Received 12 June 2016; accepted 25 July 2016; published 28 July 2016
Improvement of our understanding in the environmental and geomorphological changes’ effects on marshes and isolated waters is a critical step to address issues related to continental marshes and their responses to these changes. Also, sedimentological studies are proper tools to interpret the evolution of sedimentary environment  . Additionally, to assess the ecological impact of contamination to the environment, it is vitally important to understand the full extent and the level of pollution into the background in the area.
Regarding its capabilities in providing goods, marshes environments are classified as the most precious ecosystems on earth   . Considering the effects of climate changes and human interferences, today the future of these important landforms and ecosystems seems to be at risk and it may cause possibly irreparable transformations  -  . However, despite progress about geomorphology, sedimentology, accretionary processes and geochemistry, more work needs to be done to explain the sedimentology, stratigraphy and geochemistry of sediment in marshes on the subject of the evolution of the systems    .
The particle size and morphology of sediments are the major implements to interpret the source of sediments, transportation modes and depositional environments   . Variations in grain size distribution of isolated environments (specifically marshes habitats) may reflect air surface process such as developmental process of landforms through precipitational changes  . On the other side, mineral distributions are also standard tracers of regional geology, weathering characteristics in upstream and transport land mass  -  . Moreover, trace elemental compositions of sediments are controlled by lithologies, weathering, diagenesis, sedimentary sorting and human activities in catchments and it can be useful for identification of speciﬁc geochemical processes and provenance of clastic materials  . Also characterizing of the composition and the sedimentology of surface sediments is vital not only from geochemical point of view, but also from an environmental perspective. Thus variations in mineral compositions, trace elements and lithogenic components should be considered as valuable tools to find out the possible sediment sources and physico-chemical process affecting the geological records  .
Nowadays, Eynak marsh is strictly isolated from any riverine and oceanic sediment input (Figure 1). Anthropogenic effects (as an instance intense construction operation, sewage input to marsh and etc.) likely contribute to changing the circumstances and its natural habitat. Despite the importance of this area, there is no worthy investigation devoted to the study of geochemical, mineralogical and sedimentological signature of Eynak marsh. This investigation could be more momentous if we spot contamination of sewage entrance from the urban areas and also underground linking to GoharRood River. It is noteworthy that, GoharRood by itself is a fully contaminated river transporting sewage from upstream.
Because of its position regarding urban area, being one of the biggest marshes in north of Iran and tourism industry, this marsh represents a crucially important ecosystem in the region. Detailed sedimentological and geochemical investigations on these marshes can help us to improve our knowledge about its generation. Then it led to precise relationship being deducted between marsh and river sediments. As the other aquatic environments in south of Caspian Sea, Eynak marsh is situated in the migration way of different birds (Africa-Eurasia and Asia-Pacific skyways) then lots of bird spices fly to this region every year. Also this marsh is populated by various plant species like Myriphgllom verticillatum, Ceratophyllum submersum, Alisma plantago-aguatica, amphibians like frog and creepers like snake, turtle, lizard adapted to the environment.
Due to reflecting the privilege geology of the source area by the deposited sediments  , a comprehensive study has been conducted. This paper focuses on understanding of sedimentology, mineralogy and geochemistry variation pattern in the riverine sediment of Eynak marsh (North of Iran). So the main purposes of this paper are: 1) to provide information about the sediment size distribution, mineral composition and also the main potential source of marsh sediments; 2) to improve our understanding in trace element pattern distribution in the marsh; and 3) to assess metal contamination levels in surficial sediments and particles. To achieve these goals we have analyzed surficial sediments of the marsh thoroughly.
Figure 1. Geographical location and detailed sketch map of the study area in Eynak marsh.
2. Study Area
Marshes and bays across the Caspian Sea that are under the impact of 3 major processes of longitudinal transfer of coastal sediments, increasing the level of Caspian water, and syncline-anticline structure  are considered environment passages, from land to sea. Moreover, analysis of historical aerial photography depicts a relatively dynamic system in the area in which lateral migration of main channels caused some isolated small areas. So, Eynak marsh could be considered as such environments and it is located in Rasht countryside (Gilan province) and about 17 km away from Anzali costal lagoon, North of Iran. Also it is situated from 37˚16'25"E 49˚32'18"N to 37˚16'22"E 49˚33'31"N presumably is a separated pool from flowing rivers through time. It seems the main source of sediment in this marsh located in Kacha Mountain and sediments transported through Lakan and GoharRood Rivers. Nowadays Gohar rood and Lakan Rivers drain to Anzali coastal lagoon. Estimated area is about 214,650 m2. Due to being situated in Rasht countryside and industrial activities around the marsh, irreversible changes is happening there which effects on its habitat and it may cause to destroy the marsh completely in the future. Unfortunately it has not been a comprehensive investigation in the area to discover the origination of this marsh yet. Better to know, the upstream sewage discharging to Lakan River and its probable underground linking to Eynak marsh, may cause more negative effects on the marsh habitat. Also, there are some transects cutting across Eynak marsh and separated it to smaller areas. It means there might be no more Eynak marsh in the area in future unfortunately.
Study area has a humid subtropical climate that is one of the wettest in Iran. It has certain Mediterranean features such as a drier summer, but is also relatively continental with cooler winters and higher seasonal temperature variation than in much of Iran, in spite of its marine position. The average humidity is 81.2%, contrasting heavily with cities in many other parts of Iran. Sunshine hours, averaging roughly 1520 per year, are lower than in most places in Iran and also compared to most places at this latitude.
The oldest rocks in the domain area consists of early Carboniferous made up of creamy-brown to dark-green slate to phyletic clastic sediment which in partly are calcareous and belongs to Mobarak Formation. After that, grey to green arkozic sandstone and shaly mudstone belongs to late Triassic can be seen (Figure 2). Cretaceous rocks such as massive sandy limestone, silty limestone-siltstone and dark grey basaltic-andesitic lava occurrence
Figure 2. Geological map and the main hydrological features of the study area.
in the upstream area. Plain landscape is overlain by Quaternary deposits which  classified them in the area into: 1-Deltaic deposits and gravel, 2-Deluvial and fluvial deposits, 3-Old fluvial deposits, 4-Alluvium floodplain and deltaic deposits and finally 5-Blown sands (Figure 2).
3. Material and Method
Figure 1 shows the total 44 collected sediment sample locations along the marsh which sampling points took by GPS receiver. The primary distance between locations was about 40meters which it changed slightly based on convenient sampling. Sampling was carried out onboard small boat using a 4liter Van Veen grab sampler. Samples were taken onboard for sedimentology, mineralogy and geochemical analysis individually. Each sample was packed in polyethylene bags, tied, labeled and brought to GSI Lab for excess analyses. Detailed grain size, mineralogy and geochemical analysis has been carried out on all collected samples in order to recognize possible anomalies and basic pattern of sediment characteristics inside of the marsh.
Afterward, on the lab, samples were dried at 70˚ and dried bulk sediment was sieved to separate various fractions using wet sieving (based on standard test ASTM for determining average grain size). Grain size analysis of the 44 surficial sediment samples performed by Analysette 19 wet sieving instrument. Therefore, samples grouped into mud, sand and gravel fraction according to Udden and Wentworth. A detailed description of grain size <63 µm fractions executed by Laser Particle Seizer (model analysette 22).
Standard practice for total digestion of 44 sediment samples for chemical analysis of various metals (according to D-4698 preparing method) has been performed. So minor and major elements determined by inductively coupled plasma-optical emission spectrometry (ICP-OES-ES Varian 735) in Geological Survey of Iran chemistry lab. Moreover, X-Ray diffractions in 44 sediment samples in the area have been performed using an automatic powder EQUINOX 3000 X-ray diffractometer. Quantification and identification of the various minerals present in the crystalline fraction has been carried out following the standard procedure  .
Fractional analyses were carried out using the software package SPSS20 for windows. In addition, on all samples in Eynak marsh, detailed grain size, geochemical and mineralogical analysis have been carried out to recognize a possible correlation between their distributions and depositional environments.
4.1. Physical and Mineralogical Characteristic
Textural and size analyses are quantitative tools to determine the size frequency distribution  . Also, mineralogical and physical characteristics of the sediments in Eynak marsh can be influenced by rock assemblages in upstream such as basaltic-andesitic lava, dark grey limestone, slate and Arkozic sandstone which has been subjected into weathering, eroded and transported to downstream. In fact, due to terrestrial sources of sediments in Eynak marsh, it is characterized by similar mineralogical and physical features. Results showed that samples basically were angular to sub angular in shape (Figure 3), major component mineral were quartz, calcite, feldspar, and mica and minor mineral were pyroxene, evaporates along with some heavy minerals.
Grain Size Distribution
According to grading studies, 13 sedimentary types existed in surface sediments including: Gravelly Mud, Muddy Gravel, Gravelly Sand, Muddy Sandy Gravel, Gravelly Muddy Sand, Muddy Sand with a Little Gravel, Sandy Mud with a Little Gravel, Mud with a Little Gravel, Silty Sand, Muddy Sand, Sandy silt, Silt, Sandy Mud (Figure 4). Considering its pattern, east side of the marsh represented a variety of sedimentary types. Moreover, grain size distribution maps reveal that, silt and clay fractions are the most important sediment constitutes concentrated mostly in the middle and the east. Also, gravel size grains increased eastward approaching GoharRood River.
4.2. Statistical Parameters
Various statistical parameters of Eynak marsh sediments computed. Mean grain size: The variation in mean size reflects the variety of energy conditions to deposit and shows the average kinetic energy of the depositing agent  . Different values obtained for textural statistical parameters varying from minimum 1.5 to maximum 6.6, i.e. thus it falls between coarse sand and medium silt. Sorting: Sorting indicate the differences in kinetic
Figure 3. Sediment grains in Eynak marsh.
Figure 4. Ternary plot showing the content of gravel, sand and mud fractions in the surficial sediments of Eynak marsh.
energy associated with these mode of depositions. In the study area sediments ranges in 3 sorts: poorly sorted, very poorly sorted, and moderately sorted. The closer to GoharRood, the sorting number increases and sediments poorly sorted. Skewness: It measures the asymmetry of frequency distribution and marks the position of mean according to median  . In the present study skewness values ranges −0.43 to 0.68 with an average −0.02 represents five sorts: strongly fine skewed, fine skewed, near symmetrical, coarse skewed, strongly coarse skewed. Eastern samples showed near symmetrical to coarse skewed which it accounts as the abundance of coarse particles of energetic environment. Also, strongly fine skewed can be seen in the middle of Eynak marsh. Kurtosis: Many curves designated to minute Kurtosis and it varies from platy kurtic to mesokurtic. Also the values are among 0.5 to 2 with an average of 0.99. The platy kurtic to mesokurtic nature of sediments refers to fewer addition of finer or coarser materials to the depositional environment  . In general and regarding average values, sediments are fine grained (Figure 4), moderately to poorly sorted associated with very low current flow in eastern side of the marsh.
4.3. Statistical Parameters
Various statistical parameters of Eynak marsh sediments computed. Mean grain size: The variation in mean size reflects the variety of energy conditions to deposit and shows the average kinetic energy of the depositing agent  . Different values obtained for textural statistical parameters varying from minimum 1.5 to maximum 6.6, i.e. thus it falls between coarse sand and medium silt. Sorting: Sorting indicate the differences in kinetic energy associated with these modes of depositions. In the study area sediments ranges in 3 sorts: poorly sorted, very poorly sorted, and moderately sorted. The closer to GoharRood, the sorting number increases and sediments poorly sorted. Skewness: It measures the asymmetry of frequency distribution and marks the position of mean according to median  . In the present study skewness values ranges −0.43 to 0.68 with an average −0.02 represents five sorts: strongly fine skewed, fine skewed, near symmetrical, coarse skewed, strongly coarse skewed. Eastern samples showed near symmetrical to coarse skewed which it accounts as the abundance of coarse particles of energetic environment. Also, strongly fine skewed can be seen in the middle of Eynak marsh. Kurtosis: Many curves designated to minute Kurtosis and it varies from platy kurtic to mesokurtic. Also the values are among 0.5 to 2 with an average of 0.99. The platy kurtic to mesokurtic nature of sediments refers to fewer addition of finer or coarser materials to the depositional environment  . In general and regarding average values, sediments are fine grained (Figure 4), moderately to poorly sorted associated with very low current flow in eastern side of the marsh.
4.4. Scatter Plot
Scatter plot with mean, standard deviation and skewness can be used successfully for the distinction of the sedimentary environments, always using a large number of samples for each sedimentary body sampled  . Moreover, scatter plots are useful to identify geological signature of the grain size parameters  . Scatter plots viz. skewness versus standard deviation, mean versus standard deviation, and standard Deviation versus mean is brought in Figure 5. The scatter diagram proved that the distribution of grains belongs to fluvial and riverine sediments.
4.5. Sediment Composition
The significant correlation of elements with each other may indicate same source, chemical behavior, sediment-water interface and etc.  . Spearman’s correlation coefficient is a statistical measure of the strength of a monotonic relationship between paired data. Unlike Pearson’s correlation, there is no requirement of normality and hence it is a nonparametric statistic. Regarding unmorally in our data diversity, Spearman’s correlation analysis has been conducted on the calculated data to determine the relationship between various elements and sedimentary parameters as well as to find out the main sources of elements and grains.
4.5.1. Mineral Diversity
Eynak marsh sediments were mainly composed of muddy fractions (Figure 4). Mineralogically, quartz, calcite, feldspar, dolomite, and mica were the main constitutive minerals present in surficial sediments (Table 3). Considering opposite geochemical behavior in Quartz and Calcite, high values of quartz from the middle to east and
Figure 5. Various scatter plot of surficial sediments in the study area to show the origin of grains.
west of Eynak marsh correlated to calcite and dolomite depletion. As well as, higher amounts of calcite along with pyrite and gypsum can be seen in the middle of the marsh. Also, silicates such as feldspars, mica, pyroxene and clay minerals are distributed regularly throughout the surficial sediments. Mineralogy data diversity was proofed by geochemical analysis of sediments throughout the study area.
4.5.2. Element Diversity
Usually, fine grain sediments are common hosts and controlling factor in distribution of elements, especially metals, in aquatic sediments  . The correlation matrix, element composition and Dendrogram using Ward method are shown in Table 1 and Table 2 and Figure 6 respectively. Trace elements incorporated in heavy minerals like Y, Zr, Th, Cr, have lower content in the finer grained sediments (Figure 7) indicating depletion of
Figure 6. Dendrogram using Ward Method illustrating the relationship of elements in the study area.
Figure 7. Contour plots showing the distribution of sediment composition along the study area.
Table 1.Spearman correlation coefficient matrix for elements in the marsh sediments.
Table 2. (a) (b) Element composition in the sediment samples of Eynak marsh.
heavy minerals in fine grain size fraction. Aluminum (Al) is the major element of sediments mostly influenced by human activities and upstream feldspathic rocks (ranging 4.2% - 8.8%) (Figure 7). After that Ca (0.9% - 11.8%), Fe (2.6% - 4.9%), K (0.6 - 1.7), Mg (0.4 - 1.3), and Na (0.2 - 1.1) are the most common elements in the area. On the other hand, an important enrichment of Ca along with Fe, K, Mg, etc. indicating a proper situation for deposition of these elements.
There are significant correlations among variety of elements through the marsh sediments. As an instance Al versus Ba, Be, Cr, Fe, K, Na, Ni, and Ti displayed significant correlations. On the opposite, Al versus Ca, Mg and Mn showed negative correlations. On the other side, there are no significant correlation in some elements versus others such as Li, Cu, P, Zn, and etc. Besides, fine grained sediments, which are the fundamental sediment components, showed significant correlations with Ca, Mn, Sr and Mg indicating identical sources and the predominant associations of these elements with clay minerals  . High values for Mn concentration was observed (ranged in 462 - 1784 ppm average 1037 ppm) and it showed a significant correlation with Ca, Sr and Mg. If Mn could remobilize to the water column, it would be found in low values in the sediments  . So, a redox condition and constantly calm hydrodynamic circumstance in Eynak marsh, likely causes high concentration of these elements. Besides, it represents negative correlations versus some elements such as Al, Be, Fe, K, Na, and etc. Figure 7 summarizes the spatial distributions of some elements in surface sediments. According to these maps, some elements such as Al, Na, Be, Fe, Ba, Y, Zr, V, Sc, Cr, and Ti displayed similar patterns. It means that, an obvious increase of element values in the middle and also its depletion into the west and east side of the marsh has been observed. Unlikely, Mg, Ca, Zn, Sr and Mn presented a distribution in which values were low at the western side then increased locally, decreased again and finally showed higher concentration eastward. Moreover, Cu and Cd were highly irregular and it may depend on human activities or garbage dump to the marsh.
Pb concentration varies between 20 ppm and 58.5 ppm averaged at 34.4 ppm in the surface sediments. Its concentration showed a significant correlation with Ca and Sr. Zn values ranged from 46.6 ppm to 285 ppm with the average 168 ppm and it did not represent any correlation with the other elements. The low concentration of Zn in the eastern side is preferably attributed to the remobilization of trace elements in the water column during the change in bioturbation before reaching the sediments  . Contrary to Sr, Ca and Mg distribution pattern, some elements like Sc, Y, V, Ba, Be, etc. showed a different trend. Therefore, it could indicate the same sources among each group of these elements and mechanism controlling the pattern.
The positive association among Fe and Mn proposing a common detrital origin and a relevant transporting phase for the grains  . Regarding Mn and Fe to be the vitally important scavengers for trace metals   , trace elements like La, Gd, Th and Y showed a positive correlation with Fe. Ni distribution along the marsh decreases westward and it may be attributed to the high density of this elements and its tendency to immobilization.
In order to improve our understanding of the main sediment sources in Eynak marsh, we compared its composition to Kiakelaye marsh (located in southeast of Eynak, 70 Km away from Eynak marsh) using discrimination diagram suggested by  . Discrimination diagram (Figure 8) are more useful to evaluate dependence to geochemical end-members in the region and compare them with each other  . Sediments from Eynak marsh have Sc-Th-Cr compositions similar to what we have in Kiakelaye, representing Cr enrichment in sediments. Moreover, increasing Cr values in distribution maps suggest the upstream as a main source for the sediments and Chromium. Also Cr concentration strongly reveals that Cr-bearing minerals such as pyroxene have been deposited in the marsh and it has been proofed by mineralogy results (Table 3). Furthermore, due to the depletion of Sc in the sediments, it could not be said that the ultramafic xenolith is the probable source rock for the sediments. Moreover, Sc-Th-La indicates an enrichment of La in Eynak marsh in comparison with Kiakelaye. So this increase in La may come from a batholith-type composition in the domain area.
Considering granulometric data, its predominant grains composed by coarse sand and medium silt (Figure 3, Figure 4 and Figure 7) and it represented a low energy hydrodynamic circumstance in the marsh. A few gravels in sediments considered mostly as a gastropod shell remnants (Figure 3). Textural and statistical parameters proved the predominant fluvial origin of sediments (Figure 5). It means the probable origin of sediments is mostly related to fluvial input that have precipitated in the past. Regarding the cut off occurrence between
Table 3. The summary of mineralogical data in 44 surficial sediments in the study area.
Figure 8. Discrimination diagram of Sc-Th-La and Sc-Th-Cr for surficial sediments of Eynak marsh (black dots related to Eynak marsh and red circles related to Kiakelaye).
GoharRood River and Eynak marsh, it is not nourished by the river anymore and it can be seen a very calm hydrodynamic condition in the marsh. In addition, another possible source of material could be organism shells (as instance Gastropoda) precipitated after the death. The continental shelf sediments are characterized by the high abundance of calcite derived from biogenic mechanism  . Moreover, due to the distance between marsh and Caspian Sea beach (more than 30 Km), and the low values of biogenic calcite; there are no possibility and documented proof supporting the idea of the coastal sediment source in Eynak marsh.
Due to the main mineral involved in surficial sediments like quartz, calcite, feldspar, pyrite mica and clay minerals, chemical elements are mostly related to terrigenous input. These minerals derived from continental sources and weathered rocks such as granite that are covering the land mass in the upstream. Since muscovite reflects the influence of metamorphic and igneous rocks as a source of clastic sediments  , the existence of this mineral in the most corners of the marsh can be explained by the riverine supply from granitic rocks in the watershed. As a result, the increased abundance of biotite, muscovite and Chloritoid could be derived from igneous and metamorphic rocks weathering. Moreover, the high content of pyrite is supported by the high values of Fe detected there and this could be related to relict sediments enriched in pyrite in Gastropod infillings  . Some elements like Mg, Ca and Sr showed significant correlations with calcite distribution and it is mainly indicated by the substitution of these elements in calcite. Likely, Mg distribution shows a similar pattern, and mineralogy reported a dolomite increase to the east of Eynak marsh. Mn distribution pattern shows the maximum values in the inner part and the west side of the marsh. The existence of gypsum and pyrite in sediments could be mentioned as a proof for reduction condition in the inner side of the marsh. Considering its generation and chemical formula, the abundance of feldspars in west and east side should be related to the distribution of elements such as Al, Be, V, Na, Fe, etc.
Universally, one of the most important source of chrome to the marine environments is the household sewage and it contains about 32.2 percent of total chrome in marines  . Also cupper is an element which can enter the environment through waste water   . Likely, sewage entrance in the west and east part of the marsh may cause the increasing trend of these elements to both west and east sides. Niobium can be siderophile, chalcophile, or lithophile  , also it aggregates in Granites, Nepheline Syenite, Alkali granites, etc.  . So, the highest value of Nb in the east of the marsh as well as the majority of Quartz and Feldspars in there should be under the influence of granitic and alkali granite source rock of the domain area.
Nickel value changing pattern represented an increase trend westward. The major source of nickel exposure has a direct affiliation to organic matter  . Though, the entrance of organic and agricultural wastewater to the west side of the marsh could be a reason for high values of Ni in the area. As well as, Pb enrichment in the study area could be under the effects of anthropogenic activities around the marsh which has been conducted recently. Moreover, considering Spearman correlation coefficient of Mn versus Pb and Zn (showing a significant correlation), likely they should have similar sources.
Sedimentological, geochemical and mineralogical investigation was conducted in Eynak marsh to reconstruct the pathways of modern input from continental domain and also to find out the sediment generation. Surficial sediments integrate mineralogical, sedimentological and geochemical characteristics of the draining area by upstream and anthropogenic effects.
Textural investigations indicate that the sediments belong to the coarse sand to medium silt fractions suggesting that the sediments were deposited under calm or low energy condition. Moreover, sediments being poorly sorted to moderately sorted reveal texturally immature of a fluvial environment. The sedimentary fraction influences some elements fractionation in the surficial sediments. Distribution pattern of fine sediments is closer to Ca, Sr, and Mg pattern and it is supported by the correlation between fine grain sediments and these elements. Due to the depletion of fine grain sediment in clay minerals (which have a strong adsorption capacity), lower content of trace elements is reported from analyzed sediments. In another word, no correlation exists between the abundance of mud and concentration of some contaminations (like Fe, V, Ni, and Cr), making us believe that grain size cannot be used as a normalizer to assess contaminant sources in this area.
Mineral assemblages in sediments are truly controlled by source rocks of the domain area. The immature sediments of Eynak marsh with high feldspar relative to quartz could be classified as having an uplifted basement source. Normally, gypsum and pyrite indicate reduced environment. So the existence of these mineral along with calcite concentration represents a proper circumstance for such minerals. The chemical composition of the analyzed sediments is controlled by source composition, textural and mineralogy characteristics. The high amount of feldspar and quartz is supported by high value of Al, Fe, Na, K, etc. and decrease in Ca, Mg and Sr values representing the entrance of these minerals from east and west side of the marsh. The inner part of the marsh is characterized by presence of calcite, Pyrite and Gypsum and high concentration of Ca, Mg, Sr, etc. showing a reduction situation in the environment in which some minerals such as gypsum and pyrite representing higher amounts. In another word, higher pyrite content could be related to authigenic sources.
This is a part of Ph.D. dissertation of the senior author (A. Hazermoshar), the authors sincerely thank the GSI for the financial support. The first author would like to thank Mr. Mahmoud Noveiri for his efficient help and the kind corporation during sampling, preparation and analyzing samples.