White Paper: Common Connectivity Challenges in New England Streams
Written by Jennifer (Holton) Mongolo as an independent contractor for the Maine Department of Marine Resources in December 2008.
Executive Summary Streams are highly interactive, dynamic ecosystems, which operate across a broad range of spatial and temporal scales that can be viewed as occurring within four dimensions: longitudinal (the main channel pathway and connecting tributaries), lateral (linkages between the stream channel and the riparian/floodplain system), vertical (linkages between the stream channel and contiguous groundwaters) and temporal (continuum of time within which the stream system operates). Traditionally, the primary focus of river management and restoration has been on the longitudinal dimension, particularly in regard to fish passage; however, in order to protect and restore aquatic biodiversity in stream ecosystems it is necessary to recognize the importance of processes operating across all four dimensions. In disturbed stream systems targeted for fisheries improvement, restoration and management must be based on knowledge of the ecological processes that govern fish populations and underlie anthropogenic influences (Mann 1995). Since the four dimensions of stream ecosystems encompass and/or influence the essential ecosystem processes that generate and maintain the physical stream habitat on which fish depend, it follows that a thorough understanding of these four dimensions is essential for diagnosing stream habitat conditions.
This paper summarizes current scientific research regarding these four dimensions of stream connectivity, specifically highlighting challenges common to New England streams, in hopes of broadening the resource manager’s perspective of what constitutes stream connectivity. In order to help identify these challenges and demonstrate the scales at which they occur, a pedestrian survey of Choate Brook, a small fourth order stream located in Mid-Coast Maine, was conducted. Choate Brook is representative of small, rural New England streams that do not have the characteristic problems associated with heavily urbanized or agricultural watersheds. The survey was focused on documenting evidence of disrupted connectivity along all four dimensions. Examples from the Choate Brook study are used to demonstrate the four dimensions of a stream ecosystem, highlighting barriers, discussing their ecological implications, and where practical, suggesting recommendations for addressing these challenges.