Cache River Restoration
The Cache River, located in southernmost Illinois, is a 5th order low-gradient river that lies at the confluence four major physiographic provinces, as well as at the junction of the Mississippi and Ohio Rivers. Because of its location, the Cache River watershed provides a unique breeding and overwintering ground for migratory birds and harbors over 100 federally and state threatened and endangered species. Due to the overwhelming biodiversity in the region the watershed was designated as one of 19 wetlands in the U.S. of international importance by the RAMSAR convention in 1996. In 1915, the Cache River was disconnected and divided into two sub-watersheds to facilitate drainage of agricultural lands by the construction of the Post Creek Cutoff ditch.
This modification resulted in ongoing degradation of the river, including channel incision and loss of wetlands in the upper reaches, and lack of flow and poor water quality in the lower channel. To address the incision, 25 Newbury rock weirs were constructed in the upper Cache River. Although these weirs were initially installed to protect adjacent wetlands they are being found to have positive ecological impacts to the system. Denise Walther conducted part of her PhD research on the upper Cache River looking at the affects of the weirs on in-stream macroinvertebrates. Denise concluded that the weirs were positively influencing the macroinvertebrate communities by increasing total aquatic macroinvertebrate biomass and EPT (Ephemeroptera Plecoptera Trichoptera) biomass.
For his M.S. thesis, Kaleb Heinrich examined the effect of the rock weirs on adult insect emergence and its influence on the riparian bird community. The results of his study indicate positive numerical responses in both adult insect emergence and subsequent avian responses to the weirs. However, his study found that alterations to riparian habitat, associated with the installation of the weirs, created more edge habitat that may have a negative impact on birds through increased predation and cowbird parasitism. Along with providing one of the first studies examining riparian subsidies associated with an in-stream restoration project, Kaleb’s research indicates the need for future restoration projects to minimize disturbance, as it may offset some of the ecological benefits.
Eric Scholl, Karen Baumann and Heidi Rantala examined the potential ecological responses to an altered flow regime in the Cache River. Presently, the upper and lower parts of the Cache are drastically different in respect to in-channel hydraulics. This difference is amplified in the low-flow summer months when the lower Cache River is functioning more like a lentic habitat than a running river. Eric found the upper Cache has a more diverse macroinvertebrate community composed of larger-sized individuals compared with downstream, low-flow reaches, where production is dominated by smaller, less sensitive taxa. This difference is driven by water velocity and organic matter resources. Results demonstrate that long-term reductions in flows, even in a low-gradient river, can lead to significant shifts in macroinvertebrate communities, ultimately influencing energy flow pathways in stream food webs. The Cache River experienced a large flood in 2011 and extreme drought conditions in 2012. Karen compared macroinvertebrates between the upper and lower Cache June, July, and August of 2010-2013 to understand how hydrologic variation affects both communities. The work done on the Cache will ultimately be used to guide watershed managers on future hydrologic restoration activities.
See Kaleb and Eric’s publications for more information:
Heinrich, K. K, M. R. Whiles, and C. Roy. 2014. Cascading ecological responses to an in-stream restoration project in a Midwestern River. Restoration Ecology: 22:72-80.
Scholl, E.A., H.M. Rantala, M.R. Whiles, and G.V. Wilkerson. 2015. Influences of Flow on Community Structure and Production of Snag-Dweling Macroinvertebrates in an Impaired Low-Gradient River. River Research and Applications 32: 677-688. http://onlinelibrary.wiley.com/doi/10.1002/rra.2882/full