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Anthropogenic Impacts (anthropogenic + impact)

Distribution by Scientific Domains

Life Sciences	70%
Humanities and Social Sciences	18%
Earth and Environmental Science	7%

Selected Abstracts

Anthropogenic impacts upon plant species richness and net primary productivity in California

ECOLOGY LETTERS, Issue 2 2005
John W. Williams
Abstract We assess the importance of anthropogenic land-use, altered productivity, and species invasions for observed productivity,richness relationships in California. To this end, we model net primary productivity (NPP) c. 1750 AD and at present (1982,1999) and map native and exotic vascular plant richness for 230 subecoregions. NPP has increased up to 105% in semi-arid areas and decreased up to 48% in coastal urbanized areas. Exotic invasions have increased local species diversity up to 15%. Human activities have reinforced historical gradients in species richness but reduced the spatial heterogeneity of NPP. Structural equation modelling suggests that, prior to European settlement, NPP and richness were primarily controlled by precipitation and other abiotic variables, with NPP mediating richness. Abiotic variables remain the strongest predictors of present NPP and richness, but intermodel comparisons indicate a significant anthropogenic impact upon statewide distributions of NPP and richness. Exotic and native species each positively correlate to NPP after controlling for other variables, which may help explain recent reports of positively associated native and exotic richness. [source]

Anthropogenic impacts on lake and stream ecosystems, and approaches to restoration

JOURNAL OF APPLIED ECOLOGY, Issue 6 2007
MARTIN SØNDERGAARD
Summary 1Freshwater ecosystems have long been affected by numerous types of human interventions that have a negative impact on their water quality and ecological state. Fortunately, in most western countries the input of sewage to freshwater systems has been reduced, but hydromorphological alterations, eutrophication-related turbidity and loss of biodiversity remain major problems in many parts of the world. Such impacts prevent the achievement of a high or good ecological state, as defined by the European Water Framework Directive (WFD) or other standards. 2This paper synthesizes and links the findings presented in the seven papers of this special profile, focusing on the effects of anthropogenic stressors on freshwater ecosystems and on how to maintain and restore ecological quality. The papers cover a broad range of research areas and methods, but are all centred on the relationship between dispersal barriers, the connectivity of waterways and the restoration of rivers and lakes. 3The construction of dams and reservoirs disturbs the natural functioning of many streams and rivers and shore-line development around lakes may reduce habitat complexity. New methods demonstrate how reservoirs may have a severe impact on the distribution and connectivity of fish populations, and new techniques illustrate the potential of using graph theory and connectivity models to illustrate the ecological implications. Hydromorphologically degraded rivers and streams can be restored by addition of wood debris, but ,passive' restoration via natural wood recruitment may be preferable. The most cost-effective way to restore streams may also include information campaigns to farmers on best management practices. Removal of zooplanktivorous fish often has marked positive effects on trophic structure in lakes, but there is a tendency to return to turbid conditions after 8,10 years or less unless fish removal is repeated. 4Synthesis and applications. Development of new methods, as well as derivation of more general conclusions from reviewing the effects of previous restoration efforts, are crucial to achieve progress in applied freshwater research. The papers contained in this Special Profile contribute on both counts, as well as illustrating the importance of well-designed research projects and monitoring programmes to record the effects of the interventions. Such efforts are vital if we are to improve our knowledge of freshwater systems and to elaborate the best and most cost-effective recommendations. They may also help in achieving a good ecological state or potential in water bodies by 2015, as demanded by the European WFD. [source]

Anthropogenic impacts upon plant species richness and net primary productivity in California

Can taxonomic distinctness assess anthropogenic impacts in inland waters?

FRESHWATER BIOLOGY, Issue 9 2006
A case study from a Mediterranean river basin
Summary 1. It is increasingly recognised that adequate measures of biodiversity should include information on the ,relatedness' of species within ecological assemblages, or the phylogenetic levels at which diversity is expressed. Taxonomic distinctness measures provide a series of indices to achieve this, which are independent of sample size. Taxonomic distinctness has been employed widely in marine systems, where it has been suggested that this index can provide a reliable measure of anthropogenic impact. 2. We tested the behaviour of three related taxonomic distinctiveness indices (Average Taxonomic Distinctness, ,+; Variation in Taxonomic Distinctness, ,+; and Total Taxonomic Distinctness, s,+) in relation to putative levels of anthropogenic impact in inland waters and their potential utility in environmental monitoring, using an extensive data set for aquatic beetles from the south-east of the Iberian Peninsula. 3. Taxonomic distinctness measures were not able to identify human disturbance effects and there were no clear relationships between these new biodiversity measures and the disturbance level recorded at individual localities. Furthermore, the taxonomic distinctness measures used were apparently less sensitive to the effects of anthropogenic impact than other diversity metrics, such as species richness and rarity. 4. We conclude that taxonomic distinctness indices may not always perform as well as other metrics in the assessment of environmental quality. In addition, taxonomic distinctness measure should be interpreted with caution, as their performance and ability to detect anthropogenic disturbance may depend on the phylogenetic structure of sampled taxa within a region, and their evolutionary and ecological history. [source]

Reorganization of a large marine ecosystem due to atmospheric and anthropogenic pressure: a discontinuous regime shift in the Central Baltic Sea

GLOBAL CHANGE BIOLOGY, Issue 6 2009
CHRISTIAN MÖLLMANN
Abstract Marine ecosystems such as the Baltic Sea are currently under strong atmospheric and anthropogenic pressure. Besides natural and human-induced changes in climate, major anthropogenic drivers such as overfishing and anthropogenic eutrophication are significantly affecting ecosystem structure and function. Recently, studies demonstrated the existence of alternative stable states in various terrestrial and aquatic ecosystems. These so-called ecosystem regime shifts have been explained mainly as a result of multiple causes, e.g. climatic regime shifts, overexploitation or a combination of both. The occurrence of ecosystem regime shifts has important management implications, as they can cause significant losses of ecological and economic resources. Because of hysteresis in ecosystem responses, restoring regimes considered as favourable may require drastic and expensive management actions. Also the Baltic Sea, the largest brackish water body in the world ocean, and its ecosystems are strongly affected by atmospheric and anthropogenic drivers. Here, we present results of an analysis of the state and development of the Central Baltic Sea ecosystem integrating hydroclimatic, nutrient, phyto- and zooplankton as well as fisheries data. Our analyses of 52 biotic and abiotic variables using multivariate statistics demonstrated a major reorganization of the ecosystem and identified two stable states between 1974 and 2005, separated by a transition period in 1988,1993. We show the change in Baltic ecosystem structure to have the characteristics of a discontinuous regime shift, initiated by climate-induced changes in the abiotic environment and stabilized by fisheries-induced feedback loops in the food web. Our results indicate the importance of maintaining the resilience of an ecosystem to atmospherically induced environmental change by reducing the anthropogenic impact. [source]

Bacterial ancient DNA as an indicator of human presence in the past: its correlation with palynological and archaeological data,

JOURNAL OF QUATERNARY SCIENCE, Issue 4 2009
Jacek Madeja
Abstract Palynological investigation is one of the most important tools for reconstructing past vegetation. Some plants have proved to be relatively sensitive indicators of human activity, but most of them are not specific. In this paper we propose a method which can be used for the verification of phases of anthropogenic impact on vegetation distinguished in pollen diagrams. In this work we adopted the existing molecular methods for tracking bacterial ancient DNA of Bifidobacterium and Bacteroides-Prevotella (known as human- and cow-specific genetic markers) in palynologically and archaeologically associated sediments. This method can be helpful in determining local human presence, especially in those time periods when pollen analysis has not always been very discriminating (Palaeolithic, Mesolithic) and at sites without archaeological evidence. Copyright © 2008 John Wiley & Sons, Ltd. [source]

A high-resolution pollen and geochemical analysis of late Holocene human impact and vegetation history in southern Cumbria, England,

JOURNAL OF QUATERNARY SCIENCE, Issue 3 2009
Paul M. V. Coombes
Abstract The historic era, which in Cumbria begins with the Roman invasion of AD 71, is a frequently neglected period in palaeoecological research, but its study can bring benefits in improving knowledge of landscape history and in understanding the significance and limitations of palaeoecological records. Pollen and geochemical data are presented for late Holocene records from Deer Dyke and Hulleter Mosses in southern Cumbria. The records show initially low levels of anthropogenic impact, followed by a phase of forest clearance and mixed agriculture from the 7th to 11th centuries AD. The timing of these clearances suggests that they were initially Anglo-Saxon in origin, rather than Norse. Further clearances in the 16th century AD are interpreted as a response to monastic dissolution and late Tudor population pressures; the landscapes reached their contemporary form following extensive clearances in the 17th century AD. Silicon and titanium concentrations at Deer Dyke Moss were used to reconstruct past levels of atmospheric dust loading, which is broadly related to soil erosion. Geochemical influx was found to peak during periods of landscape transition rather than from established land use. This relationship with pollen data is thought to reflect the predominantly low levels of anthropogenic impact in the region, which changes as substantial woodland clearances during the 16th century AD and continuous land use pressure since then have greatly increased the supply of airborne dust. Copyright © 2008 John Wiley & Sons, Ltd. [source]

The importance of local-scale openness within regions dominated by closed woodland,

JOURNAL OF QUATERNARY SCIENCE, Issue 6 2007
Ralph Fyfe
Abstract New and existing pollen data from Wales, UK, are used to assess the level of landscape openness at the regional and local scale. At the regional scale, the existing pollen data support the high-forest model of vegetation structure by 6000 cal. yr. BC prior to any palynological signal for anthropogenic impact in the region. New data from two sites in southwest Wales follow the general regional pattern of early to middle Holocene vegetation succession, but are striking owing to maintenance of high non-arboreal pollen percentages (NAPs) throughout the mid-Holocene. It is argued that these NAPs indicate that a significant degree of openness can be found at the local level (and beyond the confines of the peat-forming site) within regions characterised by closed woodland. It is possible that woodland development in these areas may have been suppressed by reduced drainage, although the role of grazing animals in maintenance of clearings cannot be assessed. Implications for this local degree of openness are discussed, in particular the significance of vegetation heterogeneity at the local scale for the construction of place or locale for prehistoric communities. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Biodiversity in microbial communities: system scale patterns and mechanisms

MOLECULAR ECOLOGY, Issue 7 2009
J. JACOB PARNELL
Abstract The relationship between anthropogenic impact and the maintenance of biodiversity is a fundamental question in ecology. The emphasis on the organizational level of biodiversity responsible for ecosystem processes is shifting from a species-centred focus to include genotypic diversity. The relationship between biodiversity measures at these two scales remains largely unknown. By stratifying anthropogenic effects between scales of biodiversity of bacterial communities, we show a statistically significant difference in diversity based on taxonomic scale. Communities with intermediate species richness show high genotypic diversity while speciose and species-poor communities do not. We propose that in species-poor communities, generally comprising stable yet harsh conditions, physiological tolerance and competitive trade-offs limit both the number of species that occur and the loss of genotypes due to decreases in already constrained fitness. In species-rich communities, natural environmental conditions result in well-defined community structure and resource partitioning. Disturbance of these communities disrupts niche space, resulting in lower genotypic diversity despite the maintenance of species diversity. Our work provides a model to inform future research about relationships between species and genotypic biodiversity based on determining the biodiversity consequences of changing environmental context. [source]

Large-scale effect of aerosols on precipitation in the West African Monsoon region

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 640 2009
J. Huang
Abstract We used multi-year satellite observations to study aerosol effects on the large-scale variability in precipitation of the West African Monsoon (WAM) region, which is often impacted by high concentrations of desert dust and biomass-burning smoke. We find a statistically significant precipitation reduction associated with high aerosol concentration near the coast of the Gulf of Guinea from late boreal autumn to winter. The largest aerosol-related precipitation reduction (,1.5 mm d,1) is about 50% of the climatological mean precipitation in the region and occurs mainly at rain rates in the range of 2,17 mm d,1 off the northern coast of the Gulf of Guinea. This reduction cannot be linearly attributed to known climate and weather factors such as El Niño,Southern Oscillation, North Atlantic Oscillation, Atlantic sea-surface temperature, or water vapour. The fractional precipitation variance related to aerosol is about 13%, a value comparable to those related to the known climate factors. Based on the spatial pattern and seasonality of the observed precipitation reduction and its dependence on the rain rate, the observed negative correlation cannot be readily attributed to precipitation effects on aerosol by wet deposition or to rain and cloud contamination of satellite aerosol retrievals. We therefore suggest that our results can be taken as observational evidence of aerosol effects on precipitation. The aerosol associated with the observed precipitation reduction can be traced back to various African sources where large quantities of desert dust and biomass-burning smoke are emitted during much of the year. Given that the emissions of dust and smoke have varied considerably over the past several decades, in part attributable to human activities, our observed rainfall reduction may reflect an anthropogenic impact to some degree. Copyright © 2009 Royal Meteorological Society [source]

Multiple stressors and regime shifts in shallow aquatic ecosystems in antipodean landscapes

FRESHWATER BIOLOGY, Issue 2010
JENNY DAVIS
Summary 1. Changes in land management (land use and land cover) and water management (including extraction of ground water and diversion of surface waters for irrigation) driven by increases in agricultural production and urban expansion (and fundamentally by population growth) have created multiple stressors on global freshwater ecosystems that we can no longer ignore. 2. The development and testing of conceptual ecological models that examine the impact of stressors on aquatic ecosystems, and recognise that responses may be nonlinear, is now essential for identifying critical processes and predicting changes, particularly the possibility of catastrophic regime shifts or ,ecological surprises'. 3. Models depicting gradual ecological change and three types of regime shift (simple thresholds, hysteresis and irreversible changes) were examined in the context of shallow inland aquatic ecosystems (wetlands, shallow lakes and temporary river pools) in southwestern Australia subject to multiple anthropogenic impacts (hydrological change, eutrophication, salinisation and acidification). 4. Changes in hydrological processes, particularly the balance between groundwater-dominated versus surface water-dominated inputs and a change from seasonal to permanent water regimes appeared to be the major drivers influencing ecological regime change and the impacts of eutrophication and acidification (in urban systems) and salinisation and acidification (in agricultural systems). 5. In the absence of hydrological change, urban wetlands undergoing eutrophication and agricultural wetlands experiencing salinisation appeared to fit threshold models. Models encompassing alternative regimes and hysteresis appeared to be applicable where a change from a seasonal to permanent hydrological regime had occurred. 6. Irreversible ecological change has potentially occurred in agricultural landscapes because the external economic driver, agricultural productivity, persists independently of the impact on aquatic ecosystems. 7. Thematic implications: multiple stressors can create multiple thresholds that may act in a hierarchical fashion in shallow, lentic systems. The resulting regime shifts may follow different models and trajectories of recovery. Challenges for ecosystem managers and researchers include determining how close a system may be to critical thresholds and which processes are essential to maintaining or restoring the system. This requires an understanding of both external drivers and internal ecosystem dynamics, and the interactions between them, at appropriate spatial and temporal scales. [source]

Climatic influences and anthropogenic stressors: an integrated framework for streamflow management in Mediterranean-climate California, U.S.A.

FRESHWATER BIOLOGY, Issue 2010
THEODORE E. GRANTHAM
Summary 1. In Mediterranean and other water-stressed climates, water management is critical to the conservation of freshwater ecosystems. To secure and maintain water allocations for the environment, integrated water management approaches are needed that consider ecosystem flow requirements, patterns of human water demands and the temporal and spatial dynamics of water availability. 2. Human settlements in Mediterranean climates have constructed water storage and conveyance projects at a scale and level of complexity far exceeding those in other, less seasonal climates. As a result, multiple ecological stressors associated with natural periods of flooding and drying are compounded by anthropogenic impacts resulting from water infrastructure development. 3. Despite substantial investments in freshwater ecosystem conservation, particularly in California, U.S.A., success has been limited because the scales at which river management and restoration are implemented are often discordant with the temporal and spatial scales at which ecosystem processes operate. Often, there is also strong social and political resistance to restricting water allocation to existing consumptive uses for environmental protection purposes. Furthermore, institutions rarely have the capacity to develop and implement integrated management programmes needed for freshwater ecosystem conservation. 4. We propose an integrated framework for streamflow management that explicitly considers the temporal and spatial dynamics of water supply and needs of both human and natural systems. This approach makes it possible to assess the effects of alternative management strategies to human water security and ecosystem conditions and facilitates integrated decision-making by water management institutions. 5. We illustrate the framework by applying a GIS-based hydrologic model in a Mediterranean-climate watershed in Sonoma County, California, U.S.A. The model is designed to assess the hydrologic impacts of multiple water users distributed throughout a stream network. We analyse the effects of vineyard water management on environmental flows to (i) evaluate streamflow impacts from small storage ponds designed to meet human water demands and reduce summer diversions, (ii) prioritise the placement of storage ponds to meet human water needs while optimising environmental flow benefits and (iii) examine the environmental and social consequences of flow management policies designed to regulate the timing of diversions to protect ecosystem functions. 6. Thematic implications: spatially explicit models that represent anthropogenic stressors (e.g. water diversions) and environmental flow needs are required to address persistent and growing threats to freshwater biodiversity. A coupled human,natural system approach to water management is particularly useful in Mediterranean climates, characterised by severe competition for water resources and high spatial and temporal variability in flow regimes. However, lessons learned from our analyses are applicable to other highly seasonal systems and those that are expected to have increased precipitation variability resulting from climate change. [source]

Can macroinvertebrate rapid bioassessment methods be used to assess river health during drought in south eastern Australian streams?

FRESHWATER BIOLOGY, Issue 12 2008
PETER ROSE
Summary 1Despite significant concern about drought impacts in Australia, there have been no broad-scale studies of drought effects on river health. A severe and prolonged drought has been acting on many streams in south eastern Australia over the past decade. EPA Victoria has undertaken rapid bioassessment (RBA) of over 250 stream reference sites since 1990, providing an opportunity for a before-after-control-impact investigation of drought related changes to macroinvertebrate indices and water quality. This study uses data from 1990 to 2004 to critically evaluate the effectiveness of using RBA methods and indices, which were designed for assessment of human impacts, for monitoring streams during drought. 2Reference stream sites across Victoria (those with minimal anthropogenic disturbances and repeatedly sampled) were classified as being ,in drought' or ,not in drought' using the Bureau of Meteorology's rainfall deficiency definition. Four biological indices (SIGNAL, EPT, Family Richness and AUSRIVAS) were calculated for combined autumn and spring samples for edge and riffle habitats for the selected sites. 3General linear models and paired t -tests were used to detect drought related changes to index and water quality values at state-wide and bioregional scales. Changes in taxa constancy were examined to determine which taxa were sensitive to or benefited from drought conditions. Frequency of site failure against biological objectives specified in the State Environment Protection Policy (Waters of Victoria) (herein termed ,SEPP WoV') before and during drought was also examined to detect changes in a management context. 4Few significant changes in index values were detected for riffle habitat samples. Rates of failure against biological objectives were similar before and during drought for riffle samples. In contrast, edge habitat AUSRIVAS and SIGNAL scores were significantly reduced at the state-wide scale and most indices showed significant declines in the lower altitude forests, and foothills and coastal plains bioregions. 5Generally, more pollution tolerant, lentic taxa replaced sensitive and flow-requiring taxa in edge samples during drought. In contrast, there were few reductions in the taxa of riffle samples during drought. However, many pool preferring, but pollution sensitive taxa occurred more frequently in riffle areas. Hence, the riffle community began to resemble that of pools and edges. This was attributed to decreased flow and increased ,lentic' habitat opportunities in riffles. 6Detection of a drought effect was confined to the edge habitat and site failure could be assigned to drought and anthropogenic impacts, in conjunction or alone. The riffle sampling protocol was resistant to detection of drought effects as samples were only taken when sufficient water was present within this habitat. Therefore, biological changes at sites not meeting policy objectives for riffle habitats can be attributed to anthropogenic rather than drought impacts. [source]

Can taxonomic distinctness assess anthropogenic impacts in inland waters?

Benthic microbial respiration in Appalachian Mountain, Piedmont, and Coastal Plains streams of the eastern U.S.A.

FRESHWATER BIOLOGY, Issue 2 2002
B. H. Hill
1.,Benthic microbial respiration was measured in 214 streams in the Appalachian Mountain, Piedmont, and Coastal Plains regions of the eastern United States in summer 1997 and 1998. 2.,Respiration was measured as both O2 consumption in sealed microcosms and as dehydrogenase activity (DHA) of the sediments contained within the microcosms. 3.,Benthic microbial respiration in streams of the eastern U.S., as O2 consumption, was 0.37 ± 0.03 mg O2 m,2 day,1. Respiration as DHA averaged 1.21 ± 0.08 mg O2 m,2 day,1 4.,No significant differences in O2 consumption or DHA were found among geographical provinces or stream size classes, nor among catchment basins for O2 consumption, but DHA was significantly higher in the other Atlantic (non-Chesapeake Bay) catchment basins. 5.,Canonical correlation analyses generated two environmental axes. The stronger canonical axis (W1) represented a chemical disturbance gradient that was negatively correlated with signatures of anthropogenic impacts (ANC, Cl,, pH, SO42), and positively correlated with riparian canopy cover and stream water dissolved organic carbon concentration (DOC). A weaker canonical axis (W2) was postively correlated with pH, riparian zone agriculture, and stream depth, and negatively correlated with DOC and elevation of the stream. Oxygen consumption was significantly correlated with W2 whereas DHA was significantly correlated with W1. 6.,The strengths of the correlations of DHA with environmental variables, particularly those that are proven indicators of catchment disturbances and with the canonical axis, suggest that DHA is a more responsive measure of benthic microbial activity than is O2 consumption. [source]

The Deciduous Forest , Boreal Forest Ecotone

GEOGRAPHY COMPASS (ELECTRONIC), Issue 7 2010
David Goldblum
Ecotones have been subject to significant attention over the past 25 years as a consensus emerged that they might be uniquely sensitive to the effects of climate change. Most ecotone field studies and modeling efforts have focused on transitions between forest and non-forest biomes (e.g. boreal forest to Arctic tundra, forest to prairie, subalpine forests to alpine tundra) while little effort has been made to evaluate or simply understand forest,forest ecotones, specifically the deciduous forest , boreal forest ecotone. Geographical shifts and changes at this ecotone because of anthropogenic factors are tied to the broader survival of both the boreal and deciduous forest communities as well as global factors such as biodiversity loss and dynamics of the carbon cycle. This review summarizes what is known about the location, controlling mechanisms, disturbance regimes, anthropogenic impacts, and sensitivity to climate change of the deciduous forest , boreal forest ecotone. [source]

Stress synergy between drought and a common environmental contaminant: studies with the collembolan Folsomia candida

GLOBAL CHANGE BIOLOGY, Issue 4 2001
Rikke Højer
Summary The term global change is used predominantly in connection with the global temperature increase and associated changes in weather patterns over the next century. In a broader sense it also covers other anthropogenic impacts on the environment such as habitat fragmentation and pollution. The individual effects of each of these stress types have been extensively studied in the biota. However, organisms will frequently encounter these stress types in combination rather than alone and there is little information available on the effects of stress combinations. Here an examination is made of the interaction between realistic levels of summer drought and a common contaminant of agricultural soil (4-nonylphenol, NP), on a widespread soil invertebrate, the collembolan Folsomia candida. These stress factors were tested individually and in combination using a full factorial design. This approach revealed the existence of highly significant Bliss type synergistic interaction between the two stress types. Thus, exposure to NP significantly reduced the drought tolerance of this organism and, reciprocally, the toxicity of NP (LC50) during realistic summer drought was more than doubled in comparison to the value obtained under optimal soil moisture conditions. Furthermore, it is shown that NP has a detrimental effect on the physiological mechanisms underlying this animal's drought tolerance, thus providing some explanation for the mechanisms involved in the synergy. It is argued that this type of synergy is unlikely to be confined to this particular combination of stresses and thus there is a need to study the interactions between dominant natural stresses and pollution. The most important implication of these results is that some of the effects of global climate changes can be predicted to be most severe in polluted areas. [source]

Testing alternate ecological approaches to seagrass rehabilitation: links to life-history traits

JOURNAL OF APPLIED ECOLOGY, Issue 5 2010
Andrew D. Irving
Summary 1.,Natural resources and ecosystem services provided by the world's major biomes are increasingly threatened by anthropogenic impacts. Rehabilitation is a common approach to recreating and maintaining habitats, but limitations to the success of traditional techniques necessitate new approaches. 2.,Almost one-third of the world's productive seagrass meadows have been lost in the past 130 years. Using a combined total of three seagrass species at seven sites over 8 years, we experimentally assessed the performance of multiple rehabilitation methods that utilize fundamentally different ecological approaches. 3.,First, traditional methods of transplantation were tested and produced varied survival (0,80%) that was site dependent. Secondly, seedling culture and outplanting produced poor survival (2,9%) but reasonable growth. Finally, a novel method that used sand-filled bags of hessian to overcome limitations of traditional techniques by facilitating recruitment and establishment of seedlings in situ produced recruit densities of 150,350 seedlings m,2, with long-term survival (up to 38 months) ranging from 0 to 72 individuals m,2. 4.,Results indicate that facilitating seagrass recruitment in situ using hessian bags can provide a new tool to alleviate current limitations to successful rehabilitation (e.g. mobile sediments, investment of time and resources), leading to more successful management and mitigation of contemporary losses. Hessian bags have distinct environmental and economic advantages over other methods tested in that they do not damage existing meadows, are biodegradable, quick to deploy, and cost less per hectare (US$16 737) than the estimated ecosystem value of seagrass meadows (US$27 039 year,1). 5.,Synthesis and applications. This research demonstrates how exploring alternate ecological approaches to habitat rehabilitation can expand our collective toolbox for successfully re-creating complex and productive ecosystems, and alleviate the destructive side-effects and low success rates of more traditional techniques. Moreover, new methods can offer economic and environmental solutions to the restrictions placed upon managers of natural resources. [source]

California annual grass invaders: the drivers or passengers of change?

JOURNAL OF ECOLOGY, Issue 5 2010
Janneke HilleRisLambers
Summary 1.,The dominance of invasive species is often assumed to reflect their competitive superiority over displaced native species. However, invasive species may be abundant because of their greater tolerance to anthropogenic impacts accompanying their introduction. Thus, invasive species can either be the drivers or passengers of change. 2.,We distinguish between these two possibilities in California grasslands currently dominated by Mediterranean annuals (exotics) and subjected to livestock grazing since European settlement. We focused on native annual grasses and forbs, an understudied species-rich component of the California flora, and Mediterranean annual grasses, currently dominant and among the first non-native plants introduced to the area. 3.,We established a field experiment with fenced and unfenced blocks in a cattle pasture. We measured concentrations of limiting resources (nitrogen, phosphorus, light and soil moisture) in monoculture plots as an index of competitive ability (i.e. R*). We then quantified grazing impacts on biomass and seed production in grazed vs. ungrazed monoculture plots. Finally, we measured biomass and seed production of each species competing in mixture plots, in the presence and absence of grazers. 4.,We found that native and exotic species did not differ in R* indices of competitive ability, i.e. concentrations of limiting resources in ungrazed native monoculture plots did not differ from concentrations in ungrazed exotic monoculture plots. By contrast, exotic annuals suffered less from grazing than native annuals, perhaps reflecting their longer evolutionary history with cattle grazing. Consistent with these results, native and exotic annuals were equally abundant in ungrazed mixtures, but exotic species overwhelmingly dominated grazed mixtures. 5.,Species able to draw down nitrogen and light to lower levels in monocultures (i.e. those with lower R* values) dominated biomass and seeds in mixed plots without grazers. However, R* did not predict the relative abundance of species in grazed plots. Moreover, the relative abundance of species in mixtures did not correlate with grazing impacts on their monocultures, implying that grazing alters inter-specific competitive dynamics. 6.,Synthesis. We demonstrate that the displacement of native annuals by Mediterranean annual grasses in California may largely have been driven by cattle grazing. [source]

Plant functional types do not predict biomass responses to removal and fertilization in Alaskan tussock tundra

JOURNAL OF ECOLOGY, Issue 4 2008
M. Syndonia Bret-Harte
Summary 1Plant communities in natural ecosystems are changing and species are being lost due to anthropogenic impacts including global warming and increasing nitrogen (N) deposition. We removed dominant species, combinations of species and entire functional types from Alaskan tussock tundra, in the presence and absence of fertilization, to examine the effects of non-random species loss on plant interactions and ecosystem functioning. 2After 6 years, growth of remaining species had compensated for biomass loss due to removal in all treatments except the combined removal of moss, Betula nana and Ledum palustre (MBL), which removed the most biomass. Total vascular plant production returned to control levels in all removal treatments, including MBL. Inorganic soil nutrient availability, as indexed by resins, returned to control levels in all unfertilized removal treatments, except MBL. 3Although biomass compensation occurred, the species that provided most of the compensating biomass in any given treatment were not from the same functional type (growth form) as the removed species. This provides empirical evidence that functional types based on effect traits are not the same as functional types based on response to perturbation. Calculations based on redistributing N from the removed species to the remaining species suggested that dominant species from other functional types contributed most of the compensatory biomass. 4Fertilization did not increase total plant community biomass, because increases in graminoid and deciduous shrub biomass were offset by decreases in evergreen shrub, moss and lichen biomass. Fertilization greatly increased inorganic soil nutrient availability. 5In fertilized removal treatments, deciduous shrubs and graminoids grew more than expected based on their performance in the fertilized intact community, while evergreen shrubs, mosses and lichens all grew less than expected. Deciduous shrubs performed better than graminoids when B. nana was present, but not when it had been removed. 6Synthesis. Terrestrial ecosystem response to warmer temperatures and greater nutrient availability in the Arctic may result in vegetative stable-states dominated by either deciduous shrubs or graminoids. The current relative abundance of these dominant growth forms may serve as a predictor for future vegetation composition. [source]

The Role of Climate and Human Influences in the Dry-Up of the Jinci Springs, China,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2009
Yonghong Hao
Abstract:, One of the largest karst springs in North China, the Jinci Springs, dried up and has remained dry since 1994. We develop a correlation analysis with time-lag and a regression analysis with time-lag to study the relation between spring flow and precipitation. This allows us to obtain a better understanding of karst hydrological processes by differentiating the contribution of variation in precipitation from anthropogenic impacts on the dry-up of Jinci Springs. We divided the karstic hydrological processes into two phases: pre-1961 and post-1961. In the first phase (i.e., 1954-1960) the groundwater recharge was affected by precipitation alone, and in the second phase (i.e., 1961-1994) the groundwater recharge was influenced by both precipitation and human activities. Using precipitation and groundwater recharge data in the first phase, we set up a groundwater recharge model with time-lags. By running the time-lags model, we acquired the groundwater recharge likely to occur under the sole effect of precipitation in the second phase. Using a water-balance calculation, we conclude that the groundwater recharge exhibited statistical stationarity, and the Jinci Springs dry-up was the result of anthropogenic activities. At least three specific types of anthropogenic activities contributed to the drying-up of Jinci Springs: (1) groundwater pumping accounts for 51%, (2) the dewatering from coal mining accounts for 33%, (3) and dam-building 14%. The drying-up of Jinci Springs meant that the groundwater drained from the aquifer's fractures, and subsequently changed the structure of the karst aquifer. Although groundwater exploitation has been reduced, the flow at Jinci Springs has not reoccurred. [source]

Prediction of Lake Baikal ecosystem behaviour using an ecosystem disturbance model,

LAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2001
Eugene A. Silow
Abstract This paper combines predictions of the effects of anthropogenic impacts on the plankton of Lake Baikal with models of ecosystem disturbance. Increases in mineralization, non-toxic organic matter, nutrients, phenolic compounds, oil products and heavy metals were simulated. Significantly higher sensitivity of the community below the ice to external influences was demonstrated compared to the summer,autumn community, when there was no ice layer. Models of the distribution of aquatic pollutants demonstrate the occurrence of deviations from ecosystem state parameters in the bottom layer under the influence of pollutant input with precipitation and the distribution of perturbations over greater (up to 500 km) distances. Simulation of pollutant input at present levels shows that Lake Baikal is already perturbed. This is indicated by increases in bacterial and summer phytoplankton biomass and nutrient concentration, and by fluctuations in the zooplankton biomass. [source]

The thermal regime of soils in the north of Western Siberia

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2002
A. V. Pavlov
Abstract The results of long-term stationary observations upon the thermal regime of soils in natural and anthropogenically-disturbed tundra and northern taiga landscapes in the north of Western Siberia are discussed. Quantitative assessments of the heating effect of snow cover and the cooling effect of surface organic layer on soil temperatures in both winter and summer seasons are given. Spatial and temporal variations in the depth of seasonal thaw and soil temperatures in the tundra and taiga zones are outlined. Data on changes in soil temperature regimes following disturbance of surface organic layers are presented. Contemporary tendencies in permafrost degradation induced by climatic warming, changes in the snow cover depth, and anthropogenic impacts are shown. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Soil Nitrogen Pools Associated with Revegetation of Disturbed Sites in the Lake Tahoe Area

RESTORATION ECOLOGY, Issue 2 2002
V. P. Claassen
Abstract Thin, poorly developed soils in the high elevation, summer-dry environment near Lake Tahoe, California are easily disturbed by anthropogenic impacts. Subsoils and parent materials that are exposed by vegetation removal and topsoil erosion or by burial during construction activities are difficult to revegetate and may continue to erode for decades after disturbance. The resulting sediment loads contribute to decreased water quality in local watersheds and to the loss of clarity in Lake Tahoe. Field observations suggest that soil disturbance often results in depletion of soil nitrogen (N) reserves and that the remaining substrates may be unable to provide adequate N for revegetation. To quantify the levels of soil N that are associated with higher levels of percent plant cover on previously disturbed soils in the Lake Tahoe area, a basin-wide survey and a second paired site study were conducted. Results indicate that extractable ammonium and nitrate levels correlate poorly with percent vegetative cover, whereas the correlations of anaerobically mineralizable N and total N are stronger and account for nearly 50% of the variability in plant cover data. Sites with plant cover measuring greater than 40% are associated with total soil N levels of about 1,200 kg N/ha and anaerobic mineralizable N levels of about 26 kg N/ha. Despite high concentrations of N in the surface soils, a large fraction of the N in the 0- to 50-cm profile occurs below 30 cm, when measured on a landscape basis. [source]

Using T-PODs to assess variations in the occurrence of coastal bottlenose dolphins and harbour porpoises

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2010
Helen Bailey
Abstract 1.Assessments of anthropogenic impacts on cetaceans are often constrained by limited data on the extent to which these species use particular areas. 2.Timing porpoise detectors (T-PODs) are autonomous data recorders for detecting cetacean echolocation clicks, potentially providing cost-effective opportunities for monitoring cetacean occurrence. 3.The performance of T-PODs was assessed in three areas off the Scottish east coast, where the relative occurrence of bottlenose dolphins and harbour porpoises was known to differ. Land-based observations in one area compared visual and acoustic detections of dolphins, while direct hydrophone recordings of dolphin echolocation clicks were compared with T-POD detections during boat surveys. 4.Land-based surveys recorded 89 groups of dolphins within 900 m of the T-POD. All groups spending >30,min in the area were detected on the T-POD, and the probability of detection declined in relation to distance from the recording site. 5.The number of dolphin clicks recorded on the independent hydrophone system was significantly related to the number detected by a T-POD. Between pairs of T-PODs, there was also significant correlation with the numbers of clicks recorded in each hour, both for channels set to detect bottlenose dolphins and for channels set to detect harbour porpoises. 6.Year-round deployments of paired T-PODs detected significant geographical variation in detections for both bottlenose dolphins and harbour porpoises. This pattern reflected published data from visual surveys, where dolphins occurred most regularly within the Moray Firth Special Area of Conservation, and porpoises were sighted more regularly in offshore waters. 7.T-PODs do not detect all cetaceans in the area, and care must be taken when interpreting data from mixed species communities. Nevertheless, these results confirm that T-PODs provide an effective method for monitoring the occurrence of bottlenose dolphins and harbour porpoises, and provide excellent potential for collecting baseline data from poorly studied areas and monitoring long-term temporal change in key areas of interest. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A Marquesan coral reef (French Polynesia) in historical context: an integrated socio-ecological approach

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2009
Shankar Aswani
Abstract 1.Marine biologists are increasingly aware of the impact that even small human populations can have on coral reefs around the world, while conservationists and fisheries managers have a growing appreciation of the importance of culturally informed management strategies in coral reef conservation efforts. Despite these recognitions, however, examples of integrated field studies are limited. 2.In this paper evidence from various disciplines is used to study the interaction between humans and one of the largest reefs in the Marquesas Islands, at Anaho Bay, Nuku Hiva Island, with the aim of assessing possible anthropogenic impacts over time. 3.First, it reports on a marine biological survey of the benthic substrates of the bay and the taxonomic composition and spatial distributions of the local fish species. Second, it draws on results from an ongoing archaeological study and integrates these with interviews of village elders to gain a historical perspective on the reef and potential human impacts. 4.The biological results indicated that the reef is in a state of decline, although fish densities are moderately high. The archaeological evidence, in turn, demonstrates that human populations have occupied this valley for at least the last 700 years. Throughout this period marine resources have been an important source of both food and raw materials for tools. The archaeological study also highlights aspects of landscape change, both natural and human-induced, that probably have been detrimental to reef health. 5.Using the combined biological and anthropological data, this paper considers the nexus of factors that have led to the current reef conditions and considers management issues for the future. Key in this regard are processes that have initiated erosion and soil run-off, and fluctuations in the local human populations. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Dynamic ecosystem models and the evaluation of ecosystem effects of fishing: can we make meaningful predictions?

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2003
L.A. Robinson
Abstract 1.Fishing is one of the most widespread anthropogenic impacts on marine ecosystems. In recent times, the development of measurable metrics of the resultant ecosystem effects, has become an important aspect of fisheries management. Ecosystem models are often advocated as tools for the evaluation of system effects, but the extent to which models are able to make meaningful predictions, has not yet been fully addressed. 2.In order to assess the suitability of models, to evaluate ecosystem effects of fisheries, the direct and indirect effects were catalogued. 3.From the literature, 33 applications of marine ecosystem models were identified for analysis of their ability to fully assess these catalogued effects. Analysis was possible for only 24 of the models due to poor documentation of the other 9. 4.Each model was examined for their inclusion of nine functional groups, deemed essential for the assessment of impacts of fishing on the whole ecosystem (e.g. detritus, marine mammals). The models were also assessed for their inclusion of several additional factors, either fundamental in the regulation of marine ecosystems (e.g. environmental forcing), or important in the classification of their role as a predictor of changes in ecological processes (e.g. simulation, spatial properties). 5.No model formulation provided coverage in all the areas necessary to cover the identified effects of fisheries. Eight models provided good coverage, nutrient dynamics and benthos were the least well represented aspects of the ecosystem. 6.The ECOPATH with Ecosim family of models, the European Regional Seas Ecosystem Model (ERSEM) and the Anderson & Ursin multispecies extension to the Beverton & Holt model all seem likely to yield good insights. 7.In further developing these models, however, consideration must be given to explicitly incorporate spatial factors and extrinsic forcing functions, such as climate. Copyright © 2002 John Wiley & Sons, Ltd. [source]