Hydrologic and geochemical drivers of aluminum, barium, and copper in two drinking water reservoirs in Southwestern Virginia, USA

PCB congener dynamics in a heavily industrialized river catchment

We employ a geochemical-fingerprinting approach to estimate the source of suspended sediments collected from tributaries entering Falls Lake, a 50-km2 drinking water reservoir on the Neuse River, North Carolina, USA. Many of the major tributaries to the lake are on North Carolina’s 303(d) list for impaired streams, and in 2008, the lake was added to that list because of high values of turbidity, likely sourced from tributary streams. Suspended sediments were collected from four streams with a time-integrated sampler during high-flow events. In addition, composite sediment samples representing potential sources were collected from stream banks, forests, pastures, construction sites, dirt and paved roads, and road cuts within tributary basins. Radiocarbon dating and magnetic susceptibility measurements were used to determine the origin of stream bank alluvial deposits. Sediment samples were analyzed for the concentrations of 55 elements and two radionuclides in order to identify tracers capable of distinguishing between potential sediment sources. The relative sediment source contributions were determined by applying a Monte Carlo simulation that parameterized the geochemical tracer data in a mixing model. Radiocarbon and magnetic susceptibility measurements confirmed the presence of “legacy” sediment in the Ellerbe and New Light Creek valley bottoms. Mixing model results demonstrate that stream bank erosion is the largest contributor to the suspended sediment load in New Light Creek (62%), Ellerbe Creek (58%), and Little Lick Creek (33%), and is the second largest contributor in Lick Creek (27%) behind construction sites (43%). We find that stream bank erosion is the largest nonpoint source contributor to the suspended sediment load in three of the four catchments and is therefore a significant source of turbidity in Falls Lake. The presence of legacy sediment appears to coincide with increased contributions from stream bank erosion in Ellerbe and New Light creeks. Active construction sites and timber harvesting were also significant sources of suspended sediment. Water quality mitigation efforts need to consider nonpoint-source contributions from stream bank erosion of valley bottom sediments aggraded after European settlement.

<p>Thermal destratification of lakes and reservoirs is a primary control on dissolved-oxygen levels below the thermocline. In such waterbodies, internal biogeochemical processes are often controlled by a complex set of oxygen-controlled forcing mechanisms. Therefore, preventing stratification by artificial processes has long been an important tool in maintaining dissolved oxygen concentrations and corresponding water quality and ecosystem health in drinking water reservoirs. Blagdon Lake in Somerset, SW England is a medium-size (1.8km<sup>2</sup>), shallow depth (max: 13.1m) drinking water reservoir. An extensive 6-month field campaign was undertaken in the summer of 2019 at the reservoir, measuring depth profiles of dissolved oxygen, turbidity, conductivity, temperature and pH using an EXO3 multiparameter sonde and a CastAway® CTD. In addition, two thermistor chains were permanently installed measuring temperature and dissolved oxygen concentrations using Onset TidbiT v2 loggers (1m depth intervals) through the water column at 30-minute temporal resolution and a miniDOT oxygen logger at the sediment-water interface respectively. These thermistor chains collected data from summer 2019 – autumn 2020. The data from this field campaign were analysed to investigate the effectiveness of the installed bubble-plume destratification system present at Blagdon Lake, SW England. Similar systems are used in 66% of UK reservoirs employing artificial mixing infrastructure, though very little has been published evaluating their effectiveness in such temperate, shallow, drinking water reservoirs. Initial analysis of the results indicates that the bubble-plume system, nor wind shear is effectively preventing spring/summer destratification for long periods, and that neither are the main factor controlling thermal stratification in Blagdon Lake. The data provides a unique opportunity to directly assess the impact of bubble-plume aerators and their effectiveness at thermal destratification to control dissolved oxygen and water quality in temperate, shallow water bodies.</p>

The microbial communities within reservoir ecosystems are shaped by water quality and hydrological characteristics. However, there are few studies focused on the effects of thermal stratification on the bacterial community diversity in drinking water reservoirs. In this study, we collected water samples from the Jinpen Reservoir around the re-stratification period. To explore the functional diversity and bacterial community composition, we used the Biolog method and 16S rRNA-based 454 pyrosequencing combined with flow cytometry. The results indicated that stratification of the reservoir had great effects on temperature and oxygen profiles, and both the functional diversity and the composition of the bacterial community strongly reflected the significant vertical stratification in the reservoir. The results of the Biolog method showed a significantly higher utilization of carbon sources in the hypolimnion than in the epilimnion. The result of pyrosequencing also showed a significantly higher species diversity and richness in the hypolimnion than in the epilimnion with different dominant phylum. Redundancy analysis also indicated that the majority of environmental variables, especially pH and dissolved oxygen, played key roles in shaping bacterial community composition. Our study provides a better understanding of the functional diversity of bacterial communities, and the response of microorganisms to seasonal thermal stratification.

A numerical model has been developed to simulate the input of radionuclides into the Mediterranean Sea through the Rhone River plume. The model is fully 3D. It solves the hydrodynamic equations, which include baroclinic terms and a turbulence model, together with the suspended sediment equations and radionuclide dispersion equations. The suspended sediment sub-model includes four particle classes, settling and deposition. The radionuclide equations include the exchanges of radionuclides between water, suspended sediments and bed sediments, described using a kinetic model. The effect of salinity changes upon uptake kinetics has also been included. Computed water circulation, salinity pattern, suspended sediment distribution and sedimentation rates are in agreement with observations in the area. The model has been applied to simulate the dispersion of 137 Cs and 239,240 Pu through the plume. Computed specific activities in water, suspended matter and bottom sediments are in agreement with the measured distributions. The model can also be applied to calculate distribution coefficients. Although some water circulation models for the Rhone River plume exist in current literature, this is the first time in which a detailed hydrodynamic and suspended sediment model has been applied to simulate the dispersion of radionuclides in the plume.

<p>Radioiodine is one of the most important radionuclides released by the accidents of Fukushima Dai-ichi nuclear power plant (FDNPP). Iodine-131 elevated ambient radiation dose rate immediately after the accident, but it is extinguished due to its short half-life. The long-lived <sup>129</sup>I can be used as a tracer to retrospectively infer the level of <sup>131</sup>I. Understanding of environmental behavior of <sup>129</sup>I is important for preparedness against nuclear disaster. This study presents sampling campaigns on the Abukuma River during two high flow events, and discusses riverine <sup>129</sup>I behavior based on comparisons with that of <sup>137</sup>Cs. The study site was the Kuroiwa site locating at midstream of the Abukuma river. Its catchment area was 2886 km<sup>2 </sup>and mean <sup>129</sup>I inventory in the catchment was 0.041 Bq m<sup>-2</sup>. Five and seven river water samples were taken during high-flow events in July 2018 (JUL18) and October 2018 (OCT18), respectively. Suspended sediment and filtrate samples were obtained by decantation and subsequent filtration with 0.45 μm-mash membrane filter, respectively. The suspended sediment and filtrate samples were measured for <sup>137</sup>Cs activity concentrations with HPGe detector and then measured for <sup>129</sup>I/<sup>127</sup>I ratio with accelerator mass spectrometer and for <sup>127</sup>I concentration with ICP-QQQ-MS. Mean <sup>129</sup>I activity concentration in suspended sediment during JUL18 and OCT18 were 1.0 and 0.43 mBq kg<sup>-1</sup>, respectively. In terms of temporal trends, <sup>129</sup>I activity concentration in suspended sediment lowered in the peak water discharge phase, contrastive to those of <sup>137</sup>Cs which were the highest at peak water discharge phase. Mean dissolved <sup>129</sup>I activity concentrations during JUL18 and OCT18 were 0.18 and 0.067 μBq L<sup>-1</sup>, respectively. Both <sup>129</sup>I and <sup>137</sup>Cs activity concentrations in dissolved form tended to decrease with time during two high-flow events. Mean apparent distribution coefficient (Kd) during JUL18 and OCT18 were 4.3 ×10<sup>4</sup> and 6.1 ×10<sup>3</sup> L kg<sup>-1</sup>, respectively. The Kd values of <sup>129</sup>I were lower than those of <sup>137</sup>Cs and it reveal relatively-high solubility of <sup>129</sup>I. Total exportation of <sup>129</sup>I from the catchment during JUL18 and OCT18 were estimated as 1.0 × 10<sup>4</sup> and 2.3 × 10<sup>4</sup> Bq, respectively. Exported <sup>129</sup>I in dissolved form accounted for 80 and 27% of total exportations, respectively. By contrast, more than 95% of <sup>137</sup>Cs was exported in particulate form in the events. These results indicated an importance of dissolved form for understanding environmental behavior of radioiodine.</p>

Native brown trout populations are declining in Swiss rivers. This could be due, among other reasons, to a clogged riverbed caused by fine sediment deposition, leading to a decrease in interstitial flow and therefore in a reduced oxygen supply to the salmonid embryos. Furthermore, suspended sediment (SS) could directly harm health and fitness of free swimming fish. The aim of this dissertation was to develop and apply methods to measure SS and the effects of weekly fine sediment infiltration and net fine sediment accumulation over the entire egg incubation season on oxygen concentrations in artificial redds and the survival of the implemented brown trout eggs. Furthermore, the effects of riverbed structure, redd morphology and hydrological and hydrogeological conditions on interstitial oxygen and egg survival was assessed. In addition, source areas of SS and organic matter were assessed by C/N atomic ratio, 13Ctot, 13Corg and 15N isotopes. The study was conducted at three sites named A, B and C, from up- to downstream along the canalized and partly stabilized river Enziwigger in the Swiss Plateau. Data were collected weekly or measured continuously during two spawning seasons (2009/10 and 2010/11) from November to March in a total of 36 redds. Weekly fine sediment infiltration rates in redds were relatively high and generally increased with higher SS concentrations. Both, infiltrated sediments and SS showed strong temporal variations between low flow and peak discharge conditions. Fine sediment infiltration was at maximum during high flow events with sediments mainly in the size of sand (0.063 - 2 mm). These sediments originated for the most part in the upper watershed. Small amounts of fine sediments infiltrated during base flow periods with particles mainly in the size of silt and clay (< 63 µm) and with increasing organic matter concentrations. Organic matter was generally of allochthonous origin and major sediment source areas were pasture and arable land during those low flow periods. Less fine sediment accumulated over the entire egg incubation period in upwelling zones on the local scale and within areas of higher mean water levels due to corresponding flushing of fine sediments. Even though SS and bedloads increased from up- to downstream, less fine sediment accumulated downstream. Higher flushing of fine sediments and generally increased sediment dynamics downstream due to higher water levels are probably the reasons for this observation. Increased sediment dynamics also caused remarkably scouring of redds: 50% of the redds in the two downstream sites were excavated or buried during high flow events in early winter due to sediment movements. Redd loss at the upstream site A was substantially lower (8%). The high permeability of the redd substratum and the typical pit-tail structure of redds led to high dissolved oxygen (DO) concentrations in redds shortly after redd construction. Specific infiltration rates q decreased substantially within one month due to riverbed sediment displacements and fine sediment infiltration. This resulted in lower DO concentrations in redds. In individual redds, DO concentration decreased temporally to almost 0%, leading to a depleted redd environment unfavorable for embryo survival. Interstitial DO concentration and q generally increased during high flows. In contrast they decreased during the falling limb of the water level, likely indicating exfiltration of depleted ground- or interstitial water. Similarly, DO concentrations decreased under prolonged base flow conditions. This paralleled the higher percentage of silt and clay particles in the infiltrated sediment, probably triggering riverbed clogging and therefore reducing q. Even though organic matter in SS increased from up- to downstream due to an increase of pasture and arable land downstream of the river, egg survival was better at the downstream sites. Organic matter concentrations were with means between 5.1% at site A and 6.5% at site C relatively low. The low egg survival at site A was likely due to the high fine sediment accumulation at the site, triggering low specific infiltration rates and consequently decreased DO concentrations. This was especially true at spots with low mean water levels, where flushing of fines is inhibited. Enhanced soil erosion processes on pasture and arable land are expected with increasing heavy rain events and less snow during winter seasons due to climate change. Consequently, SS and organic matter in the river will increase, which will possibly affect brown trout negatively. Furthermore, a higher frequency of high flows in the future could potentially enhance scouring of redds especially in the downstream sites, which could further reduce egg survival rates.

The objective of this study was to evaluate the potential sources of pesticides to the Yolo Bypass, including those that could potentially impact critical life stages of resident fish. To assess direct inputs during inundation, pesticide concentrations were analyzed in water, and in suspended and bed sediment samples collected from source watersheds during high-flow events. To understand inputs from direct application on fields, pesticides were also measured in soils collected from several sites within the Bypass. Thirteen current-use pesticides were detected in water samples collected in 2004 with the highest pesticide concentrations observed at the input sites to the Bypass during high flows. Hexazinone and simazine were detected at all sites and at some of the highest concentrations. In bed and suspended sediments collected in 2004 and 2005, 13 current-use pesticides were detected, along with DDT and its metabolites. Trifluralin, DDE, and DDT were highest in the bed sediments, whereas oxyfluorfen and thiobencarb were highest in the suspended sediments. With the exception of the three organochlorine insecticides, suspended sediments had higher pesticide concentrations compared to bed sediments, indicating the potential for pesticide transport especially during high-flow events. Soil samples were dominated by DDT and its degradates but also contained a variety of current-use pesticides typically at lower concentrations. The types of pesticides detected in water and sediments were correlated with agricultural applications in each watershed. Understanding the distribution of pesticides between water and sediment is important in assessing their fate and transport within the Bypass, and in evaluating the exposure and potential effects to resident fish.

Geochemistry of sediments of the Peninsular rivers of the Ganga basin and its implication to weathering, sedimentary processes and provenance

The accurate measurement of suspended sediment (&lt;200 μm) in aquatic environments is essential to understand and effectively manage changes to sediment, nutrient, and contaminant concentrations on both temporal and spatial scales. Commonly used sampling techniques for suspended sediment either lack the ability to accurately measure sediment concentration (e.g., passive sediment samplers) or are too expensive to deploy in sufficient number to provide landscape‐scale information (e.g., automated discrete samplers). Here, we evaluate a time‐integrated suspended sediment sampling technique, the pumped active suspended sediment (PASS) sampler, which collects a sample that can be used for the accurate measurement of time‐weighted average (TWA) suspended sediment concentration and sediment particle size distribution. The sampler was evaluated against an established passive time‐integrated suspended sediment sampling technique (i.e., Phillips sampler) and the standard discrete sampling method (i.e., manual discrete sampling). The PASS sampler collected a sample representative of TWA suspended sediment concentration and particle size distribution of a control sediment under laboratory conditions. Field application of the PASS sampler showed that it collected a representative TWA suspended sediment concentration and particle size distribution during high flow events in an urban stream. The particle size distribution of sediment collected by the PASS and Phillips samplers were comparable and the TWA suspended sediment concentration of the samples collected using the PASS and discrete sampling techniques agreed well, differing by only 4% and 6% for two different high flow events. We should note that the current configuration of the PASS sampler does not provide a flow‐weighted measurement and, therefore, is not suitable for the determination of sediment loads. The PASS sampler is a simple, inexpensive, and robust in situ sampling technique for the accurate measurement of TWA suspended sediment concentration and particle size distribution.

The phosphorus content of fluvial sediment in rural and industrialized river basins

The condition of the water in drinking water source environments is critical for public health. However, in recent years, the rapid growth of algae has become a significant threat to the safety of the drinking water supply. This study investigated the temporal trends and spatial differences in algae in the Nanwan Reservoir during 2022. Regression analysis using the least-squares method demonstrated that water temperature and initial biomass concentration were critical parameters that influenced the rate of algal growth. An air–water–algal growth model (AWAM) for algal growth prediction was developed using a 30-day forecast of air temperature, an air-to-water temperature extrapolating equation, a water temperature–algal growth relationship, and only four monthly measurements of algal concentration. The results demonstrated that the model accurately predicted algal growth in the next 30 days, with an R2 of 0.738, which aligned with the monitored results. Compared to the upstream Wudaohe River inflow point, algal growth in the drinking water intake area near the downstream dam was delayed by at least 30 days. By using the upstream inflow area as a reference point, the prediction period was extended to provide a 60-day early warning. The extended prediction period and the reduced need for monitoring data make the model more convenient for guiding the prevention and control of algal blooms in drinking water reservoirs.

234Th and 7Be as tracers for the transport and dynamics of suspended particles in a partially mixed estuary

Suspended sediment remains an important variable for prediction in river studies. Knowledge of suspended sediment concentration or load at different downstream locations within a channel allows the temporal and spatial patterns of catchment sediment yield to be determined, as well as within-channel sediment budgets that provide important insight into the patterns and processes governing channel siltation and scour. However, in many rivers, the comprehensive and long-term downstream monitoring of discharge contrasts with relatively sparse and temporally discontinuous monitoring of suspended sediment. As a result, the generation of suspended sediment data through physical and empirical modelling approaches is commonplace. The emergence of a data-driven modelling paradigm in the last two decades has resulted in the adoption of new methods for suspended sediment modelling. To a large extent, these methods mirror traditional empirical approaches, except that the a priori determination of the form of the response function by the modeller is replaced by machine learning and artificial intelligence algorithms that ‘learn’ the response function (both its form and associated parameters) directly from data. Data-driven models have been shown to result in improved goodness-of-fit metric scores, but many hydrologists remain critical about the lack of attempts by data-driven modellers to demonstrate the physical rationality and operational validity of their models. In this chapter, we examine this criticism; highlight specific research challenges facing data-driven, suspended sediment modellers; and detail the research directions through which advances may be made.

The scientific and public awareness of hazardous photosynthetic prokaryotes (cyanobacteria/cyanoprokaryotes) and especially the contamination of drinking-water reservoirs with cyanotoxins is world-wide increasing. Recently much more attention has been paid to the events and results of mass proliferation of these toxic organisms even in South-East European countries in spite of the fact that, as a rule, they are not controlled by national legislation.The present paper presents a summary of results of such studies carried out in summer-autumn periods of the last 15 years (2000-2015) in Bulgarian water bodies differing by location, morphometry and trophic status, incl. drinking water reservoirs, recreational lakes and sites of nature conservation importance. A multivariate analysis allowed to outline the distribution patterns and environmental drivers of the planktonic cyanoprokaryote assemblages in relation with the available data on the water bodies, highlighting species composition and abundance of the main taxa, including potentially toxic species. Samples analysis by HPLC-DAD and/or LC/MS, ELISA and in vitro cytotoxicity tests allowed detection of microcystins, nodularins and saxitoxins. Toxin concentration ranged between 0.1 and 26.5 µg L-1 in water samples and between 10.9 and 1070 µg g-1 (d.w.) in concentrated (net) samples. Despite the fact that microcystins were not found in all studied water bodies and that the recorded levels were still lower in comparison with some other European countries, the fact that cyanotoxins were detected in 16 water bodies (incl. 3 drinking water reservoirs) could serve as an alert for the need of recognition of cyanotoxins as a new health risk factor in the country. Therefore, permanent monitoring with identification of toxins in water bodies at risk and activities for limitation and control of toxic blooms are urgently needed, in combination with increase of the attention to the effects of cyanotoxins on both human health and health of aquatic ecosystems in Bulgaria.