Thermaikos Gulf Coastal System, NW Aegean Sea: an Overview of Waterrsediment Fluxes in Relation to Air±Land±Ocean Interactions and Human Activities

Journal of Marine Systems 25Ž. 2000 47±76 www.elsevier.nlrlocaterjmarsys

Thermaikos Gulf Coastal System, NW Aegean Sea: an overview of waterrsediment fluxes in relation to air±land±ocean interactions and human activities

S.E. Poulos a,), G.Th. Chronis b, M.B. Collins c, V. Lykousis b a Faculty of Geology, Department of Geography±Climatology, Panepistimioupoli, Zografou 15784, Athens, Greece b Institute of Oceanography, National Centre for Marine Research, Agios Kosmas, Elliniko 16604, Athens, Greece c School of Ocean and Earth Science, UniÕersity of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK Received 12 January 1999; accepted 3 November 1999

Abstract

This study presents an overview of the Holocene formation and evolution of the coastal system of Thermaikos GulfŽ NW Aegean Sea. . The system is divided into the terrestrial sub-system and the oceanic sub-system; the former represents 90%, while the latter includes only 10% of the total area. This particular coastal zone includes the second most important socio-economic area of Greece and in the southern Balkans, the Thessaloniki region; this is in terms of population concentration Ž.)1 million people , industry, agriculture, aquaculture, trade and services. The geomorphology of the coastal zone is controlled by sediment inputs, nearshore water circulation, and the level of wave activity. The large quantities of sedimentsŽ with yields )500 tonnesrkm2 per year.Ž , delivered annually by the main rivers Axios, Aliakmon, Pinios, and Gallikos. and other seasonal streams are responsible for the general progradation of the coastline and the formation of the Holocene sedimentary cover over the seabed of the Gulf. Changes to the coastline can be identified on macro- and meso-time scales; the former include the evolution of the deltaic plainsŽ at )1km2ryear. , while the latter incorporates seasonal changes along sections of the coastlineŽ. e.g. sandy spits , mostly due to the anthropogenic activities. The overall water circulation pattern in Thermaikos Gulf is characterised by northerly water movement, from the central and eastern part of the Gulf; this is compensated by southerly movement along its western part. The prevailing climateŽ winds and pressure systems. appears to control the surface water circulation, while near-bed current measurements reveal a general moderate Ž.-15 cmrs southerly flow, i.e. offshore, towards the deep water Sporades Basin. Waves approaching from southerly directions play also a role in controlling the shoreline configuration. Various human activities within the coastal system place considerable pressure on the natural evolution of the coastal zone ecosystem. Thus, the construction of dams along the routes of the main rivers has reduced dramatically the waterrsediment fluxes; this caused, for example, retreat of the deltaic coastlines and seawater intrusion into the groundwater aquifers. Similarly, pollution andror eutrophication of the nearshore marine environment have resulted from the inputs of industrial wastes, urban untreated sewage, and agricultural activities on the coastal plains. This effect is demonstrated by high levels of pollutants, nutrients, and by the increased concentrations of non-residual trace-metals within the surficial sediments. Finally, climatic changes associated with a potential rise in sea level Ž.i.e. 30±50 cm will threaten a substantial part of the low-lying lands of Thermaikos Gulf. Thus, systematic and thorough

) Corresponding author. Tel.: q30-1-7247-569; fax: q30-1-7293-390. E-mail address: [email protected]Ž. S.E. Poulos .

0924-7963r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S0924-7963Ž. 00 00008-7 48 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 monitoring is needed in order to protect the coastal ecosystem; this will ensure its sustainable development and successful management, in relation to present and future socio-economic activities and climatic changes. q 2000 Elsevier Science B.V. All rights reserved.

Keywords: coastal system; coastal zone; air±land±ocean interaction; socio-economic activities; Thermaikos Gulf; Aegean Sea

1. Introduction the associated Scheldt terrestrial basinŽ SALMON, 1999. . Coastal areas are of global importance, in terms It is widely accepted that the coastal zone, includ- of their natural resources, ecological communities ing the coastal plains, extends up to the outer edge of and as regions of concentrated human activities. The the continental shelves; these are located approxi- coastal domain hosts some 60% of the human popu- mately between 200 m above and below sea level, lation, on a global scale. A gross estimation of the respectivelyŽ. Cadee et al., 1994 . However, within natural capital of the earth's ecosystemsŽ Costanza et the context of the present investigation, the broader al., 1997. accounts at least US$33 trillion worth of term coastal system is introduced; this is in order to services annually, with the majority of the value accommodate a much larger geographical area, where currently outside the market system. To this value, terrestrial environmentsŽ. terrestrial sub-system in- which is 1.8 times the current global gross capital fluence marine environmentsŽ. oceanic sub-system , productŽ. GNP , the marine coastal and wetland and vice versa. ecosystems contribute US$10.6 trillionryear and The terrestrial and marine environments of the US$4.9 trillionryear, respectively. coastal systemŽ. see below , being the products of the During the last decades, much attention has been interaction between land, sea and air processes, are given to the significance of the air±land±ocean inter- interrelated and any change to one has a direct face, in relation to the functioning of global change impact to the other. Furthermore, the terrestrial sub- of the earth's system. Examples are biological feed- system acts mainly as the provider, e.g. water and back effects on the global environment and the avail- sediment fluxes, while the marine sub-system plays ability and sustainability of living resources, for primarily the role of the receiver. The marine envi- human consumption. Furthermore, the future re- ronment influences the weather conditions of the sponse of coastal systems to changes in climate and region by affecting the level of precipitation; in other environmental factors is of direct socio-eco- combination with temperature, this determines subse- nomic importance. At the same time, pressure upon quently the vegetation cover and the type of weather- the coastal ecosystem is in terms not only of natural ing of the landmasses. Furthermore, the oceanic processes, but also due to man's use of the coastal sub-system is involved in the morphometric forma- zone for economic activities. Thus, within the con- tion and evolution of the coastline by:Ž. a affecting cept of a global change, the Land±Ocean Interac- the seaward dispersion and deposition of the riverine tions in the Coastal ZonesŽ. LOICZ Implementation suspensatesŽ. nearshore current and wave activity ; Plan has been established by The International Geo- Ž.b participating in the formation and preservation of sphere±Biosphere ProgrammeŽ. IGBP, 1993, 1995 . the estuarine and lagoon environments; andŽ. c con- Recently, localised efforts have been placed upon trolling influence on the fate of the coastal aquifers. an integrated approach to the management of the The terrestrial environment has a more pronounced coastal resources through:Ž. i the establishment of an effect on the ocean sub-system, as the main source of interdisciplinary Forum Ð such as that related to the the fresh waterrsediment fluxes and the associated Dorset coastlineŽ.Ž southern UK Dorset Coast Fo- nutrients andror pollutants. These fluxes are depen- rum, 1998.Ž. ; and ii the integration and application dent upon the area of the landscape, the morphology of numerical models capable of describing the envi- Ž.high relief , lithological characteristics Ž e.g. erodi- ronmental quality throughout a whole coastal system, bility, infiltration.Ž , the climatic conditions e.g. air on a regional scale, e.g. the Belgium coastline and temperature, precipitation. , and the types of vegeta- S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 49 tion. In particular, the levels of precipitation and of surface running water, together with the general underlying geology, are related strongly to the formation of the coastal aquifers. Within the concept of the coastal system, the coastal zone is defined as a strip of land and sea territory of varying width, depending upon the nature of these environments and their particular management needs. Furthermore, the role of the coastal zone has been recognised as a buffer in:Ž. a providing a filter, to remove pollutants and other material transported from the hinterland, before they enter to the coastal ocean; andŽ. b protecting the upland areas from storms and flooding, originating from the sea. Finally, the natural boundary between the terrestrial and marine coastal zoneŽ. the coastline changes con- stantly, in response to terrestrial and marine processes, incorporating any anthropogenic interference. The present study provides an overview of the Holocene formation and evolution of the Thermaikos Gulf Coastal System, located in the NW Aegean Sea Ž.Ž.eastern Mediterranean Sea Fig. 1 . This coastal system belongs to the southern flank of the Alpine orogenic belt, located within the humid mesothermal Fig. 1. Geographical map showing the Thermaikos Gulf Coastal climatic zone and within an essentially tideless ma- System, NW Aegean Sea, eastern MediterraneanŽ The Times .Ž' P rine environment. The coastal system is divided into Atlas of the World, 1994 , altitudes in metres; ± ±: terrestrial boundary of the coastal system; PPP: boundary of river catchment two principal components:Ž. a the terrestrial sub-sys- areas; ---: bathymetric contours, in metres. . tem; andŽ. b the oceanic sub-system. The terrestrial sub-system consists of the hinterland and the sub- aerial part of the coastal zone; the former represents synthesis of the spatial and temporal heterogeneity of mainly the catchment areas of the rivers discharging the Thermaikos coastal system, in terms of:Ž. i mass along the coastline of Thermaikos Gulf, while the Ž.water and sediment transfer from land to continen- latter consists mostly of the deltaic plains, the coastal tal shelf and, subsequently, to the deep ocean basin; plains and cliffs. The oceanic sub-system includes Ž.ii the formation and evolution of the coastal zone, the inner continental shelf Ž.-40 m and the outer in relation to land±air±ocean interaction processes; shelfrshelf-break areaŽ. 40±130 m of water depth . andŽ. iii various socio-economic aspects of the re- Further, the coastal system under investigationŽ in gion and their impact on the natural environment. particular, the coastal zone. accommodates more than More specifically, the following processes are 1 million people associated with a variety of eco- overviewed:Ž. a river waterrsediment fluxes in re- nomic activitiesŽ. e.g. agriculture, industry, and trade . sponse to weathering processes, dependent upon the Here, the county of Thessaloniki has been estab- geology and climatology of the river catchments;Ž. b lished as the second most importantŽ following the the shape of the coastline and its recent evolution, as province of Athens. socio-economic region of a result of the riverrwave interaction and littoral Greece, lying between some of the most important sedimentation processes;Ž. c the offshore transfer and areas of the southern Balkans peninsula. dispersion of suspended sediment, by the river plumes Within the framework of the various activities of and sub-surface nepheloid layers;Ž. d thermohaline the Research Foci of the LOICZ implementation and wind-induced water circulation patterns and wave Ž.IGBP, 1993, 1995 , this work presents an integrated activity;Ž. e surficial sediment characteristics, includ- 50 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 ing pollution phenomena;Ž. f shelf-sediment accumu- AliakmonŽ. the northwestern mainland of Greece , lation rates; andŽ. g the consequences of human the PiniosŽ.Ž. central Greece Fig. 1 . Among the impact upon the riverine waterrsediment fluxesŽ re- smaller rivers, the most important is the Gallikos. In lated to the evolution of the coastal zone and a Table 2, the general physiographic characteristics of potential sea-level rise. , together with pollution and the aforementioned river catchmentsŽ area, relief ra- eutrophication phenomena of the aquatic environ- tio, waterrsediment fluxes, lithology etc.. are listed. ment. 2.1.2. Regional climate and associated weathering processes The climate of the hinterland region, especially 2. Terrestrial part of the coastal system that of the drainage basin areasŽ. Table 2 , can be characterised generally as `Continental', becoming The terrestrial sub-system consists of:Ž. i the hin- `Mediterranean' towards the coastal zone. Mean an- terland; andŽ. ii the sub-aerial part of the coastal nual air temperatures vary between 98C and 17.58C, zone. It covers a total area of some 47,200 km2, while annual rainfall lie between 400 mm and 1300 representing 90% of the total area of the coastal mmŽ. the latter, especially, at high altitudes . Further- systemŽ. Table 1 . The hinterland of the Thermaikos more, the central part of the drainage basins, associ- coastal system consists mainly of the catchment ar- ated with high altitudes, is characterised by the eas of the rivers and ephemeral streams discharging exceptionally high differences of absolute tempera- along the coastline of Thermaikos Gulf. The sub- tures. For example, within the R. Axios catchment aerial part of the coastal zone includes mostly the area, the temperatures reach y458C during winter deltaic plains of the aforementioned rivers, some and q308C in summer, while for the R. Pinios low-relief late Quaternary coastal plains and cliffed Ž.located in southern latitudes they vary between areas. y108C and q458C. Different climatic conditionsŽ mainly expressed in 2.1. The hinterland area terms of air temperature and precipitation. of the catchment areas under consideration are associated The hinterland covers an area of some 44,550 with a different type and intensity of weathering km2, representing some 85% of the total area of the processes, includingŽ.Ž. Leopold et al., 1964 : i low to coastal system and almost the 95% of its terrestrial intermediate mechanical weathering;Ž. ii high to in- partŽ. Table 1 . The geomorphological and climatic termediate chemical weathering;Ž. iii intermediate to characteristics of the river catchments determine the high weathering, due to running water; andŽ. iv high weathering and fluvial processesŽ i.e. waterrsedi- weathering, in relation to mass movements caused by ment fluxes. ; these, in combination with the prevail- high relief. These intensive denudation processes are ing marine processes, control the overall morphology associated with high sediment yields, exceeding 500 of the coastal zone. tonnesrkm2 per yearŽ. see below . For comparison, a general estimate for Europe overall is a denudation 2.1.1. Geological setting rate of some 42 mmrkaŽ. Walling, 1987 ; this corre- The geological structure of the terrestrial part of sponds to a sediment1 yield approximately equal to the Thermaikos Coastal System is the result of the 112 tonnesrkm2 per year. Alpine tectogenesis, which terminated in the Miocene Another factor that controls weathering processes some 5.1 Ma agoŽ. McKenzie, 1978 . The intensive over the region is the vegetation cover. The climate tectonism, enhanced by intensive weathering pro- of the Greek peninsula favours the growth of prairies, cesses, has created an area of extreme geomorpho- grassland, savannah and some forests: coniferous logical complexity with irregular relief; the topogra- trees are present over the uplands and the mountain- phy of the mainland of the Balkan Zone exceeds 2500 m and includes numerous river networks. The most important river networks are those of the Axios 1 The specific weight of the sediment has been taken equal to Ž.lying mostly within the former Yugoslavia , the that of the quartz Žs2.65 kgrm.3. S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 51

Table 1 Morphometric characteristics of the different parts of the Thermaikos Gulf Coastal System Areaa ConstituentsŽ. % 2 Ž.km Coastal System Coastal Zone Ž.A Thermaikos Gulf Coastal System 52,300 100.0 Ž.1 Terrestrial part of the system 47,200 90.2 Ž.a Hinterland area Ž)75 m altitude . 44,550 85.2 Ž.b Sub-aerial part of coastal zone Ž-75 m altitude . 2650 70.7 Ž.2 Oceanic part of the system 5100 9.8 Ž.a Sub-aqueous part of coastal zone Ž inner continental shelf Ž-40 m . 1100 2.1 29.3 Ž.b Outer continental shelf, shelf break and upper slope Ž-200 m . 4000 7.6 Ž.B Coastal Zone Ž 1bq2a . 3750 7.2 100 Ž.C Coastline length Ž km . 360

a Based upon topographic mapsŽ. 1:500,000 and hydrographic Ž. 1:200,000 provided by the Hellenic Geographic and Hydrographic Services, respectively. ous areas. The density of the vegetation is somewhat covered by grazing and partially forested land. Such poor, with some bare areas and the remainder being sparse cover, which is even more depleted during the

Table 2 General characteristics of the main rivers discharging along the coastline of the Thermaikos Gulf Coastline Axios Aliakmon Gallikos Pinios Geomorphologya Catchment areaŽ. km2 23,747 9250 930 10,750 Maximum reliefŽ. m 2800 2200 2180 1900 Relief ratioŽ. 10y2 1.15 1.7 0.25 1.5 Deltaic plainŽ. km2 Approximately 1500 80

Lithologyb AcidŽ. % 43.5 14.5 53.1 17.5 MaficŽ. % 7.7 9.2 4.4 6.2 CarbonatesŽ. % 11.3 15.7 1.0 14.7 Flysch-MolasseŽ. % 5.6 29.6 0.0 15.8 Neogene-QuaternaryŽ. % 31.9 31.0 41.5 45.8

Climatea Mean annual temperature Ž.8C 14.5 16.5 16.5 17.0 Mean annual rainfallŽ. cm 650 750 480 710 Type Terrestrial Mediterranean to humid Continental

Hydrologya Mean annual dischargeŽ. m3rs 158 73 39.5 81 Max. annual dischargeŽ. m3rs 279 137 ? 171 Min. annual dischargeŽ. m3rs4921? 11 High water periodŽ. months De±Jn De±Ma ? De±Ap Low water periodŽ. months Jl±No Jn±No Ma±No

Sediment fluxesc Annual yield of SSLŽ. 1032 trkm 1.22 0.46 0.004 0.6 Annual yield of DLŽ. 1032 trkm 0.07 0.13 0.51 0.15

aAfter Poulos et al.Ž. 1996a,b and Poulos et al. Ž. 1994 . bAfter SkoulikidisŽ. 1993 . cAfter Poulos and ChronisŽ. 1997 . 52 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76

Fig. 2.Ž. a Monthly variation in water discharge of the Rivers Axios, Aliakmon, Gallikos and PiniosŽ.Ž. after Therianos, 1974 ; b monthly variation of water and sediment flux of the R. Aliakmon at Ilariona gauging stationŽ representing a catchment area of 5005 km2 . over the period 1962±1982Ž. Public Power . dry summer periods, may be expected to enhance for both rivers was 115 and 62 m3rsŽ Therianos, denudation and lead to the release of large amounts 1974. . of weathered detritus to the river networksŽ Tzeda- The chemistry of the water of the aforementioned kis, 1993. . rivers is controlled mainly by the climate and the petrography of the catchment areasŽ Katsiou et al., 2.1.3. Water and sediment discharges 1989; Skoulikidis, 1993. . Thus, the calcium, magnesium, hydrogen, carbonate and chlorine contentsŽ Ta- 2.1.3.1. Freshwater inputs. Most of the freshwater ble 3. originate mainly from the weathering of young inputs to the Thermaikos coastline originate from the Ž.Holocene sediments. A significant part of riverine Rivers Axios, Aliakmon, Pinios and GallikosŽ Table magnesium results from mafic rock weathering, while 2. . Comparing discharges between the Rivers Aliak- the total silicate content is attributed to mafic and mon and Pinios, with those of R. Axios, it can be acid rocks. Only a part of the potassium content of noted that the high discharges of the former rivers occur between November and May; for the latter, they occur from December to JuneŽ. Fig. 2a . This Table 3 Average river water biogeochemical compositionŽ after pattern relates to the fact that the rivers Aliakmon Skoulikidis, 1993. and Pinios, located further south, have their high Axios Aliakmon Pinios Gallikos discharges coincident with high precipitation levels; Ž.r the R. Axios peak is related to snowmelt from the Ca mval l 2.7 2.7 3.1 3.1 MgŽ. mvalrl 0.8 1.3 1.5 1.0 mountains of the former Yugoslavia region. NaŽ. mvalrl 0.8 0.2 0.3 1.4 A very important contribution to the water flux is KŽ. mvalrl 0.1 0.1 0.1 0.1 made by flood events; these follow periods of excep- ClŽ. mvalrl 0.4 0.2 0.3 0.6 Ž.r tionally high precipitation, or sudden melt of the SO4 mval l 0.7 0.3 0.3 0.6 r NO3 Ž. mg l 4.9 3.1 4.3 3.7 snow-cover. Mean daily water discharges have been r PO4 Ž. mg l 1.6 0.2 0.3 0.1 found to range from 5, up to nearly 50, times higher r SiO2 Ž. mg l 10.1 10.2 13.1 10.3 than the corresponding mean monthly values in the DOŽ. % 98.7 104.9 99.7 114.3 case of the rivers Axios and AliakmonŽ Poulos et al., DOCŽ. mgrl 1.4 1.6 1.5 2.3 1996a. . For example, between 10 and 11 November POCŽ. mgrl 0.5 0.5 1.1 0.1 Ž. 1934, the daily water discharges of the rivers Axios Cu ppb 4.8 9.3 PbŽ. ppb 4.5 2.0 2.5 4.0 3r and Aliakmon were 2440 and 3280 m s, respec- NiŽ. ppb 20.0 18.3 18.5 17.0 tively, while the corresponding mean monthly value S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 53 river water results from the weathering of acid rocks. mountainous character of the region, with high relief Carbonates and flysch-molasses play a minor role in ratiosŽ.Ž. see Table 2 and e the sparse vegetation controlling the water chemistry. Some sodium and cover. chlorine, originating from the marine spay, are added Seasonal climatic changes have a direct influence to the river water through the mechanism of a rain- on river-runoff and weathering processes, inducing water contribution. seasonal variations in sediment transport. For exam- A positive correlation between river discharge ple, monthly variations in the water and sediment levels and dissolved organic carbonŽ. DOC concen- fluxes of the R. AliakmonŽ. Fig. 2b indicate that trationsŽ. Skoulikidis, 1993 indicates that the origin sediment flux reaches its highest levels at the begin- of the DOC in the river waters is mainly terrestrial in ningŽ. within only 1 or 2 months of the wet season origin; it is transported as a soil constituent, during Ž.Oct.±June , while some months later Ž when the flood events. In general, the rivers under investiga- water levels in the rivers are still high. the sediment tion experience moderate pollution; the Axios and flux decreases rapidly to reach its minimum value Gallikos are relatively the more polluted, as they during the dry summer periodŽ. July±Sept. . receive domestic and industrial sewage from the city The seasonal variations in the sediment fluxes of Thessaloniki, together with the chemicalsrferti- may be explained in terms of sparse vegetation cover lisers from the agricultural and industrial activity of and desiccated soil conditions during the dry season. the Thessaloniki Deltaic PlainŽ Georgas and Perisso- At such times, the land surface becomes vulnerable ratis, 1993. . The pollutants include primarily sodium, to erosion, when heavy rains fall at the beginning of originating from municipal wastewater; nitrate, phos- the succeeding wet season. Subsequently, during the phate, sulphate and potassium, originating mainly wet season, the plant cover becomes dense, with a from agrochemicalsrfertilisers; and chlorine from corresponding increase in soil cohesion and a consid- sewage. erable reduction in its erodibility. Hence, it may be concluded that the majority of the sediment load of 2.1.3.2. Sediment fluxes. On an annual basis, the these mountainous rivers is transported at the begin- principal riversŽ. Axios, Aliakmon, Pinios, Gallikos ning of the wet season; the streams subsequently provide, in total, some 25=106 tonnes of suspended carry less sedimentŽ i.e. there is less weathered mate- sediment and some 5=106 tonnes of dissolved load rial available for transportation. . Further, such inten- Ž.Table 2 . In addition, some 10±15% on the total sive transport may be expected to take place within sediment load could be attributed to bed load trans- only a few days, when floods occur in response to port inputŽ. Poulos et al., 1996a . Thus, the Ther- heavy rainfall andror sudden snowmelt in the moun- maikos coastal zone receives a cumulative input of tains. 25±30=106 tonnesryear. This amount is a large contribution, particularly when Milliman and Syvit- skiŽ. 1992 have estimated that some 350=106 2.2. Sub-aerial part of the coastal zone tonnes of suspended sediment is contributed by all rivers to the southern European coastline. However, The geomorphology of the sub-aerial part of the this latter estimation has not taken into account the coastal zone and adjacent areas is shown in Fig. 3. loads of the rivers discharging along the Greek coast- The coastal-land area of the Thermaikos Gulf Coastal line, which are considered to supply some 60±70= System accounts for some 2650 km2 Ž between 0 and 106 tonnes of suspended sediment loadŽ Poulos and 75 m in altitude, above sea level. , representing only Chronis, 1997. . 5.6% of the terrestrial part of the Coastal System. The high sediment yield of the Greek rivers Ž) The length of the associated coastline exceeds 350 500 tonnesrkm2 per year.Ž. is in response to: a the km. To the west, especially the southwest, the coast- intensive weathering processes, induced by the tem- line is bounded by high mountains with altitudes perate climatic conditions;Ž. b large daily and sea- )2000 m; its eastern part is bounded by lower sonal temperature fluctuations and relatively high relief, with topographic heights of between 300 m precipitation levels;Ž. c erodible lithology; Ž. d the and 1000 m. 54 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76

Fig. 3. Generalised topography and bathymetry of the coastal zoneŽ. excluding the drainage basins of the main rivers of Thermaikos Gulf ŽŽ.based upon a topographic map 1:500,000 , produced by the Hellenic Army Geographical Service in 1979 . and an adjacent bathymetric mapŽ. 1:50,000 .

2.2.1. Climate cipitation is some 480 mmŽ in the city of Thessa- The climate of the coastal zone of Thermaikos loniki. . The mean monthly variations in air tempera- Gulf can be described as a semi-arid Mediterranean ture and precipitation in Thessaloniki are shown in type, with rather cold winters. Air temperatures range Fig. 4. In addition, the climate of the Thermaikos between 08C and 388C, while the mean annual pre- coastal zone is affected by the wind regime. Northerly S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 55

Fig. 4. Mean monthly variation of air temperatureŽ.Ž.Ž after Flocas and Arseni Papadimitriou, 1974 a , precipitation after Angouridakis and Machairas, 1973.Ž. b , and annual distribution of wind speed and direction Ž after Livadas and Sahsmanoglou, 1975 .Ž. c , in the City of Thessaloniki. winds blow throughout the year and are enhanced The lithology of the coastal zone of Thermaikos during the winter; these are Balkan cold air masses Gulf and the surrounding area is summarised in Fig. Ž.named locally the Vardaris wind , originating from 5. The eastern coastline, from the Ak. Paliourion to the northrnorthwest and following the valley of the the City of Thessaloniki, consists mainly of Mio- Axios River. During the summer, the wind climate is PlioceneŽ. 10±1.8 My lacustrine to terrestrial de- dominated by the presence of the ``Etesians'';2 these posits, changing towards the south to marine de- blow from the northrnortheast and are relatively posits. The northrnorthwesterly coastline is formed strong Ž.)6mrs . When the ``Etesians'' are not by fluvial and deltaic deposits of Holocene age. The present, small-scale ``sea breezes''Ž. of 5±10 cmrs, western shoreline, between the Aliakmon and Pinios generated by differential heating between the land Deltas, is formed of recent to present Quaternary and the sea, blow from the south and the southeast. Ž.-1.8 My formations, consisting mainly of alluvial Overall, the northerly component of winds has the and fluvial deposits. The southernmost part of the highest frequency of occurrence during every month western coastline consists of limestoneŽ mainly of the yearŽ. Fig. 4 . dolomitic. , marbles, gneisses, schists, amphibolites and metamorphic schist±chest formations, of the 2.2.2. Geological setting Pelagonian zone of Triassic±Jurassic ageŽ 230±140 The Thermaikos Gulf system forms the north- My. . western continental margin of the Aegean Sea. The region is a back-arc area in relation to the Hellenic 2.2.3. Coastal geomorphology Arc-trench; it belongs geologically to the The topographic relief of the coastal land area AxiosrVardar and Pelagonian geotectonic zones and varies considerably and is controlled by a number of developed within the QuaternaryŽ. 1.8 My±present . interrelated factorsŽ. andror processes : the general The shoreline configuration has been developed dur- geological and tectonic evolution of the region, espe- ing the Holocene, following the termination of sea cially within the Quaternary; the underlying lithol- level rise some 6000 years BCŽ Piper and Perisso- ogy; climatic conditions and the associated weather- ratis, 1991. . ing processes; and the presence of various river networks. Within the context of a global distribution, the coastal zone under investigation, as part of the

2 coast of southeastern Europe, can be characterised The Etesians are northerly winds, associated with clear skies; Ž. they blow during the warm periodŽ. May±September , reaching after Carter, 1988 as a coastal plain developed on a occasionally gale force in strength Ž.)10 mrs . The mechanism wide continental shelf. It can be further distinguished of their generation is best explained by LascaratosŽ. 1992 . geomorphologically into:Ž. i deltaic Ž Holocene . 56 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76

tudes Ž.)2000 m of the nearby mountains and their hard lithological rock-typesŽ mostly metamorphic, of the Pelagonian Zone. . Along this cliffed coastline there are some pocket beaches, formed by local ephemeral streams. In addition, within the northern part of Sector I there is a coastal areaŽ. see Fig. 5 consisting of relatively low cliffs and a broad coastal alluvial plain; its presence is associated with an ephemeral stream, which used to connect theŽ artifi- cially dried, nowadays. Lake Boibis, with the open sea. In general, coastal Sector I is associated with large nearshore water depths Ž.)200 m , while it is exposed to long easterly wave-fetch distances. Sector II includes basically the sub-aerial deltaic plain of the R. PiniosŽ. Fig. 6 , formed by the fluvial deposits of the R. Pinios within the Holocene. The lobate-shape of its shoreline reflects the dominance

Fig. 5. Lithology of the coastal zone region of Thermaikos Gulf based upon a geotectonic map produced by the IGME, 1989. wKey: Q: recent to present formations; mainly alluvial deposits, fluvial deposits, fans, dunes, volcanic agglomerates; Q1: coastal, fluvial, deltaic and moved deposits; Pt: old alluvial deposits, scree, talcus cones and terraces, mainly of Pleistocene age; N: marls, mainly limestones, clayey marls, sands, sandstones, conglomerates of Neogene andŽ. locally Pleistocene age; Kp: limestones and dolomites of Pelagonian zone; Kto: limestones of the Olonos and Pindos zone; Ba: basic, ultra basic igneous rocks; Gn: sch± gneisses, amphibolites together with crystalline schists; and Mr: marbles, crystalline limestones and cipolinsx .

plains,Ž. ii alluvial Ž Quaternary . coastal lowlands; Ž.iii low cliffed coasts; and Ž. iv high cliffed coasts. The latter two categories often incorporate pocket beaches. Thus, on the basis of the aforementioned classification, the coastal zone of Thermaikos Gulf can be divided into different geomorphological sec- torsŽ. Fig. 6 , as described below. Sector I extends between Ak. Sepia, to the south, and the commencement of the R. Pinios delta, to the north. The region incorporates mostly high cliffs, Fig. 6. Schematic representation of the different geomorphological with slopes )10%, associated with the high alti- regions of the sub-aerial coastal zone of the Thermaikos Gulf. S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 57 of the marine processes, in relation to long windr deltaic coastal plain has been formed within the wave fetches and the deep bathymetry of the narrow Holocene, presenting a very low relief -0.25%. shelfŽ.Ž see Fig. 1 for further discussion, see below . . The coastal configuration of the deltaic plain, with a Section III is located between the northern end of bird-foot shape at the river mouths, indicates the the R. Pinios delta and the promontory Ak. Atherida, dominance of fluvialŽ. waterrsediment over marine towards the northŽ. Fig. 6 ; the latter is the natural Ž.Ž.waves, longshore currents processes see below ; boundary, along the western coastline, between the this is related to the shallow offshore waters Ž-25 outer and inner shelf of Thermaikos Gulf. The cen- m. and its exposure only to high waves, approaching tral and northern part of this coastal area represents a from the south. Further, the sedimentary material of coastal plain of low reliefŽ. slopes -1% ; it consists the R. Aliakmon is relatively finerŽ. sandy silts , of alluvial deposits of a number of ephemeral streams when compared with that of the R. AxiosŽ silty with the largest being MavroneriŽ with a catchment sand. . area of some 150 km2 . . The coastline is somewhat Sector VI incorporates almost the whole of the straight, being sandy and wider to the south. The eastern coastline of Thermaikos Gulf, extending from latter characteristic is indicative of northerly littoral the City of ThessalonikiŽ. Mikro Emvolo to the sediment transport, from the R. Pinios delta area. promontory of Ak. Kassandra. The region is charac- The southern partŽ. Fig. 5 of this sector is characterised generally as a low relief coastal plain, associ- terised by a narrow coastal plain, related to the ated with some low-cliffed areas; it can be sub-di- proximity of Mount OlympusŽ. 2800 m . vided further into the following sub-sectors. Sector IV forms the western coastline of the inner ()i Sub-sector VIa Žeast coast of Thessaloniki shelf of Thermaikos GulfŽ. or Thermaikos Bay , lo- Bay.Ž relates to a sheltered and shallow water -25 cated between Ak. Atherida and Methoni BayŽ at the m. embayment, with limited wave activity. This commencement of the R. Aliakmon delta. . The stretch of coastal zone presents a rather low relief coastal zone consists of a narrow coastal plain, ex- Ž.-1.5% . tending some hundreds of metres to landwards; it is ()ii Sub-sector VIb Žeast coast of Thermaikos associated with rather shallow water depths Ž-35 Gulf. extends between the cape of Megalo Emvolo m. and is exposed to limited wave fetch distances. and the promontoryŽ. sandy spit of Ak. Epanomi; it The coastal plain is interrupted by the presence of a is characterised generally by a relatively steeper 20-m high cliff, consisting of grey sandstone, con- relief Ž.;5% and rather shallow water depths Ž-40 glomerate, sands and marls; these are of Wurm±Ris- m.. sio in ageŽ. Faugeres, 1977 . Sedimentologically, the ()iii Sub-sector VIc ŽAk. Epanomi±Ak. Kassan- section is characterised by:Ž. i coarse material mostly dra. is characterised by coastal zone slopes of be- sands of local origin; andŽ. ii fine-grained material tween 2% and 5%, while the adjacent water depths Ž.mainly silts , allochthonous in origin. Coarse- exceed 80 m. grained sediments on the beach of Makriyialo origi- Sector VII is basically a cliffed coastline, extend- nate from weathering of the aforementioned Quater- ing between Ak. Kassandra and Ak. Paliourion, fac- nary cliff; this is supported by the presence of massif ing the open NW Aegean Sea and experiencing, and speckled type of augite, which is the erosional therefore, deep water conditionsŽ water depths)200 product of the aforementioned cliff. Conversely, the m. . Geomorphologically, it is a cliffed coast bounded silts may be attributed to the southerly transport of by a lower and more erodible mountainous lithology, fine-grained material from the mouths of the rivers when compared with that of the high-cliffed coastal Axios and Aliakmon; this is indicated by the pres- zone of Sector 1Ž. see Figs. 3 and 5 . ence of green and denticulate augite originating from the volcanic rocks of the R. Axios catchment area Ž.Chronis, 1981 . 2.2.4. Ground water Sector V forms the northrnorthwestern coastline The use of ground water is associated mainly with of Thermaikos Bay consisting of the deltaic plain of the irrigation of the extended agriculturalŽ mostly the Rivers Axios, Aliakmon and Gallikos. This deltaic. areas and the provision of water to the 58 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 population established in the coastal zone. Generally, 2.2.5. Coastline changes the aquifers of the deltaic plains are supplied by The most active parts of the Thermaikos coastal water from lateral infiltration of the main rivers. In zone are those related to the evolution of the river general, the supply of freshwater to the Thessaloniki deltas and the formation of sandy spits. The former deltaic plain is satisfactory after an extended irriga- is associated primarily to the riverine sediment fluxes, tion plan for the management of the water of the while the latter is a combination of the presence of riversŽ. Axios, Aliakmon and Gallikos . Some lo- headlands and the prevailing nearshore hydrody- calised problems, which have been occurred periodi- namic conditions. cally, are associated with the occurrence of long periods of relatively lower levels of precipitation 2.2.5.1. Deltaic coasts. The sub-aerial deltaic plains andror arbitrary human utilisation of the groundwa- of the rivers Axios, Aliakmon, Pinios, together with ter. Nowadays, diversion of the R. Acheloos into the those of the Gallikos and Mavroneri, form the most R. Pinios is being considered. Such a diversion and active part of the shoreline. In particular, the deltaic the subsequent surplus of freshwater would increase complex of the rivers Axios, Aliakmon and Gallikos the agricultural productivity of the Thessalia plain form the Thessaloniki plain, which is of great socio- Ž.the agricultural area surrounding the city of Larisa economic importance to Greece. and that of the Pinios delta. Historical evidence dating from the 5th century Hydrogeological investigations undertaken in the BC indicates the rapid progradation of the aforemen- Thessaloniki deltaic plain have revealed the presence tioned deltaic complex. At this time, the ancient of three different aquifersŽ Knithakis and Tzimour- towns of SkidraŽ. to the west and Pella3 Ž to the tas, 1987.Ž. : i a shallow phreatic aquifer, at about 10 north. were located originally adjacent to the sea. m depth and a thickness of 6±8 m;Ž. ii an intermedi- Nowadays, the city of Pella is located some 30 km to ate artesian aquifer, usually observed at between 40 the northwest of the present coastline. Southerly m and 60 mŽ.Ž. locally 30±80 m ; and iii a deep progradation of the deltaic complex plain, between artesian aquifer, lying at a 100±200 m depth. The the 5th century BC and today, is presented schemati- shallow phreatic aquifer receives water from the cally in Fig. 7. Furthermore, on the basis of the rivers, streams, rainfall and through irrigation activi- comparison of hydrographic chartsŽ Poulos et al., ties. The intermediate and deep artesian aquifers 1994. , it has estimated that only within the last 150 receive also water from such lateral water movement yearsŽ. between 1850 and 1987 has the coastal deltaic and as intake from the marginalŽ. highland areas plain of R. Axios prograded to seawards; this has surrounding the plain. Furthermore, the shallow produced new land, of the order of 175 km2. Simi- phreatic horizon is characterised by high salinisation larly, the R. Aliakmon deltaic plain has increased by and alkalisation, due to the marine origin of the some 140 km2. These values correspond to annual surficial sediments. Similarly, the intermediate arte- growth rates of 1.3 and 1.0 km2ryear for the rivers sian aquifer is not suitable for drinking, as it receives Axios and Aliakmon, respectively. Such deltaic sodium chlorate through infiltration of the surface progradation is associated with high sediment fluxes waters. The deep artesian aquifer exhibits satisfac- related to: the high relief of the hinterland area; and tory quality; it is used for domestic use by the relatively erodible lithology and climatic conditions habitants of the city of Thessaloniki and its suburbs. over the river catchment areasŽ implying intense Moreover, overpumping of the ground water in the weathering processes and high rates of sediment region of KalochoriŽ a few kilometers to the north- transport. . In contrast, the smaller deltaic plain and east of the mouth of the R. Gallikos. for supply of Ž.predicted lower progradation of the deltaic plain of the city of Thessaloniki, has enhanced the subsidence R. Pinios is attributed to the presence of deep waters Ž.some 2.5 m over the past 30 years of this part of in front of the river mouth. Further, the small the coastal deltaic plain. Such movement is in response to the natural compaction of the sedimentary sequences and the reduction in sediment load deliv- 3 The city of Pella was the capital of Macedonia, during the ered by the riverŽ. IGME, 1989 . reign of the Alexander the Great. S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 59

Fig. 7. The evolution of the Thessaloniki deltaic plain within historical timesŽ.Ž. since 500 BC after Konstantinidis, 1989 .

ephemeral rivers discharging along the Katerini peak discharges occur between late autumn and early coastline have controlled the formation of the low spring, while wave energy maximum occur between relief coastal alluvial plains. Similarly, along the mid-spring and mid-autumn. Thus, during the first Chalkidiki Peninsula, most of the beaches located in period, fluvial processes dominate the evolution of front of the low cliffs are related to the action of the deltas; at such times, progradation of the river ephemeral streams and longshore currents. mouth areas may be expected to occur. In summer, The evolution and the associated morphology of when the wave power is relatively higher and the the deltaic coastline, in the case of the essentially river discharge is at its lowest levels,Ž. marine wave tideless environment of the Greek waters, results activity becomes the dominated factor. However, the mainly from interaction between the waterrsediment low levels of wave activity mean that the resulting discharge and the prevailing wave activity. Thus, the longshore currents are not strong enough to redis- deltaic shorelines of the Rivers Axios and Aliakmon tribute the sediments deposited earlier; this results in are subjected to much lower monthly wave power the formation of the bird-foot shape of the deltaic Ž-30 Wrm2 .Ž than that of the R. Pinios 70±1454 coastline, which is similar to that of Mississippi Wrm2 .Ž Fig. 8 . . This pattern relates to the restricted Ž.Galloway and Hobday, 1983 . In contrast, in the wave fetches within the semi-enclosed and shallow case of the R. Pinios, the period of high water embayment of Thermaikos Bay; in contrast, the R. dischargeŽ. December to March coincides with that Pinios is exposed to long wave fetchesŽ Poulos et al., of high wave power. Hence, in this case, the fluvial 1993. . sediment input is likely to be reworked by waves and Moreover, the monthly distribution of water dis- associated longshore currents; this creates a lobate charge and wave power for the mouths of the Rivers shape to the deltaic coastline, which is similar to that Axios and Aliakmon is out of phaseŽ. Fig. 8 : the of the R. EbroŽ. Spain . 60 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76

in response to the limited wave-fetches. Thus, the northern section of the spit undergoes gradual small-scale changes. In summer, the southerly and southeasterly wind-induced waves are associated with very long fetchesŽ. hundreds of km ; these cause intensive longshore sediment transport along the southern part of the spit. Such transport causes substantial changes in the sub-bottom profile of the spit, especially following a storm. The differences in magnitude of the changes that take place to the southern and northern part of the spit are shown on Fig. 9. To the south, the difference between the winter and summer subaquous profile exceeds 4 m at a distance of 100 m to seawards; along the northern side, it is less than 1 m and is restricted to within a distance of -30 m. In addition, the summer sub- aerial profile along the northern beach has undergone only a minimal increase; along the southern side of the spit it has increased by almost 1 m. Seasonal variation in the hydrodynamical conditions, described previously, are reflected also by the granu- lometry of the spit: coarse materialŽ coarse sand, pebbles. is abundant along the southern side, while

Fig. 8. Seasonal variation of the incoming mean offshore wave power Ž.P and river water discharge Ž.D for the Rivers Axios, Aliakmon and PiniosŽ. after Poulos et al., 1993 .

2.2.5.2. Sandy spits. Along the coastline of Ther- maikos Gulf, there are a number of small or larger sandy spits; that of the Ak. EpanomiŽ. Fig. 9 is the largest and undergoing substantial seasonal changes. Such changes relate to the fact that the promontory of Ak. Epanomi forms the natural boundary between the inner Thermaikos shelfŽ characterised by shallow waters and limited wave fetches. and the outer Ther- maikos shelfŽ associated with deeper waters and long wave fetches, especially to the south. . The Epanomi sandy spit, formed initially on a Fig. 9. Physiographic characteristics of the Epanomi sand-spit and headland, is attributed to the action of a biomodal Ž. Ž. r seasonal changes in its subaquous northern A and southern B wind wave field. Northerly winds predominate dur- beach profilewx Key: Ð: summer profile; ---: winter profileŽ after ing winter inducing moderate sediment transport rates Chronis, 1981. . S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 61 fine-grained materialŽ. mostly fine sand dominates The outer shelf area covers a much larger area, about the northern sideŽ. Chronis, 1981 . 4000 km2. On the basis of the interpretation of bathymetrical and morphological characteristics of the seafloor 3. Oceanic part of the coastal system Ž.Lykousis et al., 1981 , the subaqueous part of the Coastal System can be divided into the following The oceanic part of the Coastal systemŽ 0±200 m physiographic regionsŽ.Ž. Fig. 10 : i the continental water depth. accounts for some 5100 km2 , represent- shelf area, which extends to the shelf breakŽ at about ing almost 10% of the total area of the Thermaikos 130 m water depth.Ž. ; and ii the continental slope Gulf Coastal System and approximately two third of which extends to the deep Sporades BasinŽ with the area bounded by the 75 m topographic contour water depths of up to 1200 m. . The shelf is divided and the 200 m isobath. The sector can be divided further into the inner Ž.-40 m and the outer shelf, further into:Ž. i the inner continental shelf, with while on the slope two distinctive regions are pre- water depths of -40 m, consisting mostly of Thes- sent:Ž. a the marginal plateau, defined by the 500 m saloniki and Thermaikos Bays; andŽ. ii the outer bathymetric contour; andŽ. b the canyon and valley shelfrshelf-break areaŽ. open Thermaikos Gulf , systems, which intersect across the slope. where water depths lie between 50±200 m. Thus, the inner shelf areaŽ. subaquous part of the coastal zone 3.1. Oceanographic setting covers an area of 1100 km2, representing 21% of the oceanic part of the Coastal System and almost the 30% of the total area of the coastal zoneŽ. Table 1 . 3.1.1. Water masses The properties of the seawaters within the Ther- maikos Gulf Coastal System vary seasonally, following corresponding variations in air temperature, freshwater inputs, wind climate and the general circulation and mixing of water masses. Within the inner shelfŽ. Thermaikos Bay , the surface water temperatures vary between 258CŽ. summer and 98C Ž.winter : surface salinity are 35 psu and 28 psu during summer and winter, respectively. Near-bottom water temperature and salinity values are generally more stable throughout the year, at around 218C and 36 psu in summer and 98C and 38 psu during winterŽ. Robles et al., 1983 . An extended hydrological survey undertaken in June 1987, involving 85 CTD stations and incorporating the whole of the deep water part of the Thermaikos SystemŽ. Durrieu de Madron et al., 1992 , has revealed the existence of the following water massesŽ.Ž. Fig. 11 : i surface waters Ž.Ž. SW -40 m , with T)13.58C and high spatial variability in salinity, due mainly to the presence of the rivers Ð within the upper part of the SW, a thermocliner halocline layer is present, at depths of around 20 m; Ž.ii shelf bottom waters Ž SBW . over the continental Ž.) Fig. 10. Physiographic regions of the subaquous part of the coastal shelf water depths 40 m and, especially, near to zone of the Thermaikos Gulf Coastal SystemŽ after Lykousis et the sea bedŽ. 80±120 m Ð these are cold Ž T- al., 1981. . 12.58C.Ž. and of low salinity S-38.6 psu and their 62 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76

analyses of the tides within the Thessaloniki Bay have revealed the following amplitudes and phases Ž.Ž.Ž.Tsimplis, 1994 : M2 9 cm, 788 ; S2 6.1 cm, 988 ; K1Ž.Ž. 2.6 cm, 3578 ; and O1 1.3 cm, 3288 . Finally, records of restricted duration of water level fluctuations have attributed to strong sea breezes from the southŽ. short period oscillations and to rapid changes of barometric pressureŽ. long period oscillations Ž.Wilding et al., 1980 . Within such an essentially tideless environment, water movements are governed by the thermohaline circulation, mixing of different water masses and the prevailing wind climate. It has been observed generally that more saline, clearŽ. free of suspensates and Fig. 11. TemperatureŽ. potential ±salinity diagram of the different relatively dense waters, which originate from the water masses of Thermaikos GulfŽ after Durrieu de Madron et al., 1992. .w Key: SW: surface waters; SBW: shelf bottom waters; TW: open waters of the north Aegean Sea, enter the outer transitional water mass; SSW: sub-surface water mass; DW: shelf of Thermaikos Gulf over the central and east- deep-water massx . ern part of the plateau; then they turn towards the northeast flowing parallel to the Chalkidiki Penin- sula, finally entering the inner Thermaikos BayŽ Fig. 12a.Ž. . Conversely, fresh less saline waters flow density varies between 29.26 and 29.34;Ž. iii a transi- towards the south, along the western coastline. This tional water massŽ. TW near the shelf break and over southerly flow consists of water discharges from the the deep basin, at between 100 m and 200 m of the upper part of the water column Ð this appears to be of relatively constant densityŽ. 29.28"0.02 , despite the significant variations in both temperature and salinity;Ž. iv a sub-surface water mass Ž SSW . observed between water depths of 200±600 m Ð here, the temperature decreases, with depth, from 13.38C down to 12.68C, while the salinity is reduced slightly from 38.83 to 38.70 psu;Ž. v a deep water mass Ž.DW extending below 600 m and up to 1000 m within the water column, having temperatures of 12.7"0.018C, salinities 38.7±38.8 psu and a density increasing slightly with depthŽ from 29.34 to 29.38 psu. .

3.1.2. Water moÕement Thermaikos Gulf, as part of the northern Aegean Sea, is a microtidal marine environment. Recent analyses have shown that the major semi-diurnal constituents M2 and S2 rarely exceed 10 cm and 7 Fig. 12.Ž. a General circulation patterns of the surface waters of cm, respectively. Similarly, the major diurnal tidal Thermaikos GulfŽ.Ž after Balopoulos et al., 1987 , RRS Discovery .Ž. Ž . Ž constituentsŽ. K1 and S1 presently are of exception- Cruise 137 ; b shallow solid vectors and deep-water open vectors.Ž circulation patterns of the inner shelf Thermaikos and ally small amplitudes around 2.7 cm and 1.7, respec- Thessaloniki Bay.Ž after Ganoulis, 1987 . .w Key: v: current meter tivelyŽ. Tsimplis et al., 1995 . Moreover, harmonic stationsx . S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 63

Table 4 Current meter observations in outer Thermaikos GulfŽ. RrV DiscoÕery,5±6r83 Station Currents D Ž.Ž.m Z m -1.7a Ž. % Minimum Ž. cmrs Maximum Ž. cmrs Mean Ž. cmrs Direction Ž.8 Surface CM 1 75 50 20 -1.7 15.8 6.5 170 CM 2 85 50 27 -1.7 13.0 6.5 80 CM 3 105 95 40 -1.7 18.9 9.3 335

Bottom CM 1 75 5 32 -1.7 8.2 4.2 125 CM 2 85 5 01 -1.7 8.8 5.0 145 CM 3 105 5 32 -1.7 7.1 4.0 135

a Current meter's rotor threshold value; D: water depth; Z: distance above seabed.

Rivers Axios and Aliakmon, together with an addi- moves in the opposite directionŽ. northwards in the tional input from the R. Pinios, farther to the south. case of S±SW windsŽ. Ganoulis, 1987 . During the Moreover, this southerly movement of surface waters presence of a persistent northerly wind, the general is particularly enhanced during winter, due to the surficial flow throughout the whole embayment is prevailing northerly windsŽ. see above and the in- towards the south. The presence of a gyre, charac- creased river water dischargesŽ.Ž February±July Fig. terised by turbid waters, in the western part of the 2. . Similarly, the dominance of the southrsouthwest- Bay has been also identified in satelliteŽ. LANDSAT erly sea breezes, in summer, move water masses imageryŽ. Balopoulos et al., 1986 . from the central and eastern part of the Gulf towards the innermost part of the embayment. 3.1.3. WaÕe actiÕity Measurements of surficial currents are in accor- Wave heights, and especially the direction of dance with the circulation pattern described above, wave propagation, is governed by the existing wind although the directions are somewhat variable. In regime; this is demonstrated clearly by the wave and contrast, near-bed current measurements, obtained wind roses presented in Fig. 13. Waves related to during different seasons, have shown that there is a southerly winds are considered to be the most impor- general and southerly persistent movement of bottom tant in terms of their magnitude; these are associated waters over the shelf; this continues down the slope with the longest fetches Ž.;170 km . Hence, high and along the main submarine valleyrcanyon sys- waves of long wavelengthŽ. swell are to be expected tems towards the Sporades BasinŽ Poulos and Pana- giotopoulos, 1997. . Such water movements are indicated by observations obtained from the outer shelf Ž.Žwater depths )50 m in May 1983 RrV DiscoÕ- ery.Ž.and June 1987 RrV Aegaio . Current speeds are in the order of 5±20 cmrs near the water surface and up to 9 cmrs near the seabedŽ. Table 4 . In particular, surface water circulation over the inner shelfŽ. water depths -40 m is influenced strongly by the prevailing wind conditions. On the basis of a depth-integrated hydrodynamical model, a 2-gyre systemŽ. Fig. 12b is considered to be estab- Fig. 13. Wave and wind roses relating to Outer Thermaikos Gulf lished in Thermaikos Bay. Water moves south along and the Sporades basin areaŽ abstracted from Athanasoulis and the east and west coastline, under N±NW winds; it Skarsoulis, 1992. . 64 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76

outer shelf, primarily within the Sporades Basin, is characterised by a mean annual wave height of 0.5± 0.7 m. The frequency of occurrenceŽ. % , for different wave heights Ž.H on an annual basis is as follows: H-1 mŽ. 80% , H-2 m Ž. 95% , H)3m Ž.1% , and for H)4 m Ž.Ž 5% Athanasoulis and Skarsoulis, 1992. .

3.1.4. Nutrients The aquatic environment of Thermaikos Coastal System is characterised, in general, by high nutrient concentrations throughout the year. Especially in the inner shelf areasŽ. A±C; for locations see Fig. 14 , Fig. 14. Schematic representation of the water masses, of different nutrient concentrations, of the inner Thermaikos shelf:Ž. A Thessa- nutrients are present at levels well above the back- loniki Bay;Ž. B northwestern Thermaikos Bay; Ž. C southeastern ground values referred to the open Aegean SeaŽ Ta- Thermaikos BayŽ. after Balopoulos and Friligos, 1993 . ble 5.Ž ; most of the ratios meanrbackground values . are )2, while in some cases they exceed 4Ž Bal- opoulos and Friligos, 1993. . Furthermore, phosphate, only from southerly directions. In contrast, the ammonium and nitrate values are higher in Thessa- northerly components of the wind spectrum have a loniki BayŽ. Area A , than in Thermaikos Bay Ž Areas high frequency of occurrence; despite their smaller B and C. ; this is attributed mainly to the detergents fetches, they generate surface gravity waves influ- supplied from the existing sewage outfall of the city encing, consequently, the general water surface cir- of Thessaloniki and the relatively small amounts culation of Thermaikos Gulf. The wave field of the provided by the river inputs. Ammonium and nitrate

Table 5 Mean annual nutrient concentrationsa Ž. water column averages in mM in inner Thermaikos Gulf 3y 4yqy PhosphateŽ. PO44 Silicate Ž SiO . Ammonium Ž. NH 43 Nitrate Ž. NO Area Ab Max 0.84Ž. Su 6.02 Ž. Sp 2.13 Ž Au . 1.56 Ž Au . Min 0.35Ž. Sp 0.98 Ž Au . 0.54 Ž. Sp 0.67 Ž. Sp Mean 0.53 3.08 1.46 1.17 Ratio 4.4 2.5 4.1 2.8

Area B Max 0.30Ž. Su 4.69 Ž. Wi 1.86 Ž. Au 2.04 Ž. Wi Min 0.21Ž. Sp 3.62 Ž. Sp 0.50 Ž. Sp 1.14 Ž. Sp Mean 0.25 4.32 1.04 1.49 Ratio 2.1 3.5 2.9 3.5

Area C Max 0.15Ž. Au 4.90 Ž. Sp 1.38 Ž. Au 1.13 Ž. Sp Min 0.13Ž. Su 1.03 Ž Au . 0.44 Ž. Su 0.72 Ž. Su Mean 0.14 2.77 0.71 0.90 Ratio 1.2 2.3 2.0 2.1 Aegean Bgdc 0.12 1.22 0.36 0.42

a Concentrations values represent integrated mean nutrient values taken for the whole water column of all the stations of each physiographic area during five successive oceanographic cruisesŽ.Ž Nov. '75, Feb. '76, May '76, Aug. '76 abstracted from Balopoulos and Friligos, 1993. . bGeographical locations of Areas A±C are shown in Fig. 14. c Typical concentration values of the Aegean SeaŽ. after Friligos, 1981 . S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 65

Ž.the oxidation product of ammonium maxima occur rily, to coastal erosion in response to wave and during the autumn, due to the faster rate of decompo- current activity; their seaward dispersion is associ- sition of organic compounds. The northwestern part ated with the general water circulation patternŽ as of Thermaikos Bay hosts the highest silicate values described previously. . In general, most of the sus- throughout the year, as it is influenced mostly by the pended sediment is transferred and accumulates to- discharges of the rivers Axios and Aliakmon; in- wards the south; this influences the development of creased silicate levels coincide with periods of high the seabed sedimentary cover over the inner shelf river dischargesŽ. Dec.±May . Phosphate and ammo- and, primarily, the western part of the outer shelf. nium increased levels are usually observed within In particular, the plumes of the Rivers Axios and the Thessaloniki BayŽ. Area A . The comparatively Aliakmon overlie most of the inner shelfŽ Ther- low nutrient levels observed in the eastern part of maikos Bay. , on an annual basis; this is shown Thermaikos Bay is explained by the general water schematically by the distribution of the lower-salin- circulation, with clearer and oligotrophic Aegean ity surface watersŽ. Fig. 15a . Thus, during winter Waters to entering Thermaikos Gulf along its eastern and spring when the riversŽ. Axios and Aliakmon are coastlineŽ. see above . at their highest discharge levels, the 34 psu isohaline During a recent surveyŽ. Dec. 1995±Mar. 1996 , contour is forced by up to 10 km to the southeast, the mean nutrient concentrations of the water masses away from the river mouths. Similarly, the disper- of the inner part of Thessaloniki Bay was found to sion of the R. Pinios plume indicates the influence of be slightly increasedŽ PO444 : 0.85; SiO : 4.1; NH : the riverine sediments over the western and central 2.4. over the earlier levels, with the exception of part of the outer shelfŽ.Ž. Thermaikos Gulf Fig. 15b .

NO3 Ž.Ž 0.8 after Psylidou Giouranovits et al., 1998 . . Hence, river plumes overlie almost the whole of Thermaikos Bay and most of the inner continental shelf area. 3.2. Sedimentology Suspended particulate matterŽ. SPM is present not only in the surface waters, but relatively high SPM 3.2.1. Suspended sediment( riÕer plumes and neph- concentrations are presented as nepheloid layers as eloid layers) well, near the sea bed and at intermediate levels The presence of suspended sediments within the within the water column. Indeed, measurements un- Thermaikos Gulf Coastal System is related primarily dertaken during a period of low river discharge to the riverine waterrsediment inputs and, seconda- Ž.early July 1987 , over the whole of the study area,

Fig. 15. River plume dispersion seawards:Ž. a the river mouths of the Axios, Aliakmon, Gallikos, based upon the seasonal pattern of the salinity contour of 34 psuŽ.Ž.Ž modified from Poulos et al., 1996a,b ; and b the mouth of R. Pinios, as shown by the isopycnal contours after Balopoulos et al., 1993. .wx Key: Au: August; No: November; Fe: February; and Ap: April . 66 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76

300 and 600 m; finally, Area 5, which covers the northeastern part of the Sporades Basin Ð characterised by the presence of low surface turbidity values and the absence of intermediate and near-bed nepheloid layers. In general, Areas 3, 4 and 5 con- tain surface turbidity concentrations in the order of 0.4±0.5 mgrl. Higher values of SPM are expected to occur during the beginning of the wet seasonŽ De- cember±February.Ž and following flood events as discussed previously. . In general, the surface nepheloid layers are associated to the river waterrsediment outflows and to localised coastal erosion phenomena. The mechanisms of formation of intermediate nepheloid layers are related to the stratification and general circulation of the water masses, while nepheloid layers observed near bed are attributed to associated current activityŽ which either inhibits settling or causes resuspension. .

3.2.2. Recent sea bed sediments

3.2.2.1. Grain size. On the basis of sedimentological analysesŽ. sediment texture and composition undertaken by various investigatorsŽ Chronis, 1986; Lyk- Fig. 16. Regions of relative presence of surface, intermediate and ousis et al., 1981; Lykousis and Collins, 1987; Lyk- near bed nepheloid layersŽ. after Chronis et al., 1987 , with ousis and Chronis, 1989. , the surface sediments of representative profiles of suspended matterŽ. transmisometry from the Thermaikos Gulf marine sub-system have been Thermaikos Gulf and the adjacent Sporades Basinw Note 100±200 classified broadly into four major sedimentary ( r x mFTU 0.3 mg l. provincesŽ.Ž SP Fig. 17 .Ž. : i western shelf muds and

have revealed the presence of surficial, intermediate and bottom nepheloid layers. According to the spatial distribution and vertical location of these layers, five different areasŽ. Fig. 16 have been identified by Chronis et al.Ž. 1989 and Durrieu de Madron et al. Ž.1992 : Area 1 Ð influenced strongly by the river outflows, with surficial and bottom nepheloid layers presentŽ. concentration C)0.8 mgrl; Area 2 Ð associated with lower values of suspended matter Ž.-0.8 mgrl , within both the surficial and bottom nepheloid layers, while the latter appear not to be in direct contact with the sea bed; Area 3 Ð located over the slope and containing benthic nepheloid layers, with concentration up to 0.6 mgrl; Area 4 Ð associated with weak intermediate nepheloid layers Fig. 17. Sedimentary provincesŽ. 1 to 4 of the sea bed of the Ž.C(0.25 mgrl , lying in water depths of between Thermaikos GulfŽ. after Lykousis and Chronis, 1989 . S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 67 sandy muds;Ž. ii eastern shelf muddy sands; Ž iii . between 60% and 85%; this includes the relatively outer shelf-shelf break sandy clays and clayey sands; narrow band along the eastern shoreline of the inner andŽ. iv slope-basin muds. part of the shelfŽ Thermaikos Bay and Thessaloniki Sedimentary province 1Ž. SP-1 covers the western Bay. . The mechanisms of sedimentation are associ- part of both the inner and outer shelf, where sedi- ated with the absence of surface turbid waters andror mentation processes are dominated by the nepheloid layers, and the general northerly move- waterrsediment outflows of the major riversŽ Axios, ment of sediment-free open seawaters. Lykousis and Aliakmon, Pinios. and other ephemeral streams along ChronisŽ. 1989 have found that the proportion of the western coastline of Thermaikos GulfŽ see Fig. sand increases generally towards the eastern coast- 1. . River plumes transport seaward large quantities line; here, it is believed that there are most of the of suspended sediments; then, these are deposited sources for the coarse-grained terrigenous sediments, through gravitationalŽ. differential settling and provided by the easily erodible Neogene rocks of the physicochemicalŽ.Ž flocculation processes Poulos et coastal zone. The silt content is less than 20% and al., 1996b. . Coarser material is deposited closer to 40%, over the outer and inner shelf, respectively; the the river mouths, with the finer-grained sediments clay content is, in general, -20%. Differential set- farther offshore. MudŽ. siltrclays1:1 is the domi- tling appears to be the principal mechanism control- nant sedimentary material present, having a mean ling sediment deposition, with the coarser material grain size of 0.01 to 0.02 mm. The sand fraction of deposited nearer to the coastline. The low mud con- the deposits is generally 20% of the whole, being tent and its relatively high mean grain size Ž-0.03 terrigenous in origin; this is indicated by the rela- mm. is related to the fact that the sediment-laden tively lowŽ. about 25% carbonate content at the river plumes do not extend over the eastern part of sediments. The carbonate-free sand fraction is 0.18± the shelf, with the exception of some fine-grained 0.125 in size. The clay fraction consists mostly of material originated from the R. Pinios during peak the clay minerals illite Ž.)50% and smectite Ž) river discharges. 40%. . Sedimentary province 3Ž. SP-3 includes the south- Southerly movement of these sediments is in- ern part of the outer shelf, most of the shelf break duced by the water circulation, while the higher area and part of the marginal plateau. The Province levels of finer-grained sedimentsŽ. clay over the reveals the most complicated sedimentary pattern, in southern part of the inner Thermaikos Plateau is terms of both texture and composition; this reflects related to the presence of an anticlockwise gyre the complicated hydrodynamic conditions that usu- Ž.Balopoulos et al., 1986 . Near-bed nepheloid layers ally prevail at shelf breaks. The sand fraction varies are present over this region, indicating the abundance at between 35% and 90%; this consists partially of of suspended material and the action of near-bed terrigenous and partially of biogenic origin. Thus, current activity; this inhibits the rapid deposition of the mean size of the ``untreated'' sand fraction in the the suspensates. Elsewhere, observed current veloci- analyses is much greaterŽ. 0.35±0.18 mm than after ties are lower than 10 cmrsŽ Poulos and Pana- treatmentŽ. 0.12±0.18 mm ; this is due to the pres- giotopoulos, 1997. ; these, together with a series of ence of shell fragments. The silt and clay content photographs of the sea bedŽ Lykousis and Collins, varies between 2% and 25% and from 5% to 45%, 1987. are not indicative of any erosional processes respectively, while the mean size of mud fraction is of the sea-floor. Further, in response to the high 0.015±0.03 mm. In addition, high percentages of sedimentation rateŽ especially in the western part of sandŽ. 60±90% are present in the sediments of the the Province. , there is evidence of only minimal southern and southeastern part of the outer shelf, in bioturbation. water depths of 90±110 m. The well-sorted and Sedimentary province 2Ž. SP-2 covers the eastern well-rounded character of the sand grains, in combi- part of the shelf, with the sand fraction dominating nation with the presence of large amounts of heavy the sediment coverŽ. with percentages )50% . The minerals, leads to the conclusion that these deposits Province includes the eastern half of the outer shelf represent relict sands deposited during the late glacial Ž.Thermaikos Gulf , where the sand content varies at periodŽ.Ž WurmÈ Lykousis and Chronis, 1989 . . 68 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76

The biological texture of the seabed is conducive to the presence of hemipelagic sedimentation processes. Similarly, the very low amounts of material deposited are indicated by the presence of relict sandsŽ.Ž Lykousis and Chronis, 1989 as discussed previously. . Intensive benthic activity over parts of the outer shelf is indicative of well-oxygenated near- bed waters which, in combination with burrowing activityŽ. as indicated by the sea bed photographs , may contribute significantly to the action of diage- netic processes within the sediment depositsŽ Lykou- sis and Collins, 1987. . On the other hand, vertical turbidity profiles of this region have revealed the presence of an intermediate nepheloid layerŽ 350±450 m. extending towards the Sporades Basin; this layer indicates water movements related to current activity Fig. 18. Isopleaths of deltaic accumulations within the Holocene, or the presence of internal waves. Further, seabed in the Thermaikos Gulf Coastal SystemŽ after Lykousis and photographs obtained from the canyon floor reveal Chronis, 1987. . some erosion of the seabed sediments; this has been attributed to high near-bed current activity. Holocene, of the order of 3 mrka near to the river Sedimentary province 4Ž. SP-4 covers the lower mouths and 0.5±0.2 mrka over the prodelta area. reaches of the continental slopeŽ extending to the The thickness of the Holocene sequence in the deep Sporades Basin. and is distinct in its sedimentary Ž.Sporades basin is much less, being 1±2 ms; this character. The sediment cover consists almost en- corresponds to a mean sedimentation rate of 0.05± tirely of material of biogenous origin, as indicated by 0.15 mrkaŽ. Lykousis and Chronis, 1989 . Similar the high carbonate contentŽ. 40±45% ; this is related thickness of Holocene cover have been reported for to the relatively high coccolith composition of the the offshore areas of other Mediterranean river sys- mudsŽ. mean grain size 0.005±0.01 mm and to the tems, e.g. RhoneŽ. 30 ms , Ebro Ž. 20 ms and Po entirely biogenous sand fractionŽ Lykousis et al., Ž.Ž.20±30 ms Chronis et al. 1991 . 1981.Ž . Clay is the dominant constituent with percentages between 55% and 70%. , followed by silt 3.2.2.2. Trace metals. Coastal sediments are impor- Ž.from 30% to 40% ; the sand fraction is generally tant materials for the storage of pollutant elements of - very low Ž.5% . Seabed photographs reveal the anthropogenic origin. Thus, the higher non-residual4 presence of biological activity, in a tranquil environ- concentrations of trace metals in the surficial sediment free from suspended matter; this indicates the ments observed in the northwestern part of inner absence of near-bed currents and oxygenation of the Thermaikos Bay and in Thessaloniki Bay, when deepwater massesŽ. Lykousis and Collins, 1987 . compared with the values of the open Aegean Sea Thus, the very low percentageŽ. if not the absence of Ž.Table 6 , have been considered as the ``anthropo- very fine-grained sediments here is indicative of the genic fingerprints'' on the bottom depositsŽ Chester fact that most of the terrigenous sediments are de- and Voutsinou, 1981. ; these are related to agricul- posited within the coastal zone of Thermaikos Gulf. tural, industrial and urban activities. This assumption Holocene sequences cover most of the inner shelf is strengthened by the observation that the values of and a large portion of the western part of the outer shelfŽ. SP-1 . The thickness Ž in milliseconds of two- way travel time. of the outer deposit reaches 30 ms 4 close to the river mouths; this thins to 2±5 ms at Non-residual trace metals are not part of the silicate matrix; ) they have been incorporated into the sediment from aqueous distances 15 km to seawardsŽ. Fig. 18 . This pat- solution by processes such as adsorption and organic complexion tern implies a mean sedimentation rate, during the Ž.the latter includes those originating from polluted waters . S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 69

Table 6 ConcentrationsŽ. ppm of non-residual trace metals in the surface sediments of inner Thermaikos GulfŽ Thessaloniki Bay, northwestern Thermaikos Bay and southeastern Thermaikos Bay. Thessaloniki Bay NW Thermaikos Bay SE Thermaikos Bay Aegean Sea No. of samples: 5abaa 12 18 5 12 c Mn Min 554 535 602Ž. Ga 204 Max 1118 1322 1853Ž. Al 845 Av 787.6 826 1125.6 408.6 280 Ni Min 36 76 53Ž. Ax 35 Max 48 115 160Ž. Al 77 Av 44.2 95 79.7 52.8 28 Co Min 12 13Ž. Ax,Ga 7 Max 14 20Ž. Al 13 Av 13 14.7 9.5 Cr Min 61 196 61Ž. Ax 31 Max 107 265 103Ž. Al 96 Av 76 221 75.8 52.8 Cu Min 20 57 20Ž. Al 4 Max 37 162 31Ž. Ax 14 Av 26.2 79 23 9.6 13 Pb Min 60 46 40Ž. Al 13 Max 228 113 112Ž. Ax 38 Av 123.4 64 69.4 27.8 38 Zn Min 92 193 53Ž. Al 23 Max 158 549 299Ž. Ax,Ga 50 Av 120.8 296 102.2 31.2 45 Cd Min nd 0.55 ndŽ. Ga nd Max 1.4 4.59 3.0Ž. Ax 0.29 Av 0.54 1.33 0.7 0.06 nd: not detected; Ax: R. Axios; Al: R. Aliakmon; Ga: R. Gallikos. aAfter Chester and VoutsinouŽ. 1981 . bAfter Anagnostou et al.Ž. 1998 . cAfter Smith and CronanŽ. 1975 . trace metals, measured in 1979 by the above men- ppm. is distributed more evenly within northwestern tioned authors, has been found by Anagnostou et al. Thermaikos Bay and Thessaloniki BayŽ where it is Ž.1998 to have increased during the field campaign found to have its maximum value. . Similarly, Co and in 1995.5 Cr concentrations do not vary substantially within The highest non-residual concentrationsŽ after the aforementioned regions; their highest values of Chester and Voutsinou, 1981.Ž of Cd 1.4 ppm . , Pb 20 ppm and 107 ppm have been observed near the Ž.228 ppm and Zn Ž. 158 ppm have been observed mouth of R. Aliakmon and within Thessaloniki Bay, Ž.primarily in the sediments of inner Thessaloniki respectively. BayŽ.Ž Table 6 . Mn 1853 ppm . and Ni Ž 160 ppm . are The spatial distribution of the trace metal concen- more abundant over the northwestern part of inner trations shows clearly that the abundance of Cu, Pb, Thermaikos Bay, with their highest values close to ZnŽ especially close to the mouths of R. Axios and the mouth of the R. Aliakmon. Further, Cu Ž)95 R. Gallikos. may be attributed to anthropogenic sources, i.e. domestic sewage, together with industrial discharges. In contrast, the lowest values of 5 Some difference in the values of trace metals between the two these trace metals are found near the mouth of the R. investigations might be attributed to the different analytical meth- Aliakmon; the latter observation, combined with a ods used. relative abundance of Mn, Ni, Co and Cr in the 70 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76

Fig. 19. Schematic representation of the existed infrastructure and the various human activities along the coastal zone of Thermaikos Gulf. region, indicates their relationship to the petro- mean value for Greece is only 77.7 inhabitantsr graphic character of the surrounding catchment area, km2. The region of Chalkidiki is characterised by a as it drains a generally non-industrialised region. relatively low-density populationŽ some 30 inhabi- tantsrkm2 . ,6 while the eastern coastal zone of inner Thermaikos Gulf has 77 inhabitantsrkm2 Ž a figure 4. Socio-economic activities and their environ- close to the average value for the whole country. . In mental impact contrast, the eastern coast of the outer Thermaikos Gulf is the most rare populated area with -15 4.1. Socio-economic actiÕities inhabitantsrkm2. More than 1000 industrial units which occupy The coastal zone of Thermaikos Gulf Coastal some 50,000 employees are established in the county System is of great socio-economical importance, as of Thessaloniki; amongst these, the 35 largest are a more than one-tenth of the total population of Greece refinery, a steel mill, a canning factory, paper-mills Ž.10.5 million inhabitants live here. Most of this and chemical and cement industries. This industrial population is concentrated within the county of the activity accounts the 31% of the 26% of the GNP of City of Thessaloniki, having almost 1 million inhabi- Greece attributed to industry, in 1994.7 Furthermore, tants and being the second metropolitan centre of tourist activities are taking place along the coastline Greece; likewise, it is one of the largest in the of Chalkidiki, Pieria and some parts of the eastern southern Balkans. This region incorporates significant agricultural, industrial, tourist and tradeŽ including services.Ž. development Fig. 19 . Hence, the 6 Source: National Statistics Service of GreeceŽ. census 1991 . county of Thessaloniki presents a high figure of 7 Source: EPILOGIŽ The Greek Economy 1997 Ð The Coun- 2 density populationŽ 270 inhabitantsrkm. , while the ties of Greece.Ž in Greek . . S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 71 shoreline of Thessaloniki Bay. Such activities in- of the Rivers Aliakmon and Axios. Thus, the R. volve a great number of hotels and pensions, includ- Axios incorporates 13 dams along its lengthŽ 12 ing commercial shops and entertainment facilities. outside the Greek boarders and one within Greece at Such villages are host to a seasonalŽ. summer popu- a distance less than 30 km from its mouth. ; likewise, lation of over 45,000 touristsŽ Georgas and Perisso- the R. Aliakmon contains four main hydroelectric ratis, 1993. . dams. Low-lying land areasŽ including the Thessaloniki deltaic plain. , subjected to reclamation and subse- 4.2. Human impact on coastal enÕironment quent soil improvements during the past 50 years, are some of the most productive agricultural lands in Greece. Thus, the agricultural productionŽ. in tonnes Anthropogenic activities within the coastal system of the coastal plain area, relative to the total produc- of Thermaikos Gulf have initiated deviations to the tion of the Thessaloniki districtŽ percentage in brack- natural evolution of the terrestrial and aquatic r ets.Ž for various crops, was Prefecture of Thessa- ecosystems. Thus, the reduction in water sediment loniki, 1986.Ž. : rice Ð 76,000 100% ; sugar beet Ð fluxes to the coastline, due to the construction of 27,400Ž. 81% ; cotton Ð 31,600 Ž. 80% ; and cereals dams for electricity generation and irrigation pur- Ð 48,400Ž. 21% . Also, in the county of Thessa- poses, has initiated degradation of the coastal zone. loniki, there is a huge level of cultivation of maize, In addition, eutrophication and pollution of the tomatoes and tabacco. Hence, the agricultural activi- aquatic environment have occurred, in response to ties of this region represent one-third of the 12%Ž in the untreated flow of fertilisers, agrochemicals, in- 1994. of the GNP attributed to the agriculture. In dustrial and domestic sewage. Moreover, future cli- Ž. addition, aquacultureŽ especially that related to mol- matic changes related also to the `Greenhouse Ef- lusc production. flourishes along the Thermaikos fect' and associated with a predicted increase in air Bay; this produces, annually, some 1000±2000 temperature and sea level, could cause large-scale Ž. tonnes of oysters and molluscs. It has to be empha- changes with radical consequences within the Ther- sised that this region produces about 80% of the total maikos Gulf Coastal System. mussel production of Greece, accounting for some 27,000 tonnes in 1996; the latter corresponds to 4.2.1. Reduction in riÕer waterrsediment fluxes 3.5% of the total annual production of the E.U.8 During the past 50 years, the reduction in water The infrastructure that supports the various and sediment fluxes, in response to the dam con- socio-economic activities involves a well-developed struction along the route of the Rivers Axios and transportation network; this includes railways and Aliakmon, has affected considerably the evolution of motorways, which are under further development their deltaic coastal zones. Thus, the growth of these Ž.e.g. Egnadia motorway with the objective of con- deltas has effectively ceased, while abandoned parts necting the southern Balkan countries to the Aegean of the deltaic plain are subsiding due to compaction Sea, and the eastern countriesŽ. e.g. Turkey with the of the sedimentary sequencesŽ. Poulos et al., 1994 . Ionian Sea. Finally, air transport is served by Mikra The latter phenomenon is more pronounced in the Airport, while the Port of Thessaloniki is one of the area between the old mouths of the R. Axios and R. largest in the eastern Mediterranean; the total annual Gallikos, where some 90 km2 of land has been cargo load here is in excess of 10 million tonnes. subjected to floodingŽ. IGME, 1989 . This process Among this infrastructure is also the installation of a has been enhanced by overpumping of the deltaic biological treatment of urban sewage, expected to be groundwater, to meet the needs of the City of Thes- in full operation within 1999, together with a series saloniki, and the extended abstraction of aggregates of hydroelectric and irrigation dams along the courses from the lower route of the R. GallikosŽ for the construction industry. . Further, the drastic reduction in water discharge, andror disturbance of its natural seasonal flow regime depletes the supply of river 8 Source: Alieftika Nea 12r96Ž. magazine, in Greek . water to the sub-surface aquifers; this, in turn, leads 72 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 to the intrusion of saline water into the sub-surface global scale, could cause large-scale changesŽ with parts of the plains, deteriorating the phreatic water radical consequences. within the coastal zone of the and soil qualityŽ. as discussed in Section 2.2.4 . Thermaikos Gulf area. Thus, a possible climatic shift Finally, any reduction in surface freshwater flow towards more arid climatic conditionsŽ with longer reduces the ability of the rivers to carry and dilute summers and lower precipitation levels. will have a waste materials, increasing the possibility of occur- series of environmental impacts, such as: degrading rence of pollution andror eutrophication. the soil structureŽ i.e. by increasing salt accumulation in the top soil. , a general sort of freshwaters induc- 4.2.2. Waste discharges ing lowering of the water table, and differentŽ possi- The coastal ecosystem receives discharges of un- bly. stratification of coastal and shelf water masses. treated anthropogenic wastes, related to domestic Subsequently, the bio-climatic zonation will gradu- waters, industrial effluents and agricultural dis- ally shifts northwards, with several species forced to charges. For example, Thessaloniki Bay used to migrate or disappear and new ones to appear; the receive daily some 150=10 3 m3 of domestic and latter may include bacteria and insects. 60=10 3 m3 of untreated or partially treated indus- However, such impacts are not expected to be trial wastes, respectivelyŽ Psyllidou Giouranovits et detected until around 2030±2040, when an air tem- al., 1998. . In addition, the R. Loudias, acting as the perature increase of 1±28C will induce a sea-level main drainage canal for the main agricultural sector rise of 10±20 cmŽ. Jeftic et al., 1992 . A further of the Thessaloniki PlainŽ. Konstantinidis, 1989 , increase in mean sea levelŽ by )0.5 m, related to a transports vast amounts of pesticides, insecticides, total increment of 2±38C of air temperature. might fertilisers and some amounts of untreated industrial be catastrophic for the region, with important eco- effluents. Thus, the increased levels of trace metals nomic repercussionsŽ Georgas and Perissoratis, observed in the surficial bottom sedimentsŽ Section 1993. . A large area of the coastal agricultural zone 3.2.2.Ž. and the high nutrient levels Section 3.1.4 in will be flooded permanently, while additional areas Thessaloniki Bay and within the northwestern will suffer from temporal floodsŽ in response to nearshore zone of Thermaikos Bay, might be ex- exposure to storm surges. . Similarly, the lagoons that pected to be associated with pollution andror eu- are present nowadays, adjacent to the mouths of the trophication phenomena. Besides, some of the pollu- Rivers Axios and Aliakmon, will disappear; marshes tion in the inner Thessaloniki Bay is related also to will be converted into lagoons. The coastal section of the large activities of the Port of Thessaloniki, where the reclaimed agricultural Thessaloniki Plain there are two anti-pollution vessels to tackle acciden- Ž.defended today by a 1.5±2.0 m high dike and the tal marine pollutionŽ. related mostly to oil spills . coastal section of the County of Thessaloniki, includ- Moreover, Georgas and PerissoratisŽ. 1993 have ing the developing industrial zoneŽ protected now by stated that fishing activities have been banned in the a 1.0±1.5 m high concrete sea wall. will be threat- waters of the inner Thessaloniki Bay, as they are ened if additional measures are not taken. Finally, seriously polluted by industrial and domestic there will be an increased risk of diseases, in relation sewage,9 while estuarine environments along the to the development of ``swampy'' areas containing deltaic coastline are still attracting fish due to high warm anoxic stagnant waters. eutrophicity.

4.2.3. Climatic changes 4.3. Regional managementrscientific objectiÕes Future climatic changes, associated with a predicted increase in air temperature and sea level on a Taking into account the vulnerability of the coastal system, in response to human impact and climatic changes, an integrated regional management pro- 9 Nowadays, a biological treatment plant for the sewage of the gramme concerning the socio-economic and environ- city of Thessaloniki is in operation. mental issues should be established; this could be set S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76 73 against a background of any future planned socio- of terrestrial and oceanic sub-units, covering a total economic development and ecosystem protection. area of some 52,300 km2. Of this area, some 90% Such an approach has to place, in order: the demands belong to the terrestrial sub-system and 10% to the of energy; the required future infrastructure, in terms oceanic sub-system. The coastal zone is regarded to of transportation by land, sea and airŽ motorways, consist of the lower partŽ. altitudes -75 m of the railways, ports, marinas and fishing resorts, the ex- terrestrial sub-systemŽ 2650 km2 . and the shallow pansion of the airport at Mikra. ; the growth and partŽ. water depth -40 m of the oceanic sub-system density of the population; agriculture development; Ž1100 km2 . ; thus, its total area of 3750 km2 repre- industrial activities; tourism; and, fishing and aqua- sents only 7% of the whole system. culture. Further, such a plan has to incorporate the The present configuration of the coastal zone of associated environmental issues, such as: reduction Thermaikos Gulf is associated with:Ž. i the riverine in the waterrsediment riverine fluxes; treatment of water and sediment fluxes, dependent primarily upon city, industrial and agricultural wastes; safe sea the climate and geology of the hinterland region;Ž. ii transport and the use of the Port of Thessaloniki; the coastal geomorphologyŽ.Ž. e.g. cliffs ; iii the pre- coastal changes, in response to the disturbance of the vailing wind conditions, which relate to the surface littoral sediment; clear and safe bathing waters, for water circulation pattern and the nearshore wave and swimmers and sea-sports; and response to future wave-induced current activity;Ž. iv the overall ther- climatic changes. mosaline circulation of the water masses; and,Ž. v Such an integrated approach to coastal system anthropogenic activities. management requires, as its scientific objectives, the The observed coastal changes can be distin- careful monitoring of localised and long-term changes guished as macro-scale, being primarily inter-annual in: weather pattern and their seasonality; in characterŽ.Ž. e.g. the deltaic coasts , and seasonal freshwaterrsediment yields and fluxes; underwater meso-scale Ž.as in the case of the sandy spits . Thus, quality and water-table elevation; soil quality and the progradation of the deltaic coast of Thermaikos Bay, salinisation of any reclaimed nearshore lands, by some 35 km within only the last 2000 yearsŽ a nearshore sediment dynamics; the identification of macro-scale change. , is in response to the high sedi- background levels of nutrients in the water column ment loads delivered by the Rivers Axios, Aliakmon and trace metals on the surficial sediments; and the and Gallikos. On the other hand, meso-scale coastal monitoring of the faunal and floral communities. changes may be attributed either to the seasonal fluctuations of the wave-induced longshore transport, as in the case of sandy spits, and the localised anthropogenic influence, i.e. the construction of small 5. Synthesis and conclusions ports. The high levels of terrigenous fine-grained sedi- The coastal zone of Thermaikos Gulf, hosting ments delivered by the Rivers Axios, Aliakmon and more than 1 million people, is the second most Pinios and smaller streams, apart from their control- important socio-economic area of Greece and one of ling influence on coastal evolution are responsible the most important in the southern Balkans. The for the modernŽ. Holocene sedimentation patterns fertile deltaicŽ.Ž Thessaloniki plain )1500 km2 . over the subaqueous part of the Thermaikos Gulf provides a variety of crops, while the coastal zone Coastal System. The associated sediments in suspen- accommodates a large number of industrial, tourist sion are dispersed seawards and are then deposited and trade enterprises. The adjacent seas are used from the surfaceŽ. plumes and near-bed high-density extensively for maritime transportation, fish produc- nepheloid layers. Terrigenous sand deposition is re- tion, and fish-farmingŽ. mostly mussels . stricted to nearshore areas, originating mainly as the The Thermaikos Gulf coastal area, as in the case products of coastal erosion and supplied by ephemeral of any coastal zone, forms only part of a broader streams. Especially close to the river mouth areas, geographical unit: The Thermaikos Gulf Coastal Sys- the Holocene sedimentary cover has a thickness of tem. This complex geo-system consists of a variety between 5 m and 20 m. 74 S.E. Poulos et al.rJournal of Marine Systems 25() 2000 47±76

The substantial amounts of freshwater carried an- References nually, by the various river systems and other smaller streams, not only contribute to the evolution of the Anagnostou, Ch., Kaberi, H., Karageorgis, A., 1998. Horizontal coastal zone via the transport of high sediment loads and vertical distribution of heavy metals in sediments from but also have a major influence on the functioning of Thermaikos Gulf. Rapp. Comm. Int. Mer Medit. 35, 222±223. Angouridakis, V.E., Machairas, P.C., 1973. Precipitation in Thes- the whole coastal environment by: supporting the saloniki. Sci. Annals, Fac. Phys. Math., Univ. Thessaloniki 13, ground water table; influencing the estuarine envi- 347±380. ronments and lagoons, at the river mouth areas; Athanasoulis, G.A., Skarsoulis, E.K.Ž. Eds. , Wind and Wave Atlas participating in the offshore dispersion of the fine- of the Northeastern Mediterranean Sea. Hellenic Navy General grain sediment; enriching nutrients in the waters of Staff, Athens. 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