Freshwater Ecology Practice Test

Understanding a watershed nutrient budget means accounting for every way nutrients can move, be stored, or change form inside the system. Inputs bring nutrients into the watershed through atmospheric deposition, precipitation, point and nonpoint source runoff, and biological fixation. Outputs remove nutrients via outflow, sediment burial, and uptake by plants and microbes. But the picture isn’t complete without internal storage and transformation: nutrients can be held in soils, sediments, and living biomass, sometimes for long periods, and they can be converted between forms (for example, from organic to inorganic, or between ammonium and nitrate) by biological and chemical processes. These internal storage and transformation processes can release or retain nutrients independently of immediate input or output changes, shaping how much nutrient leaves the system over time. Therefore, the most accurate description includes inputs, outputs, plus internal storage and transformation.