This work is an attempt to evaluate the impact of the agrossystems on the quality of underground water reserves in a karstic hydrographic basin in the municipality of Colombo, part of the greater Curitiba, Parana state, Brazil.

The agrossystems system in this region revolves around intensive agriculture, geared toward commercial production, giving rise to the heavy usage of agrochemical which affect soil and water reserves. Among these chemicals, nitrogen was found to be the main pollutant, due to its mobility, and water solubility as nitrate, and consequent degradation of water quality. This because the karstic substratum presents dolines, faults and fissures that can lead to the entrance and circulation of pollutants in the aquifer.

This study was developed along two fundamental lines: (i) land vulnerability, as based on soil, landform and geological characteristics, and (ii) land occupation and use. It was defined and implemented weights to enable separation and ranking of different classes. This approach led to the generation of three maps: a map of land use and occupation, a map of land vulnerability, and an impact map which brings both types of factors together to predict areas of greater and lesser impacts.

The excess of nitrogen originating in horticulture was estimated, taking account the amounts used by farmers and the amounts extracted from crops produced over the course of a year. Nitrogen outflowing from rural households was also estimated.

Although, agriculture is the largest generator of nitrogen, water conservation in this area depends upon the ordering of activities and the disciplining of land occupation, avoiding land subdivision and urbanization.