Dissolved oxygen isotope modelling refines metabolic state estimates of stream ecosystems with different land use background

Abstract

Dissolved oxygen (DO) is crucial for aerobic life in streams and rivers and mostly depends on photosynthesis (P), ecosystem respiration (R) and atmospheric gas exchange (G). However, climate and land use changes progressively disrupt metabolic balances in natural streams as sensitive reflectors of their catchments. Comprehensive methods for mapping fundamental ecosystem services become increasingly important in a rapidly changing environment. In this work we tested DO and its stable isotope (18O/16O) ratios as novel tools for the status of stream ecosystems. For this purpose, six diel sampling campaigns were performed at three low-order and mid-latitude European streams with different land use patterns. Modelling of diel DO and its stable isotopes combined with land use analyses showed lowest P rates at forested sites, with a minimum of 17.9 mg m−2 h−1. Due to high R rates between 230 and 341 mg m−2 h−1 five out of six study sites showed a general heterotrophic state with P:R:G ratios between 0.1:1.1:1 and 1:1.9:1. Only one site with agricultural and urban influences showed a high P rate of 417 mg m−2 h−1 with a P:R:G ratio of 1.9:1.5:1. Between all sites gross G rates varied between 148 and 298 mg m−2 h−1. In general, metabolic rates depend on the distance of sampling locations to river sources, light availability, nutrient concentrations and possible exchanges with groundwater. The presented modelling approach introduces a new and powerful tool to study effects of land use on stream health. Such approaches should be integrated into future ecological monitoring.

Precipitation fuels dissolved greenhouse gas (CO2, CH4, N2O) dynamics in a peatland-dominated headwater stream: results from a continuous monitoring setup

“…Relative to concentrations at lower water levels, in-stream CO 2 was less affected by rainfall events than N 2 O and CH 4 due to anaerobic conditions in the peatland pore water, limiting microbial respiration (Drösler et al, 2008). However, the observed increase in CO 2 concentrations could be due to the input and oxidation of methane-rich peatland porewater, increasing DOC and TOC contents in the stream leached from the surrounding landscape as a C source for microbial turnover, and lower photosynthetic activities at lower PAR as compared to clear sky conditions (Figures 6E, 7B) (Dinsmore et al, 2013;Raymond et al, 2016;Piatka et al, 2021Piatka et al, , 2022bTaillardat et al, 2022). After reaching their maximum, significant decreases in GHG concentrations are probably related to reduced input of peatland soil water into the stream after the precipitation event or could be partially explained by dilution effects with rainwater and depletion of GHGs in the sediment pore waters (Hope et al, 2001;Billett et al, 2004;Wallin et al, 2010;Taillardat et al, 2022).…”

“…Rocher-Ros et al, 2020;Attermeyer et al, 2021). During the day, when photosynthesis (P) (CO 2 sink and DO source) and respiration (R) (CO 2 source and DO sink) were active, CO 2 concentrations were lowest (but still above ambient concentrations), whereas the highest values were observed at night when only R is present (Hotchkiss et al, 2015;Piatka et al, 2021Piatka et al, , 2022b. With successive rainfall events, these diurnal CO 2 cycles were strongly dampened, likely by increased k values at higher water levels and flow velocities and possibly by reduced PAR, hence P under cloudy conditions (Figures 7A, B, E) (Raymond et al, 2012;Piatka et al, 2022b).…”

Identifying the controls on nitrate and metabolic state within the Red River delta (Vietnam) with the use of stable isotopes

“…Therefore DO is quickly consumed by biodegradation and slowly replenished by atmospheric oxygen due to slow hydrodynamic condition in the deltaic rivers. This means that the remaining DO is enriched in 18 O (Quay, et al, 1995;Piatka, et al, 2022). Next, nitrification in the NH4 + concentrated water (Trinh, et al, 2007) utilises the remaining DO within the hypoxic environment (Fig.…”

“…In addition, in an aquatic ecosystem dominated by nitrification, the nitrate oxygen isotope ( 18 O of nitrate) in combination with the water oxygen isotope ( 18 O of H2O) can be used to calculate the dissolved oxygen isotope value. This oxygen isotope value can in turn be used to assess the aquatic metabolism (Venkiteswaran, et al, 2007;Piatka, et al, 2022). Here we apply nitrate isotopes and water isotopes to 1) assess the NO3sources and identify the processes governing NO3within stream water and 2) assess aquatic ecosystem metabolism within the Red River delta, which supports two of Vietnam's largest rivers, the Red River and the Day River (a significant tributary located in the heart of urban Vietnam) (Luu, et al, 2020).…”

Oxygen isotopic fractionation during dissolved oxygen consumption in the bottom layer of the Ulleung Basin, East/Japan Sea

“…Numerous studies have overcome this limitation by combining DO concentrations with stable oxygen isotopes (Levine et al, 2009;Mader et al, 2017;Li et al, 2019;Zhou et al, 2021;Piatka et al, 2022). The DO concentration, coupled with its oxygen isotopic composition, can provide additional information because it shows decoupling behaviors depending on oxygen sources and sink processes in the oxygen isotope and DO relationship (Levine et al, 2009;Zhou et al, 2021).…”