Wetland Invertebrate Biomonitoring
Although wetlands comprise only about 6% of the earth’s surface, they are one of the most valuable ecosystems on the planet. Wetlands perform important ecological functions in flood control, water storage and purification, and provide critical habitat for wildlife such as birds, amphibians, reptiles, insects, mollusks, and other organisms. Almost half of federally listed endangered animals rely on wetlands for their survival, including over 50% of America’s protected migratory bird species. Wetlands also have a significant economic value, as many commercially harvested Pacific Ocean fish and shellfish species depend on wetlands and estuaries for food, spawning, or nursery habitat. But for centuries, wetlands were seen as wastelands and health hazards to be drained, dredged, filled, or otherwise obliterated, and more than half of the 200 million acres of wetlands that existed before European settlement have been destroyed. In the past few decades the significance of wetlands has been realized, and the U.S. EPA aims “…to achieve no overall net loss of the nation’s remaining wetlands and to create and restore wetlands, where feasible…” But replacing lost wetland acreage isn’t as simple as digging a hole in the ground and filling it with water. Can a wetland be restored if the entire watershed is altered? If one type of wetland is converted to another, does it still provide the same ecological functions? How does one measure the biological health of a wetland?
One way to answer these questions is to use biological assessment (bioassessment) tools. Bioassessment evaluates the underlying health of a body of water by measuring the condition of its biological communities, such as plants, amphibians, algae, diatoms, or invertebrates. If water quality is impaired, the structure of these biological communities changes in response to the impairments, based on individual species’ sensitivity or tolerance to the impairments. Aquatic invertebrates such as insects, worms, and crayfish are excellent indicators of water quality-they are an important part of the food web, have relatively limited mobility that confines them to water for most or all of their life cycle, exhibit a range of responses to human-induced stressors, and have a short generation time that allows changes in community structure to be detected rapidly. Invertebrates have been used successfully for decades in stream bioassessment, and many people are familiar with the idea that an abundance of pollution-sensitive insects indicates a healthy stream. Much less is known about invertebrate communities in wetlands, however, and invertebrate-based bioassessment tools are not yet available for wetlands in the Pacific Northwest.
The Xerces Society is working to develop an invertebrate-based bioassessment tool (IBI) for evaluating the biological health of wetlands in the Pacific Northwest. This project began with a pilot study in 2007, when Xerces staff analyzed the invertebrate community composition at thirteen riverine wetlands in Oregon’s Willamette Valley and identified several invertebrate community attributes that differed between most-impaired and least-impaired wetlands. In 2008, the project expanded to examine invertebrate communities at 24 riverine-type wetlands in the Willamette Valley. We examined 69 different attributes of the wetland macroinvertebrate community assemblages and were able to identify six that varied reliably with the level of disturbance and were applicable to both riverine-impounding and riverine-flowthrough wetlands. These six attributes constitute a preliminary invertebrate-based IBI for wetland bioassessment. In 2009 and 2010, The Xerces Society, in partnership with the Oregon Watershed Enhancement Board and the Division of State Lands, is further testing and refining this preliminary IBI, and examining its functionality in an additional HGM class of wetland (flats). Ultimately, we hope to develop a reliable, cost-effective invertebrate-based tool that can be used by groups engaged in wetland restoration or conservation projects, to help them determine whether their efforts are improving wetland quality.