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Effects of Irradiance on Benthic and Water Column Processes in a Gulf of Mexico Estuary: Pensacola Bay, Florida, USA
Citation:
MURRELL, M. C., J. G. CAMPBELL, J. D. HAGY, AND J. M. CAFFREY. Effects of Irradiance on Benthic and Water Column Processes in a Gulf of Mexico Estuary: Pensacola Bay, Florida, USA. Estuarine Coastal and Shelf Science. Elsevier Science Ltd, New York, NY, 81(4):501-512, (2009).
Impact/Purpose:
To examine the effect of light on water column and benthic fluxes in the Pensacola Bay estuary, a river-dominated system in the northeastern Gulf of Mexico. Results from this and related studies support development of nutrient criteria under the Clean Water Act, Water Quality Multi-Year Plan, Long Term Goal 1.
Description:
We examined the effect of light on water column and benthic fluxes in the Pensacola Bay estuary, a river-dominated system in the northeastern Gulf of Mexico. Measurements were made during summer 2003 and 2004 on 16 dates at along depth and salinity gradients. Dissolved oxygen fluxes were measured in sediment and water column samples exposed to a gradient of photosynthetically active radiation. Sediment inorganic nutrient (NH4+, NO3-, PO4-) fluxes were measured. The response of dissolved oxygen fluxes to variation in light was fit to a photosynthesis-irradiance model; the parameter estimates were then used to calculate integrated production in the water column and the benthos. The results suggest that shoal environments support substantial benthic productivity, averaging 13.6 ± 4.7 mmol O2 m-2 d-1, whereas channel environments support low benthic productivity, averaging 0.5 ± 0.3 mmol O2 m-2 d-1 (± SE). Estimates of baywide microphytobenthic productivity ranged from 8.1 to 16.5 mmol O2 m-2 d-1, comprising about 16 to 32% of total system productivity. Benthic and water column dark respiration averaged 15.2 ± 3.2 and 33.6 ± 3.7 mmol O2 m-2 d-1, respectively, or 31% of baywide integrated system respiration. Inorganic nutrient fluxes were generally low compared to literature values, and responded minimally to light exposure. Across all stations, nutrient fluxes from sediments to the water column averaged 1.11 ± 0.98 mmol m-2 d-1 for NH4+, 0.58 ± 1.08 mmol m-2 d-1 for NO3-, 0.01 ± 0.09 mmol m-2 d-1 for PO43-. The results of this study illustrate how light reaching the sediments is an important modulator of benthic nutrient and oxygen dynamics in the Pensacola Bay system