\documentclass[twoside]{article}
\usepackage[silent,pdf,hyper]{elxfinal}
\usepackage{color}
\usepackage{hyperref}
\journalid{ES}{19}{6}{19}
\citnumber{}{13}
\paperid{2019ES000681}
\papertype{RAR}
\cpright{}{2019}
\lefthead{ovdina et al.}
\righthead{sarbalyk limnetic system}  
\received{31}{January}{2019}
\accepted{10}{October}{2019}
\published{28}{December}{2019}
\definecolor{brown}{RGB}{157,23,4}

\authaddr{Ekaterina A. Ovdina, Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, 3 Acad.
Koptyug Ave., 630090, Novosibirsk,  Russia. (ovdina@igm.nsc.ru)}


\begin{document}

\title{Radionuclide distribution in components of the Sarbalyk limnetic system (Baraba lowland, Western Siberia)}

\author{1}{Ovdina}{Ekaterina A.}{}{1}{}{}
\author{2}{Strakhovenko}{Vera D.}{}{1}{}{}
\author{3}{Yermolaeva}{Nadezhda I.}{}{2}{}{}
\author{4}{Zarubina}{Evgeniya Yu.}{}{2}{}{}
\author{5}{Yermolov}{Yurij V.}{}{3}{}{}

\affil{1}{Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences}{Novosibirsk}{}{Russia}
\affil{2}{Institute for Water and Environmental Problems, Siberian Branch of the Russian Academy of Sciences}{Novosibirsk}{}{Russia}
\affil{3}{Institute of Soil Science and Agrochemistry, Siberian Branch of the Russian Academy of Sciences}{Novosibirsk}{}{Russia}

\keywd{Radiogenic isotope geochemistry}
\keywd{small lake}
\keywd{Western Siberia}

\abstract{\baselineskip=12pt Geochemical and mineralogical analysis of the bottom sediment cores of small
lakes can be used as the basis for radio-ecological monitoring and environmental protection
measures. Here, features of the radionuclide activity distribution in components of the
limnetic ecosystems of the central Baraba lowland were studied, and factors affecting
radiocesium absence in the bottom sediment of Lake Sarbalyk were identified. Fieldwork
included the sampling of limnetic ecosystem components, bottom sediment weighing, and
the determination of pH, Eh, TDS and oxygen content. Subsequent laboratory investigation
involved the determination of major and trace element concentrations by atomic absorption
spectrometry and X-ray fluorescence analysis; mineral composition by X-ray diffractometry
(XRD); analysis of sample morphology and composition via scanning electron microscopy;
and natural radionuclide and radiocesium content determination by the gamma-spectrometric
method.  Radiocesium is present in all the studied lake bottom sediments of the central Baraba
lowland in the upper horizons, with the exception of Lake Sarbalyk. Limnetic ecosystem
components were analyzed using modern analytical methods, considering the distribution
features of natural and artificial radionuclides in catchment area soils, tussocks and the
bottom sediment of Lake Sarbalyk. The results revealed that the absence of radiocesium in
the bottom sediment of Lake Sarbalyk is due to two factors: the characteristics of the lake
overgrowth and the sorption of dissolved forms of $^{137}$Cs.}


\section{Introduction}

    Small lakes are an important object of study for experts in various modern scientific
fields. Bottom sediment (BS) is one of the main components of lacustrine ecosystems and
its genesis interconnects with processes occurring in both the catchment area and the lake
itself. An important feature of BS is that any change, either directly in the water system or in
its environment, will be ``documented'' by depth
%[\itc{Bo Lan et al.,} \reflink{BoLa99}{1999};
%[\itc{Lan et al.,} \reflink{Lan99}{1999};   %%% ???
[\itc{Lan et al.,} \reflink{Lan18}{2018};
\itc{Zhang et al.,} \reflink{Zhan18}{2018}].
Since small lakes are more sensitive to changes than large water bodies, their study can
provide answers to many scientific questions concerning natural and anthropogenic impacts
on the environment, occurring in the past, present or future
[\itc{Bihari et al.,} \reflink{Biha18}{2018};
\itc{Egorov et al.,} \reflink{Egor18}{2018};
\itc{Pestryakova,} \reflink{Pest16}{2016};
\itc{Solotchina,} \reflink{Solo09}{2009};
\itc{Subetto,} \reflink{Sube16}{2016};
\itc{Wang et al.,} \reflink{Wang18}{2018}].

    Southwestern Siberia contains more than 20 thousand lakes of different sizes, water
regimes and salinities. Most are inland, shallow, fresh to salt, and form the major component
of the hydrography of the Ob-Irtysh interfluve
[\itc{Bejrom et al.,} \reflink{Bejr86}{1986}; %+
\itc{Shtin,} \reflink{Shti05}{2005}]. %+
The small lakes
are characterised by active sapropel formation, which in some bodies is progressive with a
constant increase in sediment volume against terrigenous material transport and eolian
processes, mainly in humid environments
[\itc{Naumova et al.,} \reflink{Naum13}{2013};
\itc{Roslyakov et al.,} \reflink{Rosl13}{2013}].

    Sapropel is a bottom sediment of water bodies that is formed as a result of biochemical,
microbiological and mechanical processes from the remains of dying plants and animals,
which introduce organic and mineral impurities. Sapropel consists of four components:
mineral, organic, bioactive and aquatic
[\itc{Strakhovenko et al.,} \reflink{Stra16}{2016}].
Such variation in both
genesis and composition results in many different types of sapropel with varying
characteristics
[\itc{Korde,} \reflink{Kord69}{1969};
\itc{Lopotko,} \reflink{Lopo78}{1978};
\itc{Sukachyov,} \reflink{Suka43}{1943}].    %%% ???+
 The most dominant factors
include the composition of mineral particles and organic matter, as well as their ratio.
Several features characterise typical sapropelic sediments: a tobacco-green colour that
varies to black under reduction conditions, a colloidal structure, and occasionally the smell
of hydrogen sulfide. Sapropels can also be classified based on their relative organic and
mineral composition (ash content) into four main types:
{\itshape organogenic} with ash content up to
30\%;
{\itshape organomineral} (30--50\%);
{\itshape mineral-organogenic} (50--70\%);
and
{\itshape mineralised} (70--85\%).
BS with ash content above 85\%
are defined as mineral silts. The chemical composition of
the mineral component may vary, although SiO$_2$ and CaO strongly dominate, with the Si/Ca
ratio also used to allocate classes of sapropel:
{\itshape silicon} (Si~$>$~Ca);
{\itshape calcium} (Ca $>$ Si); and
{\itshape mixed}
(Si $\sim$ Ca)
[\itc{Strakhovenko et al.,} \reflink{Stra16}{2016}].


\begin{sloppypar}
 The lakes selected for analysis in the present study are located within the central part of
the Baraba lowland in Western Siberia
(\figref{1}).           % (Fig.1).
The study region is typical of Central
Baraba: In the southwest, the land surface is marked by strictly parallel, north-eastern strike,
alternating hills and hollows, with numerous small and large lakes, marshes and areas of dry
land. Because of this landscape there is local redistribution of moisture and easily soluble
salts, flowing from hills to hollows
[\itc{Il'in and Syso,} \reflink{Il'in01}{2001};
\itc{Rikhvanov,} \reflink{Rikh09}{2009}].
\end{sloppypar}

\begin{figure}[t]                     % Fig 1
\figurewidth{20pc}
\setimage{}{1.3ex}{20pc}{}{2019es000681-f01}
\caption{Location scheme of the studied lakes: 1 -- Bol. Kazatovo, 2 -- Chylym, \mbox{3~--~Barchin}, 4  -- Kambala, 5 -- Kaily, 6 -- Bergul, 7 -- Yargol,
8 -- Suetok, 9 -- Bilgen, \mbox{10 -- Bol. Kurgan}, 11 -- Sarbalyk, 12 -- Tsybovo, 13 -- Zhiloe, 14 -- Mostovoe, 15 -- Bol. Kaily, 16 -- Peschanoe, 17 -- Chistoe, 18 -- Bugristoe.}\vspace*{.1\baselineskip}
\end{figure}

\enlargethispage{-\baselineskip}

    Natural background radiation is determined by the content of natural radioactive
elements including uranium, thorium and potassium. The central part of the Western
Siberian plate belongs to a zone of low radiation, because the natural radionuclides
contained in the region's rocks and soils present low radiation dose values. However, since
these elements are found in all natural objects in certain quantities, and their increased
concentrations can be potentially dangerous, it is essential that sapropels are analysed
regarding their ecological safety, in terms of their content of toxic elements, as well as
natural and artificial radioactivity
[\itc{Rikhvanov,} \reflink{Rikh09}{2009}].

    Southwestern Siberia has been contaminated by technogenic radionuclides since the
beginning of nuclear weapons testing at the Semipalatinsk and Novaya Zemlya nuclear test
sites in 1949. The distribution of $^{137}$Cs pollution in the study area is mosaic in form, and
varies in cause and scale, depending particularly on the preservation degree of primary
mosaic contamination under the influence of secondary redistribution. The primary mosaic
radiation distribution is itself determined by nuclear test types, atmospheric conditions, the
radionuclide fractionation effect during transfer, and the nature of radioactive cloud
movement
[\itc{Strakhovenko et al.,} \reflink{Stra10}{2010}].
Soil $^{137}$Cs distribution heterogeneity was established
by comparing samples taken in the same elementary landscape type at sites equidistant from
each other and without significant differences in relief and sod layer. Radiocesium
redistribution in soil after deposition depends on many specific factors, including soil type,
rainfall, drainage, landscape and vegetation. Statistical estimates are thus more robust than
single estimates, and can be reproduced satisfactorily at a significance level of 0.05 and with
a sufficient sample size. Data can also be distributed over entire catchment areas, producing
a generalised characterisation of current radiation pollution.

    A large group of scientists have carried out work estimating the global content of $^{137}$Cs
in the total contamination of Western Siberia soils, with a value of 43~mCi/km$^{-2}$ determined
in 2000. For most studied areas, total pollution levels of $^{137}$Cs in Siberian lacustrine BS and
in the soils of their catchment area exceed the global radioactive background level.
Radiocesium distribution heterogeneity in BS is influenced by many factors, primarily the
unevenness of precipitation during nuclear tests in reaching lake waters and catchment area
soils. Furthermore, the configuration of primary habitats may vary under the influence of
erosion-accumulative processes and lithochemical migration. In the study area,
contamination of lacustrine BS is highlighted sharply against the background, especially in
Lake Sarbalyk. Indeed, an initial test in 1995 revealed that Lake Sarbalyk BS radiocesium
activity concentration was equal to zero, with re-samplings in 2012 and 2014 confirming
this first result
[\itc{Ovdina et al.,} \reflink{Ovdi16}{2016}].

    The aim of the present work was thus to study the features of radionuclide activity
concentration distribution in the lacustrine ecosystems of the central Baraba lowland and to
identify the factors affecting the radiocesium absence in Lake Sarbalyk bottom sediment.\vspace*{-.5pc}


\section{Materials and Methods}

\subsection{Materials}\vspace*{-.5pc}

\enlargethispage{-.85\baselineskip}

\subsubsection{Bottom sediments.}
\begin{sloppypar}
Stratified sediment cores were sampled in all the studied lakes, the
bottom sediments of which were identified as sapropels. Bottom sediment sampling was
carried out according to standard methods. BS were collected from a catamaran using a
cylindrical sampler with a vacuum shutter (diameter 82 mm, length 110 cm) developed by
the Taifun Research and Production Association, Russia. BS cores were sampled at an
interval of 3--5~cm to a depth of 50--120~cm; each sample was numbered in order and packed
in a plastic bag.
\end{sloppypar}

\subsubsection{Soils.}
 Soil samples were taken using a metal ring sampler
 [\itc{Malikova et al.,} \reflink{Mali05}{2005}]     %%% ???
 with a
diameter of 82~mm and height of 50~mm, through the depth of the entire soil section. All soil
samples were dried and weighed. Soil was also sampled from the catchment area of Lake
Sarbalyk, beginning on a hill and ending on the lakeshore. Soil types followed the sequence:
leached chernozem$\longrightarrow$ grey forest soil$\longrightarrow$ saline meadow carbonate soil$\longrightarrow$ meadow-marsh
carbonate soil.

\begin{figure*}[t]                     % Fig 2
\figurewidth{35pc}
\setimage{}{}{35pc}{}{2019es000681-f02}
\caption{Ferre triangle of lake water composition (\%-eq)
with respect to TDS values. Lakes: 1 -- Suetok, 2 -- Bilgen, 3 -- Sarbalyk, 4 -- Mostovoe, 5 -- Kazatovo, 6 -- Yargol, 7~--~Bergul, 
8 -- Kambala, 9 -- Chylym, 10 -- Bol. Kurgan, 11 -- Barchin, 12 -- Kaily, \mbox{13 -- Bol. Kaily}, 14 -- Tsybovo, 15 -- Chistoe, 
16 -- Zhiloe, 17 -- Bugristoe, 18 -- Peschanoe.}%%\vspace*{-\baselineskip}
\end{figure*}

\subsubsection{Water.}
Water sampling for all analyses was carried out according to standard methods. For
this purpose, bottles of volume 1, 0.5 (both plastic, to determine major and trace element
compositions) and 0.33~l (glass, to determine Hg content) were used, with water for trace
element composition and Hg tests preserved using nitric acid.

\subsubsection{Tussocks.}
Tussocks were divided into upper and lower parts, both of which were sampled:
upper part -- living reed and soil particles from the lake catchment area; lower part -- tightly
intertwined roots.

\subsubsection{Biota.}
\begin{sloppypar}
 Primary sapropel-forming material (phytoplankton, photosynthetic pigments,
zooplankton, phytoperiphyton and phytobenthos, macrophytes) was sampled for genesis
determination at each lake
[\itc{Zarubina,} \reflink{Zaru13}{2013}].
\end{sloppypar}

\subsection{Methods}

    Physical and chemical variables of water and BS material were recorded in situ (pH,
Eh, TDS) using an ANION-7000 portable liquid analyser (Biomer, Russia). Measurement of
O$_2$ content was carried out via the biochemical oxygen consumption method for five days
(BOD5), enabling the establishment of the extent of water pollution based on the amount of
oxygen consumed after the aerobic biochemical decomposition of organic substances in the
test water (at 20\deg C, in mg$^{-1}$).                %%% ???
Determination of BOD5 was carried out in the initial sample
based on the difference in oxygen content before and after incubation for five days without
access to oxygen and light. Chemical composition analyses of BS samples were carried out
at the Analytical Center for multi-elemental and isotope research SB RAS, and at the
Laboratory of Geochemistry of Noble and Rare Elements of IGM SB RAS, Novosibirsk. BS
and water major and trace element compositions were determined via atomic absorption
using a Solaar M6 instrument (Thermo Electron, UK) equipped with a Zeeman and
deuterium background corrector. Major element composition was determined by X-ray
fluorescence analysis (\mbox{ARL-9900-XP}, Applied Research Laboratories, USA). \mbox{X-ray}
diffractometry (XRD) was used to determine sample mineral composition (ARLX'TRA,
Thermo Fisher Scientific (Ecublens) SARL, Switzerland). Sample morphology, phase and
chemical composition was determined using a scanning electron microscope (TESCAN
MIRA3, Tescan, Czech Republic) equipped with an energy spectrometer (OXFORD,
Oxford Instruments, UK). Determination of natural radionuclides and radiocesium was
carried out via a gamma-spectrometric method using a well coaxial detector from ultrapure
germanium (HPGe) with preamplifier and low-background cryostat (EGPC 192-P21/SHF
00-30A-CLF-FA; EURYSIS MESURES, France).\vspace*{-.5\baselineskip}

\section{Results}\vspace*{-.5\baselineskip}

    We sampled a total of 27 lacustrine bottom sediment cores (413 samples), 15 soil cores
(60 samples) and 78 water samples.

    According to the obtained analytical data (main water ion content), water in the Baraba
lakes is mainly bicarbonate magnesium-sodium or bicarbonate sodium, alkaline (pH 8.1--10)
and fresh (0.2--0.6~g~L$^{-1}$)  %/l)
(\figref{2}),           % (Fig. 2),
with occasional brackish (TDS 1--3~g~L$^{-1}$) and salty (TDS 3.3~g~L$^{-1}$) lakes. The water composition of Lake Sarbalyk is alkaline, sodium bicarbonate
freshwater (TDS~0.3~g~L$^{-1}$).

\begin{figure}[t]                     % Fig 3
\figurewidth{20pc}
\setimage{}{1.3ex}{20pc}{}{2019es000681-f03}
\caption{Lake Sarbalyk massive-thicket type of vegetation. Tussocks.}
\end{figure}

    Field and analytical studies revealed that the BS of all the studied small lakes are
sapropels, most of which are organic-mineral or mineral-organogenic, silicon in class and
plankton-macrophyte in type. Lake Sarbalyk bottom sediment is organic-mineral silicon
sapropel, and macrophyte in type based on prevailing productivity.

    The contribution of different ecosystem biotic components to lacustrine bottom
sediment formation can vary significantly, thereby affecting the sediment's final chemical
and mechanical composition.

\begin{sloppypar}
    The main primary producers of organic matter in Lake Sarbalyk are higher aquatic
plants -- macrophytes. According to overgrowth degree and volume of primary productivity,
Lake Sarbalyk belongs to a class of lakes with massive-thicket type of vegetation
(\figref{3}).           % (Fig. 3).
Rigid air-water vegetation is represented by the communities of
{\itshape Typha latifolia}
and
{\itshape Phragmites australis (Cav.) Trin. ex Steud.} that dominate the coastal zone in shallow water.
Soft submerged vegetation communities of
{\itshape Myriophyllum sibiricum Kom., Stratiotes aloides L.}
 and
{\itshape  Ceratophyllum demersum L.} are widespread in the main water area. The lake
overgrowth area is about 70\%
[\itc{Zarubina,} \reflink{Zaru13}{2013}].
During the vegetation period, macrophytes
in Lake Sarbalyk form
1830.9~g~m$^{-2}$~per~year    %%% ???+
of organic matter, including
1014.3~gC$_{\mathrm{org}}$~m$^{-2}$,
44.5~gN~m$^{-2}$ and
4.0~gP~m$^{-2}$. Lake Sarbalyk is associated with minor phytoplankton
contribution to primary product formation. The gross primary production value of
phytoplankton during the study period was low and amounted to only 0.37~mgO$_2$~L$^{-1}$ per hour,    %%% ???+
with
665 thousand cell~dm$^{-3}$ and biomass of 0.02~g~m$^{-3}$
[\itc{Yermolaeva et al.,} \reflink{Yerm16}{2016}].    %%% ???+
Estimated values
of phytoplankton contribution to Lake Sarbalyk bottom sediments varied at 0.18~gC$_{\mathrm{org}}$~m$^{-2}$~per~year,    %%% ???+
0.03~gN~m$^{-2}$~per~year and    %%% ???+
0.004~gP~m$^{-2}$~per~year.    %%% ???+
\end{sloppypar}

    Zooplankton is actively involved in the processes of sedimentation, filtering
phytoplankton and bacterioplankton and transforming it into fecal pellets. In Lake Sarbalyk zooplankton excreted up
to 1.71 gP m$^{-2}$ , up to 17.57 gNorg m$^{-2}$, up to 145.52 gCorg m$^{-2}$ per year and due to the withering
away of zooplankton in the lake bottom sediments comes up to 1137.86 mgCorg m$^{-2}$, 264.31
mgNorg m$^{-2}$ and 3.97 mgP m$^{-2}$ per year.

    Almost the entire flow of matter, formed during the day in the upper layers of the lake,
has time to reach the lake bottom without being fully mineralized in the water column due to
the lake's shallow depth. Further transformation of both faecal and dying biological material
occurs at the lake bottom as a result of the activity of bacteria and benthic organisms.

    Thus, hydrobionts are the main source of autochthonous organic matter in the bottom
sediments, largely determining the latter's chemical composition. Macrophytes and
zooplankton make the main contribution to organic matter formation in Lake Sarbalyk.

\section{Discussion}

    Analysis of Lake Sarbalyk bottom sediment composition did not reveal any anomalies
in major and trace element distributions or mineral phases and, in general, sediment
composition does not change with depth.

\begin{table*}                                   % Table 1
\tablewidth{41pc}
\caption{Natural and Artificial Radionuclide Activity Concentrations in Small-Lake Bottom Sediments of the Central Baraba Lowland}
\vspace{5pt}
\begin{tabular}
{@{}r@{\hspace{45pt}}
l@{\hspace{62pt}}
c@{\hspace{28pt}}
c@{\hspace{28pt}}
c@{\hspace{27pt}}
c@{\hspace{23pt}}
c@{}}
\hline
\\ [-7pt]
\numero  & Lake          & $^{232}$Th,  & $^{238}$U(Ra), & $^{40}$K,     &     Ac,      & $^{137}$Cs,  \\
    &               & Bq kg$^{-1}$ & Bq kg$^{-1}$   & Bq kg$^{-1}$  & Bq kg$^{-1}$ & Bq kg$^{-1}$  \\
[7pt]  \hline   \\ [-4pt]
1   & Suetok        & 18.9         &  	28.6        &	396.4	    & 58           & 178  \\
2   & Bilgen        & 21.6	       &     24.3       &  	431.8	    & 65           & 47  \\
3   & Sarbalyk      & 24.6	       &     33.1	    &    315.1      & 59	       &  0  \\
4   & Mostovoe      & 23.1	       &     19.0       &  	250.5       & 52	       & 12  \\
5   & Kazatovo      & 14.3         &  	21.2	    &    294.4      & 44	       & 183  \\
6   & Yargol        & 16.1         &  	49.8	    &    151.3      & 34	       & 24  \\
7   & Bergul        & 13.5         &  	32.4	    &    235.5      & 38	       & 132  \\
8   & Kambala       & 22.0	       &     25.4	    &    252.9      & 50	       & 78  \\
9   & Chylym        & 13.3         & 	30.4	    &    132.5	    & 29	       & 140  \\
10  & Bol. Kurgan   & 6.7	       &     21.2	    &    170.7	    & 23	       & 114  \\
11  & Barchin       & 4.2          & 	43.1	    &    65.8	    & 11	       & 209  \\
12  & Kaily         & 13.0	       &     31.5	    &    158.3      & 30	       & 189  \\
13  & Bol. Kaily    & 28.7	       &     26.0	    &    359.3      & 68	       & 96  \\
14  & Tsybovo       & 26.7	       &     16.4	    &    292.7	    & 60	       & 168  \\
15  & Chistoe       & 34.7	       &     36.0       &  	455.4	    & 84	       & 151  \\
16  & Zhiloe        & 23.1	       &     30.3       &  	424.2       & 66	       & 115  \\
17  & Bugristoe     & 17.3	       &     24.5	    &    238.1	    & 43           & 171  \\
18  & Peschanoe     & 19.0	       &     28.1	    &    112.8	    & 35	       & 75  \\
[4pt] \hline
\end{tabular}
%%\end{table*}
%%
\vspace*{2pc}
%%
%%\begin{table*}                                   % Table 2
%%\tablewidth{41pc}
\caption{Natural and Artificial Radionuclide Activity Concentrations in Lake Sarbalyk Bottom Sediments in 1995, 2012 and 2014}
\vspace{5pt}
\begin{tabular}
{@{}l@{\hspace{22pt}}
c@{\hspace{18pt}}
c@{\hspace{22pt}}
c@{\hspace{17pt}}
c@{\hspace{20pt}}
c@{\hspace{20pt}}
c@{}}
\hline
\\ [-7pt]
Date of sampling    & Sample number	&  Depth, cm &   $^{238}$U(Ra), & $^{232}$Th,  & $^{40}$K,    & $^{137}$Cs,   \\
                    &               &            &  Bq kg$^{-1}$    & Bq kg$^{-1}$ & Bq kg$^{-1}$ &  Bq kg$^{-1}$   \\
[7pt]  \hline   \\ [-4pt]
September, 1995     & Ku22Do1	    &   0--10	 &        2.80	    & 6.00	       & 0.51	      &     0   \\
                    & Ku22Do2	    &   10--15	 &        1.80	    & 4.90	       & 0.97	      &     0   \\
                    & Ku22Do3	    &   15--25	 &        2.30	    & 5.30	       & 0.35         &     0   \\
June, 2012	        & B121Do1	    &    0--5	 &        5.0	    & 8.4	       & 1.26	      &     0   \\
                    & B121Do2	    &   5--10	 &        3.3	    & 5.6          & 1.22	      &     0   \\
                    & B121Do3       &  10--15    &        2.5	    & 6.1	       & 1.09	      &     0   \\
                    & B121Do4	    &  15--20	 &        0.7	    &              & 0.30	      &     0   \\
                    & B121Do5	    &  20--25	 &        1.9       &  6.9	       & 1.09	      &     0   \\
                    & B121Do6	    &  25--30    &        2.8	    & 6.7	       & 0.74	      &     0   \\
                    & B121Do7	    &  30--35	 &        2.1	    & 4.8	       & 0.77	      &     0   \\
                    & B121Do8	    &  35--40	 &        1.8	    & 3.7	       & 0.82	      &     0   \\
                    & B121Do9	    &  40--45	 &        2.0	    & 6.2          & 0.90	      &     0   \\
                    & B121Do10	    &  45--50	 &        1.3	    & 5.3	       & 1.05	      &     0   \\
                    & B121Do11	    &  50--55	 &        2.7       &  6.0	       & 1.10	      &     0   \\
                    & B121Do12	    &  55--60    &        3.7	    & 6.7	       & 1.04	      &     0   \\
August, 2014        & B145Do1	    &  0--10	 &        1.05	    & 5.60	       & 1.10	      &     0   \\
[4pt] \hline
\end{tabular}
\end{table*}

    The BS composition of all the studied lakes was analysed in terms of natural and
artificial radionuclide content
(\tabref{1}).           % (Table 1).
According to the data obtained, the total specific
activity (Ac) of natural radionuclides across all the lakes varies at around 11--84~Bq~kg$^{-1}$,
which corresponds to the radiation-hygienic standard for sapropels.

    Radiocesium was not detected in Lake Sarbalyk bottom sediment, in contrast to nearby
lakes (Lake Bol. Kurgan, Lake Bilgen and Lake Suetok) where radiocesium activity
concentrations in bottom sediments range from 47--178~Bq~kg$^{-1}$.

    Lake Sarbalyk bottom sediments were sampled three times in 1995, 2012 and 2014.
$^{137}$Cs was absent in all years in bottom sediments samples of Lake Sarbalyk
(\tabref{2}).           % (Table 2).

    Soils in the study catchment were also analysed in terms of their basic physical and
chemical properties (granulometric composition, humus content, pH, radionuclide activity
concentrations ($^{238}$U, $^{232}$Th, $^{40}$K, $^{137}$Cs), major and trace element composition).

\begin{figure}[t]                     % Fig 4
\figurewidth{20pc}
\setimage{}{}{20pc}{}{2019es000681-f04}
\caption{Radionuclide distribution in components of the Sarbalyk lacustrine ecosystem: 1 -- leached chernozem, 2 -- grey forest soil, 3 -- saline meadow carbonate soil, 4 -- meadow-marsh carbonate soil, 5 -- tussock, 6 -- lacustrine bottom sediments.}\vspace*{-\baselineskip}
\end{figure}


    With respect to soil chemical properties, significant $^{137}$Cs activity concentrations were
determined only in the first 0--15~cm of soil cover in the Lake Sarbalyk catchment, with no
radiocesium identified at lower depths. Radiocesium activity exceeded the global
background by at least 2 times in cores of the leached chernozem (86~Bq~kg$^{-1}$) and grey forest
soils (67~Bq~kg$^{-1}$) on the catchment hill. In contrast, concentrations in the saline meadow
carbonate soil on the slope were only 8~Bq~kg$^{-1}$, and in the meadow-marsh carbonate soil on
the lakeshore 18~Bq~kg$^{-1}$. These values likely reflect the high degree of turf cover contributing
to radiocesium retention in the upper layer, preventing the eolian transport of soil particles.

    In terms of tussock material, $^{137}$Cs activity concentrations in these samples were much
higher than those found in the saline meadow carbonate soil and meadow-marsh carbonate
soil.

    In summary, the distribution of radiocesium activity concentrations in components of
the Lake Sarbalyk ecosystem has a saltatory character
(\figref{4}),           % (Fig. 4),
with the highest levels found
in soil cover on the hill (leached chernozem) and in tussocks, and an absence of radiocesium
in lake bottom sediment. This pattern likely reflects the action of tussocks trapping soil
particles containing radiocesium due to their tightly intertwined roots.


\section{Conclusion}

    Analysis of the natural and artificial radionuclide distribution in soils, tussocks and
bottom sediment of the Lake Sarbalyk catchment area revealed that the absence of
radiocesium in the lake bottom sediments is due to several factors. In particular, the high
degree of slope vegetation cover does not allow $^{137}$Cs to enter the lake with eolian soil
particles, while direct deposition of radiocesium onto the lake area at the time of nuclear
tests did not occur.

\begin{enumerate}
\item
\begin{sloppypar}
 Features of overgrowth. The lake overgrowth area comprises around 70\%
dense
reeds, the stems, leaves and roots of which trap radiocesium-containing soil particles and
prevent their transfer from the slope. Based on the mosaic pattern of radiocesium
contamination on the surface, soils on the hill and slope are characterised by high activity
concentrations. Below the slope, due to the weathering of soil particles, radiocesium levels
are very low. Tussocks trap soil particles and prevent the deposition of radiocesium in the
bottom sediment of Lake Sarbalyk.
\item
The results indicate sorption of the dissolved forms of radiocesium and their
accumulation in tussocks. Dissolved forms of radiocesium accumulate in the roots and
lower parts of reeds, which together with soil particles from the slope increases radiocesium
activity concentrations in these features.
\end{sloppypar}
\end{enumerate}

    Considering the unique distribution of radionuclides by components of the Sarbalyk
lacustrine system, the data obtained in the present study can be used as the basis for radio-environmental monitoring and environmental protection measures.

\acknowledgements{Work is done on state assignment of IGM SB RAS and has been supported by Ministry
of Science and Higher Education of the Russian Federation and the Russian Foundation for
Basic Research (RFBR)  [grant number 18-45-540002 p$\_$a].}

% \end{document}

\begin{references}

\reference{Bejr86}
\reftype{3}
\refauthf{Bejrom}{S. G.}{}
\refauth{Vasil'ev}{I. P.}{}
\refauth{Gadzhiev}{I. M.}{}
\refyear{1986}
\refbook{Prirodnye Resursy Novosibirskoj Oblasti}
\refpubl{Na\-uka}
\reflocat{Novosibirsk, USSR}
\refpages{215}
\endreference{in Russian}

\reference{Biha18}
\reftype{2}
\refauthf{Bihari}{A.}{}
\refgroup{et al.}
\refyear{2018}
\reftitle{Fallout isotope chronology of the near-surface sediment record of Lake Bolatau}
\refjour{Journal of Environmental Radioactivity}
\refvol{181}
\refpages{32--41}
\refdoi{10.1016/j.jenvrad.2017.10.009}
\endreference{}

\reference{Egor18}
\reftype{2}
\refauthf{Egorov}{V. N.}{}
\refgroup{et al.}
\refyear{2018}
\reftitle{Rating Water Quality in Sevastopol Bay by the Fluxes of Pollutant Deposition in Bottom Sediments}
\refjour{Water Resources}
\refvol{45}
\refnumb{2}
\refpages{222--230}
\refdoi{10.1134/S0097807818020069}
\endreference{}

\reference{Il'in01}
\reftype{1}
\refauthf{Il'in}{V. B.}{}
\refauth{Syso}{A. I.}{}
\refyear{2001}
\reftitle{Pochvenno-geokhimich\-eskie provintsii v Ob'-Irtyshskom mezhdurech'e: pri\-chiny i sledstviya}
\refjour{Sibirskii Ekologicheskii Zhurnal}
\refvol{2}
\refpages{111--118}
\endreference{in Russian}

\reference{Kord69}
\reftype{3}
\refauthf{Korde}{N. V.}{}
\refyear{1969}
\refbook{Biostratigrafiya i Tipologiya Russkikh Sapropelej}
\refpubl{Izd-vo AN SSSR}
\reflocat{Mos\-cow, USSR}
\refpages{219}
\endreference{in Russian}

\reference{Lan18}
\reftype{2}
\refauthf{Lan}{B.}{}
\refauth{Zhang}{D.}{}
\refauth{Yang}{Y.}{}
\refyear{2018}
\reftitle{Lacustrine sediment chronology defined by $^{137}$Cs, $^{210}$Pb and $^{14}$C and the hydrological evolution of Lake Ailike during 1901--2013, northern Xinjiang, China}
\refjour{Catena}
\refvol{161}
\refpages{104--112}
\refdoi{10.1016/j.catena.2017.10.020}
\endreference{}

\reference{Lopo78}
\reftype{3}
\refauthf{Lopotko}{M. Z.}{}
\refyear{1978}
\refbook{Ozera i Sapropel'}
\refpubl{Nauka i Tehnika}
\reflocat{Minsk, USSR}
\refpages{88}
\endreference{in Russian}

\reference{Mali05}
\reftype{1}
\refauthf{Malikova}{I. N.}{}
\refauth{Strakhovenko}{V. D.}{}
\refgroup{et al.}
\refyear{2005}
\reftitle{Ekologicheskoe sostojanie pochv Altajskogo kraja: zagrjaznenie radioceziem}
\refjour{Sibirskii Ekologicheskii Zhurnal}
\refvol{12}
\refnumb{6}
\refpages{985--998}
\endreference{in Russian}

\reference{Naum13}
\reftype{4}
\refauthf{Naumova}{N. B.}{}
\refgroup{et al.}
\refyear{2013}
\reftitle{Donnye otlozheniya stepnykh ozer: zabytye ehkosistemy?}
\refbook{Razvitie Miner\-al'no-Syr'evoj Bazy Sibiri}
\refpubl{Tomskij Politehnicheskij Universitet}
\reflocat{Tomsk}
\refpages{276--279}
\endreference{in Russian}

\enlargethispage{-8\baselineskip}

\reference{Ovdi16}
\reftype{4}
\refauthf{Ovdina}{E. A.}{}
\refgroup{et al.}
\refyear{2016}
\reftitle{Osobennosti raspredeleniya radionuklidov v oz. Sarbalyk (Barabinskaya ravnina)}
\refbook{Materialy V Mezhdunarodnoi konferentsii Radioaktivnost' i radioaktivnye elementy v srede obitaniya cheloveka}
\refpubl{STT}
\reflocat{Tomsk}
\refpages{475--477}
\endreference{in Russian}

\reference{Pest16}
\reftype{3}
\refauthf{Pestryakova}{L. A.}{}
\refyear{2016}
\refbook{Paleoehkologiya. Metodo\-logicheskie Osnovy Paleoehkologii: Uchebno-Metodi\-cheskoe Posobie}
\refpubl{Izd-vo NEFU}
\reflocat{Yakutsk, Russia}
\refpages{84}
\endreference{in Russian}

\reference{Rikh09}
\reftype{3}
\refauthf{Rikhvanov}{L. P.}{}
\refyear{2009}
\refbook{Radioaktivnye Ehlementy v Okruzhayushhej Srede i Problemy Radioehkologii: Uchebnoe Posobie}
\refpubl{STT}
\reflocat{Tomsk, Russia}
\refpages{430}        %%% ???+
\endreference{in Russian}

\reference{Rosl13}
\reftype{4}
\refauthf{Roslyakov}{N. A.}{}
\refauth{Strakhovenko}{V. D.}{}
\refauth{Syso}{A. I.}{}
\refyear{2013}
\reftitle{Mestorozhdeniya sapropelevykh zalezhej Novosibirskoj \ oblasti}
\refbook{Razvitie \ Mineral'no-Syr'evoj Bazy Sibiri}
\refpubl{Tomskij Politehnicheskij Universitet}
\reflocat{Tomsk}
\refpages{273--276}
\endreference{in Russian}

\reference{Shti05}
\reftype{3}
\refauthf{Shtin}{S. M.}{}
\refyear{2005}
\refbook{Ozernye Sapropeli i Osnovy ikh Kompleksnogo Osvoeniya}
\refpubl{MISIS}
\reflocat{Moscow, Russia}
\refpages{373}
\endreference{in Russian}

\reference{Solo09}
\reftype{3}
\refauthf{Solotchina}{E. P.}{}
\refyear{2009}
\refbook{Strukturnyj Tipomorfizm Glinistykh Mineralov Osadochnykh Razrezov i Kor Vyvetrivaniya}
\refpubl{Geo}
\reflocat{Novosibirsk, Russia}
\refpages{236}
\endreference{in Russian}

\reference{Stra16}
\reftype{2}
\refauthf{Strakhovenko}{V. D.}{}
\refgroup{et al.}
\refyear{2016}
\reftitle{Hydrochemical characteristic of sapropels in Novosibirsk Oblast}
\refjour{Water Resources}
\refvol{43}
\refnumb{3}
\refpages{336--344}
\refdoi{10.1134/S0097807816030167}
\endreference{}

\reference{Stra10}
\reftype{2}
\refauthf{Strakhovenko}{V. D.}{}
\refgroup{et al.}
\refyear{2010}
\reftitle{The regularities of distribution of radionuclides and rare-earth elements in bottom sediments of Siberian lakes}
\refjour{Russian Geology and Geophysics}
\refvol{51}
\refnumb{11}
\refpages{1167--1178}
\refdoi{10.1016/j.rgg.2010.10.002}
\endreference{}

\reference{Sube16}
\reftype{3}
\refauthf{Subetto}{D. A.}{}
\refauth{Prytkova}{M. Ya.}{}
\refyear{2016}
\refbook{Donnye Otlozheniya Raznotipnykh Vodoemov. Metody Izucheniya}
\refpubl{KarSC RAS}
\reflocat{Petrozavodsk}
\refpages{89}
\endreference{in Russian}

\reference{Suka43}
\reftype{3}
\refauthf{Sukachyov}{V. N.}{}
\refyear{1943}
\refbook{Sapropel' i Ego Znachenie v Sel'skom Khozyajstve}
\refpubl{Izd-vo AN USSR}
\reflocat{Moscow, USSR}
\refpages{54}
\endreference{in Russian}

\reference{Wang18}
\reftype{2}
\refauthf{Wang}{J.}{}
\refauth{Baskaran}{M.}{}
\refauth{Niedermiller}{J.}{}
\refyear{2018}
\reftitle{Mobility of Cs-137 in freshwater lakes: A mass balance and diffusion study of Lake St. Clair, Southeast Michigan, USA}
\refjour{Geochimica et Cosmochimica Acta}
\refvol{218}
\refpages{323--342}
\refdoi{10.1016/j.gca.2017.09.017}
\endreference{}

\reference{Yerm16}
\reftype{2}
\refauthf{Yermolaeva}{N. I.}{}
\refgroup{et al.}
\refyear{2016}
\reftitle{Hydrobiological Conditions of Sapropel Formation in Lakes in the South of Western Siberia}
\refjour{Water Resources}
\refvol{43}
\refnumb{1}
\refpages{79--91}
\refdoi{10.1134/S0097807816010073}
\endreference{}

\reference{Zaru13}
\reftype{1}
\refauthf{Zarubina}{E. Yu.}{}
\refyear{2013}
\reftitle{Pervichnaya produktsiya makrofitov trekh raznotipnykh sapropelevykh ozer yuga Zapadnoj Sibiri (v predelakh Novosibirskoj obla\-sti) v 2012 godu}
\refjour{Mir Nauki, Kul'tury, Obrazovaniya}
\refvol{5}
\refpages{441--444}
\endreference{in Russian}

\reference{Zhan18}
\reftype{2}
\refauthf{Zhang}{Y. Q.}{}
\refauth{Long}{Y.}{}
\refauth{Li}{B.}{}
\refauth{Xu}{S. J.}{}
\refauth{Wang}{X. L.}{}
\refauth{Liao}{J.}{}
\refyear{2018}
\reftitle{Use of reservoir deposits to reconstruct the recent changes in sediment yields from a small granite catchment in the Yimeng Mountain region, China}
\refjour{Geomorphology}
\refvol{293}
\refpages{167--177}
\refdoi{10.1016/j.geomorph.2017.05.017}
\endreference{}

\vspace*{1ex}

\end{references}

\end{document}







