Changes In River Water Quality Research Articles

Distribution and Characteristic Sediment Material of Watershed Deli River-Sumatera, Indonesia

Rivers are a source of surface water and bring benefits to human life. River water quality changes along with the development of the river environment which is influenced by various activities and human life. Deli River is one of the rivers used by the people of Medan-North Sumatra as a provider of clean water and various other daily activities and is also used as a transportation route for fishermen. This study aims to determine the flooding conditions that often occur in the Deli River, this is caused by the shallowness and narrowness of the river body. In this study, the quantitative method was taking sediment samples at several points along the river starting from upstream, middle, and downstream with research time on 7 July 2023. The results obtained from this study were river sediment material along the Deli River from upstream to downstream generally has a grain size of 65% sand, a grain size of 26% clay, a grain size of silt 6.3%, and a grain size of gravel 3.7%. The upstream sediments are dominated by sand-sized sediments and in the middle (between the upstream and downstream) the sediments are dominated by clay-sand-sized sediments, while the downstream sediments are predominantly sandy loam. The flooding of the Deli River is caused by the reduced capacity of the river, high intensity of rainfall in the upper reaches, and narrowing of the river and high sediment deposits in the middle to lower reaches so flooding often occurs along the Deli River.

Kajian Dampak Penambangan Pasir Terhadap Kualitas Air Sungai Untuk Irigasi di Indonesia

The high demand for sand as a material is in line with the increase in sand mining activities. The main sand mining location commonly takes place in rivers. Even though rivers are also used as the main source for agricultural irrigation. The sand mining activities could affect river water quality, which could also impact irrigation on plant growth and crop yields. This review aimed to analyze the impact of sand mining in several locations in Indonesia on river water quality for irrigation. The data collection method was carried out by searching for articles according to the topic on Google Scholar using several predetermined keywords. Analysis and review were carried out through several stages and 6 articles were obtained according to the topic. Sand mining activities in rivers are frequently carried out using manual and mechanical techniques. The use of manual techniques in mining can have an impact on river morphology as well as the physical and chemical quality of river water. Mechanical techniques have a greater impact on changes in river water quality, where most mining is carried out using manual techniques. Therefore, the sand mining with mechanical techniques, especially using excavators, can have a higher impact on the quality of river water for irrigation.

Efficacy of point source legislation quantified for a 64-year river water quality trajectory of phosphorus loading

Changes in river water quality often follow typical trajectories characterized by sequential phases of degradation and recovery induced by management measures, typically achieved with combinations of legislative and technological interventions. However, the key question about the effectiveness of the different types of legal interventions – source control, use-related, and end-of-pipe – remains poorly understood. With the case of phosphorus (P), which is a valuable indicator of surface water quality and a widespread target of legislation at various governance levels in order to control eutrophication of water bodies, we quantified the relation between point source loading of P and resulting river water quality for a multidecadal trajectory of the river Ruhr (Germany). In particular, we analysed P-related legislation targeting point source pollution enforced at EU, national, state, and local level and linked their development with measured total phosphorus (TP) concentrations in the river Ruhr (Germany). To this end, we combined archival data with information in the literature and conducted interviews with contemporary witnesses to describe and quantify the efficacy of each legislative approach. Although not specifically targeted at P reduction, end-of-pipe measures (sewer systems and wastewater treatment plants (WWTP)) reduced TP inputs to surface waters already in the 1960s and 1970s, curbing TP inputs to the Ruhr by 38% in 1980. The first targeted source control legislation – the banning of phosphates in textile detergents in 1981 – effectively reduced TP concentrations in WWTP influents by 36% since 1990. In combination with stronger end-of-pipe legislation focusing on P elimination in WWTP since the 1990s, TP concentrations in WWTP effluents were reduced by 86% at the end of the 1990s and by 92% in 2021. Complete and successful source control for textile detergents made use-related legislation redundant. Our study demonstrates that source control measures should be prioritized, because they are the fastest way to curb emissions. These findings provide insights that can inform efficient decision-making regarding water quality in a trajectory perspective of hierarchical governance and technological needs, as well as effective policy-making and management for other pollutants requiring control from point sources.

Nitrogen and Phosphorus Pollution Discharge and Water Quality Evaluation in a Small Basin of the Upper Reaches of Lijiang River

The Lijiang River Basin is a humid, subtropical, karst landform in China and is listed as a World Heritage Site. However, with the rapid development of urbanization and tourism activities in recent years, it faces increasingly severe non-point source pollution. To understand the temporal and spatial variations in nitrogen and phosphorus pollution discharge and the changes in river water quality, the Jingui Small Basin, in the upper reaches of the Lijiang River, was chosen as a representative system. Changes in nitrogen and phosphorus concentrations were continuously monitored in the main river channel and the river water quality was evaluated using the comprehensive water quality identification index method. The results indicated that there were obvious seasonal changes in nitrogen and phosphorus discharge loads in the basin. Both nitrogen and phosphorus discharge loads were higher in the crop-growing season than in the non-growing season. No significant difference in nitrogen and phosphorus discharge load between different scales was found, and the scale was not the key factor affecting the nitrogen and phosphorus discharge load of Jingui River. As the river flowed from the initial water source to the outlet of the basin, water quality was characterized by the spatial pattern of the upper reaches > the middle reaches > the lower reaches. Except for the water quality at the outlet of the basin in November and December, which reached Class V, the comprehensive water quality of each sub-basin reached the target water quality of the water function zoning from May to December. The elucidation of the nitrogen and phosphorus pollution discharge patterns in the Jingui River and the changes in water quality provide a reference for the control and management of agricultural non-point source pollution in the Lijiang River Basin.

Lake Kivu River Tributaries Physicochemical Characteristics and Status of Waters, Democratic Republic of Congo Side

Rivers often play a vital role in the transport of major natural chemicals entering through a variety of pathways, including atmospheric inputs, chemical weathering of minerals, mechanical erosion of rocks and soil particles, and soil leaching. Increased anthropogenic activities on the shoreline of Lake Kivu combined with existing land use practices may increase changes in river water quality and composition. Knowing the physico-chemical and biological contribution of each tributary of the lake is vital for the management of its biodiversity. This study aimed at determining the physico-chemical characteristics, water quality indices and identifying the polluted tributary rivers that feed Lake Kivu on the Congo side. The physicochemical characteristics were determined for each water sample following water quantity protocol for each analysis at the Malacology Laboratory of the Biology Department of Lwiro Research Center. Two pollution level indices were used to determine the level of organic pollution in watercourses. The physico-chemical characteristics of rivers vary from one river to another depending on the anthropogenic activities around the different sub-basins of these rivers. The state of the rivers presented here reveals that the majority of them are moderately polluted and others slightly polluted. No rivers were very heavily polluted or good in the Lake Kivu basin on the DR Congo side. There is a strong or moderate correlation between certain parameters and the water quality indices used in this study (LISEC and OPI). Due to increase in anthropogenic activities near watercourses, further research is needed and the combination of several complex analytical methods should be used in the future to better characterize these waters.

Effects of land-use patterns on seasonal water quality at multiple spatial scales in the Jialing River, Chongqing, China

Land-use patterns usually impact river water quality as non-point pollution sources at both spatial and seasonal scales, which can provide important guidance for water pollution control and land-use planning after quantitative analysis. Here, surface water samples were collected from ten sampling points in the Chongqing Section of the Jialing River to monitor the physicochemical parameters of river water from March 2021 to February 2022. Our results showed significant seasonal changes in river water quality based on higher concentrations of dissolved oxygen (DO), ammonium nitrogen (NH 4+-N), and nitrate nitrogen (NO3–-N) in the wet season than those in the dry season, while the concentrations of chemical oxygen demand (CODcr) and total nitrogen (TN) in the dry season are higher than those in the wet season. Redundancy analysis (RDA) for elucidating the relationship between land-use patterns and river water quality parameters at multiple spatial (reach and riparian scale) and seasonal scales (dry and wet season) shows that water quality indices exhibited a strong positive correlation with construction land and farmland, inducing a negative impact on river water quality; while forest and grassland were inversely correlated to water quality indices, causing a positive effect on river water quality. On a seasonal scale, the land-use pattern showed more association with river water quality parameters in the wet season, compared to that in the dry season. The impact of the different buffer zones associated with land-use types on the river water quality was in the following order: 2000 > 500 ≈ 1000 m buffer. These findings contribute to sustainable land-use development and multi-scale landscape optimization to improve water quality in the Chongqing Section of the Jialing River.

Application of hybrid improved temporal convolution network model in time series prediction of river water quality

Time series prediction of river water quality is an important method to grasp the changes of river water quality and protect the river water environment. However, due to the time series data of river water quality have strong periodicity, seasonality and nonlinearity, which seriously affects the accuracy of river water quality prediction. In this paper, a new hybrid deep neural network model is proposed for river water quality prediction, which is integrated with Savitaky-Golay (SG) filter, STL time series decomposition method, Self-attention mechanism, and Temporal Convolutional Network (TCN). The SG filter can effectively remove the noise in the time series data of river water quality, and the STL technology can decompose the time series data into trend, seasonal and residual series. The decomposed trend series and residual series are input into the model combining the Self-attention mechanism and TCN respectively for training and prediction. In order to verify the proposed model, this study uses opensource water quality data and private water quality data to conduct experiments, and compares with other water quality prediction models. The experimental results show that our method achieves the best prediction results in the water quality data of two different rivers.

Landscape Patterns and Topographic Features Affect Seasonal River Water Quality at Catchment and Buffer Scales

Effects of landscape patterns or topographic features on the river water environment have been broadly studied to control non-point source (NPS) pollution and to cut off potential pathways for pollutants to affect human health. However, spatio-temporal dynamics and scale effects with respect to the impact of landscape patterns and topographic features on the aquatic environment over successive years have not been elucidated. In this study, water quality parameters and land cover data for three consecutive years mainly in Tangshan City, located in the northeast of the Haihe River Basin, China, were obtained to determine the associations between landscape patterns and topographic features with the water environment. Results indicated that seasonal differences in dissolved oxygen (DO) and total nitrogen (TN) were significant (p < 0.001), and spatial variation was generally observed for each water quality parameter. Redundancy analysis revealed that landscape patterns and topographic features have different impacts on the aquatic environment as seasonal spans and spatial scales change. Overall, the best explanatory variables explained an average of 58.6% of the variation in water quality at various spatial scales over the two seasons. Topographic features made a greater contribution to river water quality changes at the buffer scale; conversely, at the catchment scale, water quality changes stemmed primarily from differences in landscape composition and configuration. The landscape shape index of cropland (LSIcrop) was an important factor influencing seasonal river water quality changes at various spatial scales. These results suggest that considering landscape connectivity at distinct spatial scales could enhance the understanding of the alteration of hydrological processes across multiple topographic features, which in turn has an impact on seasonal river water.

Changes in River Water Quality for 30 Years in a Watershed Characterized by Population Decline

Changes in River Water Quality for 30 Years in a Watershed Characterized by Population Decline

Assessing the changes in river water quality across a land-use change (forest to oil palm plantation) in peninsular Malaysia using the stable isotopes of water and nitrate

Land conversion from natural forests to plantations (e.g., oil palm) in Southeast Asia is one of the most intensive land-use changes occurring worldwide. To clarify the effects of oil palm plantations on water quality, we conducted multipoint river and stream water sampling in peninsular Malaysia at the end of the rainy season over a 3-year period (2013–2015). We measured the major dissolved ions and stable isotope ratios of water (δ2H-H2O and δ18O-H2O) and nitrate (δ15N-NO3− and δ18O-NO3−) in water from the upper streams in mountainous forests to the midstream areas of two major rivers in peninsular Malaysia. The electrical conductivity increased, and the d-excess value (as an index of the degree of evaporation) decreased with increasing distance from the headwaters, suggesting the effect of evaporative enrichment and the addition of pollutants. We separated the sampling points into four groups (G1–G4) through cluster analysis of the water quality data. From the land use/land cover (LULC) classification maps developed from satellite images and local information, we found that G1 and G2 mainly consisted of sampling points in forested areas, while G3 and G4 were located in oil-palm-affected areas. The concentrations of major ions were higher in the oil palm areas, indicating the effects of fertilizer and limestone (i.e., pH adjustment) applications. The dissolved inorganic nitrogen concentration did not differ among the groups, but the dissolved organic carbon, total dissolved nitrogen, and δ15N-NO3− were higher in the oil palm area than in the forested area. Although the nitrogen concentration was low, even in the oil palm area, the significantly higher δ15N-NO3− in the oil palm area indicated substantial denitrification. This implies that denitrification contributed to the lowering of the NO3− concentration in rivers in the oil palm area, in addition to nutrient uptake by oil palm trees.

Detecting and explaining long‐term changes in river water quality in south‐eastern Australia

AbstractUnderstanding the temporal changes in river water quality is important for catchment water quality management. This study aims to detect and attribute long‐term trends and abrupt changes in river water quality. We used 26 years of water quality data (1994–2020) collected from 102 river monitoring sites across Victoria, south‐eastern Australia. We analysed six water quality constituents that are of key concerns for Australian catchment management, namely: electrical conductivity (EC), total suspended solids, nitrate‐nitrite, total Kjeldahl nitrogen, total phosphorous and filtered reactive phosphorus. To detect trends and abrupt changes in water quality at each site, a Bayesian ensemble modelling approach was applied, namely, the Bayesian estimator of abrupt change, seasonal change, and trend (BEAST). To explain water quality trends, we then built multivariate regressions to link water quality with streamflow and seasonality, and then compared alternative model structures with and without a change in the regression relationships informed by the changes detected by BEAST. Among the six constituents studied, EC shows the most distinct systematic trends, with 21 sites having a significant increase followed by a non‐significant trend; within the 21 sites, 14 had a significant change point in EC around Year 2010. The regression analyses between water quality and streamflow suggested that the observed systematic change in EC could be largely related to reduced streamflow during the Millennium drought, which greatly impacted the climate and hydrology of south‐eastern Australia over the first decade of 2000. The results of this study can help inform the design of effective mitigation strategies and avoid further degradation of water quality across Victoria. Besides, our trend analysis and attribution approaches are applicable to water quality time series in other regions for robust trend analysis and change point detection.

Analysis of Changes in River Water Quality Due to Weir Installation

There has been an increase in the amount of pollutants such as biochemical water and factory wastewater discharged from urban areas as a result of urbanization and industrialization. Therefore, research on securing water resources and improving water quality in rivers around cities is being actively conducted. This study analyzed the pattern of change of water quality due to the installation of overflow type weirs among the hand structures in the existing river. The target watershed was performed at Gilancheon, located in Andong-si, Gyeongsangbuk-do. The flow coefficient was calculated by analyzing the flow velocity and water level according to weir installation using the HEC-RAS. Afterwards, the QUALKO model was built, and the water quality analysis according to weir installation was performed by applying the flow coefficient calculated using HEC-RAS. As a result of the analysis, the flow rate was found to have decreased, and a stagnation section occurred due to the influence of weir installation, resulting in an increase in Chl-a. Due to the increase of Chl-a, BOD increased by 29%-32%, and T-N and T-P, which are nutrients for Chl-a, decreased. Therefore, an increase in Chl-a concentration due to weir installation can cause eutrophication due to the growth of green algae in the river, and it is believed that it can greatly affect the deterioration of water quality. Furthermore, it is considered that it will be able to help predict changes in water quality for the installation and operation of weirs in the future.

Analysing the change in water quality parameters along river Ganga at Varanasi, Mirzapur and Ghazipur using Sentinel-2 and Landsat-8 satellite data during pre-lockdown, lockdown and post-lockdown associated with COVID-19

The proper functioning of the river ecosystem has been symbolised by healthy aquatic life. The river Ganga has shown signs of rejuvenation due to lockdown. In this study, an attempt has been made to analyse the change in river water quality using Sentinel-2 and Landsat-8 imageries. The quantitative analysis has been performed for temperature and normalised difference turbidity index (NDTI). The qualitative analysis has been performed for pH, dissolved oxygen (DO) and total suspended solids (TSSs). Ghazipur, Varanasi and Mirzapur stretches have been selected for this study. In the Ghazipur stretch, the river temperature decreased by 7.14% in May 2020 (lockdown period) as compared to May 2019 (1 year before lockdown). Similarly, in the Varanasi stretch, this decrease has been by 8.62%, and in the Mirzapur stretch, this decrease has been by 12.06% in May 2020 compared to May 2019. For the same period, NDTI in the Ghazipur, Varanasi and Mirzapur stretch has been decreased by 0.22, 0.26 and 0.24, respectively. The pH and DO of the river increased, and TSS decreased for the considered time period. The lockdown during the second wave of the coronavirus disease 2019 was not helpful for river rejuvenation. This study elicited how the behaviour of the parameters changed during the lockdown.Research highlights River Ganga becomes much cleaner in the lockdown period (May 2020) compared to the pre-lockdown time.In the Mirzapur stretch, the temperature decreased most in May 2020 as compared to May 2019.In the Varanasi stretch, there is a maximum variation in the NDTI value in May 2020 in comparison with that of May 2019.The most significant task will be to maintain river conditions during post-lockdown similar to that prevailed during lockdown.In the second wave COVID-19 lockdown the river again became polluted like the pre-COVID times.

The dynamics of the first wave of COVID-19 on environment and wildlife– a boon or a bane?

Even though COVID-19 has drastically weighed upon the humankind, still there is a “silver lining” to see in this dark time. Amidst of this pandemic, most of the human activities were restricted to break the chain of infection which resulted the remarkable change in nature. It has been reported that due to halt in air travel, reduction in the use of fossil fuels, way less functioning of vehicles, shutdown of industries has complied the change in air pollution levels and also change in river water quality. Reports also showed the reduction in particulate matter (PM 2.5 and PM 10), greenhouse gases emissions, massive improvement in the Air quality index (AQI), reduction in the NOX and SOX’s level has clearly stipulated that nature has got it’s time to “revive”. Even the global carbon emission has reported to reduced reluctantly which is expected to be the biggest such drop since World War II. Despite conducting water-cleansing projects and spending a lot of money, the situation of the water bodies were far better now during first lockdown. Moreover, migration and breeding of the birds and animals have been reported to be restored to normal pattern due to depletion in man-animal conflict. Apart from the positive, negative impacts on the nature are also being experienced. Our review work is highlighting such impacts witnessed during the first wave of COVID-19, like, the significant improvement in air and water quality, reduction in environmental noise, therefore an in turn cleaner and quieter habitat for the wildlife to mate and also to quench their curiosities by their surprising excursions; but there are also some negative aspects as well, like reduction in recycling and the increase in waste, increased poaching and even lone shuttering of zoo animals.

Characterization of produced water and surrounding surface water in the Permian Basin, the United States

A thorough understanding of produced water (PW) quality is critical to advance the knowledge and tools for effective PW management, treatment, risk assessment, and feasibility for beneficial reuse outside the oil and gas industry. This study provides the first step to better understand PW quality to develop beneficial reuse programs that are protective of human health and the environment. In total, 46 PW samples from unconventional operations in the Permian Basin and ten surface water samples from the Pecos River in New Mexico were collected for quantitative target analyses of more than 300 constituents. Water quality analyses of Pecos River samples could provide context and baseline information for the potential discharge and reuse of treated PW in this area. Temporal PW and river water quality changes were monitored for eight months in 2020. PW samples had total dissolved solids (TDS) concentrations ranging from 100,800–201,500 mg/L. Various mineral salts, metals, oil and grease, volatile and semi-volatile organic compounds, radionuclides, ammonia, hydraulic fracturing additives, and per- and polyfluoroalkyl substances were detected at different concentrations. Chemical characterization of organic compounds found in Pecos River water showed no evidence of PW origin. Isometric log-ratio Na-Cl-Br analysis showed the salinity in the Pecos River samples appeared to be linked to an increase in natural shallow brine inputs. This study outlines baseline analytical information to advance PW research by describing PW and surrounding surface water quality in the Permian Basin that will assist in determining management strategies, treatment methods, potential beneficial reuse applications, and potential environmental impacts specific to intended beneficial use of treated PW.

Investigating the relationship between the river flow and dissolved solids concentration

A systematic approach was used on monthly data from three hydrometric stations located on the Gheshlagh River (west of Iran) to investigate the flow–concentration relationship and for river base flow analysis. According to the results of this study, the water quality of the Gheshlagh River has been affected by changes in river flow as well as human activities. Using the analysis of flow–concentration relationships obtained for Khalife Tarkhan station, the higher concentration of dissolved solids in groundwater (with a base flow rate from 0.1 to 0.7 m3/s) rather than surface runoff was estimated. Also, in this station, with the increase of river flow and improvement of river self-purification capacity, water quality parameters showed a decreasing trend compared to the groundwater. In Hossein Abad's upstream station, due to low average river flow and discharge of saline drainage from agricultural lands, an increasing trend in the dissolved solids both for groundwater and surface runoff was shown. The trend of spatial changes in river water quality also indicates the high impact of human activities such as fish farms and wastewater discharge of Sanandaj wastewater treatment plant, on increasing the concentration of dissolved solids in Dareh Kolleh downstream station.

Spatio-temporal distribution and correlation analysis of river water quality in City Center of Pinghu

Based on the historical data of river water quality in the central city of Pinghu from 2014 to 2018, the temporal and spatial distribution of river water quality changes and its influencing factors were analyzed, and the correlation between the main monitoring factors was identified by linear regression. The results show that water quality of the main rivers has improved significantly, and the concentrations of COD, NH3-N and TP in most rivers can reach the class III standard of surface water. In recent years, the water quality of the rivers shows a significant improvement trend, and the improvement effect of NH3-N concentration is the most obvious. The water quality of general rivers tends to improve, but the effect of treatment is relatively insufficient. Spatially, the water quality in the northern part of the flood control area is worse than that in other areas, and the main river is better than the general river. The fitting effect of COD, NH3-N and TP is good, and there is a significant correlation between the main river.

Spatio-temporal trends in the flow and water quality: response of river Yamuna to urbanization.

Urban rivers are major victims of pollution and the river Yamuna is a notable example. Effective human intervention requires an understanding of the water quality response of rivers to urbanization. To this end, the time-series data from the Central Water Commission (CWC) and the Central Pollution Control Board (CPCB) was analyzed. The dataset included 44 parameters for twelve stations on Yamuna mainstream from 1978 to 2015. Statistical tests for analysis of trends revealed decreasing monsoon flows over the past decades. Furthermore, increasing non-monsoon flows from Delhi to Agra was indicative of a significant contribution from wastewater discharge to the river. Groundwater parameters such as electrical conductivity, hardness, and sodium content were found to increase in the river over the years. This suggests the use of groundwater that gets converted into domestic wastewater flowing in surface drains discharging into the river resulting in the deterioration of water quality of river Yamuna. Dissolved oxygen (DO) and ammonical nitrogen values from Delhi to Agra stretch do not support indigenous aquatic life. A positive correlation between total and fecal coliform in this river stretch indicates the dominance of domestic sewage. The expected significant correlation between DO and biochemical oxygen demand (BOD) was not observed throughout the river stretch. High values of DO reported by CPCB indicate the presence of photosynthetic activity in the river; hence diurnal DO measurement is suggested for validation. For the rejuvenation of river Yamuna, the focus of treatment should be shifted to coliform, DO, chemical oxygen demand, and nutrients. The present study analyzed the response of the riverine ecosystem to altered flow regimes and changes in river water quality, and the findings can serve as a basis for decision-makers engaged in river restoration and conservation efforts.

An approach for decomposing river water-quality trends into different flow classes

A number of statistical approaches have been developed to quantify the overall trend in river water quality, but most approaches are not intended for reporting separate trends for different flow conditions. We propose an approach called FN2Q, which is an extension of the flow-normalization (FN) procedure of the well-established WRTDS (“Weighted Regressions on Time, Discharge, and Season”) method. The FN2Q approach provides a daily time series of low-flow and high-flow FN flux estimates that represent the lower and upper half of daily riverflow observations that occurred on each calendar day across the period of record. These daily estimates can be summarized into any time period of interest (e.g., monthly, seasonal, or annual) for quantifying trends. The proposed approach is illustrated with an application to a record of total nitrogen concentration (632 samples) collected between 1985 and 2018 from the South Fork Shenandoah River at Front Royal, Virginia (USA). Results show that the overall FN flux of total nitrogen has declined in the period of 1985–2018, which is mainly attributable to FN flux decline in the low-flow class. Furthermore, the decline in the low-flow class was highly correlated with wastewater effluent loads, indicating that the upgrades of treatment technology at wastewater treatment facilities have likely led to water-quality improvement under low-flow conditions. The high-flow FN flux showed a spike around 2007, which was likely caused by increased delivery of particulate nitrogen associated with sediment transport. The case study demonstrates the utility of the FN2Q approach toward not only characterizing the changes in river water quality but also guiding the direction of additional analysis for capturing the underlying drivers. The FN2Q approach (and the published code) can easily be applied to widely available river monitoring records to quantify water-quality trends under different flow conditions to enhance understanding of river water-quality dynamics.

Seasonal manganese transport in the hyporheic zone of a snowmelt-dominated river (East River, Colorado, USA)

Manganese (Mn) plays a critical role in river-water quality because Mn-oxides serve as sorption sites for contaminant metals. The aim of this study is to understand the seasonal cycling of Mn in an alpine streambed that experiences large spring snowmelt events and the potential responses to changes in snowmelt timing and magnitude. To address this goal, annual variations in river-water/groundwater interaction and Mn(aq) transport were measured and modeled in the bed of East River, Colorado, USA. In observations and numerical models, oxygenated river water containing dissolved organic carbon (DOC) mixes with groundwater rich in Mn(aq) in the streambed. The mixing depth increases during spring snowmelt when river discharge increases, leading to a greater DOC supply to the hyporheic zone and net respiration of Mn-oxides, despite an enhanced supply of oxygen. As groundwater upwelling resumes during the subsequent baseflow period, Mn(aq)-rich groundwater mixes with oxygenated river water, resulting in net accumulation of Mn-oxides until the bed freezes in winter. To explore potential responses of Mn transport to different climate-induced hydrological regimes, three hydrograph scenarios were numerically modeled (historic, low-snow, and storm) for the Rocky Mountain region. In a warming climate, Mn(aq) export to the river decreases, and Mn(aq) oxidation is favored in the upper streambed sediments over more of the year. One important implication is that the streambed may have an increased sorption capacity for metals over more of the year, leading to potential changes in river-water quality.