Baseflow Conditions Research Articles

Modeling Risk Dynamics of Contaminants of Emerging Concern in a Temperate-region Wastewater Effluent-dominated Stream.

Wastewater effluent-dominated streams are becoming increasingly common worldwide, including in temperate regions, with potential impacts on ecological systems and drinking water sources. We recently quantified the occurrence/ spatiotemporal dynamics of pharmaceutical mixtures in a representative temperate-region wastewater effluent-dominated stream (Muddy Creek, Iowa) under baseflow conditions and characterized relevant fate processes. Herein, we quantified the ecological risk quotients (RQs) of 19 effluent-derived contaminants of emerging concern (CECs; including: 14 pharmaceuticals, 2 industrial chemicals, and 3 neonicotinoid insecticides) and 1 run-off-derived compound (atrazine) in the stream under baseflow conditions, and estimated the probabilistic risks of effluent-derived CECs under all-flow conditions (i.e., including runoff events) using stochastic risk modeling. We determined that 11 out of 20 CECs pose medium-to-high risks to local ecological systems (i.e., algae, invertebrates, fish) based on literature-derived acute effects under measured baseflow conditions. Stochastic risk modeling indicated decreased, but still problematic, risk of effluent-derived CECs (i.e., RQ≥0.1) under all-flow conditions when runoff events were included. Dilution of effluent-derived chemicals from storm flows thus only minimally decreased risk to aquatic biota in the effluent-dominated stream. We also modeled in-stream transport. Thirteen out of 14 pharmaceuticals persisted along the stream reach (median attenuation rate constant k<0.1 h-1) and entered the Iowa River at elevated concentrations. Predicted and measured concentrations in the drinking water treatment plant were below the human health benchmarks. This study demonstrates the application of probabilistic risk assessments for effluent-derived CECs in a representative effluent-dominated stream under variable flow conditions (when measurements are less practical) and provides an enhanced prediction tool transferable to other effluent-dominated systems.

Antibiotic-Resistant Bacteria and Resistance Genes in Isolates from Ghanaian Drinking Water Sources.

The control of infectious diseases is seriously threatened by the increase in the number of microorganisms resistant to antimicrobial agents. Antibiotic-resistant bacteria have also been identified in the water environment. A field study was performed sampling drinking water sources in seven districts of southern Ghana targeting boreholes, dams, hand-dug wells, and streams during baseflow conditions. Bacteria were isolated (N = 110) from a total of 67 water samples to investigate their antimicrobial susceptibility and to determine their carriage of select antibiotic resistance genes. Bacterial identification was performed using conventional selective media methods and the analytical profile index (API) method. Antibiotic susceptibility tests were carried out using the Kirby–Bauer method. Results indicated that all water sources tested were of poor quality based on the presence of fecal indicator organisms. The most commonly occurring bacterium isolated from water was Klebsiella spp. (N = 24, 21.8%), followed by E. coli (N = 23, 20.9%). Gram-negative bacteria isolates were most commonly resistant to cefuroxime (24.5%), while the Gram-positives were most commonly resistant to meropenem (21.3%). The highest rates of bacterial resistances to more than one antibiotic were observed in Klebsiella spp. (30.0%) followed by E. coli (27.8%). PCR was used to detect the presence of a select antibiotic resistance genes in the Gram-negative isolates. The presence of blaNDM-1, sull, tet(O), and tet(W) were observed in isolates from all water sources. In contrast, ermF was not detected in any of the Gram-negative isolates from any water source. Most (28.7%) of the resistance genes were observed in E. coli isolates. Reducing microbial contamination of the various water sources is needed to protect public health and to ensure the sustainability of this resource. This further calls for education of the citizenry.

Measurable microcystin in Ozark streams was rare during summer 2018 baseflow conditions

AbstractAccelerated eutrophication due to human activity has been linked to an increase in the occurrence of cyanobacteria in freshwater systems. The purpose of this study was to document the occurrence of microcystin, a common cyanotoxin, within northwest Arkansas streams. Twenty streams were sampled from May through October 2018, and water and periphyton samples were analyzed for microcystin and chlorophyll‐a (CHL‐a). Mean microcystin concentrations in water samples were low across sites, ranging from &lt; 0.10 to 0.21 μg L−1. Mean microcystin in the periphyton across sites ranged from 2.6 to 9.9 μg m−2 and were within values observed in the literature. All microcystin concentrations measured in these Ozark streams were well below the current USEPA recreational guidelines of 8.0 μg L−1 and the drinking water guidelines of 0.3 μg L−1 for infants and 1.6 μg L−1 for adults.

Groundwater-surface water interactions and flux of organic matter and nutrients in an urban, Mediterranean stream

The chemical quality of dissolved organic matter (DOM) and the speciation of nitrogen exported from urban catchments is of great importance to biogeochemical cycling in riverine and coastal receiving waters. Many urban streams in Mediterranean climates have a flashy hydrologic regime, which would suggest a rapid pulsing and shunting of solutes downstream. However, the role of these systems both as passive pipes for solute transport or as reactors for DOM and nutrient transformation is still an open question for urban, Mediterranean streams. To address this question, we evaluated changes in concentrations of inorganic and organic solutes and DOM optical properties in Alvarado Creek, a perennially-flowing, urban, first-order tributary of the San Diego River in San Diego, CA, USA, during dry weather (baseflow) conditions and during four storm events in 2016–2018. Chloride and sulfate concentrations corroborate the supposed saline groundwater supply that maintains perennial flow and brackish nature in this urban stream. During dry weather, high proportions of protein-like fluorescent component (AC4) and downstream decreases in total dissolved nitrogen (TDN) and nitrate imply in-stream processing (nitrification and denitrification). By contrast, storm hysteresis curves indicate that the supply of DOM and TDN was not exhausted over the duration of a storm event, whereas nitrate was eventually depleted, presumably because nitrification could not keep up with the export of nitrate from source areas. Rapid decreases in chloride during the storm hydrograph coincided with a shift in specific ultraviolet absorbance (SUVA) and fluorescence index (FI) to more terrestrially-derived and aromatic carbon sources, most likely from interflow of stormwater through vadose zone soils. On an annual basis, the export of microbially-derived DOM during dry weather was higher than the export of terrestrially-derived DOM during storm events; both represent important carbon inputs to coastal waters.

The Relationship Between Delta Form and Nitrate Retention Revealed by Numerical Modeling Experiments

AbstractRiver deltas display a wide range of morphologic patterns that influence how nutrients interact in channels and wetlands on their way to the coast. To quantify the role of delta morphology on nitrate fate, we simulated reactive nitrate transport over steady base flow conditions for six synthetic, morphologically unique river‐dominated deltas created in Delft3D by varying incoming grain size distributions. We parameterized nitrate removal kinetics using an observed relationship with elevation from Wax Lake Delta (Louisiana, USA). Total nitrate retention across the six synthetic deltas and Wax Lake Delta ranged from 1.3%‐13%, suggesting that these river‐dominated deltas have limited ability to remove nitrate from incoming river water. Nitrate removal is constrained by limited hydrologic connectivity with the areas of greatest nitrate demand, which are found at higher elevation. In these synthetic numerical experiments, the efficiency of nitrate removal is greatest for deltas with more topologic complexity and greater proportions of the delta plain at higher elevation, which are both common characteristics of coarser‐grained deltas. The positive relationship between grain size and nitrate removal may help guide land reclamation projects if project goals include minimizing nitrate export to the sea.

Hydrologic controls on the accumulation of different sized microplastics in the streambed sediments downstream of a wastewater treatment plant (Catalonia, Spain)

Wastewater treatment plants (WWTPs) act as a point source of microplastics (MPs) to freshwater ecosystems. Although MP abundance has been linked to high-density population areas, the mechanisms of how river hydrodynamics and particle size influence MP accumulation in streams are still largely unknown. This study investigated the spatial distribution of MPs within streambed sediments downstream of a WWTP effluent in Cànoves stream (Montseny, Catalonia) during baseflow conditions. MP concentrations from an upstream control site were compared to the WWTP bypass that added untreated wastewater at times when stream discharge exceeded capacity. The 450 m section investigated downstream of the WWTP consisted of three geomorphically altered sub-reaches interspersed between three unaltered buffer sub-reaches, each ∼75 m that provided a range in hydrologic conditions. Measurements of MP characteristics, hydrogeomorphic variables, and fine particles were simultaneously taken. MPs were quantified following the Nile red fluorescence method for large (>64 µm) and small (10–64 µm) particles. MPs in sediment samples downstream of the WWTP were mainly fragments with a higher abundance of small MPs (85 particles/g of sediment) vs large MPs (9 particles/g of sediment). While the abundance of large MPs in streambed sediments decreased with distance from the WWTP point source, the abundance of small MPs increased. Furthermore, the area of small MPs decreased with distance from the WWTP. MPs were most abundant at the WWTP bypass, suggesting these infrequent inputs during storm events represent an important source of MPs to the stream. Higher MP abundance coincided with increased organic matter content and smaller sediment grain sizes. Overall, our results present significant findings that could help explain differences in transport and accumulation patterns of MPs that influence their retention times in streambeds, suggesting a combination of preferential filtration in the streambed sediments, and fragmentation of larger particles.

The Hydrological Urban Heat Island: Determinants of Acute and Chronic Heat Stress in Urban Streams

AbstractDuring and after rainfall events, the interaction of precipitation with hot urban pavements leads to hot runoff, and its merger with urban streams can result in an abrupt change in water temperature that can harm aquatic ecosystems. To understand this phenomenon and its relation to land cover and hydrometeorological parameters, we analyzed data spanning two years from 100 sites in the eastern United States. To identify surges, we first isolated temperature jumps of at least 0.5°C over 15 min occurring simultaneously with water flow increase. Surge magnitude was defined as the difference between peak stream temperature and baseflow temperature right before the jump. At least 10 surges were observed in 53 of the studied streams, with some surges exceeding 10°C. Our results demonstrate that the watershed developed area and vegetation fraction are the best descriptors of surge frequency (Spearman correlation of 0.76 and 0.77, respectively). On the other hand, for surge magnitude and peak temperature, the primary drivers are stream discharge and stream temperature immediately before the surge. In general, the more urbanized streams were found to be already warmer than their more “vegetated” counterparts during baseflow conditions, and were also the most affected by temperature surges. Together, these findings suggest the existence of a hydrological urban heat island, here defined as the increase in stream temperature (chronic and/or acute), caused by increased urbanization.

Variation in septic system effluent inputs to tributaries in multiple subwatersheds and approaches to distinguish contributing pathways and areas

Quantifying the contribution of septic systems to contaminant, including nutrient, loading to streams is needed in many watersheds to inform water quality management programs. However, this quantification is challenging due to the distributed locations of septic systems and uncertainties regarding the pathways delivering effluent from septic systems (functioning and failing) to a stream. The objectives of this study were firstly to evaluate how septic effluent inputs to streams vary with stream discharge conditions for multiple subwatersheds with different characteristics (i.e., geology, septic system density, and typical age), and secondly to examine new approaches for distinguishing the pathways and the contributing areas delivering septic effluent to streams. These approaches use the artificial sweetener acesulfame as a conservative tracer for septic effluent in applications of: (i) stream concentration-discharge (C-Q) relationships using low frequency sampling data, (ii) hysteresis behavior in event-based C-Q relationships, and (iii) longitudinal stream sampling. For all nine subwatersheds studied, the amount of septic effluent reaching the subwatershed outlets was considerably higher during high stream discharge (event) conditions compared to low discharge (baseflow) conditions, suggesting pathways other than groundwater may also be important. Generally, the percentage of septic effluent reaching the outlets was less for subwatersheds with newer households compared to those with older households. The combined interpretation of low frequency and event-based C-Q relationships indicate that complex pathways control the delivery of septic effluent to the subwatershed outlets. The interpretations suggest that groundwater pathways may dominate in some subwatersheds, while more rapid pathways associated with failing septic systems (e.g., overland runoff) may be important in others. Finally, longitudinal stream sampling illustrate the potential of acesulfame data to identify key areas contributing septic effluent to the stream. The novel approaches used here can be applied to guide future investigations aiming to quantify and manage water quality impairment from septic systems.

Lake water quality observed after extreme rainfall events: implications for water quality affected by stormy runoff

To investigate the effects of extreme rainfall events (EREs) on lake water quality, we analyzed the lake monthly monitoring data at the stations close to inflow rivers. We tested the hypothesis that the effects depend on rainfall magnitude, season, distance from the rivers, etc. The highest correlations with many water-quality indicators were obtained for the rainfall amount for the preceding 10 days before the water sampling days; i.e., negatively with Na+, Cl−, chlorophyll a (Chla), and COD, and positively with ortho-phosphate. We used the threshold of rainfall amount ≥ 140 mm to choose EREs and evaluate the water quality on such occasions because quite low values of Na+, Cl−, and Chla thresholds (≤ 25th percentile) were observed in some of the EREs. The event samples (group 1; G1) meeting the above thresholds probably represented the inflow waters during EREs (generally occurred in Oct–May), and the others (group 2; G2) indicated significant changes in the lakes (Jun to Sep), probably depending on the lake’s state of primary production. In the events of lower rainfall events (50 mm to 140 mm for 10 days), fast recoveries of algal production usually occurred even in Oct to May. The values of COD, total phosphorus, and ortho-phosphate in G1 were higher than the values of river water quality in the baseflow conditions, whereas both the G1 and baseflow values of nitrogen were nearly the same. The effects of ERFs on lake water quality from the viewpoints of tempo-longitudinal distributions, future monitoring, and climate change were discussed.

Habitat selection and foraging success by an endangered Mediterranean cyprinid: implications for habitat restoration

Habitat loss and degradation are causing collapses in freshwater fish in the Mediterranean region, where habitat restoration actions are still hampered by poor understanding of fish habitat selection and fitness. Here, we combined field surveys and laboratorial experiments to investigate how water velocity, body size and intra-specific interactions influence habitat selection and foraging success by the highly endangered Mira chub Squalius torgalensis. Velocity negatively affected habitat selection and fitness of chub via its negative effects on prey capture rate. Small chub occupied lower velocity ranges than large chub, and both captured the most prey at the range of velocities selected in the stream. Size-based intra-specific interactions also affected capture success, with small chub capturing proportionally less prey in the presence of large chub. Our results suggest that, during base-flow conditions, restoring low and moderate velocities up to 26 cm/s will help ensure suitable habitat and improve the fitness of small and large chub occurring in interacting groups. Integrated approaches uncovering factors directly related to habitat selection and individual fitness should guide habitat restoration for fish in Mediterranean streams and may help identify critical habitat features for other endangered species.

Long-term analysis of road salt loading and transport in a rural drinking water reservoir watershed

Chloride exports from the widespread application of road salt serve as a primary contribution to water body salinity in cold climate regions. Road salt pollution is a concern in drinking water supplies due to the relationship between chloride concentration and water corrosivity. In the Northeastern U.S., researchers and water quality managers are interested in better understanding how management practices can mitigate the negative effects of road salt pollution. This study uses regression-based chloride load estimates from LOADEST to produce mass balances and analyze transport flow-paths to the Wachusett Reservoir from a predominantly rural watershed. A chloride mass balance for 2000 through 2019 revealed that reservoir and watershed export only recently reached a level similar to estimated inputs from road salt (11,200 ton/yr). Results from hydrograph and load separation techniques show that average loading (4300 ± 1300 ton/yr) and discharge from baseflow (3.2 ± 0.9 m3/s) contributed approximately 74% and 65% of the total loading (5800 ± 1800 ton/yr) and discharge (4.93 ± 1.50 m3/s), respectively from water years 2001 through 2019. Approximately 40% of the total annual tributary load (30% baseflow; 10% runoff) occurred in the spring (March–May) and is attributed to elevated baseflow conditions from snowmelt. As indicated by a baseflow chloride index, baseflow concentrations are 14% greater than the total concentrations measured in the tributaries. Therefore, the baseflow-dominated tributary chloride loading is due to a combination of greater discharge and chloride concentration in baseflow as compared to direct surface runoff. However, a long-term trend analysis suggests a slightly increased fraction of chloride loading via overland flow in several reservoir tributaries, potentially indicative of late 20th century land development. This study offers a unique monitoring approach for management authorities to better assess road salt pollution in water systems. The decadal response of the reservoir system reflects the slow-moving nature of the baseflow-dominated chloride loading and suggests that measurable water quality improvements will only be realized with a sustained long-term decrease in the amount of road salt applied.

The role of colloids and other fractions in the below-ground delivery of phosphorus from agricultural hillslopes to streams

Colloids can be important for facilitated transfer of phosphorus (P) to groundwater (GW) and contribute to elevated P concentrations later delivered to surface water. To assess the role of colloidal P and other P fractions in delivery processes via below-ground pathways, this study investigated the influence of catchment and flow event characteristics on particulate (>450 nm), medium-sized colloidal (200–450 nm) and fine (<200 nm) P fractions in two agricultural hillslopes (TG, TA). Total and dissolved P fractions and their derivatives were also monitored. Samples in both stream and GW were taken weekly during baseflow conditions and every 2 h during storm conditions. Higher frequency monitoring of streamflow was also conducted to delineate hydrological flowpaths and determine P loads and hysteresis processes. Results indicated that during baseflow fine P was dominant in the streams (80 to 100 % of total P) and in shallow GW in TA (83 to 96 %) whereas in TG shallow GW was dominated by PP (55 to 96 %) possibly due to colloidal Fe-P complexes. Similarly, in TG shallow GW was dominated by PP (79 to 81 %) during high flow events. During a larger flow event (within the period of land fertilization) the quickflow pathway (24 % of total flow) delivered 3.2 g ha−1 of PP which was dominant in the stream (44 to 68 %). A smaller flow event (within the period of prohibited land fertilization) facilitated delivery of P via deeper baseflow pathways (87 % of total flow) as fine reactive P (1.3 g ha−1), also dominant in the stream (73 to 78 %). The research indicated a very limited presence of medium-sized colloidal P but a large presence of fine P that may contribute to elevating P concentrations above environmental thresholds. Further work should constrain the controlling factors for colloidal P presence/absence and also on the extent and speciation of coarser and finer fractions in the hillslope to stream continuum.

Do cyprinid fish use lateral flow‐refuges during hydropeaking?

AbstractHydropeaking caused by small‐scale hydropower plants creates rapid changes in the intensity, frequency, and persistence of river flows. These changes can induce stress in fish across all life‐stages and, may negatively impact fish communities. Rapid increases in the flow velocity may cause fish to avoid unstable habitats, seeking out nearby refuges to reduce their energy expenditure. A lateral flow‐refuge constructed from maritime plywood (0.4 m wide × 0.5 m long × 0.4 m high) was installed in the left river bank, 40 m downstream of the Bragado hydropower plant. A multispectral stereo underwater camera trap was installed inside the flow‐refuge to monitor fish over one‐month period. The camera recorded images continuously both during base and peak flow conditions. Two different peak‐flow conditions were detected: peak and high peak‐flow conditions. The peak flow conditions correspond to a turbine discharge of 0.67 m3/s (peak), and 2.1 m3/s (high peak) at full load. The base‐flow condition corresponded to a discharge of 0.064 m3/s. The fish presence inside the refuge was observed to be significantly higher during the peak condition when compared with the base and high peak conditions. These findings strongly indicate that the flow during the high peak condition prevented fish from using the flow‐refuge due to the increase in the current. We hypothesize that this may be due to the increase in the current velocity and increased levels of ambient turbulence near the refuge. An alternate hypothesis is that the spatial distribution of velocities and depths during the high peak condition induced fish to inhabit areas with poor access to the refuge. The results of this study indicate that fish refuges can be used to successfully mitigate hydropeaking, and that their use by fish can depend on the flow regime.

When Forests Take Over After Land Abandonment: Dissolved Organic Matter Response in Headwater Mountain Streams

Dissolved organic matter (DOM) represents the largest pool of organic carbon in fluvial ecosystems. The majority of DOM in rivers is of terrigenous origin—making DOM composition highly dependent on vegetation cover and soil properties. While deforestation is still a worldwide anthropogenic phenomenon, current land cover change in temperate regions is often characterized by secondary succession processes following the abandonment of agricultural activities including grazing on pasturelands. This results in (secondary) forest expansion with a consequent, time-lagged transformation of soil properties. Predicting the time scale and spatial scale (i.e., location in the catchment: riparian vs. upslope areas) at which such land cover changes affect the terrestrial-aquatic carbon linkage and concomitantly alter properties of fluvial DOM as drivers of carbon cycling in freshwater ecosystems represents a new scientific challenge. In an attempt to identify potential legacy effects of land cover, i.e., reaction delays of fluvial DOM to changes in land cover, we here investigate the influence of specific current and historic (2 decade-old) land cover types on molecularly resolved fluvial DOM composition in headwater mountain streams. Our analysis is based on a scale-sensitive approach weighing in the distance of land cover (changes) to the stream and ultrahigh-resolution mass spectrometric analyses. Results identified the dominance of terrigenous DOM, with phenolic and polyphenolic sum formulae commonly associated to lignins and tannins, in all the studied streams. DOM properties mostly reflected present-day gradients of forest cover in the riparian area. In more forested catchments, DOM had on average higher molecular weight and a greater abundance of O-rich phenols and polyphenols but less aliphatics. Besides the modulation of the DOM source, our results also point to an important influence of photodegradation associated to variation in light exposition with riparian land cover in defining fluvial DOM properties. Despite expectations, we were unable to detect an effect of historic land cover on present-day DOM composition, at least at the investigated baseflow conditions, probably because of an overriding effect of current riparian vegetation.

Connecting the Age and Reactivity of Organic Carbon to Watershed Geology and Land Use in Tributaries of the Hudson River

AbstractWe characterized the dissolved organic matter (DOM) under baseflow conditions from a set of rivers in the Mohawk and Hudson River watersheds. The rivers in this study drain a range of bedrock geologies and land cover. We identify how those factors influence riverine DOM reactivity and the source, age, and composition of the biolabile DOM. We performed laboratory incubation experiments to characterize each river's reactive and non‐reactive DOM pools. Measurements of dissolved organic carbon concentration, radiocarbon, Ultraviolet‐visible spectroscopy absorbance, and Fourier‐transform ion cyclotron resonance mass spectrometry (FTICR‐MS) analysis were performed at each incubation start and end, allowing us to determine the quantity, age, and composition of the reactive and nonreactive DOM pools. We find that lithology controls bulk DOM ages, with watersheds underlain by shale/limestone having the most aged DOM and crystalline/metasedimentary watersheds having the youngest DOM. We observe that for a given lithology, bulk DOM age increases with the proportion of agricultural land in the watershed–suggesting agricultural practices mobilize aged DOM. FTICR‐MS analysis reveals that both lithology and land cover influence DOM composition. Shale/limestone watersheds showed DOM compositions distinct from other watershed lithologies, and the percentage of nitrogen‐containing DOM correlated with agricultural influence. In two of the studied rivers we find that the biolabile DOM fraction is older than the bulk DOM (upwards of 7 kyr) revealing that aged DOM may be preferentially consumed in these rivers. Our findings provide insight into how riverine carbon cycles may respond to watershed disturbances that influence DOM inputs to rivers.

Fractional-derivative model simulations of reach-scale uptake and transport dynamics of natural fluorescent dissolved organic matter in a temperate forested stream in southeastern U.S.

Dissolved organic matter (DOM) entering the river networks affects aquatic ecosystems, yet it remains difficult to quantify the strength of various environmental factors in controlling reach-scale uptake and transport of DOM. This study combined reach-scale field experiments and stochastic modeling to investigate the uptake and transport dynamics of natural fluorescent DOM (FDOM) in a forested coastal plain stream located in the southeastern U.S. FDOM from litter leachate and sodium chloride (NaCl) were injected into the stream under base flow conditions (with different flow rates) on three separate occasions over a 3-month period. Field measurements showed that FDOM and NaCl exhibited different anomalous dynamics characterized by the peak and tailing behaviors of concentration breakthrough curves (BTC), indicating that the transport of FDOM was regulated more by physical retention and/or biogeochemical recycling than that of NaCl. The preferential removal of humic fluorescence than protein fluorescence before the BTC peak suggests that physical sorption was more important than biological degradation in early FDOM removal at the field site. A tempered fractional advection–dispersion-reaction model (TFADRM) was proposed to describe the FDOM migration process and estimate the FDOM spiraling metrics, and the resultant metrics were compared to those from conventionally used BTC-integrated approach. Results revealed that solute retention can lower the peak concentration and enhance the late-time tail of the FDOM BTC, whereas irreversible biogeochemical reaction processes can consume FDOM and decrease the BTC peak. Relative to the commonly used OTIS model, TFADRM can better capture the observed BTC late-time tail by considering multiple rates for the mass exchange/uptake of FDOM in streams, and therefore, this study provided a more reasonable estimate of FDOM spiraling metrics and transport dynamics at the reach scale.

Pathways and composition of dissolved organic carbon in a small agricultural catchment during base flow conditions

The amount and composition of organic carbon are major controls on water quality and ecological processes in streams. In this study we explored the fate of the quantity of dissolved organic carbon (DOC) and the composition of dissolved organic matter (DOM) in an agricultural hillslope - stream network system. We conducted our study in the 66 ha HOAL (Hydrological Open Air Laboratory) in Lower Austria. We measured DOC of the soil eluates from different land use units, water samples from the stream and from seven tributaries, and estimated DOM components by fluorescent spectrophotometry and PARAFAC analyses. Soil DOC shows the highest concentrations in summer, but DOC concentrations in the tributaries are lower in summer than in winter by between 19% and 31%. DOM composition of the soil eluate differs between land use units. The forest site exhibits the largest fractions of humic-like fluorophores and less labile DOM. DOM composition in the tributaries is, in addition to DOC, controlled by soil moisture. We estimated the DOC import from the tributaries into the stream as 125 kg during base flow conditions in the period February to December 2017 and the instream DOC production as 38 kg, considering mass balance and exchange with groundwater. Six out of seven DOM components have a positive net production along the stream, only aliphatic DOM with low molecular weight is consumed (65 % of its input). These findings suggest that agricultural land use increases DOC input into streams and alters their DOM quality. Instream processes modify DOM quality over short distances.

Phase partitioning, transport and sources of Benzotriazole Ultraviolet Stabilizers during a runoff event

Benzotriazole Ultraviolet Stabilizers (BT-UVs) are ubiquitous in the environment, given their wide use as additives in consumer products. Their bio-accumulative and toxic properties are increasingly being scrutinised, evinced by the recent proposition to add UV328 to the Stockholm Convention on Persistent Organic Pollutants. Here, we measured concentrations of six BT-UVs in the dissolved and particulate phases of stream water collected from an urban and rural stream during a runoff event. Under baseflow conditions, the less hydrophobic BT-UVs were present at low concentrations in the dissolved phase, while much higher loads of particulate BT-UVs occurred during stormflow, especially in the urban creek. Time-weighted average BT-UV concentrations were up to 4 times higher in the urban than in the rural creek. BT-UVs were found to be prevalent in water obtained from laundering textiles, which plausibly constitutes a major portion of domestic wastewater, and can serve as a BT-UV source to aquatic waterways. However, the observed dilution of a sewage tracer during the run-off event suggests that unregulated wastewater seepage is not responsible for the high BT-UV loads in storm water. High levels of UV328 and UV234 were detected in a select few plastic debris items collected from the urban watershed and in artificial turf grass, respectively. Whereas this may allow for the leaching of those BT-UVs into the creek, most plastic debris is more likely a sink than a source of BT-UVs. The observed input of particle-bound BT-UVs at the onset of the rain event indicates that most of the BT-UVs reach the creek with contaminated particles that had built up on surfaces during the antecedent dry period. UV328 was the dominant BT-UV in those particles. If such particle build-up occurs on road surfaces, it may suggest that the use of UV328 in automotive applications contributes to their presence in urban storm water.

Tandem field and laboratory approaches to quantify attenuation mechanisms of pharmaceutical and pharmaceutical transformation products in a wastewater effluent-dominated stream

Evolving complex mixtures of pharmaceuticals and transformation products in effluent-dominated streams pose potential impacts to aquatic species; thus, understanding the attenuation dynamics in the field and characterizing the prominent attenuation mechanisms of pharmaceuticals and their transformation products (TPs) is critical for hazard assessments. Herein, we determined the attenuation dynamics and the associated prominent mechanisms of pharmaceuticals and their corresponding TPs via a combined long-term field study and controlled laboratory experiments. For the field study, we quantified spatiotemporal exposure concentrations of five pharmaceuticals and six associated TPs in a small, temperate-region effluent-dominated stream during baseflow conditions where the wastewater plant was the main source of pharmaceuticals. We selected four sites (upstream, at, and two progressively downstream from effluent discharge) and collected water samples at 16 time points (64 samples in total, approximately twice monthly, depending on flows) for 1 year. Concurrently, we conducted photolysis, sorption, and biodegradation batch tests under controlled conditions to determine the major attenuation mechanisms. We observed 10-fold greater attenuation rates in the field compared to batch tests, demonstrating that connecting laboratory batch tests with field measurements to enhance predictive power is a critical need. Batch systems alone, often used for assessment, are useful for determining fate processes but poorly approximate in-stream attenuation kinetics. Sorption was the dominant attenuation process (t1/2<7.7 d) for 5 of 11 compounds in the batch tests, while the other compounds (n = 6) persisted in the batch tests and along the 5.1 km stream reach. In-stream parent-to-product transformation was minimal. Differential attenuation contributed to the evolving pharmaceutical mixture and created changing exposure conditions with concomitant implications for aquatic and terrestrial biota. Tandem field and laboratory characterization can better inform modeling efforts for transport and risk assessments.

Exposure and Transport of Alkaloids and Phytoestrogens from Soybeans to Agricultural Soils and Streams in the Midwestern United States.

Phytotoxins are naturally produced toxins with potencies similar/higher than many anthropogenic micropollutants. Nevertheless, little is known regarding their environmental fate and off-field transport to streams. To fill this research gap, a network of six basins in the Midwestern United States with substantial soybean production was selected for the study. Stream water (n = 110), soybean plant tissues (n = 8), and soil samples (n = 16) were analyzed for 12 phytotoxins (5 alkaloids and 7 phytoestrogens) and 2 widely used herbicides (atrazine and metolachlor). Overall, at least 1 phytotoxin was detected in 82% of the samples, with as many as 11 phytotoxins detected in a single sample (median = 5), with a concentration range from below detection to 37 and 68 ng/L for alkaloids and phytoestrogens, respectively. In contrast, the herbicides were ubiquitously detected at substantially higher concentrations (atrazine: 99% and metolachlor: 83%; the concentrations range from below detection to 150 and 410 ng/L, respectively). There was an apparent seasonal pattern for phytotoxins, where occurrence prior to and during harvest season (September to November) and during the snow melt season (March) was higher than that in December-January. Runoff events increased phytotoxin and herbicide concentrations compared to those in base-flow conditions. Phytotoxin plant concentrations were orders of magnitude higher compared to those measured in soil and streams. These results demonstrate the potential exposure of aquatic and terrestrial organisms to soybean-derived phytotoxins.