Major ion chemistry and dissolved inorganic carbon cycling in a human-disturbed mountainous river (the Luodingjiang River) of the Zhujiang (Pearl River), China

Major ion chemistry and dissolved inorganic carbon system (DIC, mainly HCO₃⁻ and gaseous CO₂) in the Luodingjiang River, a mountainous tributary of the Zhujiang (Pearl River), China, were examined based on a seasonal and spatial sampling scheme in 2005. The diverse distribution of lithology and anthropogenic impacts in the river basin provided the basic idea to assess the effects of lithology vs. human activities on water chemistry and carbon biogeochemistry in river systems. Major ions showed great spatial variations, with higher concentrations of total dissolved solids (TDS) and DIC in the regions with carbonate rocks and clastic sedimentary rocks, while lower in the regions with metamorphic sandstones and schists as well as granites. pCO₂ at all sampling sites was oversaturated in June, ranging with a factor from 1.6 to 18.8 of the atmospheric concentration, reflecting the enhanced contribution from baseflow and interflow influx as well as in situ oxidation of organic matter. However, in April and December, undersaturated pCO₂ was found in some shallow, clean rivers in the upstream regions. δ¹³C of DIC has a narrow range from − 9.07 to − 13.59‰, which was more depleted in the regions with metamorphic rocks and granites than in the carbonate regions. Seasonally, it was slightly more depleted in the dry season (December) than in the wet season (June). The results suggested that lithological variability had a dominant control on spatial variations of water chemistry and carbon geochemistry in river systems. Besides, anthropogenic activities, such as agricultural and urban activities and in-stream damming, as well as river physical properties, such as water depth and transparency, also indicated their impacts. The seasonal variations likely reflected the changes of hydrological regime, as well as metabolic processes in the river.     

Stable isotopes of bulk organic matter to trace carbon and nitrogen dynamics in an estuarine ecosystem in Babitonga Bay (Santa Catarina, Brazil)

The biogeochemical processes affecting the transport and cycling of terrestrial organic carbon in coastal and transition areas are still not fully understood. One means of distinguishing between the sources of organic materials contributing to particulate organic matter (POM) in Babitonga Bay waters and sediments is by the direct measurement of δ¹³C of dissolved inorganic carbon (DIC) and δ¹³C and δ¹⁵N in the organic constituents. An isotopic survey was taken from samples collected in the Bay in late spring of 2004. The results indicate that the δ¹³C and δ¹⁵N compositions of OM varied from − 21.7‰ to − 26.2‰ and from + 9.2‰ to − 0.1‰, respectively. δ¹³C from DIC ranges from + 0.04‰ to − 12.7‰. The difference in the isotope compositions enables the determination of three distinct end-members: terrestrial, marine and urban. Moreover, the evaluation of source contribution to the particulate organic matter (POM) in the Bay, enables assessment of the anthropogenic impact. Comparing the depleted values of δ¹³C_DIC and δ¹³C_POC it is possible to further understand the carbon dynamic within Babitonga Bay.     

Natural versus wastewater derived dissolved organic carbon: implications for the environmental fate of organic micropollutants

The interaction of organic micropollutants with dissolved organic carbon (DOC) can influence their transport, degradation and bioavailability. While this has been well established for natural organic carbon, very little is known regarding the influence of DOC on the fate of micropollutants during wastewater treatment and water recycling. Dissolved organic carbon-water partition coefficients (K_DOC) for wastewater derived and reference DOC were measured for a range of micropollutants using a depletion method with polydimethylsiloxane disks. For micropollutants with an octanol-water partition coefficient (log K_OW) greater than 4 there was a significant difference in K_DOC between reference and wastewater derived DOC, with partitioning to wastewater derived DOC over 1000 times lower for the most hydrophobic micropollutants. The interaction of nonylphenol with wastewater derived DOC from different stages of a wastewater and advanced water treatment train was studied, but little difference in K_DOC was observed. Organic carbon characterisation revealed that reference and wastewater derived DOC had very different properties due to their different origins. Consequently, the reduced sorption capacity of wastewater derived DOC may be related to their microbial origin which led to reduced aromaticity and lower molecular weight. This study suggests that for hydrophobic micropollutants (log K_OW > 4) a higher concentration of freely dissolved and thus bioavailable micropollutants is expected in the presence of wastewater derived DOC than predicted using K_DOC values quantified using reference DOC. The implication is that naturally derived DOC may not be an appropriate surrogate for wastewater derived DOC as a matrix for assessing the fate of micropollutants in engineered systems.     

Testing seasonal and long-term controls of streamwater DOC using empirical and process-based models

Concentrations of dissolved organic carbon (DOC) in surface waters are increasing across Europe and parts of North America. Several mechanisms have been proposed to explain these increases including reductions in acid deposition, change in frequency of winter storms and changes in temperature and precipitation patterns. We used two modelling approaches to identify the mechanisms responsible for changing surface water DOC concentrations. Empirical regression analysis and INCA-C, a process-based model of stream-water DOC, were used to simulate long-term (1986-2003) patterns in stream water DOC concentrations in a small boreal stream. Both modelling approaches successfully simulated seasonal and inter-annual patterns in DOC concentration. In both models, seasonal patterns of DOC concentration were controlled by hydrology and inter-annual patterns were explained by climatic variation. There was a non-linear relationship between warmer summer temperatures and INCA-C predicted DOC. Only the empirical model was able to satisfactorily simulate the observed long-term increase in DOC. The observed long-term trends in DOC are likely to be driven by in-soil processes controlled by SO₄²⁻ and Cl⁻ deposition, and to a lesser extent by temperature-controlled processes. Given the projected changes in climate and deposition, future modelling and experimental research should focus on the possible effects of soil temperature and moisture on organic carbon production, sorption and desorption rates, and chemical controls on organic matter solubility.     

Freshwater DOM quantity and quality from a two-component model of UV absorbance

We present a model that considers UV-absorbing dissolved organic matter (DOM) to consist of two components (A and B), each with a distinct and constant spectrum. Component A absorbs UV light strongly, and is therefore presumed to possess aromatic chromophores and hydrophobic character, whereas B absorbs weakly and can be assumed hydrophilic. We parameterised the model with dissolved organic carbon concentrations [DOC] and corresponding UV spectra for c. 1700 filtered surface water samples from North America and the United Kingdom, by optimising extinction coefficients for A and B, together with a small constant concentration of non-absorbing DOM (0.80 mg DOC L⁻¹). Good unbiased predictions of [DOC] from absorbance data at 270 and 350 nm were obtained (r² = 0.98), the sum of squared residuals in [DOC] being reduced by 66% compared to a regression model fitted to absorbance at 270 nm alone. The parameterised model can use measured optical absorbance values at any pair of suitable wavelengths to calculate both [DOC] and the relative amounts of A and B in a water sample, i.e. measures of quantity and quality. Blind prediction of [DOC] was satisfactory for 9 of 11 independent data sets (181 of 213 individual samples).     

The influence of disinfection on aquatic biodegradable organic carbon formation

The aim of this paper was to assess the extent of biodegradable dissolved organic carbon formation upon disinfection of water with chlorine dioxide. Wide diversity of natural waters has been subjected to reactions with various amounts of ClO₂. For comparison examined waters have also been treated with ozone and chlorine. The application of chlorine dioxide and ozone significantly changed the molecular weight distribution of aquatic organic matter. As a result significant amounts of biodegradable carboxylic acids and aldehydes were generated. The formic, acetic, oxalic and ketomalonic acids as well as formaldehyde, acetaldehyde, glyoxal, methylglyoxal were identified. The productivity of aldehydes calculated for all examined waters and disinfectants amounted 12.7-47.7 μg mg⁻¹ DOC in the case of ozonation, 1.3-8.1 μg mg⁻¹ DOC after chlorination and 1.7-9.4 μg mg⁻¹ DOC for ClO₂ treatment. The highest total concentration of carboxylic acids was determined after the ozonation processes. In this case the organic acids' formation potential was in the range 10.8-62.8 μg mg⁻¹ DOC. Relatively high formation potential (5.3-17.9 μg mg⁻¹ DOC) was determined after the oxidation with ClO₂ as well. In the case of chlorination, the productivity of organic acids was low and did not exceed 3.4 μg mg⁻¹ DOC. The relatively high correlation between BDOC formation and carboxylic acids' formation potential was observed. Thus, carboxylic acids' formation potential may be used as a measure of water potential to form BDOC.     

Production of dissolved organic carbon in aquatic sediment suspensions

In many water quality models production of dissolved organic carbon (DOC) is modelled as mineralisation from particulate organic matter (POM). In this paper it is argued that the DOC production from dessicated sediments by water turbulence may be of similar importance. The DOC production from sediments was measured under sterile conditions, as a function of shaking time, sediment to water ratio and OC content. Furthermore, the maximum fraction of particulate organic carbon (POC) that can be mobilised by agitation (excluding the contribution of mineralisation) was assessed. The experiments can be considered as laboratory simulations of resuspension of aquatic sediments due to turbulence caused by wind, benthivorous fish or dredging. It was found that aquatic resuspension of dessicated sediment may cause mobilisation of up to 100% of indigenous particulate carbon in a few weeks. An empirical equation was derived that expresses mobilised carbon (DOC) as a function of sediment concentration (POC), OC fraction (f(OC)) and time. At a typical value of 25mg/L suspended sediment, the halflife for mobilisation is 0.5 day, which is much faster than bacterial degradation of POM in aquatic systems.     

Sensitivity of blanket peat vegetation and hydrochemistry to local disturbances

At the ecosystem scale, peatlands can be extremely resilient to perturbations. Yet, they are very sensitive to local disturbances, especially mechanical perturbations (e.g. trampling). The effects of these disturbances on vegetation, and potential effects on hydrochemical conditions along the peat surface, however, are largely unknown.We used three research tracks (paths researchers use to access their study sites) differing in time of abandonment to investigate the impact of local disturbance (trampling) on the vegetation and its short-term (≤ 2 year) recovery in a flagship research blanket peatland. Additionally, we examined the effects of local disturbance on fluvial runoff events and the concentrations of dissolved organic carbon (DOC) and particulate organic carbon (POC) in runoff water.Local disturbance heavily impacted peat vegetation, resulting in large areas of scarred and churned peat. Recovery of vascular plants along abandoned tracks was slow, but a functional Sphagnum layer re-established after just one year.The absence of vegetation elicited an increase in the number of runoff events along the tracks, by which POC runoff from the tracks increased. POC concentrations were highest in the surface water from the recently abandoned track, while they were low in the runoff water from the track abandoned longest and the undisturbed control track. We attribute this to the relatively fast recovery of the Sphagnum vegetation. DOC concentrations did not differ significantly either spatially or temporally in surface runoff or soil solution waters.While at an ecosystem scale local disturbances may be negligible in terms of carbon loss, our data points to the need for further research on the potential long-term effects of local disturbance on the vegetation, and significant effects on local scale carbon fluxes. Moreover, the effects of disturbances could be long-lasting and their role on ecosystem processes should not be underestimated.     

Simultaneous determination of dissolved organic carbon and phosphorus in waters using flame ionization and photometric detectors

An apparatus with flame ionization and photometric detectors was assembled for the simultaneous determination of dissolved organic carbon (DOC) and phosphorus (DP) in waters. The optimum operating conditions were described. The long-term precision (relative standard deviation) is 5.8% for DOC and 5.2% for DP. The detection limits are 0.09 μg ml⁻¹ for DOC and 0.03 μg ml⁻¹ for DP. The responses for various DOC and DP compounds agreed almost with those obtained by combustion-infrared and persulfate digestion-colorimetric methods, respectively. DOC and DP in several water samples were determined by this method and other methods, and the results obtained by those methods were discussed.     

Applicability of light absorbance and fluorescence as measures of concentration and molecular size of dissolved organic carbon in humic Lake Tjeukemeer

Ultrafiltration results of humic Lake Tjeukemeer water demonstrated that light absorbance at 250 nm (E250), fluorescence (λ_ex = 365 nm; λ_em = 470 nm) (F), and concentration of dissolved organic carbon (DOC) vary with the molecular size (5–200 nm) of the dissolved organic matter. The ratio of the ultrafiltered organic fractions increased with decreasing molecular size of the DOC. However, under field conditions this ratio failed to predict molecular size distribution.These results limit the applicability of E250 and F as measures of molecular size and concentration of DOC. However, E250 measurements can be made rapidly and easily, and so are useful in estimating (30%) concentrations of DOC in humic waters.     

The multi-annual carbon budget of a peat-covered catchment

This study estimates the complete carbon budget of an 11.4 km² peat-covered catchment in Northern England. The budget considers both fluvial and gaseous carbon fluxes and includes estimates of particulate organic carbon (POC); dissolved organic carbon (DOC); excess dissolved CO₂; release of methane (CH₄); net ecosystem respiration of CO₂; and uptake of CO₂ by primary productivity. All components except CH₄ were measured directly in the catchment and annual carbon budgets were calculated for the catchment between 1993 and 2005 using both extrapolation and interpolation methods. The study shows that: Over the 13 year study period the total carbon balance varied between a net sink of − 20 to − 91 Mg C/km²/yr. The biggest component of this budget is the uptake of carbon by primary productivity (− 178 Mg C/km²/yr) and in most years the second largest component is the loss of DOC from the peat profile (+ 39 Mg C/km²/yr). Direct exchanges of C with the atmosphere average − 89 Mg C/km²/yr in the catchment. Extrapolating the general findings of the carbon budget across all UK peatlands results in an approximate carbon balance of − 1.2 Tg C/yr (± 0.4 Pg C/yr) which is larger than previously reported values. Carbon budgets should always be reported with a clear statement of the techniques used and errors involved as this is significant when comparing results across studies.     

Tracking natural organic matter (NOM) in a drinking water treatment plant using fluorescence excitation-emission matrices and PARAFAC

Natural organic matter (NOM) in water samples from a drinking water treatment train was characterized using fluorescence excitation emission matrices (F-EEMs) and parallel factor analysis (PARAFAC). A seven component PARAFAC model was developed and validated using 147 F-EEMs of water samples from two full-scale water treatment plants. It was found that the fluorescent components have spectral features similar to those previously extracted from F-EEMs of dissolved organic matter (DOM) from diverse aquatic environments. Five of these components are humic-like with a terrestrial, anthropogenic or marine origin, while two are protein-like with fluorescence spectra similar to those of tryptophan-like and tyrosine-like fluorophores. A correlation analysis was carried out for samples of one treatment plant between the maximum fluorescence intensities (F_max) of the seven PARAFAC components and NOM fractions (humics, building blocks, neutrals, biopolymers and low molecular weight acids) of the same sample obtained using liquid chromatography with organic carbon detection (LC-OCD). There were significant correlations (p < 0.01) between sample DOC concentration, UVA₂₅₄, and F_max for the seven PARAFAC components and DOC concentrations of the LC-OCD fractions. Three of the humic-like components showed slightly better predictions of DOC and humic fraction concentrations than UVA_254. Tryptophan-like and tyrosine-like components correlated positively with the biopolymer fraction. These results demonstrate that fluorescent components extracted from F-EEMs using PARAFAC could be related to previously defined NOM fractions and that they could provide an alternative tool for evaluating the removal of NOM fractions of interest during water treatment.     

Temporal dynamics of dissolved and particulate organic carbon in the northern Adriatic Sea in relation to the mucilage events

The accumulation of dissolved and particulate organic matter may play an important role in mucilage formation in the northern Adriatic. Distributions of dissolved and particulate organic carbon were therefore investigated during the period June 1999-July 2002, when massive mucilage events occurred: in the summer of 2000 and, to a greater extent, of 2002. The seasonal variations in dissolved organic carbon (DOC) concentrations were significant, doubling in summer (up to 150 micromol L(-1)) with respect to winter. The particulate organic carbon (POC) variations were also very large, with a less pronounced seasonal pattern compared to DOC, because the POC changes are much more dependent both on river discharges and on phytoplankton blooms. The comparison of the concentrations between the period before (March-May) and after the onset of mucilage events (June-August) showed that DOC, but particularly POC, were higher in the period before the event of 2002, more markedly in the surface waters of low salinity. The POC increased, reaching mean concentrations of up to 36 micromol L(-1) in March 2002 before the outbreak of the massive mucilage formation in June. This suggests that POC may have a more important role in the mucilage formation than DOC. The highest seasonal variations of organic matter concentrations took place in the upper layer of lower salinity, stressing the importance of stratification and pycnoclines for accumulation and aggregation of the organic matter in the northern Adriatic. The POC contribution to the total organic carbon was low in the oligotrophic waters (DOC/POC ratio >15) and increased with the phytoplankton biomass in the productive waters (DOC/POC ratio <10). Particulate organic carbon predominated over the dissolved inside the mucilage aggregate (DOC/POC ratio <1), probably because aggregation processes, in which colloidal organic carbon is involved, are important. The organic carbon within the aggregates reached a concentration of 13.6 mmol L(-1) which was about 100 times more than in the surrounding waters or in the waters when the mucilages were absent. This indicates that distributions of organic carbon in the northern Adriatic can be extremely patchy during mucilage events.     

Sorption and accumulation of cadmium in the sediment of the Tama River

Cadmium contents in the water and the sediment samples collected from the Tama River and several branches were measured. Cadmium (above 0.005mgl⁻¹) was detected in only four of the water samples, while the sediment samples showed cadmium content of 1.0–9.8 μg g⁻¹ dry sediment. Cadmium concentration in the sediments of the main stream was correlated against ignition loss of the samples and it was found that 1 g of ignition loss (organic matter) corresponded to 35 μg of cadmium.The batch adsorption experiment in the laboratory using an aqueous solution of cadmium for 14 sediment samples with a higher concentration of cadmium indicated that the amount adsorbed by the sediment is highly dependent on the ignition loss. The amount adsorbed on unit mass of ignition loss q_IL could be correlated by a Freundlich-type equilibrium relation as where C is the equilibrium concentration in the aqueous phase ranging between 7 × 10⁻³ and 10 mg l⁻¹, while k_IL and n are equilibrium constants.The adsorption rate measurement showed that the intraparticle diffusion coefficient of cadmium in the sediment was about 1.1 × 10⁻⁶ cm²s⁻¹, which is of a reasonable order of magnitude assuming the pore diffusion mechanism inside the particle.The results suggest that suspended solid particles of high organic content in flowing water contribute significantly to the transport of cadmium along the river.     

Preliminary laboratory investigation of disinfection by-product precursor removal using an advanced oxidation process

Natural organic matter (NOM) is ubiquitous in surface and ground waters throughout the world. During drinking water treatment, the NOM that remains in treated water can react with chlorine to form disinfection by‐products. It has been shown that titanium dioxide photocatalysis can achieve over 96% reduction in ultraviolet (UV)₂₅₄ absorbing species such as hydrophobic NOM and over 81% reduction in dissolved organic carbon (DOC). However, an additional filtration stage is required to recover the suspended catalyst before it is suitable for municipal drinking water application. To overcome this problem, we have used immobilised catalysts prepared using chemical sol–gels, and their performance has been assessed during bench‐scale experiments. An immobilised catalyst enables in situ regeneration using UV light and subsequent reuse of the catalyst. In this research, titanium dioxide sol–gels have been used to coat substrates at a laboratory scale. Results showed that the various coatings prepared had different removal efficiencies for both DOC and UV₂₅₄ absorbance. Maximum removals were 1.336 g/m² and 89%, respectively.     

Spatial and temporal variability in the relationship between water colour and dissolved organic carbon in blanket peat pore waters

The transfer of carbon from terrestrial peat to the fluvial environment forms an important component of the peatland carbon cycle, and has major implications for water quality. Dissolved organic carbon (DOC) is generally considered the largest constituent of aquatic carbon and tends to be the most intensively monitored, particularly in peatland catchments. However, many long-term records for DOC are based on proxy studies that use water colour as a surrogate. This paper tests the robustness of using spectrophotometric techniques to monitor water colour, based on absorbance from a single wavelength at 400 nm, as a surrogate for true DOC determination. The general ability of spectrophotometric analysis to measure low DOC concentrations depends on the calibration used; thus, the minimum mass of DOC detectable varies considerably and in this study was found to be as high as 10.32 mg C L^− 1. While there is often a significant correlation between water colour and DOC, it was found that the use of single or even “pooled” regressions to predict DOC concentrations could result in miscalculations of more than 50%. Further, the water colour-DOC relationship in blanket peat pore waters was found to vary significantly between peat layers, land management treatments and through time. Thus, studies using long-term water colour records as a proxy for long-term DOC concentrations in peatlands must be treated with a certain degree of caution, especially in cases where changes may have taken place to DOC production, such as those caused by land management change, during the course of investigation.     

Dissolved organic compounds in reused process water for steam-assisted gravity drainage oil sands extraction

The in situ oil sands production method called steam-assisted gravity drainage (SAGD) reuses process wastewater following treatment. However, the treatment and reuse processes concentrate contaminants in the process water. To determine the concentration and dynamics of inorganic and organic contaminants, makeup water and process water from six process steps were sampled at a facility employing the SAGD process in Alberta, Canada. In the groundwater used for the makeup water, the total dissolved organic carbon (DOC) content was 4 mg/L. This significantly increased to 508 mg/L in the produced water, followed by a gradual increase with successive steps in subsequent water treatments. The concentrations and dynamics of DOC constituents in the process water determined by gas chromatography-mass spectrometry showed that in the produced water, volatile organic compounds (VOCs) such as acetone (33.1 mg/L) and 2-butanone (13.4 mg/L) predominated, and there were significant amounts of phenolic compounds (total 9.8 mg/L) and organic acids including naphthenic acids (NAs) corresponding to the formula C_nH_2n+ZO_X for combinations of n = 4 to 18, Z = 0 and −2, and X = 2 to 4 (53 mg/L) with trace amounts of polycyclic aromatic hydrocarbons (PAHs) such as naphthalene and phenanthrene. No organic contaminants, except for saturated fatty acids, were detected in the groundwater. The concentration of DOC in the recycled water was 4.4-fold higher than that in the produced water. Likewise, the total concentrations of phenols and organic acids in the recycled water were 1.7- and 4.5-fold higher than in the produced water, whereas the total concentrations of VOCs and PAHs in the recycled water were reduced by over 80%, suggesting that phenols and organic acids are selectively concentrated in the process water treatment. This comprehensive chemical analysis thus identified organic constituents that were concentrated in the process water and which interfere with subsequent water treatments in the SAGD process.     

Influence of traditional agricultural practices on mobilization of arsenic from sediments to groundwater in Bengal delta

In the wake of the idea that surface derived dissolved organic carbon (DOC) plays an important role in the mobilization of arsenic (As) from sediments to groundwater and may provide a vital tool in understanding the mechanism of As contamination (mobilization/fixation) in Bengal delta; a study has been carried out. Agricultural fields that mainly cultivate rice (paddy fields) leave significantly large quantities of organic matter/organic carbon on the surface of Bengal delta which during monsoon starts decomposing and produces DOC. The DOC thus produced percolates down with rain water and mobilizes As from the sediments. Investigations on sediment samples collected from a paddy field clearly indicate that As coming on to the surface along with the irrigation water accumulates itself in the top few meters of sediment profile. The column experiments carried out on a 9 m deep sediment profile demonstrates that DOC has a strong potential to mobilize As from the paddy fields and the water recharging the aquifer through such agricultural fields contain As well above the WHO limit thus contaminating the shallow groundwater. Experiment also demonstrates that decay of organic matter induces reducing condition in the sediments. Progressively increasing reducing conditions not only prevent the adsorption of As on mineral surfaces but also cause mobilization of previously sorbed arsenic. There seems to be a cyclic pattern where As from deeper levels comes to the surface with irrigational water, accumulates itself in the sediments, and ultimately moves down to the shallow groundwater. The extensive and continual exploitation of intermediate/deep groundwater accelerates this cyclic process and helps in the movement of shallow contaminated groundwater to the deeper levels.     

Influence of organic carbon loading, sediment associated metal oxide content and sediment grain size distributions upon Cryptosporidium parvum removal during riverbank filtration operations, Sonoma County, CA

This study assessed the efficacy for removing Cryptosporidium parvum oocysts of poorly sorted, Fe- and Al-rich, subsurface sediments collected from 0.9 to 4.9 and 1.7-13.9 m below land surface at an operating riverbank filtration (RBF) site (Russian River, Sonoma County, CA). Both formaldehyde-killed oocysts and oocyst-sized (3 μm) microspheres were employed in sediment-packed flow-through and static columns. The degree of surface coverage of metal oxides on sediment grain surfaces correlated strongly with the degrees of oocyst and microsphere removals. In contrast, average grain size (D₅₀) was not a good indicator of either microsphere or oocyst removal, suggesting that the primary mechanism of immobilization within these sediments is sorptive filtration rather than physical straining. A low specific UV absorbance (SUVA) for organic matter isolated from the Russian River, suggested that the modest concentration of the SUVA component (0.8 mg L⁻¹) of the 2.2 mg L⁻¹ dissolved organic carbon (DOC) is relatively unreactive. Nevertheless, an amendment of 2.2 mg L⁻¹ of isolated river DOC to column sediments resulted in up to a 35.7% decrease in sorption of oocysts and (or) oocyst-sized microspheres. Amendments (3.2 μM) of the anionic surfactant, sodium dodecyl benzene sulfonate (SDBS) also caused substantive decreases (up to 31.9 times) in colloid filtration. Although the grain-surface metal oxides were found to have a high colloid-removal capacity, our study suggested that any major changes within the watershed that would result in long-term alterations in either the quantity and (or) the character of the river's DOC could alter the effectiveness of pathogen removal during RBF operations.     

Copper addition by organic matter degradation in the freshwater reaches of a turbid estuary

This study reports on the relationship between copper (Cu) behavior and organic matter (OM) transformation along the turbidity gradient in the freshwater reaches of the Gironde Estuary. During a one-year survey, surface water and suspended particulate matter (SPM) were sampled at least monthly at three sites along the Garonne Branch, representing the main fluvial branch of the Gironde Estuary. Additionally, a longitudinal high resolution profile was sampled along the Garonne Branch, covering the turbidity gradient from the river water endmember to the maximum turbidity zone (MTZ). Seasonal variability and spatial distribution of Cu in both the dissolved phases (< 0.2 μm, Cu_0.2 and < 0.02 μm, Cu_0.02) and particulate Cu (Cu_P) clearly suggested Cu_0.2 addition during summer, that increased the Cu_0.2 concentrations by a factor ~ 2, mainly manifested by an increase in the Cu_0.02 fraction. At the annual timescale (2004), this internal Cu reactivity increased Cu_0.02 fluxes in the Garonne Branch by ~ 20% (3.6 t year⁻¹), with the equivalent of ~ 2.9 t year⁻¹ derived from the Cu_P fraction and ~ 0.7 t year⁻¹ from the colloidal (0.02-0.2 μm) fraction, without involving and/or affecting the Cu_C18 (hydrophobic metal-organic complexes) fraction.Combining data on Cu speciation with the results obtained by several independent techniques (DOC and POC measurements, 3D-fluorescence, and TEM) suggested close relationships between Cu behavior and OM transformation/restructuration along the turbidity gradient in the Garonne Branch. The observed Cu_0.02 addition was related to increasing humification (humification index HIX increased from 9 to 12, network formation) and labile OM degradation (Iγ/Iα ratio decreased from 0.70 to 0.44), going along with decreasing DOC and POC concentrations. Mass-balances suggest that in the studied system, degradation of OM may account for the release of ~ 25 μmol potentially bioaccessible Cu_0.02 per mole of particulate organic carbon mineralized.