GCRC Project Summary |
Long-Term
Water Quality Sampling
of the Skidaway River Estuary
PI: Peter Verity (Skidaway Inst. of Oceanography, Savannah, Georgia, USA)
Support: The National Science Foundation, Department of Energy, and Georgia Sea Grant College Program all provided general support during the project period, although the sampling program was not a grant-funded project.
Timeframe: 1986 - ongoing
Project Overview:
Starting in 1986, samples were taken at weekly intervals, at high and low tide
on the same day at a single site from the waters adjacent to the docks at the
Skidaway Institute of Oceanography. Hydrography, nutrients, chlorophyll
a, particulate matter, and microbial and plankton biomass and composition
were measured.
Findings:
- Salinity varied inversely with river discharge and exhibited variability at all time scales, but with no long-term trend.
- Water temperature ranged over 25 degrees C, and was without apparent long-term trend.
- Seasonal cycles in concentrations of NO3, NH4, PO4, Si(OH)4 and DON were observed, with annual maxima generally occurring in late summer.
- Superimposed on seasonal cycles, all five nutrients exhibited steady increases in minimum, mean, and maximum concentrations; mean concentrations increased c. 50-150% during the decade.
- Nutrient concentrations were highly correlated with water temperature over the 10-year period, but weakly related to salinity and discharge.
- Nutrients were strongly correlated with one another, and the relative ratios among inorganic nutrients showed little long-term trend.
- Correlations among temperature and nutrient concentration exhibited considerable inter-annual variability.
- Major spikes in organic and inorganic nutrient concentrations coincided with significant rainfall events.
- All classes of particulate organic matter exhibited distinct seasonal patterns superimposed upon significant long-term increases during the study period.
- Chl a increased 18-61% over ten years (depending on size fraction).
- Particulate organic carbon and nitrogen increased 16% over the decade, and exhibited increases in annual amplitude.
- The C:N ratio was typically 6.4-6.6 (wt:wt) and did not change significatntly, while the annual mean C:Chl a ratio decreased 19% from 165 to 140.
- Temperature explained 45-50% of the variance in particulate organic matter.
- Ambient concentrations of dissolved organic nitrogen or PO4 explained 60-75% of the variance in chl a, and particulate organic carbon and nitrogen.
- These data strongly suggest that anthropogenic activities contributed to increased loading of dissolved nutrients, which became incorporated into living and nonliving particulate matter.
Publications:
Verity, P.G. 2002. A decade of change in the Skidaway River Estuary. I. Hydrography and nutrients. Estuaries 25(5): 944-960.
Verity, P.G. 2002. A decade of change in the Skidaway River Estuary. II. Particulate organic carbon, nitrogen, and chlorophyll a. Estuaries 25(5): 961-975.