The joint effect of tidal barrier construction and freshwater releases on the macrobenthos community in the northern Yellow River Delta (China)

Tidal barriers isolate intertidal areas from tides, creating distinct conditions on either side of the barrier, and freshwater releases change the receiving area's hydrology and salinity. However, the combined effect of these human actions is unknown. Using the macrobenthos community as a bioindicator, we sampled part of the northern Yellow River Delta that has been managed using tidal barriers and freshwater releases, in the spring and autumn of 2014, before and after the summer freshwater release. The macrobenthos communities differed greatly on opposite sides of the barrier. During the spring, 7 to 8 species were found inside the barrier (mainly Insecta and Crustacea), versus 22 in the intertidal area (mainly Polychaetes, Mollusca, Crustacea, and Insecta). During the autumn, 10 to 13 species were found inside the barrier and 16 in the intertidal area. Non-metric multidimensional scaling and hierarchical clustering divided the macrobenthos communities into groups that mostly agreed with the spatial distribution of the investigated areas. The characteristics of the modified ecosystems determined the similarity of the macrobenthos communities. The effects of the tidal barriers and the freshwater releases interacted: the barriers decreased sediment salinity compared with that in the intertidal area, and freshwater releases increased this differentiation. To restore the delta's original freshwater ecosystems, the tidal barriers are required to contain the freshwater releases. In addition, the effects of the freshwater releases were generally positive. Therefore, it is reasonable to retain the barriers and to continue or increase these releases.