CONTRASTING STREAM WATER NO 3 - AND CA 2+ IN TWO NEARLY ADJACENT CATCHMENTS: THE ROLE OF SOIL CA AND FOREST VEGETATION

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1 CONTRASTING STREAM WATER NO 3 - AND CA 2+ IN TWO NEARLY ADJACENT CATCHMENTS: THE ROLE OF SOIL CA AND FOREST VEGETATION By: Sheila F Christopher et al. Presented by: Hannah Scholes

2 Outline Introduction Methods Results and Discussion Factors controlling variability Conceptual model Negative feedback loop in acidification Conclusions

3 Intro High NO 3 - concentrations in stream water could be associated with high deposition, but alternate trends were observed in different watersheds such as in WV and NH

4 Factors affecting stream water NO 3 - Factors affecting atmospheric and geological sources of N Mineralization and nitrification of N influenced by soil C:N ratios and tree species composition Hydrological transport of N Climate variables and land use history

5 Site Location Nitrogen deposition in the Adirondacks ranges from 0.7 to 1.1 kmol*ha -1 *yr -1, making Adirondacks particularly sensitive to acidic deposition In the Archer Creek Catchment, atmospherically deposited N exceeded the amount lost in the water S14 had greater NO 3 -, Ca 2+, and ph than S15

6 Objective To determine the underlying mechanism regulating the N cycling in the two subcatchments Evaluated- Differences in tree species composition and soil chemistry Atmospheric deposition, hydrology, storage and land use Overall surface water-solute relationships

7 Methods Geology: glacial till Stream stage height monitored at 20 intervals Atmospheric deposition measured 2.5 km away- wet: NADP, dry: CASNET Dry adjusted for coniferous vs deciduous tree composition Mineral soil analyzed at two sites in each subcatchment (eastern and western side of stream, 3 samples per layer (Bs and C)) for Ca, Mg, Na, K and Al on ICP-AES

8 Soil (Oe and Oa horizons) sampled on 3 dates: 10/29/02, 05/29/03, 07/28/03 at 17 and 13 plots in S14 and S15 Extracted with 2M KCl, filtered (2.5um) and analyzed for NH 4+, NO 3- with continuous flow colorimetry, and TDN by persulfate oxidation DON= TDN- dissolved inorganic nitrogen Analyzed by ICP-AES for exchangeable ions like mineral soil samples Vegetation sampled in each plot in 6 different transectsbasal area calculated by species and per unit catchment area Leaf litter traps (50x50x15cm) 3cm above ground level, 2mm mesh. Collected May-July and July-November. Total surface area= 0.012% and 0.013% in S14 and S15 respectively

9 Stream samples collected monthly with more intensive sampling during hydrologic events Analyzed within 2 weeks for Cl -, SO , and NO 3 by ion chromatograhy, Ca, Mg, K, and Na by ICP-AES, NH + 4 by continuous flow colorimetry, TDN by persulfate oxidation and ph with glass electrode potentiometry Organic acids contribution to charge also determined

10 Results S14 had 1% greater area of typographic index values between 9-11 (greatest chance of water table reaching ground surface) Overall results suggest similar hydrologic responses to precipitation No difference in atmospheric N deposition

11 Mineral Soil Ca 2+ and Mg 2+ concentrations much higher in S14 than S15 Al concentrations higher in S15 than S14

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13 Soil and Forest Floor extractable N S14 soil extractable NH 4 + greater than in S15 in fall and spring (more pronounced in spring) NH 4 + differences only in the forest floor NO 3 - higher in S14 in forest floor and mineral soil as well as in spring and summer TDN greater in S14 only in the spring

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15 Soil and forest floor cations Ca 2+, Mg 2+, K + concentrations all higher in S14 vs S15 in forest floor Ca 2+ was the dominant exchangeable cation in both subcatchments ph higher in S14 vs S15 in forest floor and mineral soil

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17 Vegetation Total basal area of S14 and S15 nearly identical S14 higher mean basal areas of sugar maple, American basswood, and eastern hophornbeam S15 had higher mean basal areas of American beech and eastern white pine. S14= 96% hardwood species; S15= 79% No difference in litter biomass (3587 kg/ha and 3241 kg/ha for S14 and S15 respectively)

18 Stream Chemistry Higher concentrations of cations in S15 except Ca 2+, which was twice as high in S14 NO 3 - and TDN 2-3 times higher in S14 Mean ph higher in S14 than S15 Stream charge imbalance attributed to HCO 3 -

19 Summary Tables

20 Factors controlling variability in Ca 2+ and NO 3 - in stream waters Physiographic characteristics can describe the temporal variability of stream chemistry Land use history can have effect on NO 3 - and C:N ratios long term Between the two catchments, land use history nearly identical Atmospheric deposition affects inputs Between the two catchments, deposition nearly identical regardless of different % deciduous

21 Factors controlling variability in Ca 2+ and NO 3 - in stream waters cont. Soil and Vegetation Can affect nutrient availability, litter Litter concentrations likely higher in Ca and N in S14 vs S15 Uptake only would describe 15% of NO 3 - leaching, mineralization would describe up to 44% Species like sugar maple associated with low C:N ratios, while American beach higher C:N ratios in litter Lower C:N ratios and higher rates of NO 3 - production (nitrification) = elevated NO 3 - leaching

22 Why base rich indicator tree species found with higher exchangeable base cations The vegetation can effect site characteristics The site controls the colonization of tree species Trees like eastern hemlock have high organic acid production causing acidic forest floor, hindering decomposition, and increasing base cation leaching Base rich tree species have soils with low lignin:n ratios and high soil Ca 2+ - and NO 3 and higher soil ph Therefore, difference between Ca 2+ - and NO 3 explained by difference in vegetation and soil characteristics

23 Summary Conceptual Model Mobilization of NO 3 - and Ca 2+ is governed by the quality of the parent material and litter Parent material rich in Ca 2+ results in calciumphilic vegetation, which produce low C:N soils, promoting mineralization, nitrification, and leaching of NO 3 - and Ca 2+ Colonization of trees like American beech could cause a negative feedback loop in the acidification process

24 Conclusions The differences between Ca 2+ and NO 3 - concentrations in the subcatchments explained by tree species and soil properties Higher Ca 2+ concentrations in S14 explained by greater amount of sugar maples, and soil under these trees with higher nitrification, thus increasing NO 3 - concentrations especially in spring/summer Need for determining effect of change in climate/soil chemistry/invasive species on nutrient cycling

25 Discussion Questions Did they sample enough? The study was conducted over the course of 1 year, with soil and water sampled with different frequencies. What could be an effect of a change in the N cycling caused by climate change/invasive species etc? Could there be another factor besides bicarbonate causing the discrepancy in the charge balance?