Susceptibility of Northern Minnesota Lakes to Acid Deposition Impacts

ABSTRACT-lake chemistry surveys indicate a large number of lakes with acid neutralizing capability (ANC) below 200 μeq/L occur in northeast Minnesota where shallow soils over bedrock and exposed rock outcrops predominate, and in moraine areas having rolling to steep topography in north-central and east-central Minnesota. In the Boundary Waters area, lake chemistry is strongly associated with bedrock geology. lakes with ANC \u3c100 μeq/L are associated with granite, basalt, and gabbro formations, while lakes with ANC of 100- 200 μeq/L are associated with slate and greenstone formations. In the rest of the state where soils are deep, landform, soil type, and lake hydrology determine lake chemistry. Most low ANC lakes are found in terminal moraine areas. These lakes are generally small ( \u3c40 ha in area), have limited groundwater inflow, and typically classed as precipitation-dominated seepage lakes. Higher ANC lakes (\u3e400 μeq/L) are often associated with agricultural and residential land uses. Relationships found between ANC and bedrock geology, and between ANC and landform and soils, provided the basis for mapping the distribution of low ANC surface waters in Minnesota. Empirical and process models used to evaluate the actual susceptibility of low ANC lakes in the Upper Midwest to acid deposition impacts and indicated precipitation pH 4.6-4.7 is a threshold level for lake acidification. Modeling also indicated lakes with AN

Eutrophication Factors in North Central Florida Lakes

A small Florida lake has been receiving a regimen of nutrient addition equivalent to 500 mg/m3-yr N and 43 mg/m3-yr P since 1967. Data has been accumulated through 1969. The effect on the lacustrine ecosystem of various biogenes includes production by primary producers, species diversity of plankton and certain production estimates at the secondary trophic level using natural populations of planktivorous fish. Plankton production using isotopic carbon is ca. 58 grms/m2-yr; Species diversity is slowly changing to a mixed chlorophycean and yellow-green. Biomass of benthic green filamentous types has increased slightly. Nutrient addition has had little influence on zooplankton production. Related studies on 53 other regional lakes have been done using a multi-dimensional hybrid concept as defined by several trophic state indicators. This trophic state index has provided a means for ranking the lakes on an arbitrary scale. Cluster analysis utilizing pertinent characteristics resulted in classification of other lakes. Land use patterns and population characteristics were determined photographically and N and P budgets estimated, Using multiple regression and canonical analysis, several significant relationships were found between lake trophic state, lake basin, land use, and population characteristics. In general, trophic state of lakes can be expressed as a simple relationship incorporating N and P influx rates. This report was submitted in fulfillment of Grant #16010DON under the (partial) sponsorship of the Water Quality Office, United States Environmental Protection Agency