Monday, March 21, 2011

Bay Sediment Loads Linked to Past

Sediment loads from runoff are considered to be one of Chesapeake Bays bigger problems.  We tend to think of these problems as coming from current land uses; farming, construction, storm water, etc.  However, a body of work is starting to link sediment loads with land use decisions made decades if not centuries ago:
...Research coming out of Franklin and Marshall College in Lancaser, PA over the past several years has taken to examining the way historical land use, primarily agriculture and land clearing, has both shaped our contemporary sense of what healthy streams and creeks look like, but also how they function.

Their research has focused primarily on mill dams throughout the mid-Atlantic, and looking at how sediment released through historical land use built up behind those dams in stream valleys across the region, and is now being exported downstream. Even where mill dams were not present – and they occurred in significant numbers in Anne Arundel County – the stream valleys are covered in several feet of historical sediment which continues to make its way to tidewater.

The researchers from Franklin and Marshall issued the following stark statement in the conclusion to a 2011 publication, “incised, post-dam breach streams and fine-grained banks in the mid-Atlantic region are anthropogenic in origin, and the causes of both the accumulation of sediment in valleys and subsequent incision and erosion are not directly related to modern upland land use or cover. Conceptual and computer models that link channel condition and sediment yield exclusively with contemporaneous upland land use, sediment supply and runoff are incomplete because anthropogenic forcing has impacted valley bottom, not only upland, boundary conditions, and has done so for centuries.” ...
So who do we blame, and who do we get to fix the problem?  The landowner, who likely had nothing to do do with creation of the problem?  The county, who collected taxes on the land use that caused the problem?  Are these inputs taken into account in the sediment TMDL? 

I have a set of core data showing a distinct input of sediment into Muddy Creek (hence the name) sometime after the Civil War, after the decline in the use of water power which provided the impetus for the mill dams.

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