Low DOC Concentrations Research Articles

An iodine mass-balance for Lake Constance, Germany: Insights into iodine speciation changes and fluxes

Abstract Lake Constance is one of Europe’s largest oligotrophic lakes and provides a water source for more than 4.5 million people in Germany and Switzerland. We present here a 12 month study on iodine concentrations, speciation and fluxes to and from the lake to gain a quantitative understanding of the limnic iodine cycle. Monthly water samples were obtained from all major tributaries (14) and the outflow to construct a mass-balance model. Sediment traps were also deployed in the lake for two years at two different stations. Total soluble iodine (TSI) in aqueous samples were analysed by ICP-MS and speciation (iodide, iodate and soluble organically bound iodine, SOI) by ion chromatography–ICP-MS. Iodine concentrations in the Alpine tributaries (1–2 μg l −1 ) decreased over the summer months due to increasing proportions of snow and glacial melt water from the Alps, while iodine levels in the lowland rivers (∼2–10 μg l −1 ) increased over the summer. Deposition of TSI to the catchment (16,340 kg I yr −1 ) was similar to the TSI out-flux by rivers (16,000 kg I yr −1 ). By also including the particulate riverine iodine flux out of the catchment (∼12,350 kg I yr −1 ) it is shown that the catchment is a net source of iodine, with the highest particulate fluxes coming from the Alpine rivers. The total TSI flux to the lake was 16,770 kg I yr −1 , the largest proportion coming from the Alpenrhein (43%), followed by the Schussen (8%) and Bregenzer Ach (7.7%). Overall the mass-balance for TSI in the lake was negative, with more iodine flowing out of the lake than in (−2050 kg I yr −1 ; 12% of TSI in-flux). To maintain mass-balance, 8.8 μg I m −2 d −1 from the Obersee and 23 μg I m −2 d −1 from the Untersee must be released from the sediments into the water column. Thus, in comparison with the total iodine flux to the sediments measured by the sediment traps (4762–8075 kg I yr −1 ), up to 39% of the deposited iodine may be mobilised back into the lake. SOI was the dominant iodine fraction entering the lake, with a total flux of 10,290 kg I yr −1 (64% of TSI input), followed by iodate (3120 kg I yr −1 ) and iodide (2760 kg I yr −1 ). Net formation of SOI from iodide and iodate was also noted within the lake, with an estimated production of 6560 kg I yr −1 , suggesting a strong role for biology in iodine cycling. In conclusion, organically bound iodine was the dominant iodine species in aqueous and solid phases in Lake Constance, despite low DOC concentrations ( −1 ), and thus is expected to play an important role in iodine cycling in most freshwater environments.

Optical characterization of dissolved organic matter in tropical rivers of the Guayana Shield, Venezuela

Tropical rivers are an important source of dissolved organic matter (DOM) to coastal oceans. However, temporal and spatial variability of DOM composition and thus its quality in such rivers, on landscape and basin scales, have not been well documented. In this study, we present data on the spatial distribution of DOM quantity and quality based on source, molecular weight, and composition using optical properties including excitation emission matrix fluorescence with parallel factor analysis. We compared such DOM quantity and quality determinations in main river channels and their tributaries for three river systems of the Guayana Shield, Venezuela. Spatial variabilities of DOM parameters were strongly related to differences in the geological settings of the drainage basins and presumably their associated vegetation cover. Linear relationships between quantitative and qualitative DOM parameters were also evident, suggesting that high DOC concentration correlated with chromophoric dissolved organic matter (CDOM) characteristics of higher molecular weight associated with terrestrial sources, while low DOC concentrations correlated with CDOM characteristics of lower molecular weight associated primarily with microbial sources. Such relationships seem to imply that DOM concentrations and their sources/characteristics may be coupled in the studied fluvial systems. In addition, shifts in DOM compositions between terrestrial and microbial signals were observed with changes in water discharge and in watersheds disturbed by gold mining activities. The observed linkages between, and the changes among DOM quantity and quality, suggest that the biogeochemistry of DOM in tropical rivers may be quite sensitive to climatic and land use change.

Groundwater Al dynamics in boreal hillslopes at three integrated monitoring sites along a sulphur deposition gradient in Sweden

Summary Data from four soil water and groundwater transects from three small, boreal catchments situated along a south–north sulphur deposition gradient in Sweden were studied to assess whether the soils in the near stream zone can significantly modify the groundwater aluminium (Al) chemistry just before it enters the stream and to what extent different levels of acid deposition influences this. The results show that the groundwater aluminium species composition (Alt = total, Alo ∼ organic, Ali ∼ inorganic) and concentrations reflected the variations in groundwater pH ( r Al i 2 = 0.74 ) or TOC ( r Al o 2 = 0.93 ) or a combination of both ( r Al t 2 = 0.89 ). The highest Al concentrations were recorded in shallow groundwater, creating the prerequisites for large lateral Al-fluxes along the hillslopes during episodes of high flow when superficial flow paths are active. A downhill gradient was also seen, with increasing Alo and TOC concentrations towards the stream. Reduced Ali, in absolute as well as relative terms, but increased Alt concentrations in the discharge areas, indicate complex reactions favouring Alo formation and a local input of Alo from the soils. Results from the transect with the most detailed riparian sampling showed that in the last few meters before lateral flow reaches the stream, the mixing of superficial acid soil/groundwater and well-buffered groundwater that had moved along deeper flow paths increased pH and reduced the Ali and Alt concentrations, tangibly. The Alo concentrations were little affected by this pH increase, but at the soil and stream water interface Ali formation was favoured due to the low pH and DOC concentrations in the surface water. Hydrological and soil forming processes within the catchments were more important than acid deposition for the Al dynamics along the hillslopes.

Evaluating the effects of sample processing treatments on alkalinity measurements

summary The concentration of bicarbonate, the dominant anion in river water, is typically calculated using measured alkalinity concentrations. Alkalinity concentrations also are necessary for analytical charge balance, carbonate speciation, and PCO2 calculations. Although the Gran titration is the standard method for measuring alkalinity, previous studies have varied in how water samples have been processed prior to analysis. The purpose of this study was to determine whether variation in filtering, refrigeration, and sample storage time leads to statistically significant differences in alkalinity concentrations in oxic, low-turbidity surface waters and groundwaters ranging from undersaturated to supersaturated with respect to calcite. Samples were collected from the Blue Ridge and Piedmont Provinces of northwestern South Carolina and the Valley and Ridge Province of eastern Tennessee. Each sample was analyzed using four processing treatments: filtered and refrigerated, filtered and unrefrigerated, unfiltered and refrigerated, and unfiltered and unrefrigerated (n = 3 analyses per treatment combination). All replicates were analyzed within 24 h using the Gran titration method. Samples then were reanalyzed after 17–194 days of storage to determine if storage time affects alkalinity measurements. Overall, alkalinity concentrations ranged from 0.8 to 107 mg/L CaCO3. Statistically significant differences among the treatments and significant interactions between filtration and refrigeration were limited. For samples in which treatment means differed significantly or in which interactions were significant, differences generally were less than 10% and probably of little biogeochemical importance. For all but one sample locality, storage time did not affect alkalinity. Our results show that for oxic waters that have low concentrations of DOC and reduced metals, filtration, refrigeration and storage time are unlikely to affect measured alkalinity concentrations. However, additional research is needed to determine the degree to which sample processing treatment is important to interpreting the alkalinity concentrations of DOC- and metal-rich samples.

Rare earth elements (REE) of dissolved and suspended loads in the Xijiang River, South China

Abstract The Xijiang River is the main channel of the Zhujiang (Pearl River), the second largest river in China in terms of water discharge, and flows through one of the largest carbonate provinces in the world. The rare earth element (REE) concentrations of the dissolved load and the suspended particulate matter (SPM) load were measured in the Xijiang River system during the high-flow season. The low dissolved REE concentration in the Xijiang River is attributed to the interaction of high pH and low DOC concentration. The PAAS-normalized REE patterns for the dissolved load show some common features: negative Ce anomaly, progressively heavy REE (HREE) enrichment relative to light REE (LREE). Similar to the world’s major rivers the absolute concentration of the dissolved REE in the Xijiang River are mainly pH controlled. The degree of REE partitioning between the dissolved load and SPM load is also strongly pH dependent. The negative Ce anomaly is progressively developed with increasing pH, being consistent with the oxidation of Ce (III) to Ce (IV) in the alkaline river waters, and the lack of Ce anomalies in several DOC-rich waters is presumably due to both Ce (III) and Ce (IV) being strongly bound by organic matter. The PAAS-normalized REE patterns for the dissolved load and the SPM load in rivers draining the carbonate rock area exhibit middle REE (MREE) enrichment and a distinct maximum at Eu, indicating the preferential dissolution of phosphatic minerals during weathering of host lithologies. Compared to the Xijiang River waters, the MREE enrichment with a maximum at Eu disappeared and light REE were more depleted in the South China Sea (SCS) waters, suggesting that the REE sourced from the Xijiang River must be further fractionated and modified on entering the SCS. The river fluxes of individual dissolved REE introduced by the Xijiang River into the SCS vary from 0.04 to 4.36 × 10 4 mol a −1 .

Carbon chemistry and groundwater dynamics at natural analogue site Ruprechtov, Czech Republic: Insights from environmental isotopes

Hydrological, geochemical and environmental isotope data from groundwater wells at Ruprechtov natural analogue site were evaluated to characterize the flow pattern and C chemistry in the system. The results show that water flow in the Tertiary sediments is restricted to 1–2 m thick zones in the so-called clay/lignite horizon with two different infiltration areas in the outcropping granites in the western and south-western part of the investigated area. Generally the flow system is separated from the underlying granite by a kaolin layer up to several tens of metres thick. Differences in stable isotope signatures in the northern part of the site indicate very local connections of both flow systems via fault zones. The observed increase of δ13C values and decrease of 14C activities in dissolved inorganic C during evolution of the groundwater from the infiltration area to the clay/lignite horizon was modelled using simple open- and closed-system models as well as an inverse geochemical model (NETPATH), which included changes in other geochemical parameters. The results from both types of models provided some insights into timescales of groundwater flow, but mainly revealed that additional sources of C are active in the system. These are very likely biodegradation of dissolved and sedimentary organic C (DOC and SOC) as well as the influx of endogenous CO2. The occurrence of microbial degradation of SOC in the clay/lignite layers is indicated by the increase of biogenic DIC, DOC, and phosphate concentrations. The impact of microbial SO4 reduction on this process is confirmed by an increase of δ34S values in dissolved SO42- from the infiltration area to the clay/lignite horizon with an enrichment factor of 11‰. The very low DOC concentrations of 1–5 mg C/L in the clay/lignite horizon with an organic matter content up to 50% C is probably caused by very low availability of organic matter to the processes of degradation and DOC release, demonstrated by extraction experiments with SOC.

Sulphur leaching from headwater catchments in an eroded peatland, South Pennines, U.K

A detailed investigation into sulphur leaching in peatland headwater catchments in the South Pennines, UK shows that, despite significant reductions in sulphur emissions, sulphur remains a key acidifier. This sulphur can be considered as legacy atmospheric pollution, stored within the peat by processes of dissimilatory sulphate reduction and now being leached into the region's surface waters. Persistently lower water tables at gully edge locations define a thick erosional acrotelm that is vulnerable to aeration, oxidation and flushing throughout the year, and not solely confined to periods of drought. Stream discharge behaves as a two-end member system, whereby pre-event water, rich in DOC and sulphate, is diluted by event water as a result of event water flowing through fast flow pathways such as macropores and overland flow. A rapid increase in water table elevation during the storm and a decrease in elevation after the storm indicate that event water has infiltrated the peat and has then been released into the stream. Streamwaters in peat dominated upland catchments with high densities of gullying have high concentrations of sulphate and low concentrations of DOC, whereas the reverse is true for those catchments with low densities of gullying. This is consistent with the concept that high concentrations of sulphate can suppress the solubility of DOC. A significant store of sulphate exists within South Pennine peats, and continued gully erosion will enhance sulphur leaching meaning that the timescale involved for any depletion is uncertain. It is therefore important that models predicting recovery from acidification in these upland systems include an understanding of how this stored sulphur is being leached, especially with respect to gully erosion, climate change and reduced precipitation.

A field and experimental study on the tolerances of fish to Eucalyptus camaldulensis leachate and low dissolved oxygen concentrations

In intermittent streams, deteriorating water quality during drying influences fish survival but the specific effects of individual variables and their interactions are poorly known. During summer 2002 and 2004, fish were surveyed in isolated pools of two lowland intermittent streams in south-east Australia. Despite a low dissolved oxygen (DO, range = 0.4–6.8 mg L–1) and high dissolved organic carbon (DOC, 16–50 mg L–1) concentrations, assemblage composition and abundance of native fish appeared unaffected. In subsequent laboratory experiments, concentrations of DO and DOC were independently manipulated to identify better the tolerance of these species to extremes in environmental conditions. At low DOC concentrations (20 mg L–1), no significant effects were observed. At high DOC concentrations (50, 70 and 80 mg L–1), an interaction was observed between DOC and DO, with significant reductions in resistance (decreased time to loss of buoyancy). At extreme DOC concentrations (99 mg L–1), the effect of DO appeared to have been overridden by a strong effect from DOC (rapid loss of equilibrium). The thresholds observed suggest these species have a high resistance to ‘blackwater events’ caused by leaching of DOC from terrestrial leaf litter. Our findings are consistent with the observed tolerances of fish occupying habitats, both in Australia and elsewhere in the world, where extreme physicochemical conditions are a regular and predictable occurrence.

The impact of the water background inorganic matrix on the natural organic matter removal by nanofiltration

The impact of the water background inorganic matrix (pH and calcium hardness) on the natural organic matter (NOM) removal by nanofiltration was investigated. Pre-treated surface water and two NOM model substances of different molecular weight and hydrophilicity (salicylic acid and purified Aldrich humic acid, 2–3 mg C/L) were nanofiltered using a polypiperazine amide membrane. Results showed that the background inorganic matrix greatly influenced the NOM removal by a negatively charged membrane, regardless of the type of NOM, which caused no effect on the results. Flux showed no significant variation with running time and recovery rate, but it decreased with pH and especially in the presence of calcium. Such results were related to the low DOC concentration and the low flux that minimised the concentration polarisation, and to the pH effect on the membrane and NOM charges. The pH increase caused pore narrowing, larger NOM hydrodynamic radius and stronger repulsions between the negatively charged membrane and NOM functional groups, yielding higher rejections, which in turn, increased the osmotic gradient with a subsequent flux decline. Flux and rejections decreased further in the presence of 1 mM Ca 2+ which reduced the membrane negative charge, and decreased the sieving effects and increased the chemical interactions.

Effect of humic acid on the pH-dependent adsorption of terbium (III) onto geological materials

Mobilization of actinides by interaction with humic colloids in aquifers is essentially determined by the geochemical conditions. In this study, the pH dependence of the influence of humic acid on metal adsorption on a variety of geological solids (kaolinite, phyllite, diabase, granite, sand) was investigated for Tb(III) as an analogue of trivalent actinides, using 160Tb as a radiotracer. Humic material was radiolabelled with 131I to allow experiments at low DOC concentrations, as encountered in subsurface systems in the far-field of a nuclear waste repository. For all solids, a changeover from mobilization to demobilization is observed on acidification. Except for phyllite, the reversal occurs at slightly acidic pH values, and is thus relevant in respect of risk assessments. A composite distribution model was employed to reproduce the changeover on the basis of the underlying constituent processes. For this purpose, humate complexation of Tb(III) and adsorption of humic acid as a function of pH were investigated as well. Although the ternary systems cannot be constructed quantitatively by combining the binary subsystems, the relevant interdependences are adequately described by the composite approach. For a more general discussion in view of the diversity of natural organic colloids, adsorption isotherms of various humic and fulvic acids on sand were compared.

Salinity, depth and the structure and composition of microbial mats in continental Antarctic lakes

Summary1. Lakes and ponds in the Larsemann Hills and Bølingen Islands (East‐Antarctica) were characterised by cyanobacteria‐dominated, benthic microbial mats. A 56‐lake dataset representing the limnological diversity among the more than 150 lakes and ponds in the region was developed to identify and quantify the abiotic conditions associated with cyanobacterial and diatom communities.2. Limnological diversity in the lakes of the Larsemann Hills and Bølingen Islands was associated primarily with conductivity and conductivity‐related variables (concentrations of major ions and alkalinity), and variation in lake morphometry (depth, catchment and lake area). Low concentrations of pigments, phosphate, nitrogen, DOC and TOC in the water column of most lakes suggest extremely low water column productivity and hence high water clarity, and may thus contribute to the ecological success of benthic microbial mats in this region.3. Benthic communities consisted of prostrate and sometimes finely laminated mats, flake mats, epilithic and interstitial microbial mats. Mat physiognomy and carotenoid/chlorophyll ratios were strongly related to lake depth, but not to conductivity.4. Morphological‐taxonomic analyses revealed the presence of 26 diatom morphospecies and 33 cyanobacterial morphotypes. Mats of shallow lakes (interstitial and flake mats) and those of deeper lakes (prostrate mats) were characterised by different dominant cyanobacterial morphotypes. No relationship was found between the distribution of these morphotypes and conductivity. In contrast, variation in diatom species composition was strongly related to both lake depth and conductivity. Shallow ponds were mainly characterised by aerial diatoms (e.g. Diadesmis cf. perpusilla and Hantzschia spp.). In deep lakes, communities were dominated by Psammothidium abundans and Stauroforma inermis. Lakes with conductivities higher than ±1.5 mS cm−1 became susceptible to freezing out of salts and hence pronounced conductivity fluctuations. In these lakes P. abundans and S. inermis were replaced by Amphora veneta. Stomatocysts were important only in shallow freshwater lakes.5. Ice cover influenced microbial mat structure and composition both directly by physical disturbance in shallow lakes and by influencing light availability in deeper lakes, as well as indirectly by generating conductivity increases and promoting the development of seasonal anoxia.6. The relationships between diatom species composition and conductivity, and diatom species composition and depth, were statistically significant. Transfer functions based on these data can therefore be used in paleolimnological reconstruction to infer changes in the precipitation–evaporation balance in continental Antarctic lakes.

Nanofiltration: improvements of water quality in a large distribution system

A nanofiltration (NF) treatment was introduced during the autumn of 1999 in the Méry-sur-Oise treatment plant which feeds the northern Parisian suburbs distribution system. A study was conducted over 4 years to compare the water quality before and after nanofiltration. The results confirmed that NF treatment produced a low DOC concentration in water (average 0.7 mg C/L). This reduction of DOC concentration levels enabled an improved stability of chlorine residual that has been reduced to 0.2 mg/L at the outlet of the plant. The formation of trihalomethanes was thus reduced by 50% in the network. Moreover, the reduction of BDOC enabled an improved biological stability in the water and enhanced the microbiological water quality during distribution. In addition, the NF treatment enhanced the physico-chemical water quality.

Biogeochemical properties of a tropical swamp forest ecosystem in southern Thailand

The distributions of organic matter in the tropical swamps in southern Thailand are reported. The concentrations of particulate and dissolved organic carbon (POC and DOC) in the Bang Nara River, which drains swamp forests and nearby paddy fields, were 2.9 ± 2.0 and 6.2 ± 1.3 mg C l−1, respectively. Although the variation was large, DOC concentration in the Bang Nara River seemed to be higher than POC in November 1992 (DOC/POC ratio, 2.8 ± 2.2). River waters from the upland areas were characterized by low POC and DOC concentrations as compared with Bang Nara River water. The δ13C values of POC and river sediments were useful to distinguish between organic matter originating in upland and swamp areas. It is suggested that the distributions of organic matter and its isotopic composition reflect the difference in drainage characteristics between lowland swamp and upland areas. Isotopic analyses of plant leaves and soils revealed that the swamp forest ecosystems were characterized by low δ13C and low δ15N values, which suggested low efficiency of water use by plants and large contributions of atmospheric deposition of nitrogen, respectively. Although CO2 recycling in the forest might be an important factor determining the δ13C values of understory plants, the main process in carbon metabolism of tropical swamp forests would be CO2 exchange between the atmosphere and forest canopy.

Bacterioplankton Production in Lakes along an Altitude Gradient in the Subarctic North of Sweden.

We examined changes in bacterioplankton standing stock and production in subarctic lakes in the north of Sweden to elucidate their coupling to lake physical, chemical, and biological characteristics. Sixteen lakes situated along an altitude gradient extending from the coniferous forest to the high-alpine belt were studied during 1998 and 1999. The summer mean bacterial numbers and production varied substantially between the lakes, with a general trend toward decreasing values with increasing altitude. The results demonstrate that P probably restricted bacterial utilization of DOC in the coniferous forest lakes, while low DOC concentrations limited bacterial growth during the summer in the alpine lakes. The primary production of plankton was insufficient to support bacterial production in the lakes. High input of allochthonous DOC to the alpine lakes in spring was sufficient both to increase the bacterial production and to induce P-limitation. As a consequence, there was a tendency toward higher bacterial activity in the spring compared to the summer in the alpine lakes. The results indicate that most of the bacterial standing stock and production are supported by allochthonous DOC plus DOC from benthic production, and more or less limited by the phosphorus supply. We therefore suggest that bacteria populations in subarctic lakes may be indirectly affected by climate variations through its impact on the input of DOC and nutrients from the lake catchments.

Environmental characteristics and microbial plankton activity of freshwater environments at Kongsfjorden, Spitsbergen (Svalbard)

Physical, chemical and microbiological features of a range of High Arctic freshwater lakes, located in the vicinity of Kongsfjorden, north-west Svalbard, are described for the first time. The lakes were chosen to include both upland and coastal systems and those in proximity of human activity. Sampling was undertaken during April (late winter) and in July/August (summer). The lakes all proved to be oligotrophic with low DOC concentrations (< 2 mg/l) and most were relatively light transparent (K dPAR 0.13-0.26 m -1 ) but high inorganic particle loadings or wind-induced sediment resuspension significantly reduced light penetration in certain lakes. In the clear lakes/pools, a substantial proportion of incident UV-A and UV-B radiation often penetrated the entire water column. With short-wave radiation in High Arctic locations currently increasing the light penetration data presented here suggest that planktonic biota in the shallow lakes and pools will be subject to UV influence. Phytoplankton populations were sparse (1-3 μg chlorophyll-a/l) and virtually absent in winter with seasonal activity focussed on the short summer season. Evidence of under-ice planktonic activity was observed in only one lake. Patterns of microbial numbers and activity observed within and between lakes appeared to be related to lake volume, catchment features and high summer water temperatures (up to 15 °C). In particular, the proportion of viable (electron transport system activity) bacteria increased with temperature within each study system and a trend of increasing percentage viability was also seen in bacterioplankton along the relatively weak eutrophication gradient.

37] Influenza virus endoribonuclease

The influenza virus polymerase complex contains two associated enzymatic activities, an endoribonuclease and a RNA-dependent RNA polymerase activity. Both activities have so far been observed only with the complete polymerase complex consisting of three subunits, PB1, PB2, and PA. This chapter describes a robust and optimized procedure for the purification of active influenza virus polymerase in complex with genomic RNA and the single-stranded RNA-binding protein nucleoprotein from influenza virus particles. It also explains the synthesis of capped RNA molecules as substrates of the influenza virus endonuclease. The enzymatic properties of influenza virus-derived endoribonuclease activity have been characterized with a model RNA substrate of 20-nucleotide length, termed G20 RNA. The rate of RNA cleavage under steady state conditions appears to be limited by product dissociation. Therefore conditions have been optimized to study the chemical step of RNA cleavage under single turnover conditions. The enzyme requires divalent metal ions for activity and can use Mn(II), Co(II), and Fe(II) efficiently at pH 7, Mg(II) with intermediate efficiency, and Ni(II) and Zn(II) with lower efficiency. The reaction progress curves show slow binding of Zn(II) and Ni(II) to the protein, suggesting a conformational change of the active site as a prerequisite for endonuclease activity in the presence of these two metal ions. Low concentrations of the detergent DOC inhibit the activity and also disrupt the trimeric polymerase complex, whereas other detergents do not have a significant effect on the activity.

Surface-sediment and epilithic diatom pH calibration sets for remote European mountain lakes (AL:PE Project) and their comparison with the Surface Waters Acidification Programme (SWAP) calibration set

A modern diatom-pH calibration data-set consisting of surface-sediment diatom assemblages from 118 lakes and 530 taxa is presented. The AL:PE data-set is from high-altitude or high-latitude lakes in the Alps, Norway, Svalbard, Kola Peninsula, UK, Slovenia, Slovakia, Poland, Portugal, and Spain (pH range = 4.5‐8.0; DOC range = 0.2‐3.2 mg l ‐1 ). In addition, 92 epilithon samples from 22 high-altitude or high-latitude lakes comprise an AL:PE epilithon diatom-pH data-set. Weighted averaging partial least squares regression is used to develop pH-inference models. The AL:PE data-set has a root-mean-square-error of prediction (RMSEP) of 0.33 and a maximum bias of 0.36 pH units and r 2 of 0.82, as assessed by leave-one-out cross-validation. The epilithon data-set has, after data-screening and the deletion of one very obvious outlier, a RMSEP of 0.23 and a maximum bias of 0.18 pH units and r 2 of 0.88. The 167 sample SWAP diatom-pH data-set from lowland or upland lakes in the UK, Norway, and Sweden has a RMSEP of 0.29 and a maximum bias of 0.23 pH units and r 2 of 0.86. The pH optima, as estimated by weighted averaging and Gaussian regression, are compared for the three datasets (AL:PE, SWAP, AL:PE epilithon). There is a good correspondence between the AL:PE and the AL:PE epilithon optima, but a consistent bias between the AL:PE and SWAP optima, with the SWAP optima being lower than the AL:PE estimates. The predictive performances of the AL:PE and SWAP calibration data-sets are compared using independent test samples and six core sequences, all from high-altitude lakes, one in south-east Siberia and five in eastern Scotland. The results show the importance of using the AL:PE data-set for inferring lake-water pH from diatom assemblages in high-altitude or high latitude lakes with low DOC concentrations. * Deceased

Modelling the Radiometric Color of Inland Waters: Implications to a) Remote Sensing and b) Limnological Color Scales

Utilizing a bio-optical model previously developed for Lake Ontario, the responsiveness of chromaticity coordinates (X, Y, Z), dominant wavelength (λ dom), and associated spectral purity (p) to the abundance of color-producing agents (CPA) residing within the Lake Ladoga water column was determined. CPA considered were phytoplankton (chl), suspended minerals (sm), and dissolved organic carbon (doc). Waters that contain simultaneously low concentrations of chl, sm, and doc are shown to appear blue to turquoise in color (472–500 nm). Highly turbid waters (i.e., waters containing high concentrations of chl and/or sm) with low concentrations of doc are shown to display colors ranging from green to brown (> 500 nm). Waters with large concentrations of doc, irrespective of turbidity, are shown to be invariably brownish (560–570 nm). With increasing CPA content, X, Y, and Z (and, consequently, λ dom) asymptotically approach constant limit values. An “end-point” dominant wavelength at about 572 nm appears to be intrinsically characteristic of all natural waters. It is shown that when one or more CPA exceeds a critical concentration, the spectral purity p asymptotically approaches values in the range 0.35 to 0.45 for all waters (exceptive of those containing solely chl in the restricted concentration range < 0.5 μg/L). Optical distinctiveness, particularly with respect to indigenous doc, of natural waters, while impacting the spectral purity of the “end-point” radiometric color, does not produce a comparable impact on the “end-point” color itself. This work reinforces the restrictive application of chromaticity analyses to the remote sensing of binary aquatic systems comprised of water plus one CPA. It also illustrates that neither panchromatic nor two-channel ratio images can provide unambiguous inference of water quality parameters. Correspondence between radiometric water color descriptors (X, Y, Z, λ dom, and p) and water color scales traditionally used in limnology is established, illustrating that the platinum-cobalt scale would be most appropriate for assessing waters that were radiometrically yellow, provided that the yellow hue were not invariably attributed to doc.

Influence of NOM on copper corrosion

Experimental data suggest that NOM promotes the formation of pits in a certain narrow range of concentrations and suppresses this type of corrosion at higher dosages.Natural organic matter (NOM) profoundly affected the corrosion of copper in a moderately alkaline synthetic water. It decreased the rate of corrosion, increased the rate of copper leaching, and dispersed crystalline inorganic corrosion products. The interaction of NOM with corrosion products was modeled using separate phases of malachite and cuprous oxide. The authors concluded that NOM promotes the formation of pits in a certain narrow range of concentrations (0.1–0.2 mg/L in laboratory tests) and suppresses this type of corrosion at higher dosages. At low DOC concentrations, the main interaction between NOM and the surfaces of corroding metal and corrosion products is adsorption. The influence of NOM on corrosion of metals in real distribution systems must be studied in relation to long periods of surface aging, flow rate, concentration and type of oxidants, pH, and alkalinity.

Influence of Dissolved Organic Carbon, pH, and Microbial Respiration Rates on Mercury Methylation and Demethylation in Lake Water

Effects of changes in DOC concentrations, pH, and microbial respiration rates on specific rates of mercury methylation and demethylation in lake water were studied using radioisotopic techniques. Increased concentrations of DOC resulted in decreased specific rates of net methylation, possibly as a result of complexation of inorganic mercury with DOC. A reduction in pH from 7.0 to 5.0 had the greatest effect, causing large to moderate increases in net methylation rate at both low and high DOC concentrations (500–2600 μM). Rates of respiration (indicative of general rates of microbial activity), which were insensitive to pH change over the range tested (5.0–7.0), had the smallest effect on net methyl mercury production rates. We propose the following explanations for three situations in which high mercury concentrations are commonly found in fish. (1) in acidified dilute clear-water lakes, high fish mercury concentrations may be a result of enhanced in-lake methylation; (2) in brown-water circumneutral lakes, where in-lake methylation is inhibited by high DOC concentrations, terrestrial inputs of methyl mercury may be most important; and (3) in brown-water, low-pH lakes, both in-lake and terrestrial sources of methyl mercury may contribute to elevated mercury concentrations in fish.