Shaping Sydney Harbour: Sedimentation,dredging and reclamation 1788-1990s

Described by Governor Phillip as 'the finest harbour in the world', Sydney Harbour was affected by accelerated sedimentation very soon after settlement in 1788. Dredging began in 1842 to deal with the problems caused by sedimentation and to enhance foreshore amenity. By the end of the nineteenth century, dredging was also excavating the bottom of the Harbour and its bays to accommodate larger ships with deeper draughts, and dredged sediment was increasingly used to reclaim mudflats or marshes deemed unhealthy or unsightly, thereby creating additional useful waterfront land. There was virtually continuous dredging in some part or other of the Harbour and its tributaries for almost 140 years. With increasing costs and mounting environmental concerns, dredging is now intermittent, and carried out largely to facilitate navigation for specific projects, despite continued sedimentation. While there was an early lack of understanding of the Australian environment and the impact of clearing on soils, the causes of increased sedimentation had been documented by the 1860s. However, measures to seriously address causes were not introduced until late in the twentieth century. This paper briefly outlines the development of the Sydney estuary to 1788, considers the impact of settlement in accelerating sedimentation, traces the development of dredging and reclamation, and discusses their significance for a number of areas of current research and environmental management, as well as to social and economic history. Within the limitations of the data available, annual sediment dredged, annual expenditure, cost per tonne, and areas reclaimed by dredging and filling are included.     

陕西黄河湿地的鹭林生境与保护

2010年7月19日～8月5日,在陕西黄河湿地自然保护区发现一处鹭类繁殖地。描述了鹭类繁殖地特征并提出了保护建议。     

Hydrological drivers of wetland vegetation community distribution within Everglades National Park,Florida

The influence of hydrological dynamics on vegetation distribution and the structuring of wetland environments is of growing interest as wetlands are modified by human action and the increasing threat from climate change. Hydrological properties have long been considered a driving force in structuring wetland communities. We link hydrological dynamics with vegetation distribution across Everglades National Park (ENP) using two publicly available datasets to study the probability structure of the frequency, duration, and depth of inundation events along with their relationship to vegetation distribution. This study is among the first to show hydrologic structuring of vegetation communities at wide spatial and temporal scales, as results indicate that the percentage of time a location is inundated and its mean depth are the principal structuring variables to which individual communities respond. For example, sawgrass, the most abundant vegetation type within the ENP, is found across a wide range of time inundated percentages and mean depths. Meanwhile, other communities like pine savanna or red mangrove scrub are more restricted in their distribution and found disproportionately at particular depths and inundations. These results, along with the probabilistic structure of hydropatterns, potentially allow for the evaluation of climate change impacts on wetland vegetation community structure and distribution.     

人工补水条件下白洋淀湿地演变研究

近几十年来,在自然因素和人类活动的双重作用下,白洋淀湿地及其周边环境发生了明显变化。本文采用综合识别遥感提取技术,对近40年来白洋淀湿地面积信息进行提取并分析其变化特征,在1986—1989年间,湿地面积增加253.29 km~2;1989—1994年间,湿地面积减少181.61 km~2;1994—1997,湿地面积增加158.17 km~2;1997—2004年间,湿地面积减少170.37 km~2;2004—2016年,湿地面积增加106.09 km~2。根据湿地面积提取结果,分析湿地面积与地表水位和地下水位的关系,确定了白洋淀湿地面积变化的主要控制因子为地表水位,其与白洋淀湿地面积的相关性非常好,相关系数达0.99;白洋淀湿地面积与周边区域的地下水位动态变化呈正相关性,说明湿地渗漏量对周边区域的地下水位动态变化有一定影响。针对白洋淀湿地地表水位,采用水均衡法,分析了影响白洋淀地表水位的主控因素,主要为白洋淀湿地的入淀流量和蒸发蒸腾消耗量。通过白洋淀湿地演变及其影响因素的分析,初步揭示了白洋淀湿地与水文过程的相互影响机制,可为制定白洋淀湿地生态修复和水资源可持续利用方案等提供技术支撑和理论参考。     

Identifying environmental drivers of chlorophyll-a dynamics in Austral subtropical ephemeral ecosystems

Environmental and biological features of Austral subtropical pan types were assessed, along with the drivers of chlorophyll-a (chl-a) concentrations. Chl-a biomass varied considerably across seasons and endorheic pans had elevated chl-a concentrations compared to floodplain pans. The major driver of chl-a concentration based on generalised linear/non-linear models (GLZ) was total phosphorous and total suspended solids for all pan types and seasons combined. These results are discussed within the context of secondary productivity, aquatic ecosystem heterogeneity and endorheic pan conservation.     

Analysis of storm run-off sources using oxygen-18 in a headwater swamp

A combination of hydrometric data and observations of natural isotope (oxygen-18) variations in saturation overland flow and stream discharge were used to investigate the sources of storm run-off in a headwater swamp located in a permanent groundwater discharge zone near Toronto, Canada. The results of a two-component hydrograph separation indicated that pre-event water formed 80–90% of the stream hydrograph volume for six of the seven storms analyzed in June–November 1990. However, the instantaneous event water contribution showed considerable variability, ranging from maximum values of 20–25% for four moderate intensity storms to 63% for a high intensity thunderstorm with a return period of two years. The relative contribution of event and pre-event water to storm run-off from saturated areas and small streamlets within the swamp was similar to the main outlet stream. The dominance of pre-event water during storms could be accounted for by the mixing of a small volume of event water with a large pool of pre-event water on the surface of permanently saturated areas within the swamp. Occasional storms of high intensity or long duration produced a greater shift towards an event water signature in the saturated areas and a larger event water contribution to the outlet stream hydrograph.     

面向遥感监测的中国湿地区划初步构想

遥感技术作为对湿地进行监测的现代空间信息技术,在对湿地研究和管理中日益发挥重要作用。我国国土面积广大,在不同地带分布有不同类型的湿地。现有的湿地分类工作尚不能满足对全国开展湿地监测的需要,也缺少地理区划理论的支持。为满足全国湿地遥感动态监测的需要,以现有湿地相关研究为基础,对湿地区划的指标体系、区划的原则、方法以及区划的等级体系进行了讨论,旨在为湿地区划方案的制定和实施提供参考。     

Significance of enhanced infiltration due to groundwater extraction on the disappearance of a headwater lagoon system: Toluca Basin, Mexico

Mexico City relies significantly on groundwater resources drawn from the Sistema Lerma well field located in the Toluca Basin, Mexico. Enhanced infiltration caused by groundwater extraction is suspected to be both a prime factor in the disappearance of a lagoon system at the Toluca Basin and a potential risk to long-term groundwater quality. A combined approach of field investigation and numerical modeling was adopted to assess the groundwater-surface water interactions within the lagoon system. Potentiometric data indicate that current downward vertical hydraulic gradients below the lagoon and surrounding wetland area are extremely low suggesting very slow infiltration rates. Geochemical and isotope data from surface water and groundwater sampling also indicate that very little surface water infiltration has occurred. Numerical simulations demonstrate that enhanced surface water infiltration is unlikely to be the primary cause in the significant reduction in size of the lagoon system. Other factors such as modifications to the surface water drainage system and capture of spring flow from the surrounding mountainous regions are likely more significant. Simulations also suggest that contaminants originating in the lagoon system are currently entering nearby production wells although the total contaminant mass flux to the wells is still very low and significantly diluted.

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Resumen La Ciudad de México depende significativamente de los recursos de aguas subterráneas obtenidos del campo de pozos Sistema Lerma ubicado en la Cuenca Toluca, oeste de la Cuenca de México. Se sospecha que la infiltración estimulada causada por extracción intensiva de aguas subterráneas es un factor principal en la desaparición de un sistema de lagunas en la cabeceras del Río Lerma en el centro de México y un riesgo potencial para la calidad de aguas subterráneas a largo plazo en la región. Se adoptó un enfoque combinado de investigación de campo y modelizado numérico para evaluar las interacciones de agua superficial-agua subterránea dentro del sistema de lagunas. Datos potenciométricos indican que los gradientes hidráulicos verticales descendentes actuales, ubicados por debajo de la laguna y vecina área de humedales, son extremadamente bajos sugiriendo ritmos de infiltración muy lentos. Datos geoquímicos e isotópicos provenientes del muestreo de agua superficial y subterránea también indican que ha ocurrido muy poca infiltración de agua superficial. Las simulaciones numéricas demuestran cuantitativamente que no es probable que la infiltración estimulada de agua superficial sea la causa principal en la reducción significativa del tamaño del sistema de lagunas en la cabecera. Otros factores tal como modificaciones al sistema superficial de drenaje de agua y captura de flujo de manantial en las regiones montañosas vecinas son probablemente más significativos. Las simulaciones también sugieren que los contaminantes que se originan en el sistema de lagunas están actualmente ingresando a pozos de producción cercanos aunque el flujo de masa contaminante total a los pozos es aún muy bajo y diluido significativamente en los volúmenes grandes de extracción. La magnitud de la amenaza a largo plazo a la calidad del agua subterránea en los pozos de producción Sistema Lerma proveniente de contaminantes infiltrados es una preocupación y amerita estudios futuros.

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Résumé La Cité de Mexico dépend significativement des ressources en eau souterraine pompées au site de captages de Sistema Lerma, dans le Bassin de Toluca, à lOuest du Bassin de Mexico. Laugmentation de linfiltration, causée par lextraction extensive des eaux souterraines, est suspectée dêtre à la fois un facteur primaire de la disparition dun système de lagons en amont de la rivière Lerma au centre de Mexico, et un risque potentiel à long-terme pour la qualité de leau souterraine dans la région. Uen approche combinée détudes de terrain et de modélisation numérique a été adoptée pour estimer les interactions entre les eaux de surface et les eaux souterraines, au sein du système de lagons. Les données potentiométriques indiquent que les gradients hydrauliques verticaux descendants sont très bas au niveau des lagons, ce qui suppose un taux dinfiltration faible. Les données géochimiques et isotopiques provenant des eaux de surface et souterraines, indiquent également que peu deau de surface sinfiltrent. La simulation numérique démontre quantitativement que laugmentation de linfiltration des eaux de surface nest probablement pas la première cause de réduction des lagons. Dautres facteurs, tels que les modifications du drainage des eaux de surface, laménagement en captage des sources situées aux pieds des montagnes environnantes, sont probablement plus importants. Les simulations suggèrent également que les contaminants provenant des lagons se retrouvent également dans les captages les plus proches, bien que le flux total de contaminants entrant dans les captages reste faible. Les volumes dextraction étant très important ils diluent effectivement les contaminants. Les effets à long-terme de lextraction critique au niveau des forages de Sistema Lerma et de la dégradation de la qualité des eaux souterraines par les contaminants, nécessite une grande attention pour le futur.

     

大庆龙凤湿地须浮鸥巢址选择研究

为了认知影响须浮鸥(Chlidonias hybridus)营巢的主要环境因素,于2011年6～7月,采用直接观察法和样方法在大庆龙凤湿地自然保护区内对须浮鸥的巢区进行了调查研究.在本次调查中共发现须浮鸥巢73个,逐巢进行了常规测量,并对须浮鸥巢址及附近无巢对照区域的生境进行了调查.主成分分析和独立样本t检验的结果表明,须浮鸥属于集群营巢,而影响须浮鸥巢址选择的主要因素依次为巢下水深、巢距植物距离、巢周明水面积、植物高度、植物密度和巢距干扰源距离.其中,前3个因素影响须浮鸥生境中食物的供给条件,后3个因素影响须浮鸥巢的隐蔽条件.须浮鸥选择巢址的条件是能提供丰富食物且具有较好隐蔽条件的生境.