Dynamics of Dissolved Organic Carbon, Nitrogen and Phosphorus in a Seagrass Meadow of Laguna Madre, Texas
Seasonal and diel dynamics of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) were investigated in a Thalassia testudinum Banks & Soland. ex Koenig dominated seagrass meadow. Heterotrophic utilization was an important determinant of the seasonal and diel changes in the C, N, and P content of DOM. Bacterial growth efficiency (BGE) was positively correlated with the C:N ratio of bulk DOM and negatively correlated with the C:N ratio of bioavailable DOM. Highest BGE and DOM bioavailability were associated with the highest concentrations of DON and DOP, suggesting N and P were major components of bioavailable DOM. The concentration of DOC accounted for only ~30% of the variation in DON and DOP concentrations, indicating a decoupling of DOC cycling from that of DON and DOP. Mean residence times (Rt) of DOC were always higher (12–16 d) than those of DON (3–6 d) and DOP (1.4–5.0 d), suggesting the following reactivity of these pools: DOP>DON>DOC. Differences in mean Rt were attributed to differences in sources and processes affecting each organic nutrient. Results from this study demonstrate the importance of DOM cycling to the nutrient dynamics of a productive seagrass ecosystem, and how changes in both microbial activity and DOM source impact the biogeochemical cycling of N and P.
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Document Type: Research Article
Publication date: 01 November 2004
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