[Coral-List] New publication: Flood sedimentation in coral reef areas

[Mike Field]

Coral Listers,

A new paper by Amy Draut et al  titled "Supply and dispersal of flood 
sediment from a steep, tropical watershed: Hanalei Bay, Kaua'i, 
Hawai'i, USA" has just been published in the Geological Society of 
America Bulletin ( March 2009, v. 121, no. 3-4, p. 574-585).

This is a journal that many of you interested in this topic may not 
see, so I've taken the liberty of attaching the abstract below. A pdf 
of the article can be obtained from Amy (adraut at usgs.gov).

Mike


ABSTRACT
In contrast to many small, mountainous watersheds in temperate 
coastal regions, where fluvial discharge and wave energy commonly 
coincide, deposition and reworking of tropical flood sediment can be 
seasonally decoupled, and this has important implications for 
coral-reef ecosystems. An understanding of the interaction between 
tropical flood sedimentation and wave climate is essential to 
identifying and mitigating effects of watershed changes on coral 
reefs as urbanization and climate change proceed. Sedimentary facies 
and isotopic properties of sediment in Hanalei Bay, on the island of 
Kaua'i, Hawai'i, USA, were used to assess deposition and reworking of 
flood deposits from the Hanalei River in a case study demonstrating 
the potential ecosystem effects of runoff from a steep, tropical 
watershed.

In Hanalei Bay, the youngest and thickest terrigenous sediment was 
consistently present near the river mouth and in a bathymetric 
depression that acted as at least a temporary sediment sink. During 
this 2 yr study, the largest flood events occurred in late winter and 
spring 2006; substantial terrestrial sediment delivered by those 
floods still remained in the bay as of June 2006 because oceanic 
conditions were not sufficiently energetic to transport all of the 
sediment offshore. Additional sediment was deposited in the bay by a 
summer 2006 flood that coincided with seasonal low wave energy. In 
most years, flood sediment accumulating in the bay and on its 
fringing reefs would be remobilized and advected out of the bay 
during winter, when the wave climate is energetic. Turbidity and 
sedimentation on corals resulting from late spring and summer floods 
during low wave energy could have a greater impact on coral-reef 
ecosystems than floods in other seasons, an effect that could be 
exacerbated if the incidence and sediment load of tropical summer 
floods increase due to urbanization and climate change.




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*********************************************************
Michael E. Field
US Geological Survey
Pacific Science Center
400 Natural Bridges Drive
Santa Cruz, CA 95060
(831) 427-4737;   FAX: (831) 427-4748

http://coralreefs.wr.usgs.gov