Fertilizing the land, lagoons, and sea: A first look at human impacts on the Nile Delta fishery, Egypt
The primary focus of this dissertation is to look more closely at the influence of anthropogenic nutrients on the recovery of Egypt's Nile Delta fishery since the mid-1980's. Up to half of Egypt's fish production has come from four large coastal lagoons, which receive large amounts of nitrogen (N) and phosphorous (P) rich agricultural drainage. In Chapter 1, I provide some of the first evidence supporting a previously theoretical model that links increasing nutrient concentrations to fishery yields. Using data compiled from the literature, fish landings in the four lagoons increased with increased nutrients up to a peak at approximately 100 μM dissolved inorganic nitrogen, beyond which they declined dramatically. In the second chapter, stable isotope data (δ15N, δ13C) from fish were compared among and within the lagoons. There was a strong positive correlation between mean δ15N values of fish and estimated water residence time among lagoons, suggesting that nitrogen cycle transformations are more important than primary source δ15N signatures in determining δ15N values of lagoon fish. In the third chapter, stable isotope values of fish from inshore, offshore of the delta, and west of the delta were determined. All offshore fish had heavier δ 13C values than inshore fish, reflecting the incorporation of marine phytoplankton. In contrast, the δ15N values of the fish inshore and immediately offshore of the delta were similar, suggesting that the primary N sources were the same. Offshore fish from west of the delta were much lighter (about 5‰). As water moves from west to east in this region, the western fish represent unimpacted δ15N values while those offshore of the delta reflect anthropogenic N. Results from a simple two end-member mixing model suggest that 80% of the N in the fish captured offshore of the Nile Delta is from this land drainage. It is not known how sustainable this offshore "artificial fishery" will be for the long term, as results addressed in Chapter 1 suggest that, at some point, increasing nutrient loads may eventually contribute to the fisheries decline. ^
Biology, Oceanography|Agriculture, Fisheries and Aquaculture
Autumn Jean Oczkowski,
"Fertilizing the land, lagoons, and sea: A first look at human impacts on the Nile Delta fishery, Egypt"
Dissertations and Master's Theses (Campus Access).