Soil and Soil Solution Chemistry in the Rooting Zone of a Southern Appalachian High Elevation Spruce Fir Forest Ecosystem

Nelson, Julia

High elevation spruce-fir forests in the eastern United States appear to have been in decline since the 1960's. The coincident occurrence of relatively high amounts of acidic deposition has been implicated as a causal agent in this decline. This research was conducted to characterize the soil and soil solution chemistry of the rooting zone of a high elevation spruce-fir ecosystem (Clingman's Dome, Great Smoky Mountains National Park, N.C. elev. 1800m) and to evaluate the role that acidic deposition may be having in the apparent red spruce decline. Soil solution samples following rainfall events were collected over the course of three years using microporous carbon polymer hollow fiber samplers. The mean umolar solution concentrations were Mg 10, Ca14, Al 26, H+ 142 (pH 3.94), N0341, S04 72, and total organic carbon (TOC) 1254. For 80% of the samples the ratio of total Ca/AI was <1 (60% for (Ca+Mg)/AI). Soil solution concentrations of H+, Al, and Cawere positively correlated indicating that solution concentrations are controlled in a consistent manner over time, however, the relationships vary from location to location within the research site. Soil samples from around the hollow fiber samplers were extracted with 1M NH4CI and 1M HCL NH4CI extractable Ca and Mg were positively correlated with soil %C. HO extractable Al, Mg, Fe, Si and TOC were negatively correlated with soil %C and positively correlated with particle density. Acid extractable Al was positively correlated with HQ extractable TOC. Soil organic matter (SOM) is concluded to be the major source of exchangeable Ca and Mg. HCI extractable Mg, Fe and Si may originate from mineral sources and HCI extractable Al appears to be associated with HCI extractable SOM. Soil solution Ca and Fe were related to NH4CI extractable Ca and Fe and solution H+ was related to soil %C. The slope of the soil solution H+ vs. Al relationship was negatively correlated to soil %C indicating that the equilibrium constants of the reactions controlling Al and H+ in solution are changing with variations in SOM. Columns of soil material from the rooting zone were subject to differing concentrations and input rates of artificial acidic deposition while at 10°C (50°F). The results indicate that the volume added and the concentration if the input solution can both be determining factors of soil solution concentrations. If the input rate is high enough (6 cm/7 days), soil solution concentrations approach input concentrations. If the precipitation rate is lower, nitrification appears to control solution concentrations. The soil solution concentrations in the high elevation spruce-fir ecosystems in the southeastern U.S. are dependant on the frequency and amount of precipitation, the concentration of ions in the precipitation and on the soil characteristics. Acidic deposition may exacerbate low Ca/AI ratios by increasing Al solution concentrations. Low solution concentrations of Mg and Ca, coupled with the prevalence of total Ca/AI and (Ca+Mg)/AI molar ratios less than one, may negatively impact root growth and function, and contribute to nutritional deficiencies of Ca and Mg in red spruce growing in this ecosystem.

Soil and Soil Solution Chemistry in the Rooting Zone of a Southern Appalachian High Elevation Spruce Fir Forest Ecosystem

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