High Nitrogen and Phosphorus Concentrations in Human-Impacted Soil and Surface Runoff Negatively Affect Water Quality at Momella Lakes, Tanzania

Human land use in catchment areas has become a global concern due to its profound effects on water quality degradation. Associated eutrophication and algal bloom outbreaks in aquatic ecosystems pose an increasing threat to species that rely exclusively on water for foraging and breeding. In soda lakes, harmful algal blooms have caused fatal effects on lesser flamingos (Phoeniconaias minor), which are obligatory filter feeders and vital bio-indicators. However, little is known about how human land use affects nitrogen (N) and phosphorus (P) levels in soil and surface runoff at a watershed scale, particularly in human-dominated areas bordering the eastern African soda lakes. We aimed to understand how these levels differ between protected and unprotected land and how they might affect lesser flamingo foraging sources. We analyzed 72 surface soil and 13 surface runoff samples for N and P concentrations along valleys that potentially drain water into the Momella lakes, northern Tanzania. We found a higher soil P concentration in unprotected than in protected land, and at both sites, soil N and P concentrations were negatively related to slope. Water P concentrations in surface runoff from the unprotected land exceeded the United States Environmental Protection Agency recommended threshold (