David P. Ahlfeld
Road crossings and dams may act as barriers to movement for a wide range of aquatic organisms in lotic freshwater systems. Limited funding constrains the number of barriers that may be mitigated by repair or removal, so systematic methods of prioritization are needed for selecting barriers for mitigation. A new formulation is proposed that links the number of organisms in the watershed to the amount and quality of accessible habitat in order to quantify habitat connectivity of a watershed. The method is applied to a case study performed on the Upper West Branch of the Westfield River in Massachusetts, with multispecies measures of habitat integrity and aquatic barrier passability allowing comparison of stream segments and barriers within the network and their contributions to overall habitat availability. Optimization techniques are used to maximize the amount of high-quality habitat in the network accessible by stream-resident organisms. Results of this study demonstrate that the optimal combination of barriers for mitigation may change dramatically as budgets change, and that foreknowledge of a project’s lifetime budget and accurate data regarding mitigation costs for individual barriers are crucial to cost-effective barrier removal planning.