Mercury
Aluminum
Silica

Mercury
Mercury is an element that is found in the rocks that make up the earth's crust. Mercury is released into the air as a result of the burning of materials such as coal and the incineration of municipal and medical wastes. It is released into water through improper handling of industrial waste and is also deposited in waterbodies when it falls out of the air as rain or dust. Mercury levels in Maine's lakes are the highest in the nation. A major reason for these elevated levels is because of the weather pattern that dominates North America. As a result, the Jet Stream carries pollution from the industrial midwest and deposits them on our land and waterbodies. In varying amounts, mercury is toxic to living organisms, having significant negative impacts to reproduction, behavior, and damaging the nervous system. Large animals that are long lived are particularly in danger of mercury poisoning because mercury builds up in a body over time (called bioaccumulation), and it increases in concentration when one organism eats another (called biomagnification). As a result, very small amounts of mercury in the environment can result in extremely high amounts of mercury in animals at the top of the food chain.

There are several conditions scientists have identified that seem to make some lakes more mercury-sensitive than others. These conditions are broken down into Chemical, Physical and Biological characteristics. Chemistry: high acidity, low acid neutralizing capacity and high sulfate. Physical: Lots of wetland, small lake with large watershed, summer water fluctuations of more than 6 feet. Biological: Low zooplankton abundance, low nutrient levels, many levels in the food chain.

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Aluminum
Aluminum is a metal found in large amounts in the earth's crust, especially in igneous rock. Aluminum becomes soluble (dissolved in the water) and toxic to organisms when the pH of lake water is acidic. The amount of dissolved organic matter in the water can also have an effect on the solubility of aluminum in lake water.

Among other organisms, fish are especially sensitive to aluminum because it binds to their gills and reduces their ability to breathe. Reductions in fish populations because of aluminum poisoning disrupt the rest of the food chain in the lake.

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Conductivity
Conductivity is a measure of how easily an electric current runs through water between two electrodes. the greater amount of salts, acids and bases are in the water, the greater the conductivity will be. For this reason, conductivity is closely related to salinity (the sum of ionic compounds in water) and total dissolved solids (the weight of solids that are filtered out of water).

In general, conductivity is reduced as runoff increases, and larger lake watersheds have greater conductivity levels than lakes with smaller watersheds.

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Major Ions and Anions
Ions are atoms or molecules that have acquired an electrical charge by the loss or gain of one or more electrons. This loss or gain can be a result of a chemical reaction or an addition or subtraction of energy in the environment. Cations are ions that have a positive charge, and anions have a negative charge. The charge is usually designated with plus (+) or minus (-) signs, and a number with the plus or minus denotes how many electrons are missing or gained. The major cations that play a role in lake systems are calcium (Ca 2+), magnesium (Mg 2+), sodium (Na +), and potassium (K +). Anions are atoms or groups of atoms that carry a negative charge. Major anions in lake systems are HCO 3 - (bicarbonate), CO 3 2- (carbonate), SO 4 2- (sulfate) and Cl - (chloride). The total concentration of ions and cations in inland water is salinity, or conductivity (also called specific conductance).

One place ions are produced is in the soils or rocks of the lake catchment (watershed) and are carried by runoff into the lake. For this reason the geology of the catchment plays a major role in determining the ion content of lake water. Because different types of rock break down (weather) at different rates depending on their hardness, they contribute to salinity (or conductivity) in varying amounts. Softer sedimentary rocks such as limestone and dolomite contribute more to salinity than harder igneous rocks such as granite and gneiss.

Besides the geology, many other factors may influence the ion content of a lake, including: the climate, the age of the soil formation, the distance from the sea, human-produced atmospheric inputs of acids, trace metals and organic contaminants, fertilizers, road salt and in-lake processes.

Lakes with low salinity and acid neutralizing capacity are most sensitive to acidification from human-produced pollution. These susceptible lakes are found in areas on igneous bedrock such as quartzite, granite, basalt or gneiss or other highly insoluble rock, where the soils are made up of similar material as the bedrock. In the past 20 years lakes in these areas have been sampled in hopes of determining whether changes in environmental laws to reduce pollution are having measurable effect on acidification of sensitive lakes.

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The Trophic State Index used by many volunteer monitoring programs was developed by Dr. Robert Carlson in 1977 and is based on algal biomass in a lake. The index is a good way of comparing lakes within a region and looking at changes in trophic status through time. The Carlson index was developed for use with lakes with little non-algal turbidity and few rooted aquatic plants, so it must only be used when these conditions exist.

Three variables can be used independently to estimate algal biomass in a lake, chlorophyll pigments, Secchi depth, and total phosphorus. The Carlson method uses a log transformation of Secchi disk values as a measure of algal biomass. Each increase of ten units on the scale represents a doubling of the algal biomass.

The following text from A Coordinator’s Guide to Volunteer Lake Monitoring Methods, written by the North American Lake Management Society (NALMS), explains how trophic state index is calculated:

The index is relatively simple to calculate and to use. Three equations are used: Secchi disk, TSI(SD); chlorophyll pigments, TSI(CHL); and total phosphorus, TSI(TP). The original Secchi depth equation in Carlson (1977), reproduced below looks forbidding, but illustrates how the index was constructed.  

The basic Secchi disk index was constructed from doublings and halvings of Secchi disk transparency. The base index value is a Secchi disk of 1 meter, the logarithm of which is zero.

      ln 1 = 0                    6 - 0 = 6            10 x 6 = 60

Therefore, the TSI of a 1 meter Secchi depth is 60. If the Secchi depth were 2 meters,

      ln 2 / ln 2 = 1           6 - 1 = 5             10 x 5 = 50

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Resources:

Carlson, R.E. and J. Simpson. 1996. A Coordinator’s Guide to Volunteer Lake Monitoring Methods. North American Lake Management Society. “A Trophic State Index” found at the web address: http://dipin.kent.edu/tsi.htm, downloaded on 8/29/2005.

Evers, David C. 2005. Mercury Connections: The extent and effects of mercury pollution in northeastern North America . Biodiversity Research Institute. Gorham , Maine .

Kalff, Jacob. 2002. Limnology. Upper Saddle River, N.J. Prentice Hall.

US Environmental Protection Agency. “Carlson’s Trophic State Index” found at the web address http://www.epa.gov/bioiweb1/aquatic/carlson.html, downloaded on 8/29/2005.

USGS Geologic Glossary
http://www2.nature.nps.gov/geology/usgsnps/misc/glossaryStoZ.html#S