Turner Designs News, July 2005

Long-time Water Quaility Monitoring for the Neuse River Estuary (10AU & SCUFA)

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 website displays near real-time (2 hour update interval) data upload for these parameters from the Neuse River stations.

The CAAE has utilizes 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 (chlorophyll a) 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. US EPA 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 mL of 90% acetone, instead of the standard 10 mL. 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.

Contact Info

Mail:
620 Hutton Street Suite 104
Raleigh, NC 27606

Email:
aquatic_ecology@ncsu.edu

Nutrient Limitation Research in African Great Lakes using 10AU

Rebecca North is a doctoral student under the supervision of Dr. Stephanie Guildford and Dr. Ralph Smith at the University of Waterloo. She was awarded an International Development Research Centre (IDRC, Ottawa, Canada) doctoral research grant to continue her studies on nutrient limitation in African Great Lakes by visiting Lake Tanganyika and Lake Victoria in the fall of 2004. The goal of her thesis project is to understand the relationships between phosphorus (P), nitrogen (N), iron (Fe) and light in controlling algal biomass in temperate and tropical Great Lakes: Lake Erie, Lake Malawi, Lake Victoria and Lake Tanganyika.

Her research has identified which nutrients, P, N, or Fe, are limiting to the phytoplankton communities in the pelagic and littoral zones of the lakes. These issues are important as changing nutrient regimes can affect all freshwater systems and it is critical to understand which type of nutrient inputs can have the most impact. She investigated the nutrient status of the Lake Tanganyika phytoplankton and the role of iron in mediating nutrient uptake and interactions.

The Lake Tanganyika data will be incorporated into her Ph.D. thesis entitled “The influence of Fe bioavailability on the nutrient status of phytoplankton communities in temperate and tropical Great lakes” as well as in primary scientific journals. Her hypothesis is that the bioavailability of Fe affects N and P limitation of phytoplankton communities in Great Lakes. Lake Tanganyika is a N limited system where Fe appears to influence the availability and species of N and P utilized by the phytoplankton communities. Ammonium assimilation is the only means of meeting N demands of the phytoplankton communities that does not require Fe.

Using the 10-AU Field Fluorometer and employing a new sensitive fluorometric technique for the detection of low concentrations of ammonium [Holmes et al. 1999] has allowed her to measure the extremely low ammonium concentrations in Lake Tanganyika. Her research will build upon previous studies of Lake Tanganyika and its phytoplankton by Dr. Piet Verburg and Dr. Robert Hecky at the University of Waterloo [Verburg et al. 2003].

Verburg’s research published in 2003 has established that the nutrient regime of the lake may be changing due to a warming climate and this may be increasing the probability of iron limitation of algal growth. Her specific program for Lake Tanganyika was to measure a variety of nutrient status indicators for the nutrients N, P, and Fe and incorporate this data into a summary of the phytoplankton nutrient status of Lake Tanganyika. Her research will greatly expand on the understanding of phytoplankton-nutrient relationships on the lake to support ongoing efforts to manage the lake’s productivity and in particular, its valuable fishery.

References

Holmes, R. M., Aminot, A., Kerouel, R., Hooker, B. A., and Peterson, B. J. A simple and precise method for measuring ammonium in marine and freshwater ecosystems. Canadian Journal of Fisheries and Aquatic Sciences 56, 1801-1808. 1999.
Verburg, P., Hecky, R. E., and Kling, H. Ecological consequences of a century of warming in Lake Tanganyika. Science 301, 505-507. 2003.