Freshwater ecosystems are highly threatened by agricultural practices due to pesticide and herbicide runoff, which can have a strong effect on aquatic invertebrate communities due to them being sensitive to environmental changes and water quality. The influence of agriculture on aquatic ecosystems has been studied at length in temperate regions, but the consequences of this practice have not yet been explored in tropical regions. The purpose of this study is to compare the abundance and diversity of aquatic invertebrates between agricultural and non-agricultural (or naturally wooded) streams in Costa Rica to determine how agricultural practices influence aquatic invertebrate communities in the tropics.
This experiment was conducted at the Alberto Manuel Brenes Biological Reserve in Costa Rica, which includes 7,800 Ha of unaltered forest, but the area surrounding the reserve has experienced an intense increase in agricultural practices. In August, 2016, samples were taken on 3 separate dates at 6 streams within the reserve and 3 within the agricultural land. Streams were scored using the Biological Monitoring Working Party Method developed in Costa Rica. Both indicator score (p=0.004) and indicator category (p=0.002) were significantly different between agricultural and non-agricultural streams. While the diversity of the non-agricultural streams was higher than the diversity of the agricultural streams (p=0.026), the abundance between treatments was not significant (p=0.321). While diversity was significantly different between treatments, abundance was not, indicating that it is not the amount of invertebrates but the type that indicates stream quality.