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a b s t r a c t a r t i c l e i n f oYellow River delta (YRD) is a typical example of a valuable coastal ecosystem that is under increasing anthropogenic threat in China. To understand the current health status of this region, three surveys in 2011 for the abiotic conditions and macrobenthic assemblages were performed. The concentration of trace metals were relatively low in the sediment at all sampling stations representing a good sediment quality. A total of 159 macrobenthic species were identified during the three surveys. ABC curves showed that the macrobenthic fauna at 8 sampling stations suffered disturbances from human activities. M-AMBI index indicates that the benthic ecological quality of YRD is currently still not in a good condition. Five trace metals, water temperature and depth were the main environmental variables affecting the distribution pattern of macrobenthic assemblages. Community succession has occurred over the past 60 years, as evidenced by changes of species composition, key species, distribution pattern and range.

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Decabromodiphenyl ether (BDE209) has been subject to restrictions since 2018 in developed countries but is still manufacturing in China. Decabromodiphenyl ethane (DBDPE) is widely used as a replacement for BDE209. To better understand the behaviors and fates of these legacy and novel brominated flame retardants (BFRs), water samples were collected from the estuaries of 36 rivers that drain into the Bohai Sea (BS) and North Yellow Sea (NYS) in 2017 and 2018. The results showed that BDE209 was still the predominant compound with a median concentration of 2470 pg L À1 , whereas DBDPE had a median concentration of 129 pg L À1 . Spatially, relatively high concentrations were observed in the rivers near Laizhou Bay (LB), which is the manufacturing hub of BFRs. BDE209 concentrations were significantly higher in dry season than in wet season, which indicates a dominant process of dilution by precipitation during the wet season. DBDPE concentration showed no significant seasonal difference. This implies that wet deposition was the major additional source of DBDPE during the wet season, and the concentration increased further during the autumn as a result of a time-lag effect. The BFR concentrations in urban rivers were lower than those reported by a study undertaken in August 2013. An increase in the BFR concentrations in rural rivers since 2013 suggested increases in the use and non-point source emissions of BFRs in some remote aquatic environments. The estimated annual inputs of BDE209 and DBDPE into the BS were ~95.9 kg yr À1 and ~26.8 kg yr À1 , respectively, whereas those into the NYS were ~24.1 kg yr À1 and ~8.38 kg yr À1 . The results revealed an ecological risk of BDE209 in winter especially in the Xiaoqing River, thus suggesting the impact of BDE209 on the aquatic environment and human health.

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Since the mud snail Bullacta exarata was introduced for economic aquaculture in the Huanghe River (Yellow River) Delta in 2001, its quick population growth and expanded distribution make it a key-species in the intertidal zone of this area. This significantly contributed to the economic income of the local people, but its potential ecological impact on the benthic ecosystem remains unknown. A mesocosm study was conducted to test whether its bioturbation activities affect the microphytobenthos (MPBs; i.e., sedimentary microbes and unicellular algae) productivity and the nutrient exchange between the sediment-water interface. Our results show that the mud snail significantly impacted the dissolved oxygen (DO) flux across the sediment-water interface on the condition of normal sediment and light treatment, and significantly increased the ammonium efflux during recovery period in the defaunated sediment and dark treatment. The presence of micro-and meiofauna significantly increased the NH 4 -N flux in dark treatment. Whereas, in light treatment, these small animals had less effects on the DO and NH 4 -N flux between sediment-water interface. Our results provide better insight into the effect of the mud snail B. exarata on the ecosystem functioning via benthic fluxes.