A simple, dynamic, hydrological model of a mesotidal salt marsh
Citation:
Marois, D., Ted DeWitt, AND J. Stecher. A simple, dynamic, hydrological model of a mesotidal salt marsh. 2017 Coastal and Estuarine Research Federation Conference, Providence, RI, November 05 - 09, 2017.
Impact/Purpose:
This research was conducted to fulfill a need in the scientific modeling community for a simple way to simulate salt marsh hydrology so that other processes dependent on hydrology may be accurately modeled. We found that by using high-resolution water-level data, we could develop and calibrate a simple, low parameter model that can predict salt marsh inundation and inform other applicable marsh modeling efforts. This is relevant to protecting the environment because salt marshes provide important ecosystem services to their surrounding communities and environments. Models allow us to predict how these services may vary with environmental changes, which can provide insight into what we can expect to happen to them in various potential scenarios. This research informs SHC 2.61.3: Ecological Production Functions for Quantifying Final Ecosystem Goods and Services.
Description:
Salt marsh hydrology presents many difficulties from a modeling standpoint: the bi-directional flows of tidal waters, variable water densities due to mixing of fresh and salt water, significant influences from vegetation, and complex stream morphologies. Because of these difficulties, there is still much progress to be made in the development of a truly mechanistic model of salt marsh groundwater and surface-water hydrology. This in turn creates an obstacle for simulating other marsh processes, such as nutrient cycling, that rely heavily on hydrology as a biogeochemical control and as a mode of nutrient transport. As a solution, we have created a simplified, hourly time-step marsh hydrology model with few parameters in the dynamic modeling software Simile. The model predicts the response of marsh groundwater level to tides and precipitation as a function of elevation, soil characteristics, and distance from tidal channel. Calibration was performed with PEST automatic calibration software using observed data from 1m deep wells along a transect in Winant Slough, a 1.8-hectare salt marsh in Yaquina estuary (central Oregon coast) that experiences a mixed semidiurnal tidal cycle with a range of 2.5 m. The calibrated model adequately predicts daily flood durations when compared to observed well data (r2 = 0.89). Validation was conducted using well data from a separate transect in Winant Slough and from mesotidal marshes in Tillamook Bay, Oregon. Model outputs can predict how long an area of the marsh will be inundated given a precipitation event or high tide level. This enables scenarios of changing sea level, precipitation, and marsh surface accretion/erosion rates to be tested for their effects on surface and ground-water hydrology, which can inform further effects on vegetation, biogeochemistry, material transport, and habitat value.