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THE NITROGEN CYCLE IN SURFACE WATERS
PHYTOPLANKTON ELEMENTAL COMPOSITION
• O 53%• C 27%• K 6.2%• H 5.5%• N 4.6%• Ca 1.0%• S 0.7%• Na 0.7%• P 0.5%
• Fe 0.4%• Mg 0.4%• Zn 0.3%• Cu 0.02%• B 0.01%• Mn 0.009%• Co 0.0006%• V 0.0006%• Mo 0.0001%• Si 0.1%; DIATOMS 20%
N2
FIGURE 12-1; N2 IN GREEN LAKE AND BELOIE LAKE
N-FIXATION
CYANOBACTERIA AND N-FIXATION
OTHER MICROBIAL NITROGEN FIXERS
• Azotobacter
MEROMICTIC LAKES AND N-FIXATION
SYMBIOSIS
• N-FIXATION OFTEN THROUGH SYMBIOSIS WITH VASCULAR PLANTS e.g.– Alders (wetland plants)– Legumes– Azolla (aquatic fern)
AMMONIUM AND NITRATE
AMMONIUM
• BY-PRODUCT OF DEAMINATION• NH4
+ and NH4OH (see p233)
pH NH4
+ : NH4OH
6 3000:1
7 300:1
8 30:1
9.5 1:1
NITROGEN CYCLE
NITRIFICATION
• NH4+ NO2
- Nitrosomonas– Requires O2; wide range of temperature and pH
• NO2- NO3
- Nitrobacter– Requires O2; warm temperatures and low pH
DENITRIFICATION
• C6H12O6 + 12NO3- 12NO2
- + 6CO2 +6H2O
• C6H12O6 + 8NO2- 4N2 + 2CO2 + 4CO3
-- + 6H2O
REDUCTION IN AN ANOXIC ENVIRONMENT
NITRIFICATION AND DENITRIFICATION
ORGANIC NITROGEN
• DISSOLVED ORGANIC NITROGEN (DON)
• PARTICULATE ORGANIC NITROGEN (PON)
• DON:PON INCREASES WITH EUTROPHICATION
NITRATE AND PON
INORGANIC NITROGEN IN WINTERGREEN LAKE
NITROGEN CYCLE
NITROGEN IN STREAMS
NUTRIENT SPIRALLING
NITROGEN LOADING
NITRATE IN THE CHESAPEAKE BAY
Dead Zone summer 2011, USEPA