Decomposition of periodical cicada carcasses influences nutrient uptake rates in experimental streams

Abstract

Every 17 years, Cicadidae Magicicada emerges in forests across the eastern USA, and their subsequent die-off provides a pulsed subsidy to streams, with unknown impacts on stream ecosystem function. To explore the impact of cicada subsidies on stream ecosystem function, and compare it with leaf litter inputs, we sequentially added dead cicadas and senescent leaf litter to replicated experimental streams. We added dead cicadas and leaves as high (47 gDM/m 2 ) and low (23 gDM/m 2 ) inputs to compare with a control stream. We monitored mass loss, water column nutrients, reach-scale metabolism, and periodically measured nutrient uptake rates. Cicada decomposition rates were similar to the labile leaf species (cicada k = 0.02 d −1 ; leaf k = 0.01 d −1 ). Water column nutrients changed after cicada addition; by Day three, background ammonium-N (NH 4 + -N) increased from below detection to 9 µgN/L, while soluble reactive phosphorus was only slightly elevated. Leaf litter addition had no effect on water column nutrients. On Day three, both levels of cicadas increased areal NH 4 + -N uptake rates, and the high treatment increased reach-scale heterotrophic respiration, whereas leaves had no effect. Temporal dynamics during the decomposition of cicadas and the comparison with leaf litter expands our understanding of how resource subsidies influence stream ecosystem function.

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