GUEST COMMENTARY by THOMAS HARDYI can understand Dr. Molly Cummings’ desire to advocate for turning Cape’s Dam into another series of manmade rapids similar to Rio Vista Falls, the vision of Mr. Ben Kvanli and the kayaking community. Cummings is, after all, a former member of the U.S. Women’s Kayak Polo team, something she failed to disclose in a recent opinion piece in which she suggests science supports that aim.
But as a biology professor at Texas State University who actually studies the ecology of the San Marcos River, I am compelled to clarify where those opinions are unsupported by science-based facts.
Cummings does offers sound advice to the San Marcos City Council when she admonishes them to “depend not only on analyses by hydro-geologists, but also biologists like me [Cummings] who study local aquatic fauna and their specific habitat needs.” I have studied the impacts of dams on aquatic plants and animals in rivers for more than 30 years and specifically in the San Marcos River ecosystem for more than 15 years. I am Texas State’s Meadows Endowed Professor of Environmental Flows. I am not, nor have I ever claimed to be, a hydro-geologist as suggested by Dr. Cummings.
The San Marcos City Council and San Marcos residents deserve the truth. Here it is:
Dr. Cummings says, “This section of the river above the dam is critical for habitat protection, as the downstream sections are unsuitable due to pollution from a Superfund site and fish hatchery.”
In fact, publicly available data from the Texas Commission on Environmental Quality show that surface water samples taken downstream from the Superfund site have never found actionable levels of contamination in the river.
In addition, fish in this area have been tested and certified as being fit for human consumption. A study of aquatic insects upstream and downstream of the AE Woods Fish Hatchery by Loraine Fries and D.E. Bowles in 2011 concluded that, “benthic macroinvertebrates likewise showed no appreciable differences between upstream and downstream sampling locations, and upstream and downstream communities overlapped considerably in terms of species composition, species richness, and functional feeding group composition.”
Extensive sampling by Kenneth Behen in 2013 found 28 species of fish in both this ‘unsuitable’ section of river and in free flowing river sections below Spring Lake Dam. In addition, there are similar fish densities in both sections of the river and, in fact, this downstream section of the river below Cape’s Dam currently supports a viable sport fishery and presence of the endangered fountain darter.
Dr. Cummings says, “If the weir is destroyed, it will greatly reduce the number of plants and small fish species that can’t withstand high flow rates, and this will have dire consequences for the entire fish population here, including those that Texas’ sport fishers rely on.”
The removal of Cape’s Dam will restore natural higher-velocity flow conditions to this section of the river, but there is no evidence to support the notion that a great reduction in the number of fish will occur. Annual monitoring data collected by the Edwards Aquifer Authority since 2002, the San Marcos Observing System and Behen’s research results in 2013 clearly show that sections of the San Marcos River that are not influenced by Rio Vista or Cape’s Dam have large populations of small fish species, sustain a biodiverse fish community and provide plentiful habitat for young and juvenile fish to thrive — including the endangered fountain darter.
There is no evidence to support the notion that a great reduction in the number of plants will occur, although I do expect an increase in the number of more velocity-tolerant species. Why? As detailed in a study soon to be published, my colleagues and I found significantly increased total area of the endangered Texas wild rice as well as other native aquatic plant species restored to areas of faster water habitats of the San Marcos River where non-native plants have been removed since 2012.
To suggest that Cape’s Dam ‘weir’ is a beneficial feature necessary to maintain biodiversity in the San Marcos River ignores all the available data on fish and habitat characteristics in the San Marcos River. It also ignores decades of published literature that clearly shows that weirs and low head dams cause habitat fragmentation and loss of native biodiversity while promoting expansion of introduced non-native species. The San Marcos gambusia is extinct because of factors that include habitat alterations like dams and weirs and the introduction of non-native species like the Amazon and Sailfin mollies that thrive in the artificial slack water areas around dams and weirs.
Those of us who have actually studied the San Marcos River know that the Superfund site has no demonstrable impact on the flora or fauna of the San Marcos River and that the river downstream of Cape’s Dam and the AE Woods Fish Hatchery contains the endangered fountain darter and a healthy diverse aquatic community.
Removal of the dam is the most ecologically sound step to take for protection and recovery of endangered plants and wildlife in the river. Let’s be clear: There’s no credible science to support Cummings’ contention that weirs are essential to the biodiversity of Texas rivers.
Texas State University biology professor THOM HARDY is the chief science officer at the San Marcos-based Meadows Center for Water and the Environment. In a study commissioned by the city of San Marcos, Hardy recommends removing, rather than rebuilding, flood-damaged Cape’s Dam.
COVER: Local children revel in the San Marcos River at Stokes Park where an old mill race rejoins the river’s main channel in late summer 2012. Cape’s Dam upstream of this location is the subject of a contentious fight over whether to rebuild or remove the flood-damaged structure. MERCURY FILE PHOTO by JAMIE MALDONADO