Anthropological activities crucial to food production such as agriculture and the raising of animals have an impact on lakes. Describe which organisms may be affected there and how these abiotic features are tested by an ecologist.

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Anthropological, or human activities and actions, such as agriculture and animal husbandry, can have devastating impacts on lake ecosystems. Ecologists often measure abiotic features to provide information about the health of fresh water habitats. Abiotic (non-living) factors can be more easily and quickly determined than biotic (living) ones. For example, it is quicker and easier to measure oxygen levels in a water sample than it is to measure complex interactions between autotrophs, producers, consumers, and decomposers.

When farmers plant crops, they often use nitrate-rich fertilizers to increase the health of their harvests and the size of their yields. Nitrates from chemical fertilizers eventually make their way into rivers, lakes, and streams through rain runoff over impervious surfaces. Inorganic salts from fertilizer also dissolve into ground water, which seeps into nearby bodies of water. Likewise, animal husbandry produces lots of manure or animal feces. Animal excrement leaches into soil and make its way into lakes through the same processes. Manure can also be used as fertilizer, so commercial farms might utilize a mix of the two in their operations.

A healthy lake ecosystem is able to easily filter out moderate amounts of excess nitrates—a process known as denitrification­—but large amounts, or unusual isotopes of nitrogen, are harder to naturally neutralize. During denitrification, nitrate is converted by bacteria in the lake into nitrogen which is then released into the atmosphere. When nitrate cannot be converted back into nitrogen, nitrate levels increase, leading to eutrophication.

Eutrophication occurs when increased nitrates are absorbed by algae, causing populations to grow out of control (algal blooms). Blooms create thick layers of algae to build up and film over the top of a lake’s surface. This bloom blocks sunlight from reaching the plants below and saps the water of oxygen, effectively creating a dead zone where neither plants nor fish can live. The result is an accumulation of decay at the bottom of the lake, which further contributes to increasing levels of toxic nutrients in the water.

To examine the health of a lake, an ecologist would examine abiotic components first. Abiotic components like sunlight, temperature, salinity, nutrient levels, and altitude may all offer insights into biotic conditions. In particular, an ecologist would test a lake ecosystem near large farms for elevated nitrate levels to determine the interactions between the fish, plants, and algae living there. Studying nitrate levels would show whether denitrification was taking place or if nutrient levels were building up to dangerous levels. Ecologists might also examine oxygen levels and sunlight levels, as eutrophication causes algal blooms to deplete the ecosystem of both.

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