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1.
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2.
We provide a position paper, using a brief literature review and some new modelling results for a subset of succulent plant species, which explores why Namaqualand plant diversity might be particularly vulnerable to anthropogenic climate change despite presumed species resilience under arid conditions, and therefore a globally important test-bed for adaptive conservation strategies. The Pleistocene climate-related evolutionary history of this region in particular may predispose Namaqualand (and Succulent Karoo) plant endemics to projected climate change impacts. Key Succulent Karoo plant lineages originated during cool Pleistocene times, and projected air temperatures under anthropogenic climate change are likely to exceed these significantly. Projected rainfall patterns are less certain, and projections of the future prevalence of coastal fog are lacking, but if either of these water inputs is reduced in concert with rising temperatures, this seems certain to threaten the persistence of, at least, narrow-endemic plant species. Simple modelling approaches show strong reduction in spatial extent of bioclimates typical of Namaqualand within the next five decades and that both generalist species with large geographic ranges, and narrow-range endemics may be susceptible to climate change induced loss of potential range. Persistence of endemics in micro-habitats that are buffered from extreme climate conditions cannot be discounted, though no attempts have been made to address this shortcoming of broader scale bioclimatic modelling. The few experimental data available on elevated temperature and drought tolerance suggest susceptibility of leaf succulent species, but high drought tolerance of non-succulent shrubs. Both species-level monitoring and further experimental work is essential to test and refine projections of climate change impacts on species persistence, and the implications for conservation.  相似文献   

3.
With the development of quantitative transfer functions to relate community structure to physicochemical variables, reconstructions of past environmental conditions have been possible and have enhanced our understanding of various ecosystem processes. There are cases, however, in which this approach is not applicable, or does not provide enough information for the questions being asked. In these cases, some alternatives are to conduct experiments or to examine the distribution of species at a finer spatial resolution. These two approaches have been used as alternatives to or in conjunction with the development of transfer functions. In this review, I discuss the ways in which these two approaches are now being used in paleolimnological studies to enhance our understanding of the ecology of the species found in sediment records and thus refine interpretations of environmental change. My focus is primarily on studies that deal with establishing clearer relationships between environmental variables and the growth or distribution of organisms. I present examples of how these approaches have been integrated in a variety of studies, including those designed to: (1) refine and enhance reconstructions that are based on transfer functions; (2) develop new paleolimnological tools to reconstruct environmental change; (3) explore mechanistic links in the relationships between organisms and commonly reconstructed environmental variables; and (4) pose and test hypotheses based on patterns in the sediment record. These cases demonstrate that the use of these approaches was essential to clarify species-environment relationships as well as lake responses to disturbance. As in all disciplines, however, there are many challenges in this area of research. In particular, the quantitative integration of these approaches with the sediment record is a major challenge, due to disparate spatial and temporal scales. This research can also be quite labor-intensive, and provides information on fewer taxa than in the calibration set approach. It also requires interdisciplinary training and/or collaboration in fields that have historically been less integrated, hence they may require greater effort. These issues may hinder the use of these approaches because of the perceived difficulty. I discuss these challenges and address possible solutions.  相似文献   

4.
The Arctic has a disproportionately large response to changes in radiative forcing of climate, and arctic lacustrine ecosystems respond sensitively to these changes. The goal of this research is to generate high-resolution climate records for the past two millennia using multiple proxies in order to place 20th and 21st century climate and environmental change into a long-term context. We use a 14C- and 210Pb-dated surface core from Lake CF8 on northeastern Baffin Island, Arctic Canada to generate a high-resolution multiproxy reconstruction of climate and environmental change. Throughout the late Holocene, primary productivity in Lake CF8 was low, but increased almost 20-fold in the past 200 years. Insect (Chironomidae) assemblages also show dramatic changes since 1950 AD, with cold stenothermous chironomid taxa disappearing from the record altogether. These changes in productivity and chironomid assemblages are unprecedented in the past 5,000 years. The dramatic ecological shifts that occurred at Lake CF8 have also been observed elsewhere in the Arctic, and will likely continue at ever-increasing rates as anthropogenic inputs of green house gases continue to cause climate warming and enhanced lacustrine primary production.  相似文献   

5.
Arcellaceans have been used as indicators of a variety of paleolimnological conditions including pH, eutrophication, oxygen level, and heavy metal contamination, but there has only been limited application of the group to climate and land-use change research. The limnological evolution of Swan Lake in southwestern Ontario was documented using arcellaceans as proxies, and compared to the results of a palynological analysis, with which it closely correlated. The palynological record documents the rapid disappearance of forest by around 1850 as the area was cleared for agriculture and settlements. The change was characterized by a shift in the palynological record from the Woodland to High Diversity assemblages. Similarly the arcellacean fauna changed from the Pre-European Settlement Assemblage to the distinctive low diversity, stressed environment European Deforestation Assemblage. The introduction of high-yield chemical fertilizers in the post World War II era, and the resultant eutrophication of the lake, was clearly recognizable in the palynological record as indicated by the dramatic increase in the algae Pediastrum (High Nutrient Assemblage). This change in farming practice was also identifiable with arcellacean proxies, as indicated by the appearance of the algalphilic Eutrophication Assemblage. The arcellacean Ecologically Destabilized Assemblage dominated the lake for short intervals during the transition between the Pre-European Settlement and European Deforestation assemblages and again at the transition between the European Deforestation and Eutrophication Assemblages, indicative of periods of ecological destabilization as the lake adjusted to new trophic inputs. A stressed environment arcellacean Ecologically Destabilized Assemblage found in a portion of the core estimated to have been deposited between AD 1350 and AD 1700 may provide evidence of an earlier phase of deforestation associated with Huron Indian agricultural practices. The close correlation between the palynological and arcellacean proxy data clearly demonstrates the potential of arcellaceans as land-use change proxies, and indicates that changes in land-use had an almost immediate impact on the Swan Lake ecosystem. This observation raises concerns about the impact that rapid urbanization is having on the environmentally sensitive Oak Ridges Moraine watershed, of which Swan Lake is a part.  相似文献   

6.
The paper reassesses the role of climate as a factor shaping changes in settlement and landscape in the Swedish Iron Age (500 BC–AD 1050). Two reasons motivate this re-evaluation. First, high-resolution data based on climate proxies from the natural sciences are now increasingly available. Second, the climate-related social sciences have yielded conceptual and theoretical developments regarding vulnerability and adaptability in the present and recent past, creating new ways to analyse the effects of climatic vs. societal factors on societies in the more distant past. Recent research in this field is evaluated and the explicitly climate deterministic standpoint of many recent natural science texts is criticized. Learning from recent approaches to climate change in the social sciences is crucial for understanding society–climate relationships in the past. The paper concludes that we are not yet in a position to fully evaluate the role of the new evidence of abrupt climate change in 850 BC, at the beginning of the Iron Age. Regarding the crisis in the mid-first millennium AD, however, new climate data indicate that a dust veil in AD 536–537 might have aggravated the economic and societal crisis known from previous research.  相似文献   

7.
Global closed basins,occupying almost one fifth of the world's land area,spatially coincide with arid and semiarid areas.Paleoclimatic proxies can indicate basin-wide envi-ronmental change and human activity.However,previous studies have not approached the use of proxies in the same way to reconstruct natural and anthropogenic processes at re-gional and global scales.Here we present a regional study to investigate the basic processes of paleoclimatic proxies,from a typical closed-basin system in arid China.We use multiple paleoclimatic proxies of surface samples and sediments,as well as groundwater and sedi-ment ages to study environmental change and human activity.We then establish a dataset for paleoclimatic proxies from global closed basins and do a numerical analysis on it.Regional studies verify that human activity greatly impacts paleoclimatic proxies,especially with regard to surface samples,as well as groundwater age,but Holocene sediments are less affected.Results from global studies indicate that the major changing trend of the wet/dry status of closed basins is associated with the movement of the westerly jet streams controlled by long-term changes in winter insolation.There is an abrupt change between 1800 AD and 1900 AD,according to a numerical synthesis of paleoclimatic proxies from global closed ba-sins,which can be linked to human impact.We suggest this time period can be considered as a start point for the Anthropocene based on the sedimentary evidence of closed basins,globally.  相似文献   

8.
Playa lake systems tend to be overlooked archives of paleoenvironmental change due to the likelihood of a short and intermittent record of deposition. Groundwater-fed wetlands associated with these climate-sensitive playas, however, preserve changes in hydrologic budget and are thus valuable archives for semiarid regions. This study examines the paleoecological record of a groundwater-fed wetland from Lake Solai, Kenya. Biological proxies are used to reconstruct paleoenvironmental change and climate impacts over the past millennium. Dry conditions persisted between CE 1115 and 1490, followed by wetter conditions during the Little Ice Age. Near surface sediments indicate increasing anthropogenic impact through pastoralism.  相似文献   

9.
Subarctic and arctic lakes are the focus of many paleolimnological studies, as they are still among the least impacted lakes by humans. Hence they provide an excellent setting for studies on long-term climatic variability without the overriding effects of direct anthropogenic perturbation. On the other hand, these ecosystems are highly vulnerable to even moderate anthropogenic influence like long-distance airborne transport of nutrients and pollutants. The paleolimnological studies conducted in these areas usually include a multitude of different proxies, but so far only few have used the green algal group of Pediastrum Meyen. These algae, however, preserve well in sediments and can be identified to species level, which lends them potential as a paleo-proxy. In this study we analysed the present Pediastrum assemblages from surface-sediments of 16 subarctic lakes in Finnish Lapland as well as bottom samples from the same sediment cores, which are “spot” samples from the recent past. We found a total of 14 Pediastrum taxa, five of which occurred at moderate to high relative abundances. The majority of the taxa showed distinct relationships to environmental variables measured. Of these, pH and dissolved organic carbon (DOC) explained most of the variance in the distribution of Pediastrum and generally summarised the main environmental gradients in our data set well. Five of the studied lakes lacked Pediastrum taxa altogether, and Pediastrum occurred at low abundances in four additional lakes. All of these nine lakes have extremely low nutrient concentrations and generally lowest pH and DOC in the data set and were defined by barren catchment areas and scarce lake macrophyte growth. According to a top–bottom analysis of sediment cores, the Pediastrum assemblages of the study lakes have changed moderately, suggesting changed environmental conditions in the lakes. Although these changes appear to be climate-related, more studies are needed to confirm this hypothesis.  相似文献   

10.
Eutrophication from nutrient over-enrichment is a serious problem for the coastal zone and the estuarine environment globally. Australian estuaries are generally oligotrophic, but assessing whether they are becoming more eutrophic over time is inhibited by a lack of long-term monitoring data. The Richmond River, Australia, provided an ideal example of an estuary under anthropogenic pressure where the use of paleoecological techniques may potentially be used to reconstruct changes in nutrient status over time. Five cores were extracted from depositional areas in the Richmond River, and subjected to paleo-magnetic profiling and loss-on-ignition testing to ensure the core of greatest integrity was selected for further analytical work. Results from diatom and stable isotope analyses combined with 210Pb and AMS 14C dating show a strong indication that the total phosphorus levels in the Richmond River have fluctuated since 1940. Evidence also suggests that these fluctuations are most likely a function of climate. This study has successfully applied paleolimnological techniques to the estuarine environment to produce information that can be used by environmental managers to aid decision making in relation to nutrient control for the Richmond River. Further work using paleolimnological techniques should be aimed at the extraction of a core containing diatoms that pre-date European settlement and include analyses of specific lipids and fatty acid biomarkers.  相似文献   

11.
Arctic aquatic systems are considered to be especially sensitive to anthropogenic disturbance, which can have cascading effects on biological communities as aquatic food-web structure is altered. Bio-indicators that respond to major limnological changes can be used to detect and infer major environmental change, such as climate warming, with the use of paleolimnological techniques. A multi-proxy approach was used to quantify recent environmental changes at Baker Lake, Nunavut, Arctic Canada. Analyses of fossilized remains of chironomids and diatoms were conducted on a sediment core of 20 cm in length sampled at 0.5-cm intervals. A new surface sediment training set of subfossil chironomid assemblages from 65 lakes across the eastern Canadian Arctic generated a robust (r jack2 = 0.79) surface water paleotemperature transfer function. The transfer function was applied to stratigraphic intervals from the Baker Lake sediment core to generate a paleotemperature reconstruction of sub-decadal resolution. The surface water temperature reconstruction inferred a 2°C increase in mid-summer surface water temperature for Baker Lake over the last 60 years, which was corroborated by the local instrumental record spanning the period of 1950–2007 AD. The chironomid record shows a recent decline of several cold-water taxa and appearance of warm-water indicators. This shift in community structure began circa 1906 AD, and intensified after 1940 AD. The corresponding fossil diatom record showed an increase in small planktonic Cyclotella taxa over the past 60 years, intensifying in the last 5 years, which also suggests a warmer climate and longer ice-free periods. The shifts in the diatom assemblages began later than the shifts in the chironomid assemblages, and were of lower magnitude, reflecting differences in the mechanisms in which these two indicators respond to environmental change.  相似文献   

12.
回顾过去2000年中国气候变化的研究历史,总结了本领域在最近10年的新成果,并对未来研究动向进行了展望。主要内容包括：代用证据采集、过去2000年温度序列重建与冷暖期辨识、降水及干湿序列重建与变化特征分析、过去千年气候变化模拟与机制诊断、历史气候变化影响分析等。主要进展体现在：加密了中国气候变化代用资料的空间覆盖度,提升了2000年气候变化序列重建、资料分析和影响辨识等研究的定量化程度,深化了对中国过去2000年气候在年代—百年尺度的变化特征及其形成机制与影响的认识。为进一步揭示地球系统的变化规律,特别是更深入认识中国气候的时空变化规律提供了更好的基础。  相似文献   

13.
灌丛沙丘形成演化及环境指示意义研究的主要进展   总被引：1，自引：0，他引：1  
郎丽丽  王训明  哈斯  花婷 《地理学报》2012,67(11):1526-1536
干旱半干旱区风沙活动较强烈, 风沙地貌十分发育, 环境演变过程对气候变化响应敏感。由于缺乏高分辨率载体, 在这些地区进行环境变化重建的手段及获得的结果相对贫乏。但是在这些区域发育的灌丛沙丘是风沙堆积体, 其形成演化记录了相对丰富的区域环境演变信息。本文综述了目前在灌丛沙丘形态学特征、发育过程、以及其在区域环境变化重建中的意义等方面的研究进展。我们认为, 灌丛沙丘形成演化研究在揭示干旱区环境演变过程方面有重大的意义, 但还没有形成系统的体系, 这一方面的研究仍有较大的空间。  相似文献   

14.
Heightened public concern, pending federal legislation, and calls for an international treaty to reduce emissions of greenhouse gases have placed pressure on resource planners to mitigate the causes and impacts of anthropogenic climate change despite uncertainty over its timing and magnitude. Traditional resource planning, however, is predicated on the assumption that future environmental conditions will emulate the past, and is based on local and national, rather than global, objectives. The threat of global warming calls for a new paradigm of resource planning, including expanded sensitivity analysis, incremental response as the threat evolves, an expanded range of adjustments, and planning in a global context.  相似文献   

15.
Following deglaciation, the long-term pattern of change in diatom communities and the inferred history of the aquatic environment are affected by a hierarchy of environmental controls. These include direct climate impacts on a lake’s thermal and hydrologic budgets, as well as the indirect affects of climate on catchment processes, such as weathering, soil development, microbial activity, fire, and vegetation composition and productivity, which affect the transfer of solutes and particulates from the terrestrial ecosystem into the lake. Some of these catchment influences on lacustrine systems operate as time-dependent patterns of primary succession that are set in motion by glacier retreat. This paper provides a conceptual model of some dominant pathways of catchment influence on long-term lake development in glaciated regions and uses a series of paleolimnological examples from arctic, boreal, and temperate regions to evaluate the relative role of direct climate influences and of catchment processes in affecting the trajectory of aquatic ecosystems during the Holocene in different environmental contexts.  相似文献   

16.
Understanding the relative contributions of climatic and anthropogenic drivers of channel change are important to inform river management, especially in the context of environmental change. This global debate is especially pertinent in Australia as catchments have been severely altered since recent European settlement, and there is also strong evidence of cyclical climate variability controlling environmental systems. Corryong/Nariel Creek is an ideal setting to further study the interaction between climate and anthropogenic changes on channel evolution as it has experienced both significant periods of flood and drought, controlled by the El Niño Southern Oscillation (ENSO), and extensive anthropogenic changes. Since European settlement the floodplain has been completely cleared, the riparian zone almost entirely invaded by willows, and every reach of the channel has experienced some form of direct channel modification. Through the combined analysis of channel evolution, climate changes and anthropogenic history of the river it was found that both the ENSO-driven climate and anthropogenic drivers are significant, although at different scales of channel change. Significant straightening in response to land clearing in the early twentieth century occurred before any records of direct channel modifications. Following this, most river management works were in response to instabilities created in the clearing period, or to instabilities created by flooding triggering a new phase of instability in reaches which had already undergone stabilisation works. Overall, human activities triggered channel instability via land clearing, and management works since then generally exacerbated erosion during high flows that are driven by climate fluctuations. This research raises the interesting question of whether rivers in Australia have become more responsive to the ENSO cycle since the clearing of catchment and riparian vegetation, or whether the past response to climate variability was different.  相似文献   

17.
Global change has become a major ecological concern that has the potential to dramatically alter plant distributions and assemblages worldwide. The specific response of plants to global change will depend on their ability to move, evolve, or adjust through phenotypic plasticity. Advances in biogeographic research are on the verge of a giant leap forward if we can take advantage of emerging tools in genetics and genomics. In this review, we appraise how new, post-Sanger, high-throughput sequencing and associated technologies can be used by next generation biogeographers to assess plant responses to global change. First, we briefly review the recent advances in genome sequencing and available approaches of genomic analysis. Secondly, we discuss the three main plant responses to global change: migration, adaptation, and phenotypic plasticity. This review is intended to spark the interest of biogeographers who do not traditionally use genetics but could benefit from including genetic and genomic tools into their research. Our goal is to illustrate that their use can contribute to new perspective and add an additional level of resolution into future biogeographic research.  相似文献   

18.
Surface water resources are highly valued for their ecological services and functions. However, their quality is under threat from anthropogenic activities and climate change. A detailed understanding of natural aquatic conditions and variability is rare. This is particularly the case in Australia where the variable climate produces significant ecological changes within natural thresholds and few long-term environmental data sets exist. Palaeoecology represents a means to identify natural fluctuations of aquatic ecosystems and provide long-term data for effective environmental management. This study uses a palaeoecological approach to identify biological and sediment changes in Lake McKenzie, Fraser Island, Australia. A sediment core was extracted from the lake and the fossil diatom assemblage and sediment particle size analysed. Inferred environmental changes were detected throughout the core that pre-date European impacts. The likely causes of these changes are climatic oscillations. Further dating is required to establish a detailed chronological record and identify the timing of detected environmental change at Lake McKenzie.  相似文献   

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20.
This paper examines the use of fossil larval trichopteran communities to investigate and describe the flow environment of a paleochannel network in the middle reaches of the River Trent floodplain (UK). Previous research utilising fossil insect communities (principally O. Coleoptera, O. Chironomidae) has focussed upon climate reconstruction. However, larval trichopteran communities (O. Trichoptera) also offer an aquatic signal, giving information regarding channel habitat structure and flow environments. The taxonomic diversity of each fossil community and the categorisation of each taxon into a known flow group, using the “LIFE” methodology, facilitates the reconstruction of the river flow conditions at each site based upon known faunal associations with mean flow velocity. A total of 49 trichopteran taxa were recorded from 17 paleochannels (n = 170 samples). Detrended Correspondence Analysis (DCA) identified a environmental gradient on the first DCA axis that reflected variability in flow, from rapid/fast flow to slow flowing and standing water habitats. In addition, two distinct faunal groups were identified on the second DCA axis characteristic of (i) small nutrient rich lentic habitats; and (ii) larger water bodies displaying features of both lentic, lotic and ephemeral habitats where marginal vegetation is abundant on a mineral substratum. The results demonstrate that larval Trichoptera can be used in paleolimnological research to reconstruct a flow signal and provide additional information regarding the aquatic habitat structure. Their wider use in describing the aquatic environment, in association with other proxies (e.g., Chironomidae and Coleoptera), may provide a more holistic understanding of floodplain paleoenvironment succession.  相似文献   

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