| 1. |
- Almgren, Kjell
(author)
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Detail Surveying with GPS
- 1995
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Licentiate thesis (other academic/artistic)abstract
- Abstract In the past ten years, the Global Positioning System (GPS) has revolutionized navigation and positioning at or near the surface of the Earth. Even though it is developed and authorized by the US military forces, it has found a remarkable civilian use. In most uses of GPS, the position accuracy is in the order of metres. To achieve better accuracy (i.e. at the centimetre level), the position determination is somewhat more complicated. Firstly, centimetre accuracy can not be established with a single receiver since too many errors will affect the observations. At least two receivers have to be used, and it is the vector between the receivers which can be accurately determined. Secondly, the integer numbers of whole cycles between each satellite and receiver, called cycle ambiguities, have to be determined. This is a rather complicated procedure, which will delay the time to get a solution. Many papers have been written in the last decade about different methods for resolution of ambiguities as fast as possible and the emphasis of this thesis is put at a description of some of these theories. Ambiguities can either be determined while the receiver is at rest or while it is in motion. The latter case is called ambiguity resolution on the fly and it gives in several ways a more complicated model to solve. To aid the users, this thesis starts with a short description of the system, its history and use today followed by a list of different measuring techniques and the plans for an operational reference system in Sweden. Furthermore, observation techniques and error sources are briefly discussed together with other factors affecting the measurements such as satellite geometry and distances between receivers. In order to validate the theoretical part, some practical tests is carried out and calculated by a RlNEX-based software developed by the author for this special purpose. Parameters such as receiver compatibility, distance between receivers, number of frequencies, number of satellites and multipath effects are investigated. To enable setting out using GPS, a radio link has to send corrections to the roving receiver. This is one of the most interesting utilities for GPS in the future. To enable set outs, a real-time system has to be used. This utility is briefly explained and investigated. From the practical part, some conclusions can be drawn. Firstly, a dual-frequency receiver is superior compared to a single frequency unit when a fast solution is wanted. However, there might be some problems when initializing the second frequency due to encryption. Secondly, the time of ambiguity resolution is highly dependent of the number of satellites in view since redundant satellites give the possibility to reject false solutions at an early stage. Finally, real- time observations will significantly improve the use of GPS since otherwise, there are no possibilities to tell the user in the field when ambiguities are solved.
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| 2. |
- Elmberg, Johan, 1960-, et al.
(author)
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Do intruding predators and trap position affect the reliability of catches in activity traps?
- 1992
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In: Hydrobiologia. - 0018-8158 .- 1573-5117. - 0018-8158 ; 239:3, s. 187-193
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Journal article (peer-reviewed)abstract
- Forty lakes in Sweden and Finland were sampled in 1990 with activity traps to evaluate the effects of trapped predators on invertebrate catch. Vertebrate (fish, newts) and invertebrate (leeches, dragonflies, water beetles, backswimmers and water scorpions) predators were considered separately. Invertebrate predators affected neither the abundance nor the taxonomic diversity of the catches. Vertebrate predators had no effect on the abundance but reduced the taxonomic diversity of the catches significantly. Thus, vertebrate predators are a possible source of bias in activity trap catches, but oily concerning taxonomic diversity. Within the depth gradient studied (0.25-0.75 m), trap position (suspended in mid-water versus on the bottom) did not affect the percentages of nektonic and benthic invertebrates in the catches. The relative abundance of all taxa was similar in the catches from different trap positions, but the relative abundance of the most numerous taxa as well as the diversity of the catches differed between trap positions. We conclude that both mid-water and bottom traps are suitable for monitoring aquatic invertebrates, and that bottom traps may be preferred for practical reasons.
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| 3. |
- Elmberg, Johan, 1960-, et al.
(author)
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Factors affecting species number and density of dabbling duck guilds in North Europe
- 1993
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In: Ecography. - 0906-7590 .- 1600-0587. - 0906-7590 ; 16:3, s. 251-260
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Journal article (peer-reviewed)abstract
- We addressed how species number and pair density in guilds of co-existing species is related to habitat structure, and to the abundance and diversity of food resources. using the assemblage of seven species of dabbling ducks (genus Anas) breeding in 60 lakes distributed over six regions in temperate north Europe. Partial correlation and multiple regression revealed that species richness was best predicted by habitat structural diversity as indexed by a principal component analysis based on 18 vegetation and lake characteristics, and by the abundance of aquatic and emergent prey. We found no effect of lake size or prey size diversity on species richness. Pair density was correlated with the percentage of shoreline with horsetails (Equisetum), by habitat structural diversity and by the abundance of emergent invertebrate prey. Neither prey size diversity nor abundance of aquatic prey correlated with pair density. Species richness and pair density in North European duck guilds vary both with habitat structure and prey availability.
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| 4. |
- Elmberg, Johan, 1960-, et al.
(author)
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Interspecific interactions and co-existence in dabbling ducks : observations and an experiment
- 1997
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In: Oecologia. - 0029-8549 .- 1432-1939. - 0029-8549 ; 111:1, s. 129-136
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Journal article (peer-reviewed)abstract
- We studied the possible role of resource limitation and interspecific competition in assemblages of dabbling ducks on breeding lakes in Finland and Sweden with observational and experimental data. After initial vegetation mapping and yearly censuses of ducks in 1985-1990, we collected observational data in 1991-1994 from 28 lakes with natural populations of mallard Anas platyrhynchos and teal A. crecca. Mallard and teal co-occur over vast areas in the Holarctic and they are the only breeding dabbling ducks on many oligotrophic lakes. Both species are migratory in our study regions, teal arriving later in spring than mallards. Log-linear model analysis of observational presence/absence data revealed a positive, not a negative, association between the species. This association was independent of habitat diversity as well as of lake size. Mallard-teal interaction was also studied in a cross-over introduction experiment in 32 other lakes in two years. Wing-clipped mallards were introduced to breeding lakes before the arrival of teal to induce resource limitation and interspecific competition, hypothesized to reduce lake use by teal. The density of mallard pairs on experimental lakes was 2.9-8.0 times higher than on controls, but there was no negative response by teal to the treatment. This is the first combined observational-experimental demonstration of lack of interspecific competition in waterfowl. Our results indicate that heterospecific attraction may affect species co-existence in dabbling ducks.
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| 5. |
- Elmberg, Johan, 1960-, et al.
(author)
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Patterns of lake acidity and waterfowl communities
- 1994
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In: Hydrobiologia. - 0018-8158 .- 1573-5117. - 0018-8158 ; 279-280:1, s. 201-206
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Journal article (peer-reviewed)abstract
- Breeding waterfowl communities were studied in 28 lakes in three areas in North Europe, along gradients of acid precipitation and alkalinity that result in lake conditions ranging from unaffected to strongly acidified. Acidic lakes had generally sparser and less complex vegetation, and fewer invertebrates were caught in activity traps. There was neither correlation between pH and waterfowl species richness (genus Anas, family Anatidae, and waterfowl sensu latu tested separately), nor between pH and waterfowl diversity (Simpson's index). Further, pH and waterfowl population density (genus Anas, family Anatidae, and waterfowl sensu latu) were not correlated, but when functional rather than taxonomic groups were considered, pH and relative abundance of fish-eating species (Gaviidae and Podicipedidae) were correlated. However, the relative abundance of Bucephala clangula, a diving duck that may compete with fish for food, was not correlated with pH. Although individual species may be affected, community level responses of waterfowl to acidity are either absent or hard to detect at our sites.
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| 6. |
- Elmberg, Johan, 1960-, et al.
(author)
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Relationships between species number, lake size and resource diversity in assemblages of breeding waterfowl
- 1994
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In: Journal of Biogeography. - 0305-0270 .- 1365-2699. - 0305-0270 ; 21:1, s. 75-84
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Journal article (peer-reviewed)abstract
- Breeding waterfowl, habitat diversity and food diversity were studied in 31 boreal lakes in Finland and Sweden. Lakes were 2-48 hectares in size, and had zero to eleven waterfowl species each. In all, sixteen species of Gaviiformes, Podicipediformes, Anseriformes and Fulica were recorded. The observed species distribution deviated from the 'null' expectation derived from a model of random placement, indicating a low importance of lake area per se. However, lake area was found to be a better predictor of species number than was length of shoreline, and lake area-species number regressions gave values between 0.255 and 0.345. We further evaluated 'the area per se (sampling)' hypothesis and 'habitat diversity' hypothesis separately by multiple stepwise regressions, in which lake area explained most of the variation in species number in species dependent on the lake for brood-rearing. Richness of more mobile species and of all species was best explained by the number of prey taxa encountered in the lake.
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| 7. |
- Kindbom, Karin, et al.
(author)
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Nationell miljöövervakning av luft- och nederbördskemi
- 1997
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Reports (other academic/artistic)abstract
- I föreliggande rapport redovisas resultat från 1995 års mätningar av luftens och nederbördens sammansättning i bakgrundsmiljö i Sverige. Rapporten redovisar mätresultat från de båda nationella övervakningsnäten EMEP-nätet och Luft- och nederbördskemiska nätet. I rapporten redovisas även de spridnings- och depositionberäkningar som gjorts med MATCH-modellen, med 1995 års mätresultat som grund. Tidigare år har mätresultat och modellberäkningar rapporterats i tre skilda rapporter, men har här samlats i en rapport. Samtliga mätningar drivs av IVL, på uppdrag av Naturvårdsverket, med undantag av ozonmätningarna i Aspvreten som genomförs av ITM. Modellberäkningarna med MATCH-Sverige har utförts av SMHI. Verksamheten finansieras av Miljöövervakningsenheten vid Naturvårdsverket. I rapportens bilagor redovisas provtagnings- och analysmetoder, mätprogram och kvalitetssäkringsrutiner utförligt. Denna samlade redovisning av information rörande mätverksamheten är tänkt att fungera som referens till kommande årsrapporter.
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| 8. |
- Kindbom, Karin, et al.
(author)
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Nationell miljöövervakning av luft- och nederbördskemi 1996
- 1998
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Reports (other academic/artistic)abstract
- I föreliggande rapport redovisas resultat från 1996 års mätningar av luftens och nederbördens sammansättning i bakgrundsmiljö i Sverige. Rapporten redovisar mätresultat från de båda nationella övervakningsnäten EMEP-nätet och Luft- och nederbördskemiska nätet. I rapporten redovisas även de spridnings- och depositionberäkningar som gjorts med Sverigemodellen. Samtliga mätningar drivs av IVL, på uppdrag av Naturvårdsverket, med undantag av ozonmätningarna i Aspvreten som genomförs av ITM. Modellberäkningarna med Sverigemodellen utförs av SMHI. Verksamheten finansieras av Miljöövervakningsenheten vid Naturvårdsverket. Mätningarna har under 1996 omfattat dygnsprovtagning av svaveldioxid, kvävedioxid och partikelbundet sulfat i luft vid sex EMEP-stationer, av sot vid fem stationer samt dygnsprovtagning av totalnitrat och totalammonium vid fyra av stationerna. Månadsprovtagning av lufthalter av svaveldioxid och kvävedioxid har skett vid tolv stationer i landet. Registrering av halter av marknära ozon har skett på timbasis vid sammanlagt sex stationer. Nederbördsprovtagning, dygnsvis med lock-provtagare, har utförts hela året vid en station och veckovis vid tre stationer. Månadsprovtagning av nederbörd med öppna insamlare har skett vid 28 stationer. Nederbördsproverna har analyserats med avseende på pH, sulfat, nitrat, ammonium, klorid, kalcium, magnesium, natrium, kalium och konduktivitet. Vid fyra stationer vardera har nederbörd samlats in för analys av tungmetaller respektive av total-kvicksilver och metylkvicksilver. Genomgående visar mätresultaten ett spridningsmönster med högre halter och deposition i södra Sverige och avtagande värden mot norr. Över södra Halland, inre Skåne och östra Blekinge, där den största totaldepositionen av svavel (exkl. havssalt) uppträdde, var den maximala beräknade depositionen knappt 900 mg S/m2. I Göteborgstrakten erhölls den största totaldepositionen för oxiderat kväve, ca 800 mg N/m2, medan depositionen av reducerat kväve var störst över inre Skåne, ca 850 mg N/m2. En beräknad luftföroreningsbudget för 1996 visar en nettoimport av föroreningar till Sverige, liksom under tidigare år. Importen var för svavel och reducerade kväveföreningar 4-5 gånger så stor som exporten, medan importen av oxiderat kväve endast var ca 10% större än exporten. Årsmedelhalten av marknära ozon var, liksom tidigare år, högst i Esrange i norr, 67 µg/m3. Antalet tillfällen med timmedelhalter överskridande 120, 150 respektive 180 µg/m3 var generellt högre än 1995 men lägre än 1994. Det högsta uppmätta timvärdet under året var 210 µg/m3 i Vavihill i juni månad. Halter i nederbörd och deposition av tungmetaller och kvicksilver uppvisar, med smärre undantag, sjunkande gradienter från söder till norr i landet
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| 9. |
- Nilsson, Anders N., et al.
(author)
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Abundance and species richness patterns of predaceous diving beetles (Coleoptera, Dytiscidae) in Swedish lakes
- 1994
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In: Journal of Biogeography. - 0305-0270 .- 1365-2699. - 0305-0270 ; 21:2, s. 197-206
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Journal article (peer-reviewed)abstract
- Abundance and species richness of dytiscid water beetles were estimated with activity traps in ten lakes each in south, central and north Sweden. Partial least square regression models with two significant components explained 76.5% and 55.8% of the total variance in dytiscid abundance and species richness, respectively. For abundance as well as species richness, component 1 had its highest positive loadings for structural complexity of vegetation and abundance of Asellus and Diptera immatures, and high negative loadings for relative shore depth. Component 2 had its highest positive loadings for fish abundance, number of dipterans in emergence traps and relative shore depth, and high negative loadings for lake area. Both the number of dytiscid individuals and species were higher in the northern lakes than in the two other regions. Smaller species were not more abundant in the traps than larger ones. Species mean abundance was positively correlated with number of lakes occupied.
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| 10. |
- Nummi, Petri, et al.
(author)
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Habitat distribution of the mallard in relation to vegetation structure, food, and population density
- 1994
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In: Hydrobiologia. - 0018-8158 .- 1573-5117. - 0018-8158 ; 280:1, s. 247-252
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Journal article (peer-reviewed)abstract
- The mallard (Anas platyrhynchos Linnaeus) is a generalist feeder, breeding in a wide range of habitats, yet showing considerable between site differences in density. Variations in density and habitat use may result from inter- and intra-specific competition, habitat structure or food. We studied habitat selection of the mallard in four regions of Finland and Sweden. In each region, ten lakes were chosen ranging from oligotrophic to eutrophic. Habitat distribution of the mallard did not differ between regions despite variation in the density of the species and congenerics. Mallard density did not correlate with vegetation structure, but increased with food abundance and the number and density of congenerics although there were regional differences in mallard response.
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