Authors: A A Huss J D Wehr
Publish Date: 2004/03/25
Volume: 47, Issue: 4, Pages: 305-315
Abstract
Phytoplankton and allochthonous matter are important sources of dissolved organic carbon DOC for planktonic bacteria in aquatic ecosystems But in small temperate lakes aquatic macrophytes may also be an important source of DOC as well as a source or sink for inorganic nutrients We conducted micro and mesocosm studies to investigate the possible effects of an actively growing macrophyte Vallisneria americana on bacterial growth and water chemistry in mesotrophic Calder Lake A first microcosm 1 L study conducted under high ambient NH 4 + levels NH 4 + ≥ 10 µM demonstrated that macrophytes had a positive effect on bacterial densities through release of DOC and P A second microcosm experiment conducted under NH 4 + depleted conditions NH 4 + 10 µM examined interactive effects of macrophytes and their sediments on bacterial growth and water chemistry Nonrooted macrophytes had negative effects on bacterial numbers while rooted macrophytes had no significant effects despite significant increases in DOC and P A 70L mesocosm experiment manipulated macrophytes as well as N and P supply under surplus NH 4 + conditions NH 4 + ≥ 10 µM and measured effects on bacterial growth Chl a concentrations and water chemistry Bacterial growth and Chl a concentrations declined with macrophyte additions while bacterial densities increased with P addition with or without N Results suggest that the submersed macrophyte Vallisneria exerts a strong but indirect effect on bacteria by modifying nutrient conditions and/or suppressing phytoplankton Effects of living macrophytes differed with ambient nutrient conditions under NH 4 + surplus conditions submersed macrophytes stimulated bacterioplankton through release of DOC or P but in NH 4 + depleted conditions the influence of Vallisneria was negative or neutral Effects of living macrophytes on planktonic bacteria were apparently mediated by the macrophytes use and/or release of nutrients as well as through possible effects on phytoplankton productionWe thank Mr Michael Lambros field and Ms Molli MacDonald laboratory for their generous assistance with this study The authors also acknowledge support for this study provided by the Louis Calder Center Routh Fund the National Science Foundation DIR9002145 to JDW and Fordham University graduate fellowship to AAH This paper is contribution number 219 of the Louis Calder Center
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