Periodical cicada detritus impacts stream ecosystem metabolism

The emergence of 17-year periodical cicadas in Maryland, USA, in 2004 provided a unique opportunity to study the effect of a large, but temporally limited, resource pulse of arthropod detritus on stream ecosystem function. Cicada emergence was quantified in the forests adjacent to two small streams with different histories of riparian disturbance (Intact and Disturbed sites). We estimated the input of cicada detritus to the streams, described its retention and breakdown dynamics, and measured whole-stream respiration over the cicada flight season (May-July). Average emergence density was significantly greater at the Intact site, but average cicada detritus input rates were greater at the Disturbed site. Cicada detritus was locally retained within both streams and rapidly broke down. Daily whole-stream respiration (CR₂₄) at both sites responded dramatically to the cicada pulse, with CR₂₄ doubling pre-cicada measurements following the period of greatest cicada input (Intact: 12.82 → 23.78 g O₂ m^-2 d^-1; Disturbed: 2.76 → 5.77 g O₂ m^-2 d^-1). CR₂₄ returned to baseline levels when cicada input decreased at the Intact site, but more than doubled again at the Disturbed site (13.14 g O ₂ m^-2 d^-1), despite a decline in cicada input rate. Differences in respiration response may be a function of differences in cicada input rates as well as differences in microbial community activity. The strong effects on stream ecosystem function exerted by a short but intense input of periodical cicada detritus may provide insights regarding the response of streams to other irregular resource pulses.