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

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.

Bioavailable DOC: reactive nutrient ratios control heterotrophic nutrient assimilation—An experimental proof of the macronutrient-access hypothesis

“…Moreover, in agricultural streams, autotrophic assimilation may dominate, and these systems are often assumed to be net-autotrophic during the growing season (however, see Griffiths et al 2013). Still, there are also indications that the dominance of algae in benthic biofilms might stimulate DOC uptake either directly by priming heterotrophic assimilation with labile DOC, or indirectly by providing a better environment for heterotrophic enzymatic reactions (see Weigelhofer et al 2020) pointing to the possibility of positive feedback between autotrophic and heterotrophic assimilation. Hence, an increase in DOC:nutrient ratios may provoke a stronger response in heterotrophic nutrient assimilation in high-light systems, such as many agricultural streams, compared to low-light systems, such as many forested streams.…”

Leaves stimulate aquatic phosphorus uptake by dark‐grown but not by light‐grown microbial communities in sediments: A laboratory study

“…For example, Kamjunke et al (2015) observed responses to the quantity and quality of dissolved OM only in planktonic stream microbes but not in benthic biofilms. This indicates that sediment-associated biofilms may be more controlled by internal nutrient and carbon cycling than by the external nutrient supply (Brailsford et al, 2019;Graeber et al, 2018;Wagner et al, 2017;Weigelhofer et al, 2020). In contrast, leaf-and detritus-associated biofilms have OC directly available in their immediate surroundings (Cheever et al, 2012) and may thus require additional nutrients from the water column for enhanced growth.…”

Dry-Wet Cycles Affect Nitrous Oxide Emissions Across Aquatic-Terrestrial Interfaces: A Mesocosms Study

“…This is commonly corrected with the absorbance-based approach. From an extra absorbance measurement of the same sample (in the photometer), the effects of the absorbance influencing the fluorescence can be calculated and subsequently corrected (29,30). Absorbance scans were performed between 200 and 700 nm at 0.5 nm intervals (5 cm quartz cuvette; Shimadzu UV-1700 UV-VIS Spectrophotometer).…”