Non-conservative patterns of dissolved organic matter degradation when and where lake water mixes

Abstract

In this study, we experimentally investigated the degradation of dissolved organic matter (DOM) during lateral and vertical mixing of different water masses in a peri-alpine lake. River intrusions and vertical winter turnover in Lake Geneva (Switzerland, France) were simulated through short-term laboratory incubations by mixing riverine and lacustrine waters or lacustrine waters collected at different depths in winter. Dissolved organic carbon (DOC) degradation was monitored by dissolved oxygen (DO) measurements and changes in DOM composition were tracked by fluorescence spectroscopy in pure and mixed treatments during 72 h. Initial DOC content and DOM composition were relatively similar between end-members. The amount of DOC respired at the end of the incubation was similar between treatments, but decay constants in mixed treatments derived from a first-order decay model were significantly higher than expected values calculated based on a simple mass balance model. Fluorescent dissolved organic matter (FDOM) in mixed treatments followed non-conservative patterns that could not be predicted based on observations made in pure treatments. Hence, one protein-like and one microbial-like fluorophore that were consumed in lake waters were continuously produced in mixed treatments although lake waters represented 90% of the mix. No relationships were observed between the rate of DOC consumption and the initial DOM composition, suggesting that other factors such as nutrients and/or interactions in microbial communities were involved. Moreover, no relationships were found between DOC and FDOM patterns during incubations, suggesting that these measurements targeted different facets of microbial metabolism of DOM, respectively microbial respiration (catabolism) and microbial production (anabolism). While additional investigations are required in order to identify the drivers of these changes, this study provides evidence of non-conservative behavior of DOM degradation in mixing zones in lakes. Keywords Dissolved organic matter · Respiration · Mixing events · Metabolism · Conservative behavior · LakesPublisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Study of morphological, structural, and thermal changes of biodegradable material in simulated natural environmental conditions

“…Consequently, it has been determined that even these blends have a rate of biodegradation reduced under composting conditions, and under anaerobic digestion (Camacho‐Muñoz et al., 2020). Similar behaviors have been reported in mixtures based on PLA/PHB/ATBC (Lemos Machado et al., 2017) and PLA/PHB/PEG (Lambert & Perga, 2019; Lambert & Wagner, 2017) under the same disintegration conditions. In these studies, it has been reported that PHB slightly inhibits the degradation of PLA evaluated under the ISO 20200 standard.…”

Enhanced bioavailability of dissolved organic matter (DOM) in human-disturbed streams in Alpine fluvial networks

“…Several models can be used to characterize DOM degradation kinetic. Here we applied a first-order exponential decay model in order to derive a decay constant describing the overall dynamic of DOM degradation (Lambert and Perga, 2019;Lu et al, 2013;Shang et al, 2018) as well as the size of the short-and a long-term reactive carbon pools (STRC and LTRC, respectively). Decreasing DOC concentrations during the incubations were modeled using GraphPad Prism 8 software according to the following equation:…”

“…An alternative scenario would be that the release of simple and labile organic compounds derived from autochthonous sources enhances the degradation of terrestrial aromatic DOM by the so-called priming effect (Bianchi, 2011), inducing a final net increase of C emitted to the atmosphere. The priming effect is a process through which labile pool of DOM can enhance ("prime") the degradation of a more recalcitrant DOM pool based on interactions between microbial communities and/or changes in their functions (Guenet et al, 2010;Kuzyakov et al, 2000), but its occurrence in aquatic ecosystems is highly debated (Attermeyer et al, 2014;Bengtsson et al, 2018;Lambert and Perga, 2019). To determine how human activities may impact the mineralization of terrestrial DOM and infer the consequence on the active role of inland waters into the global C cycle, it is therefore necessary to evaluate the consequences on DOM sources, composition, but also DOM bioavailability and to identify which fraction of the DOM pool fuels respiration.…”

Loads of Pollution to Lake Toba and Their Impacts

“…A load of dissolved organic material in aquatic ecosystems is a combination of various organic compounds originating from the catchment area (allochthonous material) and the results of the primary production and decomposition process in the waters (autochthonous). During the fluvial flow, organic matter movements undergo a microbiologically continuous process and contribute to the ecological and biochemical condition [18]. The COD reflects the level of organic pollution in the waters and is associated with domestic pollutants, mainly from the catchment area.…”