InSAR to support sustainable urbanization over compacting aquifers: The case of Toluca Valley,Mexico

This paper illustrates how InSAR alone can be used to delineate potential ground fractures related to aquifer system compaction. An InSAR-derived ground fracturing map of the Toluca Valley, Mexico, is produced and validated through a field campaign. The results are of great interest to support sustainable urbanization and show that InSAR processing of open-access Synthetic Aperture Radar (SAR) data from the Sentinel-1 satellites can lead to reliable and cost-effective products directly usable by cities to help decision-making.The Toluca Valley Aquifer (TVA) sustains the water needs of two million inhabitants living within the valley, a growing industry, an intensively irrigated agricultural area, and 38% of the water needs of the megalopolis of Mexico City, located 40 km east of the valley. Ensuring water sustainability, infrastructure integrity, along with supporting the important economic and demographic growth of the region, is a major challenge for water managers and urban developers. This paper presents a long-term analysis of ground fracturing by interpreting 13 years of InSAR-derived ground displacement measurements. Small Baseline Subset (SBAS) and Persistent Scatterer Interferometry (PSI) techniques are applied over three SAR datasets totalling 93 acquisitions from Envisat, Radarsat-2, and Sentinel-1A satellites and covering the period from 2003 to 2016.From 2003 to 2016, groundwater level declines of up to 1.6 m/yr, land subsidence up to 77 mm/yr, and major infrastructure damages are observed. Groundwater level data show highly variable seasonal responses according to their connectivity to recharge areas. However, the trend of groundwater levels consistently range from −0.5 to −1.5 m/yr regardless of the well location and depth. By analysing the horizontal gradients of vertical land subsidence, we provide a potential ground fracture map to assist in future urban development planning in the Toluca Valley.     

Frontiers of urbanization: Identifying and explaining urbanization hot spots in the south of Mexico City using human and remote sensing

This article applies a multi-method approach to develop a better measurement of urbanization dynamics using remote and human sensing based on a GIS platform. The results demonstrate the benefits of bringing human and remote sensing sources together in a framework of hot spot analysis for a megacity such as Mexico City. Furthermore, our analysis suggests that human and remote sensing work well together in detecting the expansion of illegal urban settlements. Looking at the driving factors of illegal settlements, the existence of strong association between the expansion of illegal urban settlements and socioeconomic factors such as unemployment, provides some answers and reveals new questions. Illegal urban growth often leads to the loss of ecological areas in the urban frontiers, especially in areas where the urbanization potential is high. As a consequence, there are conflicts with legal settlers who dislike the illegal expansion. This approach can be extended to and replicated in new urbanizing areas, in particular in Africa and Asia.     

海南花场湾一种针叶草属亚种或变种的新记录

水鳖科针叶草属在我国海草分布记录仅有1种,即针叶草。首次在海南花场湾新发现一种海草,疑似针叶草属一亚种或变种,在水深约2 m红树林旁的泥砂中,与贝克喜盐草混生,分布集中且面积较小,面积约25 m2。比较分析了针叶草属亚种或变种、针叶草和丝状针叶草3种海草的生境、形态特征。结果表明:针叶草属亚种或变种在根和茎的形态特征与针叶草和丝状针叶草较为相似,大小上比后两者小1个数量级,果实着生在根上,初步确定该种为针叶草属亚种或变种。基于针叶草属分布面积极小,在我国海草生态保护中具有重要意义,亟需引起关注,建议将针叶草属纳入中国珍稀濒危植物名录。     

A high resolution record of storm-induced erosion from lake sediments,New Zealand

The sustainable management of erodible pastoral hill country is a major focus of land use research in New Zealand. A multi-disciplinary study, using a high resolution lake sedimentation record, is being conducted to determine the role that cyclonic storms and natural and human-induced vegetation changes play in the erosion history of a landslide-prone hill country watershed.Sediment cores from Lakes Tutira and Waikopiro in northern Hawke's Bay were analysed to construct the magnitude-frequency history of storm-induced erosion since European settlement. Pulses of sediment representing individual storms can be clearly identified and are correlated to a storm history derived from analysis of a 93 year daily rainfall record. Correlation and dating are confirmed by pollen and diatom analysis,¹³⁷Cs distribution, tephrochronology and reference to a well documented land use history. Annually laminated, organic rich deposits, which occur in the uppermost sediments and represent the annual decomposition of biogenic material associated with eutrophication, are also used to confirm the chronology.A high correlation was found between storm sediment thickness and total storm rainfall (R²=0.8). Although sediment producing storms (>150 mm) occur on a near annual basis, the two largest storms (>600 mm) contributed 54% of the total sediment thickness.The presence of well defined storm sediment pulses has enabled the lake storage component of a sediment budget to be calculated for Cyclone Bola (1988), the most recent and largest rainstorm on record. The integration of this budget with the storm-magnitude-frequency history will be used to develop watershed-based models to predict the impacts of land use changes and the erosion response to climate scenarios.This is the third paper in a series of papers published in this issue on high-resolution paleolimnology. These papers were presented at the Sixth International Palaeolimnological Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr A. F. Lotter and Dr. M. Sturm served as guest editors for these papers.     

Dilute gravity current and rain-flushed ash deposits in the 1.8 ka Hatepe Plinian deposit,Taupo, New Zealand

Two groups of poorly sorted ash-rich beds, previously interpreted as rain-flushed ashes, occur in the ca. AD 180 Hatepe Plinian pumice fall deposit at Taupo volcano, New Zealand. Two ash beds with similar dispersal patterns and an aggregate thickness of up to 13 cm make up the lowermost group (A). Group A beds extend 45 km north-east of the vent and cover 290 km². In the southern part of the group A distribution area, a coarse ash to lapilli-size Plinian pumice bed (deposit B) separates the two group A beds. The scarcity of lapilli (material seen elsewhere from the still-depositing pumice fall) in group A beds indicates that they were rapidly transported and deposited. However, this rapid transportation and deposition did not produce cross-bedding, nor did it erode the underlying deposits. It is proposed that thick (>600 m) but dilute gravity currents generated from the collapsing outer margin of the otherwise buoyant Hatepe Plinian eruption column deposited the group A beds. The upper ash beds (group C) consist of one to seven layers, attain an aggregate thickness of 35 cm, and vary considerably in thickness and number of beds with respect to distance from vent. Group C beds contain variable amounts of ash mixed with angular Plinian pumices and are genuine rain-flushed ashes. Several recent eruptions at other volcanoes (Ukinrek Maars, Vulcan, Rabaul, La Soufrère de Guadeloupe and Soufrière, St Vincent) have produced gravity currents similar in style, but much smaller than those envisaged for group A deposits. The overloaded margins of otherwise buoyant eruption plumes generated these gravity currents. Laboratory studies have produced experimental gravity current analogues. Hazards from dilute gravity currents are considerable but often overlooked, thus the recognition of gravity current deposits will contribute to more thorough volcanic hazard assessment of prehistoric eruption sequences.     

Genetic structure and recent population expansion in the commercially harvested deep-sea decapod,Metanephrops challengeri (Crustacea: Decapoda)

ABSTRACT

Determining the genetic structure and population dynamics of harvested species are key aspects of effective fisheries management. New Zealand scampi (Metanephrops challengeri) is a species of nethropid lobster that supports a commercial fishery on the continental shelf and slope around New Zealand. To determine the genetic structure and historical population demography of New Zealand scampi, we sequenced a 623 base-pair fragment of the mitochondrial gene cytochrome c oxidase subunit one (CO1) from 321 individuals across six widely separated sites off the coast of mainland New Zealand and the subantarctic Auckland Islands, representing much of the species’ distribution. The Auckland Islands population was found to be genetically distinct from all other sampled populations, potentially resulting from an absence of continuous suitable habitat between the central-eastern South Island and the Auckland Islands. An isolation-by-distance pattern of genetic structure was also detected. With the exception of the Mercury Islands, all sampled populations showed signs of recent population expansion, potentially linked to changes in habitat availability during the glacial-interglacial cycles of the Pleistocene. We recommend that the current NZ scampi management areas and harvesting rates for each remain unchanged.     

Habitats and Characteristics of the Sea Urchins Lytechinus variegatus and Arbacia punctulata (Echinodermata) on the Florida Gulf-Coast Shelf

Abstract Lytechinus variegatus and Arbacia punctulata have been studied primarily in inshore, shallow‐water areas. However, they are abundant in deeper waters on the Florida gulf‐coast shelf and seem important components of the benthic communities there. Lytechinus variegatus occurs alone on sand bottoms and A. punctulata occurs alone on rubble bottoms in these deeper waters. The species also co‐occur there on ­heterogeneous bottoms, each in a distinct microhabitat with A. punctulata on rubble and L. variegatus on surrounding sand. Characteristics of the sea urchins in these different deeper‐water habitat types and at one nearshore site with a heterogeneous rubble‐sand bottom were compared. Over the 2‐year study, offshore individuals of both species had low gut and gonad indices and the maximum size of individuals did not change. This suggests food limitation and low production. Offshore, A. punctulata had a higher Aristotle's lantern index and lower gut and gonad indices in populations where it ­co‐occurred with L. variegatus compared to populations where it occurred alone. The ­Aristotle's lantern index of L. variegatus did not differ among the offshore sites. Neither species seemed food limited at the nearshore site. Although productivity is lower at the offshore sites, both species extend their distribution and reproduction potential by existing there.     

中国马尾藻属的研究 Ⅶ.宾德种群的三个新种

在研究中国真马尾藻亚属SubgenusSargassum刺托组SectionAcanthocarpicae团徽托序亚组SubsectionGlomerulatae宾德系SeriesBinderiana宾德种群SpeciesGroupBinderia过程中，发现该种群新种3个，它们是中间马尾藻SargassumIntermediumTsengetLusp．nov.，模式标本于1975年5月15日由李伟新采自广西涸洲岛，模式标本号AST75－0594；琼海马尾藻SargassumqionghaienseTsengetLusp．nov，模式标本于1983年7月12日由陆保仁采自海南省琼海县沙，模式标本号CA83－0016；裂开马尾藻SargasumerumensTsengetLusp．nov，模式标本于1982年4月23日由陆探仁采自海南省三亚市鹿回头，模式标本号AST82－0413。模式标本均存于中国科学院海洋研究所植物标本室。     

中国栅藻属三新种

对1950，1953，1955，1957和1990年在湖北省武昌县、黄陵县、江陵县、武汉市和江苏省无锡市采集的藻类标本进行分类。鉴定表明，它们是栅藻属的3个新种：纤维藻形栅藻，球刺栅藻和湖生栅藻。模式标本保存于中国科学院水生生物研究所藻类标本室（IHBA）。     

High-resolution seismic-reflection investigation of the northern Gulf of Mexico gas-hydrate-stability zone

We recorded high-resolution seismic-reflection data in the northern Gulf of Mexico to study gas and gas-hydrate distribution and their relation to seafloor slides. Gas hydrate is widely reported near the seafloor, but is described at only one deep drill site. Our data show high-reflectivity zones (HRZs) near faults, diapirs, and gas vents and interbedded within sedimentary sections at shallow depth (<1 km). The HRZs lie below the gas-hydrate-stability zone (GHSZ) as well as within the zone (less common), and they coincide with zones of shallow water-flows. Bottom simulating reflections are rare in the Gulf, and not documented in our data.We infer HRZs result largely from free gas in sandy beds, with gas hydrate within the GHSZ. Our estimates for the base BHSZ correlate reasonably with the top of HRZs in some thick well-layered basin sections, but poorly where shallow sediments are thin and strongly deformed. The equivocal correlation results from large natural variability of parameters that are used to calculate the base of the GHSZ. The HRZs may, however, be potential indicators of nearby gas hydrate. The HRZs also lie at the base of at least two large seafloor slides (e.g. up to 250 km²) that may be actively moving along decollement faults that sole within the GHSZ or close to the estimated base of the GHSZ. We suspect that water/gas flow along these and other faults such as ‘chimney’ features provide gas to permit crystallization of gas hydrate in the GHSZ. Such flows weaken sediment that slide down salt-oversteepened slopes when triggered by earthquakes.