Stream Water Concentrations Research Articles

Influence of surface geology on phosphorus export in coastal forested headwater catchments in Akita, Japan

ABSTRACT Surface geology is a key factor regulating the geographical patterns of P export; however, geographically extensive data on P export mechanisms from natural coastal mountain regions are lacking. We compared stream-water characteristics in forested headwater catchments with different types of surface geology (marine sedimentary rocks [MSRs] and igneous rocks [IRs]) and evaluated the factors regulating soluble reactive phosphorus (SRP) concentrations in stream water. Geographically extensive stratified sampling was conducted: stream-water and sediment samples were obtained from 66 MSR catchments and 55 adjacent IR catchments along the coastal forested mountain regions in Akita, Japan. SRP and major cations and anions in stream waters were analyzed. To evaluate the effect of ionic composition on SRP, sediments were extracted with NaCl and CaCl2 solutions and the SRP concentrations in the extracts were measured. Stream SRP was significantly higher in MSR catchments (median 23 µg L−1) than in IR catchments (median 8 µg L−1) (P < 0.001), and tended to be higher in MSR catchments with younger rocks. Dissolved inorganic nitrogen (DIN) did not differ between catchments with different geologies; therefore, DIN/SRP was significantly lower in MSR catchments (median 18), close to the Redfield ratio. On a Piper diagram, high-SRP stream waters were of the NaCl water type, and stream SRP was significantly correlated with Na+ (r = 0.642, P < 0.0001). In IR catchments, stream waters had relatively higher Ca2+ and Mg2+ concentrations. SRP in the sediment extracts was significantly higher in MSR catchments and samples obtained by NaCl extraction than in IR catchments and CaCl2-extracted samples. Exchangeable Na+ in sediments was significantly higher in MSR catchments, decreasing Ca2+ in the liquid phase by an ion-exchange reaction, which is likely also key in maintaining high SRP levels. We conclude that MSR catchments in coastal Akita are a significant P source for streams even in headwater forests, and that site-specific NaCl water types and higher exchangeable Na+ concentrations in sediments result in higher SRP concentrations in stream waters. These results have critical implications for P cycles in freshwater ecosystems influenced by Na+.

Polycyclic Aromatic Hydrocarbons and Quinones in Urban and Rural Stormwater Runoff: Effects of Land Use and Storm Characteristics

Changes in streamwater concentrations in two creeks draining contrasting urbanized landscapes in southern Ontario, Canada, during a major summer rainfall event were used to assess how land use and ...

山地渓流における硝酸態窒素流出の林相による違い－トドマツ林,カラマツ林,天然林流域の比較－

山地渓流における硝酸態窒素流出の林相による違い－トドマツ林,カラマツ林,天然林流域の比較－

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.

Peatland drainage - a missing link behind increasing TOC concentrations in waters from high latitude forest catchments?

Total Organic Carbon (TOC) concentrations in stream waters from peat-covered catchments have increased over the last 15–25 years, resulting in large-scale brownification of lakes and rivers in high latitudes. While this increase has primarily been attributed to decreased acid deposition and climatic warming in most regions, we studied whether peatland drainage in forested catchments has contributed to the increasing TOC concentrations. We analysed the spatial variability of average TOC concentrations from a total of 133 peatland dominated catchments in Sweden and Finland, of which 62 were pristine and 71 were drained during the last century. In addition, we performed a trend analysis on 37 catchments for which long-term data were available. We found about 14 mg l−1 higher TOC concentrations in streams discharging from drained than undrained sites in southern latitudes, and about 8 mg l−1 higher concentrations from drained sites in northern latitudes. Trend analysis did not indicate significant differences in TOC concentration trends between drained and undrained catchments but indicated that tree stand volume correlated with increasing trends. This supports earlier findings in that the general increase in forest cover and biomass that has occurred in high latitudes during the last decades is another factor that has contributed to brownification.

Drainage for forestry increases N, P and TOC export to boreal surface waters

More reliable assessments of nutrient export to surface waters and the Baltic Sea are required to achieve good ecological status of all water bodies. Previous nutrient export estimates have recently been questioned since they did not include the long-term impacts of drainage for forestry. We made new estimates of the total nitrogen (N), total phosphorus (P) and total organic carbon (TOC) export from forests to surface waters at different spatial scales in Finland. This was done by formulating statistical equations between streamwater concentrations and climate, soil, forest management and runoff variables and spatial data on catchment characteristics. The equations were based on a large, long-term runoff and streamwater quality dataset, which was collected from 28 pristine and 61 managed boreal forest catchments located around Finland. We found that the concentrations increased with temperature sum (TS), i.e. from north to south. Nitrogen, P and TOC concentrations increased with the proportion of drained areas in the catchment; those of N and TOC also increased with the proportion of peatlands. In contrast, with the increasing concentrations of N and TOC with time, P concentrations showed a decreasing trend over the last few decades. According to our estimates, altogether 47,300 Mg of N, 1780 Mg of P and 1814 Gg of TOC is transported from forest areas to surface waters in Finland. Forest management contributes 17% of the N export, 35% of the P export and 12% of the TOC export. Our new forest management export estimates for N and P are more than two times higher than the old estimates used by the environment authorities. The differences may be explained by the long-term impact of forest drainage. The spatial results indicate that peatland forests are hotspots for N, P and TOC export, especially in the river basins draining to the Gulf of Bothnia.

Groundwater-surface water interactions and agricultural nutrient transport in a Great Lakes clay plain system

Nutrient export from agricultural land to surface waters is a significant environmental concern within the Great Lakes Basin (GLB). A field-based watershed-scale study was completed to investigate spatial and temporal variations of phosphorus and nitrate to assess nutrient transport pathways and groundwater-surface water interactions in an agriculturally dominated clay plain system. This was conducted in the 127 km2 Upper Parkhill Watershed, near Lake Huron in southwestern Ontario, Canada. Data collection occurred from June 2018 to May 2019 via continuous sensor deployment and discrete sampling of stream water, groundwater, hyporheic zone, and tile drainage water. Samples were analyzed for various nutrient species (total, total dissolved, soluble reactive, and particulate phosphorus, and nitrate-N) to examine the hydrological dynamics of principal transport pathways of agriculturally-derived nutrients. Total phosphorus and nitrate concentrations in stream water ranged from 0.007 to 0.324 mg/L and 0.32 to 13.13 mg NO3−-N/L, respectively. Tile drainage water total phosphorous concentrations varied from 0.006 to 0.066 mg/L. Groundwater total dissolved phosphorus concentrations ranged from <0.003 to 0.085 mg/L. Transport of phosphorus through tile drainage was observed to be greater than through groundwater over the study period. No distinct relationship was observed between nutrient concentrations in the hyporheic zone and the vertical hydraulic gradient within this zone in the studied stream reach. Preliminary correlations were discerned between water quality observations and recognized land management practices. Given the elevated stream nutrient concentrations, these results are consequential for the continual improvement of strategies and programs devised to conserve water resources within the GLB.

Effects of bedrock groundwater discharge on spatial variability of dissolved carbon, nitrogen, and phosphorous concentrations in stream water within a forest headwater catchment

AbstractThe quantitative evaluation of the effects of bedrock groundwater discharge on spatial variability of stream dissolved organic carbon (DOC), dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorous (DIP) concentrations has still been insufficient. We examined the relationships between stream DOC, DIN and DIP concentrations and bedrock groundwater contribution to stream water in forest headwater catchments in warm‐humid climate zones. We sampled stream water and bedrock springs at multiple points in September and December 2013 in a 5 km2 forest headwater catchment in Japan and sampled groundwater in soil layer in small hillslopes. We assumed that stream water consisted of four end members, groundwater in soil layer and three types of bedrock groundwater, and calculated the contributions of each end member to stream water from mineral‐derived solute concentrations. DOC, DIN and DIP concentrations in stream water were compared with the calculated bedrock groundwater contribution. The bedrock groundwater contribution had significant negative linear correlation with stream DOC concentration, no significant correlation with stream DIN concentration, and significant positive linear correlation with stream DIP concentration. These results highlighted the importance of bedrock groundwater discharge in establishing stream DOC and DIP concentrations. In addition, stream DOC and DIP concentrations were higher and lower, respectively, than those expected from end member mixing of groundwater in soil layer and bedrock springs. Spatial heterogeneity of DOC and DIP concentrations in groundwater and/or in‐stream DOC production and DIP uptake were the probable reasons for these discrepancies. Our results indicate that the relationships between spatial variability of stream DOC, DIN and DIP concentrations and bedrock groundwater contribution are useful for comparing the processes that affect stream DOC, DIN and DIP concentrations among catchments beyond the spatial heterogeneity of hydrological and biogeochemical processes within a catchment.

Bioaccumulation of the pesticide imidacloprid in stream organisms and sublethal effects on salamanders

Neonicotinoids are one of the most widely used classes of insecticides in the world. The neonicotinoid imidacloprid is commonly applied to hemlock (Tsuga spp.) stands in eastern North America to reduce tree mortality from infestations of the invasive hemlock woolly adelgid (HWA; Adelges tsugae). While laboratory and mesocosm studies have determined that imidacloprid can bioaccumulate in anurans and cause sublethal effects, no field studies have investigated whether salamanders or insects in streams adjacent to HWA treatments bioaccumulate imidacloprid or if sublethal effects are detectable in wild salamanders. We assessed relationships between imidacloprid exposure and stream salamander health in West Virginia, USA, using concentration of the stress hormone corticosterone and body condition indices (BCI) as response variables. Of 107 Desmognathus salamanders from 11 sites tested for bioaccumulation, we detected imidacloprid in 47 salamanders. Of 15 benthic macroinvertebrate samples tested, we detected imidacloprid, imidacloprid-urea, and imidacloprid-olefin in 15, 13, and 1 sample, respectively. Based on 115 Desmognathus salamanders sampled at 11 sites for stress hormone responses, corticosterone concentration increased with imidacloprid concentration in stream water. For 802 salamanders sampled at 48 sites, BCI decreased as concentration of imidacloprid in stream water increased, but explanatory power was low. Our study suggests that chronic leaching of imidacloprid from treated hemlock stands into adjacent streams has the potential to negatively affect aquatic organisms and may provide a route of exposure to higher trophic levels.

Determination of nitrogen and phosphorus fertilisation rates for tobacco based on economic response and nutrient concentrations in local stream water

Fertilisation, although it improves crop yield and enhances farmer income, can contribute to freshwater pollution. Thus, it is important to determine the recommended fertilisation rate that can ensure crop yield and farmer income, as well as not harm the environment. We calculated the yield and net income of tobacco and measured the nitrogen (N) and phosphorous (P) concentrations under different fertilisation rates in plot runoff and local stream water during 2017 and 2018. Tobacco yield increased with increasing fertilisation rates, but net income decreased at extremely high rates. The opposite pattern was observed for the fertiliser nutrient use efficiency (NUE). When fertilisation was applied, the N and P concentrations in the runoff exceeded the established national thresholds, and the concentrations and discharges of N and P in the runoff were positively correlated with the fertilisation rate. According to the ratio of arable land to the total watershed area, reduction characteristics of N and P in the watershed stream, and the established national thresholds, the recommended N and P2O5 annual application rates in the study area are 120 kg ha−1 for both fertilisers. The recommended rates are lower than what farmers currently apply. Therefore, reducing the synthetic fertiliser application rate should be implemented to achieve sustainable development in the study region.

Contamination of stream waters, sediments, and agricultural soil in the surroundings of an abandoned copper mine by potentially toxic elements and associated environmental and potential human health-derived risks: a case study from Agrokipia, Cyprus.

Abandoned mining areas have left a legacy of environmental damage with potential public health implications. The present study aimed at (1) assessing the level of contamination of the sites surrounding the Agrokipia abandoned copper mine in Cyprus through the mobilization of potentially toxic elements (PTEs), (2) correlating results with the mineralogy of the area, (3) discussing potential ecological and human health risks, and (4) proposing regeneration strategies. To this effect, the levels of 22 PTEs and other major elements were assessed in the acidic water of pit lakes, the tailings, the waters, and sediments of several streams originating from the mining site and flowing through the village of Agrokipia, and from agricultural soil from an impacted adjacent olive orchard. The pH values of water (pH < 2.7) in the pit lakes uncovered the acidic and oxidizing conditions that prevailed in the area. The acidity and the examined PTE concentrations in stream waters followed a decreasing trend with increasing distance from the tailing, reaching background values in a distance of 1500m. The tailing spoil-heap was significantly enriched with Cu, Zn, Pb, Cd, Cr, and Ag (e.g., enrichment factor values up to 29 for Cu and 120 for Ag). Stream sediments and agricultural soil were contaminated with PTEs (mainly Cu, Zn, Pb, Cd, Cr, Ag, and Li), as evident by several contamination indices (i.e., enrichment and contamination factor). The level of contamination was correlated with the reported mineralogy of the site. The values of the degree of contamination (Cdeg = 62) and pollution load index (PLI = 2.4) indicated contamination of the sediments of the Voulgarides stream flowing through the village, suggesting potential public health implications to the local community. In addition, the values of the ecological risk factor suggested that the studied streams pose moderate ecological risks, mainly mediated by Cd and Cu. Overall, the results highlighted the need for undertaking regeneration measures for safeguarding environmental sustainability and public health.

Do stream water solute concentrations reflect when connectivity occurs in a small, pre-Alpine headwater catchment?

Abstract. Expansion of the hydrologically connected area during rainfall events causes previously disconnected areas to contribute to streamflow. If these newly contributing areas have a different hydrochemical composition compared to the previously connected contributing areas, this may cause a change in stream water chemistry that cannot be explained by simple mixing of rainfall and baseflow. Changes in stormflow composition are, therefore, sometimes used to identify when transiently connected areas (or water sources) contribute to stormflow. We identified the dominant sources of streamflow for a steep 20 ha pre-Alpine headwater catchment in Switzerland and investigated the temporal changes in connectivity for four rainfall events based on stream water concentrations and groundwater level data. First, we compared the isotopic and chemical composition of stormflow at the catchment outlet to the composition of rainfall, groundwater and soil water. Three-component end-member mixing analyses indicated that groundwater dominated stormflow during all events, and that soil water fractions were minimal for three of the four events. However, the large variability in soil and groundwater composition compared to the temporal changes in stormflow composition inhibited the determination of the contributions from the different groundwater sources. Second, we estimated the concentrations of different solutes in stormflow based on the mixing fractions derived from two-component hydrograph separation using a conservative tracer (δ2H) and the measured concentrations of the solutes in baseflow and rainfall. The estimated concentrations differed from the measured stormflow concentrations for many solutes and samples. The deviations increased gradually with increasing streamflow for some solutes (e.g. iron and copper), suggesting increased contributions from riparian and hillslope groundwater with higher concentrations of these solutes and thus increased hydrological connectivity. The findings of this study show that solute concentrations partly reflect the gradual changes in hydrologic connectivity, and that it is important to quantify the variability in the composition of different source areas.

Chromium, manganese, nickel, and cobalt mobility and bioavailability from mafic-to-ultramafic mine spoil weathering in western Massachusetts, USA.

Fragmented ultramafic bodies in New England were important mineral resources until the early twentieth century, yet few studies have addressed their potential to release trace metals to terrestrial and aquatic environments. Here, we evaluate the release of four trace metals (Cr, Co, Mn, and Ni) from a historic serpentine-talc "soapstone" quarry in Blandford, MA, USA. Soil pits, sediment and rock samples, and stream water samples were collected from upslope undisturbed areas, within the mine spoils and mine face, and downslope of the mine. In order to provide a bottom-up approach for understanding metal release, careful petrographic analysis, electron-dispersive spectroscopy, and wavelength-dispersive spectroscopy were employed to provide first-order insight into the mineralogy of the deposit and a determination of potential metal-bearing phases. Trace metals were primarily observed in ultramafic sheet silicates, primary Fe-oxides, and interstitial weathering-related sulfates. Bulk rock concentrations were Cr (1550mgkg-1), Co (230mgkg-1), Mn (1100mgkg-1), and Ni (1960mg kg1); Cr, Co, and Ni were elevated relative to the surrounding country rock. However, soils and sediments total concentrations were comparable to background soil concentrations: Cr (119mgkg-1), Co (73mgkg-1), Mn (894mgkg-1), and Ni (65mgkg-1). Moreover, < 0.5% of the total concentrations were bioavailable (0.1M ammonium acetate extraction), implying that metals are present as insoluble forms. However, ~ 20% of the total Cr, Mn, Ni, and Co concentrations were strong acid extractable, suggesting mobilization over the coming decades. Stream water concentrations of Mn and Cr were < 50µg L-1, below concentrations outlined by USEPA drinking water standards, and WHO water guidelines for Ni. These results suggest that transport of Cr, Mn, Ni, and Co from the serpentine-talc as dissolved compounds or sediments is limited by retention within silicate and oxides.

Contribution of nitrate-nitrogen concentration in groundwater to stream water in an agricultural head watershed

This study characterized nitrate-nitrogen (NO3–N) concentrations in groundwater and stream water in an agricultural head watershed in South Korea and identified the pollution load of NO3–N as a result of the groundwater entering streams using field surveys, analyses of chemical constituents, and numerical modeling. The mean NO3–N concentration in groundwater was 7.373 mg/L, which is approximately 1.9 times higher than concentrations found in stream water. The groundwater and stream water samples belonged to the Ca–HCO3 type. The concentration of NO3–N in groundwater tended to increase in the lowland areas downstream. There was seasonal variations of NO3–N in both the groundwater and stream water samples, with increases in concentration during the dry season (January–April) and decreases during the wet season (June–October). The NO3–N load in stream water to that in groundwater (R) was higher during the wet season (September) than the dry season (March), with R distinctly increasing in upstream areas relative to downstream areas, indicating that during the wet season, a large amount of NO3–N is introduced into stream water from groundwater. By analyzing the relationship between groundwater and stream water and through NO3–N transport modeling, it was revealed that in the watershed, the nitrate-N load in stream water is greatly augmented by inputs from groundwater, particularly in the middle and downstream areas.

Shale gas development has limited effects on stream biology and geochemistry in a gradient-based, multiparameter study in Pennsylvania

The number of horizontally drilled shale oil and gas wells in the United States has increased from nearly 28,000 in 2007 to nearly 127,000 in 2017, and research has suggested the potential for the development of shale resources to affect nearby stream ecosystems. However, the ability to generalize current studies is limited by the small geographic scope as well as limited breadth and integration of measured chemical and biological indicators parameters. This study tested the hypothesis that a quantifiable, significant relationship exists between the density of oil and gas (OG) development, increasing stream water concentrations of known geochemical tracers of OG extraction, and the composition of benthic macroinvertebrate and microbial communities. Twenty-five headwater streams that drain lands across a gradient of shale gas development intensity were sampled. Our strategy included comprehensive measurements across multiple seasons of sampling to account for temporal variability of geochemical parameters, including known shale OG geochemical tracers, and microbial and benthic macroinvertebrate communities. No significant relationships were found between the intensity of OG development, shale OG geochemical tracers, or benthic macroinvertebrate or microbial community composition, whereas significant seasonal differences in stream chemistry were observed. These results highlight the importance of considering spatial and temporal variability in stream chemistry and biota and not only the presence of anthropogenic activities in a watershed. This comprehensive, integrated study of geochemical and biological variability of headwater streams in watersheds undergoing OG development provides a robust framework for examining the effects of energy development at a regional scale.

Spatial Variation of Nutrient Concentrations (NH&amp;lt;sup&amp;gt;+&amp;lt;/sup&amp;gt;&amp;lt;sub style=&amp;quot;margin-left:-5px;&amp;quot;&amp;gt;4&amp;lt;/sub&amp;gt; and Cl&amp;lt;sup&amp;gt;-&amp;lt;/sup&amp;gt;) in the Dudhkoshi River Basin, Sagarmatha National Park, Nepal

The Sagarmatha National Park (SNP) in Nepal is home to unique natural beauty and cultural significance. While the SNP has a relatively small local population, it has drawn thousands of visitors since Edmund Hillary and Tenzing Norgay reached the peak of Mt Everest in 1953. Importantly, the tourists and their concurrently generated refuse have caused massive anthropogenic pressure with serious environmental consequences for the unique SNP and SNP Buffer Zone ecosystems. This study aimed to understand the spatial variation of nutrient concentrations in stream water and drinking water (primarily shallow springs) using analyses of nitrogen as NH+4 and chlorine (Cl-) concentrations. Sampling occurred in April 2017 during the pre-monsoon dry season in the upper Dudhkoshi River Basin, SNP. Dissolved inorganic nitrogen (NH+4) concentrations in both drinking water and stream water were low with average concentrations in drinking water of 0.016 mg/L (±0.010) and 0.033 mg/L (±0.031) in stream water. Similarly, Cl- concentrations were also low with average concentrations of 0.185 mg/L (±0.045) and 0.124 mg/L (±0.051) in stream and drinking water, respectively. Importantly, nitrogen in stream waters exhibits a decreasing trend with altitude whereas Cl- values decrease with altitude in both drinking water and streams. The observed spatial variations of nitrogen and chlorine concentrations are attributed primarily to the significant variations in land use/land cover from the highest portions of the drainage basin to the lowest elevations, which are outside of the SNP boundary and therefore allow more agricultural development. Our results demonstrated that although the quality of stream water in the upper reach of Dudhkoshi River Basin meets WHO standards for drinking water, there is significant surface water contamination in the form of agricultural run-off. These results will provide base-line data for further studies and will help to improve understanding of the relationship between land use/land cover and water quality in the region.

Geochemical Characterization of Base Metals in Stream Water and Sediments in the Caddo Lake Watershed, Cass, Harrison and Marion Counties, Texas

The Caddo Lake watershed is located in northeastern Texas and encompasses much of Cass, Harrison, and Marion counties. The watershed is drained by major streams and tributaries flowing in an easterly direction over Eocene-aged rocks and sediments of the Wilcox and Claiborne groups, and empty into the western arm of Caddo Lake. Since 1995, Caddo Lake and some of its tributaries have been included on the State of Texas Clean Water Act 303(d) list by the Texas Commission on Environmental Quality (TCEQ) for impairment due to mercury content in edible tissue, depressed dissolved oxygen, base metal concentrations, and low pH values. The purpose of this multi-year study was to characterize base metal concentrations in stream water and sediments in the Caddo Lake watershed, and document the potential watershed transport and contribution to the impairment of Caddo Lake. Recent water (n = 58) and sediment (n = 116) sampling at 29 sites revealed copper, lead, and zinc concentrations within normal limits and below EPA actionable standards. Mercury concentrations were elevated at 21 of the 29 sampling sites, which could lead to methylation and bioavailability to organisms at all trophic level.

Revisiting the Determination of Percent Aspirin Lab: Using a Limiting Reactant Approach for Students To Also Determine the Amount of Iron(III) Chloride

The spectrophotometric determination of the percent composition of an aspirin tablet is a common first-year, general chemistry undergraduate laboratory procedure. The experiment requires that a known amount of pure acetylsalicylic acid be quantitatively converted into the soluble disodium salicylic acid that is further reacted with excess iron(III) chloride solution to form a deep blue tetraaqua-octahedral complex. This complex, through serial dilutions, is used to construct a Beer’s law plot that may be used to determine the concentration of aspirin. In a novel twist, this paper describes how the same Beer’s law plot can be used to determine the concentration of iron in the iron(III) complex, which is then used to determine the concentration of the original iron(III) chloride solution used to make the aspirin–iron(III) complex. The method has been adapted by high school students in determining iron concentrations in stream waters.

Effects of climate‐related variability in storage on streamwater solute concentrations and fluxes in a small forested watershed in the Southeastern United States

AbstractStreamwater quality can be affected by climate‐related variability in hydrologic state, which controls flow paths and affects biogeochemical processes. Thirty‐one years of input/output solute fluxes at Panola Mountain Research Watershed, a small, forested, seasonally water‐limited watershed near Atlanta, Georgia, were used to quantify the effects of climatic‐related variability in storage on streamwater solute concentrations and fluxes. Streamwater fluxes were estimated for ten solutes from weekly and event sample concentrations using regression‐based methods. The most pertinent storage attribute (current or antecedent watershed, shallow, and deep storage) for each solute was determined by fitting separate concentration relationships. The concentration‐discharge relationships varied more for reactive solutes such as potassium, sulfate, and DOC and less for weathering products (base cations and dissolved silica) and conservative chloride. Many solutes exhibited higher concentrations when storage levels were lower or wetting up, which was likely the result of the concentrating effects of evapotranspiration and/or the buildup and flushing of weathering products associated with longer residence times. The impacts of storage modeling on annual fluxes varied by solute, ranging from about 5% (magnesium) to 52% (nitrate) as relative standard deviations, and sufficiently removed climate‐related patterns observed in streamwater concentrations. Sulfate was particularly mobilized following growing season droughts but only if deep storage was sufficiently recharged, possibly indicating that sulfides in the deep storage pool were oxidized to sulfate during droughts and mobilized when re‐wetted. The lack of streamwater sulfate response to 61% declines in atmospheric deposition indicates the importance of watershed biogeochemical processes on controls of streamwater export of sulfate. The approach of explicitly incorporating storage in the streamwater concentration modeling elucidated the effects of climate on streamwater water‐quality and may provide insight into the effects of climatic change on future fluxes.

Metals and dissolved organic carbon (DOC) of surface waters in two adjacent watersheds in the eastern Amazon

Land-use intensification in the "Zona Bragantina" region, an area in the eastern Brazilian Amazon, has accelerated landscape changes from primary forest to a mixture of different land uses: native forest (riparian vegetation), secondary forest, pasture, annual cropland, perennial cropland, bare soil and fallow vegetation, with negative consequences for the stability and equilibrium of river systems. This study examined the temporal and spatial variation of dissolved organic carbon (DOC) and metal concentrations in stream water of the Cumaru (ICU) and São João (ISJ) watersheds from May 2014 to April 2015, to understand the chemical changes in forests and agro-ecosystems during one year. In both watersheds, higher concentrations of dissolved metals (aluminum, sodium, barium, calcium, iron, potassium, magnesium, copper and zinc) and DOC were measured in the rainy season, with considerable variability due to precipitation events. Furthermore, strong spatial variation was observed, with lower conductivity, higher pH, and higher concentrations of DOC and dissolved metals in the downstream reaches, especially for DOC in a small reservoir below a dam in ISJ. Significant human intervention was located in these downstream areas, including nearby agriculture and pasture, and use of stream resources for domestic activity. Sandy soil in these areas likely facilitated leachate processes, mainly in deforested areas, supporting the increased movement of metals from the land to the stream.