A worldwide view of organic carbon export from catchments

Abstract

Growing interest in the effects of global change on the metabolism, stoichiometry and cycling of carbon in aquatic ecosystems has motivated research on the export of organic carbon (OCE) from catchments. In this article, quantitative and functional features of the annual export rates of total, particulate and dissolved organic carbon (TOC, POC and DOC) were reviewed, and the stoichiometry of export (OC:N, OC:P and N:P) from 550 catchments worldwide was reported. TOC export ranged 2.1-92,474 kg C km -2 year -1 , POC export ranged 0.4-73,979 kg C km -2 year -1 and DOC export ranged 1.2-56,946 kg C km -2 year -1 . Exports of TOC and DOC were strongly linked, but POC export was unrelated to DOC. The DOC fraction comprised on average 73 ± 21% of TOC export. The export rates of organic carbon were poorly related to those of total nitrogen and total phosphorus. Discrete and continuous environmental variables failed to predict TOC export, but DOC export was influenced by discharge and catchment area worldwide. Models of OCE in different catchment types were controlled by different environmental variables; hydrological variables were generally better predictors of OCE than anthropogenic and soil variables. Elemental ratios of carbon export in most catchments were above the Redfield ratio, suggesting that phosphorus may become the limiting nutrient for downstream plant growth. These ratios were marginally related to environmental data. More detailed hydrological data, consideration of in-stream processes and the use of quasi-empirical dynamical models are advocated to improve our knowledge of OCE rates and those of other nutrients.

A global hotspot for dissolved organic carbon in hypermaritime watersheds of coastal British Columbia

“…However, overall DOC concentrations increased in all watersheds with both discharge and temperature indicating that the overarching drivers of DOC export are the hydrologic coupling of precipitation and runoff from the landscape with the seasonal production and availability of DOC (Fasching et al, 2016). Precipitation is a well-established driver of stream DOC export (Alvarez-Cobelas et al, 2012), particularly in systems containing organic soils and wetlands (Olefeldt et al, 2013;Wallin et al, 2015;Leach et al, 2016). Frequent, high-intensity precipitation events and short residence times are expected to result in pulsed exports of stream DOC that are rapidly shunted downstream, thus reducing time for instream processing (Raymond et al, 2016).…”

“…When compared to watersheds of similar size, DOC yields from Calvert and Hecate island watersheds are some of the highest observed (see reviews in Hope et al, 1994;Alvarez-Cobelas et al, 2012), including DOC yields from many tropical rivers, despite the fact that tropical rivers have been shown to export very high DOC (e.g., Autuna River, Venezuela, DOC yield: 56 946 kg C km −2 yr −1 ; Castillo et al, 2004) and are often regarded as having disproportionately high carbon export compared to temperate and Arctic rivers (Aitkenhead and McDowell, 2000;Borges et al, 2015). Our estimates of DOC yield are comparable to, or higher than, previous estimates from high-latitude catchments of similar size that receive high amounts of precipitation and contain extensive organic soils and wetlands (e.g., Naiman, 1982 (DOC yield: 48 380 kg C km −2 yr −1 ); Brooks et al, 1999 (DOC yield: 20 300 kg C km −2 yr −1 ); Ågren et al, 2007 (DOC yield: 32 043 kg C km −2 yr −1 )).…”

“…A. Oliver et al: A global hotspot for dissolved organic carbon coastal ocean (Cole et al, 2007), with typically > 50 % quantified as dissolved organic carbon (DOC) (Meybeck, 1982;Ludwig et al, 1996;Alvarez-Cobelas et al, 2012;Mayorga et al, 2010). Rivers draining coastal watersheds serve as conduits of DOC from terrestrial and freshwater sources to marine environments (Mulholland and Watts, 1982;Bauer et al, 2013;McClelland et al, 2014) and can have important implications for coastal carbon cycling, biogeochemical interactions, ecosystem productivity, and food webs (Hopkinson et al, 1998;Tallis, 2009;Tank et al, 2012;Regnier et al, 2013).…”

An Analysis of Terrestrial and Aquatic Environmental Controls of Riverine Dissolved Organic Carbon in the Conterminous United States

“…Forest and shrub land have positive impact, while cropland demonstrates negative influence on DOC concentrations. This may be caused by higher soil organic matter and litter inputs in natural ecosystems than in managed lands, because fresh litter decomposition is an important source of riverine DOC [67]. Additionally, intensive management activities in cropland such as tillage and irrigation may enhance soil organic matter decomposition and reduce DOC leaching from arable soils [68].…”

Hydro-ecological controls on dissolved carbon dynamics in groundwater and export to streams in a temperate pine forest

“…We could observe higher DOC concentrations in streams during early winter and high-flow periods than during growing season and late summer periods (Table 4). Increase in DOC concentrations with discharge and a high water table has been reported in the Leyre watershed (Polsenaere et al, 2013) and in many other forested catchments (Alvarez-Cobelas et al, 2012;Dawson et al, 2002;Raymond and Saiers, 2010;Striegl et al, 2005). At our study site, during periods of high flow, first-order streams exported 0.2 ± 0.2 mmol m −2 day −1 to second-order streams, a flux significantly lower than DOC exports (0.7 ± 0.7 mmol m −2 day −1 ) from groundwater to first-order streams (Table 5).…”