Nitrogen removal enhanced by benthic bioturbation coupled with biofilm formation: A new strategy to alleviate freshwater eutrophication.

Excessive nitrogen input into the water caused eutrophication thereby reducing biodiversity and degrades freshwater function. Nitrogen pollution in sediments is one key reason that makes eutrophication difficult to control. The physicochemical technologies such as dredging and coverage for sediment pollution easily destroyed and homogenized aquatic habitats. To alleviate freshwater eutrophication in ecological way, this work combined the functions of bioturbation and biofilm to test their effect on the removal of nitrogen from sediment and water. The total nitrogen removal by employing the coupled function (bioturbation + biofilm, SCB) was greater than that of the single function (bioturbation or biofilm). The mean efficiency of total nitrogen removal in SCB treatment was 3.19 times that of the control without chironomids nor biofilm medium. Chironomid bioturbation promoted nitrogen release from sediments to the overlying water. Biofilm enhanced the conversion and removal of nitrogen stirred up by chironomids, resulting the lowest concentration of total nitrogen in overlying water of SCB treatment. The enhancement of nitrogen removal may be due to the coupled function increased the abundance of denitrifying and anammox functional bacteria in sediment and biofilm. Therefore, the method of combining benthic animals with biofilm medium is not only a viable solution for reducing sedimentary nitrogen loading in freshwater ecosystems, but also a solution to mitigate eutrophication in the overlying water. The restoration and management for aquatic ecosystems should consider protecting habitat for benthic organisms while maintaining heterogeneity for biofilm.

Natural infochemical DMSP stimulates the transfer of microplastics from freshwater zooplankton to fish: An olfactory trap.

Natural infochemicals may largely affect the trophic transfer of microplastics (MPs) in ecosystems but such infochemical effect and mechanisms are poorly understood. Here, a daphnids-zebrafish freshwater microcosm was designed to elucidate whether and how an algae-derived infochemical, dimethylsulfoniopropionate (DMSP), affects the ingestion and transfer of MPs. Daphnids fast accumulated DMSP and MPs from water, and DMSP in daphnids was mainly enriched from the DMSP in water but not from MPs. DMSP did not change the MP ingestion by daphnids. A low concentration of DMSP (0.5 nM) increased predation of daphnids by zebrafish, while high concentrations of DMSP (50, 100 and 200 nM) did not increase predation rates. The concentration of DMSP in daphnids and the MP predation by zebrafish showed a unimodal relationship. The predation for MP by zebrafish in the 0.5 and 5 nM DMSP treatments was 1.89 and 1.56 times that of the control, respectively. The concentrations of DMSP in freshwater samples were lower than 50 nM. This suggests DMSP at environmentally relevant concentrations may promote the trophic transfer of MPs in freshwater ecosystems via olfactory traps.

Effects of benthic bioturbation on anammox in nitrogen removal at the sediment-water interface in eutrophic surface waters.

Anaerobic ammonium oxidation (anammox) significantly contributes to nitrogen loss in freshwater ecosystems. The sediment-water interface (SWI), known as a "hot spot" for anammox, also harbors numerous macroinvertebrates. However, the impact of their bioturbation on anammox has generally been overlooked. This study compared the effects of three representative macroinvertebrates (i.e., Propsilocerus akamusi, Branchiura sowerbyi and Radix swinhoei) with different bioturbation modes on anammox and the N-removal processes at the SWI by using a microcosmic system. The results demonstrated that all three benthic macroinvertebrates promoted anammox in addition to denitrification processes. The highest N-removal was achieved in the presence of P. akamusi considered as a gallery-diffuser, where the relative abundance of Planctomycetes (to which the anammox bacteria belong) increased by 70%. P. akamusi increased the abundance of anammox hzsB gene by 2.58-fold and promoted potential anammox rate by 12.79 nmol N g-1 h-1, which in turn facilitated total N-removal mass increased by 2.42-fold. In the presence of B. sowerbyi and R. swinhoei, the potential anammox rates increased by 4.81 and 5.57 nmol N g-1 h-1, respectively. These results underscore the substantial impact of macroinvertebrates on anammox and N-removal processes, highlighting their crucial role in N pollution control, and sustaining the overall health and stability of eutrophic water bodies.

Microplastic contamination in seawater across global marine protected areas boundaries.

Despite the relatively rich literature on the omnipresence of microplastics in marine environments, the current status and ecological impacts of microplastics on global Marine Protected Areas (MPAs) are still unknown. Their ubiquitous occurrence, increasing volume, and ecotoxicological effects have made microplastic an emerging marine pollutant. Given the critical conservation roles of MPAs that aim to protect vulnerable marine species, biodiversity, and resources, it is essential to have a comprehensive overview of the occurrence, abundance, distribution, and characteristics of microplastics in MPAs including their buffer zones. Here, extensive data were collected and screened based on 1565 peer-reviewed literature from 2017 to 2020, and a GIS-based approach was applied to improve the outcomes by considering boundary limits. Microplastics in seawater samples were verified within the boundaries of 52 MPAs; after including the buffer zones, 1/3 more (68 MPAs) were identified as contaminated by microplastics. A large range of microplastic levels in MPAs was summarized based on water volume (0-809,000 items/m3) or surface water area (21.3-1,650,000,000 items/km2), which was likely due to discrepancy in sampling and analytical methods. Fragment was the most frequently observed shape and fiber was the most abundant shape. PE and PP were the most common and also most abundant polymer types. Overall, 2/3 of available data reported that seawater microplastic levels in MPAs were higher than 12,429 items/km2, indicating that global MPAs alone cannot protect against microplastic pollution. The current limitations and future directions were also discussed toward the post-2020 Global Biodiversity Framework goals.

How do microplastics adsorb metals? A preliminary study under simulated wetland conditions.

Microplastics (MPs) are widely detected in wetlands as emerging pollutants of global concern. Co-occurrence of MPs and trace metals in wetlands is common and the vector effects of MPs on other environmental pollutants have been increasingly reported. However, the interaction of different MPs and trace metals under environmentally realistic conditions is not well understood. Here, we investigated the adsorption capacity of MPs for metals under simulated conditions of Poyang Lake wetlands in Jiang Xi, China, a Ramsar site of international importance for conservation and sustainable use. ICP-MS was used to quantify the amount of adsorbed metals onto different types of MPs. SEM-EDS and micro-FTIR were used to examine the morphological and chemical characteristics of MPs before and after metal adsorption. The influence of internal (polymer types and particle sizes of MPs) and external factors (water pH values, organic matters, ion strength, and sediment) on metal adsorption was systematically investigated. Metal adsorption equilibrium was most achieved at 72 h. The adsorption capacity of MP types to metal ions tended to decrease as PP > PE > PS, and the amount of adsorbed metals decreased as Cu > Pb > Cd. The amount of adsorbed metals generally decreased with the increase of particle size of MPs. With the increase of water pH and K+ strength, the adsorption of metals by MPs showed an increasing and then decreasing trend; the adsorption capacity of MPs increased with the increase of fulvic acid. Under the simulated sedimentary conditions, the adsorption of different metals by MPs also tended to be Cu > Pb > Cd, which was mainly determined by metal concentrations in the sediments collected in situ. The results of this study improve our understanding of metal-MP interaction under simulated environmental conditions, shedding new light on the environmental behavior of MPs and metals in wetlands.

Effect of microplastics on ecosystem functioning: Microbial nitrogen removal mediated by benthic invertebrates.

While ecotoxicological impacts of microplastics on aquatic organisms have started to be investigated recently, impacts on ecosystem functions mediated by benthic biota remain largely unknown. We investigated the effect of microplastics on nitrogen removal in freshwater sediments where microorganisms and benthic invertebrates (i.e., chironomid larvae) co-existed. Using microcosm experiments, sediments with and without invertebrate chironomid larvae were exposed to microplastics (polyethylene) at concentrations of 0, 0.1, and 1 wt%. After 28 days of exposure, the addition of microplastics or chironomid larvae promoted the growth of denitrifying and anammox bacteria, leading to increased total nitrogen removal, in both cases. However, in microcosms with chironomid larvae and microplastics co-existing, nitrogen removal was less than the sum of their individual effects, especially at microplastics concentration of 1 wt%, indicating an adverse effect on microbial nitrogen removal mediated by macroinvertebrates. This study reveals that the increasing concentration of microplastics entangled the nitrogen cycling mediated by benthic invertebrates in freshwater ecosystems. These findings highlight the pursuit of a comprehensive understanding of the impacts of microplastics on the functioning in freshwater ecosystems.

Roles of miR-432 and circ_0000418 in mediating the anti-depressant action of ADAR1.

Adenosine deaminase acting on RNA1 (ADAR1) is a newly discovered epigenetic molecule marker that is sensitive to environmental stressors. A recent study has demonstrated that ADAR1 affects BDNF expression via miR-432 and is involved in antidepressant action. However, the detailed molecular mechanism is still unclear. We have uncovered a new molecular mechanism showing the involvement of miR-432 and circ_0000418 in mediating the antidepressant action of ADAR1. We demonstrate that the ADAR1 inducer (IFN-γ) alleviates the depressive-like behaviors of BALB/c mice treated with chronic unpredictable stress (CUS) exposure. Moreover, both in vivo and in vitro studies show that ADAR1 differently impacts miR-432 and circ_0000418 expressions. Furthermore, the in vitro results demonstrate that circ_0000418 oppositely affects BDNF expression. Together, our results indicate that ADAR1 affects CUS-induced depressive-like behavior and BDNF expression by acting on miR-432 and circ_0000418. Elucidation of this new molecular mechanism will not only provide insights into further understanding the important role of ADAR1 in stress-induced depressive-like behavior but also suggest a potential therapeutic strategy for developing novel anti-depressive drugs.