Effects of Salinization Pathways upon Morphogenic and Geochemical Features of Coastal-Margin Vertisols, Aransas National Wildlife Refuge, Aransas County, Texas

Abstract

Coastal regions are predicted to experience changes in hydrology in response to climate-induced increases in sea-surface temperatures, sea-level rise, and shifts in weather patterns. These changes will likely alter pathways that marine salts enter coastal soils. This study aims to identify and quantify physical and geochemical changes in salt-affected vertisols and vertic intergrades forming on the Texas Gulf Coast. The characteristic morphogenic features of vertisols are formed as expandable clays experience seasonal fluctuations in moisture content within the profile, and smectite-group clays are more salt-sensitive than other clay types. This, coupled with their prevalence in low-lying coastal regions, makes the vertisol soil order useful for exploring how active pedogenic processes may respond to future climate scenarios. Soils were described and sampled along two transects in the Tatton Unit of Aransas National Wildlife Refuge from the coast of St. Charles Bay inland, including environments ranging from saline coastal prairie to saline-to-brackish tidal flats and tidal marshes. Macro- and micromorphological pedogenic features and geochemical patterns of major cations observed along each transect allowed for the interpretation of the relative influence of salinization pathways at the reserve based on distance from the coast and landscape position. Evidence of salinization due to underlying brackish groundwater was observed along both transects. In contrast, salinization due to surface inputs from marine sediment, tidal influence, and storm surge was more prevalent within the floodplain and at most coastal upland sites. Along both transects, slickensides and desiccation cracks appeared to be limited to the most well-drained upland sites, suggesting that a combination of increased saturation and salinization may be suppressing the formation of macroscopic vertic features.