Sigmoid Relationships between Nutrients and Chlorophyll among Lakes

1989 ◽  
Vol 46 (7) ◽  
pp. 1171-1175 ◽  
Author(s):  
Edward McCauley ◽  
John A. Downing ◽  
Susan Watson
Keyword(s):  
Algal Biomass ◽  
Chlorophyll Concentration ◽  
Management Strategies ◽  
Field Research ◽  
Phosphorus Availability ◽  
Phosphorus Concentration ◽  
Data Sets ◽  
Empirical Relationships ◽  
Dissolved Phosphorus ◽  
Freshwater Eutrophication

Previous studies of freshwater eutrophication have shown that algal biomass tends to increase with the supply of dissolved phosphorus. This concept has been condensed into empirical relationships between chlorophyll a and total phosphorus concentrations (convenient measures of algal biomass and phosphorus availability) which have become essential tools in theoretical and applied limnology. With few exceptions, ecologists accept the idea that chlorophyll concentration rises linearly with phosphorus concentration among lakes. Such a suggestion runs counter to Liebigian principles of fertilization however, and contradicts laboratory and field research indicating the influence of other nutrients. Our analysis of two large independent phosphorus–chlorophyll data sets from temperate-zone lakes shows that log phosphorus–log chlorophyll relationships are sigmoid in shape and that a second nutrient, nitrogen, has a significant impact on chlorophyll concentrations when phosphorus availability is high. Our new empirical relationships indicate that mechanisms regulating algal biomass change with enrichment, and suggest new management strategies for polluted lakes.

Periphyton as an early indicator of perturbation in recreational lakes

2008 ◽  
Vol 65 (2) ◽  
pp. 258-265 ◽  
Author(s):  
Daniel Lambert ◽  
Antonella Cattaneo ◽  
Richard Carignan
Keyword(s):  
Algal Biomass ◽  
Stoichiometric Composition ◽  
Open Water ◽  
Benthic Microalgae ◽  
Phosphorus Concentration ◽  
Empirical Relationships ◽  
Molar Ratios ◽  
Lake Development ◽  
Periphyton Biomass ◽  
Land Water

We looked for empirical relationships between periphyton biomass and recreational development in the Laurentian lakes of Quebec (Canada). We compared the response of periphyton (as chlorophyll a) on rocks and sediments with that of phytoplankton. Epilithon and epipelon biomass increased significantly with lake recreational development (as percentage of cleared land within a 50 m riparian strip) but was not related with open-water phosphorus concentration. In contrast, phytoplankton was related to open-water phosphorus but did not increase along the gradient of lake development. Periphyton stoichiometric composition also changed with increasing lake development. High C:P and C:N ratios were found in pristine lakes, whereas lower periphyton molar ratios, which approached the optimal stoichiometric composition for benthic microalgae, were observed in the most developed lakes. Our findings suggest that periphyton, positioned near the land–water interface, has access to land-derived nutrients before they are diluted in the open water. Therefore, periphyton on all substrata is the first community to respond to increased inputs resulting from lake recreational development. The measurement of littoral algal biomass and chemical composition may represent a better tool for early detection of lake perturbation than classic methods based on pelagic characteristics.

Influence of Reservoir Transit on Riverine Algal Transport and Abundance

1984 ◽  
Vol 41 (12) ◽  
pp. 1803-1813 ◽  
Author(s):  
D. M. Søballe ◽  
R. W. Bachmann
Keyword(s):  
Water Temperature ◽  
Retention Time ◽  
Standing Crop ◽  
Algal Biomass ◽  
Chlorophyll Concentration ◽  
Light Limitation ◽  
Des Moines ◽  
Flow Dependence ◽  
Major Loss ◽  
Chlorophyll Concentrations

The Des Moines River lost 65–75% of its algal standing crop (chlorophyll a) in passing through each of two impoundments (mean retention times 11 and 16 d), and chlorophyll concentrations within both impoundments were 50–90% below the predictions of empirical chlorophyll–nutrient models. Sedimentation of river-borne algae and light limitation within the impoundments were identified as major loss processes. A reduction in algal size from upstream to downstream in one reservoir paralleled the loss of algal biomass. Algal losses in each impoundment increased with both increasing retention time and water temperature so that chlorophyll concentration below the dams was uncoupled from the temperature and flow dependence seen in river reaches not influenced by impoundments. The reduction in riverine algal transport associated with reservoir transit was cumulative over the two-reservoir series; this reduction can be interpreted as a "reset" to river headwater conditions.

Light, Nutrients, and Water Temperature as Determinants of Phytoplankton Production in Two Saline, Prairie Lakes with High Sulphate Concentrations

1992 ◽  
Vol 49 (11) ◽  
pp. 2281-2290 ◽  
Author(s):  
Richard D. Robarts ◽  
Marlene S. Evans ◽  
Michael T. Arts
Keyword(s):  
Water Temperature ◽  
Photosynthetic Capacity ◽  
Chlorophyll Concentration ◽  
Euphotic Zone ◽  
Dominant Factor ◽  
Phytoplankton Production ◽  
Dissolved Phosphorus ◽  
Prairie Lakes ◽  
The Mean ◽  
Algal Productivity

Our data support empirical models indicating that algal productivity is low relative to total phosphorus (TP) levels in prairie lakes with high sulphate concentrations. Mean chlorophyll accounted for 91.1% of the variance in euphotic zone primary production (ΣA) in Humboldt Lake (total dissolved solids (TDS) = 3.3 g∙L−1; Zmax = 6 m), while TP, total dissolved phosphorus, and water temperature accounted for 82.7% of ΣA variance in Redberry Lake (TDS = 20.9 g∙L−1; Zmax = 17 m). The relative importance of these variables to ΣA resulted from biological, chemical, and physical differences of these lakes. Light usually penetrated to the bottom of Redberry Lake due to a mean euphotic zone (Zeu) chlorophyll of 1.7 mg∙m−3, while Humboldt Lake's mean Zeu was 3.4 m with a mean chlorophyll concentration of 62.6 mg∙m−3. Chlorophyll was the dominant factor correlated with light penetration in Humboldt Lake (r2 = 0.65) but not in Redberry Lake. Photosynthetic capacity was correlated (r2 = 0.72) with water temperature only in Redberry Lake. The mean ΣA was 57.1 and 230.2 mg C∙m−2∙h−1 for Redberry and Humboldt lakes, respectively.

Natural variability and the estimation of empirical relationships: a reassessment of regression methods

1995 ◽  
Vol 52 (4) ◽  
pp. 788-798 ◽  
Author(s):  
Yves T. Prairie ◽  
David F. Bird ◽  
Robert H. Peters
Keyword(s):  
Statistical Significance ◽  
Chlorophyll Concentration ◽  
Ordinary Least Squares ◽  
Natural Variability ◽  
Structural Relationship ◽  
Phosphorus Concentration ◽  
Regression Methods ◽  
Multivariate Relationships ◽  
Statistical Relationships ◽  
Fertilizing Effect

Ecologists often rely on empirically defined statistical relationships to infer how variables might be related. However, the usual method of estimating such relationships (ordinary least-squares (OLS)) is generally inappropriate because of the substantial natural variability of most ecological variables. Natural error variability in the regressor variable can artificially create a significant empirical trend where no underlying or structural relationship exists, or fail to reveal a true structural relationship. In multivariate relationships, natural variability in one variable can induce statistical significance in collinear variables even if they bear no structural relationship. We propose a simple new method, based on instrumental variables, to detect and quantify natural error variability in the regressor variables and to estimate the parameters of the structural relationship. We apply this method to two examples: (1) we show that the structural relationship between adenosine triphosphate concentration (total planktonic biomass) and chlorophyll concentration (autotrophic biomass) does not vary latitudinally in the Southern Ocean despite a significant increase in the OLS slope relating the two at more southerly stations and (2) we demonstrate that the significance of nitrogen in nutrient–chlorophyll relationships in lakes probably reflects natural variability in phosphorus concentration, and not the fertilizing effect of nitrogen.

Global Knowledge Management Technology Strategies and Competitive Functionality

2008 ◽  
pp. 126-136
Author(s):  
William Schulte ◽  
Kevin J. O'Sullivan
Keyword(s):  
Information Technology ◽  
Knowledge Management ◽  
Competitive Advantage ◽  
Positive Impact ◽  
Management Strategies ◽  
Field Research ◽  
Global Knowledge ◽  
Management Technology ◽  
Technology Applications ◽  
Technology Strategies

Information and knowledge management technologies and globalization have changed how firms in service industries formulate, implement and sustain competitive advantage. This research project contributes to our understanding of the relationships between Global Knowledge Management Technology Strategies and Competitive Functionality from Global IT. Based on field research this study found that Global Knowledge Management Technology strategies have a positive impact on Competitive Advantage from Information Technology Applications Functionality from Global IT. This study provides recommendations to International Engineering, Procurement and Construction Industry executives regarding the impact of knowledge management strategies and global information technology on competitive advantage of firms in their industry.

Empirical Models for Zoobenthic Biomass in Lakes

1987 ◽  
Vol 44 (5) ◽  
pp. 990-1001 ◽  
Author(s):  
Joseph B. Rasmussen ◽  
Jacob Kalff
Keyword(s):  
Littoral Zone ◽  
Chlorophyll Concentration ◽  
Empirical Models ◽  
Phosphorus Concentration ◽  
Lake Area ◽  
Total Phosphorus Concentration ◽  
Secchi Disk Transparency ◽  
Littoral Zones ◽  
Explained Variance ◽  
Local Variability

Estimates of macrozoobenthos from the literature were regressed against a series of limnological variables to yield empirical models for zoobenthic biomass in the profundal, sublittoral, and littoral zones of lakes. Variables indicative of phytoplankton biomass (chlorophyll concentration, total phosphorus concentration, and Secchi disk transparency) explained between 14 and 57% of the variance of zoobenthic biomass ((g/m2)0.1). Other factors such as humic colour, morphometry (slope, mean depth, ratio of mean to maximum depth, and lake area), and mean annual air temperature substantially increased the amount of explained variance. In the profundal and sublittoral zones, the best models explain 70% of the variance in zoobenthic biomass. Littoral zone models explained less than 50%, and this deficiency was attributed to sampling difficulties and to high local variability of slope and wave exposure in the littoral zone.

GRAVEL BED RIVER SCOURING ANALYSIS DOWNSTREAM OF BLOCK RAMP (EXAMPLE FROM THE PONICZANKA STREAM IN PONICE VILLAGE)

2017 ◽  
Vol 167 (47) ◽  
pp. 77-87
Author(s):  
Karol Plesiński
Keyword(s):  
Comparative Analysis ◽  
Hydraulic Structure ◽  
Field Research ◽  
Field Measurements ◽  
Field Observations ◽  
Empirical Relationships ◽  
Gravel Bed ◽  
Scouring Depth ◽  
Scouring Process ◽  
Block Ramp

The work describes the scouring process downstream of boulder block ramps on Poniczanka Stream in Ponice village. The depth of the downstream scouring rate was calculated using empirical formulae due to different authors. The results of the calculations were verified basing on the field measurements. Finally only those formulae which results were most consistent with field observations and those with were the worst consistent with field observations are presented along a paper. Thus the aim of the study was to verify the existing formulae of the scouring depth calculation downstream of block ramp hydraulic structure on the basis of the results of field research. It was found that the empirical relationships for calculating the scouring depth in observed case are not satisfied enough, however they can be used for comparative analysis for designers.

scholarly journals Modelling stock–recruitment relationships to examine stock management policies

2007 ◽  
Vol 64 (5) ◽  
pp. 870-877 ◽  
Author(s):  
A. Kimoto ◽  
T. Mouri ◽  
T. Matsuishi
Keyword(s):  
Prediction Error ◽  
Management Strategies ◽  
Fish Stock ◽  
Data Sets ◽  
Stock Management ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Management Policies ◽  
Leave One Out ◽  
High Recruitment

Abstract Kimoto, A., Mouri, T., and Matsuishi, T. 2007. Modelling stock–recruitment relationships to examine stock management policies. – ICES Journal of Marine Science, 64: 870–877. Simulation studies are used widely for fish stock management. In such studies, forecasting future recruitment, which can vary greatly between years, has become an essential part of evaluating management strategies. We propose a new forecasting algorithm to predict recruitment for short- or medium-term stochastic projections, using a stock–recruitment relationship. We address cases in which the spawning stock has dropped below previously observed levels, or in which predicted recruitment is situated close to the maximum observed level. The relative prediction error of seven existing algorithms was compared with that of the new model using leave-one-out cross-validation for 61 data sets from ICES, the Japanese Fisheries Agency, and PICES. The new algorithm had the smallest prediction error for 49 of the data sets, but was slightly biased by the precautionary treatment of predictions of high recruitment.

scholarly journals Elephants respond to resource trade-offs in an aseasonal system through daily and annual variability in resource selection

Koedoe ◽  
2017 ◽  
Vol 59 (1) ◽  
Author(s):  
Timothy J. Fullman ◽  
Gregory A. Kiker ◽  
Angela Gaylard ◽  
Jane Southworth ◽  
Peter Waylen ◽  
...  
Keyword(s):  
Resource Selection ◽  
Management Strategies ◽  
Rare Plants ◽  
Data Sets ◽  
Dynamic Selection ◽  
Daily Movement ◽  
Selection Strategies ◽  
Trade Offs ◽  
Selection Of ◽  
Annual Patterns

Animals and humans regularly make trade-offs between competing objectives. In Addo Elephant National Park (AENP), elephants (Loxodonta africana) trade off selection of resources, while managers balance tourist desires with conservation of elephants and rare plants. Elephant resource selection has been examined in seasonal savannas, but is understudied in aseasonal systems like AENP. Understanding elephant selection may suggest ways to minimise management trade-offs. We evaluated how elephants select vegetation productivity, distance to water, slope and terrain ruggedness across time in AENP and used this information to suggest management strategies that balance the needs of tourists and biodiversity. Resource selection functions with time-interacted covariates were developed for female elephants, using three data sets of daily movement to capture circadian and annual patterns of resource use. Results were predicted in areas of AENP currently unavailable to elephants to explore potential effects of future elephant access. Elephants displayed dynamic resource selection at daily and annual scales to meet competing requirements for resources. In summer, selection patterns generally conformed to those seen in savannas, but these relationships became weaker or reversed in winter. At daily scales, resource selection in the morning differed from that of midday and afternoon, likely reflecting trade-offs between acquiring sufficient forage and water. Dynamic selection strategies exist even in an aseasonal system, with both daily and annual patterns. This reinforces the importance of considering changing resource availability and trade-offs in studies of animal selection.Conservation implications: Guiding tourism based on knowledge of elephant habitat selection may improve viewing success without requiring increased elephant numbers. If AENP managers expand elephant habitat to reduce density, our model predicts where elephant use may concentrate and where botanical reserves may be needed to protect rare plants from elephant impacts.

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