LB 17-148 - The impact of water quality on aquatic ecosystem services dependent livelihoods and water hyacinth expansion using the InVEST model: A case study in the Gumara River of Lake Tana basin; Ethiopia

Aquatic ecosystems provide valuable ecosystem services to surrounding communities, including serving as habitat for fisheries. The Lake Tana basin, including the Gumara river and its associated wetlands in Ethiopia, has experienced rapid environmental change in the last several decades and is a compelling case study for understanding how changing nutrient export might be contributing to the rapid degradation of the Gumara River and Lake Tana through the expansion of water hyacinths and declines in fish biodiversity and yields. The aim of this research is to characterize patterns in the status of water quality and the impacts of human modifications and climate change on nutrient retention ecosystem services dependent livelihoods in the Gumara River and connected floodplain wetlands of Lake Tana basin, here we (1) examine trends in surface water chemistry,, watershed land use/ cover change, fish yield/diversity, and flow alterations; (2) estimate the Nutrient Delivery Ratio (NDR) as a metric of watershed nutrient retention using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model integrated with Optimization Software Toolkit for Research Involving Computational Heuristics (OSTRICH) for calibration; and (3) examine relationships between trends in water quality and fishery yields as well as water hyacinth infestation extent in Lake Tana. The surface load and export of both phosphorus and nitrogen from the Gumara River watershed were nearly stable between 1986 and 2009, but export abruptly increased between 2014 and 2019 by 88% for P and 99% for N. Some potential factors driving this increase include an expansion in irrigation agriculture, land conversion to eucalyptus plantations, decreases in dry season flow, and an increase in the magnitude of total precipitation after 2009. The increase in nutrient export in the Gumara river correlated with the decline in fish species; r=-0.96. whereas, it has happened to cause expansion of water Hyacinth in the Lake Tana. The overall prevailing relationships of watershed ecological processes to water quality changes and decline in fishery provide information to decision makers and the riparian community in managing aquatic ecosystems.