Clupeid fish hosts a Peniculus sp.(Pennellidae,Siphonostomatoida, Copepoda)—First report on new host and season dependent prevalence     

Kattambally Rijin  TMV Mumthaz  Kappalli Sudh  Anilkumar Gopinathan 《海洋学报(英文版)》2019,38(12):118-125

Pennellid copepod Peniculus fistula fistula(Nordmann, 1832)(Synonym: Peniculus fistula Nordmann, 1832,Aphia ID: 745880), a worldwide distributed species, has been recovered from at least 19 teleost families. The present paper reports for the first time from the Malabar coast(South India), not only the existence of a new host family, Clupeidae, hosting this parasitic copepod species(P. fistula fistula) but also their season dependent hosting. A total of 123 marine fish species, belonging to 77 genera and 38 families surveyed along the Malabar coast, only the clupeid, Anadontostoma chacunda(Hamilton, 1822) was shown to be infected by this copepod species; all the recovered(copepod) parasites were invariably found attached at the mid portion of the caudal fin lobes and lying parallel to the host body, indicating the strict site-specific parasitisation. There is a discrete seasonality in the prevalence(P0.05) as the sign of infection was noticed during the period from September to May with relatively high prevalence during winter months(November–January). During the monsoon months(June–August), the host fish was found completely free from Peniculus infection. Interestingly, all the 229 recovered specimens(P. fistula fistula) were gravid females having paired uniserrate egg sacs with the length more than its own body length.  相似文献   

Pricing Weather Derivatives Index based on Temperature: The Case of Bahir Dar,Ethiopia     

Tesfahun BERHANE  Aemiro SHIBABAW  Gurju AWGICHEW 《资源与生态学报(英文版)》2019,10(4):415-423

In this paper we present a stochastic model for daily average temperature to calculate the temperature indices upon which temperature-based derivatives are written. We propose a seasonal mean and volatility model that describes the daily average temperature behavior using the mean-reverting Ornstein-Uhlenbeck process. We also use higher order continuous-time autoregressive process with lag 3 for modeling the time evolution of the temperatures after removing trend and seasonality. Our model is fitted to 11 years of data recorded, in the period 1 January 2005 to 31 December 2015, Bahir Dar, Ethiopia, obtained from Ethiopia National Meteorological Services Agency. The analytical approximation formulas are used to price heating degree days (HDD) and cooling degree days (CDD) futures. The suggested model is analytically tractable for derivation of explicit prices for CDD and HDD futures and option. The price of the CDD future is calculated, using analytical approximation formulas. Numerical examples are presented to indicate the accuracy of the method. The results show that our model performs better to predict CDD indices.  相似文献   

The role of fog,orography, and seasonality on precipitation in a semiarid,tropical island          下载免费PDF全文

Sarah R. Schmitt  Diego A. Riveros‐Iregui  Jia Hu 《水文研究》2018,32(18):2792-2805

Isotopes of water (²H/¹H and ¹⁸O/¹⁶O) are commonly used to trace hydrological processes such as moisture recycling, evaporation loss, and moisture source region and often vary temporally in a given region. This study provides a first‐ever characterization of temporally variable precipitation mechanisms of San Cristóbal Island, Galápagos. We collected fog, rain, and throughfall samples over three field seasons to understand the mechanisms driving seasonal‐ and event‐based variability in the isotopic composition of precipitation in Galápagos. We establish that fog is a common phenomenon in San Cristóbal, especially during the dry season, and we found that fog, compared with cocollected rainfall, is consistently enriched. We further suggest that the relative contribution of fog formed via different mechanisms (orographic, advective, radiation) varied seasonally. We found that the source region is the most dominant control of the isotopic composition of rainfall in the Galápagos at both the seasonal and event scales, but subcloud evaporative processes (the nontraditional manifestation of the amount effect) became a dominant control on the isotopic composition of rainfall during the dry season. Overall, our findings suggest that understanding seasonally variable water‐generating mechanisms is required for effective water resource management in San Cristóbal Island and other semiarid island ecosystems under current and future regimes of climate change.  相似文献   

Quantifying the Spatial Characteristics of the Moisture Transport Affecting Precipitation Seasonality and Recycling Variability in Central Asia     

Linhao ZHONG  Lijuan HUA  Zhaohui GONG  Yao YAO  Lin MU 《大气科学进展》2022,39(6):967-984

Moisture contribution and transport pathways for Central Asia(CA)are quantitatively examined using the Lagrangian water cycle model based on reanalysis and observational data to explain the precipitation seasonality and the moisture transport variation during 1979-2015.Westerly-related(northwesterly and westerly)transport explains 42%of CA precipitation and dominates in southwest CA,where precipitation is greatest in the cold season.Southeast CA,including part of Northwest China,experiences its maximum precipitation in the warm season and is solely dominated by southerly transport,which explains about 48%of CA precipitation.The remaining 10%of CA precipitation is explained by northerly transport,which steadily impacts north CA and causes a maximum in precipitation in the warm season.Most CA areas are exposed to seasonally varying moisture transport,except for southeast and north CA,which are impacted by southerly and northerly transport year-round.In general,the midlatitude westerlies-driven transport and the Indian monsoon-driven southerly-related transport explain most of the spatial differences in precipitation seasonality over CA.Moreover,the contribution ratio of local evaporation in CA to precipitation exhibits significant interdecadal variability and a meridionally oriented tripole of moisture transport anomalies.Since the early 2000s,CA has experienced a decade of anomalously low local moisture contribution,which seems jointly determined by the weakened moisture contribution from midlatitudes(the Atlantic,Europe,and CA itself)and the enhanced contribution from high latitudes(West Siberia and the Arctic)and tropical areas(South Asia and the Indian Ocean).  相似文献   

Spatial and seasonal patterns of flood change across Brazil   总被引：1，自引：1，他引：0  

D. Bartiko  D. Y. Oliveira  N. B. Bonumá 《水文科学杂志》2019,64(9):1071-1079

Brazil has some of the largest rivers in the world and has the second greatest flood loss potential among the emergent countries. Despite that, flood studies in this area are still scarce. In this paper, we used flood seasonality and trend analysis at the annual and seasonal scales in order to describe flood regimes and changes across the whole of Brazil in the period 1976–2015. We identified a strong seasonality of floods and a well-defined spatio-temporal pattern for flood occurrence. There are positive trends in the frequency and magnitude of floods in the North, South and parts of Southeast Brazil; and negative trends in the North-east and the remainder of Southeast Brazil. Trends in the magnitude (frequency) were predominant in the winter (summer). Overall, floods are becoming more frequent and intense in Brazilian regions characterized by wet conditions, and less frequent and intense in drier regions.  相似文献   

River flood seasonality in the Northeast United States: Characterization and trends     

Mathias J. Collins 《水文研究》2019,33(5):687-698

The New England and Mid‐Atlantic regions of the Northeast United States have experienced climate‐induced increases in both the magnitude and frequency of floods. However, a detailed understanding of flood seasonality across these regions, and how flood seasonality may have changed over the instrumental record, has not been established. The annual timing of river floods reflects the flood‐generating mechanisms operating in a basin, and many aquatic and riparian organisms are adapted to flood seasonality, as are human uses of river channels and flood plains. Changes in flood seasonality may indicate changes in flood‐generating mechanisms, and their interactions, with important implications for habitats, flood plain infrastructure, and human communities. I applied a probabilistic method for identifying flood seasons at a monthly resolution for 90 Northeast U.S. watersheds with natural, or near‐natural, flood‐generating conditions. Historical trends in flood seasonality were also investigated. Analyses were based on peaks‐over‐threshold flood records that have, on average, 85 years of data and three peaks per year—thus providing more information about flood seasonality than annual maximums. The results show rich detail about annual flood timing across the region with each site having a unique pattern of monthly flood occurrence. However, a much smaller number of dominant seasonal patterns emerged when contiguous flood‐rich months were classified into commonly recognized seasons (e.g., Mar–May, spring). The dominant seasonal patterns identified by manual classification were corroborated by unsupervised classification methods (i.e., cluster analyses). Trend analyses indicated that the annual timing of flood‐rich seasons has generally not shifted over the period of record, but 65 sites with data from 1941 to 2013 revealed increased numbers of June–October floods—a trend driving previously documented increases in Northeast U.S. flood counts per year. These months have been historically flood‐poor at the sites examined, so warm‐season flood potential has increased with possible implications for aquatic and riparian organisms.  相似文献   

Flood seasonality‐based regionalization methods: a data‐based comparison     

Ali Sarhadi  Reza Modarres 《水文研究》2011,25(23):3613-3624

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Precessional forcing of tropical vegetation carbon storage     

William D. Gosling  Philip B. Holden 《第四纪科学杂志》2011,26(5):463-467

Since the Mid Pleistocene Revolution, which occurred about one million years ago, global temperatures have fluctuated with a quasi‐periodicity of ca. 100 ka. The pattern of past change in the extent of woodlands, and therefore by inference vegetation carbon storage, has been demonstrated to have a strong positive link with this global temperature change at high and mid latitudes. However, understanding of climate systems and ecosystem function indicates that the pattern of woodland change at low latitudes may follow a fundamentally different pattern. We present output from the intermediate complexity model GENIE‐1, comprising a single transient simulation over the last 800 ka and a 174‐member ensemble of 130 ka transient simulations over the last glacial cycle. These simulations suggest that while vegetation carbon storage in mid–high northern latitudes robustly follows the characteristic ca. 100 ka cycle, this signal is not a robust feature of tropical vegetation, which is subject to stronger direct forcing by the precessional (21 ka) orbital cycle (albeit with a highly uncertain response). We conclude that the correlation of palaeoenvironmental records from low latitudes with global temperature change must be done with caution. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Time series analysis of the world's longest fluvial nitrate record: evidence for changing states of catchment saturation          下载免费PDF全文

Fred Worrall  Nicholas J. K. Howden  Tim P. Burt 《水文研究》2015,29(3):434-444

Processes that drive the occurrence of nitrate concentrations in surface waters are known to operate over many decades longer than the available observations. This study considers the world's longest water quality record of nitrate concentrations in the River Thames (1868–2009) in order to understand whether the nature of the time series has changed with time and such external drivers as climate change and land use of hydrology. The study considers the linear trend, the seasonality, the memory and the impulsivity relative to river flow of the time series for moving windows of 6 years in length. The study can show that:

1. Time series analysis proved effective at discriminating controls upon the nitrate concentration in the long term as different components of the record respond to different drivers in different ways.
2. There was decoupling of the annual minimum, annual maximum and the amplitude of the seasonal cycle.
3. The nature of the time series is dominantly controlled by changes in source of nitrate and not by climate change.
4. That even similar increases in nitrate concentration in surface waters can have distinct character that illustrates that they are the result of different sources of nitrate.
5. Changes in the impulsivity of the record show that the study catchment has recovered from a state of saturation, but the memory effect shows that there is an increased contribution from a shallow groundwater.

Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Flood seasonality across Scandinavia—Evidence of a shifting hydrograph?          下载免费PDF全文

Bettina Matti  Helen E. Dahlke  Bastien Dieppois  Damian M. Lawler  Steve W. Lyon 《水文研究》2017,31(24):4354-4370

Fluvial flood events have substantial impacts on humans, both socially and economically, as well as on ecosystems (e.g., hydroecology and pollutant transport). Concurrent with climate change, the seasonality of flooding in cold environments is expected to shift from a snowmelt‐dominated to a rainfall‐dominated flow regime. This would have profound impacts on water management strategies, that is, flood risk mitigation, drinking water supply, and hydro power. In addition, cold climate hydrological systems exhibit complex interactions with catchment properties and large‐scale climate fluctuations making the manifestation of changes difficult to detect and predict. Understanding a possible change in flood seasonality and defining related key drivers therefore is essential to mitigate risk and to keep management strategies viable under a changing climate. This study explores changes in flood seasonality across near‐natural catchments in Scandinavia using circular statistics and trend tests. Results indicate strong seasonality in flooding for snowmelt‐dominated catchments with a single peak occurring in spring and early summer (March through June), whereas flood peaks are more equally distributed throughout the year for catchments located close to the Atlantic coast and in the south of the study area. Flood seasonality has changed over the past century seen as decreasing trends in summer maximum daily flows and increasing winter and spring maximum daily flows with 5–35% of the catchments showing significant changes at the 5% significance level. Seasonal mean daily flows corroborate those findings with higher percentages (5–60%) of the catchments showing statistically significant changes. Alterations in annual flood occurrence also point towards a shift in flow regime from snowmelt‐dominated to rainfall‐dominated with consistent changes towards earlier timing of the flood peak (significant for 25% of the catchments). Regionally consistent patterns suggest a first‐order climate control as well as a local second‐order catchment control, which causes inter‐seasonal variability in the streamflow response.  相似文献