The primary productivity of a lake is the productivity of the photosynthesizers at the base of the food chain in lake ecosystems. This refers to the supply of new biomass growth during a certain time period. Consumers derive all their energy from primary production, either from eating plants, or indirectly (Predators). Lakes are one of the least productive ecosystems when it comes to net primary productivity because climate and nutrients control primary productivity. Areas that are warm and wet generally are more productive. The littoral zone of a lake is the area near the shore where sunlight penetrates all the way to the lake floor and allows for aquatic plants to grow. Algae is also considered a primary producer. Autotrophs are organisms that create their own energy through the process of photosynthesis, and are more effective in primary producing than heterotrophs (Axler, 2010). Heterotrophs can only get energy by feeding on other organisms.

Primary production in relation to Lake Champlain has recently been dominated by algal blooms. Algal blooms are a result of eutrophication, or an excess of nutrients in the lake from runoff, causing rapid growth in plants and algae. Phosphorus is the primary limiting factor in the growth of primary producers in Lake Champlain. Agricultural land that drains into a sub-basin, or a basin that is only drained by one river/stream, is a major source of phosphorus. The naturally eutrophic parts of Lake Champlain are usually bordered by wetlands where decaying plants and algae cycle phosphorous back into the depths of the lake (Spahr, 2010).Water chestnut is another invasive species that crowds out native plants and is of little food value to wildlife, therefore hindering primary production.

All life on Earth is in some way reliant on primary production, but in relation to lakes, the main function of primary production is to produce oxygen for marine life and form the base of the food chain. Herbivores consume these producers, and herbivores are consumed by other predatory species, passing on the nutrients and energy that fuels the food chain (Herbert, 2007). Marine fish and animals would not be able to exist without plant life to support them.

Measuring aquatic primary production can be done in several ways. First would be to calculate oxygen concentration. Second is the incorporation of inorganic carbon. Last is to calculate fluorescence kinetics. Gross primary production value can then be determined and measures can be taken to reduce nutrient levels if eutrophication is too high. It can also be measured by recording the rate of new biomass accumulation over time. The difference between gross primary production, net primary production, and net ecosystem production is important for understanding the energy balance in plants and the rest of their ecosystem.

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