How Do Phosphates Affect Water Quality?
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Phosphorous allows plants and animals to grow and function. In animal nutrition---including human nutrition---the element is necessary for strong bones and teeth. In plants and animals alike, phosphorous is a component of Adenosine Tri-phosphate, or ATP, which is the very basic source of energy for all cellular work. As such, phosphorous is a key component of plant fertilizers---and therein begins a problem. Phosphorous that's applied to the land in large doses, as it is in farming, doesn't always stay on the land. It leaches from the soil and makes its way to rivers, streams, and eventually the ocean. As essential as it is for life, too much phosphorous in lakes and oceans can cause the food web foundation---including algae and plankton---to go into overdrive, starting an imbalance that ripples all the way through aquatic systems.
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Without added phosphorous from human activities, phosphorous cycles in a nearly closed loop from plants, to the animals that eat them, to decomposers like fungi, into the soil and back to plants again. A small amount will leach out of the soil into the water supply, but much of that falls to the bottom as sediment. It takes a very rare, major geological event to bring such sediment back to the surface again. But human activities like farming and ranching contribute much more phosphorous to the entire cycle. Through farming, more phosphorous makes it into the plants, soil and eventually the waters. Decomposing animals and their feces are another prominent source. In small amounts, a little extra phosphorous may not look like a bad thing. With a boost in plankton and algae, fish may grow larger and faster. In larger amounts, phosphorous can make aquatic systems so productive that they choke themselves out.
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Eutrophication is a term for what happens when algae becomes unusually productive in a water system. Eutrophic lakes are easy to spot, with their slimy, algae-covered rocks and even surfaces that are filled with green algae and sometimes other plants. Nitrogen, another fertilizer component, is the most likely unnatural additive to create this effect, because it is not stored in the soil as well as phosphorous. But elevated phosphorous can also contribute. The problem with a bumper crop of organisms at the base of the food chain is that it can fuel boosts in productivity at the higher levels, too. More fish may at first seem like a good thing, for example. But more fish means more death and decay. That yields increases in the animals like crabs and lobsters that thrive on the decay. Together, all of these extra, higher-level animals use a lot of oxygen. All over the world---especially in places where rivers carry agricultural runoff into the oceans---researchers are finding increasing numbers of "dead zones" that are so oxygen-deprived, fish and other marine organisms can't live in them. For their part, farmers are working hard to come up with solutions. But their challenge is daunting.
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