Stream Water Chemistry Research Articles

Spatial variations and controls on the hydrochemistry of surface waters across the Ili-Balkhash Basin, arid Central Asia

Climate variability influences both water quantity and quality in lakes and rivers, e.g., shifts in salinity caused by changes in the evaporation/precipitation ratio. However, knowledge about climate and human influences on water quality in some regions is scarce, which causes uncertainty when evaluating water resources and developing water management plans. We measured the chemical composition and stable isotope values (δD and δ18O) in water samples from the Ili-Balkhash Basin, arid Central Asia, to investigate factors that control hydrologic processes in the area, and explore how the arid environment influences local hydrochemistry and water resources. Isotope values in lake waters (−24.1‰ [δD] and −1.5‰ [δ18O]) are enriched relative to river waters (−84.6‰ [δD] and −12.4‰ [δ18O]), indicating that lake waters experience intense evaporation. In the upstream Ili River, waters with lowest δD and δ18O values are supplied mainly by glacial ice and snow melt, whereas lower reaches of the river are affected increasingly by evaporation and human water extraction. Waters of the Ili River and other small rivers that drain to Lake Balkhash are chemically similar, and of the Ca-HCO3 type. Gibbs diagrams indicate that mineral weathering is the key process that controls river water chemistry. On average, carbonate and silicate weathering contribute 55.1% and 26.7%, respectively, to the total dissolved ion load in the river waters, illustrating the strong control that regional geology exerts on streamwater chemistry. In contrast, lake waters are characterized as Na-Cl type, which results mainly from evaporation and some evaporite dissolution. Weathering in the area is controlled by climate, i.e. precipitation and temperature. Moreover, a negative correlation between lake water total dissolved solids and d-excess, and a systematic increase in chemical concentrations and stable isotope values downstream in the Ili River, reflect the fact that arid climate conditions promote evaporation and affect water quality. PCA analysis and mass balance calculation of water chemistry suggests that humans contribute only 6.6% of the major ion load to waters, which display increasing concentrations in the middle and downstream regions. There, effects of human-mediated weathering and transport of salts from agricultural irrigation are reinforced by higher temperatures and evaporation.

Hydrological, physicochemical and metabolic signatures in groundwater and snowmelt streams in the Japanese Alps

The unique hydrology and physicochemistry of alpine streams provide an important influence on the structure and function of inhabiting biological communities. A substantial body of research exists on alpine streams across many regions of the globe (e.g. Europe, North and South America and Greenland). To date, however, there have been few studies investigating the environmental conditions present in alpine streams across the Japanese archipelago. The lack of information on alpine streams in Japan is problematic as unique regional climates, e.g. some of the highest levels of snowfall globally, are likely to have repercussions for morphological, hydrological, physicochemical and metabolic signatures, causing them to differ from those observed in other regions. In this study we compare the morphology, hydrology, physicochemistry and metabolic activity of snowmelt and groundwater fed streams in the Kamikochi region of the Japanese Alps. Stream discharge, water chemistry (major ions, silica, dissolved oxygen), water temperature and channel stability were measured over a period of 16 months in 2017–2018. Metabolic activity was determined using Resazurin-Resorufin (Raz-Rru) Smart Tracer and variation in the Raz transformation rate was assessed to understand the effects of hydrology and physicochemistry on ecosystem functioning. Snowmelt streams were characterised by higher variability of water temperature, water chemistry and stream discharge, both, within and between sites. Indeed, two of the snowmelt streams experienced no flow conditions for several periods and also floods. In comparison, water chemistry, water temperature and stream discharge in groundwater fed streams were more temporally stable. Metabolic activity was higher in one groundwater fed stream, attributed to significant growth of macrophytes. These findings indicate that the patterns of morphology, hydrology, physicochemistry and metabolic activity across streams in the Japanese Alps largely resemble those identified elsewhere, although there were higher levels of inter-stream variation. The diversity and inter-site variation of hydrological and physicochemical conditions are likely responsible for the unique flora and fauna in the streams. This study therefore indicates the potential importance of habitat templates for the aquatic biodiversity hotspot in this region.

A century of change: Reconstructing the biogeochemical history of Hubbard Brook

AbstractEcosystems constantly adjust to altered biogeochemical inputs, changes in vegetation and climate, and previous physical disturbances. Such disturbances create overlapping ‘biogeochemical legacies’ affecting modern nutrient mass balances. To understand how ‘legacies’ affected watershed‐ecosystem (WEC) biogeochemistry during five decades of studies within the Hubbard Brook Experimental Forest (HBEF), we extended biogeochemical trends and hydrologic fluxes back to 1900 to provide an historical framework for our long‐term studies. This reconstruction showed acid rain peaking at HBEF in the late 1960s‐early 1970s near the beginning of the Hubbard Brook Ecosystem Study (HBES). The long‐term, parabolic arc in acid inputs to HBEF generated a corresponding arc in the ionic strength of stream water, with acid inputs generating increased losses of H+ and soil base cations between 1963 and 1969 and then decreased losses after 1970. Nitrate release after disturbance is coupled with previous N‐deposition and storage, biological uptake, and hydrology. Sulfur was stored in soils from decades of acid deposition but is now nearly depleted. Total exports of base cations from the soil exchange pool represent one of the largest disturbances to forest and associated aquatic ecosystems at the HBEF since the Pleistocene glaciation. Because precipitation inputs of base cations currently are extremely small, such losses can only be replaced through the slow process of mineral weathering. Thus, the chemistry of stream water is extremely dilute and likely to become even more dilute than pre‐Industrial Revolution estimates. The importance of calculating chemical fluxes is clearly demonstrated in reconstruction of acid rain impacts during the pre‐measurement period. The aggregate impact of acid rain on WEC exports is far larger than historical forest harvest effects, and even larger than the most severe deforestation experiment (Watershed 2) at HBEF. A century of acid rain had a calcium stripping impact equivalent to two W2 experiments involving complete deforestation and herbicide applications.

Assessment of Automatically Monitored Water Levels and Water Quality Indicators in Rivers with Different Hydromorphological Conditions and Pollution Levels in Greece

Water resources, especially riverine ecosystems, are globally under qualitative and quantitative degradation due to human-imposed pressures. High-temporal-resolution data obtained from automatic stations can provide insights into the processes that link catchment hydrology and streamwater chemistry. The scope of this paper was to investigate the statistical behavior of high-frequency measurements at sites with known hydromorphological and pollution pressures. For this purpose, hourly time series of water levels and key water quality indicators (temperature, electric conductivity, and dissolved oxygen concentrations) collected from four automatic monitoring stations under different hydromorphological conditions and pollution pressures were statistically elaborated. Based on the results, the hydromorphological conditions and pollution pressures of each station were confirmed to be reflected in the results of the statistical analysis performed. It was proven that the comparative use of the statistics and patterns of the water level and quality high-frequency time series could be used in the interpretation of the current site status as well as allowing the detection of possible changes. This approach can be used as a tool for the definition of thresholds, and will contribute to the design of management and restoration measures for the most impacted areas.

Northern landscapes in transition: Evidence, approach and ways forward using the Krycklan Catchment Study

AbstractImproving our ability to detect changes in terrestrial and aquatic systems is a grand challenge in the environmental sciences. In a world experiencing increasingly rapid rates of climate change and ecosystem transformation, our ability to understand and predict how, when, where, and why changes occur is essential for adapting and mitigating human behaviours. In this context, long‐term field research infrastructures have a fundamentally important role to play. For northern boreal landscapes, the Krycklan Catchment Study (KCS) has supported monitoring and research aimed at revealing these changes since it was initiated in 1980. Early studies focused on forest regeneration and microclimatic conditions, nutrient balances and forest hydrology, which included monitoring climate variables, water balance components, and stream water chemistry. The research infrastructure has expanded over the years to encompass a 6790 ha catchment, which currently includes 11 gauged streams, ca. 1000 soil lysimeters, 150 groundwater wells, >500 permanent forest inventory plots, and a 150 m tall tower (a combined ecosystem‐atmosphere station of the ICOS, Integrated Carbon Observation System) for measurements of atmospheric gas concentrations and biosphere‐atmosphere exchanges of carbon, water, and energy. In addition, the KCS has also been the focus of numerous high resolution multi‐spectral LiDAR measurements and large scale experiments. This large collection of equipment and data generation supports a range of disciplinary studies, but more importantly fosters multi‐, trans‐, and interdisciplinary research opportunities. The KCS attracts a broad collection of scientists, including biogeochemists, ecologists, foresters, geologists, hydrologists, limnologists, soil scientists, and social scientists, all of whom bring their knowledge and experience to the site. The combination of long‐term monitoring, shorter‐term research projects, and large‐scale experiments, including manipulations of climate and various forest management practices, has contributed much to our understanding of boreal landscape functioning, while also supporting the development of models and guidelines for research, policy, and management.

Co-variation of silicate, carbonate and sulfide weathering drives CO2 release with erosion

Global climate is thought to be modulated by the supply of minerals to Earth’s surface. Whereas silicate weathering removes carbon dioxide (CO2) from the atmosphere, weathering of accessory carbonate and sulfide minerals is a geologically relevant source of CO2. Although these weathering pathways commonly operate side by side, we lack quantitative constraints on their co-variation across erosion rate gradients. Here we use stream-water chemistry across an erosion rate gradient of three orders of magnitude in shales and sandstones of southern Taiwan, and find that sulfide and carbonate weathering rates rise with increasing erosion, while silicate weathering rates remain steady. As a result, on timescales shorter than marine sulfide compensation (approximately 106–107 years), weathering in rapidly eroding terrain leads to net CO2 emission rates that are about twice as fast as CO2 sequestration rates in slow-eroding terrain. We propose that these weathering reactions are linked and that sulfuric acid generated from sulfide oxidation boosts carbonate solubility, whereas silicate weathering kinetics remain unaffected, possibly due to efficient buffering of the pH. We expect that these patterns are broadly applicable to many Cenozoic mountain ranges that expose marine metasediments.

Stream Water Chemistry in Mixed-Conifer Headwater Basins: Role of Water Sources, Seasonality, Watershed Characteristics, and Disturbances

Understanding the transport of dissolved organic carbon (DOC) and nitrogen (N) as water flows through headwater basins is important for predicting downstream water quality. With increased recognition of climatic impact on nutrient transport, more studies are needed in headwater basins experiencing a Mediterranean-type climate, such as those of the Sierra Nevada, California. We analyzed water samples collected over 5 years from eight low-order and mixed-conifer watersheds to elucidate the temporal variation of water chemistry and evaluate their responses to prolonged drought and low-intensity forest thinning. We observed higher stream DOC concentrations in October compared to other months within water years prior to drought and thinning, suggesting the importance of antecedent moisture conditions on seasonal C export. In unthinned watersheds, stream DOC concentrations were lower (62%) and DOC aromaticity was higher (68 and 92%, depending on the index used) during drought compared to non-drought years. In thinned watersheds during drought years, stream water had higher DOC concentrations (66–94% in three consecutive years following thinning) and dissolved inorganic N (24%, in the third year following thinning) compared to unthinned watersheds during drought. Additionally, lower stream DOC concentrations were found in watersheds with higher elevations and lower drainage densities in the year with near-average precipitation; however, these correlations were not significant in years with greater or extremely low precipitation. Taken together, our results suggest that stream concentrations of DOC and dissolved N in Mediterranean headwater basins are extremely variable over time due to the high temporal climatic variabilities and periodic management practices.

Hydrochemical and stable isotopic characteristics of waters in and around an eutrophic lake—Ooty, Tamil Nadu, India

Ooty Lake, one of the famous tourist destinations in south India, deteriorates due to tourism activities and urbanisation. The present study aims in characterising the quality of lake water (both surface and depth) and groundwater besides addressing its suitability for various purposes by collecting samples during premonsoon, monsoon and post monsoon seasons of the years 2015 to 2017. Collected samples are analysed for physicochemical parameters using potentiometric technique. Major ions, trace metals and stable isotopes are determined by titrimetric, spectroscopy techniques. Statistical analysis involves principal component and cluster analysis with correlation coefficient. Major chemistry of lake water and groundwater exhibits Ca2+Na+HCO3− type and mainly dominated by silicate weathering. Water chemistry and statistical study indicate that chromium, zinc and cobalt in groundwater and lake water are attributed to the dominance of rock weathering. Copper, chromium along with zinc and lead in stream and inlet locations can be attributed to the influence of domestic waste water entering the lake. Phosphorous in the lake is also derived mainly through the domestic waste entering the lake. Water quality and heavy metal pollution indices show unsuitability of lake water for drinking, whereas, ecological risk assessment indicates that water is safe for aquatic life. Sodium absorption ratio, permeability index, residual sodium carbonate and sodium percentage of water samples indicate suitability for agricultural activities. Stable isotopic composition of lake water and groundwater samples shows possible southwest monsoon precipitation as the major source. Ineffective water treatment at inlet and stream water chemistry affects the lake water quality, which could be focussed for enriching quality.

Stream water chemistry changes in response to deforestation of variable origin (case study from the Carpathians, southern Poland)

The purpose of the study was to examine the effects of deforestation of variable origin on the stream water chemistry, with a special focus on the NO3– ion. The research was conducted in 8 small catchments in the Tatra Mountains and 7 small catchments in the Beskid Śląski Mountains (the Carpathians, Poland). Relevant deforestation events occurred in the Beskid Śląski Mountains in the 1980s and 1990s, and were caused by intense acidic atmospheric deposition in the 1970s and 1980s, while tree stands in the Tatra Mountains were damaged abruptly by hurricane-force winds in 2013 and gradually by the bark beetle since the late 1990s.We show the key role of deforestation in the concentration of base cations (Ca2+, Mg2+), base anions (SO42-, HCO3–), and NO3– in stream water in catchments affected by acidic deposition. The lack of forest reduces the release of Ca2+, Mg2+ and HCO3– due to lower weathering rates in deforested areas than in forested areas. The absence of trees capable of absorbing atmospheric SO42- and NO3– in deforested catchments leads to a higher proportion of stream water SO42- and NO3– in the anion total than in forested catchments.The time passed since deforestation and degree of deforestation play a key role in NO3– concentration in stream water. The highest concentrations of NO3– were noted in stream water in freshly and fully hurricane-deforested catchments in the Tatra Mountains. The stream water NO3– concentration was markedly lower in a beetle-deforested catchment where only 40% of the forest had become damaged while the lowest NO3– concentrations were noted in more than 60% forested catchments. The most distinct seasonal changes in NO3– concentrations in stream water and in soils were noted in freshly and fully hurricane-deforested catchments.

Variation in riparian and stream assemblages across the primary succession landscape of Mount St. Helens, U.S.A.

Abstract Although most lotic ecosystems experience frequent and sometimes large disturbances, opportunities are uncommon to study primary succession in streams. Exceptions include new stream channels arising from events such as glacial retreat, volcanism, and catastrophic landslides. In 1980, the eruption and massive landslide at Mount St. Helens (WA, U.S.A.) created an entire landscape with five new catchments undergoing primary succession. We asked if riparian and lotic assemblages at early successional stages (36 years after the eruption) showed predictable change along longitudinal gradients within catchments, and whether assemblages were similar among five replicate catchments. In July 2016, we collected environmental data and characterised riparian, algal, and benthic macroinvertebrate assemblages at 21 stream reaches distributed within and among five neighbouring catchments. We evaluated patterns of richness, abundance, biomass, multivariate taxonomic community structure, and functional traits both longitudinally and among catchments. We found minimal evidence that longitudinal gradients had developed within catchments at 36 years post‐eruption. Increases in diatom and macroinvertebrate richness with downstream distance were the only biological responses with longitudinal trends. Conversely, we documented substantial variation in community structure of riparian plants, soft‐bodied algae, diatoms, and macroinvertebrates at the among‐catchment scale. Among‐catchment differences consistently separated two eastern catchments from three western catchments, and these two groups also differed in stream water chemistry, water temperature, and geomorphology. Overall, we documented greater diversity in the young catchments than predicted by ecologists in the years immediately following the eruption, yet functional traits indicate that these catchments are still in relatively early stages of succession. Variation at the among‐catchment scale is likely to be driven in part by hydrological source variation, with the two eastern catchments showing environmental signatures associated with glacial ice‐melt and the three western catchments probably fed primarily by springs from groundwater aquifers. Contemporary flow disturbance regimes also varied among catchments and successional trajectories were probably reset repeatedly in streams experiencing more frequent disturbance. Similar to new stream channels formed following glacial retreat, our results support a tolerance model of succession in streams. However, contrasting abiotic templates among Mount St. Helens catchments appear to be driving different successional trajectories of riparian plant, algal, and macroinvertebrate assemblages among neighbouring small catchments sharing the same catastrophic disturbance history.

Long‐term hydrological, biogeochemical, and climatological data from Walker Branch Watershed, East Tennessee, USA

AbstractIn 1967, the original Walker Branch Watershed (WBW) project was established to study elemental cycling and mass balances in a relatively unimpacted watershed. Over the next 50+ years, findings from additional experimental studies and long‐term observations on WBW advanced understanding of catchment hydrology, biogeochemistry, and ecology and established WBW as a seminal site for catchment science. The 97.5‐ha WBW is located in East Tennessee, USA, on the U.S. Department of Energy's Oak Ridge Reservation. Vegetation on the watershed is characteristic of an eastern deciduous, second‐growth forest. The watershed is divided into two subcatchments: the West Fork (38.4 ha) and the East Fork (59.1 ha). Headwater streams draining these subcatchments are fed by multiple springs, and thus flow is perennial. Stream water is high in base cations due to weathering of dolomite bedrock and nutrient concentrations are low. Long‐term observations of climate, hydrology, and biogeochemistry include daily (1969–2014) and 15‐min (1994–2014) stream discharge and annual runoff (1969–2014); hourly, daily, and annual rainfall (1969–2012); daily climate and soil temperature (1993–2010); and weekly stream water chemistry (1989–2013). These long‐term datasets are publicly available on the WBW website (https://walkerbranch.ornl.gov/long‐term‐data/). While collection of these data has ceased, related long‐term measurements continue through the National Ecological Observatory Network (NEON), where WBW is the core terrestrial and aquatic site in the Appalachian and Cumberland Plateau region (NEON's Domain 7) of the United States. These long‐term datasets have been and will continue to be important in evaluating the influence of climatic and environmental drivers on catchment processes.

Sensors track mobilization of ‘chemical cocktails’ in streams impacted by road salts in the Chesapeake Bay watershed

Increasing trends in base cations, pH, and salinity of freshwaters have been documented in US streams over 50 years. These patterns, collectively known as freshwater salinization syndrome (FSS), are driven by multiple processes, including applications of road salt and human-accelerated weathering of impervious surfaces, reductions in acid rain, and other anthropogenic legacies of change. FSS mobilizes chemical cocktails of distinct elemental mixtures via ion exchange, and other biogeochemical processes. We analyzed impacts of FSS on streamwater chemistry across five urban watersheds in the Baltimore-Washington, USA metropolitan region. Through combined grab-sampling and high-frequency monitoring by USGS sensors, regression relationships were developed among specific conductance and major ion and trace metal concentrations. These linear relationships were statistically significant in most of the urban streams (e.g. R 2 = 0.62 and 0.43 for Mn and Cu, respectively), and showed that specific conductance could be used as a proxy to predict concentrations of major ions and trace metals. Major ions and trace metals analyzed via linear regression and principal component analysis showed co-mobilization (i.e. correlations among combinations of specific conductance (SC), Mn, Cu, Sr2+, and all base cations during certain times of year and hydrologic conditions). Co-mobilization of metals and base cations was strongest during peak snow events but could continue over 24 h after SC peaked, suggesting ongoing cation exchange in soils and stream sediments. Mn and Cu concentrations predicted from SC as a proxy indicated acceptable goodness of fit for predicted vs. observed values (Nash–Sutcliffe efficiency > 0.28). Metals concentrations remained elevated for days after SC decreased following snowstorms, suggesting lag times and continued mobilization after road salt use. High-frequency sensor monitoring and proxies associated with FSS may help better predict contaminant pulses and contaminant exceedances in response to salinization and impacts on aquatic life, infrastructure, and drinking water.

Simulation of the effects of forest harvesting under changing climate to inform long-term sustainable forest management using a biogeochemical model

Process ecosystem models are useful tools to provide insight on complex, dynamic ecological systems, and their response to disturbances. The biogeochemical model PnET-BGC was modified and tested using field observations from an experimentally whole-tree harvested northern hardwood watershed (W5) at the Hubbard Brook Experimental Forest (HBEF), New Hampshire, USA. In this study, the confirmed model was used as a heuristic tool to investigate long-term changes in hydrology, biomass accumulation, and soil solution and stream water chemistry for three different watershed cutting intensities (40%, 60%, 80%) and three rotation lengths (30, 60, 90 years) under both constant (current climate) and changing (MIROC5-RCP4.5) future climate scenarios and atmospheric CO2 through the year 2200. For the no future cutting scenario, total ecosystem stored carbon (i.e., sum of aboveground biomass, woody debris and soil) reached a maximum value of 207 t C ha−1 under constant climate but increased to 452 t C ha−1 under changing climate in 2200 due to a CO2 fertilization effect. Harvesting of trees decreased total ecosystem stored carbon between 7 and 36% for constant climate and 7–60% under changing climate, respectively, with greater reductions for shorter logging rotation lengths and greater watershed cutting intensities. Harvesting under climate change resulted in noticeable losses of soil organic matter (12–56%) coinciding with loss of soil nutrients primarily due to higher rates of soil mineralization associated with increases in temperature, compared with constant climate conditions (3–22%). Cumulative stream leaching of nitrate under climate change (181–513 kg N ha−1) exceeded constant climate values (139–391 kg N ha−1) for the various cutting regimes. Under both climate conditions the model projected greater sensitivity to varying the length of cutting period than cutting intensities. Hypothetical model simulations highlight future challenges in maintaining long-term productivity of managed forests under changing climate due to a potential for a deterioration of soil fertility.

Transboundary air pollution reduction rapidly reflected in stream water chemistry in forested catchment on the sea of Japan coast in central Japan

Since the 1980s, Japan has been affected by transboundary air pollution from the Asian continent due to northwesterly seasonal winds in the winter. However, after peaks in 2006 and 2011/2012, sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions began decreasing, respectively. To assess the biogeochemical response of forest ecosystems to the changing atmospheric deposition, flux observations of rainfall outside forest canopies (RF), throughfall and stemflow (TF + SF), and stream water (SW) chemistry were conducted in a Japanese cedar plantation in Kajikawa (KJK) on the Sea of Japan coast in central Japan. Fluxes of S and N by RF and TF + SF at KJK significantly decreased during the observation period (2002–2018). The non-sea salt sulfate (SO42−) flux by TF + SF peaked in 2006/2007 and decreased thereafter, which likely reflected the S emission trends. Accordingly, SO42− concentrations in SW at KJK decreased with increasing alkalinity. Similar decreases in SO42− concentrations beginning in 2006, 2007, and 2008 were observed at eight monitoring lakes in Japan. Thus, the SW chemistry at KJK and possibly that of Japanese lakes were sensitive to atmospheric S deposition reductions. However, as of late, the net S export at KJK has been increasing, exhibiting budget discrepancies in 2014/2015 and 2017/2018. Sulfur isotopic analysis suggested that the S deposited from the atmosphere was retained/cycled in the forest before it was gradually discharged into SW. Thus, a slightly weakened reaction of the output due to the internal cycle and residual effects of previous years may have caused the S budget discrepancies. The nitrate (NO3−) concentration in the SW at KJK has also been continuously increasing. N deposition and other factors, such as the maturation of the planted trees, may play an important role in NO3− leaching in plantations.

Circulation patterns of biogenic ions in Young Glacial areas.

The paper focuses on the effect of ponds (geographically isolated wetlands) on water quality within internally drained areas in a river catchment. The important part of the study was the point of formation of a periodic hydrographic network of internally drained areas linked with a main river as well as the identification of the circulation pattern of ions in such a system. The aim of the study was to examine the extent to which ponds pollute the main river upon physical connection with it. Research has shown that ponds participate actively in material circulation-including that of water and biogenic ions. The hydrographic network in Young Glacial areas is subject to very large seasonal changes. In the study area, the total length of the stream network in the dry season equaled 12 km, while in the wet season almost 75 km. At the same time, almost 50% of the internally drained areas in the catchment became connected with the surface runoff network. Such large seasonal changes in the hydrographic network yield large changes in stream water chemistry. In the study area, only 6 ponds were linked to the stream network during the dry season, while in the wet season, this number increased to 125. The parts of catchments featuring the largest changes in the hydrographic network as well as the largest number of ponds temporarily linked with surface runoff networks were characterized by a high content of total nitrogen and phosphorus-up to 244.2 kg N km2 per month and 26.2 kg P km2 per month.

Implication of Landscape Evolution Since the Middle of the 20th Century for Soil Pco2 and Stream Water Chemistry in a Karst Catchment (Pyrenees, Sw France)

Implication of Landscape Evolution Since the Middle of the 20th Century for Soil Pco2 and Stream Water Chemistry in a Karst Catchment (Pyrenees, Sw France)

Critical Shifts in Trace Metal Transport and Remediation Performance under Future Low River Flows.

Exceptionally low river flows are predicted to become more frequent and more severe across many global regions as a consequence of climate change. Investigations of trace metal transport dynamics across streamflows reveal stark changes in water chemistry, metal transformation processes, and remediation effectiveness under exceptionally low-flow conditions. High spatial resolution hydrological and water quality datasets indicate that metal-rich groundwater will exert a greater control on stream water chemistry and metal concentrations because of climate change. This is because the proportion of stream water sourced from mined areas and mineralized strata will increase under predicted future low-flow scenarios (from 25% under Q45 flow to 66% under Q99 flow in this study). However, mineral speciation modelling indicates that changes in stream pH and hydraulic conditions at low flow will decrease aqueous metal transport and increase sediment metal concentrations by enhancing metal sorption directly to streambed sediments. Solute transport modelling further demonstrates how increases in the importance of metal-rich diffuse groundwater sources at low flow could minimize the benefits of point source metal contamination treatment. Understanding metal transport dynamics under exceptionally low flows, as well as under high flows, is crucial to evaluate ecosystem service provision and remediation effectiveness in watersheds under future climate change scenarios.

Role of forests in headwater control with changing environment and society

Forest practices in headwater catchments are related to environmental and social contexts. The aim of this study is to analyse the changing protective functions of forests in the upper plain of the Jizera Mts. (North Bohemia, Czech Republic) since the second half of the 19th century. With time, forests have gradually changed from native stands to spruce plantations (Picea abies), introducing exotic conifers (more resistant to air pollution), and, recently, back to more diverse mixed stands. The priority in protective forest functions there shifted from flood protection to integrated control of water resources (quantity and quality). In the 1980s, forest – water interactions were degraded by consequences of extreme acid atmospheric deposition, forest die-back, and extensive clear-cut. In the Jizerka catchment, first signs of recovery were observed in the early 1990s, but, stream waters there are still affected by prolonged acidification. While reconstruction of stream water chemistry at Jizerka follows the drop of the acid deposition in some 5 years, the revival of stream biota takes 10–15 years. In 2071–2100, the projected climate change shows rising annual air temperatures by 3.0–4.6 °C, decreasing water yield by 65–123 mm, 60% drop in ‘minimum residual discharge’, and 20–30% rise in peak-flows. However, these projected environmental changes cannot substantially decline the high potential in water resource recharge, or, start reverse processes in recent recovery from acidification and radically affect the existence of planned mixed forests in the upper plain of the Jizera Mts.

Assessing mining impacts: The influence of background geochemical conditions on diatom and macroinvertebrate communities in subarctic streams

Mining has changed landscapes locally in northern Fennoscandia and there is an increasing pressure for exploitation of the remaining mineral deposits of the region. Mineral deposits, even if unmined, can strongly influence stream water chemistry, stream biological communities and the ability of organisms to tolerate stressors. Using data sampled from six mining areas with three active (gold and chrome), two closed (gold) and one planned mine (phosphate), we examined how mineral deposits and mining influence water chemistry and diatom and macroinvertebrate communities in subarctic streams in Finnish Lapland. We supplemented the data by additional samples compiled from databases and further assessed how variation in background geological conditions influences bioassessments of the impacts arising from mining. We found that water specific conductivity was elevated in our study streams draining through catchments with a high mineral potential. Mining effects were mainly seen as increased concentration of nitrogen. Influence of mineral deposits was detected in composition of diatom and macroinvertebrate communities, but communities in streams in areas with a high mineral potential were as diverse as those in streams in areas with a low mineral potential. Mining impacts were better detected for diatoms using a reference condition based on sites with a high than low mineral potential, while for macroinvertebrates, the responses were generally less evident, likely because of only minor effects of mining on water chemistry. Community composition and frequencies of occurrence of macroinvertebrate taxa were, however, highly similar between mine-influenced streams and reference streams with a high potential for minerals indicating that the communities are strongly structured by the natural influence of mineral deposits. Incorporating geochemistry into the reference condition would likely improve bioassessments of both taxonomic groups. Replicated monitoring in potentially impacted sites and reference sites would be the most efficient framework for detecting environmental impacts in streams draining through mineral-rich catchments.

Geochemical processes influencing stream water chemistry: a case study of Ala River, Akure, Southwestern Nigeria

Ala River is the main river that drains Akure metropolis in southwestern Nigeria. The river takes its sources from deep-seated fractures in granite and charnockite rock bodies at the North and North-western regions of Akure town, flowing through quartzite and granite gneiss exposures. This study was carried out to assess the geochemical processes influencing the quality of Ala river water. The dendritic river system, covering an area of about 427 km2, was studied and water was sampled at thirty-seven (37) points for in-situ determination of some physicochemical parameters and dissolved concentrations of the major ions. pH values obtained varied between 7.16 and 7.75, electrical conductivity ranged from 123 to 520 µs/cm, total dissolved solids varied between 62 and 260 mg/l-CaCO3 while average temperature value was 26.65 °C. Relative concentration of cations and anions were in the order of Ca2+ > Mg2+ > Na+ > K+ and HCO3− > SO42− > Cl− > NO3−. Mean values of dissolved Na+, K+, Ca2+, Mg2+, Fe2+, Cl−, HCO3−, SO42−, NO3−, and PO42− were 34.028, 8.872, 34.175, 18.289, 0.428, 16.543, 56.41, 12.503, 0.495 and 2.029 mg/l, respectively. Two hydochemical facies namely Calcium-Bicarbonate facies and mixed calcium–magnesium–chloride facies dominated the chemistry of the water. CaHCO3 facies revealed the contribution of geogenic processes while the mixed Ca(Mg)-Cl type reflected domestically induced anthropogenic activities influencing chemistry of the water. Gibbs diagrams identified rock–water interaction as an important geochemical process in the study area. Silicate weathering of rocks and carbonate weathering were identified as the important geochemical processes which influence the water chemistry of the study area.