Current Research of Dr. Bruce R. Hargreaves (updated 11/30/07)

Environmental forcing of aquatic ecosystems is the exchange of energy and matter via sun, atmosphere, and earth. Aquatic ecosystems respond by changes in transparency, temperature, dissolved oxygen and nutrient concentrations, and in trophic processes of plants, animals, and microbes. My research and that of my students involves systems analysis using advanced instrumentation and models to reveal underlying processes and interactions in lake and coastal ecosystems.

One example is my bio-optics focus on seasonal changes in ultraviolet transparency of lakes (in collaboration with Robert Moeller, Don Morris, and Craig Williamson in the Poconos, and Bob Collier, Scott Girdner, and Mark Buktenica at Crater Lake, Oregon). I am investigating abiotic and biotic factors and processes ranging from weather,
solar radiation, ozone, photobleaching, hydrologic and biotic exchange of dissolved organic matter, evaporation, thermal stratification, and UV attenuation by living and nonliving particles.  Currently I am also developing instruments for automated water column profiling of  optical, chemical and physical properties in Collaboration with Dr. Mooi Choo Chuah (Lehigh University), improving my hydrologic water budget for L. Lacawac in collaboration with Dr. Laura Toran and Dr. Jon Nyquist (Temple University), and applying a hydrologic mixing model to L. Lacawac in collaboration with Dr. Sally McIntyre (Univ. California, Santa Barbara).  Both of these new projects with improve our ability to account for changes in UV transparency through the flux of chromophoric dissolved organic matter (CDOM) from the surrounding watershed and from deeper lake water and bottom sediments.

An outgrowth of my focus on water column optics is a group of projects on optics of phytoplankton.  I have developed a field/lab instrument for characterizing the spectral absorption of phytoplankton and other particles concentrated by passing water through a particle filter.  I have also been working with Turner Designs, Inc. to improve their new C6 multichannel profiling fluorometer to record fluorescence from phytoplankton pigments (chlorophyll a, phycocyanin, phycoerythrin), chromophoric dissolved organic matter (CDOM), along with turbidity and temperature.  Recent tests during summer 2007 in lakes in Pennsylvania (L. Lacawac), in Oregon (Crater L., Odell L., Paulina L., Waldo L.) and in California (L. Tahoe) were successful at characterizing different taxonomic and depth-specific patterns, including variations consistent with some phytoplankton using photoprotective pigments to shield them from the strong UV-B radiation near the surface.

Recent streams studies have focused on climate change and landscape properties influencing stream water quality in the Delaware River Basin.   Recently completed projects focused on light penetration through the stream riparian tree canopy (Chris Forstall, M.S. 2006),  Role of forest and agricultural landcover on headwater stream dynamics for dissolved organic carbon (Shannon Haight, M.S. 2007), and quantifying hourly to annual carbon flux from a temperature peatland (Tannersville Bog, Tannersville, PA, Andrea Luebbe, M.S. 2007).  An ongoing project in collaboration with Dr. Kristen Jellison and Ph.D. candidate Elizabeth Wolyniak is investigating the interactions of the protist parasite Cryptosporidium and environmental factors such as stream pH, DOC concentration, and biofilms.

Another project using the profiling fluorometer and particle absorption spectrophotometer began in October 2007.  This project is part of a joint mission by NASA and NOAA called GASEX-III to better characterize the biological and physical factors controlling carbon dioxide flux in the Southern Ocean under extreme weather conditions (high wind and waves).   My role is to compare my new instruments with others to establish the best ground truth calibration  of satellite data to estimate phytoplankton absorption near the ocean surface, and to use this to provide a means for estimating photosynthetic uptake of carbon dioxide.   Other ecologists/physiologists are studying photosynthesis and optical properties of phytoplankton and seawater while physical oceanographers are measuring the flux of carbon dioxide and a tracer gas between the surface water and atmosphere under conditions of high wind and waves.  Data will be collected during the field campaign during a six-week cruise on the R.V. Brown (late-February to early April 2008) between the Falkland Islands and the Antarctic peninsula.  Along with data analysis from the cruise my laboratory work will continue after to cruise to measure frozen samples brought back by my colleagues Bob Vaillancourt and Veronica Lance, working with Bob Marra (all at Lamont Doherty Earth Observatory, Columbia Univ.).  I will also complete the calibration of my new instrument and application of it to a wide range of phytoplankton samples (cultured in the lab and collected from natural systems) using several techniques.  A commercial sample holder (a sample is place in the center of an integrating sphere) will be added to my field/lab particle absorption spectrophotometer to complete the critical calibration process.

Supporting Facilities (to be updated soon)

Field resources at Lacawac Sanctuary include telemetry-linked monitors of solar UV, visible, and total radiation; wind, rain, and relative humidity; temperature of air and water; lake depth. Underwater instruments include optical profilers (Biospherical Instruments PUV-501's, Focal Technologies optical plankton counter, LI-COR submersible radiometer), Benthos remotely-operated vehicle with video, Trimble global position systems (GPS), and notebook computers for use with the instruments.

Laboratory resources include a number of networked computers (PC's, PowerPC Macs, UNIX workstations). Relational database management software provides access to environmental data on PC's and workstations (ARC/INFO Geographical Information System, GIS). Optical instruments include scanning spectrophotometer, optical zooplankton counter, video microscopy digitizing system, controlled environment chambers, equipment and technical support for developing or modifying environmental instruments.