Hypolimnetic deoxygenation enhanced production and export of recalcitrant dissolved organic matter in a large stratified reservoir

Qu, Liyin; Wu, Zetao; Dahlgren, Randy A.; Ren, Mingxing; Li, Penghui; Shi, Quan; Li, Yan; Chen, Nengwang; Guo, Weidong

doi:10.1016/j.watres.2022.118537

Cited by 21 publications

(29 citation statements)

References 56 publications

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“…C3 had an excitation/emission maximum at 270/ 460 nm, which was similar to common humic-like peak A. Matches for C2 and C3 were found in seven and four published models, respectively. However, these components are ubiquitously found in aquatic DOM from watershed to deep ocean continuum (Wang et al, 2013(Wang et al, , 2021Qu et al, 2022). C4 had excitation/emission maxima at ≤ 240 and 275 nm/340 nm, which is consistent with tryptophan-like peak T (Coble, 1996).…”

Section: Parafac Resultsmentioning

confidence: 84%

“…It broke the previous result based on limited data that temperate rivers had a moderate ratio of a 350 to DOC (Lambert et al, 2015). Many factors such as climate zone, land cover, watershed morphology, climate change, and human-induced perturbation may regulate this ratio as well as the composition of riverine DOM (Guo et al, 2014;Lambert et al, 2015;Qu et al, 2020Qu et al, , 2022, thereby exerting a potentially important impact on the local coastal ecosystem.…”

Section: Factors Affecting the Sources Compositions And Levels Of Dom...mentioning

confidence: 99%

“…These allochthonous sources show large diversities in terms of the level, composition, export flux, and biogeochemical activity of DOM, resulting in distinct fates and profound implications for coastal ecosystems (Raymond and Spencer, 2015;Shen et al, 2015;Wang et al, 2018). Moreover, climate change (e.g., global warming, extreme climatic events) and human activities (e.g., damming, urbanization) have dramatically changed the composition, reactivity, and export flux of riverine (Liu et al, 2020;Qu et al, 2020Qu et al, , 2022 and groundwater DOM (Lipczynska-Kochany, 2018;McDonough et al, 2020a) delivered to sea. It is, therefore, crucial to determine the quantity, quality, and export flux of DOM at the dynamic land-sea interface, to provide a basis for a better understanding of the coastal biogeochemistry on a changing Earth.…”

Section: Introductionmentioning

confidence: 99%

“…Absorption and fluorescence spectroscopies are effective techniques for tracing DOM transport from the watershed to the open ocean (Baker, 2001;Guo et al, 2014;Li et al, 2019;Wang et al, 2021;Qu et al, 2022). They are thus widely used to characterize the sources, levels, composition, and flux of colored and fluorescent DOM (CDOM and FDOM) in groundwater (Chen et al, 2010;Tedetti et al, 2011;Nelson et al, 2015;Kim and Kim, 2017).…”

Section: Introductionmentioning

confidence: 99%

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Sources, spectral characteristics, and fluxes of dissolved organic matter in coastal groundwater and river water in western Guangdong, China

Wang

Hu²,

Liu³

et al. 2022

Front. Environ. Sci.

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Groundwater discharge and river runoff are two important ways for allochthonous dissolved organic matter (DOM) to enter the ocean, but they vary spatially. Currently, the source, composition, and efflux of groundwater and riverine dissolved organic matter to the tropical northern South China Sea remain poorly understood, preventing an accurate estimate of coastal carbon budgets. In July 2021, nine groundwater and six river water samples were collected along the coast of western Guangdong and were characterized using dissolved organic carbon (DOC) analysis, UV-visible, and fluorescence spectroscopy techniques. Atypical absorption spectra were strongly observed in groundwaters, which were mainly attributed to the high-level nitrates. An exponential-Gaussian equation showed that the average contribution of nitrate to total groundwater absorbances was up to 36% at ∼ 300 nm. Groundwater showed lower levels of DOC, colored dissolved organic matter (CDOM), and fluorescent dissolved organic matter (FDOM) as compared to river water, whereas the humic-like components dominated both groundwater and river water FDOM pools. Higher values of spectral slope S350–400, fluorescence index, biological index, and the ratio of two humic-like fluorescence jointly reveal that groundwater DOM mainly originated from microbial activities, whereas the river water DOM had considerable contribution from terrestrial soil. High precipitation, natural or agricultural land types, and a lack of seawater intrusion are expected to cause low levels of groundwater DOM in western Guangdong. Among 52 rivers from across the globe, high watershed productivity and precipitation may lead to high–moderate DOM levels in river water in western Guangdong. The DOM fluxes via fresh groundwater discharge in western Guangdong are comparable in magnitude to those by river runoff, accounting for 16%–18% of the Pearl River DOM fluxes. Based on the slopes of linear correlations between CDOM and DOC obtained in groundwater samples and 52 rivers, as well as the data on water fluxes and DOC levels, the global CDOM fluxes via groundwater discharge and river runoff are estimated to be 3.5–12.2 × 1012 m2 yr−1 and 4.3 ± 0.3 × 1014 m2 yr−1, respectively, highlighting the importance of considering groundwater discharge and river runoff in coastal carbon budgets.

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Section: Parafac Resultsmentioning

confidence: 84%

Section: Factors Affecting the Sources Compositions And Levels Of Dom...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Sources, spectral characteristics, and fluxes of dissolved organic matter in coastal groundwater and river water in western Guangdong, China

Wang

Hu²,

Liu³

et al. 2022

Front. Environ. Sci.

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show abstract

“…In addition to bulk DOC, measurements of chromophoric DOM (CDOM) and fluorescent DOM (FDOM) are widely reported from inland watersheds to the deep ocean (Massicotte et al, 2017;Wang et al, 2021a;Wang et al, 2021b;Qu et al, 2022). CDOM absorption coefficients at different wavelengths (e.g., 254, 280, 325, 350, 355, and 443 nm), and fluorescence intensities at specific excitation/emission wavelength pairs are commonly used as good indicators of DOM level (Coble, 1996;Guo et al, 2007;Yang et al, 2013b;Wang et al, 2017;Wang et al, 2021a;Wang et al, 2021b).…”

Section: Introductionmentioning

confidence: 99%

Distribution, spectral characteristics, and seasonal variation of dissolved organic matter in the northern Beibu Gulf, South China Sea

Zhu

Wei²,

Guan³

et al. 2022

Front. Mar. Sci.

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Dissolved organic matter (DOM) in the land–ocean interface plays a critical role in the global carbon cycle, yet its dynamic is not well understood. Dissolved organic carbon (DOC) in the northern Beibu Gulf was measured seasonally from April 2020 to January 2021. Chromophoric and fluorescent DOM (CDOM and FDOM) were synchronously characterized by absorption and fluorescence spectroscopy. Three fluorescent components were identified from 597 samples using parallel factor analysis, including two humic-like and one protein-like component. DOC displays a significant seasonality with the average level being highest in summer (177 μmol/L) and lowest in winter (107 μmol/L). CDOM and FDOM levels in summer are also higher than those in winter. Although the variation ranges of DOC, CDOM, and FDOM in surface water are generally greater than in bottom water, the difference between the two layers is statistically insignificant. River discharge and anthropogenic input are important external sources of DOM in the low-salinity nearshore waters (i.e., estuaries and coast), whereas DOM in offshore waters is mainly produced by in situ biological activity. The mixing behavior of DOM in the northern Beibu Gulf varies spatially but minimally on a seasonal scale. Two distinct conservative mixing behaviors of DOC, CDOM, and humic-like FDOM occur in the nearshore waters from Tieshangang Bay and excluding Tieshangang Bay, respectively. The removal of protein-like FDOM along the salinity gradient and the negative correlation between protein-like FDOM intensity and apparent oxygen utilization are pronounced in the nearshore waters excluding Tieshangang Bay, jointly indicating that oxygen is consumed by microbial communities. In contrast, a net addition of DOC occurs in the high-salinity offshore waters, whereas the CDOM and humic-like FDOM undergoes quasi-conservative mixing. Overall, this study reveals notable spatial and seasonal variations in the concentration, source, and mixing of DOM at the land–ocean interface and highlights the importance of sources and processes in shaping the amount and composition of DOM exported to the ocean margin.

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Greenhouse gas emissions (CO₂–CH₄–N₂O) along a large reservoir‐downstream river continuum: The role of seasonal hypoxia

Wu,

Yu,

et al. 2024

Limnology & Oceanography

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Recent studies suggest that hypolimnetic respiration may be responsible for greenhouse gas (GHG) emissions from deep reservoirs. Currently, quantitative evaluation of aerobic vs. anaerobic processes and priming (enhanced processing of organic matter due to the addition of labile carbon) in regulating GHG production and emissions across the reservoir‐downstream continuum remains largely unknown. High‐resolution, annual time‐series observations in a large, subtropical reservoir (Shuikou) experiencing seasonal hypoxia in southeast China indicate that aerobic hypolimnetic CO2 production dominated in most periods of the stratified spring/summer with higher rates at higher temperatures. In addition, anaerobic production of hypolimnetic CO2 occurred in the late stratified spring/summer period, which stimulated hypolimnetic production of CH4 and N2O. Incubation experiments showed that priming in spring enhanced both aerobic and anaerobic production of excess GHGs. A late spring flood event generated the highest daily efflux of CO2 through the flushing of GHG‐enriched hypolimnion waters. Turbine degassing contributed 59%, 93%, and 63% of annual CO2, CH4, and N2O effluxes, respectively. Moreover, annual downstream GHG emissions were similar to those in the transition/lacustrine zone of the Shuikou reservoir. Diurnal variation observations revealed net CO2 emissions even during algal bloom seasons. The reservoir‐downstream river continuum was a year‐round source of GHGs (218.5 ± 18.9 Gg CO2‐equivalent yr−1; CO2 contributed 91%). However, the loss of oxygen also leads to increased production and storage of recalcitrant dissolved organic carbon (RDOC). Thus, identifying mechanisms controlling both GHG emissions and RDOC production is crucial to constrain the carbon neutrality issue of hydroelectric reservoirs in the context of climate change mitigation strategies.

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Hypolimnetic deoxygenation enhanced production and export of recalcitrant dissolved organic matter in a large stratified reservoir

Cited by 21 publications

References 56 publications

Sources, spectral characteristics, and fluxes of dissolved organic matter in coastal groundwater and river water in western Guangdong, China

Sources, spectral characteristics, and fluxes of dissolved organic matter in coastal groundwater and river water in western Guangdong, China

Distribution, spectral characteristics, and seasonal variation of dissolved organic matter in the northern Beibu Gulf, South China Sea

Greenhouse gas emissions (CO₂–CH₄–N₂O) along a large reservoir‐downstream river continuum: The role of seasonal hypoxia

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Hypolimnetic deoxygenation enhanced production and export of recalcitrant dissolved organic matter in a large stratified reservoir

Cited by 21 publications

References 56 publications

Sources, spectral characteristics, and fluxes of dissolved organic matter in coastal groundwater and river water in western Guangdong, China

Sources, spectral characteristics, and fluxes of dissolved organic matter in coastal groundwater and river water in western Guangdong, China

Distribution, spectral characteristics, and seasonal variation of dissolved organic matter in the northern Beibu Gulf, South China Sea

Greenhouse gas emissions (CO2–CH4–N2O) along a large reservoir‐downstream river continuum: The role of seasonal hypoxia

Contact Info

Product

Resources

About

Greenhouse gas emissions (CO₂–CH₄–N₂O) along a large reservoir‐downstream river continuum: The role of seasonal hypoxia