Dissolved Organic Matter Quality and Biofilm Composition Affect Microbial Organic Matter Uptake in Stream Flumes

Gabriele Weigelhofer,Tania Sosa Jirón,Matthias Pucher,Gertraud Steniczka,Tz-Ching Yeh

doi:10.3390/w12113246

Abstract

Agriculture delivers significant amounts of dissolved organic matter (DOM) to streams, thereby changing the composition and biodegradability of the aquatic DOM. This study focuses on the interactive effects of DOM quality and biofilm composition on the degradation of DOM in a laboratory flume experiment. Half of the flumes were exposed to light to stimulate algal growth, the other half was shaded. Leachates of deciduous leaves, maize leaves, and cow dung were added to the flumes in a single pulse and changes of DOC (dissolved organic carbon) and nutrient concentrations, DOM composition (absorbance and fluorescence data), chlorophyll-a concentrations, bacterial abundances, and enzymatic activities were recorded over a week. DOM was taken up with rates of 50, 109, and 136 µg DOC L−1 h−1 for dung, leaf, and maize leachates, respectively, in the light flumes and 37, 80, and 170 µg DOC L−1 h−1 in the dark flumes. DOC uptake correlated strongly with initial SRP (soluble reactive phosphorus) and DOC concentrations, but barely with DOM components and indices. Algae mostly stimulated the microbial DOC uptake, but the effects differed among differently aged biofilms. We developed a conceptual model of intrinsic (DOM quality) and external (environmental) controlling factors on DOM degradation, with the microbial community acting as biotic filter.

Highlights

Worldwide, almost 40% of terrestrial surfaces have been converted to agricultural land and this trend is expected to increase in the future [1]
The current study focuses on the effects of dissolved organic matter (DOM) composition of different natural and anthropogenic sources on the microbial DOM uptake under different light conditions
Independent the biofilm community, the order of dissolved organic carbon (DOC) degradation was always the same in our experiments, with uptake rates increasing from dung to leaf and maize leachates

Summary

Introduction

Almost 40% of terrestrial surfaces have been converted to agricultural land and this trend is expected to increase in the future [1]. Natural streams are generally dominated by terrestrial, humic-like DOM originating from riparian vegetation [5]. Agriculture may shift this composition towards the dominance of protein-like labile components through the leaching of fertilized soils and plant residues and the rapid transport of this leached DOM to stream ecosystems via overland flow, preferential flow paths, or drainage waters [4,5,6,7]. The increased nutrient supply and the frequently enhanced light availability may stimulate the benthic primary production in agricultural streams, resulting in an increased autochthonous DOM production [3,8].

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Results

Conclusion