Hydric soil field indicators in interdunal wetlands of the Great Bend Sand Plains

Abstract

Interdunal wetlands form in low-lying depressions between sand dunes and provide important ecosystem services, but challenges in identifying Field Indicators of Hydric Soils (FIHS) may limit their recognition in wetland delineation and conservation. This study evaluated FIHS expression across interdunal wetlands of the Great Bend Sand Plains (MLRA 79) in south central Kansas and applied the Hydric Soil Technical Standard (HSTS) to test whether these soils are currently functioning as hydric soils. A total of 34 interdunal wetlands at the Kramer (East and West) and Pfister sites were surveyed for FIHS during 2024, with soil profiles described to 30 cm and verified using automated U.S. Army Corps of Engineers datasheets. Nine wetlands were instrumented with shallow wells, IRIS films, and dipyridyl test strips to document hydrology, anaerobic conditions, and vegetation, while precipitation normality was assessed using the Direct Antecedent Rainfall Evaluation Method (DAREM). All 34 wetlands exhibited at least one FIHS, most commonly S5 Sandy Redox, S6 Stripped Matrix, and A11 Depleted Below Dark Surface, with F3 Depleted Matrix, F6 Redox Dark Surface, and F8 Redox Depression also frequent. The study, which began in 2024, coincided with regional drought in 2022-2025, Normal precipitation amounts were observed during the spring of 2026. Despite widespread FIHS, only East Kramer's three transects met all HSTS criteria for hydrology, anaerobic conditions, and vegetation in 2026. The West Kramer and Pfister sites did not meet the HSTS despite exhibiting FIHS. This suggests FIHS at West Kramer and Pfister largely reflect a legacy of wetter conditions rather than current hydric function, plausibly linked to groundwater decline. These findings indicate FIHS are well expressed and reliable for identifying interdunal wetlands, but wetland vegetation and hydrology should be carefully examined during wetland delineations.