Road crossings and upstream and downstream aquatic macroinvertebrate communities

Culverts and bridges which let a stream pass under a road are commonly used as road crossings.  These road crossings can change the physical nature of a stream by increasing velocity and creating a downstream waterfall.  However, little is known how these road crossings affect aquatic macroinvertebrate abundance and diversity.  Hester-Dendy samplers were used to collect macroinvertebrates above and below road crossings in the Loup River drainage in central Nebraska.  Samplers were placed 100 meters above, directly above, directly below and 100 meters below the road crossing.  Single barrel culverts, double barrel culverts and bridges were sampled.  Mayflies, caddisflies and stoneflies made up 81% of the nearlt 14,000 invertebrates collected.  Although there were no significant differences in road crossing type and invertebrate abundance, location of the samplers affected catch rate and diversity.  These results show that placement of samplers can affect results of biodiversity studies.  Sampling more road crossings and different distances from the crossing could be beneficial.   Studies to assess biodiversity should be aware of these differences and adjust experimental designs accordingly.