Greg Robie: thoughts on the Sears island causeway

 On Apr 3, 2024, at 1:27 PM, Greg Robie <robie@hvc.rr.com> wrote:

Hi Ron, 

I have been engaged in some preliminary deductions about the role of the causeway and the tidal flats marine health.

Inspired by your plane ride pictures, I started this bit of educated speculation using Google Earth and off shore Gulf Stream northerly flows, near shore Arctic surface return flows, the Saint Lawrence River influence regarding onshore bottom water upwelling, and Penobscot River as the primary freshwater input. I deduced that whatever I could conclude concerning the Islesboro geological feature could be applied at a magnitude or two less, to Sears Island/Wasumkik, and this prior to the causeway, and additionally to the addition of cobbles to the intertidal bar. 

My initial intuitively modeled current dynamics concerning Islesboro seem confirmed in this study:  https://halseyburgund.com/docs/hburgund_thesis95.pdf. Due to that features and east and west channels roles, I imagine the two order of magnitude less is applicable to Wasumkik for a reasoned starting point to sort out what the causeway changed relative to the marine health of the related tidal flats. This pair of current charts from 1978 and included in the report are representative:

<Screenshot 2024-04-03 at 11.02.35 AM.png>

The impact of a reduced twice daily flushing of leached toxins in the general area of Kidder and Mack Points, and particularly reduced Stockton Harbor tidal outflows – which would not be drawing waters from Long Cove – would be cumulative. Maine’s steamer clam, Mya arenaria, as syphon feeders would likely be initially impacted by the cumulative toxicity at its larva stage, and then additionally impacted by a reduced capacity of juvenile clams to reach sexual maturity. The cumulative toxicity could also impact both sperm and egg viability. 

Similarly, the tongue of salt water of the incoming tide in the Penobscot River channel lifts and spreads the fresh water of the Penobscot River inflow into the Bay. This elevated level of fresh water, when drawn across the intertidal bar north of Wasumkik as an eddy current, would affect the salinity of both Long Cove and Stockton Harbor. Salinity is integral to both fertilization success of Mya arenaria clams, as well as where larva select as settlement sites. 

Tipping points happen, and, regardless, happened. 

Figure 1.16 demonstrates a current dynamic that went from one that could draw water across the intertidal bar due to the eddying to the east of Sears Island, to one that was stopped by the construction of the causeway. The stoppage significantly affected the estuary marine health of both Long Cove and Stockton Harbor. A relative stagnant condition in both tidal estuaries was affected. Given a collapse of these estuary systems for Mya arenaria, a disruption of a little bit of transport of brackish water across the Wasumkik cobbled intertidal bar, was significant. Prior to the cobbling the flow would have been even greater, but arguable not as significant to the Mya arenaria. 

Further study that I would find both relevant and insightful would be soil core studies of the sedimentation that constitute both Wasumkik's intertidal bar and Cape Jellison’s isthmus.  Any common geological history might demonstrate parallel sedimentation. Such common sedimentation history would significantly differ only in the quantity of the material deposited as sedimentation. The earliest sedimentation on the isthmus might be absent in the area of the bar due to the bar feature evolving at a significantly later geological time after the formation of the isthmus shifted the flow of the Penobscot exclusively to the east of the geological feature that is integral to Cape Jellison.

=)