Nutrient Dynamics in a Littoral Sediment Colonized by the Submersed Macrophyte Myriophyllum spicatum

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Abstract
The distributions of porewater reactive phosphorus (RP), NH4+, K, and inorganic carbon (ΣCO2) are compared for sediments colonized by Myriophyllum spicatum (9–40 g∙m−2) and sediments experimentally maintained plant-free. Porewater nutrients are characterized by a high spatial and temporal variability. During the summer months, root activity induces marked reductions in porewater RP and NH4+ between 5 and 38 cm. However, this trend is reversed in spring and fall when higher nutrient concentrations are observed in the colonized sediments, presumably as a result of root decay. Root activity is also associated with higher ΣCO2 and K in the porewaters. Exchangeable NH4+ is the largest pool of available N and exhibits a relatively rapid (9.5–24 d) turnover time in colonized sediments. The mineralization of organic matter is an important source of sediment NH4+ and comparable in quantity with the N requirement of the macrophytes. These results suggest that under conditions of nutrient limitation, the rate of nutrient production from sedimentary organic matter decomposition may be a good predictor of macrophyte growth.