Sediment characteristics and water physicochemical parameters of the Lysimachia Lake, Western Greece P. Avramidis, A. Samiotis, E. Kalimani, D. Papoulis, P. Lampropoulou & V. Bekiari Environmental Earth Sciences ISSN 1866-6280 Volume 70 Number 1 Environ Earth Sci (2013) 70:383-392 DOI 10.1007/s12665-012-2134-9
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Author's personal copy Environ Earth Sci (2013) 70:383–392 DOI 10.1007/s12665-012-2134-9
ORIGINAL ARTICLE
Sediment characteristics and water physicochemical parameters of the Lysimachia Lake, Western Greece P. Avramidis • A. Samiotis • E. Kalimani • D. Papoulis • P. Lampropoulou • V. Bekiari
Received: 1 March 2012 / Accepted: 18 November 2012 / Published online: 4 December 2012 Ó Springer-Verlag Berlin Heidelberg 2012
Abstract In the present paper, we present the sedimentological characteristics and the water physicochemical parameters of Lysimachia Lake, which is one of the most important lakes of Western Greece, as it is protected by international conventions and is listed in the Natura 2000 European Network. Sedimentological analysis involved grain size analyses, moment measures, total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) measurements, as well as determination of the clay minerals content. Water physicochemical parameters such as pH, temperature, conductivity and dissolved oxygen were measured in situ with portable equipment, while nutrients such as nitrates, nitrites, phosphates and ammonium ions, as well as TOC and TN were analyzed in a time period of 1 year seasonal monitoring. Geographical distribution of grain size and geochemical parameters indicated a clear partition in the northern and southern parts of the lake. This phenomenon can related to the discharging of a channel into the lake, the discharging of sewage effluents from Agrinio city during the last years as well as the type of clay minerals distribution. Clay minerals analyses indicated that smectite predominates in the northern part of the lake, whereas chlorite is more abundant in the southern parts. This explain the higher amounts of TOC and TN observed in the northern part of the lake and can be correlated with the higher external surface and adsorption capacity of P. Avramidis (&) A. Samiotis E. Kalimani V. Bekiari Laboratory of Geology for Aquatic Systems, Technological Educational Institute of Mesolonghi, Nea Ktiria, 30200 Mesolonghi, Greece e-mail:
[email protected] D. Papoulis P. Lampropoulou Department of Geology, University of Patras, 26500 Patras, Greece
minerals in the smectite-rich sediments. The four seasons monitoring of water physicochemical parameters indicates a relatively higher values of TOC and TN in the northern part of the lake, while nutrient concentrations indicate a uniform geographical distribution along the lake. Keywords Lake sediments Grain size TOC TN Nutrients Greece
Introduction Variation of the bottom sediment characteristics such as grain size and moment measures demonstrates the transport processes, selective entrainment transport and deposition (McLaren and Bowels 1985; Gao and Collins 1992; Le Roux 1994; Le Roux et al. 2002), as well as the ability of the sediments to absorb organic matter and nutrients onto mineral surfaces (Hedges and Keil 1995). Total organic carbon (TOC) is a measure of the amount of organic matter preserved within sediment, while the amount of sediment nutrients is assessed as total nitrogen (TN) and total phosphorus (TP) coming from organic and inorganic sources. Organic matter breakdown (mineralisation) reduces sediment carbon, while nutrient concentrations and dissolved nutrients are released from the sediment to the water column (Froelich et al. 1979; Golterman 2004). External surface area of minerals is a crucial factor for the amount of the present TOC as mineral surfaces help to preserve organic matter through deposition, burial, and lithification (Mayer 1994), leading to the formation of a uniform cover of the organic matter (Bishop et al. 1992). Kennedy et al. (2002) propose that abundant mineral surface area was a necessary starting condition for the burial and preservation of organic matter and that the bulk of the
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organic matter is molecular-scale adsorbed and not particulate. Sedimentation of nutrients is the reverse process of internal loading. Nitrogen settles to the sediment in organic forms, while phosphorus is either sorbed in clay minerals and settles with them on the bed sediments or reacts with Fe, Al, Mn and Ca and mineralizes (Jonsson 1997). The environmental quality of the water and the associate components of an aquatic ecosystem cannot be evaluated without the study of bottom sediments characteristics. The presence of organic matter in aquatic systems and liquid wastes has attracted an intensive research interest concerning environmental studies (Hoppe-Jones et al. 2010; Larsen et al. 2011). Thus, TOC and TN are considered as the main factors giving quantitative information for the control of water quality of an ecosystem (Vialle et al. 2011). Bottom sediments can reload the water column with nutrients via decomposition of sediment’s organic matter (Golterman 2004). TOC content in sediments has been used as an indicator of pollution and eutrophication rate (Environmental Protection Agency (EPA), USA 2002). In the present paper, we present the geographical distribution of sedimentological characteristics of the bottom lake sediments, such as grain size, moment measures, TOC, TN and TP as well as the physicochemical parameters of lake water during 1 year monitoring (October 2010 to September 2011). Moreover, sediment mineralogical and clay mineral analysis results are compared with the geochemical parameters, and an evaluation of the environmental state of Lysimachia Lake is attempted.
Study area Lysimachia Lake is situated in the area of Aitoloakarnania, near the city of Agrinio, in Western Greece (Fig. 1a, b). From the ecological point of view, Lysimachia Lake is one of the most important lakes of Western Greece as it is one of the Greek protected lakes, listed in the Natura 2000 European Network with code number GR2310009. It has a surface area of 13.6 km2, maximum depth of 8 m and mean depth of 3 m. It is a warm monomictic lake and although it was originally oligotrophic now it is characterized as an eutrophic one (Petridis 1993). A narrow channel allows outflow of clear surface water from Trichonida Lake to Lysimachia Lake, which in turn maintains an open connection to the sea via Acheloos River. Lysimachia is connected with Trichonida and Acheloos by means of two artificial ditches, known as Alampei and Dimikos, respectively (Fig. 1c). Both Trichonida and Lysimachia Lakes have a tectonic origin and occur across the tectonic graben of Agrinio (Kiratzi et al. 2008) (Fig. 1b). Sewage effluents from the town of Agrinio (population 80,000) via Katourlis stream were discharged for years into the northern part of
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Fig. 1 a General map of Greece and the location of Lysimachia Lake in western Greece, b Lysimachia and Trichonida Lakes with the main faults and c the bathymetry of the Lychimachia Lake with the sampling stations (L1–L10) and the main streams and ditches which flow into the lake
lake Lysimachia (Fig. 1c). Furthermore, the north-western part of the lake receives agricultural run-off from arable land. Lake Lysimachia has a relatively large drainage basin and is influenced by the water coming from Ermitsas stream, as well as the water of lake Trichonida (through Alampei ditch) (Fig. 1c). It exhibits strong seasonal fluctuations of its water level, which is due to the high evaporation rate during summer and drainage to the river Acheloos, while during the winter it often overflows. Previous studies for Lysimachia Lake are limited. No one focused in sediments characteristics and did not cover a monitoring period since the last 20 years. Water physicochemical parameters of the lake were presented for the first time by Overbeck et al. (1982), while an estimation on the pollution status of the lake using multivariate analysis on biological and environmental (discriminant analysis) data was made by Petridis (1993). According to the above studies, water temperature of the lake ranged between 15.5 and 26.4 °C, pH between 8.1 and 8.5, conductivity between 315 and 350 ls/cm, while nutrients of phosphates, nitrites, nitrates and ammonium ions between 7.84–22.34, 1.5–24, 21.12–88.66 and 47.74–51.59 lg/L, respectively.
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Table 1 Grain size characteristics, statistical parameters in U scale of the bottom sediments (Folk and Ward 1957), TOC, TN and TP concentrations, of the sampling stations L1–L10 Lake parts
Sampling stations
Coordinates Longitude
Northern part
L1 L2
Southern part
Grain size analysis
Statistical parameter
TOC (mg/g)
TN (mg/g)
TP (mg/g)
Latitude
Sand (%)
Silt (%)
Clay (%)
Mean
Sorting
Skewness
Kurtosis
21.36152
38.56387
1.1
85.3
13.7
7.232
1.478
0.166
21.36297
38.56885
1.7
85.9
12.4
7.070
1.545
0.153
0.931
39.34
2.93
0.76
0.960
37.51
3.06
L3
21.36655
38.57482
3.5
87.1
9.4
6.863
1.554
0.65
0.089
1.047
41.31
2.81
0.64
L4
21.3784
38.56865
2.2
86.3
11.5
6.956
L5
21.37247
38.5601
0.1
85.7
14.2
7.399
1.528
0.227
0.987
30.30
1.56
0.46
1.377
0.147
0.930
29.39
2.60
L6
21.38188
38.5555
0.6
87.9
11.4
0.45
7.081
1.508
0.085
0.901
14.22
1.28
L7
21.38923
38.54825
45.5
51.2
0.39
3.3
4.401
1.632
0.365
1.383
15.31
1.45
L8
21.39715
38.5516
0.0
0.43
87.7
12.3
7.338
1.352
0.084
0.905
15.24
1.06
0.66
L9
21.39518
38.54397
L10
21.37917
38.55385
0.0
81.7
18.3
7.850
1.216
0.029
0.921
10.69
1.26
0.64
4.5
86.8
8.7
6.435
1.708
0.162
0.907
16.87
0.79
0.31
Fig. 2 Geographical distribution of bottom lake sediments properties of a total organic carbon (TOC), b total nitrogen (TN), c total phosphorus (TP) and d mean grain size
Materials and methods Sedimentological analyses were carried out on ten samples and include grain size analysis, TOC, TN and TP. The samples were collected using a Van Veen grab, operating from a boat. Sediments were collected from the upper 1–2 cm of the bottom lake, placed in sterilized plastic
containers and then stored in the laboratory at temperatures below -4 °C. Particle size distribution was made using a Malvern Mastersizer 2000, while moment measures were calculated using GRADISTAT V.4 (Blott and Pye, 2001) and based on Folk (1974) nomenclature. TOC and TN were measured with a TOC/TN analyzer of Shimadzu TOCVCSH coupled to a chemiluminescence detector (TNM-1
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TN unit), creating a simultaneous analysis system. Oxidative combustion–infrared analysis was used for TOC (DIN 1593), while TN was estimated based on oxidative combustion-chemiluminescence method (ASTM International 2008) modified for sediments. The mineralogical composition of bulk samples (prepared by gently pressing the powder into the cavity holder) was made on all ten samples and was determined by powder X-Ray diffraction (XRD), using a Bruker D8 advance diffractometer, with Ni-filtered CuKa radiation. The scanning area covered the 2h interval 2–70°. Powders from oriented samples were prepared by the dropper method and were scanned at 1° 2h/min from 3 to 70° 2h. For each oriented specimen, the clay minerals were identified from three XRD patterns (after air-drying at 25 °C, ethylene–glycol treated and heated at 490 °C for 2 h). The water samples were collected in 1 L polypropylene bottles which were previously cleaned with HCl 5 % w/w. The samples were transferred within 1 h of collection in the laboratory and were immediately analyzed. pH, conductivity (ls/cm), temperature (T, °C) and dissolved oxygen (DO, mg/L) were field measured with a portable instrument HACH HQ40D (Loveland, Colorado USA). Ammonium ions were measured using a Hach DR2800 (Berlin, Germany) absorption spectrophotometer, using Hach cuvette test (LCK), where ammonium ions were reacted with salicylate and hydrochlorite ions in the presence of sodium nitroprusside as a catalyst and the absorbance of indophenol blue at 690 nm was measured. All anion analyses were carried out using the ICS-1100 integrated ion chromatographic system of Dionex (IC pump which is a microprocessor-based isocratic delivery system, six-port electrically activated injection valve, precolumn and separator column including chemical suppressor
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L9 L8 L7 L10 L6 L5 L4 L3 L2 L1 2
10
20
30
40
50
60
70
Fig. 4 X-ray diffraction patterns of bulk samples L1–L10. Qrtz quartz, Cc calcite, and Alb albite
device assembly). Before running a sample, the ion chromatography system was calibrated using a Dionex standard solution. By comparing the data obtained from the sample to that obtained from the known standard, sample anions are identified and quantitated automatically. TOC and TN were measured using a Schimadzu TOC analyzer (TOCVCSH) coupled to a chemiluminescence detector (TNM-1 TN unit) (APHA 2005; ASTM International 2008).
Results Sediment characteristics Grain size analysis: moment measures
Fig. 3 Plot of sediments characteristics TOC versus TN
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Figure 1c presents the bathymetry of Lysimachia Lake, the main streams and ditches which flows into the lake, as well as the location of the ten sampling stations L1–L10. The lithological types were estimated based on Folk (1974) classification. The main lithological type of the lake bottom sediments is fine silt to sandy silt, characterized by relatively uniform distribution (Table 1). The sand class is almost absent, ranging between 0.0 and 4.5 % with an
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387 b Fig. 5 Representative X-ray diffraction patterns of oriented speci-
mens of samples a L3, b L6 and c L7. Sm smectite, Illit illite, Chl chlorite
a 5
10
15
20
25
2 - Theta - Scale
exception of sample L7 where the sand portion reaches 45.5 % (Table 1). The mean grain size of Lysmachia lake sediments ranges from 4.4 to 7.7 U with an average of 6.86 U (Table 1). The distribution of mean size displays a relative uniform repartition except in the area around the channel mouth of Ermitsas stream (Fig. 1c), where the coarser material was observed, and it seems that from this channel the main sediment influx into the lake is taking place (Fig. 2a). The sorting fluctuates between 1.26 and 1.71 U with an average of 1.49 U (Table 1). The sediments are characterized as poorly sorted. This indicates that the lake sediments were not transported for considerable time or distance. The skewness varies from 0.029 to 0.365 with an average of 0.151 (Table 1). The whole part of the lagoon is covered with fine to symmetrical skewed sediments indicating deposition or a state of flux (Duanne 1964). The kurtosis varies from 0.901 to 1.383 with an average 0.987 (Table 1). The major part of the lagoon is covered with mesokurtic to leptokurtic sediments. The mesokurtic to leptokurtic nature of sediments refers to the continuous addition of finer or coarser materials after the winnowing action and retention of their original characters during deposition. Total organic carbon–total nitrogen–total phosphorus
b 5
10
15
20
25
20
25
2 - Theta - Scale
c 5
10
15
2 - Theta - Scale
Total organic carbon concentrations of the bottom lake sediments range from 10.69 to 41.31 mg C/g (Table 1) with a mean value of 25.02 mg C/g. The geographical distribution of TOC shows an important variation between the northern (samples L1–L5) and southern part (samples L6–L10) of the lake (Fig. 2b). TOC values in the northern part of the lake are twofold relatively higher compared to these in the southern one (Fig. 2b). Total nitrogen concentration varies from 0.79 to 3.06 mg N/g (Table 1)) with a mean value of 1.88 mg N/g. The geographical distribution of TN shows a strong differentiation between the northern and southern part of lake, following the differentiation of TOC values, almost in an identical way (Fig. 2c). Total phosphorus concentration ranges from 0.31 to 0.76 mg P/g with a mean value of 0.54 mg P/g showing that phosphorus is the limited sediment nutrient (Fig. 2d). The plot between TOC and TN values shows a strong positive correlation (R2 = 0.90) of the two parameters (Fig. 3), suggesting that sedimentary organic matter contributes to the accumulation of TN and that there is mainly an organic origin of nitrogen.
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Fig. 6 Seasonal mean fluctuation of physicochemical parameters in Lysimachia Lake a temperature, b pH and, c dissolved oxygen, d representative daily fluctuation of DO in mg/L during summer and e conductivity, in monitoring stations L1–L10
Mineralogical analysis: XRD XRD patterns of bulk samples (Fig. 4) showed that the mineralogical composition of all samples is characterized
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by the presence of quartz, calcite and clay minerals. The XRD patterns of oriented specimens revealed that smectite predominates and chlorite is absent in the samples collected from the northern part of the lake, samples L1–L5
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saturation conditions (Fig. 6c). In Fig. 6d we present a representative daily fluctuation of DO in August which is related to photosynthesis phenomenon. Saturating values during the day, as observed during August, are related to the photosynthesis while the lower values are the result of the stoppage of photosynthesis and taking over of respiration, which takes place from late night to early dawn hours. Conductivity values ranged from 348 to 2197 ls/cm presenting a similar distribution in all monitoring stations, while the highest values observed during winter (Fig. 6e). Chemical parameters
Fig. 7 Waters seasonal mean fluctuation of a TOC and b TN
(Fig. 5). Chlorite is the dominant clay mineral present, while smectite is absent in the samples collected from the southern part of the lake (L7–L9. In the middle part of the lake, samples L6, and L10, both smectite and chlorite are present (Fig. 5). Illite was detected in all of the samples (L1–L10), but it is abundant only in the sediments from the southern part of the lake coexisting with trace amounts of albite, while in the northern part illite is found in trace amounts and albite is absent. Water analysis: physicochemical parameters Physical parameters The mean seasonal water temperature from all the monitoring stations (L1–L10) fluctuated from 10 to 31 °C (Fig. 6a). pH values had in general similar trends to all the stations around the year, ranging between 8.19 and 8.77 (Fig. 6b). Dissolved oxygen (DO) varied between 6.3 and 10.6 mg/L indicating in general good oxygenation close to
In Fig. 7a and b we present the mean seasonal fluctuation of TOC and TN that were measured during the 1 year monitoring, while their geographical distribution is presented in Fig. 8a and b, respectively. TOC values, presented in Table 2, ranged from 1.87 to 7.94 mg C/L. As it can be seen, in Table 2, an almost uniform distribution of TOC was observed during winter, while during autumn, spring and summer the highest values were systematically observed in stations L1, L2, L3, L4 and L5, which are located in the northern part of the lake (Fig. 8a). The above-described phenomenon can be explained by the fact that during winter the water lake is 3 m higher than summer, the channel discharge larger water quantities and the winds are stronger resulting in a better circulation and mixture of water. Concerning TN, the measured concentrations fluctuated from 0.11 to 1.16 mg N/L presenting the highest values around the year in the northern part of the lake, sampling stations L3 and L4 (Table 2, Fig. 8b). The presence of nitrates was confirmed during the four seasons and in all monitoring stations (Table 2). The concentration of nitrates varied from 0.049 to 2.31 mg/L, while the mean seasonal concentrations for winter, spring, summer and autumn were 0.36, 0.087, 0.17 and 2.31 mg/L, respectively, indicating that the highest presence of nitrates takes place during autumn (Table 2). Nitrites were recorded during autumn and winter, were absent in spring and in only two stations (L1 and L3) were present in summer (Table 2). Nitrites concentrations during autumn and winter ranged from 0.02 to 0.21 mg/L with a mean value of 0.04 and 0.10 mg/L, respectively. Ammonium ions were present to all monitoring stations on autumn and winder, while was absent on spring and summer (Table 2). During the autumn and winter, ammonium ions values ranged from 0.03 to 0.77 mg/L with a mean of 0.27 and 0.11 mg/L, respectively (Table 2). Phosphates were recorded in few monitoring stations (L1, L2, L4 and L7) only in autumn and values ranged from 0.01 to 0.04 mg/L with a mean of 0.02 mg/L (Table 2).
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Fig. 8 Geographical distribution during the four seasons monitoring of water a total organic carbon (TOC) and b total nitrogen (TN)
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Table 2 Seasonal concentration in mg/L of nutrients, TOC and TN of the sampling stations L1–L10 Lake parts
Northern part
Southern part
Lake parts
Sampling stations
Winter NO3-
NO2-
NH4?
PO43-
TOC
TN
NO3-
NO2-
NH4?
PO43-
TOC
TN
L1
0.301
0.210
0.082
\DL
3.739
0.465
\DL
\DL
\DL
\DL
6.849
0.543
L2
0.341
0.196
0.078
\DL
1.865
0.420
0.134
\DL
\DL
\DL
5.666
0.495
L3
0.298
0.141
0.157
\DL
4.752
1.155
0.118
\DL
\DL
\DL
6.116
0.909
L4
0.361
0.047
0.395
\DL
3.861
0.565
0.049
\DL
\DL
0,012
7.738
1.002
L5
0.366
0.014
0.090
\DL
3.599
0.551
0.120
\DL
\DL
\DL
7.947
0.475
L6
0.386
\DL
0.033
\DL
3.809
0.503
0.055
\DL
\DL
\DL
4.999
0.306
L7
0.428
\DL
0.037
\DL
3.304
0.645
0.075
\DL
\DL
\DL
4.003
0.252
L8
0.396
0.008
0.027
\DL
3.483
0.483
0.070
\DL
\DL
\DL
3.799
0.229
L9
0.370
\DL
0.095
\DL
2.363
0.418
0.073
\DL
\DL
\DL
4.676
0.384
L10
0.403
\DL
0.057
\DL
2.491
0.352
\DL
\DL
\DL
\DL
5.066
0.426
Sampling stations
Summer -
NO3 Northern part
Southern part
Spring
Autumn NO2
-
?
3-
NH4
PO4
TOC
TN
NO3-
NO2-
NH4?
PO43-
TOC
TN
L1
0.189
0.138
\DL
\DL
5.134
0.417
2.307
0.032
0.215
0.014
2.712
0.883
L2
0.115
\DL
\DL
\DL
6.109
0.508
2.308
0.028
0.207
0.014
6.605
0.804
L3
0.068
0.076
\DL
\DL
5.786
0.604
2.013
0.063
0.769
\DL
5.581
0.722
L4
0.191
\DL
\DL
\DL
5.226
0.451
1.949
0.081
0.192
0.041
6.241
0.874
L5
0.210
\DL
\DL
\DL
7.643
0.402
1.491
0.038
0.233
\DL
5.788
0.566
L6
0.196
\DL
\DL
\DL
3.833
0.290
0.716
0.041
0.333
\DL
4.408
0.312
L7 L8
0.198 0.211
\DL \DL
\DL \DL
\DL \DL
3.992 4.663
0.310 0.352
0.553 0.271
0.037 0.017
0.375 0.163
0.014 \DL
3.146 4.577
0.196 0.108
L9
0.161
\DL
\DL
\DL
3.055
0.354
0.429
0.032
0.098
\DL
4.445
0.188
L10
0.220
\DL
\DL
\DL
3.951
0.401
1.351
0.040
0.091
\DL
5.090
0.505
? 3DL detection limits for N03 \ 0.04 mg/L, NO2 \ 0.002 mg/L, NH4 \ 0.02 mg/L, PO4 \ 0.003 mg/L
Conclusion In the present paper, we present, for the first time from our knowledge, sedimentological and water physicochemical parameters of the protected lake Lysimachia which is one of the most important lakes of western Greece and is listed in the Natura 2000 European Network. Based on the sedimentological findings and geochemical analyses, the lake is characterized by fine silt to sandy silt and is partitioning in the northern and southern parts. The bottom lake sediments are characterized by moderate to high TOC and TN concentrations, while sediments TP concentrations indicated that phosphorous (P) is the limited nutrient. These geochemical distributions are related to the sediment influx into the lake, the prolonged discharge of sewage influents of Agrinio city and the type of clay mineral content. Based on XRD analyses, smectite predominates in the northern part of the lake (samples L1–L5), whereas chlorite is more abounded in the southern parts (L7–L9). Taking into consideration that the main entrance of water as well as suspended material is the southern part of the lake, it is rather reasonable to assume that both smectite and chlorite are
originated from the suspensions inflowing from that entrance. The observed difference in the clay mineralogy in the samples from the northern and southern parts of the lake could be explained as the result of the distance from the main water entrance from Ermitsas stream and Alampei ditche (Fig. 1c). It is well known that the stability of the suspensions depends on the nature of clay minerals (Meunier 2005). Smectites form much more durable suspensions, whereas chlorite, as well as illite, settles more rapidly and this difference is due to the small size (\1 lm) of smectite crystallites as well as their ability to agglomerate into low-density aggregates (Meunier 2005). It is, therefore, expected to find closer to the main entrance (Ermitsas stream and Alampei ditche) chlorite and illite (as well as non clay minerals, in our case albite), which are characterized by the larger particle size and far from the main entrance (northern part) smectite, the clay mineral with the smaller particle size. Additionally, the presence of illite is more evident in the southern part of the lake while in the northern part is found in trace amounts. The higher amounts of TOC, TP and TN were found on the northern part of the lake in the smectite-rich sediments.
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This is reasonable because smectite minerals are characterized by the maximum cation exchange capacity and adsorption capacity relatively to all other clay minerals (except vermiculite), while chlorite and illite are characterized by relative low cation exchange capacity and adsorption capacity compared to other clay minerals and especially smectite (Bergaya et al. 2006). It is, therefore, concluded that organic C, P and N were adsorbed on smectite surfaces in the northern part of the lake rather than transport to the southern parts of the lake. From the environmental point of view, the water physicochemical parameters of the lake are characterized by high nitrates concentrations, as a result of agricultural run-off from arable land. Comparing the results of the present study with the previous one of Overbeck et al. (1982), we observe the same relatively high values of nitrates, while a decrease in the presence of phosphates, nitrites and ammonium ions is recorded, as a result of the operation of the waste water treatment plant of the Agrinion city during the last 10 years. Moreover, water TOC and TN are relatively high in the northern part of the lake as it receives effluents with high organic load, such as sewage from the overflow of the waste water treatment plant of the city of Agrinio, via Katourlis stream. The high sediments TOC and TN concentration is a point for further research and a parameter which has to be estimated, as organic matter decomposition releases nutrients and can reload with nutrients the water column, burdening environmental the lake. As it is the first time where monitoring data from the Lysimachia Lake are presented and include bottom sediment and water analyses, this study can be used as baseline data for comparison in future environmental assessment of the lake. Acknowledgments The authors would like to thank two anonymous reviewers for theirs constructive comments and suggestions, as well as the Associate Editor Dr D. Easley and Editor in Chief Dr G. Doerhoefer for the scientific editing of the manuscript.
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