Table of Contents
Journal of Ecosystems
Volume 2013, Article ID 316709, 9 pages
http://dx.doi.org/10.1155/2013/316709
Research Article

Short-Term Photochemical and Biological Unreactivity of Macrophyte-Derived Dissolved Organic Matter in a Subtropical Shallow Lake

1Programa de Pós-Graduação em Ecologia, Instituto de Pesquisas Hidráulicas, Universidade Federal do Rio Grande do Sul, 91501970 Porto Alegre, RS, Brazil
2Instituto de Pesquisas Hidráulicas, Universidade Federal do Rio Grande do Sul, 91501970 Porto Alegre, RS, Brazil

Received 7 May 2013; Revised 5 July 2013; Accepted 7 July 2013

Academic Editor: Wen-Cheng Liu

Copyright © 2013 Ng Haig They et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Macrophytes have been associated with low bacterial metabolism in the littoral zones of lake Mangueira, but an explanation for this pattern is largely unknown. In this study, macrophyte-derived DOM was incubated in situ for the measurement of the effect of grazers, bacteria, and light on its degradation in three experiments. The water was separated in bulk, bacterial, and control (+ HgCl2) fractions and exposed to or hidden from sunlight for 120 h. Unchange in bacterial variables in the bulk fraction suggested a combined control of radiation and grazing on bacteria. Light treatment increased bacterial density but not biomass and biovolume, while bacterial density decreased in the dark. Significant fading of water color in the bacterial fraction only occurred after light exposure, indicating a complementary pathway of light and bacteria. DOC and the Abs250 : 365 ratio did not change with incubation, indicating no net change of DOC pool and reactivity. Due to continuous carbon loading from macrophytes and low UV irradiance, the very low rates of DOM degradation provide the mechanistic explanation for the observed impacts of macrophytes in lake’s carbon metabolism in littoral zones.