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  • Resultat 708471-708480 av 1666853
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708478.
  • Håkanson, Lars (författare)
  • Challenges and opportunities for integrating lake ecosystem modelling approaches
  • 2010
  • Ingår i: Aquatic Ecology. - : Springer Science and Business Media LLC. - 1386-2588 .- 1573-5125. ; 44, s. 633-667
  • Tidskriftsartikel (refereegranskat)abstract
    • A large number and wide variety of lake ecosystem models have been developed and published during the past four decades. We identify two challenges for making further progress in this field. One such challenge is to avoid developing more models largely following the concept of others ('reinventing the wheel'). The other challenge is to avoid focusing on only one type of model, while ignoring new and diverse approaches that have become available ('having tunnel vision'). In this paper, we aim at improving the awareness of existing models and knowledge of concurrent approaches in lake ecosystem modelling, without covering all possible model tools and avenues. First, we present a broad variety of modelling approaches. To illustrate these approaches, we give brief descriptions of rather arbitrarily selected sets of specific models. We deal with static models (steady state and regression models), complex dynamic models (CAEDYM, CE-QUAL-W2, Delft 3D-ECO, LakeMab, LakeWeb, MyLake, PCLake, PROTECH, SALMO), structurally dynamic models and minimal dynamic models. We also discuss a group of approaches that could all be classified as individual based: super-individual models (Piscator, Charisma), physiologically structured models, stage-structured models and traitbased models. We briefly mention genetic algorithms, neural networks, Kalman filters and fuzzy logic. Thereafter, we zoom in, as an in-depth example, on the multi-decadal development and application of the lake ecosystem model PCLake and related models (PCLake Metamodel, Lake Shira Model, IPH-TRIM3D-PCLake). In the discussion, we argue that while the historical development of each approach and model is understandable given its 'leading principle', there are many opportunities for combining approaches. We take the point of view that a single 'right' approach does not exist and should not be strived for. Instead, multiple modelling approaches, applied concurrently to a given problem, can help develop an integrative view on the functioning of lake ecosystems. We end with a set of specific recommendations that may be of help in the further development of lake ecosystem models.
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708479.
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708480.
  • Håkanson, Lars, 1943- (författare)
  • Compilation and testing of tools and methods for sustainable coastal management at local and regional scales : Deliverable D2.5.4, Thresholds project, 6th framework programme, EU, 108 p.
  • 2008
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • This work describes how general methods and models for sustainable coastal ecosystem management at local to regional scales may be used to address key questions in coastal management and threshold science. The general, process-based mass-balance model (CoastMab) for substances transported to, within and from for coastal areas may be used as a tool to: 1. Combat eutrophication, 2. Rank nutrient fluxes, 3. Estimate the system response related to nutrient reductions and 4. Estimate realistic values of historical or preindustrial reference levels of key bioindicators in coastal science, including the Secchi depth, a standard measure of water clarity, the clorophyll-a concentration, an operational measure of phytoplankton biomass and the concentration of cyanobacteria, a measure of the concentration of harmful algae. CoastMab is an ecosystem model giving monthly predictions to achieve seasonal variations of basin-wide properties.  The necessary driving variables may be accessed relatively easily from standard monitoring program (e.g., salinity, water temperature and tributary water dischage) and bathymetric maps (e.g., coastal volume, area and mean depth). The selected case-study area, the Gulf of Riga, is sensitive to nutrient loading because of its shallowness and low openness towards the Baltic Proper. It has been shown that these bioindicators fulfill key criteria of operational indicators for coastal management, i.e., they should be measurable, interpretable and predictable, relevant for the ecosystem function and internationally applicable.  These four bioindicators characterize different aspects of water quality: Chlorophyll-a: Phytoplankton biomass Concentration of cyanobacteria: Harmful algal blooms Secchi depth: Depth of the photic zone; depth of macrophyte and benthic algal growth Deep water oxygen saturation: Zoobenthos survival; diffusion of phosphorus from sediments Different abiotic factors (nutrient concentrations, salinity, temperature, coastal morphometry and water exchange) influence the selected bioindicators in a logical and predictable manner. This is demonstrated by extensive data and models based on or tested against empirical data. Note that one would generally need a set of operational bioindicators to get an adequate framework to analyze changes in coastal ecosystem function and structure related to eutrophication. However, if asked if there is one candidate for a general operational bioindicator, one can argue that the Secchi depth would be a favorite for that role. A central aspect of this work concerns strategies to reduce coastal eutrophication and avoid critical thresholds and regime shift and whether remedial measures should focus on nitrogen and/or phosphorus reductions. Nitrogen reductions should not be done until the outcome of such reductions can be predicted in a relevant scientific manner using validated models.  In the present situation, costly nitrogen reductions may do more harm than good in many (but not all) coastal systems, since they will likely cause increasing concentrations of harmful algae (cyanbacteria). Phosphorus reductions should be done in a cost-effective manner. Using the CoastWeb-model, similar calculations as those presented in this work for the Gulf of Riga can be made for any given coastal area and the data necessary for such calculations are discussed in this work. To the best of the author’s knowledge, no other models use the same sedimentological criteria as the CoastMab-model discussed in this work to define fundamental model structures, e.g., the surface-water compartment, the deep-water compartment, the sediment compartment for ET-areas (where there is resuspension) and the accumulation-area compartment (where there is no wind/wave-induced resuspension). This also means that key transport processes, such as sedimentation, resuspension, mixing, diffusion and outflow, are quantified differently in this modeling approach compared to most other models. All approaches to quantify these transport processes cannot be best or most relevant from a mechanistic point of view. Such a ranking of models cannot be done by arguments, only from critical validations using reliable empirical data from a wide domain of systems. The author knows of no dynamic models which provide seasonal variations for TP, SPM and salinity in coastal areas based on other structures than those discussed in this work that have been validated over such wide domains and given results even close to what has been reported for the CoastMab-model.
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