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Nutrient Delivery to the Coastal Zone by the Altamaha River


PI: James T. Hollibaugh (Dept of Marine Sciences, Univ of Georgia, Athens, GA, USA)

Support: GA DNR Coastal Management Program (through a Coastal Incentive Grant)

Timeframe: 2005 - 2007

Project Overview:
We collected samples from the Altamaha River (at Doctortown) and its major tributaries, the Oconee, Ocmulgee and Ohoopee rivers, between October 1, 2004 and September 30, 2007. A total of ~140 samples from the Altamaha River (about 8 samples a month) were collected to determine concentrations of dissolved nutrients to determine concentrations of dissolved nutrients (NO2-, NO3-, NH4+, HPO42-, and H2SiO42-), dissolved organics (DOC, TDN, DON, TDP, and DOP), chlorophyll and particulate C and N.   

Findings:

Spatial and temporal variations over time were apparent.

  • Nitrate dominated the dissolved inorganic nitrogen (DIN) pool and concentrations varied between 0.4 and 49 micromolar (hereafter “µM” referring to micromoles per liter) and the average nitrate concentration was 18.8 (±18.05) µM.  Nitrate concentration was inversely correlated with discharge, so high flows were characterized by low nitrate concentration.
  • The average NOx concentration was 19.4 (±10.30 and the dominant component (96%) of NOx pool was nitrate; the average nitrate concentration was 18.64 (±10.5) μM. Nitrite averaged only 0.35 (±0.33) μM.
  • Ammonium concentrations were always less than 10 μM; the average concentration was 1.9 (±1.7) μM.
  • Concentrations of dissolved organic nitrogen (DON) were always equal to or greater than dissolved inorganic nitrogen (DIN) concentrations and DON concentrations were much less variable over time than DIN concentrations.
  • Concentrations of dissolved inorganic phosphorus (DIP) were typically less than 1 µM and exhibited no discernable pattern relative to DIN concentration. The average inorganic phosphate concentration was 0.54 (±0.35) μM.  The DIN:DIP ratio varied but was almost always (>91% of the time) elevated above the Redfield Ratio of 16:1; the average DIN:DIP ratio was 46.2 (±33.6) μM.
  • Concentrations of dissolved organic phosphorus (DOP) were equal to or greater than DIP concentration; the average DOP concentration was 0.99 (±0.63) μM.
  • Silicate concentrations varied significantly over time with maxima in the summer and minima in the winter and spring.  The average silicate concentration was 193.2 (±66) μM (Table 2) and the average ratio of dissolved silicate to dissolved inorganic nitrogen was 9.1 (±5) μM.
  • Dissolved organic carbon (DOC) concentrations varied substantially, ranging between 126 and 1158 μM.

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This page was updated September 1, 2009