Effect of land-cover changes on heavy metals concentration and ecological risk in sediments of Tahaddart estuary, Morocco

doi:10.21203/rs.3.rs-4460113/v1

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Effect of land-cover changes on heavy metals concentration and ecological risk in sediments of Tahaddart estuary, Morocco

https://doi.org/10.21203/rs.3.rs-4460113/v1

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Long-term trends of trace element contamination in coastal ecosystems are important for assessing the impact of land cover changes on the environment quality. In this study, the assessment of historical land cover changes and contamination status trends of Tahaddart estuary (N-W, Morocco) was investigated. Two sediment cores were selected, analyzed for trace elements (TEs), compared with sediment quality guidelines, and assessed by using environmental and ecological indices. Radiometric dating was performed on sediment core by using ²¹⁰Pb and ¹³⁷Cs isotope. Identification and description of the land cover patterns from 1984 to 2016 was analyzed using GIS methods. The geomatic results showed significant decline in agricultural land, forests, wetlands, and beaches/dunes between1984 and 2016, which are increasingly replaced by artificial land. The radio-dating of sediment core indicate that the mean sedimentation rates are 0.53 cm/years based on ²¹⁰Pb activities. The ecotoxicological risk and contamination indexes revealed a gradual deterioration in the environment quality of Tahaddart with moderate contamination level and 21% risk of toxicity. This research provides a reference database for costal area development.

Coastal land cover change

Spatial mapping

Eco-toxicological risk

Sediment quality guideline

210Pb/137Cs dating

Recently, the Morocco’s Atlantic coast is already exposing to diverse human pressures, including urban sprawl, industrial development, and over-exploitation of coastal resources, which lead to rapid changes in land cover. The decrease in natural lands and the rise in built-up and agricultural areas are some of visual evidence of modifications in land cover patterns (Dadson, 2016; Kaliraj et al., 2017; Mas, 2004). Such dynamic can contribute to the input of trace elements (TEs) in coastal areas, thus resulting in serious environmental pollution (Sarı et al., 2013; Maanan et al, 2013; Lo and Gunasiri, 2016). Trace elements emission into the environment is harmful not only to the ecosystems, but also may have long-term consequences on human health because of refractory characteristics of bioaccumulation (Şimşek et al., 2022). The information of land cover is important to overcome problems of uncontrolled pollution and environmental risk for sustainable environment.

To confirm this assumption, many studies have reported that built-up and agricultural land in coastal areas has been increased, while area under other natural land categories has decreased (Town et al., 2018; Lo and Gunasiri, 2016; Dadson, 2016). According to other studies, the improper use of land by human activities was a primary factor causing the degradation of coastal water quality (Romano et al. 2017; J. Wang et al. 2016). The rapid urbanization contributed to the input of significant amounts of TEs into the marine environment and directly affects the coastal systems in which they are often deposited and absorbed by sediments (Shi et al. 2022; Gulf et al. 2023; Vald et al. 2023). As a consequence of the land use practices, the metallic pollution has been dramatically increasing. But, the absence of long term records for TEs makes difficult to trace their behavior in coastal areas, which is the first step to prepare proactive adaptation strategies for proper marine management.

The temporal distribution of the trace elements in coastal sediments cores adjacent to populated areas can provide the evidence of the anthropogenic impacts on ecosystems and help in assessing the risks associated with discharged human waste quality (Romano et al. 2017; J. Wang et al. 2016; Gulf et al. 2023; Vald et al. 2023). Core sediments are frequently used in geochemistry and paleo-pollution research; it can serve as historical records of contamination in recent decades (Sarı et al., 2013; Gulf et al. 2023; Vald et al. 2023). The use of sediment quality index can also reveal the impact of human activity has on coastal ecosystems. Numerous studies have been done in recent years show that the use of multivariate pollution index (contamination factor (CF), pollution load index (PLI), potential ecological risk index (PER) and mean probable effect concentration quotient (m-ERM-Q) was a good tool to assess the potential risk posed by trace elements exposure in sediment (Mas et al., 2004; Vald et al., 2023; El barjy et al. 2018; Sea, Liu, Sheng, Liu, & Li, 2023; Effendi, Kawaroe, & Fauzia, 2016).

Some scientific investigations have been reported in the literature on the surface and core sediments in Tahaddart estuary (Massik et al. 2003 ; El Mrini 2004; Nachite et al. 2008; Rifai N. et al, 2018; Elbarjy et al. 2018 ). However, this is the first study to evaluate and discuss the contamination trend and eco-toxicology risk assessment in core sediments from the Tahaddart estuary. The purpose of this study is to investigate the historical variation of contamination status of TEs using sediment pollution indices, to evaluate ecological risks of TEs using ecological risk indices and guidelines for sediment quality in ²¹⁰Pb/¹³⁷Cs dated sediment cores. This study also aims to reconstruct the spatial and temporal land covers changes covering a time span of the last 32 years.

2.1. Study area

The present study has been carried out on Tahaddart estuary located between the 35°30′ − 35°40′ latitudes North and 5°55′-6°01′ longitudes West in the north of Moroccan (Fig. 1). It is 3.5 km long with a surface area of 140 km², which is occupied by temporary salted lakes, alluvial plains, and sandy coastal zones (Tahiri et al. 2014). It is one of the Moroccan sites that were considered by the RAMSAR Convention for the conservation of wetlands of international interest, and in 2005 as a RAMSAR zone under the name of “Complexe du bas Tahaddart” (Nachite et al. 2008). The anthropogenic land cover in the Tahaddart estuary is primarily dominated by agricultural areas. The rest of the study area was occupied by artificial land which used for urban areas, roads, railways, and infrastructure industry. The few villages in the area have a total population of about 45,339 inhabitants in 2014 (Barjy et al. 2018).

2.2. Land cover changes:

The analyses of land cover changes are performed using three sets of remote sensing Landsat satellite images in 1984, 2006 and 2016 obtained from the USGS official website http://glovis.usgs.gov/. All images were acquired during the dry season, with the multispectral scanner sensor (MSS), the thematic mapper sensor (TM) and the enhanced thematic mapper plus sensor (ETM+). For land cover monitoring, we have used Erdas imagine software to reproject and subset the study area. Visual interpretation is used to identify different land cover types in the satellite images. The study area in all images is classified into seven different land cover types: artificial surface, agriculture areas, forest, water bodies, beaches and sands, wetland. Each land use type is delineated using on-screen digitization of ArcGIS 10.1. The area of each land cover type is extracted by Geographic Information System (GIS) techniques. The area change occurred in each land cover type is then calculated according to the following landscape dynamic model (Lo and Gunasiri 2016): K = (So – St)/ So × 100%, where, K = area change of each land use type; So = area of initial time; St = area of end time.

2.3. Sampling and analytical methods:

2.3.1. Sample collection

Two sediment cores of 1.9 m in length and 8 cm in diameter (TC1; TC2) were collected from the Tahaddart estuary in June 2016 with the following geographical coordinates: 35°35'13.06"N, 5°58'55.32"W for CT1 and 35°36'3.03"N, 5°57'48.36"W for CT2 (Fig. 1). The coring operation was conducted using a hund-held PVC corer. Once in the LETG laboratory (UMR 6554), the cores were split lengthwise, photographed, logged, and then subsampled for further analysis.

2.3.2. Geochronology analyzes

Radio-chronological data for the last century was obtained using ¹³⁷Cs and ²¹⁰Pb_exces measurements with a gamma spectrometer (LETG Laboratory de Nantes, Géolittomer-UMR 6554-CNRS, France). Samples were collected in the first 50 cm. The CFCS (Constant Flux, Constant Sedimentation rate) model was used for the ²¹⁰Pb_exces to calculate the sedimentation rate in Tahaddart estuary (Golberg 1963).

2.3.3. Sediment contamination and risk assessment indices

The geochemical data (Trace metal concentration and local geochemical background) obtained in our previous study (Barjy et al. 2018) was used in this study. The sediment concentrations were compared with sediment quality guidelines (SQGs) proposed by Long et al. (1995) for marine ecosystems to evaluate the ecotoxicological risk. The effect range low (ERL), the effect range median (ERM), the threshold effect level (TEL), and Probable Effect Level (PEL) were used to evaluate the level of toxicity of metals in the sediment cores.

This study used the Contamination Factor (CF) and Pollution Load index (PLI) to evaluate the level of metal pollution degree of and possible anthropogenic impact on core sediments from Tahaddart estuary. The contamination factor of the studied metals was calculated by the following equation (Hakanson, 1980): CF = C_i/C_BV, Where C_i is the mean concentration of an individual metal examined and C_BV is the background value of the individual metal. The pollution load index (PLI) is a site-specific index which provides a simple comparative mean for assessing the level of metal contamination (Tomlinson et al, 1980): $\text{P}\text{L}\text{I}=\sqrt[\text{n}]{({\text{C}\text{F}}_{1}\times {\text{C}\text{F}}_{2}\times {\text{C}\text{F}}_{3}\dots {\text{C}\text{F}}_{\text{n}})}$, where n is the number of heavy metals taken into consideration and CF is the contamination factor.

The potential ecological risk Eⁱ_r was used to assess the potential risk of each metal in the sediment (Hakanson, 1980):

$$\text{E}\text{i}\text{r}=Tri\times CFi ; RI=\sum \text{E}\text{i}\text{r}$$

Where E_rⁱ is the potential ecological risk index of an individual metal, T_rⁱ is the metal toxic response factor: Zn = 1, Pb = Cu = Ni = 5, Cd = 30, ‘‘RI’’ refers to the total of all risk factors for trace metals in sediments (Hankson L. et al. 1980).

Mean sediment quality guidelines-quotient (SQG-Q) is an index that used to evaluate the possible biological effects of the coupled toxicity of trace elements in the surface sediments (Long et al. 1998). The SQG-Q was calculated for each sampling site, using the following equations:

$$\text{m}\text{E}\text{R}\text{M}-\text{Q} =\frac{{\sum }_{\text{i}}^{\text{n}}\text{C}/\text{E}\text{R}\text{M}}{\text{n}}$$

Where: C metal concentration at each sampling site, ERM is effect range median and n is the number of metals used.

3.1. Spatial-temporal LULC changes

The data obtained through the analysis of multi-temporal satellite imageries from 1984 to 2016 are illustrated in figure and Table. The land cover maps (Fig. 2) demonstrate some important spatial-temporal patterns. The artificial area experienced an increasing trend from 1984 to 2016, with a decreasing in agricultural land, forests, wetlands, and beaches/dunes. The table 1 shows that the artificial area increased from 513.3 ha in 1984 and 1284 ha in 2006, to 1762.1 ha in 2016, with a rate change of 60% during 1984–2006 and 27.1% during 2006–2016. On other hand, the forest land decreased from 2046.7 ha in 1984 to 1419.3 ha in 2016. They are lost 336.2 ha during 1984–2006 and − 291.2 ha during 2006–2016, representing a rate of change of -19.7% and − 20.5%. The wetland had a lost 396.2 ha during 1984–2006 and 80.5 ha during 2006–2016. The beaches /dunes had a lost − 174.4 ha of its area during 1984–2006 and − 68.7 ha during 2006–2016. The Scrub/ herb vegetation and the agricultural land remained relatively stable in first period (1984–2006). During 2006–2016, The Scrub/ herb vegetation increased from 1291.6 ha to of 1727.3 ha. The agricultural land had lost 450.8 ha of its area, with a rate of variation of -8.9%. Furthermore, the beaches and dunes land recorded a decreasing area during the period 1984–2016 with a rate change between − 4.5 and − 20.7%. This regression can be explained by the sediment imbalance resulting from extraction of sand for construction needs and retention of sediment by “Ibn Battuta” and “April 9, 1947” Dam at upstream site.

A detailed analysis of the intra and inter-transition of land cover classes (Table 2) reveals that 77.4% of the study area remained stable with 22.6% of change between 1984 and 2016. The most interesting change was manifested by artificial expansion at the expense of disappearance of other land-use types. For example, 1.4% of forests land was converted to artificial land and 3.1% transformed mainly into Scrub/ herb vegetation. Moreover, 5.3% agricultural land was converted also to artificial land. Another class of land cover that has undergone significant transformations was wetlands. Assessed at 28.6% in 1984, only 23.7% remained intact and 2.1% is converted into agricultural land, 1.2% into artificial land. This unconventional land cover transition is mainly linked to the construction of the thermal power station and the radio station in 1949; the TGV construction and the Rabat-Tangier highway in 2005, induced predominantly by Tangier’s urban development (Barjy et al. 2018).

3.2. Radionuclide profiles and sediment chronology

The plot of ²¹⁰Pb_xs and ¹³⁷Cs activities against depth for the Tahaddart sediment core is displayed in Fig. 3. The surface ²¹⁰Pb_xs activities was around to 34.1 Bq / kg (Fig. 5A), relatively lower compared to activities found in other coastal ecosystems (Bellucci et al. 2007; Alonso-hernandez and Ruiz-fernández 2011). A detailed analysis of the ²¹⁰Pb_xs distribution with depth suggests that the recording can be divided into two distinct segments. At the top of sediment core (0 to 20 cm), the ²¹⁰Pb_xs activities decreased exponentially with depth, indicating regular sedimentation. However, the ²¹⁰Pb_xs activities were relatively constant throughout the 20–50 cm segment of the core. A flattening of ²¹⁰Pb_xs indicates either a dilution of the atmospheric flux of 210Pbxs by mixing of sediments, acceleration of sedimentation and / or the occurrence of slumps due to, for example, heavy rains (Alonso-hernandez et al, 2011).

The ¹³⁷Cs activities range from 0.3 to 1.3 Bq / kg which are below the detection limit (2Bq / kg), which means that dating using this radionuclide is difficult (Fig. 3). This has also been observed in other coastal ecosystems such as: Yucatan Peninsula in Mexico (Ruiz-fernández, 2016) and Havana Bay in Cuba (Alonso-hernandez et al, 2011). The application of CFCS model (constant flux, constant supply), gave a sedimentation rate of 0.53 cm / year, which is comparable to that found by Khalfaoui et al. (2020) for the Tahaddart estuary. The slight difference between the two sedimentation rates is a maybe a result of the limited number of samples analyzed or located in the area (Khalfaoui et al. 2020). On the other hand, the sedimentation rate is higher than that recorded at Loukous estuary (Morocco) and Venice lagoon, but lower than the maximum rate recorded at Oum Errabia estuary and the Moulay Bousselham lagoon, Morocco (Kalloul et al, 2012; Maanan M. et al 2009; Mhammdi et al, 2010 Bellucci et al. 2007)(Table 3).

3.3. Sediment quality

The concentration of the studied metals in the dated sediment cores derived from Tahaddart estuary exhibited increasing trends, with the highest concentrations observed at the upper parts of sediment cores as obtained from our previous study (Barjy et al. 2018). To investigate the historical metals contamination, a comparative study was performed using the sediment quality guidelines (Fig. 4). The results showed that all concentrations in trace elements are below the values of ERM; thus, the concentrations of all trace elements in sediment cores do not represent any ecological risk. As indicated in figure, Zn and Cu levels in both cores were lower than TEL. Ni level in sediment exceeded the TEL values indicated in the SQG but still below the PEL values, while Pb, Cd and Cr concentrations were higher than the TEL values at upper parts of the cores.

Based on the previous results, contamination factor (CF) and pollution load index (PLI) have been calculated for each core, the results are given in Fig. 5 below. The CF varied within a range of 0.53–2.13 for Zn; 0.75–2.01 for Pb; 0.64–2.60 for Cu; 0.57–1.69 for Ni; 0.66–2.22 for As; 0.23–19.11 for Cd and 0.65–3.33 for Cr in TC1’s core ; and 0.79 and 2.11 for Ni; 0.39 and 2.10 for Cu; 0.97 and 2.10 for Zn; 0.61 and 2.95 for Cr; 0.77 and 2.13 for Pb; 0.21 and 16.09 for Cd; 0.95 and 2.63 for As in TC2’s core (Table 4). The minimum values are generally found at the base of the cores, while the maximum values are observed at the upper part. For Cd, the vertical distribution of CF reveals a strong contamination (FC ≥ 6). For As, Pb, Ni, Zn and Cr, the calculated FCs indicate moderate contamination at the top, while the base of the core is marked by low contamination.

According to table 4, the values of pollution load index (PLI) for the two cores (TC1 and CT2) are between 0.64 and 2.72 with an average of order 1.62 for the CT1 core and between 0.63 and 2.86 with an average of 1.67 for CT2 core. The results indicate that almost of the two cores have values higher than 1, which suggests the existence of anthropogenic pollution. The vertical distribution of PLI highlighted strong values at the top of the cores (Fig. 6).

As shown in Fig. 7, the ERM quotients (ERM-Q) of individual TEs indicated that Ni present a ‘‘High-medium Priority Site’ between 5–30 cm (CT1) et 0–5/15- 70cm (CT2). The others TEs (Cd, Cu and Pb) which classified them as "Medium-low priority side", except Zn and Cr have presented a "Low Priority Site". All the core sediment exhibited M-ERM-Q values > 0.1 confirming them as “medium-low priority sites”. The M-ERM-Q varied within a range of 0.06–0.18 for CT1, and 0.07–0.2 for CT2 which mean that the combination of six TEs (Cd, Cr, Cu, Ni, Pb, and Zn) might have a 21% probability of toxicity posing potential risk to the aquatic organisms (Table 5).

The vertical distribution of the potential ecological risk index (Eir) for single TES at CT1 and CT2 cores indicated decreasing pollution intensity in the following order (Fig. 6): Cd > Cu > Pb > Ni > Cr > Zn, with individual mean values of 205.1; 8.3; 6.3; 5.7; 3.3 and 1.1; respectively for CT1 core and 209.8; 6.5; 5.9; 5.7; 2.4 and 1.5 for the CT2 core. It is worth noting that the E_ir max values of all TEs were less than 40, and they posed a "low potential ecological risk", except for Cd where the risk was " high potential ecological risk" at the surface. The results highlighted the risk that Cd pose to the human body and the ecosystem. The Håkanson potential ecological risk index range for all sampling sites is from 24.4 and 608.1, indicating moderate to high potential ecological risk at surface (Table 5).

3.4. historical anthropogenic impacts on Tahaddart estuary

The results presented in this study provide important information about the historical contamination of the Tahaddart estuary in the last 150 years. Anthropogenic activities around the estuary have left their fingerprint on the geochemical records (Barjy et al. 2018). The results obtained so far confirm that the study area has experienced several changes patterns induced by urbanization and industrialization process during the past 32 years. Overall, land cover in the study area is primarily agricultural and has remained constant, while the estuary was a subject to rapid artificial intensification since the 1984s, which is reflected in reduction of agricultural land, forests, wetlands, and beaches/dunes. This degradation in the natural environment is resulting from many factors like the construction of the thermal power station and the radio station in 1949; the TGV construction and the Rabat-Tangier highway in 2005, induced predominantly by Tangier’s urban development (Barjy et al. 2018; Tahiri et al., 2014). Several authors (Cesar & al., 2002; Mas, 2004; Al-tahir, 2015; Gupta and Sprawl, 2019) have blamed population growth and some kind of exploitation as being responsible for land cover change. This situation of lands degradation in the Tahaddart estuary is also observed in other Moroccan ecosystems like Oualidia and Moulay Boussalham lagoons (Maanan et al, 2014).

Although the benefit of urbanization and agriculture development, some previous studies have suggested that the inappropriate land cover has been discussed as a factor that can affect environment quality of coastal ecosystem (M.C, 2019; Tang et al., 2022; ). Several authors argue that the data extracted from sediment cores provide important information of the contamination history over the past decades (Maanan et al., 2014; Irabien and al., 2008; Mahu et al., 2016; Hasan et al., 2023; Yang et al. 2020). However, in Tahaddart estuary, the highest values of contamination factor, pollution load index, ERM quotients (ERM-Q) and ecological risk index for all the metals studied were found at the upper portion of sediment cores confirming that there has been some anthropogenic influence on this estuary in recent times (since 1984), which receive a significant among of trace elements due to direct discharge from anthropogenic activities (Rabat-Tangier highway, thermal power station…) and the extensive use of fertilizers on farmlands around the estuary. The data obtained confirm gradually upward increasing trends in trace metal; spatially from 1984 when anthropogenic activities increased according to the evolution of land cover analyses. Recent case studies prove that some trace elements are mainly human-induced in coastal ecosystems (Zourarah B.. et al 2009; Zhuang et al. 2022; Sea et al. 2023). The result also revealed a gradual deterioration in the environment quality of Tahaddart estuary according to the sediment quality index, the studied zone was moderately impacted, with a 21% risk of biotoxic impacts. This sediment that may act in the future as a potential long term source of pollutants that could directly affect the water quality of estuary (Veerasingam et al. 2015). However, additional efforts should be made to avoid the spreading of contaminants in the lagoon and the preindustrial values obtained from the historical reconstruction provided could be used as the reference levels for environmental restoration purposes.

In this study, the coastal zone of Tahaddart estuary is taken as the research area. The changes of estuary zone over the years are analyzed, and its ecological and environmental status is scientifically evaluated, the comprehensive management and protection measures are proposed.

The main conclusions are as follows:

Based on the land cover data in the study area, it is found that artificial land area is gradually increasing, and the area of forests, wetlands, agricultural areas, beaches, and dunes during the period 1984–2016. This degradation is essentially linked to the development of socio-economic activities (sand extraction, urban expansion, etc., industrial development).

The isotope analysis of sediment core indicates that sedimentation rate is 0.53 cm/year indicated by 210 Pb, which means that one meter of sediment covers a period of 189 years.

The temporal evolution of contamination and ecological index is characterized by increasing trends over the past last 150 years. Sediment quality analyses based on contamination index and sediment quality guidelines indicated a generally moderate quality sedimentary environment in Tahaddart estuary with 21% probability of acute toxicity.

This work reveals important information about historical contamination in Tahaddart estuary that can be used to protect and improve the quality of this ecosystem.

Funding The authors received no financial support for the research, authorship, and/or publication of this article.

Competing Interests The authors have no relevant financial or non-financial interests to disclose.

Authors’ Contributions All authors contributed to the study conception. MEB, HB, NH, BH, and MeM were responsible for preparation of materials, data collection and analysis. MEB, HB, MM and MeM verified the analytical methods. MEB and MeM wrote the first draft of the manuscript and all authors commented on previous versions of it. All authors discussed the results and approved the final manuscript.

Data Availability The datasets generated and analysed during this study and its supplementary information files are available from the corresponding author on reasonable request.

Ethics Approval Not applicable.

Consent for Publication Not applicable.

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Tableau 1 : Area and amount of change in different land cover categories in the Tahaddart estuary during 1984-2016.

	1984		2006		2016		1984-2006		2006-2016
	ha	%	Km	%	Km	%	Km	%	Km	%
Artificial area	513.3	3.5	1284	8.7	1762.1	11.9	770.7	60.0	478.1	27.1
Agricultural land	5434.9	36.7	5543.7	37.5	5092.9	34.5	108.8	2.0	-450.8	-8.9
Forest land	2046.7	13.8	1710.5	11.6	1419.3	9.6	-336.2	-19.7	-291.2	-20.5
Scrub and herb Vegetation	1264.7	8.5	1291.6	8.7	1727.3	11.7	26.9	2.1	435.7	25.2
Beaches, dunes	841.2	5.7	666.8	4.5	598.1	4	-174.4	-26.2	-68.7	-11.5
Wetland	4300.3	29	3904.1	26.4	3823.7	25.9	-396.2	-10.1	-80.5	-2.1
Water body	402.1	2.7	368.4	2.5	345.7	2.3	-33.7	-9.1	-22.6	-6.5

Tableau 2: The land cover transition matrix.

		2016
		forest land	Scrub/ herb vegetation	beaches /dunes	Water body	agricultural land	artificial area	wetland	Total
1984	forest land	8,7	3,1	0,0	0,0	0,4	1,4	0,3	13,8
	Scrub/ herb vegetation	0,5	6,0	0,0	0,1	0,4	1,2	0,5	8,7
	beaches /dunes	0,1	0,2	4,4	0,1	0,2	0,0	0,0	5,1
	Water body	0,0	0,0	0,0	1,4	0,4	0,0	0,7	2,7
	agricultural land	0,1	1,0	0,1	0,2	30,5	5,3	0,5	37,7
	artificial area	0,1	0,3	0,0	0,0	0,3	2,7	0,1	3,5
	wetland	0,2	1,0		0,5	2,1	1,2	23,7	28,6
	Total	9,6	11,6	4,6	2,3	34,3	11,9	25,7	100,0

Tableau 3: Sedimentation rate in Tahaddart estuary and the related values reported in other coastal areas.

Coastal sediment	Sedimentation rate (cm/year)	Reference
Tahaddart estuary (Morocco)	0,53	Present study
Tahaddart estuary (Morocco)	0.46	Khalfaoui et al. 2020
Loukous estuary (Morocco)	0.27-0.37	Kalloul et al, 2012
Oum Er bia estuary (Morocco)	0,38 à 0,68	Maanan M. et al 2009
Moulay Bousselham logoon	0,6 – 0,70	Mhammdi et al, 2010
Venise logoon	0.25 cm y-1	Bellucci et al. 2007

Tableau 4: The ranges and averages of contamination factor (CF), Pollution Load Index (PLI) in sediment cores from Tahaddart estuary.

		Contamination factor (CF)							PLI
		Ni	Cu	Zn	Cr	Pb	Cd	As	PLI
CT1	MOY SD	1.14 0.25	1.66 0.44	1.11 0.43	1.67 0.79	1.26 0.29	6.84 4.69	1.27 0.41	1.62 0.52
CT1	MIN- MAX	0.57-1.69	0.67-2.60	0.53-2.13	0.65-3.33	0.75-2.01	0.23-19.11	0.66-2.22	0.64-2.72

CT2	MOY SD	1.29 0.35	1.48 0.51	1.46 0.24	1.21 0.45	1.23 0.32	6.99 4.84	1.64 0.47	1.67 0.55
CT2	MIN- MAX	0.79-2.11	0.39-2.42	0.97-2.10	0.61-2.95	0.77-2.13	0.21-16.09	0.95-2.63	0.63-2.86

Cf <1 indicates low contamination; 1<Cf <3 is moderate contamination; 3<Cf <6 is considerable contamination; and Cf >6 is very high contamination.
PLI >1 means that pollution exists; otherwise, if it is <1, there is no metal pollution

Tableau 5: The ranges and averages of individual ecological risk Index (Er i ), total ecological risk (RI) and Mean ERM quotients (m-ERM-Q) in sediment cores from Tahaddart estuary.

		Ecological risk Index (Er i )						RI	m-ERM-Q
		Ni	Cu	Zn	Cr	Pb	Cd	RI	m-ERM-Q
CT1	MOY SD	5.62±1.24	8.02±2.31	1.09±0.42	3.23±1.54	6.35±1.41	187.30±145.19	211.61±149.24	0.12 0.03
CT1	MIN- MAX	2.83-8.45	3.35-13.01	0.42-2.13	1.30-6.66	3.77-10.07	6.53-573.42	24.39-608.07	0.06-0.18

CT2	MOY SD	6.46±1.77	7.39±2.55	1.46±0.24	2.43±0.90	6.15±1.59	209.79±145.12	233.67±150.85	0.13 0.03
CT2	MIN- MAX	3.94-10.54	1.93-12.11	0.97-2.10	1.22-5.90	3.87-10.66	6.23-482.64	19.27-520.69	0.07-0.20

Eⁱ_r< 40 indicates a low potential ecological risk; 40 <Eⁱ_f< 80 is a moderate ecological risk; 80 <Eⁱ_r< 160 is a considerable ecological risk; 160 <Eⁱ_r< 320 is a high ecological risk and Eⁱ_r> 320 is a very high ecological risk.
R_I< 95 indicates a low potential ecological risk; 95 <R_I< 190 is a moderate ecological risk; 190 <R_I< 380 is a considerable ecological risk and R_I> 380 is a very high ecological risk.
M-ERM-Q was defined: 9% probability of toxicity (M-ERM-Q <0.1), 21% probability of toxicity (0.11 ≤ M-ERM-Q <0.5), 49% probability of toxicity (0.51 ≤ M-ERM-Q <1.5) and 76% probability of toxicity (M-ERM-Q >1.5).

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Effect of land-cover changes on heavy metals concentration and ecological risk in sediments of Tahaddart estuary, Morocco

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Abstract

Figures

1. Introduction

2. Materials and Methods

2.1. Study area

2.2. Land cover changes:

2.3. Sampling and analytical methods:

2.3.1. Sample collection

2.3.2. Geochronology analyzes

2.3.3. Sediment contamination and risk assessment indices

3. Results and discussion

3.1. Spatial-temporal LULC changes

3.2. Radionuclide profiles and sediment chronology

3.3. Sediment quality

3.4. historical anthropogenic impacts on Tahaddart estuary

4. Conclusion

Declarations

References

Tables

Status:

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