Geology topics

Marisa H. Cox

Publications and source records attributed to Marisa H. Cox.

8 recordsLinked to original sources

USGS2009

Experimental removal of wetland emergent vegetation leads to decreased methylmercury production in surface sediment

We performed plant removal (devegetation) experiments across a suite of ecologically diverse wetland settings (tidal salt marshes, river floodplain, rotational rice fields, and freshwater wetlands with permanent or seasonal flooding) to determine the extent to which the presence (or absence) of actively growing plants influences the activity of the Hg(II)-methylating microbial community and the availability of Hg(II) to those microbes. Vegetated control plots were paired with neighboring devegetated plots in which photosynthetic input was terminated 4–8 months prior to measurements, through clipping aboveground biomass, severing belowground connections, and shading the sediment surface to prevent regrowth. Across all wetlands, devegetation decreased the activity of the Hg(II)-methylating microbial community (k meth ) by 38%, calculated MeHg production potential (MP) rates by 36%, and pore water acetate concentration by 78%. Decreases in MP were associated with decreases in microbial sulfate reduction in salt marsh settings. In freshwater agricultural wetlands, decreases in MP were related to indices of microbial iron reduction. Sediment MeHg concentrations were also significantly lower in devegetated than in vegetated plots in most wetland settings studied. Devegetation effects were correlated with live root density (percent volume) and were most profound in vegetated sites with higher initial pore water acetate concentrations. Densely rooted wetlands had the highest rates of microbial Hg(II)-methylation activity but often the lowest concentrations of bioavailable reactive Hg(II). We conclude that the exudation of labile organic carbon (e.g., acetate) by plants leads to enhanced microbial sulfate and iron reduction activity in the rhizosphere, which results in high rates of microbial Hg(II)-methyation and high MeHg concentrations in wetland sediment.

Journal of Geophysical Research: Biogeosciences↗

USGS2007

Floodwater chemistry in the Yolo Bypass during winter and spring, 1998

A preliminary investigation of temporal and spatial variations in floodwater chemistry was conducted during winter and spring 1998 in the Yolo Bypass floodplain of the Sacramento River system. Samples were collected at locations along the eastern margin of the floodplain over the duration of the study and across the floodplain during major periods of inundation. Specific conductance and dissolved organic carbon concentrations along the eastern margin of the Yolo Bypass varied inversely with discharge. The Sacramento River was the greatest source of discharge to the floodplain during major periods of inundation. Increases in specific conductance and dissolved organic carbon were observed along the eastern margin during periods of lower discharge, when local streams accounted for a significant fraction of the total discharge through the Yolo Bypass. Apparent influences of local stream discharges also were observed in surface waters near the western margin of the floodplain during major periods of inundation. Although river and local stream sources of suspended particulate matter appeared important, in-floodplain processes were likely contributors to temporal and spatial variability in concentrations. Values for the C:N ratio of the particulate matter were lowest during periods of decreasing and low discharge through the floodplain, indicating production of phytoplankton in floodplain waters or supply to the floodplain by local stream sources. Phytoplankton discharged from the Yolo Bypass was detected by chlorophyll a monitors downstream in the Sacramento River during this study.

Open-File Report↗

USGS2007

Chemical and hydrologic data from the Cement Creek and upper Animas River confluence and mixing zone, Silverton, Colorado, September 1997

Cement Creek, an acidic tributary, discharges into the circum-neutral Animas River (pH>7) in Silverton, Colorado located in the high-elevation San Juan Mountains. Mixing of Animas River water with acidic metal rich Cement Creek water raises water pH and produces metal precipitates. This report presents selected anion, cation, chloride, and sulfate data along with hydrologic data highlighting the mixing of these streams during the low-flow period in late summer 1997.

Colorado↗

USGS2007

Legacy mercury in Alviso Slough, south San Francisco Bay, California: Concentration, speciation and mobility

Mercury (Hg) is a significant contaminant in the waters, sediment and biota of San Francisco Bay, largely resulting from extensive historic regional mining activities. Alviso Slough represents one of the most mercury contaminated waterways entering south San Francisco Bay, as it is associated with the drainage of the New Almaden mercury mining district. Wetland habitat restoration of former salt manufacturing ponds adjacent to Alviso Slough is currently being planned. One management scenario being considered is a levee breach between Alviso Slough and Pond A8, which will allow reconnection of the salt pond with the tidal slough. This action is projected to increase the tidal prism within Alviso Slough and result in some degree of sediment remobilization as the main channel deepens and widens. The focus of the current study is to assess: a) the current mercury species composition and concentration in sediments within the Alviso Slough main channel and its associated fringing marsh plain, b) how much of each mercury species will be mobilized as a result of projected channel deepening and widening, and c) potential changes in inorganic reactive mercury bioavailability (for conversion to toxic methylmercury) associated with the mobilized sediment fraction. The current report details the field sampling approach and all laboratory analyses conducted, as well as provides the complete dataset associated with this project including a) a quantitative assessment of mercury speciation (total mercury, reactive mercury and methylmercury), b) estimates of the quantity of sediment and mercury mobilized based on 20-foot and 40-foot levee wall notch scenarios, and c) results from a sediment scour experiment examining the changes in the reactive mercury pool under four treatment conditions (high / low salinity and oxic / anoxic water). Ancillary sediment data also collected and reported herein include bulk density, organic content, magnetic susceptibility, percent dry weight, grain size, pH, oxidation-reduction potential, core photography, and detailed lithographic descriptions.

California↗

USGS2005

Descriptions of the Animas River-Cement Creek confluence and mixing zone near Silverton, Colorado, during the late summers of 1996 and 1997

Acidic waters from Cement Creek discharge into the circum-neutral Animas River in a high-elevation region of the San Juan Mountains near Silverton, Colorado. Cement Creek is acidic and enriched in metals and sulfate because it is fed by discharges from abandoned mines and natural mineral deposits. Mixing with the Animas River raises the pH and produces precipitates of iron and aluminum (oxy)hydroxides, which in turn can adsorb other metals. This confluence was studied in 1996 and 1997 to better understand mixing and sorption processes which are common during the neutralization of acidic streams. The photographs in this report show flow braiding and other features that influenced the way the two streams mixed during the late summers of the two years. They also show 'banding' due to incomplete mixing and 'opalescence' due to chemical reactions and the formation of colloidal-size particles in the mixing zone.

Colorado↗

USGS2003

Water temperature, streamflow, and ground-water elevation in and adjacent to the Russian river between Hopland and Guerneville, California from 1998-2002

Temperature, water level elevation, stage height, and river discharge data for this report were collected in and adjacent to the Russian River from Hopland to Guerneville, CA over a four-year period from 1998 to 2002 to establish baselines for long-term water quality, water supply and habitat. Data files presented in this report were collected by the USGS and the Sonoma County Water Agency's Engineering Resource and Planning, and Natural Resource Divisions. Temperature data were collected in single-channel submersible microloggers or temperature data were collected simultaneously with water-elevation data in dual-channel down-hole data loggers. Stream stage and streamflow data were collected at USGS stream gaging stations located near Hopland, Healdsburg, and Guerneville over a 130 km reach of the Russian River. During the period of record stream flow ranged from 3 to 1458 m3/s. Stream temperature ranged from 8 to 29 oC while groundwater temperature ranged from 10 to 38 oC. Stream stage varied 5 m seasonly, while ground-water level varied 19 m over the same time scale.

California↗

USGS2003

Evaluation of tracer tests completed in 1999 and 2000 on the upper Santa Clara River, Los Angeles and Ventura Counties, California

The interaction of surface water and hyporheic water along the Santa Clara River in Los Angeles and Ventura Counties, California, was evaluated by conducting tracer tests and analyzing water-quality data under different flow conditions in October 1999 and May 2000. Tracer and water-quality samples were collected at multiple river and hyporheic sites as well as at the Los Angeles County Sanitation Districts Saugus and Valencia Water Reclamation Plants. These water reclamation plants provide the main source of base flow in the river. Rhodamine WT dye was injected into the river to determine river traveltimes and to indicate when Lagrangian water-quality sampling could be performed at each site. Sodium bromide was injected into the river at a constant rate at the water reclamation plants to evaluate the surface-water and shallow ground-water interactions in the hyporheic zone. In the upper reach of the study area, which extends 2.9 river miles downstream from the Saugus Water Reclamation Plant, traveltime was 3.2 hours during May 2000. In the lower reach, which extends 14.1 river miles downstream from the Valencia Water Reclamation Plant, traveltime was 9.6 hours during October 1999 and 7.1 hours during May 2000. The sodium bromide tracer was detected at both hyporheic locations sampled during October 1999, and at two of the three hyporheic locations sampled during May 2000. On the basis of Rhodamine dye tests, flow curves were constructed from the discharge measurements in the Valencia reach. Flow-curve results indicate net gains in flow throughout most, but not all, of the upper parts of the reach and net losses in flow at the lower part of the reach. Lagrangian water-quality sampling provides information on the changes in chemistry as the water flows downstream from the water reclamation plants. Along both reaches there is an increase in sulfate (40-60 mg/L in the Saugus reach and 160 mg/L in the Valencia reach) and a decrease in chloride (about 45 mg/L in the Saugus reach and about 10 mg/L in the Valencia reach). The increasing sulfate concentrations are consistent with discharge of higher sulfate ground water into the river. Along both reaches there is a trend of decreasing ammonia and slightly increasing nitrate concentrations. This trend is consistent with nitrification. Samples were also analyzed for numerous compounds associated with wastewater, but analysis focused on four indicators. Concentrations of wastewater indicators in the Santa Clara River were low and decreased downstream from the reclamation plants. There is general consistency between the chemical and tracer data collected from the hyporheic and the river-aquifer flow regime within a reach. The water quality at the hyporheic site in a gaining reach of the river resembled that of the local ground water and no wastewater indicators or injected tracers were observed; whereas, the water quality at the hyporheic sites in a losing reach of the river resembled the water quality of the river at the corresponding river site, and injected tracers were observed.

California↗

USGS2002

Hydrology and chemistry of floodwaters in the Yolo Bypass, Sacramento River system, California, during 2000

Discharges to and floodwaters in the Yolo Bypass were sampled during winter and spring, 2000. The primary purpose of the study was to link changes in water quality in the Yolo Bypass to inflows from the Sacramento River (over Fremont Weir) and from four local streams that discharge to the west side of the floodplain. Specific conductance, chloride, sulfate, dissolved inorganic nutrients, dissolved organic carbon, particulate carbon and nitrogen, suspended particulate matter (mass), and selected dissolved metals were measured in most of the samples. When the Sacramento River was spilling over Fremont Weir, the water chemistry in the Yolo Bypass was very similar to that in the river except along the western margin of the floodplain where influences of local stream inflow were evident. When flow over Fremont Weir stopped, floodwaters drained from the Yolo Bypass, and the local streams were the major discharges as the floodwaters receded eventually to the perennial channel along the eastern margin of the floodplain. After the initial draining of the floodplain, chemical concentrations at sites along the perennial channel showed strong influences of inflows from Cache Creek and Ridge Cut, which are sources of nutrients and contaminants that are potentially hazardous to wildlife. Runoff from spring storms increased flow in the perennial channel and flushed accumulated nutrients and organic matter to the tidal river. Releases of freshwater to the perennial channel might be beneficial in maintaining habitat quality for aquatic species during the dry seasons.

California↗