During the summer of 2007, the entire Pomme de Terre Watershed was the subject of the Minnesota Pollution Control Agency's (MPCA) Phase I intensive monitoring. This project measured water chemistry and biological diversity throughout the entire watershed. Two reaches of the Pomme de Terre have been listed as impaired for aquatic life by scoring low in the fish bioassessment. The two reaches are from Barrett Lake in Grant County down to Perkins Lake in Stevens County. The other reach is from Swift County Road 20 down to the confluence with the Minnesota River at Marsh Lake southwest of Appleton.
During the next two summers, these reaches will be the subject of phase II biological monitoring to try to document and determine what are the potential stressors on the stream and their sources.
The goal of this monitoring is to try to distinguish between naturally occurring variation and changes caused by human activities. To assess the biological condition of surface waters, the MPCA uses a multi-metric approach called the Index of Biological Integrity (IBI). Fish, insect and plant life in the stream is analyzed. This index is a scientifically validated tool using attributes of a biological assemblage related to species diversity, community composition, and reproductive function, tolerance to human disturbance, species abundance and condition.
Phase II monitoring measures and evaluates the condition of rivers and streams by studying not only water chemistry, but also fish, aquatic invertebrates, insects and plant life. Fish are sampled with the aid of electro shock equipment. Biologists then identify and release the fish. Invertebrates are collected using nets so species can be identified and tallied.
In addition to the water chemistry and biological sampling, detailed longitudinal and cross sectional stream bed mapping using laser surveying equipment is done. Bed load sampling is done to measure the composition of the stream bed, and isotope analysis of water samples are conducted to better determine how water moves through the system.
Each metric in the IBI denotes a measurable attribute of the biological assemblage that changes in a predictable way with varying levels of human influence. For example, carp or bullhead, species considered tolerant of some form of human disturbance like sedimentation could form a "tolerant" metric-degraded site which would tend to have more of these tolerant species.
Ratings are assigned to each metric and summed together; the resulting score characterizes the biological "health" of the site. A high IBI score indicates the creatures in the stream are similar to a minimally impacted (reference) site of comparable size and type in the same geographic region. A low IBI score indicates the stream is significantly different or degraded compared to a regional reference site.
In the past, chemical monitoring has been the traditional mechanism for assessing the condition of surface waters. These traditional tests include criteria such as nitrate and phosphorus levels, suspended sediment, and turbidity levels, dissolved oxygen, temperature and pH readings.
However, human actions impact a wider range of water resource attributes than water chemistry alone can measure. The degradation of Minnesota's surface waters can be attributed to a multitude of sources including: chemical pollutants from municipal and industrial discharges, agricultural runoff of pesticides, nutrients and sediment, hydrologic alterations from stream channelization, dams and artificial drainage, and habitat alteration from agricultural, urban and residential development.
Biological communities are subjected to the cumulative effects of all activities and are continually integrating environmental conditions over time. They represent the condition of their aquatic environment. Biological monitoring is often able to detect water quality impairments that other methods may miss or underestimate. We want to collect information about the watershed to link the poor fish IBI scores to the stressors in the system.
Shaun McNally is the Pomme de Terre Watershed Project Coordinator. He is located in the Stevens SWCD office in Morris. 320-589-4886 ext. 109.
The Pomme de Terre River Association maintains a website: www.pdtriver.org