Controls on stream water dissolved mercury in three mid‐Appalachian forested headwater catchments

Abstract

[1] Determining the controls on dissolved mercury (Hg D ) transport is necessary to improve estimations of export from unmonitored watersheds and to forecast responses to changes in deposition and other environmental forcings. Stream water Hg D and dissolved organic carbon (DOC) were evaluated over a range of discharge conditions in three streams within Shenandoah National Park, VA. Watersheds are distinguished by stream water pH (ranging from neutral to acidic) and soil size fractioning (ranging from clays to sands). At all sites, discharge was a significant but poor predictor of Hg D concentrations (r 2 from 0.13-0.52). Hg D was strongly coupled with DOC at all sites (r 2 from 0.74-0.89). UV absorbance at 254 nm (UV 254 ), a proxy for DOC quantity and quality, slightly improved the predictions of Hg D . Mean DOC quality differed between streams, with less aromatic DOC mobilized from the more acidic watershed. The site with less aromatic DOC and sandy soils mobilized more Hg to the stream for the same quantity and quality of DOC, likely due to the reduced capacity of the larger-grained soils to retain Hg, leaving a greater fraction associated with the organic matter. A similar amount of 0.54 ng Hg D /mg DOC is transported at all sites, suggesting the less aromatic DOC transports less Hg per unit DOC, offsetting the effects of soil type. This research demonstrates that soil composition and DOC quality influence Hg D export. We also provide evidence that soil organic carbon is a primary control on Hg-DOC ratios (0.12-1.4 ng mg À1 ) observed across the U.S. and Sweden.Citation: Riscassi, A. L., and T. M. Scanlon (2011), Controls on stream water dissolved mercury in three mid-Appalachian forested headwater catchments, Water Resour. Res., 47, W12512,

Mercury in the nation's streams - Levels, trends, and implications

“…3-17B). These findings are consistent with our understanding that organic carbon binds strongly with total and methylmercury (Grigal, 2002;Hall and others, 2008;Riscassi and Scanlon, 2011).…”

Global Meta‐Analysis on the Relationship Between Mercury and Dissolved Organic Carbon in Freshwater Environments

“…On the other hand, Stoken et al () found no relationship between ratio of Hg D :DOC and atmospheric wet Hg deposition across the US. These authors conclude that the amount of Hg freshly deposited is not the dominant factor explaining the spatial variability in the coupling between Hg and DOC and subsequent transport in the system (Riscassi & Scanlon, ; Stoken et al, ). In addition, the recent deposition may not accurately reflect the historical Hg accretion in soil due to a time lag between the two sources, which could explain the negative (or lack of) relationship between Hg:DOC and fresh Hg input (Stoken et al, ).…”

“…For the difference between Hg–DOC and Hg–Aromatic portion of DOC (UV 254 , SUVA 254 , UV 420 , and UV 320 ) in objective 3, we ran a multivariate model with DOC type as random (repeated) variable nested within the Study using the function rma.mv in the metafor package (Viechtbauer, ). We used studies that measured both DOC and a measure of aromaticity, which led to 10 studies with 16 pairwise comparisons for THg (Bravo et al, ; Burns et al, ; Dittman et al, ; Eklöf et al, ; Eklöf et al, ; Jeremiason et al, ; MacMillan et al, ; Navratil et al, ; Riscassi et al, ; Riscassi & Scanlon, ) and 4 studies with 6 pairwise comparisons for MeHg (Bravo et al, ; Eklöf et al, ; Jeremiason et al, ; MacMillan et al, ). The most widespread measure of aromaticity was SUVA 254 , which is the specific UV absorbance at 254 nm divided by DOC concentration (UV 254 /DOC).…”

“…MeHg–DOC relationships have been found to be weaker than THg–DOC relationships in the literature (Burns et al, ; Hall et al, ; Lescord et al, ), which could be due to the origin and molecular composition of DOC (Bravo et al, , ) or to photodemethylation of MeHg in presence of DOC (Girard et al, ). Stronger relationships with Hg have been found for the aromatic fraction of DOC as measured by SUVA 254 or UV 254 (Burns et al, ; Riscassi & Scanlon, ) or by specific families of compounds measured by fluorescence and analyzed by parallel factor analysis (Jiang et al, ) than for bulk DOC concentrations. As a result, DOC is generally viewed as a vector of Hg at the catchment scale in freshwater ecosystems (Grigal, ; Ravichandran, ).…”

Specific ultra-violet absorbance as an indicator of mercury sources in an Adirondack River basin

“…Fishing Brook was sampled at the outlet of County Line Flow, a small shallow impoundment just upstream of the USGS stream gage that recorded stage at 15-min intervals for conversion to streamflow through a rating curve (Rantz et al 1982). All stream samples were collected by wading to the center point of flow or reaching to the center of flow when channels were narrow or to sample groundwater seeps.…”