CHAPTER 8 

THE NITROGEN AND PHOSPHOROUS CYCLES 

    •  NITROGEN 

    •  
      •  is very important as a nutrient for both plants and animals.  It is a major component of amino acids, which forms proteins;
      •  is an essential component of genetic material ? RNA and DNA;
      • forms 20% of our body weight as proteins, hormones and enzymes;
      • mammals (humans) eliminate Nitrogen as uric acid in urine;
      • aquatic animals eliminate Nitrogen as urea and ammonia from gills;
      •  comprises 79% of the atmosphere  (when atmospheric Nitrogen exists at nitrogen oxides and dioxides = smog).
      •  A continuous cycle of reuse-renewable.
       
    • Sources of Nitrogen in the Aquatic Environment

    •  
      • Natural 
       
          1. Biological Fixation - The conversion of atmospheric gaseous Nitrogen by bacteria and blue-green algae      into nitrates primarily, but also ammonia; accounts for most of the natural transformation of Nitrogen. 

          2. Atmospheric fixation - lightning. 

          3. Nitrification - ammonia (NH3) converted by nitrosomonas to nitrite (NO3).  Nitrite converted by nitrobacteria into Nitrate.  These processes lower dissolved oxygen and pH.  What does this mean in terms of water quality testing? 

          4. Denitrification - release nitrogen from nitrates back to the atmosphere. 
           

      • Human 
       
          1. Whether through pollution of the air or land or directly into the water, manís (anthropocentric) activities generate the majority of the excess nitrogen in aquatic systems.  The effluents from domestic or municipal wastewater treatment plants are a major and direct source of nitrogen into water bodies.   Waste Water Treatment Plants (WWTP) treat approximately 9 lbs. of waste per person per year. 

          2. Runoff from feedlots and other areas where large numbers of domesticated animals are kept contains much nitrogen.  This can be a significant problem that not only results in surface water contamination but also contamination of shallow aquifers. 

          3. Also, agricultural lands are fertilized and irrigated.  Runoff carrying nitrogen can be significant.   As much as 75% of applied synthetic fertilizers can leach down and pollute subsurface waters.  In cities, storm sewer systems are also a major source of nitrogen pollution.  In rural and suburban environments, septic tanks and similar small treatment systems discharge nitrogen contamination directly to the subsurface soils. 
           

       
    • PHOSPHOROUS
    • Sources of Phosphorous in the Aquatic Environment 
       

      • Natural:
       
          1. Phosphate rock -exposed to weathering processes begin to break down the deposits. 

          2. Birds - waste from sea birds, called guano, as a result of their food chains. 

          3. Red Clay (sediment) 

          4. Detrital breakdown of phosphorous in benthic sediments (internal loading); upwelling of deep ocean waters makes this source available to organisms in the water column. 

          5. 1 mg of organic phosphorous in a lakeís cycle will require about 130 mg. of oxygen to break it down to orthophosphate.  Can cause anaerobic conditions. 
           

       
      • Human 
       
          1. Domestic and industrial wastewater discharges.  Half comes from human waste. 
                About 20-30% from detergents 

          2. Runoff. 
           

       
      • Effects 

      • Eutrophication -Phosphorous is first limiting element.  It is largely a freshwater problem in lakes and shallow water bodies.  When phosphorous levels are above .05 ppm, excessive growth of algae can occur.  Small changes in the phosphorous concentration can have dramatic effects. 

        Three categories of phosphorous: 

          1. Orthophosphates: 
            Most trouble for freshwater aquatic systems 
            The kind used in fertilizer (soluble in water) 
            Contribute significantly to Eutrophication. 

          2. Condensed phosphates: 
             Come from detergents and water treatment processes 
             Are dehydrated, and in fresh water convert slowly back to the ortho form. 

          3. Organically bound phosphorous: 
             Necessary for life 
             A component of DNA, fats and ATP 
             It can be the limiting element responsible for Eutrophication. 

       
       
      • Eutrophication: 
       
         The fertilization of water with nutrients, especially phosphorous. 
         Results in nuisance algae blooms and potentially fish kills. 
         Algae blooms can make drinking water smell and taste like petroleum and/or fish. 
         
      • Causes: 
       
          1. Sewage that contains phosphorous-rich detergents, human wastes or animal wastes. 
          2. Urban runoff contaminated by fertilizer. 
           
      • To reverse Eutrophication, must reduce phosphorous by: 
       
          1. Requiring BNR in WWTP. 
          2. Setting phosphorous limit of 1 mg/L in NPDES permits. 
          3. Buffer zones. 
          4. No more chem-lawn. 
           
         
 
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