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Measured Removal of Nitrogen from Drainage Through Riparian Buffers (per 100’) Quality of Buffer Nitrogen Removal High68-92% Medium45-68% Low15-45% From:

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1 Measured Removal of Nitrogen from Drainage Through Riparian Buffers (per 100’) Quality of Buffer Nitrogen Removal High68-92% Medium45-68% Low15-45% From: US Department of Agriculture

2 Nitrogen Removal or Accumulation Processes Storage in Vegetation Storage in Soils Biological Denitrification Chemical Denitrification Volatilization

3 Nitrogen taken up by plants is used to build tissues and is stored as protein. Woody vegetation accumulates nitrogen on a scale of decades to centuries. The greatest accumulation occurs during the transition from one steady state to another (e.g. when farmland is converted to grassland and forest). Harvesting prolongs the accumulation period. Storage in Vegetation

4 Detritivores reduce dead organic material into (detritus) simpler compounds and relatively stable residual organic materials that are collectively referred to as soil organic matter. These are generally complex long-chained organic compounds. Soil organic matter reaches a steady state with additions from dead material and losses as ammonia and nitrate. The residence time of nitrogen in soils is on a scale of decades to centuries. Storage in Soils

5 This process occurs in oxygen-depleted environments typical of saturated soils and wetlands. Anaerobic organisms utilize the oxygen in nitrate and the carbon in organic matter for their metabolism. The net result is a release of elemental nitrogen (N 2 ) nitrous oxide (N 2 O), and carbon dioxide (CO 2 ) as gases to the atmosphere. Saturated soils and wetlands could in principle supply the biomass for denitrification indefinitely. Biological Denitrification

6 In oxygen-depleted environments there are chemical as well as biochemical pathways for denitrification. In soils and wetlands it is difficult to separate these biological from chemical processes. Chemical denitrification processes are much more important in deeper aquifers than in soils, wetlands, and shallow aquifers. Chemical denitrification processes primarily involve reduced iron and sulfur compounds. Nitrate is converted to nitrogen gas (N 2 ) and iron and sulfur are oxidized. Depletion of iron and sulfur compounds in deeper aquifers will occur on a scale of decades to centuries or perhaps even millennia. Chemical Denitrification

7 Ammonia (NH 3 ) volatilization and loss to the atmosphere can occur where organic materials are decomposing under anaerobic conditions. Ammonia loss from non-agricultural soils and wetlands is generally a minor pathway for nitrogen removal. Ammonia is very soluble in water and has a short residence time in the atmosphere. Almost all of this loss to the atmosphere returns to the soil with rainfall within a few days over a dispersed area. Volatilization

8 Wells in Olmsted County that Exceeded the Nitrate Drinking Water Standard by Geologic Formation ( ) From: Olmsted County Well Index, Minnesota Geological Survey, Bedrock FormationPercent of Wells Upper Carbonate27 St. Peter 5 Prairie du Chien 7 Jordan 1

9 Cropland draining to forested hillsides

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15 Olmsted County Nutrient Balance For Agriculture ( Average)

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