Fluctuations of Nero Lake in the Holocene

Doklady Earth Sciences - The paleohydrological settings in the Rostov lowland (Yaroslavl oblast) have been the subject of long-standing of disputes. The concepts for the Holocene fluctuations in...     

Long-Term Seasonal Trends in the Prey Community of Delta Smelt (<Emphasis Type="Italic">Hypomesus transpacificus</Emphasis>) Within the Sacramento-San Joaquin Delta,California

Abiotic factors and species introductions can alter food web timing, disrupt life cycles, and change life history expressions and the temporal scale of population dynamics in zooplankton communities. We examined physical, trophic, and zooplankton community dynamics in the San Francisco Estuary, California, a highly altered Mediterranean climate waterway, across a 43-year dataset (1972–2014). Before invasion by the suspension-feeding overbite clam (Potamocorbula amurensis) in the mid-1980s, the estuary demonstrated monomictic thermal mixing in which winter turbidity and cool temperatures contributed to seasonally low productivity, followed by a late-spring-summer clearing phase with warm water and peak phytoplankton blooms that continued into early winter. Following the clam invasion, we observed a shift in peak phytoplankton bloom timing, with peak productivity now occurring in May compared to June prior to the invasion. Peak abundance of several zooplankton taxa (Eurytemora affinis, Pseudodiaptomus, other calanoids, and non-copepods) also shifted to earlier in the season. We present the first evidence of a shift in the timing of peak abundance for zooplankton species that are key prey items of delta smelt (Hypomesus transpacificus), a federally threatened pelagic fish species. These timing shifts may have exacerbated well-documented food limitations of delta smelt due to declines in primary productivity since the invasion of the overbite clam. Future conservation efforts in the estuary should consider measures designed to restore the timing and magnitude of pre-invasion phytoplankton blooms.     

Long-Term Trends of Nutrients and Phytoplankton in Chesapeake Bay

Climate effects on hydrology impart high variability to water-quality properties, including nutrient loadings, concentrations, and phytoplankton biomass as chlorophyll-a (chl-a), in estuarine and coastal ecosystems. Resolving long-term trends of these properties requires that we distinguish climate effects from secular changes reflecting anthropogenic eutrophication. Here, we test the hypothesis that strong climatic contrasts leading to irregular dry and wet periods contribute significantly to interannual variability of mean annual values of water-quality properties using in situ data for Chesapeake Bay. Climate effects are quantified using annual freshwater discharge from the Susquehanna River together with a synoptic climatology for the Chesapeake Bay region based on predominant sea-level pressure patterns. Time series of water-quality properties are analyzed using historical (1945–1983) and recent (1984–2012) data for the bay adjusted for climate effects on hydrology. Contemporary monitoring by the Chesapeake Bay Program (CBP) provides data for a period since mid-1984 that is significantly impacted by anthropogenic eutrophication, while historical data back to 1945 serve as historical context for a period prior to severe impairments. The generalized additive model (GAM) and the generalized additive mixed model (GAMM) are developed for nutrient loadings and concentrations (total nitrogen—TN, nitrate?+?nitrate—NO₂?+?NO₃) at the Susquehanna River and water-quality properties in the bay proper, including dissolved nutrients (NO₂?+?NO₃, orthophosphate—PO₄), chl-a, diffuse light attenuation coefficient (K _D (PAR)), and chl-a/TN. Each statistical model consists of a sum of nonlinear functions to generate flow-adjusted time series and compute long-term trends accounting for climate effects on hydrology. We present results identifying successive periods of (1) eutrophication ca. 1945–1980 characterized by approximately doubled TN and NO₂?+?NO₃ loadings, leading to increased chl-a and associated ecosystem impairments, and (2) modest decreases of TN and NO₂?+?NO₃ loadings from 1981 to 2012, signaling a partial reversal of nutrient over-enrichment. Comparison of our findings with long-term trends of water-quality properties for a variety of estuarine and coastal ecosystems around the world reveals that trends for Chesapeake Bay are weaker than for other systems subject to strenuous management efforts, suggesting that more aggressive actions than those undertaken to date will be required to counter anthropogenic eutrophication of this valuable resource.     

Long-Term Changes in Water Quality and Productivity in the Patuxent River Estuary: 1985 to 2003

We conducted a quantitative assessment of estuarine ecosystem responses to reduced phosphorus and nitrogen loading from sewage treatment facilities and to variability in freshwater flow and nonpoint nutrient inputs to the Patuxent River estuary. We analyzed a 19-year dataset of water quality conditions, nutrient loading, and climatic forcing for three estuarine regions and also computed monthly rates of net production of dissolved O₂ and physical transport of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) using a salt- and water-balance model. Point-source loading of DIN and DIP to the estuary declined by 40–60% following upgrades to sewage treatment plants and correlated with parallel decreases in DIN and DIP concentrations throughout the Patuxent. Reduced point-source nutrient loading and concentration resulted in declines in phytoplankton chlorophyll-a (chl-a) and light-saturated carbon fixation, as well as in bottom-layer O₂ consumption for upper regions of the estuary. Despite significant reductions in seaward N transport from the middle to lower estuary, chl-a, turbidity, and surface-layer net O₂ production increased in the lower estuary, especially during summer. This degradation of water quality in the lower estuary appears to be linked to a trend of increasing net inputs of DIN into the estuary from Chesapeake Bay and to above-average river flow during the mid-1990s. In addition, increased abundance of Mnemiopsis leidyi significantly reduced copepod abundance during summer from 1990 to 2002, which favored increases in chl-a and allowed a shift in total N partitioning from DIN to particulate organic nitrogen. These analyses illustrate (1) the value of long-term monitoring data, (2) the need for regional scale nutrient management that includes integrated estuarine systems, and (3) the potential water quality impacts of altered coastal food webs.     

现代缓坡三角洲沉积模式--以鄱阳湖赣江三角洲为例

在我国,缓坡三角洲形成了不少大油田。关于缓坡三角洲的沉积模式,前人做了大量研究,但大都针对古代地层。由于古代地层精细对比和沉积环境解释常常因人而异,因此总结出来的沉积模式五花八门,可靠性较低。鉴于此,本文从现代实例入手,选择了鄱阳湖赣江三角洲,采用野外实地测量、探槽、浅钻孔、探地雷达、粒度分析等方法,对其沉积特征进行系统研究,建立了缓坡三角洲沉积模式。本次研究主要取得了如下重要认识:①在三角洲平原上发现了两种新的砂体类型,即汊口滩和并口滩,分别位于分流河道分汊处和合并处,这意味着分流河道的分汊、合并部位也是有利的油气聚集部位;②在分流河道砂体中存在连片披覆型、孤立充填型、孤立残留型三种类型的落淤层,并提出了其形成机制;③统计了分流河道的定量参数,提出了分流河道宽度的变化规律,即从上三角洲平原到下三角洲平原,分流河道逐渐变窄,分一次分汊其宽度平均降低1/2,而且分汊频率增高,数量变多,弯度降低,沉积物变细变薄,砂体间连通性变差;④三角洲前缘不发育水下分流河道,而是发育河口坝和席状滩;⑤由于坡度平缓,湖平面小幅度变化会引起湖岸线大规模进退,可导致水下与水上沉积频繁交互,因此缓坡三角洲沉积在地震上不会有叠瓦状或反S形前积反射,而是呈平行或亚平行反射。     

Long-Term Temperature Trends and Tree Growth in the Taymir Region of Northern Siberia

The northernmost conifers in the world are located well above the Arctic Circle in the Taymir region of northern Siberia and have been recording the thermal environment for centuries to millennia. The trees respond to temperatures beyond the narrow season of actual cambial cell division by means of root growth, photosynthesis, lignification of cell walls, and other biochemical processes. Data from annual tree-ring widths are used to reconstruct May–September mean temperatures for the past four centuries. These warm-season temperatures correlate with annual temperatures and indicate unusual warming in the 20th century. However, there is a loss of thermal response in ring widths since about 1970. Previously the warmer temperatures induced wider rings. Most major warming and cooling trends are in agreement with other high-latitude temperature reconstructions based on tree-ring analyses with some regional differences in timing of cooling in the late 18th century and of warming in the late 19th century.     

Long-Term Trends of Water Quality and Biotic Metrics in Chesapeake Bay: 1986 to 2008

We analyzed trends in a 23-year period of water quality and biotic data for Chesapeake Bay. Indicators were used to detect trends of improving and worsening environmental health in 15 regions and 70 segments of the bay and to assess the estuarine ecosystem’s responses to reduced nutrient loading from point (i.e., sewage treatment facilities) and non-point (e.g., agricultural and urban land use) sources. Despite extensive restoration efforts, ecological health-related water quality (chlorophyll-a, dissolved oxygen, Secchi depth) and biotic (phytoplankton and benthic indices) metrics evaluated herein have generally shown little improvement (submerged aquatic vegetation was an exception), and water clarity and chlorophyll-a have considerably worsened since 1986. Nutrient and sediment inputs from higher-than-average annual flows after 1992 combined with those from highly developed Coastal Plain areas and compromised ecosystem resiliency are important factors responsible for worsening chlorophyll-a and Secchi depth trends in mesohaline and polyhaline zones from 1986 to 2008.     

Mechanisms of Storm-Related Loss and Resilience in a Large Submersed Plant Bed

There is a growing emphasis on preserving ecological resilience, or a system’s capacity to absorb or recover quickly from perturbations, particularly in vulnerable coastal regions. However, the factors that affect resilience to a given disturbance are not always clear and may be system-specific. We analyzed and synthesized time series datasets to explore how extreme events impacted a large system of submersed aquatic vegetation (SAV) in upper Chesapeake Bay and to identify and understand associated mechanisms of resilience. We found that physical removal of plants around the edge of the bed by high flows during a major flood event as well as subsequent wind-driven resuspension of newly deposited sediment and attendant light-limiting conditions were detrimental to the SAV bed. Conversely, it appears that the bed attenuated high flows sufficiently to prevent plant erosion at its inner core. The bed also attenuated wind-driven wave amplitude during seasonal peaks in plant biomass, thereby decreasing sediment resuspension and increasing water clarity. In addition, clear water appeared to “spill over” into adjacent regions during ebb tide, improving the bed’s capacity for renewal by creating more favorable growing conditions in areas where plant loss had occurred. These analyses demonstrate that positive feedback processes, whereby an SAV bed modifies its environment in ways that improve its own growth, likely serve as mechanisms of SAV resilience to flood events. Although this work focuses on a specific system, the synthetic approach used here can be applied to any system for which routine monitoring data are available.     

矿源层地球化学元素在黄土盖层中纵向分布的趋势提取与应用

在内蒙草原覆盖区迪彦钦阿木Mo-Ag矿床长度为106.5 m黄土覆盖层垂直岩心上等间距顺序取样106个,用Niton XL3t X-荧光仪测得每个样本的33个元素的含量.在正态性检验的基础上,用Kendallτ相关系数分析了元素含量与深度的相关性,得出黄土覆盖层中Mo、S、W、Te、Fe、Cu、Ni、Mn、Sb、Rb、Cs、Sn、Zn、Ti、V、Pb、Th、As这18种元素含量与离开矿源的距离具有显著相关性;用HP滤波法分离出这18种元素含量空间序列的长期趋势,并用变量聚类分析法对长期趋势进行了分类;用因子分析法得到了迪彦钦阿木矿床Mo-W成矿因子和Pb-Zn成矿因子,并模拟得到Mo-W成矿因子的指数分布模式.本文的研究思路与结论可为覆盖区表层地球化学异常对矿产预测的指示作用研究提供借鉴.      

Estuarine macrobenthos in Calcasieu Lake,Louisiana: Community and trophic structure

Macrobenthic assemblages in Calcasieu Lake estuary (Louisiana) were sampled at 11 sites from October 1983 through November 1985. The sites were numerically dominated by subsurface-deposit feeders, consisting mostly of polychaetes. Greater densities of macrofauna were collected at the northern (upper) stations of the lake than were collected in West Cove or the southern stations. Abundances of polychaetes, oligochaetes, and amphipods at the upper lake stations accounted for most of the differences among stations. The numerical dominance by detritivores (97% of the fauna) and lack of strong sediment or salinity gradients across the estuary, resulted in an absence of temporal pattern in trophic structure of the macrofauna.     

Living on the Edge: Increasing Patch Size Enhances the Resilience and Community Development of a Restored Salt Marsh

Foundation species regulate communities by reducing environmental stress and providing habitat for other species. Successful restoration of biogenic habitats often depends on restoring foundation species at appropriate spatial scales within a suitable range of environmental conditions. An improved understanding of the relationship between restoration scale and environmental conditions has the potential to improve restoration outcomes for many biogenic habitats. Here, we identified and tested whether inundation/exposure stress and spatial scale (patch size) can interactively determine (1) survival and growth of a foundation species, Spartina alterniflora and (2) recruitment of supported fauna. We planted S. alterniflora and artificial mimics in large and small patches at elevations above and below local mean sea level (LMSL) and monitored plant survivorship and production, as well as faunal recruitment. In the first growing season, S. alterniflora plant survivorship and stem densities were greater above LMSL than below LMSL regardless of patch size, while stem height was greatest in small patches below LMSL. By the third growing season, S. alterniflora patch expansion was greater above LMSL than below LMSL, while stem densities were higher in large patches than small patches, regardless of location relative to LMSL. Unlike S. alterniflora, which was more productive above LMSL, sessile marine biota recruitment to mimic plants was higher in patches below LMSL than above LMSL. Our results highlight an ecological tradeoff at ~LMSL between foundation species restoration and faunal recruitment. Increasing patch size as inundation increases may offset this tradeoff and enhance resilience of restored marshes to sea-level rise.     

大气-水体系统中PAR传输模式及湖泊初级生产力

给出了一种大气-水体系统中PAR的传输模式,并利用太湖的气象和实测悬浮粒资料计算水体中PAR的时空变化.模式中考虑了大气的气溶胶、臭氧、水汽和CO₂的效应以及水面风浪、水中黄质、悬浮粒和浮游藻类的多次散射和吸收过程.最后,利用生物-光模式,计算了太湖的初级生产力.结果基本上能反映水中初级生产力随水深的变化趋势.     

生油古湖泊生产力的估算方法及应用实例

文中综述了生油古湖泊生产力估算的常用方法,并以山东东营凹陷早第三纪生油湖为例进行了应用尝试。结果表明,无论是定性分析还是定量计算,均以沙三中、下亚段、沙四上亚段和沙一段沉积时期的古湖泊生产力最高,其次是沙三上亚段沉积时期,沙二段沉积时期古生产力最低。把东营湖古生产力定量计算的结果与现代不同营养类型湖泊生产力的值相比较,可以发现沙三中、下亚段、沙四上亚段和沙一段沉积时期的东营湖是超养湖,沙三上亚段沉积时期是富养湖,沙二段沉积时期是中养湖。所以沙三中、下亚段、沙四上亚段和沙一段沉积时期古湖泊最有利于生成石油,这与油气勘探的实际结果极为吻合。     

湖平面变化对王58地区浊积扇形成与演化的控制作用研究

在陆相断陷盆地内,湖平面变化、构造作用等外部因素对浊积扇体的形成与演化有明显的控制作用。以东营凹陷南斜坡王58地区沙四上浊积扇为例,分析了湖平面变化对浊积扇发育的控制作用。湖平面变化控制了沉积物供给,从而控制了扇体的发育期次。研究区纯上4砂组沉积时期,湖平面相对较低,研究区浊积扇体并不发育;浊积扇体发育在纯上2、3砂组沉积时期;纯上1砂组沉积时期,湖平面上升,研究区不再发育浊积扇。海平面变化控制了沉积物供给,控制了浊积扇体的发育类型。在纯上3砂组沉积时期,水体较浅,发育带水道的浊积扇;在纯上2砂组沉积时期,湖水较深,发育无水道的滑塌浊积扇。总之,随着湖平面的变化,王58地区沙四上浊积扇经历了从出现、发展直到消亡的整个过程,并且随着湖平面的变化,扇体由带水道的浊积扇体向元水道的滑塌浊积扇体转变。     

Long-Term Trends in Chesapeake Bay Seasonal Hypoxia,Stratification, and Nutrient Loading

A previously observed shift in the relationship between Chesapeake Bay hypoxia and nitrogen loading has pressing implications on the efficacy of nutrient management. Detailed temporal analyses of long-term hypoxia, nitrogen loads, and stratification were conducted to reveal different within-summer trends and understand more clearly the relative role of physical conditions. Evaluation of a 60-year record of hypoxic volumes demonstrated significant increases in early summer hypoxia, but a slight decrease in late summer hypoxia. The early summer hypoxia trend is related to an increase in Bay stratification strength during June from 1985 to 2009, while the late summer hypoxia trend matches the recently decreasing nitrogen loads. Additional results show how the duration of summertime hypoxia is significantly related to nitrogen loading, and how large-scale climatic forces may be responsible for the early summer increases. Thus, despite intra-summer differences in primary controls on hypoxia, continuing nutrient reduction remains critically important for achieving improvements in Bay water quality.     

湖泊沉积中的10Be含量变化——有助于识别第四纪古冰川的有无

20世纪50-70年代核试验产生的¹³⁷Cs尘埃,在现代冰川和非冰川湖泊沉积剖面中的深度分布存在明显差异.同理,大气宇宙射线成因的长半衰期¹⁰Be尘埃,在第四纪冰川和非冰川湖泊沉积剖面中的深度分布也应存在差异.第四纪冰川湖泊,冰期时流域内冰雪和¹⁰Be的累积量大于消融量,间冰期时冰雪和¹⁰Be的消融量大于累积量.因此,冰川湖泊冰期的¹⁰Be入湖通量小于间冰期.湖泊沉积剖面¹⁰Be浓度的波动,很可能表征流域内冰雪消融与累积的变化.非冰川湖泊,不存在冰川的累积与消融对¹⁰Be入湖通量的影响.开展第四纪冰川与非冰川湖泊沉积¹⁰Be含量变化的对比研究,有可能为破译中国东部中低山区古冰川和青藏高原大冰盖的世纪之争提供新的证据.     

Morphology and recent history of the Rhone River Delta in Lake Geneva (Switzerland)

The current topographic maps of the Rhone Delta—and of Lake Geneva in general—are mainly based on hydrographic data that were acquired during the time of F.-A. Forel at the end of the nineteenth century. In this paper we present results of a new bathymetric survey, based on single- and multi-beam echosounder data. The new data, presented as a digital terrain model, show a well-structured lake bottom morphology, reflecting depositional and erosional processes that shape the lake floor. As a major geomorphologic element, the sub-aquatic Rhone Delta extends from the coastal platform to the depositional fans of the central plain of the lake at 310 m depth. 9 canyons cut the platform edge of the delta. These are sinuous (“meandering”) channels formed by erosional and depositional processes, as indicated by the steep erosional canyon walls and the depositional levees on the canyon shoulders. Ripples or dune-like morphologies wrinkle the canyon bottoms and some slope areas. Subaquatic mass movements are apparently missing on the delta and are of minor importance on the lateral lake slopes. Morphologies of the underlying bedrock and small local river deltas are located along the lateral slopes of Lake Geneva. Based on historical maps, the recent history of the Rhone River connection to the sub-aquatic delta and the canyons is reconstructed. The transition from three to two river branches dates to 1830–1840, when the river branch to the Le Bouveret lake bay was cut. The transition from two to one river branch corresponds to the achievement of the correction and dam construction work on the modern Rhone River channel between 1870 and 1880.     

浅水三角洲动态生长过程模型与有利砂体分布——以鄱阳湖赣江三角洲为例

浅水三角洲是湖盆内大面积砂体分布的重要成因,但大面积砂体的非均质性较强,预测并寻找有利砂体(甜点)是现今油气勘探的重要需求。通过开展现代赣江三角洲上平原-下平原及河口区多个沉积部位探坑挖掘工作,对探坑中沉积物岩性与沉积相序进行了描述、取样以及沉积特征对比,并且对顺直河道中心的沉积物样品进行了采集与分析化验后,认为浅水三角洲上平原河道内沙洲的洲头与洲尾、堤岸近河端,下平原上游、下游的堤岸近河端,入湖河口区的水下分流河道、纵向坝、横向坝是有利砂体的发育区及有利砂体类型。由于赣江浅水三角洲的河道主要为顺直型,正韵律的分流河道砂体不发育,赣江浅水三角洲垂向上具有早期湖泊相泥-反韵律河口沙坝-下平原与上平原堤岸相沙泥质互层的沉积演化特征。结合鄱阳湖枯水期与洪水期的水文地质特征,建立了赣江浅水三角洲的动态生长过程模型,其动态成因演化过程可分为先期枯水期湖泊沉积,湖平面上升至最大洪泛期和再次枯水期三角洲进积等3阶段。该模型既为浅水三角洲沉积由静态描述向动态过程演化研究奠定了基础,又为湖盆内大面积砂体中甜点预测提供了有益参考。     

Dynamics of Bottom Boundary Layers in the Yellow River Subaqueous Delta Based on Long-Term In-Situ Observations

<正>Objective In geo-marine science,the generalized bottom boundary layer(BBL)represents a layer between sediments and seawater.The BBL plays an important role in geological,geobiochemical,geophysical and geotechnical research because it is the connection region of hydrosphere,     

Long-Term Trends in Intertidal and Subtidal Benthic Communities in Response to Water Quality Improvement Measures

Long-term monitoring studies are needed to understand changes in ecosystem status when restoration measures are implemented. A long-term data series (1996–2007) of the Tagus estuary (Portugal) intertidal and subtidal benthic communities was collected in a degraded area where mitigation measures were implemented. Multivariate analysis was used to analyze spatial and temporal patterns in benthic community composition and trends in five benthic community metrics (i.e., taxonomic richness, density, biomass, Shannon–Wiener diversity and the AMBI index) were also examined. The results revealed a clear separation between intertidal and subtidal assemblages, although they had 50% of taxa in common, including the most abundant. Significant positive trends were found for all metrics showing that both intertidal and subtidal communities responded to the restoration measures implemented. Nevertheless, biotic indices need some adaptation before being universally applied to intertidal and subtidal habitats.