A Process Based Modeling Approach to Assess Temperature Impacts of
Riparian Vegetation Management in a Southwestern Wisconsin Trout Stream
Abstract
Rising water temperatures driven by climate change threaten culturally
and economically important salmonid fisheries throughout the Upper
Midwest. Unsuitable thermal regimes degrade the effectiveness of habitat
restoration projects in the region, thus strategies for mitigating peak
summer stream temperatures are of interest to state and non-profit
fisheries managers. Using a process-based stream temperature model, this
study explores the thermal impact of riparian tree planting and tree
removal in a 179 km 2 watershed in the unglaciated
Driftless Area of southwestern Wisconsin. By creating hypothetical
riparian vegetation scenarios and systematically adding and removing
woody vegetation from the banks we explore the influence of shade and
channel geometry on July stream temperatures with an emphasis on
salmonid thermal suitability. We used this model to analyze an 18.5 km
study reach to identify management areas that have the most potential to
buffer downstream water temperatures throughout the summer with added
shade. We developed a downstream thermal change (DTC) metric to measure
the magnitude and downstream distance of temperature change following
stream alterations. The magnitude of stream cooling was mediated by
channel width in our scenarios, with more pronounced thermal changes in
narrower stream reaches (p<.05). Modeled tree planting scenarios
decreased the maximum July maximum weekly average temperature (MWAT) and
July maximum weekly maximum temperature (MWMT) within the study reach by
0.52 ℃ and 0.53 ℃ respectively. This study offers a workflow using free
and open-source modeling tools to determine the thermal impact of
restoration and prioritize future management efforts in cold water
stream ecosystems.