HR: 1340h
AN: OS13A-0515    [Abstracts]
TI: Combined Use of a Coral Reef Instrumented Platform (CRIMP) to Characterize Temporally the Biogeochemical Response of Kaneohe Bay, Hawaii to Storm Runoff Input
AU: * De Carlo, E H
EM: edecarlo@soest.hawaii.edu
AF: Department of Oceanography, University of Hawaii 1000 Pope Road, Honolulu, HI 96822
AU: Young, C W
AF: Department of Oceanography, University of Hawaii 1000 Pope Road, Honolulu, HI 96822
AU: Hoover, D J
AF: Department of Oceanography, University of Hawaii 1000 Pope Road, Honolulu, HI 96822
AU: Ringuet, S
AF: Department of Oceanography, University of Hawaii 1000 Pope Road, Honolulu, HI 96822
AU: Fagan, K
AF: Department of Oceanography, University of Hawaii 1000 Pope Road, Honolulu, HI 96822
AU: Mackenzie, F T
AF: Department of Oceanography, University of Hawaii 1000 Pope Road, Honolulu, HI 96822
AB: Pulsed inputs to coastal waters in Hawaii from storm runoff rapidly affect water quality, especially in semi enclosed coastal embayments. Traditionally the response of coastal waters to such inputs was evaluated through synoptic (low frequency) sampling that only provides snapshots of the evolution of these highly dynamic environments. In contrast, continuous in-situ measurements can potentially yield data that reflect the short-term biogeochemical response that cannot be captured through manual sampling. Data acquired by instrumented platforms facilitate the characterization of impacts of storm runoff on coastal waters and can be used to evaluate the overall ecosystem response over extended periods of time. We have deployed successfully a multi-instrument Coral Reef Instrumented Monitoring Platform (CRIMP) under conditions ranging from calm to windy dry periods through extreme rain events. Our CRIMP measures physical and biogeochemical parameters (temperature, salinity, pH, dissolved oxygen, turbidity, and chl-a, nutrients, and suspended particle distributions). Use of CRIMP in conjunction with synoptic water sampling has enabled spatial characterization of the response of Kaneohe Bay to storm inputs, the elucidation of relationships between physical, biological, and chemical processes in the bay, and the evolution of the community structure during phytoplankton blooms. In this presentation we discuss high rainfall episodes in the winter 2003-2004 that resulted in large runoff events and increased nutrient loading to coastal waters. DIN:DIP ratios in Kaneohe Bay normally range from 2 to 4, suggesting a nitrogen-limitation that has been confirmed by nutrient-enrichment experiments. Elevated DIN:DIP (25) in storm runoff changes significantly the proportion of dissolved nutrients available for biological uptake. Increases in Chl-a in the bay shortly after storms and changes in the plankton community structure reflect an evolving biological response stimulated by the inputs of excess nutrients. Extremely low phosphate levels combined with the very high DIN:DIP values in Bay waters immediately after storms imply that phosphorus becomes the ultimate limiting-nutrient. Therefore, stream runoff shifts the "normal" N-limitation to a P-limitation as the Bay is flooded with high N:P river and groundwater discharge. This shift has consequences for the management of fluvial nutrient inputs to Kaneohe Bay. A rise and persistence of elevated NH3 concentrations (10-15 æM) in the water column for several months after a rain event may also sustain longer-term bay productivity. Enhancements in primary productivity during storms also lead to drawdown of dissolved CO2 changing bay waters from a net source of CO2 to near or below atmospheric levels.
DE: 4805 Biogeochemical cycles (1615)
DE: 4815 Ecosystems, structure and dynamics
DE: 4863 Sedimentation
DE: 4219 Continental shelf processes
DE: 4235 Estuarine processes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting