Date of Award

1996

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

Jeffrey D. May

Fourth Advisor

Leonard J. Deutsch

Abstract

Soil nitrogen (N) dynamics have been shown to be quite sensitive to the soil hydrology. Creation of a mitigation freshwater wetland from an old field provided an opportunity to examine changes in N dynamics in terrestrial, aquatic (but formerly terrestrial), and transition (seasonally inundated) soils.

This thesis determined N availability using in situ incubations of soils taken from three distinct habitat conditions based on the degree of inundation following wetland creation: (1) old field (no inundation), (2) transition (seasonally inundated, initially beneath 10-20 cm of water), and (3) mitigation wetland (permanently inundated). Sample plots were located along five parallel transects with one plot of each transect located in each of these three site types for a total of 15 plots in the study. Mineral soil was incubated within polyethylene bags and buried in the ground for 28 d. Nitrogen dynamics were assessed by comparing preversus post-incubation values of extractable and. In addition, soils were analyzed for organic matter, texture (% sand, silt, and clay), and moisture content. Climatic information was observed on site on sample days and daily information was provided by the local National Weather Service office.

Soils in the old field and transition sites had similar textures; whereas, mitigation wetland soil was different with significantly higher clay and silt content and lower sand content. It was not clear whether this resulted from extended inundation or as an artifact of sampling these soils when waterlogged. Soil moisture content increased from old field to transition to mitigation wetland sites as was expected with increased levels and period of inundation. Influences on moisture content for the old field and transition soils appeared to differ. Old field soil seemed to respond to variations in precipitation in conjunction with other environmental factors, and transition soil responded to period of exposure. Soil organic matter was similar for all three site types.

Although sites were quite similar with respect to soil organic matter (the main source of N for these soils), sites differed substantially in the predominant form of available N, with dominating in the old field and late season transitional soils and dominating in the mitigation wetland and early season transition soils. Similar patterns of contrast were found for net N mineralization and nitrification. Nitrate pools decreased significantly in old field soils in May, likely related to plant uptake, and increased in September, possibly related to plant senescence. Inundated soil in April and May showed no change in pools, but instead showed substantial increases in pools. Over the length of the study mitigation wetland soil had fluctuating pools, but ended with an 87% increase in pool level, and the pool in the mitigation wetland experienced a huge increase (>200%). Seasonal draw-down of the water table exposed the transition area in June and by July N dynamics of the transition soils were similar to those of the old field sites. These results support earlier work showing that N dynamics of these alluvial soils change rapidly toward those of typical hydromorphic soils following inundation, but also demonstrate that this change is reversible.

Principal component analysis of each site type for applicable climatic, physical, and N data was used and provided a distinct separation of months. The pattern was similar for all three site types; however, some of the specific variables of influence differed. Old field sites were positively correlated to daily high temperature, average daily temperature, precipitations between samples and precipitation within 5d of sample, and negatively to precipitation within 48h of sample, extractable and extractable +. Transition sites positively correlated to daily high temperature, soil temperature, average temperature between samples, and precipitation within 5d of sample and negatively to precipitation within 48h of sample, extractable and extractable . Mitigation wetland sites correlated positively to daily high temperature, average daily temperature, precipitation between samples, and net N mineralization and negatively to net nitrification, extractable , extractable , and sample time (of day). The results of principal component analysis suggest these sites had trends in response to variations in temperature, precipitation, and soil N transformations.

Subject(s)

Soils – Nitrogen content – West Virginia.

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