Periphyton plays a significant role in heavy metal transfer in wetlands, but its contribution to cadmium (Cd) bioavailability in paddy fields remains largely unexplored. The main aim of this study was to investigate the effect of periphyton on Cd behavior in paddy fields. Periphyton significantly decreased Cd concentrations in paddy waters. Non-invasive micro-test technology analyses indicated that periphyton can absorb Cd from water with a maximum Cd²⁺ influx rate of 394 pmol cm⁻² s⁻¹ and periphyton intrusion significantly increased soil Cd concentrations. However, soil Cd bioavailability declined significantly due to soil pH increase and soil redox potential (Eh) decrease induced by periphyton. With periphyton, more Cd was adsorbed and immobilized on organic matter, carbonates, and iron and manganese oxides in soil. Consequently, Cd content in rice decreased significantly. These findings give insights into Cd biogeochemistry in paddy fields with periphyton, and may provide a novel strategy for reducing Cd accumulation in rice.

Research on the interaction of microplastics and aquatic organisms has been mainly focused on the evaluation of various impacts on animals while aquatic vascular plants have been so far understudied. In this commentary, we summarized knowledge about interactions of microplastics with aquatic vascular plants and highlighted potential ecological implications. Based on recent research, microplastics have minimal impacts on plants. However, they are strongly attracted to plant tissues, adsorbed, and accumulated by plants. Several mechanisms drive microplastics adsorption and accumulation; the most possibly electrostatic forces, leaf morphology, and presence of periphyton belong among the most important ones. Adsorbed microplastics on plant tissues are easily ingested by herbivores. Plants can thus represent a viable pathway for microplastics to enter aquatic food webs. On the other hand, the strong interactions of microplastics with plants could be used for their phytostabilization and final removal from the environment. Aquatic vascular plants have thus an important role in the behavior and fate of microplastics in aquatic ecosystems, and therefore, they should also be included in the future microplastic research.

Periphyton, composed of algae, bacteria, protozoa, epiphytes, and detritus, is widely distributed on the surfaces of paddy soils. Little is known about the interactions between the periphyton and arsenic (As) in the paddy soil. In the present study, model paddy ecosystems with and without periphyton were set up to explore the effects of periphyton on As migration and transformation in soil. According to the results, periphyton played dual roles in the mobility of As in soil. Periphyton on the surface of paddy soil could significantly increase the mobility and bioavailability of As in soils in the rice tillering stage because of the increased pH and the decreased Eh. The As uptake by rice also increased in the presence of periphyton. However, a significant fraction of the released As was further entrapped by the periphyton, significantly decreasing As concentration in pore water. As biotransformation genes, including aioA, arrA, arsC, and arsM, were identified in periphyton, with arsM being the most abundant in periphyton and soil. Periphyton significantly decreased the abundance of aioA, but increased the abundance of arsC in soils. Cupriavidus and Afipia, which are involved in As(V) cytoplasmic reduction, significantly increased in the presence of periphyton. Periphyton exerted minor effects on the highly abundant and predominant bacteria but had major effects on the less abundant bacteria in the paddy soil. The results of the present study could facilitate the regulation of As contamination in paddy soil, and enhance our understanding of the role of periphyton in the As biogeochemical cycle.

Samples of water, sediment and epilithic periphyton (EP) were collected from a lake (Dimna, DL), an intermediate canal (IC), and a river (Subarnarekha River, SR) to compare the pollution status of an urban ecosystem, and the concentrations of metal(loid) s were determined. Water characteristics were analysed by the water quality index (WQI). Sediment pollution was assessed using the ecological risk index (ERI). Accumulation of metal(loid) s in EP was determined by using bioaccumulation factor (BAF) and biota-sediment accumulation factor (BSAF). The result showed that the DL was least polluted (WQI = 30.39) and SR (WQI = 90.13) was the most polluted ecosystem. Sediment analysis revealed that Ni, Cr and Cd are the significant pollutants, especially in SR. The THQ value for fish dishes cooked in Indian style was found higher than that of raw fish, suggesting calculations considering the cooking process can provide better results. Health risk assessment shows that people inhabiting DL are vulnerable to Cr and Cu exposure, whereas people inhabiting IC and SR are susceptible to As and Co exposure due to the consumption of cooked fish. Moreover, for a developing country like India, it is important to upgrade the assessment methods and include regular monitoring of interconnecting ecosystems for the safeguard of human and ecological health.

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