Overloading in Fresh Waters 1. Nutrients and Nutrient Overloading 2. OM and BOD Overloading
river N and P cycles, revisited. The concentrations of N, P C and O in the hydrosphere are intricately related by the Redfield relationship. N (+)/P (+) = 16 CO2 (+)/N (+) = 6.6O2(+)/N(-) = 8.6
CO2 (+)/P (+) =106 O2(+)/P(-) = 138 O2 (+)/CO2 (-) = 1.3
Atmosphere exchanges. Nitrogen:¡°fixed¡± N occurs in a number of gaseous forms that are easily exchanged to the atmosphere. Natural sources of atmospheric"fixed" N (NOx and NH3) are: directemission by the biosphere and from soils minor NOx production by lightening Anthropogenic sources: NOx production by pollution (especially internal combustion) N2 + O2 + heat Phosphorous: occurs mostly in insoluble, inorganic forms (not easily exchanged to the atmosphere). NOx
Atmosphere exchanges. NH3 vapordissolves in rain to produce NH4+ and OH- (base) NOx vapor dissolves in rain to produce NO3- and H+ (acid) But, the rain flux of[N] and [P] to the landscape is very small. Marine rain: [N] and [P] of surface sea water are VERY low (consumed during photosynthesis), so [N] = [P] ~ 0 inmarine aerosols. N in terrestrial rain derives from atmospheric gasses primarily, with particulatesrunning a distant second P in terrestrial rain derives primarily from terrestrial particulates; [P]rain is very low. Changes in of NO3- and NH4+ distributions in North American Rain between 1955 and 1980. Nitrate increases in the east and decreases in the west due to increased and decreased pollutiveinput, respectively. Ammonium increases everywhere due primarily to a tripling of the use of ammonium-based fertilizerswithin the continental US over this time interval. [N] and [P] in terrestrial surface fresh waters (Rivers):
The [N] cycle has significant gas phase and biological components, with a large modern anthropogenic perturbation. [N] enters rivers primarily through discharged soil waters. Soils are an important source of NH4+ and NO3to the hydrosphere...
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