EFFECTS OF URBANIZATION ON CHANNEL INSTABILITY1

ABSTRACT: Channel instability and aquatic ecosystem degradation have been linked to watershed imperviousness in humid regions of the U.S. In an effort to provide a more process‐based linkage between observed thresholds of aquatic ecosystem degradation and urbanization, standard single event approaches (U.S. Geological Survey Flood Regression Equations and rational) and continuous hydrologic models (HSPF and CASC2D) were used to examine potential changes in flow regime associated with varying levels of watershed imperviousness. The predicted changes in flow parameters were then interpreted in concert with risk‐based models of channel form and instability. Although low levels of imperviousness (10 to 20 percent) clearly have the potential to destabilize streams, changes in discharge, and thus stream power, associated with increased impervious area are highly variable and dependent upon watershed‐specific conditions. In addition to the storage characteristics of the pre‐development watershed, the magnitude of change is sensitive to the connectivity and conveyance of impervious areas as well as the specific characteristics of the receiving channels. Different stream types are likely to exhibit varying degrees and types of instability, depending on entrenchment, relative erodibility of bed and banks, riparian condition, mode of sediment transport (bedload versus suspended load), and proximity to geomorphic thresholds. Nonetheless, simple risk‐based analyses of the potential impacts of land use change on aquatic ecosystems have the potential to redirect and improve the effectiveness of watershed management strategies by facilitating the identification of channels that may be most sensitive to changes in stream power.     

EFFECTS OF MULTI‐SCALE ENVIRONMENTAL CHARACTERISTICS ON AGRICULTURAL STREAM BIOTA IN EASTERN WISCONSIN1

ABSTRACT: The U.S. Geological Survey examined 25 agricultural streams in eastern Wisconsin the determine relations between fish, invertebrate, and algal metrics and multiple spatial scales of land cover, geologic setting, hydrologic, aquatic habitat, and water chemistry data. Spearman correlation and redundancy analyses were used to examine relations among biotic metrics and environmental characteristics. Riparian vegetation, geologic, and hydrologic conditions affected the response of biotic metrics to watershed agricultural land cover but the relations were aquatic assemblage dependent. It was difficult to separate the interrelated effects of geologic setting, watershed and buffer land cover, and base flow. Watershed and buffer land cover, geologic setting, reach riparian vegetation width, and stream size affected the fish IBI, invertebrate diversity, diatom IBI, and number of algal taxa; however, the invertebrate FBI, percentage of EPT, and the diatom pollution index were more influenced by nutrient concentrations and flow variability. Fish IBI scores seemed most sensitive to land cover in the entire stream network buffer, more so than watershed‐scale land cover and segment or reach riparian vegetation width. All but one stream with more than approximately 10 percent buffer agriculture had fish IBI scores of fair or poor. In general, the invertebrate and algal metrics used in this study were not as sensitive to land cover effects as fish metrics. Some of the reach‐scale characteristics, such as width/depth ratios, velocity, and bank stability, could be related to watershed influences of both land cover and geologic setting. The Wisconsin habitat index was related to watershed geologic setting, watershed and buffer land cover, riparian vegetation width, and base flow, and appeared to be a good indicator of stream quality Results from this study emphasize the value of using more than one or two biotic metrics to assess water quality and the importance of environmental characteristics at multiple scales.     

长江口九段沙水域环境及生物体内多氯联苯分布

对长江口九段沙湿地自然保护区的滩涂水样、泥样以及水生生物体内的多氯联苯进行GC-MS检测,研究多氯联苯各单体在不同环境介质及生物体中的分布状况. 结果表明:水样、泥样中的多氯联苯检出率为100%,其中四氯联苯(PCB52)含量最高; 与其他河口地区相比,九段沙水域水体中多氯联苯(PCBs)含量处于中等水平,ρ(PCBs)为23～95 ng/L;滩涂泥样多氯联苯含量则较低,w(PCBs)为1.77～4.51 ng/g; 该水域水生生物多氯联苯检出率为100%,w(PCBs)为0.12～9.40 μg/kg,低于国家标准限量; 软体动物、甲壳类以及鱼类检出单体均以高氯类PCB118和PCB138为主,而非环境中含量较高的PCB52,反映了水生生物对于高氯类多氯联苯富集能力强于低氯类多氯联苯.      

A simulation model for projecting changes in salinity concentrations and species dominance in the coastal margin habitats of the Everglades

Sharp boundaries typically separate the salinity tolerant mangroves from the salinity intolerant hardwood hammock species, which occupy the similar geographical areas of southern Florida. Evidence of strong feedback between tree community-type and the salinity of the unsaturated (vadose) zone of the soil suggests that a severe disturbance that significantly tilts the salinity in the vadose zone might cause a shift from one vegetation type to the other. In this study, a model based upon the feedback dynamics between vegetation and salinity of the vadose zone of the soil was used to take account of storm surge events to investigate the mechanisms that by which this large-scale disturbance could affect the spatial pattern of hardwood hammocks and mangroves. Model simulation results indicated that a heavy storm surge that completely saturated the vadose zone at 30 ppt for 1 day could lead to a regime shift in which there is domination by mangroves of areas previously dominated by hardwood hammocks. Lighter storm surges that saturated the vadose zone at less than 7 ppt did not cause vegetation shifts. Investigations of model sensitivity analysis indicated that the thickness of the vadose zone, coupled with precipitation, influenced the residence time of high salinity in the vadose zone and therefore determined the rate of mangrove domination. The model was developed for a southern Florida coastal ecosystem, but its applicability may be much broader.     

Mass balanced and dynamic simulations of trophic models of kelp ecosystems near the Mejillones Peninsula of northern Chile (SE Pacific): Comparative network structure and assessment of harvest strategies

Mass balanced trophic models for kelp ecosystems which include subsystems dominated by Macrocystis integrifolia, Lessonia trabeculata and areas of barren ground (BG) were constructed for subtidal areas near the Mejillones Peninsula (SE Pacific), Chile. Information on biomass, P/B ratios, catches, food spectrum, consumption and dynamics of commercial and non-commercial populations was obtained and examined using Ecopath with Ecosim software analyses. The biomass of blades of L. trabeculata and M. integrifolia represented the compartments most relevant to the subsystems studied. Within the herbivores, the sea urchin Tetrapigus niger was dominant, followed by the snails Turritella sp. and Tegula sp. The fishes Pinguipes chilensis and Cheilodactylus variegatus were the dominant predators, followed by the asteroids Heliaster helianthus and Meyenaster gelatinosus. The highest system throughput (72,512 g wet weight m⁻² year⁻¹) was calculated for the subsystem dominated by M. integrifolia. The mean trophic level of the catch ranged from 1.1 (subsystem dominated by L. trabeculata) to 1.3 (subsystem dominated by M. integrifolia) to 3.2 (barren ground subsystem), showing that harvesting in each system was concentrated either on primary producers (blades of kelp species) or top predator fishes. Although the values for the Relative Ascendency (A/C) fluctuated from 36.5 to 45%, suggesting that all the systems were immature, the subsystem dominated by M. integrifolia emerged as the least resistant to external disturbances (e.g. fisheries). This result agreed with the high value of the system recovery time (SRT) for the M. integrifolia subsystem as a response to combined fisheries scenarios. The results obtained using mixed trophic impact (MTI) and Ecosim [increasing the fishing mortality F_i by 4×] showed that in most of the cases the predictions had the same qualitative tendencies. One of the most important results obtained in this study was that exploitation of kelp blades as an alternative strategy to harvesting the whole plants appeared to be ecologically sustainable, since harvesting the blades propagated only small effects on the entire subsystem. The fish P. chilensis may be considered as a top predator species with a strong top-down control since an increase in its fishing mortality in the subsystem dominated by M. integrifolia produced a high SRT value, and the F_MSY was less than the originally entered F_i in Ecopath. Based on the results obtained, it was concluded that the trophic mass balanced models and simulated management scenarios offered good possibilities for the planning of interventions and manipulations or the planning of more sustainable management strategies in highly disturbed natural systems.     

Managing Aquatic Species of Conservation Concern in the Face of Climate Change and Invasive Species

Abstract:  The difficult task of managing species of conservation concern is likely to become even more challenging due to the interaction of climate change and invasive species. In addition to direct effects on habitat quality, climate change will foster the expansion of invasive species into new areas and magnify the effects of invasive species already present by altering competitive dominance, increasing predation rates, and enhancing the virulence of diseases. In some cases parapatric species may expand into new habitats and have detrimental effects that are similar to those of invading non-native species. The traditional strategy of isolating imperiled species in reserves may not be adequate if habitat conditions change beyond historic ranges or in ways that favor invasive species. The consequences of climate change will require a more active management paradigm that includes implementing habitat improvements that reduce the effects of climate change and creating migration barriers that prevent an influx of invasive species. Other management actions that should be considered include providing dispersal corridors that allow species to track environmental changes, translocating species to newly suitable habitats where migration is not possible, and developing action plans for the early detection and eradication of new invasive species.     

水生野生动物自然保护区环境规划指标体系的建立

从水生野生动物自然保护区的特点和实际情况出发,分析了水生野生动物自然保护区环境规划指标体系建立的原则,采用层次分析法筛选指标,建立了基于PSR框架模型的水生野生动物自然保护区环境规划指标体系.应用该指标体系对怀沙河、怀九河水生野生动物保护区进行环境功能区划,得到与实际情况较为符合的区划结果.说明该指标体系能够较为全面、准确地描述保护区的实际情况.     

Optimizing conservation in species-specific agricultural landscapes

Recovery of grassland birds in agricultural landscapes is a global imperative. Agricultural landscapes are complex, and the value of resource patches may vary substantially among species. The spatial extent at which landscape features affect populations (i.e., scale of effect) may also differ among species. There is a need for regional-scale conservation planning that considers landscape-scale and species-specific responses of grassland birds to environmental change. We developed a spatially explicit approach to optimizing grassland conservation in the context of species-specific landscapes and prioritization of species recovery and applied it to a conservation program in Kentucky (USA). We used a hierarchical distance-sampling model with an embedded scale of effect predictor to estimate the relationship between landscape structure and abundance of eastern meadowlarks (Sturnella magna), field sparrows (Spizella pusilla), and northern bobwhites (Colinus virginianus). We used a novel spatially explicit optimization procedure rooted in multi-attribute utility theory to design alternative conservation strategies (e.g., prioritize only northern bobwhite recovery or assign equal weight to each species’ recovery). Eastern meadowlarks and field sparrows were more likely to respond to landscape-scale resource patch adjacencies than landscape-scale patch densities. Northern bobwhite responded to both landscape-scale resource patch adjacencies and densities and responded strongly to increased grassland density. Effects of landscape features on local abundance decreased as distance increased and had negligible influence at 0.8 km for eastern meadowlarks (0.7–1.2 km 95% Bayesian credibility intervals [BCI]), 2.5 km for field sparrows (1.5–5.8 km 95% BCI), and 8.4 km for bobwhite (6.4–26 km 95% BCI). Northern bobwhites were predicted to benefit greatly from future grassland conservation regardless of conservation priorities, but eastern meadowlark and field sparrow were not. Our results suggest similar species can respond differently to broad-scale conservation practices because of species-specific, distance-dependent relationships with landscape structure. Our framework is quantitative, conceptually simple, customizable, and predictive and can be used to optimize conservation in heterogeneous ecosystems while considering landscape-scale processes and explicit prioritization of species recovery.     

Effectiveness of amphibians as biodiversity surrogates in pond conservation

Amphibian decline has led to worldwide conservation efforts, including the identification and designation of sites for their protection. These sites could also play an important role in the conservation of other freshwater taxa. In 89 ponds in Switzerland, we assessed the effectiveness of amphibians as a surrogate for 4 taxonomic groups that occur in the same freshwater ecosystems as amphibians: dragonflies, aquatic beetles, aquatic gastropods, and aquatic plants. The ponds were all of high value for amphibian conservation. Cross‐taxon correlations were tested for species richness and conservation value, and Mantel tests were used to investigate community congruence. Species richness, conservation value, and community composition of amphibians were weakly congruent with these measures for the other taxonomic groups. Paired comparisons for the 5 groups considered showed that for each metric, amphibians had the lowest degree of congruence. Our results imply that site designation for amphibian conservation will not necessarily provide protection for freshwater biodiversity as a whole. To provide adequate protection for freshwater species, we recommend other taxonomic groups be considered in addition to amphibians in the prioritization and site designation process.     

白洋淀湿地水质与水生物相关性研究

水质与水生物间关系是湿地生态学的研究热点,研究成果可为湿地水生态修复提供科学依据.在白洋淀湿地设置14个采样点,选取9个水质因子、4类11个水生物指标,利用冗余分析(RDA)方法对其进行研究.结果表明,白洋淀湿地水质和水生物相关性显著,前两个排序轴水质与水生物的相关系数分别为0.973和0.821,特征值分别是0.862和0.059.DO、NO₃^--N、SD、TN和TP是影响水生物的主要水质因子,第一排序轴与NO₃^--N和DO显著正相关;第二排序轴与SD显著正相关,与TN和TP显著负相关.比较可知,NO₃^--N、DO对浮游动植物影响显著,特征值占主要水质因子总特征值的89%;SD、TN和TP对底栖动物及大型水生植物影响大,特征值占主要水质因子总特征值的94%.