Soil Development in Created Salt Marshes; Its Spatial Patterns and Implication for Subsurface Water Flow

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Title: Soil Development in Created Salt Marshes; Its Spatial Patterns and Implication for Subsurface Water Flow
Author: Freese, Robert Carl
Advisors: Stephen W. Broome, Committee Chair
Aziz Amoozegar, Committee Member
Theodore Shear, Committee Member
Michael J. Vepraskas, Committee Member
Abstract: We examined soil development trends in a 28-year chronosequence of created salt marshes. Our objective was to determine whether created marshes reach ecological equivalence with natural marshes. Therefore, we studied soil properties that are likely indicators for ecological function. Marsh age is a good predictor of soil carbon and nitrogen levels, bulk density, macro-organic matter dry weight and nitrogen content of the 0 to 10 cm soil depth. Levels equivalent to the average natural marsh are predicted to occur within 22 years. Soil textural changes occur more slowly and are less closely predicted by marsh age. The 10 to 30 cm soil depth of created marshes does not change much with time and does not become equivalent to natural marshes within the time frame of this study. We examined spatial patterns by comparing soil properties 1 m inland from the marsh edge with soil properties 15 m inland. There were no significant differences in the 4-year old marsh but the 11- and 29-year old marshes had higher levels of soil carbon and nitrogen, silt, clay, porosity at the 1 m position than at the 15 m position. Geomorphologic characteristics of created marshes appear to account for this trend. The 29-year old marsh has a gradient in soil morphology and classification from a weakly developed Typic Psammaquent soil 30 m from marsh edge to a Mollic Psammaquent at 15 m to a Mollic Endoaquent at 1 m. Reshaping created marshes to more closely resemble natural marshes would likely enhance soil development and ecological function of the inland part of these marshes. Water tables and hydraulic properties of created marshes were studied to determine if there was greater flushing of nutrients from the soils of created marshes relative to natural marshes. The amplitude of a tidal cycle relative to marsh elevation affects the hydraulic gradients and soil water flux across the marsh. Water tables in salt marshes contiguous with upland areas have higher flux than in marshes without associated uplands due to fresh water recharge. At low tensions, a larger volume of water is released from the soil of a natural marsh relative to a 4-year old created marsh. The highest levels of discharge and nutrient export occurred from the edge of the natural marsh.
Date: 2003-01-09
Degree: PhD
Discipline: Soil Science

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