Monday, May 16, 2016

Light and sediment in the coastal ocean

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Our dive site F1, roughly 1km east of the Elwha River mouth, before (top; summer 2011) and during (bottom; summer 2013) dam removal
Included among the many things that the Elwha dam removal project is teaching us is how sediment can interact with the community of living things in the coastal environment. In particular we are interested in the role that turbidity, due to fine sediment held in suspension, played during the height of the dam removal period (2012-2014) in driving changes to the marine algae community in the Elwha nearshore. The video set above shows, for example, what we saw at many of our sites scattered around the delta - places that had coarse substrate suitable for algae to attach to...but suppressed algae growth during dam removal. The answers to these sorts of questions go beyond the Elwha in regards to their importance. Globally, humans are changing the movement of sediment from the land into the coastal oceans, ergo we may also be altering coastal ecology on a grand scale via this sediment mechanism.

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What turbidity can do to light - a video shot in May 2012 at the same site as the videos at the top of this post. Dark!

To get a better handle on the movement of fine sediment from the Elwha River into the coastal zone Andrea Ogston (from UW's Sediment Dynamics Lab) and I proposed a project to Washington Sea Grant, which was funded (full disclosure: since I work for WSG I am not funded by the project, but do act as a co-PI). The project continues the Sediment Dynamics Group's long history of work in the Elwha nearshore tracking fine sediment dispersal, but builds on that by adding in to the mix better measurements of light in the shallow coastal area around the Elwha River mouth, and partnerships with the coastal ecologists working on the project (like Helen Berry and team from the Department of Natural Resources, and Steve Rubin, Melissa Foley and Nancy Elder from the US Geological Survey).


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Emily Eidam from the UW's sediment dynamics group collects a sediment sample from the sea floor with a Shipek sampler.

Last week was the first in a series of cruises on the UW's R/V Clifford A Barnes in order to collect bottom samples (i.e. see the video above), sample the water column for turbidity and other parameters, and also deploy a series of moorings specifically designed to measure sea-floor light:


Emily with a custom made mount and light measurement cluster


Looking down at the light measurement cluster - three HOBO light intensity sensors, and two Odyssey PAR sensors (provide by Washington Department of Natural Resources) 

A few more photos from the cruise are below:

A juvenile bivalve (probably Clinocardium?) in fresh mud deposits


Sediment samples!  Ready to go...


The spacious lab on the Barnes


UW undergraduate Morgan Mackay hauling the CTD.  Bachelor Rock is in the background


Barnes, side view


Cruise plan and station map