Can we use optical sensors in highly turbid agricultural streams?

University essay from SLU/Dept. of Soil and Environment

Abstract: Optical sensors are advanced technology capable of monitoring water quality con-tinuously at high temporal resolution. Optical sensors are prone to errors when deployed in streams with high sediment content. Agricultural streams, with high and variable suspended sediment loads, can affect the performance of these instru-ments. This work aims to evaluate the capability of optical sensor measurements in highly turbid streams. The study was performed in an agricultural catchment with clay soils and high concentrations of phosphorus and sediments in stream, located in Långtora, Sweden. Sensor calibration and correction for temperature quenching effects were performed. Water samples were collected with an autosampler to be analyzed in a laboratory and the results were compared with the sensor measure-ments. Tryptophan-like fluorescence (TLF), chromophoric dissolved organic matter (CDOM), and turbidity were measured by the sensor. The results showed a strong similarity between laboratory and sensor results for TLF and turbidity. CDOM concentrations were similar apart from a linear trend present in the laboratory measurements but not sensor measurements. Additional data regarding sediment composition is presented to better understand dynamics of suspended and organic material in the stream.

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