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Paper title Multitemporal Monitoring of the impact in water quality of Lake Timsah, Ismailia (Egypt), after the construction of the New Suez Canal with the exploitation of Sentinel-2 and Landsat 8 data for the period 2014-2020.
Authors
  1. Marianthi Karantzia National Technical University of Athens
  2. Despoina Bafi Harokopio University of Athens Speaker
  3. Tarek Seleem Suez Canal University
  4. Issaak Parcharidis Department of Geography. Harokopio University of Athens
Form of presentation Poster
Topics
  • A7. Hydrology and Water Cycle
    • A7.06 EO for monitoring water quality and ecological status in inland waters
Abstract text AIM INTRODUCTION
Monitoring water quality is valuable since the changes that may occur in water bodies have severe socio-economic and environmental impacts. Such an influence is evident in Timsah lake, the biggest water body of Ismailia district in Egypt, which has been the objective of this research. The main aim of this research is to estimate the changes in the water quality of the area during the period of 2014-2020. Timsah Lake was subjected to significant environmental pressures, caused by various anthropogenic activities in Ismailia city. From satellite observations in the optical part of the spectrum, we can retrieve the concentrations of different constituents (pure water, chlorophyll, sediments, coloured dissolved organic matter) and also, we can use the satellite data to detect changes in the zone surrounding the water bodies.
Within the framework of increasing world trade, increases in the size of ships, and the need of the Egyptian economy to develop its resources, it was imperative to expand the current Suez Canal to cope with the increasing future world trade (EEAA, 2014). A new canal was implemented on the 5th of August 2014 parallel to the existing one; Suez Canal (SC). It is suspected that quality changes may be arisen due to the construction of the New Suez Canal (NSC). Timsah Lake has a strategic location on the Suez Canal, which is the main route joining the continent of Africa with Asia and Europe the evaluation of human activities, basically encompassing navigation as a pathway for trading ships with other countries, fishing which provides a vital source of food and income for local population and tourism.
DATA- METHODOLOGY
In order to achieve the goal of this study, free satellite images from Landsat 8 OLI and Sentinel-2 satellites have been exploited to analyse the objective of this research study. To be more specific, for Landsat 8 the Level-1 and Level-2 scenes were obtained from the United States Geological Survey (https://earthexplorer.usgs.gov). Landsat 8 carries the Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS) instruments.
In addition, Sentinel-2 is a European wide-swath, high-resolution, optical multi-spectral imaging mission. The full mission consists of the twin satellites flying in the same orbit but phased at 180°, is designed to give a high revisit time of 5 days and has 13 spectral bands (VIS, NIR, SWIR) (Drusch, et al., 2012). The Multispectral Instrument (MSI) Level-1C (L1C) Sentinel-2 scenes are available from the open-source of Copernicus Open Access Hub (https://scihub.copernicus.eu). Finally, the processing of the data has been carried out by the free and open ESA’s SNAP, the Harris Geospatial Solution’s ENVI and the final maps have been exported with the ESRI’s ArcGIS software.
As far as the methodologies are concerned, Principal Component Analysis (PCA) and Case 2 Regional Coast Colour (C2RCC) algorithms were applied for the purpose of monitoring the physical properties of different water characteristics encompassing pure water, chlorophyll-a, sediments, and Total Suspended Matter (TSM). In order to detect changes in the area of Ismailia city including the Suez Canal proximate area, Landsat 8 images have been used and the PCA analysis has been applied. PCA transforms an original correlated dataset into a substantially smaller set of uncorrelated variables that represent most of the information presented in the original dataset (Richards 1994; Jensen 2005). For the generation of the image-components we have adopted the PCA method by using the Landsat 8 L2 products dated 22/08/2014 and 06/08/2020 the visible and near-infrared bands, in total four bands from each date. The correlated variables (original bands) are transformed into other uncorrelated variables (principal components images). The maximum original information contained by these, with a physical meaning that needs to be explored. It is also proven, that the first three principal components may contain more than 90 percent of the information in the original seven bands.
Concerning the C2RCC, the objective of this algorithm is to determine optical properties and the concentrations of constituents of case 2 waters. Case 2 water is defined as a natural water body, which contains more than 1 component of water constituents, which determine the variability of the spectrum of the water leaving radiance and is presented in coastal seas, estuaries, lagoons and inland waters (Morel & Prieur, 1977; Gitelson et al. 2007). For this study, 7 Sentinel 2 A & B, Level 1C products were used and acquired by the satellite during August month each year from 2015 to 2020. Also, Landsat 8 Level 1 products, for month August 2014 and 2020 have been processed using the C2RCC. The processing of the Sentinel 2 and Landsat 8 images could be divided into two steps. The first one is the pre-processing including resampling (in this case resample in 40 m/pixel) so that all bands have the same spatial resolution and then is the subset of the image over the study area. The second one concerns application of the C2RCC algorithm in order to detect the amount of seawater suspended matters and chlorophyll-a and also perform the atmospheric correction. The final product is a thematic facilitating the knowledge content the unit is cubic gm-3 which is unit of volume cubic gigametre. Finally, the data were exported in GeoTIFF format and then imported into ArcGIS software, where the final maps are produced.
RESULTS -DISCUSSION
The results of the present work and the figures that emerged revealed that the original hypothesis of this research was proven correct, which presumed that the main source of pollution was the NSC. The obtained values of the different water characteristics that the Western Lagoon -located to the Western part of Timsah lake and connected with it through one inlet in the western side- and its emerging streams (Abu Atwa drain) are considered as contamination starting points. Generally, TSM and Chlorophyll-a results from Sentinel-2 data, indicate that during August 2015 there are lower values of TSM and Chlorophyll-a, with a range between 4 and 17 g m-3 and 2 and 11 g m-3, respectively. While the higher values of the TSM and Chlorophyll-a concentration, appears during August 2018 for the TSM, around 23 and 50 g m-3 and for Chlorophyll-a during August 2016 and 2018, around 20 and 40 g m-3. Specifically, high levels of TSM are evident and concentrated in the Western Lagoon. These values are at their pick especially during August 2018, 2019 and 2020. Regarding the Landsat-8 results, the TSM in August 2014 is lower than the following periods until 2020, where higher values are attributed mainly to the Western Lagoon and the inlet of the Timsah lake. For Chlorophyll-a, the highest value is recorded in 2014 than any other year, concentrated in NSC and the Western Lagoon.
Concerning the results of PCA, from the analysis of eigenvalues and eigenvectors, in combination with the interpretation of the principal components, the component images which are suitable in order to perceive the possible spatial changes, are selected. Moreover, the first component (PC1) corresponds to the brightness image (information concerning topography and albedo) and contains 78.35% of the information. The second component (PC2) calculates the spectral information related to all the transformations that took place during the period 2014 to 2020 and contains 11.12% of the information. There is the difference image between the two dates, resulting from the negative contribution of the original spectral bands of the first date (2014) and the positive contribution of the original spectral bands of the second date (2020). The last PC images contain a small amount of information relative to other applications and “noise” (Psomiadis et al. 2005).
To conclude, this study demonstrates a correlation between the results and the overall change in the area, since human activity and technological development is increasing. The contaminants of aquatic and wetland environments are a common situation due to the changes in the surrounding area. Such changes are tourism, agriculture, hotels, leisure infrastructures, which are built throughout the last years. As is confirmed from El-Serehy et al. (2018) and Abd El-Azim et al. (2018), there are three major sources responsible for water quality changes in Timsah Lake (area of interest) such as agricultural drainage, anthropogenic activities, untreated domestic and industrial waste discharges. Due to the lack of in situ data, the results cannot thoroughly confirm this hypothesis.
In line with the main goal, the recorded values of the TSM have shown that in the past years the connection between the Western Lagoon, the Abu Atwa Drain, Ismailia Canal and the Timsah lake appears to be the contamination sources that degrade the quality of water. This might reveal that Lake Timsah is a high eutrophic lake, as it was also pointed out by Mehanna et al. (2016). In our future work, we would like to add in situ data to prove our hypothesis.