THREE‐DIMENSIONAL KRIGING ANALYSIS OF SEDIMENT MERCURY DISTRIBUTION: A CASE STUDY¹

Abstract

This study presents an application of a three‐dimensional kriging technique to estimate spatial distribution of total mercury (Hg) in the Cedar‐Ortega Rivers watershed located in the lower St. Johns River basin, Florida. The kriging procedures, including preliminary data analysis, structural data analysis and the log kriging estimation, are presented. Results show watershed wide Hg contamination of river sediment to a depth of 1.0 m. A three‐dimensional plot of Hg against the Florida Sediment Assessment Guidelines (i.e., the probable effect level or PEL) demonstrates that the Cedar River is more contaminated with Hg than the rest of the watershed. The maximum sediment depth with Hg concentrations above PEL value (0.696 mg/kg) is 1.5 m. Hg concentrations at or above this level could pose a significant hazard to aquatic organisms. Analysis of the spatial distribution of Hg in the watershed finds multiple input sources. This study suggests that there is a need to identify the major sources of Hg in the watershed, and to determine the pathways that allow Hg to enter the river.

Naturalization as a strategy for improving soil physical characteristics in a forested urban park

“…The gstat package in R (www.r-project.org) and Geostatistical Analyst (ArcGIS 9.2 extension; ESRI Inc.) were used to estimate and fit models to our empirical semivariograms: spherical, exponential, or Gaussian (Ouyang et al 2003). The presence of anisotropy (greater autocorrelation in one direction when compared with another) was assessed using an interactive semivariogram modeling tool in Geostatistical Analyst by viewing hypothetical fits of anisotropic models to several directions simultaneously (Waller and Gotway 2004).…”

“…A total of 12 lags and a lag size of 10 m were specified for each analysis. The model best suited to each particular variable was evaluated through visual examination of the shape of the empirical semivariogram and through a cross-validation comparing the error terms for each of the models evaluated (Hooker and Nathanail 2006;Ouyang et al 2003) using an iterative procedure.…”

Assessing historical versus contemporary mercury and lead contamination in Lake Huron sediments

“…Few however have applied this tool for the estimation of sediment contamination distribution. Some recent examples for river environments include Ouyang et al (2003a), andOuyang et al (2003b). In the Great Lakes Basin, Jakubek and Forsythe (2004), Forsythe et al (2004), and Forsythe and Marvin (2005) utilized kriging to estimate sediment contamination levels.…”

Estimation of dynamic load of mercury in a river with BASINS-HSPF model

“…Two steps were used for the model calibration and validation processes in this study, one for the hydrologic component and the other for the sediment transport component. Surface loading and stream routing of Hg are primarily associated with sediment transport as no Hg was detected in the surface water samples in our previous studies (Ouyang et al 2003). Therefore, calibration of sediment loading and routing in the surface water would be adequate for sediment associated Hg loading.…”

“…In recent years, the St. Johns River Water Management District (SJRWMD) of Florida has sampled sediments in the LSJR and its tributaries to determine the presence and concentration of anthropogenic pollutants (Durell et al 2004). Based on the results of these efforts, both the Cedar and Ortega Rivers, tributaries of the LSJR, were determined to be contaminated with Hg (Ouyang et al 2003;Durell et al 2004) and other compounds. However, the potential sources, loading rates, and environmental health impacts of Hg contamination have not yet been thoroughly investigated.…”