Overview
Phragmites growth in marsh watersheds due to increased salinity is a crucial issue worldwide. This study investigated salinity movement in the ungauged Mentor Marsh of Ohio, USA, where salinity had increased from a number of potential sources — causing a decline in native vegetation and increased invasive phragmites growth.
Model Setup
A detailed bathymetric survey was conducted and several monitoring stations were established to record hourly environmental data. Because Mentor Marsh has complex hydrologic characteristics and interacts with Lake Erie through a backwater effect, an Environmental Fluid Dynamics Code (EFDC+) model was developed to simulate the western marsh’s salinity distribution. The model was calibrated and validated using measured time-series water temperature, water level, and salinity data from December 2019 to March 2020, with good performance (calibration R² = 0.82; validation R² = 0.84).
Key Findings
The calibrated model was used to investigate salinity distributions under different inflow and lake level rise conditions. During high-flow conditions, advection of saline water from Marsh Creek was vigorous, pushing salinity toward Mentor Marsh. When lake level rise occurred, the model predicted a significant decrease in marsh salinity near Lake Erie — averaging −45.8% near the lake and −21.2% within Mentor Marsh — as the high lake level pushed Marsh Creek toward the marsh. The analysis suggests the phragmites growth in the western section is likely due to road salt used for winter deicing.