Linking water quality with agricultural intensification in a rural watershed

Agricultural intensification was linked to streamwater pollution in a case study watershed using GIS and nutrient budgeting techniques. The results showed that surplus nitrogen applications from fertilizers and manure averaged 120 kg ha(-1) yr(-1). In some parts of the watershed surplus applications exceeded 300 kg ha(-1) yr(-1). A consistent increase in pig and chicken numbers (59 and 165% increase between 1986 and 1996) is considered the main reason for the surplus. Water quality was impacted in two ways: nitrate contaminated groundwater contributed to high nitrates in a major tributary during the summer, while in the wet winter season ammonia, phosphate and coliform levels were high throughout the drainage system. Significant negative relationships were found between surplus nitrogen applications and dissolved oxygen while ammonia and nitrate concentrations during the wet season were positively correlated to surplus applications. Soil texture and drainage type were also significantly correlated with the water quality indicators suggesting that it is possible to use the budget/GIS linked techniques for pollution risk assessment from agricultural non-point sources.