HR: 11:05h
AN: H51F-04    [PDF]
TI: Runoff nutrient and suspended sediment fluxes, cycling, and management in southern Kaneohe Bay, Hawaii
AU: * Ringuet, S
EM: ringuet@soest.hawaii.edu
AF: Department of Oceanography, 1000 Pope Road University of Hawaii, Honolulu, HI 96822
AU: Young, C W
EM: cwyoung@soest.hawaii.edu
AF: Department of Oceanography, 1000 Pope Road University of Hawaii, Honolulu, HI 96822
AU: Hoover, D J
EM: dhoover@soest.hawaii.edu
AF: Department of Oceanography, 1000 Pope Road University of Hawaii, Honolulu, HI 96822
AU: De Carlo, E H
EM: edecarlo@soest.hawaii.edu
AF: Department of Oceanography, 1000 Pope Road University of Hawaii, Honolulu, HI 96822
AU: Mackenzie, F T
EM: fredm@soest.hawaii.edu
AF: Department of Oceanography, 1000 Pope Road University of Hawaii, Honolulu, HI 96822
AB: Urban runoff and its impact on water quality in Hawaii, especially after heavy rainfall, is highly dynamic. In the past, water quality was determined through "grab samples" that were merely snapshots in time of an ever-changing environment. In contrast, continuous measurements of water quality can capture data that reflect the effects of significant storm runoff events unobtainable using even frequent manual sampling. Continuous multiparameter monitoring facilitates investigation of the both the magnitude and persistence of impacts of storm runoff on coastal waters, which can eventually be related to the health of coral reef ecosystems. Taking advantage of recent technological developments in oceanographic instrumentation, our study assembled an instrument package dubbed Coral Reef Instrumented Monitoring Platform (CRIMP). CRIMP was designed to include probes that measure physical and biological parameters (temperature, salinity, pH, dissolved oxygen, turbidity, and chlorophyll-a), nutrient analyzers (nitrate and phosphate), and a particle analyzer based on laser in-situ scattering and transmissometry. Various components of the CRIMP were previously used in conjunction with grab samples with the objective of elucidating the water quality of southern Kaneohe Bay and its relationship to physical, biological, and chemical processes operating in the bay, and to coral reef ecosystems. All instruments are now being combined on the CRIMP, and will allow us to study in near real time changes in fluvial inputs to the bay during storm runoff conditions and their impact on bay water quality and the coral reef ecosystem. In this presentation we discuss effects of freshwater delivery on adjacent coastal waters during high rainfall episodes (May 2002 and Feb 2003) that result in large runoff events and increased nutrient loading to coastal waters. Dissolved inorganic nitrogen to phosphorus ratios (DIN:DIP) in the Bay normally range from 2 to 4, suggesting a nitrogen-limitation that has been confirmed by nutrient-enrichment experiments. Elevated DIN:DIP values for storm runoff (25) change significantly the proportion of dissolved nutrients available for biological uptake. Significant increases in Chl-a concentrations in the bay a few days after storms suggest that phytoplankton growth was stimulated by the excess nutrients. The extremely low phosphate levels combined with the very high DIN:DIP values in Bay waters imply that phosphorus was the ultimate limiting-nutrient. Therefore, stream runoff has the potential of shifting the "normal" nitrogen-limited environment into a phosphorus-limited ecosystem. This shift has consequences for the management of fluvial nutrient inputs to Kaneohe Bay.
DE: 1803 Anthropogenic effects
DE: 1860 Runoff and streamflow
DE: 4825 Geochemistry
DE: 4845 Nutrients and nutrient cycling
DE: 4894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting