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Title: Sediment-submersed macrophyte relationships in freshwater systems
Authors: Aquatic Plant Control Research Program (U.S.)
Barko, John W.
Smart, R. Michael.
Matthews, M. Susan.
Hardin, Dwilette G.
Keywords: Aquatic plants
Freshwater ecology
Freshwater flora
Issue Date: Jun-1982
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: The capabilities of four species of submersed freshwater macrophytes in mobilizing nitrogen (N), phosphorus (P), and potassium (K) from three different sediments were comparatively examined in relation to their requirements for these nutrients during a 10-week period of growth under controlled environmental conditions. With all species, N and P were readily mobilized from each of the sediments and concentrated in plant shoots at levels well above those required for growth. However, the mobilization of K from all sediments was much less effective and may have limited the growth of the species considered. Sediments represent a large and important source of N and P for rooted aquatic macrophytes, but K is probably supplied to these plants primarily from the water. Only small quantities, or none at all, of N and P were excreted from the species considered during active growth. However, considerable quantities of these nutrients can be released to the water due to plant senescence and associated decay processes. Since a large fraction of the total nutrients, in particular N and P, released during decay may derive f rom the sediment, this mechanism represents an important mode of sediment-nutrient recycling in aquatic systems. In a subsequent related investigation, K uptake by Hydrilla verticillata Royle from sediment versus overlying water was evaluated in relation to the K demands incurred by this species during an 8-week period of growth. The investigation was conducted on a heterogeneous assemblage of sediments and in two solutions differing fundamentally in the presence (2.3 mg/l⁻¹) and absence of K. Both biomass production and shoot morphology in Hydrilla varied significantly between solutions and among sediments. In contrast to N and P, which were readily mobilized from most sediments, K was mobilized from all sediments to only a minor extent by this species. Mobilization of K was proportional to interstitial water K concentrations ; yet on at least four of the six sediments examined, K supplied from sediments was insufficient to support the maximal growth of Hydrilla. The open water rather than the sediment appears to be the primary source of K supply to this species and perhaps to most other submersed freshwater macrophytes. Where K was supplied in solution, sediment-related differences in the growth of Hydrilla negatively correlated with sediment organic matter content over the range of 1.6 tc 56.2 percent dry sediment mass. It is tentatively suggested that the organic composition of sediments may influence the species composition of aquatic macrophyte communities.
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