Evaluating the effects of applied stream restoration: Instream habitat and scales of influence in two streams with partially developed watersheds.

摘要

In developed watersheds, degraded water quality, altered hydrology and sediment transport, and impaired physical habitat are often present, and the use of stream restoration has been rapidly increasing over the past 50 years to ameliorate these effects. Only recently have researchers begun to formally address complex questions to improve the science of stream restoration, and more work is needed to evaluate the project effectiveness of popular practices and determine the important scales of influence. I present the results of comparative upstream-downstream studies in the upper Norwalk River (urban-forest watershed) and Merrick Brook (agriculture-forest watershed), two 4 th order streams in Connecticut, U.S., that have received habitat rehabilitation (i.e., instream structures, streambank stabilization, and meander re-creation). At the time of monitoring, projects had been in place for 2 to 5 years. A comprehensive set of physical, chemical, and biological variables were monitored at control, enhanced (treatment sites that were originally controls), impaired, and rehabilitated (treatment sites that were originally impaired) sites over the course of three field seasons to identify the effects of the projects and establish monitoring strategies. In general, some small improvements in local habitat and macroinvertebrate assemblages were observed at rehabilitated sites; however, control conditions were never fully attained. Changes to stream condition were less evident when investigating reach-averaged instream variables. At this larger scale, variables linked to watershed process, such as water temperature, magnesium concentration, and the amount of impervious cover in the upstream watershed 100-m stream buffer, were more closely related to instream condition. This finding confirms the need for more holistic stream restoration and watershed management, where disturbances at multiple spatial scales are considered. Additional scientific study of stream restoration is recommended to improve methods of application and meet the goal of improving the many facets of streams, and a three-tiered monitoring strategy is proposed with varying levels of detail and scales of observation to efficiently accomplish this task.