Life Down Under: The Forgotten Hyporheic Zone in Stream Restoration and Development of a Bioindicator of Subsurface Recovery

Billions of dollars are spent every year on stream restoration projects aimed at restoring the hydraulic and ecological diversity of natural stream systems. Usually restoration goals are focused on bank erosion and improving fish habitat. But, what effects are there on the subsurface environment? Streams are not simply surface flow over a stream bed, but include complex interactions with and within the stream bed. What effects do these man-made rock structures have on biological communities within the bed itself? Do they restore the habitat and biological diversity like we hope they do?

These engineered stream restoration structures may induce hyporheic exchange—the mixing of surface and groundwater flows—within the stream bed. No one has ever studied the effects of these structures on the living world within the stream bed (an entire and complex fauna of invertebrates lives down there). Kathleen McGrath and her team at SUNY College of Environmental Science and Forestry partnered with Laura Lautz at Syracuse University to study Ninemile Creek in Marcellus, NY, an ideal field “laboratory” to examine the effects of restoration structures on subsurface invertebrates.

The team of researchers at Ninemile Creek found that cross vane structures, or carefully placed V-shaped rock structures built across the channel to funnel flow toward the center and away from eroding stream banks, do appear to affect the nature of the environment in a positive way. By mimicking natural riffle pool flow patterns with carefully placed rock structures, flow patterns in and out of the bed, and associated hyporheic habitats do appear to be more diverse. Invertebrate communities may be more diverse and healthy as well.

A better understanding of stream restoration effects on the hyporheic zone allows us to guide future stream restoration efforts to restore not just the surface environment of a healthy stream, but also the subsurface environment as well.