Geology topics

Christopher D. Knightes

Publications and source records attributed to Christopher D. Knightes.

4 recordsLinked to original sources

USGS2015

Optimizing fish sampling for fish - mercury bioaccumulation factors

Fish Bioaccumulation Factors (BAFs; ratios of mercury (Hg) in fish (Hg fish ) and water (Hg water )) are used to develop Total Maximum Daily Load and water quality criteria for Hg-impaired waters. Both applications require representative Hg fish estimates and, thus, are sensitive to sampling and data-treatment methods. Data collected by fixed protocol from 11 streams in 5 states distributed across the US were used to assess the effects of Hg fish normalization/standardization methods and fish sample numbers on BAF estimates. Fish length, followed by weight, was most correlated to adult top-predator Hg fish . Site-specific BAFs based on length-normalized and standardized Hg fish estimates demonstrated up to 50% less variability than those based on non-normalized Hg fish . Permutation analysis indicated that length-normalized and standardized Hg fish estimates based on at least 8 trout or 5 bass resulted in mean Hg fish coefficients of variation less than 20%. These results are intended to support regulatory mercury monitoring and load-reduction program improvements.

Chemosphere↗

USGS2013

Climate change and watershed mercury export: a multiple projection and model analysis

Future shifts in climatic conditions may impact watershed mercury (Hg) dynamics and transport. An ensemble of watershed models was applied in the present study to simulate and evaluate the responses of hydrological and total Hg (THg) fluxes from the landscape to the watershed outlet and in-stream THg concentrations to contrasting climate change projections for a watershed in the southeastern coastal plain of the United States. Simulations were conducted under stationary atmospheric deposition and land cover conditions to explicitly evaluate the effect of projected precipitation and temperature on watershed Hg export (i.e., the flux of Hg at the watershed outlet). Based on downscaled inputs from 2 global circulation models that capture extremes of projected wet (Community Climate System Model, Ver 3 [CCSM3]) and dry (ECHAM4/HOPE-G [ECHO]) conditions for this region, watershed model simulation results suggest a decrease of approximately 19% in ensemble-averaged mean annual watershed THg fluxes using the ECHO climate-change model and an increase of approximately 5% in THg fluxes with the CCSM3 model. Ensemble-averaged mean annual ECHO in-stream THg concentrations increased 20%, while those of CCSM3 decreased by 9% between the baseline and projected simulation periods. Watershed model simulation results using both climate change models suggest that monthly watershed THg fluxes increase during the summer, when projected flow is higher than baseline conditions. The present study's multiple watershed model approach underscores the uncertainty associated with climate change response projections and their use in climate change management decisions. Thus, single-model predictions can be misleading, particularly in developmental stages of watershed Hg modeling.

South Carolina↗

USGS2012

Data visualization, time-series analysis, and mass-balance modeling of hydrologic and water-quality data for the McTier Creek watershed, South Carolina, 2007-2009

The McTier Creek watershed is located in the headwaters of the Edisto River Basin, which is in the Coastal Plain region of South Carolina. The Edisto ecosystem has some of the highest recorded fish-tissue mercury concentrations in the United States. In an effort to advance the understanding of the fate and transport of mercury in stream ecosystems, the U.S. Geological Survey, as part of its National Water-Quality Assessment Program, initiated a field investigation of mercury in the McTier Creek watershed in 2006. The initial efforts of the investigation included the collection of extensive hydrologic and water-quality field data, along with the development of several hydrologic and water-quality models. This series of measured and modeled data forms the primary source of information for this investigation to assess the fate and transport of mercury within the McTier Creek watershed.

South Carolina↗

USGS2010

Total mercury, methylmercury, and selected elements in soils of the Fishing Brook watershed, Hamilton County, New York, and the McTier Creek watershed, Aiken County, South Carolina, 2008

Mercury is an element of on-going concern for human and aquatic health. Mercury sequestered in upland and wetland soils represents a source that may contribute to mercury contamination in sensitive ecosystems. An improved understanding of mercury cycling in stream ecosystems requires identification and quantification of mercury speciation and transport dynamics in upland and wetland soils within a watershed. This report presents data for soils collected in 2008 from two small watersheds in New York and South Carolina. In New York, 163 samples were taken from multiple depths or soil horizons at 70 separate locations near Fishing Brook, located in Hamilton County. At McTier Creek, in Aiken County, South Carolina, 81 samples from various soil horizons or soil depths were collected from 24 locations. Sample locations within each watershed were selected to characterize soil geochemistry in distinct land-cover compartments. Soils were analyzed for total mercury, selenium, total and carbonate carbon, and 42 other elements. A subset of the samples was also analyzed for methylmercury.

Data Series↗