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| 2. |
- Humborg, Christoph, et al.
(författare)
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Nutrient land-sea fluxes in oligothrophic and pristine estuaries of the Gulf of Bothnia, Baltic Sea
- 2003
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Ingår i: Estuarine, Coastal and Shelf Science. - 0272-7714 .- 1096-0015. ; 56:3-4, s. 781-793
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Tidskriftsartikel (refereegranskat)abstract
- Estuaries are often seen as important filters between land and the sea for inorganic and organic nutrients. This paper aims at estimating the estuarine fluxes of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) and dissolved silicate for the major oligothrophic and pristine rivers running into the Bothnian Bay (BB) and the Bothnian Sea (BS), the northern subarctic subbasins of the Baltic Sea. Long-term data sets for these rivers and their estuaries as well as for the BB and BS were analyzed to assess whether these estuaries are sinks for inorganic nutrients. Most studied estuaries can be characterized as salt wedge estuaries with little exchange between the fresh seaward-flowing river water and the inward-flowing seawater. Estimates of water transit times ranged between 1 and 14 days. In most estuaries of the BB, N-depleted river water meets P-depleted seawater during the growth period. These findings were corroborated by mixing diagrams showing that the inner areas of the estuaries were N-depleted in summer. In the BS, on the other hand, both rivers and seawater were mostly N-depleted during summer. Thus, for most estuaries of this region of the Baltic Sea, primary productivity is presumably lower than or equal to that of offshore. The low productivity is also reflected in the sediments. The coastal sediments did not differ from the offshore stations in accumulation rates as well as the content of organic matter and nutrients, indicating that estuarine nutrient burial is not always higher as normally observed in other temperate systems. Finally, the estuaries of the pristine rivers in the northernmost part of the BB import DIN during summer, whereas the estuaries of the rivers in the BS import DIP during winter, from the sea. ⌐ 2003 Elsevier Science B.V. All rights reserved.
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| 3. |
- Humborg, Christoph, et al.
(författare)
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Nutrient variations in boreal and subarctic Swedish rivers : Landscape control of land–sea fluxes
- 2004
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 49:5, s. 1871-1883
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Tidskriftsartikel (refereegranskat)abstract
- We examined the hypothesis that the extent of vegetation cover governs the fluxes of nutrients from boreal and subarctic river catchments to the sea. Fluxes of total organic carbon (TOC) and dissolved inorganic nitrogen, phosphorus, and dissolved silicate (DIN, DIP, and DSi, respectively) are described from 19 river catchments and subcatchments (ranging in size from 34 to 40,000 km2) in northern Sweden with a detailed analysis of the rivers Lulea¨lven and Kalixa¨lven. Fluxes of TOC, DIP, and DSi increase by an order of magnitude with increasing proportion of forest and wetland area, whereas DIN did not follow this pattern but remained constantly low. Principal component analysis on landscape variables showed the importance of almost all land cover and soil type variables associated with vegetation, periglacial environment, soil and bedrock with slow weathering rates, boundary of upper tree line, and percentage of lake area. A cluster analysis of the principal components showed that the river systems could be separated into mountainous headwaters and forest and wetland catchments. This clustering was also valid in relation to river chemistry (TOC, DIP, and DSi) and was confirmed with a redundancy analysis, including river chemistry and principal components as environmental variables. The first axis explains 89% of the variance in river chemistry and almost 100% of the variance in the relation between river chemistry and landscape variables. These results suggest that vegetation change during interglacial periods is likely to have had a major effect on inputs of TOC, DIP, and DSi into the past ocean.
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| 5. |
- Höglander, Helena, 1973-
(författare)
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Studies of Baltic Sea plankton - spatial and temporal patterns
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examines the spatial and temporal patterns of Baltic Sea phyto- and zooplankton. Studies of such patterns are important to gain a better understanding of the offshore nutrient dynamics of the Baltic Sea (Papers I and II) and how to manage eutrophication and invasive species in coastal areas (Papers III and IV). During the spring phytoplankton bloom, diatoms rapidly depleted inorganic nitrogen in the shallow mixed layer, but were replaced by dinoflagellates when a seasonal pycnocline developed early in spring due to riverine freshwater inputs (Paper I). The settling of diatoms from the mixed water column was species-specific (Paper I). Vertically migrating dinoflagellates were able to exploit nutrients to considerable depth. The settling of primary produced carbon was low, only 12% as particulate organic carbon (POC) at 100 m and 2% as identifiable cells (Paper I). Profound alterations in species composition during settling will hinder interpretation of paleoecological records. During summer cyanobacterial blooms, vertically separated diazotrophic and mixotrophic species dominated the phytoplankton community. Unicellular and colony-forming picocyanobacteria, a hitherto underestimated group, made up a substantial part of phytoplankton biomass late in the bloom (Paper II). Dominant species during the blooms exhibited species-specific depth distributions, suggesting niche-separation to decrease competition. Management of coastal eutrophication is of major concern, particularly in estuaries and enclosed seas with limited water exchange. In Himmerfjärden, a eutrophicated Baltic Sea bay, filamentous nitrogen-fixing cyanobacteria increased substantially following a drastic reduction in nitrogen load from a modern sewage treatment plant (STP). Seston <10 µm responded to the 15N-enriched nitrogen from the STP with a δ15N-value of near 8‰ close to the discharge point, compared to only 2‰ in the open Baltic. In contrast, filamentous nitrogen-fixing cyanobacteria had δ15N-values of -3.0‰ to -0.2‰ (average -1.5‰) independent of distance to the STP (Paper III), indicating that they used only dinitrogen for growth. When cyanobacteria were abundant, total nitrogen concentrations increased and δ15N decreased in seston <10 µm and zooplankton >200 µm (Paper III), indicating that fixed nitrogen was transferred to other trophic levels. During a later deliberate experimental discharge of nitrogen designed to suppress cyanobacterial growth, cyanobacteria used some dissolved inorganic nitrogen but their biomass was not markedly reduced (Paper III). The cladoceran zooplankton Cercopagis pengoi, a recent invader to the Baltic Sea, is a potential competitor with fish for zooplankton prey. Stable nitrogen isotope studies imply that invasion by C. pengoi has changed the pelagic food web structure in the bay Himmerfjärden by competing with small pelagic fishes for zooplankton, and by providing a new prey for these fishes (Paper IV). These results indicate the risk of cascading effects on other trophic levels and the necessity of whole ecosystem analysis when evaluating effects of invasive species (Paper IV).
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| 6. |
- Ittekot, Venu, et al.
(författare)
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Carbon Silicon Interactions.
- 2003. - 1
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Ingår i: Interactions of the Major Biogeochemical Cycles: Global Change and Human Impacts. - New York : Island Press. - 1559630655 - 9781559630658 ; , s. 311-336
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The circulation and interactions of major elements such as carbon, nitrogen, phosphorus, sulphur, oxygen, and hydrogen are critical for the maintenance of the earth's ecosystems. Human activities including agriculture, industry, and urbanization alter element interactions and contribute to major environmental problems ranging from climate change and depletion of the ozone layer to acidification of soils to the destruction of coral reefs.Interactions of the Major Biogeochemical Cyclesis a new scientific assessment of element interactions in the biosphere. It provides an up-to-date review of biogeochemistry and its effects on earth's systems, with leading experts in biogeochemical cycling in atmospheric, land, freshwater, and marine environments offering chapters that summarize and synthesize information in each discipline.The book opens with chapters on cross-cutting issues that have significance in understanding global change effects and their potential management. These chapters address:* trends in element interactions in response to global changethe effects of natural disturbancesnew approaches and methods for advancing our understanding of element interactionsthe potential for managing element interactions to address major environmental issues
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| 7. |
- Rahm, Lars, 1948-, et al.
(författare)
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Ecological Economic Interactions : Considerations for Coastal Zone Management
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Coastal zones are the meeting point for land and ocean. Besides these land-ocean interactions, the coastal zone can also be distinguished by the many and strong interactions between the biotic and abiotic systems and the regional economy. Around the world coastal systems are coping with ncreased human pressures in the form of an increased demand for space and other resources as a result of for example population growth, migration and an expansion of tourism. In addition, coastal areas have to deal with natural pressures resulting from large scale interactions of the atmospheric, water, soil and biological systems including climatic change.Derivations from the natural material and energy flows in the coastal zone are often a result of changes in land-use and other man-induced impacts within the watershed, the coastal zone or in the ocean. A considerable part of the changes do not originate in the coastal zone itself but are caused by land based activities upstream in the catchment area (see for example the case studies below of the Baltic Sea and the Black Sea). In general, there is a lack of understanding of the interdependence of natural and human systems and processes, especially for river basins and coasts. Furthermore, there is only limited knowledge of how activities in the catchment area influence the coastal zone. Consequently, in order to aid policy formulation and decision-making, the interactions between natural and human systems in respectively the catchment area and the coastal zone as well as the connection between them, need to be identified, studied, and at least partly understood.In attempting a linked analysis of natural and human processes, special attention should be paid to the different temporal and spatial scales on which they operate. One of the most important issues that needs further studying is the temporal and spatial disparity between processes and activities in the catchment area and effects in the coastal zone. This includes the time lags and spatial disparity between activities and their effects as well as the time ags between effects of activities and the time decision makers need to take action to identify, study and eventually reduce these impacts. Each of these issues will now be elaborated upon.
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