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 sh owed that surplus nitrogen applications from fertilizers and manure average d 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 nu mbers (59 and 165% increase between 1986 and 1996) is considered the main r eason for the surplus. Water quality was impacted in two ways: nitrate cont aminated groundwater contributed to high nitrates in a major tributary duri ng the summer, while in the wet winter season ammonia, phosphate and colifo rm levels were high throughout the drainage system. Significant negative re lationships 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 ty pe were also significantly correlated with the water quality indicators sug gesting that it is possible to use the budget/GIS linked techniques for pol lution risk assessment from agricultural non-point sources.