Community Response to Cumulative Toxic Impact: Effects of Acclimation on Zinc Tolerance of Aufwuchs

1992 ◽  
Vol 49 (10) ◽  
pp. 2155-2163 ◽  
Author(s):  
B. R. Niederlehner ◽  
John Cairns Jr.
Keyword(s):  
Second Generation ◽  
Community Response ◽  
Artificial Substrates ◽  
Community Respiration ◽  
Additional Stress ◽  
Total Biomass ◽  
Secondary Stress ◽  
Initial State ◽  
Zinc Tolerance ◽  
Zn Stress

Aufwuchs communities were developed on artificial substrates in a local pond. Second-generation communities were developed on identical substrates in laboratory systems receiving three levels of zinc (Zn): background, 73, and 172 μg∙L−1. After 21 d, second-generation communities were exposed to five concentrations of Zn ranging from background to 10 078 μg∙L−1 for 48 h. Protozoan communities developed under Zn stress were initially less rich taxonomically but subsequently lost fewer species in response to acute Zn exposures. Richness remaining after exposure to high Zn levels [Formula: see text] was similar for all groups. Taxonomic composition changed less in acclimated communities than in the control in response to secondary stress. Gross primary productivity was less impaired by secondary stress in communities acclimated to Zn. Community respiration, algal biomass, total biomass, respiration to biomass ratios, and ratios of soluble to total reactive phosphates did not differ in response to secondary stress. In general, communities developed under Zn stress were initially impaired but changed less in response to additional stress relative to their initial state.

Homeostatic Characteristics of Single Species Fish Stocks in Arctic Lakes

1983 ◽  
Vol 40 (7) ◽  
pp. 987-1024 ◽  
Author(s):  
Lionel Johnson
Keyword(s):  
Stock Returns ◽  
Dominant Species ◽  
Size Structure ◽  
Arctic Charr ◽  
Arctic Lakes ◽  
Large Individual ◽  
Total Biomass ◽  
Length Frequency ◽  
Initial State ◽  
Fish Stocks

The results of investigations on the fish stocks of seven Arctic lakes covering a period of 23 yr are described. These lakes have remained largely undisturbed since their formation in late glacial times; all but one are completely autonomous and of comparatively small size. Such lakes provide a unique opportunity for the development and testing of conceptual models. In all cases the only fish species present is Arctic charr, Salvelinus alpinus. Length frequency distributions derived from gillnet catch curves are shown to be, within reasonable limits, representative of the actual populations in the lake, and not artifacts of the sampling procedure. Length frequency curves show a unimodal or bimodal distribution and this structure, in the absence of perturbation, appears to remain constant indefinitely. Individuals are of great age but age-at-length is highly variable. Age and size structure are shown to be comparable with the age and size structure of the dominant tree species in a climax forest; it is concluded that forces of great generality fashion these configurations. It is hypothesized that all species tend to move towards a state of least energy dissipation; this can be most readily seen in the dominant species at the climax in an autonomous system. The dominant species is characterized by large individual size, a high degree of uniformity, high total biomass, great mean age, indeterminate age-at-death, and a low incidence of replacement stock. After severe perturbation it is shown that the charr stock returns to a state of least dissipation without oscillation. Absence of oscillation during the return to the initial state, combined with the long-term stability shown in control lakes, indicates the presence of an effective damping mechanism; this in turn indicates the existence of organization within the stock as a whole. Organization develops through an interactive mechanism described under the doctrine of homeokinesis, which is responsible for energy equipartitioning and the maintenance of uniformity. These concepts help to explain phenomena observed in more complex systems and help our understanding of ecosystem functioning.

scholarly journals Patterns of carbon processing at the seafloor: the role of faunal and microbial communities in moderating carbon flows

2016 ◽  
Vol 13 (15) ◽  
pp. 4343-4357 ◽  
Author(s):  
Clare Woulds ◽  
Steven Bouillon ◽  
Gregory L. Cowie ◽  
Emily Drake ◽  
Jack J. Middelburg ◽  
...  
Keyword(s):  
Bacterial Biomass ◽  
Coarse Grained ◽  
Community Respiration ◽  
Total Biomass ◽  
Coastal Zones ◽  
Organic C ◽  
Sand Flat ◽  
Permeable Sediments ◽  
C Cycling ◽  
Wide Range

Abstract. Marine sediments, particularly those located in estuarine and coastal zones, are key locations for the burial of organic carbon (C). However, organic C delivered to the sediment is subjected to a range of biological C-cycling processes, the rates and relative importance of which vary markedly between sites, and which are thus difficult to predict. In this study, stable isotope tracer experiments were used to quantify the processing of C by microbial and faunal communities in two contrasting Scottish estuarine sites: a subtidal, organic C rich site in Loch Etive with cohesive fine-grained sediment, and an intertidal, organic C poor site on an Ythan estuary sand flat with coarse-grained permeable sediments. In both experiments, sediment cores were recovered and amended with 13C labelled phytodetritus to quantify whole community respiration of the added C and to trace the isotope label into faunal and bacterial biomass. Similar respiration rates were found in Loch Etive and on the Ythan sand flat (0.64 ± 0.04 and 0.63 ± 0.12 mg C m−2h−1, respectively), which we attribute to the experiments being conducted at the same temperature. Faunal uptake of added C over the whole experiment was markedly greater in Loch Etive (204 ± 72 mg C m−2) than on the Ythan sand flat (0.96 ± 0.3 mg C m−2), and this difference was driven by a difference in both faunal biomass and activity. Conversely, bacterial C uptake over the whole experiment in Loch Etive was much lower than that on the Ythan sand flat (1.80 ± 1.66 and 127 ± 89 mg C m−2, respectively). This was not driven by differences in biomass, indicating that the bacterial community in the permeable Ythan sediments was particularly active, being responsible for 48 ± 18 % of total biologically processed C. This type of biological C processing appears to be favoured in permeable sediments. The total amount of biologically processed C was greatest in Loch Etive, largely due to greater faunal C uptake, which was in turn a result of higher faunal biomass. When comparing results from this study with a wide range of previously published isotope tracing experiments, we found a strong correlation between total benthic biomass (fauna plus bacteria) and total biological C processing rates. Therefore, we suggest that the total C-cycling capacity of benthic environments is primarily determined by total biomass.

scholarly journals The gravitational stability of the Earth

1907 ◽  
Vol 79 (529) ◽  
pp. 194-199 ◽  
Keyword(s):  
Initial Stress ◽  
Gravitational Instability ◽  
Direct Method ◽  
Elastic Solid ◽  
Frequency Equation ◽  
The Body ◽  
Additional Stress ◽  
Initial State ◽  
Planetary Body ◽  
The Earth

The problem of determining the conditions, as regards elasticity, in which a body of planetary dimensions can be gravitationally unstable, was attacked by J. H. Jeans. To turn the difficulty arising from the fact that such a body is necessarily in a state of “ initial stress,” by which gravitation is balanced throughout its interior, he introduced an artificial external field of force to balance gravitation in the undisturbed body, and he thus dispensed with initial stress. A more direct method of treating the problem has been advocated by Lord Rayleigh. In this method the stress at any point of the body, when disturbed from its equilibrium state, is taken to be com­pounded of two stress-systems ; an initial stress of the nature of hydrostatic pressure, balancing gravitation in the undisturbed body, and an additional stress connected with the strain (reckoned from the initial state) by the same formulæ as connect stress with strain in a homogeneous isotropic elastic solid body which is slightly strained from an initial state of zero stress. In the first part of the present paper the equations of vibratory motion of the planetary body, assumed to be initially spherical, are formed in accordance with this method, and they are solved by means of spherical harmonics. The frequency equation is obtained, and the conditions that it may be satisfied by a zero value of the frequency are found. When these conditions are fulfilled the body is in a state of gravitational instability.

scholarly journals To Modulate Survival under Secondary Stress Conditions, Listeria monocytogenes 10403S Employs RsbX To Downregulate σBActivity in the Poststress Recovery Stage or Stationary Phase

2015 ◽  
Vol 82 (4) ◽  
pp. 1126-1135 ◽  
Author(s):  
Ye Xia ◽  
Yongping Xin ◽  
Xiaoliang Li ◽  
Weihuan Fang
Keyword(s):  
Listeria Monocytogenes ◽  
Stationary Phase ◽  
Parent Strain ◽  
Recovery Period ◽  
Negative Regulator ◽  
Secondary Stress ◽  
Initial State ◽  
Recovery Stage ◽  
Content Type ◽  
Primary Stress

ABSTRACTListeria monocytogenesis a saprophytic bacterium that thrives in diverse environments and causes listeriosis via ingestion of contaminated food. RsbX, a putative sigma B (σB) regulator, is thought to maintain the ready state in the absence of stress and reset the bacterium to the initial state in the poststress stage inBacillus subtilis. We wondered whether RsbX is functional inL. monocytogenesunder different stress scenarios. Genetic deletion and complementation of thersbXgene were combined with survival tests and transcriptional and translational analyses of σBexpression in response to stresses. We found that deletion ofrsbXincreased survival under secondary stress following recovery of growth after primary stress or following stationary-phase culturing. The ΔrsbXmutant had higher expression of σBthan its parent strain in the recovery stage following primary sodium stress and in stationary-phase cultures. Apparently, increased σBexpression had contributed to improved survival in the absence of RsbX. There were no significant differences in survival rates or σBexpression levels in response to primary stresses between thersbXmutant and its parent strain during the exponential phase. Therefore, we provide clear evidence that RsbX is a negative regulator ofL. monocytogenesσBduring the recovery period after a primary stress or in the stationary phase, thus affecting its survival under secondary stress.

scholarly journals A Trait-Based Clustering for Phytoplankton Biomass Modeling and Prediction

Diversity ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 295
Author(s):  
Crispin M. Mutshinda ◽  
Zoe V. Finkel ◽  
Claire E. Widdicombe ◽  
Andrew J. Irwin
Keyword(s):  
Phytoplankton Biomass ◽  
Environmental Changes ◽  
Community Response ◽  
Total Biomass ◽  
Prediction Errors ◽  
Functional Type ◽  
Modeling And Prediction ◽  
Functional Types ◽  
Biomass Dynamics

When designing models for predicting phytoplankton biomass or characterizing traits, it is useful to aggregate the myriad of species into a few biologically meaningful groups and focus on group-level attributes, the common practice being to combine phytoplankton species by functional types. However, biogeochemists and plankton ecologists debate the most applicable grouping for describing phytoplankton biomass patterns and predicting future community structure. Although trait-based approaches are increasingly being advocated, methods are missing for the generation of trait-based taxa as alternatives to functional types. Here we introduce such a method and demonstrate the usefulness of the resulting clustering with field data. We parameterize a Bayesian model of biomass dynamics and analyze long-term phytoplankton data collected at Station L4 in the Western English Channel between April 2003 and December 2009. We examine the tradeoffs encountered regarding trait characterization and biomass prediction when aggregating biomass by (1) functional types, (2) the trait-based clusters generated by our method, and (3) total biomass. The model conveniently extracted trait values under the trait-based clustering, but required well-constrained priors under the functional type categorization. It also more accurately predicted total biomass under the trait-based clustering and the total biomass aggregation with comparable root mean squared prediction errors, which were roughly five-fold lower than under the functional type grouping. Although the total biomass grouping ignores taxonomic differences in phytoplankton traits, it predicts total biomass change as well as the trait-based clustering. Our results corroborate the value of trait-based approaches in investigating the mechanisms underlying phytoplankton biomass dynamics and predicting the community response to environmental changes.

Use of Artificial Substrates to Estimate Prey Resources available to a Visually Feeding Benthivorous Fish

1990 ◽  
Vol 47 (4) ◽  
pp. 789-793 ◽  
Author(s):  
Blake R. Konkle ◽  
Nicholas C. Collins ◽  
Robert L. Baker
Keyword(s):  
Prey Availability ◽  
Lepomis Macrochirus ◽  
Stomach Contents ◽  
Artificial Substrates ◽  
Total Biomass ◽  
Benthivorous Fish ◽  
Taxonomic Range ◽  
Prey Resources ◽  
Lake Variation ◽  
Food Exploitation

Empirically derived estimates of prey resources using conventional sampling methods are generally poor indices of actual food available to visually feeding benthivorous fish. We preferentially sampled the most active fraction of the benthos (presumably that most detectable by fish) utilizing short-term (4 d) colonization of artificial substrates, and used colonist biomass to explain temporal variation in stomach contents of bluegill sunfish (Lepomis macrochirus) in Lake Opinicon, Ontario. Simple linear regressions showed that total biomass of colonists explained 75% of the variance in the biomass of stomach contents. Independent variables using a limited taxonomic range or size range of colonists explained less variance in stomach contents. The convenience and simplicity of this methodology, and its ability to explain within-lake variation in food exploitation by visual benthivores, suggest that artificial substrate colonization could be useful for surveys of prey availability to benthivorous fishes.

scholarly journals Patterns of carbon processing at the seafloor: the role of faunal and microbial communities in moderating carbon flows

2016 ◽  
Author(s):  
C. Woulds ◽  
S. Bouillon ◽  
G. L. Cowie ◽  
E. Drake ◽  
Jack J. Middelburg ◽  
...  
Keyword(s):  
Bacterial Biomass ◽  
Coarse Grained ◽  
Community Respiration ◽  
Total Biomass ◽  
Coastal Zones ◽  
Organic C ◽  
Sand Flat ◽  
Permeable Sediments ◽  
C Cycling ◽  
Wide Range

Abstract. Marine sediments, particularly those located in estuarine and coastal zones, are key locations for the burial of organic carbon (C). However, organic C delivered to the sediment is subjected to a range of biological C-cycling processes, the rates and relative importance of which vary markedly between sites, and which are thus difficult to predict. In this study, stable isotope tracer experiments were used to quantify the processing of C by microbial and faunal communities in two contrasting Scottish estuarine sites: a subtidal, organic C rich site in Loch Etive with cohesive fine-grained sediment, and an intertidal, organic C poor site on an Ythan estuary sand flat with coarse- grained permeable sediments. In both experiments, sediment cores were recovered and amended with 13C labelled phytodetritus to quantify whole community respiration of the added C and to trace the isotope label into faunal and bacterial biomass. Similar respiration rates were found in Loch Etive and on the Ythan sand flat (0.64±0.04 and 0.63±0.12 mg C m−2 h−1, respectively), which we attribute to the experiments being conducted at the same temperature. Faunal uptake of added C over the whole experiment was markedly greater in Loch Etive (204±72 mg C m−2) than on the Ythan sand flat (0.96±0.3mg C m−2), and this difference was driven by a difference in both faunal biomass and activity. Conversely, bacterial C uptake over the whole experiment in Loch Etive was much lower than that on the Ythan sand flat (1.80±1.66 and 127±89 mg C m−2 respectively). This was not driven by differences in biomass, indicating that the bacterial community in the permeable Ythan sediments was particularly active, being responsible for 48±18% of total biologically processed C. This type of biological C processing appears to be favoured in permeable sediments. The total amount of biologically processed C was greatest in Loch Etive, largely due to greater faunal C uptake, which was in turn a result of higher faunal biomass. When comparing results from this study with a wide range of previously published isotope tracing experiments, we found a strong correlation between total benthic biomass (fauna plus bacteria) and total biological C processing rates. Therefore, we suggest that the total C cycling capacity of benthic environments is primarily determined by total biomass.

Benthic Responses to Wet-Weather Discharges in Urban Streams in Southern Ontario

2004 ◽  
Vol 39 (4) ◽  
pp. 374-391 ◽  
Author(s):  
Lee Grapentine ◽  
Quintin Rochfort ◽  
Jiri Marsalek
Keyword(s):  
Spatial Scales ◽  
Sediment Toxicity ◽  
Benthic Communities ◽  
Community Response ◽  
Artificial Substrates ◽  
Urban Stream ◽  
Toxicity Tests ◽  
Biological Degradation ◽  
Response Dynamics ◽  
Wet Weather

Abstract Urban stormwater and combined sewer overflow (CSO) discharges are important sources of sediment and contaminants (trace metals, PAHs, nutrients and road salts), and cause changes in flow, sediment, chemical and thermal regimes of receiving waters. Over the past several years, benthic conditions of streams representing a range of exposure environments were assessed in Hamilton, Toronto, Oshawa and Kingston, Ontario. Studies progressed from initial surveys of sediment contaminant levels, sediment toxicity and benthic invertebrate community structure to more spatially intensive sampling and experimental approaches that included the use of artificial substrates, in situ water toxicity tests and measurements of contaminant bioaccumulation. Results showed that while sediments and some biota at sites exposed to wet-weather discharges were often contaminated with metals and PAHs and enriched with nutrients, significant biological degradation measured by sediment toxicity or depauperated benthic communities was not evident. Exposure to stormwater discharges at sites below outfalls could alter the composition of benthic communities, but these effects were not strongly related to contaminant concentrations in sediment or invertebrate tissue. No outfall-associated toxicity was observed for caged amphipods held in the water column. Effects of wet-weather discharges on benthic communities at the urban stream sites studied appear to be small, and their detection was limited by several inherent conditions, including natural heterogeneity in the distribution of benthic invertebrates, episodic (intermittent) exposure to discharges and contaminant fluxes allowing some recovery, “background” levels of disturbance, poorly delineated changes in communities caused by physical effects such as flow and sediment transport, and community response dynamics. Detection of stormwater discharge effects should be improved by sampling on smaller temporal and multiple spatial scales to better quantify stressor exposure and invertebrate responses.

scholarly journals Next-generation cellulosic ethanol technologies and their contribution to a sustainable Africa

2011 ◽  
Vol 1 (2) ◽  
pp. 196-211 ◽  
Author(s):  
W. H. van Zyl ◽  
A. F. A. Chimphango ◽  
R. den Haan ◽  
J. F. Görgens ◽  
P. W. C. Chirwa
Keyword(s):  
Cellulosic Ethanol ◽  
Second Generation ◽  
Consolidated Bioprocessing ◽  
Low Cost ◽  
Electricity Production ◽  
Transport Sector ◽  
Total Biomass ◽  
Wealth Creation ◽  
Human Needs ◽  
The Past

The world is currently heavily dependent on oil, especially in the transport sector. However, rising oil prices, concern about environmental impact and supply instability are among the factors that have led to greater interest in renewable fuel and green chemistry alternatives. Lignocellulose is the only foreseeable renewable feedstock for sustainable production of transport fuels. The main technological impediment to more widespread utilization of lignocellulose for production of fuels and chemicals in the past has been the lack of low-cost technologies to overcome the recalcitrance of its structure. Both biological and thermochemical second-generation conversion technologies are currently coming online for the commercial production of cellulosic ethanol concomitantly with heat and electricity production. The latest advances in biological conversion of lignocellulosics to ethanol with a focus on consolidated bioprocessing are highlighted. Furthermore, integration of cellulosic ethanol production into existing bio-based industries also using thermochemical processes to optimize energy balances is discussed. Biofuels have played a pivotal yet suboptimal role in supplementing Africa's energy requirements in the past. Capitalizing on sub-Saharan Africa's total biomass potential and using second-generation technologies merit a fresh look at the potential role of bioethanol production towards developing a sustainable Africa while addressing food security, human needs and local wealth creation.

Tensile Failure of 55-Nitinol Wire

1975 ◽  
Vol 33 ◽  
pp. 46-47
Author(s):  
F. I. Grace
Keyword(s):  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Stoichiometric Composition ◽  
Tensile Failure ◽  
Initial State ◽  
Initial Shape ◽  
Nitinol Wire ◽  
Cscl Type ◽  
Shear Transformation

An interest in NiTi alloys with near stoichiometric composition (55 NiTi) has intensified since they were found to exhibit a unique mechanical shape memory effect at the Naval Ordnance Laboratory some twelve years ago (thus refered to as NITINOL alloys). Since then, the microstructural mechanisms associated with the shape memory effect have been investigated and several interesting engineering applications have appeared.The shape memory effect implies that the alloy deformed from an initial shape will spontaneously return to that initial state upon heating. This behavior is reported to be related to a diffusionless shear transformation which takes place between similar but slightly different CsCl type structures.

Sign in / Sign up

Export Citation Format

Share Document