See the Paper: Rice Creek: Differences in chemical properties and aquatic macroinvertebrate  populations between forested and agricultural sites

Photo from MN Pollution Control Agency

Background

Freshwater macroinvertebrates include insects that are in their larval or nymph (young) stages. Macroinvertebrates make excellent indicators of the health of an ecosystem, meaning that their abundance and diversity can help people assess the water quality of the location they are in. This is because they are an important part of the food web, recycling nutrients and providing food for other animals. Macroinvertebrates are also sensitive to pollutants, and the presence of certain species can indicate if there is agricultural runoff or other chemicals in the water. In general, a higher diversity of macroinvertebrates means a more healthy ecosystem. 

Rice Creek in Northfield is the only stream in Rice county that is home to native brook trout, and the health of this creek is of interest to many people. This creek drains approximately seven square miles of agricultural land, and there are concerns over the potential pesticide and fertilizer runoff impacting the health of the creek. In 2017, a St. Olaf student investigated if land use affected the health of Rice Creek. They compared the water quality of multiple sites at Rice Creek that were surrounded by forest or agricultural land. 

The Study

Sarah Bond (Class of 2019, B.A. Biology) surveyed macroinvertebrates at four sites along Rice Creek. Two sites were surrounded by forest and two sites were surrounded by agricultural land. Bond used a probe to take measurements of the dissolved oxygen, the temperature, the pH, and the conductivity of the water at every site three times over the course of October and November. 

The Findings

The study expected to find that forested sites would have higher diversity of macroinvertebrates. However, Bond found that there was a higher diversity of macroinvertebrates at the two agricultural sites. Ideal dissolved oxygen for brook trout is 11mg/L, whereas the average dissolved oxygen levels across all sites was 9.88 mg/L. The ideal pH of the water for brook trout is 6.5-8, and the average pH across all sites was 8.75. Healthy streams tend to have a conductivity between 150 – 500 uS, and conductivity in all sites was above 504 uS.

The water quality tests indicate that Rice Creek can support brook trout but does not have ideal conditions. All sites showed a low diversity of macroinvertebrates, suggesting that Rice Creek may not be functioning healthily. 

Relevance

This research indicates that the water quality of Rice Creek is not ideal. Regardless of the small forested areas along the creek, this is likely caused by the surrounding agriculture. Knowing the status of Rice Creek is important for managers and policy makers to set buffer laws and other regulations that protect the health of streams in this area. 

Citation

Bond, S. 2017. Rice Creek: Differences in chemical properties and aquatic macroinvertebrate  populations between forested and agricultural sites. St. Olaf College Local Ecology Papers.