| 1. |
- Ahlgren, Joakim, et al.
(author)
-
Orsaker till minskande syrehalter i Bottenhavet
- 2017
-
Reports (peer-reviewed)abstract
- Resultat från den nationella miljöövervakningen visar att syrehalterna i Bottenhavet har minskat sedan 1970-talet, en minskning som accelererat från 1990. För att ha möjlighet att på något sätt kunna åtgärda denna försämring av den marina miljön är det nödvändigt att identifiera orsakerna till denna syreminskning, eftersom olika orsaker kan kräva olika former av åtgärder. Om orsaken till exempel är ökad syreförbrukning beroende på regional övergödning, skulle detta innebära ökat behov av regionala reningsåtgärder. Målsättningen med projektet var därmed att ge en tillförlitlig förklaring till de sjunkande syrehalterna i Bottenhavet under de senaste 20 åren genom att använda data från de nationella miljöövervakningsprogrammen. De huvudhypoteser som undersöktes som orsaker till de sjunkande syrehalterna var: • Ökad regional gödning av Bottenhavet och därmed ökad produktion. • Tillförsel av syrefattigt och fosfatrikt från Egentliga Östersjön. • Starkare haloklin och försämrad ventilation av Bottenhavets djupvatten. • Ökad temperatur och ökad tillförsel av löst organiskt kol. Analys av tidsserier och modellanalyser utifrån miljöövervaknings- och forskningsdata visade att den observerade syrehaltsminskningen i Bottenhavets djupvatten främst beror på en ökning av vattentemperaturen och delvis på en ökning av löst organiskt kol i vattnet, samt tillflöde från Egentliga Östersjön. Dataanalysen visade däremot inget tydligt stöd för att ökad produktion av biomassa i Bottenhavet orsakat de minskande syrehalterna. Detta gäller indikatorer för växtplankton, sedimentation och bakterieplankton som alla förväntas öka vid ökad produktion och det finns således inga direkta indicier för att stödja hypotesen om ökad gödning av Bottenhavet. Sammantaget visar de analyser som gjorts inom projektet att Bottenhavets framtida hälsa främst gynnas av en kombination av åtgärder för att motverka globala klimatförändringar, samt åtgärder för att förbättra vattenkvaliteten i Egentliga Östersjön. Näringstillförsel från Bottenhavets avrinningsområden bedöms främst ha haft betydelse för syresituationen i kustnära vattenförekomster. Den bedöms därför inte i betydande omfattning ha orsakat de minskande syrehalterna i Bottenhavets utsjöområden.
|
|
| 2. |
- Ahlgren, Joakim, et al.
(author)
-
Temperature, DOC level and basin interactions explain the declining oxygen concentrations in the Bothnian Sea
- 2017
-
In: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 170, s. 22-30
-
Journal article (peer-reviewed)abstract
- Hypoxia and oxygen deficient zones are expanding worldwide. To properly manage this deterioration of the marine environment, it is important to identify the causes of oxygen declines and the influence of anthropogenic activities. Here, we provide a study aiming to explain the declining oxygen levels in the deep waters of the Bothnian Sea over the past 20 years by investigating data from environmental monitoring programmes. The observed decline in oxygen concentrations in deep waters was found to be primarily a consequence of water temperature increase and partly caused by an increase in dissolved organic carbon (DOC) in the seawater (R-Adj(2). = 0.83) as well as inflow from the adjacent sea basin. As none of the tested eutrophication-related predictors were significant according to a stepwise multiple regression, a regional increase in nutrient inputs to the area is unlikely to explain a significant portion of the oxygen decline. Based on the findings of this study, preventing the development of anoxia in the deep water of the Bothnian Sea is dependent on the large-scale measures taken to reduce climate change. In addition, the reduction of the nutrient load to the Baltic Proper is required to counteract the development of hypoxic and phosphate-rich water in the Baltic Proper, which can form deep water in the Bothnian Sea. The relative importance of these sources to oxygen consumption is difficult to determine from the available data, but the results clearly demonstrate the importance of climate related factors such as temperature, DOC and inflow from adjacent basins for the oxygen status of the sea.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Grimvall, Anders, et al.
(author)
-
Sjöar och vattendrag i Skåne– går utvecklingen åt rätt håll? : Statistisk utvärdering av vattenkvalitet ochprovtagningsprogram i Skåne län
- 2002
-
Reports (other academic/artistic)abstract
- 1. SammanfattningEn statistisk utvärdering av tidsserier av vattenkvalitetsdata från sjöar och vattendrag iSkåne län visar att det skett tydliga miljöförändringar under tjugoårsperioden 1981-2000. I två viktiga avseenden har vattenmiljön förbättrats. Försurningen har gåtttillbaka, åtminstone i vissa områden, och övergödningen av sjöar och vattendrag harkulminerat. Återhämtningen går dock långsamt och vissa andra förändringar sominträffat under studieperioden kan uppfattas som mindre önskvärda.Ljusförhållandena i sjöar och vattendrag har på vissa håll försämrats genom attmängden partiklar eller färgat organiskt material ökat. Det finns även en statistisktsäkerställd ökning av mängden syreförbrukande ämnen i vissa sjöar och vattendrag.En närmare granskning av försurningsrelaterade data visar att det främst är densyraneutraliserande kapaciteten (ANC-värdet) som ökat, medan förändringarna i pHär mindre systematiska. Dessutom föreligger stora skillnader mellan olikaavrinningsområden.Det nuvarande provtagnings- och analysprogrammet för sjöar och vattendrag i Skånelän är ändamålsenligt i den bemärkelsen att det kunnat klarlägga hur obetydligaförändringar från år till år ackumulerats till statistiskt säkerställda förändringar avvattenmiljön under en tjugoårsperiod. Det är också uppenbart att provtagning ochanalyser i de flesta fall skett med god noggrannhet. Bara ett mindre antal mätvärdenavviker på ett oförklarligt sätt från merparten av mätvärdena från samma plats, och delångtidstrender som identifierats för olika platser och tillståndsvariabler bildar med fåundantag ett trovärdigt mönster.Om provtagningen i vattendragen glesas ut från ett prov per månad till ett prov perkvartal minskar självfallet sannolikheten att miljöförändringar upptäcks. Grovt räknatkommer det då att ta ca 50 % längre tid att upptäcka en viss given årlig förändring avmiljötillståndet. Dessutom skulle programmet ge ett sämre underlag för att fastställaom de av riksdagen fastställda miljömålen uppfylls.
|
|
| 6. |
- Nordgaard, Anders, 1962-, et al.
(author)
-
A resampling technique for estimating the power of non-parametric trend tests
- 2006
-
In: Environmetrics. - : Wiley. - 1180-4009 .- 1099-095X. ; 17:3, s. 257-267
-
Journal article (peer-reviewed)abstract
- The power of Mann-Kendall tests and other non-parametric trend tests is normally estimated by performing Monte Carlo simulations in which artificial data are generated according to simple parametric models. Here we introduce a resampling technique for power assessments that can be fully automated and accommodate almost any variation in the collected time series data. A rank regression model is employed to extract error terms representing irregular variation in data that are collected over several seasons and may contain a non-linear trend. Thereafter, an autoregressive moving average (ARMA) bootstrap method is used to generate new time series of error terms for power simulations. A study of water quality data from two Swedish rivers illustrates how our method can provide site- and variable-specific information about the power of the Hirsch and Slack test for monotonic trends. In particular, we show how to clarify the impact of sampling frequency on the power of the trend tests. Copyright (c) 2006 John Wiley & Sons, Ltd.
|
|
| 7. |
|
|
| 8. |
- Asker, Christian, 1979-, et al.
(author)
-
Electronic and atomic structure of Mo from high-temperature molecular dynamics simulations
-
Other publication (pop. science, debate, etc.)abstract
- By means of ab initio molecular dynamics (AIMD) simulations we carry out a detailed stdly of the electronic and atomic structure of Mo upon the thermal stabilization of its dynamically unstable face-centered cubic (fcc) phase, Wc calculate how the atomic positions, radial distribution function, and the ei
|
|
| 9. |
- Asplund, Gunilla, et al.
(author)
-
Soil Peroxidase-Mediated Chlorination of Fulvic Acid
- 1991
-
In: Humic substances in the aquatic and terrestrial environment : proceedings of an international symposium, Linköping, Sweden, August 21-23, 1989. - Berlin Heidelberg New York : Springer. - 3540537023 ; , s. 474-483
-
Book chapter (peer-reviewed)abstract
- Humic matter has recently been shown to contain considerable quantities of naturally produced organohalogens. The present study investigated the possibility of a non-specific, enzymatically mediated halogenation of organic matter in soil. The results showed that, in the presence of chloride and hydrogen peroxide, the enzyme chloroperox1dase (CPO) from the fungus Caldariomyces fumago catalyzes chlorination of fulvic acid. At pH 2.5 - 6.0, the chlorine to fulvic acid ratio in the tested sample was elevated from 12 mg/g to approximately 40-50 mg/g. It was also shown that this reaction can take place at chloride and hydrogen peroxide concentrations found in the environment. An extract from spruce forest soil was shown to have a measurable chlorinating capacity. The activity of an extract of 0.5 kg soil corresponded to approximately 0.3 enzyme units, measured as CPO activity. Enzymatically mediated halogenation of humic substances may be one of the mechanisms explaining the w1despread occurrence of adsorbable organic halogens (AOX) in soil and water.
|
|
| 10. |
- Bergström, Lena, et al.
(author)
-
Interim Report of the ICES/HELCOM Working Group on Integrated Assessments of the Baltic Sea (WGIAB) : 18-22 April 2016 Helsinki, Finland
- 2016
-
Reports (other academic/artistic)abstract
- The ICES/HELCOM Working Group on Integrated Assessments of the Baltic Sea (WGIAB) meeting was held in Helsinki (Finland), 18-22 April 2016. The meeting was attended by 26 participants from five countries and chaired by Laura Uusitalo, Fin-land, Saskia Otto, Germany, Martin Lindegren, Denmark, and Lena Bergström, Swe-den. This was the first year of the new three-year Terms of Reference (ToR) for WGIAB. The main working activities in 2016 were to A) develop the trait-based ap-proach of understanding the ecosystem function, and B) explore the social-ecological system, including indicator development, revising the conceptual model, and devel-oping case studies. As a primary outcome of the ToR A, we built on our previous work on integrated ecosystem assessments (IEAs) in the Baltic Sea, but extended it beyond considering changes in abundances of a few dominant species, to accounting for community-wide changes in a number of key traits across multiple trophic levels. These traits represent various ecosystem functions upon which we derive important ecosystem services. By investigating temporal changes in the community weighted mean traits of phyto-plankton, zooplankton, zoobenthos, and fish, we demonstrated whether trait reor-ganizations at the level of entire communities occurred in the Central Baltic Sea as a result of the 1980s regime shift. Using in total 29 traits combined for all groups we found indications of two breakpoints across all four taxonomic groups over the last decades, i.e. one around 1990 and one around 2000. Further work will focus on ex-ploring the nature of the changes in trait composition and on standardizing the num-ber of traits and data types (i.e. binary, continuous or categorical) across taxonomic group.In addition, we collected data on key functional groups and abiotic variables in all main sub-basins of the Baltic Sea, setting the stage for a cross-regional comparison of temporal patterns and trends in lower trophic level in the face of recent develop-ments in climate-related drivers.With reference to Tor B, to explore how social indicators could be used in parallel with biological indicators in an integrated assessment framework, we developed a conceptual model of interrelationships between ecosystem and society. We used the model as a basis for mapping factors to be accounted for in the ecosystem-based management using the Baltic salmon and clupeid species as case studies. The models depict 1) the structure of the foodweb relevant to the target species, 2) the key com-munity level and population traits that contribute to the state of the species, 3) main pressures affecting the foodweb and their effects on the species, 4) key management measures, and 5) benefits that the species can produce for society.To support the development of Ecosystem Overview the group members evaluated the probability of occurrence and the magnitude of the effect of 15 pressures occur-ring in the Baltic Sea. The top five pressures identified were input of nutrients, in-creased temperature, decreased salinity, input of hazardous substances, and input or spread of non-indigenous species.The work will continue intersessionally and the next meeting of WGIAB is planned to be held in Lisbon, Portugal, back-to-back with WGCOMEDA and WGEAWESS.
|
|
| 11. |
- Bergström, Lena, et al.
(author)
-
Report of the ICES/HELCOM Working Group on Integrated Assessments of the Baltic Sea (WGIAB)
- 2015
-
Reports (other academic/artistic)abstract
- The ICES/HELCOM Working Group on Integrated Assessments of the Baltic Sea(WGIAB) was established in 2007 as a forum for developing and combining ecosystembasedmanagement efforts for the Baltic Sea. The group intends to serve as a scientificcounterpart and support for the ICES Baltic Fisheries Assessment Working Group(WGBFAS) as well as for efforts and projects related to Integrated Ecosystem Assessments(IEA) within ICES and HELCOM. The group works in cooperation with similargroups within the ACOM/SCICOM Steering Group on Integrated Ecosystem Assessments(SSGIEA).The 2015 WGIAB meeting was held in Cádiz, Spain, from 9–13 March, back-to-backwith the meeting of its counterpart in the Working Group on Ecosystem Assessmentof Western European Shelf Seas (WGEAWESS). The meetings had joint sessions as wellas WG specific work, and some participants effectively participated in both meetings.The WGIAB meeting was attended by 27 participants from nine countries. The meetingwas chaired by Christian Möllmann, Germany, Laura Uusitalo, Finland and Lena Bergström,Sweden.This was the last year of the ongoing three-year Terms of Reference (ToR) for WGIAB.The main working activities in 2015 were to i) conduct studies on Baltic Sea ecosystemfunctioning with the goal to publish case studies from different parts of the Baltic Seain peer-reviewed journals, ii) work on the demonstration exercise to develop ecosystem-based assessment and advice for Baltic fish stocks focusing on cod (DEMO) withmultiple approaches, iii) plan further how to integrate the social and economic aspectsmore tightly in the WGIAB work, and iv) discuss the future focus and format of theWGIAB work.The Baltic ecosystem functioning activity focused on identifying and exploring keytrends and linkages in the Baltic Sea foodweb. This was pursued by presentation andfurther discussion of ongoing intersessional work on foodweb modelling and integratedanalyses, and by exercises to develop conceptual models Baltic Sea foodwebsand the links to ecosystem function. Long-term monitoring datasets on the abiotic andbiotic parts of the Baltic Sea Proper ecosystem were updated for use in the continuedwork to develop environmental indicators for fisheries and marine management.The focus of the DEMO 3 (DEMOnstration exercise for Integrated Ecosystem Assessmentand Advice of Baltic Sea cod) was on finding a way to use the results from theDEMO1 and DEMO2 workshops in short and midterm projections/scenarios of Balticcod dynamics based on different types of modelling, as well as designing methodologyand modelling data for practical implementation of Integrated Advice for Baltic cod.The WGIAB was positively inclined towards including social and economic aspectsinto the integrated assessment. Openings to this path were provided by presentationon ongoing project work, and discussing their linkages to ecological aspects. It wasseen as crucial that experts on social and economic analysis should be included andtake an active part in the future work of the group.The group concluded that its upcoming work should focus more closely on functionaldiversity, which was identified as a recurring issue in the Baltic Sea. This approach wasalso identified as a useful connection point between scientific and management aspectsin order for the group to continue serving as a forum for developing ecosystem-basedmanagement efforts in the Baltic Sea. A focus on functional diversity was also seen as2 | ICES WGIAB REPORT 2015a potentially feasible way of bringing together management aspects for different sectors,by linking to ecosystem services concepts.The group proposed Saskia Otto, Germany and Martin Lindegren, Denmark as newincoming Chairs, together with Lena Bergström, Sweden and Laura Uusitalo, Finland.Having four Chairs is justified due to the wide scope of the group's work, as well asthe increased work load due to the planned new foci.
|
|
| 12. |
- Burauskaite-Harju, Agne, 1981-, et al.
(author)
-
A test for network-wide trends in rainfall extremes
- 2012
-
In: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 32:1, s. 86-94
-
Journal article (peer-reviewed)abstract
- Temporal trends in meteorological extremes are often examined by first reducing daily data to annual index values, such as the 95th or 99th percentiles. Here, we report how this idea can be elaborated to provide an efficient test for trends at a network of stations. The initial step is to make separate estimates of tail probabilities of precipitation amounts for each combination of station and year by fitting a generalised Pareto distribution (GPD) to data above a user-defined threshold. The resulting time series of annual percentile estimates are subsequently fed into a multivariate Mann-Kendall (MK) test for monotonic trends. We performed extensive simulations using artificially generated precipitation data and noted that the power of tests for temporal trends was substantially enhanced when ordinary percentiles were substituted for GPD percentiles. Furthermore, we found that the trend detection was robust to misspecification of the extreme value distribution. An advantage of the MK test is that it can accommodate non-linear trends, and it can also take into account the dependencies between stations in a network. To illustrate our approach, we used long time series of precipitation data from a network of stations in The Netherlands.
|
|
| 13. |
- Burauskaite-Harju, Agne, et al.
(author)
-
Characterizing and visualizing spatio-temporal patterns in hourly precipitation records
- 2012
-
In: Journal of Theoretical and Applied Climatology. - : Springer. - 0177-798X .- 1434-4483. ; 109:3-4, s. 333-343
-
Journal article (peer-reviewed)abstract
- We develop new techniques to summarize and visualize spatial patterns of coincidence in weather events such as more or less heavy precipitation at a network of meteorological stations. The cosine similarity measure, which has a simple probabilistic interpretation for vectors of binary data, is generalized to characterize spatial dependencies of events that may reach different stations with a variable time lag. More specifically, we reduce such patterns into three parameters (dominant time lag, maximum cross-similarity, and window-maximum similarity) that can easily be computed for each pair of stations in a network. Furthermore, we visualize such threeparameter summaries by using colour-coded maps of dependencies to a given reference station and distance-decay plots for the entire network. Applications to hourly precipitation data from a network of 93 stations in Sweden illustrate how this method can be used to explore spatial patterns in the temporal synchrony of precipitation events.
|
|
| 14. |
- Burauskaite-Harju, Agne
(author)
-
Characterizing Temporal Changes and Inter-Site Correlations in Daily and Sub-Daily Precipitation Extremes
- 2011
-
Doctoral thesis (other academic/artistic)abstract
- Information on weather extremes is essential for risk awareness in planning of infrastructure and agriculture, and it may also playa key role in our ability to adapt to recurrent or more or less unique extreme events. This thesis reports new statistical methodologies that can aid climate risk assessment under conditions of climate change. This increasing access to high temporal resolution of data is a central factor when developing novel techniques for this purpose. In particular, a procedure is introduced for analysis of long-term changes in daily and sub-daily records of observed or modelled weather extremes. Extreme value theory is employed to enhance the power of the proposed statistical procedure, and inter-site dependence is taken into account to enable regional analyses. Furthermore, new methods are presented to summarize and visualize spatial patterns in the temporal synchrony and dependence of weather events such as heavy precipitation at a network of meteorological stations. The work also demonstrates the significance of accounting for temporal synchrony in the diagnostics of inter-site asymptotic dependence.
|
|
| 15. |
- Burauskaite-Harju, Agne, et al.
(author)
-
Diagnostics for tail dependence in time-lagged random fields of precipitation
- 2013
-
In: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 112:3-4, s. 629-636
-
Journal article (peer-reviewed)abstract
- Weather extremes often occur along fronts passing different sites with some time lag. Here, we show how such temporal patterns can be taken into account when exploring inter-site dependence of extremes. We incorporate time lags into existing models and into measures of extremal associations and their relation to the distance between the investigated sites. Furthermore, we define summarizing parameters that can be used to explore tail dependence for a whole network of stations in the presence of fixed or stochastic time lags. Analysis of hourly precipitation data from Sweden showed that our methods can prevent underestimation of the strength and spatial extent of tail dependencies.
|
|
| 16. |
- Burauskaite-Harju, Agne, et al.
(author)
-
Statistical framework for assessing trends in sub-daily and daily precipitation extremes
-
Other publication (other academic/artistic)abstract
- Extreme precipitation events vary with regard to duration, and hence sub-daily data do not necessarily exhibit the same trends as daily data. Here, we present a framework for a comprehensive yet easily undertaken statistical analysis of long-term trends in daily and sub-daily extremes. A parametric peaks-over-threshold model is employed to estimate annual percentiles for data of different temporal resolution. Moreover, a trend-durationfrequency table is used to summarize how the statistical significance of trends in annual percentiles varies with the temporal resolution of the underlying data and the severity of the extremes. The proposed framework also includes nonparametric tests that can integrate information about nonlinear monotonic trends at a network of stations. To illustrate our methodology, we use climate model output data from Kalmar, Sweden, and observational data from Vancouver, Canada. In both these cases, the results show different trends for moderate and high extremes, and also a clear difference in the statistical evidence of trends for daily and sub-daily data.
|
|
| 17. |
- Burdakov, Oleg, 1953-, et al.
(author)
-
A generalised PAV algorithm for monotonic regression in several variables
- 2004
-
In: COMPSTAT. Proceedings in Computational Statistics. - Heidelberg, NY : PhysicaVerlag/Springer. - 3790815543 ; , s. 761-767
-
Conference paper (peer-reviewed)abstract
- We present a new algorithm for monotonic regression in one or more explanatory variables. Formally, our method generalises the well-known PAV (pool-adjacent-violators) algorithm from fully to partially ordered data. The computational complexity of our algorithm is O(n2). The goodness-of-fit to observed data is much closer to optimal than for simple averaging techniques.
|
|
| 18. |
- Burdakov, Oleg, 1953-, et al.
(author)
-
An algorithm for isotonic regression problems
- 2004
-
In: European Congress on Computational Methods in Applied Sciences and Engineering ECCOMAS. - Jyväskylä : University of Jyväskylä. - 9513918688 ; , s. 1-9
-
Conference paper (peer-reviewed)abstract
- We consider the problem of minimizing the distance from a given n-dimensional vector to a set defined by constraintsof the form xi xj Such constraints induce a partial order of the components xi, which can be illustrated by an acyclic directed graph.This problem is known as the isotonic regression (IR) problem. It has important applications in statistics, operations research and signal processing. The most of the applied IR problems are characterized by a very large value of n. For such large-scale problems, it is of great practical importance to develop algorithms whose complexity does not rise with n too rapidly.The existing optimization-based algorithms and statistical IR algorithms have either too high computational complexity or too low accuracy of the approximation to the optimal solution they generate. We introduce a new IR algorithm, which can be viewed as a generalization of the Pool-Adjacent-Violator (PAV) algorithm from completely to partially ordered data. Our algorithm combines both low computational complexity O(n2) and high accuracy. This allows us to obtain sufficiently accurate solutions to the IR problems with thousands of observations.
|
|
| 19. |
- Burdakov, Oleg, 1953-, et al.
(author)
-
An O(n2) algorithm for isotonic regression
- 2006
-
In: Large-Scale Nonlinear Optimization. - New York : Springer Science+Business Media B.V.. - 0387300635 ; , s. 25-33
-
Conference paper (other academic/artistic)abstract
- We consider the problem of minimizing the distance from a given n-dimensional vector to a set defined by constraints of the form xi ≤ xj. Such constraints induce a partial order of the components xi, which can be illustrated by an acyclic directed graph. This problem is also known as the isotonic regression (IR) problem. IR has important applications in statistics, operations research and signal processing, with most of them characterized by a very large value of n. For such large-scale problems, it is of great practical importance to develop algorithms whose complexity does not rise with n too rapidly. The existing optimization-based algorithms and statistical IR algorithms have either too high computational complexity or too low accuracy of the approximation to the optimal solution they generate. We introduce a new IR algorithm, which can be viewed as a generalization of the Pool-Adjacent-Violator (PAV) algorithm from completely to partially ordered data. Our algorithm combines both low computational complexity O(n2) and high accuracy. This allows us to obtain sufficiently accurate solutions to IR problems with thousands of observations.
|
|
| 20. |
- Burdakov, Oleg, et al.
(author)
-
An O(n2) algorithm for isotonic regression problems
- 2006
-
In: Large-Scale Nonlinear Optimization. - : Springer-Verlag. - 9780387300634 ; , s. 25-33
-
Book chapter (peer-reviewed)abstract
- Large-Scale Nonlinear Optimization reviews and discusses recent advances in the development of methods and algorithms for nonlinear optimization and its applications, focusing on the large-dimensional case, the current forefront of much research.The chapters of the book, authored by some of the most active and well-known researchers in nonlinear optimization, give an updated overview of the field from different and complementary standpoints, including theoretical analysis, algorithmic development, implementation issues and applications
|
|
| 21. |
|
|
| 22. |
- Burdakov, Oleg, 1953-, et al.
(author)
-
Data preordering in generalized PAV algorithm for monotonic regression
- 2006
-
In: Journal of Computational Mathematics. - 0254-9409 .- 1991-7139. ; 24:6, s. 771-790
-
Journal article (peer-reviewed)abstract
- Monotonic regression (MR) is a least distance problem with monotonicity constraints induced by a partially ordered data set of observations. In our recent publication [In Ser. {\sl Nonconvex Optimization and Its Applications}, Springer-Verlag, (2006) {\bf 83}, pp. 25-33], the Pool-Adjacent-Violators algorithm (PAV) was generalized from completely to partially ordered data sets (posets). The new algorithm, called GPAV, is characterized by the very low computational complexity, which is of second order in the number of observations. It treats the observations in a consecutive order, and it can follow any arbitrarily chosen topological order of the poset of observations. The GPAV algorithm produces a sufficiently accurate solution to the MR problem, but the accuracy depends on the chosen topological order. Here we prove that there exists a topological order for which the resulted GPAV solution is optimal. Furthermore, we present results of extensive numerical experiments, from which we draw conclusions about the most and the least preferable topological orders.
|
|
| 23. |
- Burdakov, Oleg, 1953-, et al.
(author)
-
Generalized PAV algorithm with block refinement for partially ordered monotonic regression
- 2009
-
In: Proceedings of the Workshop on Learning Monotone Models from Data. ; , s. 23-37
-
Conference paper (other academic/artistic)abstract
- In this paper, the monotonic regression problem (MR) is considered. We have recentlygeneralized for MR the well-known Pool-Adjacent-Voilators algorithm(PAV) from the case of completely to partially ordered data sets. Thenew algorithm, called GPAV, combines both high accuracy and lowcomputational complexity which grows quadratically with the problemsize. The actual growth observed in practice is typically far lowerthan quadratic. The fitted values of the exact MR solution composeblocks of equal values. Its GPAV approximation has also a blockstructure. We present here a technique for refining blocks produced bythe GPAV algorithm to make the new blocks more close to those in theexact solution. This substantially improves the accuracy of the GPAVsolution and does not deteriorate its computational complexity. Thecomputational time for the new technique is approximately triple thetime of running the GPAV algorithm. Its efficiency is demonstrated byresults of our numerical experiments.
|
|
| 24. |
- Burdakov, Oleg, et al.
(author)
-
Hasse diagrams and the generalized PAV-algorithm for monotonic regression in several explanatory variables
- 2005
-
In: Computational Statistics and Data Analysis. - 0167-9473.
-
Journal article (peer-reviewed)abstract
- Monotonic regression is a nonparametric method for estimation ofmodels in which the expected value of a response variable y increases ordecreases in all coordinates of a vector of explanatory variables x = (x1, …, xp).Here, we examine statistical and computational aspects of our recentlyproposed generalization of the pool-adjacent-violators (PAV) algorithm fromone to several explanatory variables. In particular, we show how the goodnessof-fit and accuracy of obtained solutions can be enhanced by presortingobserved data with respect to their level in a Hasse diagram of the partial orderof the observed x-vectors, and we also demonstrate how these calculations canbe carried out to save computer memory and computational time. Monte Carlosimulations illustrate how rapidly the mean square difference between fittedand expected response values tends to zero, and how quickly the mean squareresidual approaches the true variance of the random error, as the number of observations increases up to 104.
|
|
| 25. |
- Burdakov, Oleg, 1953-, et al.
(author)
-
Monotonic data fitting and interpolation with application to postprocessing of FE solutions
- 2007
-
In: CERFACS 20th Anniversary Conference on High-performance Computing,2007. ; , s. 11-12
-
Conference paper (other academic/artistic)abstract
- In this talk we consider the isotonic regression (IR) problem which can be formulated as follows. Given a vector $\bar{x} \in R^n$, find $x_* \in R^n$ which solves the problem: \begin{equation}\label{ir2} \begin{array}{cl} \mbox{min} & \|x-\bar{x}\|^2 \\ \mbox{s.t.} & Mx \ge 0. \end{array} \end{equation} The set of constraints $Mx \ge 0$ represents here the monotonicity relations of the form $x_i \le x_j$ for a given set of pairs of the components of $x$. The corresponding row of the matrix $M$ is composed mainly of zeros, but its $i$th and $j$th elements, which are equal to $-1$ and $+1$, respectively. The most challenging applications of (\ref{ir2}) are characterized by very large values of $n$. We introduce new IR algorithms. Our numerical experiments demonstrate the high efficiency of our algorithms, especially for very large-scale problems, and their robustness. They are able to solve some problems which all existing IR algorithms fail to solve. We outline also our new algorithms for monotonicity-preserving interpolation of scattered multivariate data. In this talk we focus on application of our IR algorithms in postprocessing of FE solutions. Non-monotonicity of the numerical solution is a typical drawback of the conventional methods of approximation, such as finite elements (FE), finite volumes, and mixed finite elements. The problem of monotonicity is particularly important in cases of highly anisotropic diffusion tensors or distorted unstructured meshes. For instance, in the nuclear waste transport simulation, the non-monotonicity results in the presence of negative concentrations which may lead to unacceptable concentration and chemistry calculations failure. Another drawback of the conventional methods is a possible violation of the discrete maximum principle, which establishes lower and upper bounds for the solution. We suggest here a least-change correction to the available FE solution $\bar{x} \in R^n$. This postprocessing procedure is aimed on recovering the monotonicity and some other important properties that may not be exhibited by $\bar{x}$. The mathematical formulation of the postprocessing problem is reduced to the following convex quadratic programming problem \begin{equation}\label{ls2} \begin{array}{cl} \mbox{min} & \|x-\bar{x}\|^2 \\ \mbox{s.t.} & Mx \ge 0, \quad l \le x \le u, \quad e^Tx = m, \end{array} \end{equation} where$e=(1,1, \ldots ,1)^T \in R^n$. The set of constraints $Mx \ge 0$ represents here the monotonicity relations between some of the adjacent mesh cells. The constraints $l \le x \le u$ originate from the discrete maximum principle. The last constraint formulates the conservativity requirement. The postprocessing based on (\ref{ls2}) is typically a large scale problem. We introduce here algorithms for solving this problem. They are based on the observation that, in the presence of the monotonicity constraints only, problem (\ref{ls2}) is the classical monotonic regression problem, which can be solved efficiently by some of the available monotonic regression algorithms. This solution is used then for producing the optimal solution to problem (\ref{ls2}) in the presence of all the constraints. We present results of numerical experiments to illustrate the efficiency of our algorithms.
|
|
| 26. |
- Burdakov, Oleg, 1953-, et al.
(author)
-
New optimization algorithms for large-scale isotonic regression in L2-norm
- 2007
-
In: EUROPT-OMS Conference on Optimization,2007. - University of Hradec Kralove, Czech Republic : Guadeamus. ; , s. 44-44
-
Conference paper (other academic/artistic)abstract
- Isotonic regression problem (IR) has numerous important applications in statistics, operations research, biology, image and signal processing and other areas. IR in L2-norm is a minimization problem in which the objective function is the squared Euclidean distance from a given point to a convex set defined by monotonicity constraints of the form: i-th component of the decision vector is less or equal to its j-th component. Unfortunately, the conventional optimization methods are unable to solve IR problems originating from large data sets. The existing IR algorithms, such as the minimum lower sets algorithm by Brunk, the min-max algorithm by Lee, the network flow algorithm by Maxwell & Muchstadt and the IBCR algorithm by Block et al. are able to find exact solution to IR problem for at most a few thousands of variables. The IBCR algorithm, which proved to be the most efficient of them, is not robust enough. An alternative approach is related to solving IR problem approximately. Following this approach, Burdakov et al. developed an algorithm, called GPAV, whose block refinement extension, GPAVR, is able to solve IR problems with a very high accuracy in a far shorter time than the exact algorithms. Apart from this, GPAVR is a very robust algorithm, and it allows us to solve IR problems with over hundred thousands of variables. In this talk, we introduce new exact IR algorithms, which can be viewed as active set methods. They use the approximate solution produced by the GPAVR algorithm as a starting point. We present results of our numerical experiments demonstrating the high efficiency of the new algorithms, especially for very large-scale problems, and their robustness. They are able to solve the problems which all existing exact IR algorithms fail to solve.
|
|
| 27. |
|
|
| 28. |
- Forsman, Åsa, 1972-, et al.
(author)
-
Generic structures of decision support systems for evaluation of policy measures to reduce catchment-scale nitrogen fluxes
- 2003
-
In: Physics and Chemistry of the Earth. - 1474-7065 .- 1873-5193. ; 28:14-15, s. 589-598
-
Journal article (peer-reviewed)abstract
- Decision support systems (DSSs) for evaluation of different policy measures have two important functions: To assess how considered policy measures may influence the behavior of actors, and to predict the effects of a given set of actions generated from the anticipated behavior. So far, almost all attempts to construct DSSs for environmental management have focused on assessing the impact of a set of actions on the environment. Here, we describe the generic structure of a DSS that enables more complete evaluation of regional or national policies to reduce nitrogen inputs to water. In particular, we expound the principles for linking models of farm economic behavior to catchment-scale models of the transport and transformation of nitrogen in soil and water. First, we define system boundaries for nitrogen fluxes through the agricultural sector and the ambient environment to create a basis for model integration. Thereafter, we show how different modules operating on different temporal and spatial scales can be interlinked. Finally, we demonstrate how statistical emulators or meta-models can be derived to reduce the computational burden and increase the transparency of the DSS. In particular, we show when and how the temporal or spatial resolution of model inputs can be reduced without significantly influencing the estimates of annual nitrogen fluxes on a catchment scale.
|
|
| 29. |
- Forsman, Åsa, 1972-, et al.
(author)
-
Reduced models for efficient simulation of spatially integrated outputs of one-dimensional substance transport models
- 2003
-
In: Environmental Modelling & Software. - 1364-8152 .- 1873-6726. ; 18:4, s. 319-327
-
Journal article (peer-reviewed)abstract
- We examined under what circumstances the results of a large number of runs of the one-dimensional, physics-based SOIL/SOILN nitrate transport model can be combined into a reduced (or meta) model. We considered the total flow of nitrate from a given area and investigated when and how hidden linear structures can be extracted from the underlying model. The presence of such structures can justify the use of spatially aggregated inputs to compute spatially aggregated outputs. Extensive Monte-Carlo simulations showed that some linear structures emerged when the outputs for a long period of time were summed. Other linear structures appeared as relationships between two different components of the model outputs. However, different cropping systems respond differently to changes in anthropogenic or meteorological forcings. Therefore, we derived a reduced model of long-term leaching of nitrogen from the root zone in an agricultural area by combining each combination of soil type and cropping system. Reduced models can help make process-oriented models more transparent, and they are particularly suitable for incorporation into decision support systems.
|
|
| 30. |
- Grimvall, Anders, et al.
(author)
-
Ekosystembaserad förvaltning som metod för att hantera negativa miljötrender och oklara orsakssamband
- 2019
-
Reports (other academic/artistic)abstract
- Havsmiljöinstitutet har på uppdrag av Miljömålsberedningen tagit fram denna underlagsrapport om ekosystembaserad förvaltning som metod för att hantera miljöstörningar och oklara orsakssamband. Rapporten utgår från ett urval negativa miljötrender som dokumenterats i forskningsrapporter och fortlöpande miljöövervakning i Östersjön och Västerhavet.Sedan mer än tjugo år tillbaka har röster höjts inom såväl förvaltning som forskning och i ideella organisationer för att miljöförvaltningen ska bli mer ekosysteminriktad. En ekosystembaserad förvaltning ska präglas av en helhetssyn på bevarande och hållbart nyttjande av ekosystemen. Det innebär bland annat att den ska ta hänsyn till att olika arter i ett ekosystem påverkar varandra och att samspelet mellan människa och miljö ofta spänner över flera sektorer i samhället.Trots ett ambitiöst arbete för en bättre havsmiljö finns det flera miljöstörningar som har förvärrats under senare år. Den samlade fiske-och miljöförvaltningen har tillexempel inte kunnat hindra att viktiga torskbestånd utarmats eller att stora arealer av det viktiga ålgräset försvunnit längs västkusten. Reproduktionsskador hos lax och sjöfågel, vilka kopplats till brist på vitamin B1(tiamin), och dramatiska förändringar i djurlivet på Östersjöns bottnar har fått än fler varningsklockor att ringa. Det är svårt att peka ut klara orsaker till dessa observerade störningar och att ta steget från forskningsresultat och miljöövervakning till åtgärder inom förvaltningen. Rapporten visar därför på betydelsen av en systemsyn inom den svenska havsmiljöförvaltningen och vikten av att skapa förvaltningsprocesser som beaktar vidden av interaktioner i ekosystemen, inklusive mänsklig påverkan, samtidigt som vi främjar ekosystemens funktionalitet och ett hållbart nyttjande av havets resurser.
|
|
| 31. |
|
|
| 32. |
|
|
| 33. |
|
|
| 34. |
- Grimvall, Anders, et al.
(author)
-
Intensiv trafik i haven runt Sverige
- 2014
-
In: Sjöfarten kring Sverige och dess påverkan på havsmiljön. - : Havsmiljöinstitutet. - 9789163757389 ; , s. 4-7
-
Book chapter (other academic/artistic)abstract
- Sverige omges av hav med en omfattande fartygstrafik. Under 2013 besökte fler än 10 200 unika fartyg Östersjön och Västerhavet, och då är fiskefartygen inte inräknade. En stor majoritet av fartygen var registrerade i länder med höga krav avseende säkerhet och miljö. Men det fanns undantag.
|
|
| 35. |
|
|
| 36. |
- Grimvall, Anders, et al.
(author)
-
Långsamma transporter kan ge snabba förändringar i rätt riktning
- 2017
-
In: Johansen Lilja, T., Lundberg, F., Sundblad, E-L., (Red.) Åtgärder för att minska sjöfartens påverkan på havsmiljön. Havsmiljöinstitutets rapport 2017:2. - Göteborg : Havsmiljöinstitutet. - 9789198229158 ; :2017:2, s. 29-30
-
Other publication (other academic/artistic)abstract
- Sjöfarten kan spara bränsle och minska belastningen på miljön genom att fartygen håller en lägre fart än vad de är designade för. Statistik från Östersjön och Västerhavet visar att sänkt hastighet redan blivit praxis. Den visar också att det blir fler och fler stora fartyg i haven runt Sverige.
|
|
| 37. |
- Grimvall, Anders, et al.
(author)
-
Mitigating marine eutrophication in the presence of strong societal driving forces. Report no 2017:3 Swedish Institute for the Marine Environment
- 2017
-
Reports (other academic/artistic)abstract
- Man-made eutrophication of lakes, coastal waters, and oceans occurs in practically all populated parts of the world, and in many regions the problem is increasing. The ecological effects of excessive input of nutrients include massive algal blooms, extensive oxygen depletion, and recurrent incidences of fish kills. The East China Sea, the Gulf of Mexico, the Bay of Bengal, and the Baltic Sea are some examples of sea basins in which nutrient over-enrichment has resulted in unnaturally large hypoxic zones, where the oxygen concentration is so low that animal life suffocates and dies. Such serious effects are negative not only for ecological reasons, but they also mean the loss of economically valuable resources. Measures to prevent or reduce fluxes of nutrients into marine waters were first undertaken in some parts of Europe and North America. Wastewater treatment plants in urban areas were upgraded to enable the efficient removal of nutrients, and discharges from industry were substantially reduced. Step by step, diffuse emissions from agriculture, transport, and other sectors were also addressed. A brief review of the measures currently in place in a number of countries showed that, despite progress in some areas, the targets of international conventions and other agreements are rarely completely achieved. One reason might be that the flow of nutrients through society and into coastal waters is strongly intertwined with basic human needs, especially the production and consumption of food. Another reason might be that all relevant actors do not participate in the mitigation efforts. In addition, the impact of global social and economic trends is rarely addressed by the authorities who are developing programs of measures (POMs). This report elucidates how politicians, numerous decision-makers in both authorities and enterprises, and conscious consumers can help to reduce eutrophication of coastal waters and oceans. This is done by first reviewing the current measures and instruments in place to mitigate marine eutrophication. Thereafter, it is explored how the range of intervention options can be expanded by systematically linking the flows of substances and goods to the relevant actors and by assessing these actors’ potential to influence nutrient fluxes. Selected global trends and innovative technologies of relevance are also considered. Moreover, the need and benefit of simultaneously working toward different sustainable development goals is addressed. Current measures in selected countries. Sweden, which is one of the nine Baltic Sea countries, has developed a very complex mix of physical measures and policy instruments to combat marine eutrophication. Efficient wastewater treatment has been accomplished by simultaneously paying attention to institutions, legislation, and financing of measures. Leakage of nutrients from agriculture has been reduced by combining legislation and ordinances from the Government and national agencies with inspections and guidance from county administrative boards and municipalities. Voluntary actions by farmers are to some extent subsidized. Emissions from shipping, especially nitrogen emissions from fuel combustion, are another major source of marine eutrophication, and national regulations have been decided upon and implemented. Collaboration with other countries is needed to achieve unified actions, but such actions take time. Denmark, which is another Baltic Sea nation, produces large amounts of pig meat, and this has made it necessary to address the leakage of nutrients from agriculture. Originally, nitrate pollution of inland waters and groundwater was in focus, but measures to protect such waters have also resulted in the improved status of marine waters. Politically, Denmark has met the challenges by employing two different abatement strategies. Detailed regulation of agricultural practices using almost identical rules in the whole of Denmark is now being replaced by spatially differentiated regulation. The Netherlands by the North Sea is another country with large-scale and intensive animal farming. Because livestock production generates considerably more manure than is required by agriculture in the immediate vicinity, the cycling of nutrients is disrupted. To reduce regional imbalances in nutrient fluxes, Dutch farmers are now required to have a certain percentage of their surplus manure treated for sale outside the Dutch fertilizer market. In the US, POMs have long had a strong focus on point-source emissions, including emissions from concentrated animal feeding operations. Extensive outreach activities, voluntary actions, and strong ambitions to involve a wide range of stakeholders characterize several of the POMs. However, the overall progress to reduce fundamental imbalances in nutrient fluxes in food production has been slow. India and Bangladesh, which border the Bay of Bengal, are two countries with a rapidly increasing population and rapid urbanization. Urban sanitation and wastewater treatment for the large cities are in focus, but without upgrading the treatment systems so that they include efficient removal of nutrients, there is a substantial risk of increased eutrophication problems. China has changed faster than any other large country over the past few decades. New environmental laws and substantial investments in wastewater treatment plants indicate an increased willingness to address water pollution, including marine eutrophication. However, implementation of new environmental standards is lagging behind changes in nutrient fluxes. The impact of urbanization, transitions in agriculture, and dietary shifts are so strong that fundamental imbalances in nutrient fluxes are likely to persist for a long time. Generally, abatement of eutrophication problems starts with efforts to eliminate hot spots of nutrient pollution by regulating point-source emissions and agricultural practices. Addressing eutrophication by considering large-scale imbalances in nutrient fluxes and desirable transitions in society usually comes later. Increased cooperation within sea conventions, stronger involvement of major enterprises, and coordinated efforts to simultaneously achieve several sustainable development goals represent a way forward. Cooperation within international sea conventions and watershed task forces In Europe, the contracting partners of the HELCOM and OSPAR conventions are cooperating to reduce eutrophication in the Baltic Sea and the Northeast Atlantic, respectively. Such regional sea conventions are important platforms for mutual decisions between the member states. They also form bodies large enough to push forward issues in global organizations such as the International Maritime Organization. The European Union broadens the cooperation possibilities by offering more partners and by providing unified legislation and financial support. India and Bangladesh participated in the Bay of Bengal Large Marine Ecosystem project as a way to share visions and objectives and to engage in discussion concerning the measures to be implemented. This project ended in 2015, and future work related to the project is currently being discussed. In the US and China, the Mississippi and Yangtze river basins are so large that watershed task forces play a key role in abatement programs. Expansion of intervention options The human pressure on many coastal and offshore water bodies remains unacceptably high even though several measures have already been implemented. This indicates that there is a need to expand the range of intervention options. Systems analysis of fluxes of nutrients through society can reveal a multitude of activities and behavioral patterns of institutions, organizations, and individuals that affect the pressure on marine environments. When developing policy instruments and measures to reduce the pressure on marine environments, it is important to identify actors who have the potential to change their behaviors. By analyzing product chains, it is often possible to identify such actors or groups of actors. A case study of the product chain for meat produced and consumed in Sweden revealed that although the number of activities in the chain is large, the actual number of influential actors is rather small. This study also showed that it is not only the actors who actually release nutrients into the sea who can influence the nutrient loads. Large food retailers, for example, can influence what is consumed and thereby also the fluxes of nutrients along the entire chain from production of animal feed and food to emissions from sewage systems. Chefs with a media presence, NGOs, and conscious consumers are other examples of key actors. Taking stock of the current measures as well as our general procedure for linking key actors to fluxes of substances and products, we propose new measures to mitigate the eutrophication of marine waters. In contrast to many of the current measures that can be characterized as endof- pipe solutions or cleanup operations, these new measures have the potential to transform society into becoming more ecologically, economically, and socially sustainable. The proposed measures all relate to dietary issues or to better recycling of nutrients. Three proposed measures A. Protein consumption adjusted to health requirements. People in many countries have increased their average protein consumption to levels far higher than needed. Phosphorus and nitrogen fluxes through society and from society to nature increase with increased protein consumption. Taking Sweden as an example, a 20% lower production and consumption of protein could substantially lower the nutrient input into the Baltic Sea without increasing the risk of protein deficiency. Such dietary changes are in the hands of many actors such as legislators, agencies, market actors, and NGOs. B. Increased aquaculture with minimal loss of nutrients. Aquaculture has considerable potential to e
|
|
| 38. |
|
|
| 39. |
|
|
| 40. |
- Grimvall, Anders, et al.
(author)
-
Phytotoxic Substances in Runoff from Forested Catchment Areas
- 1991
-
In: Humic substances in the aquatic and terrestrial environment : proceedings of an international symposium, Linköping, Sweden, August 21-23, 1989. - Berlin Heidelberg New York : Springer. - 3540537023 ; , s. 397-406
-
Book chapter (peer-reviewed)abstract
- Runoff from different catchment areas in southem Sweden was tested in a root bioassay based on solution cultures of cucumber seedlings. Water samples from agricultural catchment areas produced no signs at all or only weak signs of inhibited root growth, whereas several water samples from catchmcnt areas dominated by mires or coniferous forests produced visible root injuries. The most severe root injuries (very short roots, discolouration, swelling of root tips and lack of root hairs) were caused by samples from a catchment area without local emissions and dominated by old stands of spruce. Fractionation by ultrafiltration showed that the phytotoxic effect of these samples could be attributed to organic matter with a nominal molecular-weight exceeding 1000 or to substances associated with organic macromolecules. Experiments aimed at concentrating phytotoxic compounds from surface water indicated that the observed growth inhibition was caused by strongly hydrophilic substances. Previous reports on phytotoxic, organic substances of natura! origin have emphasized interaction between plants growing close together. The presence of phytotoxic substances in runoff indicates that there is also a large-scale dispersion of such compounds.
|
|
| 41. |
- Grimvall, Anders, et al.
(author)
-
Semiparametric smoothers for trend assessment of multiple time series of environmental quality data
- 2008
-
In: Environmetrics. - 1180-4009 .- 1099-095X.
-
Journal article (other academic/artistic)abstract
- Multiple time series of environmental quality data with similar, but not necessarily identical, trends call for multivariate methods for trend detection and adjustment for covariates. Here, we show how an additive model in which the multivariate trend function is specified in a nonparametric fashion (and the adjustment for covariates is based on a parametric expression) can be used to estimate how the human impact on an ecosystem varies with time and across components of the observed vector time series. More specifically, we demonstrate how a roughness penalty approach can be utilized to impose different types of smoothness on the function surface that describes trends in environmental quality as a function of time and vector component. Compared to other tools used for this purpose, such as Gaussian smoothers and thin plate splines, an advantage of our approach is that the smoothing pattern can easily be tailored to different types of relationships between the vector components. We give explicit roughness penalty expressions for data collected over several seasons or representing several classes on a linear or circular scale. In addition, we define a general separable smoothing method. A new resampling technique that preserves statistical dependencies over time and across vector components enables realistic calculations of confidence and prediction intervals.
|
|
| 42. |
- Grimvall, Anders, et al.
(author)
-
Time scales of nutrient losses from land to sea - A European perspective
- 2000
-
In: Ecological Engineering. - 0925-8574 .- 1872-6992. ; 14:4, s. 363-371
-
Journal article (peer-reviewed)abstract
- Empirical data regarding the time scales of nutrient losses from soil to water and land to sea were reviewed. The appearance of strongly elevated concentrations of nitrogen and phosphorus in major European rivers was found to be primarily a post-war phenomenon. However, the relatively rapid water quality response to increased point source emissions and intensified agriculture does not imply that the reaction to decreased emissions will be equally rapid. Long-term fertilisation experiments have shown that important processes in the large-scale turnover of nitrogen operate on a time scale of decades up to at least a century, and in several major Eastern European rivers there is a remarkable lack of response to the dramatic decrease in the use of commercial fertilisers that started in the late 1980s. In Western Europe, studies of decreased phosphorus emissions have shown that riverine loads of this element can be rapidly reduced from high to moderate levels, whereas a further reduction, if achieved at all, may take decades. Together, the reviewed studies showed that the inertia of the systems that control the loss of nutrients from land to sea was underestimated when the present goal of a 50% reduction of the input of nutrients to the Baltic Sea and the North Sea was adopted. (C) 2000 Elsevier Science B.V.
|
|
| 43. |
|
|
| 44. |
- Hoffmann, M., et al.
(author)
-
Leaching of nitrogen in Swedish agriculture - A historical perspective
- 2000
-
In: Agriculture, Ecosystems & Environment. - 0167-8809 .- 1873-2305. ; 80:3, s. 277-290
-
Journal article (peer-reviewed)abstract
- There is a need to examine long-term changes in nitrogen leaching from arable soils. The purpose of this study was to analyse variations in specific leaching rates (kg ha-1 per year) and gross load (Mg per year) of N from arable land to watercourses in Sweden from a historical perspective. The start of the study was set to 1865 because information on crop distribution, yield and livestock has been compiled yearly since then. The SOIL/SOILN model was used to calculate nitrogen leaching. Calculations were done for cereals, grass and bare fallow for three different soil types in nine agricultural regions covering a range of climatic conditions. Results indicate that both specific leaching rates and gross load of nitrogen in the middle of 19th century were approximately the same as they are today for the whole of south and central Sweden. Three main explanations for this were (1) large areas of bare fallow typical for the farming practice at the time, (2) enhanced mineralisation from newly cultivated land, and (3) low yield. From 1865, i.e. the start of the calculations, N leaching rates decreased and were at their lowest around 1930. During the same period, gross load was also at its lowest despite the fact that the acreage of arable land was at its most extensive. After 1930, average leaching increased by 60% and gross load by 30%, both reaching a peak in the mid-1970s to be followed by a declining trend. The greatest increase in leaching was in regions where the increase in animal density was largest and these regions were also those where the natural conditions for leaching such as mild winters and coarse-textured soils were found. Extensive draining projects occurred during the period of investigation, in particular an intensive exploitation of lakes and wetlands. This caused a substantial drop in nitrogen retention and the probable increase in net load to the sea might thus have been more affected by this decrease in retention than the actual increase in gross load. (C) 2000 Elsevier Science B.V.
|
|
| 45. |
|
|
| 46. |
|
|
| 47. |
|
|
| 48. |
- Hussian, Mohamed, et al.
(author)
-
Estimation of the human impact on nutrient loads carried by the Elbe River
- 2004
-
In: Environmental Monitoring and Assessment. - 0167-6369 .- 1573-2959. ; 96:1-3, s. 15-33
-
Journal article (peer-reviewed)abstract
- The reunification of Germany led to dramatically reduced emissions of nitrogen (N) and phosphorus (P) to the environment. The aim of the present study was to examine how these exceptional decreases influenced the amounts of nutrients carried by the Elbe River to the North Sea. In particular, we attempted to extract anthropogenic signals from time series of riverine loads of nitrogen and phosphorus by developing a normalization technique that enabled removal of natural fluctuations caused by several weather-dependent variables. This analysis revealed several notable downward trends. The normalized loads of total-N and NO3-N exhibited an almost linear trend, even though the nitrogen surplus in agriculture dropped dramatically in 1990 and then slowly increased. Furthermore, the decrease in total-P loads was found to be considerably smaller close to the mouth of the river than further upstream. Studying the predictive ability of different normalization models showed the following: (i) nutrient loads were influenced primarily by water discharge; (ii) models taking into account water temperature, load of suspended particulate matter, and salinity were superior for some combinations of sampling sites and nutrient species; semiparametric normalization models were almost invariably better than ordinary regression models.
|
|
| 49. |
- Hussian, Mohamed, 1969-
(author)
-
Monotonic and Semiparametric Regression for the Detection of Trends in Environmental Quality Data
- 2005
-
Doctoral thesis (other academic/artistic)abstract
- Natural fluctuations in the state of the environment can long conceal or distort important trends in the human impact on our ecosystems. Accordingly, there is increasing interest in statistical normalisation techniques that can clarify the anthropogenic effects by removing meteorologically driven fluctuations and other natural variation in time series of environmental quality data. This thesis shows that semi- and nonparametric regression methods can provide effective tools for applying such normalisation to collected data. In particular, it is demonstrated how monotonic regression can be utilised in this context. A new numerical algorithm for this type of regression can accommodate two or more discrete or continuous explanatory variables, which enables simultaneous estimation of a monotonic temporal trend and correction for one or more covariates that have a monotonic relationship with the response variable under consideration. To illustrate the method, a case study of mercury levels in fish is presented, using body length and weight as covariates. Semiparametric regression techniques enable trend analyses in which a nonparametric representation of temporal trends is combined with parametrically modelled corrections for covariates. Here, it is described how such models can be employed to extract trends from data collected over several seasons, and this procedure is exemplified by discussing how temporal trends in the load of nutrients carried by the Elbe River can be detected while adjusting for water discharge and other factors. In addition, it is shown how semiparametric models can be used for joint normalisation of several time series of data.
|
|
| 50. |
|
|
