对中欧草地系统演替的17年量化研究(英文)

本文旨在用17年的观测数据检验三个有关草地系统演替的假设:(1)物种多样性在演替早期不断增加;(2)伴随着演替的推进,样方植物群落间的相似度逐渐增加(样方间的差异度随着演替不断降低);(3)在演替早期,植物群落的物种组成有趋同之势。包括植物群落的总体发展、Shannon多度与均度、Bray-Curtis差异度和群落周转率在内的量化统计结果显示:经过早期5年的演替,各样方的物种多样性表现出快速的趋同,多度均值逐渐由8增加至25个物种;同时,所有样方的物种总数由23增加至55个物种,标准方差由4.6降至0.3。此外,样方间的差异度逐渐降低,物种多度与组成呈明显的趋同。停止除草的一个重要效应是,人工设置的由1到16个物种的多样性梯度因物种入侵至多度较低的样地而减弱。     

Detecting potential changes in the meridional overturning circulation at 26˚N in the Atlantic

We analyze the ability of an oceanic monitoring array to detect potential changes in the North Atlantic meridional overturning circulation (MOC). The observing array is ‘deployed’ into a numerical model (ECHAM5/MPI-OM), and simulates the measurements of density and wind stress at 26^°N in the Atlantic. The simulated array mimics the continuous monitoring system deployed in the framework of the UK Rapid Climate Change program. We analyze a set of three realizations of a climate change scenario (IPCC A1B), in which – within the considered time-horizon of 200 years – the MOC weakens, but does not collapse. For the detection analysis, we assume that the natural variability of the MOC is known from an independent source, the control run. Our detection approach accounts for the effects of observation errors, infrequent observations, autocorrelated internal variability, and uncertainty in the initial conditions. Continuous observation with the simulated array for approximately 60 years yields a statistically significant (p < 0.05) detection with 95 percent reliability assuming a random observation error of 1 Sv (1 Sv = 10⁶ m³ s^?1). Observing continuously with an observation error of 3 Sv yields a detection time of about 90 years (with 95 percent reliability). Repeated hydrographic transects every 5 years/ 20 years result in a detection time of about 90 years/120 years, with 95 percent reliability and an assumed observation error of 3 Sv. An observation error of 3 Sv (one standard deviation) is a plausible estimate of the observation error associated with the RAPID UK 26^°N array.     

Credited forest carbon sinks: how the cost reduction is allocated among countries and sectors

Forest carbon sinks have been included in the Kyoto Protocol as one of the mechanisms for mitigating climate change. Consequently, credited sinks decrease the need to reduce emissions. We analyse in detail both the economywide and the sectoral effects of inclusion of carbon sinks as agreed upon in Bonn and Marrakesh for the first commitment period of 2008–2012. The focus of our analysis is the special treatment for Canada and Japan that allows them larger sinks. The analysis is performed with the multi-region computable general equilibrium (CGE) model GTAP-E.New Zealand benefits most from the inclusion of sinks as it gains large carbon sinks from afforestation. Also in Sweden, Canada and Japan the costs of achieving the emission target are considerably reduced. Of these countries, only Canada has high costs without sinks. Thus credited sinks partly reduce the difference in economic burden of achieving the Kyoto target among countries. Even though larger sinks clearly benefit Canada and Japan, their effect on other countries, either on the economywide or on the sectoral level, remains marginal. Allowing larger sinks is, indeed, of relatively minor importance for the world economy and emission reduction, compared to the US withdrawal from the Kyoto Protocol.     

Diagenetic Alteration of Magnetic Signals by Anaerobic Oxidation of Methane Related to a Change in Sedimentation Rate

Geochemical and rock magnetic investigations of sediments from three sites on the continental margin off Argentina and Uruguay were carried out to study diagenetic alteration of iron minerals driven by anaerobic oxidation of methane (AOM). The western Argentine Basin represents a suitable sedimentary environment to study nonsteady-state processes because it is characterized by highly dynamic depositional conditions. Mineralogic and bulk solid phase data document that the sediment mainly consists of terrigenous material with high contents of iron minerals. As a typical feature of these deposits, distinct minima in magnetic susceptibility (κ) are observed. Pore water data reveal that these minima in susceptibility coincide with the current depth of the sulfate/methane transition (SMT) where HS⁻ is generated by the process of AOM. The released HS⁻ reacts with the abundant iron (oxyhydr)oxides resulting in the precipitation of iron sulfides accompanied by a nearly complete loss of magnetic susceptibility. Modeling of geochemical data suggest that the magnetic record in this area is highly influenced by a drastic change in mean sedimentation rate (SR) which occurred during the Pleistocene/Holocene transition. We assume that the strong decrease in mean SR encountered during this glacial/interglacial transition induced a fixation of the SMT at a specific depth. The stagnation has obviously enhanced diagenetic dissolution of iron (oxyhydr)oxides within a distinct sediment interval. This assumption was further substantiated by numerical modeling in which the mean SR was decreased from 100 cm kyr⁻¹ during glacial times to 5 cm kyr⁻¹ in the Holocene and the methane flux from below was fixed to a constant value. To obtain the observed geochemical and magnetic patterns, the SMT must remain at a fixed position for ∼9000 yrs. This calculated value closely correlates to the timing of the Pleistocene/Holocene transition. The results of the model show additionally that a constant high mean SR would cause a concave-up profile of pore water sulfate under steady state conditions.     

Reviews

Book reviewed in this article:
Green Politics By S. Rainbow.
Keeping New Zealand Green: Recent Environmental Reforms By P.A. Memon.
Environmental Planning in New Zealand Edited by P.A. Memon and H. C. Perkins.     

Paleolimnological assessment of the impact of logging on small boreal lakes

In Finland a great number of forest lakes are affected by silvicultural practices such as logging. Logging affects water chemistry and thus the ecological state of lakes by causing nutrient loads and increasing erosion and humic substances in water. Water quality assessment requires definition of natural background conditions and ecological status of water bodies. Therefore it is necessary to determine the impact of these practices on aquatic organisms. In the absence of long-term monitoring data, paleolimnological methods provide a powerful tool for determining human-induced changes in lakes. In this study diatom assemblages, diatom-inferred water total phosphorus and total organic carbon, and sediment chemistry were analyzed from the sediments of six lakes with a logged catchment area (11-53%). According to one-way analysis of similarities (ANOSIM) the diatom communities of three lakes were different before, immediately after and more than 10 years after logging and diatom assemblages in remaining three lakes did not show statistically significant differences between these times. However, all changes were minor, and at present the diatom assemblages and diatom-inferred water chemistry of all the lakes are close to the pre-logging conditions. The minor alterations are probably due to the wide protective zones around the lakes.     

Hydrologic and climatic implications of stable isotope and minor element analyses of authigenic calcite silts and gastropod shells from a mid-Pleistocene pluvial lake, Western Desert, Egypt

Authigenic calcite silts at Wadi Midauwara in Kharga Oasis, Egypt, indicate the prolonged presence of surface water during the Marine Isotope Stage 5e pluvial phase recognized across North Africa. Exposed over an area of  4.25 km², these silts record the ponding of water derived from springs along the Libyan Plateau escarpment and from surface drainage. The δ¹⁸O values of these lacustrine carbonates (− 11.3‰ to − 8.0‰ PDB), are too high to reflect equilibrium precipitation with Nubian aquifer water or water of an exclusively Atlantic origin. Mg/Ca and Sr/Ca of the silts have a modest negative covariance with silt δ¹⁸O values, suggesting that the water may have experienced the shortest residence time in local aquifers when the water δ¹⁸O values were highest. Furthermore, intra-shell δ¹⁸O, Sr/Ca, and Ba/Ca analyses of the freshwater gastropod Melanoides tuberculata are consistent with a perennially fresh water source, suggesting that strong evaporative effects expected in a monsoonal climate did not occur, or that dry season spring flow was of sufficient magnitude to mute the effects of evaporation. The input of a second, isotopically heavier water source to aquifers, possibly Indian Ocean monsoonal rain, could explain the observed trends in δ¹⁸O and minor element ratios.     

Organochlorine, Heavy Metal and Polyaromatic Hydrocarbon Pollutant Concentrations in the Great Barrier Reef (Australia) Environment: a Review

Past monitoring of heavy metals, organochlorine compounds and polyaromatic hydrocarbons (PAHs) has found that pollutant concentrations are generally low within the Great Barrier Reef Marine Park and World Heritage Area and are indicative of a relatively unpolluted environment. The exceptions are sites that are adjacent to human activity such as ports and harbours, urban centres and areas adjacent to intensive agricultural activity. These sites have elevated concentrations of a range of pollutants. Concentrations of dioxins have also been found to be elevated in marine park sediments. Elevated pollutant concentrations are generally the consequence of effluent discharge, urban stormwater, and agricultural and industrial runoff. However, a majority of Great Barrier Reef pollutant data are now dated, and contemporary information is required concerning the distribution and impact of pollutants in the Queensland marine environment. The utility of specialized monitoring tools such as biomarkers for tropical marine environments urgently needs to be examined. With this information, appropriate risk assessment and monitoring can be implemented and effective management strategies developed to protect tropical marine ecosystems including the Great Barrier Reef.     

Climate Variability and Land-use Change in Danangou Watershed, China—Examples of Small-Scale Farmers' Adaptation

With global concern on climate change impacts, developing countries are given special attention due their susceptibility. In this paper, change and variability in climate, land use and farmers' perception, adaptation and response to change are examined in Danangou watershed in the Chinese Loess Plateau. The first focus is to look at how climate data recorded at meteorological stations recently have evolved, and how farmers perceived these changes. Further, we want to see how the farmers respond and adapt to climate variability and what the resulting impact on land use is. Finally, other factors causing change in land use are considered. Local precipitation and temperature instrumental data and interview data from farmers were used. The instrumental data shows that the climate is getting warmer and drier, the latter despite large interannual variability. The trend is seen on the local and regional level. Farmers' perception of climatic variability corresponds well with the data record. During the last 20 years, the farmers have become less dependent on agriculture by adopting a more diversified livelihood. This adaptation makes them less vulnerable to climate variability. It was found that government policies and reforms had a stronger influence on land use than climate variability. Small-scale farmers should therefore be considered as adaptive to changing situations, planned and non-consciously planned.