Surface Water Catchment Research Articles

The influence of different tree species and age on the surface water balance of a small commercial forestry catchment

Acacia mearnsii and Eucalyptus dunnii plantations play an important role in the South African economy as a source for a variety of wood products. However, these species are commonly associated with high evapotranspiration (ET) which may cause streamflow reduction, affecting downstream water users who are reliant on the stream for survival. The potential future increase in exotic plantations worldwide necessitates understanding the impact of these different species on the water balance, hence the streamflow. At the Two Streams research catchment in South Africa, intense hydrological observations (streamflow, ET and weather) have been conducted on A. mearnsii for almost two decades. In 2018, the catchment was clear-felled with subsequent replanting of E. dunnii and hydrological measurements continued. This provided an opportunity to present observations of the surface water balance of the catchment. However, gaps in the data at various times prevented a compilation of a continuous hydrological record. Therefore, three window periods, with complete records of streamflow, ET and precipitation, and with similar weather conditions, were compared. Only the interception loss (Il) was estimated using the Von Hoyningen-Huene method. First window, A. mearnsii trees were three years old (Amear3), second window, A. mearnsii trees were seven years old (Amear7) and the third window, E. dunnii trees were three years old (Edun3). Results indicated a negative catchment surface water balance for all window periods. During the Amear7 window period, the Il was highest compared to the young crops, which reduced effective precipitation, in turn contributing to the lowest measured streamflow. The negative surface water balance and high ET, suggests that trees were accessing water not quantified in the surface water balance. Crops of all three window periods were found to have the potential to significantly reduce the streamflow, which may in turn affect downstream water users. Further research using isotopes to trace the sources of water used by trees in the system is suggested.

Effects of Deforestation and Anthropogenic Aspects on Streamflow in the Mau Forest Catchments in Kenya: Hydrological Modelling of Surface Water Yields from Sondu River Basin

Climatic factors determine the amount and distribution of atmospheric water received at the land surface while the land cover conditions determine the partitioning of this water into different hydrological components and ultimately the catchment surface water yields. This study assessed the effects of deforestation of a tropical catchment on surface water yields to address fluctuating flows of the rivers emanating from Mau Forest, the largest water tower in Kenya. Sondu basin traverses Southwest Mau Forest covering an area of 3500 km2. The main channel in the basin flows in a southwest direction into Lake Victoria in an altitudinal range of 2900 to 1130 m a.s.l over a length of 173 km. Different deforestation scenarios over the basin were integrated with climate data to form inputs to a hydrologic model, Soil and Water Assessment Tool (SWAT). Using model outputs, the effects of deforestation on annual and seasonal surface water yields, represented by changes in streamflow volumes under different deforestation scenarios, were evaluated. Deforestation scenarios were derived from a supervised classification scheme of time series of LANDSAT images (1970-2020) to show deforestation trends. Effects of deforestation on the catchment water-yielding capacity were estimated as the ratio of the difference between simulated yields under different deforestation scenarios and those simulated under the pre-deforestation scenario of the 1970s decade. Results show that forest cover declined by 21% and a corresponding growth in land under agriculture by 26% in the period 1970-2020. The decline in forest coverage resulted in an increase in the annual surface water yields of about 23% (from 152 to 187 MCM/year) throughout the period of study. This implies that there is less recharge of groundwater due to decreased infiltration and subsequent storage leading to lower flows during the dry seasons and increased flood frequencies in the basin during the wet seasons. The study has therefore, demonstrated that deforestation has reduced the stability of Mau Forest as a water tower and conservation of the forest will enhance its water-holding capacity thereby ensuring a stable water supply to rivers emanating from it as a way of combating floods and low flows in the basin. The resultant impacts on environment and society are displacements from floods and destruction of properties.

Surface water catchment deformation—toward a conceptual model: the case study of Zarqa river catchment, Jordan

Surface water catchment deformation—toward a conceptual model: the case study of Zarqa river catchment, Jordan

Comparison of measured and predicted herbicide concentrations in surface water catchments in Belgium.

In the process of approval of active substances and authorization in the European Union and at the member state level, it must be shown by the applicant that an unacceptable risk for nontarget organisms in the aquatic environment by the active substance can be excluded. To achieve this aim, standardized models, scenarios, and agreed pesticide input parameters have to be used to calculate the exposure as defined by the FOrum for the Co-ordination of pesticide fate models and their Use (FOCUS). During a period of daily surface water sampling lasting 3.5 years, a survey was conducted among farmers in the highly vulnerable catchment of Grote Kemmelbeek in Belgium to collect agronomic data on crops, application dates, and application rates of 12 applied herbicides and one metabolite. Daily surface water concentrations for the same herbicides were measured over 2.5 years for a second, much larger but less vulnerable, catchment of Kleine Aa (KAa). A comparison of realistic worst-case predicted environmental concentrations in surface water (PECsw) according to FOCUS with measured concentrations shows that, in the GKb catchment, the PECsw was never exceeded for six substances, was exceeded on only 1-2 days for five substances, and was exceeded on 9-27 days for two substances. For the KAa catchment, the PECsw was only exceeded on twodays for one compound and never for the other 12 compounds. These numbers correspond to a level of protection of the FOCUS PECsw between 100% and 97% and are much higher than the regulatory protection goal of 90%. These two case studies demonstrate the protectiveness of the FOCUS surface water approach. Integr Environ Assess Manag 2024;20:1447-1462. © 2024 Bayer AG. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Recession constants are non-stationary: Impacts of multi-annual drought on catchment recession behaviour and storage dynamics

Recession analysis is commonly adopted to characterise catchment behaviour, particularly in relation to the role of catchment storage in streamflow production. Recession techniques are data hungry and characterise average behaviour over long periods of recorded data, making them generally unsuitable in transient conditions. Nevertheless, in the context of multi-annual drought, sufficient data may be available to characterise temporal change by examining different subperiods. In this work, we assessed changes in recession behaviour of catchments affected by multi-annual drought in south-eastern Australia, focusing on how changes in recession patterns over time correlate to drought-induced shifts in annual rainfall-runoff relationships. We applied two methods, drawn from the vast methodological literature on recession analysis. They consider different information and entail different assumptions; one is based on average daily recession rates and the other on hourly recession slope plots. Despite the differences, their results are consistent: catchments that exhibited significant changes in rainfall-runoff relationship during the drought also display significantly steeper recessions during and after the drought. Subsequent investigation suggests that only a portion of the increases in recession speed are attributable to increased evaporative demand. Rather, they are likely caused by decreased connectivity between subsurface storage and catchment surface water and increased transmission losses through the streambed. With this work, we demonstrate the usefulness of recession analysis to investigate sources and effects of non-stationary behaviour, providing insights into the impacts of long-term drought on streamflow production and catchment storage dynamics.

Identification and estimation of hydrological contributions in a mixed land‐use catchment based on a simple biogeochemical and hydro‐meteorological dataset

AbstractWater pathways and water contamination in mixed land‐use catchments are complex to understand. Runoff‐generating sources can be numerous and water pathways modified by anthropogenic elements. Monitoring surveys considering geochemical and microbial parameters, are often carried out on such catchment, but are often simple in terms of studied parameters. Nonetheless, they can be helpful to identify the specific signatures of the main runoff‐generating sources and estimate their contribution to total runoff at the outlet of mixed land‐use catchments. Based on a monthly biogeochemical monitoring program conducted between 2017 and 2019 in the Ratier catchment (19.8 km2) near Lyon (France), a step‐by‐step approach was developed to: (1) identify the main runoff‐generating sources using a perceptual model of the Ratier catchment, (2) identify the respective biogeochemical signatures of each source using this biogeochemical dataset and hydro‐meteorological indicators and (3) estimate their contribution to the stream total runoff using an End‐Member Mixing Analysis method. We identified three main runoff‐generating sources outside of rainy periods: a colluvium aquifer, a fractured gneiss aquifer and a saprolite layer. The monitored geochemical datasets were found divided into three groups matching these sources. Contributions of these sources were estimated based on representative tracer concentrations. Microbial parameters showed a homogeneous agricultural and anthropogenic contamination among the catchment surface water, but also deeper into the fractured gneiss groundwater. This approach showed the potential of using simple monitoring datasets to identify runoff‐generating sources and estimate their contribution to total runoff.

A Systems Approach to Identifying Hazards in the Management of Stream Buffers for the Protection of Drinking Water Quality

In drinking water catchments, exploiting ecosystem services provided by stream buffers has the potential to complement conventional engineering solutions such as water treatment and reduce the overall public health risks to consumers. These stream buffers interrupt the movement of contaminants and sediments from non-point source sources, such as agricultural land, to surface waters. Effectively managing stream buffers can be challenging due to the complexity and diversity of factors that can directly and indirectly impact efficacy. This study uses System Theoretic Process Analysis (STPA) and Early Warning Signal Analysis based on STPA (EWaSAP) methodology to systematically examine the sociotechnical structures for managing stream buffers in surface water catchments using a theoretical scenario representative of typical surface water supplies. The combination of STPA and EWaSAP provides a practical approach for developing requirements for stream buffers in drinking water catchments, focusing on hazard assessment and management measures. The evaluation considers the complex management arrangements for land uses within catchment areas. The performance and effectiveness of these actions can be tracked through the selected sensors and early warning measures. As a practical matter, this approach would help specify requirements for catchment management and drinking water source protection that can be systematically integrated into relevant management strategies.

Microbial source tracking using molecular and cultivable methods in a tropical mixed-use drinking water source to support water safety plans

Microbial contamination deteriorates source water quality, posing a severe problem for drinking water suppliers worldwide and addressed by the Water Safety Plan framework to ensure high-quality and reliable drinking water. Microbial source tracking (MST) is used to examine different microbial pollution sources via host-specific intestinal markers for humans and different types of animals. However, the application of MST in tropical surface water catchments that provide raw water for drinking water supplies is limited. We analyzed a set of MST markers, namely, three cultivable bacteriophages and four molecular PCR and qPCR assays, together with 17 microbial and physicochemical parameters, to identify fecal pollution from general, human-, swine-, and cattle-specific sources. Seventy-two river water samples at six sampling sites were collected over 12 sampling events during wet and dry seasons. We found persistent fecal contamination via the general fecal marker GenBac3 (100 % detection; 2.10–5.42 log10 copies/100 mL), with humans (crAssphage; 74 % detection; 1.62–3.81 log10 copies/100 mL) and swine (Pig-2-Bac; 25 % detection; 1.92–2.91 log10 copies/100 mL). Higher contamination levels were observed during the wet season (p < 0.05). The conventional PCR screening used for the general and human markers showed 94.4 % and 69.8 % agreement with the respective qPCR results. Specifically, in the studied watershed, coliphage could be a screening parameter for the crAssphage marker (90.6 % and 73.7 % positive and negative predictive values; Spearman's rank correlation coefficient = 0.66; p < 0.001). The likelihood of detecting the crAssphage marker significantly increased when total and fecal coliforms exceeded 20,000 and 4000 MPN/100 mL, respectively, as Thailand Surface Water Quality Standards, with odds ratios and 95 % confidence intervals of 15.75 (4.43–55.98) and 5.65 (1.39–23.05). Our study confirms the potential benefits of incorporating MST monitoring into water safety plans, supporting the use of this approach to ensure high-quality drinking water supplies worldwide.

Agricultural Pressures on the Quality of Ground and Surface Waters in Catchments of Artificial Reservoirs

Changes in nutrient concentrations in groundwater were investigated to determine the impact of agriculture on water quality in artificial lakes. The study covered three reservoirs in an agricultural area of Wielkopolska (central-western part of Poland). Assessing the agricultural impact required a network of piezometers around the reservoirs, used to determine the degree of groundwater pollution from nutrients supplied to the reservoirs. Moreover, the analysis covered the quality of water in streams flowing into the reservoirs, and in the reservoirs themselves. Field research was conducted every month of the growing season from March to November. The analysis covered land inclination, ground permeability, and soil type. Detailed objectives included: (1) assessment of the agricultural impact on the chemical parameters of ground and surface water quality, and (2) evaluation of the impact of different sources of agricultural pollution on water quality in artificial reservoirs in regards to their management. This study revealed high dynamics of nutrient concentrations, particularly for nitrates and phosphates, in groundwater and surface water. A significant effect of maize cultivation on an increase in nitrate concentrations in the groundwater of the catchment of the Przebędowo Reservoir was evidenced, as well as a substantial effect of the functioning of an animal farm on the quality of groundwaters in the catchment of the Lachotka Reservoir. The nutrient load of agricultural origin in the catchment of the Miedzichowo Reservoir was relatively low. Our study revealed elevated amounts of nutrients such as nitrogen and phosphorus, detected more frequently in groundwater than in running waters, which confirms our hypothesis of the importance of groundwater analysis in detecting the source of pollution of the studied lakes. High nutrient concentrations recorded in groundwater leached from arable fields were also observed in the summer period, failing to confirm the hypothesis that the greatest effect of factors would be related to the spring effect of arable fields on water quality (lack of compact vegetation cover, high water level, etc.). Our study also indicated a greater importance of the type of land use than lithology or permeability of deposits.

Design of groundwater catchments. Case study: the water supply of Adjud

The use of groundwater to supply water to citizens is an important component of a country's security strategy, as groundwater is less vulnerable to pollution and can be used even in difficult climatic conditions. Groundwater catchments involve additional investment in research, compared to surface water catchments, because they use an underground source that must be identified through geological and hydrogeological research: the aquifer. From the geological and hydrogeological studies that were carried out in the area, the conclusion is that these aquifers can appear at depths between 15 and 120 m and there is a possibility that they manifest themselves artesian.

Quantifying MCPA load pathways at catchment scale using high temporal resolution data

Detection of the agricultural acid herbicide MCPA (2-methyl-4-chlorophenoxyacetic acid) in drinking water source catchments is of growing concern, with economic and environmental implications for water utilities and wider ecosystem services. MCPA is poorly adsorbed to soil and highly mobile in water, but hydrological pathway processes are relatively unknown at the catchment scale and limited by coarse resolution data. This understanding is required to target mitigation measures and to provide a framework to monitor their effectiveness. To address this knowledge gap, this study reports findings from river discharge and synchronous MCPA concentration datasets (continuous 7 hour and with additional hourly sampling during storm events) collected over a 7 month herbicide spraying season. The study was undertaken in a surface (source) water catchment (384 km2—of which 154 km2 is agricultural land use) in the cross-border area of Ireland. Combined into loads, and using two pathway separation techniques, the MCPA data were apportioned into event and baseload components and the former was further separated to quantify a quickflow (QF) and other event pathways. Based on the 7 hourly dataset, 85.2 kg (0.22 kg km−2 by catchment area, or 0.55 kg km−2 by agricultural area) of MCPA was exported from the catchment in 7 months. Of this load, 87.7 % was transported via event flow pathways with 72.0 % transported via surface dominated (QF) pathways. Approximately 12 % of the MCPA load was transported via deep baseflows, indicating a persistence in this delayed pathway, and this was the primary pathway condition monitored in a weekly regulatory sampling programme. However, overall, the data indicated a dominant acute, storm dependent process of incidental MCPA loss during the spraying season. Reducing use and/or implementing extensive surface pathway disconnection measures are the mitigation options with greatest potential, the success of which can only be assessed using high temporal resolution monitoring techniques.

A research and development roadmap to support applications of the enhanced BIOMASS methodology

The International Atomic Energy Agency has coordinated an international project addressing enhancements of methods for modelling the biosphere in post-closure safety assessments of solid radioactive waste disposal. This has resulted in the enhanced BIOMASS methodology that is described elsewhere in this special issue. To a large degree, the enhancements to the BIOMASS methodology arose from experience gained in applying the original methodology, both in the context of other international projects and in assessments of existing or proposed disposal facilities for solid radioactive wastes. Here, this experience is used, together with information on the status of solid radioactive waste disposal programmes worldwide, to identify opportunities for applying the enhanced methodology and for learning from those applications. This provides a basis for identifying research and development to support application of the enhanced methodology in a variety of environmental settings. These research and development requirements include aspects related to climate change under a variety of forcing scenarios, landform development in climatic regimes ranging from cold, polar to arid, tropical, modelling of groundwater flow and contaminant transport in surface-water catchments where both fractured rock and porous sediments are present, and studies of the transport of key radioisotopes of elements central to major biogeochemical cycles, such as those of carbon, chlorine, sulphur and iodine. In addition, some remarks are made on aspects of the application of the enhanced methodology that could imply review and updating of regulations and regulatory guidance, e.g. in relation to the definition of representative persons or groups to be considered in assessments and in respect of approaches to the assessment of radiological impacts on non-human biota. Furthermore, consideration is given as to how the scientific and technical experience that has been gained and methods that have been developed in the context of solid radioactive disposal facilities could support management of contaminated sites and legacy facilities that are likely to require long-term management and stewardship.

Surface Water Contamination and Catchment Protection in Lower Manyame Sub-Catchment of Zimbabwe

Surface Water Contamination and Catchment Protection in Lower Manyame Sub-Catchment of Zimbabwe

Mass Balance of Perfluoroalkyl Acids, Including Trifluoroacetic Acid, in a Freshwater Lake.

Perfluoroalkyl acids (PFAAs) are highly persistent chemicals that are ubiquitously found in the environment. The atmospheric degradation of precursor compounds has been identified as a source of PFAAs and might be an important pathway for contamination. Lake Vättern is one of Sweden’s largest lakes and is an important source for drinking water. In addition to contamination via atmospheric deposition, the lake is subject to several potential contamination sources via surface water inflow. The relevance of different sources is not well understood. A mass balance of selected PFAAs was assembled based on measured concentrations in atmospheric deposition, surface water from streams that constitute the main inflow and outflow, and surface water in the lake. The largest input was seen for trifluoroacetic acid (150 kg/year), perfluoropropanoic acid (1.6 kg/year), perfluorobutanoic acid (4.0 kg/year), and perfluoro-octanoic acid (1.5 kg/year). Both atmospheric deposition and surface water inflow was found to be important input pathways. There was a positive correlation between the input of most perfluoroalkyl carboxylic acids via atmospheric deposition and global radiation and between the input via surface water inflow and catchment area. These findings highlight the importance of atmospheric oxidation of volatile precursor compounds for contamination in surface waters.

Numerical modeling of groundwater‐driven stream network evolution in low‐relief post‐glacial landscapes

AbstractIn the low‐relief post‐glacial landscapes of the Central Lowlands of the United States, fluvial networks formed and expanded following deglaciation despite the low slopes and large fraction of the land surface occupied by closed depressions. Low relief topography allows for subtle surface water divides and increases the likelihood that groundwater divides do not coincide with surface water divides. We investigate how groundwater transfer across subtle surface water divides facilitates channel network expansion using a numerical model built on the Landlab platform. Our model simulates surface and subsurface water routing and fluvial erosion. We consider two end‐member scenarios for surface water routing, one in which surface water in closed depressions is forced to connect to basin outlets (routing) and one in which surface water in closed depressions is lost to evapotranspiration (no routing). Groundwater is modeled as fully saturated flow within a confined aquifer. Groundwater emerges as surface water where the landscape has eroded to a specified depth. We held the total water flux constant and varied the fraction of water introduced as groundwater versus precipitation. Channel growth is significantly faster in routing cases than no‐routing cases given identical groundwater fractions. In both routing and no‐routing cases, channel expansion is fastest when ~30% of the total water enters the system as groundwater. Groundwater contributions also produce distinctive morphology including steepened channel profiles below groundwater seeps. Groundwater head gradients evolve with topography and groundwater‐fed channels can grow more quickly than channels with larger surface water catchments. We conclude that rates of channel network growth in low‐relief post‐glacial areas are sensitive to groundwater contributions. More broadly, our findings suggest that landscape evolution models may benefit from more detailed representation of hydrologic processes.

Predicting mass loadings of sulfamonomethoxine, sulfamethoxazole, and lincomycin discharged into surface waters in Japanese river catchments

Japanese strategies for the management of livestock waste suggest effluent discharge from livestock farms as major pathways of entry of veterinary antibiotics into surface waters. To aid control of their sources, we developed a model for predicting annual loads of antibiotics discharged into surface waters as effluent from livestock farms, sewage treatment plants, and households, using population, usage, excretion, removal, and fraction of livestock waste treated as wastewater. To verify the model, we monitored three antibiotics which are much used for livestock in Japan and are stable during river transport—i.e., sulfamonomethoxine (SMM), sulfamethoxazole (SMX), and lincomycin (LCM)—over one year in the Oyodo River, which has the most active swine farming area in Japan in its catchment. Concentrations and mass flows of SMM and SMX showed a sharp peak in winter, and those of LCM were also higher in winter than in summer in the river. Annual mass flows observed in the river and reported in three other Japanese rivers were within a range of ½ to 2 times the model estimates. Effluent from swine farms contributed largely to mass flows of SMM and LCM in the rivers, while human wastewater from sewage treatment plants and households contributed partly to substantially to those of SMX. Estimated contributions of surface runoff from agricultural land to the annual mass flows in the rivers were < 1%, in agreement with the prediction made by limiting sources to effluent. Although other locations and antibiotics should be studied in the future, this first attempt at modeling the load of veterinary antibiotics discharged from livestock farms provides a new perspective on how to reduce movement of these compounds into surface waters in catchments where wastewater treatment is or could be used in managing livestock waste. • A model of veterinary antibiotics in effluents was developed. • Observed riverine flux of SMM, SMX, and LCM increased in winter in a river. • The model estimates agreed well with annual mass flows of the antibiotics in rivers. • Effluent from swine farms was the largest source of the antibiotics. • Agricultural land was a negligible source of the antibiotics.

Effects of Topographic Resolution and Geologic Setting on Spatial Statistical River Temperature Models

AbstractRiver temperature exerts a critical control on habitat for aquatic biota. As the climate warms in eastern Canada, threats to habitats of cold‐water species will increase, underpinning the necessity to develop an understanding of landscape‐scale, thermal regimes of flowing waters. We assessed the performance of spatial statistical network (SSN) models of river temperature using high‐resolution thermal infrared imagery (0.6 m) and LiDAR (1 m) compared to NASA's Shuttle Radar Topography Mission (SRTM—30 m) topographic data and interrogate LiDAR derived fine‐scale models (3 ha) to describe groundwater connectivity to surface waters in catchments with shallow overburden and varied bedrock geology. LiDAR improved model performance in a catchment underlain by a homogeneous, high hydraulic conductance bedrock (Cains River) but did not improve model performance in a catchment with heterogeneous bedrock and variable hydraulic conductance (North Pole Stream). We hypothesize that differences in bedrock conductance modified topographic controls on subsurface flows and discharge patterns to the rivers and thus produced the mixed performance of the SSN models. At finer scales, river reaches in steep valleys incising high conductance bedrock produced groundwater discharge, which was absent in incised valleys with low conductance bedrock. These findings indicate that while topography exerts an important control on landscape‐scale hydrological processes, geologic setting is a similarly important influence on hydrological processes. We suggest the inclusion of a third dimension of spatial autocorrelation, representative of the vertical plane that captures the geologic setting, would broaden the geographic applicability of spatial statistical models for river temperature studies.

Stakeholders Reach Consensus in Troubled Waters

Surface water and groundwater catchments rarely align with the boundaries of cities, states, or nations. More often, water runs through, over, and under man-made sociopolitical divisions, making the governance of transboundary waters a formidable task. Although much of the public conversation regarding the availability and management of shared waters may appear to be dire (e.g., reports of “water wars”), there are transboundary basin water management strategies across the globe which offer hope. These include the efforts of the Apalachicola-Chattahoochee-Flint Stakeholders (ACFS) in the southeastern United States, which may serve as a useful template for future conversations around the water sharing table. The Apalachicola-Chattahoochee-Flint Basin (ACF Basin) is a vital economic engine in the southeastern United States. The waters of the ACF are shared between three states—Alabama, Florida, and Georgia—and harbor some of the richest freshwater biodiversity in North America, including sturgeon, rock bass, madtom, sculpin, bass, darters, and the highest densities of freshwater mussels in the world. Many of these are species of concern or threatened or endangered species; therefore, water management strategies in multiple portions of the ACF must comply with habitat protection plans under the U.S. Environmental Protection Act of 1970 (https://www.enr.gov.nt.ca/en/environmental-protection-act). The ACFS was organized in 2009 in the hopes of overcoming a decades-long stalemate between Alabama, Florida, and Georgia, regarding the use of shared waters in the ACF Basin. Despite years of litigious relationships among these three states, the ACFS managed to bring a diverse and previously contentious set of water users to the table and build consensus on a shared water management plan for the entire ACF Basin. While the ACFS holds no regulatory power, they made more progress in breaking through existing distrust and deadlock than any previous efforts in this basin to date. In the end, they developed cooperation, respect, and a sustainable and adaptive water management plan which included input and buy-in from all identified water sectors in the ACF Basin. It is, therefore, a valuable exercise to examine the ACFS model and contemplate whether it contains exportable methodologies for other catchments challenged with managing transboundary waters.

The water chemistry and microbiome of household wells in Medawachchiya, Sri Lanka, an area with high prevalence of chronic kidney disease of unknown origin (CKDu)

Chronic kidney disease (CKD) of unknown etiology (CKDu) mostly affects agricultural communities in Central America, South Asia, Africa, but likely also in North America and Australia. One such area with increased CKDu prevalence is the Medawachchiya District Secretariat Division of the Anuradhapura District in the North Central Province of Sri Lanka. Recent research has focused on the presence of various microbial pathogens in drinking water as potential causal or contributing factors to CKDu, yet no study to date has performed a more comprehensive microbial and water chemistry assessment of household wells used for domestic water supply in areas of high CKDu prevalence. In this study, we describe the chemical composition and total microbial content in 30 domestic household wells in the Medawachchiya District Secretariat Division. While the chemical composition in the tested wells mostly lies within standard drinking water limits, except for high levels of fluoride (F), magnesium (Mg), sodium (Na), chloride (Cl) and calcium (Ca) in some samples, we find a frequent presence of cyanotoxin-producing Microcystis, confirming earlier studies in Sri Lanka. Since the total microbial content of drinking water also directly influences the composition of the human gut microbiome, it can be considered an important determinant of health. Several bacterial phyla were previously reported in the gut microbiome of patients with CKD. Using these bacteria phyla to define operational taxonomic units, we found that these bacteria also occur in the microbiome of the sampled well water. Based on available environmental data, our study demonstrates associations between the abundances of these bacteria with geographical distribution, well water temperature and likely fertilizer use in the local surface water catchment area of the individual household wells. Our results reinforce the recommendation that household wells with stagnant or infrequently used water should be purged prior to use for drinking water, bathing and irrigation. The latter is suggested because of the reported potential accumulation of bacterial toxins by agricultural crops. The observation that bacteria previously found in chronic kidney disease patients are also present in household wells requires a more detailed systematic study of both the human gut and drinking water microbiomes in CKDu patients, in relation to disease prevalence and progression.

Approaches to herbicide (MCPA) pollution mitigation in drinking water source catchments using enhanced space and time monitoring

Freshwater occurrences of the selective acid herbicide 2-methyl-4-chloro-phenoxyacetic acid (MCPA) are an ongoing regulatory and financial issue for water utility industries as the number and magnitude of detections increase, particularly in surface water catchments. Assessments for mitigating pesticide pollution in catchments used as drinking water sources require a combination of catchment-based and water treatment solutions, but approaches are limited by a lack of empirical data. In this study, an enhanced spatial (11 locations) and temporal (7-hourly to daily sampling) monitoring approach was employed to address these issues in an exemplar surface water source catchment (384 km2). The spatial sampling revealed that MCPA was widespread, with occurrences above the 0.1 μg L−1 threshold for a single pesticide being highly positively correlated to sub-catchments with higher proportions of ‘Improved Grassland’ land use (r = 0.84). These data provide a strong foundation for targeting catchment-based mitigation solutions and also add to the debate on the ecosystems services provided by such catchments. Additionally, of the 999 temporal samples taken over 12 months from the catchment outlet, 25% were above the drinking water threshold of 0.1 μg L−1. This prevalence of high concentrations presents costly problems for source water treatment. Using these data, abstraction shutdowns were simulated for five scenarios using hydrometeorological data to explore the potential to avoid intake of high MCPA concentrations. The scenarios stopped abstraction for 4.2–9.3% of the April–October period and reduced intake of water containing over 0.1 μg L−1 of MCPA by 16–31%. This represents an important development for real-time proxy assessments for water abstraction in the absence of more direct pesticide monitoring data.