Continuing Acidification of Organic Soils Across and 2001: Fact or Fiction. Richard A. F. Warby (Ph.D.)

Transcription

1 Continuing Acidification of Organic Soils Across the Northeastern U.S. between 1984 and 2001: Fact or Fiction Richard A. F. Warby (Ph.D.)

2 Overall Approach Resample organic soils and surface waters in 2001 originally sampled as part of the DDRP in Using the same chemical analyses where possible, compare the 1984 and 2001 chemical data. Determine the chemical response of surface waters and organic soils over the study period following reduced inputs of acidic deposition.

3 Chemical Changes in Oa-Horizon Soils Specific Hypotheses: 1. CEC in Organic soils may have increased between 1984 and 2001; 2. Exchangeable base cations, Ca in particular, will have shown a greater increase than exchangeable acidity, resulting in increased base saturation; and 3. The ph of soils across the northeastern U.S. will have increased over the study period.

4 The DDRP The DDRP was started in 1984 under the National Acid Precipitation Assessment Program at the request of the Administrator of the U.S. Environmental Protection Agency (EPA) The central question that t the DDRP hoped to address was: How many surface waters would become acidic due to current or altered levels of acidic sulfur deposition, and on what time scales? However the central questions in this project focus on the However, the central questions in this project focus on the chemical responses of these ecosystems

5 The three DDRP Study Regions

6 DDRP Watershed Selection Criteria The DDRP watersheds were a subset of 768 watersheds studied during the Eastern Lakes Survey Phase I; Lakes with ANC less than 400 μeql -1 ; Lakes deeper than 1.5 m; Lakes with surface area greater than 4 ha; Culturally disturbed lakes were not sampled; and Lakes with a watershed area > 3000 ha were not sampled.

7 DDRP Watershed Selection Criteria The DDRP used a random stratified approach to select lakes. Using preliminary results from the ELS Phase I, lakes were divided into three strata based on ANC class. A random sample of 50 lakes was selected from each ANC class. Refusal of access and other factors ultimately reduced the total to 145 lake watersheds. The random stratified sampling approach allowed the lakes to be extrapolated to a population of 3666 lakes across the northeastern U.S.

8 DDRP Soil Sampling The DDRP identified about 600 soil mapping units on the 145 watersheds in the northeastern U.S.; The soils were grouped into 38 sampling classes based on how they might respond to acidic deposition; and In total, approximately 280 pedons and 1400 horizons were sampled by the DDRP.

9 DDRP Soil Sampling Scheme The DDRP used a three-part scheme for randomly selecting sites for each of the sampling classes: 1) they randomly selected a watershed in which the soil class of interest occurred; 2) they randomly selected a potential location in that watershed using soil maps and; 3) h d l l d di i i hi h 3) they randomly selected a direction in which to move if the field crew found that the sampling class did not occur within 5 m of the potential sampling site.

10 DDRP Soil Sampling Scheme Because of this site selection scheme, some watersheds were not sampled at all, while others were the site of multiple pits. In the Northeast region, the DDRP sampled all horizons thicker than 3 cm downtobedrockorto15m or 1.5 m, thesamples were cooled to 4 o C within 12h, and transported to laboratories for further analysis.

11 Approach to the 2001 Soils Study As outlined earlier, a total of 139 watersheds hd were sampled ldduring the summer of 2001 and In each watershed we dug a soil pit, chose a face which was cleaned, and each horizon was sampled. The samples were bagged and sent back to The samples were bagged and sent back to Syracuse University for analysis.

12 Unknown Pond in the Adirondacks

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16 Soil Profile at Unknown Pond in the Adirondacks

17 Data Screening Oa Horizons DDRP sampled horizons greater than 3-cm in thickness Watersheds in the SNE subregion typically did not have Oa horizons Omitted samples with total carbon < 16% Final data set: 1984 (DDRP): 75 Oa horizons from 47 watersheds 2001: 55 Oa horizons from 55 watersheds 3 Sub-regions: Adirondacks, Cat/Poc, CNE/Maine

18 Soil Sampling Sites

19 Why the Oa Horizon? The Oa horizon is not diagnostic of any particular soil type so we could make comparisons across soil types; Conditions across the northeastern U.S. allow for the development of Oa horizons, at most locations; The Oa horizon contains an important pool of exchangeable Calcium in forest soils in the Northeast; and The Oa horizon is the first to acidify and the first to recover following reductions in acidic deposition.

20 Soil Chemical Measurements Same as DDRP to the extent possible Soil ph (DI water and 0.01 M CaCl 2 ) Total C and N (combustion/gas chromatography) Exchange Acidity (1 M KCl) Exchangeable Ca, Mg, K, Na, Al (1 M NH 4 Cl) BC = Ca + Mg + Na + K (cmol c kg -1 ) CEC e = BC + EA Base Saturation

21 Data Analysis Non-Parametric Statistics Medians for central tendency Mann-Whitney U test Exchangeable Concentrations Normalized to Carbon Units: cmol c (kg C) -1

22 Region-Wide Results Significance Median Median Calcium, cmol c (kg C) P < 0.01 Aluminum, cmol -1 c (kg C) P< Acidity, cmol c (kg C) P < 0.01 CEC e, cmol c (kg C) None ph P < 0.05 Base Saturation, % P < 0.01

23 Region-Wide Results Cumulative Frequency Diagram for Ca N (cmol c/kgc) Cumulative Frequency Diagram for Exch. Acidity (cmol c/kgc) % Les Less than thab Ca Ca N N Acidity % Less than Exch Ca N (cmol c /kgc) Exchangeable Acidity (cmol c /kgc) Cumulative Frequency Diagram for ph s Cumulative Frequency Diagram for Al N (cmol c /kgc) H s % Less than ph N % Less than Al ph s Exchangeable Aluminum (cmol c /kgc)

24 Sub-Regional Results * Indicates P < 0.05 CEC C e (cmol c /kgc) Base Satura ation (%) * * * Sample Size (N): Region All ADR CATPOC 10 8 CNE/Maine Calcium (cmolc c /kg gc) Acid dity (cmolc c /kgc) Aluminum (c cmolc c /kgc) * * * * * * * * Whole Region ADR CATPOC CNE/Maine

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26 Acidification Most Profound in Watersheds with Moderate ANC Lakes ANC < 0 0 < ANC < 25 ANC > Number of Samples Base Saturation ** 36.24** CEC en Acidity N ** 38.02** Ca N ** 17.14** Al N ** 16.20** ph s ** 2.96** ** Indicates P < 0.01

27 Comparison of Changes in Ca and Al Concentrations (Neutral Salt Extractions) Adirondacks Study Horizon (n) Element Unit ~ % Change Warby (2001) Oa 28 Ca cmol c /kgc 35 Johnson (2008) Oa 36? Ca ~8 ~6.5 cmol c /kg (ODW) 15 Warby (2001) Oa 28 Al cmol c /kgc 60 Johnson (2008) O 24 Al cmol c /kg (ODW) 70 Alleghney Plateau Study Horizon (n) Element Unit ~ % Change Bailey 2005 Oa 4 Ca cmol c /kg 75 Bailey 2005 Oa 4 Al cmol c /kg 80

28 Overview Oa horizons in the northeastern USA experienced substantial decreases in exchangeable Ca, and increases in exchangeable Al between 1984 and These changes are consistent with other long-term monitoring i results in the region. Acidification of Oa horizon soils was most profound in the CNE/Maine sub-region, and in watersheds that supported moderate-anc lakes. The continuing acidification of Oa soils may help explain the sluggish recovery of ANC in regional surface waters.

29 Final Thoughts Understanding the extent, if any, of the acidification of mineral soils across the northeastern U.S. will provide valuable insight into the possible future recovery of both aquatic and terrestrial ecosystems. While Stoddard et al. (2000) believes that true recovery of soils may take centuries, I believe that some soils may never recover to pre-industrial revolution conditions.

30 Future Research Question Why do we continue to see chemical recovery of surface waters while soils continue to acidify? Does this phenomenon indicate that soil are more sensitive to acidic deposition than surface waters? Will the continuing acidification of soils result in the future decline in surface water quality? What land management and land use has the greatest impact on how these ecosystems respond to decreases in acidic deposition?

31 Questions?