A HYDROCLIMATIC APPLICATION STRATEGY FOR THE POISSON PARTIAL DURATION MODEL1

ABSTRACT: A strategy for formulating and testing the Poisson partial duration extreme value model is presented. The procedure is demonstrated using recorded Streamflow series from a humid subtropical region of the southern United States. The observed data series are partitioned by climatic causes and tested for both the Poisson assumption and the validity of the exponential as marginal distributions. Several statistical tests are utilized in making these determinations. Some important aspects of the model as applied to humid climates are demonstrated. It was found that a majority of Streamflow series could be represented by the model and that significant differences do exist between the arrival structures of floods resulting from different climatic mechanisms. However, these differences generally do not exist in the distribution of the flood magnitudes. In addition, it is possible that model validity is restricted by drainage basin size.     

PRACTICAL IMPLICATIONS IN THE USE OF STOCHASTIC DYNAMIC PROGRAMMING FOR RESERVOIR OPERATION1

ABSTRACT: A stochastic dynamic programming model is applied to a small hydroelectric system. The variation in number of stage iterations and the computer time required to reach steady state conditions with changes in the number of storage states is investigated. The increase in computer time required to develop the storage probability distributions with increase in the number of storage states is reviewed. It is found that for an average of seven inflow states, the largest number of storage states for which it is computationally feasible to develop the storage probability distributions is nine. It is shown that use of the dynamic program results based on a small number of storage states results in unrealistically skewed storage probability distributions. These skewed distributions are attributed to “trapping” states at the low end of the storage range.     

当代河流系统研究中稳定性同位素的应用

对天然存在的稳定碳、氮同位素在河流系统中的有机物质（POM和DOM）来源、转换、运移规律、与沿岸生态系统的关系、河口区不同来源颗粒有机质的混合过程、河流系统中富营养的污染来源和土壤中的微生物过程、系统中的营养行为和食物来源途径以及河流有机物质在陆架上的分配、积累和运移规律的应用研究作了较为系统的论述。     

Why Critical Loads of Acidity and N for Soils Should be Based on Pollutant Effective Concentrations Rather Than Deposition Fluxes

Numerous assumptions have been made over the past 17 years when calculating critical loads for soils, both for acidity (based upon base cation steady state mass balances (SMB)) and for N (eutrophication, based upon N mass balances), often without all the assumptions being explicitly stated. The tacit assumptions that the author believes to be implicit in the SMB approach are critically reviewed, with particular reference to upland regions where slope processes are highly significant. It is concluded that many of them cannot be justified, especially those that involve ignoring many key processes known to be important to biogeochemical cycling and soil evolution in upland catchments. The evidence presented suggests that critical loads of acidity and of N for soils should be based upon effective pollutant and, for acidity, also effective base cation deposition concentrations, rather than upon pollutant deposition fluxes. This is because of the dominant role of cation exchange equilibria, rather than weathering rate, in regulation of the pH and base status of the more acidification-sensitive soils, and because of the importance of transport down slope of base cations, alkalinity and N species.     

REDUCING THE RISK OF FISHERY RESOURCE DISASTERS: A BIOECONOMIC APPROACH TO SUSTAINABLE RESOURCE MANAGEMENT1

Abstract: Recognition is growing that fisheries must be both ecologically and commercially sustainable. The bioeconomic models proposed herein constitute an analytic framework capable of integrating the ethics and Societal values associated with fisheries preservation. Specifically, we focus on the normalized optimal (equilibrium) fish population, z*, a dimensionless variable representing biomass as a proportion of environmental capacity. We model z* as a function of (a) the dimensionless "bionomic growth ratio", γ, which is the ratio of the discount rate to the intrinsic population growth rate, and (b) the preservation coefficient, Ω, which is the ratio of the preservation value (a measure of Society's value for the stock) to price, assuming that the population growth rate and intrinsic growth rate are fixed. It is shown that increasing Ω significantly impacts z*, particularly for moderate values of γ (2 γ 4). Finally, stochastic population models are used to analyze the risk of a fish stock collapse due to harvesting pressures. The bioeconomic models and simulations herein described improve the accuracy and reliability of maximum sustainable yield management.     

资源开发与技术效率:以中西部地区为例

利用1985—2004年省际统计数据,应用随机前沿分析技术估算了中西部地区和辽宁省的技术效率,研究了资源对技术效率的影响。结果表明,产业结构、外商直接投资的数量、企业的所有制结构和资源禀赋决定技术效率水平。分析表明,资源优势妨碍了技术效率的提高,资源开发战略不利于经济的长期增长。     

A Vegetation-Based Method for Ecological Diagnosis of Riverine Wetlands

/ The management of riverine wetlands, recognized as a major component of biodiversity in fluvial hydrosystems, is problematic. Preservation or restoration of such ecosystems requires a method to assess the major ecological processes operating in the wetlands, the sustainability of the aquatic stage, and the restoration potential of each riverine wetland. We propose a method of diagnosis based on aquatic macrophytes and helophytes. Plant communities are used because they are easy to survey and provide information about (1) the origin of a water supply (i.e., groundwater, seepage, or surface river water) and its nutrient content, (2) effects of flood disturbances, and (3) terrestrialization processes. The novelty of the method is that, in contrast to available typologies, it is based on the interference of gradients resulting from several processes, which makes it possible to predict wetland sustainability and restoration potential. These predictions result from knowledge of the processes involved in terrestrialization, i.e., the influence of flood disturbances, occurrence of groundwater supplies, trophic degree, and water permanency of the habitat during a yearly cycle. The method is demonstrated on five different river systems.     

Model-based analysis of the influence of ecological processes on forest point pattern formation—A case study

Many different spatio-temporal individual-based models (IBM) for forests have been developed for studying the development of trees in space and time. Such models typically depend on various numerical parameters that represent the ecological processes of growth (G), inter-plant competition (C) and birth-and-death (B&D; also called regeneration and mortality). Until now little work has been done to systematically trace the influence of these processes and their model parameters on the spatial structure of forest ecosystems.This paper attempts to fill this gap by addressing an important aspect of forest structure, spatial variability, characterised by the mark variogram as a summary characteristic. The model used was inspired by components of various well-established IBMs including a shot-noise competition field. Time series data from monospecies forests in three different countries of the northern hemisphere provided ecological reference scenarios. Though a case study, the paper's methodology is rather general and can be applied to any model and forest ecosystem.Methods of sensitivity analysis revealed that only a small number of model parameters is crucial for forming spatial variability. Particularly important is the range of competition between trees; with increasing range the variability increases. Growth processes have considerable importance particularly with short observation periods and in young forests, whereas mortality processes become more influential in the long-term. Naturally, these statements depend upon the initial structure and on the length of the observation period.     

Fragmentation drives tropical forest fragments to early successional states: A modelling study for Brazilian Atlantic forests

Land use leads to massive habitat destruction and fragmentation in tropical forests. Despite its global dimensions the effects of fragmentation on ecosystem dynamics are not well understood due to the complexity of the problem. We present a simulation analysis performed by the individual-based model FORMIND. The model was applied to the Brazilian Atlantic Forest, one of the world's biodiversity hot spots, at the Plateau of São Paulo. This study investigates the long-term effects of fragmentation processes on structure and dynamics of different sized remnant tropical forest fragments (1-100 ha) at community and plant functional type (PFT) level. We disentangle the interplay of single effects of different key fragmentation processes (edge mortality, increased mortality of large trees, local seed loss and external seed rain) using simulation experiments in a full factorial design.Our analysis reveals that particularly small forest fragments below 25 ha suffer substantial structural changes, biomass and biodiversity loss in the long term. At community level biomass is reduced up to 60%. Two thirds of the mid- and late-successional species groups, especially shade-tolerant (late successional climax) species groups are prone of extinction in small fragments. The shade-tolerant species groups were most strongly affected; its tree number was reduced more than 60% mainly by increased edge mortality. This process proved to be the most powerful of those investigated, explaining alone more than 80% of the changes observed for this group. External seed rain was able to compensate approximately 30% of the observed fragmentation effects for shade-tolerant species.Our results suggest that tropical forest fragments will suffer strong structural changes in the long term, leading to tree species impoverishment. They may reach a new equilibrium with a substantially reduced subset of the initial species pool, and are driven towards an earlier successional state. The natural regeneration potential of a landscape scattered with forest fragments appears to be limited, as external seed rain is not able to fully compensate for the observed fragmentation-induced changes. Our findings suggest basic recommendations for the management of fragmented tropical forest landscapes.