Determining water level management strategies for lake protection at the ecosystem level

To prevent lake degradation, water level management has been a major focus of research in the past several decades. There are, however, some shortcomings in the traditional studies, and the protection of entire ecosystems is difficult to achieve in practice. In this paper, the framework of a new method for determining ecosystem-based water level regimes (WLRs) for lake protection is proposed. First, historical WLRs are divided into several sub-stages. Then, ecosystem statuses corresponding to different WLRs are quantified and compared. Finally, parameters of optimal and acceptable WLRs are used to determine water level management goals. The proposed method was applied to Baiyangdian Lake, the largest shallow lake in the North China Plain, to test its effectiveness. Results showed that to protect the ecosystem at the optimal status, 50% of the parameter values should fall within the range of the 25th and 75th percentiles of Stage I; and to protect the ecosystem from reverse succession, 50% of the water level parameter values should fall within the range of the 25th and 75th percentiles of Stage II. This method takes ecosystem status into account, and has high practicability in water resources management.     

Carbon dioxide increase: the implications at the ecosystem level*

Abstract Possible effects of increased atmospheric concentrations of CO₂ on forest ecosystems are discussed and as an example a simulation case study using a set of mixed-age and mixed-species forest stand models is presented. The responses of the models to a simple scenario (uniform growth increase of all trees as a response to CO₂ enrichment) include increases in biomass that are considerably less than the increases in growth rate of the trees. These simulations and more general discussion of the possible effects of increased photosynthetic production identify the problem of scaling-up small time-scale and space-scale measurements of plant responses to CO₂ enrichment to the ecosystem level.     

An ecosystem organization model explaining diversity at an ecosystem level: Coevolution of primary producer and decomposer

Ecological complexity of species interactions and habitat heterogeneity creates and maintains biodiversity at a trophic level in an ecosystem. This biodiversity simultaneously serves as raw material on which selective forces for organizing ecosystems operate. As a result of this organization process, differences in structure and functioning of ecosystems (diversity at ecosystem level) are generated. Although understanding diversity at the ecosystem level has attracted great interest, recent theoretical advances toward this aim have not been fully appreciated yet. Following Higashi et al. (1993), this report presents a theoretical framework that deals with the organization process of an ecosystem as a consequence of the interactions among its biotic components and their modification of ecological traits. Specifically, the ecosystem organization process of a terrestrial ecosystem is analyzed, including primary producers and decomposers. This model sheds new insight into the differences between temperate and tropical forest ecosystems.     

Effect at the ecosystem level of elevated atmospheric CO2in an aquatic microcosm

We studied the responses of an aquatic microcosm in two different eutrophic conditions to elevated atmospheric CO₂concentration. We used microcosms, consisting of Escherichia coli(bacteria), Tetrahymena thermophila(protozoa) and Euglena gracilis(algae), in salt solution with 50 and 500 mg l^–1of proteose peptone (eutrophic and hypereutrophic conditions, respectively) under ambient and elevated CO₂(1550±100 l l^–1) conditions. The density of E. gracilisincreased significantly under elevated CO₂in both eutrophic and hypereutrophic microcosms. In the eutrophic microcosm, the other elements were not affected by elevated CO₂. In the hypereutrophic microcosm, however, the concentrations of ammonium and phosphate decreased significantly under elevated CO₂. Furthermore, the density of T. thermophilawas maintained in higher level than that in the microcosm with ambient CO₂and the density of E. coliwas decreased by CO₂enrichment. Calculating the carbon biomasses of T. thermophilaand E. colifrom their densities, the changes in their biomasses by CO₂enrichment were little as compared with large increase of E. graciliscarbon biomass converted from chlorophyll a. From the responses to elevated CO₂in the subsystems of the hypereutrophic microcosm consisting of either one or two species, the increase of E. graciliswas a direct effect of elevated CO₂, whereas the changes in the density of E. coliand T. thermophilaand the decreases in the concentration of ammonium and phosphate are considered to be indirect effects rather than direct effects of elevated CO₂. The indirect effects of elevated CO₂were prominent in the hypereutrophic microcosm.     

Cortical control of motor behavior at the cellular level

The studies reviewed in this paper describe the relations of single-cell activity in central motor structures to complex visuomotor tasks and document the fact that various cortical areas process visuomotor information in parallel. Moreover, the studies provide clear evidence that the map in the motor cortex is modifiable and dynamically maintained.     

Effects of resource availability on plant recruitment at the community level in a Mediterranean mountain ecosystem

Coexisting plant species usually differ in resource requirements, which may also vary within species at successive demographic stages. Such differences become extremely important during the early life stages, since these are the most critical phases in woody-species recruitment, they depend heavily on resources, and they may determine future community composition. Under a global-change scenario, where climatic conditions, nutrient availability, and habitat characteristics are expected to be altered, it is difficult to predict the way in which plant recruitment will be affected. To understand the impact of different global-change drivers on community recruitment, we sowed a set of species representative of the different successional groups of a complete Mediterranean woody community under field conditions, and studied their emergence, growth, and survival along the main resource gradients of light, water, and nutrients. The light and nutrient gradients followed the natural range of conditions in the study area, but water availability was manipulated to simulate three contrasting climatic scenarios: wetter, drier, and current conditions. Structural equation modelling was used to provide a comprehensive analysis of the factors and relations governing plant recruitment. Overall, seedling emergence was determined directly by light; growth was determined by light and summer soil moisture; and survival was determined by summer soil moisture. Light was the main factor indirectly affecting the demographic stages of all species. However, the magnitude of the direct and indirect relationships varied among species. Particularly, species differed in their response to the expected drier climatic conditions, some (e.g. Pinus sylvestris, Acer opalus) being much more vulnerable than others (e.g. Cytisus scoparius, Salvia lavandulifolia). These differential responses could translate as major shifts in the structure of the overall plant community. Our results support the idea that the analysis of complex relations among essential resources is critical for accurate forecasts of the impact of climate change on community dynamics.     

The Oosterschelde estuary: an evaluation of changes at the ecosystem level induced by civil-engineering works

The interest in storm-flood protection has recently gained momentum, owing to the wide international discussion on the impact of sea-level rise on society. The Oosterschelde project is technically and scientifically unique. The storm-surge barrier represents an important breakthrough in marine civil engineering. The project also offered ample opportunities to perform integrated physical, chemical, geological and biological research. Integration of the knowledge gained, raised the entire project to the level of a case study of a changing estuarine ecosystem, and demonstrated the effects of human interference in a non-polluted estuary. Notwithstanding considerable changes in the environment, the Oosterschelde has retained most of its favourable abiotic factors, labeling the estuary as a high quality marine system. The water quality in the post-barrier period more closely resembles that of the North Sea than in the period before. Significant changes in erosion and sedimentation and the consequent redistribution of fine sediments, are continuing. The ecosystem has shown responses to various factors. Effects of severe winters and impact of mussel- and cockle fisheries could be distinguished from other factors. The physical response of the ecosystem to the civil-engineering project could be quantified in terms of changes in habitat availability, maintenance of biological productivity, and restricted maintenance of the carrying capacity as an internationally recognized wetland and fisheries area.     

The transpososome: control of transposition at the level of catalysis

Studies of several transposable genetic elements have pinpointed the importance of the transpososome, a nucleoprotein complex involving the transposon ends and a transposon-encoded enzyme--the transposase--as a key in regulating transposition. Transpososomes provide a precise architecture within which the chemical reactions involved in transposon displacement occur. Data are accumulating that suggest they are dynamic and undergo staged conformational changes to accommodate different steps in the transposition pathway. This has been underpinned by recent results obtained particularly with Tn5, Tn10 and bacteriophage Mu.     

Water release through plant roots: new insights into its consequences at the plant and ecosystem level

Hydraulic redistribution (HR) is the passive movement of water between different soil parts via plant root systems, driven by water potential gradients in the soil-plant interface. New data suggest that HR is a heterogeneous and patchy process. In this review we examine the main biophysical and environmental factors controlling HR and its main implications at the plant, community and ecosystem levels. Experimental evidence and the use of novel modelling approaches suggest that HR may have important implications at the community scale, affecting net primary productivity as well as water and vegetation dynamics. Globally, HR may influence hydrological and biogeochemical cycles and, ultimately, climate.     

Natural ecosystem design and control imperatives for sustainable ecosystem services

Sustainability of ecosystem services to humanity will depend on knowledge of how ecosystems work in their natural states, which can then be carried over to managed states. The objective of this paper is to describe four properties of ecosystems taken as natural conditions to be maintained under exploitation. Three of these are design properties: near-steady-state or extremal dynamics, dominance of indirect effects, and positive utility in network organization. One is a regulatory property: distributed multivariable control. The methodology of the paper is mathematical modeling. The design properties are drawn from the inherent formalism in models. The control property is demonstrated by manipulating model parameters to achieve a management goal. The results show that: (1) natural ecosystems operate near, but not at, steady states or extrema, and ecosystems exploited for human purposes should be similarly maintained (near-steady-state imperative); (2) indirect effects are dominant in natural ecosystem networks, and should be taken into account in managing ecosystems for human benefits (nonlocal imperative); (3) natural ecosystems enhance positive relationships among their constituents, and ecosystems maintained for human services should be managed to maximize their expression of mutualistic and synergistic network properties (nonzero imperative); and (4) natural ecosystems are regulated by checks and balances distributed across many control variables in interactive networks, so that obtaining human services from ecosystems should similarly be through coordinated use of many, not few, control variables (multifactorial control imperative). The conclusion from these results is that ecosystems under natural conditions evidence organizational properties evolved over evolutionary time, and management for sustainable extraction of ecosystem services should seek to preserve and emulate these properties in the new exploited states.     

Protein synthesis and translational control: at eye level with the ribosome

At the EMBO Conference on 'Protein Synthesis and Translational Control' held in Heidelberg in September 2011, scientists shared their latest findings on the structure and function of the ribosome, mRNA-specific regulation of translation and the numerous quality control mechanisms that ensure accurate protein synthesis.     

Long-term ecosystem level experiments at Toolik Lake, Alaska, and at Abisko, Northern Sweden: generalizations and differences in ecosystem and plant type responses to global change

Long‐term ecosystem‐level experiments, in which the environment is manipulated in a controlled manner, are important tools to predict the responses of ecosystem functioning and composition to future global change. We present the results of a meta‐analysis performed on the results of long‐term ecosystem‐level experiments near Toolik Lake, Alaska, and Abisko, Sweden. We quantified aboveground biomass responses of different arctic and subarctic ecosystems to experimental fertilization, warming and shading. We not only analysed the general patterns but also the differences in responsiveness between sites and regions. Aboveground plant biomass showed a broad similarity of responses in both locations, and also showed some important differences. In both locations, aboveground plant biomass, particularly the biomass of deciduous and graminoid plants, responded most strongly to nutrient addition. The biomass of mosses and lichens decreased in both locations as the biomass of vascular plants increased. An important difference between the two regions was the smaller positive aboveground biomass response of deciduous shrubs in Abisko as compared with Toolik Lake. Whereas in Toolik Lake Betula nana increased its dominance and replaced many of the other plant types, in Abisko all vascular plant types increased in abundance without major shifts in relative abundance. The differences between the responses of the dominant vegetation types of the Toolik Lake region, i.e. tussock tundra systems, and that of the Abisko region, i.e. heath systems, may have important implications for ecosystem development under expected patterns of global change. However, there were also large site‐specific differences within each region. Several potential mechanistic explanations for the differences between sites and regions are discussed. The response patterns show the need for analyses of joint data sets from many regions and sites, in order to uncover common responses to changes in climate across large arctic regions from regional or local responses.     

淡水水域富营养化及其治理

简要介绍了淡水水域富营养化的成因与危害,近年来我国淡水水域富营养化现状,以及水域富营养化的主要预防与治理措施。