Dissolved Organic Matter

   ·    Dahm, Clifford N., Baker, Michelle A., Moore, Douglas I., and Thibault, James R.  2003.  Coupled Biogeochemical and Hydrological Responses of Streams and Rivers to DroughtFreshwater Biology.  48(7):1219-1231.

Abstract
:  1. Severe or extreme droughts occurred about 10% of the time over a 105-year record from central New Mexico, U.S.A., based on the Palmer Drought Severity Index.
2. Drought lowers water tables, creating extensive areas of groundwater recharge and fragmenting reaches of streams and rivers. Deeper groundwater inputs predominate as sources of surface flows during drought. Nutrient inputs to streams and rivers reflect the biogeochemistry of regional ground waters with longer subsurface residence times.
3. Inputs of bioavailable dissolved organic carbon to surface waters decrease during drought, with labile carbon limitation of microbial metabolism a byproduct of drought conditions.
4. Decreased inputs of organic forms of carbon, nitrogen and phosphorus and a decrease in the organic:inorganic ratio of nutrient inputs favours autotrophs over heterotrophs during drought.
5. The fate of autotrophic production during drought will be strongly influenced by the structure of the aquatic food web within impacted sites.  (Author’s Summary)

Keywords:
biogeochemistry; dissolved organic carbon; drought;  hydrology; nutrient cycling; surface water;  groundwater interactions; water table; regional; water quality

 

     ·    Dilling, Jörg and Kaiser, Klaus.  2002.  Estimation of the Hydrophobic Fraction of Dissolved Organic Matter in Water Samples Using UV PhotometryWater Research.  36(20):5037-5044.

Abstract
:  In this study, we tested a simple and rapid method for the estimation of carbon in the hydrophobic fraction of dissolved organic matter (DOM) of different origin (spruce, pine, and beech litter) in soil water. The method is based on the fact that the hydrophobic fraction of DOM contains almost entirely the aromatic moieties of DOM. Thus, it showed a clearly distinct light absorption at 260nm compared to the hydrophilic fraction. This light absorption was directly proportional to the concentration of the hydrophobic fraction. Moreover, it was independent of the concentration of the hydrophilic fraction. We compared the concentrations of hydrophobic DOM estimated by the UV method with those of the conventional fractionation using chromatographic columns of XAD-8 macroporous resin and found an excellent agreement between the two methods for both solutions from laboratory sorption experiments and field samples of forest floor leachates and subsoil porewaters. In addition, the absorption at 260nm of hydrophobic DOM proved to be independent of pH values ranging from 2.0 to 6.5. Compared to the conventional chromatographic fractionation, the method using the UV absorption at 260nm is less time consuming, needs a much smaller sample volume, and showed a better reproducibility. However, its use is restricted to water samples of low nitrate (<25mgL-1) and Fe (<5mgL-1) concentrations and, probably, with the hydrophobic fraction dominated by aromatic compounds deriving from degradation of lignin.  (Author’s Abstract)

Keywords:
dissolved organic carbon; fractionation of dissolved organic matter; XAD-8 macroporous resin; UV absorption;  hydrophobic fraction; hydrophilic fraction; water quality; research methodology

 

 ·    Hejzlar, Josef, Dubrovsky, Martin, Buchtele, Josef, and Růžiča, Martin.  2003.  The Apparent and Potential Effects of Climate Change on the Inferred Concentration of Dissolved Organic Matter in a Temperate Stream (the Malše River, South Bohemia)The Science of the Total Environment.  310(1-3):143-152.

Abstract
:  Long-term and seasonal changes in concentration of dissolved organic matter (DOM) and their possible drivers were evaluated for an upland stream in central Europe during 19692000. Two periods have been detected within this data setyears with decreased DOM until the middle of 1980s and then years with increased DOM until 2000. Temperature, hydrological regime of runoff from the catchment (namely the amount of interflow), and changes in atmospheric deposition of acidity coincided with the variations in DOM concentrations. The analysis of single runoff events confirmed the relation between the export of increased DOM concentrations from the catchment and interflow. A multiple linear regression model based on monthly averages of temperature and interflow explained 67% of DOM variability. This model suggested a 7% increase in DOM concentration under the scenarios of possible future climate change related to doubled CO2 concentration in the atmosphere. The scenarios were based on results of several global circulation models.  (Author’s Abstract)

Keywords:
dissolved organic carbon; stream; hydrology; flow components; climate change; scenario modelling; regional ; water quality; research methodology

 

 ·    Neirop, Klaas G. J., Jansen, Boris, and Verstraten, Jacobus M.  2002.  Dissolved Organic Matter, Aluminum and Iron Interactions: Precipitation Induced by Metal/Carbon Ratio, pH and CompetitionThe Science of the Total Environment.  300(1-3):201-211.

Abstract
:  To better understand the precipitation behaviour of dissolved organic matter induced by interactions with metals, a systematic titration experiment was conducted mimicking the soil solution conditions in an acidic, sandy soil. The variables of interest included the type of metal species (Al, Fe), the redox state [Fe(II), Fe(III)], the pH (3.5, 4.0, 4.5), the metal to organic carbon (M/C) ratio and the competition between Al and Fe. Precipitation of DOMAl appeared to be strongly correlated with M/C ratio and the pH. For Fe(II) only little precipitation occurred, while the strongest flocculation degree was found after addition of Fe(III). In contrast to Al, hardly any correlation between DOMFe precipitation and pH was observed. Both reduction and oxidation of Fe was found and exhibited a strong effect on the precipitated amounts of DOM and Fe. In competetion, Al determined the precipitation behaviour at lower M/C ratios (<0.10), while at higher M/C ratios Fe determined the flocculation. Below a M/C ratio of 0.06 Al was the dominant metal in the precipitates, especially at lower pH levels, while the opposite trend was found at M/C ratios above 0.06. Overall, Fe(III) gave the strongest flocculation, although Al influenced the impact of Fe(III) interactions with DOM in relation to pH and M/C ratio.  (Author’s Abstract)

Keywords:
Al; Fe; dissolved organic matter ; precipitation; pH; metal-carbon ratio; water quality

 

 ·    Page, D. W., van Leeuwen, J. A., Spark, K. M., and Mulcahy, D. E.  2002.  Application of Pyrolysis-Gas Chromatography/Mass Spectrometry for Characterisation of Dissolved Organic Matter Before and After Alum TreatmentJournal of Analytical and Applied Pyrolysis.  67(2):247-262.

Abstract
:  Aqueous extract samples of organic matter from southeastern Australia were isolated from the vegetation and soils of five catchments of drinking water reservoirs. Vegetation types sampled included mixtures of Australian native vegetation (Eucalypts) and exotic species (pines) in both sandy and clayey soils. After dilution, the samples were treated with alum, using a jar test procedure. This was used to determine alum doses required for target removal of colour and turbidity. Water samples from the reservoirs were similarly tested using the jar test procedure. Pyrolysisgas chromatography/mass spectrometry was performed on freeze-dried material from the raw samples, flocs and treated waters. Pyrolysis products of dissolved organic matter (DOM) were qualitatively compared to those derived from biomacromolecules such as lignin and cellulose. Semi-quantitative comparisons were made on the organic matter component removed by coagulation/flocculation with that recalcitrant to alum treatment. All samples produced relatively large amounts of alkylbenzenes, alkylphenols and polycyclic hydrocarbons. The organic matter that flocculated with alum treatment was determined to be predominantly aromatic, producing methoxyphenols, which were possibly derived from lignin and tannin-like materials. Nitrogen containing compounds were detected from the reservoir-derived DOM but not the terrestrially-derived DOM. Alum treatment had no observed effect on the relative abundance of the detected nitrogenous compounds. The non-coagulable organic matter was found to have a higher proportion of polysaccharide-derived molecular tracer compounds, consistent with a higher hydrophilic character.  (Author’s Abstract)

Keywords:
dissolved organic matter (DOM); pyrolysis; gas chromatography; mass spectrometry; water treatment; water quality; regional

 

·    Page, D. W., van Leeuwen, J. A., Spark, K. M., and Mulcahy, D. E.  2002.  Pyrolysis Characterisation of Plant, Humus and Soil Extracts From Australian CatchmentsJournal of Analytical and Applied Pyrolysis .  65(2):269-285.

Abstract
:  Dissolved organic matter (DOM) from vegetation, humus layers and soils of four reservoir catchments in south-eastern Australian were characterised by flash pyrolysis and off-line thermochemolysis using tetramethylammonium hydroxide (TMAH). The aim of this work was to identify organic compounds which might act as tracers of terrestrially derived bio-macromolecules to the drinking water reservoirs. Organic matter in reservoirs is a key issue to the water industry due to it being a precursor of disinfection by-products, causing taste and odours and is a substrate for microbial growth in a distribution system. Of the pyrolysis products detected from all three sample types (vegetation, humus and soils) most were molecular tracers of polysaccharides and to a lesser extent lignin and protein. Several benzyl and methoxyphenol compounds were detected from these samples that might enable tracing of terrestrial organic input to reservoirs. Compounds detected from vegetation, humus and soil samples by thermochemolysis were predominantly methoxy benzene structures, indicative of lignin sources and tannin, though compounds indicative of polysaccharides, lipids and resins acids were also detected. Ratios of syringyl to courmaryl moieties were found to be highest from locations with native hardwoods and these ratios consistently decreased from vegetation to humus to soil samples.  (Author’s Abstract)

Keywords:
dissolved organic matter (DOM); pyrolysis-gas chroatography-mas spectrpmetry; off-line thermochemolysis; Australian catchments; regional ; water quality

 

·    Pokrovsky, O. S. and Schott, J.  2002.  Iron Colloids/ Organic Matter Associated Transport of Major and Trace Elements in Small Boreal Rivers and their Estuaries (NW Russia)Chemical Geology.  190:141-179.

Abstract
:  The chemical status of major and trace elements (TE) in various boreal small rivers and watershed has been investigated along a 1500-km transect of NW Russia. Samples were filtered in the field through a progressively decreasing pore size (5, 0.8 and 0.22 μm; 100, 10, and 1 kD) using a frontal filtration technique. All major and trace elements and organic carbon (OC) were measured in filtrates and ultrafiltrates. Most rivers exhibit high concentration of dissolved iron (0.24 mg/l), OC (1030 mg/l) and significant amounts of trace elements usually considered as immobile in weathering processes (Ti, Zr, Th, Al, Ga, Y, REE, V, Pb). In (ultra)filtrates, Fe and OC are poorly correlated: iron concentration gradually decreases upon filtration from 5 μm to 1 kD whereas the major part of OC is concentrated in the <110 kD fraction. This reveals the presence of two pools of colloids composed of organic-rich and Fe-rich particles. According to their behavior during filtration and association with these two types of colloids, three groups of elements can be distinguished: (i) species that are not affected by ultrafiltration and are present in the form of true dissolved inorganic species (Ca, Mg, Li, Na, K, Sr, Ba, Rb, Cs, Si, B, As, Sb, Mo) or weak organic complexes (Ca, Mg, Sr, Ba), (ii) elements present in the fraction smaller than 110 kD prone to form inorganic or organic complexes (Mn, Co, Ni, Zn, Cu, Cd, and, for some rivers, Pb, Cr, Y, HREE, U), and (iii) elements strongly associated with colloidal iron in all ultrafiltrates (P, Al, Ga, REE, Pb, V, Cr, W, Ti, Ge, Zr, Th, U). Based on size fractionation results and taking into account the nominal pore size for membranes, an estimation of the effective surface area of Fe colloids was performed. Although the total amount of available surface sites on iron colloids (i.e., 110 μM) is enough to accommodate the nanomolar concentrations of dissolved trace elements, very poor correlation between TE and surface sites concentrations was observed in filtrates and ultrafiltrates. This strongly suggests a preferential transport of TE as coprecipitates with iron oxy(hydr)oxides. These colloids can be formed on redox boundaries by precipitation of Fe(III) from inflowing Fe(II)/TE-rich anoxic ground waters when they meet well-oxygenated surface waters. Dissolved organic matter stabilizes these colloids and prevents their aggregation and coagulation. Estuarine behavior of several trace elements was studied for two small iron- and organic-rich rivers. While Si, Sr, Ba, Rb, and Cs show a clear conservative behavior during mixing of freshwaters with the White sea, Al, Pb and REE are scavenged with iron during coagulation of Fe hydroxide colloids.  (Author’s Abstract)

 Keywords:
iron colloids; trace elements; organic matter; boreal river; estuary;  regional; habitat; water quality

 

·     Schönfelder, Ilka, Gelbrecht, Jörg, Schönfelder, Jörg, and  Steinberg, Christian E. W.  2002.  Relationships between Littoral Diatoms and Their Chemical Environment in Northeastern German Lakes and RiversJournal of Phycology .  38(1):66-82.

Abstract
:  We explored statistical relationships between the composition of littoral diatom assemblages and 21 chemical and physical environmental variables in 69 lakes and 15 river sites in the lowland of northeastern Germany. Canonical correspondence analysis with single treatment and with forward selection of environmental variables was used to detect 11 important ecological variables (dissolved inorganic carbon [DIC], Na+ , total phosphorus [TP], dissolved organic carbon [DOC], total nitrogen [TN], pH, oxygen saturation, dissolved iron, SO42-, NH4+, soluble reactive silicium) and maximum water depth or Ca2+ or soluble reactive phosphorus that most independently explain major proportions of the total diatom variance among the habitats. Monte Carlo permutation tests showed that each contributed a significant additional proportion (P< 0.05) of the variance in species composition. Together, these 11 most important environmental variables explained 34% of the total variance in species composition among the sites and captured 73% of the explained variance from the full 21 parameters model. Weighted-averaging regression and calibration of 304 indicator taxa with tolerance down-weighting and classic deshrinking was used to develop transfer functions between littoral diatoms and DIC, pH, TP, TN, and Cl-
.   The DOC:TP ratio was introduced and a weighted-averaging model was developed to infer allochthonous DOC effects in freshwater ecosystems. This diatom-DOC/TP model was significant (< 0.001) and explained 7.6% of the total diatom variance among the sites, surpassing the inferential power of the diatom-TP-transfer function (7.3% explained variance). The root-mean-square errors of prediction of the models were estimated by jack-knifing and were comparable with published data sets from surface sediment diatom samples. The data set of littoral diatoms and environmental variables allows use of the diatom-environmental transfer functions in biomonitoring and paleolimnological approaches across a broad array of natural water resources (such as floodplains, flushed lakes, estuaries, shallow lakes) in the central European lowland ecoregion.  (Author’s Abstract)
Keywords:
biodiversity; calibration data set; canonical correspondence analysis; dissolved organic carbon; interference models; littoral diatoms; total nitrogen; total phosphorus; weighted averaging; diatom; water quality; regional

 

·    Sutton, Susan D. and Findlay, Robert H.  2003.  Sedimentary Microbial Community Dynamics in a Regulated Stream: East Fork of the Little Miami River, OhioEnvironmental Microbiology .  5(4):256-266.

Abstract
:  A field study was conducted in the Lower East Fork of the Little Miami River, a regulated stream in Clermont county, Ohio, to determine how changes in streamflow, water temperature and photo-period affect sediment microbial community structure. Surface sediment cores were collected from sampling stations spanning 60 river kilometers three to four times per year between October 1996 and October 1999. During the final year of the field study, water temperature, water depth, conductivity, total suspended solids, dissolved organic carbon, instantaneous streamflow velocity, sediment grain size and sediment organic matter were determined. Total microbial biomass was measured using the phospholipid phosphate technique (PLP) and ranged between 2 and 134nmol PLP•g-1 dry weight with a mean of 25 nmol PLP•g-1. Microbial community structure was determined using the phospholipid fatty acid analysis and indicated seasonal shifts in sedimentary microbial community composition. January to June sedimentary microbial biomass was predominately prokaryotic (60%±2), whereas microeukaryotes dominated samples collected during the late summer (55%±2.4) and fall (60%±2). These changes were correlated with stream discharge and water temperature. Microbial community structure varied spatially about a reservoir with prokaryotic biomass dominant at upstream stations and eukaryotic biomass dominant at downstream stations. These findings reveal that sedimentary microbial communities in streams are dynamic responding to the seasonal variation of environmental factors.  (Author’s Summary)

Keywords:
  microbial community structure; streamflow; water temperature; photo-period; misc; regional; water quality

 

·    Taylor, Lisa N., Baker, Daniel W., Wood, Chris M., and McDonald, D. Gordon.  2002.  An In Vitro Approach for Modelling Branchial Copper Binding in Rainbow TroutComparative Biochemistry and Physiology, Part C.  133(1-2):111-124.

Abstract
:  The main objective of this study was to characterize the individual effects of water chemistry (Ca2+, Na+, dissolved organic matter (DOM), pH, alkalinity) on the rapid binding of copper to the gill surface of rainbow trout using an in vitro gill binding assay. In this assay, individual gill arches were exposed for 5 min to 64Cu labelled copper solutions ranging from 0.02 to 0.16 μM in water chemistries reflecting the full range of fresh water values for the Great Lakes. The gills displayed saturable Cu binding within this Cu range but gillCu binding was completely unaffected over the full range of calcium, sodium and alkalinity concentrations used. Only low pH (pH 4.0) and commercial DOM (Aldrich humic acid at =3 mgC/l) altered copper binding to rainbow trout gills in vitro. These findings were consistent with the results of geochemical modelling of our water chemistry (using mineql+, Version 4.5) which showed that H+ and DOM affected the free cupric ion concentration. However, DOM (up to 80 mgC/l) was only able to reduce Cu on the gills by 50%. We hypothesize that in the range of 0.020.16 μM Cu there are two high affinity Cu binding sites on the gills, one having a substantially higher affinity for copper than DOM. The absence of a calcium effect on gill copper binding was in accord with in vivo evidence that calcium primarily acts to alter the physiology of the gill binding sites through acclimatory processes, rather than through competitive interactions. It was a surprise that water chemistry parameters influence rapid gillmetal binding in a manner different to their influence on acute toxicity and different from the effects on long-term binding reported in other studies. Currently, the biotic ligand model uses the rapid increase of gill copper (believed to reflect binding to the physiologically active receptor sites) to model gill binding characteristics. The distinction between rapid surface binding and metal uptake obviously plays an important role in determining the toxic effects of copper, especially when regulators need to predict the modifying effects of water chemistry.  (Author’s Abstract)

Keywords:
trout; copper; modelling; gill binding; toxicity; water chemistry; biotic ligand model; research methodology; water quality

 

·    Zsolnay, Ádám.  2003.  Dissolved Organic Matter: Artefacts, Definitions, and FunctionsGeoderma.  113(3-4):187-209.

Abstract
:  In this concept paper, some basic problems in the obtaining of the dissolved organic matter (DOM) are described. Some of them are fairly obvious such as adsorption and desorption on the filters used to isolate DOM. However, some are subtler such as alteration in the tertiary physicochemical structure of DOM because of cavitation (filtration), concentration (ultrafiltration, reverse osmosis), or decomposition (electrophoresis). These structure changes may not have an influence on a variety of analytical techniques, but they may alter the ability of DOM to interact with certain ecosystem components such as the biota and pollutants. Therefore, the interpretation of the analyses done with such DOM cannot necessarily be extrapolated to in situ conditions. Fluorescence has been found to be a sensitive tool to follow such tertiary structure changes.
In structured matrices with pore spaces such as soils and sediments, DOM may have different fates and functions depending on the pore spaces in which it is located. This again needs to be considered in sampling strategies. For example, DOM in macropores may play important roles in groundwater quality but presumably does not play a major role in the in situ production of the greenhouse gas N2O via denitrification, since this pore space tends to be well aerated. A protocol for the separate sampling of the different pore spaces is presented. Another difficulty, which is shown here, is that minor changes in extraction methodology (such as the extractant-soil ratio) can have a serious effect on the apparent amount of DOM.
DOM samples from a field can have considerable temporal and spatial variability, which is complicated by the fact that DOM from unsaturated systems can be strongly influenced by ambient water content. This again needs to be considered, especially when fields from different regions are sampled and compared. Another important point is that the results obtained from one DOM source cannot necessarily be extrapolated to the DOM from another source. For example, soil pore water DOM differs both from aquatic DOM and from the material, which can be extracted as the humic substance fraction. Finally, with the increasing awareness of the ecological functions of DOM, which are briefly presented here, there is also an increase in DOM research being done in different disciplines. This is laudable, but presentations of results need to define DOM more precisely to prevent misunderstandings.  (Author’s Abstract)

Keywords:
artefacts; dissolved organic matter; extraction. functions; pore space; water quality