Soil Solution Chemical Response to Two Decades of Experimental Acidification at the Bear Brook Watershed in Maine

We examined long-term changes in soil solution chemistry associated with experimental, whole watershed-acidification at the Bear Brook Watershed in Maine (BBWM). At BBWM, the West Bear (WB) watershed has been treated with bimonthly additions of ((NH₄)₂ SO₄) since 1989. The adjacent East Bear (EB) watershed serves as a biogeochemical reference. Soil solution chemistry in the EB watershed was relatively stable from 1989?C2007, with the exception of declining SO₄?CS concentrations associated with a progressive decline in SO₄?CS deposition during this period. Soil solution chemistry in WB reflected a progressive change in acid-neutralization mechanisms from base cation buffering to Al buffering associated with treatment during this period. Total dissolved Al concentrations progressively increased over time and were ~4× higher in 2007 than in 1989. Treatment of WB was also associated with long-term increases in soil solution H⁺, SO₄?CS, and NO₃?CN, whereas soil solution dissolved organic carbon (DOC) was unresponsive to treatment. For solutes such as Ca, H⁺, and SO₄?CS, changes in stream chemistry were generally parallel to changes in soil solution chemistry, indicating a close coupling of terrestrial and aquatic processes that regulate the chemistry of solutions in this first-order stream watershed. For other solutes such as Al and DOC, solute concentrations were higher in soil solutions compared with streams, suggesting that sorption and transformation processes along hydrologic flow-paths were important in regulating the chemistry of solutions and the transport of these solutes.     

施用碱稳定污泥污水土壤经γ-辐照后土壤溶液中Cu和Zn

Soil samples collected from several acid soils in Guangdong, Fujian, Zhejiang and Anhui provinces of the southern China were employed to characterize the chemical species of aluminumions in the soils. The proportion of monomeric inorganic Al to total Al in soil solution was in the range of 19% to 70%, that of monomeric organic Al (Al-OM) to total Al ranged from 7.7% to 69%, and that of the acid-soluble Al to total Al was generally smaller and was lower than 20% in most of the acid soils studied. The Al-OM concentration in soil solution was positively correlated with the content of dissolved organic carbon (DOC) and also affected by the concentration of Al³⁺. The complexes of aluminum with fluoride (Al-F) were the predominant forms of inorganic Al, and the proportion of Al-F complexes to total inorganic Al increased with pH. Under strongly acid condition, Al³⁺ was also a major form of inorganic Al, and the proportion of Al³⁺ to total inorganic Al decreased with increasing pH. The proportions of Al-OH and Al-SO₄ complexes to total inorganic Al were small and were not larger than 10% in the most acid soils. The concentration of inorganic Al in solution depended largely on pH and the concentration of total F in soil solution. The concentrat ions of Al-OM, Al³⁺, Al-F and Al-OH complexes in topsoil were higher than those in subsoil and decreased with the increase in soil depth. The chemical species of aluminumions were influenced by pH. The concentrations of Al-OM, Al³⁺, Al-F complexes and Al-OH complexes decreased with the increase in pH.     

Aluminum species in porewaters of Kejimkujik and Mountain Lakes,Nova Scotia

Sediment porewaters were recovered by the membrane dialysis technique from Kejimkujik Lake and Mountain Lake in Nova Scotia and analyzed for pH, dissolved organic carbon (DOC), total (acid soluble) aluminum, total reactive monomeric aluminum (TRM-Al), organic monomeric aluminum and inorganic monomeric aluminum. The results show that in the colored lake water (Kejimkujik), close to 100% of the TRM-Al fraction is bound to organic matter and that 10 to 60% of the total-Al is in the monomeric form. In the clearwater lake (Mountain), 50 to 65% of TRM-Al fraction is associated with organic matter and less than 4 to 5% of the Total-Al is in the monomeric form. The concentrations of reactive monomeric species in organic-rich porewaters decrease with time of storage due to the precipitation of organo-Al compounds. Model calculations using the porewater profiles for Al suggest that the sediment can be an important source of dissolved Al to the overlying water.     

Hydrologic pathways and chemical composition of runoff during snowmelt in Loch Vale Watershed,Rocky Mountain National Park,Colorado, USA

Intensive sampling of a stream draining an alpine-subalpine basin revealed that depressions in pH and acid neutralizing capacity (ANC) of surface water at the beginning of the spring snowmelt in 1987 and 1988 were not accompanied by increases in strong acid anions, and that surface waters did not become acidic (ANC<0). Samples of meltwater collected at the base of the snowpack in 1987 were acidic and exhibited distinct ‘pulses’ of nitrate and sulfate. Solutions collected with lysimeters in forest soils adjacent to the stream revealed high levels of dissolved organic carbon (DOC) and total Al. Peaks in concentration of DOC, Al, and nutrient species in the stream samples indicate a flush of soil solution into the surface water at the beginning of the melt. Infiltration of meltwater into soils and spatial heterogeneity in the timing of melting across the basin prevented stream and lake waters from becoming acidic.     

Effects of lime applications to parts of an upland catchment on soil properties and the chemistry of drainage waters

The liming of soils in the lower part of an upland catchment was found to have a major effect on both soil properties and the chemistry of drainage waters. Exchangeable Al was closely correlated with soil pH and showed a very steep rise from 2.6-4.8 meq 1⁻¹ over the pH range 5.5-4.5. As streams flowed from unimproved through improved land there was an increase in pH and the concentration of all major anions and basic cations. The greatest increase was in Ca (approximately 3.5-fold). The concentrations of all dissolved Al species decreased, with inorganic monomeric Al falling to near zero. Leachates were examined from soils representative of the most acidic and the least acidic. Calcium concentrations differed by almost tenfold. Aluminium was present in leachates from the limed soil, but most was unreactive and none was inorganic monomeric. Most of the Al leached from the acid soil was monomeric.
A model of soil acidification is proposed in which soil Ca is depleted at a rate of 8% of the exchangeable Ca per annum. The model predicts that liming a soil to neutrality would be likely to influence drainage water chemistry for 30-40 years and that the most acidic soils of the catchment show no net loss of Ca to drainage.     

Geochemical Mobility and Bioavailability of Heavy Metals in a Lake Affected by Acid Mine Drainage: Lake Hope, Vinton County, Ohio

Sandy Run (Vinton County, southeastern Ohio, USA) is a stream receiving acid mine drainage (AMD) from an abandoned coal mine complex. This stream has been dammed to form Lake Hope. The heavy metal composition of waters (benthic and pore), sediments, and macroinvertebrates in the lake reservoir sediments were analyzed. Lake waters contained Mn as the heavy metal present in higher concentrations followed by Fe, Al, and Zn. Depletion of Fe and Al occurred from precipitation of less soluble Fe and Al oxides and hydroxides along Sandy Run before entering the lake, producing a high Mn water input into the reservoir. Concentrations of heavy metals in the sediments increased toward the dam area. Sequential extraction of metals in the sediments showed that the highest fractions of metals corresponded to the detrital fraction or eroded material from the watershed and metals associated with iron and manganese hydroxides. Heavy metals in the organic sediment fraction were low. Heavy metals from the AMD source, as well as sediments rich in heavy metals eroded from the watershed, were transported to the downstream dam area and stored at the bottom, producing the observed chemistry. Heavy metals in benthic waters also were sourced from the diffusion of ions from sediments and lake waters as variation in pH and redox conditions determined the flux at the sediment–water interface. Metal concentrations were measured within two deposit feeders, oligochaetes and chironomids, and compared to trends in physical metal concentration across the lake. For the four heavy metals with higher concentration in both benthic animals, the concentrations followed the trend: Fe?>?Al?>?Mn?>?Zn, which were similar to the bioavailable metals in the sediments rather than the pore or the benthic water where Mn was the most abundant heavy metal. Ingestion of sediment, not exposure to pore or benthic waters, appeared to be the main transfer mechanism for metals into the biota. Trends and patterns in animal metal concentrations across the lake were probably a complex process controlled by metabolic needs and metallic regulation and tolerance. Even when Mn was the highest concentration heavy metal in the pore waters, it was the lowest to bioconcentrate in the organisms. In comparison, Cd, the lowest concentration metal in the sediments, presented one of the highest bioaccumulation factors.     

Changes in the concentrations and speciation of aluminum in response to an experimental addition of ammonium sulfate to the bear Brook Watershed,Maine, USA

An understanding of the biogeochemistry of aluminum (Al) in acid-sensitive terrestrial and aquatic ecosystems is critical to assessments of the effects of acidic deposition. Bear Brook Watershed, Maine, USA includes paired watersheds, East Bear and West Bear. Starting in November 1989, experimental additions of ammonium sulfate ((NH₄)₂SO₄; 900 mol/ha-yr) have been made to West Bear Brook Watershed. Chemical analysis of soil and stream waters were conducted to evaluate the speciation of Al prior to (1987–89) and following (1989–92) the experimental treatments. Before the treatments, soilwater Al occurred largely as inorganic monomeric Al (Ali). Concentrations of organic monomeric Al (Alo), Ali and dissolved organic C (DOC) were high in soil solutions draining the E horizon, and decreased in the lower mineral soilwater (Bs horizon) and streamwater. Streamwater concentrations of monomeric Al (Alm) were largely in the form of Alo. After the (NH₄)₂SO₄ treatments were initiated in the West Bear Brook Watershed, concentrations of Alm increased in soilwater and streamwater, largely as Ali. These increases in Al accompanied decreases in pH and increases in concentrations of SO₄ ^2? and NO₃ ^? in drainage waters. Increases in stream concentrations of Al were particularly evident during high flow events. This pattern, coupled with the increases in concentrations of Ali in upper soilwaters in response to the (NH₄)₂SO₄ addition, suggests that episodic increases in Ali were due to inputs of water entering the stream from shallow hydrologic flowpaths.     

A Comparison of the Temporally Integrated Monitoring of Ecosystems and Adirondack Long-Term Monitoring Programs in the Adirondack Mountain Region of New York

This paper compares lake chemistry in the Adirondack region of New York measured by the Temporally Integrated Monitoring of Ecosystems (TIME) and Adirondack Long-Term Monitoring (ALTM) programs by examining the data from six lakes common to both programs. Both programs were initiated in the early 1990s to track the efficacy of emission reduction policies and to assess the full impacts of acid deposition on surface water chemistry. They now serve to inform on the emerging chemical recovery of these waters. The Adirondack TIME program utilizes a probability-based approach to assess chronic acidification in a population of lakes using one summer sample per year. The ALTM attempts to track changes in both chronic and episodic acidification across a gradient of lake types using monthly samples. The ALTM project has two important attributes that contrast with the TIME program in the Adirondacks: higher temporal resolution (monthly versus once during the summer or fall) and speciation of aluminum. In particular, the ALTM program provides inorganic monomeric aluminum (Al_IM), the fraction of Al that is most toxic. The monthly sampling of the ALTM program includes the spring snowmelt period when acid-neutralizing capacity and pH are near their lowest and Al levels are near their highest. We compare chemistry trends (1992?C2008) for sulfate, nitrate, base cations, dissolved organic carbon, hydrogen ion, acid neutralizing capacity, and Al for the six lakes common to both programs. We also compare relatively high springtime Al_IM concentrations from the ALTM with relatively low summertime total Al concentrations from the TIME, showing that the ALTM program provides a more biologically relevant indicator of the effects of acid deposition, illustrating the value of the complementary monitoring efforts in the Adirondack region.     

Modeling the Concentration of Aluminum in Surface Waters

Although the increased mobilization of aluminum from soils to surface waters is widely recognized as one of the most important ecological effects of acidic deposition, lumped-parameter mathematical models of acidification response typically overestimate the change in Al concentration under changing deposition by a considerable margin. The assumption of equilibrium with gibbsite (Al(OH)₃) in the MAGIC model and other models of acid-base chemistry is shown to be inconsistent with measured values for a large variety of lake and stream databases. A modified algorithm for predicting Al concentration, based on empirical relationships evident in field data, provided superior estimates of changes in Al concentration in three long-term monitoring data sets and under experimental conditions at two experimental watershed manipulation sites.     

Modelling pH buffering and aluminium solubility in European forest soils

The pH buffering and aluminium solubility characteristics of acid soil are important in determining the soil's response to changes in precipitation acidity. The chemistry of soil organic matter (humic substances) plays a key role in both processes, yet is complex and still poorly understood. Nevertheless, models of humic substance chemistry have been developed, one of which is WHAM–S, which contains a model (Model V) of proton and metal binding at discrete sites on humic substances and considers electrostatic effects on the binding strength. Here we have tested the ability of WHAM–S to model solution pH and Al using batch titration studies on organic and mineral soil horizons from forested sites in Norway, Germany and Spain, with ambient pH values from 3.73 to 5.73. We optimized the model predictions by adjusting the amounts of soil aluminium and humic substances within defined limits, taking the contents of copper chloride‐extractable Al and the base‐extractable organic matter as starting values. The model simulated both pH and dissolved Al well with optimized amounts of aluminium and humic substances within the defined limits (root mean squared error for pH from 0.01 to 0.22, for p[Al]_aq (total dissolved Al) from 0.03 to 0.49, five data points). Control of dissolved Al by dissolved organic matter was important particularly at above‐ambient pH. In two mineral horizons we improved the fits by assuming that Al could precipitate as Al(OH)₃. The optimized model also gave reasonable predictions of pH and dissolved Al in supernatants obtained by repeated leaching of the soil horizons. The results show that humic substances dominate the control of pH and dissolved Al in most of the horizons studied. Control by Al(OH)₃ occurs but is the exception.     

The effects of stream liming on water chemistry and anadromous yellow perch spawning success in two Maryland coastal plain streams

Automated stream dosers that deliver a wet slurry of calcite were installed in 1987 on two Maryland Coastal Plain streams subject to acidic pulses during rainstorms to evaluate the use of stream liming technology to maintain suitable water quality for early life stages of anadromous fish. Results of water quality sampling during baseflow conditions and hydrologic events indicated that significant changes in water chemistry occurred at the upstream (untreated) site during elevated flows on each stream. Observed responses in stream chemistry during the events included declines in pH, acid neutralizing capacity (ANC), and Ca, and increases in monomeric Al concentrations. With the addition of calcite, stream chemistry conditions at the downstream (treated) sites during each event were similar to those observed during baseflow. In situ bioassay experiments indicated that survival of yellow perch eggs and newly-hatched larvae may be enhanced by stream liming.     

Effects of acid,aluminium and lime additions on fish and invertebrates in a chronically acidic welsh stream

A chronically acidic stream, mean pH 5.2, in upland mid-Wales was subjected to an induced episode of acidity, during which acid, Al and limestone were added at different points along the stream length. An upstream reference zone (A), an acid zone (B), an acid plus Al zone (C) and a downstream zone of Al at low pH with added limestone to increase pH (D) were created for a 24 hr period. Four species of fish and 10 species of invertebrates were exposed in each zone and response criteria measured included mortality, metal uptake, feeding and the ability of stressed animals to recover. Fish mortalities were greater in zones B and C than in zone A and were greatly reduced by the addition of lime in zone D. Overall mortality was low amongst the invertebrate species found in acid waters. Greatest mortalities were recorded for Gammarus pulex. G. pulex infected with the acanthocephalan parasite Pomphorhynchus laevis exhibited greater mortality than uninfected animals. The feeding rate of G. pulex was suppressed in all zones during the dosing period; uninfected G. pulex consumed more than infected animals, and the feeding rate of all gammarids increased post-dosing but not to the level of unexposed animals. Aluminium concentrations in fish gills increased with time. Invertebrate body burdens of Al were greatest in zone D, with significant increases over the dosing period for both G. pulex and Isoperla grammatica. No significant patterns were observed in the concentration of Ca, Na or K for either fish or invertebrates.     

Temporal Variations of Aluminium Fractions in Streams in the Delsbo Area, Central Sweden

Stream waters were sampled weekly during spring and monthly during summer and autumn in 1998. The streams are more or less acidified, and some have been treated with lime. The aluminium fractions (total monomeric Al, organic monomeric Al, inorganic monomeric Al) were determined colourimetrically with pyrocatechol violet combined with cation exchange using Continuous Flow Analysis (Autoanalyzer I). The levels of inorganic monomeric aluminium varied substantially, between <3 to 271 µg/l. The levels were higher in untreated than in limed waters and twice as high in the most humic waters as in less humic waters. The importance of aluminium mobilisation from the catchments was obvious, with higher aluminium concentrations in surface runoff (unbalanced stream waters) compared to lake outlets (balanced and precipitated lake water). The highest mean levels were measured at spring, whereas the highest single peaks occurred during summer. Inorganic monomeric and total monomeric aluminium was best correlated to ion ratio and pH whereas acid soluble aluminium and organic monomeric aluminium was best correlated to TOC, water colour and iron.     

Quality of soluble organic C,N, and P produced by different types and species of litter: Root litter versus leaf litter

In forested ecosystems, the quality of dissolved organic matter (DOM) produced by freshly senesced litter may differ by litter type and species, and these differences may influence the amount of DOM that is respired versus that which may either contribute to soil organic matter accumulation or be leached from the ecosystem. In this study, we investigated the effect of litter type (including freshly senesced fine root, leaf, fine woody, and reproductive litter) and species (5 species of leaf litter) on several measures of the quality of DOM produced at a site along a primary successional chronosequence at Mt. Shasta, California. We measured differences in solid litter chemistry (C, N, and P concentration) and differences in the concentration of dissolved organic C, N, and P (DOC, DON, and DOP, respectively), water-soluble monomeric carbohydrates, polyphenols, proteins, fractions of DOC, as well as UV absorbance. For several aspects of DOC quality, DOM from fine roots was less labile than DOM from leaf litter. In contrast to DOC quality, soluble material originating from fine roots was high in labile forms of dissolved N and P in comparison to leaf litter. We also found that leaf litter with greater total %N or %P in solid litter had higher DON or DOP concentration (and higher total soluble P concentration). A very high percentage, on average 72% (up to 89%) of the total P in leaf litter was water-soluble and mostly inorganic P. Concentrations of soluble polyphenols were strongly related to DOC, and concentrations of soluble proteins were significantly related to DON in leaf litter of different species. During primary succession at the Mt. Shasta site, an increasing ratio of root to leaf litter production and shifting species composition has been found to occur, and the results of this study suggest that some aspects of DOC quality reflect a decrease in labile forms of DOC originating from both above and belowground litter. In contrast, dissolved N and P reflect an increase in labile forms with increasing inputs of root litter. In particular, our study has demonstrated important differences in the quality of inputs of DOM from freshly senesced root and leaf litter, and these differences have implications for C and nutrient cycling.     

Stabilization of dissolved organic matter by aluminium: a toxic effect or stabilization through precipitation?

Carbon mineralization in acidic forest soils can be retarded by large concentrations of aluminium (Al). However, it is still unclear whether Al reduces C mineralization by direct toxicity to microorganisms or by decreased bioavailability of organic matter (OM) because dissolved organic matter (DOM) is precipitated by Al. We conducted an incubation experiment (6 weeks) with two DOM solutions (40 mg C litre^?1) derived from two acidic forests and possessing large differences in composition. Aluminium was added to the solutions in realistic ranges for acidic soils (1.6–24 mg Al litre^?1) at pHs of 3.8 and 4.5, to achieve differences in Al speciation. We determined different Al species, including the potentially toxic Al³⁺, by Diffusive Gradients in Thin Films (DGT) to evaluate toxic effects on microorganisms. Precipitation of OM increased with larger amounts of added Al and higher pH, and we measured a larger fraction of dissolved ‘free’ Al at pH 3.8 than at pH 4.5. Organic matter degradation decreased significantly with Al addition, and we found more organic matter degraded at pH 3.8 than at pH 4.5 for the respective Al additions. Consequently, the observed reduction in OM degradation (i.e. stabilization) cannot be explained by toxic effects of ‘free’ Al. However, C stabilization correlated significantly with C precipitation. The pH did not influence C stabilization directly, but determined the amount of C being precipitated. Phosphorus was removed along with OM by precipitation, which possibly also affected C stabilization. We conclude that C stabilization upon Al addition did not result from toxic effects, but was caused by reduced bioavailability of OM after its precipitation. The reduction in OM degradation by 65% is of great relevance for the overall C stabilization in acidic forest soils. Increasing pH and decreasing Al concentrations upon recovery from acidic deposition should therefore not result in decreased stabilization of precipitated OM.     

低分子量有机酸对高岭石中铝释放的影响

选择了几种土壤中可能存在的低分子量脂肪羧酸 ,研究了它们对高岭石中铝释放的影响。结果表明 ,有机酸可以通过络合作用促进高岭石中铝的释放。几种有机酸对体系中可溶性铝影响的大小顺序为 :草酸 >柠檬酸 >丙二酸 >苹果酸 >乳酸。草酸、柠檬酸和乳酸对可溶性铝释放的促进作用随体系pH的升高而减小 ,其中草酸体系中可溶性铝随pH的变化幅度最大。在苹果酸体系中 ,可溶性铝随pH的升高而稍有增加。体系中的可溶性铝随有机酸浓度的增加而增加 ,而交换性铝随柠檬酸浓度的增加而减少 ,先随苹果酸浓度增加而增加 ,然后又逐渐减少。与对照相比 ,柠檬酸和草酸使交换性铝的量减小 ,苹果酸和乳酸在低pH下使交换性铝明显增加 ,而苹果酸在较高pH下使交换性铝减少。有机酸影响释放出的铝在固液相间的分配比 ,苹果酸在低pH下使体系中释放出的大部分铝以交换性形态存在 ,而在较高pH下 ,大部分铝以可溶形态存在。在草酸体系中 ,释放出铝的大部分都以可溶形态存在。不同有机酸的不同表现与体系中铝的溶解平衡、铝的吸附 -解吸平衡、有机酸的吸附 -解吸平衡、有机酸的离解平衡和铝与有机酸的络合 -离解平衡有关。     

Extreme acidification of a lake in southern Norway caused by weathering of sulphide-containing bedrock

In 1986 Lake Langedalstjenn in southern Norway was a weakly acidified lake with a pH of 5.2–5.6, and an average concentration of SO₄ of 330 μeq L^?1. The total Al concentration varied between 10 and 20 μeq L^?1 (expressed as Al³⁺). The lake supported populations of brown trout and perch and had supplied about 100 people with drinking water until the late 1980's. During 1986–1989, a dramatic change in the water chemistry occurred because of blasting of and weathering of sulphidic gneisses in the watershed. The oxidation of sulphide to sulphate (sulphuric acid) caused an increase in the SO₄ concentration of the draining stream of up to ≈ 4800 μeq L^?1. Weathering and/or cation exchange of Ca and Mg neutralized approximately 52% of the protons from the sulphuric acid production, while about 46% were consumed by mobilization of aluminium and iron. Nevertheless, about 2% of the hydrogen ions from the sulfuric acid were still present, which resulted in a stream pH of 4.0. In the lake, the pH was 4.4, and the concentrations of all major cations and anions were significantly lower than in the heavily affected stream. Mixing of the stream water with lake water, formation of aluminium-sulphate complexes and coprecipitation of Ca may explain the resulting concentrations of major ions in the lake.     

Characterizing Episodic Stream Acidity During Stormflows in the Great Smoky Mountains National Park

Episodic acidification of surface waters has been observed in the Great Smoky Mountains National Park, similar to other forested watersheds with base-poor bedrock in the eastern US receiving acids from atmospheric deposition. Three remote, forested, high-elevation streams were selected in the Little Pigeon River watershed for study; two of which brook trout have extirpated, and believed to have resulted from severe acidity during stormflows. This research characterized stream chemistry during episodes in order to better understand potential factors that contribute to rapid drops in pH and acid neutralizing capacity (ANC) during stormflows. Autosamplers initialized by sondes, collected samples during storm events for analysis of pH, ANC, cations, and anions over a 15-month period. ANC and pH depressions, and increased concentrations in sulfate, nitrate, and organic acids were observed for all storms at each study site. ANC contribution analysis indicated sulfate was the strongest contributor to ANC depressions, but nitrate, cation dilution, and organic acids were also significant in some cases. Acidic deposition appears to be the primary source of episodic acidification, supported also by the finding that larger stormflows preceded by long, dry periods resulted in significantly larger pH depressions. It appears stream acidification episodes may be driven by acid deposition. However, this study documents the variability of several ion contributors to observed stormflow ANC depressions illustrating the spatial and temporal complexity of watershed processes that influence this phenomenon.     

Responses of atlantic salmon (Salmo salar) alevins to dissolved organic carbon and dissolved aluminum at low pH

Mortality of Atlantic salmon alevins in solutions containing Al and dissolved organic anions (both synthetic and natural) was correlated with Al accumulation in alevin tissues. Both mortality and accumulation could be related to the concentration differences between Al and organic anions. Mortality and body accumulation of Al both increased dramatically as total Al concentrations increasingly exceeded organic anion concentrations. Alevin growth and yolk utilization were both less rapid at inorganic monomeric Al concentrations exceeding 2 μM (50 μg L^-1). The acidic fractions of dissolved organic matter (DOM) are more effective in protecting alevins against Al toxicity than are the neutral and basic fractions. Ambient inorganic monomeric Al is probably not toxic to salmon alevins in acidic Nova Scotian streams, even during snow-melt.     

Urban Influences on Stream Chemistry and Biology in the Big Brushy Creek Watershed, South Carolina

Naturally high total dissolved solids and upstream agricultural runoff often mask the influence of urban land cover on stream chemistry and biology. We examined the influence of headwater urbanization on the water chemistry, microbiology, and fish communities of the Big Brushy Creek watershed, a 96 km² drainage basin in the piedmont of South Carolina, USA. Concentrations of most major anions and cations (especially nitrate, sulfate, chloride, sodium, potassium, and calcium) were highest in the urban headwaters and decreased downstream. Generally, the highest concentrations of suspended coliform bacteria occurred in the urban headwaters. In contrast, stream habitat quality and the abundance, species richness, and species diversity of fishes did not differ significantly between urban and rural sites. Discharge of wastewater treatment plant effluent at one rural location caused an increase in concentrations of many solutes and possibly the abundance of benthic algae. We hypothesize that atmospheric dry deposition and domestic animal wastes are important sources of stream solutes and of coliform bacteria, respectively, in the urban headwaters. The lack of significant differences in fish abundance and diversity between urban and rural sites may indicate that urban development in the Big Brushy Creek watershed has not yet degraded habitat conditions greatly for stream fishes. Alternatively, agriculture or other land uses may have degraded stream habitat quality throughout the watershed prior to urbanization.