The Mentor marsh was the first declared a National Natural Landmark in 1966 and became a nature preserve in 1971 in the State of Ohio. Despite being affected by salt pollution and other physical challenges, it still has a tremendous economic value, and will rise if it is restored. The Marsh was specifically dominated by catastrophic salt pollution due to the development of different human and industrial activities, especially between the late 1950’s and late 1970’s. The water salinity of the marsh varied from oligosaline (500 to 5,000) mg/L to hypersaline (above 40,000 mg/L) during that period. Salinity is a crucial environmental problem in the Mentor Marsh leading to profound consequences in wetland plants and aquatic habitats; including the rapid development of Phragmites australis in the downstream marshland. These Phragmites australis were very vulnerable to capture fire. While several studies were conducted in the past in the Mentor marsh, hydrologic investigation of the watershed has not been conducted yet, due to the lack of monitoring stations and long-term data records. Since the Mentor marsh watershed is a small ungaged watershed, and data is only being collected for a short duration, the prediction of flow with limited data invites certain degree of uncertainty. Therefore, monitoring stations were established in two small tributaries of Blackbrook Creek and Marsh Creek, for real time data recording of flow stage, water conductivity, water temperature, and atmospheric pressure in hourly mode using Levelogger and Barologger data logging devices. Similarly, the creek cross-section, water velocity and water stage were recorded intermittently with direct field observation to develop a rating curve and generate the continuous streamflow data. The hydrologic model, Soil and Water Assessment Tool (SWAT), was developed using climate data from National Climatic Data Center (NCDC) and Digital Elevation Model (DEM), land cover and soil data from the United States Department of Agriculture (USDA). The model was calibrated on the monthly scale with a Nash Sutcliffe Efficiency (NSE) of 0.86, the Root Mean Square Error (R2 ) of 0.87, and Percentage bias (PBIAS) of -2.9% using the observed data from Blackbrook monitoring station from the period of November 2016 to August 2017. Similarly, it was validated with NSE (0.78), R2 (0.87) and PBIAS (-13%), respectively, using the observed data records from the period of September 2017 to March 2018. The total monthly salinity loading from Blackbrook Creek was in the range of 10.23 ton to 163.98 ton, whereas it was in the range of 65.63 ton to 2028.13 ton in Marsh Creek. The median monthly salinity loading in Blackbrook Creek and Marsh Creek were 55 ton and 329 ton, respectively. The analysis showed that the Marsh creek had higher salinity loading than that of Blackbrook creek during direct field bservation. This was mainly because of the relatively large size of Marsh Creek catchment compared to Blackbrook Creek. However, the salinity concentration was higher in Blackbrook Creek compared to the Marsh Creek except in the month of winter and early spring seasons. The salinity loading was linearly correlated with streamflow in daily (R2 = 0.72) and monthly scale (R2= 0.83) in Blackbrook Creek. Similarly, the daily and monthly R2 of streamflow with salinity in Marsh Creek was 0.86 and 0.76, respectively. Furthermore, the correlation of salinity loadings with simulated streamflow from the SWAT model was utilized to generate the salinity loadings in streamflow events of various years at historical period. The monthly simulated salinity loading in Blackbrook and Marsh Creek in the historical period (2000-2016) illustrated that Marsh Creek contributed more than 10 times higher
salinity loading than that of Blackbrook Creek. Similarly, the results showed that Blackbrook and Marsh Creek had higher median salinity loading in spring season. The salinity loading simultaneously decreased in summer and fall in both creeks and vice versa in winter season, most likely due to road salt application. The result also showed that wet years such as 2008 and 2011, experienced higher salinity loading in both creeks. Likewise, the analysis showed that annual median salinity loading in a historical period of 2000 to 2016 from Blackbrook and Marsh Creek were 620 ton and 8334 ton salt load respectively, which contributed to downstream marsh.