Research Interests: Time Series, Water quality, Wastewater Treatment, Environmental Monitoring, Multidisciplinary, and 12 morePhosphorus, Atmospheric deposition, Nitrogen Fixation, Land Use, Nitrogen, Data Collection, Natural Sciences, Marine Algae, Environmental monitoring and assessment, Nutrient Loading, Water Quality, and Nutrient Concentration
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... This article shows how information about the riverine load of pollutants at different sites in a study area can be combined with data on the spatial distribution of sources and selected river basin characteristics to carry out a... more
... This article shows how information about the riverine load of pollutants at different sites in a study area can be combined with data on the spatial distribution of sources and selected river basin characteristics to carry out a statistical source apportionment of the load observed at ...
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Riverine transport is the, most important pathway for input of nutrients to the Gulf of Riga. The present study focused on updating existing estimates of the riverine nutrient contributions and on improving the favailable information on... more
Riverine transport is the, most important pathway for input of nutrients to the Gulf of Riga. The present study focused on updating existing estimates of the riverine nutrient contributions and on improving the favailable information on temporal and spatial variation in such input. The results show that the gulf received an average of 113,300 tons of nitrogen, 2050 tons of phosphorus and 64,900 tons of dissolved silica (DSi) annually during the time period 1977-1995. There was large interannual variation in loads, e.g., a factor two difference was found between the two most extreme years (1984 and 1990); this was attributed mainly to natural variation in water discharge. The seasonal distribution of nutrient loads exhibited a distinct pattern for practically all studied constituents, especially nitrate. Loads were high during the spring-flow and relatively low during the low-flow summer period. Examination of the spatial variation of nutrient loads showed that the Daugava River alone accounted for approximately 60% of the total riverine load. The highest area-specific loads of nitrate and phosphate were observed in the agriculturally dominated Lielupe River, and the highest loads of organic-nitrogen (org-N) and total phophorus (tot-P) were found in the Pärnu River. However, the values for all the studied rivers and constituents were rather low (phosphorus) or moderate (nitrogen and silica) compared to those reported for many other drainage areas of the Baltic Sea. This was true despite the inefficient sewage treatment and intensive agriculture in the studied basins in the 1970s and 1980s.
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ABSTRACT The demands on monitoring systems have gradually increased, and interpretation of the data is often a matter of controversy. As an example of this, we investigated water quality monitoring and the eutrophication issue in Sweden.... more
ABSTRACT The demands on monitoring systems have gradually increased, and interpretation of the data is often a matter of controversy. As an example of this, we investigated water quality monitoring and the eutrophication issue in Sweden. Our results demonstrate that powerful statistical tools for trend analysis can reveal flaws in the data and lead to new and revised interpretations of environmental data. In particular, we found strong evidence that long-term trends in measured nutrient concentrations can be more extensively influenced by changes in sampling and laboratory practices than by actual changes in the state of the environment. On a more general level, our findings raise important questions regarding the need for new paradigms for environmental monitoring and assessment. Introduction of a system in which conventional quality assurance is complemented with thorough statistical follow-up of reported values would represent a first step towards recognizing that environmental monitoring and assessment should be transformed from being a system for sampling and laboratory analyses into a system for interpreting information to support policy development.
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ABSTRACT
Changes in observational data over time can be seve rely distorted by errors in measurements, sampling, or reporting. Here, we show how smooth trends in vector time series can be separated from one or two abrupt leve l shifts that occur... more
Changes in observational data over time can be seve rely distorted by errors in measurements, sampling, or reporting. Here, we show how smooth trends in vector time series can be separated from one or two abrupt leve l shifts that occur simultaneously in all coordinates. Trends are modelled nonparametrica lly, whereas abrupt changes and the impact of covariates are modelled parametrically. T he model is estimated using a back- fitting algorithm in which estimation of smooth tre nds is alternated with estimation of regression coefficients for covariates and assessme nt of sudden level shifts. The proposed method is adaptive in the sense that the degree of smoothing over time and across coordinates is controlled by a roughness penalty an d cross-validation procedure that automatically identifies the interdependence of the analysed data. Furthermore, it uses a resampling technique that can accommodate correlated error terms in the assessment of the uncertainty of both smooth trends and...
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Since the late 1980s, the use of commercial fertilisers in most Eastern European countries has decreased at an unprecedented rate. We examined the impact of this dramatic reduction in agricultural inputs on concentrations of nutrients in... more
Since the late 1980s, the use of commercial fertilisers in most Eastern European countries has decreased at an unprecedented rate. We examined the impact of this dramatic reduction in agricultural inputs on concentrations of nutrients in four rivers in Eastern Europe: the Emajogi and Ohnejogi (Estonia), the Daugava (Latvia), and the Tisza (Hungary). Time series of nitrate (NO3-N) and phosphate (PO4-P) concentrations and data on runoff were selected to represent catchments with substantial areas of agricultural land and available time series of sufficient length and frequency. The study period was 1987-1998. We detected downward trends in nitrate-N and phosphate-P in only two of the four rivers. Our results imply that the response to the extensive decrease in agricultural intensity since the late 1980s has been slow and limited in many rivers. Corresponding results in the literature are inconclusive and comprise several examples of both decreasing and non-decreasing nutrient concentr...
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Riverine transport is the, most important pathway for input of nutrients to the Gulf of Riga. The present study focused on updating existing estimates of the riverine nutrient contributions and on improving the favailable information on... more
Riverine transport is the, most important pathway for input of nutrients to the Gulf of Riga. The present study focused on updating existing estimates of the riverine nutrient contributions and on improving the favailable information on temporal and spatial variation in such input. The results show that the gulf received an average of 113,300 tons of nitrogen, 2050 tons of
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... This article shows how information about the riverine load of pollutants at different sites in a study area can be combined with data on the spatial distribution of sources and selected river basin characteristics to carry out a... more
... This article shows how information about the riverine load of pollutants at different sites in a study area can be combined with data on the spatial distribution of sources and selected river basin characteristics to carry out a statistical source apportionment of the load observed at ...
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ABSTRACT The demands on monitoring systems have gradually increased, and interpretation of the data is often a matter of controversy. As an example of this, we investigated water quality monitoring and the eutrophication issue in Sweden.... more
ABSTRACT The demands on monitoring systems have gradually increased, and interpretation of the data is often a matter of controversy. As an example of this, we investigated water quality monitoring and the eutrophication issue in Sweden. Our results demonstrate that powerful statistical tools for trend analysis can reveal flaws in the data and lead to new and revised interpretations of environmental data. In particular, we found strong evidence that long-term trends in measured nutrient concentrations can be more extensively influenced by changes in sampling and laboratory practices than by actual changes in the state of the environment. On a more general level, our findings raise important questions regarding the need for new paradigms for environmental monitoring and assessment. Introduction of a system in which conventional quality assurance is complemented with thorough statistical follow-up of reported values would represent a first step towards recognizing that environmental monitoring and assessment should be transformed from being a system for sampling and laboratory analyses into a system for interpreting information to support policy development.
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This article presents the results of the first critical examination of time series of riverine nutrient-load data for the entire Baltic Sea drainage area. Water quality data collected by or for the different national environmental... more
This article presents the results of the first critical examination of time series of riverine nutrient-load data for the entire Baltic Sea drainage area. Water quality data collected by or for the different national environmental agencies were compiled and analysed statistically to identify and remove inconsistent or obviously incorrect observations. Moreover, sampling tours were undertaken to acquire additional information about
Research Interests: Time Series, Water quality, Wastewater Treatment, Environmental Monitoring, Multidisciplinary, and 12 morePhosphorus, Atmospheric deposition, Nitrogen Fixation, Land Use, Nitrogen, Data Collection, Natural Sciences, Marine Algae, Environmental monitoring and assessment, Nutrient Loading, Water Quality, and Nutrient Concentration
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If a computer model is run many times with different inputs, the results obtained can often be used to derive a computationally cheaper approximation, or surrogate model, of the original computer code. Thereafter, the surrogate model can... more
If a computer model is run many times with different inputs, the results obtained can often be used to derive a computationally cheaper approximation, or surrogate model, of the original computer code. Thereafter, the surrogate model can be employed to reduce the computational cost of a variance-based sensitivity analysis (VBSA) of the model output. Here, we draw attention to a procedure in which an adaptive sequential design is employed to derive surrogate models and estimate sensitivity indices for different sub-groups of inputs. The results of such group-wise VBSAs are then used to select inputs for a final VBSA. Our procedure is particularly useful when there is little prior knowledge about the response surface and the aim is to explore both the global variability and local nonlinear features of the model output. Our conclusions are based on computer experiments involving the process-based river basin model INCA-N, in which outputs like the average annual riverine load of nitrogen can be regarded as functions of 19 model parameters.
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... Yet other techniques are restricted to specific types of isotonic regression problems (Restrepo and Bovik, 1993; Schell and Singh, 1997; Pardalos and ... approach to MR/IR problems in which the PAV algorithm was generalized from fully... more
... Yet other techniques are restricted to specific types of isotonic regression problems (Restrepo and Bovik, 1993; Schell and Singh, 1997; Pardalos and ... approach to MR/IR problems in which the PAV algorithm was generalized from fully to partially ordered data. ...
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... Page 7. A generalised PAV algorithm 7 [10] Maxwell WL and Muchstadt JA (1983). ... Proceedings Book, International Society of Clinical Biostatistics, 19-23 August, Sweden, Stockholm, 162. [15] Schell MJ and Singh B. (1997). The... more
... Page 7. A generalised PAV algorithm 7 [10] Maxwell WL and Muchstadt JA (1983). ... Proceedings Book, International Society of Clinical Biostatistics, 19-23 August, Sweden, Stockholm, 162. [15] Schell MJ and Singh B. (1997). The reduced monotonic regression method. ...