Role of Hydrous Iron Oxide Formation in Attenuation and Diel Cycling of Dissolved Trace Metals in a Stream Affected by Acid Rock Drainage

Mining-impacted streams have been shown to undergo diel (24-h) fluctuations in concentrations of major and trace elements. Fisher Creek in south-central Montana, USA receives acid rock drainage (ARD) from natural and mining-related sources. A previous diel field study found substantial changes in dissolved metal concentrations at three sites with differing pH regimes during a 24-h period in August 2002. The current work discusses follow-up field sampling of Fisher Creek as well as field and laboratory experiments that examine in greater detail the underlying processes involved in the observed diel concentration changes. The field experiments employed in-stream chambers that were either transparent or opaque to light, filled with stream water and sediment (cobbles coated with hydrous Fe and Al oxides), and placed in the stream to maintain the same temperature. Three sets of laboratory experiments were performed: (1) equilibration of a Cu(II) and Zn(II) containing solution with Fisher Creek stream sediment at pH 6.9 and different temperatures; (2) titration of Fisher Creek water from pH 3.1 to 7 under four different isothermal conditions; and (3) analysis of the effects of temperature on the interaction of an Fe(II) containing solution with Fisher Creek stream sediment under non-oxidizing conditions. Results of these studies are consistent with a model in which Cu, Fe(II), and to a lesser extent Zn, are adsorbed or co-precipitated with hydrous Fe and Al oxides as the pH of Fisher Creek increases from 5.3 to 7.0. The extent of metal attenuation is strongly temperature-dependent, being more pronounced in warm vs. cold water. Furthermore, the sorption/co-precipitation process is shown to be irreversible; once the Cu, Zn, and Fe(II) are removed from solution in warm water, a decrease in temperature does not release the metals back to the water column.     

Photosynthetically Mediated Zn Removal from the Water Column in High Ore Creek, Montana

We collected cobbles covered in biofilm from High Ore Creek, Montana, placed them in 12 transparent PVC plastic chambers, and exposed the chambers to four treatments: Sunlight, Sunlight-occluded, DCMU (photosynthesis inhibited), and Formalin. Total aqueous zinc (Zn) concentrations in the Sunlight treatment decreased during the 4-h experiment and were significantly lower (P?≤?0.05) than in the other three treatments, in which the total aqueous Zn concentrations did not decrease significantly. Therefore, we believe photosynthesis in the biofilm played a role in causing total aqueous Zn concentrations in the Sunlight treatment to decrease, and we believe a similar process contributes to diel Zn cycling in High Ore Creek and some other metals-contaminated streams.     

Processes Controlling Trace-Metal Transport in Surface Water Contaminated by Acid-Mine Drainage in the Ducktown Mining District, Tennessee

Former mining activities lasting 140 years in the Ducktown Mining District, Tennessee, USA, has contaminated the streams draining the district with acid-mine drainage (AMD). North Potato Creek and its major tributary, Burra Burra Creek, are two of the most heavily AMD-impacted streams in the district. The removal of dissolved metals from the water in these creeks is largely attributable to the sorption of Cu, Zn, Co, Al, and Mn on suspended hydroxide precipitates of Fe. The fraction of trace metals remaining in solution decreases with increasing pH in the sequence Pb?<?Cu?<?Zn?<?Co. The concentration of Fe in solution also decreases with increasing pH due to the formation of ferric hydroxide precipitates which accounted for up to 81.4% by weight of the total suspended sediment. The concentration of suspended sediment substantially decreases as the water of North Potato Creek flows through a large settling basin, where 1.3 (±0.3)?×?10⁶ kg/year of trace-metal-laden suspended sediment would be annually deposited. In spite of this attempt to purify it, the water discharged into the river is acidic (pH 3.6) and still contains high concentrations of dissolved trace metals, which would resorb on to suspended sediment and be ultimately transported to a downstream reservoir, Ocoee No. 3 Lake.     

Acidification and anadromous fish of Atlantic estuaries

The Hudson River Foundation convened a conference to evaluate evidence pertaining to the roles played by acid deposition and stream acidification in the decline of anadromous fish populations along the Atlantic coastal plain. The stimuli for the conference were that (1) some populations of Atlantic salmon, American shad, hickory shad, alewives, blueback herring and striped bass as well as a few species resident in coastal streams (yellow perch and white perch) are in a state of severe decline along portions of the east coast of North America; (2) several of these species have declined more or less simultaneously since about 1970; and (3) severe episodic pH depressions are observed in some streams of the Chesapeake Bay system. For example, the pH of Lyons Creek decreased from 7.0 to 5.9 in 1 hr during a rain event, returning to 7.0 a day later. After discussing several possible mechanisms for these observations, the conferees agreed that a combination of factors including stream and river acidification, toxic metals and organic compounds, eutrophication and overfishing appears to be contributing to the reduction in fish stocks. The essential point resulting from the conference is that the acid deposition hypotheses for stream acidification and declines of anadromous fish populations, a potential mechanism that has received very little attention heretofore, was shown to be viable for these coastal areas. Specific recommendations for research were agreed upon by the conferees.     

Relationship Between Benthic Fluxes and Macrophyte Cover in a Shallow Brackish Lagoon

The relationship between macrophyte cover and benthic fluxes of oxygen. nutrients and sulphide has been examined in a shallow fishpond with a nearly homogeneous meadow ofRuppia cirrhosa (Pelagna) Grande (Bassin d'Arcachon. western France). In 1993 and 1994, benthic fluxes were treasured in early and late summer. These periods were selected to represent the production and decay phases ofRuppia in order to determine the effect on benthic processes. Benthic fluxes of elements were measured by means of multiple dark and light benthic chambers in the presence or absence of community components. In summer 1994. at the end of the incubation period, profiles of acid volatile sulphide (AVS) and chromium reducible sulphur (CRS) were measured also in the 0–5 cm sediment horizon in cores withdrawn from the dark benthic chambers and from the sediment outside the chambers. Oxygen production and consumption were closely related to macrophyte cover, whilst the contributions of plankton and microphytobenthic communities were less significant. In the water column, dissolved inorganic nutrients were almost totally depleted, while dissolved organic nitrogen attained concentrations up to 200 μM. In late summer.Ruppia biomass underwent a significant decay due to the build up of a thick epiphyte layer, mostly around floating leaves. The epiphyte slime was rich in labile organic matter, the decomposition of which led to a significant oxygen uptake as well as to sulphide production. Therefore, we postulate that epiphyte growth can cause disturbance in the aquatic system keeping dissolved sulphide at very high levels. Biogeochemical reactions, such as precipitation of iron sulphide, can exert a control lowering the amplitude of such disturbances.     

Diel turbidity cycles in a headwater stream: evidence of nocturnal bioturbation?

Purpose

A small number of recent studies have linked daily cycles in stream turbidity to nocturnal bioturbation by aquatic fauna, principally crayfish, and demonstrated this process can significantly impact upon water quality under baseflow conditions. Adding to this limited body of research, we use high-resolution water quality monitoring data to investigate evidence of diel turbidity cycles in a lowland, headwater stream with a known signal crayfish (Pacifastacus leniusculus) population and explore a range of potential causal mechanisms.

Materials and methods

Automatic bankside monitoring stations measured turbidity and other water quality parameters at 30-min resolution at three locations on the River Blackwater, Norfolk, UK, during 2013. Specifically, we focused on two 20-day periods of baseflow conditions during January and April 2013 which displayed turbidity trends typical of winter and spring seasons, respectively. The turbidity time-series, which were smoothed with 6.5-h Savitzky-Golay filters to highlight diel trends, were correlated against temperature, stage, dissolved oxygen and pH to assess the importance of abiotic influences on turbidity. Turbidity was also calibrated against suspended particulate matter (SPM) over a wide range of values via linear regression.

Results and discussion

Pronounced diel turbidity cycles were found at two of the three sites under baseflow conditions during April. Spring night-time turbidity values consistently peaked between 21:00 and 04:00 with values increasing by ~10 nephelometric turbidity units (NTU) compared with the lowest recorded daytime values which occurred between 10:00 and 14:00. This translated into statistically significant increases in median midnight SPM concentration of up to 76 % compared with midday, with night-time (18:00–05:30) SPM loads also up to 30 % higher than that recorded during the daytime (06:00–17:30). Relating turbidity to other water quality parameters exhibiting diel cycles revealed there to be neither any correlation that might indicate a causal link nor any obvious mechanistic connections to explain the temporal turbidity trends. Diel turbidity cycles were less prominent at all sites during the winter.

Conclusions

Considering the seasonality and timing of elevated turbidity, visual observations of crayfish activity and an absence of mechanistic connections with other water quality parameters, the results presented here are consistent with the hypothesis that nocturnal bioturbation is responsible for generating diel turbidity cycles under baseflow conditions in headwater streams. However, further research in a variety of fluvial environments is required to better assess the spatial extent, importance and causal mechanisms of this phenomenon.

     

Chemical characteristics and temporal trends in eight streams of the Catskill Mountains,New York

Discharge to concentration relationships for eight streams studied by the U.S. Geological Survey (USGS) as part of the U.S. Environmental Protection Agency's (U.S. EPA) Long-Term Monitoring Project (1983–89) indicate acidification of some streams by H₂SO₄ and HNO₃ in atmospheric deposition and by organic acids in soils. Concentrations of major ions in precipitation were similar to those reported at other sites in the northeastern United States. Average concentrations of SO₄ ^2? and NO₃ ^? were similar among streams, but base cation concentrations differed widely, and these differences paralleled the differences in acid neutralizing capacity (ANC). Baseflow ANC is not a reliable predictor of stream acidity at high flow; some streams with high baseflow ANC (>150 Μeq L^?1) declined to near zero ANC at high flow, and one stream with low baseflow ANC (<50 Μeq L^?1) did not approach zero ANC as flow increased. Episodic decreases in ANC and pH during peak flows were associated with increased concentrations of NO₃ ^? and dissolved organic carbon (DOC). Aluminum concentrations exceeding 300 Μg L^?1 were observed during peak flows in headwater streams of the Neversink River and Rondout Creek. Seasonal Kendall Tau tests for temporal trends indicate that SO₄ ^2? concentrations in streamwater generally decreased and NO₃ ^? concentrations increased during the period 1983–1989. Combined acid anion concentrations (SO₄ ^2? + NO₃ ^?) were generally unchanged throughout the period of record, indicating both that the status of these streams with respect to acidic deposition is unchanged, and that NO₃ ^? is gradually replacing SO₄ ^2? as the dominant acid anion in the Catskill streams.     

Seasonal patterns of mineral and organic acidification in two streams in Southwestern Nova Scotia

DOC concentrations in two streams of different hydrologic order are highly variable with the higher order stream exhibiting approximately a 3 mo response lag. Seasonal variation of SO⁴ concentration and flux are similar in both streams and do not reflect the seasonal patterns in precipitation. The basins store SO₄ from May to November and lose SO₄ from December to April. Consequently, SO⁴ concentrations and flux are maximum during January to March and reach a minimum during July to September. The highly organic lower order stream exhibits relatively stable pH controlled by two competing mechanisms. The pH is dominated by organic acids during the summer and autumn and by mineral acids during the late winter and early spring. In the higher order system, the pH tends to be inversely related to changes in SO₄ concentration. These observations suggest that organic systems do respond to acidic deposition but that in some systems mineral acid influence may be restricted to the winter and spring.     

Relationship Between pH and Stream Water Total Mercury Concentrations in Shenandoah National Park

The purpose of this study was to gather information on the spatial and temporal variation of stream water total mercury concentrations ([THg]) and to test the hypothesis that stream water [THg] increases as stream pH decreases in the Shenandoah National Park (SNP). We based our hypothesis on studies in lakes that found mercury methylation increases with decreasing pH, and studies in streams that found total mercury and other trace metal concentrations increase with decreasing pH. Stream water was collected at baseflow in SNP in April, July, and October 2005 and February 2006. Contrary to our hypothesis, stream water [THg] decreased with decreasing pH and acid neutralizing capacity. In SNP, stream pH and acid neutralizing capacity are strongly influenced by bedrock geology. We found that bedrock also influences stream water [THg]. Streams on basaltic bedrock had higher [THg] (0.648 ng L^?1?±?0.39) than streams on siliciclastic bedrock (0.301 ng L^?1?±?0.10) and streams on granitic bedrock (0.522 ng L^?1?±?0.06). The higher pH streams on basaltic bedrock had the highest [THg]. The variation in stream water [THg] occurred despite no known variation in wet deposition of mercury across the SNP. The findings of this study indicate that the SNP can be an important area for mercury research with significant variations in mercury concentrations across the park.     

In-Stream Processing of Sediment-Associated Metals in Peatland Fluvial Systems

The interaction between fluvially transported, metal contaminated peat particulates and acidic waters draining peatland catchments has received limited attention. Potential in-stream processing of sediment-associated metals in acidic stream water was investigated in laboratory based mixing experiments, designed to represent conditions of fluvial sediment transport in a highly contaminated and severely eroding peatland catchment in the Peak District (UK). Over the initial 20 min of the first experiment, stream water Cr and Zn concentrations increased by at least an order-of-magnitude and remained elevated for the full duration (24 h) of the experiment. Stream water As, Mo, Pb, Ti and V concentrations increased between 43% (As) and 440% (V) over the first hour of the experiment. After 24 h most of the metals appeared to have reached equilibrium in the water column. Results of the second experiment revealed that when the concentration of metal contaminated peat particulates is increased, there is an associated increase in the stream water As, Cr, Mo, Pb, Ti, V and Zn concentrations. The experimental data suggest that As, Cr, Mo, Pb, Ti, V and Zn are liable to desorption from metal contaminated peat into acidic stream water. The solubilisation of contaminated peat particulates may also contribute to elevated stream water metal concentrations. The laboratory based approach used in this study may indicate that when there is erosion of metal contaminated peat into acidic fluvial systems there is a concomitant increase in dissolved metal levels, especially when suspended sediment concentrations are high. Further laboratory and field based experiments are required to evaluate the relative importance of physical and chemical processes in the interaction between contaminated peat particulates and stream water in peatland fluvial systems.     

Dynamics of Dissolved Forms of Carbon and Inorganic Nitrogen in Small Watersheds of the Coastal Atlantic Forest in Southeast Brazil

Based on the fact that streamwater quality reflects landscape conditions, the objectives of this study were: to investigate nitrogen (N), carbon (C), and major ion concentrations in six streams crossing minimally disturbed Atlantic Forest areas, with similar geomorphological characteristics; to determine N and C fluxes in one of these pristine streams (Indaiá); and assess the impact of human activity on the biogeochemistry of two other streams in the same region, crossing urbanized areas. The distribution pattern of carbon and inorganic nitrogen dissolved forms, as well as the major ion and biogenic gas concentrations in the streamwater, was similar in pristine streams, indicating that the C and N dynamics were determined by influence of some factors, such as climate, atmospheric deposition, geology, soil type, and land covering, which were analogous in the forested watersheds. The urban streams were significantly different from the pristine streams, showing low dissolved oxygen concentrations, high respiration rates, and high concentrations of carbon dioxide, dissolved inorganic nitrogen, dissolved inorganic carbon, and major ion. These differences were attributed to anthropogenic impact on water quality, especially domestic sewage discharge. Additionally, in the Indaiá stream, it was possible to observe the importance of rainfall over temporal dynamics of dissolved carbon forms, and also, the obtained specific flux of dissolved inorganic nitrogen was relatively elevated (approximately 11 kg ha^?1 year^?1). These results reveal the influence of human activity over the biogeochemistry of coastal streams and also indicate the importance N export of Atlantic Forest to the ocean.     

SOURCES OF TRACE METALS IN STREAMS AND HEADWATER LAKES IN FINLAND

Distributions of Mn, Zn, Cu, Ni, Cr, Pb, As, and Cd in Finnish surface waters were studied by comparing two data sets: samples from 154 headwater lakes collected by the Water and Environment Administration in 1992 and samples from 1165 headwater streams collected during the environmental geochemical mapping program of the Geological Survey of Finland in 1990. It was expected that headwater lakes with catchments smaller than 1 km² and high lake percentage (ratio of lake area to catchment size) would be more influenced by atmospheric trace metal deposition than the streams, with average catchment size of 30 km². The lakes with highest arsenic concentrations lie in an area with greenstones and arsenic-rich black schists. The same lakes have high copper concentrations, which evidently are derived from the Cu-rich greenstones of the catchment. The high copper concentrations of streams and lakes in the industrialized region of the southwest coast are due to several anthropogenic sources. The highest concentrations of chromium occur in brown stream and lake waters rich in humic matter, while manganese and zinc concentrations, which are controlled by acidity, tend to be elevated in low-pH waters. The high nickel concentrations in lakes in southwestern Finland probably are due to anthropogenic input, while Ni anomalies in stream and lake water in eastern Finland are correlated with high Ni contents of glacial till. The lead concentrations in lakes are mainly of airborne anthropogenic origin. The pattern of atmospheric deposition is reflected in the concentrations of Cd, As, Cu, Zn, and Ni in headwater lakes, but land-use, the natural distribution of metals in the overburden, water acidity, and the amount of humic substances influence the distribution of trace metals in both lakes and streams. Thus the trace metal distribution in headwater lakes cannot be used alone to estimate the contribution of anthropogenic atmospheric deposition to metal anomalies in Finnish surface waters.     

Groundwater Contribution of Metals from an Abandoned Mine to The North Fork of The American Fork River, Utah

Surface water discharge measurements and metals concentrations in the North Fork of the American Fork River, Utah, its tributaries, and the groundwater in the vicinity of the Pacific Mine were used to evaluate the impact of groundwater on loading rates of metals and As to the river. Fish in the river contain As, Cd, and Pb at concentrations that are hazardous to human health if consumed. The results suggest that dissolved As, Cd, Cu, Fe, Mn, Pb, and Zn enter the river when it is a gaining stream. However, the suspended metals load is significantly greater than the dissolved load, and generally decreases through the reach of river adjacent to the mine site. Cadmium and Mn travel as dissolved species while Cu, Fe, Pb, and Zn travel as suspended solids. Arsenic seems to travel both with the suspended solids and in the dissolved state. The geochemical modeling program PHREEQC and a diffuse double layer surface complexation model were used to investigate the chemical controls on metals mobility and attenuation in the surface and groundwaters at the site. Based on the PHREEQC results, the most important process in these waters is the precipitation of ferrihydrite, also referred to as hydrous ferric oxide (HFO). Copper, Pb, most importantly Zn, and to a lesser degree As sorb to HFO.     

Variations in the Diurnal Flux of Greenhouse Gases from Soil and Optimizing the Sampling Protocol for Closed Static Chambers

There is no standardized method for the sampling of greenhouse gas fluxes from soil. Two methods are primarily used: closed dynamic chamber (CDC) and closed static chamber (CSC) systems. The most complex and costly are the CDC systems, which can sample gases in situ. However, the low-cost CSC systems are being increasingly used in which the gas samples are collected manually and analyzed off-site at a later date. Given their growing popularity, it is important to optimize the sampling procedure of the CSC systems to ensure that the measurements are both repeatable and representative. Samples from a commercial potato crop were collected in the morning and afternoon at 0, 15, 30, 60, 90, and 120 min after the chambers were closed, and the concentrations of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) were determined using gas chromatography. The concentrations of CO₂ and N₂O inside chambers increased linearly over time, whereas the concentration of CH₄ remained constant. The fluxes of CO₂ and N₂O from soil were greater in the afternoon than the morning, whereas the flux of CH₄ was greater in the morning. For longer-term single-point soil flux monitoring using CSCs with a volume of 6.3 L, it is recommended that samples are collected in the morning at 0, 30, and 60 min after chambers are closed. This approach will ensure that the concentration of the gases are representative and will allow for a high level of repeatability and certainty in the results.     

Influence of Natural Sources on Mercury in Water, Sediment and Aquatic Biota in Seven Tributary Streams of the East Fork of the Upper Carson River, California

The East Fork of the Upper Carson River (EFUCR) drainagebasin contains the Leviathan mine site, a known source of acidmine drainage, and numerous small prospects and mineralizedareas, some of which are enriched in mercury. In 1999 aninvestigation was undertaken to characterize total mercuryconcentrations in water, sediment, and whole aquaticmacroinvertebrates from seven tributaries of the EFUCR watershedon a seasonal time step. In the fall, methyl mercury in water,sediment and Stoneflys was determined for three sites. Both total and dissolved mercury in water at all sites, notimpacted by acid mine drainage, exhibited a seasonal trend withthe lowest concentrations occurring in the winter, higherconcentrations in the summer, and the highest concentrationsrecorded in the fall. Winter samples were taken during a periodof ice melt. It is hypothesized that the high fall concentrations were due to elevated mercury concentrations ingroundwater, which was recharging the stream under baseflow conditions and had interacted with substrate naturally enrichedin mercury. Mercury concentrations in Leviathan Creek wereelevated when acid mine drainage was being discharged directlyinto the Creek. Mercury concentrations in individual stoneflyscollected from specific stream reaches were similar, and methylmercury and total mercury concentrations in macroinvertebratetissue were roughly equivalent. Comparison of mercury bodyburden of macroinvertebrates between tributaries showed thatmacroinvertebrates in the Cottonwood Creek watershed had highermercury concentrations relative to the other sites. Thistributary had higher sediment mercury concentrations than allsimilar tributaries not impacted by acid mine drainage.     

Aluminum speciation in running waters on the Canadian pre-Cambrian Shield: Kinetic aspects

To evaluate the extent to which chemical disequilibrium may exist in stream waters following naturally occurring short-term pH changes, surface water samples were collected from two streams in the Lake Laflamme watershed north of Quebec City, placed in large polyethylene containers and stirred continuously at the in situ temperature; changes in Al speciation were followed with time for up to 24 hr. The original samples were collected during the spring snow-melt period and during summer low flows. In this latter case, a pH depression was induced by artificial acidification (H₂SO₄; pH 4) and changes in Al speciation with time were followed in both the acidified and the unacidified samples. Aluminum speciation as operationally defined did respond to artificial acidification (pH lowered; non-exchangeable and non-extractable Al decreased), and these pH-induced changes occurred rapidly (< 4 hr). During storage of natural water samples at in situ T for up to 24 hr, little change in Al speciation was noted, even in the case of samples collected during spring snow-melt; no clear cases of chemical disequilibrium existed among the studied samples. The distribution of Al among its various physico-chemical forms thus appears to be established within the stream itself; at a given stream sampling point the speciation of A1 will not necessarily reflect its geochemical origins, but rather the prevailing in situ conditions (e.g. pH, ligand concentrations).     

Geochemical Behavior of Dissolved Organic Carbon under Baseflow Conditions at the Corbeira Stream Water,Spain

Geochemical processes related to dissolved organic carbon (DOC) under baseflow are studied in Corbeira Stream (northwestern Spain). The stream drains a catchment occupied by forest and agricultural fields. Dissolved organic carbon and other chemical parameters were analyzed. Seasonally, DOC values show a gradual rising background beginning in late spring to summer, finishing with major anomalies in the early to middle autumn. Suspended solids (SS) values exhibit a steady to falling background. The greatest DOC peaks seem be a function of rising temperatures and degradation of organic matter in wet soils. Divergent DOC and SS backgrounds in dry season and synchronicity between DOC-SS peaks associated with negative correlation of SS to pH in autumn seem be conspicuous geochemical signatures in perennial streams under temperate climates. The first one indicates the predominance of subsurface flows in streams, and the second one indicates the predominance of overland runoff.     

The effect of pH and atmospheric deposition on concentrations of trace elements in acidified freshwaters: A statistical approach

A statistical evaluation of 5 338 analysis of freshwaters from little polluted stream basins in the Czech Republic indicated a relationship between the Pb, Cu, Zn, Cd, Be, As, Mn, Sr, F^? and Fe concentrations and the pH, over a range of pH 3.6 to 9.6. Except for Sr, the median concentrations of all the trace metals increase with decreasing pH, but the increase never extends over the whole studied acidic range (pH 3.6 to 7.0). Acid deposition related mobilization of Mn and Be into freshwaters explains the sharp increase in their concentrations with decreasing pH. Cadmium and Zn are also mobilized n strongly acidic environment. The concentrations of Be, As, F^? and Mn in strongly acidic waters and those of Zn and Cd in weakly acidic ones are considerably higher in areas receiving a higher atmospheric loading. For Be and Mn, the higher concentrations are caused by higher acid deposition rates, while for As and F^?, the concentrations are probably greater due to higher atmospheric deposition of these elements over more intensely acontaminated areas of the Czech Republic. In extremely acidic waters (pH < 4.2), the concentrations of Mn, Be, Cd, Zn and Al no longer increase with decreasing pH; on the contrary, those of Mn and Be actually decrease. This seems to be primarily caused by a decrease in their concentrations within the surface horizons of soils and vegetation induced by prolonged leaching. The Cd and Zn concentrations are independent of pH over an interval of pH 5.4 to 6.0 and thus the increase in the mean concentrations of Cd and Zn with decreasing pH involves two separate stages, at pH > 6.0 and at pH < 5.4. The concentrations of Cu in acid freshwaters are controlled by both the presence of high molecular weight organics plus biota uptake and by their atmospheric deposition levels; the concentrations of As and Pb are in addition controlled by sorption on Fe - oxyhydroxides. These elements accumulate in the topsoil, even under conditions of severe acidification. The surprisingly lower concentrations of Pb and Cu were found in acidic waters of more contaminated areas.     

Geochemical multifractal distribution patterns in sediments from ordered streams

For geochemical exploration, the stream sediment survey is of great importance for the delineation of geochemical anomalies and the distribution patterns of chemical elements are critical for anomaly recognition and mineral resource assessment. To study the distribution patterns of elements, we collected 7113 stream sediment samples along stream networks with seven orders from an area in the Qulong region of Tibet in southwest China where numerous polymetallic Cu deposits have been found. Thirteen elements, including Cu, Ag, As, Au, Ba, Bi, Hg, Mo, Pb, Sb, Sn, Zn, and W, were measured in each sample. The distribution patterns of the element concentrations are represented by multifractal spectrum estimated by the method of moments and characterized by six quantitative multifractal parameters. The multifractalities and inhomogeneity of the elements grow stronger as the elements transported from the main streams to the streams of order 1. Our study shows that the Cu anomalies delineated by the multifractal inverse distance weighted interpolation analysis correspond from streams of order 1 to streams of order 5, which indicates the self-similarity of geochemical variables. These results strongly suggested that the multifractal model and the multifractal parameters might be useful in estimating other stream sediments' properties and studying the geochemical dynamic transport behaviors of elements in stream sediments, which also might be extended to study the physical and chemical properties of soils from different horizons and other kinds of media at different scales as well.     

Trace Elements in Coalbed Methane Produced Water Interacting with Semi-Arid Ephemeral Stream Channels

The objective of this study was to examine the chemistry of trace elements in coalbed methane (CBM) discharge water reacting with semi-arid ephemeral stream channels in Powder River Basin, Wyoming. The study area consisted of two ephemeral streams, Burger Draw and Sue Draw. These streams are tributaries to the perennial Powder River, Wyoming. Samples were collected bimonthly from three CBM discharge points and seven channel locations in Burger Draw and Sue Draw. Samples were also collected bimonthly from the Powder River above and below the confluence of Burger Draw. Before sample collection, pH, temperature, dissolved oxygen (DO), and turbidity were measured in the field. Samples were transported to the laboratory and analyzed for dissolved trace elements including iron (Fe), manganese (Mn), boron (B), arsenic (As), selenium (Se), and fluoride (F). Results suggest pH of discharge water was 7.1 and increased significantly in the downstream channel of Burger Draw to 8.84 before joined with the Powder River. Temperature of CBM produced water at discharge points ranged between 20.3 and 22.7 ^°C. Before discharge, DO concentrations of CBM produced water were between 1.42 and 1.5 mg/L. No significant differences in temperature, DO, and turbidity were found between Burger Draw flow and Powder River flow. However, significant differences were found within the sampling period in temperature and turbidity in flow of Burger Draw. The temperature, DO, and turbidity were all significantly different in Powder River within the sampling period. The CBM discharge water consisted of higher concentrations of F, Fe and B compared to other components. Significant changes were observed for Fe, Mn, and As; and seasonally for B. Dissolved Fe and Mn decreased, while As and Se increased in downstream channel flow. These findings will be useful in proper management of CBM produced water in semi-arid environments.