The Adirondack Manipulation and Modeling Project (AMMP): design and preliminary results

Forest Ecology and ' Management ELSEVIER

Forest Ecology and Management 68 (1994) 87-100

The Adirondack Manipulation and Modeling Project (AMMP)" design and preliminary results M.J. Mitchell *'a, C.T. Driscoll b, J.H. Porter c, D.J. Raynal a, D. Schaefer d, E.H. W h i t e a aSUNY, College of Environmental Science and Forestry, Syracuse, NY 13210, USA bSyracuse University, Syracuse, NY 13244, USA cNYC-DEP, Graharnsville Laboratory, Grahamsville, NY 12740, USA dCenter for Energy and Ecological Research, San Juan, 00936, Puerto Rico

Abstract

The Adirondack Manipulation and Modeling Project (AMMP) was initiated in 1990 to investigate the effects of changing chemical inputs in the Adirondack Mountains of New York (USA). The four study sites are located across a west to east gradient of declining atmospheric deposition, increasing acid neutralizing capacity (ANC) and decreasing NO j- concentration in surface waters in the Adirondacks. We hypothesize that the two sites in the western Adirondacks (Woods Lake (WL) and Pancake-Hall Creek ( P H C ) ) exhibit lower critical loads of N, S and H ÷ than the central and eastern sites (Huntington Forest (HF) and Pack Forest (PF), respectively). To test this hypothesis, chemical treatments of plots were initiated in 1990 including (NH4)2SO4 ( 1000 and 2000 eq h a - t year- i ), H2SO4 ( 1000 eq h a - t year- ~), HNO3 ( 1000 eq h a - ~year- ~), Ca + Mg + SO~e- ( 1000 eq h a - ~year- t ). Three of the sites (WL, PHC and HF) are northern hardwood ecosystems underlain by Spodosols. The PF site is a Pinus resinosa plantation on a glacial outwash plain (Typic Udipsamment). Ions in total deposition, throughfall and soil leachates were monitored continuously. Changes in the solid phase chemistry of the mineral soil were assessed annually using the buried soil-bag approach. Vegetation responses to chemical treatments were analyzed by ascertaining changes in growth, composition and nutrient concentrations of both the overstory and understory. Elemental cycling models used in the AMMP include NuCM and VEGIE-CHESS. Preliminary results of bulk precipitation and throughfall from 1991-1992 suggest that the western sites may have greater inputs of SO 2- and have lower capacity to retain NO j- passing through the foliage. Soil solutions (1991-1992) in reference plots of the western sites (WL and PHC) had higher concentrations of NOj- in soil solution than the central and eastern Adirondack sites (HF and PF). For all sites except PF, ammonium sulfate additions resulted in increased concentrations of SO~- and NOj- in soil solutions. Results of model simulations with NuCM for HF are presented which suggest that the model adequately simulated the pattern of increasing SO~- concentrations in response to (NH4)2SO 4 treatment, but that the increase in NOj- was underestimated. Keywords: Chemical manipulation; Model simulation; Atmospheric deposition; Nutrient concentration; Soil

1. Introduction

The Adirondack Manipulation and Modeling

Project (AMMP) was initiated in response to previous and ongoing investigations which established baseline information on the effect of air quality, including acidic deposition, on element

*Corresponding author. 0378-1127/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSD10378-1127 ( 94 ) 06076-U

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M.J. Mitchell et al. / Forest Ecology and Management 68 (I 994) 8 7-1 O0

cycling in the Adirondack Mountains of New York, USA as well as in other regions. The status of the surface waters in the Adirondack Mountains and their responses to acidic deposition have been summarized by Driscoll et al. ( 1991 ). Synoptic surveys of surface waters including the Eastern Lake Survey (Landers et al., 1988) and the Adirondack Lakes Study (Krester et al., 1989 ) as well as detailed studies of solute flux in forested ecosystems have indicated that there is a range of acid neutralizing capacity (ANC) and concentrations of NO~- and basic cations across the Adirondacks. Lakes in the western part of the Adirondack Park generally have lower pH and ANC values and higher NO~- concentrations (Driscoll et al., 1991 ). Concentrations of SO42are relatively more uniform across the region. The relative contributions of air pollutants, meteorological conditions, soil processes and vegetation characteristics in affecting the spatial distribution of acidic waters have not been determined. Elevated inputs of atmospheric deposition of N is of concern within New York State. In the Adirondack Region high concentrations of surface water NO~- have been reported in synoptic surveys and time-series analyses have demonstrated increasing leaching losses of this anion in recent years (Driscoll and Van Dreason, 1993 ). However, this excess N may be due not only to atmospheric deposition of N, but also to a declining N demand by the biota with a decrease in forest growth (Aber et al., 1989; Schulze et al., 1989; Stoddard, 1994). Thus, policies which mandate the maintenance of old age forests may contribute to elevated concentrations of solutes in soil solutions and surface waters. Presently, there is limited information to quantify the relative contributions of internal sources of N and atmospheric deposition to NOw leaching in the Adirondack region. The loss of basic cations from forest soils may be accelerated by inputs of strong inorganic acids derived from atmospheric pollutants. With the available data it is not possible to make accurate predictions of how changing these acid inputs (either increase or decrease) will influence the chemistry of forest soils and surface waters, and

thus impact forest health and water quality. The linkage between atmospheric pollutants and forest health has been the subject of considerable debate both by scientists and policy makers. For example, declines of sugar maple in Ontario, Quebec and Vermont have been reported, especially by individuals engaged in commercial sugar maple production. Bernier and Brazeau (1988) hypothesized that some of this decline may be linked to nutrient deficiencies which may have been exacerbated by acidic deposition. However, Barnard et al. (1990) summarized information on sugar maple decline and found that most sugar maple stands in North America are not in a state of decline. Nevertheless, decline episodes may be severe and coincide with insect defoliation, severe weather and nutrient deficiencies, but acidic deposition has not yet been shown to be a significant contributing factor. The development of the AMMP coincides with other projects within the United States and Europe which are using experimental chemical manipulations to evaluate the effects of air pollutants and climatic change on ecosystem processes. In addition to the regional approach of the AMMP, there are important linkages to global concerns on elemental cycles and environmental changes that can be made within the framework of this project. For example, it has been suggested that temperate forest ecosystems with high N loadings may contribute to increasing CH4 concentrations in the atmosphere (Steudler et al., 1989). Forest ecosystems may also influence the atmospheric exchange of other infrared-absorptive gases including CO2 and N20 (Bowden, 1986).

2. A M M P sites

The study sites were selected to represent different regions of the Adirondacks. Deposition of N and S is thought to be highest in the western Adirondacks, decreasing in the eastern Adirondacks. Western watersheds exhibit high NO~leaching compared with those in the central and eastern Adirondacks (Driscoll and Van Dreason, 1993). An additional factor in choosing

M.J. Mitchell et al. / Forest Ecology and Management 68 (1994) 8 7-1 O0

89

Sum • )

--~-

Huntington

~

(

f

~ ~

( f

Adlrond:LckPark

Fig. 1. Location of A M M P sites in the Adirondack Park of New York State. Table 1 Selected characteristics of A M M P sites Site (abbreviation) Woods Lake (WL) Pancake-Hall Creek (PHC) Huntington Forest (HF) Pack Forest (PF)

Elevation (m)

Dominant overstory vegetation at site

Soil type

43 ° 53 'N, 74 ° 57' W 43 ° 50'N, 74 ° 51 ' W

678

Typic Haplorthod

43 ° 59'N, 74 ° 14'W

530

43 ° 33' N, 73°48'W

245

Betula alleghaniensis, Acer rubrum Acer saccharum, Picea rubens, Fagus grandifolia A. rubrun, B. alleghaniensis, A. saccharum Pinus resinosa

635

these specific sites was that each has an extensive biogeochemical database which serves as an important foundation for the experimental manipulations in the AMMP. The locations of the four sites are given in Fig. 1 and the major features of each site are summarized in Table 1. Further information on each of the A M M P sites is given below.

2.1. Pack Forest (PF) The research site is on a 48.5 ha glacial outwash plane within the 1500 ha Charles Lathrop

Typic Haplorthod

Typic Haplorthod

Typic Udipsamment

Pack Demonstration Forest in the eastern Adirondacks near Warrensburg, NY. Conifer plantations, established on abandoned farm land, have been the sites of continuous research on forest nutrition and soil-site relationships since the late 1930s, when growth abnormalities were first observed in the young trees. The results of more than 40 years of research have shown that K fertilizer was the only treatment that produced a growth response. Recent investigations are summarized by Nowak et al. ( 1991 ). The outwash soil at the Pack Forest site is a deep, highly

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M.J. Mitchell et al. / ForestEcologyand Management 68 (1994)87- I O0

stratified, Plainfield loamy sand (Typic Udipsamment). These soils have low cation exchange capacity and thus might be expected to be susceptible to acidic deposition. Recent work at PF has included stem analysis of historical patterns of growth patterns in the pine plantations (LeBlanc et al., 1987 ) and research on biogeochemical cycling (Shepard and Mitchell, 1990, 1991 ). These previous studies indicated that this forest does not exhibit high rates of cation leaching since there is a high demand for N and thus there is little NO~- leaching. The AMMP plots are located within a Pinus resinosa (Ait.) (red pine) stand which is 60 years old and was fertilized with 212 kg ha -I of KC1 in 1951. The PF site is the only AMMP site dominated by conifers, making for an interesting comparison of responses in pine versus the hardwood ecosystems at the other three sites. In addition the response of the pine system to chemical manipulations will provide valuable information on the effects of changing chemical inputs to conifer ecosystems.

siderable coarse fragments and high organic concentrations in the upper mineral horizons. This site has been the location of a series of studies, such as the IFS (Johnson and Lindberg, 1992), which have evaluated the effects of acidic deposition (Raynal et al., 1985; Shepard et al., 1989; Foster et al., 1992 ) including detailed studies on S (David et al., 1987), N (Shepard et al., 1990; Mitchell et al., 1992a,b) and A1 cycling (David and Driscoll, 1984). The HF is an National Atmospheric Deposition Program (NADP) and National Trends Network (NTN) site and has extensive instrumentation (Shepard et al., 1989) for monitoring meteorology, wet deposition inputs and gaseous pollutant concentrations (i.e. NOx, SO2, ozone). The hardwood site has been extensively characterized as part of the IFS project including the elemental content of the vegetation and solute flux (including event chemistry) through all strata of the ecosystem. The AMMP plots are located within 500 m of the IFS study plots.

2.2. Huntington Forest (HF)

2.3. Pancake-Hall Creek watershed (PHC)

This experimental forest (6066 ha) property is located in western Essex County and eastern Hamilton County within the Adirondack State Park of New York. Since 1940, basic meteorological data have been collected on a regular basis at the Huntington Forest. The regional climate is cool, moist and continental. The mean annual temperature is 4.4°C with a dormant mean of - 2 . 8 ° C and a growing season mean of 14.3 ° C. Total annual precipitation averages 101 cm (Shepard et al., 1989). The mixed northern hardwood site is typical of much of the Adirondack region since it was heavily cut about 100 years ago and deciduous forest has regenerated dominated by Fagus grandifolia Ehrh. (American beech) and Acer saccharum Marsh. (sugar maple). The soil is a Becket bouldery fine sandy loam, a Typic Haplorthod. Similar soils are found in much of the Adirondack Region and other areas of the northeastern United States. The soil overlies a bedrock of gneiss, is shallow (less than 1 m depth) and contains a hardpan derived from the parent material of glacial till. There are con-

This 74 ha watershed is in the western Adirondacks and is a mixed hardwood stand with A. saccharum, F. grandifolia, Betula alleghaniensis Britton (yellow birch), Picea rubens Sarg. (red spruce), Abies balsamea (L.) Mill (balsam fir) and Tsuga canadensis (L.) Carr. (Canadian hemlock). This site is equipped with snow and zero tension lysimeters beneath the Oa and Bs2 horizon which are monitored weekly with more intensive monitoring during the snow melt period (Driscoll et al., 1987). Information on atmospheric deposition was available from the Utilities Acid Precipitation Program (UAPSP) network at Big Moose Lake (approximately 2 km from the Pancake-Hall watershed). Soils have been characterized chemically at this site. Work on this site has focused on the 'Evaluation of the Source of Nitric Acid Inputs to Adirondack Surface Waters' under the direction of C. Driscoll. A comparison of PHC and HF has suggested that the former is more sensitive to strong acid inputs (Driscoll et al., unpublished data, 1993). This difference is largely due to the greater availabil-

M.J. Mitchellet al. / ForestEcologyand Management 68 (1994) 87-1O0

ity of base cations in the latter system. Because of elevated concentrations of strong acid anions relative to basic cations, streamwater at PHC contains higher concentrations than HF of labile monomeric A1 which may be toxic to aquatic biota. The AMMP plots are located in the western portion of PHC watershed. 2.4. Woods Lake watershed (WL)

This watershed is in the western Adirondacks and has a basin area of 2.1 km 2. The mean depth to till is about 2.1 m underlain by granitic bedrock and the soils are predominantly Haplorthods. The watershed is 88% hardwood forest with smaller amounts of coniferous, mixed forest types and wetlands. The hardwood community is dominated by F. grandifolia and Acer rubrum L. (red maple). The most important subdominants are A. saccharum with P. rubens, Acer pensylvanicum L. (striped maple), and B. alleghaniensis being of less importance. The average basal area of the hardwood stands is 20.9 m 2 ha- 1with an average diameter at breast height (dbh) of 16.5 cm (Cronan and DesMueles, 1985 ). This area has received intensive study owing to its use in the Integrated Lake-Watershed Acidification Study (ILWAS) (Goldstein and Gherini, 1984) and the Lake Acidification Mitigation Program (LAMP) (Driscoll et al., 1989). Solute fluxes, vegetation characteristics, geology and hydrology have been extensively characterized for this watershed. The AMMP plots are adjacent to the southeast edge of the Woods Lake watershed.

3. Approach The overall approach of the project is to couple experimental manipulations with modeling to test hypotheses relating to the effect of atmospheric pollutants on forest ecosystems. These hypotheses are as follows. (1) Atmospheric deposition. There are decreases in atmospheric inputs of NO~-, SO4z- , and acidity from west to east across the Adirondack Mountains.

91

(2) Vegetation. Increased inputs of N, P, Ca, K and Mg will cause increased nutrient uptake and enhance primary production. Response will be site-specific and depend upon forest age, deposition inputs and soil nutritional status. (3) Soil (solid phase). Increased loadings of mobile anions (SO42- and NO~- ) will result in changes in the solid phase of the soil. These changes will be greater in forests in the western Adirondacks since these systems exhibit higher leaching rates of mobile anions and show limited retention of N and S compared with sites in the central and eastern Adirondacks. (4) Soil (solution). Increased loadings of N and S will result in increased concentrations and fluxes of NO~- and SOl- in soil solution as well as associated cations with greater increases in sites in the western Adirondacks. (5) Soil (microbial). Increased loading of N will be reflected in changes in microbially mediated processes with greatest response in those sites with lower initial N availability. The treatments and measurements which have been implemented for testing these hypotheses are described below.

3. I. Chronic treatments

These hypotheses are tested by experimental manipulation of field plots which were performed in 1991 and 1992 (and will continue through 1993) at the four sites: WL, PHC, HF and PF (Table 2 ). The experimental design was a randomized complete block with three replicates. Solutions were sprayed biweekly from June through October. A single addition of (NH4)2SO4 was applied in spring (late May or early June) as a dry salt. Some minor burning of foliage on seedlings and ground flora has been observed where salt crystals adhered to moisture on the foliage. Otherwise, there were no visible effects of treatments (including the acid solution additions). Stable ~SN isotopes are used to help quantify N dynamics at PHC where the added (NH4) 2SO4 was enriched with 0.5% 15N.

M.J. Mitchell et al. / Forest Ecology and Management 68 (1994) 87-100

92

Table 2 Chronic treatments used in the AMMP

wood stand which regenerated naturally after clear-cutting in 1966.

Treatment (plot size)

Rate (eq h a - l year-l )

Sites (abbreviations as in text)

Reference

Ambient only

H2SO4 (5 m × 5 m) Ca + Mg + SO4 (5m×5m) HNO3 (5 m × 5 m) Low (NH4)2804 (10m×10m) except at PHC (5m×5m) High (NH4) 2SO4 (10m×10m) except at PHC (5mXSm)

1000+ambient 1000 + ambient

WL, PHC, HF, PF WL, HF WL, HF

1000+ambient 1000 + ambient

2000 + ambient

WL, HF WL, PHC, HF, PF

WL, PHC, HF, PF

Table 3 Acute treatments at Huntington Forest Designation Description Reference N NS NP NPK

Ca

No fertilizer N at 336 kg h a - ~from NH4NO 3 N at 336 kg h a - 1 from (NH4)2804 N at 336 kg h a - ~from (NH4)zSO4 and P at 112 kg h a - ~from triple superphosphate (TSP) N at 336 kg ha-~ of N from (NH4)2SO4, P at 112 kg ha- t of P from TSP, and K at 224 kg ha-1 from KC1 Agricultural limestone at 10 Mg ha-

3.2. Acute treatments The objective of this portion of the AMMP is to determine whether the addition of nutrient elements at levels used in commercial fertilization (Table 3) will result in increased production and increased elemental uptake of these elements at HF. A minus element approach was utilized in selecting the treatments including the use of two N sources, (NH4)2SO4 and NH4NO3. The experiment was established in a complete randomized block design with three replications for each treatment. Eighteen plots, 15 m × 15 m with an interior l0 m × l0 m central measurement plot, were established in a northern hard-

4. Sampling and analyses 4.1. Meteorological monitoring, air quality, and trace gas fluxes Meteorological monitoring was performed at HF, PF and Number Four (N4) sites. The N4 site is located just west of the Adirondack Park Boundary and was used only for meteorological and deposition monitoring. Air chemistry was monitored at the HF and N4 using three-stage filter packs (Teflon® filters for aerosols, nylon filters for H N O 3 vapor, carbonate-treated cellulose filters for SO2 vapor). Dry deposition inputs at HF were estimated using the IFS dry deposition model (Johnson and Lindberg, 1992 ). Equilibrium chambers were used to estimate fluxes of trace gases (CH4, N20 and CO2). Gas collections were made monthly during the growing season at PHC and HF in reference, low ( NH4 ) 2SO4 and high (NH4) 2SO4 plots.

4.2. Precipitation and throughfall Bulk throughfall (TF) was sampled biweekly at all experimental sites from May through November starting in August 1991 using three collectors in each reference plot. After this period bottles were replaced with snow buckets which were sampled approximately every 6 weeks as weather and scheduling permit access to the sites. At HF wet-only TF samples (using AeroChem Metrics (ACM) collectors) were obtained weekly during warmer weather and biweekly in winter. Precipitation was monitored using individual ACMs (wet-only) at N4, HF and PF and funnelbottles at N4, HF, and PF. In addition, there are several other sources of wet deposition input data (UAPSP, NADP, NYDEC) in the Adirondack area, which can be compared with our results.

M.J. Mitchell et al. / Forest Ecology and Management 68 (1994) 87-100

93

PrecipitaLion 60

I

40 k_

(D

a_ 20

N4

HF

PF

SITE

Throughfall I

ISulfate Nitrate

80

60 k_

0D

4~

o©

40

20

WL

PHC

HF

PF

SITE Fig. 2. Mean concentrations of SO~- and NO~ in bulk precipitation and throughfall at AMMP sites from 1990 to 1992. Different letters indicate mean separation among sites (t~ = 0.05 ) by Tukey's Honestly Significant Difference (HSD) test. Vertical lines are standard errors.

4.3. Vegetation response, foliar litter and litter bags The forest overstory (trees over 5 cm dbh) and understory (including trees 1-5 cm dbh) have

been measured. Two 0.25 m 2 herbaceous layer plots were established within each of the 5 m X 5 m plots at HF, PHC and WL; four 0.25 m 2 plots were established within each of the 10 m X 10 m plots at HF and WL. During the growing season,

94

M.J. Mitchell et al. / Forest Ecology and Management 68 (1994) 87-100

Table 4 Number of lysimeter collections at AMMP sites from 1991 to 1992 Treatment

Lysimeter depth

Woods Lake

Pancake-Hall Creek

Huntington Forest

Pack Forest

83 66 77 59 72 91

56 76 45 85 52 66

53 56 44 63 49 39

41 69 43 62 53 71

(era) Reference Low (NH4)2SO4 High (NH4)2SO4

15 50 15 50 15 50

percent cover and frequency of all species within the herbaceous layer (less than 0.5 m in height), and density of tree seedlings were estimated using the quadrat frame method. In August, foliage was collected with pole pruners from the overstory (individuals of at least 5.0 cm dbh) or from large trees by shooting down a branch. Litter flux was quantified through use of littertraps, 0.25 m E in size. Two traps were placed in each plot. Litter for mass and chemical analyses was collected biweekly in August, September, and October and monthly during the other snow-free months. Nylon-mesh litter bags were installed during late autumn 1991 with B. alleghaniensis or A. rubrum litter at the three hardwood sites and Pinus resinosa litter at PF.

4.4. Soil solution A total of 432 lysimeters (0.1 MPa, high-flow ceramic cups; Soil Moisture Corporation, Santa Barbara, CA) was installed in July and August 1990. In the l0 m × l0 m plots, lysimeters were restricted to a 5 m × 5 m central area to be consistent with the design of small plots (the full 10 m × 10 m area was utilized for vegetation studies). In the 5 m × 5 m plots, a 50 cm buffer was maintained between lysimeters and the plot boundary to avoid sampling solution from a transition zone between treated and untreated areas. Four lysimeters were installed with their cups 15 cm below the mineral soil surface and four were placed at 50 cm in each plot. The shallow lysimeters are in the upper Bh horizon and in a zone of moderate root density, while the deep

lysimeters are in the Bs horizon and below the majority of roots. Lysimeters were installed at a 45 ° angle to the ground surface to minimize preferential flow of throughfall and treatment solutions. Lysimeter solutions are collected monthly between June and December. During the winter, samples are collected as permitted by weather conditions. Solutions are collected approximately biweekly during snowmelt from late March through early May. Bulking lysimeter samples by plot and depth was initiated in December 1991.

4.5. Mineral soil It is important to quantify the response of soil to changes in chemical inputs because these processes are important in regulating the acid-base status of soil leachates and plant nutrient availability. Adsorption of SO24- can strongly influence the mobility of anions and hence of cations. Treatment-induced changes in soil solid phase chemistry are being monitored via use of buried soil-bags (David et al., 1990). Bulk B-horizon soil was acquired from each site during late August and September 1990. Soil was passed through a 6 mm sieve and homogenized. Approximately 200 g dry weight equivalent was placed into Nitex ® nylon bags (250/ira mesh) and installed beneath the Oa horizon. In addition to each site receiving its own soil, at WL and PHC bags of H F soil were placed within reference plots. Buried soil-bags have been collected in October 1991 and 1992 for analysis of chemi-

M.J. Mitchell et al. / Forest Ecology and Management 68 (1994) 87-1 O0

95

Sulfate 600

i

i

'

b

15 cm depfh

500

b

400 L

@

b 300

T

\\\

,~

b

\\x

©

&

\\" I \ \ \~.

a

\ \ \

b

200

\\\ \\\ \\\ \\\ \\\ \\\

a b.~

100

\\\ \\\ \\\

WL

PHC

HF

PF

SITE 600

500

50 cm depfh ~ - ~ Reference ~ ] L o w Ammonium Sulfafe ~High Ammonium Sulfate

400 L

© 300 o©

~t

b

200

b

a

ab a

ab

a

100

WL

PHC

HF

PF

SITE Fig. 3. Mean concentrations of SO42- in soil solutions from AMMP plots in 1991-1992 in reference, low (NH4)2SO4 ( 1000 eq h a - 1 year - 1) and high (NH4) 2SO4 (2000 eq h a - ~ year- ~) plots. Different letters indicate mean separation among treatments ( a = 0.05 ) by Tukey's Honestly Significant Difference ( H S D ) test. Vertical lines are standard errors.

cal and microbial biomass determinations; an additional collection will be made in 1993.

4.6. Modeling Data analysis and predictions were facilitated by the application of simulation models. The IFS

model NuCM (Liu et al., 1992) has previously been calibrated for the HF and we have conducted some initial simulations to evaluate some of the early results of the AMMP. The Chemical Equilibria in Soils and Solutions (CHESS) model (Santore and Driscoll, 1994), and the Vegetation Effects on Groundwater In Ecosys-

M.J. Mitchell et al. / Forest Ecology and Management 68 (1994) 8 7-1 O0

96

NitraLe 175

T

b T

- - T - -

150

15 cm depfh 125

b

L_

©

b

100 b

oqp

:3.

75

50

25 0

0

0

0

_

WL

PHC

HF

PF

SITE

175

150

50 cm depfh ~T/~ Reference ~ : ~ L o w Ammonium SulfGte ~High Ammonium Sulfafe

125 L_

100 0-

©

x.

75

50

a

b

b

25 0

0

0

I

0 WL

PHC

HF

PF

SITE Fig. 4. Mean concentrations of NOj- in soil solutions from AMMP plots in 1991-1992 in reference, low (NH4)2804 ( 1000 eq ha-1 year-1 ) and high (NH4)2SO4 (2000 eq ha-I year-~ ) plots. Different letters indicate mean separation among treatments (a = 0.05 ) by Tukey's Honestly Significant Difference (HSD) test. Vertical lines are standard errors.

tems (VEGIE) model (Aber et al., 1991 ) are also being utilized. The CHESS and VEGIE models are designed to work independently of each other, but can also be linked into an integrated nutrient cycling model. The CHESS model is a chemical equilibrium model designed to simulate reactions in soils and solutions. We will also examine some of the critical for-

mulations of the models employed in DDRP. Through a systematic assessment of the representation of individual processes regulating the release/retention of solutes, we evaluate process formulations and utilize these models to predict how changes in atmospheric pollutants will affect the Adirondack region. This information will also be used in interpreting differences in surface

M.J. Mitchell et al. / Forest Ecology and Management 68 (1994) 87-100

97

900

90

800

-

80

700

-

70

500

-

60

-

50

C"

C"

©

~J

®

CT © 500

3

©

CT ©

:Z. 400

-

40

© 500

50

200

20

1O0

10

~h

© 0

z

REFERENCE

LOW AMMONIUM SULFATE

HIGH AMMONIUM SULFATE

Treatment

•

Sulfate Measured

VT~sulfate Simulated (2 yr)

~:T~ Sulfate Simulated (10 yr)

[~

Nitrate Measured

~Nitrate

f~

Simulated (2 yr)

Nitrate Simulated (10 yr)

Fig. 5. Simulated concentrations of SO~- and N O ; in soil solution at HF at addition rates of (NH4)2SO4 at 0, 1000 a n d 2000 eq h a - ~ y e a r - ~ above ambient inputs for 2 and 10 years compared with measured concentrations with 2 years of addition.

water chemistry in the Adirondacks. In addition, this information should enhance interactions with resource managers and policy makers in making assessments of the effects of pollutants on forest ecosystems and their respective watersheds for other regions of North America as well as Europe.

5. Preliminary results and future directions

5.1. Bulk precipitation and throughfall chembstry Preliminary information is presented on mean concentrations of NO~- and SO~- in bulk precipitation and throughfall (Fig. 2) based on 29, 23 and 31 precipitation collections at N4, HF and

PF, respectively, and 83 throughfall collections at WL, PHC and PF and 90 collections at HF. Samples were collected from August 1991 through November 1992. Site differences were determined using ANOVA with mean separations ( a = 0.05 ) by Tukey's Honestly Significant Difference (HSD) multiple comparison procedure (Statistical Analysis Systems Institute Inc., 1985 ). There were no significant differences in SO4z- or NO~- concentrations in bulk precipitation at N4, HF and PF sites, although the most western site (N4) tended to have greater concentrations. It is anticipated, however, that when these concentration data are converted to fluxes that differences among the sites will be shown since the western sites likely have greater inputs

98

M.J. Mitchell et aL / Forest Ecology and Management 68 (1994) 87-100

of precipitation. PHC has significantly lower concentrations of SO4z- than the WL, H F and PF sites. The WL site is the most westerly site for which throughfall data were collected and it tended to have higher concentrations than the other sites. Among the four sites, NO~- concentrations in throughfall were significantly greater at the WL and PHC and significantly lower at PF. The differences in N O ; concentrations in throughfall suggest that the foliar demand for N is less at WL and P H C than at H F and PF. The low N O ; concentrations at the PF reflect the tight cycling of N which has been documented previously at this site (Shepard and Mitchell, 1991).

5.2. Soil solution chemistry In an effort to demonstrate the results of chemical treatments for the AMMP, we present preliminary results on mean N O ; and SO24concentrations from lysimeter collections in the reference, low (NH4)2804 and high (NH4)2504 plots at WL, PHC, H F and PF. Means are from samples from January 1991 through November 1992 with the number of samples given in Table 4. Variation in the number of samples among treatments, sites and depth was due to differences in the collection efficiency of individual lysimeters at different depths and soil moisture regimes. Treatment effects were determined for each site using statistical analysis similar to that used for precipitation and throughfall. For reference plots at H F the concentrations of SO 2- and N O ; in soil solution at depths of 15 and 50 cm were similar to those reported previously (E horizon, 13 cm depth, 99/teq 1- ~ and 39/teq 1- ~; B horizon, 63 cm depth, 136 #eq 1and 18 #eq l -a, respectively) by Mitchell et al. (1992b). For reference plots at PF the concentrations of S O l - in soil solution at 15 and 50 cm depth were higher than those reported previously, but NO~- concentrations were similar and very small (15 cm, 102 lteq l -~ and 0.7 #eq 1-~; 45 cm, 89/~eq 1-~ and 1.2/~eq 1-~, respectively; Shepard and Mitchell, 1991 ). These results suggest that installation effects which may cause elevated NO~- concentrations (Shepard et al.,

1990) had diminished during the intervening period between solution sampling and lysimeter installation in the spring of 1990. The SO42- concentrations in the reference plots of the three hardwood sites (WL, P H C and H F ) were relatively uniform at both 15 and 50 cm, but substantially lower than at the conifer site at PF. As predicted, the reference plots of the western sites, WL and PHC, had greater concentrations of N O ; at both 15 and 50 cm compared with H F and PF. For all sites except PF the ammonium sulfate treatment resulted in increased concentrations ofSO~- (Fig. 3 ) a n d N O ~ - (Fig. 4). These preliminary results do not clearly demonstrate that the western sites are more sensitive to increased loadings of nitrogen and sulfur as hypothesized. Solute fluxes are being calculated to refine this evaluation since the hydrological regimes differed during the 199 l 1992 period both between years as well as among the four sites. These hydrological determinations as well as an additional chemical treatment in 1993 should help clarify patterns of solute concentration and flux for the AMMP sites.

5.3. Modeling An example of model application in the AMMP is shown in Fig. 5. For the H F site the NuCM model was run for 10 years. Results of the simulations for the second and tenth year as well as actual measurements from the second year of treatment are presented. Comparisons were made of NuCM simulations at additions of 0, 1000 and 2000 eq ha-~ year-1 of ammonium sulfate above ambient addition levels versus measurements at the AMMP plots at H F for the 50 cm depth. For the reference plots the simulated SO~- and N O ; concentrations were higher than those measured. For both the low and high ammonium sulfate treatment plots, simulated values of N O ; and SO 2- concentrations were lower than those measured. The simulated concentrations for the tenth year increased and their relative values reflected the levels of SO 2- addition. In contrast, even after 10 years, N O ; concentrations did not increase and, moreover, showed a decrease. These simulations suggest

M.J. Mitchell et al. /Forest Ecology and Management 68 (1994) 87-100

that the model with its present formulations and parameters underestimated nitrification rates and resulting NOj- loss at HF. 5.4. Future directions

We are presently focusing model evaluation on the conceptualization and parameterization of those processes which regulate nitrogen fluxes since this element plays a central role in affecting overall biogeochemical cycles within the AMMP sites as well as explaining variation in surface water concentrations of NOj-. We anticipate that the concomitant utilization of experimental data from field manipulations in conjunction with the testing of the two biogeochemical simulation models will serve as a powerful tool in predicting how elemental cycling will be affected by altered loadings of nitrogen and sulfur in the Adirondack Mountains.

Acknowledgments The Adirondack Manipulation and Modeling Project (AMMP) is funded by the New York State Energy Research and Development Authority (NYSERDA), Empire State Electric Energy Research Corporation (ESEERCO) and National Council of the Paper Industry for Air and Stream Improvement, Inc. (NCASI). We also thank Todd Anthony, Bhesh Dhamala, Donald H. Bickelhaupt, Anthony Brach, Linda M. Galloway, Azharul Mazumder, Jeffrey S. Owen, Robert C. Santore, Andre Tanguay and Richard van Dreason for their assistance in this research.

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