In-situ long-term deployment of water quality sensors adversely affected by biological fouling

In-situ, long-term, water quality monitoring is necessary to determine natural ranges of environmental variables, evaluate environmental impacts resulting from coastal projects, and correlate changes in water quality as a function of coastal hydrodynamics. Existing methods for water quality monitoring are limited to short-term duration mainly due to biological fouling and/or limited life of system components. Optical instruments are the most susceptible to biological fouling. Long-term data are necessary to accurately determine natural conditions which include the impacts of seasonal variations, meteorological effects, and storm conditions. Long-term data may be compared with data collected throughout coastal operations to evaluate impacts resulting from the operations. A methodology for in-situ, long-term, water quality monitoring was developed based on the requirement that instrumentation be resistant to biological fouling. The design focused on instrumentation requiring optical sensors for measurement. A prototype sensor for in-situ, long-term turbidity measurement was developed implementing this methodology. Evaluation of the sensor was conducted through laboratory testing. This paper describes the methodology for in-situ long-term deployment of water quality sensors, and application of the methodology to the measurement of turbidity.