Long‐term dynamics of Chernobyl ¹³⁷Cs in freshwater fish: quantifying the effect of body size and trophic level

Abstract

Summary 1.Freshwater fish are a potentially important link in the transfer of radionuclides from polluted ecosystems to people. A pulsed contamination event such as the Chernobyl fallout in 1986 is a challenge to the prediction of radioactivity in biota, because activity concentrations of radionuclides can change dynamically among populations during an initial equilibration phase. This was demonstrated from time-series of 137 caesium (Cs) in fish from three Swedish lakes (1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000), eight species, > 7600 individuals). In addition, we used these data to test hypotheses about the influence of fish size and trophic level on the temporal patterns of 137 Cs. 2. In order to facilitate comparisons, a pulse-response model was developed to extract key parameters from field data: the timing ( t max ) and level ( Cs max ) of the peak concentrations, the near steady-state level ( Cs base ) and the long-term decline rate ( λ ). 3. Peak concentrations in different fish were attained 56 -806 days after the fallout. This delay ( t max ) increased with body size and trophic level. Cs max increased with fish size but was highest at intermediate trophic levels. Cs base increased by a factor of 1·8 per trophic level, but was not influenced by size across species. The 137 Cs-size relationship within species, however, shifted from negative to positive during the first 2 years. 4. The apparent ecological half-life ( T 1/2 ) for 137 Cs increased after t max and initially differed among fish and lakes. About 10 years after the fallout T 1/2 was no longer significantly different among fish or lakes, suggesting that steady-state among 137 Cs levels in fish had been reached. The mean T 1/2 during 1996-2000 was 46 years, implying that the future recovery from present 137 Cs levels (more than 10-fold higher than preChernobyl levels) will be dominated by the physical decay of 137 Cs (30 years). 5. The influence of fish size and trophic level on 137 Cs dynamics has been consistent among the three lakes. The duration of the 137 Cs pulse in fish appeared to be regulated by fish ecophysiology, whereas the amplitude also appeared to be regulated by lake characteristics. 6. Synthesis and applications. These data have implications for the predictive modelling of pulsed contaminants in lake ecosystems and show that (i) complex temporal concentration trends in fish can be adequately modelled by a combination of simple firstorder equations; (ii) a one-component decline function is insufficient to describe the observed increase in ecological half-life over time; (iii) fish weight and trophic level can and should be treated as independent variables because their influence differs and changes over time. For management purposes, a pulse-response model for fish can be scaled to different systems by using established relationships to account for differences in fallout and catchment biogeochemistry.

Transfer of 137Cs into fish in small forest lakes

“…After entering lakes, 137 Cs transferred into food chains and raised the activity concentrations in lake water, fish and other biota. The activity concentrations of fish in boreal lakes reached peak values at various times after the deposition, first in non-predatory fish and then, after one to two years, also in predatory fish (Sundbom et al, 2003).…”

Cesium accumulation by aquatic organisms at different trophic levels following an experimental release into a small reservoir

“…Furthermore, each fish species will lose >30% of their Cs content on day 70 before reaching their maximum concentrations. Clearly, there is a large and continuing flux of Cs through the unsampled biota such as the larger benthic and freeswimming aquatic insects (Voshell et al, 1985), detritivores (Hakonson and Whicker, 1975), and the small-body fishes such as those sampled by Sundbom et al (2003) that is required to replace the losses and continue the increases in the Cs concentrations of L. macrochirus and M. salmoides.…”

“…A major emphasis of these studies has been Cs accumulation by fish (e.g., Hakanson et al, 1992;Smith et al, 2002;Sundbom et al, 2003;Saxen, 2007) because of their importance in the human diet and their convenient use as indicator organisms. Less emphasis has been placed on the biota comprising the food chains that lead to fish.…”

Effects of nutrient enrichment on C and N stable isotope ratios of invertebrates, fish and their food resources in boreal streams

“…Specimens of Eurasian minnow Table 2 Trophic level classification of invertebrates according to Moog (1995), Schmedtje & Colling (1996) and the AQEM Consortium (2005) and of fish according to Sundbom et al (2003) [Phoxinus phoxinus (Linnaeus)] were too small to provide sufficient tissue mass for analysis; thus the five specimens caught were pooled. Functional feeding groups were assigned according to Sundbom et al (2003) and FishBase.se (http://artedi.nrm.se/fishbase_ se) ( Table 2). All samples were freeze-dried, ground in a mortar and weighed to nearest 0.001 mg in tin capsules for stable isotope (d 13 C and d 15 N) analyses.…”