Paleoecological reconstruction of changes in the productivity of a small,meromictic lake in Southern Ontario,Canada

Some aspects of the paleoproductivity of meromictic Crawford Lake, near Toronto, are inferred from a study of its sedimentary pigments, and diatoms. Several stages of lake development are observed over the 35 cm-deep sediment core removed from the center of Crawford Lake. Evidence of changes in lake productivity during the last 300 years was reflected by significant stratigraphic sediment pigment changes which were associated with European settlement in the Crawford Lake watershed and recent alterations associated with the area's operation by the Conservation Authority (1969 — present). One of the most important factors correlated with paleoproductivity was land clearance (mainly logging of white oak and pine). Deforestation during the last century is correlated with an increase in the amount of algal pigments deposited in the lake's sediments during the 1800's. During the last 10 years a striking increase in the accumulation of chlorophyll derivatives was observed. This is correlated with a dramatic increase in the number of visitors to the lake.Stratigraphic changes in the ratio of cyanobacterial to phototrophic bacterial pigment accumulation are used to infer changes which occurred during the shift from mesotrophy to eutrophy in Crawford Lake.     

Combining limnological and palaeolimnological data to disentangle the effects of nutrient pollution and climate change on lake ecosystems: problems and potential

1. As long‐term observational lake records continue to lengthen, the historical overlap with lake sediment records grows, providing increasing opportunities for placing the contemporary ecological status of lakes in a temporal perspective. 2. Comparisons between long‐term data sets and sediment records, however, require lake sediments to be accurately dated and for sediment accumulation rates to be sufficiently rapid to allow precise matching with observational data. 3. The critical role of the sediment record in this context is its value in tracking the changing impact of human activity on a lake from a pre‐disturbance reference through to the present day. 4. Here, we use data from a range of lakes across Europe presented as case studies in this Special Section. The seven sites considered all possess both long‐term observational records and high‐quality sediment records. Our objective is to assess whether recent climate change is having an impact on their trophic status and in particular whether that impact can be disentangled from the changes associated with nutrient pollution. 5. The palaeo‐data show clear evidence for the beginning of nutrient pollution varying from the mid‐nineteenth century at Loch Leven to the early and middle twentieth century at other sites. The monitoring data show different degrees of recovery when judged against the palaeo‐reference. 6. The reason for limited recovery is attributed to continuing high nutrient concentrations related to an increase in diffuse nutrient loading or to internal P recycling, but there is some evidence that climate change may be playing a role in offsetting recovery at some sites. If this is the case, then lake ecosystems suffering from eutrophication may not necessarily return to their pre‐eutrophication reference status despite the measures that have been taken to reduce external nutrient loading. 7. The extent to which future warming might further limit such recovery can be evaluated only by continued monitoring combined with the use of palaeo‐records that set the pre‐eutrophication reference.     

Using palaeolimnological and limnological data to reconstruct the recent history of European lake ecosystems: introduction

1. As future climate change is expected to have a major impact on freshwater lake ecosystems, it is important to assess the extent to which changes taking place in freshwater lakes can be attributed to the degree of climate change that has already taken place. 2. To address this issue, it is necessary to examine evidence spanning many decades by combining long‐term observational data sets and palaeolimnological records. 3. Here, we introduce a series of case studies of seven European lakes for which both long‐term data sets and sediment records are available. Most of the sites have been affected by eutrophication and are now in recovery. 4. The studies attempt to disentangle the effects of climate change from those of nutrient pollution and conclude that nutrient pollution is still the dominant factor controlling the trophic state of lakes. 5. At most sites, however, there is also evidence of climate influence related in some cases to natural variability in the climate system, and in others to the trend to higher temperatures over recent decades attributed to anthropogenic warming. 6. More generally and despite some problems, the studies indicate the value of combining limnological and palaeolimnological records in reconstructing lake history and in disentangling the changing role of different pressures on lake ecosystems.     

城市湖泊湿地温湿效应——以武汉市为例

选择武汉城市三环内主城区14块湖泊湿地为研究对象,采用小尺度定量测定的方法,研究城市湖泊湿地与温湿效应间的关系。结果表明:(1)城市湿地温度值与面积指数、距离指数呈显著负相关,与景观形状指数呈显著正相关(P0.05);湿度值与面积指数、距离指数、环境类型指数呈显著正相关,与景观形状指数呈显著负相关(P0.05)。其中面积指数的贡献值最大。(2)14块湖泊湿地的降温增湿效应排序为湖泊11—14湖泊6—10湖泊1—5。当湖泊湿地面积为9.2—12.2 hm2时,其降温增湿效应明显;当湖泊湿地面积为308.4hm2左右时,降温效应显著且趋于稳定,湖泊湿地面积为67.6hm2左右时,增湿效应显著且趋于稳定(P0.05)。当湖泊湿地面积达到临界值之后,多斑块离散型(Dispersive)湖泊湿地布局对整个城市环境的降温增湿效应更为显著。     

Assessing the impacts of agricultural intensification on biodiversity: a British perspective

Agricultural intensification is best considered as the level of human appropriation of terrestrial net primary production. The global value is set to increase from 30%, increasing pressures on biodiversity. The pressures can be classified in terms of spatial scale, i.e. land cover, landscape management and crop management. Different lowland agricultural landscapes in Great Britain show differences among these pressures when habitat diversity and nutrient surplus are used as indicators. Eutrophication of plants was correlated to N surplus, and species richness of plants correlated with broad habitat diversity. Bird species diversity only correlated with habitat diversity when the diversity of different agricultural habitats was taken into account. The pressures of agricultural change may be reduced by minimizing loss of large habitats, minimizing permanent loss of agricultural land, maintaining habitat diversity in agricultural landscapes in order to provide ecosystem services, and minimizing pollution from nutrients and pesticides from the crops themselves. While these pressures could potentially be quantified using an internationally consistent set of indicators, their impacts would need to be assessed using a much larger number of locally applicable biodiversity indicators.     

Harnessing the potential of the multi‐indicator palaeoecological approach: an assessment of the nature and causes of ecological change in a eutrophic shallow lake

相似文献   

A hybrid zone revisited: molecular and morphological analysis of the maintenance, movement, and evolution of a Great Plains avian (Cardinalidae: Pheucticus) hybrid zone

Black-headed grosbeaks ( Pheucticus melanocephalus ) and rose-breasted grosbeaks ( Pheucticus ludovicianus ) are passerine bird species known to hybridize in the Great Plains of North America. Both extrinsic (environmental) and intrinsic factors (pre- and postzygotic reproductive isolation) have been credited for the generation and maintenance of the grosbeak hybrid zone, but little is known about the genetic characteristics of this hybrid zone. To investigate the stability and extent of the grosbeak hybrid zone, we constructed clines from both molecular sequence data (mtDNA, three autosomal intron loci, and one Z-linked locus) and morphological data (morphometric analyses and hybrid index scores) to determined zone centre and width. Hybrid zone centre and width were also determined for samples collected across the zone 40 years ago from morphological data. The present and past clines were compared and provided support for stability in hybrid zone location and width, and the evolutionary implications of this are discussed. Three models of hybrid zone maintenance were investigated to consider the influence of intrinsic and extrinsic factors on this zone. Our results suggest low hybrid frequencies, a stable zone location and narrow width, and reduced hybrid fitness over the past 40 years best categorize the grosbeak hybrid zone as a tension zone.     

Nonlinear response of nitric oxide fluxes to fertilizer inputs and the impacts of agricultural intensification on tropospheric ozone pollution in Kenya

Crop yields in sub‐Saharan Africa remain stagnant at 1 ton ha^?1, and 260 million people lack access to adequate food resources. Order‐of‐magnitude increases in fertilizer use are seen as a critical step in attaining food security. This increase represents an unprecedented input of nitrogen (N) to African ecosystems and will likely be accompanied by increased soil emissions of nitric oxide (NO). NO is a precursor to tropospheric ozone, an air pollutant and greenhouse gas. Emissions of NO from soils occur primarily during denitrification and nitrification, and N input rates are a key determinant of emission rates. We established experimental maize plots in western Kenya to allow us to quantify the response function relating NO flux to N input rate during the main 2011 and 2012 growing seasons. NO emissions followed a sigmoid response to fertilizer inputs and have emission factors under 1% for the roughly two‐month measurement period in each year, although linear and step relationships could not be excluded in 2011. At fertilization rates above 100 kg N ha^?1, NO emissions increased without a concomitant increase in yields. We used the geos‐chem chemical transport model to evaluate local impacts of increased NO emissions on tropospheric ozone concentrations. Mean 4‐hour afternoon tropospheric ozone concentrations in Western Kenya increased by up to roughly 2.63 ppbv under fertilization rates of 150 kg N ha^?1 or higher. Using AOT40, a metric for assessing crop damage from ozone, we find that the increased ozone concentrations result in an increase in AOT40 exposure of approximately 110 ppbh for inputs of 150 kg N ha^?1 during the March–April–May crop growing season, compared with unfertilized simulations, with negligible impacts on crop productivity. Our results suggest that it may be possible to manage Kenyan agricultural systems for high yields while avoiding substantial impacts on air quality.     

Algal response to a thermal effluent: study of a power station on the provo river,Utah, USA

The effect of a thermal effluent on the attached algae of the Provo River, Utah, USA, was studied from 1975 to 1977. Data for macroscopic and microscopic algae were collected and analyzed. Diatoms, Cladophora glomerata, and Hydrurus foetidus dominated the flora. The thermal effluent significantly affected the algal flora in a section of river 100 to 135 meters long immediately below the discharge point. Cladophora growth was increased and Hydrurus was absent in this area. In addition, diatom production was often higher and diversity lower than in the rest of the river. Community structure was unique from all other adjacent areas. Small temperature increases which occured as effluent and river waters mixed farther downstream were apparently not as important to the algal flora as other environmental factors.     

Effects of agricultural diversification on the abundance, distribution, and pest control potential of spiders: a review

A review of the literature showed that spider abundance was increased by diversification in 63% of studies. A comparison of diversification modes showed that spider abundance in the crop was increased in 33% of studies by `aggregated diversification' (e.g. intercropping and non-crop strips) and in 80% of studies by `interspersed diversification' (e.g., undersowing, partial weediness, mulching and reduced tillage). It is suggested that spiders tend to remain in diversified patches and that extending the diversification throughout the whole crop (as in interspersed diversification) offers the best prospects for improving pest control. There is little evidence that spiders walk in significant numbers into fields from uncultivated field edges, but diversification at the landscape level serves to foster large multi-species regional populations of spiders which are valuable as a source of aerial immigrants into newly planted crops. There are very few manipulative field studies where the impact of spiders on pests has been measured in diversified crops compared with undiversified controls. It is encouraging, however, that in those few studies an increased spider density resulted in improved pest control. Future work needs are identified.     

Permeability of the urban matrix to arboreal gliding mammals: Sugar gliders in Melbourne,Australia

Habitat corridors that facilitate functional connectivity are a fundamental component of wildlife conservation in fragmented landscapes. However, the landscape matrix separating suitable habitat is not uniformly impermeable to movement and management to increase matrix permeability could be an alternative means to maintain connectivity. Gliding mammals are particularly sensitive to fragmentation because their movements are constrained by glide distance thresholds. Populations of gliders in cities are at risk of being isolated by increasing habitat loss and urban development, yet little is known about how the urban matrix affects glider movement. Here we investigate how the level of urbanization and tree cover in the matrix influence matrix permeability to sugar gliders (Petaurus breviceps) within suburban forest reserves. Twenty‐two sugar gliders were radio‐tracked over winter and summer at four reserves. Boundary crossing behaviour was measured as the number of times each glider crossed into the matrix, and matrix permeability was determined as the maximum distance travelled by gliders into the matrix. The majority of gliders (81%) were located in the matrix at least once, and rates of boundary crossing were consistent across urbanization and tree cover levels. Matrix permeability was negatively affected by matrix urbanization, but not by matrix tree cover, and no interaction effects were found. Although distances travelled by gliders into the matrix did not exceed 180 m, they were comparable with typical movement distances by gliders in reserves. Our results demonstrate that the urban matrix can provide suitable habitat for gliding mammals to move and forage, but that increased urbanization may inhibit glider use of the matrix irrespective of tree cover. This finding has implications for conservation planning and suggests that structurally connected areas may not be used if movement behaviour is inhibited. Conversely, management of matrix permeability could be used to maintain connectivity without needing to construct physical corridors.     

大气污染规制对城市空气污染的防治成效——基于准实验分析

以2003年实施的大气污染防治重点城市政策为准自然实验,运用双重差分模型从区域层面分析了大气污染规制对城市空气污染治理的影响,研究发现：（1）大气污染规制在1%的显著性水平下降低了重点城市的工业二氧化硫排放强度,工业二氧化硫排放量以及城市PM2.5年均浓度值。（2）大气污染防治重点城市政策实施后的9年时间内有效减少了12215.8万t城市工业二氧化硫排放量,并且使得城市PM2.5年均浓度改善2.97μg/m3,下降比分别达到了36.2%和8.5%,平均每年减少了3.7%的城市工业二氧化硫排放量并降低0.944%的城市PM2.5浓度值。（3）大气污染防治重点城市政策对于城市空气污染治理主要是通过减少能源消耗量、增加城市污染治理力度、促进规制地区产业结构转型升级和提升生产技术水平等渠道予以实现。     

Plant community responses to bison reintroduction on the Northern Great Plains,United States: a test of the keystone species concept

Keystone species restoration, or the restoration of species whose effect on an ecosystem is much greater than their abundance would suggest, is a central justification for many wildlife reintroduction projects globally. Following restoration, plains bison (Bison bison L.) have been identified as a keystone species in the tallgrass prairie ecoregion, but we know of no research to document similar effects in the mixed‐grass prairie where restoration efforts are ongoing. This study addresses whether Northern Great Plains (NGP) mixed‐grass prairie plant communities exhibit traits consistent with four central keystone effects documented for bison in the tallgrass prairie. We collected species composition, diversity, abundance, bare ground cover, and plant height data in three treatments: where livestock (Bos taurus L.) continuously grazed, livestock were removed for 10 years, and bison have been introduced and resident for 10 years. We observed mixed support for bison acting as keystone species in this system. Supporting the keystone role of bison, we observed higher species richness and compositional heterogeneity (β‐diversity) in the bison treatment than either the livestock retention or livestock removal treatments. However, we observed comparable forb, bare ground, and plant height heterogeneity between bison‐restored sites and sites where livestock were retained, contradicting reported keystone effects in other systems. Our results suggest that after 10 years of being restored, bison partially fulfill their role as a keystone species in the mixed‐grass prairie, and we encourage continued long‐term data collection to evaluate their influence in the NGP.     

The Influence of Climate, Soils, Weather, and Land Use on Primary Production and Biomass Seasonality in the US Great Plains

Identifying the conditions and mechanisms that control ecosystem processes, such as net primary production, is a central goal of ecosystem ecology. Ideas have ranged from single limiting-resource theories to colimitation by nutrients and climate, to simulation models with edaphic, climatic, and competitive controls. Although some investigators have begun to consider the influence of land-use practices, especially cropping, few studies have quantified the impact of cropping at large scales relative to other known controls over ecosystem processes. We used a 9-year record of productivity, biomass seasonality, climate, weather, soil conditions, and cropping in the US Great Plains to quantify the controls over spatial and temporal patterns of net primary production and to estimate sensitivity to specific driving variables. We considered climate, soil conditions, and long-term average cropping as controls over spatial patterns, while weather and interannual cropping variations were used as controls over temporal variability. We found that variation in primary production is primarily spatial, whereas variation in seasonality is more evenly split between spatial and temporal components. Our statistical (multiple linear regression) models explained more of the variation in the amount of primary production than in its seasonality, and more of the spatial than the temporal patterns. Our results indicate that although climate is the most important variable for explaining spatial patterns, cropping explains a substantial amount of the residual variability. Soil texture and depth contributed very little to our models of spatial variability. Weather and cropping deviation both made modest contributions to the models of temporal variability. These results suggest that the controls over seasonality and temporal variation are not well understood. Our sensitivity analysis indicates that production is more sensitive to climate than to weather and that it is very sensitive to cropping intensity. In addition to identifying potential gaps in out knowledge, these results provide insight into the probable long- and short-term ecosystem response to changes in climate, weather, and cropping.     

Assessment of European streams with diatoms, macrophytes, macroinvertebrates and fish: a comparative metric-based analysis of organism response to stress

1. Periphytic diatoms, macrophytes, benthic macroinvertebrates and fish were sampled with standard methods in 185 streams in nine European countries to compare their response to degradation. Streams were classified into two main stream type groups (i.e. lowland, mountain streams); in addition, the lowland streams were grouped into four more specific stream types. 2. Principal components analysis with altogether 43 environmental parameters was used to construct complex stressor gradients for physical–chemical, hydromorphological and land use data. About 30 metrics were calculated for each sample and organism group. Metric responses to different stress types were analysed by Spearman Rank Correlation. 3. All four organism groups showed significant response to eutrophication/organic pollution gradients. Generally, diatom metrics were most strongly correlated to eutrophication gradients (85% and 89% of the diatom metrics tested correlated significantly in mountain and lowland streams, respectively), followed by invertebrate metrics (91% and 59%). 4. Responses of the four organism groups to other gradients were less strong; all organism groups responded to varying degrees to land use changes, hydromorphological degradation on the microhabitat scale and general degradation gradients, while the response to hydromorphological gradients on the reach scale was mainly limited to benthic macroinvertebrates (50% and 44% of the metrics tested correlated significantly in mountain and lowland streams, respectively) and fish (29% and 47%). 5. Fish and macrophyte metrics generally showed a poor response to degradation gradients in mountain streams and a strong response in lowland streams. 6. General recommendations on European bioassessment of streams were derived from the results.     

Effects of N : P loading ratios on phytoplankton community composition, primary production and N fixation in a eutrophic lake

相似文献   

Effects of seasonality on the species–area relationship: a case study with birds in urban parks

Aim To examine how parameters of the species–area curve and factors determining bird species richness are affected by seasonality. Location One hundred and thirty urban parks of the city of Valencia (Spain) ranging between 0.03 and 18.6 ha. Methods Bird censuses were conducted monthly during 1998 and 2004. For each park, 27 variables were recorded as measures of size, structure and isolation. Linear regression was used to test for patterns in species richness relative to independent variables. The results of each season were compared. Results Curves corresponding to the breeding period (spring–summer) had significantly higher intercepts, but slopes did not change across seasons. Turnover rates of resident species were dependent on patch size and isolation considering spring, but not autumn, from different years. Additionally, turnover rates in spring were lower in parks in close proximity to others than in isolated ones. In all seasons, the number of bird species showed a strong relationship with park area, which explained c. 60% of the variation in species numbers. Habitat variables and park isolation explained a small amount of the variation in species numbers. The data did not give support to the random placement hypothesis. Main conclusions The overall conclusions of this study give little support to the possible influence of seasonality on species–area relationship or on the three main hypotheses explaining it. This lack of influence of seasonality could be explained by the seasonal stability of the bird populations of the parks within the study area as a consequence of different factors, mainly the characteristics of the species pool, similarity in the features of the parks irrespective of their size, and stability of resources and conditions across seasons. The question of whether this lack of influence of seasonality on the species–area relationship occurs in those ecological systems that have a larger seasonal variation than the urban parks of the study area remains unresolved. Closer examination of the seasonal patterns reported in this study is likely to be useful in increasing our understanding of the species–area relationship.     

城市绿地空间格局及其环境效应——以宜昌市中心城区为例

城市绿地在改善城市环境及维护城市生态系统平衡中起着极为重要的作用 ,而当绿地覆盖率小于 4 0 %时 ,绿地整体生态效益的发挥主要取决于绿地的内部结构和空间布局 ,但迄今为止缺乏绿地景观分布格局与环境效应关系的研究报道。本研究应用景观生态学原理 ,分析了湖北省宜昌市中心城区斑优格局、斑匀格局、廊道格局和对照格局等四种景观结构及其绿地分布格局 ,选取了气温、相对湿度、环境噪声和大气 SO2 、NOx、TSP含量等环境监测指标 ,观测了不同绿地景观格局下的环境效应 ,并对比分析了绿地分布格局指标与综合环境效应间的关系 ,以便提出城市绿地系统布局合理性指标 ,为城市绿地系统的景观结构优化提供依据。研究结果表明 ,斑优格局、斑匀格局、廊道格局和对照格局等四种不同景观在斑块总面积、建筑斑块面积和无绿化道路面积等景观总体格局上较均衡 ,但由于其绿化覆盖率及绿地景观分布格局差异较大 ,致使其环境效益也表现出明显的差异。其中 ,对照格局景观的绿地斑块总面积最小 ,绿地破碎化指数最高 ,绿化覆盖率仅为 1.0 0 % ,以建筑铺装斑块和无绿化道路廊道为主要景观构成。因此 ,对照格局景观的环境气温较高、空气相对湿度低、环境噪声较大、大气 TSP含量高 ,景观环境恶劣。斑优格局景观主要表现为绿     

Land-use influence on stream water quality and diatom communities in Victoria, Australia: a response to secondary salinization

Diatom communities were analyzed in 39 streams located in drainages with varied land-use practices throughout Victoria, Australia. Thirteen water quality parameters were also measured in each stream. Most streams had low HCO₃ ^1- concentrations (low buffering capacity) with >90% of the waters dominated by Na¹⁺ and Cl^1-. Phosphate concentrations ranged from 0.003 to 2.0 mg/L. Diatom communities (245 taxa) were strongly correlated with land-use practices, i.e. historic clear cutting, and secondary salinization. Streams influenced by heavy irrigation practices and dryland farming had reduced species diversity and richness compared to systems with low to moderate land use. A nonmetric multidimensional ordination of diatom communities in the 39 streams was conducted. An ANOSIM on the ordination showed that diatom communities in upland watersheds with native forest canopies and low salinization, lowland streams in watersheds with cleared forest canopies, moderate agricultural utilization and salinization, and lowland streams in areas with high irrigation and salinization were all significantly different (p<0.001) from one another. Community ordination techniques showed that both specific conductance (salinity) and phosphorus interacted to determine stream diatom community structure in drainages with high secondary salinization. Drainages with low to moderate agricultural activity and low nutrients, but with a wide range of salinities showed strong associations with the diatom taxa Amphora coffeaeformis, Cymbella pusilla and Entomoneis paludosa, whereas, streams in regions with heavy agricultural practices and high phosphorus had Bacillaria paradoxa, Nitzschia hungarica, N. frustulum and Aulacoseira granulata as numerically important diatoms. In contrast, Rhizosolenia eriensis, Frustulia rhomboides, Eunotia pectinatus and Tabellaria flocculosa were strongly associated with upland streams with fast current, relatively low O-PO₄ ^3- concentrations, low pH, low salinity, and low temperature. In general, the diatom communities in saline streams (3 mS) were similar to those previously reported in saline lakes in Victoria.     

Nature in the city,city in the nature: case studies of the restoration of urban nature in Tokyo,Japan and Toronto,Canada

Increasing demands for the restoration of nature in cities have led planners to seek an effective form, configuration and maintenance scheme for parks and open spaces in urban areas. This paper aims to introduce two contrasting examples of ways that planners have met the challenge of restoring nature in the city. It takes Tokyo Bay Bird Sanctuary Park (TBBSP), Tokyo, Japan, and Tommy Thompson Park (TTP), Toronto, Canada, as case studies. TBBSP is located on reclaimed land facing Tokyo Bay, and is surrounded by heavily industrialized areas. The absence of green corridors which connect TBBSP to surrounding green patches have turned TBBSP into an isolated oasis for migrating birds. TTP in Toronto is also located on reclaimed land facing Lake Ontario. However, TTP has become to be an indispensable green patch of the open space network of Toronto because it is located at the node of green corridors. The principles of landscape ecology may dictate that TTP, integrated in the green network of the area, is in far better condition than isolated TBBSP. However both case studies are based on the same early post-war parks and open space planning concept, which aimed to clearly separate urban greens from surrounding urban fabrics. To restore nature in cities it is important to understand that alternative models of parks and open space planning can exist. We therefore refer to the authentic urban pattern found in Japanese cities, which historically have not intended to clearly separate each land use types but have sustained a mix of open spaces and urban fabrics. In the context of the global concern to realize ecological cities, restoring a city by integrating greens in the urban fabric should be understood as a way of achieving a city in nature.