The Herring Run

News and Information about the
HERRING RIVER RESTORATION
 November 2017

 
In this issue: reasons why trees are dying in the Lower Pole Dike Creek and mid-Herring River sub-basins, sustained low dissolved oxygen levels in Herring River, and a loss of marsh bird habitat.  The alarming trends demonstrate a loss of habitat health and productivity in Herring River.  

Now "A barren wasteland for marsh birds," restoration will vastly improve avian habitat

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WHAT'S WITH ALL THE DEAD TREES?
The Herring River estuary was stable, productive and a major asset to human residents for 2000 years, until the building of the Chequessett Neck Road dike disconnected the wetland from the Bay just 108 years ago.
 
An abundance of highly visible dying trees in the Lower Pole Dike Creek and mid-Herring River sub-basins is a good example of how a salt marsh that becomes isolated behind a dike results in vegetation changes that do not support a stable and productive ecosystem. 
 
The dead trees are mostly black cherry, an upland species that cannot tolerate water-saturated soils. The species has invaded the flood plain between Bound Brook Island and Pole Dike to the north, and High Toss Rd to the south.  The trees took root following diking and intense mosquito-control drainage activities that effectively de-watered the wetland.  
 
Around 1984, the Cape Cod Mosquito Control Project voluntarily stopped the drainage activities when National Park Service scientists had found that the drainage was causing the marsh to decompose and release acids into the surrounding soils and surface waters.  Decomposing marsh has also contributed to extremely low dissolved oxygen levels (see article below.)  The acidification and low dissolved oxygen have caused massive juvenile herring kills. 
 
There has been no further dredging of the river or its tributaries since then.  Over time, shoaling and plant growth in the river and other waterways has slowed drainage and allowed the wetland to again become wet.  The re-wetting of soils would in turn cause plants like black cherry, which require an unsaturated root zone, to die.  A closer look may show that other upland plants are dying too.

Note that all the dead trees are at low flood-plain elevations, while the same species at higher elevations along Pole Dike Road look fine.  This supports the idea that the mortality is caused by root-zone flooding and not disease or insect infestation, although these latter two could be secondary stresses on already flood-stressed trees.

While some have argued that the upper Herring River system has evolved into a healthy freshwater wetland, these vegetation trends do not support that conclusion.

Low Dissolved Oxygen 
 Recorded in Herring River
For 108 years now the dike has blocked tides and seawater from the 1100-acre estuary upstream.  Nevertheless, most of the organic matter that accumulated within this expansive wetland over thousands of years remains.

Meanwhile, oxygen-rich Cape Cod Bay water, which would normally flood the river and creeks on every high tide, is greatly restricted by the dike at Chequesset Neck Road.  

In summer, decomposition of this organic matter puts a serious strain on the river's dissolved oxygen budget.  Indeed, during periods of low light for photosynthetic oxygen production, i.e. nighttime or cloudy weather, the river can be poised for complete oxygen depletion; the latter has been observed since at least the mid-1980s, accompanied by fish kills, in 1985 wiping out the entire juvenile river herring run when they attempted to journey from the kettle ponds to the sea.  This has likely been going on for the past 100-plus years, severely damaging aquatic habitat throughout the flood plain, and perhaps explaining the apparent abundance of nuisance mosquitoes.  Mosquito larvae and pupae don't require dissolved oxygen (they breathe air) and thrive in the absence of predatory estuarine fish.

The graph below shows dissolved oxygen trends from this past summer (2017), collected by the US Geological Survey.  Readings below the yellow line are within a range that is chronically stressful to fish and other aquatic animals that "breathe water"; below the red line is a range that is acutely lethal to aquatic life.  Oxygen varies with tides: the little bit of seawater that enters the river at high tide boosts dissolved oxygen, but during every low tide oxygen plummets as the water column becomes dominated by oxygen-depleted river water.
On nearly every low tide in summer the river water becomes highly stressful to fish and other aquatic animals.  (Imagine being in a room without air.)  The problem will continue, quietly and lethally, until the river is re-connected with the marine environment.

Don't Miss The 15th Annual 
State of Wellfleet Harbor Conference 

The 15th annual State of Wellfleet Harbor Conference will be held on Saturday, November 4 from 8:30 am  to 2:00 pm   at the Wellfleet Elementary School. The event is free and open to all.

This year's conference has a water theme: how to protect and improve local waterways, how best to manage wastewater, as well as the threat of rising seawater as the climate warms.

Here is a sample of the topics that will be discussed:
  • Sea Level is Rising and Wellfleet Harbor is Sinking: What Will the Future Look Like? 
  • Herring River Restoration Can Open Closed Shellfish Beds: the Seawater Solution 
  • Update on Wellfleet Harbor Dredging 
  • Can Sea Run Brook Trout Return to Wellfleet? 
  • The Who, What, When, Where, and Why of Horseshoe Crabs in Wellfleet Harbor: Results of a Three-Year Study 
And much more....We hope to see you there!
For more information visit: http://www.friendsofherringriver.org

Or email us at: info@herringriver.org