Current Research of Dr. Bruce R. Hargreaves
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
ozone, photobleaching, hydrologic
and biotic exchange of dissolved organic matter, evaporation, thermal
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.