Environmental hydrogeology of the southern sector of the Samborombon Bay wetland,Argentina

The Samborombon Bay wetland is located on the west margin of the Rio de la Plata estuary, in the Province of Buenos Aires, Argentina. This paper analyses the geological, geomorphologic, soil and vegetation characteristics of the southernmost sector of this wetland and their influence on surface water and groundwater. The study area presents three hydrologic units: coastal dunes, sand sheets and coastal plain. Coastal dunes and sand sheets are recharge zones of high permeability with well-drained, non-saline soils, and a few surface water flows. Changes in the water table are related to rainfall. Groundwater in coastal dunes is Ca–Mg–HCO₃ to Na–HCO₃, and of low salinity (590 mg/l). Groundwater in sand sheets is mainly Na–HCO₃ with a salinity of about 1,020 mg/l. The coastal plain exhibits medium to low permeability sediments, with submerged saline soils poorly drained. Groundwater is Na–Cl with a mean salinity of 16,502 mg/l. A surface hydrological network develops in the coastal plain. Surface water levels near the shoreline are affected by tidal fluctuations; far from the shoreline water accumulates because of poor drainage. Both sectors have Na–Cl water, but the former is more saline. Human intervention and sea level rise may affect the wetland severely.     

Nutrients and zooplankton composition and dynamics in relation to the hydrological pattern in a confined Mediterranean salt marsh (NE Iberian Peninsula)

The role of the hydrological regime in the nutrients and zooplankton composition and dynamics has been analysed in five lagoons of La Pletera salt marshes (NE Iberian Peninsula) during a complete hydrological cycle (2002–2003). Two of the lagoons have their origin in the old river mouths while the other three were recently created in the framework of a Life Restoration project. This fact has also allowed us to study the effect of the lagoon age on nutrient and zooplankton composition and dynamics. The salt marsh hydrology is determined by a prolonged period of confinement without water inputs, irregularly interrupted by sudden water inputs due to flooding events (sea storms or intense rainfalls). While the dynamics of oxidized nitrogen compounds in the lagoons depends on the water inputs variability within each hydrological cycle, the internal load of phosphorus, total nitrogen and organic matter is related more to the cumulative mechanisms during the confinement periods. Accumulation processes may be easily related to lagoon age, since old lagoons have higher content of nutrients and organic matter, suggesting that these lagoons progressively accumulate nutrients during the successive confinement events. This is the usual case for most Mediterranean salt marshes without an artificially manipulated water regime. The zooplankton community in La Pletera integrates the effects of both the hydrological regime and the lagoon age since the former determines the temporal pattern of the main zooplankton species and the latter explains differences in composition and structure between old and new lagoons.     

Geochemical modeling of coal mine drainage, Summit County, Ohio

 Geochemical modeling was used to investigate downstream changes in coal mine drainage at Silver Creek Metro-park, Summit County, Ohio. A simple mixing model identified the components that are undergoing conservative transport (Cl^–, PO₄ ^3–, Ca²⁺, K⁺, Mg²⁺ and Na⁺) and those undergoing reactive transport (DO, HCO₃ ^–, SO₄ ^2–, Fe²⁺, Mn²⁺ and Si). Fe²⁺ is removed by precipitation of amorphous iron-hydroxide. Mn²⁺ are removed along with Fe²⁺ by adsorption onto surfaces of iron-hydroxides. DO increases downstream due to absorption from the atmosphere. The HCO₃ ^– concentration increases downstream as a result of oxidation of organic material. The rate of Fe²⁺ removal from the mine drainage was estimated from the linear relationship between Fe⁺² concentration and downstream distance to be 0.126 mg/s. Results of this study can be used to improve the design of aerobic wetlands used to treat acid mine drainage. Received: 4 June 1996 · Accepted: 17 September 1996     

Sodium Arsenite Induced Alteration of Hemocyte Density of Lamellidens marginalis – An Edible Mollusk from India

Lamellidens marginalis (Molluska Bivalvia Eulamellibranchiata) is an important member of the freshwater ecosystem of India, which is sustained by filtering phytoplankton, bacteria and other particulate organic matter from the available water. Hemocytes, the circulating blood cells of bivalves, function as immunological effector cells under exposure to toxins and/or parasites. The hemocytes of Lamellidens marginalis have been identified morphologically and enumerated as being qualified for use as a biomarker to analyze the threat of freshwater contamination by sublethal concentrations of sodium arsenite, a natural pollutant of freshwater ecosystems. Diverse subpopulations of hemocytes were identified as blast‐like cells, granulocytes, agranulocytes, hyalinocytes and asterocytes. Supression in the total count of hemocytes and blast‐like cells was recorded under the exposure of all the concentrations of sodium arsenite tested. Sodium arsenite elevated the relative density of granulocytes, hyalinocytes, and asterocytes. Partial restoration of the total count of the hemocytes was recorded after the post‐treated animals were maintained in arsenic‐free water for periods of 15 and 30 days. The data predict a shift in the immunological parameters of this bivalve in arsenic contaminated environments. The present study is aimed at quantifying the arsenic induced stress in Lamellidens marginalis and establishing the hemocyte density as a biomarker of aquatic pollution in selected geographical regions of India.     

Use of WorldView-2 time series to establish a wetland monitoring program for potential offsite impacts of mine site rehabilitation

The Ramsar-listed wetlands of the Magela Creek floodplain, situated in the World Heritage Kakadu National Park, in northern Australia are recognised for their biodiversity and cultural values. The floodplain is also a downstream receiving environment for Ranger uranium mine, which is entering closure and rehabilitation phases. Vegetation on the floodplain is spatially and temporally variable which is related to the hydrology of the region, primarily the extent and level of inundation and available soil moisture. Time-series mapping of the floodplain vegetation will provide a contemporary baseline of annual vegetation dynamics to assist with determining whether change is natural or a result of the potential impacts of mine closure activities such as increased suspended sediment moving downstream. The research described here used geographic object-based image analysis (GEOBIA) to classify the upper Magela Creek floodplain vegetation from WorldView-2 imagery captured over four years (2010–2013) and ancillary data including a canopy height model. A step-wise rule set was used to implement a decision tree classification. The resulting maps showed the 12 major vegetation communities that exist on the Magela Creek floodplain and their distribution for May 2010, May 2011, June 2012 and June 2013 with overall accuracies of over 80% for each map. Most of the error appears to be associated with confusion between vegetation classes that are spectrally similar such as the classes dominated by grasses. Object-based change detection was then applied to the maps to analyse change between dates. Results indicate that change between dates was detected for large areas of the floodplain. Most of the change is associated with the amount of surface water present, indicating that although imagery was captured at the same time of year, the imagery represents different stages of the seasonal cycle of the floodplain.     

北京野鸭湖湿地不同植被退化区的土壤种子库特征

2010年5月,在北京野鸭湖湿地自然保护区选择废弃鱼塘、耕作苜蓿(Medicago)地、撂荒苜蓿地、天然退化湿地和天然湿地作为实验地,其中,天然湿地作为对照。通过土壤种子库萌发实验,对实验地土壤种子库的基本特征以及与地上植被的关系进行了对比研究。结果表明,5种实验地的土壤种子库共有60种植物,隶属于23科46属。其中,萌发物种最多的是菊科(Compositae)、禾本科(Poaceae)和莎草科(Cyperaceae),分别为11种、10种和8种。废弃鱼塘、耕作苜蓿地、撂荒苜蓿地和天然退化湿地种子平均密度为6 885粒/m~2,天然湿地种子的平均密度为16 083粒/m~2,5种实验地的种子库密度差异极显著(n=300,F=4.828,p=0.001<0.05);各实验地的种子库垂直分布有一致的规律性,各实验地0～6 cm土层的种子库密度明显高于6～12 cm土层;各实验地的土壤种子库与地上植被的相似性系数都不高,土壤种子库物种组成的稳定性要高于地上植被。通过研究发现,退化湿地的土壤种子库中有大量的植物种子储藏和湿地植物的种子,这为野鸭湖退化湿地恢复提供了重要的保障,这些潜在的植物种子在野鸭湖退化湿地生态输水过程中会起到应有的恢复作用。建议野鸭湖湿地自然保护区管理部门继续加强退化湿地区域的土壤种子库保护工作,必须重视水环境的恢复、各种人为干扰的消除以及系统保护的加强。     

我国湿地的主要生态问题及治理对策

在参阅相关文献和实地调查的基础上,分析了我国湿地面临的主要生态问题,将湿地生态系统结构与功能的退化划分为缺水萎缩、污染退化、泥沙淤积退化、疏干排水退化、生物资源过度利用与生物多样性受损、红树林破坏、生物入侵退化等7个类型。在此基础上,提出湿地生态保育与治理的若干对策。     

Hydrodynamic characteristics of the western Doñana Region (area of El Abalario), Huelva,Spain

The Doñana region, in southwestern Spain, comprises a large and important nature reserve, the wetlands of which are affected by human activity. Planting of an extensive eucalyptus forest in the 1950s and, more recently, the use of aquifers for irrigation and water supply for some coastal tourist resorts, have altered the natural groundwater-flow system. The area of the study is the western sector of the region, called El Abalario, which is a gentle topographic elevation between the Atlantic coast and La Rocina Creek (Arroyo de la Rocina). Underneath a variable layer of eolian sands with high dunes near the coast, thick Plio-Quaternary detritic strata, mostly fine silica sands, overlie marls. Near the base there is a variable, deltaic-origin layer of coarse sands and gravels. The dome-shaped water table, inside the sands, is close to the surface everywhere except beneath the dune belt, and small, temporary, shallow lagoons are numerous. The coarse sand and gravel layer conditions groundwater flow and behaves as a semiconfined layer between sands. A cross section through the area was simulated with a model to check the validity of the conceptual groundwater-flow pattern and its sensitivity to the hydraulic parameters. The model was calibrated using parameter values obtained by pumping tests and multilevel piezometric data, and checked against the estimated groundwater discharge into La Rocina Creek. Groundwater flows peripherally to the sea coast, to La Rocina Creek, or directly east and southeastward into the Doñana marshlands, in the Guadalquivir River delta. The average net aquifer recharge rate was calculated to be between 100 and 200 mm year^–1 for the area covered by brush, but is remarkably lower in the areas of eucalyptus trees. The transient-state model shows that recharge varies spatially and is not clearly proportional to annual precipitation. Phreatic evapotranspiration plays an important role in decreasing the net value of aquifer recharge to approximately 0.4–0.6 of that calculated with a soil-balance model. The cross section model was used to study the effect of groundwater abstraction on water-table depth by subtracting the contribution of vertical flow, calculated by a well-hydraulics formula, to the semiconfined deep aquifer. The result was a decrease in phreatic evapotranspiration, flow into La Rocina Creek, and lagoon-inundation frequency. Replacement of the eucalyptus forest with native vegetation may raise water-table levels and even reactivate old tributaries to La Rocina Creek.

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Resumen La región de Doñana, situada en el sudoeste de España, incluye una gran e importante reserva natural, cuyos humedales están siendo afectados por la actividad humana. La extensa plantación de eucaliptus en la década de 1950 y el uso más reciente de los acuíferos para riego y para abastecimiento de centros turísticos costeros han modificado el sistema de flujo del agua subterránea en esta zona. Este estudio se ha realizado en el sector occidental, llamado El Abalario. Se trata de una elevación suave situada entre el océano Atlántico y el arroyo de La Rocina. Debajo de un manto variable de arenas eólicas, que forma un alto cordón dunar costero, se encuentran sedimentos detríticos plio-cuaternarios formados por arenas silíceas finas, que hacia la base incluyen una capa de arenas gruesas y gravas de origen deltrico, los que a su vez yacen sobre margas. El flujo de agua subterránea está relacionado con niveles de gravas y gravillas semiconfinadas por las arenas fluvio-marinas que contienen el nivel freático. El nivel freático es somero excepto debajo del cordón dunar. Son frecuentes pequeñas lagunas temporales. Se ha simulado el flujo de agua subterránea en una sección para comprobar el modelo de flujo conceptual y la sensibilidad a variaciones de los parámetros. El modelo fue calibrado usando los valores de los parámetros hidráulicos obtenidos en ensayos de bombeo y datos piezométricos medidos a diferentes profundidades, y la descarga estimada al arroyo de La Rocina. La recarga de agua subterránea drena lateralmente, por un lado hacia la costa y por otro lado a través del arroyo de La Rocina, o directamente hacia las Marismas de Doñana situadas en el delta del río Guadalquivir. Con una lluvia media anual entre 550 y 600 mm, la recarga neta media estacionaria anual del acuífero, considerando periodos de tiempo largos, se estima entre 100 y 200 mm en las zonas de vegetación autóctona, y es notablemente menor en las zonas de plantación de eucaliptos. El modelo transitorio indica que la recarga varia espacialmente y no es claramente proporcional a la precipitación para periodos de un año. La evapotranspiración freática varia espacialmente y juega un papel importante; disminuye el valor neto de la recarga al acuífero para dejarlo en 0,4 a 0,6 de lo que se calcula mediante un balance de agua en el suelo. La sección modelada sirve para estudiar el efecto de la extracción de agua subterránea sobre la profundidad del nivel freático mediante la substracción del flujo vertical, que se calcula mediante una fórmula de hidráulica de pozos para el acuífero semiconfinado profundo. El resultado es una disminución de la evapotranspiración freática, del flujo al arroyo de la Rocina y de la frecuencia de inundación de las lagunas. La substitución del bosque de eucaliptus por vegetación nativa puede elevar los niveles freáticos e incluso reactivar antiguos "caños" tributarios al arroyo de La Rocina.

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Résumé La région de Doñana, située dans le sud ouest de l'Espagne, comprend une importante réserve naturelle avec des zones humides, affectée par l'activité humaine. L'exploitation de vastes plantations d'eucalyptus pendant les années 50 et l'usage plus récent des nappes souterraines pour l'irrigation et l'alimentation en eau des centres touristiques côtiers ont modifié le système de flux d'eau souterraine dans cette zone. La présente étude a été réalisée dans le secteur occidental, appelé El Abalario. Ce secteur consiste en une légère élévation située entre l'Océan Atlantique et la ravine de La Rocina. Une couverture variable de sables éoliens, formant une haute crête dunaire côtière, recouvre des sédiments detritiques plio-quaternaires, déposés eux même sur des sables siliceux lesquels reposent à leur tour sur des marnes. Près de la base se trouvent des sables grossiers et des graviers d'origine deltaïque, dont l'épaisseur varie spatialement. Le flux d'eau souterraine est conditionné par l'aquifère semi confinés des graviers et des sables grossiers. Le niveau phréatique de l'aquifère libre des sables fluvio-marins est peu profond, excepté sous les dunes. On y trouve souvent des petites lagunes temporaires peu profondes. Le flux de l'eau souterraine a été simulé dans une section verticale pour vérifier le modèle hydrogéologique conceptuel et la sensibilité aux variations des paramètres. Le modèle a été calé en utilisant d'une part les valeurs des paramètres hydrauliques obtenus par des essais de pompage et d'après les données piezométriques mesurées à différentes profondeurs, et d'autre part l'apport estimé de la ravine de La Rocina. L'écoulement d'eau souterraine s'effectue par drainage latérale dans trois directions, d'une part vers la côte, d'autre part à travers la ravine de La Rocina et finalement directement vers les Marais de Doñana situés à l'est et sud-est dans le delta du fleuve Guadalquivir. Avec une pluviométrie moyenne comprise entre 550 et 600 mm, la recharge nette moyenne annuelle des nappes, pour des périodes de temps assez longues, est estimée entre 100 et 200 mm dans les aires de végétation autochtone, et elle est nettement inférieure dans les aires plantées d´eucalyptus. Le modèle transitoire montre que la recharge varie dans l'espace et qu'elle n'est pas clairement proportionnelle aux précipitations annuelles. L'évapotranspiration phréatique joue un rôle important et diminue la valeur nette de la recharge des nappes de 0,4 à 0,6 de la valeur calculée avec un modèle de bilan d'eau dans le sol. La section modélisée est utilisée pour étudier l'effet de l'extraction d'eau souterraine sur la profondeur du niveau phréatique en soustrayant le flux vertical, calculé grâce à une formule d'hydraulique des puits, de la nappe profonde semi-confinée. Le résultat de cette extraction est une diminution de l'évapotranspiration phréatique, du flux au niveau de la ravine de La Rocina et de la fréquence d'inondation des lagunes. La substitution de forêts d'eucalyptus par de la végétation autochtone peut permettre la remonté des niveaux phréatiques et même réactiver d'anciens ravins affluents à La Rocina.

     

云南省鹤庆盆地2.78Ma以来的环境演化

通过构建于新沂河河漫滩上的表面流人工温地系统处理污染河水的现场中试研究表明,在CODMn和NH4 -N进水浓度分别为11．69-60．00 mg／L和1．37-20．18 mg／L时,种植千屈菜、美人蕉、香蒲、水葱4种不同植物的表面流人工湿地系统,对CODMn的平均去除效率分别为26．44％、40．12％、46．71％、28．23％,对NH4 -N的平均去除效率分别为64．27％、70．49％、66．78％、58．52％,其中香蒲和美人蕉的净化能力较强．4种植物中水葱的耐淹能力最强,在完全淹水达22 d以上时,水葱依然生长良好;千屈菜的耐淹能力最弱,在完全淹水7 d后就开始枯萎,淹水17 d后地上、地下部分全部死亡．     

Characterizing wetland dynamics: a post-classification change detection analysis of the East Kolkata Wetlands using open source satellite data

The East Kolkata Wetlands is a unique resource recovery system. The Ramsar Convention recognized it as a ‘Wetland of International Importance’ in August 2002. However, the long-term resource exploitation and land use changes in the dynamic ecosystem have resulted in non-linear environmental responses. This is an attempt using open source remote sensing datasets to capture the spatio-temporal transformation of the wetland resulting from various anthropogenic activities. Landsat MSS and TM imageries of 1973, 1980, 1989, 2001 and 2010 were classified using Maximum Likelihood Classifier to monitor the wetland change; however, to study wetland dynamics, the post-classification wetland change detection maps have been generated for two temporal phases, i.e. 1973–1989 and 1989–2010. This study finds that the area under wetlands has reduced comprehensively in the past 40 years due to the conversion of wetlands into various other uses such as urban expansion of the Kolkata metropolitan city.