SEER: The Role of Natural Versus Anthropogenic Factors in Assessing Ecological Risk in Agricultural WatershedsEPA Grant Number: R827784E02
Title: SEER: The Role of Natural Versus Anthropogenic Factors in Assessing Ecological Risk in Agricultural Watersheds
Investigators: Watzin, Mary C. , Gotelli, Nicholas J. , Hoffmann, James
Institution: University of Vermont
EPA Project Officer: Hunt, Sherri
Project Period: November 1, 1999 through April 30, 2002
Project Amount: $268,633
RFA: EPSCoR (Experimental Program to Stimulate Competitive Research) (1999) RFA Text | Recipients Lists
Research Category: EPSCoR (The Experimental Program to Stimulate Competitive Research)
Our overall goal was to develop a conceptual framework for watershed systems that can be used to predict where agricultural disturbances pose a significant risk to the stream community and where restoration activities have the greatest likelihood of success.
Objective 1 - Assess the influence of stream connectivity and adjacent land use on stream benthic macroinvertebrate and periphyton communities; Objective 2 - Evaluate colonization processes in natural and agriculturally influenced stream reaches to determine which factors might be most important in assessing the potential for recovery in damaged stream systems; and Objective 3 - specifically evaluate the impacts of phosphorus and suspended sediments on stream periphyton and macroinvertebrates using a manipulative field experiment.
To address Objective 1, samples were collected at 13 stream confluences with different mixes of land use during the summer of 2000. To address Objective 2, specially configured sample collectors were deployed in 2001 to sample drifting macroinvertebrates, macroinvertebrates moving through the hyporheic zone, emerging adults, and ovipositing adults in both agricultural and reference streams. To address Objective 3, a manipulative field experiment adding phosphorus, suspended sediments, and a combination of the two to experimental flumes deployed in a reference stream reach was conducted. Macroinvertebrates and periphyton were collected in the flumes over a 30-day experiment.
Our work documents increased densities of stream periphyton and macroinvertebrates at agricultural sites and a shift in species composition towards pollution tolerant taxa. It also shows that downstream communities are constantly receiving potential colonists from upstream reaches and that the diversity and abundance of the upstream macroinvertebrate colonists moving both as drift and through the hyporheos is influenced by land use, with generally more movement at agricultural sites. The high rates of movement and rapid colonization of new substrates suggests that when restoration provides appropriate substrate, recovery of stream communities may be rapid. Using a simple mixing model, we could predict the species composition expected in downstream reaches based on the relative abundances of taxa in the upstream reaches. Because discharge controls the delivery of drifting colonists, it explained a large percentage of the variation in the contribution of the upstream reaches. Those upstream reaches with a larger discharge contributed proportionally more to the composition of the downstream community. Land use of the upstream reaches was also important. In general, community composition below confluences reflected the total amount of agricultural land use upstream; however, sites with contrasting land use in upstream reaches had higher taxa richness than sites with uniformly undisturbed or uniformly agricultural land use in the upstream drainage area. Taken together, our results support a watershed approach to stream restoration. They suggest that restoration sites selected based on a full understanding of upstream land use and local habitat conditions will have the highest probability of success. If local habitat and water quality conditions are remediated, recovery of the biota should be rapid.