INTRODUCTION
Dr. Olie Gokeeta, Biology professor at Ramford University and member of the Renapi Tribe and his students have been studying the physical, biological and chemical characteristics of six lakes in Northwestern Ramford County for the past 20 years. This area is forested upland and mountainous region that receives relatively large inputs of precipitation (100-150 cm annually) and acidic deposition (e.g., typical pH is about 4.1 to 4.2).
The primary objective of the efforts of Dr. Olie Gokeeta and his students was to provide an accurate data base that would establish a basis for assessing future environmental impacts and provide scientific data for making fisheries management decisions. The basic approach examined relationships observed in the data base among watershed characteristics, lake chemistry and fish status.
Lake Classification
Dr. Olie Gokeeta decided to use the lake classification system devised in New York State to study the acid rain problem in their state. The classification system is based on chemical and hydrological conditions.
Lakes fall into two major groups: seepage lakes and drainage lakes. Drainage lakes have an outlet, while seepage lakes do not. Both lake types receive water from various sources including surface runoff, groundwater, and direct precipitation, although in different relative amounts. Drainage lakes receive a higher proportion of water from surface runoff, whereas seepage lakes receive water primarily from direct precipitation and groundwater. All six lakes in the Ramford study are drainage lakes.
The condition of the waters in a lake is a function of the relative contributions of acids and bases. These acids are derived from both atmospheric deposition and natural processes, such as organic matter decay and the oxidation of organic nitrogen. The bases result from reactions occurring within the watershed soils (e.g., weathering and cation exchange reactions) and from atmospheric deposition. The degree to which the incoming precipitation interacts with the watershed soils and the routing of the water through these soils, are major determinants of the base supply rate. In watersheds with thick soils, acids – whether natural or from acidic deposition – will be largely neutralized by bases within the soils. In contrast, in watersheds with thin soils, much of the incoming precipitation passes only through the shallow organic horizons and into the lakes and streams. Such systems would generally be expected to be more responsive to increases or decreases in atmospheric acid inputs.
Another characteristic of the classification is the lake’s Acid Neutralizing Capacity (ANC). Acid neutralizing capacity is a measure of the net strong base in solution, or net strong acid if its value is negative. As a result, additions of strong acids or bases to surface waters have a direct effect on ANC. Depending on the initial ANC of the solution, this addition may also significantly influence pH. Sulfate is the dominant mineral acid anion in the lakes in the Ramford study, with sulfate concentrations between about 80 and 140 µeq/L, indicating that sulfuric acid is the major source of mineral acidity. Some portion of this sulfate is attributable to acidic deposition.