Watersheds Underlain Research Articles

English

This work evaluates the use of the biotic ligand model (BLM), an aquatic toxicity model, to predict toxic effects of metals on aquatic biota in areas underlain by different rock types. The chemical composition of water, soil, and sediment is largely derived from the composition of the underlying rock. Geologic source materials control key attributes of water chemistry that affect metal toxicity to aquatic biota, including: 1) potentially toxic elements, 2) alkalinity, 3) total dissolved solids, and 4) soluble major elements, such as Ca and Mg, which contribute to water hardness. Miller (2002) compiled chemical data for water samples collected in watersheds underlain by ten different rock types, and in a mineralized area in western Colorado. He found that each rock type has a unique range of water chemistry. In this study, the ten rock types were grouped into two general categories, igneous and sedimentary. Water collected in watersheds underlain by sedimentary rock has higher mean pH, alkalinity, and calcium concentrations than water collected in watersheds underlain by igneous rock. Water collected in the mineralized area had elevated concentrations of calcium and sulfate in addition to other chemical constituents. Miller's water- chemistry data were used in the BLM (computer program) to determine copper and zinc toxicity to Daphnia magna. Modeling results show that waters from watersheds underlain by different rock types have characteristic ranges of predicted LC50 values (a measurement of aquatic toxicity) for copper and zinc, with watersheds underlain by igneous rock having lower predicted LC50 values than watersheds underlain by sedimentary rock. Lower predicted LC50 values suggest that aquatic biota in watersheds underlain by igneous rock may be more vulnerable to copper and zinc inputs than aquatic biota in watersheds underlain by sedimentary rock. For both copper and zinc, there is a trend of increasing predicted LC50 values with increasing dissolved organic carbon (DOC) concentrations. Predicted copper LC50 values are extremely sensitive to DOC concentrations, whereas alkalinity appears to have an influence on zinc toxicity at alkalinities in excess of about 100 mg/L CaCO3. These findings show promise for coupling the BLM (computer program) with measured water-chemistry data to predict metal toxicity to aquatic biota in different geologic settings and under different scenarios. This approach may ultimately be a useful tool for mine-site planning, mitigation and remediation strategies, and ecological risk assessment.

Use of the Biotic Ligand Model to Predict Metal Toxicity to Aquatic Biota in Areas of Differing Geology

This work evaluates the use of the biotic ligand model (BLM), an aquatic toxicity model, to predict toxic effects of metals on aquatic biota in areas underlain by different rock types. The chemical composition of water, soil, and sediment is largely derived from the composition of the underlying rock. Geologic source materials control key attributes of water chemistry that affect metal toxicity to aquatic biota, including: 1) potentially toxic elements, 2) alkalinity, 3) total dissolved solids, and 4) soluble major elements, such as Ca and Mg, which contribute to water hardness. Miller (2002) compiled chemical data for water samples collected in watersheds underlain by ten different rock types, and in a mineralized area in western Colorado. He found that each rock type has a unique range of water chemistry. In this study, the ten rock types were grouped into two general categories, igneous and sedimentary. Water collected in watersheds underlain by sedimentary rock has higher mean pH, alkalinity, and calcium concentrations than water collected in watersheds underlain by igneous rock. Water collected in the mineralized area had elevated concentrations of calcium and sulfate in addition to other chemical constituents. Miller's water- chemistry data were used in the BLM (computer program) to determine copper and zinc toxicity to Daphnia magna. Modeling results show that waters from watersheds underlain by different rock types have characteristic ranges of predicted LC50 values (a measurement of aquatic toxicity) for copper and zinc, with watersheds underlain by igneous rock having lower predicted LC50 values than watersheds underlain by sedimentary rock. Lower predicted LC50 values suggest that aquatic biota in watersheds underlain by igneous rock may be more vulnerable to copper and zinc inputs than aquatic biota in watersheds underlain by sedimentary rock. For both copper and zinc, there is a trend of increasing predicted LC50 values with increasing dissolved organic carbon (DOC) concentrations. Predicted copper LC50 values are extremely sensitive to DOC concentrations, whereas alkalinity appears to have an influence on zinc toxicity at alkalinities in excess of about 100 mg/L CaCO3. These findings show promise for coupling the BLM (computer program) with measured water-chemistry data to predict metal toxicity to aquatic biota in different geologic settings and under different scenarios. This approach may ultimately be a useful tool for mine-site planning, mitigation and remediation strategies, and ecological risk assessment.

Nitrogen loss from watersheds of interior Alaska underlain with discontinuous permafrost

We constructed annual nitrogen budgets for four years for three watersheds underlain with discontinuous permafrost in interior Alaska. During all years, nitrogen export in stream flow exceeded input from deposition, with loss rate greatest from the two watersheds with the lowest spatial extents of permafrost. Elevated nitrogen export appears to be common in regions with discontinuous permafrost, based on nitrogen concentration in streams spanning a latitudinal gradient in permafrost coverage. This pattern of nitrogen loss is counter to temperate regions, where watersheds retain nitrogen even with elevated atmospheric deposition, and unexpected, given that terrestrial primary production appears to be nitrogen limited.

Coupling of runoff processes and sediment transport in mountainous watersheds underlain by different sedimentary rocks

AbstractRunoff and sediment transport were observed in two mountainous watersheds with different lithologies. One watershed is underlain by chert and the other by sandstone and shale. The chert watershed consists of bedrock cliffs and shallow regolith (0–2 m), whereas the sandstone–shale watershed is covered with a deeper regolith (1–5 m). In the sandstone–shale watershed, a large spring located in the channel head contributed to storm runoff. Tensiometric response in regolith above the spring showed negative pressure head throughout storm runoff, thus implying that the subsurface flow in bedrock predominated even during storm runoff. In the chert watershed, the runoff coefficient was larger than in the sandstone–shale watershed. Tensiometric response in regolith showed positive pressure head during storm runoff, indicating generation of rapid subsurface stormflow. Concentration of subsurface flow from side slopes increased peak streamflow in the downstream direction. In these two watersheds, different subsurface flowpaths, including bedrock fractures, facilitated different modes of sediment transport. Groundwater outflow at the spring caused seepage erosion in the sandstone–shale watershed, whereas peak streamflow transported bedload supplied by rockfall in the chert watershed. Copyright © 2004 John Wiley & Sons, Ltd.

Comparative major ion geochemistry of Piedmont streams in the Atlanta, Georgia region: possible effects of urbanization

The major ion stream chemistry for an urbanized basin (Peachtree Creek) in the Atlanta (Georgia, USA) metropolitan region was analyzed and compared upon a time-series basis with the stream chemistry of a nearby, but far less developed basin (Sweetwater Creek). The major ion chemistry from both streams indicated that all parameters fell below safe drinking water standards as would be expected in watersheds underlain by low-solubility aluminosilicate bedrock. Base flow TDS concentrations for the urbanized basin (Peachtree Creek) were ~30% greater than Sweetwater Creek and were characterized by elevated concentrations of base cations (Ca, Mg, Na), alkalinity, sulfate, and chloride. The less-urbanized Sweetwater Creek basin is underlain by a higher percentage of more soluble amphibolite and, therefore, the higher concentration of solutes within the urban base flow can not readily be explained by differential mineral weathering. The increased inorganic solute loads might have resulted from pollution input (leaky underground sewer lines?) and/or evaporative concentration; however, these explanations are presently speculative. Major ion concentrations within the urban Peachtree Creek basin were diluted by an average of ~50% compared with only ~25% in the Sweetwater Creek basin as a result of the increased contribution of direct surface runoff. The regression correlation coefficients for the ions that evolve through mineral weathering (Ca, Mg, Na, and HCO3) are much higher in urban stream flow than in Sweetwater Creek waters. This might indicate that storm waters in the urban basin are more closely derived from a two end member mixture (groundwater and street runoff) than waters from Sweetwater Creek, which represent a more complex mixture.

The role of subsurface runoff through bedrock on storm flow generation

AbstractThe influence of bedrock subsurface flow on storm runoff generation was investigated in Japan in two regions in Japan underlain by three bedrock types. One region, with approximately 2500 m of relief, is located in the Japan Alps, central Japan (In a region), where six small forest‐covered watersheds underlain by granite and Mesozoic shale were studied. Two of these watersheds were instrumented to monitor stream discharge and the other four are springs occurring at the bedrock exposure. The other study area is in northern Kyoto prefecture, western Japan (Oe region). Here, spring distribution and seasonal flow were monitored in two steep basins underlain by serpentinite rocks. Distinctly different runoff responses were observed: the granite watershed exhibited a large and rapid runoff peak that coincided with the rainfall peak (type 1); and the shale and serpentinite basins exhibited small initial runoff peaks followed by a maximum peak discharge five to ten times greater with a convex recession limb (type 2). Runoff response from bedrock springs had characteristics similar to type 1 hydrographs; however, discharge increased only when the antecedent precipitation index was large and the runoff peak was delayed between 10 h and 1 week after rain events. The specific discharge of the springs decreased with increase in altitude in the Oe region, especially in dry periods. This decline in discharge with elevation suggests that a deep subsurface flow system through bedrock fissures contributes to the storm water flow in serpentinate basins. When comparing runoff response and spring discharge, slow or double peak runoff response may be a good indicator of the influence of bedrock subsurface outflow on storm runoff generation in steep mountainous regions. Copyright © 2001 John Wiley & Sons, Ltd.

Geochemical Study of a Granitic Area – The Margeride Mountains, France: Chemical Element Behavior and 87Sr/86Sr Constraints

A small watershed (89 km2) underlain by granite or granite-gneiss in the Margeride mountains, southern Massif Central (France), has been studied using the chemical and isotopic composition of its dissolved load, bed sediments and soils. Dissolved concentrations of major ions (Cl, SO4, NO3, HCO3, Ca, Na, Mg, K, Al and Si), trace elements (Rb and Sr) and strontium isotopes have been determined for three different hydrologic periods in the main stream of the Desges river and its tributaries.

Regional test of a model for shallow landsliding

Landslides mapped in 14 watershed analyses in Oregon and Washington provide a regional test of a model for shallow landsliding. A total of 3224 landslides were mapped in watersheds covering 2993 km2 and underlain by a variety of lithologies, including Tertiary sedimentary rocks of the Coast Ranges, volcanic rocks of the Cascade Range and Quaternary glacial sediments in the Puget Lowlands. GIS (geographical information system) techniques were used to register each mapped landslide to critical rainfall values predicted from a theoretical model for the topographic control on shallow landsliding using 30 m DEMs (digital elevation models). A single set of parameter values appropriate for simulating slide hazards after forest clearing was used for all watersheds to assess the regional influence of topographic controls on shallow landsliding. Model performance varied widely between watersheds, with the best performance generally in steep watersheds underlain by shallow bedrock and the worst performance in generally low gradient watersheds underlain by thick glacial deposits. Landslide frequency (slides/km2) varied between physiographic provinces but yielded consistent patterns of higher slide frequency in areas with lower critical rainfall values. Simulations with variable effective cohesion predicted that high root strength effectively limits shallow landsliding to topographic hollows with deep soils and locations that experience excess pore pressures, but that low root strength leads to higher probabilities of failure across a greater proportion of the landscape. © 1998 John Wiley & Sons, Ltd. Language: en

Nitrogen Loading from Coastal Watersheds to Receiving Estuaries: New Method and Application

In this paper we develop a model to estimate nitrogen loading to watersheds and receiving waters, and then apply the model to gain insight about sources, losses, and transport of nitrogen in groundwater moving through a coastal watershed. The model is developed from data of the Waquoit Bay Land Margin Ecosystems Research project (WBLMER), and from syntheses of published information. The WBLMER nitrogen loading model first estimates inputs by atmospheric deposition, fertilizer use, and wastewater to surfaces of the major types of land use (natural vegetation, turf, agricultural land, residential areas, and impervious surfaces) within the landscape. Then, the model estimates losses of nitrogen in the various compartments of the watershed ecosystem. For atmospheric and fertilizer nitrogen, the model allows losses in vegetation and soils, in the vadose zone, and in the aquifer. For wastewater nitrogen, the model allows losses in septic systems and effluent plumes, and it adds further losses that occur during diffuse transport within aquifers. The calculation of losses is done separately for each major type of land cover, because the processes and loss rates involved differ for different tesserae of the land cover mosaic. If groundwater flows into a freshwater body, the model adds a loss of nitrogen for traversing the freshwater body and then subjects the surviving nitrogen to losses in the aquifer. The WBLMER model is developed for Waquoit Bay, but with inputs for local conditions it is applicable to other rural to suburban watersheds underlain by unconsolidated sandy sediments. Model calculations suggest that the atmosphere contributes 56%, fertilizer 14%, and wastewater 27% of the nitrogen delivered to the surface of the watershed of Waquoit Bay. Losses within the watershed amount to 89% of atmospheric nitrogen, 79% of fertilizer nitrogen, and 65% of wastewater nitrogen. The net result of inputs to the watershed surface and losses within the watershed is that wastewater becomes the largest source (48%) of nitrogen loads to receiving estuaries, followed by atmospheric deposition (30%) and fertilizer use (15%). The nitrogen load to estuaries of Waquoit Bay is transported primarily through land parcels covered by residential areas (39%, mainly via wastewater), natural vegetation (21%, by atmospheric deposition), and turf (16%, by atmospheric deposition and fertilizers). Other land covers were involved in lesser throughputs of nitrogen. The model results have implications for management of coastal landscapes and water quality. Most attention should be given to wastewater disposal within the watershed, particularly within 200 m of the shore. Rules regarding setbacks of septic system location relative to shore and nitrogen retention ability of septic systems, will be useful in control of wastewater nitrogen loading. Installation of multiple conventional leaching fields or septic systems in high-flow parcels could be one way to increase nitrogen retention. Control of fertilizer use can help to a modest degree, particularly for optional uses such as lawns situated near shore. Conservation of parcels of accreting natural vegetation should be given high priority, because these environments effectively intercept atmospheric deposition. Areas upgradient from freshwater bodies should be given low priority in plans to control nitrogen loading, because ponds intercept much of the nitrogen transported from upgradient.

NITROGEN LOADING FROM COASTAL WATERSHEDS TO RECEIVING ESTUARIES: NEW METHOD AND APPLICATION

In this paper we develop a model to estimate nitrogen loading to watersheds and receiving waters, and then apply the model to gain insight about sources, losses, and transport of nitrogen in groundwater moving through a coastal watershed. The model is developed from data of the Waquoit Bay Land Margin Ecosystems Research project (WBLMER), and from syntheses of published information. The WBLMER nitrogen loading model first estimates inputs by atmospheric deposition, fertilizer use, and wastewater to surfaces of the major types of land use (natural vegetation, turf, agricultural land, residential areas, and impervious surfaces) within the landscape. Then, the model estimates losses of nitrogen in the various compartments of the watershed ecosystem. For atmospheric and fertilizer nitrogen, the model allows losses in vegetation and soils, in the vadose zone, and in the aquifer. For wastewater nitrogen, the model allows losses in septic systems and effluent plumes, and it adds further losses that occur during diffuse transport within aquifers. The calculation of losses is done separately for each major type of land cover, because the processes and loss rates involved differ for different tesserae of the land cover mosaic. If groundwater flows into a freshwater body, the model adds a loss of nitrogen for traversing the freshwater body and then subjects the surviving nitrogen to losses in the aquifer. The WBLMER model is developed for Waquoit Bay, but with inputs for local conditions it is applicable to other rural to suburban watersheds underlain by unconsolidated sandy sediments. Model calculations suggest that the atmosphere contributes 56%, fertilizer 14%, and wastewater 27% of the nitrogen delivered to the surface of the watershed of Waquoit Bay. Losses within the watershed amount to 89% of atmospheric nitrogen, 79% of fertilizer nitrogen, and 65% of wastewater nitrogen. The net result of inputs to the watershed surface and losses within the watershed is that wastewater becomes the largest source (48%) of nitrogen loads to receiving estuaries, followed by atmospheric deposition (30%) and fer- tilizer use (15%). The nitrogen load to estuaries of Waquoit Bay is transported primarily through land parcels covered by residential areas (39%, mainly via wastewater), natural vegetation (21%, by atmospheric deposition), and turf (16%, by atmospheric deposition and fertilizers). Other land covers were involved in lesser throughputs of nitrogen. The model results have implications for management of coastal landscapes and water quality. Most attention should be given to wastewater disposal within the watershed, par- ticularly within 200 m of the shore. Rules regarding setbacks of septic system location relative to shore and nitrogen retention ability of septic systems, will be useful in control of wastewater nitrogen loading. Installation of multiple conventional leaching fields or septic systems in high-flow parcels could be one way to increase nitrogen retention. Control of fertilizer use can help to a modest degree, particularly for optional uses such as lawns situated near shore. Conservation of parcels of accreting natural vegetation should be given high priority, because these environments effectively intercept atmospheric deposition. Areas upgradient from freshwater bodies should be given low priority in plans to control nitrogen loading, because ponds intercept much of the nitrogen transported from upgradient.

Use of geochemical mass balance modelling to evaluate the role of weathering in determining stream chemistry in five mid-atlantic watersheds on different lithologies

The importance of mineral weathering was assessed and compared for five mid-Atlantic watersheds receiving similar atmospheric inputs but underlain by differing bedrock. Annual solute mass balances and volume-weighted mean solute concentrations were calculated for each watershed for each year of record. In addition, primary and secondary mineralogy were determined for each of the watersheds through analysis of soil samples and thin sections using petrographic, scanning electron microscope, electron microprobe and X-ray diffraction techniques. Mineralogical data were also compiled from the literature. These data were input to NETPATH, a geochemical program that calculates the masses of minerals that react with precipitation to produce stream water chemistry. The feasibilities of the weathering scenarios calculated by NETPATH were evaluated based on relative abundances and reactivities of minerals in the watershed. In watersheds underlain by reactive bedrocks, weathering reactions explained the stream base cation loading. In the acid-sensitive watersheds on unreactive bedrock, calculated weathering scenarios were not consistent with the abundance of reactive minerals in the underlying bedrock, and alternative sources of base cations are discussed. © 1997 John Wiley & Sons, Ltd.

Comparison of Hydrograph Deconvolutions using Residual Alkalinity, Chloride, and Oxygen 18 as Hydrochemical Tracers

Hydrograph deconvolution using geochemical tracers is currently widely used for determining the hydrologic mechanisms occurring in watersheds. However, few chemical parameters can be used as tracers because their involvement in biogeochemical processes prevents them from behaving in a conservative way. The aim of this study was to combine several geochemically controlled parameters into a single tracer. Residual alkalinity is a combination of several controlled parameters and is conservative in a wide range of natural environments. It was used in this study for quantifying the contributions of surface runoff and of groundwater flow during a flood in a Mediterranean watershed underlain by sedimentary rock. A preliminary geochemical study revealed that interactions with calcite, dolomite, and the clay‐humus complex controlled calcium and magnesium concentrations as well as carbonate alkalinity (Alkc), which prevented using them as tracers. Nevertheless, although residual alkalinity (Alkresidual) is a combination of these three parameters (Alkresidual = Alkc ‐ 2[Ca2+]T‐2[Mg2+]T), it provided results that were highly comparable to those obtained using chloride and δ18O. Contrary to the most cases in the literature, the contribution of direct runoff was dominant (about 80% at peak discharge). Accuracy estimates, which took into account analytical errors, temporal variations in the isotopic signature of rainfall, and the spatial variability of chemical elements, supported this result and confirmed that residual alkalinity is a useful concept in hydrology.

Spatial Variation in Specific Discharge of Base Flow in a Small Catchments, Oe-Yama Region, Western Japan.

Base flow from 66 tributaries in watersheds underlain by serpentinite, granite, and Paleozoic shale were measured in Oe-yama region, Kyoto Prefecture, Western Japan. The base flow measurements sufficiently after rainfall were conducted during the snowmelt season (April) and summer dry season (August). Spatial variation of specific discharge was greater in the serpentinite basins than those in the granite and the Paleozoic shale basins. In addition, there are many tributaries without discharge in serpentinite basins, even though they have large drainage areas and well-defined valleys. On the contrary, the specific discharges in the granite and the Paleozoic shale basins are relatively constant among tributaries. The average specific discharges in the serpentinite basin are smaller in August than that in April, whereas little difference between base flow discharges of April and August were observed in both the granite and the Paleozoic shale basins. These findings suggest that the seasonal variation of groundwater table level in bedrock is larger in serpentinite mountainous region than that of the granite and Paleozoic shale areas. Hence, we expect that lithology has a crucial effect on spatial variation, quantity and seasonal change of base flow.

Effects of climate on chemical_ weathering in watersheds

Climatic effects on chemical weathering are evaluated by correlating variations On solute concentrations and fluxes with temperature, precipitation, runoff, and evapotranspiration ( ET) for a worldwide distribution of sixty-eight watersheds underlain by granitoid rock types. Stream solute concentrations are strongly correlated with proportional ET loss, and evaporative concentration makes stream solute concentrations an inappropriate surrogate for chemical weathering. Chemical fluxes are unaffected by ET, and SiO 2 and Na weathering fluxes exhibit systematic increases with precipitation, runoff, and temperature. However, warm and wet watersheds produce anomalously rapid weathering rates. A proposed model that provides an improved prediction of weathering rates over climatic extremes Os the product of linear precipitation and Arrhenius temperature functions. The resulting apparent activation energies based on SiO 2 and Na fluxes are 59.4 and 62.5 kJ · mol -1, respectively. The coupling between temperature and precipitation emphasizes the importance of tropical regions On global silicate weathering fluxes, and suggests it is not representative to use continental averages for temperature and precipitation On the weathering rate functions of global carbon cycling and climatic change models. Fluxes of K, Ca, and Mg exhibit no climatic correlation, implying that other processes, such as ion exchange, nutrient cycling, and variations On lithology, obscure any climatic signal. The correlation between yearly variations On precipitation and solute fluxes within individual watersheds Os stronger than the correlation between precipitation and solute fluxes of watersheds with different climatic regimes. This underscores the significance of transport-induced variability On controlling stream chemistry, and the importance of distinguishing between short-term and long-term climatic trends. No correlation exists between chemical fluxes and topographic relief or the extent of recent glaciation, implying that physical erosion rates do not have a critical influence on chemical weathering rates.

Effects of Climate on Chemical Weathering in Watersheds Underlain by Grantoid Rocks

Effects of Climate on Chemical Weathering in Watersheds Underlain by Grantoid Rocks

Comparison of episodic acidification of Mid‐Atlantic Upland and Coastal Plain streams

Episodic acidification was examined in five mid‐Atlantic watersheds representing three physiographic provinces: Coastal Plain, Valley and Ridge, and Blue Ridge. Each of the watersheds receives a similar loading of atmospheric pollutants (SO42− and NO3−) and is underlain by different bedrock type. The purpose of this research was to quantify and compare the episodic variability in storm flow chemistry in Reedy Creek, Virginia (Coastal Plain), Mill Run and Shelter Run, Virginia (Valley and Ridge), and Fishing Creek Tributary and Hunting Creek, Maryland (Blue Ridge). Because episodic responses were similar from storm to storm in each of the watersheds, a representative storm from each watershed was discussed. Acidification, defined as the loss of acid‐neutralizing capacity (ANC), was observed in all streams except Mill Run. Mill Run chemistry showed little episodic variability. During storms in the other streams, pH decreased while SO42−, NO3−, and K+ concentrations increased. Concentrations of Mg2+ and Ca2+ increased in Reedy Creek and Fishing Creek Tributary, but decreased in Shelter Run and Hunting Creek. Therefore the net effect of episodic changes on the acid‐base status differed among the streams. In general, greater losses of ANC were observed during storms at Shelter Run and Hunting Creek, watersheds underlain by reactive bedrock (carbonate, metabasalt); comparatively smaller losses in ANC were observed at Reedy Creek and Fishing Creek Tributary, watersheds underlain by quartzites and unconsolidated quartz sands and cobbles. Increased SO42− concentrations were most important during storms at Reedy Creek and Fishing Creek Tributary, but organic anions (inferred by anion deficit) were also a factor in causing the loss of ANC. Dilution of base cations was the most important factor in the loss of ANC at Shelter Run. Both increased sulfate and dilution of base flow were important in causing the episodic acidification at Hunting Creek. The role of SO42− in contributing to episodic acidification in these watersheds is similar to that documented in studies conducted in other regions of the United States, Scandinavia, Canada, and the United Kingdom. The importance of SO42− in mid‐Atlantic United States streams contrasts with northeastern United States streams, in which increased NO3‐ derived from snowpack is more important in causing episodic acidification. Results support the importance of shallow subsurface processes in determining storm flow chemistry, regional climatic characteristics in determining the different sources of acidity during episodes, and the importance of bedrock geology in determining the amount of ANC loss.

Silicate dissolution influence on Filson Creek chemistry, northeastern Minnesota

The chemistry of surface water, precipitation, and ground water in Filson Creek watershed was studied to evaluate the kinetics of dissolution of silicate minerals in a natural watershed underlain by troctolite. Annual chemical budgets in 1977 showed net losses of dissolved silica, bicarbonate, calcium, magnesium, and sodium of about 31.0, 19.6, 4.8, 3.8, and 2.1 kg per hectare per year, respectively, and net gains of dissolved potassium and sulfate of 0.4 and 8.9 kg/ha/yr. On a molar basis, about 1.5 times as much magnesium was lost as was calcium, even though the amount of mafic minerals in till and bedrock underlying the watershed is about 10 times less than the amount of calcic plagioclase. Molar concentrations of magnesium in base flow and ground water were about the same as concentrations of calcium and sodium. These field data indicate that magnesium loss from the mafic minerals may be faster than either calcium or sodium loss from plagioclase. Stoichiometric “reconstruction” of primary minerals from base-flow water chemistry and kaolinite was done as a first approximation to evaluate the rates of loss. The calculations indicated that the release of magnesium from mafic minerals would have to be more than ten times faster than the release of calcium and sodium from plagioclase to account for the amount of magnesium in base flow. These calculations compare favorably with experimental linear rates of cation and silica release from forsterite, enstatite, augite, and labradorite.

MINE DRAINAGE AND ROCK TYPE INFLUENCES ON EASTERN OHIO STREAM WATER QUALITY1

ABSTRACT: Stream water during fair weather (base flow) is largely ground water discharge, which has been in contact with minerals of the underlying aquifer. Base flow water quality should therefore reflect aquifer mineralogy as well as upstream land use. Three upstream mining categories (unmined lands, abandoned coal mines, and reclaimed coal mines) differed in pH, specific conductance, sulfate, iron, aluminum, and alkalinity for 122 streams in eastern Ohio. Aquifer rock type influenced pH, specific conductance, sulfate, iron, and alkalinity. Reclamation returned many components of acid mine drainage to near unmined levels, although sulfate and specific conductance were not improved. Acid mine drainage problems were less severe in watersheds underlain by the calcareous Monogahela Formation. These results should ayply to other Appalachian coal regions having similar rock units.The water quality data distributions were neither consistently normal nor lognormal. Statistical tests utilizing ranks of the water quality data, instead of the data themselves, proved useful in analyzing the influences of mining category and rock type.

Chemical character of headwater streams in Vermont and New Hampshire

Stream water samples were collected from headwater streams in Vermont and New Hampshire during low‐flow periods in the fall and analyzed for principal dissolved constituents. Dissolved solids are qualitatively and quantitatively related to bedrock type. Streams draining watersheds underlain by plutonic bedrock are acid, mixed cation sulfate waters with little buffering capacity and very low solute content (about 16 mg/1). Streams draining metamorphic and sedimentary terrains are characterized by neutral pH, alkaline earth cations, and mixed anions or bicarbonate. Concentrations of Ca + Mg + Na + K and pH of streams draining granitic bedrock are lower than those of streams draining similar rock types in small watersheds in the Sierra Nevada and Sangre de Cristo mountains.

Sustained flow in small Appalachian watersheds underlain by carbonate rocks

The groundwater release from storage as it relates to sustained flows in surface streams was investigated for 57 carbonate basins within the Appalachian Highlands. Comparisons were made between sustained flow and the aerial extent of limestone and dolomite rock outcrop within the basins and with the degree of karst development as measured by internal drainage through dolines and sinking streams. Data analyses by direct correlation, by factor analysis and cluster analysis showed that the basins investigated fell into two distinct populations, those with sustained flows comparable to flows observed in non-carbonate basins and those with exceptionally low sustained flows. Basins with a high degree of karst development tended to have low sustained flow because of poor groundwater storage and short residence times in carbonate aquifers with conduit-type permeability. Higher sustained flows were associated with aquifers of the diffuse-flow type.