Monitoring ungauged watersheds for investigating the variability of flow and salinity to implement the possible removal of salt fill sites

Salinity is a crucial environmental problem leading to profound consequences in wetland plants and aquatic habitats including the rapid development of Phragmites australis in the marshland. These Phragmites australis are extremely vulnerable to capture fire, which might eventually affect the overall ecosystem of the marsh. However, in order to restore the marsh, a hydrologic investigation is needed, which is possible if a watershed is gauged, and long-term data are available. In this study, a systematic approach has been presented to conduct hydrologic modeling and salinity prediction in an ungauged watershed in order to implement the possible removal of salt fill sites. The stage and electrical conductivity were measured continuously, whereas stream cross sections and velocity of the streamflow were recorded intermittently in the Blackbrook Creek to develop a rating curve and generate continuous streamflow data. The watershed model Soil and Water Assessment Tool (SWAT) was calibrated and validated to a monthly scale with good model performance. In the next step, critical sources of salinity were identified from the two tributaries in order to implement the removal of salt fill sites for the possible reduction of salinity in the marsh. While salinity loading was approximately 10 times higher from Marsh Creek (65.63 tons to 2028.13 tons per month) compared with Blackbrook Creek (10.23 tons to 163.98 per month), the analysis suggested that salinity concentration was higher from Blackbrook Creek, which was particularly due to abandoned salt fill sites near the Creek. The salinity loadings were linearly correlated with streamflow on a monthly (R² = 0.81) scale, which was utilized to generate the salinity loadings that were diverted due to the rerouting of the Creek through the new location in order to avoid salt fill sites and reduce salinity in the Mentor Marsh. Our analysis suggested that approximately 74 kg/day salinity was being rerouted from the Marsh; however, the salt fill sites contribute salinity to the Marsh equivalent to 63 kg/day, which still needs to be removed. The research findings are expected to be helpful for monitoring small ungauged watersheds.