Food Web Responses to Stream Simulation Design of Road-Stream Crossings: Moving Beyond Aquatic Organism Passage

Typical goals of aquatic organism passage (AOP) projects include providing adequate passage of aquatic orgamisms and rarely consider whether stream function is improved.  We examined differences in habitat and food web responses (periphyton, organic matter, and invertebrates) in upstream, downstream, and culvert reaches at two restored road-stream crossings on the Little Popple River, WI.  One culvert was constructed using the Stream Simulation Design (SSD) which mimics natural channel structure, while the other was left to fill on its own.  Habitat characteristics within the SSD crossing included shallower depths, faster velocities, and cobble/pebble/gravel substrate (95%), while silt dominated (91%) the non-SSD crossing.  Periphyton standing crop was 5x greater in the SSD crossing than the non-SSD crossing.  Fine benthic organic matter was significantly greater at the non-SSD crossing than at all other reaches.  Coarse organic matter and invertebrate abundances were significantly lower at the non-SSD crossing compared to upstream and downstream reaches and similar among all reaches at the SSD site.  Collector-gatherer chironomids dominated invertebrate communities at the non-SSD crossing, while mayflies, stoneflies, and caddisflies dominated reaches at the SSD site.  Food webs at the SSD road-stream crossing more closely reflected reference reaches demonstrating that SSD can provide ecological functions beyond AOP.