Nitrogen and Phosphorus Dynamics in the Waters of the Great Ruaha River, Tanzania

Abstract

This study assessed the levels of nitrogenous (ammonia, nitrite and nitrate) and phosphate compounds in the water column in the Great Ruaha River (GRR) in response to natural and human pressures. Water were sampled using Teflon capped plastic containers and analysed using standard methods. High levels of ammonia were observed in the Mtera dam and low in the GRR and its tributaries as well as at Ruaha Mbuyuni. Nitrite levels were observed only in Mswiswi and Luwosi tributaries in the upstream and in the Mtera and Ruaha Mbuyuni in the downstream. High levels of nitrite were observed in the Mtera dam probably due to increased microbial activity. Levels of nitrates were high in the Mtera dam and in the Mswiswi and Lunwa tributaries and low in the Little Ruaha, Ruaha Mbuyuni and in other tributaries. Nitrate levels were increasing from the tributaries to the main river and later decreasing at Ruaha Mbuyuni probably indicative of some changes in land cover, land use, soil type and groundwater level. Observed levels of phosphate followed an irregular pattern and were relatively were high probably due to anthropogenic activities and absence of Ca, Mg, Al and Fe minerals that can precipitate phosphate. Levels of nitrogen and phosphorus in the GRR were lower than the US EPA and Health Canada set standards, indicative of a natural source. Principal Component Analysis (PCA) indicate that the nitrite and ammonia are so closely related to each other than to nitrate, indicating probably that most nitrites originate from the nitrification of ammonia than the denitrification of nitrate. Similarly, nitrate and phosphate were observed in the same principal component clearly indicative of the same source, which could be fertiliser application in agricultural fields. However, increasing agricultural and livestock activities as aggravated by increasing human population pose a threat on the future dynamics of the nitrogen and phosphorus in the area.