Aristomenis P. Karageorgis holds a Ph.D. in Oceanography. He works with the Hellenic Centre for Marine Research-Institute of Oceanography since 1994, and currently he holds a position of Research Director. He has participated/coordinated several national and EU projects with particular focus on sedimentology, geochemistry, and particle dynamics.
Abstract: The Axios River delta and the Inner Thermaikos Gulf coastal zone have experienced a long period of human interventions during the past 100 years. A post-evaluation of long run coastal zone changes under the Drivers-Pressures-State-Impacts-Response (DPSIR) conceptual framework is presented. The DPSIR approach is then used to project out into possible futures in order to connect with policy and management options proposed for the improvement of the current conditions and the achievement of sustainable development, in the coastal zone. Socio-economic driving forces with their origins in the end of the 19th century have generated numerous pressures in the coastal environment that changed the state of the environment. In the first part of the last century, there was no coupling between change of state and policy. Due to increasing environmental awareness, a coupling became more apparent over the last thirty years. Human interventions include river route realignment, extensive drainage of the plains, irrigation network, roads and dam constructions. The consequences were positive for the economic development of the area, human health, and navigation for the port of Thessaloniki. In contrast, the manipulation and over-use of natural resources has led to a reduction of wetlands, biodiversity loss, stress on freshwater supplies, and subsidence of coastal areas, aquifer salinization, and rapid coastal erosion. Three plausible future scenarios are utilised in order to investigate the implications of this environmental change process and possible socio-economic consequences.
Abstract: The Inner Thermaikos Gulf is located in the northwestern Aegean Sea, receiving water and sediment fluxes from the Axios, Aliakmon, Gallikos and Loudias Rivers. The geomorphological and sedimentological evolution of the system is reconstructed for the last 150 years (1850-2000), on the basis of detailed analysis of historical bathymetric charts. Late Holocene history is considered within the context of changing riverine sediment supply and human activities. Three evolutionary stages are identified. Stage I (1850-1916) corresponds to a natural phase of rapid deltaic progradation and sea-floor deposition, with an average sediment accumulation rate of 6.5 × 106 m3 a-1. During Stage II (1946-1956), human interference (e.g. artificial changes in river delta plains, realignment of channels and land reclamation schemes) to the deltaic system increased sediment delivery to the coastal waters by a factor of three; this, in turn, enhanced the progradation of the active river mouth areas. In contrast, Stage III (1956-2000) is characterized by significant coastline (deltaic) retreat and erosion of the adjacent sea floor (net loss of 2.5 × 106 m3 a-1); this was as a result of extensive river damming, which trapped a significant part of the sediment moving seaward. Furthermore, these human impacts have affected the character of the surficial sea-bed sediments of the Gulf, by reducing the proportion of mud. The response of the deltaic margin of the Inner Thermaikos Gulf to various anthropogenic interventions seems to be analogous to that of other deltas in the Mediterranean region where large drainage projects, the development of irrigation networks and dam construction have taken place within their river basins.
Abstract: Respiration and sequestering of organic carbon was investigated in northern Aegean Sea sediments (NE Mediterranean), Benthic total carbonate (C T, also called ?CO2 or dissolved inorganic carbon, DIC) fluxes and O2 uptake rates were measured in situ using a benthic lander. Dissolved organic carbon (DOC) fluxes were calculated from pore water gradients, taking into account the influence of biodiffusion/bioirrigation. Macrofaunal biomass was determined in the sediment collected by the chambers of the benthic lander. Chl a distributions were used as a tracer of high-quality sedimentary organic carbon. The measured benthic CT fluxes were positively correlated with the O2 uptake rates. The obtained average apparent respiration ratio (CT flux:O2 flux) of 0.90 ± 0.36 suggests a clear dominance of aerobic respiration in these organic carbon-poor shelf sediments. The CT efflux, the O2 uptake rate, and the DOC flux were significantly higher in spring than in fall at 2 of the stations. The Black Sea water, which enters the Aegean Sea in the study area, did not influence benthic respiration rates or organic carbon sequestering rates. A strong positive correlation between both the CT and O 2 fluxes and the mean chl a concentration in surficial sediment suggests that benthic respiration, to a large extent, was controlled by the availability of labile phytodetrital organic matter. There was no influence of macrofaunal biomass (dry weight) on CT fluxes or oxygen uptake rates. The calculated benthic DOC fluxes made up 7.2 to 27% (average 14 ± 8.1%) of the CT fluxes, indicating that their contribution to the overall recycling of organic carbon in these sediments was important. The organic carbon burial efficiency ranged from 0.1 to 5.3%, but at Stn KA1 it was considerably higher (average 4%) than at the other stations (average 0.3%). Except for this station, the obtained burial efficiencies were very low compared to other sediments with similar accumulation rates. The average burial flux of organic carbon corresponded to less than 1% of the annual mean primary production (PP) for the Aegean Sea at Stn KA1, and to less than 0.1% of PP at the other stations.
Abstract: CTD /transmissometer profiles were made on four cruises in the northwest Aegean Sea to study seasonal and spatial distribution patterns of particulate matter (PM). Water samples were filtered to obtain particulate matter concentrations and subsequently to calibrate transmissometer readings. Continental runoff is a major particle source during high river discharge seasons (winter and spring). Resuspended particles predominate in the water column during summer and autumn. Particulate matter distribution patterns consist in well-defined surface, intermediate and bottom nepheloid layers (SNL, INL, and BNL, respectively). The SNL is intense during spring and winter, while it is very weak during summer and autumn. The prevailing wind-driven cyclonic circulation regulates the PM distribution over the shelf, whereas the pycnocline depth controls mainly the vertical PM distribution. The resuspension of modern loosely consolidated sediments, under the forcing of near-bottom currents, forms consistent BNLs over the continental shelf throughout the year. The detachment of these BNLs at the shelf break generates weak INLs, which account for an important shelf-basin transport mechanism during winter and spring. The total particulate standing crop is estimated to be between 484 × 103 and 830 × 103 tons. During summer and autumn, the PM on the shelf results largely from resuspension.
Abstract: Volos city and its port are situated in the northern part of Pagassitikos Gulf, a shallow, semi-enclosed marine area in central Greece. A wastewater treatment plant (WWTP) and pipeline operate in the same area. Muddy sediments with low carbonate contents cover most of the seabed, except for the Volos embayment and the western part of the gulf where sandy carbonates prevail. Bulk organic carbon contents and the organic carbon contents of the clay fractions are high in the vicinity of Volos embayment. High element (Pb, Cu, and Zn) contents and Igeo (geoaccumulation index) values were found for the clay fractions in the northern part of Pagassitikos Gulf. This enrichment is attributed to the discharge of raw domestic and industrial effluents of Volos city and port before the WWTP was installed. The dispersal of pollutants is essentially controlled by diffusion from point sources (city, port and WWTP) and is limited to Volos Bay. Relatively high Mn levels are ascribed to diagenetic formation of manganese carbonates (authigenic phase), whereas Cr and Ni are elevated due to weathering of ultrabasic formations on land.
Abstract: The Cretan Basin can be characterized as a back-arc basin of the Hellenic Trench System, that is related to the subduction zone of the African Plate under the Eurasia Plate. The study area includes the narrow and relatively steep (gradient 1.5°) continental shelf of the island of Crete followed by the steep slope (2°-4°) and the rather flat deeper part of the Cretan basin (water depths > 1700 m). Surficial sediments of the coastal zone are coarser and of terrigenous origin, while in deeper waters finer sediments, of biogenic origin, are more abundant. Sand-sized calcareous sediment accumulations, identified in middle-lower slope, may be attributed to the aggregation of seabed biogenic material related to the near bed current activity. High resolution profiles (3.5 kHz) taken from the inner shelf shows a typical sigmoid-oblique progradational configuration, implying prodelta sediment accumulation during the Holocene. In the upper-middle slope, sub-bottom reflectors indicate continuous sedimentation of alternating fine and/or coarse grained material. Small-scale gravity induced synsedimentary faults appeared, locally. In contrast, a series of gravity induced faults, identified in the lower slope, are associated with sediment instabilities due to seismotectonic activity. Sediment cores taken from the shelf-break consists of calcareous muddy sand with small amounts of terrigenous silt and fine sand, while the cores recovered from the middle slope has revealed a more homogeneous fine sediment texture of hemipelagic deposition. The prevailing accumulation processes in the southern margin of the Cretan basin are: (i) Prodelta deposition in the inner-middle shelf; (ii) settling from bottom nepheloid layers in the shelf and upper slope; (iii) calcareous sediment formation due to settling from suspension and post accumulation aggregation (middle-lower slope); (iv) long-term episodic sediment gravity processes in the lower slope; and (v) to a lesser extent, redeposition from resuspension due to gravity processes and bottom currents. (C) 2000 Elsevier Science Ltd.
Abstract: Suspended particulate matter (SPM) patterns in the surface waters of the NW Aegean Sea were studied by (1) determining SPM concentration by water filtration, (2) measuring light transmission, and (3) evaluating satellite images. The SPM signals of the three major rivers discharging into the study area were recorded by all three methods, thereby providing information about the sources, transport pathways, and regional dispersion patterns of the SPM. The filtration of water samples and light transmission measurements were found to be good indicators of SPM concentrations in surface waters. Most of the SPM is composed of terrigenous minerals, thus explaining the correlation between the beam attenuation coefficient and the SPM concentration. A Landsat image obtained for the study period was found to adequately reveal regions with high SPM concentrations. Low concentrations, on the other hand, remain obscured.
Abstract: This work aims at studying the geochemistry and mineralogy of Milos bay surface sediments. The bay forms an enclosed marine area, supplied totally by Volcanic formations. Totally 16 samples were subjected to sedimentological (grain size), mineralogical (microscope examination and X-ray diffraction of the bulk sample and the pelitic fraction), and geochemical analyses (X-ray fluorescence in the pelitic fraction). Also the carbonate content was determined. Sediments were sandy with a high carbonate content (14-58%). The dominant minerals recognized in the pelitic fraction were smectite, kaolinite and illite, followed by chlorite, quartz, calcite, Mg-calcite and feldspars. In general, element concentrations appeared to be within the normal range, except Pb and Zn, which exhibited relatively high values. The Index of Geoaccumulation I(geo) was computed, in order to investigate a possible enrichment of the surface sediments in metals. The analysis revealed again high values of I(geo) class for both Pb and Zn. A careful Study of the area, in relation to the quality of the catchment basins petrology, lead to a non-anthropogenic origin of these high concentrations. The enrichment of the surface sediments in Pb and Zn is attributed to the weathering of several mineral deposits, pyroclastic rocks and lavas, covering almost all Milos vicinity. A study of the geochemical data correlation coefficient matrix revealed three major groups of elements: (i) the elements of detrital origin represented by Si, Al, K and a part of the metals; (ii) the carbonates group; and (iii) a Fe-Mn oxyhydroxides-oxides group, which attracts a part of Pb, Cr and Ni.
Abstract: A suite of 68 surface sediment samples from the South Evvoikos (SEG), North Petation (NPG) and South Petalion (SPG) gulfs was analyzed for grain size, meneralogy, major and minor elements in the bulk sample and the < 2 ?m fraction. Grain size analysis distinguished two sedimentary provinces: 1) SEG with fine grained sediments; and ii) NPG, SPG dominated by relict sandy sediments. Abundants minerals are quartz, feldspars, calcite and Mg-calcite. Heavy minerals identified were epidote, hornblende, zircon and glaucophane. Factor analysis revealed that chemical elements of the total sample are mainly of terrigenous origin, supplied by the Asopos river, which discharges in SEG. The southern part is dominated by residual Si and biogenic components. Metals are generally present in low concentrations. I(geo) index computation for the trace elements indicated relatively high concentrations of Ni and Cr in the SEG are, which are in all probability related to the erosion of laterite formations and ultramatic rocks.
Abstract: The area under investigation is the gulf and the bay of Thessaloniki which comprise the northern part of Thermaikos gulf. During the last years the area is being loaded with heavy metals and organic pollutants coming from industrial and domestic discharges of Thessaloniki city. As a result of the anthropogenic activities, the seabed properties are changed and moreover the marine ecosystem is disturbed. The aim of the study was to determine the environmental impact on the surface sediments so that the extent of heavy metal pollution is quantified and the whole area could be characterized according to the geoaccumulation index (Igeo). For this purpose, thirty three sediment samples were collected from the bay and the gulf of Thessaloniki. The diameter <2 ?m sediment fraction of the samples was analyzed for the heavy metal content (Zn, Cu, Ni, Cr, Pb, Cd, Fe and Mn). The geoaccumulation index was then calculated comparing the concentration of the respective elements to that of unpolluted sediments, the so called `background value'. According to the Igeo classification, the bay of Thessaloniki was characterized as moderately polluted to strongly polluted for the metals Zn, Cd, Pb and unpolluted to moderately polluted in Cu, Ni and Cr, while the gulf of Thessaloniki was characterized as an unpolluted to unpolluted to moderately polluted marine area.