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

The distributions of porewater reactive phosphorus (RP), NH 4 + , K, and inorganic carbon (ΣCO 2 ) 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 NH 4 + 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 ΣCO 2 and K in the porewaters. Exchangeable NH 4 + 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 NH 4 + 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.