The Effect of Climate Change on an Arctic Marine Food Web

Climate change in the Arctic affects the distribution of organic contaminants and their bioaccumulation (the net result of contaminant uptake and purging by an organism). Borga et al. (2009) investigate the effect of increased temperature and primary production on bioaccumulation of organic contaminants at various trophic levels. The authors base their investigation on the idea that temperature can alter partitioning of organic compounds, which can affect the bioavailability of contaminants for direct uptake by aquatic organisms. Similarly, climate change can also affect the transport of contaminants in Polar Regions, as well as an increase in new species due to overall temperature gain. Clara Lyashevsky
Borga, K., Saloranta, T., and Ruus, A., 2010. Simulating climate changeinduced alterations in bioaccumulation of organic contaminants in an arctic marine food web. Environmental Toxicology and Chemistry 29, 1349–1357.

The study focused on the marine food web of the Arctic. This includes primary producers (phytoplankton), secondary producers (calanoid copepods and krill), predators (pelagic amphipods), and piscivorous seabirds (kittiwake, Rissa tridactyla). The model used in the study was based in spring because it is the most productive period of the year. The authors predicted the magnitude and direction of change in bioaccumulation of organic contaminants for three substances (HCH, PCB-52, PCB-153). These three substances were chosen due to their differences in molecular structure, solid-water partitioning properties, and persistence in fish and birds. The experiment was carried out at different trophic levels in an Arctic shelf sea food web (Barents Sea), in two different future climate change scenarios with increased temperature and amount of particulate organic carbon (POC).
The bioaccumulation model was used to estimate six different contaminant rate constants governing the intake and elimination of POPs in an organism; uptake (kI) and elimination (kO) to water or air via respiratory surfaces, dietary uptake (kD), and elimination due to excretion (kE), biotransformation (kM), and growth dilution (kG).
The simulation model was used to measure bioaccumulation and contaminant concentration changes in a projected future climate for each food web organism. The ratio of contaminant concentrations in a future climate scenario (cb_scen) and in the present state (cb_ctrl; control simulation) was introduced in order to create the model. The rate constants are linear, resulting in the total water concentration (cwat_tot) to be set to 1pg/L.
The control scenario measured HCH, PCB-52, and PCB-153 concentrations in the Barents Sea food web in May 1999. The model performance was based on the standardization of both simulated control scenario results and the measured data against the herbivorous copepod. This process permitted the bioaccumulation processes of the animals in the food web to be addressed independently from the total water and air concentrations. The standardized concentrations are referred to as biomagnification factors (BMFs).
Based on the projected increase in temperature in the Arctic, the authors defined two scenarios where temperature in water (Twater) and air (Tair) is increased by 2.0 oC in scenario 1, and by 4.0oC in scenario 2. The temperature in the control simulation (present state) is assumed to be at the point at which ice melts (0 oC) for both Twater and Tair. The body temperatures of all the food web organisms are assumed to be the same as Twater, except seabirds, which are assumed to have a constant body temperature of 40 oC. Temperature change directly affects the partitioning coefficients, which in turn affect the bioavailable POP concentrations in water and air. The temperature change in invertebrates and fish is anticipated to affect the feeding (GD) and ventilation (GV) rates as well as biotransformation and growth (kG) rate constants. The doubling of primary production in the Arctic shelf, due to the reduced sea ice cover and enhanced upwelling of nutrient-rich water, changed the water POC.
The control model agreed with the observed data. The PCB-52 showed a higher degree of biomagnification than the HCH in both modeled and measured values. The PCB-153 had higher modeled and measured BMF values than the PCB-52. In the seabird, the modeled BMF of HCH and PCB-52 were higher than measured. This suggests that the actual biotransformation rate for these compounds in kittiwake is faster than the conservative half-life values. The opposite was found for PCB-153, implying that biotransformation may be slower than assumed.
The factors of change (F) based on wet weight concentrations were below 1, implying that bioaccumulation decreased compared to the control scenario. The decline in bioaccumulation was seen in lipid weight based concentrations for the PCBS, while there was no change in bioaccumulation for that of HCH. CPOC had a much higher influence on the simulated future bioaccumulation of the PCBs, compared to HCH. The compounds would have more similar future bioaccumulation scenarios if CPOC stopped increasing.

The increase in temperature and POC would reduce the bioaccumulation of PCBs in the Arctic food web, due to reduced bioavailable fraction of PCBs. The PCBs showed the largest reduction in bioaccumulation based on the climate change simulations. The HCH, however, showed less or close to no reduction in bioaccumulation as well as less variability due to season and trophic levels.

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