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