COLBY BI 493 - LECTURE NOTES
School name Colby College
Course Bi 493-
Pages 7

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Salmon Lake and McGrath Pond Watershed StudyColby Environmental Assessment TeamExecutive SummaryDecember 10, 2009In the summer and fall of 2009, the Colby Environmental Assessment Team (CEAT) studiedthe water quality of Salmon Lake and McGrath Pond, located in the Belgrade Lakes Region ofMaine. The physical, chemical and biological characteristics of water quality were measured andanalyzed to evaluate the current health of these lakes. Water quality data collected during thesummer and fall of 2009 were compared with data from previous years to study the historicwater quality trends. Land use patterns in the Salmon/McGrath watershed were also examined toinvestigate their impact on the lake water quality.The water quality trends suggest an improvement in the transparency of Salmon Lake andMcGrath Pond over the last 34 years. Improvements in transparency have been greater forMcGrath Pond than for Salmon Lake. In 1975, McGrath Pond and Salmon Lake hadtransparencies of 4 m and 5 m, respectively. In 2009, both water bodies had transparencies ofapproximately 5.5 m. Data from 2009 show the productivity of Salmon Lake to be higher.Consequently the threat of eutrophication is higher in Salmon Lake than in McGrath Pond.Mean phosphorus levels recorded in this study were 13 ppb for Salmon Lake and 10.6 ppb forMcGrath Pond. In September of 2009, phosphorus levels at the deepest part of Salmon Lakeapproached 300 ppb compared to less than 10 ppb for McGrath Pond. Phosphorus from thebottom can be mixed into the water column during spring and fall mixing events. Whenphosphorus levels exceed 12-15 ppb, the lake is at risk for algal blooms. The last recorded algaebloom in Salmon Lake was in 2002-2003. The decreasing trends in productivity of Salmon Lake and McGrath Pond indicate decreasinglevels of phosphorus, but concentrations are still near the 12-15 ppb tipping point, at which algalblooms may occur. Algal blooms can be detrimental to the health of organisms in the lake, maydecrease the aesthetic value of the lake and can reduce the value of shoreline homes. Effortsshould be taken to decrease nutrient levels in the water. Salmon Lake is much more likely todevelop algal blooms than McGrath Pond because of higher phosphorus levels. In late summer 2009, Salmon Lake experienced very low dissolved oxygen levels in thehypolimnion—the bottom layer of lake water. The lack of oxygen on the bottom during thesummer months is due to stratification of the water column, which prevents mixing of oxygenrich water from the surface. When the lake is stratified and mixing is not occurring, existingoxygen on the bottom of the water column is depleted by populations of decomposers that thrivebecause of the availability of organic matter in aging lakes. Following is a brief summary of findings from the 2009 CEAT study of Salmon Lake andMcGrath Pond and their watershed:- Salmon Lake and McGrath Pond have a combined surface area of 2,043 hectares (ha).Salmon Lake has one deep basin, with the deepest point of the two lakes reaching 17.4 m.The deepest section of McGrath Pond reaches 7 m.- The recent discovery of Eurasian watermilfoil in Kozy Cove of Salmon Lake isparticularly troubling for Great Pond because water flows from Salmon Lake to GreatPond by way Kozy Cove and Hatchery Brook. Once discovered, the Maine Departmentof Environmental Protection took actions to eradicate the presence of Eurasianwatermilfoil in Kozy Cove, on the southeast side of Salmon Lake. Because the majorityof Salmon Lake and McGrath Pond is shallow (less than 8 m) and invasive macrophytessuch as Eurasian watermilfoil prefer shallow water for colonization and establishment,these lakes are at high risk of invasive species colonization. Continued monitoring andvigilance of volunteers, researchers and residents is critical for the prevention of furtherinvasive species establishment.- The mean epicore phosphorus concentration in Salmon Lake and McGrath Pond was 13.0ppb and 10.6 ppb respectively. The largest external contributors to phosphorus loading aspercentages of the total external load into the water body are shoreline residential septicsystems (14.9%), atmospheric input (13.1%), cropland (11.1%), shoreline development(10.1%), non-shoreline development (9.1%), logged areas (8.7%) and youth camp septicsystems (8.6%).- Salmon Lake and McGrath Pond have a flushing rate of 0.47 flushes per year, based onthe water budget calculated by CEAT, with 66% of water inputs coming from runoff and34% from precipitation.- Land use has undergone several changes in the period between 1965/66 and 2007:o Non-shoreline residential area has increased 142.9% and now covers 135 ha ofthe watershed. Shoreline residences have increased by only 29.5% (54.9 ha),likely because much of the shoreline was already developed by 1965/66. o CEAT estimates that there are 19 shoreline lots that could be developed. Thereare also other non-shoreline areas where potential development might occurwithin the watershed. Limits to development include lack of municipal sewageand water treatment, the topography of the watershed, shoreline zoningordinances and the current economic downturn. o Agricultural land decreased 60.1% since 1965/66, which is consistent with trendsin surrounding watersheds and throughout central Maine. o Logged area in the northwestern part of the watershed has increased significantly,from 3.3% to 8.2%. o Forested land in the watershed has significantly decreased from 71.5% to 65.1%(a decrease of 71 ha) due to logging and development. o High impact development, which includes commercial and municipal land uses,increased from 2.23 ha in 1965/66 to 14.2 ha (0.69%) in 2007. - There are 66 camp roads, 3 state roads and 12 town roads in the Salmon/McGrathwatershed. Camp roads cover 13.2 miles, and state and town roads cover 27.7 miles.Many of the camp roads could have a negative impact on the watershed due to theirproximity to the shoreline. Camp roads are generally privately owned and maintained byresidents living on each road. Many camp roads fall into disrepair because residents lackthe funding and knowledge of road repair to keep the road well maintained. - Based on the CEAT road survey, over half of the camp roads are in fair (35%) or poor(23%) condition, and are


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COLBY BI 493 - LECTURE NOTES

Course: Bi 493-
Pages: 7
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