Measurement and modeling of the hydrology of cypress wetlands - pine uplands ecosystems in Florida flatwoods.

摘要

The goals for this dissertation were to document the hydrology of cypress wetlands-pine uplands ecosystems in north central Florida and develop a simulation model (FLATWOODS). Three cypress wetland/pine upland systems embedded in a flatwoods landscape were extensively instrumented and monitored. Annual average canopy interception rates on a monthly basis for cypress wetlands and pine uplands were 12% (8-40%) and 14% (6-43%) of rainfall, respectively. An quantitative index was presented to describe the high dynamics of wetland hydroperiod. Groundwater table fluctuations were classified into four categories. Shallow groundwater flow velocity was low ({dollar}<{dollar}10 cm/day) due to low hydraulic gradients ({dollar}<{dollar}1.0%), although the soil hydraulic conductivity was high (0.5-20 m/day). Groundwater flows followed the overall topographic gradients during the wet seasons, while during the spring transition season from wet to dry conditions, surface water tended to recharge the surrounding uplands for some distance. Surface runoff was generated only from saturated variable source areas (VSA) associated with cypress wetlands in winter. The VSA increased 8-32% in a single storm. Monthly water balances showed that rainfall and/or surface inflow were the major inputs to the wetland/upland ecosystems, while ET and surface outflow were the main outputs.; The existing COASTAL model with the following modifications was used to construct the FLATWOODS model: (1) algorithms for the calculation of initial soil moisture content in unsaturated zones were added; (2) algorithms for unsaturated water drainage from unsaturated zone to the surficial aquifer were modified; (3) evapotranspiration procedures were modified by adding plant leaf area index (LAI) and root components; (4) soil evaporation was set as a function of groundwater table depth and LAI; (5) smaller grid systems, dynamic aquifer parameters of hydraulic conductivity and specific yield were employed to account for the surface-groundwater interactions; and (6) surface flow routing procedures for each modeling unit were added. In addition, FLATWOODS was calibrated and verified with field data of ground water table and daily runoff from two different research sites.; Simulation by the FLATWOODS model showed that clear-cutting both pine uplands and wetlands had the greatest effect on groundwater table and runoff, especially during the first six years after treatment. Following the regrowth of young plantations, the hydrologic regime may recover to the pre-treatment conditions within about ten years. Partial harvesting of wetlands or uplands significantly reduced hydrologic impacts in pine flatwoods. Forest harvesting had the most pronounced effects on groundwater tables during dry periods.