Litterfall Mercury in Two Forested Watersheds at Acadia National Park, Maine, USA

Litterfall can be an important flux of mercury (Hg) to soils in forested landscapes, yet typically the only available data to evaluate Hg deposition is from precipitation Hg monitoring. Litterfall was collected at 39 sampling sites in two small research watersheds, in 2003 and 2004, and analyzed for total Hg. Four vegetation classes were designated in this study as hardwoods, softwoods, mixed and scrub. The mean litter Hg concentration in softwoods (58.8 ± 3.3 ng Hg g^?1 was significantly greater than in mixed (41.7 ± 2.8 ng Hg g^?1 and scrub (40.6 ± 2.7 ng Hg g^?1, and significantly lower than in hardwoods (31.6 ± 2.6 ng Hg g^?1. In contrast, the mean weighted litter Hg flux was not significantly different among vegetation classes. The lack of a significant difference in litter Hg flux between hardwoods and softwoods was attributable to the large autumnal hardwood litter Hg flux being balanced by the higher softwood litter Hg concentrations, along with the higher chronic litterfall flux throughout the winter and spring in softwoods. The estimated annual deposition of Hg via litterfall in Hadlock Brook watershed (10.1 μg m^?2 and Cadillac Brook watershed (10.0 μg m^?2 was greater than precipitation Hg deposition and similar to or greater than the magnitude of Hg deposition via throughfall. These results demonstrate that litterfall Hg flux to forested landscapes can be at least as important as precipitation Hg inputs.     

Chemistry differences in two streams entering an acidic lake in the Adirondack Mountains,New York (U.S.A.)

Solution chemistry was measured in two major inlets, lake water column, lake outlet, and soils of the South Lake watershed in the Adirondack Mountains, New York. The east inlet had greater concentrations of H⁺, sulfate-S, and Al and smaller concentrations of base cations and silica than the west inlet (70, 116, 25, 90, 64 and 4, 99, 8, 228, 148 μeq L^?1 of H⁺ and sulfate-S, μmol L^?1 Al, μeq L^?1 total base cations and μmol L^?1 silica in east and west inlets, respectively). Concentrations of base cations in C horizon soil solutions (157 μeq L^?1 total base cations) were smaller and greater than west and east inlets, respectively. This suggests that water flowing into the west inlet contacted deeper mineral layers, whereas water reaching the east inlet did not. Lake and lake outlet concentrations were also intermediate between the two inlets, and the lake was acidic (pH 4.9 to 5.1) with relatively high total monomeric Al concentrations (8 to 9 μmol Al L^?1). The east inlet also had greater DOC concentrations than the west (0.38 and 0.24 μmol C L^?1, respectively), again indicating that soil solutions entering the east inlet passed through the forest floor but had more limited contact with deeper mineral layers in comparison with the west inlet. Differences between the streams are hypothesized to be related to contact of percolating solutions with mineral soil horizons and underlying glacial till, which provides neutralization of acidic solutions and releases base cations. This work indicates that processes controlling surface water acidification can be spatially quite variable over a small watershed.     

Patterns of acid deposition to a Danish spruce forest

Bulk precipitation and bulk throughfall was collected during the period September to November 1984 in a Danish spruce forest. Samples were analyzed for all major anions and cations as well as strong and total acidity. The acid load to the forest ecosystem was estimated adding the throughfall fluxes of protons (79 eq ha^?1mo^?1), ammonium (99 eq ha^?1mo^?1) and a calculated estimate oflthe protons buffered by exchange processes in the canopy (75 eq ha^?1 mo^?1). This is still a minimum estimate but it exceeds the proton load determined by pH measurement in bulk throughfall and bulk precipitation by factors 3 and 6, respectively. Throughfall fluxes of all major cations and anions except ammonium decreased with distance from the trunk.     

Acid deposition and throughfall fluxes of elements as related to tree species in deciduous forests of South Sweden

The influence of tree species and soil properties on throughfall fluxes were studied for 5 tree species, growing on initially identical soil. In three mixed deciduous forests with different soil properties, throughfall fluxes of 11 elements were measured during 2 yr for 100 to 150 yr old individuals of Fagus sylvatica L., Quercus robur L., Carpinus betulus L., Tilia cordata Mill. and Acer platanoides L.. Throughfall : precipitation flux ratios were: PO₄ ^3? (11 to 37), K⁺ (7 to 22), Mn²⁺ (5 to 14), Mg²⁺ (3 to 9), Ca²⁺ (3 to 5), Cl^? (1.9 to 2.6), Na⁺ (1.1 to 2.2), NH₄ ⁺ (1.5 to 2), SO₄ ^2? (1.5 to 2.1), NO₃ ^? (0.7 to 1.3) and H⁺ (0.1 to 0.5). The annual input of S to the soil by throughfall was for Fagus 22 to 29, Quercus 25 to 37, Carpinus 20 to 25, Tilia 24 and Acer 29 kg ha^?1. The annual input of N to the soil by throughfall was for Fagus 20 to 29, Quercus 14 to 22, Carpinus 15 to 22, Tilia 22 and Acer 20 kg ha^?1. Throughfall fluxes of Na⁺ and Cl^? differed between species, depending on different canopy filtering capacity of sea aerosol, and were greatest for Fagus and Quercus. Throughfall of Ca²⁺, Mg²⁺ and K⁺ were characterized by increased flux from poor to rich sites, with the greatest soil effect on Carpinus, and by a high leaching part, which increased in the same manner. Manganese throughfall showed especially soil effects, characterized of decreased flux from poor to rich sites, but also species effects, of which Carpinus had the greatest flux. pH in throughfall showed a pronounced seasonal variation with pH 6 to 6.5 for Fagus in the foliated season and pH 4.0 to 4.3 in the defoliated season. Carpinus and especially Quercus had lower pH at the poor site, but the differences decreased at the richer sites. The calculated annual acid input to the trees was 4 to 12 times greater than the H⁺ flux measured as pH in throughfall. An inorganic anion deficit in throughfall, probably due to the presence of organic anions, was proportional to K⁺, Ca²⁺ and Mg²⁺.     

Acidity neutralization mechanism in a forested watershed in Central Japan

The contributions of cation exchange and mineral weathering to the neutralization of acidity in the Jingahata watershed in central Japan were estimated through a laboratory weathering experiment and runoff chemistry measurements. The laboratory experiment was conducted in a stirred-flow reactor for a whole soil sample collected from the C horizon in the watershed. The concentration ratios of base cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺) to Si (BC/Si) released during the steady-state stage of the laboratory experiment were in good agreement with the ratios of the net flux of base cations to the flux of Si in the streamwater (BC _{N ET}/Si _L).This result suggests that the acidity in the watershed is neutralized primarily by mineral weathering without causing a net loss of base cations from exchange sites. The alkalinity/acidity balance estimated for the watershed shows that the total weathering rate of base cations is approximately 3.26 keq ha^?1 yr^?1. Weathering of plagioclase (An₄₁) contributes 83% of the total weathering rate. The dominant acidity source is CO₂ released within the soil horizons, accounting for roughly 85% of the total acidity flux (3.20 keq ha^?1 yr^?1). This high internal production of acidity suppresses the relative importance of atmospheric acidity inputs (0.3 keq ha^?1 yr^?1).     

Atmospheric deposition in forest edges measured by monitoring canopy throughfall

Atmospheric dry deposition in two forest edges was studied by means of monitoring canopy throughfall in Douglas Fir stands. Throughfall fluxes in the first 50 to 100 m of forest edges were found to be substantially higher than fluxes in the interior of forest stands. Sodium and chloride showed the steepest throughfall flux gradients. Ions important for soil acidification and eutrophication showed relatively less steep but still significant gradients. The mean increase of the throughfall flux at 10 m, with respect to the flux at 200 m from the forest edge amounted to 150% for Na⁺, 119% for Cl^?, 54% for S0₄ ^2?, 38% for NO₃ ^? , and 39% for NH₄ ⁺ The enhancement of dry deposition in forest edges strongly depends on wind velocity and wind direction during dry deposition. Particularly trees in forest edges exposed to prevailing wind directions receive relatively large amounts of dry deposition.     

The role of organic horizons and canopy to modify the chemistry of acidic deposition in some forest ecosystems

To clarify the mechanisms of pH buffering in forest ecosystems, field observations of pH and ionic concentrations in precipitation (R), throughfall (Tf), stemflow (Sf), and leachates from organ c horizons (Lo) were conducted for three years at three stands in Tomakomai (TK) and Teshio (TS) in Hokkaido, northern Japan. Weighted mean rates of H⁺ input as wet deposition at TK and TS were estimated in the range from 0.3 to 1.0 and 0.4–0.6 kmol_c ha^?1 y^?, respectively. While the net H⁺ flux was reduced significantly by the forest canopy, net fluxes of other ions by throughfall, especially for Na⁺, Cl^?, and SO₄ ^2?, were apparently greater than those by precipitation. The canopy modification of the H⁺ flux was more remarkable under deciduous stands than under coniferous stands, suggesting that the efficiency of conifers as the collectors of dry deposition is greater than that of deciduous ones. More than 50% of H⁺ flux due to throughfall was absorbed by the organic horizons and the weighted mean pH of Lo at TK and TS was in the range from 4.9 to 5.5 and 5.0–5.5, respectively. Results from field observation and field leaching experiments, showed that the major H⁺ sinks of the organic horizons are exchange reaction of Ca²⁺, Mg²⁺ and K⁺. Organic acids or organo-metallic complexes of lower pK(=5.0–5.5) played a significant role as counter anions in O horizons leachate in coniferous forests. Our results indicate the importance of biogeochemical modifications in the canopy and organic horizon in acid buffering mechanisms of forest ecosystems.     

Primary production in a eutrophic acid lake

Total P concentrations, chlorophyll concentrations, and phytoplankton production were investigated bi-weekly in Tibbs Run Lake, Monongalia County, West Virginia, from March 1977 to March 1978. Mean H⁺ concentration in the lake was 25.1 μeq 1^?1 (pH 4.6). The acidic condition of the lake is attributed to inputs of acid via precipitation (mean H⁺ concentration of the bulk precipitation was 79 μeq 1^?1, pH 4.1), and the low buffering capacity of the watershed (bedrock composition of sandstone). Effect of the watershed is shown by the net retention of imput of P (ca. 26%) and H⁺ (ca. 68%). Total P loading to the lake was 0.495 g P m^?2 yr^?1. The single inflow accounted for 95% of the total loading while bulk precipitation accounted for the remainder. Mean summer chlorophyll concentration was 22.2 mg m^?2. Phytoplankton production expressed volumetrically as aP-vol-x value was 9.78 mg C m^?3 h^?1. Regression analysis indicated that H⁺ do not affect chlorophyll concentrations or phytoplankton production but rather that P limits algal biomass. Trophic status of Tibbs Run Lake based on a P budget model, chlorophyll concentration, and volumetric production all indicate that the lake is meso-eutrophic.     

Changes in water quality in the Laflamme Lake Watershed Area,Canada

The Laflamme Lake Watershed Area is located in a sensitive region on the Canadian Shield and is subjected to wet atmospheric loading between 17 and 25 kg ha^?1 yr^?1. From 1981 to 1988, the level and fluctuations of the atmospheric deposition of acidifying substances has led to various responses in the water chemistry of headwater lakes in the area. The general trend in atmospheric inputs is a gradual increase of acidifying substances from 1981 to 1985 followed by a 2 yr decrease then a return to previous values. In the two lakes with almost no alkalinity acidification has occured throughout the 1983 to 1988 period. In the four lakes with slightly higher alkalinity values, a reversal in acidification is seen when atmospheric loading decreased in 1986. Along with the interannual trends, seasonal variability to acidification occurs with sensitivity of surface waters being highest during spring melt. Sensitivity to acidification can also be altered by watershed processes and in the Laflamme Lake Watershed, soil processes are effective in altering the acidity of precipitation before it reached the lake. In this watershed, wet atmospheric inputs of H⁺ and NO₃ ^? are larger than surface water outputs while the reverse occurs for Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^? and SO₄ ^2?.     

Response to a smelter closure in Cascade mountain lakes

A statistically significant decrease in sulfate was observed in high elevation Cascade lakes during 1983 through 1988. The total decrease averaged 2.2 μeq L^?1 in two slow-flush lakes and 4.2 μeq L^?1 in three fast-flush lakes for 1983–1985 vs 1986–1988, respectively. Coincident with these changes in sulfate concentrations were a sharp decrease of SO₂ emissions from the ASARCO smelter (100 km SE of the lakes), from 87 to 70 kt yr^?1 during 1983–1984 to 12 in 1985, the year of its closure, and a gradual change in SO₂ emissions from Mt. St. Helens, from 39 to 27 during 1983–1984 to 5 in 1988. The sharpest decreases occurred in non-marine sulfate in fast-flush lakes from 1984 to 1985 (about 2 μeq L^?1) and in slow-flush lakes from 1985 to 1986 (1 μeq L^?1, which point to the ASARCO closure as the sole cause. However, some of the more gradual decline in non-marine sulfate observed during 1983 through the 1988 sampling periods may have been due to a slow washout of sulfate enriched ash from the 1980 Mt. St. Helens' eruption. Sulfate concentrations in precipitation also declined significantly by about 2 μeq L^?1, but changes in volume-weighted sulfate content were not significant. Lake alkalinity did not show a consistent increase in response to decreased sulfate. This was probably due to either watershed neutralization of acidic deposition or the greater variability in alkalinity measurements caused by small changes in acidic deposition making it difficult to detect changes.     

Precipitation and streamwater chemistry from undisturbed watersheds in the cascade mountains of Oregon

Long-term records of precipitation and streamwater chemistry are rare; such records from forested watersheds relatively free of acidic deposition are even rarer. Precipitation and streamwater chemistry have been measured on two undisturbed forested watersheds at the H. J. Andrews Experimental Forest located on the western slopes of the Cascade Mountains of Oregon. Data from one watershed spans the period 1973–1985, the other 1969–1985. The mean annual pH of precipitation was 5.5 with a range of 4.7 to 6.0. HCO₃ ^? was the dominant anion; Ca²⁺ and Na⁺ were the dominant cations. The mean annual pH of streamwater was 7.3, and was dominated by HCO₃ ^? and Ca²⁺. These data contrast sharply with data from other calibrated watersheds in the north Cascade Mountains of Washington and British Columbia, and with data from New Hampshire and North Carolina where pH of precipitation averages 4.14 and 4.43, respectively, with SO₄ ^2? the dominant anion.     

Long-Term Annual and Seasonal Patterns of Acidic Deposition and Stream Water Quality in a Great Smoky Mountains High-Elevation Watershed

The recovery potential of stream acidification from years of acidic deposition is dependent on biogeochemical processes and varies among different acid-sensitive regions. Studies that investigate long-term trends and seasonal variability of stream chemistry in the context of atmospheric deposition and watershed setting provide crucial assessments on governing biogeochemical processes. In this study, water chemistries were investigated in Noland Divide watershed (NDW), a high-elevation watershed in the Great Smoky Mountains National Park (GRSM) of the southern Appalachian region. Monitoring data from 1991 to 2007 for deposition and stream water chemistries were statistically analyzed for long-term trends and seasonal patterns by using Seasonal Kendall Tau tests. Precipitation declined over this study period, where throughfall (TF) declined significantly by 5.76?cm?year^?1. Precipitation patterns play a key role in the fate and transport of acid pollutants. On a monthly volume-weighted basis, pH of TF and wet deposition, and stream water did not significantly change over time remaining around 4.3, 4.7, and 5.8, respectively. Per NDW area, TF SO₄ ^2- flux declined 356.16?eq?year^?1 and SO₄ ^2- concentrations did not change significantly over time. Stream SO₄ ^2- remained about 30???eq L^?1 exhibiting no long-term trends or seasonal patterns. SO₄ ^2- retention was generally greater during drier months. TF monthly volume-weighted NH₄ ⁺ and NO₃ ^- concentrations significantly increased by 0.80???eq L^?1?year^?1 and 1.24???eq L^?1?year^?1, respectively. TF NH₄ ⁺ fluxes increased by 95.76?eq?year^?1. Most of NH₄ ⁺ was retained in the watershed, and NO₃ ^- retention was much lower than NH₄ ⁺. Stream monthly volume-weighted NO₃ ^- concentrations and fluxes significantly declined by 0.56???eq L^?1?year^?1 and 139.56?eq?year^?1, respectively. Overall, in NDW, inorganic nitrogen was exported before 1999 and retained since then, presumably from forest regrowth after Frazer fir die-off in the 1970s from balsam wooly adelgid infestation. Stream export of NO₃ ^- was greater during winter than summer months. During the period from 1999 to 2007, stream base cations did not exhibit significant changes, apparently regulated by soil supply. Statistical models predicting stream pH, ANC, SO₄ ^2-, and NO₃ ^- concentrations were largely correlated with stream discharge and number of dry days between precipitation events and SO₄ ^2- deposition. Dependent on precipitation, governing biogeochemical processes in NDW appear to be SO₄ ^2- adsorption, nitrification, and NO₃ ^- forest uptake. This study provided essential information to aid the GRSM management for developing predictive models of the future water quality and potential impacts from climate change.     

Annual Element Budget of Soil in Snow-Dominated Forested Ecosystem

Seasonal fluctuation of concentration and flux of major inorganic ions in throughfall, stem flow, snowpack and soil solution was investigated at a natural cool temperature mixed forest in Hokkaido, northern Japan, in order to clarify the effect of snowmelt on the solute dynamics in the forest soil in snow-dominated region. Na⁺, Ca²⁺, Mg²⁺, Cl^? and SO₄ ^2? concentrations in soil solution showed a large fluctuation in the snowmelt period. The percentage of output of these elements from soil during the snowmelt period in the annual output was as follows. Mg²⁺: 51%, Na⁺ and Cl^?: 59 and 60%, SO₄ ^2?: 65%, Ca²⁺: 77%. Our results indicated that the snowmelt event was very important to quantify the annual elemental budgets in this region. Although the leaching of base cation from the soil was larger than that of inputs and accumulation into the vegetation, annual decreasing rate of acid neutralization capacity (ANC_(s)) from the soil was mostly affected by the base cation accumulation into the vegetation, related that the base cations weathering accompanied with bicarbonate was slow due to the acidic and weathered soil in the studied site. It is suggested that the weakly acidic soil which has low ANC_(s) in snow-dominated region will be relatively sensitive to the future increase of acidic deposition.     

Estimation of the Maximum Critical Load for Sulfur in South Korea

The maximum critical load of sulfur and its exceedance by the sulfur deposition of 1994–1997 were mapped for South Korea with a spatial resolution of 11 × 14 km using the steady-state mass balance method. The Korean soil and geological maps were used as basis for the estimations of the critical alkalinity leaching and the weathering rate of base cations. The normalized difference vegetation index data obtained from the Advanced Very High Resolution Radiometer (AVHRR) together with the observed primary productivity of plants were used for the estimation of the critical uptake of base cations. Wet deposition of the non-sea-salt base cations was derived from measured base cation concentrations in precipitation, precipitation rate and air concentration of total suspended particulate while dry deposition of base cations was estimated using the inferential technique using scavenging ratios. The predominant ranges of base cation weathering, uptake and deposition were estimated to be of 200 – 600 eq ha^?1 yr^?1, 200 – 400 eq ha^?1 yr^?1 and 400 – 600 eq ha^?1 yr^?1, respectively. Critical alkalinity leaching was mainly in the range of 1000 – 2000 eq ha^?1 yr^?1 due to relatively high value of precipitation runoff. Exceedance of sulfur critical load was found at 40 % of the ecosystems considered mainly in the southeastern part of Korea, and about 60 % of Korea ecosystems were sustainable against sulfur acidity loadings.     

Chemical composition of hoarfrost,rime and snow during a winter inversion in Utah,U.S.A.

We present data on the chemical composition of hoarfrost, rime, and snow grains that accumulated during an eighteen-day long temperature inversion event in Salt Lake City, Utah in December 1985 and January 1986. Chemical analyses show that the precipitation formed during this inversion event was acidic (as low as pH 3.85) and had nitrate and sulfate contents up to 1680 and 1290 μeq · L^?1, respectively. Ammonia, nitrate, and sulfate deposition of 361, 615, and 792 μeq · m^?2, respectively, occurred in a six-day period due to the accumulation of snow grains during this inversion.     

Episodic acidification of a coastal plain stream in Virginia

This study investigates the episodic acidification of Reedy Creek, a wetland-influenced coastal plain stream near Richmond, Virginia. Primary objectives of the study were to quantify the episodic variability of acid-base chemistry in Reedy Creek, to examine the seasonal variability in episodic response and to explain the hydrological and geochemical factors that contribute to episodic acidification. Chemical response was similar in each of the seven storms examined, however, the ranges in concentrations observed were commonly greater in summer/fall storms than in winter/spring storms. An increase in SO _inf4 ^sup2? concentration with discharge was observed during all storms and peak concentration occurred at or near peak flow. Small increases in Mg²⁺, Ca²⁺, K⁺ concentrations and dissolved organic carbon (DOC) were observed during most storms. At the same time, ANC, Na⁺ and Cl^? concentrations usually decreased with increasing discharge. In summer/fall storms, the absolute increase in SO _inf4 ^sup2? concentration was one-third to 15 times the increase observed in winter/spring storms; the decrease in ANC during summer/fall storms was usually within the range of the decrease observed in winter/spring storms. In contrast, the decrease in Na⁺ and Cl^? concentrations during winter/spring storms was much greater than that observed during summer/fall storms. Data show that while base flow anion deficit was higher in summer/fall than in winter/spring, anion deficit decreased during most summer/fall storms. In contrast, base flow anion deficit was lower in spring and winter, but increased during winter/spring storms. Increased SO _inf4 ^sup2? concentration was the main cause of episodic acidification during storms at Reedy Creek, but increased anion deficit indicates organic acids may contribute to episodic acidification during winter/spring storms. Changes in SO _inf4 ^sup2? concentration coincident with the hydrograph rise indicate quick routing of water through the watershed. Saturation overland flow appears to be the likely mechanism by which solutes are transported to the stream during storm flow.     

Polluted precipitation and the geochronology of mercury deposition in lake sediment of northern Minnesota

Elevated Hg levels in game fish from wilderness lakes in northern Minnesota led to the present study of sediment cores from two lakes to ascertain the source and history of Hg deposition. Natural background levels of Hg were found to range from 0.03 to 0.06 μg g^?1, with cultural levels as high as 0.16 μg g^?1. Reconstructed geochronologies reveal a dramatic two-fold increase in Hg flux, from 0.008 to 0.017 μg cm^?2 yr^?1, occuring after the year 1880, suggesting an anthropogenic influence. No industrial or geologic source of Hg is found in the study watersheds. The entire historical increase in Hg flux can be accounted for by atmospheric loading provided that 1/5 of all the Hg presently supplied to the watershed via precipitation is ultimately deposited in lake sediment. Hg levels in fish are not correlated with Hg levels in lake sediment, although there is a link to acid-sensitivity of lake water, amount of acid-neutralizing geologic material exposed in the watershed, and watershed area/lake volume ratio. Thermal stratification of lake water and a complexation-adsorption mechanism are proposed to account for variations in Hg levels observed in sediment collected from different sites.     

Physical and chemical characteristics of three acidic,oligotrophic lakes and their watersheds in Kejimkujik National Park,Nova Scotia

Southwestern Nova Scotia receives acidic precipitation (average pH 4.5 to 4.6), and there are many waterbodies that are susceptible to acidification. This study characterizes the physical and chemical features of three remote, oligotrophic lakes and their watersheds in this region, in order to provide baseline information against which assessments can be made of changes caused by atmospheric depositions. Two of the lakes are small (<0.5 km²) and on headwater watersheds: Beaverskin Lake has an almost completely forested watershed and is moderately acidic and clear (pH 5.3, 5 Hazen units), while the watershed of Pebbleloggitch Lake is about 2/3 forested and 1/3 covered by a Sphagnum-heath bog, and its water is very acidic and highly colored (pH 4.3, 87 Hazen units). Kejimkujik Lake is much larger, its watershed is mostly forested but also contains some boggy terrain, its water is intermediate in acidity and color (pH 4.9, 65 Hazen units), and because it drains a much larger area of watershed it has relatively large concentrations of Ca, Mg, Na, Cl, and SO₄.     

A Preliminary Assessment of Wet Deposition and Episodic Transport of Total and Methyl Mercury from Low Order Blue Ridge Watersheds,S.E. U.S.A.

Results from a preliminary sampling program designed to investigate total (THg) and methyl Hg (MeHg) deposition, cycling and transport at the Coweeta Hydrologic Laboratory western North Carolina are presented. Wet deposition samples were collected in June and July 1994 and throughfall, seep and streamwaters were intensively collected during and after a rainfall event in June 1994. All water samples were collected using ultra clean trace sampling protocol. Low elevation Watershed 18 streamwater THg concentrations peaked with discharge, increasing 6 fold to 9 ng L^-1. High elevation Watershed 27 which received less than one half the precipitation Watershed 18 received during the event, exhibited THg concentrations only 1.3 times over base flow conditions. Methyl Hg concentrations remained near detection limits (≤ 0.025 ng L^-1) in both streams. Dissolved MeHg concentrations were higher in shallow seep (0.097 ng L^-1), throughfall (0.135 ng L^-1) and precipitation (0.16 – 0.035 ng L^-1) than streamwaters. Initial estimates of annual THg and MeHg deposition and transport indicate >90% retention of Thg and a >80% retention or demethylation of wet deposition MeHg is occurring in these low order watersheds.     

Manganese Biogeochemistry in a Central Czech Republic Catchment

Mn biogeochemistry was studied from 1994 to 2003 in a small forested catchment in the central Czech Republic using the watershed mass balance approach together with measurements of internal stores and fluxes. Mn inputs in bulk deposition were relatively constant during a period of sharply decreasing acidic deposition, suggesting that the Mn source was terrestrial, and not from fossil fuel combustion. Mn inputs in bulk deposition and Mn supplied by weathering each averaged 13 mg m^?2 year^?1 (26 mg m^?2 year^?1 total input), whereas Mn export in streamwater and groundwater averaged 43 mg m^?2 year^?1. Thus an additional Mn source is needed to account for 17 mg m^?2 year^?1. Internal fluxes and pools of Mn were significantly greater than annual inputs and outputs. Throughfall Mn flux was 70 mg m^?2 year^?1, litterfall Mn flux was 103 mg m^?2 year^?1, and Mn net uptake by vegetation was 62 mg m^?2 year^?1. Large pools of labile or potentially labile Mn were present in biomass and surficial soil horizons. Small leakages from these large pools likely supply the additional Mn needed to close the watershed mass balance. This leakage may reflect an adjustment of the ecosystem to recent changes in atmospheric acidity.