Spatial and temporal dynamics of mercury in Precambrian Shield upland runoff

Methylated and total Hg, and TOC concentrations were measured in precipitation and runoff in a first order Precambrian Shield watershed, and in precipitation, throughfall, shallow groundwater and runoff in a zero Precambrian Shield watershed. Plots dominated by open lichen-covered bedrock and another containing small patches of conifer forest and thin discontinuous surficial deposits were monitored within the zero order catchment. Methyl (3–10 fold) and non-methyl (1.4–2.8 fold) Hg concentrations changed irregularly during rainfall and snowmelt runoff events in all catchments. Temporal patterns of Hg concentration in runoff included flushing and subsequent dilution as well as peak concentrations coinciding with peak or recession flow. Mercury export was highest from lichen-covered bedrock surfaces as a result of high runoff yields and minimal opportunity for physical retention and in the case of MeHg demethylation. Forest canopy and lichen/bedrock surfaces were often net sources for Hg while forest soils were mostly sinks. However, upland soils undergoing periodic reducing conditions appear to be sites for the in situ production of MeHg.     

Some factors controlling the major ion chemistry of small lakes: Examples from the prairie parkland of Canada

The management of recreational lakes in the prairie region of Canada requires that their physical, chemical and biological setting be clearly defined. This study relates the major ion chemistry of two lakes to significant ion contributions from groundwater, surface runoff and snow. The major ion concentrations in addition are related to several important limnological processes.Lake Wabamun is a 84.6 km² lake with a basin set in Cretaceous bedrock. Groundwater studies in the watershed indicate that rather large quantities of groundwater enter the lake from fractured coal and bedrock units. Hastings Lake has a considerably smaller surface area and is formed in a shallow depression in glacial drift. Generally, smaller quantities of groundwater enter this lake because the glacial drift has a low permeability.Evaluation of the data indicates that relative quantity and quality of groundwater inflow is probably the most important factor controlling the major ion chemistry of the lakes. Other factors are mineral precipitation, freezing out and the timing of major water inflows.     

Lake-watershed acidification in the North Branch of the Moose River: Introduction

An integrated analysis of a terrestrial-aquatic ecosystem, the North Branch of the Moose River in the Adirondack region of New York, was conducted. This basin contains a large number of interconnected surface waters that exhibit marked gradients in pH and acid neutralizing capacity (ANC). As a result, the basin has been the focus of research activity, including the Regional Integrated Lake-Watershed Acidification Study (RILWAS). The objective of the current analysis was to use the North Branch of the Moose River as a case study to:

1. Evaluate processes regulating the acid-base chemistry of surface waters.
2. To assess the effects of surface water acidification on fish populations.

The observations of this study were consistent with the model of surface water acidification developed during the Integrated Lake-Watershed Acidification Study (ILWAS). The processes depicted in the original ILWAS simulation model were adequate to describe the acid-base chemistry of surface waters in the North Branch of the Moose River. However, the reduction of SO ₄ ^2? in lake sediments, a process not represented in the original model, proved to be a significant source of acid neutralizing capacity (ANC) for some of these waters. As a result, reduction processes were added to the model. Analysis of in-situ bioassay and survey data indicate that acid-sensitive fish species have disappeared from the more acidic areas of the basin over the last half century. Paleoecological analyses indicate that pH has decreased from the high 5's to about 5 in Big Moose Lake during this period. ILWAS model simulations indicate that the pH of Big Moose Lake would increase by at least 0.1 to 0.5 pH units (depending on the season) in response to a 50% reduction in total atmospheric S deposition. Considerable variability in processes regulating acid/base chemistry was evident in the North Branch of the Moose River. Therefore, regional assessments of past or possible future effects of acidic deposition require widespread application of ILWAS theory within the Adirondack region and other potentially acid-sensitive areas.     

Geology and environmental significance of sediment distributions in an area of the submerged Niagara escarpment,Georgian Bay

The study site covers a spur of the submerged Niagara escarpment and part of the Flowerpot basin of Georgian Bay. Bedrock outcrops occur on islands and shoals but much of the area is covered by glacial till (10–20 m thick). Glaciolacustrine clay occurs in thin patches on the spur; in the deepest parts of the area, however, it is nearly 70 m thick. The distributions of Recent sediments which comprise lag-gravels, sands and silty clays, reflect major postglacial lake level changes in the Huron — Georgian Bay basin.Sediment geochemistry in Georgian Bay is similar to many other parts of the Great Lakes but calcium charbonate levels are lower than expected, except in some deposits of gaciolacustrine clay. There is little evidence of anthropogenic impact in the content of trace metals, although Pb likely includes a portion derived from atmospheric loading; Hg is usually present at very low levels but there are anomalously high values in some deepwater modern muds.In the bottom sediment habitat of modern benthos, the distribution of chironomids seems to reflect silt content. Oligochaetes are least in areas of thin Recent mud or exposed glaciolacustrine clay. Pontoporeia and sculpins are most numerous at depths between 50–110 m. Bottom tracks and other bed marks cover extensive areas of the deepwater lake sediments.     

Microbial communities across a hillslope‐riparian transect shaped by proximity to the stream,groundwater table,and weathered bedrock

Watersheds are important suppliers of freshwater for human societies. Within mountainous watersheds, microbial communities impact water chemistry and element fluxes as water from precipitation events discharge through soils and underlying weathered rock, yet there is limited information regarding the structure and function of these communities. Within the East River, CO watershed, we conducted a depth‐resolved, hillslope to riparian zone transect study to identify factors that control how microorganisms are distributed and their functions. Metagenomic and geochemical analyses indicate that distance from the East River and proximity to groundwater and underlying weathered shale strongly impact microbial community structure and metabolic potential. Riparian zone microbial communities are compositionally distinct, from the phylum down to the species level, from all hillslope communities. Bacteria from phyla lacking isolated representatives consistently increase in abundance with increasing depth, but only in the riparian zone saturated sediments we found Candidate Phyla Radiation bacteria. Riparian zone microbial communities are functionally differentiated from hillslope communities based on their capacities for carbon and nitrogen fixation and sulfate reduction. Selenium reduction is prominent at depth in weathered shale and saturated riparian zone sediments and could impact water quality. We anticipate that the drivers of community composition and metabolic potential identified throughout the studied transect will predict patterns across the larger watershed hillslope system.     

Groundwater nitrate removal in riparian buffer zones: a review of research progress in the past 20 years

This review evaluates research in the past 20 years focusing on groundwater nitrate removal in the riparian zones of agricultural watersheds. Studies have reported a large range in the magnitude of groundwater and nitrate fluxes to buffers in different hydrogeologic settings. An earlier focus on buffers with shallow subsurface flow has expanded to include sites with deep flow paths and groundwater-fed overland flow. Nitrate removal efficiency and the width required for removal have been linked to riparian sediment texture and depth to an impervious layer. Denitrification has been identified as the dominant mechanism of nitrate removal based on evidence that this process occurs at depth in many buffers which contain buried organic-rich deposits. Several studies have assessed the cumulative effect of riparian buffers on nitrate removal at the watershed scale. Despite considerable research progress areas of uncertainty still remain. Buffers with coarse-textured sediments located in landscapes with upslope sand aquifers have received most attention. In contrast, few sites have been analysed in weathered bedrock and glacial till landscapes. Many studies have reported nitrate removal efficiency based on nitrate concentrations rather than measuring groundwater fluxes which assess the magnitude of nitrate removal. More information is needed on interactions between riparian hydrological flow paths and biogeochemical processes. Further research is recommended on the effect of riparian zone nitrate removal at the watershed scale and long-term monitoring with respect to buffer restoration, the ability to sustain nitrate removal and responses to land use and climate change.

     

Hydrogeologic controls of surface-water chemistry in the Adirondack region of New York State

Relationships between surface-water discharge, water chemistry, and watershed geology were investigated to evaluate factors affecting the sensitivity of drainage waters in the Adirondack region of New York to acidification by atmospheric deposition. Instantaneous discharge per unit area was derived from relationships between flow and staff-gage readings at 10 drainage basins throughout the region. The average chemical composition of the waters was assessed from monthly samples collected from July 1982 through July 1984. The ratio of flow at the 50-percent exceedence level to the flow at the 95-percent exceedence level of flow duration was negatively correlated with mean values of alkalinity or acid-neutralizing capacity (ANC), sum of basic cations (SBC), and dissolved silica, for basins containing predominantly aluminosilicate minerals and little or no carbonate-bearing minerals. Low ratios are indicative of systems in which flow is predominately derived from surface- and ground-water storage, whereas high ratios are characteristic of watersheds with variable flow that is largely derived from surface runoff.In an evaluation of two representative surface-water sites, concentrations of ANC, SBC, and dissolved silica, derived primarily from soil mineral weathering reactions. decreased with increasing flow. Furthermore, the ANC was highest at low flow when the percentage of streamflow derived from ground water was maximum. As flow increased, the ANC decreased because the contribution of dilute surface runoff and lateral flow through the shallow acidic soil horizons to total flow increased. Basins having relatively high ground-water contributions to total flow, in general, have large deposits of thick till or stratified drift. A major factor controlling the sensitivity of these streams and lakes to acidification is the relative contribution of ground water to total discharge.     

Polycyclic aromatic hydrocarbons in surficial sediments and caged mussels of the St. Marys River, 1985

During 1985, a biological monitoring study was conducted in the St. Marys River to determine the availability and source areas of polycyclic aromatic hydrocarbons (PAHs) and the relative importance of water and sediment to tissue contaminant concentrations. Clean unionid mussels (Elliptio complanata) were exposed in cages for three weeks at 14 stations and surficial sediments were obtained at 12 of these. The highest concentrations of total PAHs as well as many individual compounds were found in sediments and mussels from the Algoma Steel Slip above St. Marys Falls and in sediments below the discharge of the Edison Sault Electric Co. Canal. Although concentrations were lower below the Falls, elevated levels persisted downstream along the Ontario shore into Lake George. PAHs were also accumulated by mussels exposed along the Michigan shoreline, but at lower levels than along the Ontario shore. From 23 to 63 percent of the PAHs in sediments and 6 to 27 percent of those in mussels were comprised of compounds with mutagenic and/or carcinogenic properties. The predominance of higher molecular weight PAHs in both sediments and mussels as well as lower molecular weight PAHs and nitrogen- and sulfur-containing PAHs in certain areas, indicates that high temperature combustion of fossil fuels is the major source of PAHs, augmented by localized spills of fossil fuels and coke oven by-products.Mussels contained fewer PAHs (up to 18 vs. 25) at lower concentrations (µg kg^-1 vs. mg kg^-1) than the associated surficial sediments. Also, mussels suspended at mid-depth in the water column accumulated similar concentrations to those exposed to sediments, indicating that the major exposure pathway is via the water filtered by these organisms, and hence, is due primarily to external industrial inputs.     

Longitudinal patterns of fish assemblages in small unregulated subbasins: evaluating reach- and watershed-scale parameters

Fish assemblage relationships with environmental parameters were studied in four small unregulated subbasins in the speciose Upper Green River Basin of central Kentucky, USA. One subbasin drains into a tributary of the Green River and produced the lowest species (28) richness. The three other subbasins drain directly into the Green River and supported 41−59 species. Parameters were partitioned into watershed- and reach-scale spatial categories. Watershed area per stream segment and stream-size related environmental parameters at the reach scale produced the highest loadings of a principle components analysis (PCA), and both PCA Axes 1 and 2 for all subbasins were reflective either of watershed area or stream-size parameters. Small loadings were produced by all watershed-scale land-use parameters and all reach-scale water chemistry parameters. Fish richness and diversity were positively correlated with watershed area for the two largest subbasins and for the three Upper Green River subbasins combined. The lack of a linear relationship, however, between the residuals of multiple linear regression models between richness and diversity versus stream width, percent bedrock, percent pool and percent fine substrates indicated that a simple species area relationship was not operating. A detrended correspondence analysis (DCA) performed for each subbasin showed that several fish species were associated mainly either with small, upland segments or conversely the largest, deeper segments, and each subbasin yielded significant correlations between the environmental PCA loadings and fish assemblage DCA site scores. These results indicated that within the regional scale, and in absence of steep disturbance gradients, stream fish assemblages can reflect natural hydrologic and geomorphic gradients.     

Recreational water quality analyses of the Colorado River corridor in Grand Canyon.

We intensively examined the recreational water quality of the Colorado River and 26 tributaries in Grand Canyon National Park over four consecutive summers. Highly ephemeral precipitation cycles and arid watershed hydrologies were the principal factors influencing water quality. Fecal coliforms (FC) in the river and in most tributaries were less than or equal to 10 FC 100 ml-1 and less than or equal to 20 FC 100 ml-1, respectively, during drought cycles. During rainfall cycles, FC densities were highly variable and often exceeded recreational contact standards. FC were not found to vary significantly in response to diurnal fluctuations in river stage height which resulted from hydroelectric stream flow regulation. River and tributary bottom sediments harbored FC in densities averaging 10 to 100 times those in the overlying waters. Sediment FC densities were not found to be reliable indicators of overlying water quality when storm flow and nonstorm flow periods were compared.     

Longitudinal and temporal trends in the water chemistry of the North Branch of the Moose River

Surface water acidification is potentially a problem in regions with low ionic strength drainage waters. Atmospheric deposition of sulfuric acid has generally been implicated as the causative agent of this problem, although other sources of acidity may contribute. The Adirondack region of New York State is an area with acid-sensitive surface waters and an abundance of acidic lakes. The intent of this study was to evaluate the processes regulating the acid/base chemistry of a series of lakes draining a large heterogeneous watershed in the Adirondack region of New York.The study site, the North Branch of the Moose River, is heterogeneous in its soil and geological characteristics. This variability was reflected through differences in water chemistry that occurred within the basin. The northern headwaters generally drain subcatchments with shallow, acidic soils. The resulting water chemistry was acidic (equivalence of acidic anions exceeded equivalence of basic cations) with high concentrations of Al and dissolved organic carbon (DOC). As this water migrated through a large lake (Big Moose Lake) with a moderate hydrologic retention time (0.5 yr), considerable loss of DOC was evident.As acidic water was transported through the drainage area, it mixed with waters that were enriched in concentrations of basic cations from the eastern subbasins. As a result, there was a successive increase in the acid neutralizing capacity (ANC) and a decrease in Al concentrations as water migrated from the northern reaches to the outlet of the watershed.In addition to these general trends, short-term changes in water chemistry were evident. During low flow summer periods concentrations of basic cations were elevated, while concentrations of SO ₄ ^2– and NO ₃ ^– were relatively low. These conditions resulted in less acidic waters (higher ANC) with relatively low concentrations of Al. During high flow winter/spring conditions, elevated concentrations of SO ₄ ^2– and NO ₃ ^– were evident, while concentrations of basic cations were reduced resulting in low pH (low ANC) waters with high concentrations of Al.Variability in the processes regulating the pH buffering of waters was apparent through these short-term changes in water chemistry. In the northern subbasin short-term fluctuations in ANC were minimal because of the buffering of Al under low pH conditions. Seasonal changes in the ANC were more pronounced in the eastern subbasin because of the predominance of inorganic carbon buffering in the circumneutral pH waters.Lakes in the west-central Adirondacks have characteristically short hydraulic residence times and elevated nitric acid inputs. As a result these waters may be more susceptible to surface water acidification than other acid-sensitive lake districts in eastern North America. Given the apparent interregional differences, extrapolation of chemical trends in the Adirondacks to other areas may be tenuous.     

Fire and the relative roles of weather,climate and landscape characteristics in the Great Lakes‐St. Lawrence forest of Canada

Question: In deciduous‐dominated forest landscapes, what are the relative roles of fire weather, climate, human and biophysical landscape characteristics for explaining variation in large fire occurrence and area burned? Location: The Great Lakes‐St. Lawrence forest of Canada. Methods: We characterized the recent (1959–1999) regime of large (≥ 200 ha) fires in 26 deciduous‐dominated landscapes and analysed these data in an information‐theoretic framework to compare six hypotheses that related fire occurrence and area burned to fire weather severity, climate normals, population and road densities, and enduring landscape characteristics such as surficial deposits and large lakes. Results: 392 large fires burned 833 698 ha during the study period, annually burning on average 0.07%± 0.42% of forested area in each landscape. Fire activity was strongly seasonal, with most fires and area burned occurring in May and June. A combination of antecedent‐winter precipitation, fire season precipitation deficit/surplus and percent of landscape covered by well‐drained surficial deposits best explained fire occurrence and area burned. Fire occurrence varied only as a function of fire weather and climate variables, whereas area burned was also explained by percent cover of aspen and pine stands, human population density and two enduring characteristics: percent cover of large water bodies and glaciofluvial deposits. Conclusion: Understanding the relative role of these variables may help design adaptation strategies for forecasted increases in fire weather severity by allowing (1) prioritization of landscapes according to enduring characteristics and (2) management of their composition so that substantially increased fire activity would be necessary to transform landscape structure and composition.     

Some physical and chemical characteristics of an arctic beaded stream

Imnavait Creek is a tundra stream in the Arctic Foothills of Alaska. The stream is beaded, i.e. consists of pools (up to ∼ 2 m deep) connected by narrow channels. Peat dominates pool and channel substrate materials with occasional rock and moss substrates. The watershed is underlain by ice-bonded till and is hydrologically watertight. Because of low rates of weathering, bedrock and till do not contribute significantly to ionic composition of the stream water. Breakup occurs in late May to early June with surface flow until September. During periods of low rainfall, channel flow is reduced and pools become hydrologically isolated and thermally stratified (with very high surface water temperatures). Streamwater is acidic (pH values 5.3–6.1) with very low alkalinity (≤3 mg l⁻¹). The major transport of ions occurs in early flow derived from snow melt. Organic carbon concentrations are high with very high ratios of dissolved to particulate organic carbon. Dissolved inorganic nitrogen concentrations appear to be very low. High concentrations of dissolved organic material may indicate a central role for DOM in trophic dynamics.     

A landscape approach to examining spatial patterns of limnological variables and long-term environmental change in a southern Canadian lake district

1. We explored patterns of limnological variables (physical, chemical and biological) with relation to landscape position (expressed as lake order) in 86 study lakes located on shield bedrock in south‐central Ontario, Canada. 2. Using anova s with lake order as the categorical variable, landscape position explained significant amounts of variation in major ion chemistry, physical and catchment characteristics, hypolimnetic oxygen, and community composition in algal (diatom, chrysophyte) and invertebrate (chironomid) assemblages preserved in surficial sediments. Several nutrient variables (TP, total phosphorus and TN, total nitrogen) and dissolved organic carbon did not have significant relationships with lake order. 3. The strongest relationships with lake order (as a fraction of variation explained in anova s) included silica concentrations (r² = 0.40) and SO₄ (r² = 0.29) concentrations, surface area (r² = 0.50) and hypolimnetic oxygen (r² = 0.29). 4. Bedrock geology (carbonate metasedimentary versus non‐carbonate bedrock) had strong influences on spatial gradients of pH and major ion chemistry. It was difficult to separate geological influences from spatial influences on limnological variables in this study, as drainage patterns in the region are highly influenced by surface features of underlying geological formations because of the very thin glacial till or exposed bedrock that exists in most catchments. 5. Patterns of limnological variables indicated that low‐order, headwater lakes had the lowest concentrations of major ions, and, from algal inferences of pH change, had been most susceptible to acidic deposition. High‐order, downstream lakes were larger and deeper, and had higher concentrations of hypolimnetic oxygen, indicating that optimal lake trout habitat was primarily located in high‐order lakes. 6. Variance partitioning analyses indicated that lake order as a metric of landscape position explained comparable portions of community variation in algal and invertebrate assemblages compared with geographic position (latitude, longitude) and Cartesian coordinate position (e.g. x, y, x², y², etc.) metrics. Lake order explained more community variation in chironomid assemblages compared with other landscape metrics, possibly because of the strong relationships between lake order and lake morphometry variables.     

Relationships between lakewater pH and sedimentary diatoms in the Matamek Watershed,Northeastern Quebec,Canada

Twenty lakes in the Matamek and nearby watersheds were sampled in the summer of 1983 for water chemistry and surficial sediments. Thirty-two physical and chemical variables, including pH, alkalinity, cations and metal concentrations were measured on samples from the epilimnion and hypolimnion of each lake. In three lakes, two to four replicate cores were collected to estimate spatial variability of the sediment flora.All lakes were acidic (pH 4.59 to 5.80), highly colored and poorly buffered. Aluminum and magnesium concentrations reached 494 and 70 µg l^-1, respectively. The pH of the lakes appears to be declining, as indicated by a comparison of our results with those from a survey done in 1970. An empirical chemical model based on the alkalinity/sulfate ratio and the regression of pH on calcium also indicated that these lakes may be undergoing acidification.Analyses of the diatom flora of the surficial sediments showed strong dominance of 6 species that cooccurred with a large number of rare species (in all, 229 taxa were found). Variability among samples within a lake was as high as among lakes. Calculation of Nygaard's alpha index for each sample and the regression of its log-transformed value on surface pH yielded a relationship that was significantly from other published models. The regression model was applied to a down-core analysis of the diatom flora of the sediments of two lakes. Although the large confidence intervals on pH values predicted by the model obscured any evidence of pH change with sediment depth, there was a significant increase of acidophilous and a decrease of circumneutral species over time, suggesting that a change in the flora, possibly correlated with pH, is taking place.In making comparisons among lakes, the surficial-sediment flora did not provide clear evidence of a relationship with the pH of surface water. Indices computed from the surficial-sediment flora are apparently insensitive to differences in pH over a narrow range, particularly when the lakes being compared are similar chemically. Nygaard's alpha index is shown to be unduly sensitive to outliers. The currently accepted assumption of a progressive linear change in communities may be inadequate for the quantification of acidification processes. Other models, derived from catastrophe theory, may prove more fruitful.     

Dilution and acidification effects during the spring flood of four Swedish mountain brooks

The seasonal variation in water chemistry was followed during 1980 and 1981 in four mountain brooks in the southern part of Swedish Lapland. In the area investigated the soil is calcareous and the brook water is very well buffered during the major part of the year, with alkalinity varying between 0.4 and 1.0 milliequivalents per liter and with pH values about 7.5. These years the snow had a pH of approximately 5.2, which was considerably higher than has been reported from adjacent areas in the lower, coniferous region. During snowmelt the water discharge increased drastically, and although the net transport of bicarbonate increased, alkalinity showed low values due to dilution with meltwater. pH decreased, but not further than to 6.3–6.5, far from values reported in 1979 (pH less than 5), apparently due to the comparatively clean snow. A slight deficit in alkalinity, as compared to the nonmarine calcium and magnesium content, points to an acidification impact on the area. During maximum runoff some chemical variables, like aluminium, iron, nitrogen and phosphorus, behaved reversely to what might be expected during dilution and reached maxima in concentrations. It is concluded that the extreme runoff characteristics of high mountain areas make brook water more sensitive to acid precipitation than might be expected when regarding only the calcareous properties of soil and bedrock.     

基于农业气象学原理的林地生态需水量估算——以泾河流域为例

从农业气象学原理出发 ,森林植被的生态需水可以理解为林地的蒸散耗水量。根据土壤水分有效性的划分 ,林木暂时凋萎含水量和生长阻滞含水量分别是能保证林木基本生存和正常生长时土壤含水量的下限 ,据此可以作为林地最小生态需水定额和适宜生态需水定额计算的依据 ,其数值通过计算林地的潜在蒸散并利用土壤水分修正系数和林木系数进行订正获得。根据遥感图像资料 ,在 GIS支持下 ,计算了泾河流域现有林地生长季的最小生态需水量和适宜生态需水量 ,分别为 2 0 396 0× 10 4 m3和340 330× 10 4 m3。     

Species richness of aquatic macrophyte communites in Central Canada

Aquatic macrophyte species richness (SR) was examined at 430 sites in the central Canadian region in relation to water body type, bottom substrate and 8 water chemistry parameters. SR was highest in rivers and lakes, intermediate in creeks, and lowest in ponds. The highest values occurred where granitic bedrock, highly organic substrates or sand predominated. SR was significantly inversely correlated in the study area as a whole with 7 of the water chemistry parameters; of these, total alkalinity was the most important. However, the relative importance of the respective parameters differed for various water body types. The relationship between SR and phosphorus was positive in ponds, but negative for all other water body types. Stepwise sultiple regression analysis identified phosphorus, total alkalinity and dissolved organic matter as important factors in ponds; sulphate, total alkalinity and chloride in lakes, and sulphate and phosphorus in lotic habitats. Log transformations improved the correlations for some variables. However, the water chemistry parameters examined accounted for less than half of the total variability in SR. Apparently SR depends on many different factors, including surface areaand bottom type, whose relative contributions vary with situation.     

Sediment microbial enzyme activity as an indicator of nutrient limitation in the great rivers of the Upper Mississippi River basin

We compared extracellular enzyme activity (EEA) of microbial assemblages in river sediments at 447 sites along the Upper Mississippi, Missouri, and Ohio Rivers with sediment and water chemistry, atmospheric deposition of nitrogen and sulfate, and catchment land uses. The sites represented five unique river reaches—impounded and unimpounded reaches of the Upper Mississippi River, the upper and lower reaches of the Missouri River, and the entire Ohio River. Land use and river chemistry varied significantly between rivers and reaches. There was more agriculture in the two Upper Mississippi River reaches, and this was reflected in higher nutrient concentrations at sites in these reaches. EEA was highest in the two Upper Mississippi River reaches, followed by the lower Missouri River reach. EEA was generally lowest in the upper Missouri River reach. Canonical correlation analysis revealed a strong correlation between EEA and the suite of water and sediment chemistry variables, and the percent of the catchment in anthropogenically dominated land uses, including agriculture and urban development. Nutrient ratios of the waters and sediments suggested carbon (C), nitrogen (N), or phosphorus (P) limitation at a large number of sites in each reach. C-limitation was most pronounced in the unimpounded Mississippi River and lower Missouri River reaches; N-limitation was prevalent in the two Missouri River reaches; and P-limitation dominated the Ohio River. Linking microbial enzyme activities to regional-scale anthropogenic stressors in these large river ecosystems suggests that microbial enzyme regulation of carbon and nutrient dynamics may be sensitive indicators of anthropogenic nutrient and carbon loading.     

Application of the integrated lake-watershed acidification study model to watershed liming at woods Lake,New York

Woods Lake, in the Adirondack Mountains of New York, was the site of the Experimental Watershed Liming Study (EWLS) in which base addition was investigated as a method for mitigation of lake acidity. In an effort to predict the duration of effects, the treatment was simulated using the Integrated Lake-Watershed Acidification Study (ILWAS) model. To simulate terrestrial liming, calcite was applied to treated subcatchments as a rapidly weathering mineral in the upper horizon. Soil solution and lake outlet chemistry showed a response to calcite addition within four months of the start of the simulation. Calcium concentrations, acid neutralizing capacities (ANC), and pH increased in the upper soil layer and aluminum concentrations decreased in the upper three soil layers (0–70 cm). The response of ANC was delayed in lower soil layers due to proton production associated with aluminum hydrolysis. Moreover, soil water pH in the third soil layer decreased in response to calcite treatment due to the displacement of hydrogen ions by calcium added to the exchange complex. Calcium concentrations, ANC and pH increased and aluminum concentrations decreased in the simulated lake outlet. The modeled effects of calcite treatment on the soil and lake outlet chemistry were not as great as field observations. This was, in part, attributed to the model representation of the watershed, which did not include streams, ponds, or wetlands located in the treated subcatchments. Calcite applied to these saturated areas in the field readily dissolved, supplying ANC to lake water. Additionally, incorporation of calcite into a thick organic layer in the model diminished the possibility of dissolution by contact with overland flow. Observed concentrations of calcium, ANC, and pH in the outlet decreased after high values in the two years after treatment. Although the model failed to match observed short-term data, it may simulate the long-term response as calcium is transported through the soil. A long-term simulation of the model suggests that effects of base treatment will persist for at least 50 years.