| 1. |
- Bryhn, Andreas C., 1971-, et al.
(författare)
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A comparison of predictive phosphorus load-concentration models for lakes
- 2007
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 10:7, s. 1084-1099
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Tidskriftsartikel (refereegranskat)abstract
- Lake models that predict phosphorus (P) concentrations from P-loading have provided important knowledge enabling successful restoration of many eutrophic lakes during the last decades. However, the first-generation (static) models were rather imprecise and some nutrient abatement programs have therefore produced disappointingly modest results. This study compares 12 first-generation models with three newer ones. These newer models are dynamic (time-dependent), and general in the sense that they work without any further calibration for lakes from a wide limnological domain. However, static models are more accessible to non-specialists. Predictions of P concentrations were compared with empirical long-term data from a multi-lake survey, as well as to data from transient conditions in six lakes. Dynamic models were found to predict P concentrations with much higher certainty than static models. One general dynamic model, LakeMab, works for both deep and shallow lakes and can, in contrast to static models, predict P fluxes and particulate and dissolved P, both in surface waters and deep waters. PCLake, another general dynamic model, has advantages that resemble those of LakeMab, except that it needs three or four more input variables and is only valid for shallow lakes.
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| 2. |
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| 4. |
- Håkanson, Lars, 1943-
(författare)
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A general process-based mass-balance model for phosphorus/eutrophication as a tool to estimate “natural” reference values for key bioindicators, as exemplified using data for the Gulf of Riga
- 2009
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Ingår i: Ecological Modelling. - : Elsevier BV. - 0304-3800 .- 1872-7026. ; 220:2, s. 226-244
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Tidskriftsartikel (refereegranskat)abstract
- This work describes how a general, process-based mass-balance model (CoastMab) for phosphorus for coastal areas may be used as a tool to estimate realistic values of “natural” 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. The CoastMab-model is an ecosystem model giving monthly predictions to achieve seasonal variations of basin-wide properties. 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. The morphometry of any coastal area, as given by the size and form parameters, influences all internal processes, such as sedimentation, resuspension, diffusion in water and from sediments to water, biouptake and retention in biota, stratification, mixing and outflow. There has been no mass-balance modeling for nitrogen (N) in this work because empirical data (from the HELCOM database) clearly indicate that the monthly primary production in the Gulf of Riga is regulated by phosphorus (P) – the mean monthly total-N to total-P ratios are well over 7.2 (the Redfield-ratio) and generally higher than 15 for the data used in this study (from 1992 to 2005). At present anthropogenic loads, the average modeled monthly values for Secchi depth, chlorophyll (Chl), cyanobacteria (CB) and total-P (TP) are 3.2 m, 3.8 µg/l, 78 µg/l and 31.3 µg/l, respectively. If 50% of all anthropogenic sources to the Gulf of Riga via rivers, point sources and diffuse sources were to be removed, these values would be 3.6 m, 3.4 µg Chl/l, 63 µg CB/l and 29.1 µg TP/l. If 60% of the anthropogenic phosphorus fluxes to the Baltic Proper were to be omitted and as well as 75% of all direct anthropogenic sources to the Gulf of Riga, the values would be 4.6 m, 2.7 µg Chl/l, 45 µg CB/l and 25.4 µg TP/l. These values represent the “natural” reference levels and it is not realistic to expect that remedial measures would improve the conditions more than that. Using the CoastWeb-model, similar calculations can be made for any given coastal area and the data necessary for such calculations are discussed in this work.
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| 5. |
- Håkanson, Lars, 1943-, et al.
(författare)
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A new general approach to quantify nitrogen fixation exemplified for the Baltic Proper
- 2009
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Ingår i: The Open Marine Biology Journal. - : Bentham. - 1874-4508. ; 3, s. 36-48
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Tidskriftsartikel (refereegranskat)abstract
- This work uses empirical data from the HELCOM database and a new empirically-based model to predict the concentration of cyanobacteria in the Baltic Proper. The aim has been to estimate nitrogen fixation. The inherent variabilities/patchiness in the variables regulating nitrogen fixation are great. This means that different approaches may provide complementary information so that several relatively uncertain estimates may together provide less uncertainty in the estimate for nitrogen fixation in a given system. We show that there is marked variability in nitrogen fixation among different years (a factor of 20 between the year 2001 with the smallest value and 2005 with the highest value of about 900 kt/yr of N-fixation). The mean value for the period from 1997 to 2005 was 190 kt/yr. TN/TP based on median monthly data has been higher than the Redfield ratio of 7.2 since 1994. 6.5% of all individual data (n = 3001) from the surface-water layer (44 m) in the Baltic Proper for samples with temperatures higher than 15°C (when risks of getting cyanobacteria blooms are favoured) have TN/TP lower than 7.2. The mean TN/TP is 20 for surface-water sites with temperatures higher than 15°C, indicating that the average trophic conditions in the Baltic Proper are likely more limited by phosphorus than nitrogen. Nitrogen fixation is an important contributor to the nitrogen concentration and we give overall budgets for nitrogen and phosphorus in the Baltic Proper, including nutrient data from land uplift, which is the most important contributor for nutrients and often neglected in discussions about sources of nutrients to the Baltic Sea.
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| 6. |
- Håkanson, Lars, 1943-
(författare)
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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
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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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| 7. |
- Håkanson, Lars, 1943-, et al.
(författare)
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Data variability and uncertainty limits the capacity to identify and predict critical changes in coastal systems : A review of key concepts
- 2008
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Ingår i: Ocean and Coastal Management. - : Elsevier BV. - 0964-5691 .- 1873-524X. ; 51:10, s. 671-688
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Tidskriftsartikel (refereegranskat)abstract
- How do inherent variations and uncertainties in empirical data constrain approaches to predictions and possibilities to identify critical thresholds and points of no return? This work addresses this question in discussing and reviewing key concepts and methods for coastal ecology and management. The main focus is not on the mechanisms regulating the concentration of a given variable but on patterns in variations in concentrations for many standard variables in entire lagoons, bays, estuaries or fjords (i.e., on variations at the ecosystem scale). We address and review problems related to: (1) The balance between the changes in predictive power and the accumulated uncertainty as models grow in size and include an increasing number of x-variables. (2) An approach to reduce uncertainties in empirical data. (3) Methods to maximize the predictive power of regression models by transformations of model variables and by creating time and area compatible model variables. (4) Patterns in variations within and among coastal systems of standard water variables. (5) Based on the results of the review, we also discuss the concept “Optimal Model Scale” (OMS) and an algorithm to calculate OMS, which accounts for key factors related to the predictive power at different time scales (daily to yearly prediction) and to uncertainties in predictions in relation to access to empirical data and the work (sampling effort) needed to achieve predictive power at different time scales.
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| 8. |
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| 9. |
- Håkanson, Lars, 1943-
(författare)
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Factors and criteria to quantify the bioproduction potential of coastal areas and presentation of a simple operational Index of Biological Value (IBV) for coastal management
- 2009
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Ingår i: The Open Marine Biology Journal. - : Bentham Science Publishers Ltd.. - 1874-4508. ; 3, s. 6-15
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Tidskriftsartikel (refereegranskat)abstract
- There are major differences in the bioproduction potential of different coastal areas. The aim of this work is to review and discuss simple, operational criteria related to the bioproduction potential of coastal areas and to present and motivate an Index of Biological Value (IBV) for coastal management. This index is based on two key variables, which can be determined easily from bathymetric maps and data from standard monitoring programs: (1) the bottom area of the coast above the Secchi depth and (2) the topographical openness (or exposure) of the coastal area. The exposure is defined by the ratio between the section area of the coast and the enclosed coastal area. The boundaries of the coastal area should not be defined in an arbitrary manner but according to the topographical bottleneck method so that the exposure attains a minimum value. IBV is meant to be used to identify coastal areas with a high production potential so that preservation plans and remedial actions can be directed to such areas in a cost-efficient manner. Applying the index using a dataset including 478 coastal areas from the Baltic Sea, there were 5 (1%) extremely productive coastal areas (IBV > 50), 43 (9%) very productive coastal areas (25 < IBV < 50), 209 (43.7%) productive coastal areas (10 < IBV < 25), 214 (63.0%) moderately productive coastal areas (1 < IBV < 10) and 7 (1.5%) low-productive coastal areas (IBV < 1).
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| 10. |
- Håkanson, Lars, 1943-, et al.
(författare)
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Helcom gör dyra systemfel
- 2008
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Ingår i: Hufvudstadsbladet. - 0356-0724. ; :28/10
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Tidskriftsartikel (populärvet., debatt m.m.)
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