A Watershed Analysis of Togus Pond

Executive Summary

 

Problems in Environmental Science Class

Colby College

 

December 9, 2004

 

     The Colby Environmental Assessment Team (CEAT) investigated the water quality and factors affecting water quality in the surrounding watershed of Togus Pond in Augusta, Maine from June through September 2004.  CEAT analyzed several physical, chemical and biological water quality parameters, land use patterns in the watershed, and the impact of residential and commercial development on water quality.  Data collected were used to produce models of the watershed that enabled CEAT to identify possible sources of degradation to the current and future water quality of Togus Pond.  To obtain a historical perspective, all data collected this summer were compared to data collected in previous years by the Maine Department of Environmental Protection.  Lake water quality is most affected by the accumulation of external nutrients, particularly phosphorus, resulting from surface runoff and land erosion.  Internal nutrient loading is an important factor to consider since a large amount of the phosphorus in the lake comes from internal sediment loading.  When concentrations of phosphorus approach threshold levels (15 ppb), a lake may experience algal blooms that decrease the aesthetic, recreational, ecological, and economic value of the lake and land areas surrounding the lake.

 

A brief summary of the CEAT findings in the Togus Pond study:

      Dissolved oxygen and mean transparency (3 m) readings for Togus Pond were consistent with other lakes in the surrounding area.  The range of transparency over the summer months was from 6 m in June decreasing to 2 m in September.

      The dissolved oxygen level during the mid-summer months was 0 ppm at 8 m and below giving a volume of approximately 1,836,000 m3 of the anoxic water in the lake (12% of the total volume).  This anoxia allows significant phosphorus release from the sediments.

      Conductivity was 58 mMHOs/cm, which is well above the means for other lakes in the area, suggesting that runoff is contributing particulate matter to Togus Pond.

      Mean hardness (22.2 mg/L) was very high compared to surrounding lakes in the area.

      Phosphorus data were collected from June-September 2004 at the surface, mid-depth, and bottom of the lake, as well as by epicore samples.  Mean total phosphorus was found to be 28 ppb in epicore samples.  Phosphorus levels increased in epicore and bottom samples throughout the course of the summer.  Phosphorus levels peaked at 401 ppb in the bottom samples at Site 1 at about 14.7 m (48.2 ft) of depth. 

      A phosphorus loading model was used to assess the inputs and outputs of phosphorus in the Togus Pond watershed in 2004.  The budget is based on the amount of phosphorus entering the lake from the different land use types in the watershed.  It also takes into account internal recycling of phosphorus.  The model predicts that the land area in the Togus Pond watershed contributes 410 kg/yr of phosphorus to the lake and that 328 kg phosphorus/yr is released from the sediments within the lake. The mean phosphorus concentration predicted by the model ranged from 19 ppb to 28 ppb, which was similar to actual water quality data obtained by CEAT. 

      The mean septic suitability of the watershed soil was 5.0 on a scale of 1-9, with 1 being the least suitable and 9 being the most suitable for septic systems.

      Roads within the watershed disproportionately contribute to the phosphorus loading of Togus Pond.  Paved state and municipal roads contribute approximately four percent of the total phosphorus load entering the lake, and camp roads contribute five percent of the total phosphorus load.  This is a substantial amount for the relatively small percent of the watershed land use devoted to roads (1.5%).  Because of the relatively small road area, road improvement would be an easy way to decrease the total phosphorus load entering the lake to help improve water quality.  Camp roads and driveways should be a priority for repair because of their proximity to the water.

      CEAT found a total of 283 houses in the Togus Pond watershed.  184 of these houses (65%) are considered shoreline (within 200 feet of the lake) and 99 houses (35%) are non-shoreline.  There are 221 year-round residences (78% of the houses) and 62 seasonal residences (22%) in the Togus Pond watershed.

      CEAT found that 43% of the buffer strips on developed residential lots are inadequate.  The majority of buffer strips need to be enhanced to decrease nutrient runoff.  Many of the older homes do not meet current setback standards, and shoreline septic systems may contribute disproportionately to high lake phosphorus levels.

      The little commercial development that exists in the Togus Pond watershed is primarily found along Route 3 and Route 105.  The proposed expansion of the golf course is of potential concern for lake water quality.  Clusters of shoreline residences exist in the northern and southern sections of the lake, eliminating the potential for any major future increase in residences along the shore.  Future increases in the Togus Pond watershed population will likely occur outside the shoreline zone.

      The four remediation methods deemed most applicable to Togus Pond are:

-     Alum treatment to reduce the concentration of phosphorus in the water column chemically and to seal the sediment to prevent internal recycling of phosphorus;

-     Fish stock manipulation to decrease fish that consume zooplankton to attain higher levels of zooplankton to reduce the intensity of algal blooms.  This method will not reduce the level of phosphorus in the lake;

-     Drawdown to remove nutrient-rich water from the lake;

-     Vegetative mats that trap phosphorus in aquatic plant biomass and remove it from the lake.

 

The Colby Environmental Assessment Team presentation, A Watershed Analysis of Togus Pond will be available online at: http://www.colby.edu/biology/BI493/.  The complete report will be available in the spring.