Cost-Effective Approach for Continuous Major Ion and Nutrient Concentration Estimation in a River

Major ion and nutrient concentration monitoring and estimation are important factors in management and interpretations on river health, particularly in the context of total maximum daily load limits. Spatial and temporal (daily, seasonally, yearly, etc.) variations commonly complicate investigations and can produce unrepresentative results, particularly in systems with large seasonal or daily variation in river parameters or concentrations as a result of physical loading or biogeochemical activity (e.g., photosynthesis and respiration). This study combines an observed relationship between electrical conductivity and major ions, including nitrate, and continuous colorimetric estimation of ammonium and phosphate to permit cost-effective real-time estimation of river concentrations for major ions and nutrients for surface water quality monitoring. Data collected from sites both up- and downstream of a major city were used to evaluate the method. Constant total dissolved solids (TDS) to electrical conductivity (EC) relationships were observed at both the upgradient (TDS = 696EC; r2 = 0.93) and downgradient (TDS = 684EC; r2 = 0.90) sites. The resulting predicted estimations of major ion and nutrient concentrations for each site had average errors of less than 5%. Combining this method with a modified continuous colorimetric method for ammonia and phosphate allows for the continuous estimation of major ion and nutrient concentrations in a river system.