The natural flow regime concept has contributed significantly to environmental flows (e‐flows) science and applications over the last 20 years. Natural flow regimes reflect long‐term, historical ...patterns of flow variability that have shaped riverine species’ adaptations and continue to shape community and ecosystem structure and function. This scientific perspective, however, carries with it important assumptions about climatic and ecological stationarity in terms of “reference” conditions that provide a basis for comparing success or outcomes of e‐flow interventions.
Non‐stationarity in climate and other environmental conditions (temperature, sediment, nutrients) and in ecological features (non‐native species spread) presents important challenges for environmental flows science. Reliance on the assumption of restoration to reference conditions for either hydrologic or ecological conditions is no longer tenable, and an expanded e‐flows science foundation is needed to meet several challenges facing future e‐flows implementations.
Currently recognised limitations of e‐flows science contribute to the emergence of research frontiers that need further development. These are (1) shifting from static, regime‐based flow metrics to dynamic, time‐varying flow characterisations; (2) expanding the ecological metrics (and space–time scales) used in e‐flows from primary reliance on ecosystem states to include process (population) rates and species traits; (3) incorporating other “non‐flow” environmental features (e.g. temperature, sediment) to guide prioritisation of e‐flows applications with a likelihood of success; and (4) broadening the ecological foundation of e‐flows to incorporate more ecological theory that will contribute to a more predictive science.
The natural flow regime perspective of managing for historical variability will remain important to understand ecological response to hydrologic alterations and to inform e‐flows management. However, under shifting hydro‐climatic and ecological conditions, a new imperative of managing for resilience is emerging, that is, identifying and prescribing e‐flows to sustain robust, persistent and socially valued ecological characteristics in a flexible and adaptive management framework.
How dams can go with the flow LeRoy Poff, N.; Schmidt, John C.
Science (American Association for the Advancement of Science),
09/2016, Letnik:
353, Številka:
6304
Journal Article
Recenzirano
The world's rivers are regulated by about 58,000 large dams (more than 15 m high) that provide water supplies for municipalities and irrigation, allow downstream navigation, and enable hydropower ...production (1). New dams are widely seen as sources of green energy. An estimated 75% of the world's potential hydropower capacity is unexploited (2), and some 3700 new dams are currently proposed in developing economies (3, 4). But dams also cause substantial and often unacknowledged environmental damage. Recent research affords insight into how dams might be strategically operated to partially restore some lost ecosystem functions and services.
Species richness is greatest in the tropics, and much of this diversity is concentrated in mountains. Janzen proposed that reduced seasonal temperature variation selects for narrower thermal ...tolerances and limited dispersal along tropical elevation gradients Janzen DH (1967) Am Nat 101:233–249. These locally adapted traits should, in turn, promote reproductive isolation and higher speciation rates in tropical mountains compared with temperate ones. Here, we show that tropical and temperate montane stream insects have diverged in thermal tolerance and dispersal capacity, two key traits that are drivers of isolation in montane populations. Tropical species in each of three insect clades have markedly narrower thermal tolerances and lower dispersal than temperate species, resulting in significantly greater population divergence, higher cryptic diversity, higher tropical speciation rates, and greater accumulation of species over time. Our study also indicates that tropical montane species, with narrower thermal tolerance and reduced dispersal ability, will be especially vulnerable to rapid climate change.
1. In an effort to develop quantitative relationships between various kinds of flow alteration and ecological responses, we reviewed 165 papers published over the last four decades, with a focus on ...more recent papers. Our aim was to determine if general relationships could be drawn from disparate case studies in the literature that might inform environmental flows science and management. 2. For all 165 papers we characterised flow alteration in terms of magnitude, frequency, duration, timing and rate of change as reported by the individual studies. Ecological responses were characterised according to taxonomic identity (macroinvertebrates, fish, riparian vegetation) and type of response (abundance, diversity, demographic parameters). A 'qualitative' or narrative summary of the reported results strongly corroborated previous, less comprehensive, reviews by documenting strong and variable ecological responses to all types of flow alteration. Of the 165 papers, 152 (92%) reported decreased values for recorded ecological metrics in response to a variety of types of flow alteration, whereas 21 papers (13%) reported increased values. 3. Fifty-five papers had information suitable for quantitative analysis of ecological response to flow alteration. Seventy per cent of these papers reported on alteration in flow magnitude, yielding a total of 65 data points suitable for analysis. The quantitative analysis provided some insight into the relative sensitivities of different ecological groups to alteration in flow magnitudes, but robust statistical relationships were not supported. Macroinvertebrates showed mixed responses to changes in flow magnitude, with abundance and diversity both increasing and decreasing in response to elevated flows and to reduced flows. Fish abundance, diversity and demographic rates consistently declined in response to both elevated and reduced flow magnitude. Riparian vegetation metrics both increased and decreased in response to reduced peak flows, with increases reflecting mostly enhanced non-woody vegetative cover or encroachment into the stream channel. 4. Our analyses do not support the use of the existing global literature to develop general, transferable quantitative relationships between flow alteration and ecological response; however, they do support the inference that flow alteration is associated with ecological change and that the risk of ecological change increases with increasing magnitude of flow alteration. 5. New sampling programs and analyses that target sites across well-defined gradients of flow alteration are needed to quantify ecological response and develop robust and general flow alteration-ecological response relationships. Similarly, the collection of pre- and post-alteration data for new water development programs would significantly add to our basic understanding of ecological responses to flow alteration.
The Natural Sediment Regime in Rivers WOHL, ELLEN; BLEDSOE, BRIAN P.; JACOBSON, ROBERT B. ...
Bioscience,
04/2015, Letnik:
65, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Water and sediment inputs are fundamental drivers of river ecosystems, but river management tends to emphasize flow regime at the expense of sediment regime. In an effort to frame a more inclusive ...paradigm for river management, we discuss sediment inputs, transport, and storage within river systems; interactions among water, sediment, and valley context; and the need to broaden the natural flow regime concept. Explicitly incorporating sediment is challenging, because sediment is supplied, transported, and stored by nonlinear and episodic processes operating at different temporal and spatial scales than water and because sediment regimes have been highly altered by humans. Nevertheless, managing for a desired balance between sediment supply and transport capacity is not only tractable, given current geomorphic process knowledge, but also essential because of the importance of sediment regimes to aquatic and riparian ecosystems, the physical template of which depends on sediment-driven river structure and function.
ABSTRACT
GRANDMA (Global Rapid Advanced Network Devoted to the Multi-messenger Addicts) is a network of 25 telescopes of different sizes, including both photometric and spectroscopic facilities. The ...network aims to coordinate follow-up observations of gravitational-wave (GW) candidate alerts, especially those with large localization uncertainties, to reduce the delay between the initial detection and the optical confirmation. In this paper, we detail GRANDMA’s observational performance during Advanced LIGO/Advanced Virgo Observing Run 3 (O3), focusing on the second part of O3; this includes summary statistics pertaining to coverage and possible astrophysical origin of the candidates. To do so, we quantify our observation efficiency in terms of delay between GW candidate trigger time, observations, and the total coverage. Using an optimized and robust coordination system, GRANDMA followed-up about 90 per cent of the GW candidate alerts, that is 49 out of 56 candidates. This led to coverage of over 9000 deg2 during O3. The delay between the GW candidate trigger and the first observation was below 1.5 h for 50 per cent of the alerts. We did not detect any electromagnetic counterparts to the GW candidates during O3, likely due to the very large localization areas (on average thousands of degrees squares) and relatively large distance of the candidates (above 200 Mpc for 60 per cent of binary neutron star, BNS candidates). We derive constraints on potential kilonova properties for two potential BNS coalescences (GW190425 and S200213t), assuming that the events’ locations were imaged.
ABSTRACT
We present a new strategy to optimize the electromagnetic follow-up of gravitational wave triggers. This method is based on the widely used galaxy targeting approach where we add the stellar ...mass of galaxies in order to prioritize the more massive galaxies. We cross-matched the Galaxy List for the Advanced Detector Era (GLADE) galaxy catalogue with the AllWISE catalogue up to 400 Mpc with an efficiency of ∼93 per cent, and derived stellar masses using a mass-to-light ratio using the WISE1 band luminosity. We developed a new grade to rank galaxies combining their 3D localization probability associated with the gravitational wave event with the new stellar mass information. The efficiency of this new approach is illustrated with the GW170817 event, which shows that its host galaxy, NGC 4993, is ranked at the first place using this new method. The catalogue, named MANGROVE, is publicly available and the ranking of galaxies is automatically provided through a dedicated website for each gravitational wave event.
Ecology Letters (2010) 13: 267-283 Predicting changes in community composition and ecosystem function in a rapidly changing world is a major research challenge in ecology. Traits-based approaches ...have elicited much recent interest, yet individual studies are not advancing a more general, predictive ecology. Significant progress will be facilitated by adopting a coherent theoretical framework comprised of three elements: an underlying trait distribution, a performance filter defining the fitness of traits in different environments, and a dynamic projection of the performance filter along some environmental gradient. This framework allows changes in the trait distribution and associated modifications to community composition or ecosystem function to be predicted across time or space. The structure and dynamics of the performance filter specify two key criteria by which we judge appropriate quantitative methods for testing traits-based hypotheses. Bayesian multilevel models, dynamical systems models and hybrid approaches meet both these criteria and have the potential to meaningfully advance traits-based ecology.
Tamarix ramosissima is a naturalized, nonnative plant species which has become widespread along riparian corridors throughout the western United States. We test the hypothesis that the distribution ...and success of Tamarix result from human modification of river-flow regimes. We conducted a natural experiment in eight ecoregions in arid and semiarid portions of the western United States, measuring Tamarix and native Populus recruitment and abundance at 64 sites along 13 perennial rivers spanning a range of altered flow regimes. We quantified biologically relevant attributes of flow alteration as an integrated measure (the index of flow modification, IFM), which was then used to explain between-site variation in abundance and recruitment of native and nonnative riparian plant species. We found the likelihood of successful recruitment of Tamarix to be highest along unregulated river reaches and to remain high across a gradient of regulated flows. Recruitment probability for Populus, in contrast, was highest under free-flowing conditions and declined abruptly under even slight flow modification (IFM > 0.1). Adult Tamarix was most abundant at intermediate levels of IFM. Populus abundance declined sharply with modest flow regulation (IFM > 0.2) and was not present at the most flow-regulated sites. Dominance of Tamarix was highest along rivers with the most altered flow regimes. At the 16 least regulated sites, Tamarix and Populus were equally abundant. Given observed patterns of Tamarix recruitment and abundance, we infer that Tamarix would likely have naturalized, spread, and established widely in riparian communities in the absence of dam construction, diversions, and flow regulation in western North America. However, Tamarix dominance over native species would likely be less extensive in the absence of human alteration of river-flow regimes. Restoration that combines active mechanical removal of established stands of Tamarix with a program of flow releases conducive to native species establishment and persistence is hypothesized to facilitate the codominance of Populus in reaches where it has become rare. Our findings have implications for planning flow-related stream restoration, for developing realistic expectations for yield on investment in prescribed flow releases, and for planning flow-related interventions that might be possible if control and management of invasive plant species along rivers is a goal.
Humans have altered the natural flow of rivers, adversely affecting biodiversity and the services that these watercourses provide. The mapping of millions of kilometres of rivers reveals the extent ...of human interference.
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