Hydrobiologia (2009) 622:147–171 DOI 10.1007/s10750-008-9682-8

NORTH AFRICAN COASTAL LAGOONS

Application of remote sensing to site characterisation and environmental change analysis of North African coastal lagoons

M. H. Ahmed Æ B. M. El Leithy Æ J. R. Thompson Æ R. J. Flower Æ M. Ramdani Æ F. Ayache Æ S. M. Hassan

Published online: 22 January 2009 Ó Springer Science+Business Media B.V. 2009

Abstract This article describes the use of satellite (1972–2004). Following geometric correction and imagery for identifying key environmental character- enhancement, the interpretation of the most recent istics within three North African coastal lagoons image acquired for each of the three lagoons provides (Merja Zerga, Morocco; Ghar El Melh, Tunisia and important insights into their current conditions. For Lake Manzala, Egypt) and for detecting the major Merja Zerga, these include the distribution of the environmental changes within these environments. A largest channels which drain extensive inter-tidal combination of Landsat MSS, Landsat TM, Landsat mudflats and the two major depositional features ETM? and ASTER imagery was acquired for the associated with sources of freshwater. The distribu- three sites for a period covering the last three decades tion of marginal aquatic vegetation is highlighted as is the intensive use of the surrounding landscape for agriculture. Intensive agriculture around Ghar El Guest editors: J. R. Thompson & R. J. Flower Melh is also indicated. The influence of the Mejerda Hydro-ecological Monitoring and Modelling of North African River, which was diverted away from the lagoon over Coastal Lagoons 100 years ago, is shown to persist as a residual area M. H. Ahmed (&) Á B. M. El Leithy Á S. M. Hassan of deltaic deposits in shallow water that has been Department of Marine Sciences, National Authority for eroded over time. Coastal processes including the Remote Sensing and Space Sciences, 23 Josef Burrows direction of the alongshore sediment transport and the Tito Street, El Nozha, Al Gadida, PO Box 1654, Cairo, Egypt influence of engineering work associated with port e-mail: [email protected] construction can also be recognised. Within Lake Manzala, vegetated islands divide the lake into a J. R. Thompson Á R. J. Flower series of sub-basins which can be clearly distin- Wetland Research Unit/Environmental Change Research Centre, UCL Department of Geography, University guished. The large influence of human activities College London, Gower Street, London WC1E 6BT, UK within this lake can be identified and include reclamation for agriculture and the conversion of M. Ramdani parts of the lake bed for fish farms. The historical Department of Zoology and Animal Ecology, Institute Scientifique, University Mohamed V, Charia Ulan Batota, images available for the three lagoons provide Rabat BP703, Morocco important insights into decadal scale changes, which have been greatest at Lake Manzala. Since the early F. Ayache 1970s large parts of the lake, in particular in the Faculte´ des Lettres et Sciences Humaines de Sousse, De´partement de Ge´ographie, Universite´ de Sousse, southwest where the shoreline has migrated north- Cite´ Erryad, B.P. 547, 4029 Sousse, Tunisia wards, have been reclaimed. Major engineering 123 148 Hydrobiologia (2009) 622:147–171 works, such as the El Salam Canal and road coverage of a specific geographic area, 16 days in the embankments, are shown to have resulted in signif- case of Landsat TM) from such sources permits icant lake change. The distribution of emergent regular image acquisition over the same area enabling vegetation within the lake has also changed. Classi- change detection at relatively high temporal fre- fication of images for this lake into open water, quency (Lillesand et al., 2008). vegetation and land enables the quantification of Common types of detectable land cover change, these changes. Between 1973 and 2003, the lake which can be monitored using remotely sensed data, declined in area by approximately 50%. Changes at include vegetation disturbance and regeneration, Merja Zerga over the last three decades include agricultural intensification, urban expansion, spatial reconfiguration of the marine outlet and the expan- changes in aquatic ecosystems and hence surface sion of the internal delta at the end of the Nador water extent, as well as a variety of soil disturbance Canal. The images of this site clearly demonstrate the processes including overgrazing and soil erosion (e.g. intensification of agriculture around the lagoon. The Milne, 1988; Hall et al., 1991). The application of most marked changes evident within the images of remote sensing for biodiversity and conservation over Ghar El Melh concern the sand bars that separate the a range of spatial scales is reviewed by Turner et al. lagoon from the sea. Geomorphological processes (2003), who emphasised the great potential of the operating within the coastal zone have resulted in the approach. Remote sensing techniques can enable straightening of the bars with central sections ecologists and resource managers to monitor the migrating out towards the sea. Remote sensing is vegetation condition and detect environmental change established as a promising application for detecting trends in regions where difficult terrain, poor access, the quantitative surface cover changes in coastal and extreme climate conditions make regular field lagoons and their near landscapes. investigations difficult. Satellite data are also suitable for inventorying the type, quality, distribution, pro- Keywords Coastal lagoons Á North Africa Á ductivity and biomass condition of natural as well as Remote sensing Á Environmental change Á planted vegetation at a range of spatial scales (Hobbs, Image interpretation and classification 1990; Milne & O’Neill, 1990; Franklin, 1991; Hall et al., 1991;, Turner et al., 2003). Land cover change detection and overall land use classification (e.g. Introduction Ambrose & Shag, 1990; Teng, 1990; Petit & Lambin, 2001) have global applications especially regarding Remotely sensed images can be used as a tool to map assessments of the magnitude and rate of conversion ecosystems and to detect, monitor and evaluate of natural landscapes into high productivity agricul- changes within them thereby supporting the devel- tural or urbanised systems. Satellite and/or airborne opment of resource management strategies. Satellite data has been demonstrated to have particular use for and airborne systems offer major opportunities for monitoring water and vegetation changes within monitoring large scale, earth surface characteristics aquatic ecosystems including wetlands (e.g. Hardisky and provide a database for change detection studies. et al., 1986; Howman, 1988; Hess et al., 2003; Ozemi Remotely sensed data can be used to span temporal & Bauer, 2004,Co´zar et al., 2005). and spatial scales ranging from local to aggregated In Africa, remote sensing has made major contri- global systems (Graetz, 1990). Monitoring global, butions to monitoring a variety of wetland systems regional and local areas can be performed by (e.g. Fuller et al., 1998; Munyati, 2000; De Roeck restricting the analysis to a single sensor series or et al., 2008). Landsat data, for example, has enabled by using different satellite data. With the availability the identification of the impacts of both natural of data from remote sensing satellites such as the processes and human interventions on African lakes, Landsat series, it has become cost effective and freshwater ecosystems and wetlands (UNEP, 2005). convenient to acquire multi-date images over a Results from studies utilising data from these sources greater array of spatial and temporal scales than have revealed that pollution resulting from land-use was possible with aerial photography. The temporal changes, environmental modification and other prac- resolution of data (the ability to obtain repeated tices associated with rapid population increase, and 123 Hydrobiologia (2009) 622:147–171 149 water abstraction have caused or accelerated many The MELMARINA primary lagoons negative changes in the continent’s lakes (e.g. Randazzo et al., 1998, Scheren et al., 2000). The Three primary lagoons, one in each of the three North main threats to water quality in Africa are perceived African countries who participated in the MELMA- to include eutrophication, pollution, increasing water RINA project, were identified: Merja Zerga demand and the proliferation of invasive aquatic (Morocco), Ghar El Melh (Tunisia) and Lake Manz- plants such as the water hyacinth (e.g. Albright et al., ala (Egypt) (Fig. 1). These lagoons were the focus of 2004). One study of Lake Chad carried out within field survey and monitoring activities (e.g. Ramdani NASA’s earth observing system programme showed et al., 2009, Thompson et al., 2009) as well as hydro- that the lake shrank to one-twentieth of its original ecological modelling (e.g. Rasmussen et al., 2009a, size during the last 35 years (NASA, 2001). In North b) and the remote sensing reported in this article. A Africa, remote sensing has been used to monitor the series of secondary sites was also identified to development of Lake Nasser including the new delta provide context for the primary sites (see Flower & in its southern section and environmental changes in Thompson, 2009). They were not, however, subjected Lake Ichkeul, Tunisia, (NASA, 2005a, b). The use of to remote sensing analysis. remotely sensed data for monitoring North African Detailed descriptions of the three primary lagoons wetlands has much potential (Flower, 1998) when are provided by Ayache et al. (2009). They are combined with ground surveys and existing field strongly contrasted according to their physical and data. Turner et al. (2003) stressed the importance of biological characteristics. All three are shallow water obtaining validatory ground evidence to help to bodies (\2 m deep) linked to the sea through one or interpret remote sensing products. For the manage- more well-defined connections. They vary in size ment of North African coastal lagoons, remote from c.13 (Merja Zerga) to c.700 km2 (Manzala) and sensing techniques provide an exceptional means of differ in water quality. Merja Zerga is flushed daily distinguishing spatial vegetation cover as well as by the relatively large Atlantic tides whereas Ghar El determining the extent of open water, marginal Melh and Lake Manzala, being confluent with the disturbance and water quality (Ahmed & Donia, Mediterranean, are much less affected by tidal cycles 2007; Ahmed & El-Leithy, 2008). This study aims to (see Thompson et al., 2009). All three lagoons occur apply remote sensing techniques to three North at the termini of inland drainage systems, which have African lagoons to both assess spatial status and to all been subjected to significant human modification. detect recent environmental change. It was under- Merja Zerga receives freshwater from two highly taken as part of MELMARINA (Monitoring and seasonal inflows, one of which (the Nador Canal) is Modelling Coastal Lagoons: Making Management artificial comprising drainage water. The volumes of Tools for Aquatic Resources in North Africa), a these inflows are smaller in comparison to those 3-year integrated hydro-ecological monitoring and associated with tidal flushing by sea water. Freshwa- modelling project funded through the EU INCO-Med ter inflows to Ghar El Melh are also seasonal and programme (see Flower & Thompson, 2009). usually very small except when exceptional floods

Primary site Secondary site

2 c 1 b d a

3 e

f

Primary: 1. Merja Zerga, 2. Ghar El Melh, 3. Lake Manzala Secondary: a. Sidi Bou Ghaba, B. Lagune de Nador, c. Lac de Korba, d. Halk el Mijil, e. Lake Bardawil, f. Lake Qarun

Fig. 1 The MELMARINA lagoons 123 150 Hydrobiologia (2009) 622:147–171 link the lagoon with the Mejerda River, which 2.35 lm), 60 m for band 6 (thermal infrared, 10.40– historically discharged into the lagoon. As a result 12.50 lm) and 15 m for band 8 (panchromatic, 0.52– of the relatively small and seasonal freshwater 0.90 lm) (Graetz, 1990). A suitable, cloud free image inflows, both Merja Zerga and Ghar El Melh are of Lake Manzala was available from this source for usually dominated by marine water, especially in 05/02/2003. However, an unsuccessful review of summer. On the other hand, Lake Manzala has available data for the other two lagoons, combined become predominantly freshwater since it now with the failure of the Scan Line Corrector on the receives large volumes of agricultural and domestic sensor in May 2003 which impacted data quality (e.g. drainage from drains along its southern borders (e.g. Maxwell et al., 2007; Zhang et al., 2007) necessitated Ayache et al., 2009; Stanley, 1996; Stanley and the use of alternative imagery. Therefore, data from Warne, 1993; Thompson et al., 2009). This last site is the Advanced Spaceborne Thermal Emission and characterised by extensive within lake emergent Reflection Radiometer (ASTER) instrument on the vegetation, which is largely restricted to marginal Terra satellite were employed. This instrument areas within Merja Zerga and Ghar El Melh. records data from 14 spectral bands from the visible to the thermal infrared wavelengths. The visible and near infrared (VNIR) bands (1–4) cover a similar Methods wavelength range as bands 1–5 of Landsat ETM? (0.52–0.86 lm) at 15 m resolution, higher than that This study employed remotely sensed image process- provided by Landsat ETM? (Abdeen et al., 2002; ing supported by expert opinion on site characteristics Marc¸al et al., 2005; Gao & Liu, 2008). ASTER obtained during the course of MELMARINA field images from 23/07/2004 and 01/09/2003 were programs within each of the three primary lagoons. acquired for Merja Zerga and Ghar El Melh, The aims were twofold; first to demonstrate the utility respectively. of remotely sensed imagery for identifying key A suite of historical images for the three lagoons environmental features within coastal lagoons. This were acquired to facilitate the identification of was undertaken for all three of the MELMARINA decadal scale change (Table 1). One Landsat lagoons using imagery acquired during or immedi- ETM? scene from 2001 was available for both ately before the initiation of the field programs (June Merja Zerga and Ghar El Melh. Landsat Thematic 2003–September 2004). The second aim was to Mapper (TM) imagery was acquired for the mid- employ historical remotely sensed data to reveal the 1980s to the early 1990s. The predecessor of Landsat long-term changes in the bio-physical characteristics ETM?, Landat TM’s seven bands cover a similarly of the lagoons. Although this was undertaken for all wide range of the electromagnetic spectrum from the three MELMARINA primary lagoons, a particular visible range (0.45–0.69 lm), to near infrared (0.76– focus was Lake Manzala for which image classifica- 0.90 lm) and mid infrared (1.55–2.35 lm), up to the tion techniques were applied. This was due to the thermal infrared band (10.4 – 12.5 lm) (Jensen, particular characteristics of the site and the large 1986). With the exception of the thermal infrared changes witnessed within the lake over the last three band (120 m), the spatial resolution of the data is decades (e.g. Ayache et al., 2009). The following 30 m. Landsat Multi-Spectral Scanner (MSS) imag- sections describe the different stages of the analysis. ery were acquired for the 1970s and early 1980s. The four bands of this sensor cover the visible to near Image identification and acquisition infrared part of the electromagnetic spectrum (0.5– 1.1 lm) at the larger pixel size of 79 m (Jensen, The initial aim for the analysis of contemporary 1986). As summarised in Table 1, in total four images was to employ data from the same sensor, the images covering the period 1979–2004 and 1972– Enhanced Thematic Mapper Plus (ETM?) on the 2003 were available for Merja Zerga and Ghar El Landsat 7 platform, for each lagoon. Images for this Melh, respectively. Six images (1973–2003) were sensor consist of eight spectral bands with spatial employed for Lake Manzala. More images for this resolutions of 30 m for bands 1–5 (recording wave- last site were employed since they were already lengths between 0.45 and 1.75 lm) and 7 (2.09– available within the data archive of the National 123 Hydrobiologia (2009) 622:147–171 151

Table 1 Summary of remotely sensed imagery available for the MELMARINA primary lagoons Merja Zerga Ghar EL Melh Lake Manzala Date Sensor Date Sensor Date Sensor

15/05/1979 Landsat MSS 11/08/1972 Landsat MSS 03/01/1973 Landsat MSS 07/05/1987 Landsat TM 05/08/1987 Landsat TM 10/05/1978 Landsat MSS 06/06/2001 Landsat ETM? 31/05/2001 Landsat ETM? 16/05/1983 Landsat MSS 23/07/2004a ASTER 01/09/2003a ASTER 07/11/1987 Landsat TM 04/08/1990 Landsat TM 05/02/2003a Landsat ETM? a Image acquired during or immediately before the MELMARINA field programs

Authority for Remote Sensing and Space Sciences correspondence between ground features and their (NARSS), Egypt. Where possible, the images correct position throughout the image. As a result, it selected for each lagoon were acquired at approxi- has the scale and projection properties (geometric mately the same time of year with spring and summer integrity) of a map. Image rectification is typically (i.e. the growing season) being preferred. The images accomplished on the basis of well-distributed ground of Merja Zerga fall within the three months between control points (GCPs) located on both the images May and July whilst those for Ghar El Melh are from and a map of the corresponding area (Olmanson May to September. Images for Lake Manzala are, et al., 2001). For each image of the three MELM- however, from a wider spread of months. ARINA primary lagoons, a number of GCPs (between 5 and 19 depending on image) were identified. These points comprised static features Image processing visible in both an image (source points) and the corresponding 1:50:000 topographic map (reference Image processing, which comprised three principal points). GCPs included road and canal intersections, steps of geometric correction, spectral enhancement bridges and other large man-made features. More and, in the case of the images of Lake Manzala, natural, dynamic features such as river bends and image classification was undertaken using ERDAS lagoon–marine connections were not used as GCPs Imagine (v 8.7). since they are more prone to movement between map production and image acquisition. Since both Geometric correction the source and corresponding reference points rep- resented the same features with different coordinate The geometric correction of each image was carried systems, they were used to generate a transformation out using standard procedures. Geometric distortions polynomial using the regression analysis method are normally introduced to satellite data during (Milne, 1988). A first degree polynomial transfor- acquisition. They result from several factors includ- mation was considered appropriate, given the low ing attitude (roll, pitch, and yaw), the Earth’s relief of the lagoons and their surrounding land- rotation and panoramic distortions (e.g. Curran, scapes. Acceptance of the transformation polynomial 1985; ERDAS, 1999). The coordinates of a remotely was based upon the root mean square (RMS) error sensed scene do not therefore correspond to a reported between the two sets of points. The RMS standard map projection and the coordinates of a errors for the transformations employed in this study fixed point vary from image to image. Geometric were in the range 0.7–0.9 of the pixel sizes. correction (rectification) is therefore necessary in Subsequently, the transformation polynomial was order to remove geometric anomalies and create a used to rectify the image to the map coordinate faithful representation of the original scene by system using the nearest neighbour re-sampling correcting pixel location errors and establishing a technique (Christensen et al., 1988).

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Image enhancement open water each of the remotely sensed images of Lake Manzala were subjected to a classification Enhancement techniques are often employed in order procedure. This was not undertaken for the images of to enhance image display properties, identify differ- Merja Zerga and Ghar El Melh as emergent vegeta- ent features in an image and thereby enhance the tion covers a much smaller part of both the lagoons subsequent visual interpretation. Enhancement of and, as noted above, is largely restricted to marginal each of the remotely sensed images of the MELM- areas. The basic premise of multi-spectral image ARINA lagoons was undertaken by applying a linear classification is that different surfaces have suffi- stretching technique to the different spectral bands. ciently different reflectance properties in different This procedure modifies the distribution and range of regions of the electromagnetic spectrum (i.e. spectral digital numbers (DNs) of the image pixels so that the signatures). An unsupervised classification approach potentially limited range of DN values within the was adopted (e.g. Lillesand et al., 1998) in which original image covers a larger range within the pixels were classified based upon their spectral stretched image (Lillesand et al., 2008). False colour signatures alone without any prior knowledge of the composite (FCC) images were derived in which three different surfaces within the images. Classification selected image bands were assigned to red, green and was undertaken using image bands with the highest blue (R, G, B), respectively. The selection of the FCC spatial resolution. These comprised all four bands (1– spectral bands is usually based on the features of 4) of the three MSS images (resolution 79 m) and interest. Table 2 summarises the bands used within bands 1–5 and 7 of the two Landsat TM and Landsat the false colour composite images of the MELMA- ETM? images (resolution 30 m). The classification RINA lagoons. Although the range of wavelengths was restricted to a digitised lake boundary for each recorded in each band vary between sensors, the image identified from the false colour composites. bands employed within the false colour composites The unsupervised classification procedure was per- were selected to provide as close an overlap as formed using the ISODATA (‘Iterative Self- possible. These band combinations have been applied Organising Data Analysis Technique’) algorithm in similar studies (Rawan & Mars, 2001; Hewson within ERDAS Imagine with an initial specified 15 et al., 2002). arbitrary classes. This algorithm repeatedly performs an entire classification from which clusters of pixels Image classification with similar spectral signatures are identified. A minimum spectral distance formula is used to define Review of the false colour composites of Lake these clusters (e.g. Calvo et al., 2003;Mu¨llerova´, Manzala (discussed below) highlighted major 2005). After initial unsupervised classification, clas- changes over time in the distribution of the within ses were combined based upon knowledge of the lake emergent vegetation, which is a characteristic characteristics of the site to provide three major feature of this particular site. The extensive islands of classes of open water, emergent vegetation and dry vegetation divide the lake into different sub-basins so land. Although cloud cover was not significant in the that they play an important ecological role. There- majority of the images, conspicuous clouds were fore, in order to more clearly illustrate these changes evident over the northeastern corner of Lake Manzala and to provide quantitative information on the in the 1983 image. Comparisons with the preceding relative extent of emergent vegetation compared to and proceeding images (1978 and 1987, respectively)

Table 2 Bands used in the false colour composite images of the three MELMARINA primary lagoons RGB Landsat ETM? Landsat TM Landsat MSS ASTER Band Wavelengths (lm) Band Wavelengths (lm) Band Wavelengths (lm) Band Wavelengths (lm)

R 4 0.77–0.90 4 0.76–0.90 4 0.70–0.80 3 0.76–0.86 G 3 0.63–0.69 3 0.63–0.69 3 0.60–0.70 2 0.63–0.69 B 2 0.52–0.60 2 0.52–0.60 1 0.50–0.60 1 0.52–0.60

123 Hydrobiologia (2009) 622:147–171 153 enabled a reclassification of cloud covered pixels to the three land cover classes are assumed to be the one of the three major classification classes. In most result of persistent trends in lake development. cases, pixels were reclassified as water. The images from 1978 and 1987 show very little change over this period in this particular part of the lake. Subse- Results quently, the area and percentage cover of each of the classes were evaluated for each image. Seasonal Recent remotely sensed imagery for each lagoon changes in vegetation within Lake Manzala are relatively smaller due to the relative constancy of The most recent remotely sensed images of the three the climate whilst the small tidal range (e.g. Thomp- MELMARINA primary lagoons (Figs. 2, 3, 4) enable son et al., 2009) exerts a minimal effect on the extent the identification of some of the key features within of open water within the lake. Therefore, changes in these environments and in their immediate

Fig. 2 False colour composite ASTER image of Merja Zerga (23/07/2004) Red Band 1, Green Band 2, Blue Band 3. Specific locations discussed in the text: (1) gullet, (2) inland within the gullet, (3) major in-lagoon drainage channels, (4) Merja Kahla, (5) Drader River, (6) Drader delta distibutaries, (7) Nador Canal, (8) Nador Delta, (9) Dayet Roureg, (10) Moulay Bou Selham

123 154 Hydrobiologia (2009) 622:147–171

Fig. 3 False colour composite ASTER image of Ghar El Melh (01/09/2003) Red Band 1, Green Band 2, Blue Band 3. Specific locations discussed in the text: (1) Jbel Nadhour, (2) old Mejerda delta, (3) former Mejerda channel, (4) Sebkht El Ouafi, (5) coastal sand bar, (6) dredged channel, (7) former mouth of Mejerda River, (8) Sebkhat Sidi Ali El Mekki, (9) new port, (10) Ghar El Melh town

surroundings at the time of image acquisition. are clearly evident within the image. The relatively Specific areas discussed in the text are labelled deep water channel (known as the ‘‘gullet’’), which within the images. links the lagoon with the Atlantic Ocean, is shown cutting through the coastal sand dunes (1). The Merja Zerga channel, which varies from 60 to 300 m in width, has variable bathymetry up to 3 m depth. An island Figure 2 provides a false colour composite image of feature within the channel at its Atlantic end (2) is the ASTER data acquired for Merja Zerga on 23/07/ visible within Fig. 2 suggesting that the image was 2004. Within the image, red can be broadly classified acquired near low tide. As noted in Ayache et al. as vegetation, green as dry bare surfaces and blue as (2009), the seaward section of this channel was predominantly either water or wet surfaces. A regularly blocked in the past by moving coastal sand number of the characteristic features of Merja Zerga bars although, more recently, the ‘‘gullet’’ has been 123 Hydrobiologia (2009) 622:147–171 155

Fig. 4 False colour composite Landsat ETM? image of Lake Manzala (05/ 02/2003) Red Band 4, Green Band 3, Blue Band 2. Specific locations discussed in the text: (1) vegetated islands, (2) channels cut through islands, (3)El Gamil channels, (4) Port Said, (5) Damietta, (6) intensive fish farms, (7)Bahr El-Baqar drain, (8) El Salem Canal, (9) Matariya, (10) fish farms

actively managed in order to maintain marine con- of Merja Kahla (4) to the north of the main lagoon nectivity. The southward extending sand bar at the (Ayache et al., 2009) is also clearly visible. The end of the ‘‘gullet’’ as well as the southward centre of the lagoon, indicated in light blue within deflection of the channel itself suggests that the Fig. 2, retains no or only a few centimetres of water predominant direction of the alongshore sediment at low tide. Its irregular shape is indicative of the transport is north–south. complex bathymetric characteristics of the lagoon Drainage channels in Merja Zerga, which extend depression. These reflect the drainage features on the from the ‘‘gullet’’ towards the centre of the lagoon, inter-tidal mudflats, which extend from the centre of are clearly distinguishable. Two major channels run the lagoon towards the marginal areas. On these due south along the western edge of the lagoon mudflats, areas indicated in darker blue within Fig. 2 towards the less shallow central area (3) (Ayache denote the presence of shallow standing water or et al., 2009; Thompson et al., 2009). Another major drainage channels. channel initially runs east–west from the ‘‘gullet’’ Figure 2 shows the two major depositional fea- also before being diverted to the south and splitting tures within Merja Zerga, which are associated with into two branches. The channel which at high spring freshwater inflows. The deltaic feature at the end of tides links Merja Zerga with the smaller wetland area the Drader River, which can be seen meandering 123 156 Hydrobiologia (2009) 622:147–171 towards the lagoon from the east, is clearly visible Nador Canal. Ayache et al. (2009) reports on the (5). One primary channel crosses the delta before vegetation in these areas beyond the Juncus zone; a splitting into four main distributaries (6). Elsewhere, belt of heavily grazed often water-logged grassland is dry channels and former drainage across the delta are particularly extensive on the eastern border of the indicated by the presence of linear-vegetated features lagoon, beyond which lies predominantly cultivated (typified mainly by Juncus). The most notable of land. Individual fields in this area, as well as to the these is associated with the levee which separates immediate north of the lagoon, are clearly evident Merja Kahla from the main body of the lagoon. Since within Fig. 2. Figure 2 also illustrates the presence of the ASTER image was acquired in July, when flows vegetation on the coastal dunes (beyond the darker within the Drader River are very low and made up red-coloured Juncus zone) to the west of the lagoon. almost entirely of irrigation return flows (e.g. Ayache The largest of these vegetated areas are plantations of et al., 2009; Thompson et al., 2009), water appears to Eucalyptus and Acacia, which were planted in the be restricted to the main channel. It is, however, early 1970s, (Ayache et al., 2009) although there are possible that during winter floods, water spills into also some smaller areas of agriculture as indicated by other channels and even across the surface of the the rectangular field outlines. The linear vegetated delta. The lower reaches of the delta (the light blue features on the dunes mark cactus hedge tracks. The and white areas in Fig. 2) have little vegetation largest settlement in the area, Moulay Bou Selham except for algae and some patches of Arthrocnemum. (10), is visible to the immediate north of the ‘‘gullet’’. These extensive mudflats are inundated by spring Similarly, the smaller villages of Ouled Mesbah (to tides. The upper, higher elevation areas are shown to the south of the Dayet Roureg wetland) and Merhi- be extensively vegetated with field surveys (under- tene (south of the lagoon and adjacent to the taken in 2003) showing that the dominant species motorway which is also clearly visible) are also were Juncus maritimus and J. acutus. distinguishable within the image. The much straighter course of the Nador Canal can be identified in Fig. 2 entering the lagoon from the Ghar El Melh south (7). It has also created an extensive prograding deltaic depositional structure (8). Unlike the delta of Figure 3 provides a false colour composite of the the Drader River, the most downstream parts of the most recent (01/09/2003) image available for Ghar El Nador Canal’s delta are shown to be densely Melh. It shows that the boundary between the lagoon vegetated. This could suggest that they are at a and the surrounding landscape is much more distinct higher elevation permitting the colonisation by Jun- than it is for Merja Zerga. This is especially so in the cus and some Phragmites which characterises the north where the scrub covered hills of the Jbel margins of the canal. The land lateral to the Nador Nadhour (1) provide a structural limit to the lagoon delta is a sparsely vegetated mudflat. Grasses (Spar- (see Ayache et al., 2009). The low tidal range of the tina and Panicum) together with Arthrocnemum are Mediterranean ensures that within the lagoon the common on the western side whilst isolated stands of tidally induced fluctuations in water levels are very Phragmites and Typha and widespread Arthrocne- small (0.13–0.07 m; Thompson et al., 2009). This mum occur on the eastern side. In contrast, in the consequentially accounts for the lack of extensive upstream of the Nador Canal delta, the vegetation inter-tidal habitats within the remotely sensed image gives way to grazed grassland on the eastern side and of Ghar El Melh. Unlike Merja Zerga, the bathymetry Eucalyptus groves and agriculture on the western of this lagoon is relatively uniform with most areas side. The small (c. 0.1 km2) shallow wetland area, being between 1.0 and 1.5 m deep (Thompson et al., Dayet Roureg (9), to the west of the canal is also 2009). With the exception of the old delta of the clearly indicated in Fig. 2 as an area of open water Mejerda River (2) and the area immediately adjacent fringed by (Juncus) vegetation. Generally, marginal to the coastal sand bar little bathymetric information vegetation of Juncus characterises much of the edge is shown within Fig. 3, but some turbidity features of Merja Zerga beyond the mudflats. In particular, are indicated. Fig. 2 indicates wide bands of vegetation along the The former delta of the Mejerda is clearly visible shores between the deltas of the Drader River and the in the south indicating the location where the river 123 Hydrobiologia (2009) 622:147–171 157 discharged into the lagoon before its diversion to the The distinct sub-lagoon of Sebkhat Sidi Ali El south during a major flood at the end of the Mekki in the northeast (8) is shown to contain a series nineteenth century (Ayache et al., 2009). The channel of small vegetated islands which are probably former into which the river shifted can be seen to the south of sand bars composed of sediment derived from the Ghar El Melh (3) although it is now largely dry Jbel Nadhour (Ayache et al., 2009). This basin was following another flood in 1973, which resulted in the effectively cut off from the main Ghar El Melh river moving 10 km to the south. Within Ghar El lagoon due to the stabilisation of the sand bar along Melh, the former channel can be distinguished as a its western margin to enable the construction of a linear feature extending approximately 1.7 km into road. This was undertaken in the early 1970s to the lagoon between what are assumed to be shallower provide access to a new port built for sea going areas made up of historic levees. The shallower water vessels (9). Much of this sand bar has since been in these areas encourages the growth of vegetation cultivated by local people growing fruit and vegeta- that was shown in field surveys to be dominated by bles within small plots which are visible within sparse Arthrocnemum and abundant benthic algae. Fig. 3. The new port can be seen on the southern edge Further into the lagoon, former delta distributaries are of the Sebkhat Sidi Ali El Mekki as can the jetties suggested by the widening of the area of shallow constructed to prevent blockage of the port’s mouth. water. Ayache et al. (2009) suggest that the delta The build up of sand to the north of the jetties further (now partly eroded) was once more extensive with indicates the north–south direction of alongshore one branch extending towards the coastal sand bars sand transport. The entrapment of this sand may have and, in the first half of the twentieth century, long-term implications for Ghar El Melh’s main sand effectively isolating a small southern lagoon basin bar. For example, it is evident in Fig. 3 that the most (Sebkhet El Ouafi, 4). The gently shelving lagoon northerly section of the sand bar, adjacent to the margin in the vicinity of the delta, which is indicated dredged channel, is thinner (\50 m) than further by the progressively darker blue from the lagoon shore south (c. 100 m), which might indicate its erosion in towards the lagoon’s centre, provides for some mar- the face of reduced up-current sediment supply. ginal plants including benthic macro-algae and The intensive nature of the agricultural landscape fringing Arthrocnemum. These can extend up to around Ghar El Melh is clearly evident in Fig. 3. For 100 m into the lagoon. The benthic macro-algae example, to the west of the Ghar El Melh town (Enteromorpha and Ulva) are particularly abundant (which, along with its port, is visible on the northern on the north shore of the lagoon as indicated by a thin shore of the lagoon, 10) the numerous rectangular red marginal band in Fig. 3 and probably results from areas of vegetation correspond to small agricultural excessive nutrient pollution (Ayache et al., 2009). plots that extend almost to the lagoon’s shore. The Vegetation is also present on the lagoon side of the intensively cultivated Utica floodplain lies to the sand bar which separates Ghar El Melh from the south and west of Ghar El Melh. The complex Mediterranean (5). This gently shelving shore is irrigation and drainage infrastructure in this area consistent with the seaward movement of the sand necessitates larger field sizes than those to the bars over the last century which is described by immediate north of the lagoon. Since the image was Ayache et al. (2009) and discussed below. The dredged acquired in September, after many crops had been channel towards the northern end of the sand bar is harvested, a large number of the fields in this area are clearly distinguished in Fig. 3 (6). To the immediate shown to lack vegetation. south of this channel, one of the low-lying sections of the bar which provides ephemeral marine connectivity Lake Manzala during periods of high tide or major flood events is visible. Impacts of the diversion of the Mejerda River Figure 4 shows a false colour composite of the upon coastal processes are also clearly demonstrated Landsat ETM image of Lake Manzala acquired on in Fig. 3. The former mouth of the river (7) has been 05/02/2003. As in Figs. 2 and 3, red can be broadly blocked by the sand bar as a result of the north–south classified as vegetation, green as dry bare surfaces alongshore currents. This has, in turn, created a smaller and blue as predominantly either water or wet coastal lagoon south of Ghar El Melh. surfaces. The image demonstrates that Lake Manzala 123 158 Hydrobiologia (2009) 622:147–171 is very different from the other two MELMARINA In Fig. 4, the impact of reclamation can also be primary lagoons. The lake is substantially larger distinguished along the southern margins of the lake. presently covering around 700 km2 compared to c. 13 Although in some places, the margins of the lake are and c. 36 km2 for Merja Zerga and Ghar El Melh, relatively ill defined, such as in the southwest where respectively. Unlike these other two lagoons, Lake the Bahr El-Baqar drain (7) discharges into the lake Manzala is divided into a series of sub-basins which and open water areas are fringed by marshes dom- are delineated by numerous vegetated islands dom- inated by Phragmites and Typha (e.g. Randazzo et al., inated by Phragmites and Typha. These islands are 1998; Ramdani et al., 2001), elsewhere there is a clearly distinguished in Fig. 4 and are coloured red- more distinct division between the lake and dry land. brown (1). They comprise a mixture of dry land just This is most clearly demonstrated by the straight above the lake water surface and fringing emergent east–west aligned lake margin in the southwest. Here, vegetation. It has been suggested that those islands in the embankments of the El Salam Canal (8), which the north with long axes roughly parallel to the coast delivers water to the North Sinai Agricultural Devel- are former coastal sand ridges whist further south opment Project (NSADP, World Bank/Ministry of those which trend in a more north–south direction are Public Works and Water Resources, 1992; FAO, remnants of deposition along former branches of the 2005) delineate the boundary of Lake Manzala. The Nile (Sestini, 1976; Abdel-Kader, 1982; Randazzo canal, which receives water from the Damietta et al., 1998). The islands within the lake influence Branch of the Nile and intercepts water from some circulation patterns and each of the different sub- of the main drains crossing the delta towards Lake basins consequentially have different hydrochemical Manzala, can be seen turning to the south before and sedimentological characteristics (Tennessee Val- again heading east where it eventually passes via a ley Authority, 1997). In a number of locations, siphon beneath the Suez Canal beyond the eastern channels cut through the islands to aid navigation can edge of Fig. 4. be identified (2). Similarly, the channels at El Gamil To the south of Lake Manzala, Fig. 4 displays an dredged through the coastal sand bars, which in intricate field system which is characteristic of the places are 2-km wide, can also be distinguished (3) Nile Delta. Much reclamation has occurred in this whilst, to the south, the main Nile Delta drains, which area over the last few decades and a significant part of provide freshwater to the lake, are also visible. the agricultural land to the immediate south of Lake The strong influence of human activities on Lake Manzala was reclaimed from the lake. Figure 4 Manzala and its immediate surroundings is clearly suggests that at the time of image acquisition most evident in Fig. 4. For example, the construction of the of the agricultural land to the west was under crops new road running along an embankment, which can whilst to the east, which includes some of the most be seen from Port Said (visible on the coast on the recently reclaimed land, many field systems were not eastern edge of the image, 4) to Damietta (located to cultivated. The substantial town of Matariya on the the west on both banks of the Damietta branch of the southern shore of the lake is also visible (9). Linear River Nile, 5), has isolated the large northwestern vegetated features within the lake are particularly sector of the lake except for a few locations when the dense in the lake region immediately east and north road passes over bridges. It has also created an of this town and indicate the presence of extensive elongated strip of open water approximately 1-km fish farming and associated ad hoc management of wide between the coastal sand bars and the embank- the particularly luxuriant emergent vegetation in this ment in the east. Isolation has permitted the extensive area (10). reclamation of lake bed in the northwest of the lake for aquaculture development. The numerous rectan- Decadal scale lagoon change gular divisions in this part of the lake are indicative of the widespread and largely uncoordinated construc- The false colour composite images of the three tion of embankments to enclose engineered fish farms MELMARINA primary lagoons acquired on different (6). These enclosures are shown in Fig. 4 to also be dates within a period of up to 30 years duration extending into the northwestern part of the main body enable the identification of environmental changes at of Lake Manzala from the road embankment. each site. These changes relate to changes in both the 123 Hydrobiologia (2009) 622:147–171 159 lagoons and in their surrounding near landscapes. three months of May–July, the large tidally induced Despite varying resolution (from as small as 15 m for oscillations in lagoon water level (see Thompson the recent ASTER images to 79 m for the Landsat et al., 2009) make recognition of some within lagoon MSS images) and differences in timing, some prin- changes more difficult. Perhaps most apparent are the cipal environmental change features can be discussed physical changes associated with the channel which which augment the observations reported in Ayache links the lagoon with the Atlantic Ocean. A beach et al. (2009). sand spit on the southern side of this channel is shown to be well developed in 1979. Subsequent images Merja Zerga show that this feature diminished in size, as the channel was deflected to the south. By 2001, a The four false colour composite images of Merja prominent spit had developed on the northern side of Zerga are shown in Fig. 5. These include the most the channel and, as discussed above, an island of sand recent ASTER image discussed above. Significant had accumulated in the channel’s mouth by 2004. changes in a number of specific features are discern- Also clearly shown in Fig. 5 is the extension into able. Although all the images are from the Merja Zerga of the delta of the Nador Canal. The

Fig. 5 False colour composite images of Merja Zerga (a) 15/05/1979, Landsat MSS; (b) 07/05/ 1987, Landsat TM; (c) 06/ 06/2001, Landsat ETM?; (d) 23/07/2004, ASTER

123 160 Hydrobiologia (2009) 622:147–171 eastern side of the delta appears to have experienced image, available for Ghar El Melh. Probably, the considerable infilling with a commensurate increase most marked changes recorded in the years between in salt marsh vegetation cover. The 1979 image 1972 and 2003 are associated with the geomorpho- suggests that deposition has previously been concen- logical development of the sand bar which delimits trated in the west locally raising surface elevations the lagoon from the Bay of Tunis and the southern and permitting the colonisation by vegetation prob- extension of this bar beyond the old Mejerda River ably dominated by Juncus and Phragmites. By 1987, mouth. Over time, the sand bar has straightened as its the vegetation had expanded by approximately 1 km central sections have migrated to the east. The central to the east, a process which appears to have continued part of the bar moved by as much as 320 m between towards the present day. The delta–lagoon margin is 1972 and 2003 resulting in an increase in the now much straighter than it was in the late 1970s. In combined area of the main lagoon and Sebkhet El the northeast, sediment from the Drader River has Ouafi of nearly 4 km2 (30.70 km2 in 1972 and accumulated in both westerly and southwesterly 34.65 km2 in 2003). Ayache et al. (2009) provides directions. The expansion of the Drader’s delta in a evidence from historical maps which suggest that this westerly direction has effectively closed off the process, so clearly evident in Fig. 6, characterised northerly Merja Kahla sub-basin. Whilst in the 1979 much of the twentieth century development of the image, a nearly continuous 600-m long connection lagoon. As the sand bar has become less concave in with the main lagoon along the southern edge of the the south of the lagoon, the southerly alongshore smaller body of water is discernable, over time this currents have become less diverted out to sea as they has closed so that within the 2004 image connection is cross the former mouth of the Mejerda River. As a limited to the previously discussed vegetation (Jun- result, the sand spit which has developed in this area cus) fringed channel extending to the proximal section has migrated inland almost completely isolating a of the ‘‘gullet’’. Beyond the lagoon, the sequence of body of coastal water creating another lagoonal images in Fig. 5 clearly show the intensification of environment. However, at times, as indicated in the agriculture in the adjacent landscape. The develop- 2001 image, low lying parts of this sand bar provide ment of field systems on the gently sloping ground to connections between this lagoon and the sea. Further the east of Merja Zerga can be identified. In 1979, very north, another change affecting the coastal sand bars little vegetation is indicated on the dunes that lie to the has been the construction of the new port. In 1972, west of the lagoon. By contrast, in 2001, large parts of the coastal sand bars were uninterrupted between the the dunes are covered in rectangular shaped fields, Jbel Nadhour in the north and the former Mejerda which in turn appear to have increased in number and mouth in the south. Within the 1987 image, a sharp extent four years later. Flower et al. (1992)suggested change in the shape of the sand bars including an that Dayet Roureg, the small wetland to the west of the increase in their width can be identified around the Nador Canal, had experienced recent rapid siltation. new port. Other features of the coastal sand bar This could be attributable to its location near the canal include changes in the channels which cross it and or enhanced agricultural activity in the surrounding link the lagoon with the sea. The images from 1972 area. Figure 5 shows that in both the 1979 and 1987 and 1987 suggest that the main lagoon–sea connec- images, the wetland can be clearly distinguished as a tions were towards the central, most concave parts of dark area of open water. The more recent images the sand bar. By 2001, these connections are no suggest a potential reduction in its extent as well as longer visible and instead the major lagoon–sea colonisation by fringing vegetation, reported above to connectivity is provided by the dredged channel to be dominated by Juncus. This would be consistent with the immediate south of the new port. Within the the infilling of the wetland by sediment. lagoon, the former delta of the Mejerda appears to show little change since 1972. This suggests that its Ghar El Melh rate of erosion has declined from that experienced in the first half of the twentieth century when the delta Figure 6 provides the four false colour composite effectively isolated the southern part of the lagoon. images, including the previously discussed ASTER Ghar El Melh town on the northern shore has grown

123 Hydrobiologia (2009) 622:147–171 161

Fig. 6 False colour composite images of Ghar El Melh (a) 11/08/1972, Landsat MSS; (b) 05/08/1987, Landsat TM; (c) 31/05/2001, Landsat ETM?;(d) 01/09/2003, ASTER between 1972 and 2003 with development being much larger extent of this lake compared to the other concentrated in the west. two MELMARINA primary lagoons, Fig. 8 provides details from the same areas within the earliest and Lake Manzala latest images to illustrate the specific changes which can be identified. The most marked changes within The six false colour composite images for Lake the lake concern the extent of open water and the Manzala, including the 2003 Landsat ETM? image development of islands of emergent vegetation. In the previously discussed, are shown in Fig. 7. Due to the 1973 image, this vegetation is largely restricted to 123 162 Hydrobiologia (2009) 622:147–171

Fig. 7 False colour composite images of Lake Manzala (a) 03/01/1973, Landsat MSS; (b) 10/05/ 1978, Landsat MSS; (c) 316/05/1983, Landsat MSS; (d) 07/11/1987, Landsat TM; (e) 04/08/1990, Landsat TM; (f) 05/02/ 2003, Landsat ETM? (boxes indicate location of insets on Fig. 8)

123 Hydrobiologia (2009) 622:147–171 163

Fig. 8 Sections of the oldest (03/01/1973, Landsat MSS) and El Baqar drain, (c) northwest corner of the lake before road most recent (05/02/2003, Landsat ETM?) false colour construction and reclamation for fish farms; (d) northeast composites of Lake Manzala. Locations of insets are indicated section of the lake including new embankments and engineered on Fig. 7.(a) Southwestern lake margin showing impact of marine connections Salam Canal; (b) lake bed reclamation to the east of the Bahr the western and southern sectors of the lake with Major changes have occurred around the margins several irregular strips of vegetation in the central area. of the lake, including the vegetation in these areas, Within 10 years (1983) this vegetation had expanded since the early 1970s. Perhaps, the most profound has dividing the lake into the sub-basins which now resulted from the construction of the El Salam Canal characterise Lake Manzala. In contrast, the spatial which, as described above, now runs eastward along pattern of the vegetated islands within the main body the southwestern margin of the lake. In 1973, the lake of the lake changed relatively little in the following margin in this area was relatively ill defined with 20 years (1983 compared to 2003). These changes are open water giving way to emergent vegetation before further demonstrated in Fig. 9, which shows the results agricultural land further south (Figs. 7, 8a). By 1983, of the classification of Lake Manzala into the three the engineering work associated with the canal had land cover classes of open water, vegetation and bare shifted the lagoon’s margin by as much as 6 km to land. The concentration of large areas of wetland the north in some locations. Figure 7 shows that the vegetation in 1973 within the southern part of the lake land reclaimed from the lake to the south of the canal is clearly demonstrated. Within the main body of the was rapidly converted to agricultural production. As lake, vegetation is concentrated in thin linear bands indicated above, large areas in the southeastern parts which are shown to have increased in width by 1978. of the lake have similarly been reclaimed. For This process continued till 1983 with patches of example, a large wetland area to the east of the Bahr vegetation coalescing. Over the next 20 years, the El Baqar drain has been reclaimed since 1990 and is boundaries of these sub-basins were retained. now (2003) partly under agriculture (Fig. 8b). The 123 164 Hydrobiologia (2009) 622:147–171

Fig. 9 Classified remotely sensed images of Lake Manzala (a) 03/01/1973; (b) 10/05/1978; (c) 316/05/ 1983; (d) 07/11/1987; (e) 04/08/1990; (f) 05/02/2003

isolation of the northwestern part of Lake Manzala transport and waste water control for the Port Said from the main lake is illustrated in Fig. 7. The earliest area together with the sluice gates on the two main images show that although a wide unvegetated bar, marine channels (Fig. 8d). probably a former coastal sand ridge, ran along the Table 3 demonstrates that the combined impact of southern margin of the roughly triangular section of the activities discussed above has been a substantial the lake, there were numerous relatively wide con- decline in the overall area of the lake from more than nections between it and the main lake. Construction 1,400 km2 in the early 1970s to less than 700 km2 in of the road linking Port Said to Damietta began in 2003. This decline in lake area should be considered 1990 with the work being completed by 2000. This when interpreting the relative importance of the land road is shown to have been constructed on the top of cover classes shown in Table 3. For example, the the sand bar in the most recent image. Many of the total area of vegetation has declined consistently connections between these two different parts of the since 1973 (with the exception of 1990), so that its lake have therefore been lost. Improved access to this total extent in 2003 was almost 50% of that in 1973. part of the lake due to the new road is probably a However, due to the decline in the total lake area, the major factor in the conversion of extensive areas of percentage cover of vegetation has remained rela- lake bed to fish farming. Figure 8c shows that this tively stable although showing a small increase in the process has resulted in major changes in this part of late 1980s/early 1990s. Similarly, the proportions of the lake. The northeastern section of the lake has both water and land have remained very approxi- been under development since the 1970s with the mately the same over the period 1973–2003 construction of embankments associated with (Table 3). 123 Hydrobiologia (2009) 622:147–171 165

Table 3 Area and percentage of the total classified area of three land cover classes within Lake Manzala: 1973–2003 Image Area (km2) Percentage of classified area Water Vegetation Land Total Water Vegetation Land

03/01/1973 1070 243 128 1441 74.3 16.9 8.9 10/05/1978 819 191 86 1096 74.7 17.4 7.8 16/05/1983 709 165 151 1025 69.1 16.1 14.8 07/11/1987 580 164 65 809 71.7 20.3 8.0 04/08/1990 520 190 57 767 67.8 24.8 7.4 05/02/2003 491 125 63 679 72.3 18.4 9.3

Discussion sensors such as Landsat MSS has been used success- fully for large wetlands (Hardisky et al., 1986), its use The application of remote sensing techniques to is more limited for small scale studies (e.g. vegetation landscape characterisation, habitat monitoring and community identification and mapping) within wet- spatial analysis of surface cover change has made lands. These environments, such as the major advances in the past three decades (e.g. MELMARINA primary lagoons, are typically spa- Schowengerdt, 2007). However, the use of simple tially diverse and exhibit complex communities of remote sensing techniques are still relatively under- aquatic vegetation as well as wide variations in water used in ecology and particularly in hydrobiology and quality within relatively small areas. Higher resolu- wetland systems within less developed regions. Here, tion such as Landsat TM, Landsat ETM? and they have particular relevance to informing environ- ASTER enable the discrimination of smaller areas mental management. This study has utilised remotely within these environments (Turner et al., 2003;De sensed data in a comparative way in the assessment Roeck et al., 2008). of three coastal lagoons in North Africa. Here, some of the principal attributes of remote Contemporary status of the coastal lagoons sensing, including spatial coverage, availability of archives of historic imagery and relative cost effec- Within this study, the spatial features of each of the tiveness compared to field programmes, make it an three MELMARINA primary lagoons were identified attractive option for mapping and monitoring. The using a variety of satellite data (Landsat MSS, TM, relatively large size of many North African coastal ETM? and ASTER, cf. Table 1) following appro- lagoons, especially Lake Manzala, means that whole priate image processing and (for Lake Manzala) site ground surveys cannot be undertaken easily and classification. The false colour composite images of repeatedly. Furthermore, extensive areas of shallow the three lagoons capture the major biogeographical water mean that boat access is hindered whilst the features. The large tidal cycle at Merja Zerga is a large tidal regime of sites such as Merja Zerga means complicating factor that affects the spatial analysis that access to many areas is limited to high tide. since the extent of the exposed mudflats beyond the When coupled with the frequently fine cloudless fringing Juncus communities varies substantially weather in North Africa, remotely sensed data according to water levels and hence the time of combined with appropriate targeted ground survey image acquisition. Extensive fringing salt marsh can provide uniquely detailed spatial information on communities are largely absent at the other two sites surface features across entire wetland landscapes. where tidal fluctuations are small and where water Comparison of images from different dates over the margins are less variable and more easily delineated. last few decades provides a means of assessing the Contemporary images of all three lagoons display the changes in site characteristics including near land- geomorphological characteristics of the sandy bars, scape geomorphology, lagoon hydromorphology and spits and dunes that separate them from the sea. Only the distribution of aquatic and marginal vegetation. at Merja Zerga is some agriculture developed on the Although the first available satellite information from very substantial coastal dune strip but elsewhere land 123 166 Hydrobiologia (2009) 622:147–171 surrounding each lagoon is intensively cultivated and hyperspectral data could be applied (e.g. Underwood field systems encroach almost to the water margins of et al., 2006; Jollineau & Howarth, 2008). Ghar El Melh and Lake Manzala. Within-lagoon vegetation at Merja Zerga or Ghar Environmental change El Melh is characterised by submerged communities that are exposed during low tide only at the first of The multi-temporal satellite images show consider- these two sites. The relatively low density of this able changes associated with the geomorphological benthic aquatic vegetation compared to the dense development of all three lagoons, but changes in the stands of emergent vegetation at Lake Manzala total lake area and in the areas of open water and resulted in less clear discrimination within the emergent vegetation have been greatest in Lake satellite images although the FCC images do indicate Manzala. The largest single recent change within the fringing vegetation (Juncus and/or green macro- Merja Zerga, the construction the Nador Canal in the algae, see Ramdani et al., 2001). The situation in 1950s (Ayache et al., 2009), predates the availability Lake Manzala is very different and this site is of satellite imagery. However, the suite of images characterised by the presence of more than 1,000 available for this site from the 1970s onward small irregular islands, which consists of clay, sand or demonstrate the lasting impact of this major hydro- mollusc shells. These island range up to several logical engineering project in the form of the square kilometres in area and many are densely expanding delta where the canal discharges into the vegetated (Zahran et al., 1988, 1990). An extensive lagoon. Similarly, the growth of the delta associated community of emergent vegetation (mainly Phrag- with the more natural inflowing channel, the Drader mites and Typha) occurs on and around these islands. River, is also demonstrated. The shape of the channel These vegetated areas are clearly distinguished connecting the lagoon with the sea is also shown to within the satellite image. Thus, the extent of have changed over the same period. The most emergent vegetation within the lake is well captured dramatic changes, however, have been within the by the satellite image as are the linear navigation near landscape and are associated with the intensifi- channels which pass through the vegetation and cation of agriculture and expansion of the field between the islands. Floating plants, particularly system around the lagoon. Over a similar period, water hyacinth (Eichhorina crassipes as well as Ghar El Melh has seen some extension of agriculture Azolla and Lemna spp.), are also common in standing around its northern and western shores, but the most water between the islands, but together with the persistent change is associated with sediment dynam- submerged vegetation (Potomogeton and Ceratophyl- ics and the easterly migration of the sand spit lum, see Khedr, 1997) these communities are not as delimiting the lagoon from the sea. This movement well discriminated within the FCC image. Collec- has probably been exacerbated by the building of the tively, however, the aquatic vegetation of the lake new fishing port in the northeast and alterations to the plays an important role in maintaining varied habitat marine inlet channel since the 1970s (see Ayache for fish and bird species. Local modifications to et al., 2009). emergent plant cover are particularly intense in the Due to its larger size, the changes within Lake southern central sector of the lake and result from fish Manzala were examined in more detail. Images of farming activities where selective reed cutting has this lake from 1973 to 2003 (Fig. 7) show a marked created rectangular features at the scale of 100 m or contraction of the lake margins and major changes in less. Estimating the cover provided by aquatic plants the distribution of emergent aquatic vegetation. is important because it promotes fish stocks (Kraı¨em According to the morphometric measurements made et al., 2009) as well as restricting water movements from the classified images of the Lake Manzala (Thompson et al., 2009). The latter help in assimi- (Fig. 9), the overall size of the lake decreased by c. lating the excessive dissolved nutrients and in 50% between 1973 and 2003. Major reclamation in restricting the distribution of water pollutants (cf. the northwest, southeast and south central areas of the Duning et al., 1996). For further discrimination, lake since the early 1970s is clearly evident. These assessment and mapping of these aquatic plant changes principally result from: (1) annexation of the communities in Lake Manzala, higher resolution northwestern sub-basin that existed prior to the late 123 Hydrobiologia (2009) 622:147–171 167

1980s as a result of building the Trans-Manzala central parts of the lake. At the same time the major highway over the sandy ridges that marked the inner reclamation activities have removed vegetation zones northern margin of the lake until the mid-1980; (2) by encroachment into the former lake bed. While fish construction of the El Salam Canal to the south of the production has not changed markedly in the late lake across once extensive marshlands, which has twentieth century (Kraiem et al., 2009), the species since allowed reclamation of former lake bed on the composition has shifted in response to water quality landward side of the canal since 1983 (El-Quosy, and to changes in fisheries practices. Development of 2006); and (3) rapid extension of land development tilapia fisheries, particularly during the last 30 years, westwards from the southeastern border of the lake has been accompanied by increasing modification of since 1973. In the first of these areas, engineered fish the emergent vegetation. These modifications are farms were established but the northern tip of the El mostly marked by the development of engineered fish Deeba area has been affected by coastal erosion at farming in the annexed northwestern part of the lake least since 1973. Eroded material is transported east and also by the linear vegetation features in the by long-shore currents (e.g. Stanley, 1988, 1996) central southern part of the lake (especially around causing siltation problems that affect the marine inlet the lake port of Matariya). The expansion of these channels to the lake. In the south, more than 250 km2 activities is evident within the remotely sensed of land were reclaimed for agriculture east of images of the lake. Matariya when the El Salam Canal was constructed Although the extensive area of emergent vegeta- east from the Damietta Branch of the Nile. This tion in central Lake Manzala has expanded since the development has allowed for improved agriculture 1970s, much of this habitat has been lost from the and road access to the town, but removal of surface marginal zones. As a result, the proportion of the lake water from newly reclaimed land in the area remains covered in wetland vegetation has changed relatively a persistent problem. In the southwest, the El Bshteer little. The post-1970s spread of Phragmites reed area is one of the fastest developing areas around the swamp in the central area is a significant change that lake and the images show that between 1987 and has doubtless affected water circulation patterns and 2003 quantitative changes amounted to local loss of water quality. Interestingly, this increase parallels more than 100 km2 of lake area. In contrast, in the changes recorded in the Lauentian Great Lakes where early the wetlands in this region of the lake extended the dominance of several opportunistic plant species, to within \500 m of the Suez Canal. The overall including the common reed (Phragmites australis), contraction of Lake Manzala has reduced its water has increased in recent decades (e.g. Wilcox et al., storage capacity, and other post-1970s hydrological 2003). Temperature and water level regime have been modifications have affected water distribution (see implicated in the spread of common reed in North Ayache et al., 2009). The engineered marine inlet America, but in Lake Manzala reduced salinity seems channels in the El Gamil area permit Lake Manzala the most plausible causative agent. In contrast to the water to flow seawards and this can be tracked by Great Lakes, no specific management of the common satellite imagery. When the El Gamil sluices are reed has been undertaken in Lake Manzala, yet a open, the lake water, rich in nutrients and phyto- combined field and remote sensing-based approach to plankton, can be seen to escape into the coastal zone develop a semi-automated detection and mapping (cf. the February 2003, Fig. 8d). technique to support monitoring and assessment of As a consequence of the recent changes in the emergent plants (mainly Phragmites and Typha) lake’s morphology and hydrology, the distribution of offers an attractive way to tackle management of aquatic emergent vegetation in and around Lake these reed beds. Manzala has changed significantly. At least two major factors appear to be involved. The first is the Implications freshening of the lake since the early twentieth century (see Flower, 2001) due to the inflow of large Results of this study show that remote sensing when volumes of water from the drains in the south integrated with field survey and knowledge of site (Ayache et al., 2009; Thompson et al., 2009). This characteristics can offer a convenient approach for has permitted emergent vegetation to extend into the assessing North African coastal lagoons and 123 168 Hydrobiologia (2009) 622:147–171 monitoring environmental change. Detecting geo- experience acute water stress (Shindell, 2007) with morphological and hydrological changes at the important implications for aquatic ecosystems includ- drainage basin scale has important implications for ing those in the densely populated coastal zone. All site management and near landscape development. three sites investigated in the MELMARINA Project The loss of lagoon habitat area is most alarming for (Flower & Thompson, 2009) urgently require conti- Lake Manzala and together with major changes in the nuity of the integrated monitoring and modelling distribution of emergent aquatic plants and water programme as initiated by this project. Remote circulation this must exert a major stress on the lake sensing is undoubtedly of major importance in this ecosystem. The fishery status is questioned at all respect and, combined with new developments in this three sites and likely further increases in eutrophica- rapidly advancing field, will provide information tion, siltation and reclamation will diminish lagoon needed by environmental planning and management habitats further. Predicted sea level rise may inter- authorities as well as environmental law enforcement vene but the ecosystems will surely change further so agencies to help ensure the sustainability of these that monitoring into the future is essential. systems. Water quality and vegetation, which includes phytoplankton, macro-algae and submerged and Acknowledgments The MELMARINA Project was financed emergent plants, are crucial aspects of aquatic by the EU Framework V INCO-Med Programme (Grant ICA3- CT2002-10009). The authors acknowledge the assistance of all biodiversity. The value of remote sensing to biodi- the partner institutions in the project. Particular thanks are versity and nature conservation is potentially extended to Prof. A. El-Dessouki, Chairman of NARSS for demonstrated by tracking the nature and pace of the facilitating the project work in Egypt. spatial changes in the lagoon habitat structure and quality. 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