Introduction

Lake Bafa is a natural reserve situated in southwestern (37°31′N, 27°27′E) Turkey, the southern part of it within the boundaries of Milas district of Mugla Province and the northern part within Aydin Province’s Soke district. It is one of the largest coastal lakes in Turkey. Having a maximum depth of roughly 20 m, its surface covers an area of approximate 75 km2. The lake developed as a result of the delta progradation of the Buyuk Menderes (Meander) River which is the longest river in the Aegean region Menderes for 584 km through western part of Turkey before reaching the Aegean Sea with a large delta ecosystem. Buyuk Menderes has a total drainage area of 24,000 km2. The overall runoff capacity, for instances the erosion potential of the river is so high that, it could be able to change the geomorphology of the former Latmian Bay radically [1]. In the past six or so millennia, the river sediments have gradually filled nearly the whole marine embayment of the so-called Latmian Gulf, thereby separating its southeastern part from the off shore [2]. Lake Catchment is comprised of the residential and agricultural areas and there is also olive oil factory, fish hatchery, restaurant in catchment in Fig. 1. showing that it has been affected by the human activities. The industry has been gradually grown in catchment land in recent years. Lake is under the influence of waters runoff coming from the Buyuk Menderes River. Beside this, some small streams contribute to the water input [1]. Salinity of the lake water differs in a range between 0.17 and 0.04 % [3], summer and winter seasons respectively.

Fig. 1
figure 1

Study area and core locations

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The radionuclides 210Po (half-life: 138.38 days), 210Pb (half-life: 22.30 years) and 137Cs (half-life: 30.14 years) have widely and successfully used in environmental investigations. In this study radiometric measurements are shedded light on evaluation of lake sediments, especially recent chronology, residence time of 210Pb, radionuclide ratios, pollution degree and supply of pollution.

Materials and methods

Sample preparation and measurement

Four sediment cores (C-1, C-2, C-3 and C-4) were collected from different locations of Lake Bafa via a gravity corer in 2010. Study area is shown in Fig. 1. Bottom currents were measured in each station at different depths (6, 8, 10, 12 m) by using Teledyne 150 kHz RDI WH Mariner ADCP (Acoustic Doppler Current Profiler). The core length is varied from 32 to 51 cm and water depth is from 3 to 17 m. Cores were sliced at 1 cm intervals in the laboratory. The wet weights of the samples were recorded and then oven dried at 70 °C for 24 h to obtain dry weights. Then water content and porosity were calculated for each slice.

The sediment samples were ground and passed through a 63 µm mesh followed by homogenization. After the addition of a standardized amount of 209Po (half-life: 103 years) tracer, sediment samples were completely dissolved with HF:HNO3 (1:1) and HCl. Polonium was spontaneously plated onto copper discs in 0.5 M HCl in the presence of ascorbic acid to reduce Fe+3 to Fe+2 in order to get the optimum conditions for plating 210Po on discs the standard technique used which was modified by Flynn [4]. Measurements of 210Po concentrations were made through its 5.30 MeV alpha particle emission, using 209Po (4.88 MeV alpha emission) as the internal tracer (National Institute of Standards and Technology, <500 Bq in 7 % hydrochloric acid). Alpha particles from 210Po were counted in PIPS (Passivated Implanted Planar Silicon) detector (Ortec Octete Plus-450 mm2 ULTRA-AS) and analyzed by utilizing a Canberra 7401 spectrometer. After the first deposition of 210Po residual 0.5 M HCl was stored for one year to allow of 210Po in-growth from the 210Pb contained in the sample solution. Each sample was re-plated to determine the 210Po activity. Counting period was adjusted to keep the standard error under the 10 % (relative standard error was approximately 5 %). In determination of 210Po, the results of 209Po recovery and Bateman equations [5, 6] were used.

137Cs activities were determined as gamma spectroscopic using the high resolution gamma spectrometer consist of a 184 cc HPGe detector, ORTEC-671 model spectroscopy amplifier and a Canberra PC based multi-channel analyzer with a 8 K spectral memory. The specification of the p-type coaxial detector was 1.85 keV full width at half maximum (FWHM) at the 1.33 MeV gamma energy of 60Co and a 25 % relative efficiency. Minimum detectable activity (MDA) was 2.21 Bq kg−1 for 200000 s. To reduce the background, the detector was shielded by a 100 mm thick lead shield with a fixed bottom and a moving cover. The detector efficiency calibration was performed by using the IAEA quality assurance reference materials produced by IAEA [7]. Sample was comprised of 10 g sediment and 4 g starch (Merck). Geometry was formed by using presser as a disc (thickness was 6 mm and diameter was 40 mm). Reference material with same geometry was IAEA-156.

Residence time calculation

Residence time of 210Pb in lake water was calculated using the first order kinetic relation as shown below:

$$ {{dI_{w} } \mathord{\left/ {\vphantom {{dI_{w} } {dt}}} \right. \kern-0pt} {dt}} = \varPhi_{w} - \left\{ {\left[ {\lambda_{\text{pb}} + \left( {{1 \mathord{\left/ {\vphantom {1 {T_{\text{w}} }}} \right. \kern-0pt} {T_{\text{w}} }}} \right)} \right]I_{w} } \right\} $$
(1)
$$ {{dI_{s} } \mathord{\left/ {\vphantom {{dI_{s} } {dt}}} \right. \kern-0pt} {dt}} = \varPhi_{s} - \left\{ {\left[ {\lambda_{\text{pb}} + \left( {{1 \mathord{\left/ {\vphantom {1 {T_{s} }}} \right. \kern-0pt} {T_{s} }}} \right)} \right]I_{s} } \right\} $$
(2)

where Φw and Φs (Bq cm−2 year−1) are the fluxes of 210Pb in the lake water and sediments respectively, and their corresponding inventories I w and I s (Bq cm−2). λ pb is the radioactive decay constant (= ln2/22.3 year−1), T w and T s are the residence times of the 210Pb in the lake water and lake sediments respectively. At steady state, the inventory of unsupported 210Pb in the lake water, I w , can be found by subtraction the mean sedimentary unsupported 210Pb inventory of the lake, I s from the atmospherically supported inventory, I atm . If dI w and dI s /dt are equal to zero residence time of 210Pb in lake water can be obtained using above equations as:

$$ T_{w} \approx \frac{{I_{atm} - I_{s} }}{{\lambda_{Pb} I_{s} }} $$
(3)

Since λ pb ≪ 1/T w , λ pb ≪ 1/T s and I w  = I a  − I s [8].

Results and discussions

Nevertheless there is not any study of sedimentation rates and historical sediment records in Lake Bafa using such models at present. In this study, we have examined the applicability of the 210Pb dating models for determination of past sedimentation rates in Lake Bafa in Turkey. The use of 210Pb dating models was tested with 137Cs dating. We have not only aimed to comprise out sedimentation pattern but also realized the works that are mentioned following sentences. 210Po/210Pb rates and porosities were determined in cores and consequences were used in evaluation of sediment content and supply of pollution. The residences time of 210Pb in lake water were calculated In this research the most important point is that above mentioned evaluations for instances dating, sedimentation pattern, the residences time of radionuclide (210Pb) and determination of sediment pollution degree (210Po/210Pb rates) were especially realized by only using radiometric measurements.

Porosity

The porosity profile indicates that sediment structure in C-4 station consist of three types divisions with have different mass densities. Porosity is lower than the other three cores (Fig. 2).

Fig. 2
figure 2

Porosities of the sediment cores at C-1, C-2, C-3 and C-4 stations

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Porosity displays more or less same value along the core profile. According to us it can be said that sediment structure which is accumulated to the lake floor is the same material along the core profile in C-3 station. When we compare porosity with the profile distribution of 210Pb concentration, it is seen that sharply decrease in porosity corresponds to decrease in 210Pb concentration (Table 1) and increase in sedimentation rate (Tables 2, 3).

Table 1 210Po, 210Pb concentrations and 210Po/210Pb ratios are summarized in table
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Table 2 Sedimentation rates and dating in cores C-1, C-3, C-4 using CIC model
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Table 3 Sedimentation rates and dating in cores C-1, C-3, C-4 using CRS model
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C-2 station has successive increase and decrease in porosity and the values are relatively equal to each other. According to us it implies that sediment structure which is accumulated to the lake floor has been changed periodically and it is related to the Menderes River that its flow to the lake has periodically been banned for the irrigation. Beside of this it may be related to the collapse of the successive accumulated sediment layers and mixing them.

When examining the C-1 station it is seen that porosity along to core profile is more or less the same. In each core, porosities are free from the others due to the lack of bottom current in the lake. Measured flows were recorded between 3.046 and 4.905 cm s−1. Speed of the bottom currents is very low. According to us, it has not any impression on sediment accumulation. Differences of the sedimentation rates among the stations are free from the bottom currents. So it can be stated as the lake has different sediment depositional zones.

Athy [9] argue that the porosity profile for homogeneous sediments with uniform compaction usually shows an exponential decrease with depth (obtained from [8]). Similarly Begy et al. [10] investigated that porosity profile shows an exponential decrease with depth in Red Lake (Romania). Contrary Klump et al. [11] calculated the fifteen porosity profiles, when glimpsed to the profiles they did not display exponential decrease with depth in eastern Lake Superior.

In this study porosities have not displayed the exponential decreases along to sediment profiles. Porosity varies between 0.82 and 0.77 from top to bottom levels in central area of the lake and between 0.70 and 0.68 from top to bottom levels in near shore. When glimpsed to the Fig. 2. it can be seen that the sediments accumulated to the lake floor are homogenous in C-1 and C-3 stations separately. Since the porosity is consistent at layer by layer along to core profile. In C-2 station first part which is long 23 cm of the core, displays the fluctuations on porosity so it can be said that C-2 has a stratified construction.

Radionuclides

The relation between 210Po concentrations and porosities along to the core profiles can be seen that, however profile distributions of 210Po displayed the exponential decrease with increasing depth (Table 1), in C-1 and C-3 stations porosity shows more or less constant line from top to bottom along to the profiles on the Fig. 2. In other cores (C-2 and C-4) profile distribution of 210Po concentrations do not display exponential decrease with increasing depth and porosity showed sequentially increases and decreases along to the core profile. So we think that exponential decrease in porosity for exponential decrease with increasing depth in 210Po concentrations conversely to Begy et al. [10] is not necessary.

210Po/210Pb ratios in sediment cores provide the important information which is related to the sediment nature. According to Boisson et al. [12] the ratio is generally close to 1 in sediments, approximately 2 in fecal pellets (fecal pollution or dead plankton), 7 in phytoplankton and 30 in zooplankton detrital material. Further information about the 210Po/210Pb ratios in surficial waters can be found in Masque et al. [13]. The ranges of ratios in the sediment cores obtained from the Lake Bafa were 2.27–1.32, 1.52–0.90, 2.78–0.79, 1.84–0.76 in C-4, C-3, C-2, C-1 stations respectively (Table 1). They indicate that nature of the precipitated particles to the lake floor is close to fecal pellets especially in C-4 station in Lake Bafa. Heussner et al. [14] and Wei and Murray [15] were reported that the average ratio in particles were 0.68–1.13 for North-western Mediterranean and the Black Sea. Average 210Po/210Pb ratios in C-3, C-2 and C-1 (0.96, 1.15, and 1.13 respectively) stations are more or less at same interval with North-western Mediterranean and Black Sea. However, in C-4 (1.58) station it is higher than the above ratio.

Some radionuclides like 210Pb and 137Cs have been used in environmental studies. 210Pb is the important natural radionuclide for determining marine and fresh water sedimentation and it provides well-established mathematical models [16–21]. These models have been extensively used in dating the chemical changes, trace or heavy metal, organic matter and any other kind of pollution that have occurred in recent lake sediments [22–24]. Application of radiometric methods to sedimentary geochronology resulted successfully. According to the Krishnaswami et al. [25] 210Pb is ideal for dating lake sediments as far back as a century or so [26].

The 210Pb dating is generally supported by the marker 137Cs since the use of both radiotracers improves accuracy by providing two independent means of measuring the same burial processes occurring within a given sediment core. The artificial radionuclide 137Cs aroused from the atmospheric testing of thermo nuclear weapons and Chernobyl reactor accident then precipitated to environment. Significant fallout on a global scale began after the initial test in the early 1950s, reached peak value in 1963 and then declined because of the implementation of the international treaty banning such tests. Next nuclear weapons tests in the atmosphere between 1966 and 1974 were performed by France. Other substantial fallout originated with 1986 Chernobyl Reactor Accident.

Although 210Pb can be determined by alpha (via indirectly its grand-daughter, 210Po), beta (via its beta emitting daughter, 210Bi (half-life: 5.01 days)) or gamma spectrometric methods 210Po analysis is widely realized using alpha spectrometric methods [27, 28]. So in this study 210Pb and 137Cs were determined by alpha and gamma spectrometric methods respectively.

The total 210Pb activity in sediments has two components, namely supported and unsupported components. Unsupported 210Pb is that part of the measured activity of the 210Pb which exceeds the supported activity that derives from in situ decay of the parent radionuclide 226Ra and it will usually be in radioactive equilibrium with the 226Ra. Unsupported 210Pb is determined by subtracting supported activity from the total activity at every levels. 210Pb is scavenged from the atmosphere by both wet and dry processes as 210Po [29–32].

The total 210Pb activity is varied between 170.74 ± 4.78 mBq g−1 and 54.80 ± 2.57 mBq g−1 along the core in C-1 station. 226Ra activity was determined as 54.80 ± 2.57 mBq g−1 from the deepest layer of the core (the layer is defined that the total 210Pb activity decreases to level of 226Ra activity as deepest layer in dating and remained part of the core is ignored.). Unsupported 210Pb activities were plotted on logarithmic scale versus depth profile and slope of the graph was 0237 (Fig. 3.). Inclination of the graph was determined by the regression line (r 2 = 0.884). This line is sufficiently fit for logarithmic 210Pb concentrations in core C-1. So in calculation of sedimentation rates all models (CRS, CIC and CF;CS) are more or less compatible with each other. Sedimentation rate which is calculated by the CF;CS model is 0.131 cm year−1 but CIC and CRS models are useable rather than CF;CS. Beside of the 210Pb dating models, 137Cs method utilized to confirm the sedimentation rates or sediment dating in C-1 station. The most suitable model is the CIC in this core. Since the results of the 210Pb dating (CIC model) are a bit more compatible with the results of the 137Cs dating than the other one (CRS model). When it is glanced to the 137Cs activities Chernobyl and nuclear test peaks are seen in Fig. 4. 137Cs activities reached to a peak value (50.00 ± 2.78 mBq g−1) at the fifth cm under the sediment surface in core C-1 (Fig. 4.). It indicates that fifth cm under the sediment surface corresponds to the 1986 (Chernobyl reactor accident). As it can be clearly seen from Tables 2 and 3. It is necessary 23.04 ± 0.97 years and 22.91 ± 0.97 years according to CIC and CRS models respectively for sediment deposition from surface to fifth cm under the sediment surface. Second peak (10.17 ± 1.37 mBq g−1) is seen at the twelfth cm under the surface. This peak belongs to the nuclear test attempts. It corresponds to 59.79 ± 3.48 and 60.06 ± 3.49 years before according to CRS and CIC models respectively (Tables 3 and 2). It can be seen that the each sediment dating techniques, natural radionuclide 210Pb (CIC and CRS models) and artificial radionuclide 137Cs have shown good agreement in this station.

Fig. 3
figure 3

Unsupported 210Pb concentrations were plotted on logarithmic scale versus mass depth in Lake Bafa cores (C-1, C-3 and C-4). Slope of the regression line and regression coefficient were indicated upper right-hand corner in each graph

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Fig. 4
figure 4

Profile distribution of 137Cs activity concentrations in C-1, C-3 and C-4 cores

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Sedimentation rate is varied between 1.999 ± 0.626 cm year−1 and 0.036 ± 0.002 cm year−1 along to core. 210Pb flux (21.24 mBq cm−2 year−1) was calculated by using core inventory (683.34 mBq cm−2). Although sedimentation rate displays the successive increases and decreases, in general it increases until the seventh layer (0.491 ± 0.058 cm year−1) than decreases through to the deeper parts of the core except seventeenth layer (1.999 cm year−1). Sediment deposition has displayed the increasing inclination until 1969 and it has showed successive fluctuations at last thirty years. The reasons of the fluctuations on sediment deposition may be related to the growing agricultural areas and changing irrigation policy around the lake. According to Persson and Holm [33] phosphate fertilizers are derived from phosphate ores containing 210Pb and 210Po [34, 35]. Most of the contaminants are left in the solid gypsum waste, and some of the 210Pb and 210Po and in the fertilizers [36, 37]. Disposing gypsum waste directly into the environment and the use of phosphate fertilizers may affect the levels of 210Pb and 210Po in water sediments and soil [36, 38–40]. The phosphate industry is claimed to be a major source of enhancement of 210Pb and 210Po in the surrounding environment [41].

Distribution of the total 210Pb activity is varied between 44.81 ± 2.63 mBq g−1 and 42.12 ± 2.84 mBq g−1 along the core in C-2 station. Vertical distribution of 210Pb activity along to core is not display the exponential decrease so dating or sedimentation rate cannot be calculated in this station. According to us overlapping sediment layers have collapsed and sediment layers have mixed each other. Average 210Po/210Pb ratio (1.15) displays the sediment type. Accumulated sediment is not comprised the soft material. In this case collapsing of the sediment layers may be related to the geologic features of the lake floor. For instance, an earthquake may have triggered the collapse of the sediment layers accumulated on sloping lake floor.

The total 210Pb activity is varied between 187.84 ± 4.83 mBq g−1 and 58.46 ± 2.56 mBq g−1 along the core in C-3 station. 137Cs activity concentrations gave the Chernobyl and nuclear test peak. 137Cs concentrations reached to a peak value (46.32 ± 3.25 mBq g−1) at the fifth cm under the sediment surface in core C-3 (Fig. 4.). It is indicated that fifth cm under the sediment surface corresponds to the 1986 (Chernobyl reactor accident). As it can be clearly seen from Tables 2 and 3. It is necessary 24.02 ± 0.79 years and 23.82 ± 0.78 years according to CIC and CRS models respectively for sediment deposition from surface to fifth cm under the sediment surface. The next peak (9.67 ± 1.63 mBq g−1) which is belong to nuclear test attempts (1957), is at eleventh cm under the surface. It corresponds to 63.07 ± 1.94 and 62.92 ± 1.93 years before according to CRS and CIC models respectively. If error range (Tables 2 and 3) is considered it is very close to beginning of the first nuclear test reaction (1951) or to 1963 peak (late 1950s/early 1960s). Sedimentation rate is varied between 2.606 ± 0.120 and 0.039 ± 0.002 cm year−1 along to core. 210Pb flux (27.72 mBq cm−2 year−1) was calculated by using core inventory (892.09 mBq cm−2).

Distribution of the total 210Pb activity ranged between 126.34 ± 3.42 mBq g−1 and 74.25 ± 2.66 mBq g−1 along the core in C-4 station. When it is glanced to the 137Cs activities, Chernobyl and nuclear test peaks are seen obviously. 137Cs activities reach to a peak value (24.35 ± 1.28 mBq g−1) at the fifth cm under the sediment surface in core C-4 (Fig. 4.). According to the CIC model fifth cm under the sediment surface corresponds to the 1983. If error range (Table 2) is considered it is very close to the 1986 (Chernobyl reactor accident). Second peak is seen at tenth cm (13.09 ± 1.03 mBq g−1) under the sediment surface corresponds to beginning of the first nuclear test reactions (1951). It can be clearly seen from Table 2. It is necessary 59.41 ± 2.81 years according to CIC model for sediment deposition from surface to tenth cm under the sediment surface. It can be seen that the each sediment dating techniques natural radionuclide 210Pb (CIC and CRS models) and artificial radionuclide 137Cs have shown good agreement in this station. Small differences may be related to the sediment structure or particle reactive feature of the 137Cs. Sediment structure is close to fecal pellets as different from the other stations. Water depth is 3 m in this station. Direction of the wind has affected the accumulated materials such as peat and algae for C-4 station. Because algae are comprised on the surface of lake water and they are moved to C-4 station by wind. Sedimentation rate is varied between 0.343 ± 0.011 and 0.016 ± 0.001 cm year−1 along to core. 210Pb flux (10.22 mBq cm−2 year−1) is calculated by using core inventory (328.82 mBq cm−2).

Max. unsupported 210Pb activities in Lake Bafa are slightly higher than those in Lake Puyehue and Lake Icalma (80–120 Bq kg−1 and 90 Bq kg−1 respectively) [42], Red Lake (Romania) (137.34 Bq kg−1) [10], more or less same with Lough Carra (Ireland) (200 Bq kg−1) [43] and lower than Lake Hongfeng (248-371 Bq kg−1) [23].

Although inventories are different in each core, central ones (C-1, C-3) are close to each other and higher than the near shore one (C-4). Difference might be aroused from beside of the maximum core depths (short cores have lower 210Pb inventory than the deeper one) sediment types. It is familiar that sediment type is directly related to the radionuclide absorbance. It is stated by Persson and Holm [33] that, soil consists of particles of different minerals as well as organic matter in various stages of degradation.

The 210Pb fluxes (21.24, 27.72, 10.22 mBq cm−2 year−1) in Lake Bafa are higher than the ones at Northern Patagonia Lakes (it ranged from 4 to 48 Bq m−2 year−1) [20], and lower than Lake Zurich; Center of lake 3 (375 ± 38 Bq m−2 year−1) [44] (obtained from Guevara et al. [20] ). According to Appleby and Oldfield [18] global average atmospheric flux was estimated as 185 Bq m−2 year−1. Therefore we can say that average 210Pb flux (19,73 mBq cm−2 year−1) obtained from Lake Bafa is a bit higher than the global average. However it is more or less in the range of average atmospheric flux values of the Mediterranean area that was reported by Garcia-Orellana et al. [45]. It is a bit lower than average (204,30 Bq m−2 year−1) atmospheric flux of Monaco [46].

In general, sedimentation rates along to core profile are more or less same in central cores (C-1 and C-3). They exhibited a stable character. According to us differences arouse from the maximum core depths and the distributions of 210Pb concentration along to core profiles. Since measured bottom currents are almost same in central stations of the lake and not sufficient for an impression on the sedimentation pattern. However sedimentation rates along to core profile are not systematic in C-4 station. Two different trends are seen in C-4 core. First, sedimentation rates show sharp increase and decrease between 1966 and 2010. Second, it is decreased from 1966 to 1813. Average sedimentation rate in central area cores are slightly higher than the near shore one. The sedimentation rates in more recent times are two and three times higher than the earlier years. The increasing inclination of the sedimentation rate among the sediment layers in near shore is higher than the central area of the lake. According to us, it should be related to the sediment types of stations and the prevailing winds. Since the usual wind direction for the lake is towards to C-4 station. Beside of this in hydrothermal areas sedimentation rates in upper layers are up to seven times higher than the bottom ones [47]. So we can say that Lake Bafa has not hydrothermal activity.

In entire study site mean atmospheric flux (24.48 mBq cm−2 year−1) in central area and near shore (10.22 mBq cm−2 year−1) are not close to each other. So it is indicated that the atmospheric flux is not the dominant factor controlling the 210Pb supply. In this situation CIC model should be utilized for sediment dating [16–18, 48]. These models are compatible but CIC model also is displayed better convenience with 137Cs method in general. In another research conducted by Müllenhoff et al. [2] two sediment cores were obtained from the lake. The first one (Baf S1) was taken from the eastern part of the lake, the second one (Baf S6) from the Midwestern part. Both cores have been analyzed with sedimentological, micro-faunistical and paly-nological methods. Dating has been realized by using radiocarbon technique (AMS-technique) in both cores. Their results are indicated that sedimentation rate increases from 0.11 cm year−1 (11 cm/100a) in the Geometric-Archaic periods (Baf S1) and 0.22 cm year−1 (22 cm/100a) in the Classical-Hellenistic periods (Baf S6), respectively, to 1.35 cm year−1 (135 cm/100a) in the Roman era. However in our study average sedimentation rate is found as 0.351 cm year−1 in central area and 0.137 cm year−1 in near shore station by using together 210Pb and 137Cs techniques.

Other knowledge about Lake Bafa is residence time of 210Pb in lake water. According to Kumar et al. [8] in a lake sediment core, lower values of 210Pb concentration at the sediment–water interface compared to values at lower depths and/or a non-monotonic 210Pb profile at any location beside of the other things may be attributable to higher residence time of the radionuclide in lake water. It was calculated by using profile distribution of 210Pb concentrations as 1.9 months for Lake Bafa. The residence time of 210Pb in Lake Bafa waters is very short. So it is convenient with non-lower values of 210Pb concentration at the sediment–water interface in lake. According to us it is next indicator to explain sedimentation pattern and accumulated sediment type.

Conclusions

The study has focused on to answering the question “How to describe recent changes on Lake Bafa using especially radiometric techniques?” In order to response the question, sediment porosities were calculated, radionuclide concentrations were determined, bottom currents were measured, and residence time of 210Pb was calculated in lake water. The results showed that sediment structure had a stratified construction in C-2 and homogenous one in C-1 and C-3 along to cores. The evaluation of relation between porosities and 210Po concentrations in cores indicated that exponential decrease with increasing depth was not an obligation on porosity and 210Po concentrations in a parallel manner. The other important information was received from radionuclide (210Po/210Pb) ratios in sediment cores. The range of ratios could be said that nature of the precipitated particles to the lake floor as sediment is close to fecal pellets (fecal pollution). It may be related to the buildings around the lake or salinity difference of the lake water between in summer and winter seasons. Because entry of waters that are coming from Menderes River to lake has been blocked for irrigation in summer months, in recent years. A hydraulic barrier controlling the lake’s water level with two regulators at both ends have been installed. So salinity difference has caused uncontrolled reproduction of alga on the water surface and than dead algae have sunk towards to bottom as sediment. It has been also supported by radiometric techniques (210Po/210Pb ratio). It should be taken some protective measure related to the fecal pollution around the lake. In this study the sedimentation rates and sedimentation pattern of Lake Bafa were studied using natural 210Pb models and tested by utilizing 137Cs technique. Sedimentation rates were evaluated with respected to bottom currents, porosities, profile distribution of 210Pb concentrations, relations between 210Po/210Pb and sediment types, prevailing winds. Average sedimentation rate in central area of the lake was higher than the near shore region. According to us residence time of 210Pb in lake water was next indicator to explain sedimentation pattern and accumulated sediment type. It was very short (1.9 months). So it was convenient with non-lower values of 210Pb concentration at the sediment–water interface in lake. Sedimentation pattern was also evaluated with respect to the bottom currents. It was pointed out that speed of the bottom currents was very low and it was not sufficient to make any impression on sediment accumulation. Differences of the sedimentation rates among to stations were free from the bottom currents. So it can be said that the lake has different sediment depositional zones.

Although there is a study related to the sediment dating using radiocarbon technique. Due to the lack of available data about detailed sediment dating in Lake Bafa, we performed this detailed recent sediment dating of the lake. We provided the different point of view to Lake Bafa via using radiometric techniques. We think that the present study will provide to available and comparable data for next studies on this subject.