Testing the influence of sediment granulometry on heterotrophic respiration with a new laboratory flow-through system

Abstract

Purpose Increased sedimentation due to land use intensification is increasingly affecting carbon processing in streams and rivers around the globe. This study describes the design of a laboratory-scale flow-through incubation system as a tool for the rapid estimation of sediment respiration. The measurements were compared with those obtained using an in situ closed chamber respiration method. The influence of sediment size on respiration rates was also investigated. Materials and methods Measurements were conducted on a pre-alpine gravel-bed river sediment separated into the following grain size fractions: > 60 mm (14.3%), 60-5 mm (60.2%), 5-2 mm (13.7%), 2-0.063 mm (11.1%) and <0.063 mm (0.6%). Concurrently, in situ and laboratory measurements were carried out on a naturally heterogeneous sediment. In situ respiration was determined in closed chambers as O 2 consumption over time, while in the laboratory, respiration was determined using flow-through respiration chambers. Oxygen concentrations were measured using a fibre-optic oxygen meter positioned at the inflow and outflow from the chamber. Results and discussion The mean respiration rates within naturally mixed riverbed sediments were 1.27 ± 0.3 mg O 2 dm −3 h −1 (n = 4) and 0.77 ± 0.1 mg O 2 dm −3 h −1 (n = 3) for the flow-through chamber system and closed chamber system, respectively. Respiration rates were statistically significantly higher in the flow-through chamber system (t test, p < 0.05), indicating that closed chamber measurements underestimated the oxygen consumption within riverbed sediments. Sediment grain size was found to significantly affect respiration rates in both systems (ANOVA, p < 0.001) with the fine sediment fraction (particle size <0.063 mm) having the highest respiration rate (r flow-through = 51 ± 23 mg O 2 dm −3 h −1 ). The smallest fractions (2-0.063 and <0.063 mm), which represent approximately 12% of total sediment volume, contributed 60% of total respiration. Conclusions The study demonstrated that flow-through respiration chambers more accurately estimate the respiration rate within riverbed sediments than in situ closed chambers, since the former experiment imitates the natural conditions where continuous interstitial flow occurs in the sediments. We also demonstrated that fine sediments (<5 mm) substantially contribute to heterotrophic respiration in the studied gravel-bed river.

Spatiotemporal heterogeneity of actual and potential respiration in two contrasting floodplains

“…This factor was determined by analyzing gravel samples and considers that the size fraction >8 mm accounted on average 46% and 50%, respectively, of the sediment volume in each river. The factors were applied to avoid overestimation of the area respiration because larger size fractions represent substrate with low metabolic activity (Mori, Debeljak, Kocman, & Simčič, ).…”

Preface

“…Six published papers are dealing with soils focusing on organic matter composition in rice-paddy soils (Cheng et al 2017) and degradation of organic matter in Andisol and Inceptisol paddy soils (Tang et al 2017), morphology of fly-ash contaminated soil (Weber et al 2017), the relationship between soil properties and plant community in a lagoon (Antisari et al 2017), methane transformation in a drained wetland soil (Jerman et al 2017), and the sources of soil CO 2 above a subterranean cave (Krajnc et al 2017). Five published papers consider biogeochemical processes in freshwater sediments focusing on metals in sediments of several areas, including the largest mercury mine district in Almaden area (Garcia-Ordiales et al 2017), in the Zrmanja River estuary (Fiket et al 2017) and in the Sava River (Vidmar et al 2017), as well as the characteristics of ammonia oxidizers in aquaculture ponds (Zhou et al 2017) and the effect of sediment grain size on heterotrophic respiration (Mori et al 2017). Five papers are devoted to marine sediments comprising hydrocarbons in coastal area (Bajt 2017), microbial mercury transformation processes (Hines et al 2017), historical deposition of trace elements in saltmarshes (Covell et al 2017) and the accumulation of metal(loid)s in halophytes (Petranich et al 2017), and the characteristics of microbial mats in a marine mangrove (Gontharet et al 2017).…”

Machine Learning Photogrammetric Analysis of Images Provides a Scalable Approach to Study Riverbed Grain Size Distributions

“…The grain size distribution (GSD) of sediments in streams and rivers, often represented by the median of the GSD (d50), plays many important roles that regulate fluvial hydrology and biogeochemistry, and their interactions. Grains ranging from clays to boulders control the locations and rates of groundwater-surface water exchange, which can influence stream metabolism, as well as gas (e.g., oxygen and carbon dioxide) and solute sources, fate, and transport (Glaser et al, 2020;Gomez-Velez et al, 2015;Harvey et al, 2011;Mori et al, 2017;Son et al, 2022;Xia et al, 2017). Because of these roles, GSD is a key metric for predicting hydraulic conductivity (J.-P. Wang et al, 2017), flow resistance (Rickenmann & Recking, 2011), microbial respiration and denitrification in streambeds (Son et al, 2022), and parameterizing hydromorphological models (Lepesqueur et al, 2019).…”