『Abstract
The watershed of the Altamaha River, Georgia, is one of the largest
in the southeastern U.S., draining 36,718 km2 (including
parts of metro Atlanta). We calculated both nitrogen (fertilizer,
net food and feed import, atmospheric deposition, and biological
N fixation in agricultural and forest lands) and phosphorous (fertilizer
and net food and feed import) inputs to the watershed for 6 time
points between 1954 and 2002. Total nitrogen input rose from 1,952
kg N km-2 yr-1 in 1954 to a peak of 3,593kg
N km-2 yr-1 in 1982 and then declined to
2,582kg N km-2 yr-1 by 2002. Phosphorus
inputs rose from 409 kg P km-2 yr-1 in 1954
to 532 kg P km-2 yr-1 in 1974 before declining
to 412 kg P km-2 yr-1 in 2002. Fertilizer
tended to be the most important input of both N and P to the watershed,
although net food and feed import increased in importance over
time and e\was the dominant source of N input by 2002. When considered
on an individual basis, fertilizer input tended to be highest
in the middle portions of the watershed (Little and Lower Ocmulgee
and Lower Oconee sub-watersheds) whereas net food and feed imports
were highest in the upper reaches (Upper Oconee and Upper Ocmulgee
sub-watersheds). Although the overall trend in recent years has
been towards decreases in both N and P inputs, these trends may
be offset due to continuing increase in animal and human populations.
Keywords: Altamaha River; Nitrogen budgets; Nutrient inputs; Phosphorus
budgets; spatial distribution; Temporal trends』
Introduction
Methods
Watershed delineation
Nutrient budgets
Fertilizer
Net food and feed import
Net atmospheric N deposition
Nitrogen fixation
Non-food crop export
Results
Temporal trends
Fertilizer
Net food and feed import
Net atmospheric N deposition
Biological N fixation
Non-food crop export
Dominant sources
Spatial distribution
Fertilizer
Food and feed import
Net atmospheric N deposition
Biological N fixation
Overall nutrient distribution
Discussion
Acknowledgments
References