Land Use Patterns in Relation to Lake Water Quality in the Lake George and Oaks Pond Watersheds

Problems in Environmental Science – Biology 493

Colby College, Waterville, Maine 04901

December 3, 2001 Presentation

Project Summary

The water quality of Lake George and Oaks Pond is currently below the critical range for phosphorus (12 to 15 ppb), which is the primary cause of algal blooms.  These low levels of phosphorus are one of several characteristics that classify both lakes as mesotrophic.  The results of other physical and chemical tests were also within acceptable ranges for healthy lakes with the exception of dissolved oxygen and alkalinity.  Oxygen depletion is occurring in deep areas of both lakes, which can affect the cold water fisheries negatively and is an early warning sign of eutrophication.  Alkalinity helps to buffer a lake by mitigating the effects of acid deposition.  Our study indicates low alkalinity for both lakes and a resulting sensitivity to acid inputs. We calculated a water budget and annual flushing rate for both lakes.  The flushing rate is a measure of how fast water is replaced within the lake and reflects the nutrient/pollution cleansing ability of the lake.  The flushing rate for Oaks Pond is more than five times faster then that of Lake George. Consequently, Lake George has a higher sensitivity to nutrient loading than Oaks Pond.  However the water quality of Lake George and Oaks Pond are closely related because Lake George drains into Oaks Pond.

A primary objective of our study was to identify land use patterns within the watersheds and document their effects on water quality because land use influences the magnitude of phosphorus inputs into the lakes.  A Geographic Information System (ArcView) was an invaluable tool for analyzing land use and development trends, through the construction of composite maps and models.  Land use in the watersheds changed dramatically over the 42-year period studied.  A comparison of 1955 and 1997 land use patterns, made possible from aerial photographs, showed a major increase in mature forests in the Lake George watershed and a drastic decrease in agricultural land in both watersheds.  The mature forests help to mitigate erosion and phosphorus loading that can affect water quality.

Active logging of these mature forests within the Lake George watershed, particularly, is a concern and use of best management practices is recommended.  Compliance with the Natural Resources Protection Act is also important.  Future logging is more likely but less suitable in the Lake George watershed and more suitable but less likely in the Oaks Pond watershed as determined by the logging suitability model.  The model integrates soil types and slope of the land to project areas that could support logging with minimal detrimental effects on lake water quality.  

Shoreline residential land increased from very few residences in 1955 to approximately 34 houses today.  Oaks Pond has experienced a similar increase in the number of shoreline residences.  This land use type is of particular concern because of the greater potential for nutrient loading from shoreline development and septic systems than from these activities in non-shoreline areas of the watershed.  Shoreline development may cause increased erosion and phosphorus loading caused by the presence of impervious surfaces and by disturbance of shoreline vegetation.  Oaks Pond is at a higher risk for these problems because of the high number of shoreline camps and the potential for conversion of camps from seasonal to year round use.  Lake George is at less risk due to the Lake George Regional Park, which owns a substantial portion of the lake shoreline and subsequently reduces the potential for problems related to shoreline development.  Installation of adequate shoreline buffer strips in front of residences is an economical and effective way to mitigate erosion and subsequent nutrient loading.  Based on our analysis, 69 percent of buffer strips on Lake George and 33 percent of buffer strips on Oaks Pond were adequately buffered.              Roads are significant pathways for nutrients to enter the lakes. Most of the roads surrounding Oaks Pond run in close proximity to the shoreline and are an immediate threat to water quality.  Two of these roads are classified as high risk.  The majority of all roads in the combined Lake George and Oaks Pond watershed were classified as being a risk to lake water quality.  There is one high-risk road in proximity to Lake George.            

We believe that the Lake George Regional Park has been practicing ecologically sound stewardship of the land under its control.  However, the public boat launch, gravel parking lots, and the east side access road are of particular concern for water quality management.  These areas all contribute to erosion and potential nutrient loading. The Regional Park can play an important role in protecting Lake George by working to enhance buffering around the boat launch, parking areas, and along the park access roads.  The park septic systems on the east and west sides of the park are under their projected capacity. However, increased park visitation could threaten their ability to function optimally and result in a negative impact on lake water quality.  This issue is especially of concern on the east side where visitation rates are highest and the septic field is located close to the shoreline.

The Colby Environmental Assessment Team developed a phosphorus model as part of our study to project current and future phosphorus inputs into Lake George and Oaks Pond.  Current projections were approximately equal to the values determined by our chemical analysis.  The greatest contributors of phosphorus to the lakes determined by the model were roads, shoreline and non-shoreline residences, commercial/municipal lands, and the park.   Our phosphorus model showed current inputs to be below the critical value of 12 to 15 ppb, which is the threshold for potential algal blooms.  Future predictions from our model for several development and logging scenarios suggest that resulting phosphorus inputs are not likely to exceed this critical value

Invasive plant species are not present in either lake. However, there is the potential for accidental introduction through the launching of contaminated boats.  Invasive aquatic plant species can cause serious economic and ecological damage to lake communities and to the recreational resources of the lakes.  Education of boat owners is an important preventative measure that should be undertaken to address this potential threat.            

In summary, Lake George and Oaks Pond are presently within acceptable ranges of good water quality as defined by the study.  To maintain present levels, appropriate actions to limit erosion and nutrient loading should be taken.  Community awareness through educational initiatives will help lake stakeholders prevent future degradation of water quality.

 

Project Recommendations

The Colby Environmental Assessment Team has compiled the following recommendations for the stakeholders in the Lake George and Oaks Pond watersheds.  These recommendations identify potential problem sources of nutrient inputs in both lakes and suggest actions that can be undertaken to mitigate these problems.  We believe that these precautionary steps to reduce erosion from runoff and subsequent phosphorus loading will help maintain the water quality of Lake George and Oaks Pond for future generations.

Phosphorus Control

Buffer Strips and Erosion Reduction

Roads

Boat launches

 

Septic Systems

Land Use

Monitoring and Education

Lake George Regional Park

Invasive Species

Fish Populations

Community Awareness