Hydrologic and soil conditions across hydrogeomorphic settings

Abstract

Though it is well accepted that hydrology, soil temperature, and soil reducing conditions are critical controlling factors in determining growing season and wetland status, inadequate data exist on regional scales. Even less is known about the temporal and spatial variability in these controlling factors in different landscape positions and hydric regimes. Hence, there is a need to develop more appropriate and reliable scientific-based data on wetland hydrology, soil temperature, and soil redox potential within specific regions. In addition, relationships between long-term measurements of these controlling factors and indicators of their presence or absence need to be established. Consequently, a study was undertaken to determine the correspondence between wetland hydrology, soil temperature, and soil redox potential, and ultimately, the expression of these factors in the form of field indicators. |The goal of the study was to identify the variation in hydrologic and soil conditions across hydrogeomorphic gradients in the southern Piedmont physiographic province, USA. Research objectives were to identify predominant subclasses of riverine systems, determine the correspondence between hydrology, soil temperature, and soil redox potential within the subclasses, establish relationships between measured parameters and indicators of federal wetland jurisdiction, and propose additional research needs. |The study was conducted at two different scales: regional and intensive. The regional study consisted primarily of identifying subclasses of Piedmont riverine wetlands, indicators of federal wetland jurisdiction, and comprehensive vegetational surveys. Relationships were developed between soil properties and hydrologic indicators as compared to vegetative response. The intensive survey was initiated based on the findings of the regional study and included automated instrumentation designed to measure water table, air and soil temperature, and soil redox potential. |Based on hydrogeomorphic settings, water source and transport, hydrodynamics, particle size distribution, and mineralogy, four subclasses of Piedmont riverine systems were identified: overbank, depression, fine seep, and coarse seep. Excellent correspondence between hydrophytic vegetation and redoximorphic features such as masses, pore linings, chroma of 2 or less, and concretions was observed. However, the correspondence between hydrophytic vegetation and hydrologic indicators such as water-stained leaves, drift, and deposition was fair. |A regional dimensionless rating curve specific to the Piedmont was found to be useful in determining flood frequency and discharge onto adjacent riverine wetlands. Flood frequency and discharge were observed to be dependent on channel capacity and geomorphology. |Mean, minimum, and maximum soil temperature at all depths could be estimated annually and during any season from mean air temperature by simple linear regression. A lower air temperature was required to reduce the soil temperature at the overbank and forested seep to non-growing season conditions as compared to the depression and emergent seep. |In general, soil redox potential was observed to be negatively related to air temperature and positively related to increases in water table elevation. Water table was lower and soil redox potential was higher at the overbank as compared to the other subclasses. Optimal soil temperature in combination with adequate water table which occurred in the spring in the depression resulted in the lowest redox potential observed in the subclasses during the study.