Comparison of total mercury and methylmercury cycling at five sites using the small watershed approach

Abstract

Martin M., "Comparison of total mercury and methylmercury cycling at five sites using the small watershed approach" (2008 High-flow sampling reveals strong contrasts in total mercury and methylmercury cycling in five diverse USA watersheds. AbstractThe small watershed approach is well-suited but underutilized in mercury research. We applied the small watershed approach to investigate total mercury (THg) and methylmercury (MeHg) dynamics in streamwater at the five diverse forested headwater catchments of the US Geological Survey Water, Energy, and Biogeochemical Budgets (WEBB) program. At all sites, baseflow THg was generally less than 1 ng L À1 and MeHg was less than 0.2 ng L À1. THg and MeHg concentrations increased with streamflow, so export was primarily episodic. At three sites, THg and MeHg concentration and export were dominated by the particulate fraction in association with POC at high flows, with maximum THg (MeHg) concentrations of 94 (2.56) ng L À1 at Sleepers River, Vermont; 112 (0.75) ng L À1 at Rio Icacos, Puerto Rico; and 55 (0.80) ng L À1at Panola Mt., Georgia. Filtered (<0.7 mm) THg increased more modestly with flow in association with the hydrophobic acid fraction (HPOA) of DOC, with maximum filtered THg concentrations near 5 ng L À1 at both Sleepers and Icacos. At Andrews Creek, Colorado, THg export was also episodic but was dominated by filtered THg, as POC concentrations were low. MeHg typically tracked THg so that each site had a fairly constant MeHg/THg ratio, which ranged from near zero at Andrews to 15% at the low-relief, groundwater-dominated Allequash Creek, Wisconsin. Allequash was the only site with filtered MeHg consistently above detection, and the filtered fraction dominated both THg and MeHg. Relative to inputs in wet deposition, watershed retention of THg (minus any subsequent volatilization) was 96.6% at Allequash, 60% at Sleepers, and 83% at Andrews. Icacos had a net export of THg, possibly due to historic gold mining or frequent disturbance from landslides. Quantification and interpretation of Hg dynamics was facilitated by the small watershed approach with emphasis on event sampling.

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

“…3a). This finding is especially surprising because FTHg concentrations and DOC concentrations in streams and lakes with largely forested watersheds in Sweden, the Adirondacks, northeastern US, and upper Midwest typically show stronger relations with r 2 values of 0.6-0.93 (Selvendiran et al , 2009Shanley et al 2008;Brigham et al 2009;Dittman et al 2009;Eklöf et al 2012). However, previous investigations in Fishing Brook and the upper Hudson basin noted relatively weak THg-DOC relations (Schelker et al 2011;Burns et al 2012).…”

“…Although dissolved Hg and DOC concentrations are often strongly correlated in many surface waters with r 2 values of 0.7-0.9 (Grigal 2002;Shanley et al 2008;Dittman et al 2010;Riscassi and Scanlon 2011), not all waters show such strong a strong association. For example, Hg and DOC concentrations are weakly related in the Everglades where a diversity of organic matter sources and complex biogeochemical processes are observed .…”

The Correlations Between Mercury Speciation and Dissolved Organic Matter in the Sediment of the Red Sea

“…Both dissolved and particulate C plays an essential role in the transport of Hg fractions. The result of the this study is in agreement with other studies in the region that report DOC as an important transport mechanism for THg (Driscoll et al, 1995;Selvendiran et al, 2008b;Shanley et al, 2008).…”

Impact of collection container material and holding times on sample integrity for mercury and methylmercury in water

“…Within a stream, concentrations of Hg and methylmercury (MeHg) vary spatially (e.g., downstream versus upstream at a single point in time) (Bonzongo et al 1996;Southworth et al 2004;Zagar et al 2006;Flanders et al 2010;Tsui et al 2010;Kocman et al 2011) as well as temporally at an individual location. For a specific stream site, concentrations have been shown to vary seasonally (Balogh et al 2002), on diel timescales (Nimick et al 2007) and on hourly timescales with rapid changes in discharge (and associated changes in water chemistry) due to precipitation or snow melt events Shanley et al 2008;Riscassi and Scanlon 2011). Though relatively scarce in the literature, high-frequency storm event sampling has been used to assess Hg and MeHg source areas within a watershed (Bushey et al 2008;Demers et al 2010), and paired with discharge measurements, to calculate hourly downstream fluxes over an annual cycle (Riscassi and Scanlon 2013).…”

“…Different flow conditions correspond to different sources of water within a stream watershed system and concentrations of water quality parameters, including Hg and MeHg, are known to vary in concentration and speciation; baseflow is typically associated with a smaller fraction of Hg in the particulate form compared to snowmelt or storm flow conditions Riscassi and Scanlon 2013). Basic water quality parameters were also measured for each sample, specifically, total suspended sediment (TSS) and DOC were evaluated due to the known association of particulate Hg and MeHg to TSS (Balogh et al 1997(Balogh et al , 1998Mason and Sullivan 1998;Scherbatskoy et al 1998;Whyte and Kirchner 2000;Lawson and Mason 2001;Balogh et al 2003;Wall et al 2005); similarly, filtered Hg and MeHg is commonly associated with dissolved organic carbon (DOC) (Mierle and Ingram 1991;Joslin 1994;Bishop et al 1995;Driscoll et al 1995;Hurley et al 1995;Allan and Heyes 1998;Babiarz et al 1998;Kolka et al 1999;Grigal 2002;Shanley et al 2002;Galloway and Branfireun 2004;Mast et al 2005;Nelson et al 2007;Shanley et al 2008;Brigham et al 2009;Dittman et al 2009;Demers et al 2010;Dittman et al 2010;Riscassi and Scanlon 2011). To capture a more complete range of field conditions experienced throughout an entire year in this stream system (i.e., changes in air temperature during sample storage, percent of Hg and MeHg in particulate versus the dissolved form), samples taken concurrently with established manual techniques and container material were compared with samples taken with the automated sampler and stored in LDPE bags for a variety of holding times throughout a 10-month period (Sep 2012 through July 2013).…”