Hydro‐Climatological Influences on Long‐Term Dissolved Organic Carbon in a Mountain Stream of the Southeastern United States

Abstract

In the past decade, significant increases in surface water dissolved organic carbon (DOC) have been reported for large aquatic ecosystems of the Northern Hemisphere and have been attributed variously to global warming, altered hydrologic conditions, and atmospheric deposition, among other factors. We analyzed a 25-yr DOC record (1988-2012) available for a forested headwater stream in the United States and documented two distinct regimes of stream DOC trends. From 1988 to 2001, annual mean volume-weighted DOC concentration (DOC, mg L) and annual DOC flux (kg ha yr) declined by 34 and 56%, respectively. During 1997 to 2012, the decline in DOC and DOC flux increased by 141 and 165%, respectively. Declining DOC from 1988 to 2001 corresponded to a decline in growing season runoff, which has the potential to influence mobilization of DOC from uplands to streams. Increasing DOC from 1997 to 2012 corresponded to increased precipitation early in the growing season and to an increase in the number and intensity of short-duration fall storms capable of mobilizing long-accrued DOC from forest litter and soils. In contrast, total annual runoff declined throughout the period. Rising air temperature, atmospheric acid deposition, and nitrogen depositions did not offer any plausible explanation for the observed bidirectional annual trends of stream DOC. Our study highlights the critical role of long-term datasets and analyses for understanding the impacts of climate change on carbon and water cycles and associated functions of aquatic and terrestrial ecosystems.

Ecological response to hydrological variability and catchment development: Insights from a shallow oxbow lake in Lower Mississippi Valley, Arkansas

“…Global circulation models predict increases in air temperature and hydrological extremes for most part of United States (IPCC, 2014). Recent studies suggest that changes in precipitation patterns can significantly influence the water quality for range of aquatic habitats (e.g., Whitehead et al, 2009;Singh et al, 2016). Increase in large precipitation events and associated flooding can mobilize pollutants from the cultivated sections of RFEs and can adversely impact water quality and productivity of floodplain lakes (Knight et al, 2007;Kröger et al, 2013).…”

Multitemporal Relationships Between the Hydroclimate and Exports of Carbon, Nitrogen, and Phosphorus in a Small Agricultural Watershed

“…Few studies have investigated water quality response to local climatic conditions considering (i) multiple elements (Michalak, 2016; Singh et al, 2016; Whitehead et al, 2009) with contrasting sources, mobilization, and reactivity, such as DOC, NO 3 , and SRP, and (ii) several temporal scales (from 1 day to decades). Such studies require high‐frequency multielement sampling in small‐scale watersheds over a long period (>10 years).…”

Photodegradation disproportionately impacts biodegradation of semi‐labile DOM in streams

“…Terrestrially derived dissolved organic matter (DOM) sourced from decaying plant and soil organic matter fuels heterotrophic microbial degradation in streams (Battin et al ). Export of terrestrially derived DOM to streams in many regions has increased in response to changes in climate, land‐use, or other processes (Monteith et al ; Laudon et al ; Singh et al ). However, controls on the biodegradation of DOM to CO 2 remain too poorly understood to predict changes in CO 2 emissions from streams in response to increasing DOM export from watersheds (Oni et al ; Biddanda ).…”