Lars Brydsten

Effects of Additions of DOC on Pelagic Biota in a Clearwater System: Results from a Whole Lake Experiment in Northern Sweden

An oligotrophic clearwater lake, initially characterized by a pronounced dominance of autotrophic phytoplankton and mostly by one species, the green alga Botryococcus, was subject to additions of dissolved organic carbon in the form of white sugar (sucrose) during two consecutive years. The hypothesis tested was that it is organic carbon per se, and not other possible effects of humic substances, that determines the differences in structure of the planktonic ecosystem between humic and clearwater lakes. The additions of DOC resulted in a significant increase in bacterial biomass and a decrease in the biomass of autotrophic phytoplankton. The biomass of mixotrophic and heterotrophic flagellates instead increased significantly, whereas no effects were found to propagate to higher trophic levels. As a result of the changes among biota, total planktonic biomass also decreased to a level typical of nearby humic lakes. We suggest that it is the carbon component of humic material and its utilization by bacterioplankton that determines the structure and function of the pelagic food web in humic lakes.

Landscape Development During a Glacial Cycle: Modeling Ecosystems from the Past into the Future

Understanding how long-term abiotic and biotic processes are linked at a landscape level is of major interest for analyzing future impact on humans and the environment from present-day societal planning. This article uses results derived from multidisciplinary work at a coastal site in Sweden, with the aim of describing future landscape development. First, based on current and historical data, we identified climate change, shoreline displacement, and accumulation/erosion processes as the main drivers of landscape development. Second, site-specific information was combined with data from the Scandinavian region to build models that describe how the identified processes may affect the site development through time. Finally, the process models were combined to describe a whole interglacial period. With this article, we show how the landscape and ecosystem boundaries are affected by changing permafrost conditions, peat formation, sedimentation, human land use, and shoreline displacement.

Studies of estuarine sediment dynamics using 137Cs from the Tjernobyl accident as a tracer

Sediment dynamics in the Ore River estuary in northern Sweden were studied by monitoring the turnover of particles associated with 137Cs in surface sediment and sediment traps during the period following the Tjernobyl accident in late April until late November 1986. River transported material was deposited in the estuary and then frequently redistributed due to resuspension-redeposition processes during the ice-free period. There was a slow net transport of particles out of the estuary which was delayed by at least one event with a significant particle redistribution to the inner part of the estuary. Wind and wave induced water dynamics are responsible for resuspension and transport of particles.

Wave-induced sediment resuspension in the Öre estuary, northern Sweden

Material transported by the Öre River in northern Sweden is all deposited within the estuary which means that resuspension is necessary for the transport of particles out of the estuary. Wave-induced sediment resuspension in the estuary was studied by monitoring the distribution of suspended particles during a resuspension-redeposition cycle. The particle concentration in the water mass was measured with a light scattering probe, calibrated by comparison with the amount of particles collected on a filter.After a long period with calm weather and a low river input less than 100 tonne of suspended particulate matter was present in the estuary. However, during a period with stormy conditions significant resuspension of sediment particles occurred within the estuary. Two days after the storm approximately 1125 tonne of suspended particulate matter was found in the estuary. Most (61%) of the suspended matter was found in the deepest third of the water column, although up to 17% was present in the top third of the water column. The total load of particulate matter in the water column remained constant until day four after the storm, but a significant redistribution of the particulate matter occurred both in the vertical and horizontal directions. Nine days after the storm, a significant amount of particles (c. 350 tonnes) was still in suspension.

Retention and long term accumulation of EOCl from pulp mill effluents in a Baltic Sea recipient

The total inventory and distribution of ExtractableOrganic Chlorine (EOCl) has been investigated in anestuary exposed to pulp mill effluents for over 50 yr.The estuarine turnover of suspended particulate matter(SPM) and associated pollutants was studied using a modeldescribing important processes for EOCl accumulation. Therecipient has a low retention of SPM due to dominatingstratified conditions in the water column. The totalinventory of EOCl in the sediment is therefore relativelylow as compared with the total discharge. It was foundthat the vertical distribution of EOCl has a closerelationship to the extent of chlorine use at the mill.Discharges of SPM from the pulp production process play amajor role in establishing the chronology of the sediment.A modernisation of the mill from 1986 to 1991 considerablyreduced the discharges of chlorinated substances. In the near future there will be an accumulation of EOCl in the estuary.

Characterization of sediments by high-frequency echo-sounding

A high-frequency echo-sounder (200 kHz) was used to characterize the sediments of the shallow Öre Estuary in the Gulf of Bothnia, northern Sweden. The acoustic signal patterns of the echogram were used to differentiate between fine-grained and coarse-grained sediment bottoms according to four major criteria: roughness of the line surface, line thickness, and occurrence of white line and double echo. The echogram characteristics were calibrated against physical properties of the sediment determined in the laboratory. It can be concluded that high-frequency echo-sounding offers an easily applied and reliable method for determining the spatial extent of different bottom sediments (e.g., fine-grained) in shallow waters.

Sedimentation of river-transported particles in the Öre estuary, northern Sweden

Sedimentation of river transported particles in the Öre Estuary was studied during spring flow (April–May, 1989). River input was calculated as the product of discharge and particle concentration in the river water. The concentration of suspended matter in the estuary water was determined with a light-scattering probe at 25 depth profiles throughout the estuary. The sedimentation was measured using sediment traps on 5 stations along a line from the river mouth to the mouth of the estuary. Sampling was carried out on four dates with different water discharge.The extension of the particle plume varied during the observation period mainly due to variation in river discharge. The maximum extension of the river plume occurred during the peak of the spring flow and covered approximately 70% of the estuary area. The sedimentation rates were generally high and the average retention time for a particle in the water column was less than 1 day which verifies that the river transported fine-grained particles are primary deposited within the estuary. The major part of the river input of suspended matter was deposited near the river mouth. There was a surplus of the total sedimentation compared to the river input which was due to wave-induced resuspension, especially in the eastern part of the estuary.

Turnover of particulate matter in a Baltic estuary

The turnover of particulate material in Gardsfjarden, a semi-enclosed, non-tidal estuary of the Baltic Sea, was studied during 1 year. Large temporal variation characterized the particle dynamics. The estuary had a stable stratification during most of the year, being mainly controlled by temperature. Under stratified conditions, inflowing particulate material of fluvial origin was largely transported straight through the estuary to the sea. At the spring and autumn turnover of the water column, there was a net erosion of the surface sediment due to re-suspension. Barotropbically forced seawater intrusions destabilized the stratification on a few occasions in the summer, and probably more often in the winter, causing increased retention of suspended particulate matter in the summer, and increased re-suspension and erosion of the surface sediment in the winter. The morphology of the basin, the bi-annual turnover of the water column and irregular seawater intrusions were the three most important factors governing the turnover of particulate material in Gardsfjarden.

Landscape modeling for dose calculations in the safety assessment of a repository for spent nuclear fuel

The Swedish Nuclear Fuel and Waste Management Co., (SKB), pursues site investigations for the final repository for spent nuclear fuel at two sites in the south eastern part of Sweden, the Forsmark- and the Laxemar site (figure 1). Data from the two site investigations are used to build site descriptive models of the areas. These models describe the bedrock and surface system properties important for designing the repository, the environmental impact assessment, and the long-term safety, i.e. up to 100,000 years, in a safety assessment. In this paper we discuss the methodology, and the interim results for, the landscape model, used in the safety assessment to populate the Forsmark site in the numerical dose models. The landscape model is built upon ecosystem types, e.g. a lake or a mire, (Biosphere Objects) that are connected in the landscape via surface hydrology. Each of the objects have a unique set of properties derived from the site description. The objects are identified by flow transport modeling, giving discharge points at the surface for all possible flow paths from the hypothetical repository in the bedrock. The landscape development is followed through time by using long-term processes e.g. shoreline displacement and sedimentation. The final landscape model consists of a number of maps for each chosen time period and a table of properties that describe the individual objects which constitutes the landscape. The results show a landscape that change over time during 20,000 years. The time period used in the model equals the present interglacial and can be used as an analogue for a future interglacial. Historically, the model area was covered by sea, and then gradually changes into a coastal area and, in the future, into a terrestrial inland landscape. Different ecosystem types are present during the landscape development, e.g. sea, lakes, agricultural areas, forest and wetlands (mire). The biosphere objects may switch from one ecosystem type to another during the modeled time period, from sea to lake, and from lake to mire and finally, some objects are transformed into agricultural area due to favorable farming characteristics.Copyright