Dynamics and sources of reduced sulfur, humic substances and dissolved organic carbon in a temperate river system affected by agricultural practices
Graphical abstract
Introduction
Dissolved organic matter (DOM) is formed from the decay of intact or remnant and transformed compounds released from living and decaying biota. Because it participates in many biogeochemical processes in the environment, i.e. photochemical reactions, metal complexation, microbial growth, and nutrient and contaminant transport, DOM is an important component of marine and terrigenous aquatic ecosystems. Therefore, determining its composition and reactivity is essential for understanding environmental processes, for example metal complexation. Moreover, the riverine export of DOM through estuaries has a major impact on the biogeochemical cycles in the coastal ocean (Canuel et al., 2012, Hansell and Carlson, 2002, Volkman, 2006). Despite its importance, the composition and fate of riverine DOM have been poorly determined and remain one of the major concerns in contemporary biogeochemistry (Bianchi, 2011).
A significant proportion of riverine DOM is composed of more stable compounds produced either in the soil or in the water body. Because of their resistance to degradation, these compounds are sometimes called refractory organic matter (ROM), but they are most often referred to as humic acids (HA), fulvic acids (FA) or humic substances (HS). As mentioned recently (Filella, 2014), although HS are the most widely used type of DOM in laboratory studies, attempts to quantify them in natural waters are scarce. The only quantification method that will theoretically allow measurement of ‘true’ HA and FA concentrations should be based on exactly the same fractionation procedure used in defining them. However this requires large volumes of water, and is tedious and time-consuming, so is rarely used. Due to an update of an old electroanalytical method (Quentel et al., 1986), a few studies of the HS behavior in the aquatic environment have appeared (Chanudet and Filella, 2007, Filella et al., 2013, Waeles et al., 2013).
Besides, reduced sulfur substances (RSS), particularly thiols have aroused interest mainly because they are important complexing ligands for metals and therefore significantly control the speciation of many trace elements in natural waters by competing with other potential binders such as HS (Buffle, 1988). Thiols are ubiquitous at the mmol level in intracellular media and participate in a wide range of biochemical reactions due to their detoxifying effect as metal ligands and reactive oxygen species scavengers (Jacob et al., 2003). It was long assumed that the concentration of thiols would be quite low or even below detection in oxic waters as these compounds are readily oxidized (Abedinzadeh et al., 1989, Winterbourn and Metodiewa, 1999), easily metabolized by bacteria (Visscher and Taylor, 1993) and/or quickly photo-oxidized (Laglera and van den Berg, 2006, Moingt et al., 2010). It has been demonstrated, however, that thiols like glutathione may be stabilized via metal complexation or even DOM conjugation (Moingt et al., 2010, Tang et al., 2004). Most studies reporting on thiols in aquatic systems have been conducted on marine, estuarine and coastal environments, and have generally found a correlation between some thiols and indicators of phytoplankton abundance, particularly chlorophyll (Chl-a) concentration (Al-Farawati and van den Berg, 2001, Dupont et al., 2006, Laglera and van den Berg, 2003, Le Gall and van den Berg, 1993, Tang et al., 2000, Tang et al., 2004). Only three studies have reported thiols in freshwater: Connecticut lakes (Hu et al., 2006), the St Lawrence system (Moingt et al., 2010) and one focusing on sediment porewater in a wetland area (Zhang et al., 2004).
Determination of the individual components of RSS mixtures in the range pmol L-1 to μmol L-1 may be performed using high performance liquid chromatography (HPLC) after derivatization (Dupont et al., 2006, Tang et al., 2003, Tang et al., 2004). However, uncertainty about the recovery rates and the common presence of unidentified thiol peaks may pose some concern about the ability of HPLC to determine the overall concentration of RSS. The huge affinity of reduced sulfur for mercury facilitates the analysis of RSS using cathodic stripping voltammetry (CSV) with mercury electrodes. However, CSV is severely limited by coalescence at neutral pH, i.e. thiol peaks merge together at environmental pH. Recent electroanalytical improvements by way of cathodic pseudopolarography (Laglera et al., 2014, Laglera and Tovar-Sanchez, 2012), enabled the characterization and quantification of individual components of RSS mixtures at neutral pH. The duration of the analysis (several h per sample) is, however, too restrictive for environmental applications. Nevertheless it has been shown recently that acidification of the samples to pH 1.95 and addition of molybdenum (VI) allow the rapid and direct simultaneous identification and quantification of glutathione (GSH), thioacetamide (TA) and HS using differential pulse CSV (DP-CSV) (Pernet-Coudrier et al., 2013).
In this study, we investigated the behavior of DOC, HS and RSS in the Penzé River (NW France) using DP-CSV and liquid chromatography coupled to an organic carbon detector. Despite its low discharge regime, this river can be regarded as a typical temperate system affected by agricultural practices (Waeles et al., 2005, Waeles et al., 2013). Moreover, studies on such small watersheds over a wide range of hydrologic conditions also allow understanding relative short-term components of carbon cycling (Dalzell et al., 2005). Therefore, the Penzé River had been sampled at high frequency over a 1 year period (45 sampling campaigns in 2012) in order to take into account the potential strong variability. To our knowledge, such an approach has not been undertaken before. Our objectives were to (i) determine the annual dynamics of DOC, RSS and HS in this kind of temperate river system affected by agricultural activity, (ii) to examine the sources of these compounds and (iii) to assess their flux towards the coastal area.
Section snippets
Study area
The Penzé River (N Brittany, France) has a drainage area of 141 km2 and is 28 km long, with an estuary of 10 km (Fig. 1). This river system collects the water from a poorly industrialized catchment but where extensive agricultural activity has been developed for decades. Soil occupancy is mainly agricultural with arable and permanently cultivated areas representing 36% and heterogeneous agricultural areas accounting for 33%. Meadows (7%), moor and peat bogs (3%) and forests (0.7%) are the
Hydrological variation
The annual mean water discharge from the Penzé River over 2012 was 3.09 m3 s− 1 which was not significantly different from the average of 2.82 ± 0.68 m3 s− 1 calculated from 1967 to 2013. Usually, the hydrological cycle of the river has two distinct periods: November–March, characterized by relatively high discharge and April–October, which is the drier period (Fig. 2). The daily water discharge normally fluctuated between 0.66 m3 s− 1 and 14.5 m3 s− 1 (Fig. 3A). During the winter of 2012, the discharge (Q)
Comparison with other systems
Humic substances, and more particularly FA, represent a significant proportion of dissolved organic matter in freshwater. This had been demonstrated over a wide range of systems (Table 1). In agricultural streams, DOC can reach up to 16 mg L− 1 and HS like FA may account up to 80% (Table 1). The Penzé River fell within this range, with DOC ranging between 2 and 8 mgC L− 1 and HS ranging between 44 and 69% of DOC.
For GSHs and TAs, comparison with the literature is difficult, due mainly to the scarcity
Conclusions
The differential pulse cathodic stripping voltammetry and the liquid chromatography coupled to an organic carbon detector were applied to quantify respectively the concentrations of glutathione-like, thioacetamide-like, humic substances and dissolved organic carbon in the temperate Penzé River system affected by agricultural practices. Concentration-flow charts, poly-component analysis and flux analysis allowed us to discriminate the source and dynamics of each compound type. Our results
Acknowledgments
We thank N. Cabon, C. Bassoulet, C. Liorzou, M.-L. Rouget and C. Tissot for their assistance in the sampling campaigns and analysis. This work was financially supported by the Region Bretagne and the Université de Bretagne Occidentale (Ph.D. grant to L. Marie) and the Marie Curie FP7 (Dynamite project CIG 333737).
References (63)
- et al.
Fate of natural and anthropogenic dissolved organic carbon in the macrotidal Elorn estuary (France)
Mar. Chem.
(1990) - et al.
Cadmium lets increase the glutathione pool in bryophytes
J. Plant Physiol.
(2001) - et al.
Submicron organic matter in a peri-alpine, ultra-oligotrophic lake
Org. Geochem.
(2007) - et al.
The role of hydrology in annual organic carbon loads and terrestrial organic matter export from a midwestern agricultural watershed
Geochim. Cosmochim. Acta
(2007) - et al.
Distributions of dissolved and particulate biogenic thiols in the subartic Pacific Ocean
Deep-Sea Res. I
(2006) Understanding what we are measuring: standards and quantification of natural organic matter
Water Res.
(2014)- et al.
Natural organic matter quantification in the waters of a semiarid freshwater wetland (Tablas de Daimiel, Spain)
J. Environ. Sci.
(2013) - et al.
The role of climate on inter-annual variation in stream nitrate fluxes and concentrations
Sci. Total Environ.
(2010) - et al.
Characterisation of aquatic humic and non-humic matter with size-exclusion chromatography–organic carbon detection–organic nitrogen detection (LC–OCD–OND)
Water Res.
(2011) - et al.
Direct recognition and quantification by voltammetry of thiol/thioamide mixes in seawater
Talanta
(2012)
Copper complexation by thiol compounds in estuarine waters
Mar. Chem.
Photochemical oxidation of thiols and copper complexing ligands in estuarine waters
Mar. Chem.
Cathodic pseudopolarography: a new tool for the identification and quantification of cysteine, cystine and other low molecular weight thiols in seawater
Anal. Chim. Acta
Composition of dissolved organic matter in groundwater
Geochim. Cosmochim. Acta
Role of ultra-violet radiation, mercury and copper on the stability of dissolved glutathione in natural and artificial freshwater and saltwater
Chemosphere
Simple and simultaneous determination of glutathione, thioacetamide and refractory organic matter in natural waters by DP-CSV
Sci. Total Environ.
River discharge of humic substances and humic-bound metals to the Gulf of Bothnia
Estuar. Coast. Shelf Sci.
Origin and mobility of fulvic acids in the Gorleben aquifer system: implications from isotopic data and carbon/sulfur XANES
Org. Geochem.
The geochemistry of rare earth elements in groundwater from the Carnmenellis area, southwest England
Geochim. Cosmochim. Acta
Identification and on-line monitoring of reduced sulphur species (RSS) by voltammetry in oxic waters
Talanta
Determination of dissolved thiols using solid-phase extraction and liquid chromatographic determination of fluorescently derivatized thiolic compounds
J. Chromatogr. A
Groundwater contamination by trace elements
Agric. Ecosyst. Environ.
Seasonal variations of dissolved and particulate copper species in estuarine waters
Estuar. Coast. Shelf Sci.
Annual cycle of humic substances in a temperate estuarine system affected by agricultural practices
Geochim. Cosmochim. Acta
Sediment concentration versus water discharge during single hydrologic events in rivers
J. Hydrol.
Reactivity of biologically important thiol compounds with superoxide and hydrogen peroxide
Free Radic. Biol. Med.
Kinetic study of the oxidation mechanism of glutathione by hydrogen peroxide in neutral aqueous medium
Can. J. Chem.
Glutathione and other low molecular weight thiols in marine phytoplankton under metal stress
Mar. Ecol. Prog. Ser.
Thiols in coastal waters of the Western North sea and English channel
Environ. Sci. Technol.
Quantitative and qualitative changes of organic matter in an Ando soil induced by mineral fertilizer and cattle manure applications for 20 years
Soil Sci. Plant Nutr.
Humic substances in the Suwannee River, Georgia; interactions, properties, and proposed structures
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