Influence of colonizing benthos on physical properties and chemical diagenesis of the estuarine seafloor

Abstract

Two sampling stations were established on the top and edge of a newly dumped dredge spoil deposit in 12 and 18 meters of water in central Long Island Sound. These stations were sampled periodically from June 1974 to April, 1975. The spoil pile represents over 10$sup 6$M$sup 3$ of organic-rich sand, silt, and clay, dumped between October 1973 and April 1974. A control station was established 5.5 km NW from the dump in 14 meters of water. The colonization of the dump surface may be divided into three stages: Stage I (June-July) represents initial recruitment of shallow burrowing surface deposit feeders, suspension feeders, and meiofauna. Stage II (August-November) is a phase of exponential recruitment of stage I populations and new recruitment of deeper-feeding infauna. Stage III (December-April) is a period of leveling-off in population densities. The control station shows relative constant standing crops of deep-feeding deposit feeders over the sampling period. Late stage II and stage III abundances and diversities on the dump exceed those at the control station. Habitat modification related to the three colonization stages are: Stage I--Fecal pellet production starts and the redox potential discontinuity (RPD) is depressed to about one centimeter by feeding, bioturbation, and respiration activities. Stage II--The surficial layer of pellets experiences some destruction by meiofaunal grazing. The RPD is depressed to 2-3 cm and pore water profiles in SO$sub 4$$sup 2-$ and NH$sub 4$ approach constant values to a depth of 3-6 cm. Sediment water content increases to 2-3 cm. The seafloor is bound by microbial exudates. Stage III - The pelletal surface decays, the RPD rebounds to a depth of 1-2 cm. Pore water profiles are diffusion-altered relicts of late summer irrigation activity. Microbial binding decreases. Several hypotheses are stated regarding the potential importance of these habitat modifications to the colonization sequence. (auth)