Chemically, the waters of these lakes are very dilute (Armstrong and Schindler 1971) with conductivities typically ranging from 10 to 100 micromhos cm-1 at 25o Celsius and total dissolved solids less than 100 mg L-1 (Cleugh and Hauser 1971, Prokopowich 1979). Epilimnetic nutrient concentrations are naturally very low and phosphorus is usually limiting. By weight, N:P concentrations range from 20:1 to 50:1 and C:N ratios from 2:1 to 7:1 (Prokopowich 1979). The granitic bedrock is low in C, N and P, and is very slowly weathered. Thus much of the nutrient input to these ecosystems is via the precipitation or directly from the atmosphere (C and N).
Epilimnetic pH values for these lakes are typically between 6 and 7, except in the shallow humic lakes, such as 225 and 624, where the pH may be between 5 and 6 (Schindler and Ruszczynski 1983). However, buffering is poor in these dilute waters and natural alkalinities are extremely low. Dissolved inorganic carbon (DIC) concentrations range from 25 to 275 umol L-1 and alkalinity from 20 to approximately 200 ueq L-1 (Schindler and Ruszczynski 1983).
Light transmission in these waters is typically high, with Secchi depths of from 1 to 10 metres (Cleugh and Hauser 1971, Cruikshank 1988), the lower values occurring in lakes with high natural colour. Vertical attenuation coefficients typically range from 0.25 to 2.0 in natural ELA lakes. With low nutrient concentrations, algal productivity and biomass are also low in epilimnetic waters, and natural chlorophyll a concentrations typically range from 1 to 15 ug L-1 (Prokopowich 1979). The slow weathering and low productivity of these systems results in low suspended particulate concentrations, such that most of the light attenuation is caused by dissolved coloured matter. This natural colour is largely a function of the watershed vegetation and the amount of precipitation. Humic colouring, particularly from wetland vegetation, is flushed into the lakes as dissolved organic matter during periods of heavy precipitation. During prolonged dry periods, this colour is gradually bleached from the epilimnetic waters by solar radiation.
