Artificial mouth opening fosters anoxic conditions that kill small estuarine fish     

Alistair Becker  Laurie J.B. Laurenson  Kylie Bishop   《Estuarine, Coastal and Shelf Science》2009,82(4):566-572

Fish kills are not uncommon within estuaries in many regions of the world. In seasonally open systems, which are common in temperate areas, they are often associated with mouth openings. Such a kill occurred in July 2005 in the Surrey Estuary following a closed mouth period of seven months resulting in the loss of many thousands of fish. At the time the fish community within the estuary was under investigation which provided comprehensive data of this population prior to the kill. Monthly water quality monitoring was also being conducted prior to the kill and also carried out on a daily basis following the mouth opening. The Surrey was stratified during the closed mouth phase, isolated waters below the halocline had stagnated and become anoxic. As a result only waters above the halocline contained oxygen concentrations capable of sustaining most fish. It appears that if a mouth opening happens under low flow conditions, a shearing effect occurs within the water column where surface waters flow out to sea leaving deeper waters behind. This resulted in only anoxic waters being present for in excess of six days and was responsible for the fish kill. Fish sampling of the Surrey Estuary was conducted three and six months following the kill and those data were compared to that collected in the 12 months prior to the event. Three months after the kill few fish were collected within the estuary and included marine opportunists near the mouth and estuarine resident species in the far upper reaches of the system. However six months following the kill large numbers of estuarine resident species were collected throughout the Surrey Estuary. As many species were euryhaline, it is believed that some individuals migrated into freshwater reaches of the Surrey to escape the anoxic conditions within the estuary. As conditions improved they recolonised the Surrey Estuary. The high fecundity and rapid growth of these small, short lived species probably aided in their re-establishing populations within the estuary. It is clear from this research that artificial openings of estuaries should be avoided during low flow periods when oxygen concentrations are low. It also appears that many of the small estuarine resident species common in seasonally open estuaries are capable of recolonising estuaries following fish kills. The effects on larger, longer lived resident species are not known but likely to be more detrimental due to longer time required for them to reach sexual maturity.  相似文献   

The nitrogen isotopic composition of dissolved nitrate in the Yangtze River (Changjiang) estuary,China     

Xiujuan Liu  Zhiming Yu  Xiuxian Song  Xihua Cao 《Estuarine, Coastal and Shelf Science》2009

The nitrogen isotopic composition of dissolved nitrate (δ¹⁵N-NO₃⁻) in surface water of the Yangtze River estuary was determined in four seasons of 2006. δ¹⁵N-NO₃⁻ ranged from 0.4‰ to 6.5‰ and varied with seasons and geographic regions, reflecting the dynamics of nitrogen cycling in the estuarine ecosystem. δ¹⁵N-NO₃⁻ was markedly lower in February than in other seasons and exhibited conservative mixing, which was probably attributed to the NO₃⁻ being sourced from the atmospheric deposition and agricultural fertilizer. In the upper estuary, the influence of riverine inputs was important during all surveys. In the turbidity maximum zone, nitrification was found with nitrate depleted in ¹⁵N in May, whereas denitrification resulting in heavy δ¹⁵N-NO₃⁻ played an important role in August. More enriched δ¹⁵N-NO₃⁻ values coinciding with losses of nitrate concentrations based on the conservative mixing model were found in the adjacent marine area in May, and may reflect obvious phytoplankton assimilation of dissolved nitrate. In this manner, δ¹⁵N-NO₃⁻ may be a sensitive indicator of nitrogen sources and biogeochemical processing existing in this estuary in conjunction with the variations of dissolved nitrate and other environmental factors.  相似文献   

Temporal and spatial variability of sea level and volume flux in the Murderkill Estuary     

Kuo-Chuin Wong  Brian Dzwonkowski  William J. Ullman 《Estuarine, Coastal and Shelf Science》2009,84(4):440-446

The instantaneous sea level determined at two sites in the Murderkill Estuary, a tributary of Delaware Bay, results from the superposition of temporal variability operating over different time and spatial scales. Over the relatively short tidal time scales, the semidiurnal tides that represent the dominant tidal constituents in lower Delaware Bay show a modest increase in tidal amplitudes from the bay mouth (Lewes, Delaware), up to Bowers Beach (the mouth of the Murderkill Estuary). However, as the tides propagate into the Murderkill Estuary, the semidiurnal constituents undergo heavy attenuation, resulting in a 48% reduction in tidal amplitude from Bowers to Frederica (approximately the extent of saline intrusion). The diurnal tide, on the other hand, experiences only a 25% reduction in amplitude. The limited tidal asymmetry that is observed may be a result of interaction between flows in the tidal channel and the adjacent salt marsh. At longer time scales, the subtidal sea level experiences no attenuation. The Murderkill Estuary thus behaves like a low pass filter to preferentially damp out high frequency sea level forcing from lower Delaware Bay. The subtidal volume flux in the Murderkill is highly coherent with the time rate of change of sea level, indicating that the Murderkill basically co-oscillates with Delaware Bay in a standing wave fashion over the subtidal time scale. This remote coupling controls more than 90% of the variance in subtidal sea level in the estuary. The surface slopes in the lower bay and the Murderkill Estuary are closely correlated with winds along the orientation of the two waterways, consistent with the effect of local wind on subtidal sea level.  相似文献   

Reconstruction of incomplete satellite SST data sets based on EOF method   总被引：1，自引：0，他引：1  

DING Youzhuan  WEI Zhihui  MAO Zhihu  WANG Xiaofei  PAN Delu 《海洋学报(英文版)》2009,28(2):36-44

As for the satellite remote sensing data obtained by the visible and infrared bands inversion, the clouds coverage in the sky over the ocean often results in missing data of inversion products on a large scale, and thin clouds di?cult to be detected would cause the data of the inversion products to be abnormal. Alvera et al.(2005) proposed a method for the reconstruction of missing data based on an Empirical Orthogonal Functions (EOF) decomposition, but his method couldn’t process these images presenting ex...  相似文献   

Influence of allochthonous input on autotrophic–heterotrophic switch-over in shallow waters of a tropical estuary (Cochin Estuary), India     

Shoji D. Thottathil  K.K. Balachandran  G.V.M. Gupta  N.V. Madhu  Shanta Nair 《Estuarine, Coastal and Shelf Science》2008

Bacterial productivity (BP) and respiration (BR) were examined in relation to primary productivity (PP) for the first time in a shallow tropical ecosystem (Cochin Estuary), India. The degree of dependence of BP (6.3–199.7 μg C L⁻¹ d⁻¹) and BR (6.6–430.4 μg C L⁻¹ d⁻¹) on PP (2.1–608.0 μg C L⁻¹ d⁻¹) was found to be extremely weak. The BP/PP (0.05–8.5) and PP/BR (0.02–7.9) ratios widely varied in the estuary depending on the season and location. There was a seasonal shift in net pelagic production from autotrophy to heterotrophy due to terrestrial organic matter input through rivers which enhanced the bacterial heterotrophic activity and very high pCO₂ (106–6001 μatm) levels. The heterotrophic zones were characterized by low PP but high bacterial production and respiration leading to oxygen undersaturation and exceptionally high pCO₂. We propose that the CO₂ supersaturation caused by increased bacterial respiration (in excess of PP) was a result of bacterial degradation of allochthonous organic matter. This indicates that sources other than planktonic compartment need to be explored to understand the C-cycling in this estuary. These results are of particular relevance to tropical ecosystems in general, where the bulk of world's river discharges occur.  相似文献   

Surface evolution and carbon sequestration in disturbed and undisturbed wetland soils of the Hunter estuary,southeast Australia   总被引：2，自引：0，他引：2  

A.J. Howe  J.F. Rodríguez  P.M. Saco 《Estuarine, Coastal and Shelf Science》2009

The aim of this work was to quantify the soil carbon storage and sequestration rates of undisturbed natural wetlands and disturbed wetlands subject to restriction of tidal flow and subsequent rehabilitation in an Australian estuary. Disturbed and undisturbed estuarine wetlands of the Hunter estuary, New South Wales, Australia were selected as the study sites for this research. Vertical accretion rates of estuarine substrates were combined with soil carbon concentrations and bulk densities to determine the carbon store and carbon sequestration rates of the substrates tested. Relationships between estuary water level, soil evolution and vertical accretion were also examined. The carbon sequestration rate of undisturbed wetlands was lower (15% for mangrove and 55% for saltmarsh) than disturbed wetlands, but the carbon store was higher (65% for mangrove and 60% for saltmarsh). The increased carbon sequestration rate of the disturbed wetlands was driven by substantially higher rates of vertical accretion (95% for mangrove and 345% for saltmarsh). Estuarine wetland carbon stores were estimated at 700–1000 Gg C for the Hunter estuary and 3900–5600 Gg C for New South Wales. Vertical accretion and carbon sequestration rates of estuarine wetlands in the Hunter are at the lower end of the range reported in the literature. The comparatively high carbon sequestration rates reported for the disturbed wetlands in this study indicate that wetland rehabilitation has positive benefits for regulation of atmospheric carbon concentrations, in addition to more broadly accepted ecosystem services.  相似文献   

Integrated remote sensing and GIS techniques for biogeochemical characterization of the Tinto-Odiel estuary system,SW Spain     

M.?Chica-OlmoEmail author  F.?Rodriguez  F.?Abarca  J.?P.?Rigol-Sanchez  E.?deMiguel  J.?A.?Gomez  A.?Fernandez-Palacios 《Environmental Geology》2004,45(6):834-842

The Tinto-Odiel estuary area in SW Spain presents a high concentration of industrial, agricultural and mining activities that seriously affect water quality, producing significant concentrations in trace metals and other contaminant elements. Previous studies have highlighted the important environmental effect of these contaminated waters discharged into the Gulf of Cadiz, contributing in a marked way to trace-metal concentrations in the Mediterranean Sea by water inflow through the Strait of Gibraltar. A global biogeochemical characterization of these waters was the main objective of a multidisciplinary research study funded by the European Union, in which remote sensing and GIS techniques, among other methodologies, were jointly applied. The main results confirmed the usefulness of this integrated methodological approach as an effective tool for the assessment of current biogeochemical conditions. Digital image processing provided valuable thematic information for temporal hydrodynamic analysis and water quality parameters mapping, which was integrated into a GIS database together with experimental information sampled in oceanographic cruises.  相似文献   

2003年江南干旱的成因分析   总被引：7，自引：0，他引：7  

袁晓玉  马德贞 《气象》2005,31(7):37-41

在对2003年夏季江南干旱进行客观评估的基础上,利用天气学方法对该年夏季江南干旱成因进行分析。结果表明,干旱同期北半球500hPa极涡偏于西半球,欧亚中高纬度大气环流呈两槽一脊型,东亚西风锋区位于40°N附近,西太平洋副热带高压长时间稳定控制江南地区。  相似文献   

两个登陆粤西台风对深圳影响的比较分析     

曹春燕  江崟  朱小雅 《气象》2005,31(9):71-74

比照路径相似台风的降雨制作台风降雨预报是台风业务预报的常规方法之一。但0307号台风伊布都和0312号台风科罗旺的路径虽然极为相似，降雨强度却有明显差异。分析显示：0307号台风伊布都在西进过程中，副热带高压持续控制江南、华南大部至南海地区并不断加强西伸，东风急流减弱和口。值较小不利于台风降水云系的发展；而0312号台风科罗旺在进入南海前，南海受辐合带控制，在其西进过程中副热带高压不断减弱东退，东风急流加强，有利于台风右前方螺旋云带发展。这是造成科罗旺距离深圳虽远于伊布都，但降水却更大的主要原因。  相似文献   

热带海表温度持续异常对东亚初夏大气环流的影响   总被引：3，自引：1，他引：3  

袁佳双  郑庆林 《气象》2005,31(12):10-17

利用NCEP/NCAR月平均海表温度及北半球大气环流分析资料,系统研究了热带海洋表面温度持续异常状况下东亚初夏（5、6月份）大气环流的异常特征.研究发现,暖海温年,南亚高压、西太平洋副热带高压明显偏强,冷海温年明显偏弱;暖海温年,欧亚大陆南支西风急流明显减弱北移,东亚大陆对流层低层温度偏高或接近常年,青藏高原近地面温度偏高,而冷海温年,东亚大陆对流层低层温度偏低,5月份青藏高原近地面温度偏低.研究表明,海表温度的持续异常对东亚初夏大气环流的季节转换有重要影响.  相似文献