Addressing the fouling of in situ ultraviolet-visual spectrometers used to continuously monitor water quality in brackish tidal marsh waters.

The introduction of portable in situ ultraviolet-visual spectrometers has made possible the collection of water quality parameters at a high frequency in dynamic systems such as tidal marshes. The usefulness of this technology is inhibited by fouling of the instrument's optics. In this study, a spectrometer fitted with manufacturer-recommended compressed air optical cleaning was installed in a brackish marsh to determine if fouling interfered with measurements between bi-weekly servicing. During a 2-wk period, the absorbance measured in air at 220 nm increased from 9 to 549 m, indicating major fouling. An antifouling system was developed that reduced the time of exposure of the optics to stream water and used a pressurized fresh water cleaning. After implementation of the system, the absorbance in air increased to at most 63 m after 2 wk of data collection. The dramatic reduction in fouling will allow quality long-term data to be collected using this technology.