Relationship between land use and Ohio stream fish diversity

Background/Question/Methods

Stream habitats are highly influenced by watershed land use. Agricultural land use increases nutrient concentrations in streams and may increase algal biomass or affect algal community composition. This may have a positive bottom-up effect on the stream productivity. However, changes algal community composition towards less edible species may negatively affect herbivores, with potentially minor effects on other trophic guilds. Do fish at different trophic positions respond differently to changes in stream structure engendered by changing land use? To analyze this question, we used water quality and land use data to model fish abundance, first by species and then by trophic position, using long-term monitoring data from the Ohio Environmental Protection Agency’s Fish Database and the USGS Land Cover Institute. Predictor variables were chosen as indicators of agricultural land use and other anthropogenic influences.  

Results/Conclusions

Land cover composition and nutrient concentration were both strong predictors in fish abundance across all trophic positions. Higher nutrient concentrations did not increase herbivore densities. Instead, the abundance of a tolerant and ubiquitous herbivorous fish (Campostoma anomalum) was negatively correlated with nutrient concentrations, indicating that detrimental effects of such land use outweigh any potential increase in food availability. The abundance of most common fish species was negatively correlated with ammonia concentration and unimodally related to stream phosphorus concentrations. With current data, we cannot determine which negative effects reduced herbivore densities, and these effects may vary by species. Overall, species responded in a highly individualistic way to land use and water quality patterns.