Field Tests Show Strong Agreement Between EXO and 6-Series Time-Series Data in South Carolina Estuary

Continuous water quality monitoring platform in estuary

Continuous water quality monitoring platform in estuary

In March 2012, YSI (a Xylem brand) released its next-generation water quality sonde, the EXO2, which represents a number of advances in sensor and anti-fouling technology. To ensure that a transition to the EXO2 would not introduce discontinuities into long-term data sets established with existing YSI 6-Series sondes, a field comparison of the two sonde platforms was established at a system-wide monitoring program (SWMP) station within the North Inlet–Winyah Bay NERR.

Beginning in July 2012, an EXO2 sonde was deployed in a stand-pipe immediately adjacent to the stand-pipe housing the NI-WB NERR’s YSI 6600V2 sonde. The EXO2 was deployed for intervals of one month. Data from these deployments were compared to the 6600V2, deployed at a two-week interval, as well as a second 6600V2 maintained at one-month deployment intervals. Sonde performance, post-deployment QA/QC and biofouling were quantified for each sonde deployment.

The comparisons revealed a strong agreement between EXO2 and 6600V2 time-series data and suggest longer deployment intervals are possible with the EXO2, relative to the 6600V2.

In addition, the new FDOM sensor available on the EXO2 shows great promise for time-series monitoring of dissolved organic carbon dynamics in estuarine environments.

Side-by-side comparison of YSI water quality sondes in estuary

Side-by-side comparison of YSI water quality sondes in estuary

Since DOC is often the largest pool of fixed organic carbon in aquatic ecosystems, time-series measurements of FDOM allow the dynamic nature of this pool to be quantified at time-scales not previously possible with conventional grab-sampling techniques. This dynamic is illustrated in time-series data that spans a dry period of no rainfall followed by three successive rain events (as evidenced in the salinity data). During dry periods, the magnitude and variability in FDOM was driven by salt marsh export and its dilution with coastal waters, but during wet periods significant discharge from adjacent upland wetlands contributed substantially to FDOM concentrations and variability. In contrast, this wet-dry cycle had little effect on particulate matter dynamics (as evidenced by the turbidity data) or on chlorophyll concentrations (which decreased during wet periods as a result of enhanced flushing and reduced growth due to substantial light attenuation produced by high FDOM concentrations).

 

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