Anthropogenic nitrogen pollution in mangrove ecosystems along Dar es Salaam and Bagamoyo coasts in Tanzania

Abstract

Mangroves are among the most productive coastal ecosystems; however, they are prone to anthropogenic pollution due to their land-sea interface position. We used stable nitrogen isotopes and spectrophotometric nitrate analysis to study the anthropogenic pollution in five mangrove ecosystems in Tanzania, including two polluted (Mzinga and Kizinga), one moderate (Kunduchi) and non-polluted (Mbegani and Ras Dege) sites. Also, we tested the suitability of mangrove leaves, roots, sediment, and gastropod as indicators of anthropogenic nitrogen pollution using stable δ15N isotope analysis. Results revealed higher than 10‰ δ15N values in all analysed components and the highest nitrate concentrations of 16.44 mg L−1 in the interstitial waters at the polluted sites, indicating anthropogenic nitrogen inputs. The δ15N enrichment increased in the order: non-polluted < moderate < polluted. The polluted sites are fed by freshwater creeks and probably receive high loads of domestic sewage from the surrounding communities, industries, and agricultural effluents. Therefore, to protect mangrove ecosystems, proper waste and wastewater management upstream are recommended.