Steven J. Eisenreich

Mobility and diagenesis of Pb and 210Pb in peat

Peatlands long have been considered to preserve the record of atmospheric deposition of anthropogenic contaminants such as Pb. In the past two decades, {sup 210}Pb has been widely used to data recent strata of peat and to calculate accumulation rates. The assumption that Pb and {sup 210}Pb are immobile and not subject to diagenesis in peat has been questioned but not rigorously tested. The authors attempted to determine if Pb is mobile in peatlands and if Pb profiles are altered by diagenic processes by constructing a mass balance for Pb about a small peatland, by comparing inventories, concentrations, and accumulation rates of Pb and {sup 210}Pb in peatlands across northeastern North America, and by examining the relationship between concentrations of Pb in bog waters and peat in numerous sites. The results clearly demonstrate that Pb and {sup 210}Pb are mobilized by the organic-rich waters of peatlands. Profiles of Pb and {sup 210}Pb at depths below the water table do not preserve the record of atmospheric deposition, and inventories of Pb and {sup 210}Pb are depleted in peatland hollows. Concentrations of Pb in bog waters are regulated by the concentration of Pb in the peat and the concentration of dissolved organicmorexa0» carbon. The mass balance for one bog indicated that over the specific three-year period of study more than 30% of inputs of Pb were not retained within the peat. As a result of this mobility, dates based on {sup 210}Pb can be biased and inaccurate by as much as 30 years. Dates based on {sup 210}Pb should be verified by other techniques, especially when the inventory of {sup 210}Pb is less than that expected from local rates of deposition.«xa0less

Dynamics of gaseous semivolatile organic compounds in a terrestrial ecosystem - effects of diurnal and seasonal climate variations

The dynamics of gas-phase semivolatile organic compounds (SOCs) were examined in a forested bog in northern Minnesota. A strong diurnal variation in the gas-phase concentration was observed for over 100 compounds including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and other organochlorines. This diurnal variation, whereby afternoon concentrations exceeded early morning levels by factors of 2–10, is a likely result of volatilization and deposition of SOCs to and from local plant surfaces. The variation cannot be explained by air turbulence, wind direction, photoreactivity, or plant stomatal activity. Gas-phase SOC concentrations ([SOCg]) are strongly correlated with both local temperature and relative humidity. The correlation between [SOCg] and temperature was examined separately from the correlation between [SOCg] and relative humidity (RH). Only during the winter sampling period, when snow covered the forest surface, was relative humidity not a significant predictor of [SOCg]. For sampling periods when relative humidity was significant, the following relationship was found: In [SOCg] = a + mT + c RH, where T is the ambient temperature (K) at ∼1 m, a, m, and c are constants that vary with compound and season. This study suggests that surface adsorption processes dominate atmospheric SOC cycling, rather than absorptive or stomatal partitioning processes.

Sulfur cycling in a forested Sphagnum bog in northern Minnesota

The mass balance and internal cycle of sulfur within a small forested,Sphagnum bog in northern Minnesota are presented here based on a 4-year record of hydrologic inputs and outputs (precipitation, throughfall, streamflow, upland runoff) and a 3-year measurement of plant growth and sulfur uptake. Concentrations and accumulation rates of inorganic and organic sulfur species were measured in porewater. The bog is a large sink for sulfur, retaining 37% of the total sulfur input. Because of the relatively large export of organic S (21% of inputs), retention efficiency for total-S (organic S + SO4=; 37%) is less than that for SO4= (58%). There is a dynamic cycle of oxidation and reduction within the bog. Annual oxidation and recycling of S is equal to total inputs in the center of the bog. Plants receive 47% of their uptake requirement from atmospheric deposition, 5% from retranslocation from foliage, and the remainder from sulfur remineralized from peat. Mineralization is most intense in the aerobic zone above the water table. Inorganic sulfur species comprise <5% of the total sulfur burden within the peat.

PCBQ: Computerized quantification of total PCB and congeners in environmental samples

Abstract Computerized methodologies for the quantification of total PCBs, PCB in Aroclor mixtures and individual PCB congeners in environmental samples are presented. The method for total PCBs is based on a multiple-linear regression analysis using data from capillary gas chromatography of Arocolor standards. PCB congeners were identified and their weight percentages determined in Aroclor mixtures by GC/MS. PCB congeners and total PCBs were accurately quantified in predetermined test data and environmental samples.

Atmospheric input of trace metals to Lake Michigan

Atmospheric bulk deposition was collected on a monthly basis in the Lake Michigan basin from September 1975 through December 1976 to determine the atmospheric loading of trace elements to Lake Michigan. The sampling network consisted of bulk collectors located at 21 locations in the northern and southern basin. Atmospheric loading rates to Lake Michigan were estimated as (in units of 105 kg yr−1): Al-50; Fe-28; Mn-6.4; Zn-11; Cu-1.2; Pb-6.4; Cd-0.11; Co- <0.25; Ca-798; Mg-155; Na-110; K-64. Atmospheric deposition of all elements measured was greater in the southern basin than in the northern basin as a result of intense urban/industrial activity in the former. The percentage of total atmospheric deposition falling in the southern basin was: Fe-74%, Al-71%; Mn-75%; Zn-67%; Cu-62%; Pb-78%; Cd-74%; Co- ti 56%; Ca-79%; Mg-62%; Na-65%; K-61 %. Atmospheric loading rates reported are in general agreement with estimates made by others from emission inventories and aerosol concentrations. Atmospheric loadings were estimated to represent 10% or more of the total loadings to Lake Michigan from tributary and erosion sources for the trace elements Mn, Zn, Cu, Cd and Pb. Also, atmospheric deposition may account for recent accumulations of Zn, Cu, Cd, Pb and Co in southern Lake Michigan surficial sediments. The atmospheric Ph flux to southern Lake Michigan was estimated as ∼1.7 μg sm−2 yr−1 for 1975–1976 which compares favorably with the 1972 anthropogenic Pb flux of 1.3 μg cm−2 yr−1 (total − ∼1.5 μg cm−2 yr−1) as determined from Pb-210 dating (Edgington and Robbins, 1976). The geographical distribution of trace element loading implicates the southern periphery of Lake Michigan as the principal emission source area.

PCBs and PAHs as Tracers of Particulate Dynamics in Large Lakes

Internal cycling of particles within the water columns of the Great Lakes results in spatial and temporal variability in concentrations of hydrophobic organic contaminants. Concentrations of organic carbon, fourteen polycyclic aromatic hydrocarbons (PAHs), and thirty-five polychlorobiphenyl (PCBs) congeners were measured in particles collected in detailed vertical profiles of the atmosphere, water column, and sediments of Lake Superior to assess the dynamics of organic matter and particle transport in large lakes. A benthic nepheloid layer (BNL), a particle-rich zone extending up from the lake floor, was observed from a manned submersible during a NOAA National Undersea Research Program cruise on Lake Superior in 1986. This region contains large numbers of both living organisms and detritus, indicating that the BNL is supplied with significant quantities of reduced carbon from above. Patterns of organic contaminants associated with particles were examined by principal components analysis to determine the sources of particles to the BNL. Settling of surface water particles is the dominant source of solids containing PAHs and PCBs to the BNL during stratification, while resuspension of surf icial sediments also contributes to BNL formation. Large vertical fluxes of organic-rich particles serve to rapidly transport hydrophobic organic contaminants to the benthic region. Once in the BNL, however, particulate organic matter is rapidly degraded and is largely not incorporated into underlying sediments. Rates of particulate organic matter utilization in the BNL are estimated to be orders of magnitude faster than corresponding rates in Lake Superior surf icial sediments. Internal cycling of particles and organic matter significantly impacts the behavior and residence times of nutrients and contaminants in the water column of large lakes.

Silica in Lake Superior: mass balance considerations and a model for dynamic response to eutrophication

Abstract The dissolved silica concentration in waters of Lake Superior probably is in a steady state because it is not influenced significantly by man, and the climate, topography and vegetation in the drainage area of the lake have been stable for the past 4000 years. Therefore the rate at which dissolved silica is introduced to the lake should equal the output rate. The primary inputs are: tributaries (4.1–4.6 × 10 8 kg SiO 2 / yr ), diffusion from sediment pore waters (0.21−0.78 × 10 8 kg SiO 2 / yr ) and atmospheric loading (0.26 × 10 8 kg SiO 2 / yr ). Silica is lost from the lake waters by: outflow through the St. Marys River, diatom deposition, adsorption onto particulates in the sediments, and authigenic formation of new silicate minerals. Tributary outflow accounts for less than one half the annual input of silica, and diatom deposition and silica adsorption withdraw less than 10% of the annual input. Therefore the formation of new silicate phases must be the dominant sink for dissolved silica in Lake Superior. The specific phases formed are not identified in the bottom sediments. X-ray diffraction studies suggest that smectite is one product, and amorphous ferroaluminum silicates may be another product. Mathematical modeling of the dissolved silica response to lake eutrophication suggests that the phosphate loading to Lake Superior would have to increase by about 250-fold to cause a silica depletion rate equal to that reported for Lake Michigan, assuming no change in the rate of upwelling of deep waters.

Atmospheric deposition of toxaphene to Eastern North America derived from peat accumulation

Abstract Dated peat cores from Minnesota east to Nova Scotia analyzed for toxaphene provided spatial variation in historical and recent atmospheric fluxes and an atmospheric input function for toxaphene extending over the past 40 years. This input function is consistent with toxaphene production data and the input of a well documented insecticide, DDT. Total core burdens of toxaphene across a west to east transect were highest in the upper midwest and Nova Scotia, with recent peat accumulation rates ranging from 0.5 to 9 μg m −2 a −1 . Atmospheric concentrations of toxaphene, back-calculated from accumulation rates in peat, range from 8 to 150 pg m −3 , in agreement with recently-measured concentrations in remote atmospheres. Recent atmospheric inputs of toxaphene are two to four times those of PCBs and DDT, respectively.

Sedimentation Rates and Depositional Processes in Lake Superior from 210Pb Geochronology

Sedimentation rates range from 0.01 to 0.32 cm/yr in 17 sediment box cores from Lake Superior, as determined by 210Pb geochronology. Shoreline erosion and resuspension of nearshore sediments causes moderate to high (0.05–0.11 cm/yr) sedimentation rates in the western arm of Lake Superior. Sedimentation rates are very high (> 0.15 cm/yr) in marginal bays adjoining Lake Superior; and moderate to very high (0.07–0.19 cm/yr) in open lake regions adjacent to marginal bays. Resuspension of nearshore and shoal top sediments in southern and southeastern Lake Superior by storms is responsible for depositional anomalies in 210Pb profiles corresponding to 1905, 1916–1918, and 1940 storms. Sedimentation rates are very low (0.01–0.03 cm/yr) in the central basins due to isolation from sediment sources. These data indicate that sedimentation rates and processes vary significantly in different regions of Lake Superior. The sedimentation rates provided by this study, in conjunction with previously-reported sedimentation rates, yield a better understanding of the Lake Superior depositional environment.

Proton Cycling in Bogs: Geographic Variation in Northeastern North America

A detailed hydrogen ion budget has been constructed for the Marcell bog in north-central Minnesota based on a 5-year, intensive study of element cycles. Major features of the acidity balance for this site include the following: (1) production of organic acids (263 meg.m−2.y−1) is the dominant source of acidity and serves to buffer the bog water at pH 4; (2) seguestering of elements in peat is also a significant source of acidity (42.9 meg.m−2.y−1); (3) weathering of dustfall inputs is an important source of alkalinity (<76 meg.m−2.y−1) at this site which is situated near the major agricultural area of the plains; (4) nitrate and sulphate reduction contribute little alkalinity (<39.2 meg.m−2.y−1) because inputs (NO3 and SO4) to this bog are low. Analysis of peat and surface water from bogs across northeastern North America (Manitoba to Newfoundland) reveals the following: (1) production of organic acids across this region varies between 104 and 263 meg.m−2.y−1; (2) acidity-generation associated with net biological uptake (NBU, excluding nitrogen = 20–117 meg.m−2.y−1) varies in proportion to the rate of peat accumulation; (3) NBU-acidity exhibits high values in maritime bogs and lower values in mid-continental bogs; (4) bogs have a large capacity for sulphate reduction, and sulphate reduction becomes an increasingly important source of alkalinity as rates of sulphate deposition increase. From 60 to 93% of annual sulphate loadings are retained as reduced sulphur in bogs across eastern North America.