Ecological Implications

How Wetlands Reduce Excess Nutrients

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Wetlands are home to many different species of plants which are adept at living in saturated, low oxygen conditions. Many different microorganisms and plants house bacteria that uptake and utilize nitrogen through the processes of nitrification and ammonification. Nitrification either results in absorption and conversion into organic matter or immobilized on negatively charged soil particles. (Mitsch, 1999). The semi-stagnant quality of wetlands also allows sediment and phosphorous settling into the benthos. To assist with the excess nutrients, wetlands can be established as sinks, or a wetland that exports lower nutrients than are imported into said wetland (Mitsch, 1999). High nutrient discharge amounts generally occur only during and directly after storm events (Raisin, 1995). During the rest of the year, these sink wetlands function as a nutrient absorber, or a “natural kidney”. The time in between storm events affects how much nutrient absorption occurs, because the longer time water resides in the wetland, the more nutrients are utilized (Raisin, 1995). Mitigation and creation of wetlands is a difficult process, and obviously requires a great deal of research into what type of wetland should be created, as well as factors such as hydrology, flow measurements and more. Much research has been used to determine how created wetlands deal with nutrient loading. Raisin et al. created a gravel-based wetland to determine nutrient loading and compare levels of inflows and outflows. Knowing that storm events drastically affect nutrient loading, they tested levels both prior to the event and at peak event flow. Total phosphorous prior to the event was 0.2-0.4 mg1-1, at peak flow increased to 1.0mg1-1. In contrast, measuring outflows, total phosphorous prior to the event was 0.1 mg 1-1, and during peak flow was measured at only 0.68mg 1-1. Storm flows also affect nitrogen levels. In between February 1994 and January 1995, nitrogen inflows measured 90.3 kilograms. 29.2 kg entered solely during storm events, primarily from agriculture runoff. 10.3 kg, or 11% of total nitrogen was succesfully retained (Raisen, 1997). Out of 33 separate storm events, 22 of them resulted in wetland nitrogen retention. Types of nitrogen that were retained began with organic nitrogen, less commonly ammonia and nitrate (Raisen, 1997).

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