Greek case studies: Geomorphological changes on the coastal area of the Inner Thermaikos Gulf over the past 150 years

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Introduction

This article presents the geomorphological evolution of the deltaic coastal zone of the Inner Thermaikos Gulf, northern Greece, over the past 150 years (1850–2000). It should be read in conjunction with the article Greek case studies: Long term geomorphological changes in the coastal zone of the Thermaikos Gulf, Salonika Region, North Greece.


The reconstruction of the geomorphological evolution is based on a detailed analysis of historical bathymetric charts (Albanakis et al., 1993; Poulos et al., 1994; Kapsimalis et al., 2005). The evolution is mainly caused by human-induced modifications in the basins of two main rivers (Axios and Aliakmon) and two smaller rivers (Gallikos and Loudias), which discharge into the Gulf (Poulos et al., 2000; Karageorgis et al., 2005; Karageorgis et al., 2006). Over the past 150 years, the Gulf has accumulated a net sediment volume of 1230 x 106 m3, at an average rate of accretion of 8 x 106 m3 a-1 or 12 x 106 tons a-1. Some 85% of this load is deposited around the active river mouths, with approximately 15% being dispersed offshore (Kapsimalis et al., 2005). Over this period of time, three evolutionary ‘stages’ are identified on the basis of changes in sediment supply and associated human interference.

Stage I: 1850–1916

From the middle of the 19th century to the early 20th century, the coastal system of the Gulf evolved naturally. A net marine sediment supply of some 430 x 106 m3 resulted from fluvial discharge at an average rate of 6.5 x 106 m3 a-1 or 10 x 106 t a-1 (Kapsimalis et al., 2005; Karageorgis et al., 2006). This input resulted in the progradation of the delta complex, especially near the active river mouths.

Stage II: 1916–1956

Subsequently, human intervention to the natural system of the deltaic plain was at a maximum, especially in the second part of stage II (1934–1956). Major causes were:

  • artificial realignment of the main river channels (1934);
  • drainage of the Yiannitsa Lake and the Loudias Swamps (1935);
  • the instigation of other land reclamation projects (Karageorgis et al., 2006).

The net riverine sediment supply increased considerably, up to 900 x 106 m3; this corresponds to an average input of 18 x 106 m3 a-1 or 28 x 106 t a-1 (Kapsimalis et al., 2005). Over this period, rapid progradation occurred at the active mouths of the Axios and Aliakmon Rivers. At the same time, some of the fine-grained components of the sediment load were dispersed over the Inner Thermaikos Gulf.

Stage III: 1959–2000

The last stage is strongly characterized by a further ‘cycle’ of human interference (Georgas and Perissoratis, 1992; Poulos et al., 2000; Karageorgis et al., 2005). This includes the construction of irrigation reservoirs and hydroelectric dams. Such structures caused a significant reduction in sediment supply, leading to an overall erosional phase over the Gulf and a mean sediment loss of 2.5 x 106 m3 a-1 or 4 x 106 t a-1 (Kapsimalis et al., 2005). During this period, the river mouths underwent rapid retreat. The ‘active’ rivers prograded only minimally, while the lower reaches of the deltaic plain were subjected to coastal flooding. Furthermore, human activities affected the circulation pattern of the Gulf (Nikolaidis et al., 2006) and the texture of the offshore sea-bed sediments (Kapsimalis et al., 2005). This resulted in the alteration of the associated benthic habitats (Voutsinou-Taliadouri and Varnavas, 1995).


References

Albanakis K., Vavliakis E., Psilovikos A., Sotiriadis L., 1993. Mechanisms and evolution of the delta of Axios River during the 20th Century. Proceedings of the 3rd Hellenic Geography Conference, Hellenic Geographical Society, Athens, 311–325.

Georgas D., Perissoratis C., 1992. Implications of future climatic changes on the Inner Thermaikos Gulf. In: Jeftic L., Milliman J. (eds.), Climatic change and the Mediterranean. UNEP, Edward Arnold, London, 495–534.

Kapsimalis V., Poulos S.E., Karageorgis A.P., Pavlakis P., Collins M.B., 2005. Recent evolution of a Mediterranean deltaic coastal zone: human impacts on the Inner Thermaikos Gulf, NW Aegean Sea. Journal of Geological Society, London, 162: 897-908.

Karageorgis, A.P., Skourtos M.S., Kapsimalis V., Kontogianni A.D., Skoulikidis N.T., Pagou K., Nikolaidis N.P., Drakopoulou P., Zanou B., Karamanos H., Levkov Z., Anagnostou C., 2005. An integrated approach to watershed management within the DPSIR framework: Axios River Catchment and Thermaikos Gulf. Regional Environmental Change, 5:138–160.

Karageorgis A.P., Kapsimalis V., Kontogianni A., Skourtos M., Turner K.R., Salomons W., 2006. Impact of 100-year human interventions on the deltaic coastal zone of the Inner Thermaikos Gulf (Greece): a DPSIR framework analysis. Environmental Management, 38(2): 304-315.

Nikolaidis N.P., Karageorgis A.P., Kapsimalis V., Marconis G., Drakopoulou P., Kontoyiannis H., Krasakopoulou E., Pavlidou A., Pagou K., 2006. Circulation and nutrient modeling of Thermaikos Gulf, Greece. Journal of Marine Systems, 60: 51-62.

Poulos S.E., Papadopoulos A., Collins M. B., 1994. Deltaic progradation in Thermaikos Bay, Northern Greece and its socio-economic implications. Ocean and Coastal Management, 22: 229–247.

Poulos, S.E., Chronis G.T., Collins M.B., Lykousis V., 2000. Thermaikos Gulf coastal system, NW Aegean Sea: an overview of water/sediment fluxes in relation to air–land–ocean interactions and human activities. Journal of Marine Systems, 25: 47–76.

Voutsinou-Taliadouri F., Varnavas S.P., 1995. Geochemical and sedimentological patterns in the Thermaikos Gulf, North-west Aegean Sea, formed from a multisource of elements. Estuarine and Coastal Shelf Science, 40: 295–320.

The main author of this article is Kapsimalis, Vasileios
Please note that others may also have edited the contents of this article.