Most of us care about whether or not our water is pure enough to drink. You may wonder if the pond near your house, or the river that runs through your city is healthy enough to support fish and other aquatic life. If you are reading this guide, you probably care enough to want some sort of tool or mechanism to determine just how healthy a body of water may be.

What is bioassessment?
Bioassessment, or biomonitoring, is the process of evaluating the health of a water body based on the life it can support. Water quality can also be monitored by taking a water sample and testing it for the presence of various nutrients, chemicals or pollutants.

Unfortunately, water may appear chemically pure but lack the diversity of aquatic life expected in a pristine habitat. The chemical characteristics of a water body alone will not necessarily reflect its biological condition. By looking at what kind of life a wetland can support, we can get a picture of its overall health. For example, a wetland may have high ater quality but poor diversity of species, due to the presence of an aggressive invasive species that is out-competing and displacing the native species. Biological assessment can be thought of as providing a motion picture of a habitat that integrates the cumulative effects of human activities on aquatic systems, while chemical monitoring alone is akin to a snapshot, recording only the information at a single point in time. It is important to combine a biological monitoring sampling scheme with chemical monitoring, along with an assessment of some of the physical characteristics to help you understand the condition of a wetland and how human stressors are affecting its ability to support life.

Why are invertebrates good water quality indicators?
Invertebrates are excellent water quality indicators because they are ubiquitous, relatively easily sampled, and abundant in most bodies of water. There is a wide diversity of invertebrates, each with a slightly different response to pollutants or other stressors that may be present in the water body.  Invertebrates have shown responses to stressors such as chemical pollutants, increased turbidity, changes in hydrology, input from stormwater runoff, invasive species, and nutrient enrichment, among others. Some invertebrates have very short life spans (i.e. a few weeks) and will reflect recent stressors more quickly; others can live for years. and will integrate stressors over time.

While there has been less research on the responses of wetland invertebrates to human impacts than on the responses of stream invertebrates, wetland invertebrates have the potential to be very good indicators of water quality. They have been used successfully, along with other biological assemblages (such as plants or amphibians), as bioindicators of wetlands in other parts of the country. Many wetland invertebrates are tightly linked to their habitat, completing their entire life cycle in a single wetland, and those taxa will integrate stressors in a specific wetland site.

There is a large body of literature available on the tolerance levels of stream invertebrates to various pollutants and stressors, and a growing amount of knowledge on the tolerance levels of wetland invertebrates (link to literature on wetland invertebrate tolerance). Since many of the same organisms found in streams can also be found in wetlands, some stream invertebrate tolerance information can be extrapolated and used for wetland invertebrates. However, many invertebrates that are considered tolerant in streams have that label because they can withstand low levels of dissolved oxygen. Wetlands can have highly fluctuating dissolved oxygen levels, including very low levels at times. Many wetland invertebrates have adapted to cope with low levels of dissolved oxygen, and these animals will be found in even the most pristine wetlands. Additionally, there is very little information available on tolerance of wetland specialists, such as water boatmen, fingernail clams, certain snails, backswimmers, etc. The EPA has an excellent database, compiled by Adamus and Gonyaw, summarizing the literature available on wetland invertebrates and their responses to a variety of stressors.

Wetland invertebrate bioassessment Scientists and citizen monitoring groups around the country have begun to monitor the health of their wetlands using invertebrates, diatoms, algae, amphibians and plants as indicators. States that have done substantial wetland biomonitoring include Minnesota, Maine, Ohio, Montana and Florida (literature on case studies). Other studies have been done in a variety of other states, although very little work has been done in the Pacific Northwest on using invertebrates as wetland bioindicators. The Xerces Society is currently involved in an effort to develop the use of invertebrates as a tool in wetland bioassessment in the Pacific Northwest, and conducted a pilot study in 2007.

The pilot study focused on macroinvertebrates in 13 riverine-impounding wetlands in the Willamette Valley of Oregon. The main goals of this project were 1) to test a single sampling method in one subclass of wetlands, 2) to characterize the macroinvertebrate community and 3) to evaluate the amount of variability that exists in that community among wetlands.