Articles | Volume 9, issue 6
Research article 08 Jun 2012
Research article | 08 Jun 2012
Organic matter sources, fluxes and greenhouse gas exchange in the Oubangui River (Congo River basin)
S. Bouillon et al.
Related subject area
Biogeochemistry: Rivers & StreamsIncreased carbon capture by a silicate-treated forested watershed affected by acid depositionThermokarst amplifies fluvial inorganic carbon cycling and export across watershed scales on the Peel Plateau, CanadaSoil organic carbon decomposition rates in river systems: effect of experimental conditionsTemporary and net sinks of atmospheric CO2 due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithologyFrom canals to the coast: dissolved organic matter and trace metal composition in rivers draining degraded tropical peatlands in IndonesiaDistribution and flux of dissolved iron in the peatland-draining rivers and estuaries of Sarawak, Malaysian BorneoComparisons of dissolved organic matter and its optical characteristics in small low and high Arctic catchmentsHigh-frequency measurements explain quantity and quality of dissolved organic carbon mobilization in a headwater catchmentDissolved inorganic nitrogen in a tropical estuary in Malaysia: transport and transformationBehaviour of Dissolved Phosphorus with the associated nutrients in relation to phytoplankton biomass of the Rajang River-South China Sea continuumSynchrony in catchment stream colour levels is driven by both local and regional climateThe post-monsoon carbon biogeochemistry of the Hooghly–Sundarbans estuarine system under different levels of anthropogenic impactsRiverine particulate C and N generated at the permafrost thaw front: case study of western Siberian rivers across a 1700 km latitudinal transectGeochemistry of the dissolved loads during high-flow season of rivers in the southeastern coastal region of China: anthropogenic impact on chemical weathering and carbon sequestrationCO2 partial pressure and CO2 emission along the lower Red River (Vietnam)Stable isotopes of nitrate reveal different nitrogen processing mechanisms in streams across a land use gradient during wet and dry periodsRiverine carbon export in the arid to semiarid Wuding River catchment on the Chinese Loess PlateauUse of argon to measure gas exchange in turbulent mountain streamsReviews and syntheses: Anthropogenic perturbations to carbon fluxes in Asian river systems – concepts, emerging trends, and research challengesShifts in stream hydrochemistry in responses to typhoon and non-typhoon precipitationQUAL-NET, a high temporal-resolution eutrophication model for large hydrographic networksDiel fluctuations of viscosity-driven riparian inflow affect streamflow DOC concentrationA comprehensive biogeochemical record and annual flux estimates for the Sabaki River (Kenya)Hydro-ecological controls on dissolved carbon dynamics in groundwater and export to streams in a temperate pine forestRegional-scale lateral carbon transport and CO2 evasion in temperate stream catchmentsCarbon and nutrient export regimes from headwater catchments to downstream reachesInfluence of infrastructure on water quality and greenhouse gas dynamics in urban streamsHydromorphological restoration stimulates river ecosystem metabolismQuantifying nutrient fluxes with a new hyporheic passive flux meter (HPFM)Sources, cycling and export of nitrogen on the Greenland Ice SheetVariability in runoff fluxes of dissolved and particulate carbon and nitrogen from two watersheds of different tree species during intense storm eventsShift in the chemical composition of dissolved organic matter in the Congo River networkTechnical note: Assessing gas equilibration systems for continuous pCO2 measurements in inland watersSource and flux of POC in a karstic area in the Changjiang River watershed: impacts of reservoirs and extreme droughtSediment trap efficiency of paddy fields at the watershed scale in a mountainous catchment in northwest VietnamAlong-stream transport and transformation of dissolved organic matter in a large tropical riverGlobal riverine N and P transport to ocean increased during the 20th century despite increased retention along the aquatic continuumOptical properties and bioavailability of dissolved organic matter along a flow-path continuum from soil pore waters to the Kolyma River mainstem, East SiberiaTrace element transport in western Siberian rivers across a permafrost gradientEffects of different N sources on riverine DIN export and retention in a subtropical high-standing island, TaiwanStream biogeochemical and suspended sediment responses to permafrost degradation in stream banks in Taylor Valley, AntarcticaRunoff- and erosion-driven transport of cattle slurry: linking molecular tracers to hydrological processesDissolved organic carbon lability and stable isotope shifts during microbial decomposition in a tropical river systemMap-based prediction of organic carbon in headwater streams improved by downstream observations from the river outletModel-aided quantification of dissolved carbon and nitrogen release after windthrow disturbance in an Austrian karst systemNitrogen export from a boreal stream network following forest harvesting: seasonal nitrate removal and conservative export of organic formsSalinization alters fluxes of bioreactive elements from stream ecosystems across land useReviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystemsBiodegradability of dissolved organic carbon in permafrost soils and aquatic systems: a meta-analysisControls on dissolved organic matter (DOM) degradation in a headwater stream: the influence of photochemical and hydrological conditions in determining light-limitation or substrate-limitation of photo-degradation
Lyla L. Taylor, Charles T. Driscoll, Peter M. Groffman, Greg H. Rau, Joel D. Blum, and David J. Beerling
Biogeosciences, 18, 169–188,Short summary
Enhanced rock weathering (ERW) is a carbon dioxide removal (CDR) strategy involving soil amendments with silicate rock dust. Over 15 years, a small silicate application led to net CDR of 8.5–11.5 t CO2/ha in an acid-rain-impacted New Hampshire forest. We accounted for the total carbon cost of treatment and compared effects with an adjacent, untreated forest. Our results suggest ERW can improve the greenhouse gas balance of similar forests in addition to mitigating acid rain effects.
Scott Zolkos, Suzanne E. Tank, Robert G. Striegl, Steven V. Kokelj, Justin Kokoszka, Cristian Estop-Aragonés, and David Olefeldt
Biogeosciences, 17, 5163–5182,Short summary
High-latitude warming thaws permafrost, exposing minerals to weathering and fluvial transport. We studied the effects of abrupt thaw and associated weathering on carbon cycling in western Canada. Permafrost collapse affected < 1 % of the landscape yet enabled carbonate weathering associated with CO2 degassing in headwaters and increased bicarbonate export across watershed scales. Weathering may become a driver of carbon cycling in ice- and mineral-rich permafrost terrain across the Arctic.
Man Zhao, Liesbet Jacobs, Steven Bouillon, and Gerard Govers
Revised manuscript accepted for BGShort summary
We investigated the relative importance of two individual factors (mechanical disturbance and aquatic microbial organisms) that possibly control SOC decomposition rates in river systems. We found aquatic microbial organisms led to rapid SOC decomposition, while effect of mechanical disturbance is relative minor. We propose a simple conceptual model: mechanical disturbance is only important when soil aggregates are strong enough to withstand the disruptive forces imposed by immersion in water.
Yingjie Cao, Yingxue Xuan, Changyuan Tang, Shuai Guan, and Yisheng Peng
Biogeosciences, 17, 3875–3890,Short summary
About half of the global CO2 sequestration due to chemical weathering occurs in warm and high-runoff regions. To evaluate the temporary and net sinks of atmospheric CO2 due to chemical weathering, we selected a typical subtropical catchment as our study area and did fieldwork to sample surface water along the main channel and major tributaries in 1 hydrological year. The result of mass balance calculation showed that human activities dramatically decreased the CO2 net sink.
Laure Gandois, Alison M. Hoyt, Stéphane Mounier, Gaël Le Roux, Charles F. Harvey, Adrien Claustres, Mohammed Nuriman, and Gusti Anshari
Biogeosciences, 17, 1897–1909,Short summary
Worldwide, peatlands are important sources of dissolved organic matter (DOM) and trace metals (TMs) to surface waters, and these fluxes may increase with peatland degradation. In Southeast Asia, tropical peatlands are being rapidly deforested and drained. This work aims to address the fate of organic carbon and its role as a trace metal carrier in drained peatlands of Indonesia.
Xiaohui Zhang, Moritz Müller, Shan Jiang, Ying Wu, Xunchi Zhu, Aazani Mujahid, Zhuoyi Zhu, Mohd Fakharuddin Muhamad, Edwin Sien Aun Sia, Faddrine Holt Ajon Jang, and Jing Zhang
Biogeosciences, 17, 1805–1819,Short summary
This study offered detailed information on dFe concentrations, distribution and the magnitude of yield in the Rajang River, the largest river in Malaysia. Three blackwater rivers, draining from peatlands, were also included in our study. Compared with the Rajang River, the dFe concentrations and yield from three blackwater rivers were much higher. The precipitation and agricultural activities, such as palm oil plantations, may markedly increase the concentration dFe in these tropical rivers.
Caroline Coch, Bennet Juhls, Scott F. Lamoureux, Melissa J. Lafrenière, Michael Fritz, Birgit Heim, and Hugues Lantuit
Biogeosciences, 16, 4535–4553,Short summary
Climate change affects Arctic ecosystems. This includes thawing of permafrost (ground below 0 °C) and an increase in rainfall. Both have substantial impacts on the chemical composition of river water. We compared the composition of small rivers in the low and high Arctic with the large Arctic rivers. In comparison, dissolved organic matter in the small rivers is more susceptible to degradation; thus, it could potentially increase carbon dioxide emissions. Rainfall events have a similar effect.
Benedikt J. Werner, Andreas Musolff, Oliver J. Lechtenfeld, Gerrit H. de Rooij, Marieke R. Oosterwoud, and Jan H. Fleckenstein
Biogeosciences, 16, 4497–4516,Short summary
Increased dissolved organic carbon (DOC) concentration in streams can pose a threat to downstream water resources. Analyzing data from an in-stream probe we found that hydroclimatic and hydrological drivers can describe up to 72 % of the observed DOC concentration and composition variability. Variability was found to be highest during discharge events with warm and dry preconditions. The findings suggest an impact of climate change on DOC exports and thus also on downstream water quality.
Shan Jiang, Moritz Müller, Jie Jin, Ying Wu, Kun Zhu, Guosen Zhang, Aazani Mujahid, Tim Rixen, Mohd Fakharuddin Muhamad, Edwin Sien Aun Sia, Faddrine Holt Ajon Jang, and Jing Zhang
Biogeosciences, 16, 2821–2836,Short summary
Three cruises were conducted in the Rajang River estuary, Malaysia. The results revealed that the decomposition of terrestrial organic matter and the subsequent soil leaching were the main sources of dissolved inorganic nitrogen (DIN) in the fresh river water. Porewater exchange and ammonification enhanced DIN concentrations in the estuary water, while intensities of DIN addition varied between seasons. The riverine DIN flux could reach 101.5 ton(N) / d, supporting the coastal primary producers.
Edwin Sien Aun Sia, Jing Zhang, Shan Jiang, Zhuoyi Zhu, Gonzalo Carrasco, Faddrine Holt Jang, Aazani Mujahid, and Moritz Müller
Revised manuscript not acceptedShort summary
Nutrient loads carried by large rivers and discharged into the continental shelf and coastal waters are vital to support primary production. Our knowledge of tropical river systems is fragmented with very few seasonal studies available for Southeast Asia (SEA). We present data from three sampling campaigns on the longest river in Malaysia, the Rajang river. Our results show the generalization of SEA as a nutrient hotspot might not hold true for all regions and requires further investigation.
Brian C. Doyle, Elvira de Eyto, Mary Dillane, Russell Poole, Valerie McCarthy, Elizabeth Ryder, and Eleanor Jennings
Biogeosciences, 16, 1053–1071,Short summary
This study explores the drivers of variation in the water colour of rivers, and hence organic carbon export, in a blanket peatland catchment. We used 6 years of weekly river water colour data (2011 to 2016) from three proximate river sub-catchments in western Ireland. in tandem with a range of topographical, hydrological and climate data, to discover the principle environmental drivers controlling changes in colour concentration in the rivers.
Manab Kumar Dutta, Sanjeev Kumar, Rupa Mukherjee, Prasun Sanyal, and Sandip Kumar Mukhopadhyay
Biogeosciences, 16, 289–307,Short summary
The study focused on understanding C biogeochemistry of two adjacently located estuaries undergoing different levels of anthropogenic stresses. Different parameters related to C cycling were measured in an anthropogenically influenced and a mangrove-dominated estuary. Although the entire estuarine system acted as a source of carbon dioxide to the regional atmosphere, emission approximately 17 times higher was noticed from the anthropogenically affected estuary compared to mangrove-dominated one.
Ivan V. Krickov, Artem G. Lim, Rinat M. Manasypov, Sergey V. Loiko, Liudmila S. Shirokova, Sergey N. Kirpotin, Jan Karlsson, and Oleg S. Pokrovsky
Biogeosciences, 15, 6867–6884,Short summary
We tested the effect of climate, permafrost and physio-geographical landscape parameters on particulate C, N and P concentrations in small- and medium- sized rivers in the Western Siberian Lowland (WSL). We discovered a maximum of particulate C and N concentrations at the beginning of the permafrost appearance. A northward shift of permafrost boundaries may increase the particulate C and N export by WSL rivers to the Arctic Ocean by a factor of 2.
Wenjing Liu, Zhifang Xu, Huiguo Sun, Tong Zhao, Chao Shi, and Taoze Liu
Biogeosciences, 15, 4955–4971,Short summary
The southeastern coastal region is the top acid-rain-impacted area in China. It is worth evaluating the acid deposition impacts on chemical weathering and CO2 consumption there. River water geochemistry evidenced an overestimation of CO2 sequestration if H2SO4/HNO3 involvement was ignored, which accounted for 33.6 % of the total flux by silicate weathering in this area. This study quantitatively highlights the anthropogenic acid effects on chemical weathering and associated CO2 consumption.
Thi Phuong Quynh Le, Cyril Marchand, Cuong Tu Ho, Nhu Da Le, Thi Thuy Duong, XiXi Lu, Phuong Kieu Doan, Trung Kien Nguyen, Thi Mai Huong Nguyen, and Duy An Vu
Biogeosciences, 15, 4799–4814,Short summary
The Red River is a typical south-east Asian river, strongly affected by climate and human activity. This study showed the spatial and seasonal variability of CO2 emissions at the water–air interface of the lower part of this river due to natural conditions (meteo-hydrological-geomorphological characteristics) and human activities (dam impoundment, population, land use). The Red River water was supersaturated with CO2, providing a mean water–air CO2 ﬂux of 530 ± 17 mmol m−2 d−1.
Wei Wen Wong, Jesse Pottage, Fiona Y. Warry, Paul Reich, Keryn L. Roberts, Michael R. Grace, and Perran L. M. Cook
Biogeosciences, 15, 3953–3965,Short summary
Over-enrichment of nitrate can pose substantial risk to the quality of freshwater ecosystems. Hence, understanding the dynamics of nitrate is the key to better management of waterways. This study evaluates the relationship between the effects of land use and rainfall on the major sources and processing of nitrate within and between five streams in five catchments spanning an agricultural land use gradient. We found that rainfall exerted significant control over the fate of nitrate.
Lishan Ran, Mingyang Tian, Nufang Fang, Suiji Wang, Xixi Lu, Xiankun Yang, and Frankie Cho
Biogeosciences, 15, 3857–3871,Short summary
We systematically assessed the transport and fate of riverine carbon in the moderate-sized Wuding catchment on the Chinese Loess Plateau by constructing a riverine carbon budget and further relating it to terrestrial ecosystem productivity. The riverine carbon export accounted for 16 % of the catchment's net ecosystem production (NEP). It seems that a significant fraction of terrestrial NEP in this catchment is laterally transported from the terrestrial biosphere to the drainage network.
Robert O. Hall Jr. and Hilary L. Madinger
Biogeosciences, 15, 3085–3092,Short summary
Streams exchange oxygen with the atmosphere, but this rate is difficult to measure. We added argon to small mountain streams to estimate gas exchange. We compared these rates with sulfur hexafluoride, an intense greenhouse gas. Argon worked well to measure gas exchange, but had higher-than-predicted rates than sulfur hexafluoride. Argon exchange is more likely to represent that for oxygen because they share similar physical properties. We suggest argon to measure gas exchange in small streams.
Ji-Hyung Park, Omme K. Nayna, Most S. Begum, Eliyan Chea, Jens Hartmann, Richard G. Keil, Sanjeev Kumar, Xixi Lu, Lishan Ran, Jeffrey E. Richey, Vedula V. S. S. Sarma, Shafi M. Tareq, Do Thi Xuan, and Ruihong Yu
Biogeosciences, 15, 3049–3069,Short summary
Human activities are drastically altering water and material flows in river systems across Asia. This review provides a conceptual framework for assessing the human impacts on Asian river C fluxes and an update on anthropogenic alterations of riverine C fluxes, focusing on the impacts of water pollution and river impoundments on CO2 outgassing from the rivers draining South, Southeast, and East Asian regions that account for the largest fraction of river discharge and C exports from Asia.
Chung-Te Chang, Jr-Chuan Huang, Lixin Wang, Yu-Ting Shih, and Teng-Chiu Lin
Biogeosciences, 15, 2379–2391,Short summary
Our analysis of ion input–output budget illustrates that hydrochemical responses to typhoon storms are distinctly different from those of regular storms. In addition, even mild land use change may have large impacts on nutrient exports/losses. We propose that hydrological models should separate hydrochemical processes into regular and extreme conditions to better capture the whole spectrum of hydrochemical responses to a variety of climate conditions.
Camille Minaudo, Florence Curie, Yann Jullian, Nathalie Gassama, and Florentina Moatar
Biogeosciences, 15, 2251–2269,Short summary
We developed the model QUALity-NETwork (QUAL-NET) to simulate water quality variations in large drainage networks. This model is accurate enough to represent processes occurring over short periods of time such as storm events and helps to fully understand water quality variations in stream networks in the context of climate change and varying human pressures. It was tested on the Loire River and provided good performances and a new understanding of the functioning of the river.
Michael P. Schwab, Julian Klaus, Laurent Pfister, and Markus Weiler
Biogeosciences, 15, 2177–2188,Short summary
We studied the diel fluctuations of dissolved organic carbon (DOC) concentrations in a small stream in Luxembourg. We identified an increased proportion of DOC from terrestrial sources as responsible for the peaks in DOC in the afternoon. Warmer water temperatures in the riparian zone in the afternoon increased the amount of water flowing towards the stream. Consequently, an increased amount of DOC-rich water from the riparian zone was entering the stream.
Trent R. Marwick, Fredrick Tamooh, Bernard Ogwoka, Alberto V. Borges, François Darchambeau, and Steven Bouillon
Biogeosciences, 15, 1683–1700,Short summary
A 2-year biogeochemical record provides annual sediment and element flux estimates for the non-dammed Sabaki River, Kenya, establishing a baseline for future research in light of impending construction of the first major upstream reservoir. Over 80 % of material fluxes occur across the wet season, with annual yields comparable to the adjacent, and dammed, Tana River. Observations at low-flow periods suggest large mammalian herbivores may be vectors of terrestrial subsidies to the water column.
Loris Deirmendjian, Denis Loustau, Laurent Augusto, Sébastien Lafont, Christophe Chipeaux, Dominique Poirier, and Gwenaël Abril
Biogeosciences, 15, 669–691,Short summary
Carbon leaching to streams represents a very small (~ 2 %) fraction of forest net ecosystem exchange (NEE). Such weak export of carbon from forest ecosystems, at least in temperate regions, is at odds with recent studies that attempt to integrate the contribution of inland waters in the continent carbon budget. Understanding why local and global carbon mass balances strongly diverge on the proportion of land NEE exported to aquatic systems is a major challenge for research in this field.
Katrin Magin, Celia Somlai-Haase, Ralf B. Schäfer, and Andreas Lorke
Biogeosciences, 14, 5003–5014,Short summary
We analyzed the relationship between terrestrial net primary production (NPP) and the rate at which carbon is exported from catchments in a temperate stream network. The carbon exported by streams and rivers corresponds to 2.7 % of the terrestrial NPP. CO2 evasion and downstream transport contribute about equally to this flux. A review of existing studies suggests that the catchment-specific carbon export varies in a relatively narrow range across different study regions and spatial scales.
Rémi Dupas, Andreas Musolff, James W. Jawitz, P. Suresh C. Rao, Christoph G. Jäger, Jan H. Fleckenstein, Michael Rode, and Dietrich Borchardt
Biogeosciences, 14, 4391–4407,Short summary
Carbon and nutrient export regimes were analyzed from archetypal headwater catchments to downstream reaches. In headwater catchments, land use and lithology determine land-to-stream C, N and P transfer processes. The crucial role of riparian zones in C, N and P coupling was investigated. In downstream reaches, point-source contributions and in-stream processes alter C, N and P export regimes.
Rose M. Smith, Sujay S. Kaushal, Jake J. Beaulieu, Michael J. Pennino, and Claire Welty
Biogeosciences, 14, 2831–2849,Short summary
Urban streams receive excess nitrogen from numerous sources. We hypothesized that variations in carbon availability and subsurface infrastructure influence emissions of N2O and other greenhouse gases (CH4 and CO2) as excess N is utilized by microbes. We sampled eight streams draining four categories of stormwater and sanitary infrastructure. Dissolved nitrogen concentration was the strongest predictor of CO2 and N2O concentrations, while C : N ratio was the strongest predictor of CH4 in streams.
Benjamin Kupilas, Daniel Hering, Armin W. Lorenz, Christoph Knuth, and Björn Gücker
Biogeosciences, 14, 1989–2002,Short summary
Modern ecosystem restoration should consider a wide range of environmental characteristics, including functional ones, such as rates and patterns of ecosystem metabolism. We show that hydromorphological river restoration enhanced habitat availability and abundance of macrophytes, promoting river primary productivity and respiration. Incorporating ecosystem functioning into monitoring programs enables a more holistic assessment of river health and a better understanding of restoration effects.
Julia Vanessa Kunz, Michael D. Annable, Jaehyun Cho, Wolf von Tümpling, Kirk Hatfield, Suresh Rao, Dietrich Borchardt, and Michael Rode
Biogeosciences, 14, 631–649,Short summary
The hyporheic zone, the subsurface region of streams, is a key compartment for in-stream nutrient retention. Knowledge on actual hyporheic processing rates is still limited due to methodological restrictions which are mainly related to the high local and temporal variability of subsurface flow patterns and nutrient transformation processes. We present a new device which allows quantitative assessment of hyporheic nutrient fluxes and demonstrate its advantages in an exemplary field testing.
Jemma Louise Wadham, Jonathan Hawkings, Jon Telling, Dave Chandler, Jon Alcock, Emily O'Donnell, Preeti Kaur, Elizabeth Bagshaw, Martyn Tranter, Andre Tedstone, and Peter Nienow
Biogeosciences, 13, 6339–6352,Short summary
Fjord and continental shelf environments in the polar regions are host to some of the planet's most productive ecosystems and support economically important fisheries. A key limiting nutrient for many of these marine phytoplankton is nitrogen. Here we evaluate the potential for a melting Greenland Ice Sheet to supply nitrogen to Arctic coastal ecosystems. We show nitrogen fluxes of a similar order of magnitude to one large Arctic river but yields that are double those typical of Arctic rivers.
Mi-Hee Lee, Jean-Lionel Payeur-Poirier, Ji-Hyung Park, and Egbert Matzner
Biogeosciences, 13, 5421–5432,Short summary
Heavy storm events may increase the organic matter fluxes from forested watersheds and deteriorate water quality. Our study in two forested watershed in Korea revealed, that a larger proportion of coniferous forests likely leads to less organic carbon and larger of inorganic nitrogen fluxes to the receiving surface water bodies. More severe monsoon storms in the future will increase the fluxes of dissolved organic matter.
Thibault Lambert, Steven Bouillon, François Darchambeau, Philippe Massicotte, and Alberto V. Borges
Biogeosciences, 13, 5405–5420,Short summary
This paper aims to investigate the spatial variability in dissolved organic matter (DOM) in terms of both concentration and composition in the Congo River network. Stable carbon isotopes and absorption and fluorescent properties of DOM were used as proxies for DOM composition. This study shows that DOM degradation within the Congo Basin results in the transition from aromatic to aliphatic DOM as well as the role of landscape and water residence time on this transition.
Tae Kyung Yoon, Hyojin Jin, Neung-Hwan Oh, and Ji-Hyung Park
Biogeosciences, 13, 3915–3930,Short summary
Spray- and marble-type equilibrators and a membrane-enclosed CO2 sensor were compared to assess their suitability for continuous pCO2 measurements in inland waters. The results suggest that the fast response of the equilibration systems facilitates capturing large spatial variations in pCO2 during short underway measurements. The membrane-enclosed sensor would be suitable for long-term continuous measurements if biofouling could be overcome by antifouling measures such as copper mesh coverings.
Hongbing Ji, Cai Li, Huaijian Ding, and Yang Gao
Biogeosciences, 13, 3687–3699,Short summary
The mineral composition, C / N ratios as well as 13C and 15N, of POC was firstly analyzed in suspended and surface sediments in the Wujiang River after the Three Gorges Dam began impounding sediment in 2004. A comparison of POC yield was made between karstic rivers and non-karstic rivers to evaluate the influence of carbonate distribution on POC transport. Considering the cascade reservoir and climate in the Wujiang River, the impacts of reservoirs and extreme drought were estimated in this study.
Johanna I. F. Slaets, Petra Schmitter, Thomas Hilger, Tran Duc Vien, and Georg Cadisch
Biogeosciences, 13, 3267–3281,Short summary
Maize production on steep slopes causes erosion. Where the eroded material ends up is not well understood. This study assessed transport of sediment in mountainous Vietnam, where maize is cultivated on slopes and rice is cultivated in valleys. Per year, 64 tons per hectare of sediments are brought into the rice fields and 28 tons of those are deposited there. The sediment fraction captured by the paddies is mostly sandy, while fertile silt and clay are exported. Upland erosion thus impacts rice production.
Thibault Lambert, Cristian R. Teodoru, Frank C. Nyoni, Steven Bouillon, François Darchambeau, Philippe Massicotte, and Alberto V. Borges
Biogeosciences, 13, 2727–2741,Short summary
This manuscript presents a detailed analysis of transport and transformation of dissolved organic matter along the Zambezi River and its largest tributary. A particular focus is put on the effects of floodplains/wetlands and reservoirs as well as low-flow vs. high-flow conditions on the longitudinal patterns in DOM concentration and composition. It is the first study to present such a detailed analysis for a whole, large river system, and in particular for a tropical river other than the Amazon.
Arthur H. W. Beusen, Alexander F. Bouwman, Ludovicus P. H. Van Beek, José M. Mogollón, and Jack J. Middelburg
Biogeosciences, 13, 2441–2451,Short summary
Intensifying anthropogenic activity over the 20th century including agriculture, water consumption, urbanization, and aquaculture has almost doubled the global nitrogen (N) and phosphorus (P) delivery to streams and steadily increased the N : P ratio in freshwater bodies. Concurrently, the cumulative number of reservoirs has driven a rise in freshwater nutrient retention and removal. Still, river nutrient transport to the ocean has also nearly doubled, potentially stressing coastal environments.
Karen E. Frey, William V. Sobczak, Paul J. Mann, and Robert M. Holmes
Biogeosciences, 13, 2279–2290,Short summary
In this study, we provide new findings with regards to the spatial distribution of dissolved organic matter (DOM) concentration, bioavailability, and optical properties during mid-summer hydrologic conditions throughout the Kolyma River basin in northeast Siberia. This is particularly critical for this region, where the future fate of organic carbon currently frozen in permafrost soils (and whether it ultimately is released as CO2 and CH4) is tightly linked to the lability of this material.
Oleg S. Pokrovsky, Rinat M. Manasypov, Sergey V. Loiko, Ivan A. Krickov, Sergey G. Kopysov, Larisa G. Kolesnichenko, Sergey N. Vorobyev, and Sergey N. Kirpotin
Biogeosciences, 13, 1877–1900,Short summary
Climate change in western Siberia and permafrost boundary migration will essentially affect the elements controlled by underground water feeding (DIC, alkaline earth elements (Ca, Sr), oxyanions (Mo, Sb, As) and U). The thickening of the active layer may increase the export of trivalent and tetravalent hydrolysates in the form of organo-ferric colloids.
Jr-Chuan Huang, Tsung-Yu Lee, Teng-Chiu Lin, Thomas Hein, Li-Chin Lee, Yu-Ting Shih, Shuh-Ji Kao, Fuh-Kwo Shiah, and Neng-Huei Lin
Biogeosciences, 13, 1787–1800,Short summary
The mean riverine DIN export of 49 watersheds in Taiwan is ∼ 3800 kg N km−2 yr−1, 18 times the global average. The mean riverine DIN export ratio is 0.30–0.51, which is much higher than the average of 0.20–0.25 of large rivers around the world, indicating excessive N input relative to ecosystem retention capacity. The DIN export ratio is positively related to agriculture input, and levels of human disturbance and watersheds with high DIN export ratios are likely at advanced stages of N excess.
Michael N. Gooseff, David Van Horn, Zachary Sudman, Diane M. McKnight, Kathleene A. Welch, and William B. Lyons
Biogeosciences, 13, 1723–1732,Short summary
The landscape of the McMurdo Dry Valleys, Antarctica has been considered quite stable. In 2012, we discovered extensive permafrost degradation along several km of Crescent Stream. Here we document the responses to water quality, specifically changes to dissolved major ion and suspended sediment characteristics. Stream nitrate concentrations were greater than observed in the stream over the previous ~ 20 years, suggesting potentially significant impacts for stream and downstream lake ecosystems.
C. E. M. Lloyd, K. Michaelides, D. R. Chadwick, J. A. J. Dungait, and R. P. Evershed
Biogeosciences, 13, 551–566,Short summary
Our interdisciplinary research brings together methodologies from hydrology, soil science and biogeochemistry to address key questions about the transport of cattle slurry in the environment. The paper provides a novel approach to trace dissolved and particulate components of cattle slurry through an experimental hillslope system. This work provides one of the first examples of using biomarkers to assess the effects of slope gradient and rainfall intensity on the movement of slurry derived-OM.
N. Geeraert, F. O. Omengo, G. Govers, and S. Bouillon
Biogeosciences, 13, 517–525,Short summary
Rivers transport a large amount of carbon as dissolved organic carbon (DOC). Our incubation experiments on water of the Tana River, Kenya, showed that microbial decomposition of 10–60 % of the initial DOC occurred within the first 24–48 h. Simultaneously, there was a decrease in isotopic composition, indicating that DOC derived from C4 vegetation is preferentially decomposed. This has implications for the assessment of vegetation in a catchment based on isotope signatures of riverine carbon.
J. Temnerud, C. von Brömssen, J. Fölster, I. Buffam, J.-O. Andersson, L. Nyberg, and K. Bishop
Biogeosciences, 13, 399–413,Short summary
In this study we test whether river outlet chemistry can be used as an additional source of information to improve the prediction of the total organic carbon (TOC) of headwaters, relative to models based on map information alone. Including river outlet TOC as a predictor in the models gave 5-15 % lower prediction errors than using map information alone. Thus, data on water chemistry measured at river outlets offer information which can complement GIS-based modelling of headwaters chemistry.
A. Hartmann, J. Kobler, M. Kralik, T. Dirnböck, F. Humer, and M. Weiler
Biogeosciences, 13, 159–174,Short summary
We consider the time period before and after a wind disturbance in an Austrian karst system. Using a process-based flow and solute transport simulation model we estimate impacts on DIN and DOC. We show that DIN increases for several years, while DOC remains within its pre-disturbance variability. Simulated transit times indicate that impact passes through the hydrological system within some months but with a small fraction exceeding transit times of even a year.
J. Schelker, R. Sponseller, E. Ring, L. Högbom, S. Löfgren, and H. Laudon
Biogeosciences, 13, 1–12,Short summary
The scientific question that is addressed in this study is how forest disturbance affects organic and inorganic nitrogen export from a boreal landscape. The key findings are that the mobilization of inorganic nitrogen from the terrestrial environment to streams increased strongly as a response to harvesting, but the stream network removed a major fraction of this load before it reached the outlet, while organic nitrogen was not removed and transported downstream.
S. Duan and S. S. Kaushal
Biogeosciences, 12, 7331–7347,Short summary
There has been increased salinization of fresh water over decades during the urban evolution of watersheds. This study finds that salinization consistently increased sediment releases of labile organic carbon and total dissolved Kjeldahl nitrogen and sediment transformations of nitrate, and the salinization effects increased with percentage watershed urbanization. These findings are will be critical for forecasting changes in carbon and nutrient exports due to salt use in urban watersheds.
J. E. Vonk, S. E. Tank, W. B. Bowden, I. Laurion, W. F. Vincent, P. Alekseychik, M. Amyot, M. F. Billet, J. Canário, R. M. Cory, B. N. Deshpande, M. Helbig, M. Jammet, J. Karlsson, J. Larouche, G. MacMillan, M. Rautio, K. M. Walter Anthony, and K. P. Wickland
Biogeosciences, 12, 7129–7167,Short summary
In this review, we give an overview of the current state of knowledge regarding how permafrost thaw affects aquatic systems. We describe the general impacts of thaw on aquatic ecosystems, pathways of organic matter and contaminant release and degradation, resulting emissions and burial, and effects on ecosystem structure and functioning. We conclude with an overview of potential climate effects and recommendations for future research.
J. E. Vonk, S. E. Tank, P. J. Mann, R. G. M. Spencer, C. C. Treat, R. G. Striegl, B. W. Abbott, and K. P. Wickland
Biogeosciences, 12, 6915–6930,Short summary
We found that dissolved organic carbon (DOC) in arctic soils and aquatic systems is increasingly degradable with increasing permafrost extent. Also, DOC seems less degradable when moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly bioavailable DOC is lost in headwater streams. We also recommend a standardized DOC incubation protocol to facilitate future comparison on processing and transport of DOC in a changing Arctic.
R. M. Cory, K. H. Harrold, B.T. Neilson, and G. W. Kling
Biogeosciences, 12, 6669–6685,Short summary
This study investigates how sunlight, dissolved organic matter (DOM) concentration and composition, and hydrology interact to control DOM degradation in headwater streams. In Imnavait Creek, a shallow, low-relief stream in the Arctic, DOM degradation by sunlight was limited by light under all conditions. Study results were used to synthesize controls on DOM degradation by sunlight for a river reach, expressed as a function of light attenuation and water residence times.
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