Water quality condition monitoring - Long-term wetland monitoring

Since 1995, the Biological Monitoring Unit has been repeatedly sampling a small set of depressional wetlands located within each of Minnesota’s three main ecoregions. All of these sites are located within relatively stable land use settings, broadly categorized as urban, agricultural, or natural. Information gained from these sites is used to help determine whether any large-scale factors (e.g., climate, atmospheric deposition) are affecting the condition of Minnesota’s wetlands. Specifically, these sites are monitored over time (approximately every three years) using plant and macroinvertebrate IBIs to look for trends in the indicators. If indicators exhibit a similar pattern (increasing or decreasing) from year to year across the long term monitoring sites, then regional-scale factors in addition to any site specific factors may be influencing the condition of these sites. The results from long term monitoring sites can be used for a variety of purposes, including:

• Assess the influence of changing climate patterns on wetland condition
• Provide context (i.e., background conditions) for other monitoring activities designed to evaluate effectiveness of management activities or policies
• Assess variability of indicators through time
• Evaluate the need for re-calibrating indicators

For more information on the purpose and rationale for long term monitoring of wetlands in Minnesota see the following fact sheet:

• Long Term Depressional Wetland Monitoring Sites

Monitoring sites

A total of 18 long term depressional wetland monitoring sites have been established throughout the state.  Six sites are located within each of Minnesota’s three major ecoregions and these are monitored approximately every three years. Within each ecoregion sites have been located in areas representative of least-disturbed conditions (= natural) as well as agricultural and urban settings. These sites are semi-permanent to permanently inundated depressional wetlands that have a fringe of emergent vegetation as well as floating-leaved and submerged aquatic plant communities (i.e., marshes).

Methods

During each site visit biological, chemical, and physical information about the wetland is collected. The composition and structure of the plant community at each study site is characterized using releve sampling methodology. Releve sampling is a technique where an observer selects an area representative of the overall community to place a sampling plot (or multiple plots) where plant data can be quantified. Plots typically straddle the emergent/aquatic vegetation interface. Aquatic macroinvertebrates are also sampled from the emergent/aquatic vegetation interface using D-frame dip nets. Samples are collected by sweeping the net through the water column over a horizontal distance of approximately 1 m. Several sweeps at various locations within the wetland are collected and combined into a single sample. Two macroinvertebrate samples are collected in this manner during each site visit. Biological data are used to calculate separate plant and macroinvertebrate index of biological integrity (IBI) scores. These scores are then compared to results obtained from least-disturbed regional reference sites in order to assess the condition or ecological health of each long term wetland monitoring site.

Chemical and physical data collected from each monitoring site are used to evaluate the extent and severity of any environmental stressors that may be impacting the biological communities. For instance, if biological data indicate that a wetland is in poor condition, the chemical and physical measurements can be used to determine potential causes of the impairment. Water chemistry measurements include dissolved oxygen, temperature, specific conductance, pH, nutrients, chloride, and sulfate. Water clarity is also measured using a transparency tube.

For more details on the methods and equipment used to collect data at long term wetland monitoring sites see the following standard operating procedure (SOP) documents:

• Plants
• Macroinvertebrates
• Water Chemistry

Site reports

WMA = Wildlife Management Area (Minnesota Department of Natural Resources)
WPA = Waterfowl Production Area (US Fish and Wildlife Service)