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Long-time Water Quality Monitoring for the Neuse River Estuary

Parameters: Chlorophyll

The Center for Applied Aquatic Ecology (CAAE) is part of the Botany Department of North Carolina State University and is dedicated to research involving aquatic botany, ecology and water quality. One of the Center's key water quality research projects is the long-term water quality monitoring and modeling of the mesohaline Neuse River Estuary. The Neuse River is a highly eutrophied system in eastern North Carolina and was listed as one of the 20 most threatened rivers in the nation in from 1995 - 1997. Sections of the river are currently classified by the USEPA as "nutrient sensitive". The monitoring has been conducted since 1994 and includes 20 stations, seven of which are permanent solar powered platforms (see photo) that house a sonde sensor bundle from Hydrolab, a Turner Designs corporate partner. These stations provide continuous measurement and vertical profiling of temperature, dissolved oxygen, redox, salinity, and turbidity. The CAAE has recently purchased a Turner Designs, Self Contained Underwater Fluorescence Apparatus (SCUFA®) for in-vivo chlorophyll-a measurement in the field. The system allows for quick calibration with a very stable solid form standard. The Center's field crews are currently performing SCUFA® casts at key stations as part of routine sampling. The data values and trends will be compared to chlorophyll data from extracted chlorophyll-a measurements of water samples collected in parallel with the SCUFA measurements. Deployment of the SCUFA® on a platform is planned to enable continuous vertical profiling of chlorophyll, which will also provide an opportunity to evaluate the unit's antifouling system. The resulting data will be available in the near future via the website link referenced above.

Discrete water samples are also collected from all stations for analysis in the CAAE analytical chemistry lab. Samples are routinely collected for nutrients, solids, BOD, and extracted pigment (chla) analysis. A Turner Designs 10-AU Fluorometer is employed for routine analysis of chlorophyll extracts and has proven to be highly stable and versatile for over seven years of use in our laboratory. USEPA method 445.0 (acidification - optical kit 10-037) has been the method historically employed within the laboratory and recent side-by-side studies have shown good agreement with the Welschmeyer method (optical kit 10-040). The Welschmeyer method produced results approximately 5% higher on average. Algae and therefore chlorophyll will tend to demonstrate significant spatial heterogeneity in the environment, more so than the other analytical parameters/indicators we measure. This trait makes it advisable to collect and filter of a significant sample volume (200 -500 ml). A large sample volume from a eutrophied system, such as the Neuse River produces high levels of analyte. We extract the sample into 14 mls. of 90% acetone, instead of the standard 10 mls. in order to lower the extract concentration, however, the pre-acidification measurements in particular are still high enough to warrant calibration at high levels. The wide dynamic range of the instrument allows us to achieve high linearity at high levels over a large range with low residuals. Calibration in the high range with a span of approximately 20% and removal of the reference filter enables these high yet accurate measurements, which minimizes the number of samples requiring error vulnerable dilution. The table and graph below includes the data from a recent calibration. The calibration standard used was diluted from a spinach extract stock prepared in 90% acetone, which was purity adjusted via spectrophotometric measurement.

Institution:The Center for Applied Aquatic Ecology (CAAE), North Carolina, USA

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