Mount Holyoke's Lakes and Streams
The other, perhaps most picturesque parts of Mount Holyoke’s landscape, is its two lakes, matter-of-factly named Upper Lake and Lower Lake based on their respective elevations. Both lakes are man-made, created by the damming of Stony Brook, a stream that runs through campus and still connects them. Upper Lake is also fed by a stream known among campus faculty as “Project Stream” because of the wetlands restoration project it is part of.
An aerial view of Mount Holyoke's Campus, Google maps
For years, the lakes and streams have been plagued by pollution from organic compounds, particularly nitrogen and phosphorus. Between 2008 and 2012, the nitrate (a nitrogen compound) levels averaged 3.6 mg/L, roughly five times the Environmental Protection Agency’s recommended level of 0.71 mg/L. The average phosphorous levels were 0.035 mg/L, a level close but still in excess of the EPA’s recommended level of 0.031 mg/L.
Nitrogen and phosphorous are essential nutrients for life and are taken up in ecosystems by plants. However, in excess, they become pollutants; the environment has some capacity to absorb them but once that has been exceeded they can accumulate in an ecosystem. This is the case in Mount Holyoke’s lakes, particularly Lower Lake. Lower Lake has never been dredged to remove the mud and sediment that have built up over the years, so it is very shallow and the sediments at the bottom of the lake mix with a large portion of the lake water when stirred up, polluting it. In a deeper lake, sediments and pollutants would settle out onto the bottom of the lake and mix only a little with the layer of water directly above the bottom of the pond, leaving the surface waters comparatively clean and pure.
Information from: Professor Kate Ballantine
In Lower Lake, the mixing of pollutant-rich sediments with surface waters causes eutrophication, an excess of nutrients in the water. This leads to large algal blooms that can be highly damaging to the ecosystem. As the algae dies, it is decomposed by bacteria that consume oxygen. This depletes the levels of oxygen in the water, sometimes to the point that the water can’t sustain other aquatic life. Additionally, while the algae are living they can become so thick that they block the sunlight needed by photosynthesizing organisms in the lake. To try to mitigate these issues, facilities management adds algaecides and herbicides three times each growing season. They also add alum, a chemical flocculent that causes the algae to precipitate out, clearing the water. Although this keeps the lake ecosystem functioning on some level, these man-made materials are no replacement for a healthy ecosystem that is self-sustaining.
Efforts are under way to try to improve the water quality of the lake and the overall quality of the lake ecosystems by restoring wetlands and altering water flow to improve ecosystem services. Project Stream, mentioned earlier, has higher levels of pollutants than the lakes, meaning that it’s bringing pollutants from off campus and depositing them in the lakes. This summer, Professor Kate Ballantine and her assistants are hoping to begin reconstructing wetlands around where Project Stream meets Upper Lake. They will slow the water from Project Stream down, allowing pollutants to settle out of it before it enters Upper Lake. Professor Ballantine and her crew also plan to put logs in the streambed to raise the water levels and make the stream a little wider, which will also decrease the speed at which the water flows and give pollutants and sediments time to settle out.
Information from: Professor Kate Ballantine
An example of an algal bloom caused by eutrophication (picture not taken at Mount Holyoke)
http://www.soil-net.com/album/Water/Lakes_Rivers/slides/Eutrophication%2001.html
The area of Project Stream to which wetlands will be restored as it looks at present, pre-wetlands.
Photo: from Mount Holyoke College Wetland Restoration's Facebook page