Water: Monitoring & Assessment
7. Synthesis and Recommendations for Indicators
Bioindicators for Assessing Ecological Integrity of Prairie Wetlands
Report # EPA/ 600/ R-96/ 082
Determining the ecological integrity of a prairie wetland and diagnosing possible causes of impairment should involve monitoring of multiple indicators. In most prairie wetlands the possibility of ongoing or recent past exposure to excessive sedimentation is probably best indicated by species composition of algae and invertebrates, with emphasis on the epibenthic forms (taxa that live on the top surfaces of the sediment). Epibenthic and epiphytic algae and invertebrates are also useful indicators of excessive enrichment, removal of vegetative cover, and turbidity that is occurring either currently or during past years as determined by analysis of decay-resistant remains. Ongoing or recent past changes of water regime and salinity, as well as overgrazing, in individual wetlands are perhaps best indicated by vascular plant species composition. Longer-term changes in these factors can be inferred by examining seed banks and decay-resistant remains of invertebrates. Exposure to pesticides and heavy metal contaminants can sometimes be inferred from species composition of invertebrates and from various biomarkers in amphibians and birds. For bioaccumulative contaminants, tissues of individual plants and birds can be examined. Birds are also uniquely valuable for spatially integrating information on the hydrologic stresses to wetlands across entire regions.
Although the choice of indicators and sampling methods is vital to establishing monitoring programs, equally important are questions of how to interpret the collected data. Information provided throughout this document is intended to support data interpretation, and potentially diagnostic symptoms of the ecological integrity of prairie wetlands are summarized in Table 5.
Table 5. Symptoms of Changes in the Ecological Integrity of Prairie Wetlands, and Examples of Possible Causes
Responses of wetland communities to environmental change are extremely variable and difficult to interpret or predict. Following are some examples of symptoms that sometimes are associated with particular causes. Because of a generally poor understanding of prairie wetland variability, these examples are anecdotal, not definitive.
Plant species richness or number of functional groups (Boutin and Keddy 1993) is declining or is low relative to reference areas.
Plant species richness or number of functional groups is increasing or is high relative to reference areas.
Blooms of algae occur more often, for longer periods, and/or at atypical times of year.
Percent cover and stem density of emergents and associated epiphytic algae is relatively small or declining, coinciding with larger or increasing cover of submersed and floating-leaved species and (perhaps) phytoplankton and epipelic algae.
Percent cover and stem density of emergents extensive or increasing, coinciding with small or declining cover of submersed and floating-leaved species and/or phytoplankton and epipelic algae.
The number of species and dominance of algae, vascular plants, and/or invertebrates known to be characteristically tolerant of turbidity and sediment deposition (Appendices A, B) is increasing relative to species that are not, or is
Wetland is being exposed (or recently has been exposed) to contaminants, increasing or decreasing water levels, excessive nutrient or sediment inputs, or intense grazing.
Wetland is being exposed (or recently has been exposed) to increasing or decreasing water levels, moderate nutrient inputs, or moderate levels of grazing or other vegetation-thinning activities.
Nutrient loading of the wetland from external sources has increased recently, AND/OR
Enriched sediment or decaying vegetation is being reflooded following a drier period, AND/OR
Grazing, mowing, herbicides, or other factors have removed vegetation that formerly shaded the water column, AND/OR
Contaminants or other factors have reduced populations of zooplankton and other organisms that otherwise control algae by grazing.
Recent years have been wetter than normal, AND/OR
Wetland has recently been burned, mowed, tilled, treated with herbicides, or intensely grazed.
Recent years have been drier than normal, AND/OR
Wetland has not been disturbed by fire, tillage, or similar disturbance for many years, AND/OR
Water is very turbid due to sediment runoff, wind resuspension of bottom sediments, or previous algal blooms triggered by excessive nutrient inputs.
Wetland is being exposed (or recently has been exposed) to increasing runoff of sediment, shoreline erosion, resuspension of bottom sediments by wind or livestock.