Stream Water Data Research Articles

Tellus regional stream water geochemistry: environmental and mineral exploration applications

Regional stream water geochemistry acquired as part of the Tellus programme in Ireland has been analysed to assess its potential for application to environmental assessment and mineral exploration. Interpolated geochemical maps and multivariate statistical analysis, including principal component analysis and random forest classification, demonstrate broad geogenic control of stream water chemistry, with both bedrock and subsoil contributing to the patterns observed. Surface water regulations set Environmental Quality Standard values for individual Priority Substances and Specific Pollutants that may depend on background concentrations and/or water hardness. The high resolution of Tellus stream water data and their location on low-order streams have allowed estimation of background concentrations and water hardness in the survey area, with significant implications for water monitoring programmes. Anthropogenic inputs to stream water in the survey area come mainly from agricultural sources and Tellus data suggest few catchments are unaffected. Comparison of Tellus stream water geochemistry with stream sediment and topsoil geochemistry suggest that stream water geochemistry has strong potential for use in mineral exploration, with the same base metal and gold pathfinder anomalies apparent in all three data sets. Cluster analysis indicates that base metals in stream water are associated with organic matter but statistical analysis may be employed to distinguish mineralization-related signatures. Supplementary material: Comparison of cation/anion associations using Piper plots and principal component analysis is available at https://doi.org/10.6084/m9.figshare.c.5683094 Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Uranium partitioning from contaminated wetland soil to aqueous and suspended iron-floc phases: Implications of dynamic hydrologic conditions on contaminant release

Environmental mobility of anthropogenic heavy metal releases is governed by site-specific hydrobiogeochemical factors. Uranium (U) releases from 1965 to 1988 resulted in contamination of the Tims Branch wetland at the United States Department of Energy Savannah River Site (SRS) near Aiken, South Carolina. Today, 80% of the 43,000 kg released remain sequestered in soils of two former ponds, Beaver Pond and Steed Pond. The objective of this study was to understand U partitioning from contaminated wetland sediments to aqueous and particulate iron-floc phases. The approach was to correlate U, iron (Fe), and organic matter (OM) in soil cores at key depositional areas; determine U and Fe concentrations in aqueous- and solid-phases in the stream; and compare these stream water data following two storm events. Uranium was released into an outfall canal leading away from the SRS M-Area and first deposited in a topographically low area where a beaver pond is frequently in place. Uranium soil concentrations in Beaver Pond exceed 14,000 µg/g and a second deposition area 1 km downgradient in a former farm pond (Steed Pond) has U soil concentrations near 300 µg/g. Uranium releases to the stream are minimal at Beaver Pond, but U incorporation into Fe-OM colloids, or flocs, at Steed Pond results in appreciable fluxes of U from the wetland. This work yields four key conclusions. At the kilometer and meter scales, geochemistry cannot be the sole predictor of U mobility, as the anthropogenic U deposition is geologically young relative to Fe and OM. Storm intensity and duration do not appear to be directly proportional to U releases from the wetland, as flooding decreases U inclusion in mobile flocs. The mass of suspended solids present in a stream reach often governs how much U moves. The solid-bound U inventory at Beaver Pond does not enter the mobile aqueous phase as easily as Steed Pond U, resulting in U sequestration amid wetland metal cycling in Tims Branch. This work expands upon studies conducted in the 1990′s and early 2000′s, improving our understanding of the geochemical controls of uranium migration through Tims Branch, particularly with respect to the changes over the last 30+ years. Current wetland conditions do not favor significant U movement, but long-term changes in local and regional hydrology may alter this delicate biogeochemical balance.

Altitude isotope effects in Mediterranean high-relief terrains: a correction method to utilize stream water data

ABSTRACT Quantification of the isotope altitude effect from precipitation allows the identification of recharge altitudes in high-relief areas. However, steep terrains frequently limit the use of this precipitation-based approach. Perennial rivers often provide easy, year-round access for water sampling. However, in high-relief regions rivers may not adequately represent regional precipitation isotope patterns because they integrate isotope signals along their course. This prevents the calculation of an altitudinal isotope gradient from river water samples alone. We present a study that shows how a river-based sampling approach served to determine the altitude effect. Replacing the original sample site altitude with the mean upstream catchment elevation as calculated from a digital elevation model allowed us to establish a plausible altitude isotope effect from stream water. The correction approach was verified independently using precipitation isotope data. This approach can potentially be transferred to other regions where precipitation sampling at various elevations is difficult to determine.

The impacts of historical land-use on phosphorus movement in the Calhoun Critical Zone Observatory in the southeastern US Piedmont

Human actions through land-use can alter soil phosphorus (P) distribution over time and space as vegetation is altered and added fertilizer P is translocated downslopes by runoff and erosion, or through the soil profile by leaching. In the southeastern US Piedmont, a more than 100-year period of human land-use of forest clearing and farming, which included P fertilization, caused severe surface erosion before reforestation. This history resulted in elevated surface soil P in farmed ridge tops, even after 70 years of reforestation, but little data exists on redistribution of this P downslope or down profile during these 70 years. We aimed to investigate the effect of different land-use histories on soil P losses over time. Combined with multiple years of current soils, soil solution, and stream water data from two small watersheds in the Calhoun Critical Zone Observatory (Calhoun CZO) in South Carolina, USA, we use the soil and water assessment tool (SWAT) to simulate a trajectory of seven different land-uses on P movement. Results indicated annual solution total P loss under 100% agriculture (3.7 kg ha−1 year−1) was six times greater than under 100% forest while mixed forest and agriculture experienced about one-third the loss observed under agricultural land. Furthermore, the model predicted P leaching that ranged from 0.036 to 0.1 kg ha−1 year−1 with the highest rates during early reforestation. These increased leaching rates could account for 7–20 kg ha−1 of vertical P movement through the soil profile over 200 years. This content of P leaching is consistent with observed differences in the content of extractable soil P in the 2 m of soil under farmed vs. never farmed locations. Simulation under high rainfall indicated wet periods or events could augment P mobilization and better approximated observed increases in soil extractable P content. These land-use change simulations indicate reforestation reduces surface runoff and erosion but increases vertical leaching and, despite soil P retention mechanisms, may move P deep into the soil profile.

Distribution and potential ecological risk assessment of trace elements in the stream water and sediments from Lanmuchang area, southwest Guizhou, China.

Trace elements contamination in sediment is regarded as the global crisis with a large share in developing countries like China. Water and sediment samples were collected during (2016) from Qingshui Stream and analyzed for major physicochemical properties and trace elements by using ICP-MS. Our result of sediments showed that studied trace elements (except Pb, Cd, Co) had a concentration higher than Chinese sediment guideline as well as stream water data for studied trace elements (except Cr, Pb, Cd, Cu, and Zn) had a higher concentration than the maximum permissible safe limit of WHO. Contamination factor (CF) confirmed a moderate to high contamination in the sediment samples due to As and Tl, respectively. The values of pollution load index (PLI) were found above one (> 1), describing the progressive sediment quality decline. Pearson correlation showed that there was a significant positive association between Tl and As (r = 0.725, p < 0.05) in sediment samples. Results revealed that water-rock interaction, weathering of Tl sulfide mineralization, and hydrogeological conditions were major sources of stream water and sediments contamination in the study area. This experimental study contributes to a better understanding of the geochemistry and prevention of trace element contamination in sediments from Lanmuchang area.

Occurrence of the herbicide glyphosate and its metabolite AMPA in surface waters in Switzerland determined with on-line solid phase extraction LC-MS/MS.

Glyphosate is currently one of the most important herbicides worldwide. Its unique properties provide for a wide range of uses in agriculture but also in non-agricultural areas. At the same time, its zwitterionic nature prevents the inclusion in multi-residue analytical methods for environmental monitoring. Consequently, despite its extensive use, data on occurrence of glyphosate in the aquatic environment is still scarce. Based on existing methods, we developed a simplified procedure for the determination of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) in water samples using derivatization with fluorenylmethyl chloroformate FMOC-Cl, combined with on-line solid phase extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS) detection. This method was extensively tested on over 1000 samples of surface water, groundwater, and treated wastewater and proved to be simple, sensitive, and reliable. Limits of quantification of 0.005μg/L were routinely achieved. Glyphosate and AMPA were detected in the vast majority of stream water samples in the area of Zurich, Switzerland, with median concentrations of 0.11 and 0.20μg/L and 95th percentile concentrations of 2.1 and 2.6μg/L, respectively. Stream water data and data from treated wastewater indicated that non-agricultural uses may significantly contribute to the overall loads of glyphosate and AMPA in surface waters. In the investigated groundwater samples, selected specifically because they had shown presence of other herbicides in previous monitoring programs, glyphosate and AMPA were generally not detected, except for two monitoring sites in Karst aquifers, indicating that these compounds show much less tendency for leaching.

How does temporal variation affect the value of stream water as a medium for regional geochemical survey?

Stream water is a key medium for regional geochemical survey for mineral exploration and environmental protection. However, stream waters are transient, and measurements are susceptible to various sources of temporal variation. In a regional geochemical survey stream water data comprise ‘snapshots’ of the state of the medium at a sample time. For this reason the British Geological Survey (BGS) has included monitoring streams in its regional geochemical baseline surveys (G-BASE) at which daily stream water samples are collected, over variable time intervals, to supplement the spatial data collected in once-off sampling events.In this study we present results from spatio-temporal analysis of spatial stream water surveys and the associated monitoring stream data. We show that the variability of monitoring stream data from the G-BASE surveys has a temporally correlated component which can be treated as independent between streams, and therefore as a component of the nugget (spatially uncorrelated variance) of the spatial variograms of stream water survey data. For the variables examined this component was small relative to the spatial variability, which indicates that the value of stream water data to provide spatial geochemical information is not compromised by temporal variability. However, these conclusions are conditioned on the particular data set which was collected only in the summer months, specifically to limit temporal variability. Temporal variation in stream water analyses may be less tractable in wetter conditions. We show how the spatial data from stream water surveys can be mapped by ordinary kriging, with the predictions interpreted as an estimate of the temporal (summer months) mean, and the kriging variance reflecting the partition of the nugget variance of the spatial variogram between spatial and temporal components.

Fine-scale temporal characterization of trends in soil water dissolved organic carbon and potential drivers

Long-term monitoring of surface water quality has shown increasing concentrations of dissolved organic carbon (DOC) across a large part of the Northern Hemisphere. Several drivers have been implicated including climate change, land management change, nitrogen and sulphur deposition and CO2 enrichment. Analysis of stream water data, supported by evidence from laboratory studies, indicates that an effect of declining sulphur deposition on catchment soil chemistry is likely to be the primary mechanism, but there are relatively few long term soil water chemistry records in the UK with which to investigate this, and other, hypotheses directly. In this paper, we assess temporal relationships between soil solution chemistry and parameters that have been argued to regulate DOC production and, using a unique set of co-located measurements of weather and bulk deposition and soil solution chemistry provided by the UK Environmental Change Network and the Intensive Forest Monitoring Level II Network. We used statistical non-linear trend analysis to investigate these relationships at 5 forested and 4 non-forested sites from 1993 to 2011. Most trends in soil solution DOC concentration were found to be non-linear. Significant increases in DOC occurred mostly prior to 2005. The magnitude and sign of the trends was associated qualitatively with changes in acid deposition, the presence/absence of a forest canopy, soil depth and soil properties. The strongest increases in DOC were seen in acidic forest soils and were most clearly linked to declining anthropogenic acid deposition, while DOC trends at some sites with westerly locations appeared to have been influenced by shorter-term hydrological variation. The results indicate that widespread DOC increases in surface waters observed elsewhere, are most likely dominated by enhanced mobilization of DOC in surficial organic horizons, rather than changes in the soil water chemistry of deeper horizons. While trends in DOC concentrations in surface horizons have flattened out in recent years, further increases may be expected as soil chemistry continues to adjust to declining inputs of acidity.

Does the spatial arrangement of disturbance within forested watersheds affect loadings of nitrogen to stream waters? A test using Landsat and synoptic stream water data

Remotely sensed maps of forest disturbance provide a powerful tool for predicting spatial and temporal variability in the loading of nitrogen to receiving waters, key data needed for effective watershed management of nutrient pollution. We hypothesize that the spatial arrangement of disturbances within small-forested watersheds can affect N loadings. To test this, we developed schemes for spatially weighting maps of yearly disturbance produced through change analysis of the Landsat Tasseled Cap Disturbance Index (DI), and evaluated the ability of each scheme to predict N concentrations, and subsequently estimated N loads, from forty low-order streams within the Savage River drainage of western Maryland, USA during the 2006–2010 water years, a period encompassing extensive defoliations by gypsy moths (Lymantria dispar). We generated a base scheme of unweighted, watershed averaged change in DI (ΔDI), and five other schemes that weighted ΔDI by either a pixel's flow accumulation value, the distance to the watershed outlet, or proximity to the stream. Over the five years, the flow accumulation scheme tended to perform better than other weighting schemes, and even explained slightly more variability than the base scheme during years of moderate N loads (R2=0.15 vs. 0.03 in 2007 and R2=0.30 vs. 0.18 in 2010). However, this best spatial weighting scheme explained comparable or less variability during the two post-defoliation years with larger N loads (R2=0.43 vs. 0.44 in 2008 and R2=0.31 vs. 0.48 in 2009). Thus, for the purposes of utilizing remote sensing information within watershed management of nutrient pollution, these results suggest that coarse-scale, high temporal frequency data such as MODIS could be well suited for characterizing forest disturbance and predicting the resultant episodic N loads.

Assessments of natural and anthropogenic controls on the spatial distribution of stream water quality in Southeastern Korea

Hydrogeochemical and geostatistical analyses were conducted to evaluate natural and anthropogenic effects using stream water data of Southeastern Korea acquired through the Hydrogeochemical Survey Program of the Korea Institute of Geoscience & Mineral Resources. The results of a variographic analysis of the spatial structure of stream water quality show that the semivarigrams of Ca, Mg, and HCO3 have similar patterns and regional distributions, reflecting the same geogenic source of Paleozoic, Tertiary, and Cretaceous sedimentary rocks. Although Ca and Mg originated from Paleozoic sedimentary rocks, the distribution of Mg is significantly different from that of Ca due to the presence of dolomite in northeastern area of Korea, which enhances the Mg concentration in stream water. Studies of mineralization and acid mine drainage resulting from previous mining activities reveal a high Ba in sedimentary rock from of Kyongsang basin, as well as anomalous concentration of Al, Fe, and SO4 in the Ogcheon and Tabaeksan mineralization areas. Saturation indices of barite determined using average Ba and SO4 concentrations in stream water suggest the existence of barite mineralization deposits in sedimentary rock of Kyongsang Group. Na, Cl, K, NO3, and Cl, exhibit effects of anthropogenic and marine sources in the stream water, with increasing values near residential, agricultural, and coastal areas. Cokriging analyses employing Ca-HCO3, Ca-Sr, Ba-SO4, and Na-Cl also revealed the nature of bedrock geology, mineralization, and anthropogenic and marine sources.

Impact of wildfire on source water contributions in Devil Creek, CA: evidence from end‐member mixing analysis

AbstractA geochemical and end‐member mixing analysis (EMMA) is undertaken in Devil Canyon catchment, located in southern California, to further understanding of watershed behaviour and source water contributions after an acute and extensive wildfire. Physical and chemical transformations in post‐fire watersheds are known to increase overland flow and decrease infiltration, mainly due to formation of a hydrophobic layer at, or near, the soil surface. However, less is known about subsurface flow response in burned watersheds. The current study incorporates EMMA to evaluate and quantify source water contributions before, and after, a catchment affected by wildfires in southern California during the fall of 2003. Pre‐ and post‐fire stream water data were available at several sampling sites within the catchment, allowing the identification of contributing water sources at varying spatial scales. Proposed end‐member observations (groundwater, overland flow, shallow subsurface flow) were also collected to constrain and develop the catchment mixing model. Post‐fire source water changes are more evident in the smaller and faster responding sub‐basin (interior sampling point). Early post‐fire storm events are dominated by overland flow with no significant soil water or groundwater flow contribution. Inter‐storm streamwater in this smaller basin shows an increase in groundwater and a decrease in soil water. In the larger, baseflow‐dominated system, source water components appear less affected by fire. A slight increase in lateral flow is observed with only a slight decrease in baseflow. Changes in the post‐fire flow regimes affect nutrient loading and chemical response of the basin. Relatively rapid recovery of the chaparral ecosystem is evidenced, with active re‐growth and evapotranspiration evidenced by the fourth post‐fire rainy season. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Use of neural networks for monitoring surface water quality changes in a neotropical urban stream

This paper reports the using of neural networks for water quality analysis in a tropical urban stream before (2002) and after sewerage building and the completion of point-source control-based sanitation program (2003). Mathematical modeling divided water quality data in two categories: (a) input of some in situ water quality variables (temperature, pH, O2 concentration, O2 saturation and electrical conductivity) and (b) water chemical composition (N-NO2(-); N-NO3(-); N-NH4(+) Total-N; P-PO4(3-); K+; Ca2+; Mg+2; Cu2+; Zn2+ and Fe+3) as the output from tested models. Stream water data come from fortnightly sampling in five points along the Ipanema stream (Southeast Brazil, Minas Gerais state) plus two points downstream and upstream Ipanema discharge into Doce River. Once the best models are consistent with variables behavior we suggest that neural networking shows potential as a methodology to enhance guidelines for urban streams restoration, conservation and management.

Isotopic characteristics of meteoric waters in the Belgrade region

The stable isotope composition of hydrogen (δ2H) and oxygen (δ18O) in monthly precipitation and river water (Sava River and Danube) samples in the Belgrade area gathered between 1992 and 2005 are determined. The local meteoric water line δ2H=7.8 (±0.2) δ18O+7.3(±1.6) (r 2=0.98, n=60, σ=0.52) for the whole period of observation is close to the global meteoric water line. The amount-weighted mean δ2H and δ18O values of precipitation were−65±27 ‰ and−9.4±3.4 ‰, respectively. Good correlation between δ18O values (r>rsim0.67) and ambient temperature and relative humidity was obtained. Stream-water data ranged from−94 to−60 ‰ for δ2H and from−11.0 to ∼5.7 ‰ for δ18O with highly statistically significant difference (p>0.01) between the Sava River and the Danube. In addition, the isotopic compositions of local precipitation and adjacent river water at monitoring sites were compared. Obtained data will give an opportunity to improve the knowledge of mixing stream water and local groundwater, and assessment of potential groundwater risks and pressures in the Belgrade basin.

Inferring nitrate sources through end member mixing analysis in an intermittent Mediterranean stream

We monitored 24 storms during the period 1998–2002 in order to elucidate whether the origin of nitrate could be inferred from water sources in the catchment. The study was performed in the Fuirosos catchment (10.5 km2) drained by an intermittent stream. Water sources were estimated through end member mixing analysis (EMMA) using chloride, sulfate and dissolved organic carbon as tracers. Three end members were identified in the catchment: event water, hillslope groundwater and riparian groundwater. Streamwater data encompassed the mixing space defined by the end members only during the 12 storms occurred during the wet period (from December to May). Water sources were related to stream nitrate concentrations during 6 of the 12 storms indicating a linkage between hydrological and nitrate sources. However, there was not a consistent pattern of a particular end member being a source of nitrate. EMMA was used to determine expected nitrate concentrations in stream water based on conservative mixing of the different water sources. The effect of the near- and in- stream zones on stream nitrate was inferred by comparing predicted nitrate concentrations to measured stream nitrate concentration. At discharges below 80 l s−1 stream nitrate concentrations were lower than expected from catchment sources in 82% of the cases suggesting nitrate retention in the near stream zones. The trend was the opposite at higher discharges.

A conceptual model of spatially heterogeneous nitrogen leaching from a welsh moorland catchment

Soil- and stream-water data from the Plynlimon research area, mid-Wales, have been used to develop a conceptual model of spatial variations in nitrogen (N) leaching within moorland catchments. Extensive peats, in both hilltop and valley locations, are considered near-complete sinks for inorganic N, but leach the most dissolved organic nitrogen (DON). Peaty mineral soils on hillslopes also retain inorganic N within upper organic horizons, but a proportion percolates into mineral horizons as nitrate (NO−3), either through incomplete immobilisation in the organic layer, or in water bypassing the organic soil matrix via macropores. This NO−3 reaches the stream where mineral soilwaters discharge (via matrix throughflow or pipeflow) directly to the drainage network, or via small N-enriched flush wetlands. NO−3 in hillslope waters discharging into larger valley wetlands will be removed before reaching the stream. A concept of catchment ‘nitrate leaching zones’ is proposed, whereby most stream NO−3 derives from localised areas of mineral soil hillslope draining directly to the stream; the extent of these zones within a catchment may thus determine its overall susceptibility to elevated surface water NO−3 concentrations.

Long‐term trends in stream water and precipitation chemistry at five headwater basins in the northeastern United States

Stream water data from five headwater basins in the northeastern United States covering water years 1968–1996 and precipitation data from eight nearby precipitation monitoring sites covering water years 1984‐1996 were analyzed for temporal trends in chemistry using the nonparametric seasonal Kendall test. Concentrations of SO4declined at three of five streams during 1968–1996 (p &lt; 0.1), and all of the streams exhibited downward trends in SO4 over the second half of the period (1984–1996). Concentrations of SO4 in precipitation declined at seven of eight sites from 1984 to 1996, and the magnitudes of the declines (−0.7 to −2.0 µeq L−1 yr−1) generally were similar to those of stream water SO4. These results indicate that changes in precipitation SO4 were of sufficient magnitude to account for changes in stream water SO4. Concentrations of Ca + Mg declined at three of five streams and five of eight precipitation sites from 1984 to 1996. Precipitation acidity decreased at five of eight sites during the same period, but alkalinity increased in only one stream. In most cases the decreases in stream water SO4 were similar in magnitude to declines in stream water Ca + Mg, which is consistent with the theory of leaching by mobile acid anions in soils. In precipitation the magnitudes of SO4 declines were similar to those of hydrogen, and declines in Ca +Mg were much smaller. This indicates that recent decreases in SO4 deposition are now being reflected in reduced precipitation acidity. The lack of widespread increases in stream water alkalinity, despite the prevalence of downward trends in stream water SO4, suggests that at most sites, increases in stream water pH and acid‐neutralizing capacity may be delayed until higher soil base‐saturation levels are achieved.

Effect of groundwater springs on NO3− concentrations during summer in Catskill Mountain streams

Groundwater and stream water data collected at three headwater catchments in the Neversink River watershed indicate that base flow is sustained by groundwater from two sources: a shallow flow system within the till and soil and a deep flow system within bedrock fractures and bedding planes that discharges as perennial springs. Data from eight wells finished near the till/bedrock interface indicate that saturated conditions are not maintained in the shallow flow system during most summers. In contrast, the discharge of a perennial spring remained constant during two summer rainstorms, providing evidence that the deep flow system is disconnected from the shallow flow system in summer. Discharge from perennial springs was the principal source of streamflow in a headwater reach during low flow. Mean NO3− concentrations were 20–25 μmol L−1 in five perennial springs during the summer but only 5–10 μmol L−1 in shallow groundwater. Thus the deep flow system does not reflect typical NO3− concentrations in the soil during summer. A hydrologic budget at a headwater drainage reveals that March and late fall are the principal groundwater recharge periods. Residence time modeling based on analyses of 18O and 35S indicates that groundwater in the deep flow system is 6–22 months old. These data indicate that summer base flow largely originates from previous dormant seasons when available soil NO3− is greater. In these Catskill watersheds, high base flow concentrations of NO3− during summer do not provide sufficient evidence that the atmospheric N deposition rate exceeds the demand of terrestrial vegetation.

Measured and modelled retention of inorganic sulfur in soils and subsoils (Harz Mountains, Germany)

Atmospheric deposition has resulted in an accumulation of inorganic sulfur (S) in many forest soils. At Sosemulde (Harz Mountains) samples from 5–240 cm depth were analysed. Most sulfate (SO4) is accumulated at about 30–60 cm depth: 8.5–9.5 mmolc kg−1. Large amounts can also be retained in > 100 cm. To assess changes in SO4 dynamics in time,adsorption isotherms have been included in several process-oriented models, e.g., in MAGIC. The Lange Bramke (LB) Model is the first model used on the catchment scale containing solubility products for the hydroxosulfate minerals jurbanite and alunite. By reconstructing the long-term acidification history (140 years) both models were successfully calibrated to a 14-year deposition, soil and streamwater data set at Lange Bramke catchment (Harz Mountains). According to MAGIC the present accumulation of SO4 in 0 –80 cm is 8.7 mmolc kg−1, while according to the LB-Model 10.2 mmolc kg−1 are stored as jurbanite. Both models predicted 4.5 mmolc kg−1 SO4 in the subsoil layer, retained as alunite in the LB Model. These values correspond to the amounts measured in soil and subsoil samples at Sosemulde, respectively. However, for future scenarios with decreasing S inputs the models show different developments in SO4 concentrations. Changes in MAGIC are gradual whereas the LB model predicts stepwise decreasing SO4 values as soon as previously stored hydroxosulfates are fully dissolved. Such concentration “jumps” have not been observed.

Simulated effects of atmospheric sulfur deposition on nutrient cycling in a mixed deciduous forest

The effects of three S deposition scenarios — 50% reduction, no change, and 100% increase — on the cycles of N, P, S, K, Ca, and Mg in a mixed deciduous forest at Coweeta, North Carolina, were simulated using the Nutrient Cycling model (NuCM). The purpose of this exercise was to compare NuCM's output to observed soil and streamwater chemical changes and to explore NuCM's response to varying S deposition scenarios. Ecosystem S content and SO42− leaching were controlled almost entirely by soil SO42− adsorption in the simulations, which was in turn governed by the nature of the Langmuir isotherm set in the model. Both the simulations and the 20-year trends in streamwater SO42− concentration suggest that the ecosystem is slowly becoming S saturated. The streamwater data suggest S saturation is occurring at a slower rate than indicated by the simulations, perhaps because of underestimation of organic S retention in the model. Both the simulations and field data indicated substantial declines in exchangeable bases in A and BA soil horizons, primarily due to vegetation uptake. The correspondence of model output with field data in this case was a result of after-the-fact calibration (i.e. setting weathering rates to very low values) rather than prediction, however. Model output suggests that soil exchangeable cation pools change rapidly, undergoing annual cycles and multi-decade fluctuations.

Limitations to the understanding of ion-exchange and solubility controls for acidic Welsh, Scottish and Norwegian sites

A summary of soilwater and streamwater data from acidic catchments in Wales, Scotland and Norway is presented. It is concluded that insufficient detail has been established to describe quantitatively the ion-exchange and weathering processes in determining streamwater chemistry: such a description is required before reliance can be placed on mathematical models describing short- and long-term changes. The need for manipulative studies is highlighted, emphasis being placed on minimizing perturbation of the system from field conditions. An appeal is made for the use of a standardized method for determining the exchangeable cations. The studies provide overwhelming evidence showing the incorrectness of the commonly used modelling assumption that Al(OH) 3 solubility determines inorganic aluminium levels in the soil and streams. The importance of simple mixing of soil and ground water, in explaining streamwater aluminium-hydrogen ion relationships, is emphasized.