Diagnosis of the Land Cover/Use Effect on Nutrient Discharge from Three Biobio River Sub-Basins

Water is an essential resource for developing several human activities. The increase in nutrients transport to surface waters is one of the leading factors promoting water quality loss; mainly caused due to land-use changes. In this study, the contribution of nitrogen and total phosphorus to the surface water bodies in three sub-basins of the Biobio River dominated by native forests, forestry, and agriculture are compared. Nutrient sampling points were taken at each sub-basin during the summer of 2013 and 2014; obtained results were compared using the Mann-Whitney statistical analysis. Noticeable differences in total nitrogen concentration were observed between the sub-basins with agricultural and forestry dominance in summer 2013. Additionally, significant differences in the total nitrogen concentration are reported in the sub-basin dominated by agricultural coverage when compared to those dominated by forest lands and native forests in 2014 summer. No significant differences were found between the sub-basins of the Biobio River for the study period in the total phosphorus records. The study depicts that different soil covers play an important role in the total nitrogen retention, however, in the case of total phosphorus, results suggest that concentration is given by geological factors.