Contemporary changes in dissolved organic carbon (DOC) in human‐dominated rivers: is there a role for DOC management?

Abstract

1. Dissolved organic carbon (DOC) plays a central role in the dynamics of stream and river ecosystems, affecting processes such as metabolism, the balance between autotrophy and heterotrophy, acidity, nutrient uptake and bioavailability of toxic compounds. However, despite its importance to stream processes, restoration and management activities rarely incorporate DOC as a major management criterion. 2. Lotic DOC pools reflect terrestrial organic carbon accumulation, transfer to the river channel and aquatic processing. In pristine landscapes, characteristics such as topography, climate, and landscape composition are strong predictors of terrestrial accumulation and transfer. Within aquatic systems, the quantity and form of DOC are altered by a variety of processes including primary production, microbial breakdown, sorption to particles and photodegradation. 3. Terrestrial accumulation, transfer and aquatic processing of DOC in agricultural and other human-dominated landscapes are all subject to substantial change. Consequently, DOC pools in agricultural streams likely differ from historic conditions and now include more labile material and low concentrations of a variety of ubiquitous synthetic organic compounds (e.g. pesticides, antibiotics). 4. Although DOC change in agricultural streams and associated ecological consequences are expected to be widespread, current understanding and relevant data needed to manage affected systems are surprisingly scarce. 5. Wetland and riparian restoration projects have variable effects on fluvial DOC regimes, but management at this intermediate scale is a realistic compromise between the small extent of most restoration projects and the large spatial scale over which organic carbon impairment occurs.

Effects of human land use on the terrestrial and aquatic sources of fluvial organic matter in a temperate river basin (The Meuse River, Belgium)

“…All these fundamental aspects can potentially be impacted by human activities (Stanley et al 2012). In this study, we showed that human activities in the Walloon region have affected both terrestrial and aquatic sources of fluvial OM, leading to a shift in composition toward a more microbial/algal and less plant/soil-derived character in streams and rivers.…”

“…A similar pattern was observed at the scale of the Meuse basin whereby F Max of terrestrial components were slightly higher during S2 (summer period, low specific discharge) relative to S1 (winter period, high specific discharge). This likely reflects modification and/or reorganization of hydrological flow paths that connect terrestrial soils to aquatic ecosystems by agricultural practices and urbanization engineering (Kaushal and Belt 2012;Stanley et al 2012).…”

“…The terrestrial (allochthonous) or aquatic (autochthonous) origin of OM determines its composition that in turn drives its reactivity and its impact on stream metabolism (Strauss and Lamberti 2002;Tranvik and Bertilsson 2001). Terrestrial inputs as well as autochthonous primary production of OM are the result of the interplay of several catchment attributes such as soil properties (Autio et al 2016;Nelson et al 1992), land cover (Giling et al 2014;Wilson and Xenopoulos 2009), hydrology and water residence time (Lambert et al 2014;Sanderman et al 2009) and nutrient availability (Reche et al 1998), all of these basic drivers being altered by human activities (Carpenter et al 2011;Stanley et al 2012). The conversion of natural landscapes for human use has thus been shown to alter the sources, composition and reactivity of fluvial OM with significant effects on carbon cycling in freshwaters (Parr et al 2015;Petrone et al 2011;Rosemond et al 2015;Wilson and Xenopoulos 2009).…”

Beyond the urban stream syndrome: organic matter budget for diagnostics and restoration of an impaired urban river

“…Organic matter may also be directly deposited into streams and can contribute to depleted dissolved oxygen (DO) concentrations, thus threatening ecosystem health (Imberger et al 2014). Investigating and controlling concentrations of both nutrients and OM should be considered when developing eutrophication mitigation strategies (e.g., Smith et al 1999;Dodds 2007;Stanley et al 2012).…”

Allochthonous dissolved organic carbon in river, lake and coastal systems: transport, function and ecological role

“…Given the role of allochthonous DOC in supporting and structuring aquatic ecosystems, there are a wealth of opportunities to incorporate DOC to support process-based river rehabilitation and management (Stanley et al 2012). To build on this interest in allochthonous DOC in management, Baldwin et al (2016) present a review paper on the use of environmental flows to restore allochthonous DOC to lowland river systems.…”