S28

Water quality along the Ganga is critically impacted by multiple stressors, including agricultural, industrial and domestic pollution inputs, a lack and failure of water and sanitation infrastructure, increasing water demands in areas of intense population growth and migration, as well as the severe implications of land use and climate change. We report the findings of a collaborative effort to monitor the evolution of emerging and legacy pollutants along the 2500 km length of the Ganga and its major tributaries that was carried out over a six-week period in 2019 by three teams of more than 30 international researchers from 10 institutions. Surface water and sediment were sampled from more than 80 locations along the river and analysed for organic contaminants, nutrients, metals, pathogen indicators, microbial activity and diversity as well as microplastics, integrating in-situ fluorescence and UV absorbance optical sensor technologies with laboratory sample preparation and analyses. Water and sediment samples were analysed to identify the co-existence of pollution hotspots, quantify their spatial footprint and identify potential source areas, dilution, connectivity and thus, derive understanding of the interactions between proximal and distal of sources of solute and particulate pollutants.

Our results reveal the co-existence of distinct pollution hotspots that coincided for different contaminant groups but not others (e.g., microplastics). Interestingly, the downstream footprint of specific pollution hotspots from contamination sources along the main stem of the Ganga varied between contaminants bearing significant implications for the spatial reach and legacy of pollution hotspots. Furthermore, the comparison of the downstream evolution of multi-pollution profiles between surface water and sediment samples support interpretations of the role of in-stream fate and transport processes in comparison to patterns of pollution source zone activations across the channel. In reporting the development of this multi-dimensional pollution dataset, we aim to stimulate a discussion of the value of large river network surveys to better understand the relative contributions, footprints and impacts of complex pollution sources for integrated approaches in water resources and pollution management.

How to cite: Krause, S. and the Team SAPTANADI: Taking the pulse of mother Ganga – The evolution of water pollution along the Ganges River, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-93, https://doi.org/10.5194/iahs2022-93, 2022.

Ecological study of Mediterranean wetland: Sediment dynamics and blue carbon storage

Aya Hammami¹, Kerim Ben mustapha¹, Oula Amrouni ¹, Amjad Kallel²

¹ University of Carthage, National Institute of Marine Sciences and Technologies, LR16INSTM04,2025, Tunis, Tunisia

² University of Sfax, National School of Engineering, 3038 Sfax, Tunisia

                   Abstract

The aim of this study is to monitor the sediment dynamic and to estimate the percentage of carbon sequestered by macrophytes in the coastal lagoon of Ghar El Melh, Gulf of Tunis Mediterranean. A total of 21 surface sediment samples were collected during the winter campaign, completed by a second floristic campaign in April 2021 for the identification of the spatial distribution of the phanerogam Posidonia oceanica. The results showed that the lagoon is characterized by two types of sedimentary facies: dominant silty facies (65%) with an average size D50 which varies from 4.3 µm to 8.7 µm and sandy facies (35%) with an Mz grain sized ranges from 2Φ to 3Φ. The mineralogical identification of the lagoon sediments shows the presence of a biogenic calcium carbonate (CaCO3) :4% to 100%. The rate of organic matter OM: 2% to 11%. Sedimentological and mineralogical analysis of the coastal lagoon shows the coupled origin of sediment supplies. At the level of the banks of the lagoon, the silty facies enriched in carbonated fraction are allochthonous via the fluvial yields of the lower valley of Medjerda. The muddy deposits in the center of the OM-enriched lagoon are formed by the phytoplanktonic primary production of zooplankton, indicative of bacterial activity in the water column. Floristic investigation of the coastal lagoon reveals the presence of the Posidonia oceanica species in sandy areas. The average carbon capture rate of Posidonia in the lagoon is estimated to be ~15.6 t/ha. Nevertheless, Posidonia meadows are absent in central areas and adjacent to urban areas, characterized by muddy facies with a relatively high level of organic matter.

Key words: Ghar El Melh lagoon, phanerogams, blue carbon, Mediterranean, Ecohydrology.

How to cite: Hammami, A., Ben mustapha, K., Amrouni, O., and Kallel, A.: Ecological study of Mediterranean wetland: Sediment dynamics and blue carbon storage, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-161, https://doi.org/10.5194/iahs2022-161, 2022.

The coastal lagoon system is undergoing pronounced shoreline retreats and floods as a consequence of the ongoing sea level rise resulting from global warming. The aim of this study is to assess shoreline changes, land use occupation and to evaluate socioeconomic vulnerability in the urbanized coastal lagoon in Ghar El Melah, Tunisia in central Mediterranean. Methods are based on the diachronic shoreline changes monitoring from satellite scene, aerial photograph, topographic, and bathymetric maps during the period 1882, 1936, 1974 and 2021. Shoreline movement is acquired according to the statistical Digital Shoreline Analysis System (DSAS) from 1882 to 2021 data sets. Land use classification was established from supervised algorithm using multiple satellites scenes of Landsat 5 (1985) and Landsat 8 (2021). The Socioeconomic Vulnerability Index (SVI) is calculated from five socioeconomic parameters: (1) population density, (2) land use, (3) coastal fishing (4) road network and (5) settlement. Our results reveal alarming erosion of the sandy barrier with a maximum value of Net Shoreline Movement (NSM) − 1580 m (± 6 m) between 1882 to 2021. Temporal classification of the Ghar El Melah landscape from 1985 to 2021 revealed the extended urban class over the lagoon internal ridge from 5.4% to 14 % respectively. Whereas the vegetation crops are decreasing by 10%. The statistical coastal (SVI) map reveals that 87% of the lagoon area are characterized by high to very high vulnerability (class 5). These high coastal vulnerabilities risk is primarily induced by the extensive land occupation since the last few decades.

How to cite: Hzami, A., Mahé, G., Amrouni, O., and Missaoui, H.: Socioeconomic vulnerability of a Mediterranean coastal lagoon : case of Ghar El Melah, Tunisia, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-195, https://doi.org/10.5194/iahs2022-195, 2022.

Coastal wetland ecosystems are complex environments subject to physical factors and multiple yield supplies. The climate change impacts are strongly visible in those low-lying areas, in close relationships with the decrease of the continental water and sediment supply, marine storms and submersion. To understand the interactions between the coastal components we adopt the ecohydrology approach for a lagoon ecosystem in North Africa. The ecohydrology approach is based on as a compeling of well-experimented data as the sediment dynamics, the hydrology of the watershed basin and the coastal aquifer, and the biodiversity and the remote sensing observations in relation with the socioeconomic activities. The ecohydrology concept is focused in our research on the coastal ‘hot spot’ areas on the deltaic-lagoon and sandy barrier areas identified as very highly vulnerable to the sea level rise and marine disasters. The main goal is to establish a shared database and an innovative Nature Based Solution with the regional communities to enhance the coastal resilience and to better explore the aquatic resource for a sustainable blue economy, in the context of rapid environmental changes in the Mediterranean arid-regions, driven by both climate change and anthropogenic negative impacts on natural landscapes.

How to cite: Amrouni, O., Heggy, E., and Mahé, G.: The ecohydrological approach for Integrated Vulnerable Coastal Zone Resilience in arid regions, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-208, https://doi.org/10.5194/iahs2022-208, 2022.

The Suez Canal is a major bottleneck of global shipping. The stranding of the Ever Given, one of the world's largest container ships, in early 2021 showed how much global supply chains depend on the Suez Canal. The canal navigability directly depends on the incoming fluxes of sediments, either through the entrance on the Mediterranean Sea or from smaller tributaries along the canal. Here we model the hydrodynamics of the southeastern Mediterranean Sea, Suez canal and northern Gulf of Suez with the multi-scale ocean model SLIM (www.slim-ocean.be). The model can locally achieve a resolution of about 50 m and hence explicitly describes the flow through the narrow branches of the canal. The hydrodynamic model is then used to drive a sediment transport model that represents the dynamics of several types of sediments originating from the Nile delta, from shorelines along the Mediterranean Sea, and from inland channels connecting the Nile to the Suez Canal. Model results allow us to estimate the sediment deposition rate within the canal under present and future climate, and for different land and river management scenarios. The latter include the impact of existing and future dams along the Nile River and irrigation practices within the Nile Delta. Our result suggest that the Nile River management directly impacts the Suez canal navigability. This interconnection between the Nile River and the Suez Canal calls for an integrative management strategy. 

How to cite: Hanert, E., Randresihaja, R., Amrouni, O., Hzami, A., S. Fouad, S., and Heggy, E.: Assessing sediments export from the Nile to the Suez Canal and the associated risk to global shipping, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-227, https://doi.org/10.5194/iahs2022-227, 2022.

The city of Cotonou (Benin) in the delta of the River Ouémé and the city of Lomé (Togo) closed to the River Zio and depending lagoons have hydrosystems include aquifers and urban ecology under pressure of annual floods and discharge. So, bad sanitation and hygiene, poor physicochemical and bacteriological groundwater quality and occurrence of health risks (malaria, gastroenteritis, diarrheal) are observed ecohydrological characteristics. Well water quality data, sanitation and hygiene related public health data linking to the flow data of referred rivers are used to highlight a complexity of the ecohydrological state of the cities. With regard to the global agenda 2030 specifically the SDG 3, 6 and 11, an ecohealth model was developed to contribute in improvement of well water quality and to promote sustainable healthy living in the study area. Elaborated ecohealth model supports pathways on how improved human health could be attained from better groundwater and waste management in the whole west African coastal cities. In Cotonou and Lomé, recurrent floods, controlled by hydrological variation on the depending river basin affects urban ecology and human settlements. The footprint of the interactions is deterioration of environment patterns, of groundwater quality and higher prevalence of waterborne diseases. Referring to knowledge on public health (current and expected status), the model ecohealth is generated by establishing a relationship between floods, aquifers (hydrosystem) and sanitation and hygiene systems (disposal). Given that the urban population faces problems of unsafe sanitation and hygiene, and well water quality degradation, adequate information-education-communication (IEC) for social change approach was used to help in adoption of socio-ecological sanitation systems for water security and its accessibility. Dry toilets, above ground and watertight pit latrines and polyethylene septic tanks are the proposed sanitation disposals. Effective implementation of developed ecohealth model could have great social impacts and help in sustainable well-being in the coastal West African cities.

Keywords: River delta, coastal city, groundwater quality, floods, ecohealth model 

How to cite: Totin Vodounon, H. S., Houédakor, K. Z., Amoussou, E., Odoulami, L., and Makoutodé, C. A. A. P.: Ecohealth model for groundwater quality improvement on the coastal cities of Cotonou and Lomé in West Africa, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-596, https://doi.org/10.5194/iahs2022-596, 2022.