General Lake Chenistry-Part I

The chemical compoition of a lake is a function of its climate and its basin geology. Each lake has an ion balance of the three major anions and four major cations, including HCO3-, SO4-2, Cl-, Ca+2, Mg+2, Na+,and K+. Ion balance means the sum of the negative ions equals the sum of the positive cations when express as equivalents. These ions are usually present at concentration expressed as mg/L (ppm) whereas other ions such as the nutrients phosphate, nitrate, and ammonium are present at ug/L (ppb) levels.

Humans can influence lake chenistry with excessive land disturbance around a lake which causes higher rates of leaching and erosion by removing vegetation, exposing soil, and increasing water runoff. Lawn fertilizers, and urban runoff add micronnutrients such as nitrogen and phosphorous, chloride and potassium, and where highways and parking lots are close to the lake, oils and heavy metals. Emissions from motor vehicles, fossil-burning utilities and industry, and other sources produce compounds attecting lake chemistry. One important consideration to this is the fact pollution can occur many miles away from your faviorite lake and can be blown by the winds or carried by streams.

The best understood ions are hydrogen (H+, which indicates acidity), sulfate (SO4-2) and nitrate (NO3-), which are associated with acid rains. Mercury (Hg) is a significant air pollutant affecting aquatic ecosystems by accumulation in the food web in the lake. Lakes with hight concentration of calcium (Ca+2) and magnesium (Mg+2) are labled "hardwater" lakes, while those with low levels of these ions are called "softwater" lakes. Concentration of other ions, especially bicarbonate, are highly correlated with the concentration of the hardness ions, especially Ca+2. The ionic concentration influence the lake's ability to assimilate pollutants and maintain nutrients in solution. Calcium carbonate in the form of "marl" can precipitate phosphate from the water and thereby remove this important nutrient from the water.

The total amount of ions in lake water is called TDS (total dissolved salt, or total dissolved solids concentration). Both the concentration of TDS and the relative amounts or ratios of different ions influence every living creature in a lake, as well as, affect important chemical reactions that occur normally in the water.

So what is your take on conductivity of water and how it relates to fishing?

Since Kentucky is famous for its limestone waters, I would assume that the native fish here are accustomed to waters with high alkalinity and neutral to basic pH's. I know that as water gets more acidic, various toxins in the water increase, such as aluminum. If anything, the precipitation of phosphate by 'marl' is probably a good thing. The lakes in KY suffer from enough eutrophication as it is.

Motalot, this is a good question. I can't find much on the affects of condutivity on fish, but pH is related to water conductivity. If the pH changes, the water conductivity changes. Rain water in its pure state is distilled water and neutral (pH 7), and its conductivity close to pure water. But when the atmosphere is polluted with sulfur oxide and nitrogen, the rain goes through oxidation with ozone or hydrogen peroxide before falling to into the lake and forms surlfuric acid (H2SO4) and nitric acid (HNO3). Rain water with pH below 5.5 or 5.6 is called acid rain. Some acid rain has a conductivity of 50 millisec/cm, while other acid rain of 5 can have conductivity of 100 millisec/cm. So, conductivity can be at different levels at the same pH. Now, how this affects fish, I am not really sure other than the fact that these pH changes that affect water conductivity will certainly affect a fish's comfortability. It has been proven paddlefish will avoid aluminium objects, and researchers think any large unprotected aluminium structure around locks and dams will interfer with migratory fish. Is this a electroconductivity dectection by these fish? Most likely.

Whew.....way over my head!