Effects of Grass Seed Agriculture on Aquatic Invertebrate Communities Inhabiting Seasonal Wetlands of the Southern Willamette Valley, Oregon

Abstract

Wetland loss throughout the United States has contributed substantially to landscape fragmentation and loss in biodiversity. In Oregon’s Willamette Valley, only 1 % of native-wet prairie habitat still exists, though seasonal wetlands are still common. These hydrogeomorphic Flats wetlands predominately occur on privately owned and actively farmed lands. We studied these wetlands in spring of 2009 and 2010 in order to quantify and compare aquatic invertebrate communities in two agricultural land-use groups (annual and perennial-grass-seed fields) with native-wet prairie habitat. Community composition in native-prairie, including higher taxa richness and greater diversity, differed from farmed wetlands. Invertebrate densities did not differ among land-uses. However, biomass in perennial-grass wetlands was greater than in annual-grass wetlands both years, and during 2009, it was more than in native-prairie. Lower turbidity, lower conductivity levels, and greater availability of rooted vegetation in native-prairie habitat were conditions associated with differences in invertebrate composition among land-uses. Though invertebrate communities in farmed wetlands differed from native-prairie, the importance of these seasonal wetlands in an altered and fragmented Willamette Valley landscape speaks to their potential contribution for the region’s biodiversity and to their inclusion for management of agricultural lands.