The Offshore Chemical Monitoring Program is largely an open-water testing program. That is, the sites selected are a series of deep-water locations along the south to north axis of the lake from Tea Island in the south to Rogers Rock in the north and a series of shallower bay locations around the lake. This monitoring program represents the backbone of the Lake George limnological database. It provides a yearly barometer of the chemical water quality of the lake.
Lake George is considered an oligotrophic lake, meaning in lay terms that the lake possesses high water clarity indicative of very low turbidity and algal productivity in its open waters. However, human activity and changing land use around the lake (perturbation of the watershed) in the last 30 years is suspected of increasing the rate at which nutrients and other pollutants are coming into the lake. Slowing or moderating these impacts will require the utmost vigilance on the part of the Lake George community if the pristine character of the lake is to be saved for later generations to enjoy.
As in past years, major changes in chemical and physical parameters of the epilimnetic (surface) waters of mid-lake sites were not observed. However, some areas sampled as a part of this program show signs of decreased water quality, namely the deep waters at the southernmost site (Tea Island). This site has continued to show near anaerobic conditions in the deep waters (hypolimnion) beneath the thermocline concomitant with phosphorus and nitrate accumulation during the later stages of summer stratification. Such conditions are stressful to cold-water fish (e.g. trout and salmon), which require oxygen levels above 4.0 mg/l. As hypolimnetic oxygen depletion rises higher in the water column, the range of these fish will be significantly diminished. Hypolimnetic oxygen depletion also promotes the dissolution of nutrients from lake-bottom sediments. Nutrients, primarily nitrogen and phosphorus, which are normally tied-up in the sediments under aerobic conditions, are available to promote greater algal growth (productivity) when oxygen levels are depleted.
Nutrient limitation of algal growth has always been attributed to lack of phosphorus. The 2010 data supports this supposition, however more interesting are the differences between basins of the lake. Ratios of total nitrogen (TN) to total phosphorus (TP) support the contention that more phosphorus is available in the south basin. Identification of the sources of phosphorus to the basin and means to curtail inputs is warranted. A FUND supported effort by the Lake George Park Commission to improve the quality of phosphorus budgets for the lake, thereby identifying sources of phosphorus and their relative contributions, was completed in 2001. The conclusions of this report stress that although urbanized lands only account for 5% of the land area in the basin, they account for 43% of the phosphorus loading to the lake via surface runoff. Continuing efforts to incorporate stormwater management into any and all construction within the basin is critical. Monitoring to evaluate the success or failure of mitigation efforts is also necessary.
Trophic State Indices on a South to North Axis for Lake George.
Seasonal trends observed in dissolved nutrients and other essential constituents can be attributed in many cases to primary production among the phytoplankton. Soluble nutrients have shown maximum concentrations in past years following snowmelt episodes and the resulting terrestrial runoff. Heavy rains in October of 2010, causing widespread erosion, affected the composition of various components in the water column, particularly when coupled with Fall overturn. This in turn can affect other biological and chemical qualities of the water. For example, chlorophyll and phosphorus distributions throughout the water column might be elevated for a longer period of time in the spring due to the runoff caused by the increased precipitation. Higher phosphorus levels provide more nutrients for the algae. This in turn can affect zooplankton populations, and so on up the food chain. Differences in overall water quality were observed between the north and south basins of Lake George in 2010. Principle among the observed differences were:
- Less clarity in the south basin as measured by secchi disk and photometry,
- More chlorophyll, phosphorus, nitrogen and salts in the south basin, and
- Less deep-water (hypolimnetic) dissolved oxygen in the Caldwell (Tea Island) sub-basin of the south basin.
These differences indicate poorer water quality in the southern, more urbanized portion of the lake. The ultimate consequences of human activity in the basin will be demonstrated through continued long-term monitoring of the sites contained within this program.