Release of treated effluent into streams: A global review of ecological impacts with a consideration of its potential use for environmental flows

1. Worldwide, the addition of treated wastewater (i.e. effluent) to streams is becoming more common as urban populations grow and developing countries increase their use of wastewater treatment plants. Release of treated effluent can impair water quality and ecological communities, but also could help restore flow and maintain aquatic habitat in water-stressed regions. To assess this range of potential outcomes, we conducted a global review of studies from effluent-fed streams to examine the impacts of effluent on water quality and aquatic and riparian biota.
2. We identified 147 quantitative studies of effluent-fed streams, most of which were from the U.S.A. and Europe. Over 85% of the studies identified water quality as a primary study focus, including basic physical and chemical parameters, as well as trace organic contaminants. Nearly 60% of the studies had at least some focus on aquatic or riparian biota, primarily fish, aquatic invertebrates, and basal resources (e.g. algae).
3. Effluent inputs generally impaired water quality near discharge points, mainly through increased water temperature, nutrients, and concentrations of trace organic contaminants, but also via decreased dissolved oxygen levels. The majority of ecological studies found that basal resources, aquatic invertebrates, and fish were negatively affected in a variety of ways (e.g. biodiversity losses, replacement of sensitive with tolerant species). However, several studies showed the importance of effluent in providing environmental flows to streams that had been dewatered by anthropogenic water withdrawals, especially in semi-arid and arid regions.
4. Knowledge gaps identified include the abiotic impacts of effluent, such as changes in channel morphology and hydrology (e.g. how nutrient-rich and warmer effluent affects infiltration rates or interactions with groundwater), the effects of effluent on plants and vertebrates (e.g. amphibians, birds), and the impact of effluent-induced perennialisation on naturally intermittent or ephemeral streams.
5. Although effluent-fed streams often exhibit signs of ecological impairment, there is great potential for these systems to serve as refuges of aquatic biodiversity and corridors of ecological connectivity when wastewater treatment standards are high, especially in semi-arid and arid regions where natural streams have been dewatered.

     

Impacts of climatic stability on the structural and functional aspects of macroinvertebrate communities after severe drought

1. Unpredictable, extreme climatic events (e.g. droughts) can potentially destabilize aquatic communities. From 1998 to 2002, southwestern Georgia, U.S.A., experienced the third worst drought of the last 100 years, leading to loss of surface flow in many small streams. We sampled macroinvertebrates, flow and water chemistry in small headwater streams from 2001 to 2007 in two adjacent coastal plain streams of contrasting headwater type (wetland and groundwater‐fed seep) following resumption of flow. 2. Decreasing water temperature, conductivity and nutrient concentrations within the first 2 years of the study indicated flushing of the streambed associated with increased discharge. Invertebrate community composition became less variable over time and during wetter years, reflecting water chemistry, hydrological and climate conditions. 3. A core set of species appeared immediately following breaking of the drought in both streams, reflecting a shared species pool. These species exhibited resilience traits, including short life cycles and resistance to desiccation, which allowed for rapid recovery from disturbance. Such species, which were small‐bodied, sclerotized and abundant in the drift, were then replaced as flows increased by those that were larger, soft‐bodied and rare in drift, suggesting a more stable and less ephemeral habitat. 4. Hydrologic regime and long‐term precipitation indices were strongly correlated with invertebrate community and trait structure. Long‐term data allowed for better interpretation of the effects of infrequent disturbances on aquatic ecosystems. Additionally, long‐term precipitation indices (i.e. 48‐month standardized precipitation index) can indicate the likelihood of a return to drought, allowing for the collection of pre‐disturbance data.     

广东车八岭国家级自然保护区大型底栖动物多样性

大型底栖动物在当地生物多样性、食物链构成、水质指示和物质循环中有重要的作用, 但目前国内对森林内陆水体(湖泊、水库、溪流)中的大型底栖动物综合调查较少。作者于2019、2020年对广东车八岭国家级自然保护区的9个采样点开展了大型底栖动物的定性调查, 采样点涵盖保护区不同功能区、海拔、水体环境和水体底质。共鉴定出大型底栖动物4门6纲18目38科57种, 水生昆虫稚虫占大多数, 且多喜好清洁流动水体。在低海拔实验区即可采集到种类与数量可观的清洁水体指示物种。当地的大型底栖动物以亚热带森林典型物种为主, 多偏好栖息于流动水体, 反映了保护区的物种区系及其水体环境。本研究可为保护区的物种编目、环境评估和长期监测提供基础资料。     

Structural and functional development of twelve newly established floodplain pond mesocosms

Ecosystems are complex structures with interacting abiotic and biotic processes evolving with ongoing succession. However, limited knowledge exists on the very initial phase of ecosystem development and colonization. Here, we report results of a comprehensive ecosystem development monitoring for twelve floodplain pond mesocosms (FPM; 23.5 m × 7.5 m × 1.5 m each) located in south‐western Germany. In total, 20 abiotic and biotic parameters, including structural and functional variables, were monitored for 21 months after establishment of the FPMs. The results showed evolving ecosystem development and primary succession in all FPMs, with fluctuating abiotic conditions over time. Principal component analyses and redundancy analyses revealed season and succession time (i.e., time since ecosystem establishment) to be significant drivers of changes in environmental conditions. Initial colonization of both aquatic (i.e., water bodies) and terrestrial (i.e., riparian land areas) parts of the pond ecosystems occurred within the first month, with subsequent season‐specific increases in richness and abundance for aquatic and terrestrial taxa over the entire study period. Abiotic environmental conditions and aquatic and terrestrial communities showed increasing interpond variations over time, that is, increasing heterogeneity among the FPMs due to natural environmental divergence. However, both functional variables assessed (i.e., aquatic and terrestrial litter decomposition) showed opposite patterns as litter decomposition rates slightly decreased over time and interpond differences converged with successional ecosystem developments. Overall, our results provide rare insights into the abiotic and biotic conditions and processes during the initial stages of freshwater ecosystem formation, as well as into structural and functional developments of the aquatic and terrestrial environment of newly established pond ecosystems.     

A Conceptual Framework for Using Mussels as Biomonitors in Whole Effluent Toxicity

As a main source of direct and continuous input of pollutants in the aquatic ecosystem, studying the effects of effluents on receiving ecosystems has a high ecological relevance. While ecological risk assessment procedures are usually based on a chemical-based single component approach, their application for complex mixtures and effluents is less straightforward. A chemical-based approach has to rely on the knowledge of what chemicals are present in effluents, their potential toxicity, how all of these individual chemicals interact and what their individual and combined contribution to the mixture is. Whole effluent toxicity (WET) testing, however, is an integrative tool that measures the toxic effect of an effluent as a whole and accounts for uncharacterized sources of toxicity and for interactions. This paper addresses the use of transplanted bivalves, i.e., caged mussels, as a biomonitoring tool in WET testing with special reference to field situations in both freshwater and marine environments. We indicate how endpoints at different levels of biological organization within exposed mussels can give an integrative overview of effects. Finally, we will provide a framework for future research using mussels and discuss a multitude of instream responses for routine, efficient and cost-effective active biomonitoring applications.     

Structural and functional aspects of treated mine water and aquaculture effluent streams

Multiple effluent streams may flow into a single receiving stream making it difficult to understand the effects of a single effluent source or the interactions between effluents. In this study, we examined benthic community structure and function in an effluent stream formed by the release of treated mine water, in treated mine water that had been used as a water source for flow-through aquaculture and below the confluence of the two. This study demonstrated that macroinvertebrate communities, while taxonomically simple, developed in treated mine water. The addition of aquaculture effluent to the treated mine water allowed colonization by additional taxa, increased leaf decomposition rates and may have conferred resistance to a turbidity event. Ecosystem responses were mediated by the surrounding terrestrial environment. In shaded conditions macroinvertebrate densities could be as much as 10× higher and the taxa were dominated by simuliids and chironomids, while in open conditions filamentous algae flourished and the taxa were dominated by hydroptilids and chironomids. Consequently, consideration of stream processes that promote preferred ecological processes, such as macroinvertebrate production and organic matter processing, when siting effluent streams may reduce impacts on receiving streams.     

流域水质管理系统构建的理论、方法和实践

随着工农业的发展及乡村都市化 ,淡水资源的短缺成为全球性的问题。淡水资源的短缺 ,一方面是对淡水需求量增加 ,供不应求。另一方面是水体水质恶化 ,水资源退化。保护淡水资源是一项持久性的艰巨任务 ,其中水资源管理工具评价预测各种管理措施对水资源的影响 ,是必不可缺少的。工业和生活废水对水体的点源污染问题 ,早在2 0世纪 2 0年代就被意识到 ,并开展了一些水资源的保护和管理研究工作。自 192 5第一个水质数学模型Ｓｔｒｅｅｔｅｒ Ｐｈｅｌｐｓ[1] 用于模拟水环境中ＢＯＤ和ＤＯ的动态变化研究以来 ,出现了许多水质模型并用于河流、…     

Biological monitoring of water quality in Australia: Workshop summary and future directions

Abstract Biological methods are widely accepted in water quality monitoring programmes worldwide; however, some concern remains over their effectiveness in predicting the effects of contaminants on aquatic ecosystems. While the so-called‘early warning’ approaches, such as bioassays and biomarkers, have been used in Australia to demonstrate mechanisms of toxic action and exposure to contaminants, as elsewhere, little attempt has been made to link observed effects at these lower levels of biological organization to real impacts on aquatic systems. The ecological consequences of exposure to contaminants is undoubtedly best studied at higher levels of biological organization (i. e. at the population or community level). However, monitoring aquatic communities is labour intensive and inadequate for the early detection of impacts. Research is needed to identify links between the bioassessment measures used, so that changes at the lowest biological level (e. g. using biomarkers and bioassays) can be translated into likely‘real’ impacts on the aquatic system, as measured at the population or community level. Monitoring the genetic structure of populations of aquatic organisms, particularly invertebrates, may provide a potential link between subtle effects observed in bioassay tests and subsequent changes in population density and/or community structure. A streamlined approach to monitoring changes at the community level needs to be developed to improve predictive ability and to make this approach more responsive to the early detection and prevention of unacceptable impacts. In addition, research on the use of ecosystem level parameters, such as production/respiration ratios or community metabolism, should be undertaken to determine their suitability for routine biomonitoring of water quality in Australian inland waters.     

Shifts in leaf litter breakdown along a forest–pasture–urban gradient in Andean streams

Tropical montane ecosystems of the Andes are critically threatened by a rapid land‐use change which can potentially affect stream variables, aquatic communities, and ecosystem processes such as leaf litter breakdown. However, these effects have not been sufficiently investigated in the Andean region and at high altitude locations in general. Here, we studied the influence of land use (forest–pasture–urban) on stream physico‐chemical variables (e.g., water temperature, nutrient concentration, and pH), aquatic communities (macroinvertebrates and aquatic fungi) and leaf litter breakdown rates in Andean streams (southern Ecuador), and how variation in those stream physico‐chemical variables affect macroinvertebrates and fungi related to leaf litter breakdown. We found that pH, water temperature, and nutrient concentration increased along the land‐use gradient. Macroinvertebrate communities were significantly different between land uses. Shredder richness and abundance were lower in pasture than forest sites and totally absent in urban sites, and fungal richness and biomass were higher in forest sites than in pasture and urban sites. Leaf litter breakdown rates became slower as riparian land use changed from natural to anthropogenically disturbed conditions and were largely determined by pH, water temperature, phosphate concentration, fungal activity, and single species of leaf‐shredding invertebrates. Our findings provide evidence that leaf litter breakdown in Andean streams is sensitive to riparian land‐use change, with urban streams being the most affected. In addition, this study highlights the role of fungal biomass and shredder species (Phylloicus; Trichoptera and Anchytarsus; Coleoptera) on leaf litter breakdown in Andean streams and the contribution of aquatic fungi in supporting this ecosystem process when shredders are absent or present low abundance in streams affected by urbanization. Finally, we summarize important implications in terms of managing of native vegetation and riparian buffers to promote ecological integrity and functioning of tropical Andean stream ecosystems.     

The role of oligochaetes in the management of waters

To better understand the role of an aquatic oligochaete in the management of water quality, it was determined if oligochaetes were representative of water quality, if indices based on oligochaetes were widely applicable to access water quality, and if oligochaete assemblages were related to environmental factors other than organic pollution. It was found that if only one monitoring sample a year was taken in December, about 73% of the more common species were collected. Seasonality did not seem to affect the taxa collected except for forms in low presence, e.g., Nais. Several indices we used were not applicable to regulated streams. Oligochaete ordination procedures revealed only a partial picture of the environmental conditions of regulated streams.     

Ecosystem measures of river health and their response to riparian and catchment degradation

1. Measurements of ecological patterns are often used as primary biological indicators of river health. However, these patterns provide little information about important stream ecosystem processes (e.g. the sources and fate of energy and nutrients). The direct measurement of these processes is considered fundamental to the determination of the health of stream and river ecosystems. 2. In this paper we used two basic approaches to assess stream ecosystem response to catchment disturbance and, particularly, to the loss of riparian vegetation in different forested biomes across Australia. Benthic gross primary production (GPP) and respiration (R₂₄) provided measures of the amounts of organic carbon produced and consumed within the system, respectively. Stable isotope analysis was used to trace the fate of terrestrial and instream sources of organic matter in the aquatic food web. In a focal catchment in SE Queensland, additional measurements were taken of riparian attributes, catchment features and water quality. 3. Baseline measurements of GPP and R₂₄ from undisturbed forest streams provided reference values for healthy streams for comparison with sites where the catchment or riparian vegetation had been disturbed. These values of metabolism were low by world standards in all biomes examined. Preliminary data from the Mary River catchment in SE Queensland indicated that these parameters were sensitive to variations in riparian canopy cover and, to a lesser extent, catchment clearing, and predictive models were developed. The ratio P : R (GPP : R₂₄) was used to determine whether sites were net consumers (P < R) or producers (P > R) of carbon but this was not considered a reliable indicator of stream health on its own. 4. Although forest streams were typically net consumers of carbon (P < < R), stable isotope analysis of metazoan food webs indicated a high dependence on inconspicuous epilithic algae in some biomes. 5. A dramatic decline in the health of forest streams was observed when GPP substantially exceeded R₂₄, especially when instream primary producers shifted from palatable unicellular algae to prolific filamentous green algae and macrophytes. These sources of instream production do not appear to enter aquatic food webs, either directly through grazing or indirectly through a detrital loop. Accumulation of these plants has led to changes in channel morphology, loss of aquatic habitat and often a major decline in water quality in some of the streams studied.     

How Much Is Enough? Minimal Responses of Water Quality and Stream Biota to Partial Retrofit Stormwater Management in a Suburban Neighborhood

Decentralized stormwater management approaches (e.g., biofiltration swales, pervious pavement, green roofs, rain gardens) that capture, detain, infiltrate, and filter runoff are now commonly used to minimize the impacts of stormwater runoff from impervious surfaces on aquatic ecosystems. However, there is little research on the effectiveness of retrofit, parcel-scale stormwater management practices for improving downstream aquatic ecosystem health. A reverse auction was used to encourage homeowners to mitigate stormwater on their property within the suburban, 1.8 km² Shepherd Creek catchment in Cincinnati, Ohio (USA). In 2007–2008, 165 rain barrels and 81 rain gardens were installed on 30% of the properties in four experimental (treatment) subcatchments, and two additional subcatchments were maintained as controls. At the base of the subcatchments, we sampled monthly baseflow water quality, and seasonal (5×/year) physical habitat, periphyton assemblages, and macroinvertebrate assemblages in the streams for the three years before and after treatment implementation. Given the minor reductions in directly connected impervious area from the rain barrel installations (11.6% to 10.4% in the most impaired subcatchment) and high total impervious levels (13.1% to 19.9% in experimental subcatchments), we expected minor or no responses of water quality and biota to stormwater management. There were trends of increased conductivity, iron, and sulfate for control sites, but no such contemporaneous trends for experimental sites. The minor effects of treatment on streamflow volume and water quality did not translate into changes in biotic health, and the few periphyton and macroinvertebrate responses could be explained by factors not associated with the treatment (e.g., vegetation clearing, drought conditions). Improvement of overall stream health is unlikely without additional treatment of major impervious surfaces (including roads, apartment buildings, and parking lots). Further research is needed to define the minimum effect threshold and restoration trajectories for retrofitting catchments to improve the health of stream ecosystems.     

Invasion of temperate deciduous broadleaf forests by N-fixing tree species – consequences for stream ecosystems

Biological invasions are a major threat to biodiversity and ecosystem functioning. Forest invasion by alien woody species can have cross-ecosystem effects. This is especially relevant in the case of stream–riparian forest meta-ecosystems as forest streams depend strongly on riparian vegetation for carbon, nutrients and energy. Forest invasion by woody species with dissimilar characteristics from native species may be particularly troublesome. The invasion of temperate deciduous broadleaf forests with low representation of nitrogen (N)-fixing species by N-fixers has the potential to induce ecosystem changes at the stream level. Although effects of tree invasion on stream ecosystems have been under assessed, knowledge of native and invasive tree characteristics allows prediction of invasion effects on streams. Here we present a conceptual model to predict the effects of forest invasion by alien N-fixing species on streams, using as a background the invasion of temperate deciduous broadleaf forests by leguminous Acacia species, which are among the most aggressive invaders worldwide. Effects are discussed using a trait-based approach to allow the model to be applied to other pairs of invaded ecosystem–invasive species, taking into account differences in species traits and environmental conditions. Anticipated effects of N-fixing species invasions include changes in water quality (increase in N concentration) and quantity (decrease in flow) and changes in litter input characteristics (altered diversity, seasonality, typology, quantity and quality). The magnitude of these changes will depend on the magnitude of differences in species traits, the extent and duration of the invasion and stream characteristics (e.g. basal nutrient concentration). The extensive literature on effects of nutrient enrichment of stream water, water scarcity and changes in litter input characteristics on aquatic communities and processes allows prediction of invasion effects on stream structure and function. The magnitude of invasion effects on aquatic communities and processes may, however, depend on interactions among different pathways (e.g. effects mediated by increases in stream nutrient concentration may contrast with those mediated by decreases in water availability or by decreases in litter nutritional quality). A review of the literature addressing effects of increasing cover of N-fixing species on streams suggests a wide application of the model, while it highlights the need to consider differences in the type of system and species when making generalizations. Changes induced by N-fixing species invasion on streams can jeopardize multiple ecosystem services (e.g. good quality water, hydroelectricity, leisure activities), with relevant social and economic consequences.     

Beta diversity of aquatic invertebrates increases along an altitudinal gradient in a Neotropical mountain

Mountains harbor rich biodiversity and high levels of endemism, particularly due to changes in environmental conditions over short spatial distances, which affects species distribution and composition. Studies on mountain ecosystems are increasingly needed, as mountains are highly threatened despite providing ecosystem services, such as water supply for half of the human population. We aimed to understand the patterns and drivers of alpha and beta diversities of aquatic invertebrates in headwater streams along an altitudinal gradient in the second largest South American mountain range, the Espinhaço mountains. Headwater streams were selected at each 100 m of elevation along an altitudinal gradient ranging from 800 to 1400 m asl, where three substrate types per stream were sampled: leaf litter, gravel, and cobbles. Environmental variables were sampled to represent local riparian canopy cover, instream physical habitat, water quality, climatic data, and land use. Generalized linear models and mixed models were used to test relationships between altitude and the richness and abundance of invertebrates and to assess the influence of environmental variables on the same metrics. Patterns of spatial variation in aquatic invertebrate assemblages along the altitudinal gradient were assessed using multiplicative beta diversity partitioning. The richness and abundance of aquatic invertebrates decreased with increasing altitude, whereas beta diversity increased with increasing altitude. Significant differences in assemblage composition and in relative abundance of invertebrates were observed for both substrates and altitude. We thus show that the high regional beta diversity in aquatic ecosystems in the studied site is due to the high turnover among areas. Abstract in Portuguese is available with online material.     

Impact of climatic variability on parameters used in typology and ecological quality assessment of surface waters—implications on the Water Framework Directive

In most cases the negative impacts of climate change to aquatic ecosystems cannot be mitigated by measures in the river basin management. Ignoring climate change by the Water Framework Directive may have strong implications for the typology and quality assessment systems used for water bodies. As a result of climate change, water bodies, especially those located near the type boundaries may change their type. Compared to typology characteristics, water quality parameters are even more labile and may be easily affected by climate change. The paper exemplifies that the anticipated deterioration of water quality within the time frame relevant for WFD implementation may be large enough to endanger the fulfillment of the set water quality objectives. The review of the river basin characterization every six years, as required by the WFD, might also include re-evaluation of reference conditions according to the changes observed at pristine reference sites. As a consequence, the restoration targets (i.e., the good ecological status) would also need to be evaluated periodically.     

微型生物群落eDNA-PFU监测

微型生物群落在水生态系统中起着至关重要的作用, 是水生态系统食物链的关键环节, 其结构和功能可以很好地反映不同生境的水质特征。《水质 微型生物群落监测 PFU法》是我国首个生物监测国家标准, 被证明是一种快速、经济、准确的监测方法。然而, 由于PFU法对专业知识要求较高、费时耗力且不易标准化, 严重阻碍了该方法进一步的推广与应用。近年来, 环境DNA(eDNA)技术的快速发展突破了微型生物形态鉴定的瓶颈, 能高效、准确地鉴定出水环境中包括微型生物在内的各种水生生物。为此, 文章提出微型生物群落eDNA-PFU法, 即基于eDNA技术改进的PFU法, 对微型生物群落进行监测。为了对eDNA-PFU法进行验证, 文章针对武汉东湖水体中的原生动物群落开展了预实验, 结果表明eDNA-PFU法较传统PFU法覆盖度与灵敏度均更高, 可以真实、全面、准确地揭示水体中微型生物群落结构特征。因此, 基于eDNA-PFU法的微型生物群落监测有望为湖泊、河流、水库等水体的生态考核提供新一代的生物监测标准。     

森林溪流倒木生态学研究进展

溪流倒木是指在河流中长度大于1 m、直径大于10 cm的死木。溪流倒木在森林河流中(特别是较小的河流中)是一个常见且重要的结构成分。该文综述了近30年溪流倒木的研究成果(主要来自北美),总结溪流倒木在河流形态、碳循环、泥沙与养分拦截、水生生境的形成、水生生物多样性等方面的生态功能,倒木的时间动态性与空间变异性,以及干扰(包括自然干扰与人为干扰)与倒木存留量及分布的关系。此外,该文也探讨了溪流倒木的生态管理模式及未来研究方向。大量的研究证明,溪流倒木对森林水生生态系统具有重要的生态功能,但它的存留量、分布以及它的生态意义因所研究的森林生态系统、河流大小不同而异。随着河流宽度的增加, 倒木的存留量及它对河流的影响减少,并且倒木的分布以单个为主变为聚集体为主。单个倒木的直径则随河流宽度增加而增大。倒木也呈现十分明显的时间动态性,而这种动态往往是由大规模毁灭性的森林干扰(火、风倒等)所驱动的。研究倒木的时空变异性及自然干扰与人为干扰对倒木的不同影响对于保持倒木的生态功能是十分必要的。该文还对中国开展溪流倒木的生态研究提出一些建议。