Marine ecosystem modeling beyond the box: using GIS to study carbon fluxes in a coastal ecosystem

Studies of carbon fluxes in marine ecosystems are often done by using box model approaches with basin size boxes, or highly resolved 3D models, and an emphasis on the pelagic component of the ecosystem. Those approaches work well in the ocean proper, but can give rise to considerable problems when applied to coastal systems, because of the scale of certain ecological niches and the fact that benthic organisms are the dominant functional group of the ecosystem. In addition, 3D models require an extensive modeling effort. In this project, an intermediate approach based on a high resolution (20x20 m) GIS data-grid has been developed for the coastal ecosystem in the Laxemar area (Baltic Sea, Sweden) based on a number of different site investigations. The model has been developed in the context of a safety assessment project for a proposed nuclear waste repository, in which the fate of hypothetically released radionuclides from the planned repository is estimated. The assessment project requires not only a good understanding of the ecosystem dynamics at the site, but also quantification of stocks and flows of matter in the system. The data-grid was then used to set up a carbon budget describing the spatial distribution of biomass, primary production, net ecosystem production and thus where carbon sinks and sources are located in the area. From these results, it was clear that there was a large variation in ecosystem characteristics within the basins and, on a larger scale, that the inner areas are net producing and the outer areas net respiring, even in shallow phytobenthic communities. Benthic processes had a similar or larger influence on carbon fluxes as advective processes in inner areas, whereas the opposite appears to be true in the outer basins. As many radionuclides are expected to follow the pathways of organic matter in the environment, these findings enhance our abilities to realistically describe and predict their fate in the ecosystem.     

使用罗斯比中心海洋模型检测波罗的海次盆地的周转时间

尤其在判断气候变化可能带来的影响时,事实证明有必要对受到显著的外部影响的有限海域的水更新速度进行评估.随SWECLIM项目一起,上述工作已在波罗的海的两个生态敏感的次盆地(即里加湾和格但斯克湾)中开展.为此目的,我们已分别以质量平衡收支和拉格朗日轨迹线为基础,采用了两种方法上不同的做法.与采用拉格朗日技术获取的结果相比,事实证明,在作为一个在形态上受到极大约束的盆地的里加湾中,使用这种箱状模型方法非常合适,而在将它用于以更加开阔的地形条件为特点的格但斯克湾时却表现出一些不足.     

Naturally and hatchery produced European trout Salmo trutta: do their marine survival and dispersal differ?

We tested whether marine survival and migration pattern differed between naturally and hatchery produced European trout Salmo trutta of different origins. The hatchery fish were released 150 m above the river estuary of the southwestern, Norwegian River Imsa, the home of the local population. Recaptures were used as proxy for survival. Wild and local hatchery fish survived better than transplanted hatchery stocks. Trout that were 1 year at release survived less well than 2-year olds, and small individuals less well than larger ones. Relative to their body size at release, populations that originated most distant from the River Imsa, the Baltic River Emån and the Norwegian mountain Lake Tunhovd, exhibited the poorest sea survival. At sea, trout chiefly moved less than 240 km from the river of release, but there were significant differences in dispersal among populations. Hatchery-produced River Emån and Lake Tunhovd trout moved farther from the River Imsa than the south Norwegian sea trout populations, and the marine distributions of the former were similar to that of the natural River Imsa trout. Large fish moved farther from the river than smaller ones. Straying to other rivers was low among wild and local hatchery-produced fish, and significantly lower than among most transplanted populations, and River Emån trout in particular. Thus, the River Imsa trout appeared better adapted to survival under the local conditions than non-local trout with consequences for optimal population management.     

Baltic sub-basin turnover times examined using the Rossby Centre Ocean model

Not least when judging the possible effects of climate change it proves necessary to estimate the water-renewal rates of limited marine areas subject to pronounced external influences. In connection with the SWECLIM programme this has been undertaken for two ecologically sensitive sub-basins of the Baltic, viz. the Gulf of Riga and Gdansk Bay. For this purpose two methodologically different approaches have been employed, based on mass-balance budgets and analysis of Lagrangian trajectories, respectively. When compared to the results obtained using the Lagrangian technique, the box-model approach proved to be adequate for the Gulf of Riga representing a morphologically highly constrained basin, whereas it demonstrated certain shortcomings when applied to the more open topographic conditions characterizing Gdansk Bay.     

The formation of solid solutions in surface layers: An important adsorption mechanism?

After a short presentation of the relevant thermodynamic theory for solid solutions, the equations used for the computation of mass transfers are presented as well as methods for their solution. Two simple test programs, solusol and solumix, were constructed for the calculation of equilibria involving non-ideal solid solutions, the last taking exsolution processes into account. In another minor program, solidsol, the formation of ideal solid solutions is considered, as well as the simultaneous speciation in the aqueous phase.Based on estimated mass transfers, the experimental evidence in favour of the interpretation of some adsorption phenomena as being due to the formation of “surface solutions” is presented and discussed.     

Does juvenile experience affect migration and spawning of adult Atlantic salmon?

Summary This paper documents differences in seasonal time of river ascent and descent, and instream behavior of adult wild and sea-ranched Atlantic salmon (Salmo salar) of the Norwegian River Imsa stock during the period 1981–1989. Wild fish use River Imsa as a nursery, and at an age of 2 years most of them migrate to the sea as smolts. The sea ranched fish are hatchery reared offspring of the River Imsa stock and are released as smolts at the mouth of the river. They are thus deprived of juvenile river life and a downstream smolt migration. Wild and sea ranched salmon feed for 1 or more years in the Norwegian Sea before homing as spawners. Both groups returned simultaneously to coastal Norway, but sea ranched fish ascended the river later and descended sooner after spawning than wild fish. All wild females and almost all wild males (96.2%) spawned in the river, whereas 13.5% and 36.7%, respectively, of the mature sea-ranched females and males left the river unspawned. The annual number, but not the proportion, of unspawned fish increased with increasing density of adult salmon in the river. Unspawned females were medium sized and small (45–70 cm); unspawned males were medium sized and large (50–90 cm). Independent of the density of spawners in the river, sea ranched fish moved up- and downstream the river more often than wild fish. More than 20% of the sea-ranched salmon and less than 1% of the wild salmon passed a trap 100 m above the river outlet more than once in each direction during the same spawning reason. Moreover, sea-ranched salmon were about twice as often seriously injured during spawning as wild fish. Lack of juvenile experience from the river may be the main reason for the behavioral differences between sea-ranched and wild fish. Offprint requests to: B. Jonsson