Spatial and Temporal Coupling of Nutrient Inputs to Estuarine Primary Production: The Role of Particulate Transport and Decomposition
Spatial and temporal aspects of the coupling of nutrient inputs to estuarine primary production are discussed in terms of formation, transport and decomposition of particulate material in the Patuxent River estuary. Mixing diagrams of dissolved and particulate nitrogen and phosphorus (DIN, PN, DIP, PP) versus salinity indicate rapid removal of DIN and DIP with parallel formation of PN and PP in the slightly brackish (0–5‰) region. However, plankton production (per m2) tends to be inversely related to salinity between 0 and 10‰. While most of the annual nutrient inputs to the Patuxent occur between December and April, peak plankton production occurs in the summer. Deposition and resuspension of particulate substances in this system are dynamic processes which decrease in a seaward direction. Regeneration of DIN and DIP from particulate decomposition in the sediments similarly decreases toward the estuary's mouth; however, highest rates are in the 5–10‰ region. Temporal patterns of benthic regeneration and plankton production are congruent (being generally related to temperature), and rates of sediment NH4 + recycling represent about 60–80% of the plankton assimilative demand in the 5–10‰ region. On the basis of these observations we propose a conceptual model in which annual inputs of dissolved nutrients from runoff are converted into particulate forms which are gradually transported seaward through cycles of deposition and resuspension. As temperatures rise in the summer these particulates are decomposed, releasing dissolved nutrients to the euphotic zone where they support the major annual blooms of plankton. By comparing these patterns for the Patuxent with those reported for other estuaries, it is suggested that this model may be relatively general for many coastal systems.
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Document Type: Research Article
Publication date: 01 November 1984
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