Free-flowing rivers (FFRs) support diverse, complex and dynamic ecosystems globally, providing important societal and economic services. Infrastructure development threatens the ecosystem processes, ...biodiversity and services that these rivers support. Here we assess the connectivity status of 12 million kilometres of rivers globally and identify those that remain free-flowing in their entire length. Only 37 per cent of rivers longer than 1,000 kilometres remain free-flowing over their entire length and 23 per cent flow uninterrupted to the ocean. Very long FFRs are largely restricted to remote regions of the Arctic and of the Amazon and Congo basins. In densely populated areas only few very long rivers remain free-flowing, such as the Irrawaddy and Salween. Dams and reservoirs and their up- and downstream propagation of fragmentation and flow regulation are the leading contributors to the loss of river connectivity. By applying a new method to quantify riverine connectivity and map FFRs, we provide a foundation for concerted global and national strategies to maintain or restore them.
Why Should We Care About Temporary Waterways? Acuña, V.; Datry, T.; Marshall, J. ...
Science (American Association for the Advancement of Science),
03/2014, Letnik:
343, Številka:
6175
Journal Article
Recenzirano
Intermittently flowing streams and rivers should be recognized, afforded protection, and better managed.
A proposed ruling by the U.S. Environmental Protection Agency (EPA), aimed at clarifying which ...bodies of water that flow intermittently are protected under law (
1
), has provoked conflict between developers and environmental advocates. Some argue that temporary streams and rivers, defined as waterways that cease to flow at some points in space and time along their course (see the figure, left) ( Fig. 1) (
2
), are essential to the integrity of entire river networks. Others argue that full protection will be too costly. Similar concerns extend far beyond the United States. Debate over how to treat temporary waterways in water-policy frameworks is ongoing (
3
), particularly because some large permanent rivers are shifting to temporary because of climate change and extraction of water (
4
). Even without human-induced changes, flow intermittency is part of the natural hydrology for streams and rivers globally.
Conservation planners need reliable information on spatial patterns of biodiversity. However, existing data sets are skewed because some ecosystems, taxa, and locations are underrepresented. We ...determined how many articles have been published in recent decades on the biodiversity of different countries and their constituent provinces. We searched the Web of Science catalogues Science Citation Index (SCI) and Social Science Citation Index (SSCI) for biodiversity‐related articles published from 1993 to 2016 that included country and province names. We combined data on research publication frequency with other provincial‐scale factors hypothesized to affect the likelihood of research activity (i.e., economic development, human presence, infrastructure, and remoteness). Areas that appeared understudied relative to the biodiversity expected based on site climate likely have been inaccessible to researchers for reasons, notably armed conflict. Geographic publication bias is of most concern in the most remote areas of sub‐Saharan Africa and South America. Our provincial‐scale model may help compensate for publication biases in conservation planning by revealing the spatial extent of research needs and the low cost of redoing this analysis annually.
Efectos del Sesgo de Publicación sobre la Planeación de la Conservación
Resumen
Los planeadores de la conservación necesitan información confiable sobre los patrones espaciales de la biodiversidad. Sin embargo, los conjuntos de datos existentes están distorsionados porque algunos ecosistemas, taxones y localidades están subrepresentados. Determinamos cuántos artículos sobre la biodiversidad de diferentes países y sus provincias constituyentes han sido publicados en décadas recientes. Buscamos artículos relacionados con la biodiversidad publicados entre 1993 y 2016 que incluyeran el nombre de países y provincias en los catálogos SCI y SSCI de la Web of Science. Combinamos los datos de frecuencia de publicación de investigaciones con otros factores de escala provincial que creemos afectarían la probabilidad de la actividad de investigación (es decir, desarrollo económico, presencia humana, infraestructura y lejanía). Las áreas que aparentaron estar poco estudiadas en relación con la biodiversidad esperada basada en el clima del sitio probablemente han estado inaccesibles para los investigadores por diferentes razones, notablemente los conflictos armados. El sesgo geográfico en las publicaciones es un tema de importancia para las áreas más remotas del África subsahariana y América del Sur. Nuestro modelo de escala provincial puede ayudar a compensar los sesgos de publicación en la planeación de la conservación al revelar la extensión espacial de las necesidades de investigación y los bajos costos de repetir este análisis cada año.
摘要
保护规划者需要生物多样性空间格局的可靠数据。然而, 目前的数据集还存在偏差, 这是因为一些生态系统、类群或地理位置没有充足的代表性信息。我们统计了近几十年来不同国家及其省份与生物多样性有关的文章的数量。我们在 Web of Science 网站上搜索了 1993 ‐ 2016 年间, 包含了国家和省份名称且与生物多样性有关的 SCI 和 SSCI 论文。我们将研究发表频率与省份尺度上其它可能影响研究活动的因素 (经济发展、人类活动、基础设施和偏远性) 的数据相结合, 发现那些与基于区域气候数据估计的生物多样性水平相比, 相关研究较少的地区, 许多是因为某些原因, 特别是武装冲突, 研究人员无法进入。其中, 在撒哈拉沙漠以南的非洲和南美洲最偏远的地区, 地理上的发表偏倚最令人担忧。本研究中省份尺度的模型揭示了空间范围内的研究需求, 加之每年都能以低成本重复这项研究, 这可以帮助弥补保护规划中发表偏倚的问题。【翻译: 胡怡思; 审校: 聂永刚】
Riverine landscape diversity WARD, J. V.; TOCKNER, K.; ARSCOTT, D. B. ...
Freshwater biology,
April 2002, Letnik:
47, Številka:
4
Journal Article
Recenzirano
1. This review is presented as a broad synthesis of riverine landscape diversity, beginning with an account of the variety of landscape elements contained within river corridors. Landscape dynamics ...within river corridors are then examined in the context of landscape evolution, ecological succession and turnover rates of landscape elements. This is followed by an overview of the role of connectivity and ends with a riverine landscape perspective of biodiversity.
2. River corridors in the natural state are characterised by a diverse array of landscape elements, including surface waters (a gradient of lotic and lentic waterbodies), the fluvial stygoscape (alluvial aquifers), riparian systems (alluvial forests, marshes, meadows) and geomorphic features (bars and islands, ridges and swales, levees and terraces, fans and deltas, fringing floodplains, wood debris deposits and channel networks).
3. Fluvial action (erosion, transport, deposition) is the predominant agent of landscape evolution and also constitutes the natural disturbance regime primarily responsible for sustaining a high level of landscape diversity in river corridors. Although individual landscape features may exhibit high turnover, largely as a function of the interactions between fluvial dynamics and successional phenomena, their relative abundance in the river corridor tends to remain constant over ecological time.
4. Hydrological connectivity, the exchange of matter, energy and biota via the aqueous medium, plays a major though poorly understood role in sustaining riverine landscape diversity. Rigorous investigations of connectivity in diverse river systems should provide considerable insight into landscape‐level functional processes.
5. The species pool in riverine landscapes is derived from terrestrial and aquatic communities inhabiting diverse lotic, lentic, riparian and groundwater habitats arrayed across spatio‐temporal gradients. Natural disturbance regimes are responsible for both expanding the resource gradient in riverine landscapes as well as for constraining competitive exclusion.
6. Riverine landscapes provide an ideal setting for investigating how complex interactions between disturbance and productivity structure species diversity patterns.
1. Global warming has increased the mean surface temperature of the Earth by 0.6 °C in the past century, and temperature is probably to increase by an additional 3 °C by 2100. Water temperature has ...also increased, which in turn can affect metabolic rate in rivers. Such an increase in metabolic rate could alter the role of river networks in the global C cycle, because the fraction of allochthonous organic C that is respired may increase. 2. Laboratory-based incubations at increasing water temperature were used to estimate the temperature dependence of benthic respiration in streams. These experiments were performed on stones taken from seven reaches with different thermal conditions (mean temperature ranging 8-19 °C) within the pre-alpine Thur River network in Switzerland, June-October 2007. 3. The activation energy of respiration in different reaches along the river network (0.53 ± 0.12 eV, n = 94) was similar, indicating that respiration was constrained by the activation energy of the respiratory complex (E = 0.62 eV). Water temperature and the thickness of the benthic biofilm influence the temperature dependence of respiration and our results suggest that an increase of 2.5 °C will increase river respiration by an average of 20 ± 1.6%.
Intermittent rivers and ephemeral streams (IRES) may represent over half the global stream network, but their contribution to respiration and carbon dioxide (CO2) emissions is largely undetermined. ...In particular, little is known about the variability and drivers of respiration in IRES sediments upon rewetting, which could result in large pulses of CO2. We present a global study examining sediments from 200 dry IRES reaches spanning multiple biomes. Results from standardized assays show that mean respiration increased 32‐fold to 66‐fold upon sediment rewetting. Structural equation modeling indicates that this response was driven by sediment texture and organic matter quantity and quality, which, in turn, were influenced by climate, land use, and riparian plant cover. Our estimates suggest that respiration pulses resulting from rewetting of IRES sediments could contribute significantly to annual CO2 emissions from the global stream network, with a single respiration pulse potentially increasing emission by 0.2–0.7%. As the spatial and temporal extent of IRES increases globally, our results highlight the importance of recognizing the influence of wetting‐drying cycles on respiration and CO2 emissions in stream networks.
Key Points
Sediment respiration in intermittent rivers and ephemeral streams increases substantially in response to rewetting
Respiration pulses are driven by sediment properties, which, in turn, are influenced by climate and catchment characteristics
Effects of wetting‐drying cycles on respiration and CO2 emissions in stream networks need consideration in upscaling and modeling efforts
Non-technical summary
There has been a long history of conflicts, studies, and debate over how to both protect rivers and develop them sustainably. With a pause in new developments caused by the ...global pandemic, anticipated further implementation of the Paris Agreement and high-level global climate and biodiversity meetings in 2021, now is an opportune moment to consider the current trajectory of development and policy options for reconciling dams with freshwater system health.
Technical summary
We calculate potential loss of free-flowing rivers (FFRs) if proposed hydropower projects are built globally. Over 260,000 km of rivers, including Amazon, Congo, Irrawaddy, and Salween mainstem rivers, would lose free-flowing status if all dams were built. We propose a set of tested and proven solutions to navigate trade-offs associated with river conservation and dam development. These solution pathways are framed within the mitigation hierarchy and include (1)
avoidance
through either formal river protection or through exploration of alternative development options; (2)
minimization
of impacts through strategic or system-scale planning or re-regulation of downstream flows; (3)
restoration
of rivers through dam removal; and (4) mitigation of dam impacts through biodiversity
offsets
that include restoration and protection of FFRs. A series of examples illustrate how avoiding or reducing impacts on rivers is possible – particularly when implemented at a system scale – and can be achieved while maintaining or expanding benefits for climate resilience, water, food, and energy security.
Social media summary
Policy solutions and development pathways exist to navigate trade-offs to meet climate resilience, water, food, and energy security goals while safeguarding FFRs.
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