From Recharge to Rivers: Groundwater Fauna Sampling across Flowpaths

Synopsis: See representative/ important groundwater fauna sites in the San Marcos area as we move from the Contributing Zone of the Edwards Aquifer down a flowpath that even takes us off of the karst but never outside its influence to see aquatic habitats, management issues, and sampling techniques for rare groundwater species.

Logistics: Due to a need to get up close and personal to see sampling techniques and groundwater invertebrates, group size will be limited to 20 people. We will depart promptly at 9:00AM from the San Marcos Activity Center, returning at 5:00PM. Lunch will be provided. No special gear is needed (we will not be going in caves), but some sites require a short walk. Comfortable hiking shoes, a water bottle, and sun protection are suggested. You will have the option of getting your feet wet, but water should be avoidable. Details below are preliminary and subject to change. Although we will be sampling for groundwater organisms, successful capture is not guaranteed.

Details: The Edwards Aquifer is a global hotspot of groundwater biodiversity. It is also a critically importance water source for large, metropolitan areas. This results in substantial management conflict, but also novel conservation approaches. We will visit a diversity of sites within 35 minutes of San Marcos to see different segments of the aquifer system, including the contributing zone (where surface waters flow onto the recharge zone), the recharge zone (where surface water sinks to recharge the aquifer), the confined zone (where Edwards limestones are overlain by non-karstic lithologies), Edwards springs, and Edwards-dependent surface streams. Specific sites include: Jacobs Well (an iconic spring and underwater cave in the contributing zone), Freeman Ranch (a working ranch in the recharge zone, operated by Texas State University), Ezell’s Cave (a historic and biologically important cave in the recharge zone), the San Marcos artesian well (a flowing artesian well in the confined portion of the aquifer and the most biodiverse groundwater site in North America), Comal Springs (the largest Edwards spring and habitat for several federally protected species), and the San Marcos River (a culturally and biologically important river fed by the San Marcos Springs). At each site, we will briefly discuss the hydrogeologic setting and salient management and conservation issues. In more detail, we will introduce sampling strategies for collecting aquatic subterranean organisms without physically entering caves.

Preliminary schedule:

Wednesday November 3, 2021 9am-5pm