Anthropological activities crucial to food production that can have significant impact on lakes are agriculture and raising animals. Which organisms may be affected, and how are these abiotic features tested by an ecologist?
The term “lake” may be applied to bodies of water of many different sizes and configurations. Limnology is the science that studies lakes. One abiotic feature is the type of ecosystem in which the lake is located. Along with location, the size has a strong effect on the organisms that live in and around it. For example, Lake Titicaca, shared by Peru and Bolivia at about 3,800 meters (more than 12,000 feet) above sea level, has a unique ecosystem in part because of its very high-altitude location.
In all lakes, fluctuations in water level mean that the shoreline constantly changes, which affects the kinds and amounts of plants and animals that will thrive there as well as in the deeper part of the lake. The close interactions among all aspects of a given ecosystem, which may be described as an ecological pyramid, mean that changes to one abiotic feature are likely to impact every organism. The decayed organic material, or detritus, within lake systems is crucial, because of its role in sustaining life.
The world’s largest freshwater lake by volume is Russia’s Lake Baikal, which holds more than 23,000 cubic kilometers (about 5,670 cubic miles) of water; its far northern location means that it is frozen for at least one-third of the year. This clearly demonstrates the importance of another abiotic feature: temperature.
The abiotic features characteristic in a given ecosystem include wind and current. These effect temperature and the surface and subsurface movement of water. Light is another abiotic feature which is crucial to the biota, because plants need it for photosynthesis. This process is related to the abiotic feature of chemistry, including oxygen production. Changes may occur because nutrients, such as nitrogen and phosphorous from fertilizer, have been added; this process is called eutrophication. Other changes include salinization from erosion or runoff, which may affect the terrain of the lake, whether along the shore or at the lake’s bottom.
The tests that would determine how pollution, often from runoff resulting from farming and ranching activities, would vary according to specific factors. Some of the most commonly applied tests are for E. coli bacteria, total dissolved solids, pH, hardness, iron and manganese, aluminum, and sulfates. Temperature is tested with a thermometer. Specific meters or less-expensive kits can measure dissolved oxygen. A Secchi test for cloudiness, indicating sediment, is done by lowering the black-and-white Secchi disk into the water.