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James P. Hurley

Publications and source records attributed to James P. Hurley.

15 recordsLinked to original sources
USGS2025

Ecological factors decouple Great Lakes fish mercury concentrations trends decadal declines in mercury emissions

Atmospheric mercury (Hg) deposition has been declining in North America but remains the dominant delivery mechanism to the Great Lakes. The Lakes are highly efficient at bioaccumulating methylmercury, making the fish excellent sentinels for tracking shifts in atmospheric Hg deposition. Invasive mussels have altered biogeochemical processes, prey populations and fish dietary strategies asynchronously and to varied extents across the lower four lakes, impacting fish Hg exposure. To test if fish are adapting to new biogeochemical conditions, we analyzed a 40 year fish archive for carbon and nitrogen isotope ratios and amino acid-specific nitrogen isotope ratios. To assess Hg sources, we measured Hg isotope ratios. We reconstructed and compared energetic pathways that impact fish Hg concentrations to Hg-source trends. We found fish-Hg concentrations are declining but not monotonically due to ecological disturbances. Fish-Hg isotope values, unimpacted by ecological disturbance, confirm that sources of bioaccumulated Hg shift contemporaneously with changes in atmospheric Hg concentrations. Across Lakes, the degree of responsiveness to changes in atmospheric Hg concentrations mirrors the proportion of atmospheric-delivered Hg we previously modeled. Changes in both fish concentrations and fish isotope values outpace paleolimnetic reconstructions suggesting declines in atmospheric Hg concentrations impact fish Hg more than sediment.

Great Lakes↗
USGS2023

Competition between dissolved organic matter and freshwater plankton control methylmercury isotope fractionation during uptake and photochemical demethylation

Isotope fractionation related to photochemical reactions and planktonic uptake at the base of the food web is a major uncertainty in the biological application of mercury (Hg) stable isotopes. In freshwater systems, it is unclear how competitive interactions among methylmercury (MeHg), dissolved organic matter (DOM), and phytoplankton govern the magnitude of mass-dependent and mass-independent fractionation. This study investigated how DOM alters rates of planktonic MeHg uptake and photodegradation and corresponding Hg isotope fractionation in the presence of freshwater phytoplankton species, Raphidocelis subcapitata . Outdoor sunlight exposure experiments utilizing R. subcapitata were performed in the presence of different DOM samples using environmentally relevant ratios of MeHg-DOM thiol groups. The extent of Δ 199 Hg in phytoplankton incubations (2.99‰ St. Louis River HPOA, 1.88‰ Lake Erie HPOA) was lower compared to paired abiotic control experiments (4.29 and 2.86‰, respectively) after ∼30 h of irradiation, resulting from cell shading or other limiting factors reducing the extent of photodemethylation. Although the Δ 199 Hg/Δ 201 Hg ratio was uniform across experiments (∼1.4), Δ 199 Hg/δ 202 Hg slopes varied dramatically (from −0.96 to 15.4) across incubations with R. subcapitata and DOM. In addition, no evidence of Hg isotope fractionation was observed within R. subcapitata cells. This study provides a refined examination of Hg isotope fractionation markers for key processes occurring in the lower food web prior to bioaccumulation, critical for accurately accounting for the photochemical processing of Hg isotopes across a wide spectrum of freshwater systems.

ACS Earth and Space Chemistry↗
USGS2022

Methylmercury stable isotopes: New insights on assessing aquatic food web bioaccumulation in legacy impacted regions

Through stable isotope measurements of total mercury (HgT), identification of crucial processes and transformations affecting different sources of mercury (Hg) has become possible. However, attempting to use HgT stable isotopes to track bioaccumulation of Hg sources among different food web compartments can be challenging, if not impossible, when tissues have varying methylmercury (MeHg) contents. We measured HgT and MeHg stable isotope ratios within the lower Fox River to examine how these values differed across the food web and if isotope values in biota were influenced by legacy contamination. We showed that seston, invertebrates, and fish had a large range of δ 202 HgT (−0.74 to 0.15 ‰, n = 11) due to varying MeHg contents in tissues but a commonly conserved MeHg isotope value (δ 202 MeHg ave = 0.01 ± 0.12 ‰, 1 standard deviation, n = 11). We also examined some mathematical approaches to estimate the MeHg isotope values, which were mostly comparable to measured MeHg isotope values in the Fox River, with some exceptions. In this study, we observed that the MeHg isotope values can elucidate links between different food web compartments and provide insight on aquatic Hg cycling that can be masked by the sole use of HgT isotopes in contaminated sites.

Wisconsin↗
USGS2022

Using carbon, nitrogen, and mercury isotope values to distinguish mercury sources to Alaskan lake trout

Lake trout ( Salvelinus namaycush ), collected from 13 remote lakes located in southwestern Alaska, were analyzed for carbon, nitrogen, and mercury (Hg) stable isotope values to assess the importance of migrating oceanic salmon, volcanic activity, and atmospheric deposition to fish Hg burden. Methylmercury (MeHg) bioaccumulation in phytoplankton (5.0–6.9 kg L –1 ) was also measured to quantify the basal uptake of MeHg to these aquatic food webs. Hg isotope values in lake trout revealed that while the extent of precipitation-delivered Hg was similar across the entire study area, volcanic Hg is likely an important additional source to lake trout in proximate lakes. In contrast, migratory salmon ( Oncorhynchus nerka ) deliver little MeHg to lake trout directly, although indirect delivery processes via decay could exist. A high level of variability in carbon, nitrogen, and Hg isotope values indicates niche partitioning in lake trout populations within each lake and that a complex suite of ecological interactions is occurring, complicating the conceptually linear assessment of the contaminant source to the receiving organism. Without connecting energy and contaminant isotope axes, we would not have understood why lake trout from these pristine lakes have highly variable Hg burdens despite consistently low water Hg and comparable age-length dynamics.

Alaska↗
USGS2021

Experimental evidence for recovery of mercury-contaminated fish populations

Anthropogenic releases of mercury (Hg) 1,2,3 are a human health issue 4 because the potent toxicant methylmercury (MeHg), formed primarily by microbial methylation of inorganic Hg in aquatic ecosystems, bioaccumulates to high concentrations in fish consumed by humans 5,6 . Predicting the efficacy of Hg pollution controls on fish MeHg concentrations is complex because many factors influence the production and bioaccumulation of MeHg 7,8,9 . Here we conducted a 15-year whole-ecosystem, single-factor experiment to determine the magnitude and timing of reductions in fish MeHg concentrations following reductions in Hg additions to a boreal lake and its watershed. During the seven-year addition phase, we applied enriched Hg isotopes to increase local Hg wet deposition rates fivefold. The Hg isotopes became increasingly incorporated into the food web as MeHg, predominantly from additions to the lake because most of those in the watershed remained there. Thereafter, isotopic additions were stopped, resulting in an approximately 100% reduction in Hg loading to the lake. The concentration of labelled MeHg quickly decreased by up to 91% in lower trophic level organisms, initiating rapid decreases of 38–76% of MeHg concentration in large-bodied fish populations in eight years. Although Hg loading from watersheds may not decline in step with lowering deposition rates, this experiment clearly demonstrates that any reduction in Hg loadings to lakes, whether from direct deposition or runoff, will have immediate benefits to fish consumers.

Experimental Lakes Area↗
USGS2020

Aqueous elemental mercury production versus mercury inventories in the Lake Michigan airshed: Deciphering the spatial and diel controls of mercury gradients in air and water

Atmospheric delivery of mercury (Hg) is important to the Upper Great Lakes, and understanding gaseous Hg exchange between surface water and air is critical to predicting the effects of declining mercury emissions. Speciated atmospheric Hg, dissolved gaseous Hg (DGM), and particulate and filter passing total Hg were measured on a cruise in Lake Michigan. Low mercury levels reflected pristine background conditions, especially in offshore regions. In the atmosphere, reactive and particle-associated fractions were low (1.0 ± 0.5%) compared to gaseous elemental Hg (1.34 ± 0.14 ng m–3) and were elevated in the urbanized southern basin. DGM was supersaturated, ranging from 17.5 ± 4.8 pg L–1 (330 ± 80%) in the main lake to 33.2 ± 2.4 pg L–1 (730 ± 70%) in Green Bay. Diel cycling of surface DGM showed strong Hg efflux during the day due to increased winds, and build-up at night from continued DGM production. Epilimnetic DGM is formed from photochemical reduction, while hypolimnetic DGM originates from biological Hg reduction. We found that DGM concentrations were greatest below the thermocline (30.8 ± 13.6 pg L–1), accounting for 68–92% of the total DGM in Lake Michigan, highlighting the importance of nonphotochemical reduction in deep stratified lakes.

Lake Michigan↗
USGS2020

Resolving atmospheric mercury loading and source trends from isotopic records of remote North American lake sediments

The strongest evidence for anthropogenic alterations to the global mercury (Hg) cycle comes from historical records of mercury deposition preserved in lake sediments. Hg isotopes have added a new dimension to these sedimentary archives, promising additional insights into Hg source apportionment and biogeochemical processing. Presently, most interpretations of historical changes are constrained to a small number of locally contaminated ecosystems. Here, we describe changes in natural Hg isotope records from a suite of dated sediment cores collected from various remote lakes of North America. In nearly all cases, the rise in industrial-use Hg is accompanied by an increase in δ 202 Hg and Δ 199 Hg values. These trends can be attributed to large-scale industrial emission of Hg into the atmosphere and are consistent with positive Δ 199 Hg values measured in modern-day precipitation and modeled increases in δ 202 Hg values from global emission inventories. Despite similar temporal trends among cores, the baseline isotopic values vary considerably among the different study regions, likely attributable to differences in the fractionation produced in situ as well as differing amounts of atmospherically delivered Hg. Differences among the study lakes in precipitation and watershed size provide an empirical framework for evaluating Hg isotopic signatures and global Hg cycling.

North America↗
USGS2019

Isolation of methylmercury using distillation and anion-exchange chromatography for isotopic analyses in natural matrices

The development of mercury (Hg) stable isotope measurements has enhanced the study of Hg sources and transformations in the environment. As a result of the mixing of inorganic Hg (iHg) and methylmercury (MeHg) species within organisms of the aquatic food web, understanding species-specific Hg stable isotopic compositions is of significant importance. The lack of MeHg isotope measurements is due to the analytical difficulty in the separation of the MeHg from the total Hg pool, with only a few methods having been tested over the past decade with varying degrees of success, and only a handful of environmentally relevant measurements. Here, we present a novel anion-exchange resin separation method using AG 1-X4 that further isolates MeHg from the sample matrix, following a distillation pretreatment, in order to obtain ambient MeHg stable isotopic compositions. This method avoids the use of organic reagents, does not require complex instrumentation, and is applicable across matrices. Separation tests across sediment, water, and biotic matrices showed acceptable recoveries (98 ± 5%, n = 54) and reproducible δ 202 Hg isotope results (2 SDs ≤ 0.15‰) down to 5 ng of MeHg. The measured MeHg pools in natural matrices, such as plankton and sediments, showed large deviations from the non-speciated total Hg measurement, indicating that there is an important isotopic shift during methylation that is not recorded by typical measurements, but is vital in order to assess sources of Hg during bioaccumulation.

Analytical and Bioanalytical Chemistry↗
USGS2019

Mercury source changes and food web shifts alter contamination signatures of predatory fish from Lake Michigan

To understand the impact reduced mercury (Hg) loading and invasive species have had on methylmercury bioaccumulation in predator fish of Lake Michigan, we reconstructed bioaccumulation trends from a fish archive (1978 to 2012). By measuring fish Hg stable isotope ratios, we related temporal changes in Hg concentrations to varying Hg sources. Additionally, dietary tracers were necessary to identify food web influences. Through combined Hg, C, and N stable isotopic analyses, we were able to differentiate between a shift in Hg sources to fish and periods when energetic transitions (from dreissenid mussels) led to the assimilation of contrasting Hg pools (2000 to present). In the late 1980s, lake trout δ 202 Hg increased (0.4‰) from regulatory reductions in regional Hg emissions. After 2000, C and N isotopes ratios revealed altered food web pathways, resulting in a benthic energetic shift and changes to Hg bioaccumulation. Continued increases in δ 202 Hg indicate fish are responding to several United States mercury emission mitigation strategies that were initiated circa 1990 and continued through the 2011 promulgation of the Mercury and Air Toxics Standards rule. Unlike archives of sediments, this fish archive tracks Hg sources susceptible to bioaccumulation in Great Lakes fisheries. Analysis reveals that trends in fish Hg concentrations can be substantially affected by shifts in trophic structure and dietary preferences initiated by invasive species in the Great Lakes. This does not diminish the benefits of declining emissions over this period, as fish Hg concentrations would have been higher without these actions.

Lake Michigan↗
USGS2019

Rapid pre-concentration of mercury in solids and water for isotopic analysis

The precise quantification of mercury (Hg) stable isotope compositions in low concentration or dilute samples poses analytical challenges due to Hg mass limitations. Common Hg pre-concentration procedures require extended processing times, making rapid Hg stable isotope measurements challenging. Here we present a modified pre-concentration method that combines commonly used Hg reduction and gold trap amalgamation followed by semi-rapid thermal desorption (less than 1 h) and chemical trapping. This custom designed system was demonstrated to perform adequately on multiple trapping matrices including a new bromine monochloride (BrCl) wet oxidant trap (40% 3HNO 3 :BrCl), capable of trapping consistently in 2 mL volume over a wide range of Hg masses (5–200 ng). The procedure was also shown to work effectively on natural matrices, waters and sediments, producing comparable isotope results to the direct digestion analyses. Here, we present a method that can effectively triple sample throughput in comparison to traditional procedures, and also access lower concentration matrices without compromising the accuracy or precision of Hg isotope measurements.

Analytica Chimica Acta↗
USGS2018

Factors affecting mercury stable isotopic distribution in piscivorous fish of the Laurentian Great Lakes

Identifying the sources of methylmercury (MeHg) and tracing the transformations of mercury (Hg) in the aquatic food web are important components of effective strategies for managing current and legacy Hg sources. In our previous work, we measured stable isotopes of Hg (δ 202 Hg, Δ 199 Hg, and Δ 200 Hg) in the Laurentian Great Lakes and estimated source contributions of Hg to bottom sediment. Here, we identify isotopically distinct Hg signatures for Great Lakes trout ( Salvelinus namaycush ) and walleye ( Sander vitreus ), driven by both food-web and water-quality characteristics. Fish contain high values for odd-isotope mass independent fractionation (MIF) with averages ranging from 2.50 (western Lake Erie) to 6.18‰ (Lake Superior) in Δ 199 Hg. The large range in odd-MIF reflects variability in the depth of the euphotic zone, where Hg is most likely incorporated into the food web. Even-isotope MIF (Δ 200 Hg), a potential tracer for Hg from precipitation, appears both disconnected from lake sedimentary sources and comparable in fish among the five lakes. We suggest that similar to the open ocean, water-column methylation also occurs in the Great Lakes, possibly transforming recently deposited atmospheric Hg deposition. We conclude that the degree of photochemical processing of Hg is controlled by phytoplankton uptake rather than by dissolved organic carbon quantity among lakes.

Environmental Science & Technology↗
USGS2016

Distribution and geochemical speciation of soil mercury in Wanshan Hg mine: Effects of cultivation

The distribution and speciation of mercury (Hg) were investigated in contaminated soils collected from two adjacent land use systems (arid land and rice paddy) near the Wanshan Mercury mine, SW China. In both sites, fine soil aggregate size fractions (<231μm) showed higher total Hg concentrations and higher soil organic matter contents than in larger aggregate size fractions (231 to 2000μm). Compared to arid land, paddy soils are characterized by higher proportions of fine soil aggregates, higher soil organic matter and higher total Hg content. Soil Hg speciation, based on X-ray absorption spectroscopy (XANES) analysis, indicated that the majority (64–81%) of Hg in soils under both land use systems was associated with metacinnabar (β-HgS), indicating the precipitation of β-HgS in soils. We also observed the presence of bioavailable HgCl 2 and Hg(0) in soils at both sites, which may represent a considerable environmental concern. Our study clearly showed that different cultivation practices can largely change the distribution and speciation of Hg in agriculture soils.

Guizhou Province↗
USGS2015

Use of stable isotope signatures to determine mercury sources in the Great Lakes

Sources of mercury (Hg) in Great Lakes sediments were assessed with stable Hg isotope ratios using multicollector inductively coupled plasma mass spectrometry. An isotopic mixing model based on mass-dependent (MDF) and mass-independent fractionation (MIF) (&delta; 202 Hg and &Delta; 199 Hg) identified three primary Hg sources for sediments: atmospheric, industrial, and watershed-derived. Results indicate atmospheric sources dominate in Lakes Huron, Superior, and Michigan sediments while watershed-derived and industrial sources dominate in Lakes Erie and Ontario sediments. Anomalous &Delta; 200 Hg signatures, also apparent in sediments, provided independent validation of the model. Comparison of &Delta; 200 Hg signatures in predatory fish from three lakes reveals that bioaccumulated Hg is more isotopically similar to atmospherically derived Hg than a lake&rsquo;s sediment. Previous research suggests &Delta; 200 Hg is conserved during biogeochemical processing and odd mass-independent fractionation (MIF) is conserved during metabolic processing, so it is suspected even is similarly conserved. Given these assumptions, our data suggest that in some cases, atmospherically derived Hg may be a more important source of MeHg to higher trophic levels than legacy sediments in the Great Lakes.

Lake Erie, Lake Huron, Lake Michigan, Lake Ontario↗
USGS2009

Cycling of mercury across the sediment-water interface in seepage lakes: Chapter 13, Advances in Chemistry

The magnitude and direction of Hg fluxes across the sediment&mdash;water interface were estimated by groundwater, dry bulk sediment, sediment pore water, sediment trap, and water-column analyses in two northern Wisconsin seepage lakes. Little Rock Lake (Treatment Basin) received no groundwater discharge during the study period (1988&mdash;1990), and Follette Lake received continuous groundwater discharge. In Little Rock Lake, settling of particulate matter accounted for the major Hg delivery mechanism to the sediment&mdash;water interface. Upward diffusion of Hg from sediment pore waters below 2&mdash;4-cm sediment depth was apparently a minor source during summer stratification. Time-series comparisons suggested that the observed buildup of Hg in the hypolimnion of Little Rock Lake was attributable to dissolution and diffusion of Hg from recently fallen particulate matter close to the sediment&mdash;water interface. Groundwater inflow represented an important source of new Hg, and groundwater outflow accounted for significant removal of Hg from Pallette Lake. Equilibrium speciation calculations revealed that association of Hg with organic matter may control solubility in well-oxygenated waters, whereas in anoxic environments sulfur (polysulfide and bisulfide) complexation governs dissolved total Hg levels.

Wisconsin↗