Origin, enzymatic response and fate of dissolved organic matter during flood and non-flood conditions in a river-floodplain system of the Danube (Austria)

Abstract

Spectroscopic techniques and extracellular enzyme activity measurements were combined with assessments of bacterial secondary production (BSP) to elucidate flood-pulse-linked differences in carbon (C) sources and related microbial processes in a river-floodplain system near Vienna (Austria). Surface connection with the main channel significantly influenced the quantity and quality of dissolved organic matter (DOM) in floodplain backwaters. The highest values of dissolved organic carbon (DOC) and chromophoric DOM (CDOM) were observed during the peak of the flood, when DOC increased from 1.36 to 4.37 mg l−1 and CDOM from 2.94 to 14.32 m−1. The flood introduced DOC which consisted of more allochthonously-derived, aromatic compounds. Bacterial enzymatic activity, as a proxy to track the response to changes in DOM, indicated elevated utilization of imported allochthonous material. Based on the enzyme measurements, new parameters were calculated: metabolic effort and enzymatic indices (EEA 1 and EEA 2). During connection, bacterial glucosidase and protease activity were dominant, whereas during disconnected phases a switch to lignin degradation (phenol oxidase) occurred. The enzymatic activity analysis revealed that flooding mobilized reactive DOM, which then supported bacterial metabolism. No significant differences in overall BSP between the two phases were detected, indicating that heterogeneous sources of C sufficiently support BSP. The study demonstrates that floods are important for delivering DOM, which, despite its allochthonous origin, is reactive and can be effectively utilized by aquatic bacteria in this river-floodplain systems. The presence of active floodplains, characterized by hydrological connectivity with the main channel, creates the opportunity to process allochthonous DOC. This has potential consequences for carbon flux, enhancing C sequestration and mineralization processes in this river-floodplain system.

From isolation to connectivity: the effect of floodplain lake restoration on sediments as habitats for macroinvertebrate communities

“…Cut-offs quickly become filled with sediments as a result of autogenic processes and/or allogenic processes, i.e., accumulation of the material carried by the river during inundation events and by ground water (Sieczko and Peduzzi 2014). Soon after, the isolated water bodies undergo eutrophication and then terrestrialization (Obolewski et al 2016;Palmer et al 2005).…”

River bacterioplankton community responses to a high inflow event

“…They couple abiotic components of terrestrial environments (such as flood plains) with biotic processes in aquatic systems (Junk et al 1989, Tockner et al 2000, Sieczko & Peduzzi 2014. The frequency, variability, volume and quality of river inflows ultimately determine the ecological character of rivers and their associated estuaries (Poff & Zimmerman 2010).…”

Spatial variability of chromophoric dissolved organic matter in a large floodplain river: control factors and relations with phytoplankton during a low water period

“…The hydrological connectivity of water bodies influences the concentration and molecular weight (MW) of CDOM in a variable way according to the magnitude of several factors. These factors include: evapoconcentration, dilution by water inflow, exports and inputs of CDOM, and water residence time that affects CDOM transformations (Mladenov et al ., ; Peduzzi et al ., ; Cawley et al ., ; Sieczko and Peduzzi, ). As in other studies (Mladenov et al ., op.…”

“…Chromophoric dissolved organic matter (CDOM) is also affected by hydrological connectivity in floodplain fluvial systems (Depetris and Kempe, 1993;Mladenov et al, 2005;Peduzzi et al, 2008;Cawley et al, 2012;Sieczko and Peduzzi, 2014). Most of these studies focus on CDOM temporal variability.…”