Stream Water Chemistry Research Articles

Concentration–discharge relationships vary among hydrological events, reflecting differences in event characteristics

Abstract. Studying the response of streamwater chemistry to changes in discharge can provide valuable insights into how catchments store and release water and solutes. Previous studies have determined concentration–discharge (cQ) relationships from long-term, low-frequency data of a wide range of solutes. These analyses, however, provide little insight into the coupling of solute concentrations and flow during individual hydrologic events. Event-scale cQ relationships have rarely been investigated across a wide range of solutes and over extended periods of time, and thus little is known about differences and similarities between event-scale and long-term cQ relationships. Differences between event-scale and long-term cQ behavior may provide useful information about the processes regulating their transport through the landscape. Here we analyze cQ relationships of 14 different solutes, ranging from major ions to trace metals, as well as electrical conductivity, in the Swiss Erlenbach catchment. From a 2-year time series of sub-hourly solute concentration data, we determined 2-year cQ relationships for each solute and compared them to cQ relationships of 30 individual events. The 2-year cQ behavior of groundwater-sourced solutes was representative of their cQ behavior during hydrologic events. Other solutes, however, exhibited very different cQ patterns at the event scale and across 2 consecutive years. This was particularly true for trace metals and atmospheric and/or biologically active solutes, many of which exhibited highly variable cQ behavior from one event to the next. Most of this inter-event variability in cQ behavior could be explained by factors such as catchment wetness, season, event size, input concentrations, and event-water contributions. We present an overview of the processes regulating different groups of solutes, depending on their origin in and pathways through the catchment. Our analysis thus provides insight into controls on solute variations at the hydrologic event scale.

How does climate variability affect water quality dynamics in Canada's oil sands region?

In Canada's oil sands region, classic boreal hydrology (i.e., winter low flow followed by peaks during spring freshet and then summer flow recession) combined with erosion of both natural and anthropogenically-exposed bitumen results in seasonal and inter-annual variability in stream water chemistry. Using data collected from all seasons over three years (2012–2015), we investigated the mechanisms driving spatial and temporal change in the concentration of 26 water quality parameters for six rivers draining Canada's oil sands region. Mantel tests showed a strong spatial aggregation of climatic drivers (average daily precipitation, accumulated precipitation, snow water equivalent) associated with west versus east discharge patterns. Wavelet analysis highlighted unique watershed attributes, in particular the importance of developed area in lowering responsiveness to seasonal precipitation. Concentrations of most chemical parameters (20 of 23) showed distinct temporal patterns that were correlated with seasonal changes in hydrology which, in turn, were related to changes in weather. Comparison of concentrations observed in this study with those reported in the scientific literature for the same watersheds showed 81% of comparisons differed significantly. This was likely due to the short duration of previous field campaigns and thus the sampling of a very narrow window of the annual streamflow regime.

Stream water quality in relation to watershed‐scale practical forest management in a cool‐temperate natural forest in northern Japan

AbstractThe water chemistry of a stream reflects the biogeochemical processes occurring in upstream forests. Anthropogenic disturbances in forests, such as cutting trees, altering the nitrogen (N) cycle, and increase in N leaching from the soil to streams, potentially cause acidification or eutrophication downstream. In forests with dense understory vegetation, mechanical site preparation following tree cutting is commonly used to improve the early establishment of tree seedlings. In cool‐temperate forests in northern Hokkaido, Japan, dense understory vegetation (mainly comprising Sasa dwarf bamboo) inhibits forest regeneration after tree cutting. Soil scarification is a common site preparation technique for eliminating Sasa bamboo and improving forest regeneration. Long‐term data are useful for examining the temporal changes in stream water chemistry exposed to different specific forest management practices under changing environment (e.g., climate change and atmospheric N deposition). For 14 years (2003–2016), we observed the stream water chemistry in naturally forested watersheds and at one point after the confluence of all streams in Uryu Experimental Forest of Hokkaido University (North Hokkaido Experimental Forests Site of JaLTER) in northern Japan. We also monitored stream discharge, water level and stream water temperature in each watershed. Water samples were collected from the outlets of 10 watersheds. The forest management practice in each watershed includes clear‐cutting, soil scarification in sparse forest with dense understory Sasa, and clear‐cutting and soil scarification followed by soil replacement. Long‐term data in the six unmanaged watersheds are also valuable as a background information to analyze the effect of long‐term climate, environment and vegetation changes on stream water chemistry. The measured water quality data of 1,873 water samples include the ion concentrations (Cl−, NO3−, SO42−, Na+, NH4+, K+, Mg2+, and Ca2+), pH, and electrical conductivity (EC) in the stream water. The range of the concentrations of Cl−, NO3−, SO42−, Mg2+, and Ca2+ in the stream water across all the watersheds throughout the observed periods (minimum to maximum) were 3.35–23.67, 0.01–8.68, 0.83–4.01, 0.45–2.55 and 0.72–6.16 mg L−1, respectively. Similarly, the stream pH and EC ranged from 6.04 to 7.53 and 3.14 to 9.47 mS m−1, respectively.The complete data set for this abstract published in the Data Paper section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/datapaper%202020‐04.1/jalter‐en. [Correction added on 7 September 2020, after first online publication: JaLTER URL has been updated.]

Riparian land use and stream habitat regulate water quality

Riparian land use is a key driver of stream ecosystem processes but its effects on water quality are still a matter of debate when proposing measures to improve freshwater quality. The aim of this study was to examine the influence of riparian land use on stream habitat and water chemistry, and to assess in what extent stream habitat also affects water quality. To that end, we selected eight reaches in the Ave River basin (northwestern Portugal) and compared longitudinal variations in water chemistry and stream habitat between reaches with different land use (urban, agricultural and natural), and between reaches with natural riparian areas and different habitats. Stream habitat was assessed using the Fluvial Functional Index, the HABSCORE, and the Riparian Forest Quality Index. Longitudinal variations in water chemistry were determined measuring differences in concentrations of ammonium, nitrate, phosphate and oxygen, and conductivity, pH and temperature between the downstream and the upstream ends of each reach. Nitrate concentration tended to decrease along reaches with more natural riparian areas and to increase along reaches with more urban and agricultural land uses. Longitudinal variations in water chemistry also differed between reaches with natural riparian areas, suggesting that water quality also depends on stream habitat. Moreover, longitudinal variation in water chemistry was proven a simple, useful and low-cost approach to assess the influence of land cover and stream habitat on water quality. Overall results demonstrated that both riparian land use and stream habitat influence water quality and that riparian forests are essential to reduce nutrient export to downstream ecosystems.

Aqueous inorganic uranium speciation in European stream waters from the FOREGS dataset using geochemical modelling and determination of a U bioavailability baseline

The concentration of the bioavailable uranium fraction (Ubio) at the European scale was deduced by geochemical modelling considering several definitions found in the literature and the FOREGS European stream waters geochemical atlas dataset to produce a Ubio baseline. A sensitivity analysis was performed using three thermodynamic databases. We also investigated the link between total dissolved uranium (Uaq) concentrations, speciation and global stream water chemistry on the one hand, and the lithology and ages of the surrounding rocks on the other.The more U-enriched the stream sediments or rock type contexts are, which tends to be the case with rocks containing silicates (4.1 mg/kg), the less U-concentrated the stream waters are (0.15 μg/L). Sedimentary rocks lead to slightly higher Uaq concentrations (0.34 μg/L) even if the concentration in sediment (Used) is relatively low (1.6 mg/kg). This trend is reversed for Ubio, with higher concentrations in a crystalline context. The mean estimated Ubio value ranges from 1.5.10−3 to 65.3 ng/L and can fluctuate by 3 orders of magnitude depending on the considered definition as opposed to by 2 orders of magnitude accountable to differences between thermodynamic databases. The classification of the water in relation to the two surrounding rock lithologies makes it possible to reduce the mean variability for the Ubio concentrations.Irrespective of the definition of Ubio considered, in 59% of cases the Ubio fraction represents less than 1% of Uaq. Several threshold values relating to Ubio were proposed, assuming knowledge only of the aqueous concentrations of the major elements and Uaq.

The response of stream ecosystems in the Adirondack region of New York to historical and future changes in atmospheric deposition of sulfur and nitrogen

The present-day acid-base chemistry of surface waters can be directly linked to contemporary observations of acid deposition; however, pre-industrial conditions are key to predicting the potential future recovery of stream ecosystems under decreasing loads of atmospheric sulfur (S) and nitrogen (N) deposition. The integrated biogeochemical model PnET-BGC was applied to 25 forest watersheds that represent a range of acid sensitivity in the Adirondack region of New York, USA to simulate the response of streams to past and future changes in atmospheric S and N deposition, and calculate the target loads of acidity for protecting and restoring stream water quality and ecosystem health. Using measured data, the model was calibrated and applied to simulate soil and stream chemistry at all study sites. Model hindcasts indicate that historically stream water chemistry in the Adirondacks was variable, but inherently sensitive to acid deposition. The median model-simulated acid neutralizing capacity (ANC) of the streams was projected to be 55 μeq L-1 before the advent of anthropogenic acid deposition (~1850), decreasing to minimum values of 10 μeq L-1 around the year 2000. The median simulated ANC increased to 13 μeq L-1 by 2015 in response to decreases in acid deposition that have occurred over recent decades. Model projections suggest that simultaneous decreases in sulfate, nitrate and ammonium deposition are more effective in restoring stream ANC than individual decreases in sulfur or nitrogen deposition. However, the increases in stream ANC per unit equivalent decrease in S deposition is greater compared to decreases in N deposition. Using empirical algorithms, fish community density and biomass are projected to increase under several deposition-control scenarios that coincide with increases in stream ANC. Model projections suggest that even under the most aggressive deposition-reduction scenarios, stream chemistry and fisheries will not fully recover from historical acidification by 2200.

Wastewater treatment plant effluent inputs induce large biogeochemical changes during low flows in an intermittent stream but small changes in day-night patterns

Wastewater treatment plant (WWTP) effluents alter stream water chemistry and metabolic activity. Yet, essential aspects influencing the biogeochemical response of receiving streams such as hydrology and diel oscillations of light and temperature remain largely unexplored. We measured day vs night water chemistry and in-stream net nutrient uptake velocity (Vf) in an intermittent forested stream, upstream and downstream of a WWTP effluent under contrasting hydrological conditions. The WWTP effluent negatively influenced stream water chemistry, especially during the dry period. Despite large diel oscillations in light inputs, day-night differences in nutrient and oxygen concentrations were small, suggesting that heterotrophic respiration drove stream metabolism with a minor contribution of gross primary production. The magnitude of Vf was similar between day and night at the two reaches. Yet, at the downstream reach, in-stream net DIN uptake occurred more often at night, and values of Vf for ammonia and nitrite indicated enhanced in-stream nitrification. The two reaches showed a small capacity to retain DIN and soluble reactive phosphorus from the water column. Positive values of in-stream net nutrient uptake (i.e. uptake > release) occurred mostly during the dry period, highlighting that in-stream biogeochemical processing can contribute to improve water quality in streams receiving point-sources effluents in regions with low water availability.

Dilution and precipitation dominated regulation of stream water chemistry of a volcanic watershed

Dilution, chemical precipitation, biological uptake and inflow inputs are important processes regulating stream water chemistry but quantitative evaluations of their relative contributions are rare. We examined stream water chemistry and discharge in two streams, one heavily affected by volcanic activities, one much less so, and their confluence to evaluate the importance of these processes, with special emphasis on dilution and precipitation, on reducing solute concentrations in northern Taiwan. We found that differences in the relative importance of the four processes led to three scenarios of upstream-downstream patterns of solute concentrations and fluxes. In Scenario I, solute concentration was greater but flux was smaller in the upstream than the downstream, likely due to dilution through the input of lateral inflows with low solute concentrations. In Scenario II, both solute concentration and flux were greater in the downstream, likely because the inflow water contained high solute concentrations. In Scenario III, both solute concentration and flux were greater in the upstream, likely because chemical precipitation dominated the upstream-downstream pattern. Dilution accounts for 63.7 ± 1.1% of the reduction of concentrations of all solutes in the confluence due to the input of relatively “clean” water from the less contaminated stream. Net precipitation effect was solute-specific and was positive only for Fe and PO43−. It reduced concentration of Fe by 79 ± 0.07% and PO43− by 49 ± 0.25%, likely due to decreases of solubility with increases in pH. Frequent mild rainfall is more effective than more extreme rainfall on lowering solute concentrations because the dilution effects of even large rainfall are short lived. The projected increases in drought events will reduce dilution effects when the need for diverting water from “clean” streams for anthropogenic uses is greater, making water resource management more challenging.

Stream health assessment using chemical and biological multi-metric models and their relationships with fish trophic and tolerance indicators

Abstract Nonsan Stream is a tributary of the Geum River that is strongly affected by urbanization and agricultural activities in the watershed. The present study was performed to diagnose the chemical and biological health of the stream from 2010 to 2016 using the multi-metric water pollution index (WPI) and index of biotic integrity (IBI) models. Monthly and annual variations in stream water chemistry were directly influenced by the monsoon season. Inputs of total phosphorus, suspended solids, and ionic substances, as well as dilution of total nitrogen, occurred during July and August. Chlorophyll increase was largely influenced by total phosphorus (R2 = 0.43, p

Temporal and spatial variability of stream water chemistry on Subantarctic Marion Island

Concentrations of major ions in stream water from the Soft Plume River on Subantarctic Marion Island were measured. During the annual relief voyage, samples were collected daily over a 16-day period (21 April–6 May 2015) from three sites along the stream to better understand temporal and spatial variability of stream water chemistry on the island. The chemical composition of the stream is dominated by the sea salts Na+ and Cl−. Mean solute concentrations for Na+ and Cl− are 7 ± 0.58 and 12.5 ± 0.84 mg/L, respectively. The mean molar Na:Cl ratio for all samples is 0.86 ± 0.05, with a range from 0.71 to 0.99 (n = 47), and there is a strong, significant positive correlation between Na+ and Cl− concentrations (r = 0.80; p < 0.001). These values are consistent with previous studies from Marion Island and other Subantarctic islands. Temporal variation in ion concentrations was small. The largest detected change was a decrease in most solute concentrations that coincided with two precipitation events. This decrease was largest at the highest altitude and the shallowest site, suggesting that there was more rainfall at this location. These findings confirm the dominance of the surrounding ocean as the main source of the island’s stream water chemistry and illustrate spatiotemporal patterns that provide an insight into mechanisms affecting their composition on Subantarctic Marion Island.

Coupling Concentration‐ and Process‐Discharge Relationships Integrates Water Chemistry and Metabolism in Streams

AbstractStream ecosystem processes, such as metabolism, are dynamically impacted by flow intensity. Therefore, without integrating ecosystem processes with water quality, we miss opportunities to develop frameworks to understand metabolic responses to changing flow. Flow simultaneously affects the material transport and biological opportunities for material transformation. Combining the strengths of ecohydrology and stream ecology to understand how flow variation alters ecosystem processes, we analyzed more than 5 years of water quality and stream metabolism data. We created segmented process‐discharge (P‐Q) relationships to examine how metabolism rates vary across discharge and compared them to concentration‐discharge (C‐Q) relationships to explore the dynamic effects of discharge on processes and physicochemical parameters. Within the segmented P‐Q relationships, we found the behavior of ecosystem respiration (ER), gross primary production (GPP), and net ecosystem production (NEP) to be different at high and low flows with varying degrees of statistical significance, demonstrating the potential for divergent metabolic responses across changing flows. GPP declined with increasing discharge. The rate of ER declined with discharge initially but then became unchanging at higher flows. NEP reflected the divergent trends between ER and GPP, as the relationship of NEP to Q was flat at lower discharge and declined at higher flows. Interrelated physicochemical parameters and ecosystem processes, such as pH and NEP, had mirrored responses to discharge. Coupling analyses of flow, water quality, and metabolism offers a more complete picture of interrelated ecosystem processes, allowing for a better understanding of ecosystem response to the physical and chemical changes that occur across flows.

Coupling Concentration‐ and Process‐Discharge Relationships Integrates Water Chemistry and Metabolism in Streams

Coupling Concentration‐ and Process‐Discharge Relationships Integrates Water Chemistry and Metabolism in Streams

Seasonal Variations of Streams Hydrochemistry and Relationships with Morphometric/Landcover Parameters in the Bhagirathi Watersheds, Garhwal Himalaya, India

ABSTRACT The Bhagirathi streams are a major source of fresh water in the form of glaciers meltwater streams and monsoonal phenomena. The watersheds of the Bhagirathi basin is trending towards water chemistry as well as changing morphological and land cover features due to the climatic and anthropogenic activity. To understand seasonal hydrochemistry and the impact of watershed morphology a total of 32 stream water samples collected during post and pre-monsoon seasons. The bicarbonate is the most dominant ion in the streams water followed by Na+, Ca+2, SO4-2, Cl-, SiO2, K+, and Mg+2. The results were found that HCO3- is in very good correlation with the base cations Ca+2, Mg+2 and Na+ in both pre and post-monsoon seasons. The higher concentration of HCO3- in Bhagirathi stream water and its positive correlation with Ca+2 and Mg+2 indicates that their main source comes from the dissolution of carbonates. Most of the hydro-chemical parameters (EC, pH) and ions (Ca+2, Mg+2, Na+, K+, HCOf-, SO4-2, Cl-, and F-) indicated a relationship with morphometric and land cover and these parameters vary with the season. It is observed that elevation, relief, basin length, area, and perimeter impact on stream water chemistry. Due to the processes of chemical weathering, mixing of the groundwater, snow/glacier meltwater, and surface water components responsible for the seasonal variation in the hydrochemistry of streams. Impact of agriculture land is more dominant than any land cover followed by barren land and glacier cover that influence the hydrochemistry of streams.

Major ion chemistry and atmospheric CO2 consumption deduced from the Batal glacier, Lahaul–Spiti valley, Western Himalaya, India

This study mainly focuses on the source identification of various ions in meltwater and estimation of CO2 consumption rate by chemical weathering in the Batal glacier basin on the basis of 2 years of study (2015 and 2017). The glacier meltwater has been monitored as slightly acidic in nature having mean pH value of 6.6. Ca2+ was observed as the most dominant cation contributing about 76% of TZ+ (total cations), whereas SO42− was observed as the most dominant anion contributing about 70% of TZ− (total anions) in the stream meltwater. High ratios of (Ca + Mg) versus TZ+ (mean value: 0.89 ± 0.02) and (Ca + Mg) versus (Na + K) (mean value: 8.51 ± 2.07) elucidate that stream water chemistry of the Batal glacier is largely controlled by carbonate weathering. Concentration of total dissolved solid in the glacial stream water was higher during the low-melt season (September) and lower during the high-melt period (July). The average value of daily mean TDS flux of the study area was calculated to be 12.4 t/day. The mean values of CWR (carbonate weathering rate) and SWR (silicate weathering rate) for the Batal glacier basin were calculated to be 97.4 and 22.8 t/km2/year, showing higher contribution of CWR as compared to SWR in the investigation area. CO2 consumption rate by the combined silicate and carbonate (chemical) weathering was estimated to be 11.1 × 105, 28.8 × 105 and 35.5 × 105 mol/km2/year during the study period September 2015, June 2017 and July 2017, respectively. The annual CO2 drawdown by the Batal glacier basin on the basis of CO2 consumption rate by chemical weathering is much lower as compared to the Gangotri glacier, which may be due to bigger size and higher meltwater runoff of the Gangotri glacier as compared to the Batal glacier.

Interannual Variation of Benthic Macroinvertebrate Communities at Long-Term Monitoring Sites Impacted by Human Activities: Implications for Bioassessment

Bioassessment assumes that ecological conditions remain stable in the absence of environmental changes. Evidence suggests this assumption may hold for reference streams, but knowledge gaps remain for impacted streams. Our study quantified interannual variation of benthic macroinvertebrate communities, monitored for at least 14 years in eight impacted streams in the Upper Thames River watershed in Ontario, Canada. Benthic communities exhibited moderate interannual variation in relative abundance of EPT (Ephemeroptera, Plecoptera and Trichoptera) and Chironomidae taxa. Year-to-year changes were reflected in lower community persistence than that observed in studies of reference streams. In contrast, tolerance-based metrics showed minimal interannual variation, suggesting compositional changes were because of taxonomic substitutions, in which one tolerant taxon replaced another. Analyses indicated limited directionality in temporal variation for most bioassessment metrics. An exception was taxa richness, which increased at most sites, possibly because of changes in subsampling. However, no associations between calculated bioassessment metrics and measured environmental factors (stream flow and water chemistry) or sampling procedures were observed. We conclude interannual variation in ecological conditions can be substantial and may not be associated with deterministic factors routinely measured in stream assessments. We recommend increased sampling frequency and traits-based assessment as options for limiting effects of interannual variation on assessment results.

Spatial variability in specific discharge and streamwater chemistry during low flows: Results from snapshot sampling campaigns in eleven Swiss catchments

AbstractCatchments consist of distinct landforms that affect the storage and release of subsurface water. Certain landforms may be the main contributors to streamflow during extended dry periods, and these may vary for different catchments in a given region. We present a unique dataset from snapshot field campaigns during low‐flow conditions in 11 catchments across Switzerland to illustrate this. The catchments differed in size (10 to 110 km2), varied from predominantly agricultural lowlands to Alpine areas, and covered a range of physical characteristics. During each snapshot campaign, we jointly measured streamflow and collected water samples for the analysis of major ions and stable water isotopes. For every sampling location (basin), we determined several landscape characteristics from national geo‐datasets, including drainage area, elevation, slope, flowpath length, dominant land use, and geological and geomorphological characteristics, such as the lithology and fraction of quaternary deposits. The results demonstrate very large spatial variability in specific low‐flow discharge and water chemistry: Neighboring sampling locations could differ significantly in their specific discharge, isotopic composition, and ion concentrations, indicating that different sources contribute to streamflow during extended dry periods. However, none of the landscape characteristics that we analysed could explain the spatial variability in specific discharge or streamwater chemistry in multiple catchments. This suggests that local features determine the spatial differences in discharge and water chemistry during low‐flow conditions and that this variability cannot be assessed a priori from available geodata and statistical relations to landscape characteristics. The results furthermore suggest that measurements at the catchment outlet during low‐flow conditions do not reflect the heterogeneity of the different source areas in the catchment that contribute to streamflow.

Riparian wetland rehabilitation and beaver re-colonization impacts on hydrological processes and water quality in a lowland agricultural catchment

Quantifying the catchment water balance and the characterization of its water quality changes are effective tools for establishing the response of catchments to shifting land management practices. Here we assess long-term hydrological partitioning and stream water chemistry over a 30-year period in a rural mixed land use catchment in northern Germany undergoing riparian wetlands and widespread re-colonization by beavers (Castor fiber) along the river network. We used long-term spatially distributed stream discharge, groundwater levels and surface water quality data with a simple monthly water balance model, changes in the variability in discharge measurements, and statistical analysis of spatio-temporal changes in stream water quality to assess long-term changes. Water balance estimates indicated high proportions of evapotranspiration loss (~90% of total precipitation) and relatively low groundwater recharge (<5% of total precipitation) prior to riparian rehabilitation in 2000. Increasing groundwater levels from 2000 to 2017 and the relatively linear nature of the catchment storage – discharge relationship, indicate a gradual increase in groundwater recharge (buts still <10% of total precipitation). Wetland rehabilitation, greatly enhanced by increasing beaver populations, resulted in longer water transit times in the stream network, less linear storage-discharge relationship and a loss of daily stream variability, increased DOC concentrations, isotopic evaporative enrichment downstream, and moderated stream temperatures. There was limited long-term water quality improvements from wetland rehabilitation on either nitrate or total phosphorus concentrations, with unchanged seasonal summer and winter peak concentrations for phosphorus and nitrate, respectively. This likely reflects the long-term legacy of fertilizer use on nutrient reservoirs in the catchment's soils, aquifers, and stream network. These long-term changes in hydrology and stream chemistry resulting from riparian rehabilitation and changes in agricultural management practices provide invaluable insights into catchment functioning and an evidence base for future planning in relation to long-term climatic changes.

Contrasting Patterns in the Decrease of Spatial Variability With Increasing Catchment Area Between Stream Discharge and Water Chemistry

AbstractUnderstanding how spatial variability in stream discharge and water chemistry decrease with increasing catchment area is required to improve our ability to predict hydrological and biogeochemical processes in ungauged basins. We investigated differences in this decrease of variability with increasing catchment area among catchments and among specific discharge (Qs) and water chemistry parameters. We defined the slope of the decrease in the variability with increasing catchment area as the rate of decrease in the standard deviation and coefficient of variation (δSD and δCV, respectively), both of which are −0.5 for the simple mixing of random variables (random mixing). All δSD and δCV values of Qs were less than −0.5, while those of most water chemistry values were greater than −0.5, indicating that with increased catchment area the spatial variability of Qs decreased more steeply than for random mixing, while for water chemistry they decreased less steeply. δSD and δCV had linear relationships with both the spatial dissimilarity index and relative changes in parameters' mean values with increasing catchment area. It suggested that differences in δSD or δCV for Qs and water chemistry can be explained by the different spatial structures, where dissimilar values of Qs and similar values of water chemistry, respectively, are located close together in space. Differences in δSD and δCV according to Qs and water chemistry should significantly affect the determination of representative elementary area and therefore need to be considered when predicting representative elementary area from spatial variability of low‐order streams.

Spatially resolved soil solution chemistry in a central European atmospherically polluted high-elevation catchment

Abstract. We collected soil solutions by suction lysimeters in a central European temperate forest with a history of acidification-related spruce die-back in order to interpret spatial patterns of soil nutrient partitioning, compare them with stream water chemistry and evaluate these parameters relative to concurrent loads of anions and cations in precipitation. Five lysimeter nests were installed in the 33 ha U dvou loucek (UDL) mountain catchment at different topographic positions (hilltops, slopes and valley). Following equilibration, monthly soil solution samples were interrogated over a 2-year period with regard to their SO42-, NO3-, NH4+, Na+, K+, Ca2+, Mg2+ and total dissolved Al concentrations, organic carbon (DOC) and pH. Soil pits were excavated in the vicinity of each lysimeter nest to also constrain soil chemistry. For an estimation of phosphorus (P) availability, ammonium oxalate extraction of soil samples was performed. Cation exchange capacity (CEC ≤58 meq kg−1) and base saturation (BS ≤13 %) were found to be significantly lower at UDL than in other monitored central European small catchments areas. Spatial trends and seasonality in soil solution chemistry support belowground inputs from mineral-stabilized legacy pollutants. Overall, the soil solution data suggest that the ecosystem was still chemically out of balance relative to the concurrent loads of anions and cations in precipitation, documenting incomplete recovery from acidification. Nearly 30 years after peak acidification, UDL exhibited similar soil solution concentrations of SO42, Ca2+ and Mg2+ as median values at the Pan-European International Co-operative Program (ICP) Forest sites with similar bedrock lithology and vegetation cover, yet NO3- concentrations were an order of magnitude higher. When concentrations of SO42-, NO3- and base cations in runoff are compared to soil pore waters, higher concentration in runoff points to lateral surficial leaching of pollutants and nutrients in excess than from topsoil to subsoil. With P availability being below the lowest range observed in soil plots from the Czech Republic, the managed forest ecosystem in UDL probably reflects growing inputs of C from regenerating vegetation in the N-saturated soil, which leads to P depletion in the soil. In addition, the observed spatial variability provides evidence pointing to substrate variability, C and P bioavailability, and landscape as major controls over base metal leaching toward the subsoil level in N-saturated catchments.

Response of Water Chemistry and Young-of-Year Brook Trout to Channel and Watershed Liming in Streams Showing Lagging Recovery from Acidic Deposition

Reductions in sulfur emissions have initiated chemical recovery of surface waters impacted by acidic deposition in the Adirondack region of New York State. However, acidified streams remain common in the region, which limits recovery of brook trout (Salvelinus fontinalis) populations. To investigate liming as a method to accelerate recovery of brook trout, the channels of two acidified streams were limed annually from 2012 to 2015, and an entire watershed of a third acidified tributary was limed by helicopter in 2013. Stream flow, water chemistry, and density of young-of-year (YOY) brook trout were measured in limed streams, an untreated acidified stream, and a buffered reference stream. Lime additions increased pH and acid-neutralizing capacity and decreased inorganic monomeric aluminum concentrations to less than 2.0 μmol/L, the minimum concentration at which in situ brook trout mortality has been documented. However, of the two channel-limed streams, only stream T8 showed a significant response (P < 0.01) in YOY density, increasing from a mean of 0.4 fish/m2 before liming to 2.7 fish/m2 after liming. No YOY brook trout response was observed in the stream within the limed watershed. Groundwater inputs to streams were identified by relative differences in temperature and concentrations of silica and sodium. YOY brook trout densities increased only in the channel-limed stream (T8) with suitable groundwater inputs for fall spawning and a summer nursery. Results suggest that targeted liming of acidified streams with the necessary groundwater habitat could be beneficial in accelerating recovery of brook trout populations.