Biouptake pelagic-benthic

There are some interesting principles for metals in general that could be addressed, using Hg and Cs as type elements - e.g., the difference between a continuous contamination, like that for Hg, and the sudden peak in contamination for Cs, the fundamental differences between pelagic and benthic biouptake, the difference that Hg has an organic/lipophilic phase, which Cs has not, the importance of the partition coefficient and the differences in retention times between the two elements in biota. 

Fig. 9.4. The new mixed model for metals in lakes. Load (or dose) parameters are related to the input of metals to the lake (direct load and load from the catchment), the metal amount in the lake water is distributed into dissolved and particulate phases by the partition coefficient (Kd). Sedimentation is net sedimentation per unit of time (the calculation unit is set to 1 year for Hg and 1 month for Cs). The sensitivity parameters influence biouptake of metals from water to phytoplankton (but they may also be used in other contexts, e.g., to influence the Kd-values, as illustrated by the dotted line, or the rate of sedimentation). The biological or ecosystem variables include pelagic and benthic uptake, bioaccumulation and retention time in the five compartments (lake water, active sediments, phytoplankton, prey and predator fish). The ejfect parameter is the concentration of the metal in predatory fish (used for human consumption). One panel gives the calculation of concentrations, another the driving parameters (model variables should, preferably, not be altered for different lakes, while environmental variables must be altered for each lake). The arrows between these two panels illustrate the phytoplankton biomass submodel...

The focus will now be set on the role of (1) the partition coefficient, (2) a changing pH (related to liming), (3) differences in biouptake pattern (pelagic or benthic) and (4) differences in retention (turnover) in the biological compartments (a slower retention for Hg and a faster retention for Cs). All data on rates and model variables are given in Table 9.5, and interesting data on amounts and fluxes in Table 9.7. 

There are several possible strategies to reduce metal concentrations in freshwater fish. Great and principally interesting differences exist between metals like Hg, which partly appear in an organic (lipophilic) phase (and not just as Hg , Hg ", etc.) and metals like Cs, which only appear in inorganic phases. The amount of metals in fish depends foremost on the biouptake route (pelagic or benthic uptake) and the retention of the metal in fish. The bioavailability can be regulated by a number of chemical and physical variables, such as pH, total-P and color. 

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