ISSN:
1573-515X
Keywords:
aluminum
;
calcium
;
leaching
;
magnesium
;
potassium
;
soil
;
sulfur
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
Notes:
Abstract The effects of three S deposition scenarios — 50% reduction, no change, and 100% increase — on the cycles of N, P, S, K, Ca, and Mg in a mixed deciduous forest at Coweeta, North Carolina, were simulated using the Nutrient Cycling model (NuCM). The purpose of this exercise was to compare NuCM's output to observed soil and streamwater chemical changes and to explore NuCM's response to varying S deposition scenarios. Ecosystem S content and SO4 2− leaching were controlled almost entirely by soil SO4 2− adsorption in the simulations, which was in turn governed by the nature of the Langmuir isotherm set in the model. Both the simulations and the 20-year trends in streamwater SO4 2− concentration suggest that the ecosystem is slowly becoming S saturated. The streamwater data suggest S saturation is occurring at a slower rate than indicated by the simulations, perhaps because of underestimation of organic S retention in the model. Both the simulations and field data indicated substantial declines in exchangeable bases in A and BA soil horizons, primarily due to vegetation uptake. The correspondence of model output with field data in this case was a result of after-the-fact calibration (i.e. setting weathering rates to very low values) rather than prediction, however. Model output suggests that soil exchangeable cation pools change rapidly, undergoing annual cycles and multi-decade fluctuations. Varying S deposition had very little effect upon simulated vegetation growth, nutrient uptake, or N cycling. Varying S deposition strongly affected simulated Ca2+. Mg2+, K+, and P leaching but caused little change in soil exchangeable pools of Ca2+ K+, or P because soil exchangeable pools were large relative to fluxes. Soil exchangeable Mg2+ pools were reduced by high rates of S deposition but remained well above levels sufficient for tree growth. Although the total soil pools of exchangeable Ca2+ and K+ were only slightly affected by S deposition, there was a redistribution of Ca2+ and K+ from upper to lower horizons with increasing S deposition, causing increased base saturation in the deepest (BC) horizon. The 100% increased S deposition scenario caused increasing peaks in simulated Al3+ concentrations in A horizons after 25 years as a result of large seasonal pulses of SO4 2− and lowered base saturation. Simulated soil solution Al3+ concentrations remained well below toxicity thresholds for selected tree species at the site.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00023751
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