Christopher S. Cronan

Chemistry and transport of soluble humic substances in forested watersheds of the Adirondack Park, New York

Abstract Studies were conducted in conjunction with the Integrated Lake-Watershed Acidification Study (ILWAS) to examine the chemistry and leaching patterns of soluble humic substances in forested watersheds of the Adirondack region. During the summer growing season, mean dissolved organic carbon (DOC) concentrations in the ILWAS watersheds ranged from 21–32 mg C l−1 in O/A horizon leachates, from 5–7 mg C l−1 in B horizon leachates, from 2–4 mg C l−1 in groundwater solutions, from 6–8 mg C l−1 in first order streams, from 3–8 mg C l−1 in lake inlets, and from 2–7 mg C l−1 in lake outlets. During the winter, mean DOC concentrations dropped significantly in the upper soil profile. Soil solutions from mixed and coniferous stands contained as much as twice the DOC concentration of lysimeter samples from hardwood stands. Results of DOC fractionation analysis showed that hydrophobia and hydrophilic acids dominate the organic solute composition of natural waters in these watersheds. Charge balance and titration results indicated that the general acid-base characteristics of the dissolved humic mixture in these natural waters can be accounted for by a model organic acid having an averagepKa of 3.85, an average charge density of 4–5 μeq mg−1 C at ambient pH, and a total of 6–7 meq COOH per gram carbon.

Nitrogen Pollution in the Northeastern United States: Sources, Effects, and Management Options

Abstract The northeastern United States receives elevated inputs of anthropogenic nitrogen (N) largely from net imports of food and atmospheric deposition, with lesser inputs from fertilizer, net feed imports, and N fixation associated with leguminous crops. Ecological consequences of elevated N inputs to the Northeast include tropospheric ozone formation, ozone damage to plants, the alteration of forest N cycles, acidification of surface waters, and eutrophication in coastal waters. We used two models, PnET-BGC and WATERSN, to evaluate management strategies for reducing N inputs to forests and estuaries, respectively. Calculations with PnET-BGC suggest that aggressive reductions in N emissions alone will not result in marked improvements in the acid–base status of forest streams. WATERSN calculations showed that management scenarios targeting removal of N by wastewater treatment produce larger reductions in estuarine N loading than scenarios involving reductions in agricultural inputs or atmospheric emissions. Because N pollution involves multiple sources, management strategies targeting all major pollution sources will result in the greatest ecological benefits.

Impervious Surface Area as a Predictor of the Effects of Urbanization on Stream Insect Communities in Maine, U.S.A.

The influence of urbanization on stream insect communities was determined by comparing physical, chemical, and biological characteristics of streams draining 20 catchments with varyinglevels of urban land-cover in Maine (U.S.A). Percent total impervious surface area (PTIA), which was used to quantify urbanland-use, ranged from ∼1–31% among the study catchments.Taxonomic richness of stream insect communities showed an abruptdecline as PTIA increased above 6%. Streams draining catchmentswith PTIA < 6% had the highest levels of both total insect and EPT (Ephemeroptera + Plecoptera + Trichoptera) taxonomic richness. These streams contained insect communities with a totalrichness averaging 33 taxa in fall and 31 taxa in spring; EPT richness ranged from an average of 15 taxa in fall and 13 taxa inspring. In contrast, none of the streams draining catchments with6–27% PTIA had a total richness > 18 taxa or an EPT richness> 6 taxa. Insect communities in streams with PTIA > 6% were characterized by the absence of pollution-intolerant taxa. The distribution of more pollution-tolerant taxa (e.g.Acerpenna (Ephemeroptera); Paracapnia, Allocapnia (Plecoptera); Optioservus, Stenelmis (Coleoptera); Hydropsyche, Cheumatopsyche (Trichoptera)), however, showed little relation to PTIA. In contrast to the apparent threshold relationship between PTIA and insect taxonomic richness, both habitat qualityand water quality tended to decline as linear functions of PTIA.Our results indicate that, in Maine, an abrupt change in stream insect community structure occurs at a PTIA above a threshold ofapproximately 6% of total catchment area. The measurement of PTIA may provide a valuable tool for predicting thresholds for adverse effects of urbanization on the health of headwater streams in Maine.

Comparative soil CO2 evolution, litter decay, and root dynamics in clearcut and uncut spruce-fir forest

Abstract An investigation was conducted in a northern spruce-fir forest to examine the impact of forest clearcutting on soil CO2 efflux, litter decay, and root dynamics in the first year following harvesting. During a 6-month sampling period from May-November, clearcut plots released 16% more carbon dioxide than did uncut spruce-fir reference plots. Aboveground litterfall was much greater in the uncut site; however, unit decay rates for Oi horizon surface litter in cut and uncut sites were similar. Thus, excess CO2 efflux from the harvested site did not result from increased decomposition of litter and forest floor organic matter. Fine root (≤ 3 mm) biomass and necromass varied over the sampling period between cut and uncut sites, and live root biomass declined steeply over the growing season in the clearcut plots. Fine root decomposition in the O horizon of harvested plots equalled 35% of the initial standing crop of fine root biomass + necromass in the forest floor of the cut site, and accounted for about one-third of total soil CO2 efflux from the clearcut site during the study period.

Biogeochemical controls on aluminum chemistry in the O horizon of a red spruce (Picea rubens Sarg.) stand in central Maine, USA

This study examined the biotic and abiotic processes controlling solution chemistry and cycling of aluminum (Al) in the organic horizons of a northern coniferous forest ecosystem. A mass balance budget indicated that aboveground inputs of Al to the O horizon averaged 0.9 kg ha−1 1 yr−1, with major inputs accounted for by litterfall (69%), followed by precipitation (21%), and net canopy throughfall plus stemflow (10%). Estimated leaching losses of Al from the O horizon averaged 2.1 kg Al ha-1 yr1. We hypothesize that the difference between measured Al inputs and outputs can be accounted for by Al release from weathering of soil minerals admixed into the O horizon. Variations in O horizon solution Al chemistry were influenced by a number of factors, including pH, Al equilibria with different solid-phase organic exchange sites, and Al complexation with humic ligands in soil solution.

Comparative effects of precipitation acidity on three forest soils: carbon cycling responses

SummaryThis comparative soil microcosm study examined the effects of precipitation acidity on decomposition processes in three contrasting eastern North American forest soils: a Becket series Haplorthod, an Unadilla series Dystrochrept, and an Adams series Haplorthod. Results from all three soils showed that soil respiration is quantitatively unaffected by differences in precipitation acidity over the range of pH 5.7 to 3.5 (annual loading rates of 36 to 5,520 eq H+ · ha−1). Soil respiration did vary as a function of edaphic differences between soils. Data from all three soils also indicated that precipitation acidity (at pH≧3.5 and lime potential ≧1.11) had no consistent quantitative effect upon total dissolved organic carbon leaching. Again, differences in DOC flux were related to inter-soil edaphic variations. Carbon turnover budgets for the three soils indicated that 54–68% of the forest floor carbon loss occurred through respiration, while DOC leaching accounted for the remaining 32–46% of carbon loss. Finally, results from all three soils showed that increased inputs of strong acids to the forest floor caused distinct decreases in the hydrophobic acid (fulvic acid) content of leachate dissolved organic carbon.

Chemical Weathering and Solution Chemistry in Acid Forest Soils: Differential Influence of Soil Type, Biotic Processes, and H+ Deposition

In this investigation, weathering rates were calculated for three eastern North American forest soils using five separate estimation techniques. In addition, leaching experiments were performed to examine the influence of selected environmental variables on the weathering process. Weathering rates varied five-fold between soils, ranging from approximately 0.5 Keq ha–1 yr–1 in a sandy Adams Spodosol, to 1.2 Keq ha yr–1 in a sandy loam Becket Spodosol, to 2.7 Keq ha–1 yr–1 in a silty Unadilla Inceptisol. Inter-soil differences in weathering rate were inversely correlated with mean soil particle size and positively correlated with total exchangeable bases in the soil profile. Study results also demonstrated major differences in weathering rates between soil horizons.

Apparent differences in binding site distributions and aluminum(III) complexation for three molecular weight fractions of a coniferous soil fulvic acid

Abstract A soil fulvic acid isolated from a northern coniferous forest (NCFA) was fractionated into three different molecular sizes ranging from less than 500 to 10 000 daltons by ultrafiltration and the fractions were studied by synchronous scan fluorescence spectroscopy (SSFS). The SSFS gives three distinct emission peaks (I, II and III) for these fractions of NCFA, which are attributed to different fluorophores. The lower-wavelength peaks (315 and 370 nm) are attributed to fluorophores that consist of a single aromatic ring with carboxyl and/or hydroxyl groups attached to it, whereas the longest-wavelength peak (470 nm) is associated with a fluorophore containing three or four condensed aromatic rings with substituted groups. The ratio of the intensity of peak III to II increases from the lower to higher molecular weight fraction which indicates a higher content of condensed aromatic rings in the high molecular weight fraction. This study also included aluminum(III) binding experiments with the different molecular weight fractions of NCFA. Results showed that the high molecular weight fraction has a stronger affinity for aluminum(III) than the low molecular weight fraction.

A kinetic study of aluminum adsorption by aluminosilicate clay minerals

Abstract The adsorption kinetics of Al 3+ by montmorillonite, kaolinite, and vermiculite were investigated as a function of the initial Al concentration, the surface area of the clay, and H + concentration, at 25°, 18°, and 10°C. In order to minimize complicated side reactions the pH range was kept between 3.0 and 4.1. Results showed that the adsorption rate was first order with respect to both the initial Al concentration and the clay surface area. Changes in pH within this narrow range had virtually no effect on adsorption rate. This zero order reaction dependence suggested that the H + , compared to Al, has a weak affinity for the surface. The rates of adsorption decreased in the order of montmorillonite > kaolinite > vermiculite when compared on the basis of equal surface areas, but changed to kaolinite > montmorillonite > vermiculite when the clays were compared on an equal exchange capacity basis. The calculated apparent activation energies were −1 , indicating that over the temperature range of the study the adsorption process, is only marginally temperature sensitive. The mechanism is governed by a simple electrostatic cation exchange involving outer sphere complexes between adsorbed Al and the clay surface. Vermiculite, may have a second reaction step governed by both electrostic attraction and internal ion diffusion. Equilibrium constants for the formation of an adsorbed Al clay complex were also estimated and are 10 5.34 , 10 5.18 , and 10 4.94 for kaolinite, montmorillonite, and vermiculite, respectively, suggesting that these clays could play a significant role in controlling soil solution Al concentrations.

Forest vegetation in relation to surface water chemistry in the North Branch of the Moose River, Adirondack Park, N.Y.

The Regional Integrated Lake-Watershed Acidification Study (RILWAS) was conducted to identify and to quantify the environmental factors controlling surface water chemistry in forested watersheds of the Adirondack region of New York. The RILWAS vegetation research was designed to: (1) compare the quantitative patterns of forest cover and tree community structure in the study catchments of the Moose River drainage system; and (2) identify important vegetation differences among study watersheds that might help to explain inter-watershed differences in water chemistry and aquatic responses to acidic deposition. Field transect data indicated that the overall drainage system includes 50% mixed forest cover, 38% hardwood forest, 10% coniferous forest, and 2% wetland cover. Major tree species include yellow birch, red spruce, American beech, sugar maple, eastern hemlock, and red maple. Analysis of forest structure indicated that mean weighted basal area estimates ranged two-fold from 24–48 m2ha−1 among watersheds. Likewise, mean weighted estimates for aboveground biomass and aboveground annual productivity ranged among watersheds from 160 to 320 MT ha−1 and from 8 to 18 MT ha−1 yr−1, respectively. Results showed that differences in surface water chemistry were independent of vegetation differences among watersheds.