Glossary

adsorption: adhesion of molecules or ions on a surface.

alum: potassium aluminum sulfate dodecahydrate, KAl(SO₄)₂\(\cdot\)12H₂O

anoxic: no oxygen. Anoxic waters are areas of natural waters that are depleted of dissolved oxygen.

chlorophyll: green pigment present in all plant life and necessary for photosynthesis. The amount present in lake water depends on the amount of algae and is therefore used as a common indicator of water quality.

colorimetry: quantitative chemical analysis using color (visible spectroscopy).

coprecipitation: precipitation of substances normally soluble under the conditions employed. There are three main mechanisms of coprecipitation: inclusion, occlusion, and adsorption. Inclusion occurs when the impurity occupies a lattice site in the crystal structure of the carrier. Occlusion occurs when an adsorbed impurity gets physically trapped inside the crystal as it grows. Adsorption is an impurity that is weakly bound (adsorbed) to the surface of the precipitate.

cyanobacteria: phylum of bacteria that obtain energy through photosynthesis (also known as blue-green algae).

epilimnion: the top-most layer in a thermally stratified lake, occurring above the deeper hypolimnion. It is warmer and typically has a higher pH and dissolved oxygen concentration than the hypolimnion during the summer.

eutrophic: a eutrophic body of water, commonly a lake or pond, has high primary productivity due to excessive nutrients and is subject to algal blooms resulting in poor water quality. The bottom waters of such bodies are commonly deficient in oxygen, ranging from hypoxic to anoxic.

eutrophication: the process by which lakes are enriched with nutrients, increasing the production of rooted aquatic plants and algae. The extent to which this process has occurred is reflected in a lake’s trophic classification: oligotrophic (nutrient poor), mesotrophic (moderately productive), and eutrophic (very productive).

fall and spring turnover: fall cooling and spring warming of surface water increases density, and gradually makes temperature and density uniform from top to bottom. This allows wind and wave action to mix the entire lake. Mixing allows bottom waters to contact the atmosphere, raising the water’s oxygen content.

hypolimnion: the dense, bottom layer of water in a thermally-stratified lake. Being at depth, it is isolated from surface wind-mixing during summer, and usually receives insufficient light for photosynthesis to occur.

hypoxic: oxygen depleted. In an aquatic environment, a state in which the dissolved oxygen concentration is so low, it is detrimental to aquatic organisms living in the system.

limiting factor: the nutrient or condition in shortest supply relative to plant growth requirements. Plants will grow until stopped by this limitation. Phosphorus is typically limiting in summer, and temperature or light is limiting in fall or winter.

marl: white to gray accumulation on lake bottoms caused by precipitation of calcium carbonate (CaCO₃) in hard water lakes. Marl may contain many snail and clam shells, which are also calcium carbonate. While it gradually fills in lakes, marl also precipitates phosphorus, resulting in low algae populations and good water clarity

mesotrophic: mesotrophic lakes have an intermediate level of productivity, greater than oligotrophic lakes, but less than eutrophic lakes.

Milli-Q water: water that has been purified and deionized to a high degree by a water purification system manufactured by Millipore Corporation.

nonpoint source (NPS) pollution: pollution affecting a water body from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and human-made pollutants, depositing them into lakes and other natural waters. These pollutants include excess fertilizers from agricultural lands and residential areas; sediment from improperly managed construction sites, crop lands, and eroding streambanks; and bacteria and nutrients from livestock, pet wastes, and faulty septic systems.

occlusion: coprecipitation where an adsorbed impurity gets physically trapped inside the crystal as it grows.

oligotrophic: oligotrophic lakes have low nutrient levels and low primary productivity.

point source pollution: a single, identifiable localized source of pollution, such as pollution released from industrial plants, commercial businesses or wastewater treatment plants.

primary productivity: the production of organic compounds from atmospheric or aquatic carbon dioxide, principally through the process of photosynthesis.

Secchi disk: an 8-inch diameter plate with alternating quadrants painted black and white that is used to measure water clarity (light penetration). The disk is lowered into water until it disappears from view. It is then raised until just visible. An average of the two depths, taken from the shaded side of the boat, is recorded as the Secchi disk reading.

stratification: the layering of water due to differences in density. Water’s greatest density occurs at 4°C. As water warms during the summer, it remains near the surface while colder water remains near the bottom. Wind mixing determines the thickness of the warm surface water layer (epilimnion), which usually extends to a depth of about 20 feet. The narrow transition zone between the epilimnion and cold bottom water (hypolimnion) is called the metalimnion or thermocline.