Recovery from acidification of lakes in Finland, Norway and Sweden 1990?1999

International audienceSulphate deposition has decreased by about 60% in the Nordic countries since the early 1980s. Nitrogen deposition has been roughly constant during the past 20 years, with only a minor decrease in the late 1990s. The resulting changes in the chemistry of small lakes have been followed by national monitoring programmes initiated in the 1980s in Finland (163 lakes), Norway (100 lakes) and Sweden (81 lakes). These lakes are partly a subset from the survey of 5690 lakes in the Northern European lake survey of 1995. Trend analyses on data for the period 1990-1999 show that the non-marine sulphate concentrations in lakes have decreased significantly in 69% of the monitored lakes. Changes were largest in lakes with the highest mean concentrations. Nitrate concentrations, on the other hand, were generally low and showed no systematic changes. Concentrations of non-marine base cations decreased in 26% of the lakes, most probably an ionic-strength effect due to the lower concentrations of mobile strong-acid anions. Acid neutralising capacity increased in 32% of the lakes. Trends in recovery were in part masked by large year-to-year variations in sea-salt inputs and by increases in total organic carbon concentrations. These changes were most probably the result of climatic variations. Nordic lakes, therefore, show clear signs of recovery from acidification. Recovery began in the 1980s and accelerated in the 1990s. Reductions in sulphur deposition are the major "driving force" in the process of recovery from acidification. Further recovery can be expected in the next 10 years if the Gothenburg protocol on emissions of acidifying pollutants is implemented. Keywords: Nordic countries, sulphur deposition, lakes, recover

Detection of plagiarism in computer programming using abstract syntax trees

Plagiarism in connection with computer programming education is a serious problem. This problem is common to many universities around the world, and the University of Oslo (UoO) makes no exception. The major problem is that students plagiarize homework programming assignments written by fellow students. To deal with this situation plagiarism detection software has been developed to assess the similarity between program listings. Such software is exposed to the daunting task of minimizing the numbers of false negatives and false positives at the same time, i.e. finding the highest number of copies while avoiding those which are not. UoO uses a distributed system for delivering such assignments, called Joly. This system compares program listings by using an attribute counting metric. This is a very general metric and here I investigate whether a less general-purpose metric tuned to the particularities of programming code may perform better than the one currently being used in Joly. To this end I have developed two new structure based similarity measures which quantify the structural similarity between abstract syntax trees (AST). More specifically, I have (i) modified the standard AST representation to ease the comparison between trees, (ii) identified the most common cheating strategies employed by students, (iii) assessed the changes these strategies have on the AST structures, (iv) developed and implemented two new AST similarity measuring algorithms, ASTSIM-NWand ASTSIM-LCS, focused on uncovering plagiarism based on the most common cheating strategies leaving the most distinct AST footprints, and (v) compared the performance of the two new algorithms relative to the one being currently used in Joly. Even though the test results need to be interpreted with caution, the combined use of the two new algorithms appears to perform better in terms of false negatives and false positives. This suggests that they should be considered as candidates for complementing the current attribute counting approach in Joly and thus be exposed to more extensive testing and polishing

Long-term changes in acidification and recovery at nine calibrated catchments in Norway, Sweden and Finland

International agreements to reduce the emissions of acidifying pollutants have resulted in major changes in deposition of sulphur and nitrogen in southern Scandinavia over the past 25 years. Long-term monitoring of deposition and run-off chemistry over the past 12-25 years at nine small calibrated catchments in Finland, Norway and Sweden provide the basis for analysis of trends with special attention to recovery in response to decreased sulphur and nitrogen deposition in the 1980s and 1990s. During the 1980s and 1990s sulphate deposition in the region decreased by 30 to 60%, whereas inorganic nitrogen deposition showed very little change until the mid-1990s. Deposition of non-marine base cations (especially calcium) declined in the 1990s most markedly in southern Finland. Run-off response to these changes in deposition has been rapid and clear at the nine catchments. Sulphate and base cations (mostly calcium) concentrations declined and acid neutralising capacity increased. Occasional years with unusually high inputs of sea-salt confound the general trends. Trends at all the catchments show the same general picture as that from small lakes in Scandinavia and in acid-sensitive waters elsewhere in Europe.</p> <p style='line-height: 20px;'><b>Keywords: </b>acidification, recovery, Scandinavia, catchment, trend analysi

Trace metals in Norwegian surface waters, soils, and lake sediments - relation to atmospheric deposition

Årsliste 2006This report presents results from simultaneous trace metal surveys 1995 in Norway on atmospheric deposition based on moss analysis, the humic layer of soils, lake sediments, and surface waters. The samples of sediment and water were not taken at the same geographical locations as the moss and soil samples, but a direct comparison of the data sets is still feasible. Retrospective studies indicate that long-range transport has been a significant source of heavy metal contamination in southern Norway for the last couple of centuries, but has been considerably reduced over the last 20 years. Long-range transboundary air-pollution (LRTAP) is a very important source of of heavy metal contamination in the Norwegian environment, in particular for As, Cd, Sb, Hg, Pb, and Bi but also to some extent for V, Zn, Se, Mo, Sn, Te, and Tl. The corresponding geographic trend is reflected in samples of moss, surface soil, lake sediment, and lake water. A similar geographic trend is also indicated in the water samples for Be and Co, but not in samples of moss or soil humus. This is interpreted as a possible result of higher acidic deposition in the south wich leads to enhanced weathering of mineral matter and subsequent leaching to the lakes.Norges forskningsråd, (PROFO

Recovery from acidification of lakes in Finland, Norway and Sweden 1990–1999

Sulphate deposition has decreased by about 60% in the Nordic countries since the early 1980s. Nitrogen deposition has been roughly constant during the past 20 years, with only a minor decrease in the late 1990s. The resulting changes in the chemistry of small lakes have been followed by national monitoring programmes initiated in the 1980s in Finland (163 lakes), Norway (100 lakes) and Sweden (81 lakes). These lakes are partly a subset from the survey of 5690 lakes in the Northern European lake survey of 1995. Trend analyses on data for the period 1990-1999 show that the non-marine sulphate concentrations in lakes have decreased significantly in 69% of the monitored lakes. Changes were largest in lakes with the highest mean concentrations. Nitrate concentrations, on the other hand, were generally low and showed no systematic changes. Concentrations of non-marine base cations decreased in 26% of the lakes, most probably an ionic-strength effect due to the lower concentrations of mobile strong-acid anions. Acid neutralising capacity increased in 32% of the lakes. Trends in recovery were in part masked by large year-to-year variations in sea-salt inputs and by increases in total organic carbon concentrations. These changes were most probably the result of climatic variations. Nordic lakes, therefore, show clear signs of recovery from acidification. Recovery began in the 1980s and accelerated in the 1990s. Reductions in sulphur deposition are the major &quot;driving force&quot; in the process of recovery from acidification. Further recovery can be expected in the next 10 years if the Gothenburg protocol on emissions of acidifying pollutants is implemented. Keywords: Nordic countries, sulphur deposition, lakes, recover

Long-term changes in acidification and recovery at nine calibrated catchments in Norway, Sweden and Finland

International audienceInternational agreements to reduce the emissions of acidifying pollutants have resulted in major changes in deposition of sulphur and nitrogen in southern Scandinavia over the past 25 years. Long-term monitoring of deposition and run-off chemistry over the past 12-25 years at nine small calibrated catchments in Finland, Norway and Sweden provide the basis for analysis of trends with special attention to recovery in response to decreased sulphur and nitrogen deposition in the 1980s and 1990s. During the 1980s and 1990s sulphate deposition in the region decreased by 30 to 60%, whereas inorganic nitrogen deposition showed very little change until the mid-1990s. Deposition of non-marine base cations (especially calcium) declined in the 1990s most markedly in southern Finland. Run-off response to these changes in deposition has been rapid and clear at the nine catchments. Sulphate and base cations (mostly calcium) concentrations declined and acid neutralising capacity increased. Occasional years with unusually high inputs of sea-salt confound the general trends. Trends at all the catchments show the same general picture as that from small lakes in Scandinavia and in acid-sensitive waters elsewhere in Europe. Keywords: acidification, recovery, Scandinavia, catchment, trend analysi

Chemistry of lakes in the Nordic region - Denmark, Finland with Åland, Iceland, Norway with Svalbard and Bear Island, and Sweden

This report presents the first common evaluation of water chemistry in the Nordic countries (except for the Faroe Islands and Greenland): Denmark, Finland including Åland, Iceland, Norway including Svalbard and Bear Island, and Sweden. The Nordic countries exhibit large gradients in many chemical constituents in lake water, from Iceland in the west, Svalbard and Bear Island in the north via Denmark to Sweden, Finland and Norway, due to large differences in geology, hydrology, vegetation and air pollution. The data are interpreted relative to these factors

Hydro Aluminium Sunndal. PAH, metaller og vannkvalitet i innsjøer i regionen rundt aluminiumverket

Årsliste 2007HYDRO ALUMINIUM AS

Norwegian lakes show widespread recovery from acidification; results from national surveys of lakewater chemistry 1986-1997

International audienceSurveys of 485 lakes in Norway conducted in 1986 and again in 1995 reveal widespread chemical recovery from acidification. Sulphate concentrations in lakes have decreased by 40% in acidified areas in southern Norway. This decrease has been compensated about 25% by decreases in concentrations of base cations and of 75% by increased Acid Neutralising Capacity (ANC). The increased ANC in turn reflects lower concentrations of acidic cations Aluminum (ALn+) and Hydrogen (H+). A sub-set of 78 of the 485 lakes sampled yearly between 1986 and 1997 shows that, at first most of the decrease in non-marine sulphate (SO4*) was compensated by a decrease in base cations, such that ANC remained unchanged. Then as SO4* continued to decrease, the concentrations of non- marine calcium and magnesium ((Ca+Mg)*) levelled out. Consequently, ANC increased, and H+ and Aln+ started to decrease. In eastern Norway, this shift occurred in 1989?90, and came slightly later in southern and western Norway. Similar shifts in trends in about 1991?92 can also be seen in the non-acidified areas in central and northern Norway. This shift in trends is not as pronounced in western Norway, perhaps because of the confounding influence of sea-salt episodes on water chemistry. This is the first documented national-scale recovery from acidification due to reduced acid deposition. Future climate warming and potentially increased N-leaching can counteract the positive trends in recovery from acidification