Geology topics
Katherine Walton-Day
Publications and source records attributed to Katherine Walton-Day.
The interaction of natural organic matter with iron in a wetland (Tennessee Park, Colorado) receiving acid mine drainage
Pore water from a wetland receiving acid mine drainage was studied for its iron and natural organic matter (NOM) geochemistry on three different sampling dates during summer 1994. Samples were obtained using a new sampling technique that is based on screened pipes of varying length (several centimeters), into which dialysis vessels can be placed and that can be screwed together to allow for vertical pore-water sampling. The iron concentration increased with time (through the summer) and had distinct peaks in the subsurface. Iron was mainly in the ferrous form; however, close to the surface, significant amounts of ferric iron (up to 40% of 2 mmol L-1 total iron concentration) were observed. In all samples studied, iron was strongly associated with NOM. Results from laboratory experiments indicate that the NOM stabilizes the ferric iron as small iron oxide colloids (able to pass a 0.45μm dialysis membrane). We hypothesize that, in the pore water of the wetland, the high NOM concentrations (>100 mg C L-1) allow formation of such colloids at the redoxcline close to the surface and at the contact zone to the adjacent oxic aquifer. Therefore, particle transport along flow paths and resultant export of ferric iron from the wetland into ground water might be possible.
Physical and chemical characteristics of Terrace Reservoir, Conejos County, Colorado, May 1994 through May 1995
Terrace Reservoir receives drainage of low-pH, metal-enriched water from mineralized areas, including the Summitville Mine, within the Alamosa River Basin. Drainage from the Summitville Mine has contributed a substantial part of the metal load to Terrace Reservoir. From May 1994 through May 1995, a study was done by the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, to evaluate the physical and chemical characteristics of Terrace Reservoir. Terrace Reservoir was thermally stratified from about mid-May through August 1994. Thermal stratification was absent from September\x111994through March 1995. During periods of stratification, underflow of the Alamosa River was predominant, and residence times of the underflow were shortened by 40 to 75\x11percent of the theoretical residence times for a well-mixed reservoir. Transport and deposition of suspended solids in Terrace Reservoir varied spatially and temporally. Most of the suspended solids were deposited in Terrace Reservoir. The concentration of dissolved oxygen in the reservoir varied little spatially or temporally and generally was within a few tenths of the dissolved-oxygen concentration of the inflow. The pH of water in the reservoir generally ranged from about 4.0 to about 7.0, depending on date, depth, and location. The largest pH values were measured during May. A markeddecrease of about 1.5\x11pH units occurred at site T5 in the reservoir about mid-June. The pH of the reservoir remained at or below 5.5 from mid-June through November. Dissolved-metal concentrations varied spatially and temporally in response to several factors, which included inflow characteristics, reservoir stratification and mixing, inflow-routing and flow-through patterns, residence times, sedimentation, dissolved oxygen, and pH.Inflow chemistry is the dominant controlling factor of metal chemistry within Terrace Reservoir.During periods of stratification, large vertical variations in metal concentrations occurred. The highest metal concentrations in the reservoir generally were measured in the hypolimnion between June and August. During June, epilimnetic water of the reservoir had pH values greater than 6.0, and metal concentrations were lower than hypolimnetic concentrations. In the hypolimnion, pH values were less than 5.5. The difference between the chemistry of the epilimnion and the hypolimnion was due to differences in flow routing and residence times of water in those respective layers. The dissolved-metal concentrations were larger during July and August than during June.During September, small vertical variations in metalconcentrations occurred, and the dissolved-metal concentrations were nearly equivalent to the average August metal concentrations, indicatingthat the metal concentrations measured during September resulted largely from reservoir mixing.During March, the largest metal concentrationsoccurred in the epilimnion, where pH was about 5.5; in the hypolimnion, where the pH was about 6.0, dissolved-metal concentrations were substantially lower and reflected inflow concentrations.
Geochemistry of the processes that attenuate acid mine drainage in wetlands
Because conventional treatment of acid-mine drainage (AMD) involves installation and maintenance of water treatment plants, regulators and mine operators have sought lower cost and lower maintenance technologies. One ecological engineering technology that has received increasing research attention is the use of natural and constructed wetlands for remediation of some of the water-quality problems associated with AMD. As surface water flows through a wetland, several processes can occur to decrease the elevated concentrations of sulfate, trace metals, arsenic, and hydrogen ions that characterize AMD. These processes range from precipitation of mineral phases to the active uptake of solutes by vegetation. The relative importance of these processes between different wetlands depends on the hydrologic and geochemical characteristics of the wetlands. This paper describes the geochemistry of the processes that contribute to AMD attenuation in wetlands and presents some of the case studies that have identified these processes. The attenuation of AMD in wetlands has been studied in natural and in man- made (constructed) wetlands. In this paper, case studies of both are presented. A discussion of some of the general characteristics of wetlands is followed by more detailed discussions of the processes and geochemistry that contribute to the treatment of AMD in wetlands, relevant case studies, and a brief discussion of constructed wetland design. The physical, chemical, and hydrologic characteristics of a wetland that affect its potential for supporting specific types of reactions are also emphasized.
Physical and chemical characteristics of Terrace Reservoir, Conejos County, Colorado, May 1994 through May 1995; interim report
Terrace Reservoir receives drainage of low-pH, metal-enriched water from mineralized areas, including the Summitville Mine, within the Alamosa River Basin. Drainage from the Summitville Mine has contributed a substantial part of the metal load to Terrace Reservoir. From May 1994 through May 1995, a study was done by the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, to evaluate the physical and chemical characteristics of Terrace Reservoir. Terrace Reservoir was thermally stratified from about mid-May through August 1994. Thermal stratification was absent from September\x111994through March 1995. During periods of stratification, underflow of the Alamosa River was predominant, and residence times of the underflow were shortened by 40 to 75\x11percent of the theoretical residence times for a well-mixed reservoir. Transport and deposition of suspended solids in Terrace Reservoir varied spatially and temporally. Most of the suspended solids were deposited in Terrace Reservoir. The concentration of dissolved oxygen in the reservoir varied little spatially or temporally and generally was within a few tenths of the dissolved-oxygen concentration of the inflow. The pH of water in the reservoir generally ranged from about 4.0 to about 7.0, depending on date, depth, and location. The largest pH values were measured during May. A markeddecrease of about 1.5\x11pH units occurred at site T5 in the reservoir about mid-June. The pH of the reservoir remained at or below 5.5 from mid-June through November. Dissolved-metal concentrations varied spatially and temporally in response to several factors, which included inflow characteristics, reservoir stratification and mixing, inflow-routing and flow-through patterns, residence times, sedimentation, dissolved oxygen, and pH. Inflow chemistry is the dominant controlling factor of metal chemistry within Terrace Reservoir. During periods of stratification, large vertical variations in metal concentrations occurred. The highest metal concentrations in the reservoir generally were measured in the hypolimnion between June and August. During June, epilimnetic water of the reservoir had pH values greater than 6.0, and metal concentrations were lower than hypolimnetic concentrations. In the hypolimnion, pH values were less than 5.5. The difference between the chemistry of the epilimnion and the hypolimnion was due to differences in flow routing and residence times of water in those respective layers. The dissolved-metal concentrations were larger during July and August than during June. During September, small vertical variations in metal concentrations occurred, and the dissolved-metal concentrations were nearly equivalent to the average August metal concentrations, indicatingthat the metal concentrations measured during September resulted largely from reservoir mixing.During March, the largest metal concentrationsoccurred in the epilimnion, where pH was about 5.5; in the hypolimnion, where the pH was about 6.0, dissolved-metal concentrations were substantially lower and reflected inflow concentrations.
Geochemistry of sediments from coastal marshes of Louisiana
As a part of the U.S. Geological Survey Global Change and Climate History Program we have been studying the biogeochemistry of coastal marshes in Terrebonne Basin, Louisiana. Louisiana has about 40 percent of the coastal wetlands in the conterminous U.S. and it is losing wetlands at one of the highest rates in the U.S. with the conversion of about 65 km2/yr of marsh to open water (Britsch and Dunbar, 1993). The losses have been attributed to human and natural causes including saltwater intrusion through man-made canals, reduced sediment input, and regional subsidence. The net effect of these influences is to change the salinity of interior marshes in a fashion similar to a eustatic sea level rise. We are studying the cycling of carbon, sulfur, and other elements in sediments, waters, and marsh macrophytes in fresh, intermediate/brackish, and saltwater marshes in order to better understand how sea level rise, one aspect of global change, will influence and in turn be influenced by cycling of these elements. By characterizing the critical biogeochemical processes and the recent past environments in these rapidly changing marshes, we can improve predictions of future changes and interpretations of the historic geologic record in similar environments. In this report we describe our coastal marsh study sites in Louisiana, the types of samples collected, the collection methods, the chemical analysis methods, and selected chemical analysis results. Also included are summaries of the project quality control results. The raw chemical analysis results are provided in this report without interpretation. Interpretations will be provided in subsequent reports.