Andrew J. Friedland

Lead Migration in Forest Soils: Response to Changing Atmospheric Inputs

Decreased use of leaded gasoline has caused a rapid reduction in atmospheric Pb deposition to terrestrial and aquatic ecosystems of the northeastern United States. In forest soils, the response to decreased Pb deposition has been more rapid than was anticipated based on previous studies of Pb cycling in forested ecosystems. To better understand the observed ecosystem response, we estimated both short-(25 y) and long-term (190 y) time series of the regional average atmospheric Pb concentrations in precipitation, cloudwater, and air. We combined these time series with modeled wet and dry deposition velocities to calculate the time-dependent Pb flux at different elevations in montane forests of the northeastern United States

Trace metal content of the forest floor in the green mountains of Vermont: Spatial and temporal patterns

The organic horizons of forest soils in eleven stands along an elevational gradient on Camels Hump Mountain, Vermont, were analyzed for Pb, Cu, Zn, Ni, Cd, organic matter and organic C. Lead concentration and amount increased with elevation. Vertical profiles of forest floor in the boreal forest showed that highest concentrations for most metals occurred in the upper F horizon. Comparison with 1966 and 1977 samples from the same stands showed that concentrations of Pb, Cu, and Zn and percent organic matter increased by as much as 148% in the intervening 14 yr. Estimates of 1966 amounts of Pb, Cu, and Zn indicated that increases in trace metal amounts over the 14 yr period are consistent with annual deposition rates reported in the literature.

Nitrogen deposition, distribution and cycling in a subalpine spruce-fir forest in the Adirondacks, New York, USA

Nitrogen inputs, fluxes, internal generation and consumption, and outputs were monitored in a subalpine spruce-fir forest at approximately 1000-m elevation on Whiteface Mountain in the Adirondacks of New York, USA. Nitrogen in precipitation, cloudwater and dry deposition was collected on an event basis and quantified as an input. Throughfall, stemflow, litterfall and soil water were measured to determine fluxes within the forest. Nitrogen mineralization in the forest floor was estimated to determine internal sources of available N. Lower mineral horizon soil water was used to estimate output from the ecosystem. Vegetation and soil N pools were determined.During four years of continuous monitoring, an average of 16 kg N ha−1 yr−1 was delivered to the forest canopy as precipitation, cloudwater and dry deposition from the atmosphere. Approximately 30% of the input was retained by the canopy. Canopy retention is likely the result of both foliar uptake and immobilization by bark, foliage and microorganisms. Approximately 40 kg of N was made available within the forest floor from mineralization of organic matter. Virtually all the available ammonium (mineralized plus input from throughfall) is utilized in the forest floor, either by microorganisms or through uptake by vegetation. The most abundant N component of soil water solutions leaving the system was nitrate. Net ecosystem fluxes indicate accumulation of both ammonium and nitrate. There is a small net loss of organic N from the ecosystem. Some nitrate leaves the bottom of the B horizon throughout the year. Comparisons with other temperate coniferous sites and examination of the ecosystem N mass balance indicate that N use efficiency is less at our site, which suggests that the site is not severely limited by N.

ACCUMULATION AND DEPLETION OF BASE CATIONS IN FOREST FLOORS IN THE NORTHEASTERN UNITED STATES

Loss of base cations from forest soils can be accelerated by acid rain, by forest regrowth following harvest removals, and by declining inputs of base cations from atmospheric deposition. Calcium losses from forest floors have been reported at several sites in the northeastern United States. To test for loss of base cations from forest floors at the Hubbard Brook Experimental Forest in New Hampshire (USA), we analyzed samples collected on seven dates between 1976 and 1997. Calcium and magnesium contents of the forest floor did not decline significantly; a change >0.9%/yr would have been detectable. Concentrations of Ca were 40% higher in 1969-1970 than in the current study, but the difference is partly due to changes in collection methods. Magnesium concentrations were too variable to detect a loss of <47% over the 21-yr interval. To determine whether base- cation losses were associated with forest growth, we resampled a chronosequence of north- ern hardwood stands in the White Mountains of New Hampshire. The 13 stands did not show consistent changes in Ca, Mg, and potassium over the 15-yr interval. Losses of these cations were most pronounced in stands logged more than 25 yr earlier. Younger stands, contrary to our expectation that rapid forest growth should cause cation depletion, all gained base cations in the forest floor. Early in stand development these forest floors appeared to accumulate biomass along with living vegetation, rather than serving as a net source of nutrients. Finally, in a regional survey of 28 mature stands in the northeastern United States, some lost significant forest-floor Ca and Mg between 1980 and 1990, while others gained. The average change in Ca and Mg content was not significant; a loss of 1.4%/yr would have been detectable. Forest floors in the region are not currently experiencing rapid losses of base cations, though losses may have preceeded the onset of these three studies.

Atmospheric deposition to forests along an elevational gradient at Whiteface Mountain, NY, U.S.A.

Abstract Atmospheric deposition rates of pollutants are known to be greater at high elevations than at low elavations in the same region, but the pattern of the deposition rate increase with elevation has not been established. This study was conducted to estimate nutrient and pollutant transfer rates from the atmosphere to forests along an elevational gradient at a site in the Adirondack Mountains of NY, U.S.A. Widely used models of cloud droplet, dry aerosol and gas phase SO 2 and HNO 3 deposition processes were modified for use in this application. An extensive data set describing the elevational variation in forest canopy composition and structure and microclimatic variables was assembled from measurements made by us during seven years of research activities at Whiteface Mountain, NY. Model estimates of total atmospheric deposition of S and N increased by factors of 4 and 5, respectively, over the elevational range 600–1275 m. Steep gradients in wind speed and cloud immersion frequency contributed to a nearly exponential increase in ion deposition by cloud water interception, which was responsible for most of the increase in total ion deposition rates with elevation. An additional factor contributing to increased deposition rates at high elevations was an increasing percentage of total leaf area attributable to coniferous vegetation, which is more effective at scavenging aerosol particles and cloud droplets than broad-leaved vegetation. Dry deposition contributed 13% and cloud water 61% of the 29.5 kg N ha −1 yr −1 estimated total N deposition at 1275 m elevation as opposed to 22 and 5% of the 7 kg N ha −1 yr −1 total N deposition estimated for surrounding low-elevation (600 m) forests. The dry deposition component accounted for 5% and the cloud water component 64% of the estimated 31 kg S ha −1 yr −1 total deposition at 1275 m elevation, in comparison with a 21% dry and 5% cloud contribution to the 8.4 kg S ha −1 yr −1 estimated deposition to low-elevation forests.

Nitrogen isotope variation of tree rings as a potential indicator of environmental change

Abstract The δ 15 N-values of tree rings have been measured for two eastern hemlocks ( Tsuga canadensis ) from a site in Hanover, New Hampshire, U.S.A. δ 15 N-values of tree rings show a total range of −0.1 to +6.8%. Both trees show a systematic decrease of δ 15 N-values from the early 1960s to the last year of growth. Possible explanations for the observed decrease of δ 15 N-values over the last 30 years include a decrease in the δ 15 N-values of available nitrogen, or isotope fractionation accompanying translocation. The results demonstrate the potential utility of nitrogen isotope analysis of tree rings as a method to investigate the long-term biogeochemical behavior of nitrogen. Tree-ring δ 15 N-values signatures can potentially procide information concerning the effects of atmospheric deposition of nitrogen upon forested ecosystems at actual levels of nitrogen deposition, as opposed to high levels of pulsed nitrogen addition over a relatively short period, as is typically the case in fertilizer studies. Additional advantages of tree-ring studies over fertilizer studies include the ability to study very long time periods, wide geographical application and the lack of need for a long-term, intensive experimental effort.

Red spruce (Picea rubens Sarg.) foliar chemistry in Northern Vermont and New York, USA

Current and one-year-old foliage was collected from sixty-five red spruce trees growing in thirteen stands at different elevations in the Green Mountains of Vermont and Adirondacks of New York. Sample trees were randomly selected from visually healthy trees at each site. Foliage was analyzed for major and minor elements. In July 1984, foliar Ca, Mg, and Zn concentrations were significantly greater at low than at high elevations. In October 1984, Ca, Mg, and Zn concentrations were higher at low elevations and Ca and Mg concentrations varied significantly among locations within elevational groups. Nitrogen concentration was significantly higher in the high-elevation group in July but not in October. The average red spruce foliar Mg concentration at the end of the growing season in the high elevation stands (442 mg kg−1) is much lower than values reported for other mature red spruce stands in the eastern United States.

MAJOR-ELEMENT CYCLING IN A HIGH-ELEVATION ADIRONDACK FOREST: PATTERNS AND CHANGES, 1986-1996

High-elevation forests in the northeastern United States have received large amounts of atmospheric deposition of pollutants that may alter natural element cycling and retention rates in a variety of ways. This study examined atmospheric deposition of N, S, and base cations (Ca2+, Mg2+, K+, Na+), and their impact on element cycling, in a high-elevation forest on Whiteface Mountain, New York, USA. Ten years of element cycling data (1986–1996) showed that at our study site (1050-m elevation) precipitation and cloud water contributed most of the atmospheric deposition relative to dry deposition. Input–output budgets revealed a net retention of N in this forest. In contrast, annual variations in outputs of K+ were roughly balanced by atmospheric inputs. Potassium output seemed to be strongly related to and dependent on K+ inputs. There was a net loss of Ca2+, Mg2+, and SO42− from the site. Calcium and SO42− outputs were related to one another and to water inputs to the forest. Net loss of 2.9 kg S·ha−1·yr−1 w...

Threshold increases in soil lead and mercury from tropospheric deposition across an elevational gradient.

Atmospheric deposition is the primary mechanism by which remote ecosystems are contaminated, but few data sets show how fluxes change and control soil metal burdens at the landform scale. We present mercury (Hg), lead ((210)Pb and total Pb), and cosmogenic beryllium-7 ((7)Be) measurements in organic (O) soil horizons at high-resolution elevation intervals of ∼60 m from 540 to 1160 m on Camels Hump in northern Vermont, USA. Across this gradient, average O horizon Hg ranges from 0.99 mg m(-2) in the low elevation deciduous forest zone to 7.6 mg m(-2) in the higher elevation coniferous forest at 1030 m. We measure two pronounced threshold increases in soil metal burdens above 801 and 934 m, corresponding to the two most common altitudes of cloud base, which coincide with changes in vegetation species. Lead-210, a unique tracer of tropospheric deposition, also increased from 3200 Bq m(-2) to 11500 Bq m(-2) in O horizons, exhibiting threshold responses at the same elevations as Hg and total Pb. Concentrations of (210)Pb and Hg in foliage double from 760 to 900 m elevation, indicating enhanced deposition across the transition from deciduous to coniferous forest. In contrast, (7)Be is constant across the entire elevational gradient because of its upper atmospheric source. This indicates that the effects of orographic precipitation have a smaller control on soil contaminant burdens than the coupled cloudwater deposition-vegetation scavenging effect in the presence of upwind sources. By measuring soil contaminants and unique tracers of atmospheric deposition, we show that tropospheric fluxes of Hg and Pb are higher by a factor of 2 in high-elevation coniferous forests than in adjacent lowlands. Total O horizon Hg and Pb burdens increase by over 4-fold with elevation because of the compounding effects of enhanced deposition and longer metal residence times at higher elevations (>50 years).

Spatial and vertical distribution of mercury in upland forest soils across the northeastern United States

Assessing current Hg pools in forest soils of the northeastern U.S. is important for monitoring changes in Hg cycling. The forest floor, upper and lower mineral horizons were sampled at 17 long-term upland forest sites across the northeastern U.S. in 2011. Forest floor Hg concentration was similar across the study region (274 ± 13 μg kg(-1)) while Hg amount at northern sites (39 ± 6 g ha(-1)) was significantly greater than at western sites (11 ± 4 g ha(-1)). Forest floor Hg was correlated with soil organic matter, soil pH, latitude and mean annual precipitation and these variables explained approximately 70% of the variability when multiple regressed. Mercury concentration and amount in the lower mineral soil was correlated with Fe, soil organic matter and latitude, corresponding with Bs horizons of Spodosols (Podzols). Our analysis shows the importance of regional and soil properties on Hg accumulation in forest soils.