A catchment‐scale perspective of plastic pollution

Plastic pollution is distributed across the globe, but compared with marine environments, there is only rudimentary understanding of the distribution and effects of plastics in other ecosystems. Here, we review the transport and effects of plastics across terrestrial, freshwater and marine environments. We focus on hydrological catchments as well‐defined landscape units that provide an integrating scale at which plastic pollution can be investigated and managed. Diverse processes are responsible for the observed ubiquity of plastic pollution, but sources, fluxes and sinks in river catchments are poorly quantified. Early indications are that rivers are hotspots of plastic pollution, supporting some of the highest recorded concentrations. River systems are also likely pivotal conduits for plastic transport among the terrestrial, floodplain, riparian, benthic and transitional ecosystems with which they connect. Although ecological effects of micro‐ and nanoplastics might arise through a variety of physical and chemical mechanisms, consensus and understanding of their nature, severity and scale are restricted. Furthermore, while individual‐level effects are often graphically represented in public media, knowledge of the extent and severity of the impacts of plastic at population, community and ecosystem levels is limited. Given the potential social, ecological and economic consequences, we call for more comprehensive investigations of plastic pollution in ecosystems to guide effective management action and risk assessment. This is reliant on (a) expanding research to quantify sources, sinks, fluxes and fates of plastics in catchments and transitional waters both independently as a major transport routes to marine ecosystems, (b) improving environmentally relevant dose–response relationships for different organisms and effect pathways, (c) scaling up from studies on individual organisms to populations and ecosystems, where individual effects are shown to cause harm and; (d) improving biomonitoring through developing ecologically relevant metrics based on contemporary plastic research.     

Microplastic effects on carbon cycling processes in soils

Microplastics (MPs), plastic particles <5 mm, are found in environments, including terrestrial ecosystems, planetwide. Most research so far has focused on ecotoxicology, examining effects on performance of soil biota in controlled settings. As research pivots to a more ecosystem and global change perspective, questions about soil-borne biogeochemical cycles become important. MPs can affect the carbon cycle in numerous ways, for example, by being carbon themselves and by influencing soil microbial processes, plant growth, or litter decomposition. Great uncertainty surrounds nano-sized plastic particles, an expected by-product of further fragmentation of MPs. A major concerted effort is required to understand the pervasive effects of MPs on the functioning of soils and terrestrial ecosystems; importantly, such research needs to capture the immense diversity of these particles in terms of chemistry, aging, size, and shape.

This Essay proposes that a major concerted effort is required to understand the pervasive effects of microplastics on the functioning of soils and terrestrial ecosystems, including the immense diversity of microplastic particles in terms of their chemistry, aging, size, and shape.     

Current research trends on microplastic pollution from wastewater systems: a critical review

Microplastics have been widely considered as contaminants for the environment and biota. Till now, most previous studies have focused on the identification and characterization of microplastics in freshwater, sea water, and the terrestrial environment. Although microplastics have been extensively detected in the wastewater, research in this area is still lacking and not thoroughly understood. To fill this knowledge gap, the current review article covers the analytical methods of microplastics originating from wastewater streams and describes their sources and occurrences in wastewater treatment plants (WWTPs). Studies indicated that microplastic pollution caused by domestic washing of synthetic fibers could be detected in the effluent; however, most microplastics from personal care and cosmetic products (PCCPs) can be efficiently removed during wastewater treatment. Moreover, various techniques for sampling and analyzing microplastics from wastewater systems are reviewed; while, the implementation of standardized protocols for microplastics is required. Finally, the fate of microplastics during wastewater treatments and the environmental contamination of effluent to environment are presented. Previous studies reported that the advanced wastewater treatment (e.g., membrane bioreactor) is needed for improving the removal efficiency of small-sized microplastics (<?100 µm). Although the role of microplastics as transport vectors for persistent organic pollutants (POPs) is still under debate, they have demonstrated abilities to absorb harmful agents like pharmaceuticals.

     

Ecosystem engineering effects on species diversity across ecosystems: a meta‐analysis

Ecosystem engineering is increasingly recognized as a relevant ecological driver of diversity and community composition. Although engineering impacts on the biota can vary from negative to positive, and from trivial to enormous, patterns and causes of variation in the magnitude of engineering effects across ecosystems and engineer types remain largely unknown. To elucidate the above patterns, we conducted a meta‐analysis of 122 studies which explored effects of animal ecosystem engineers on species richness of other organisms in the community. The analysis revealed that the overall effect of ecosystem engineers on diversity is positive and corresponds to a 25% increase in species richness, indicating that ecosystem engineering is a facilitative process globally. Engineering effects were stronger in the tropics than at higher latitudes, likely because new or modified habitats provided by engineers in the tropics may help minimize competition and predation pressures on resident species. Within aquatic environments, engineering impacts were stronger in marine ecosystems (rocky shores) than in streams. In terrestrial ecosystems, engineers displayed stronger positive effects in arid environments (e.g. deserts). Ecosystem engineers that create new habitats or microhabitats had stronger effects than those that modify habitats or cause bioturbation. Invertebrate engineers and those with lower engineering persistence (<1 year) affected species richness more than vertebrate engineers which persisted for >1 year. Invertebrate species richness was particularly responsive to engineering impacts. This study is the first attempt to build an integrative framework of engineering effects on species diversity; it highlights the importance of considering latitude, habitat, engineering functional group, taxon and persistence of their effects in future theoretical and empirical studies.     

Transport and fate of microplastics in wastewater treatment plants: implications to environmental health

Global studies of microplastic (MP) pollution confirm wastewater treatment plants serve as pathways for microplastics entering terrestrial and aquatic ecosystems. The behaviour, transport and fate of microplastics in wastewater effluents remain mostly unknown, rendering wastewater-derived microplastics as a contaminant of significant concern. We critically examine the literature to understand the sources and fate of microplastics in wastewater treatment plants (WWTPs) and the implications of treated effluents admitted to soil and aquatic systems. The transport of chemical and biological contaminants is also discussed in detail, using fundamental principles of vector relationships. For the removal and reduction of microplastics, profound knowledge is required from source to solution. This review presents a comprehensive overview of the significance of microplastics as a vector of water-borne contaminants in WWTPs.     

陆地生态系统凋落物分解对全球气候变暖的响应

陆地生态系统凋落物分解是全球碳收支的一个重要组成部分, 主要受气候、凋落物质量和土壤生物群落的综合控制。科学家们普遍认为全球气候变化将对陆地生态系统凋落物分解产生复杂而深远的影响。该文结合凋落物分解试验的常用方法——缩微试验、原位模拟实验和自然环境梯度实验, 归纳现有研究结果, 意在揭示全球气候变化对陆地生态系统凋落物分解的直接影响(温度对凋落物分解速率的影响)和间接影响(温度对凋落物质量、土壤微生物群落及植被型的影响)的普遍规律。各种研究方法都表明: 在水分条件理想的情况下, 温度升高往往能加快凋落物的分解速率; 原位模拟实验中, 凋落物分解速率因物种、增温方法和地理方位而异; 全球气候变化能改变凋落物质量, 但可能不会在短期内影响凋落物的分解速率; 凋落物质量和可分解性的种间差异远大于增温所引发的表型响应差异, 那么, 气候变化所引发的植物群落结构和物种组成的变化将对陆地生态系统凋落物分解产生更强烈的影响; 土壤生物群落如何响应全球气候变化, 进而怎样影响凋落物分解过程, 这些都还存在着极大的不确定性。     

Perspectives and challenges of micro/nanoplastics‐induced toxicity with special reference to phytotoxicity

Plastic pollution has become a global concern for ecosystem health and biodiversity conservation. Concentrations of plastics are manifold higher in the terrestrial system than the aquatic one. Micro/nanoplastics (M/NP) have the ability to alter soil enzymatic system, soil properties and also affect soil borne microorganisms and earthworms. Despite, the knowhow regarding modulatory effects of plastics are acquired from the study on aquatic system and reports on their phytotoxic potentials are limited. The presence of cell wall that could restrict M/NP invasion into plant roots might be the putative cause of this limitation. M/NP inhibit plant growth, seed germination and gene expression; and they also induce cytogenotoxicity by aggravating reactive oxygen species generation. Dynamic behavior of cell wall; the pores formed either by cell wall degrading enzymes or by plant–pathogen interactions or by mechanical injury might facilitate the entry of into roots M/NP. This review also provides a possible mechanism of large sized microplastics‐induced phytotoxicity especially for those that cannot pass through cell wall pores. As M/NP affect soil microbial community and soil parameters, it is hypothesized that they could have the potential to affect N₂ fixation and research should be conducted in this direction. Reports on M/NP‐induced toxicity mainly focused only on one polymer type (polystyrene) in spite of the toxicological relevancies of other polymer types like polyethylene, polypropylene etc. So, the assessment of phytotoxic potential of M/NP should be done using other plastic polymers in real environment as they are known to intract with other environmental stressors as well as can alter the the soil–microbe–plant interaction.     

海洋微塑料污染的生态效应研究进展

海洋微塑料污染已成为全球性环境问题。微塑料粒径小,易与海洋生物发生相互作用,可通过多种途径进入海洋生物体内,并在其组织和器官中蓄积和转移,对机体产生毒害。微塑料可沿食物链进行传递,威胁海洋生态系统的健康与稳定。因此,海洋生物与微塑料的相互作用以及海洋微塑料污染的生态效应成为当前研究的热点。综述微塑料的生物附着、生物摄入、对海洋生物的毒性效应及其与化学污染物的复合毒性效应研究的基础上,提出未来微塑料生态效应研究应重点关注我国海洋环境中微塑料的污染现状及生物摄入状况、微塑料的生物效应及其毒理学机制研究、微塑料与其他污染物的复合效应、以及微塑料在海洋生态系统中的作用及其生物地球化学行为等。     

Nanoplastics alter ecosystem multifunctionality and may increase global warming potential

Although the presence of nanoplastics in aquatic and terrestrial ecosystems has received increasing attention, little is known about its potential effect on ecosystem processes and functions. Here, we evaluated if differentially charged polystyrene (PS) nanoplastics (PS-NH₂ and PS-SO₃H) exhibit distinct influences on microbial community structure, nitrogen removal processes (denitrification and anammox), emissions of greenhouse gases (CO₂, CH₄, and N₂O), and ecosystem multifunctionality in soils with and without earthworms through a 42-day microcosm experiment. Our results indicated that nanoplastics significantly altered soil microbial community structure and potential functions, with more pronounced effects for positively charged PS-NH₂ than for negatively charged PS-SO₃H. Ecologically relevant concentration (3 g kg⁻¹) of nanoplastics inhibited both soil denitrification and anammox rates, while environmentally realistic concentration (0.3 g kg⁻¹) of nanoplastics decreased the denitrification rate and enhanced the anammox rate. The soil N₂O flux was always inhibited 6%–51% by both types of nanoplastics, whereas emissions of CO₂ and CH₄ were enhanced by nanoplastics in most cases. Significantly, although N₂O emissions were decreased by nanoplastics, the global warming potential of total greenhouse gases was increased 21%–75% by nanoplastics in soils without earthworms. Moreover, ecosystem multifunctionality was increased 4%–12% by 0.3 g kg⁻¹ of nanoplastics but decreased 4%–11% by 3 g kg⁻¹ of nanoplastics. Our findings provide the only evidence to date that the rapid increase in nanoplastics is altering not only ecosystem structure and processes but also ecosystem multifunctionality, and it may increase the emission of CO₂ and CH₄ and their global warming potential to some extent.     

微塑料污染对浮游生物影响研究进展

微塑料作为一种新型的环境污染物,大量存在于水环境中,给水生生物带来了极大的危害。浮游生物是水生食物链的基础,是水生生态系统物质循环和能量流动的重要环节;同时,浮游生物也是对各种环境污染物最敏感的类群。了解微塑料对浮游生物的影响是评价其生态风险的重要依据。本文介绍了环境中微塑料来源、特征及水生态系统微塑料污染现状,阐述了微塑料对水生生物的直接和间接危害,并重点聚焦于浮游植物和浮游动物,从个体、种群和群落的层次详细总结了微塑料的影响及其作用机制。最后,本文指出当前针对浮游生物微观基因和蛋白质组学,以及宏观种群和群落响应等方面的研究还非常缺乏,为今后开展微塑料危害研究提供参考。     

城乡景观中土壤生态系统微塑料的来源、迁移特征及其风险

土壤微塑料污染的持久性、复杂性及其对土壤生态系统的影响受到越来越广泛的关注,但对其来源、迁移过程等仍有许多问题尚未理清。从复合生态系统的角度,通过对城乡景观中土壤微塑料的来源、迁移过程及其风险等相关研究进展进行了系统梳理,分析了城乡不同景观中土壤微塑料的主要来源和特点,讨论了土壤微塑料在城乡景观中的迁移特征及其驱动力,探讨了土壤微塑料在城乡景观中的生态和健康风险。今后需进一步明确城乡景观中土壤微塑料污染的物质流过程与环境归趋特征,加强微塑料对土壤生态系统的作用过程及生态系统服务影响的研究,揭示土壤微塑料对人类健康的直接或间接影响,建立城乡复合生态系统土壤微塑料污染预测模型,以维护土壤生态安全与人居环境健康。     

Freshwater wild biota exposure to microplastics: A global perspective

1. Current understanding on the exposure of freshwater organisms to microplastics (plastics sized between 1 µm and 5 mm) has arisen mostly from laboratory experiments—often conducted under artificial circumstances and with unrealistic concentrations. In order to improve scientific links through real ecosystem exposure, we review field data on the exposure of free‐living organisms to microplastics.
2. We highlight that the main outputs provided by field research are an assessment of the occurrence and, at times, the quantification of microplastics in different animal taxa. Topics of investigation also include the causes of contamination and the development of biological monitoring tools. With regard to taxa, fish, mollusks, and arthropods are at the center of the research, but birds and amphibians are also investigated. The ingestion or occurrence of microplastics in organs and tissues, such as livers and muscles, are the main data obtained. Microorganisms are studied differently than other taxa, highlighting interesting aspects on the freshwater plastisphere, for example, related to the structure and functionality of communities. Many taxa, that is, mammals, reptiles, and plants, are still under‐examined with regard to exposure to microplastics; this is surprising as they are generally endangered.
3. As biota contamination is acknowledged, we contribute to an interdisciplinary scientific discussion aimed at a better assessment of knowledge gaps on methodology, impact assessment, and monitoring.

     

Plastic pollution in croplands threatens long‐term food security

Plastic pollution is a global concern given its prevalence in aquatic and terrestrial ecosystems. Studies have been conducted on the distribution and impact of plastic pollution in marine ecosystems, but little is known on terrestrial ecosystems. Plastic mulch has been widely used to increase crop yields worldwide, yet the impact of plastic residues in cropland soils to soil health and crop production in the long term remained unclear. In this paper, using a global meta‐analysis, we found that the use of plastic mulch can indeed increase crop yields on average by 25%–42% in the immediate season due to the increase of soil temperature (+8%) and moisture (+17%). However, the unabated accumulation of film residues in the field negatively impacts its physicochemical properties linked to healthy soil and threatens food production in the long term. It has multiple negative impacts on plant growth including crop yield (at the mean rate of ?3% for every additional 100 kg/ha of film residue), plant height (?2%) and root weight (?5%), and soil properties including soil water evaporation capacity (?2%), soil water infiltration rate (?8%), soil organic matter (?0.8%) and soil available phosphorus (?5%) based on meta‐regression. Using a nationwide field survey of China, the largest user of plastic mulch worldwide, we found that plastic residue accumulation in cropland soils has reached 550,800 tonnes, with an estimated 6%–10% reduction in cotton yield in some polluted sites based on current level of plastic residue content. Immediate actions should be taken to ensure the recovery of plastic film mulch and limit further increase in film residue loading to maintain the sustainability of these croplands.     

Responses of belowground communities to large aboveground herbivores: Meta‐analysis reveals biome‐dependent patterns and critical research gaps

The importance of herbivore–plant and soil biota–plant interactions in terrestrial ecosystems is amply recognized, but the effects of aboveground herbivores on soil biota remain challenging to predict. To find global patterns in belowground responses to vertebrate herbivores, we performed a meta‐analysis of studies that had measured abundance or activity of soil organisms inside and outside field exclosures (areas that excluded herbivores). Responses were often controlled by climate, ecosystem type, and dominant herbivore identity. Soil microfauna and especially root‐feeding nematodes were negatively affected by herbivores in subarctic sites. In arid ecosystems, herbivore presence tended to reduce microbial biomass and nitrogen mineralization. Herbivores decreased soil respiration in subarctic ecosystems and increased it in temperate ecosystems, but had no net effect on microbial biomass or nitrogen mineralization in those ecosystems. Responses of soil fauna, microbial biomass, and nitrogen mineralization shifted from neutral to negative with increasing herbivore body size. Responses of animal decomposers tended to switch from negative to positive with increasing precipitation, but also differed among taxa, for instance Oribatida responded negatively to herbivores, whereas Collembola did not. Our findings imply that losses and gains of aboveground herbivores will interact with climate and land use changes, inducing functional shifts in soil communities. To conceptualize the mechanisms behind our findings and link them with previous theoretical frameworks, we propose two complementary approaches to predict soil biological responses to vertebrate herbivores, one focused on an herbivore body size gradient, and the other on a climate severity gradient. Major research gaps were revealed, with tropical biomes, protists, and soil macrofauna being especially overlooked.     

Microplastics reduce soil microbial network complexity and ecological deterministic selection

Microplastics have been proposed as emerging threats for terrestrial systems as they may potentially alter the physicochemical/biophysical soil environments. Due to the variety of properties of microplastics and soils, the microplastic-induced effects in soil ecosystems are greatly manifold. Here, we studied effects of three polymer microplastics (polyamide-6, polyethylene, and polyethylene terephthalate) on soil properties with four different soil types. The success patterns, interaction relationships, and assembly processes of soil bacterial communities were also studied. Microplastics have the potential to promote CO₂ emissions and enhance the soil humification. Even though microplastics did not significantly alter the diversity and composition of the soil microbial community, the application of microplastics decreased the network complexity and stability, including network size, connectivity, and the number of module and keystone species. The bacterial community assembly was governed by deterministic selection (77.3%–90.9%) in all treatments, while microplastics increased the contribution of stochastic processes from 9.1% in control to 13.6%–22.7%. The neutral model results also indicated most of the bacterial taxa were present in the predicted neutral region (approximately 98%), suggesting the importance of stochastic processes. These findings provided a fundamental insight in understanding the effects of microplastics on soil ecosystems.     

Food or just a free ride? A meta-analysis reveals the global diversity of the Plastisphere

It is now indisputable that plastics are ubiquitous and problematic in ecosystems globally. Many suggestions have been made about the role that biofilms colonizing plastics in the environment—termed the “Plastisphere”—may play in the transportation and ecological impact of these plastics. By collecting and re-analyzing all raw 16S rRNA gene sequencing and metadata from 2,229 samples within 35 studies, we have performed the first meta-analysis of the Plastisphere in marine, freshwater, other aquatic (e.g., brackish or aquaculture) and terrestrial environments. We show that random forest models can be trained to differentiate between groupings of environmental factors as well as aspects of study design, but—crucially—also between plastics when compared with control biofilms and between different plastic types and community successional stages. Our meta-analysis confirms that potentially biodegrading Plastisphere members, the hydrocarbonoclastic Oceanospirillales and Alteromonadales are consistently more abundant in plastic than control biofilm samples across multiple studies and environments. This indicates the predilection of these organisms for plastics and confirms the urgent need for their ability to biodegrade plastics to be comprehensively tested. We also identified key knowledge gaps that should be addressed by future studies.Subject terms: Microbial ecology, Soil microbiology, Water microbiology, Microbial ecology, Microbiome     

Engineering role models: do non-human species have the answers?

A shift from traditional engineering approaches to ecologically-based techniques will require changing societal values regarding ‘how and what’ is defined as engineering and design. Non-human species offer many ecological engineering examples that are often beneficial to ecosystem function and other biota. For example, organisms known as ‘ecosystem engineers’ build, modify, and destroy habitat in their quest for food and survival. Similarly, ‘keystone species’ have greater impacts on community or ecosystem function than would be predicted from their abundance. The capacity of these types of organisms to affect ecosystems is great. They exert controlling influences over ecosystems and communities by altering resource allocation, creating habitats and modifying relative competitive advantages.Species’ effects in ecosystems, although context-dependent, can be evaluated as ‘beneficial’ or ‘detrimental’. The evaluation depends on whether effects on other species or ecosystem function are more or less desirable from a given perspective. Organisms with beneficial impacts facilitate the presence of other species, employ efficient nutrient cycling, and are sometimes characterized by specific mutualisms. In contrast, many cases of detrimental engineering are found from introduced (i.e., exotic) species and are characterized by a loss of species richness, a lack of nutrient retention and the degradation of ecosystem integrity. Species’ impacts on ecosystems and community traits have been quantified in ecological studies and can be used similarly to understand, design and model human engineering structures and impacts on the landscape. Emulation of species with beneficial impacts on ecosystems can provide powerful guidance to the goals of ecological engineering. Using role model organisms that have desirable effects on species diversity and ecosystem function will be important in developing alternatives to traditional engineering practices.     

Antarctic terrestrial biodiversity in a changing world

Recent analyses of Antarctic terrestrial biodiversity data, in combination with molecular biological studies, have created a new paradigm that long-term persistence and regional isolation are general features of most of the major groups of Antarctic terrestrial biota, overturning the previously widely assumed view of a generally recent colonisation history. This paradigm, as well as incorporating a new and much longer timescale in which to consider the evolution and adaptation of Antarctic terrestrial biota, opens important new cross-disciplinary linkages with geologists and glaciologists seeking to unravel the history of the continent itself. This unique biota now faces the twin challenges of responding to the complex processes of climate change facing some parts of the continent, and the direct impacts associated with human occupation and activity. In many instances, this biota is likely to benefit, initially at least, from the current environmental changes, and there is an expectation of increased production, biomass, population size, community complexity, and colonisation. However, the impacts of climate change may themselves be outweighed by other, direct, impacts of human activities, and in particular, the introduction of non-indigenous organisms from which until recently the terrestrial ecosystems of the continent have been protected. The Antarctic research community and those responsible for governance under the Antarctic treaty system are faced with the pressing challenges of (1) ensuring there is sufficient baseline monitoring and survey activity to enable identification of these changes, however caused and (2) ensuring that effective operational management and biosecurity procedures are in place to minimise the threat from anthropogenic activities.     

Marine incursion into East Asia: a forgotten driving force of biodiversity

Episodic marine incursion has been a major driving force in the formation of present-day diversity. Marine incursion is considered to be one of the most productive ‘species pumps’ particularly because of its division and coalescence effects. Marine incursion events and their impacts on diversity are well documented from South America, North America and Africa; however, their history and impacts in continental East Asia largely remain unknown. Here, we propose a marine incursion scenario occurring in East Asia during the Miocene epoch, 10–17 Ma. Our molecular phylogenetic analysis of Platorchestia talitrids revealed that continental terrestrial populations (Platorchestia japonica) form a monophyletic group that is the sister group to the Northwest Pacific coastal species Platorchestia pacifica. The divergence time between the two species coincides with Middle Miocene high global sea levels. We suggest that the inland form arose as a consequence of a marine incursion event. This is the first solid case documenting the impact of marine incursion on extant biodiversity in continental East Asia. We believe that such incursion event has had major impacts on other organisms and has played an important role in the formation of biodiversity patterns in the region.