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51Journal of Siberian Federal University. Biology 2019 12(2): 120-129
УДК 630.228.7:582.475.4(571.51)
Some Peculiarities of Foraminifera Species Distribution Associated with Concentrations of 226Ra, 238U, 232Th in the Deryugin Basin (the Sea of Okhotsk)
Mikhail M. Domanov* and Tatyana A. Khusid
P.P. Shirshov Institute of Oceanology RAS 36 Nakhimovskiy, Moscow, 117997, Russia
Received 05.04.2016, received in revised form 23.06.2017, accepted 19.06.2018, published online 09.07.2018
An analysis of composition and quantitative distribution offoraminifera in bottom sediments collected in the Deryugin Basin (the Sea of Okhotsk) has demonstrated that specific foraminiferal assemblages at the depths of 691 to 1786 m are associated with distribution of natural radionuclides. A comparison of the percentage of Saccorhiza ramosa (Brady) as a dominant species in the community of benthic foraminifera and the concentrations of radionuclides in the sediments showed that the quantity of S. ramosa correlates with the concentrations of238U, 232Th and 226Ra in the sediments. The correlation coefficients for concentrations of238U, 232Th and 226Ra are 0.75, 0.83 and 0.86, respectively. Calcareous foraminifera abundance decreases with radioactivity growth and correlates with common radioactivity with the negative coefficient of -0.82.
Keywords: foraminifera, community of foraminifera, biocoenosis, radionuclides, 238U, 232Th, 226Ra, sediment, abundance.
Citation: Domanov M.M., Khusid T.A. Some peculiarities of foraminifera species distribution associated with concentrations of 226Ra, 238U, 232Th in the Deryugin Basin (the Sea of Okhotsk). J. Sib. Fed. Univ. Biol., 2019, 12(2), 120-129. DOI: 10.17516/1997-1389-0063.
© Siberian Federal University. All rights reserved
* Corresponding author E-mail address: [email protected]
Особенности распределения бентосных видов фораминифер и 226Ra, 238и, 232Th в донных осадках впадины Дерюгина (Охотское море)
М.М. Доманов, Т.А. Хусид
Институт океанологии им. П.П. Ширшова РАН Россия, 117997, Москва, пр. Нахимовский, 36
Анализ состава и количественного распределения фораминифер в донных осадках впадины Дерюгина (Охотское море) показал, что специфический комплекс фораминифер впадины Дерюгина на глубине от 691 до 1786 м связан с распределением природных радионуклидов. Сопоставление процентного содержания Saccorhiza ramosa (Brady), доминирующей в сообществе бентосных фораминифер, и концентрации радионуклидов в донных осадках показало, что количество фораминифер S. ramosa коррелирует с концентрацией в осадках 238U, 232Th и 226Ra. Коэффициенты корреляции с концентрацией 238U, 232Th и 226Ra равны 0,75, 0,83 и 0,86 соответственно. Обилие известковых фораминифер с ростом радиоактивности снижается и коррелирует с общей радиоактивностью с отрицательным коэффициентом -0,82.
Ключевые слова: фораминиферы, сообщество фораминифер, биоценоз, радионуклиды, 238U, 232Th, 226Ra, морские осадки.
Introduction
Zones of increased natural radioactivity are of interest for research into evolutionary transformations in the history of the Earth biosphere (Odum, 1959; Neruchev, 1982). Benthic organisms living directly in the bottom sediments or on the sediment surface are mostly exposed to the influence of radiation from radionuclides concentrated in bottom sediments. Benthic organisms can accumulate radionuclides, which intensifies the effect ofradiation. Xenophyophores, a group of protists of the benthic community, are able to concentrate naturally occurring radionuclides 238U, 232Th, 210Po, 226Ra, 210Pb in the cytoplasm and the shell (Levin et al., 1986; Swinbanks, Shirayama, 1986; Lecrog et al., 2009). It was shown that concentrations of 226Ra and 232Th in these protists depend on the following:
the species of the organism, the composition of the material utilized in agglutination, and the concentration of radionuclides in the environment (Domanov, 2015).
Swinbanks & Shirayama (1986) demonstrated that high levels of natural radiation occur in xenophyophores, as a result of presence of 226Ra in intracellular barite crystals, and suggested that this radiation would induce numerous genetic mutations. Multidirectional influence of radioactivity on biodiversity and abundance of meiobenthos (particularly in the community of foraminifera) was noted in the Kara Sea (Alexeev, Galtsova, 2012). Thus, to assess the impact of various factors on functioning of benthic foraminiferal communities, radionuclides are to be taken into account.
One of the areas with high natural radioactivity of bottom sediments is the Deryugin Basin in the Sea of Okhotsk. The concentrations of 238u, 232Xh are 2-3 times higher and 226Ra concentration is 10-25 times higher in the central part of the Deryugin Basin than in the periphery (Domanov, 2009).
In this area, a particular community of benthos foraminifera with a small amount of species and a predominance of agglutinated foraminifera was discovered (Khusid et al., 2006, 2013).
The research was aimed to study a correlation between distribution of benthic foraminifera and radionuclides 238U, 232Th, and 226Ra in the Deryugin Basin in order to identify a connection of dominant foraminifera species with the distribution of natural radionuclides in bottom sediments.
Materials and methods
The Deryugin Basin (Fig. 1) is bounded in the west by the northern Sakhalin continental slope and in the north by the Staretsky Trough
and the Kashevarov Bank of the North Okhotsk margin.
The structure and composition of benthic foraminiferal communities from the Deryugin Basin were analyzed in 11 samples taken with the bottom grab "Okean" at the depths of 691 to 1786 m from the surface 0-2 cm sediment layer. Samples were collected during the 50th and 51st cruises of the R/V Professor Khromov. The location of the stations, their depths, and sediment description are given in Table 1. The majority of samples were collected in the deepest part of the Deryugin Basin at a small range of depths (from 1420 to 1786 m) (Fig. 2) and only one sample (St. 51-23) was taken at the southern edge of the basin, from the depth of 691 m.
Sediment samples (40-60 g) were washed and passed through a 0.05 mm mesh size sieve. Taxonomical identification of foraminifera was based on the accepted classification (Loeblich and Tappan, 1964, 1986, 1987). The planktonic and benthic foraminifers were studied under a Leica WILD M3C light microscope at x100 magnification. The taxonomic composition,
r'iSh 'W '
Fig. 1. Location of the study area
Table 1. Description of the bottom sediments and position of the stations in Deryugin Basin
Station Latitude, N Longitude, E Depth, m Comment
50-29 53o57.818 144 o58.266 1420 Diatom sediment with sand inclusions
50-36 53o54.547 145o54.214 1650 Sediment with sand inclusions deep-brown, oxidated
50-37 53o30.936 146 o05.599 1750 Diatom sediment with sand inclusions deep-brown, oxidated
50-38 53o18.158 146o33.756 1733 Sediment with sand inclusions, pelite
50-39 53o00.204 146 o04.462 1736 Diatom silt with path of sediment feeding
51-17 53o00.264 146 o24.356 1749 Sediment pelite deep-brown, oxidated
51-19 53o14.982 146 o06.600 1786 Sediment pelite deep-brown to black, oxidated
51-20 53o14.782 145o42.265 1731 Sediment with sand inclusions, pelite light gray, olive-green
51-21 53o30.928 146o05.658 1783 Sediment pelite deep-brown to black, oxidated
51-22 54o54.645 145o54.131 1648 Sediment pelite deep-brown to black, oxidated
51-23 52o30.001 144 o49.995 691 Pelitic diatom ooze, greenish brown
Longitude E
Fig. 2. Position of the stations in thedeepest partofthe DeryuginBasin
proportion of all foraminiferal species, and Laboratory of Dosimetry and Environmental their total abundance (individuals per g dry Radioactivity of the Chemistry Department of sediment) were determined in each sample. The Moscow State University. The radioactivity of radioactivity analysis was performed in the natural radionuclides (238U, 232Th and 226Ra) in
- 123 -
bottom sediments was measured on a gamma-spectrometer with a super pure germanium GC-3020 detector with a relative efficiency of 30% (Co-60 line - 1.332 Me) and a resolution of 1.8 Kev. The software GENIE-400 PC was used. The accuracy of measurements for Ra, Th and U was 5-7%, 10-15% and 15-20% respectively.
Results
The bottom sediments from 1420 to 1786 m were represented by dark brown pelitic diatom silt. The sample from the depth of 691 m had an olive-brown colour and contained more diatoms (Table 1).
The abundance and species composition of benthic foraminiferal communities and the concentration of radionuclides in sediments are shown in Table 2. The composition of foraminiferal assemblages varied significantly. In most of the samples the abundance varied from 9 to 25 individuals per g, and the number of species was from 7-8 to 17. The sample from the depth of 691 m was characterized by the highest abundance 35 individuals per g and the highest number of species 30. The lowest number of species (7) and the lowest abundance of
foraminifera (9-11 individuals/g) was observed in the samples from stations 36 and 17 located in the central part of the basin at the depths of 1650 and 1749 m, respectively.
The ratio of the main species is presented in Fig. 3. At all studied stations, except 51-23 (691 m), the fauna was generally represented by agglutinated species. Saccorhiza ramosa (Brady) was a dominant species making 47-92% of the total quantity of foraminifera. The largest percentage of S. ramosa (76-92%) was observed in the samples with the lowest number of species. In addition to S. ramosa, a significant number of representatives of other agglutinated species (Cyclammina cancellata, C. bradyi, Recurvoides contortus) were found.
Foraminiferal assemblages in some samples were characterized by clear dominance (82-99%) of agglutinated fauna. In other samples from central and peripheral parts of the basin the share of S. ramosa was much smaller (i.e. did not exceed 47-67%) and this species made only 5% at the depth of 691 m (Table 2). The shells of S. ramosa were composed of sand grains of different size glued with low quantities of secreted calcareous cement (Fig. 4).
Fig. 3. Species composition of the foraminiferal assemblages (others: Cyclammina cancellata Brady, C. brady Cushman, Recurvoides contortus Earland, Globobulimina auriculata (Bailey), Alabaminella weddellensis (Earland), Valvulineria sadonica Asano, Nonionella labradorica (Dawson), Elphidium sp.)
Table 2. Abundance and species composition of benthic foraminifera community and concentration of the natural radionuclides in sediments.
Station no. Station depth, m Abundance, ind./g Number of species Agglutinated foraminifera, % of total abundance Calcareous foraminifera Concentration of radionuclides in sediments, Bq/kg
S. raniosa Other agglutinated 232Th 23SU 226Ra
29 1420 14 17 47 4 49 11.90 35.30 603.10
36 1650 9 7 76 12 12 13.70 89.30 910.20
37 1750 16 14 71 19 10 14.80 64.10 884.30
38 1733 21 13 67 13 20 14.00 5.40 1069.30
39 1736 10 12 74 2 24 16.50 94.70 880.60
17 1749 11 7 82 0 18 17.50 133.00 1417.10
19 1786 16 14 78 2 20 21.10 92.30 1047.10
20 1731 23 16 81 9 10 23.90 111.60 1439.30
21 1783 25 8 92 7 1 20.80 152.80 2057.20
22 1648 12 8 89 7 4 19.90 122.80 1639.10
23 691 35 30 5 7 88 23.50 77.60 139.50
Fig. 4. Agglutinated foraminifera Saccorhiza ramosa (Brady)
Among calcareous species, Uvigerina auberiana d'Orbigny (Fig. 5) and Gyroidina orbicularis d'Orbigny were the most common in the associations of the basin; these species are known as ubiquitous (able to exist in very different environmental conditions).
Calcareous species including Uvigerina peregrina Cushman and Cassidulina spp. predominated in the assemblages from the upper Sakhalin slope (station 51-23) (Fig. 3). The species U. peregrina is considered to be an indicator of highly productive regions but it was missing from the Deryugin Basin.
Common radioactivity of key elements in uranium-thorium families (238U, 232Th and 226Ra) in the bottom sediments of the Deryugin Basin varied from 650 to 2231 Bq/kg. Major contribution to radioactivity was made by 226Ra (89-93%) (Table 2). A comparison of the percentage of S. ramosa in the community of benthic
foraminifera and concentration of radionuclides in the sediments showed that the quantity of S. ramosa correlated with the concentration of 238U, 232Th and 226Ra in the sediments. The correlation coefficients for 232Th, 238U, and 226Ra concentration were equal to 0.75, 0.83 and 0.86, respectively (Table 3).
Discussion
With the increase of common radioactivity in the sediments, the percentage of S. ramosa in the community increased from 47 to 92%. The correlation coefficient was equal to 0.84 (Table 3). The abundance of calcareous foraminifera with the growth of common radioactivity decreased and had a negative correlation coefficient of -0.82. Thus, radionuclides 238U, 232Th and 226Ra may have a depressing effect on calcareous foraminifera. Radioactivity of natural radionuclides has an impact on the functioning
Table 3. Correlation matrix for benthic foraminifers (% of total abundance) and concentration of natural radionuclides in sediments (Bq/kg) (correlation is significant at p< 0.05)
232Th 238U 226Ra Common radioactivity
S. ramosa 0.75 0.83 0.86 0.84
Calcareous - - -0.84 -0.82
- not identified
of the benthic community. Both the positive effect (radiation hormesis) (Kuzin, 1991), and the depressing effect depend on the internal factors of an organism (age, state of cells, resistance of an organism). These vary in different species of the benthic community (in this case in foraminifera species). Stimulation of development of S. ramosa may be more pronounced than a negative effect of radiation on it, which may lead to domination of this species.
A stimulating influence of radioactive 226Ra contained in natural sea barite on the
development of heterotrophic bacteria from the Barents Sea was described in the previous paper (Domanov et al., 2015). Earlier, multidirectional influence of artificial radioactivity on biodiversity and abundance of meiobenthos in the Russian Arctic shelf was noted in the paper by Alexeev and Galtsova (2012). However, for a number of meiobenthic organisms, the effect of radioactivity changed from positive to negative. The taxonomic diversity of meiobenthic communities increased and the population density decreased with the growth
of concentration of 137Cs. It was suggested that meiobenthic communities can react very quickly to deterioration of environmental radioactivity by changing their taxonomic composition and quantitative characteristics (Galtsova et al., 2004).
Radionuclide concentration in organisms can vary depending on the species, their feeding habits, physiological processes, body size and seasonal changes (Alam, Mohamed, 2011).
The way of feeding may also be a factor which determines the correlation between S. ramosa abundance and radioactivity. S. ramosa feeds on detritus in the surface sediment layer and in comparison with the species feeding on seston is more subjected to the influence of both external and internal radiation.
Conclusion
A correlation analysis between the percentage of S. ramosa in the community of
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