Application of estuarine ecohydrology approach for Studying the key hydrological and ecological Processes of the Wami estuary, Tanzania

Abstract

This study was conducted in the Wami Estuary in Saadani National Park (SANAPA) to understand the key hydrological and ecological processes that influence the ecosystem functioning. It focused at the dynamics of water quantity, quality and their impact to the organisms, the fate of riverine nutrients and the role of the mangrove ecosystem. Data obtained from the fieldwork, laboratory analyses and secondary sources were used to assess the estuarine condition. The land-ocean Interaction in the Coastal Zone (LOICZ) and UNESCO- Estuarine Ecohydrology (UEE) models were used to study the nutrients processing within the estuarine food web, estimating the nutrients budget, the residence time and the net ecosystem metabolism (NEM). The results indicate the declining trend of freshwater flow to the estuary particularly during the dry season and increasing sediment loading that result to seasonal and tidal variations in the plankton community structure. Seasonal variations in salinity gradient indicate a highly stratified system and a well- mixed system during the wet and dry seasons respectively. The model results indicate the estuary shifts from an autotrophic, denitrifying, flushed in ~ 0.5 day and freshwater-dominated to a heterotrophic, nitrifying, flushed in ~ 7 days, marine-water dominated system from the wet to dry season. The presence of mangroves doubles the shrimp and phytoplankton communities. The mangroves trapped about 12% of the riverine sediments during the wet season while during the dry season the riverine sediment sediment inflow accounted for only 10% of the sediment trapped. The mangrove litter contributes to nutrient recycling whereby crabs recycled 57% of the mangrove litter, 32% was exported to the estuary and 11% remained to decomposed in the mangrove floor. The findings indicate that water quality parameters are within the acceptable levels recommended to sustain a healthy aquatic ecosystem. The study provides a scientific understanding of the Wami Estuary ecosystem functioning for proper management and decision-making process. It recommends an effective governance mechanism in the Wami River basin, emphasizing on sustainable use of water, and reducing sediment loading. Under the worst-case scenario, SANAPA should construct a water reservoir to serve for the estuarine ecosystem, wildlife, and people during the dry season.