Recovery of lotic periphyton communities after disturbance

Periphyton communities represent potentially excellent candidates for assessing the recovery of lotic ecosystems after disturbance. These communities are ubiquitous, relatively easy to sample and measure (in terms of total community biomass), have short generation times, and may influence the recovery rates of higher trophic levels. The first section of this article analyzes how site availability, species availability, and differential species performance influence periphyton successional dynamics. This background information provides a foundation for understanding how periphytic organisms respond after a disturbance. The second section of this article analyzes how periphyton communities respond to four different types of disturbance (flood events, desiccation, organic nutrient enrichment, and toxic metal exposure). Although data are limited, it is concluded that the fast growth rates and short generation times of periphytic organisms, coupled with their flexible life history strategies and good dispersal ability, allow lotic periphyton communities to recover relatively quickly after a disturbance. In addition, disturbance type and severity, local environmental conditions, and site-specific factors also will influence recovery rates. Future research needs include a better understanding of: (1) what periphyton property(ies) would serve as the best index of recovery; (2) whether or not the robustness of this index varies among different environments and different disturbances; (3) interactions between autotrophs and heterotrophs within the periphyton mat, particularly with respect to nutrient cycling; (4) competitive interactions among organisms; (5) functional redundancy of organisms; and (6) the influence of the riparian zone and channel geomorphology on periphyton recovery rates.     

Recovery of lotic macroinvertebrate communities from disturbance

Ecosystem disturbances produce changes in macrobenthic community structure (abundances, biomass, and production) that persist for a few weeks to many decades. Examples of disturbances with extremely long-term effects on benthic communities include contamination by persistent toxic agents, physical changes in habitats, and altered energy inputs. Stream size, retention, and local geomorphology may ameliorate the influence of disturbances on invertebrates. Disturbances can alter food webs and may select for favorable genotypes (e.g., insecticidal resistance). Introductions of pesticides into lotic ecosystems, which do not result in major physical changes within habitats, illustrate several factors that influence invertebrate recovery time from disturbance. These include: (1) magnitude of original contamination, toxicity, and extent of continued use; (2) spatial scale of the disturbance; (3) persistence of the pesticide; (4) timing of the contamination in relation to the life history stages of the organisms; (5) vagility of populations influenced by pesticides; and (6) position within the drainage network. The ability of macroinvertebrates to recolonize denuded stream habitats may vary greatly depending on regional life histories, dispersal abilities, and position within the stream network (e.g., headwaters vs larger rivers). Although downstream drift is the most frequently cited mechanism of invertebrate recolonization following disturbance in middle- and larger-order streams, evidence is presented that shows aerial recolonization to be potentially important in headwater streams. There is an apparent stochastic element operating for aerial recolonization, depending on the timing of disturbance and flight periods of various taxa. Available evidence indicates that recolonization of invertebrate taxa without an aerial adult stage requires longer periods of time than for those that possess winged, terrestrial adult stages (i.e., most insects). Innovative, manipulative experiments are needed in order to address recolonization mechanisms of animals inhabiting streams that differ in size, latitude, disturbance frequency and magnitude, as well as the potential influence of early colonists on successional sequences of species following disturbance.     

Post-fire seeding on Wyoming big sagebrush ecological sites: regression analyses of seeded nonnative and native species densities

Since the mid-1980s, sagebrush rangelands in the Great Basin of the United States have experienced more frequent and larger wildfires. These fires affect livestock forage, the sagebrush/grasses/forbs mosaic that is important for many wildlife species (e.g., the greater sage grouse (Centrocercus urophasianus)), post-fire flammability and fire frequency. When a sagebrush, especially a Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis (Beetle & A. Young)), dominated area largely devoid of herbaceous perennials burns, it often transitions to an annual dominated and highly flammable plant community that thereafter excludes sagebrush and native perennials. Considerable effort is devoted to revegetating rangeland following fire, but to date there has been very little analysis of the factors that lead to the success of this revegetation. This paper utilizes a revegetation monitoring dataset to examine the densities of three key types of vegetation, specifically nonnative seeded grasses, nonnative seeded forbs, and native Wyoming big sagebrush, at several points in time following seeding. We find that unlike forbs, increasing the seeding rates for grasses does not appear to increase their density (at least for the sites and seeding rates we examined). Also, seeding Wyoming big sagebrush increases its density with time since fire. Seeding of grasses and forbs is less successful at locations that were dominated primarily by annual grasses (cheatgrass (Bromus tectorum L.)), and devoid of shrubs, prior to wildfire. This supports the hypothesis of a "closing window of opportunity" for seeding at locations that burned sagebrush for the first time in recent history.     

Recovery of lotic communities and ecosystems from disturbance—A narrative review of case studies

We present a narrative account of case studies of the recovery of flowing water systems from disturbance, focusing on the investigators' conclusions about recovery time and the factors contributing to recovery. We restrict our attention to case studies in which the recovery of some biological property of the system has been examined, excluding those that deal only with physical or chemical properties. Although natural processes and rates of recovery are emphasized, studies of reclamation or restoration of damaged ecosystems are included where they contribute to an understanding of recovery processes. For the majority of studies examined, the systems recovered quite rapidly. The most commonly cited reasons for short recovery times were: (1) life history characteristics that allowed rapid recolonization and repopulation of the affected areas, (2) the availability and accessibility of unaffected up-stream and downstream areas and internal refugia to serve as sources of organisms for repopulation, (3) the high flushing rates of lotic systems that allowed them to quickly dilute or replace polluted waters, and (4) the fact that lotic systems are naturally subjected to a variety of disturbances and the biota have evolved life history characteristics that favor flexibility or adaptability. In general, longer recovery times were observed in disturbances, such as channelization, that resulted in alterations to physical conditions. This review also indicates that much of our knowledge of recovery in lotic ecosystems is fragmented and uncoordinated. In addition to establishing the bounds of recovery time, our review identifies some research gaps that need to be filled.     

Fire hazard after prescribed burning in a gorse shrubland: implications for fuel management

Prescribed burning is commonly used to prevent accumulation of biomass in fire-prone shrubland in NW Spain. However, there is a lack of knowledge about the efficacy of the technique in reducing fire hazard in these ecosystems. Fire hazard in burned shrubland areas will depend on the initial capacity of woody vegetation to recover and on the fine ground fuels existing after fire. To explore the effect that time since burning has on fire hazard, experimental tests were performed with two fuel complexes (fine ground fuels and regenerated shrubs) resulting from previous prescribed burnings conducted in a gorse shrubland (Ulex europaeus L.) one, three and five years earlier. A point-ignition source was used in burning experiments to assess ignition and initial propagation success separately for each fuel complex. The effect of wind speed was also studied for shrub fuels, and several flammability parameters were measured. Results showed that both ignition and initial propagation success of fine ground fuels mainly depended on fuel depth and were independent of time since burning, although flammability parameters indicated higher fire hazard three years after burning. In contrast, time since burning increased ignition and initial propagation success of regenerated shrub fuels, as well as the flammability parameters assessed, but wind speed had no significant effect. The combination of results of fire hazard for fine ground fuels and regenerated shrubs according to the variation in relative coverage of each fuel type after prescribed burning enabled an assessment of integrated fire hazard in treated areas. The present results suggest that prescribed burning is a very effective technique to reduce fire hazard in the study area, but that fire hazard will be significantly increased by the third year after burning. These results are valuable for fire prevention and fuel management planning in gorse shrubland areas.     

Recovery of temperate-stream fish communities from disturbance: A review of case studies and synthesis of theory

To evaluate the relative effect of autecologic factors, site-specific factors, disturbance characteristics, and community structure on the recovery of temperate-stream fish communities, we reviewed case histories for 49 sites and recorded data on 411 recovery end points. Most data were derived from studies of low-gradient third- or fourth-order temperate streams located in forested or agricultural watersheds. Species composition, species richness, and total density all recovered within one year for over 70% of systems studied. Lotic fish communities were not resilient to press disturbances (e.g., mining, logging, channelization) in the absence of mitigation efforts (recovery time >5 to >52 yr) and in these cases recovery was limited by habitat quality. Following pulse disturbances, autecological factors, site-specific factors, and disturbance-specific factors all affected rates of recovery. Centrarchids and minnows were most resilient to disturbance, while salmonid populations were least resilient of all families considered. Species within rock-substrate/nest-spawning guilds required significantly longer time periods to either recolonize or reestablish predisturbance population densities than did species within other reproductive guilds. Recovery was enhanced by the presence of refugia but was delayed by barriers to migration, especially when source populations for recolonization were relatively distant. Median population recovery times for systems in which disturbances occurred during or immediately prior to spawning were significantly less than median recovery times for systems in which disturbances occurred immediately after spawning. There was little evidence for the influence of biotic interactions on recovery rates.     

A landscape analysis of cougar distribution and abundance in Montana, USA

Recent growth in the distribution and abundance of cougars (Puma concolor) throughout western North America has created opportunities, challenges, and problems for wildlife managers and raises questions about what factors affect cougar populations. We present an analysis of factors thought to affect cougar distribution and abundance across the broad geographical scales on which most population management decisions are made. Our objectives were to: (1) identify and evaluate landscape parameters that can be used to predict the capability of habitats to support cougars, and (2) evaluate factors that may account for the recent expansion in cougar numbers. Habitat values based on terrain ruggedness and forested cover explained 73% of the variation in a cougar abundance index. Indices of cougar abundance also were spatially and temporally correlated with ungulate abundance. An increase in the number and total biomass of ungulate prey species is hypothesized to account for recent increases in cougars. Cougar populations in Montana are coping with land development by humans when other components of habitat and prey populations are sufficient. Our analysis provides a better understanding of what may have influenced recent growth in cougar distribution and abundance in Montana and, when combined with insights about stakeholder acceptance capacity, offers a basis for cougar management at broad scales. Long-term conservation of cougars necessitates a better understanding of ecosystem functions that affect prey distribution and abundance, more accurate estimates of cougar populations, and management abilities to integrate these components with human values.     

Short- and Longer-Term Effects of Fire and Herbivory on Sagebrush Communities in South-Central Montana

To better understand the role of herbivory and fire as potential disturbance processes in sagebrush communities, we examined responses of a grazing ungulate, elk (Cervus elaphus), following prescribed burning of sagebrush (Artemisia tridentata ssp. vaseyana) in south-central Montana (USA.) with concurrent monitoring of changes in plant production, nutritional quality, and community diversity from 1989–1999. Burning transformed low-diversity, sagebrush-dominated communities into high-diversity, graminoid-forb communities that persisted for 10 years without significant reestablishment of sagebrush. Elk increased use of burned sites one year after burning, but elk use returned to pre-burn levels over the next two to nine years. Forage biomass and nutritional quality declined after initial increases that coincided with increased elk use. Increases in elk use appeared to be influenced by increases in combined graminoid and forb production and changes in structural vegetation characteristics that permitted greater foraging efficiency. Declines in use were associated with loss of nutritional enhancement and declines in combined graminoid and forb production. Managers may observe only short-term responses from grazing ungulates to prescribed fire in sagebrush communities, but can expect longer-term increases in plant diversity and establishment of graminoid-forb communities.     

Effects of land clearing methods on the properties and productivity of an Alfisol in south-western Nigeria

Summary This study investigated the impact of manual and mechanical land clearing methods on the soils and the yield of maize in a part of the rainforest belt of south-western Nigeria. The results of the study revealed that the mean values of such soil properties as the organic matter, bulk-density, total porosity, soil moisture and to some extent the exchangeable actions in the mechanically cleared farms differed significantly at (P 0.05) from those in the manually cleared farms and the rainforest vegetation used in the control plot. There was no significant difference in the average yield of maize for the three years for which records were available.Dr Adeniyi Gbadegesin is a Senior Lecturer in the Department of Geography, University of Ibadan, where Miss B. B. Olusesi was a recent graduate.     

The multiple communities of low-carbon transition: an assessment of communities involved in forest carbon measurement

In recent writing on sociotechnical transitions theory communities are mostly conceived of as being local and place-based (“grassroots”). In this paper the implications for sociotechnical transitions theory of having multiple communities operating at different geographical scales, and with different objectives, are examined through a case study of low-carbon innovation in forests. The focus of analysis is the communities promoting sociotechnical innovations in the measurement of forest carbon. Innovation is being driven by the international United Nations climate policy initiative “Reducing Emissions from Deforestation and forest Degradation” (REDD+). The rise of REDD+ policy has prompted a flurry of activity in related scientific research, especially in the field of remote sensing. But other types of community are also actively positioning themselves as experts in forest carbon measurement: there are multiple communities at work, each with varying claims to innovation and expertise, from local (place-based) forest communities to international communities of foresters and forest ecologists. Recognition of the multiple communities operating within sociotechnical systems usefully draws our attention to the politics of innovation.     

Analysis of the prescribed burning practice in the pine forest of northwestern Portugal

The ignition of low-intensity fires in the dormant season in the pine stands of north-western Portugal seeks to reduce the existing fuel hazard without compromising site quality. The purpose of this study is to characterise this practice and assess its effectiveness, based on information resulting from the normal monitoring process at the management level, and using operational guidelines, fire behaviour models and a newly developed method to classify prescribed fire severity. Although the region's humid climate strongly constrains the activity of prescribed fire, 87% of the fires analysed were undertaken under acceptable meteorological and fuel moisture conditions. In fact, most operations achieved satisfactory results. On average, prescribed fire reduces by 96% the potential intensity of a wildfire occurring under extreme weather conditions, but 36% of the treated sites would still require heavy fire fighting resources to suppress such fire, and 17% would still carry it in the tree canopy. Only 10% of the prescribed burns have an excessive impact on trees or the forest floor, while 89% (normal fire weather) or 59% (extreme fire weather) comply with both ecological integrity maintenance and wildfire protection needs. Improved planning and monitoring procedures are recommended in order to overcome the current deficiencies.     

Beer,beef, and boards: the role of intermediaries in payment for ecosystem services arrangements in northwestern Montana

Payments for ecosystem or ecological services (PES) are voluntary, often market-based approaches to protecting environmental values. In the rural United States, some landowners receive PES through government led conservation programs, but little is known about their involvement in market based arrangements. We analyzed three examples of market based PES arrangements in northwestern Montana: watershed restoration and craft brewing, niche meat production, and certified timber supplies. We find that intermediaries were working between buyers and sellers in each case to set conditions for transactions and undertake the mechanics of implementation. These findings align with existing conceptualizations of intermediaries as crucial links in PES arrangements, but also suggest that intermediaries for market based PES arrangements are not always facilitators or neutral nongovernmental actors; they may actually be from the private sector and drive the process by serving as buyers. This research contributes to stronger understanding of the possibilities for local market based conservation in the rural West.     

PRB在地下水污染修复中的应用

本文综述了可渗透反应墙(PRB)的基本结构及其不同浓度的安装方法、反应材料的选择、零价铁和微生物修复的原理，并提出须通过进一步的研究以提高对该系统长期性能的了解。     

Social learning and sustainable communities: An interim assessment of research into sustainable communities projects in the UK

Abstract

The delivery of many of the most pressing environmental issues will rely on changes in environmental attitudes and behaviour at community level. At a UN Special Session in 1997, the British Government highlighted its initiatives on Local Agenda 21 (LA21) and Going for Green (GFG) as significant advances. This paper adds a new perspective, drawing on the range of experiences of some of the research teams that have been working with local authorities on pilot Sustainable Community Projects (SCPs) in England and Scotland. It sheds light on three substantive themes: the tensions inherent in the implementation of internationally and nationally agreed goals through local action; the ambiguity of local agencies acting as facilitators of community ownership of processes, and the requirements for successful partnership between local authorities and higher education.     

Social learning and sustainable communities: An interim assessment of research into sustainable communities projects in the UK

The delivery of many of the most pressing environmental issues will rely on changes in environmental attitudes and behaviour at community level. At a UN Special Session in 1997, the British Government highlighted its initiatives on Local Agenda 21 (LA21) and Going for Green (GFG) as significant advances. This paper adds a new perspective, drawing on the range of experiences of some of the research teams that have been working with local authorities on pilot Sustainable Community Projects (SCPs) in England and Scotland. It sheds light on three substantive themes: the tensions inherent in the implementation of internationally and nationally agreed goals through local action; the ambiguity of local agencies acting as facilitators of community ownership of processes, and the requirements for successful partnership between local authorities and higher education.     

The role of learning in sustainable communities of practice

This paper adds to the literature on skills for sustainable communities by examining the role and processes of learning in “communities of practice” that exist within a “grassroots association”. Interviews were conducted with participants in the communities of practice of a student group called Green Action, which engages with environmental issues in practical ways. The findings demonstrate how learning occurred in the communities of practice, how participants gained skills and knowledge for sustainable consumption, and how learning in the communities of practice appeared to help Green Action to sustain itself in the long-term. This paper could serve as a useful demonstration to others as to how to apply the theories and concepts from the literature on communities of practice when researching skills and knowledge for sustainable communities. It also has some value for grassroots associations themselves in understanding their own activities.     

Characterization of turf practices in five North Carolina communities

Limited information exists on specific urban lawn care practices in the United States. We conducted a door-to-door lawn care survey in five North Carolina communities to determine suburban fertilizer, pesticide, and water use. These communities, Cary, Goldsboro, Kinston, New Bern, and Greenville, are mostly located within the Neuse River basin, a nutrient-sensitive water resource. Residents in Cary used lawn care companies more than twice as frequently as residents in the other communities (43 compared with 20%). Cary had the smallest mean lawn size (445 m2), while the largest was in Goldsboro (1899 m2). Tall fescue [Festuca arundinacea Schreb.] was the predominant grass type in Cary (99%), and centipedegrass [Eremochloa ophiuroides (Munro) Hack.] or centipedegrass mixtures were the predominant grass types in Greenville and New Bern. Kinston had the lowest fertilizer usage with only 54% of the residents using fertilizer; Cary had the highest rate of 83%. The average N fertilizer rate applied to the lawns was dissimilar ranging from 24 to 151 kg N ha(-1). Analysis of variance results for fertilizer rates and household income indicated a significant difference (P < 0.05) in application rate between high- and medium-income levels and the low-income level. Cary, Goldsboro, and Greenville had approximately the same number of fertilizer applications per year (1.5), whereas the average number of fertilizer applications per year in New Bern was 3.0. Most household residents (53%) used instructions on the bag and either grass type and/or lawn area to guide them on fertilizer application rates.     

我国废电池的回收与处理

本文详细介绍了国内外常见的各种废电池的种类、有害成分，处理方法，分析了目前我国在度电池回收处理过程中所存在的诸多问题，并有针对性的提出建议。     

Influence of Llamas, Horses, and Hikers on Soil Erosion from Established Recreation Trails in Western Montana, USA

/ Various types of recreational traffic impact hiking trails uniquely and cause different levels of trail degradation; however, trail head restrictions are applied similarly across all types of packstock. The purpose of this study was to assess the relative physical impact of hikers, llamas, and horses on recreational trails. Horse, llama, and hiker traffic were applied to 56 separate plots on an existing trail at Lubrecht Experimental Forest in western Montana. The traffic was applied to plots at intensities of 250 and 1000 passes along with a no-traffic control under both prewetted and dry trail conditions. Soil erosion potential was assessed by sediment yield and runoff (using a Meeuwig type rainfall simulator), changes in soil bulk density, and changes in soil surface roughness. Soil moisture, slope, and rainfall intensity were recorded as independent variables in order to evaluate the extent that they were held constant by the experimental design. Horse traffic consistently made more sediment available for erosion from trails than llama, hiker, or no traffic when analyzed across wet and dry trail plots and high and low intensity traffic plots. Although total runoff was not significantly affected by trail user, wet trail traffic caused significantly greater runoff than dry trail traffic. Llama traffic caused a significant increase in sediment yield compared to the control, but caused erosion yields not significantly different than hiker traffic. Trail traffic did not increase soil compaction on wet trails. Traffic applied to dry trail plots generally resulted in a significant decrease in soil bulk density compared to the control. Decreased soil bulk density was negatively correlated with increased sediment yield and appeared to result in increased trail roughness for horse traffic compared to hiker or llama traffic. Differences described here between llama and horse traffic indicate that trail managers may want to consider managing packstock llamas independent of horses.KEY WORDS: Recreational impacts; Sediment yield; Trail degradation