Storage and Dynamics of Subsurface Detritus in a Sand-Bottomed Stream

Abstract

Annual mean storage of buried detritus (0–20 cm depth) in a first-order, sand-bottomed stream was 4.8 kg AFDM/m2, approximately one order of magnitude greater than surface storage. Forty percent of the buried detritus was wood > 8 mm; much of the remainder was 1–8 mm particles. Exchange of detritus between surface and shallow sediments occurred throughout the year; exchange between surface and deep sediments occurred only during spates Heavy rainfall during a September hurricane caused a mean scour depth of 6 cm (range = 0–27 cm) and contributed to a 0 94 kg/m2 reduction of buried detritus. Buried leaves were processed slower than leaves on the sediment surface (25% of initial buried leaves remained after 1 yr). Particles < 8 mm were processed faster from January to March (19% mass reduction) than at other times (8–9% mass reduction). Except during the September spate burial was approximately offset by decomposition. About 21% of estimated autumnal leaf input to the stream became buried. Given the large quantity of detritus stored in the subsurface, its slow processing rate and the episodic nature of its release from deep storage, the hyporheic area of this stream has an important effect on the stream's carbon spiralling length, energetics, and trophic dynamics.