Stable isotopes reveal effects of natural drivers and anthropogenic pressures on isotopic niches of invertebrate communities in a large subtropical river of China.

Isotopic niches reflect the basic structure and functioning of river food webs; however, their response to riverine environments remains unclear. We used stable isotope analysis and community-wide metrics to quantify how invertebrate niches vary with environmental changes along a large subtropical river in China. Eight niche metrics, which had higher values in the wet than in the dry season, increased from headwaters to the middle river and decreased sharply near the estuarine industrial zones. The δ13C value of > - 23.8‰, which indicated consumption of epilithic diatoms, separated the invertebrates between the upper and mid-lower reaches. The δ15N values > 9.4‰ identified site-specific nitrogen sources from manure (e.g., animal effluent) and domestic sewage in agricultural area. The output of mixing models showed a downstream shift in carbon utilization by invertebrates from autochthonous periphyton and submerged hydrophytes to allochthonous C3 plants. Principle component (PC) and cluster analysis decomposed and grouped 40 environmental variables into 4 PCs that explained 84.5% of the total variance. Hierarchical partitioning revealed that the second and first PCs, which were driven mainly by biological indicators and habitat characteristics, had the highest explanatory power for niche ranges and areas (e.g., Bayesian ellipse), respectively. Our results suggest that reducing anthropogenic pressures (e.g., habitat loss and water pollution) on river ecosystems through measures, such as protecting diatom-dominated biofilms in riffles and controlling nitrogen loading in rural regions, may produce the greatest impact for river management. Graphical abstract.

Bioaccumulation of endocrine disrupting compounds in fish with different feeding habits along the largest subtropical river, China.

Endocrine disrupting compounds (EDCs) are becoming an increasing concern regarding bioaccumulation in aquatic biota. However, the effects of regional pollution levels and specific feeding habits on the bioaccumulation of EDCs in fish are rarely reported. 4-Nonylphenol (4-NP), bisphenol A (BPA), 4-tert-octylphenol (4-t-OP), triclocarban (TCC) and triclosan (TCS) were determined in abiotic compartments [water, sediment, suspended particulate matter (SPM)] and fish with different feeding habits along the Pearl River, China. EDCs in abiotic compartments exhibited significant (p < 0.05) spatial variations, forming five zones clustered based on site-specific EDC concentrations. 4-NP was the dominant compound, contributing 58-98% of the EDCs in fish, followed by BPA (<41%), 4-t-OP (<13%), and TCC and TCS (<4.7%). The concentrations of 4-NP and 4-t-OP, BPA, and TCC and TCS were the highest in brackish carnivorous, planktivorous, and detritivorous fish, respectively. The bioaccumulation factors (BAFs) showed that 4-NP accumulated (BAF > 5000) in all fish except for suck-feeding detritivores, while 4-t-OP and TCC accumulated in filter-feeding planktivores. The concentration of 4-NP in carnivores was significantly higher than that in detritivores, indicating the potential biomagnification of 4-NP along food chains. EDCs in sediment and SPM and those in water were most positively correlated with those in detritivores and planktivores, respectively, suggesting the potential of fish with these two feeding habits to act as bioindicators of EDC pollutants.

Longitudinal variation in fish prey utilization, trophic guilds, and indicator species along a large subtropical river, China.

Due to the heterogeneous distribution of resources along large rivers, understanding prey utilization by basin-scale fish assemblages remains a challenge, and thus, recognizing regional fish trophic guilds and indicator species is important. We analyzed the stomach contents of 96 fish species along the subtropical East River in China and identified 8 prey items (29 subcategories). Site-specific differences in fish diet composition (DC) revealed longitudinal shifts in utilized prey taxa, from upstream lotic to downstream semi-lentic items, and these were characterized by a decrease in the proportions of epilithic diatoms and aquatic insect larvae (Ephemeroptera and Chironomidae) accompanied by an increase in bivalves (Corbicula and Limnoperna), shrimps and fishes, and organic sediments. The relative prey consumption weighted by fish abundance and biomass indicated that decreasing insect consumption and increasing detritus consumption were two fundamental vectors governing fish-centered feeding pathways. Seventeen prey-oriented fish guilds that were clustered based on DC matrix determined the spatial variation in the fish trophic structure. The cumulative presence of (a) upstream guilds reliant on insects and epiphytes, (b) midstream guilds reliant on hydrophytes, molluscs, and nekton, and (c) downstream guilds reliant on detritus, annelids, and plankton resulted in a longitudinal increase in guild richness, but this continuity was interrupted near the industrialized estuary. The most abundant 28 fish species across the guilds were selected as trophic indicator species; their spatial distribution significantly (p < 0.05) explained >80% of the environmental and prey variables identified. These species signified the availability of predator-prey links in distinct habitats and the key environmental factors supporting these links. With a high contribution (>51%) of exotic species, an increase in detritivores downstream distinguishes the subtropical East River from temperate rivers. Particularly, in the disturbed lower reaches, the dominance of detritivores prevailed over the predicted increase in other feeding groups (e.g., omnivores and carnivores).

[Spatio-Temporal Patterns and Environmental Risk of Endocrine Disrupting Chemicals in the Liuxi River].

This study aimed to investigate the occurrence and spatio-temporal distribution of 4-tert-octylphenol (4-t-OP), 4-nonylphenol (4-NP), triclosan (TCS), estrone (E1), 17ß-estradiol (E2), and bisphenol-A (BPA) as endocrine disrupting chemicals (EDCs) in the water of the Liuxi River and to evaluate the risks for estrogenic activity. The results showed that EDCs had been detected at the 14 monitoring sites and the total concentration ranged from 26.07 ng·L-1 to 7109.5 ng·L-1, with the highest contribution rate coming from 4-NP (78.62%), followed by BPA (11.91%), and the other four EDCs (≤ 4.92%). On a spatial and temporal scale, the EDC contents increased longitudinally from upstream to downstream, especially in the heavily-polluted Baiyun section where the water quality was lower than level Ⅴ. The EDC contents in the tributaries were much higher than those in the main channels. Influenced by the monsoon precipitation, the contents of 4-NP, 4-t-OP, and total EDCs in the rainy season were significantly (P<0.05) higher than those in the dry season, while the seasonal changes of E1 and E2 followed the opposite tendency. A Pearson correlation analysis showed that DO was significantly negatively correlated with all the EDCs, suggesting that the EDCs and reductive organic pollutants might coexist. As TN, TP, NH4+-N, permanganate index, and EC were significantly positively correlated with E1, E2, BPA, and TCS but not obviously correlated with 4-NP (P>0.05), we presumed that the pollution source of E1, E2, BPA, and TCS might be the same with nitrogen and phosphorus nutrition, originating from the point source emission of the domestic sewage, industrial, and agricultural wastewater. In contrast, 4-NP and 4-t-OP more likely originated from the non-point source pollution from agriculture. RDA results showed that the variation of the EDCs contents by season was more obvious than that in space (RDA1 56.14%>RDA2 14.20%), which was much more influenced by 4-NP in the rainy season and by BPA in the dry season. As E1, E2, and TCS were positively correlated with the Cu, Zn, cyanide, and fecal coliform, these three target compounds could be used to indicate the multiple pollution components for water quality. Compared with the worldwide reported EDC contents in waters, 4-NP, BPA, and TCS contents in the middle and lower reaches of the Liuxi River were at higher levels, while E1, E2, and 4-t-OP were at the middle and lower levels. The risk assessment for estrogenic activity showed that the RQ values in the middle and lower reaches of the Liuxi River were all greater than 1, indicating that the downstream river sections were under high risk for estrogenic activity. As a result, appropriate precautions are needed to improve environmental management.