Temporal analysis of the frequency and duration of low and high streamflow: years of record needed to characterize streamflow variability     

Seungho Huh  David A. Dickey  M.R. Meador  K.E. Ruhl 《Journal of Hydrology》2005,310(1-4):78-94

A temporal analysis of the number and duration of exceedences of high- and low-flow thresholds was conducted to determine the number of years required to detect a level shift using data from Virginia, North Carolina, and South Carolina. Two methods were used—ordinary least squares assuming a known error variance and generalized least squares without a known error variance. Using ordinary least squares, the mean number of years required to detect a one standard deviation level shift in measures of low-flow variability was 57.2 (28.6 on either side of the break), compared to 40.0 years for measures of high-flow variability. These means become 57.6 and 41.6 when generalized least squares is used. No significant relations between years and elevation or drainage area were detected (P>0.05). Cluster analysis did not suggest geographic patterns in years related to physiography or major hydrologic regions. Referring to the number of observations required to detect a one standard deviation shift as ‘characterizing’ the variability, it appears that at least 20 years of record on either side of a shift may be necessary to adequately characterize high-flow variability. A longer streamflow record (about 30 years on either side) may be required to characterize low-flow variability.  相似文献   

Growth pattern and maturation in arctic char (Salvelinus alpinus L.) of Lake Walenstadt,Switzerland     

Christian Ruhlé 《Aquatic Sciences - Research Across Boundaries》1989,51(4):296-305

Within one decade the yield in arctic char fishery of Lake Walenstadt (Switzerland) has dropped from 1.7 kg · ha^–1 to 0.7 kg · ha^–1. In the same period growth decreased by about 15%. The fish considered as degenerated dwarfed chars by fishermen are supposed to mature in very young ages.The change of the growth pattern can be related to reoligotrophication of the lake and impoverishments of the food source. Compared to other arctic char populations in Switzerland maturation takes place at least one year later.  相似文献   

Enhancement and inhibition of iron photoreduction by individual ligands in open ocean seawater     

Micha J.A. Rijkenberg  Loes J.A. Gerringa  Ilona Velzeboer 《Geochimica et cosmochimica acta》2006,70(11):2790-2805

In laboratory experiments, we investigated the effect of five individual Fe-binding ligands: phaeophytin, ferrichrome, desferrioxamine B (DFOB), inositol hexaphosphate (phytic acid), and protoporphyrin IX (PPIX) on the Fe(II) photoproduction using seawater of the open Southern Ocean. Addition of 10-100 nM Fe(III) to open Southern Ocean seawater without the model ligands and containing; 1.1 nM dissolved Fe(III), 1.75 ± 0.28 equivalents of nM Fe of natural ligands with a conditional stability constant (log K′) of 21.75 ± 0.34 and a concentration DOC of 86.8 ± 1.13 μM C leads to the formation of amorphous Fe(III) hydroxides. These amorphous Fe(III) hydroxides are the major source for the photoproduction of Fe(II). The addition of the model ligands changed the Fe(II) photoproduction considerably and in various ways. Phaeophytin showed higher Fe(II) photoproduction than ferrichrome and the control, i.e., amorphous Fe(III) hydroxides. Additions of phytic acid between 65 and 105 nM increased the concentration of photoproduced Fe(II) with 0.16 nM Fe(II) per nM phytic acid, presumably due to the co-aggregation of Fe(III) and phytic acid leading via an increasing colloidal surface to an increasing photoreducible Fe(III) fraction. DFOB and PPIX strongly decreased the photoproduced Fe(II) concentration. The low Fe(II) photoproduction with DFOB confirmed reported observations that Fe(III) complexed to DFOB is photo-stable. The PPIX hardly binds Fe(III) in the open Southern Ocean seawater but decreased the photoproduced Fe(II) concentration by complexing the Fe(II) with a binding rate constant of k_Fe(II)PPIX = 1.04 × 10⁻⁴ ± 1.53 × 10⁻⁵ s⁻¹ nM⁻¹ PPIX. Subsequently, PPIX is suggested to act as a photosensitizing producer of superoxide, thus increasing the dark reduction of Fe(III) to Fe(II). Our research shows that the photochemistry of Fe(III) and the resulting photoproduced Fe(II) concentration is strongly depending on the identity of the Fe-binding organic ligands and that a translation to natural conditions is not possible without further characterization of the natural occurring ligands.  相似文献   

Estimation of the Continuous Ranked Probability Score with Limited Information and Applications to Ensemble Weather Forecasts     

Michaël Zamo  Philippe Naveau 《Mathematical Geosciences》2018,50(2):209-234

The continuous ranked probability score (CRPS) is a much used measure of performance for probabilistic forecasts of a scalar observation. It is a quadratic measure of the difference between the forecast cumulative distribution function (CDF) and the empirical CDF of the observation. Analytic formulations of the CRPS can be derived for most classical parametric distributions, and be used to assess the efficiency of different CRPS estimators. When the true forecast CDF is not fully known, but represented as an ensemble of values, the CRPS is estimated with some error. Thus, using the CRPS to compare parametric probabilistic forecasts with ensemble forecasts may be misleading due to the unknown error of the estimated CRPS for the ensemble. With simulated data, the impact of the type of the verified ensemble (a random sample or a set of quantiles) on the CRPS estimation is studied. Based on these simulations, recommendations are issued to choose the most accurate CRPS estimator according to the type of ensemble. The interest of these recommendations is illustrated with real ensemble weather forecasts. Also, relationships between several estimators of the CRPS are demonstrated and used to explain the differences of accuracy between the estimators.  相似文献   

New insights into lake responses to rapid climate change: the Younger Dryas in Lake Gościąż, central Poland     

Daniela Müller  Rik Tjallingii  Mateusz Płóciennik  Tomi P. Luoto  Bartosz Kotrys  Birgit Plessen  Arne Ramisch  Markus J. Schwab  Mirosław Błaszkiewicz  Michał Słowiński  Achim Brauer 《Boreas: An International Journal of Quaternary Research》2021,50(2):535-555

The sediment profile from Lake Gościąż in central Poland comprises a continuous, seasonally resolved and exceptionally well-preserved archive of the Younger Dryas (YD) climate variation. This provides a unique opportunity for detailed investigation of lake system responses during periods of rapid climate cooling (YD onset) and warming (YD termination). The new varve record of Lake Gościąż presented here spans 1662 years from the late Allerød (AL) to the early Preboreal (PB). Microscopic varve counting provides an independent chronology with a YD duration of 1149+14/–22 years, which confirms previous results of 1140±40 years. We link stable oxygen isotopes and chironomid-based air temperature reconstructions with the response of various geochemical and varve microfacies proxies especially focusing on the onset and termination of the YD. Cooling at the YD onset lasted ~180 years, which is about a century longer than the terminal warming that was completed in ~70 years. During the AL/YD transition, environmental proxy data lagged the onset of cooling by ~90 years and revealed an increase of lake productivity and internal lake re-suspension as well as slightly higher detrital sediment input. In contrast, rapid warming and environmental changes during the YD/PB transition occurred simultaneously. However, initial changes such as declining diatom deposition and detrital input occurred already a few centuries before the rapid warming at the YD/PB transition. These environmental changes likely reflect a gradual increase in summer air temperatures already during the YD. Our data indicate complex and differing environmental responses to the major climate changes related to the YD, which involve different proxy sensitivities and threshold processes.  相似文献   

Patterns of cornulitid encrustation on the Late Devonian brachiopod shells from Russia     

Sabiela Musabelliu  Michał Zatoń 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(2):227-234

Upper Devonian brachiopods from the Central Devonian Field, Russia have been investigated with respect to encrustation patterns of cornulitids. These Palaeozoic encrusters were very characteristic component of shelly substrates during the Devonian and may serve as valuable objects for palaeoecological studies, especially those concerning the encrusters-host relationships. On the basis of rich material, it has been shown that cornulitid abundance significantly increased in the lower Famennian. Their disparity also increased from one morphotype (robust) present in the upper Frasnian to two distinct morphotypes (robust and slender, presumably representing two different species) in the lower Famennian. The analysis of the spatial occurrence of cornulitids on two dominant lower Famennian brachiopod species (Cyrtospirifer zadonicus and Ripidiorhynchus huotinus) showed, that these encrusters preferred the marginal parts of the shells. This, together with a dominant directional growth of cornulitids toward the commissure, indicates that cornulitids benefited from food brought by feeding currents produced by the brachiopod’s lophophore. The unequivocal evidence for syn vivo association of the cornulitids and their brachiopod hosts is the presence of distinct shell malformations caused by cornulitid growth affecting the host’s shell-secreting epithelium, preserved on some lower Famennian specimens. Interestingly, these malformations were caused by a slender cornulitid morphotype only. Thus, it is evident that during food gathering from the inhalant currents, this cornulitid species exerted a distinct, negative effect on the brachiopod – a deviation of its shell growth. In this case, we may consider this particular cornulitid species as ectoparasite rather than commensal with respect to its host.  相似文献   

Seasonal deposition of authigenic calcite out of isotopic equilibrium with DIC and water,and implications for paleolimnological studies     

Apolinarska  Karina  Pleskot  Krzysztof  Pełechata  Aleksandra  Migdałek  Michał  Pełechaty  Mariusz 《Journal of Paleolimnology》2021,66(1):41-53

Journal of Paleolimnology - We conducted year-round, monthly monitoring of the stable isotope composition of DIC and water in hypereutrophic Lake Kierskie, western Poland, along with isotope...  相似文献   

The effect of fish stocking on mountain lake plankton communities identified using palaeobiological analyses of bottom sediment cores     

Elwira Sienkiewicz  Michał Gąsiorowski 《Journal of Paleolimnology》2016,55(2):129-150

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Evolution of Mesozoic fluvial systems along the SE flank of the West Siberian Basin, Russia     

Daniel Paul Le Heron  Micha M. Buslov  Clare Davies  Keith Richards  Inna Safonova 《Sedimentary Geology》2008,208(1-2):45-60

The Mesozoic stratigraphy in the subsurface of the West Siberian Basin contains prolific hydrocarbon accumulations, and thus the depositional environments of marine and marginal marine Jurassic and Cretaceous age sediments are well-established. However, no information is currently available on strata of equivalent age that crop out along the SE basin margin in the Mariinsk–Krasnoyarsk region, despite the potential of these exposures to supply important information on the sediment supply routes into the main basin. Detailed sedimentological analysis of Jurassic–Cretaceous clastic sediments, in conjunction with palaeo-botanical data, reveals five facies associations that reflect deposition in a range of continental environments. These include sediments that were deposited in braided river systems, which were best developed in the Early Jurassic. These early river systems infilled the relics of a topography that was possibly inherited from earlier Triassic rifting. More mature fluvial land systems evolved in the Mid to Late Jurassic. By the Mid Jurassic, well-defined overbank areas had become established, channel abandonment was commonplace, and mudrocks were deposited on floodplains. Coal deposition occurred in mires, which were subject to periodic incursions by crevasse splay processes. Cretaceous sedimentation saw a renewed influx of sand-grade sediment into the region. It is proposed that landscape evolution throughout the Jurassic was driven simply by peneplanation rather than tectonic processes. By contrast, the influx of sandstones in the Cretaceous is tentatively linked to hinterland rejuvenation/ tectonic uplift, possibly coeval with the growth of large deltaic clinoform complexes of the Neocomian in the basin subsurface.  相似文献   

Nonapplicability of the viscous approximation method in homogeneous cosmological models     

Michał Ostrowski 《Astrophysics and Space Science》1984,105(2):253-257

By considering two conceptually important instances it is shown that one cannot use the viscous approximation method to estimate the effects of nonequilibrium processes in homogeneous cosmological models. Despite the widespread acceptance of this method, it is argued that not even qualitative estimates can be obtained by its use.  相似文献