Land uses, Nitrogen and Phosphorus estimated fluxes in a Brazilian semi-arid watershed.

Abstract This paper presents the estimates of nitrogen and phosphorus loads associated with different land uses in a semi-arid watershed in the Brazilian northeast (NE). To calculate the annual loads and calibrate de estimates, we used emission factors related to natural processes and human activities from land uses and monitored the nutrient concentrations in surficial waters. The concentrations of TN were above the 2.18 mg N L−1 limit for lotic environments while the TP exceeded the limit value of 0.15 mg P L−1 established in the Brazilian legislation. The total loads L e N , P corresponded to 16,621 t N yr−1 and 3,211 t P yr−1 or 1,292 t N km−2 yr−1 and 250 t P km−2 yr−1. The anthropogenic emissions accounted for 82.1% of the N and 91.3% of the P emitted. The results for the Salgado river basin are lower than those estimated globally, but exceed the values obtained for the South American continent in an order of magnitude. The use of nutrient loads instead of concentrations, particularly in areas where detailed studies on nutrient concentrations are unavailable, such as in the semi-arid NE Brazil, may become a satisfactory approach to evaluate the sensitivity of aquatic systems to a further introduction of anthropogenic effluents. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]