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Title: Effects of endothall treatment of phosphorus concentration and community metabolism of aquatic communities
Authors: Aquatic Plant Control Research Program (U.S.)
James, William F.
Keywords: Aquatic plants
Aquatic plant control
Aquatic ecology
Environmental effects
Issue Date: Feb-1984
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Miscellaneous Paper
Abstract: Herbicide treatment and macrophyte senescence may result in the recycling of phosphorus from aquatic weeds to nontarget species because the nutrient is rapidly leached from plant tissue. A field study and two microcosm experiments were conducted to examine changes in phosphorus, oxygen, and chlorophyll α concentrations after the application of the herbicide endothall. In each microcosm experiment, Potamogeton crispus communities were housed in 57-l aquaria containing known standing crops of the test plant and sediment with a specific phosphorus-adsorbing capacity. In the first microcosm experiment (experiment I), the application of 2.0 ppm endothall caused plant death and a rapid, short-term increase in soluble reactive phospho rus, presumably from excessive leaching during senescence. Although the sediment-adsorbing capacity for KH2PO4 wa s high and the microzone appeared to be oxidized throughout the experiment, leached soluble reactive phosphorus was still directly available for algal uptake. This resulted in an epipelic chlorophyll α increase after herbicide application. A second microcosm experiment, which employed six control and six experimentally treated systems, differed from microcosm experiment I in that the sediment used had a weak phosphorus-adsorbing capacity. In addition, the metabolism of the total microcosm and three autotrophic components (macrophyte-epiphyte, planktonic, and benthic) were monitored to assess the effects of an herbicide perturbation on nontarget assemblages. Unlike experiment I, no soluble reactive phosphorus pulse was observed during plant senescence. However, benthic gross productivity and chlorophyll α again increased, suggesting a rapid transfer of leached phosphorus and other nutrients to the sediment algae. The apparent differences in the soluble reactive phosphorus responses between the two microcosm experiments may be attributed to differences in the standing crops of macrophyte phosphorus since the concentration was three times higher in microcosm experiment I. Endothall also caused a significant deflection in microcosm productivity rates but an increase in microcosm respiration relative to control rates. The opposite deflection pattern was attributed to destruction of photo synthetic activities by the macrophytes and an abundance of leached labile organic material which potentially stimulated heterotrophic consumption. Microcosm metabolism recovered from herbicide treatment because photosynthetic dominance shifted from the macrophyte-epiphyte component to the benthic algae. Furthermore, the shift in photosynthetic dominance appeared to be stimulated by the uptake of leached macrophyte phosphorus by the sediment algae which were resistant to the herbicide perturbation. These results indicated that phosphorus was rapidly leached from herbicide killed plants and algae could potentially assimilate this phosphorus for growth.
Appears in Collections:Miscellaneous Paper

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