researchers, water managers and policy makers. A general consensus is emerging that FS is a global ecological and societal challenge that urgently requires effective management. However, there are still many unanswered questions that hamper our ability to make progress. In this talk I will tackle some of these questions. For example: Which human activities are contributing the most to FS in different regions of the world? How does FS interacts with other stressors (including climate change)? What is the effect of FS on trophic interactions and ecosystem functioning? Which are the economic costs and human health risks associated with FS? How should we monitor FS? Which technical and nature-based solutions are available to prevent and mitigate FS and to restore salinised ecosystems?

How to cite: Cañedo-Argüelles, M.: Freshwater salinisation: a global challenge with multiple causes and drastic consequences, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-710, https://doi.org/10.5194/egusphere-egu21-710, 2021.

Salinization of freshwater ecosystems due to seawater intrusion and/or man-driven activities (e.g. salt use as de-icers) has gained much attention in the last years as it may lead to the loss of important services aside the evident lessen of biodiversity.

As an easier way to deliver information on the potential ecotoxicological effects of increased osmotic stress in freshwaters, many studies used sodium chloride (NaCl) as a surrogate salt.  Despite, other ions are present in salt mixtures and, it has been suggested that ion-specific guidelines must be developed in order to construct more effective and environmentally protective frameworks. Yet, ecotoxicity data available for other salts is quite poor, outdate, and neglects the effects that may be caused to important ecological groups. A broader range of ecological groups and up-to-date information is urgently needed. Thus, this work aimed at: i) delivering new data on the ecotoxicity effects of other major salts sharing a common anionic form with NaCl (MgCl₂, KCl, and CaCl₂); ii) deriving hazard concentrations that protect 5% of population (HC₅) for each salt in order to compare and provide future working and discussion material intended to be integrated in the so long wanted ion-specific guidelines; iii) evaluating the suitability of other(s) salts as a substitute for NaCl, and that might constitute a more conservative approach for the protection of freshwater ecosystems; and, iv) within the perspective of climate-change associated sea level rise, induced salinization to compare the aforementioned HC₅ values with that obtained for natural seawater (NSW).

To our knowledge, we provide here median effective concentrations for MgCl₂, KCl, and CaCl₂ notreported before for two freshwater species: Brachionus calyciflorus (a filter-feeder) and Hydra viridissima (cnidarian). Furthermore, the following HC₅ (in mg Cl^-/L; and respective confidence limits at 95% and R² - curve fitness) were obtained: 0.56 (0.38-0.83; R²=0.92) for NaCl; 0.12 (0.02-0.88; R²=0.77) for MgCl₂; 0.26 (0.19-0.34; R²=0.95) for KCl; and 0.53 (0.32-0.82; R²=0.90) CaCl₂. These values indicate firstly that the lack of data points is reflected in the spread of the confidence limits and the lowest adjustment of the curve to the model (e.g., MgCl₂) but also that the integration of different species is of great relevance due to the broad inter-species variability; secondly, that ecotoxicity induced by KCl is lower than that induced by NaCl and so, KCl might be in the future proposed as a surrogate for NaCl, although ecotoxicity data must be largely expanded so that solid conclusions can be withdrawn. Finally, the comparison of the HC₅ here derived with those derived in previous works for NSW (1.17 and 6.64 mg Cl^-/L at sublethal and lethal levels) suggested that along with NaCl, also KCl might be used as a surrogate for NSW (with the cautions above mentioned).

This work aside from providing new data liable to be included in guidelines for the protection of freshwater systems, shows that this topic continues to require investment from laboratory (and field) research, but that this knowledge must be shared with regulatory agents and stakeholders, aiming accurate and targeted management actions.

How to cite: Venâncio, C. and Lopes, I.: An integrated perspective on salinization of freshwater ecosystems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7470, https://doi.org/10.5194/egusphere-egu21-7470, 2021.

Water resources are deteriorating across the world, which is of particular concern in water-scarce arid and semi-arid regions. Saline lakes often lack outflow, and are vulnerable to environmental change. When they start to shrink, salinity levels increase, due to evapoconcentration of salts in the reduced water volumes. This may harm the aquatic environment and limit the usability for humans. The associated exposure of their dry lakebeds may also bring severe regional problems of wind-blown saline dust and soil degradation. Although some of the world’s major cases of lake drying have been well studied, like the case of the Aral Sea desiccation, there is a lack of coherent assessments made at the global scale. Such assessments are critical for identifying vulnerable regions and main drivers of change, which may contribute to the prevention of future catastrophes. We here synthesise information on and analyse the desiccation status of 28 major saline lakes, each one of them having a surface area of ≥ 100 km² and salinity of ≥ 10 g·L^-1. They are geographically distributed over the world’s all continents, except Europe and Antarctica. In total, our results show that more than half of the world’s major saline lakes have dried up considerably in the last couple of decades. Out of these, 36 % are already, or are close to being completely desiccated. Preliminary analyses show correlations between original lake depth, lake bathymetry and resulting lakebed exposure from drying, suggesting that a lake’s general resilience to drying may be predictable. Our estimates further show that the world’s major saline lakes together contain 1177 billion tonnes of salt, of which 79 billion tonnes are currently in drying or already dried up lakes. If all of these lakes would desiccate, around 1 billion people are currently living within reach of saline dust storms that could spread from dry lakebeds.

How to cite: Jarsjö, J. and Thorslund, J.: Global drying of major saline lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15270, https://doi.org/10.5194/egusphere-egu21-15270, 2021.

Mine waters are a significant point source stressor for aquatic environments. Acid mine drainage has long been considered a big environmental issue, but recent studies suggest that the salinity of mine waters may also be harmful particularly to small, dimictic lakes which are abundant in the boreal region. The denser saline mine waters may cause a shift in the mixing regime of a lake, leading to a permanent stratification of the water column, i.e. meromixis. As the demand for raw materials increases, mining companies, policy makers, and environmental regulators need to be more aware of these harmful effects of saline mine waters. In this study, two lakes receiving drainage waters from closed copper-nickel mines are investigated. Lake Valkeinen and Lake Sortavalanjärvi are situated in Eastern Finland near the mines Kotalahti (active 1959–1987) and Laukunkangas (active 1986–1994), respectively. The waters from the mines have been managed according to the permit conditions and in the case of Lake Valkeinen are primarily discharged elsewhere. Nevertheless, the mixing regimes of the lakes have seemingly shifted to meromictic.

To study the present conditions of the lakes, water samples and in-situ water column measurements were collected seasonally. Lake Valkeinen was sampled in 2017 and 2018, and Lake Sortavalanjärvi in 2018. Inflowing and outflowing streams were also sampled at both locations. Element concentrations and other chemical properties were analysed from the water samples. The stability of meromixis under varying conditions in the lakes was modelled with MATLAB-based open source model code MyLake that was modified to account for the changing density caused by increased salinity. This was done using conductivity as an explaining quantity.  

The results suggest that the lakes are permanently stratified at present with a chemocline separating the circulating, well-oxygenated upper water (mixolimnion) from the non-circulating, hypoxic bottom water (monimolimnion). The maximum depth of both lakes is ca. 16 m and the chemocline is situated at the depth of 8-10 m with some seasonal shifting in both lakes. In Lake Valkeinen, electrical conductivity (EC) was ca. 500 mS m^-1 in the mixolimnion on all occasions and ca. 600 mS m^-1 or more in the monimolimnion. In Lake Sortavalanjärvi, EC was ca. 600 mS m^-1 in the mixolimnion and ca. 1200 mS m^-1 in the monimolimnion. pH was circumneutral, with a slightly lower pH in the monimolimnia of the lakes on most occasions. Main anions were S and SO₄ in both lakes, while main cations were Ca, Mg, Na, and K. SO₄ concentrations were 250-280 mg l^-1 in the deepest part of Lake Valkeinen and 520-640 mg l^-1 in Lake Sortavalanjärvi. The results from MyLake scenarios suggest that the meromixis would be sustained even if external load ceased completely and a change in prevailing wind conditions is the only factor that could significantly alter the situation. The elevated concentrations of the conservative elements inflowing from the mine area coupled with a favourable position of the lakes in relation to main wind directions seem to sustain the meromictic conditions in these lakes.

How to cite: Kehusmaa, K., Juntunen, J., Saarni, S., Österholm, P., and Kauppila, T.: Modelling the properties and stability of meromixis induced by saline mine waters in two boreal lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5118, https://doi.org/10.5194/egusphere-egu21-5118, 2021.

The increasing global effort to overcome the reliance on fossil fuels is driving the demand for ‘green’ metals such as lithium. This study aims to develop a repeatable and seamless workflow to track the mass of lithium from its source in the watershed surrounding South American salt lakes (“salars”) to the nucleus of the salar itself. The area of interest is in and around the Salar de Uyuni, Bolivia, the largest salt flat in the world. We aim to create an understanding of how Li brine deposits develop, where the water and solute comes from, how the brines are created and how does abstraction affect the mass balance within the salar. For this research, open source Earth observation (EO) data is analysed to support geological and hydrological research. We explore the potentials of EO data for several research aspects, such as (1) Jointing: it may influence fracture-flow of groundwater and also be significant in terms of surface-area for water-rock interaction, i.e. potentially increasing the ‘leaching’ rates of Li from the bedrock into the water; (2) Weathering: the degree and style of weathering may influence the liberation of Li from rocks into the water; (3) Distribution of clays: the distribution of clays that may restrict the liberation of Li from weathered rock, or may scavenge Li from passing water; (4) Water and moisture: the distribution of water-bodies and sources, including active streams, springs etc. We are building a groundwater recharge model having as input soil moisture content; (5) Geological structure: the presence of neotectonic faults that may disrupt the salar, as well as structures that may provide pathways for the flow of fluids; (6) Lithological mapping and classification: possible refinement of existing geological maps. This workflow will support the sustainable management of lithium in the region. Moreover, the provision of “fit for purpose” systems of tracking Li helps in filling gaps in existing methods to enable Li brines resources to be correctly reported.

How to cite: Rossi, C., Ford, J., Bayaraa, M., Bateson, L., Butcher, A., Petavratzi, E., and Huges, A.: Using Earth Observation to track lithium movements in the Salar de Uyuni region, Bolivia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12111, https://doi.org/10.5194/egusphere-egu21-12111, 2021.

Increased salinisation of surface waters poses growing threats to agro- and aquatic ecosystems around the world. One extreme example is Lake Urmia, in northwestern Iran, which is one of the largest hypersaline lakes. Due to anthropogenic and climate-induced changes, the salinity of Lake Urmia has reached a maximum level of 420 PSU in recent years. This high salinity has endangered the food web and biodiversity in the regional ecosystem and caused an ecological regime shift. However, salinisation processes in the lake have not been well-explored yet. To address this, a combination of in-situ and remote sensing observations along with a numerical hydrodynamic model was used to study the salinity dynamics of the lake. To simulate the water salinity distribution, a three-dimensional hydrodynamic model of the lake was developed based on Finite Volume Community Ocean Model (FVCOM) and validated using field data. Wind field, heat flux, precipitation, and surface water evaporation were constructed based on meteorological data. The PHREEQC inverse modeling was then applied to obtain the precipitation and dissolution rates of minerals species. Simulated results indicate that the sedimentation and dissolution of minerals have a significant effect on the salinity levels of the lake. Although brine discharges of rivers to the lake increase the salinity of the lake, the elevated salinity of the lake is dominantly caused by the salt precipitation/dissolution processes. The results of this study provide a better understanding of the impact of precipitation and dissolution mechanisms on salinity dynamics in saltwater bodies.

How to cite: Chamanmotlagh, F. and Safaie, A.: Drivers of spatio-temporal salinity distribution in a hypersaline lake, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10641, https://doi.org/10.5194/egusphere-egu21-10641, 2021.

Increasing population, growth of cities and intensifying irrigated agriculture in the world’s deltas promote the demand for fresh water resources, accelerating groundwater extraction. This, in turn, leads to sea water intrusion and salt water upconing, which threaten near-future water and food security. Proper water management in deltas requires precise knowledge about the current status of the deltas’ fresh groundwater resources, in the form of a groundwater salinity distribution. However, this knowledge is scarcely present, especially at larger depths. In this research, we applied three-dimensional variable-density groundwater model simulations over the last 125 ka to estimate present-day fresh groundwater volumes for several major deltas around the world. We also compared these to current extraction rates and estimated the time until in-situ fresh groundwater resources are completely exhausted (ignoring local-scale problems), partly leading to groundwater level decline and mostly replacement with river water or saline groundwater. In this presentation we will share our findings, for example which deltas’ groundwater reserves presumably are under stress.

How to cite: van Engelen, J., Oude Essink, G., and Bierkens, M.: The sustainability of fresh groundwater resources in major deltas around the world, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10738, https://doi.org/10.5194/egusphere-egu21-10738, 2021.

In coastal areas, seawater intrusion is a main driver of groundwater salinization and numerical models are widely used to support sustainable groundwater management. Sharp interface models, in which mixing between freshwater and seawater is not explicitly simulated, have fast run times which enable the implementation of parameter estimation and uncertainty analysis. These are essential steps for decision-support modeling, however their implementation in sharp interface models has remained limited. Few guidelines exist regarding which observations to use, and what processing and weighting strategies to employ. We developed a data assimilation framework for a regional, sharp interface model designed for management purposes. We built a sharp interface model for an island aquifer using the SWI2 package for MODFLOW. We then extracted freshwater head observations from shallow wells, pumping wells and deep open wells, and observations of the seawater-freshwater interface from deep open wells, time-domain electromagnetic (TDEM) and electrical resistivity tomography (ERT) surveys. After quantification of measurement uncertainties, parameter estimation was conducted with PEST and a data worth analysis was carried out using a linear approach. Model residuals provided insight on the potential of different observation groups to constrain parameter estimation. The data worth analysis provided insight on these groups’ importance in reducing the uncertainty of model forecasts. Overall a satisfying fit was obtained between simulated and observed data, but observations from deep open wells were biased. While observations from deep open wells and geophysical surveys had a low signal-to-noise ratio, parameter estimation effectively reduced predictive uncertainty. Interface observations, especially from geophysical surveys, were essential to reduce the uncertainty of model forecasts. The use of different types of observations is discussed and recommendations are provided for future data collection strategies in coastal aquifers. This framework was developed in the Magdalen Islands (Quebec, Canada) and could be carried out more systematically for sharp interface seawater intrusion modeling.

How to cite: Coulon, C., Pryet, A., and Lemieux, J.-M.: Parameter Estimation of a Decision-Support Seawater Intrusion Model Using Multiple Well and Geophysical Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6024, https://doi.org/10.5194/egusphere-egu21-6024, 2021.

Compound anthropogenic pressures are driving critical mangrove degradation worldwide, threatening the wellbeing of coastal human populations historically associated with these systems. The Ramsar and Biosphere Reserve, Ciénaga Grande de Santa Marta (CGSM) is located in the northern of Colombia and is the largest coastal lagoon-delta in the Caribbean. It is inhabited by stilt communities that have developed intricate livelihood and cultural relationships with the mangroves. The CGSM has experienced sustained social and ecological degradation during the last six decades, triggered by land-use change and disruption of hydrological connections. This study integrates Social-ecological Memory from fishing communities and Paleoenvironmental frameworks to develop a historical perspective of the biophysical and social dimensions of environmental change in the CGSM. Integrating X-ray fluorescence (XRF) geochemical sediment analysis, C¹⁴ radiocarbon dating, and demographic inferences from archaeological evidence revealed three distinct periods over the last ~5000 years where sea-level rise and hydroclimatic variability shaped the transition between freshwater to prevailing marine conditions and modulated human occupation patterns in the area. Specifically, the period with the highest hydroclimatic variability and precipitation minima (4000 – 2500 yr BP) is consistent with the lowest human population estimates, whereas sea-level increase (~ 2000 yr BP) corresponds with a sustained increase in estimated population growth. In connection, participatory oral reconstructions conducted in the stilt-house communities of Buenavista and Nueva Venecia, offered nuanced descriptions about the spatial, temporal, and contextual aspects generating and reinforcing hypersalinization of the system, and their profound social-ecological consequences over the past several decades. The interdisciplinary approach of this study indicates that the CGSM is a highly dynamic socio-ecological system that has been changing and reconfiguring across different time scales in response to both natural and human-induced processes. Finally, it reveals the relative effects of biophysical and social drivers on driving social-ecological change on millennial to decadal time scales.

How to cite: Gutierrez-Cala, L., Zúñiga, A. C., Gonzalez, C., Salgado, J., Saavedra-Díaz, L. M., Ricaurte, C., Zipper, S. C., and Jaramillo, F.: Looking for the present in the past: Paleoenvironmental analyses and Social-ecological memory to explore changes in the mangroves of the Ciénaga Grande de Santa Marta - Colombia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12908, https://doi.org/10.5194/egusphere-egu21-12908, 2021.

The secular change of ocean salinity is regarded as an indicator of the global water cycle by measuring the surface freshwater flux which is the most important component of earth hydrological budget. Under the effect of remarkable global warming, the surface salinity patterns in ocean basins illustrated that the intensified water cycle resulted in the continuous and significant freshening phenomena in tropical ocean. With the recent boom in salinity measurements and observations, the variability of surface salinity was examined to explore its relationship with anthropogenic warming. In this paper, we found that the salinity varied on the decadal to centurial time scales and responded significantly to the global warming in tropical Pacific Ocean by using the multi-source reanalysis datasets. An unexpected distribution was figured out and what is noteworthy is that, the robust salinification occurred in the central tropic Pacific in the first two decades of 21^st which was demonstrated by Argo observations. Nevertheless, it did not follow the typical salinity patterns that ‘wet get wetter’ mentioned by several literatures and illustrated a significant trend shift. Similarly, the subsurface ocean salinity revealed the same shift but an opposite tendency to that on surface. It may involve that the controlling influence of surface freshwater reduced and the impact of ocean thermodynamic adjustment became gradually pronounced to the upper ocean. The salinity budget suggested that salinity advection and subsurface entrainment played key roles to induce the reversed trend of salinity change. In addition, the isopycnals variability caused by wind-driven ocean pumping and subtropical gyre may be acted as a trigger of the salinity enhancement in the upper ocean. What’s more, the impact of PDO decadal shift and the moderate global warming was seemed to be the essential factors to change the feedback of ocean-atmosphere processes, potentially and was finally reflected on ocean salinity field.

How to cite: Shi, H. and Du, L.: The unexpected salinity trend shifts in upper Tropical Pacific Ocean under the global hydrological cycle framework, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14698, https://doi.org/10.5194/egusphere-egu21-14698, 2021.