Vegetation response to rainfall seasonality and interannual variability in tropical dry forests

Projected changes in rainfall seasonality and interannual variability are expected to have severe impacts on arid and semi‐arid tropical vegetation, which is characterized by a fine‐tuned adaptation to extreme rainfall seasonality. To study the response of these ecosystems and the related changes in hydrological processes to changes in the amount and seasonality of rainfall, we focused on the caatinga biome, the typical seasonally dry forest in semi‐arid Northeast Brazil. We selected four sites across a gradient of rainfall amount and seasonality and analysed daily rainfall and biweekly Normalized Difference Vegetation Index (NDVI) data for hydrological years 2000 to 2014. Rainfall seasonal and interannual statistics were characterized by recently proposed metrics describing duration, timing and intensity of the wet season and compared to similar metrics of NDVI time series. The results show that the caatinga tends to have a more stable response with longer and less variable growing seasons (3.1 ± 0.1 months) compared to the duration wet seasons (2.0 ± 0.5 months). The ecosystem ability to buffer the interannual variability of rainfall is also evidenced by the stability in the timing of the growing season compared to the wet season, which results in variable delays (ranging from 0 to 2 months) between the peak of the rainfall season and the production of leaves by the ecosystem. The analyses show that the shape and size of the related hysteresis loops in the rainfall–NDVI relations are linked to the buffering effects of soil moisture and plant growth dynamics. Finally, model projections of vegetation response to different rainfall scenarios reveal the existence of a maximum in ecosystem productivity at intermediate levels of rainfall seasonality, suggesting a possible trade‐off in the effects of intensity (i.e. amount) and duration of the wet season on vegetation growth and related soil moisture dynamics and transpiration rates. Copyright © 2016 John Wiley & Sons, Ltd.     

香港地区晚更新世的构造活动性

河沥背西北走向的断层最近期的构造活动发生于晚更新世时期,至全新世已经完全停止.晚更新世后期香港地区(如河沥背、黄竹洋、南山和贝澳)滑坡、泥石流和巨型滚石等重力地质事件频繁发生,而且还有原地重复的情况.按照地面地质破坏现象的分布范围、规模和数量等指针综合分析,在晚更新世后期香港地区可能曾经遭受过强烈地震的袭击,其烈度估计可达Ⅸ-Ⅹ度,而且在数万年之内曾经多次发生.1万年以来,构造运动减弱,地震活动降低,地面运动的最大强度相应减小.     

Aquatic prey subsidies to riparian spiders in a stream with different land use types

Land use related habitat degradation in freshwater ecosystems has considerably increased over the past decades, resulting in effects on the aquatic and the riparian communities. Previous studies, mainly in undisturbed systems, have shown that aquatic emergent insects contribute substantially to the diet of riparian predators. To evaluate the effect of land use on aquatic prey subsidies of riparian spiders, we performed a longitudinal study from June to August 2012 along a first order stream (Rhineland-Palatinate, Germany) covering three land use types: forest, meadow and vineyard. We determined the contribution of aquatic and terrestrial resources to the diet of web-weaving (Tetragnathidae spp.) and ground-dwelling (Pardosa sp.) riparian spiders using stable isotope analyses of aquatic emergent insects and terrestrial arthropods. The contribution of aquatic and terrestrial sources differed between Tetragnathidae spp. and Pardosa sp. as well as among land use types. Tetragnathidae spp. consumed 80–100% of aquatic insects in the meadows and 45–65% in the forest and vineyards. Pardosa sp. consumed 5–15% of aquatic insects in the forest, whereas the proportions of aquatic and terrestrial sources were approximately 50% in the meadow and vineyard. Thus, aquatic emergent insects are an important subsidy to riparian spiders and land use is likely to affect the proportion of aquatic sources in the spider diet.     

The importance of aquatic macrophytes in a eutrophic tropical shallow lake

Inlay Lake is the second largest natural lake in Myanmar. Located in Shan State, in the eastern part of the country, it is a known biodiversity hotspot. The lake is negatively affected by an increasing local human population and rapid growth in both agriculture and tourism. In recent decades, several studies have listed faunistic and floristic groups in Inlay Lake, but there is still a general lack of knowledge about the aquatic macrophyte and phytoplankton community composition and abundance, and their interactions. To fill this knowledge gap, field surveys of biological and physical and chemical parameters were carried out in the period 2014–2017. They show that Inlay Lake is a shallow, clear water and calcareous lake, with nutrient concentrations indicating mesotrophic-eutrophic conditions. However, close to the shore, nutrient concentrations are generally higher, reflecting pollution from inflowing rivers, shoreline villages and floating gardens. Both the richness and abundance of aquatic macrophytes in Inlay Lake were high, with several species forming extensive stands in most of the lake over the whole survey period. Total phytoplankton and cyanobacterial biomass were low, but cyanobacteria included toxin-producing strains of Microcystis, suggesting that cyanobacterial and total phytoplankton biomass need to be kept low to avoid potentially harmful cyanobacterial blooms. Submerged macrophyte abundance and phytoplankton biomass were inversely correlated in the heavily vegetated northern lake area. Our survey suggests a great importance of the submerged macrophytes to the general water quality and the clear water state in Inlay Lake. Maintaining high macrophyte abundances should therefore be a goal in management strategies, both for Inlay Lake and other lakes in Myanmar. It is highly desirable to include macrophytes and phytoplankton in the lake monitoring in Myanmar.     

The toxicity of marine sediments in Victoria Harbour, Hong Kong

When the toxicity of marine sediment in Hong Kong was evaluated, it was found that the seven sediments collected within Victoria Harbour were severely contaminated with heavy metals, at concentrations many times higher than those in sediments collected from outside the harbour. The highest metal content was recorded in site VS14 (located near the airport runway and the industrialized area), with copper, zinc, lead and chromium values of 3789, 610, 138 and 601 mg kg⁻¹ dry wt, respectively. This site also had the greatest alkaline phosphatase activities (15 fluorescent intensity unit g⁻¹ wet wt), the largest number of total coliforms (910 CFU g⁻¹ wet wt) and sulphate-reducing bacteria (8.5 × 10⁴ cells g⁻¹ wet wt), implying that site VS14 was also contaminated with organic matter and nutrients. Sediment bioassays, Microtox and algal tests, demonstrated that sediment elutriates obtained from site VS14 were of greatest toxicity. The EC₁₀ value in Microtox tests was 17% elutriate, and the 96-h IC₅₀ values using Skeletonema costatum and Dunaliella tertiolecta were 40 and 79% elutriate, respectively. No toxic effects were found in sediment samples collected from the control site outside Victoria Harbour. Significant correlations were found between the results of the algal toxicity test (using S. costatum) and the coliform count and metal content of the sediments. The Microtox test was less sensitive than the algal bioassay, and no sediment elutriate, even from the site mostly contaminated by heavy metals, caused more than 50% inhibition of the light-emitting activity of the bacteria. In this study, S. costatum (the diatom) provided a more sensitive and reliable test species than D. tertiolecta (the flagellate) in differentiating the toxicity of marine sediments.     

Hydraulic habitat use with respect to body size of aquatic insect larvae: Case of six species from a French Mediterranean type stream

Macroinvertebrates play a key role in lotic ecosystems, as fish prey and processors of organic material. Therefore, their hydraulic preferences have to be integrated in instream habitat models for ecological stream management. This study characterized physical habitat use in terms of shear velocity for the larvae of three Ephemeropteran (Ephoron virgo, Oligoneuriella rhenana, and Serratella ignita), two Trichopteran (Cheumatopsyche lepida and Hydropsyche exocellata) and one Dipteran species (Blepharicera fasciata) in a Mediterranean stream at a relatively low water discharge. O. rhenana, C. lepida, H. exocellata, and B. fasciata larvae were mainly found in high shear velocity conditions, whereas E. virgo and S. ignita larvae were found in low shear velocity conditions. Knowing that habitat preferences should vary during ontogenesis (with respect to changes in biological requirements and/or morphological abilities to withstand high flow, for example), our second objective was to characterize differences in the hydraulic habitat use (in terms of shear velocity) for different size classes of these six species.Larvae of H. exocellata and B. fasciata mainly colonized high shear velocity conditions and numerous individuals of these species also used medium shear velocity conditions, independent of size class.The use of high shear velocity conditions increased with larval size for C. lepida and O. rhenana, whilst the use of low shear velocity conditions increased for larger larvae of E. virgo and S. ignita. Various hypotheses are proposed to explain these different strategies of habitat use during ontogenesis. We point out the lack of knowledge about physical habitat shifts during the larval growth of freshwater invertebrates.These results highlight the interest to consider the respective habitat requirements of different size classes of invertebrates in instream habitat models. Population bottlenecks should be overcome if hydraulic conditions are kept suitable for all size classes by stream managers.     

The role of fog,orography, and seasonality on precipitation in a semiarid,tropical island

Isotopes of water (²H/¹H and ¹⁸O/¹⁶O) are commonly used to trace hydrological processes such as moisture recycling, evaporation loss, and moisture source region and often vary temporally in a given region. This study provides a first‐ever characterization of temporally variable precipitation mechanisms of San Cristóbal Island, Galápagos. We collected fog, rain, and throughfall samples over three field seasons to understand the mechanisms driving seasonal‐ and event‐based variability in the isotopic composition of precipitation in Galápagos. We establish that fog is a common phenomenon in San Cristóbal, especially during the dry season, and we found that fog, compared with cocollected rainfall, is consistently enriched. We further suggest that the relative contribution of fog formed via different mechanisms (orographic, advective, radiation) varied seasonally. We found that the source region is the most dominant control of the isotopic composition of rainfall in the Galápagos at both the seasonal and event scales, but subcloud evaporative processes (the nontraditional manifestation of the amount effect) became a dominant control on the isotopic composition of rainfall during the dry season. Overall, our findings suggest that understanding seasonally variable water‐generating mechanisms is required for effective water resource management in San Cristóbal Island and other semiarid island ecosystems under current and future regimes of climate change.     

与香港地区地震危险性相关的汶川地震灾害调查的五点认识

在2008年汶川地震灾害凋查和认识的基础上,研究了与香港地区地震危险性相关的五点认识.香港地区虽然有较大断裂,但是它的断裂处于较为完整的花岗岩和火山岩岩体中,深部不具备产储大型高压人然气囊,因此,它不具备发生中强地震的充分条件.香港地区的岩石类型、周边和内部海水体、周边岛屿和建筑楼顶水体的均有利于抗震减灾.     

香港海啸监测及警报系统的发展

地震监测、海啸数值模拟和海平面监测是监测和预报海啸的主要工具。为了有效监测南海北部可能发生的地震海啸,香港天文台（HKO）正在香港筹建一个宽频地震站,同时通过太平洋海啸警报及减灾系统（PTWS）的框架取得美国加州综合地震网（CISN）显示系统的实时地震信息,并通过世界气象组织（WM0）的全球通信系统（GTS）接收南海和西北太平洋的验潮站和海啸浮标数据以监测海面的波动情况。香港天文台通过联合国教科文组织（UNESCO）政府间海洋学委员会（IOC）取得海啸漫滩模式交换计划（TIME）下的海啸数值模式,把香港本地的高分辨率水深和地形数据融合在模式之内,并利用这个模式计算南海多处地区在不同地震情景下的海啸传播,为海啸预报提供重要的参考数据。     

Diving associated coral breakage in Hong Kong: Differential susceptibility to damage

We conducted the first quantitative assessment of coral breakage along a gradient of diving activities in Hong Kong, the most densely populated city in southern China. A survey of six 1 × 25 m transects at seven sites revealed a total of 81 broken corals, among which 44% were branching, 44% plate-like and 12% massive. There were 3–19 broken colonies per site. At most study sites, the percentage of broken corals exceeded the recommended no-action threshold of 4%, suggesting that management intervention is justified. There was a significant positive correlation between the number of broken coral colonies and the number of divers visiting the site. The branching Acropora and the plate-like Montipora suffered from much higher frequency of damage than their relative abundance, raising the concern that the cumulative impact of such differential susceptibility to breakage may affect coral community composition.     

Toxicity testing of oil slick dispersants in Hong Kong

In Hong Kong, the toxicity of oil spill dispersants was assessed in a preliminary screening test, based upon TD₅₀ values in samples of ten fish. Later, an improved test was introduced, based upon new procedures developed in the United Kingdom and modified to suit conditions in Hong Kong. Products approved elsewhere were usually, but not always, approved in Hong Kong. Further work is needed to relate the test results to oil-spill damage in local waters.     

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in sediments from Hong Kong

Concentrations of 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in 14 sediment samples collected from four sites in the Mai Po Marshes Nature Reserve (within a RAMSAR Site) and from another six sites in Victoria Harbour and along the Hong Kong coastline. Elevated levels of PCDDs, and particularly OCDD, were detectable in all samples collected from the Mai Po Marshes and five of the six sites. In contrast to PCDDs, PCDFs were mainly found in sediment samples collected from industrial areas (Kwun Tong and To Kwa Wan) in Victoria Harbour. PCDD/F levels and congener profiles in the samples from the Mai Po Marshes Nature Reserve in particular show strong similarities to those reported in studies which have attributed similar elevated PCDD concentrations to nonanthropogenic PCDD sources.     

Environmental management of marine fish culture in Hong Kong

Marine fish farming is an important commercial practice in Hong Kong. Marine fish farms located in eutrophic coastal waters often face the threat of severe dissolved oxygen depletion associated with algal blooms and red tides. On the other hand, mariculture activities also contribute to pollution. The sustainable management of mariculture requires proper siting of the fish farms and stocking density control. Both of these are related to the carrying capacity of the water body concerned, which is mainly governed by its flushing characteristics. A simple method to determine the carrying capacity of a fish farm has been developed by using three-dimensional (3D) hydrodynamic modelling and its effective coupling with a diagenetic water quality model. A systematic methodology using numerical tracer experiments has been developed to compute the tidal flushing in a fish farm. The flushing time is determined from the results of a numerical tracer experiment using robust 3D hydrodynamic and mass transport models. A unit tracer concentration is initially prescribed inside the region of interest and zero elsewhere; the subsequent mass transport and the mass removal process are then tracked. The fish farms are usually situated in well-sheltered shallow embayments and may not connect directly to the open water. It is found that it is necessary to define both "local" and "system-wide" flushing times to represent the effectiveness of the mass exchange with the surrounding water body and the open sea respectively. A diagenetic water quality model simulating the sediment-water-pollutant interaction is employed to address the response of the water column and the benthic layer to pollution discharges. With the flushing rate reliably computed, the carrying capacity of the fish farm can be determined in terms of key water quality parameters: chlorophyll-a, dissolved oxygen, organic nitrogen and potential lowest dissolved oxygen level on a day of negligible photosynthetic production. The predictions are well-supported by field data.     

The interpretation of body trace metal concentrations in neogastropods from Hong Kong.

Three species of neogastropods, i.e., Thais clavigera, Thais luteostoma and Morula musiva, were collected from 12 sites in the coastal waters of Hong Kong, including clean and known metal-enriched ones. Accordingly, body trace metal concentrations varied greatly. Copper and zinc body concentrations compared poorly with those of accepted biomonitors and presumed metal contamination profiles. Much is known about the feeding ecology of neogastropods on local shores and where direct observational data were not available, their diets could, nevertheless, be estimated reliably. Accumulated metal concentrations can be interpreted with regard to dietary history. T. luteostoma, for example, had body copper concentrations of 51.8 microg g(-1) on an exposed shore and a diet of mainly barnacles. In contrast, on a sheltered shore (but only some 250 m distant) where the diet consisted mainly of oysters, body copper concentrations were approximately 15 times greater at 833 microg g(-1). Similar results were obtained for T. clavigera. The results of this analysis suggest that neogastropods can play a significant role in trace metal trophic transfer studies, especially as their representatives are intertidally and subtidally ubiquitous and can be spatially separated into tropical specialists and temperate generalists.     

Concentrations of PCBs in coastal mangrove sediments of Hong Kong

The concentrations of polychlorinated biphenyls (PCBs) in surface sediments of ten mangrove sites in Hong Kong were determined by Congener-specific and Arcolor methods. Spatial variations were found between mangrove sites and within the same site, indicating that the sediment samples were heterogeneous and total PCBs concentrations in mangrove sediments should be normalised to compensate for natural variability and for identifying serious anthropogenic contamination. In addition to total organic carbon, Al, Fe and Mn were possible normalisers. Based on PCB/normaliser ratio and 95% prediction limits of scatter plots between total PCB and normaliser, all mangrove sites were not seriously contaminated by human activities. The estimated total PCBs concentrations (quantified by Congener-specific method) for most sediment ranged from 0.5 to 5.8 ng g(-1) (dry weight, n = 92). However, very high concentrations of PCB were found in sub-samples from Yi O, Tolo Pond and Lai Chi Wo, suggesting that these samples represented the PCB contaminated "hot spots".     

Some effects of sewage discharge upon phytoplankton in Hong Kong

The coastal waters of Hong Kong constitute a transition from estuarine conditions in the west to more oceanic conditions in the east, with a major discharge of untreated sewage located at the mid-point. Chlorophyll a was determined and net phytoplankton was sampled at 45 stations throughout this transition. Over a period of 20 months, chlorophyll a values rarely exceeded 2 μg l.^?1 in unpolluted coastal waters. Estuarine waters generally contained 2–6 μg l.^?1 and, in waters influenced by sewage discharge, values sometimes exceeded 20 μg l.^?1. There was no evidence of a reduction in taxonomic diversity in polluted areas except in summer, when the net phytoplankton was dominated by Chaetoceros spp. In the autumn and early winter, Skeletonema costatum was abundant in the central polluted areas.     

Monitoring of toxic substances in the Hong Kong marine environment

A long-term programme for monitoring toxic substances in the marine environment was established in Hong Kong in 2004, focusing on chemicals of potential ecological and health concern. The programme ran on 3-year cycles, with the first two years monitoring marine water, sediment, biota, and the third year monitoring pollution sources. Twenty-four priority chemicals were measured, including dioxins/furans, dioxin-like PCBs, total PCBs, PAHs, DDTs, HCHs, TBTs, phenol, nonylphenol (NP), NP ethoxylates, PBDEs and metals. Results from the first three years of monitoring indicate that toxic substances in the Hong Kong marine environment were within the range reported for the coastal waters in China and other regions, but generally lower than in the Pearl River Estuary. The levels met the standards for protecting aquatic life and human consumption. Sewage effluent, stormwater and river water were possible sources of phenolic compounds; whereas air deposition or regional pollution, rather than local discharges, may contribute to the dioxins/furans, PAHs and PCBs found in the marine environment.