The goal of the study was to develop a method to estimate long-term variability of nitrate levels in the Aconcagua River watershed in Chile. The researchers used available data on hydrology, land use, and point sources from 1986 to 2006 to model nitrate concentrations. They found that the model accurately represented nitrate levels in the upper and lower parts of the watershed, but had limitations in the lower part. The study also developed criteria for optimizing monitoring stations and frequencies to improve water quality monitoring in the area.