Science Serving Maryland's Coasts
Roger Newell, Ph.D.
Horn Point Laboratory
The Effects of Nutrient Availability on Bacterial Growth Efficiency in Aquatic Salt Marsh Ecosystems
The purpose of this study was to determine the influence of nutrients on bacterial metabolism in salt marsh water with respect to the natural system and under conditions of experimental nutrient enrichments. Water samples were collected from the Monie Bay National Estuarine Reserve in Maryland during June and August 1999. Control and enriched samples were incubated over a 36 hour period in an environmental growth chamber at ambient temperature. Nitrogen and phosphorus were added to samples to achieve 80μM (NH4) 2SO4 and 5μM KH2PO4 concentrations. Bacterial production rates were measured using the 3H-leucine uptake method (Smith et al. 1992) and bacterial respiration was measured as changes in Oz concentrations using membrane inlet mass spectrometry (Kana et al. 1994), 4 gradient of nutrients was found in the natural system with a corresponding gradient of bacterial growth efficiency and bacterial production. Total nutrient concentrations (N and P) and average growth efficiencies were highest in Little Monie Creek, a tidal creek in close proximity to a chicken farm, and lowest in the Open Bay. Little Monie Creek was not limited by nutrients while the Open Bay waters and Little Monie Creek was not limited by nutrients while the Open Bay waters and Little Creek, a relatively pristine tidal creek were limited by nitrogen, phosphorus, or both. The experimental nutrient additions of nitrogen, phosphorus and nitrogen and phosphorus resulted in increased growth efficiencies for the Open Bay and Little Creek, but not for Little Monie Creek. The results suggest that bacterial growth efficiency is positively related to nutrient concentrations in Monie Bay National Estuarine Reserve.
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