Date of Award

2003

Degree Name

Biological Sciences

College

College of Science

Type of Degree

M.S.

Document Type

Thesis

First Advisor

Frank S. Gilliam

Second Advisor

Dan K. Evans

Third Advisor

Jeff D. May

Abstract

Soil processes often exhibit spatial heterogeneity within ecosystems and this heterogeneity may influence community structure. This study was conducted to determine spatial patterns and variability of soil nutrients and plant communities within different vegetation types in a stream floodplain in southwestern West Virginia. One 5-m × 5-m site was established in each of three vegetation/drainage types: pasture (PA), old field (OF), and wetland scar (SC). Pasture and SC sites were located ~25 m apart on flat bottomland; the OF site was located on a moderate slope 6.3 m above bottomland, ~200 m from PA and SC. A 10-m × 1-m transect was also established perpendicular to the visible boundary between PA and SC drainage types, but not within the PA and SC sites. Each site was divided into 1-m2 plots (n = 25) and the transect was divided into 0.25-m2 plots (n = 40). For sites, mineral soil was taken to a 5-cm depth with a 2-cm diameter soil corer centrally from each 0.25-m2 quadrant of and combined into a single composite sample per plot (n = 25 per site). For transect, mineral soil was taken to ~5-cm depth using a hand trowel and samples for each plot were kept separate (n = 40). Soil organic matter was measured as loss-on-ignition. Extractable NH4+ and NO3- were determined before and after laboratory incubation (28 days at 27 C) to determine net N mineralization and nitrification. Cations were analyzed using inductively coupled plasma emission spectrometry. Vegetation was assessed using estimated percent cover (sites) and aboveground harvested biomass (transect). Mean organic matter was significantly higher (P <0.05) in SC than in OF and PA (10.6, 8.1, and 8.3%, respectively). Nitrification was nearly 100% of mineralization in all soils, and was significantly lower (P <0.05) in PA than in OF and SC (0.7, 1.6, and 1.8 µg NO3--N/g soil/d, respectively). Aluminum was significantly higher (P <0.05) in SC than in OF and PA (202.1, 4.8, and 0.5 µg Al3+/g soil, respectively). Calcium, magnesium, and pH were all significantly higher (P <0.05) in OF (1035.7 and 334.8 µg/g soil, and 4.6, respectively). Transect results were similar to PA and SC sites and an abrupt transition was found between PA and SC site types. Vegetation analysis revealed three distinct communities with SC dominated by wetland species, OF dominated by upland species, and PA dominated by a mixture with slightly more upland species. Transect vegetation also consisted of largely wetland species within wetland and a mixture in pasture, however Arthraxon hispidus dominated for ~1 m at the boundary. Spatial variability of organic matter was much lower than spatial variability of nitrification, which was higher in PA than in OF and SC. Thus, availability of organic substrates to N-processing microbes is less variable than N processing itself, underlining the complexity of biotic factors responsible for regulating soil N processes.

Subject

Spatial ecology

Subject

Nitrogen - Environmental aspects

Subject

Floodplain ecology

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