Abstract Concern is resurfacing in the United States over the long-term effects of excess nitrogen (N) deposition and mobility in the environment. We present here a new synthesis of existing data sets for the northeastern United States, intended to answer a single question: Is N deposition altering the N status of forest ecosystems in this region? Surface water data suggest a significant increase in nitrate losses with N deposition. Soil data show an increase in nitrification with decreasing ratio of soil carbon to nitrogen (C:N) but weaker relationships between N deposition and soil C:N ratio or nitrification. Relationships between foliar chemistry and N deposition are no stronger than with gradients of climate and elevation. The differences in patterns for these three groups of indicators are explained by the degree of spatial and temporal integration represented by each sample type. The surface water data integrate more effectively over space than the foliar or soil data and therefore allow a more comprehensive view of N saturation. We conclude from these data that N deposition is altering N status in northeastern forests.

Is Nitrogen Deposition Altering the Nitrogen Status of Northeastern Forests

Concern is resurfacing in the United States over the long-term effects of excess nitrogen (N) deposition and mobility in the environment We present here a new synthesis of existing data sets for the northeastern United States, intended to answer a single question: Is N deposition altering the N status of forest ecosystems in this region? Surface water data suggest a significant increase in nitrate losses with N deposition Soil data show an increase in nitrification with decreasing ratio of soil carbon to nitrogen (C:N) but weaker relationships between N deposition and soil C:N ratio or nitrification Relationships between foliar chemistry and N deposition are no stronger than with gradients of climate and elevation The differences in patterns for these three groups of indicators are explained by the degree of spatial and temporal integration represented by each sample type The surface water data integrate more effectively over space than the foliar or soil data and therefore allow a more comprehensive view of N saturation We conclude from these data that N deposition is altering N status in northeastern forests

https://udel.edu/~inamdar/nps2007/n_discussion.pdf

A synthesis of the biogeochemistry of Ca was done during 1963–1992in reference and human-manipulated forest ecosystems of the Hubbard BrookExperimental Forest (HBEF), NH. Results showed that there has been a markeddecline in concentration and input of Ca in bulk precipitation, an overalldecline in concentration and output of Ca in stream water, and markeddepletion of Ca in soils of the HBEF since 1963. The decline in streamwaterCa was related strongly to a decline in SO\(_4^{2 - } \) +NO\(_3^ - \) in stream water during the period. The soildepletion of Ca was the result of leaching due to inputs of acid rain duringthe past 50 yr or so, to decreasing atmospheric inputs of Ca, and tochanging amounts of net storage of Ca in biomass. As a result of thedepletion of Ca, forest ecosystems at HBEF are much more sensitive tocontinuing inputs of strong acids in atmospheric deposition than expectedbased on long-term patterns of sulfur biogeochemistry. The Ca concentrationand input in bulk precipitation ranged from a low of 1.0 µmol/land 15 mol/ha-yr in 1986–87 to a high of 8.0 µmol/l and 77mol/ha-yr in 1964–65, with a long-term mean of 2.74 µmol/lduring 1963–92. Average total atmospheric deposition was 61 and 29mol/ha-yr in 1964–69 and 1987–92, respectively. Dry depositionis difficult to measure, but was estimated to be about 20% of totalinput in atmospheric deposition. Streamwater concentration reached a low of21 µmol/l in 1991–92 and a high of 41 µmol/l in1969–70, but outputs of Ca were lowest in 1964–65 (121mol/ha-yr) and peaked in 1973–74 (475 mol/ha-yr). Gross outputs of Cain stream water were positively and significantly related to streamflow, butthe slope of this relation changed with time as Ca was depleted from thesoil, and as the inputs of sulfate declined in both atmospheric depositionand stream water. Gross outputs of Ca in stream water consistently exceededinputs in bulk precipitation. No seasonal pattern was observed for eitherbulk precipitation or streamwater concentrations of Ca. Net soil releasevaried from 390 to 230 mol/ha-yr during 1964–69 and 1987–92,respectively. Of this amount, weathering release of Ca, based on plagioclasecomposition of the soil, was estimated at about 50 mol/ha-yr. Net biomassstorage of Ca decreased from 202 to 54 mol/ha-yr, and throughfall plusstemflow decreased from 220 to 110 mol/ha-yr in 1964–69 and1987–92, respectively. These ecosystem response patterns were relatedto acidification and to decreases in net biomass accretion during the study.Calcium return to soil by fine root turnover was about 270 mol/ha-yr, with190 mol/ha-yr returning to the forest floor and 80 mol/ha-yr to the mineralsoil. A lower content of Ca was observed with increasing elevation for mostof the components of the watershed-ecosystems at HBEF. Possibly as a result,mortality of sugar maple increased significantly during 1982 to 1992 at highelevations of the HBEF. Interactions between biotic and abiotic controlmechanisms were evident through elevational differences in soil cationexchange capacity (the exchangeable Ca concentration in soils wassignificantly and directly related to the organic matter content of thesoils), in soil/till depth, and in soil water and in streamwaterconcentrations at the HBEF, all of which tended to decrease with elevation.The exchangeable pool of Ca in the soil is about 6500 mol/ha, and itsturnover time is quite rapid, about 3 yr. Nevertheless, the exchangeablepools of Ca at HBEF have been depleted markedly during the past 50 years orso, >21,125 mol/ha during 1940–1995. The annual gross uptake oftrees is about 26–30% of the exchangeable pool in the soil.Some 7 to 8 times more Ca is cycled through trees than is lost in streamwater each year, and resorption of Ca by trees is negligible at HBEF. Of thecurrent inputs to the available nutrient compartment of the forestecosystem, some 50% was provided by net soil release, 24% byleaching from the canopy, 20% by root exudates and 6% byatmospheric deposition. Clear cutting released large amounts of Ca tostream water, primarily because increased nitrification in the soilgenerated increased acidity and NO\(_3^ - \), a mobileanion in drainage water; even larger amounts of Ca can be lost from theecosystem in harvested timber products. The magnitude of Ca loss due towhole-tree harvest and acid rain leaching is comparable for forests similarto the HBEF, but losses from harvest must be superimposed on losses due toacid rain.

The biogeochemistry of calcium at Hubbard Brook

Increased losses of nitrate from watersheds may accelerate the depletion of nutrient cations and affect the acidification and trophic status of surface waters. Patterns of nitrate concentrations and losses were evaluated in four forested watersheds (East Bear Brook Watershed, Lead Mountain, ME; Watershed 6, Hubbard Brook Experimental Forest, White Mountains, NH; Arbutus Watershed, Huntington Forest, Adirondack Mountains, NY; Biscuit Brook, Catskill Mountains, NY) located across the northeastern United States. A synchronous pattern was observed in nitrate concentrations of drainage waters from these four sites from 1983 through 1993. Most notably, high concentrations and high drainage water losses followed an anomalous cold period (mean daily temperature −11.4 to −16 °C in December 1989) for all four sites. After high nitrate losses during the snowmelt of 1990, nitrate concentrations and fluxes decreased at all sites. These results suggest that climatic variation can have a major effect on nitrogen flux an...

Climatic Control of Nitrate Loss from Forested Watersheds in the Northeast United States

https://www.esf.edu/efb/mitchell/Myron%20Ref/Evn.Pol.123.327.336.pdf

Effects of acidic deposition on forest and aquatic ecosystems in New York State.

Long-term changes in the chemistry of precipitation (1978–94) and 16 lakes (1982–94) were investigated in the Adirondack region of New York, USA. Time-series analysis showed that concentrations of SO4
2−, NO3
−, NH4
+ and basic cations have decreased in precipitation, resulting in increases in pH. A relatively uniform rate of decline in SO4
2− concentrations in lakes across the region (1.81±0.35 μeq L−1 yr−1) suggests that this change was due to decreases in atmospheric deposition. The decrease in lake SO4
2− was considerably less than the rate of decline anticipated from atmospheric deposition. This discrepancy may be due to release of previously deposited SO4
2− from soil, thereby delaying the recovery of lake water acidity. Despite the marked declines in concentrations of SO4
2− in Adirondack lakes, there has been no systematic increase in pH and ANC. The decline in SO4
2− has corresponded with a near stoichiometric decrease in concentrations of basic cations in low ANC lakes. A pattern of increasing NO3
− concentrations that was evident in lakes across the region during the 1980's has been followed by a period of lower concentrations. Currently there are no significant trends in NO3
− concentrations in Adirondack lakes.

W.J Kretser

Papers

Long-term trends in the chemistry of precipitation and lake water in the Adirondack Region of New York, USA

The response of lake water in the Adirondack region of New York to changes in acidic deposition