Sediment and trace element trapping in a forested wetland, Chickahominy River, Virginia

Abstract

Abstract:The Chickahominy River, arising near Richmond, Virginia, flows southeast toward Newport News, which impounds the river for much of its water supply. Much of the bottomland between the two cities is flooded for extended periods annually. Sediment-deposition rates estimated from tree rings were used in conjunction with multi-element analyses of sediments and of selected growth rings from oak trees to estimate amounts of trapped sediment and trace elements. Mean rates of deposition at eight study sites range from 0.7 to 5.7 mm/yr and are related to stream gradient, stream power, percent wetland, hydroperiod, and land use. Deposition rates are highest downstream from the confluence of upper basin tributaries near Richmond, where stream power is low and there is a high percentage of emergent/shrub-scrub wetlands; rates decrease along downstream reaches toward the Chickahominy reservoir. Tree-ring data suggest that mean sedimentation rates were greater during the last 50 years than during the previous 30-year period, possibly because of urban expansion in the upper basin. Sites nearest the urban area have the highest rates of sedimentation and the highest concentrations of most trace elements in sediments. Trace elements concentrated in sediment include zinc, lead, chromium, copper, nickel, tin, and cadmium. Concentrations in tree rings of zinc, copper, nickel, and lead were generally proportional to those in sediment at a site, and some inter-site correlations were also observed. Unusually high concentrations of zinc were detected in some tree rings, including some that formed before 1950. Concentrations of zinc and lead in the most recently formed rings of those trees suggest that sediment concentrations of those elements may have declined relative to earlier periods. The trapping of substantial amounts of sediment and trace elements by these forested wetlands demonstrates their importance in the maintenance of water-quality.

Hydrogeomorphic processes affecting riparian habitat within alluvial channel–floodplain river systems: a review for the temperate zone

“…The significance of both geomorphology and hydrology as controls on sedimentation, which may moderate or override the impact of vegetation, are identified (Hupp et al, 1993;Kleiss, 1996;Steiger et al, 2001a). For example, according to Chow (1959), meanders and, therefore, river planform can increase Manning's n by as much as 30% where flow is confined within the river channel.…”

“…The riparian zone may function as an important sediment (clay, silt and sand) sink during flood events (Hupp et al, 1993;Kleiss, 1996;Steiger and Gurnell, 2003) and may buffer rivers from washload produced within uplands (e.g. Lowrance et al, 1985).…”

Sedimentation in created freshwater riverine wetlands: 15 years of succession and contrast of methods

“…While the SET method did show that erosion occurred in the wetlands throughout the year, the average rate of 5.0 cm yr À1 is probably too high to be considered an accurate measurement of net elevation change. Elevation change in other freshwater, riparian wetlands in the United States has varied between 0.07 and 0.57 cm yr À1 (Hupp et al, 1993). A possible reason for the overestimation may be that the sites were not spread equidistantly throughout the wetland.…”

“…Sedimentation has been measured with several methodologies, including: rare-earth stable tracer horizons like Cs-137 and Pb-210 (Craft and Richardson, 1993;Bernal and Mitsch, 2012), horizon markers (Knaus and Van Gent, 1989;Harter and Mitsch, 2003;Hupp et al, 2008), sediment traps and bottles (Mitsch et al, 1979a;Brueske and Barrett, 1994;Fennessy et al, 1994;Braskerud et al, 2000;Braskerud, 2001;Nahlik and Mitsch, 2008), dendrogeomorphic techniques (Hupp and Morris, 1990;Hupp et al, 1993), and sedimentation plates (Mitsch et al, 1979b;Braskerud et al, 2000;Braskerud, 2001). Variable methodologies have led to inconsistent and poorly comparable sedimentation rates.…”

Design and Construction of Wetlands for Aqueous Transfers and Transformations of Selected Metals

“…For example, constructed wetlands may serve as buffer zones between valued aquatic systems and potential point or nonpoint source materials that cause adverse effects in the downstream portions of these aquatic systems (Rodgers and Dunn, 1994). Constructed wetlands have been used for treatment of many materials including metals and have been effective in removing metals with primarily lithic geochemical cycles from wastewater and acid mine drainage areas (Brodie et al, 1990;Gambrell et al, 1991;Hammer, 1992;Hupp et al, 1993;Lapakko and Eger, 1988;Masscheleyn et al, 1992;Niering, 1985;Puckett et al, 1993;Sinicrope et al, 1993;USEPA, 1988). Full-scale demonstration constructed wetlands have successfully treated industrial effluents and other recalcitrant materials (East, 1993;Gillette, 1992;Rogozinski et al, 1992).…”