Long Pond Water Quality Assessment Study
Completed for the Town of Brewster Conservation Commission
For more information, please contact Ed Eichner at the Cape Cod Commission. Send e-mail to: water@capecodcommission.org
Long Pond is the largest great pond on Cape Cod covering over 740 acres and split between the Towns of Brewster and Harwich. Long Pond has begun to experience water quality problems that threaten the environmental health and the enjoyment of the pond by town residents. A large algal bloom occurred on the lake during 1996 and a significant fish kill (> 100 fish) occurred in June 1997. To help address concerns about these events, the Towns, the Cape Cod Commission, and the Long Pond Watershed Association contributed matching funds and staff and volunteer time to help obtain a state Department of Environmental Management grant to complete an analysis of factors influencing the water quality in Long Pond. This analysis includes collection and analysis of water quality data and a phosphorus loading assessment. This assessment focussed on phosphorus because it is the key nutrient in pond ecosystems.
Based on these efforts, the Commission has concluded that Long Pond is a mesotrophic lake (see diagram of eutrophication cycle), which is experiencing low oxygen conditions in its bottom waters during summer stratification due to bacterial respiration during the decomposition of organic sediment materials. Limited oxygen is a habitat impairment for bullheads, trout, and other creatures who live in the colder bottom waters during summer months and is the likely cause of the 1997 fish kill. Low oxygen conditions also cause the release of phosphorus from the sediments.
Phosphorus loads from land uses surrounding Long Pond are approximately half of the load regenerated from the sediments, and the regenerated load is between 44 and 60% of the entire phosphorus load in the pond water column. Since phosphorus regeneration plays such a central role in determining water quality in Long Pond, efforts to limit regeneration should be the focus of in-lake water quality efforts. There are a number of options to reduce the phosphorus regeneration and improve the deep water dissolved oxygen conditions, including:
In-lake phosphorus reductions will improve water quality in the short run, but phosphorus reductions within a 250 ft deep buffer strip around Long Pond are necessary to sustain good water quality in the long term. The phosphorus in the pond came from land uses within this strip over a number of years and buildout within this area is projected to increase the load by 28%. Options to reduce these phosphorus loadings include:
Water quality monitoring of Long Pond should continue as public discussions consider which are the most appropriate options to protect water quality in Long Pond. Commission staff are available to assist the towns in the development of management options and review of potential remedial solutions.
Web page last updated May 27, 1999