Understanding the effects of hydrological processes on the benthic macroinvertebrates in salt marshes can
provide theoretical basis for species diversity restoration, coastal environment protection, and comprehensive
exploitation and utilization of salt marsh ecosystems. In this study, 4 fixed-point sampling sites were set up in the
salt marsh of the East Nanhui tidal flat in the Yangtze Estuary for benthic macroinvertebrate survey, hydrological
monitoring and sedimentary parameter collection over two short-time scales (semidiurnal and fortnightly cycles).
Based on the results of these surveys, we analyzed the effects of hydrological processes on the benthic
macroinvertebrates over different timescales. The results showed that benthic macroinvertebrates assemblages
varied significantly over the semidiurnal and fortnightly tide periods but not between sites. The number of
species and the abundance of the benthic macroinvertebrates during spring tide period were significantly lower
than that during neap tide period, although the biomass during both tidal periods were not significantly different.
There was no significant variation in the number of species, abundance, and biomass of benthic macroinvertebrates
over the semidiurnal tidal scale in general with few exceptions. However, there were significant
differences in most of the hydrological and sedimentary parameters between the spring and neap tide periods, as
well as between semidiurnal tides in these two periods. Two principal components, the intensity of hydrological
processes (PC1) and the physicochemical properties of water and sediment (PC2), were derived from principal
component analysis on hydrological factors and sedimentary physicochemical parameters. The results show that
PC1 had a significant effect on abundance of benthic macroinvertebrate community; while PC2 had a significant
effect on biomass. The best combined environmental factors, which exhibited significant correlations with the
characteristics of the benthic macroinvertebrates and also their taxonomic classes, varied across the sampling
periods. This study indicates that short-term hydrological processes can not only directly affect the benthic
macroinvertebrates, but also indirectly affect the communities by altering sedimentary physicochemical factors.
There were significant differences in the effects of the hydrological processes on the benthic macroinvertebrate
community over the semidiurnal and fortnightly tidal scales, and it could be inferred that the scale effect still
exists in the short-time scale.