Abstract. Human activities, among which dredging and land use change in river basins,
are altering estuarine ecosystems. These activities may result in changes in
sedimentary processes, affecting biodiversity of sediment macrofauna. As
macrofauna controls sediment chemistry and fluxes of energy and matter between
water column and sediment, changes in the structure of macrobenthic
communities could affect the functioning of an entire ecosystem. We assessed
the impact of sediment deposition on intertidal macrobenthic communities and
on rates of an important ecosystem function, i.e. sediment community oxygen
consumption (SCOC). An experiment was performed with undisturbed sediment
samples from the Scheldt river estuary (SW Netherlands). The samples were
subjected to four sedimentation regimes: one control and three with a
deposited sediment layer of 1, 2 or 5 cm. Oxygen consumption was measured
during incubation at ambient temperature. Luminophores applied at the
surface, and a seawater–bromide mixture, served as tracers for bioturbation
and bio-irrigation, respectively. After incubation, the macrofauna was
extracted, identified, and counted and then classified into functional groups
based on motility and sediment reworking capacity. Total macrofaunal
densities dropped already under the thinnest deposits. The most affected
fauna were surficial and low-motility animals, occurring at high densities in
the control. Their mortality resulted in a drop in SCOC, which decreased
steadily with increasing deposit thickness, while bio-irrigation and
bioturbation activity showed increases in the lower sediment deposition
regimes but decreases in the more extreme treatments. The initial increased
activity likely counteracted the effects of the drop in low-motility, surficial
fauna densities, resulting in a steady rather than sudden fall in oxygen
consumption. We conclude that the functional identity in terms of motility
and sediment reworking can be crucial in our understanding of the regulation
of ecosystem functioning and the impact of habitat alterations such as
sediment deposition.
Numerical Study on the Expansion and Variation of Changjiang Diluted Water in Summer and Autumn
