Nestos River Delta Research Articles

Index-Based Groundwater Quality Assessment of Nestos River Deltaic Aquifer System, Northeastern Greece

The Nestos River delta is one of the most important and sensitive basins in Greece and Europe due to its ecosystem functions, combining intensive agricultural production with low-enthalpy geothermal energy and important ecotopes. High water quality is of paramount importance to the sustainability of the system. Systematic and continuous assessment of water quality needs to be carried out in a way that is easy and quick for decision makers and non-expert societal partners to comprehend. In this way, decisions may be made more rapidly, and involved water users may be sensitized to rational water use. To this end, this paper presents the assessment of groundwater quality in the Nestos River’s western delta with the use of Poseidon (PoS), a versatile, index-based method. Groundwater samples collected from 24 and 22 wells tapping the unconfined and the confined aquifers, respectively, in four time periods (May and October 2019 and 2020) were analyzed. Using the PoS index, groundwater samples were classified according to their quality status, highlighting the parameters driving quality degradation issues, thus assisting water managers in obtaining an overview of quality status and evolution through datasets that were often large. PoS index is applied in the study area for the first time and provides a groundwater quality assessment through a unique score representative of the overall water quality status regardless of processes (anthropogenic or natural) or any kind of pressures.

New Records of Tetraselmis sp. Strains with Biotechnological Potential Isolated from Greek Coastal Lagoons

In the pursuit of sustainable sources for food, energy, and health products, microalgae have gained attention. In the present study, the lagoonal system of the Nestos River delta was selected as a sampling point in order to search for opportunistic and robust species. Two new strains of Tetraselmis are described with regards to their taxonomic features (as observed using light and transmission electron microscopy and molecular phylogenetics) and their biochemical properties (total lipid, total protein, and total carbohydrate content, photosynthetic pigments, and antioxidant capacity). The studied strains were identified as representatives of Tetraselmis verrucosa f. rubens. Furthermore, both strains exhibited an interesting biochemical profile coupled with high growth rates and promising antioxidant activity, without the use of enhancement and induction culture methods, warranting further investigation and showing potential for biotechnological use.

A Detailed Liquefaction Susceptibility Map of Nestos River Delta, Thrace, Greece Based on Surficial Geology and Geomorphology

The existence of high potential onshore and offshore active faults capable to trigger large earthquakes in the broader area of Thrace, Greece in correlation with the critical infrastructures constructed on the recent and Holocene sediments of Nestos river delta plain, was the motivation for this research. The goal of this study is twofold; compilation of a new geomorphological map of the study area and the assessment of the liquefaction susceptibility of the surficial geological units. Liquefaction susceptibility at regional scale is assessed by taking into account information dealing with the depositional environment and age of the surficial geological units. In our case, available geological mapping shows a deficient depiction of Pleistocene and Holocene deposits. Taking into consideration the heterogeneously behavior of active floodplains and deltas in terms of liquefaction, a detailed classification of geological units was mandatory. Using data provided by satellite and aerial imagery, and topographic maps, dated before the 1970’s when extensive modifications and land reclamation occurred in the area, we were able to trace fluvial and coastal geomorphological features like abandoned stream/meanders, estuaries, dunes, lagoons and ox-bow lakes. This geomorphological-oriented approach clearly classified the geological units according to their depositional environment and resulted in a more reliable liquefaction susceptibility map of 4 classes of susceptibility; Low, Moderate, High and Very High. The sediments classified as very high liquefaction susceptibility are related to fluvial landforms, the high to moderate liquefaction susceptibility ones in coastal and floodplain landforms, and low susceptibility in zones of marshes. The sediments classified in the highest group of liquefaction susceptibility cover 85.56 km2 of the study area (16.6%). Particular attention was drawn to critical infrastructure (Kavala International Airport “Alexander the Great”) constructed on the most prone to liquefaction areas.

Chemical and isotopic characterization of the thermal fluids emerging along the North\u2013Northeastern Greece

Hydrochemical and isotopic characteristics of fluids from major geothermal fields of middle/low temperature in N/NE Greece are examined [basins: Strymon River (SR), Nestos River Delta (ND), Xanthi–Komotini (XK), Loutros–Feres–Soufli (LFS) and Rhodope Massif]. The geodynamic context is reflected to isotopic/chemical composition of fluids, heat flow values and elevated CO2 concentrations in emitted fluids. B and Li are derived from leaching of the geothermal systems hosting rocks. δ18OH2O, δ18OSO4, δ13CCO2 values and chemical compositions of Cl, B and Li of geothermal discharges suggest two distinct source fluids. Fluids in SR exhibit high B/Cl and Li/Cl ratios, suggesting these constituents are derived from associated magmas of intermediate composition (andesitic rocks). Geothermal discharges in LFS exhibit low B/Cl and Li/Cl ratios, implying acid (rhyolitic) magmatism. δ13CCO2 and CO2/(CO2 + 105He) ratios in the west part, suggest fluids affected by addition of volatiles released from subducted marine sediments. For the eastern systems, these ratios suggest gas encountered in systems issued from mixing of crustal and mantle-derived volatiles. Isotopic geothermometers reflect, for the same direction, equilibrium processes more (LFS, XK) or less (SR) pronounced and discriminate the geothermal field from low to middle [SR, ND (Erasmio)] and middle to high enthalpy [ND (Eratino), LFS, XK].

Relating Hydro-Meteorological Variables to Water Table in an Unconfined Aquifer via Fuzzy Linear Regression

This study aims to assess the short-term response of groundwater to the main hydro-meteorological variables of drought in a coastal unconfined aquifer. For this purpose, a multiple fuzzy linear regression-based methodology is implemented in order to relate rainfall, streamflow and the potential evapotranspiration to groundwater. Fuzzy regression analysis is recommended when there is a lack of data. The uncertainty of the system is incorporated into the regression coefficients which, in this study, are considered to be fuzzy symmetrical triangular numbers. Two objective functions are used producing a fuzzy band in which all the observed data must be included. The first objective function, based on Tanaka’s model, minimizes the total width of the produced fuzzy band. The second one includes the first while additionally minimizing the distance between the central value of the fuzzy output of the model and the observed value. Validity of the model is checked through suitability measures. The present methodology is applied at the east part of the Nestos River Delta in the Prefecture of Xanthi (Greece), where the observed values of the depth of groundwater level of four wells are examined.

Assessing the Vulnerability of a Deltaic Environment due to Climate Change Impact on Surface and Coastal Waters: The Case of Nestos River (Greece)

In deltaic areas, riverine and coastal waters interact; hence, these highly dynamic environments are particularly sensitive to climate change. This adds to existing anthropogenic pressures from irrigated agriculture, industrial infrastructure, urbanization, and touristic activities. The paper investigates the estimated future variations in the dynamics of surface and coastal water resources at a Mediterranean deltaic environment for the twenty-first century. Therefore, an Integrated Deltaic Risk Index (IDRI) is proposed as a vulnerability assessment tool to identify climate change impact (CCI) on the study area. For this purpose, three regional climate models (RCM) are used with representative concentration pathways (RCPs) 4.5 and 8.5 for short-term (2021–2050) and long-term (2071–2100) future periods. Extensive numerical modeling of river hydrology, storm surges, coastal inundation, water scarcity, and heat stress on irrigated agriculture is combined with available atmospheric data to estimate CCI on the Nestos river delta (Greece). The IDRI integrates modeling results about (i) freshwater availability covering agricultural demands for three water consumption scenarios, i.e., a reference (REF), a climate change (CC), and an extended irrigation (EXT) scenario, combining river discharges and hydropower dam operation; (ii) inundated coastal areas due to storm surges; and (iii) heat stress on cultivated crops. Sustainable practices on irrigated agriculture and established river basin management plans are also considered for the water demands under combinatory scenarios. The differentiations of model outputs driven by various RCM/RCP combinations are investigated. Increased deltaic vulnerability is found under the RCP8.5 scenario especially for the long-term future period. The projected IDRI demonstrates the need for integrated water resources management when compared with risk indexing of individual water processes in the study area.

Assessing the impact of dams on riparian and deltaic vegetation using remotely-sensed vegetation indices and Random Forests modelling

Abstract Riparian and deltaic areas exhibit a high biodiversity and offer a number of ecosystem services but are often degraded by human activities. Dams, for example, alter the hydrologic and sediment regimes of rivers and can negatively affect riparian areas and deltas. In order to sustainably manage these ecosystems, it is, therefore, essential to assess and monitor the impacts of dams. To this end, site-assessments and in-situ measurements have commonly been used in the past, but these can be laborious, resource demanding and time consuming. Here, we investigated the impact of three dams on the riparian forest of the Nestos River Delta in Greece by employing multi-temporal satellite data. We assessed the evolution in the values of eight vegetation indices over 27 years, derived from 14 dates of Landsat data. We also employed a modelling approach, using a machine learning Random Forests model, to investigate potential linkages between the observed changes in the indices and a host of climatic and terrestrial predictor variables. Our results show that low density vegetation (0–25%) is more affected by the construction of the dams due to its proximity to anthropogenic influences and the effects of hydrologic regime alteration. In contrast, higher density vegetation cover (50–75%) appears to be largely unaffected, or even improving, due to its proximity to the river, while vegetation with intermediate coverage (25–49%) exhibits no clear trend in the Landsat-derived indices. The Random Forests model found that the most important parameters for the riparian vegetation (based on the Mean Decrease Gini and the Mean Decrease Accuracy) were the distance to the dams, the sea and the river. Our results suggest that management plans of riparian and deltaic areas need to incorporate and take into consideration new innovative management practices and monitoring studies that employ multi-temporal satellite data archives.

Ecohydraulic modelling of Nestos River Delta under low flow regimes

The determination of a proper minimum environmental flow in a river basin is one of the most critical components of sustainable water resources management, with hydraulic and habitat modelling being the most advance methods for that analysis. The present study illustrates the ecohydraulic modelling of Nestos River Delta at the deltaic zone of a heavily modified watershed under various low flow scenarios, using the RIVER2D Model. RIVER2D is a two-dimensional, depth averaged hydrodynamic and fish habitat model, widely used in environmental flow assessment studies. A detailed digital model of the river channel and its surrounding area was developed, including all the morphological characteristics of the river channel, as well as its various sandy islets. Field surveys in combination with Digital Elevation Model data were used for the development of the digital terrain used as input to RIVER2D model. Several different steady state hydraulic simulations were conducted under typical low flow conditions, producing water depth and water velocity (direction and magnitude) maps for each discharge scenario, while results were verified with the use of field measurements. In the next step, RIVER2D was used for the fish habitat modelling of the study area, with the application of fish preference curves developed specifically for the study area. Finally, the fish habitat modelling was conducted for four different fish species, divided into two age groups, forced under the same five typical low flow conditions. Results reveal that the ecohydraulic modelling of river basins should be considered as an indispensable component in sustainable water resources management.

Μορφολογικά και ιζηματολογικά χαρακτηριστικά του ενεργού Δέλτα του ποταμού Νέστου, μετά τη κατασκευή των φραγμάτων

The purpose of this paper is the geomorphological and sedimentological study of modern Nestos River Delta, to examine the effect of the dams to the sedimentological regime of the coastal zone. Nestos Delta suffered a series of anthropogenic influences; the most significant was the channeliza-tion of the river bed, which prevents avulsion and enforces the river to discharge to the sea with one main channel. A DGPS with accuracy better than 1m (GMS-2- Topcon), was used for mapping the coastline, along with sampling the coastal sediments. Sedimentological analysis revealed that the mean size of the sandy material of the coastline reduces with increasing the eastward distance from the river mouth. The western coastline revealed a more complex situation, since it had inherited characteristics from older, abandoned river mouths, bars, spits etc, existed prior to anthropogenic influence. Comparison between the DGPS survey and the 1970 topographic maps revealed some areas with erosional and some with depositional tendencies. A clear erosional tendency was not rec-orded. Furthermore comparison, between 2000 GPS survey, and the present 2009 DGPS survey, recorded a stability of the coastline within the resolution and the accuracy of the instruments. A pos-sible explanation, is the dramatic reduction of the active area of the delta, due to anthropogenic influ-ence, where at its natural stage, was dispersing sediments with avulsion and multiple river channels in an area of 500 km2, but now the active area, where deposition is possible, is only 45.84 km2.

HYDROGEOLOGICAL ASSESSMENT OF GROUNDWATER DEGRADATION AT THE EASTERN NESTOS RIVER DELTA, N.E. GREECE.

This paper deals with the hydrogeological study of the evolution of groundwater salinisation - degradation at the eastern Nestos River Delta. Relevant field works including in-situ measurements of groundwater level, pH, Specific Electrical Conductivity (SEC) and temperature took place in the years 2008 and 2009. Groundwater samples were also collected for chemical analysis at the Engineering Geology Laboratory of the Department of Civil Engineering of D.U.Th. (July of 2009). Important conclusions regarding the progress of the groundwater degradation at the study area were drawn based on the analysis of all the available data and the elaboration of the designed piezometric maps and the various maps showing the distribution of SEC, Chloride, SAR (Sodium Absorption Ratio) and Revelle coefficient values. Some managerial suggestions for the confrontation of the seawater intrusion regime of the study area are also included.

Assessment of Shoreline Changes and Evaluation of Coastal Protection Methods to Mitigate Erosion

In this paper, the combined use of satellite images and morphodynamic models is applied to assess the coastline changes of an erosion-prone deltaic zone in Northern Greece (Nestos River delta). Satellite images over the last 31 years were used to estimate the erosion rates at the eastern, central and western parts of the delta. The numerical model LITPACK, coupled with wave and hydrodynamic nearshore models, was calibrated based on these results, and was further utilized to predict the shoreline evolution with and without “hard” protection works. Results show that the model underestimated erosion rates over all studied sub-sections, but showed fair agreement to remote sensing analysis when focusing on the zones of major erosion. “Hard” coastal protection structures were tested to assess their mitigation efficiency in terms of longshore and cross-shore sediment transport reduction. LITPACK considered that the scenario of seven rubble-mound breakwaters with low seaward and lee-side slopes, positioned between 9 m and 19 m depicted the best results, even reversing coastline retreat process.

Assessment of soil salinization at the eastern Nestos River Delta, N.E. Greece

This paper analyses land degradation phenomena at the SE part of R. Nestos Delta, Greece. The work includes geological, hydrological and hydrogeological data interpretation in the study area, including field and laboratory measurements and soil samples analyses during 2007, 2008 and 2009. The study also involved the correlation of certain soil parameters such as pH, ECe and chemical characteristics of both soils and groundwaters while spatial analysis was proved useful for the estimation of soil salinization progress in the study area. Management proposals that could be implemented by relevant institutions and stakeholders are also presented, such as control of groundwater table, improvement of soil drainage potentials, use of calcium for leaching out the exchangeable sodium, cultivation of salt tolerant crops, prevention of salts and sodium accumulation, soil improvement by using compost, organic matter, etc. Also, novel strategies for reclamation and improvement of the salt-affected soils are evaluated in order to determine the most promising strategy for field application including irrigation with treated waste water, bio-drainage, use of fungi, suitable plants, genetically modified plants and automated irrigation control.

Assessment of reservoir sedimentation effect on coastal erosion in the case of Nestos River, Greece

Coastal erosion that is generated by the reduction of the annual sediment yield at river outlets, due to the construction of reservoirs, constitutes one of the main environmental problems in many parts of the world. Nestos is one of the most important boundary rivers, flowing through Bulgaria and Greece, characterized by its great biodiversity. In the Greek part of the river, two reservoirs, the Thisavros Reservoir and the Platanovrysi Reservoir, have already been constructed and started operating in 1997 and 1999, respectively. The present paper constitutes the first attempt where the assessment of reservoir sedimentation effect on the coastal erosion for the case of the Nestos River delta and the adjacent shorelines is addressed in detail, through mathematical modeling, modern remote sensing techniques and field surveying. It is found that the construction and operation of the considered reservoirs have caused a dramatic decrease (about 83%) in the sediments supplied directly to the basin outlet and indirectly to the neighbouring coast and that this fact has almost inversed the erosion/accretion balance in the deltaic as well as the adjacent shorelines. Before the construction of the reservoirs, accretion predominated erosion by 25.36%, while just within five years after the construction of the reservoirs, erosion predominates accretion by 21.26%.

Exploring for geothermal resources in Greece

In Greece the geothermal areas are located in regions of Quaternary or Miocene volcanism and in continental basins of high heat flow. The existence of high-temperature (>200 °C) resources has been proven by deep drilling on the islands of Milos and Nisyros and inferred on the island of Santorini by its active volcanism. Elsewhere, geological investigations, geochemical analyses of thermal springs and shallow drilling have identified many low-temperature (<100 °C) reservoirs, utilized for spas and greenhouse/soil heating. Ternary K–Na–Mg geothermometer data suggest deep, medium-temperature resources (100–200 °C) in Sousaki, the islands of Samothraki, Chios and Lesvos, in the basins of Nestos River Delta and Alexandroupolis and in the graben of Sperchios River. In the basins of northern Greece these resources are also inferred from deep oil exploration well data.

Application of Stepwise Discriminant Analysis for the Identification of Salinity Sources of Groundwater

Statistical analysis can be an important tool to identify and classify different sources of groundwater salinisation. This paper refers to the application of Stepwise Discriminant Analysis (SDA) as an effective technique for the identification of major constituent ratios which can be used for efficiently identifying various salinity sources. The effectiveness of the SDA method was tested on five groups of groundwater samples known for their salinisation. Three were taken from the brackish groundwater of the Nestos River delta, from the geothermal field of Nea Kessani and the brackish groundwater of the western coastal area of Rhodope, in Greece. The remaining two groups were taken from bibliographic sources and they refer to the degraded groundwater of the Wittmund area in coastal NW Germany as well as from the underground brines of Sichuan Basin in China. The method of SDA has demonstrated its effectiveness of classifying different groundwater groups, and its usefull contribution to the groundwater contamination. In this way, possible expensive field investigations and analyses of chemical parameters can be eliminate.

Simulation and Trend Analysis of the Water Quality Monitoring Daily Data in Nestos River Delta. Contribution to the Sustainable Management and Results for the Years 2000–2002

The transboundary River Nestos in the Balkan Peninsula is a surface water resource shared by Hellas and Bulgaria. The Public Power Corporation of Hellas (DEH) proceeded to the dams' construction of Thesaurus in 1997 and Platanovrissi in 2000, to satisfy the increased needs for power production and irrigation in the Regions of Eastern Macedonia and Thrace in the Hellenic Territory. DEH following the Ministerial Agreement of the Hellenic Parliament ';KYA 18492/19-09-1996'' funded a series of Research Projects concerned on the monitoring of the water quantity and quality data of Nestos from the Hellenic-Bulgarian borders to its estuaries in the Thracian sea. ';PERSEAS'' Research Group from Aristotle University of Thessaloniki, carried out the research, design, construction, installation, operation and maintenance of the ';R.E.MO.S.'' (Remote Environmental MOnitoring System) networks. Three REMOS networks have been installed in the areas of (a) the River Nestos deltaic channel, (b) Thesaurus dam-lake in the intramountainous valley and (c) Potamoi (Despat) and Pagoneri (Nestos) villages close to the borders between Hellas and Bulgaria. They record water level (H), water and air temperature (T), water conductivity (ECw), Redox potential (RP) and dissolved oxygen (DO) on a 24h basis, since the beginning of the year 2000. The research carried out in this paper, is focused on the REMOS station in the final course of Nestos in the deltaic area. The continuous monitoring and the data analysis yield useful results for the quality and quantity of the hydrologic regime of Nestos after the dams' construction, as well as for the trends detected of the quality parameters (ECw, RP and DO) and the water level, using the nonparametric Spearman's criterion. The best fitted model of time trend, for each variable, was chosen. The statistical sample of each one of the quality variables consisted of about 1000 values based on daily measures on a three years monitoring program (1/1/2000-31/12/2002). Further research and analysis for the other network stations of REMOS should provide useful results for the sustainable management of the transboundary River Nestos.

Geomorphological classification of the Thrace coasts after Valentin

An attempt is made in this paper to elucidate the geologic evolution of the coastal zone at the North Aegean Sea (Thrace area) during the Holocene period and its géomorphologie classification. Various classification systems were applied but the Valentin system found to be the most applicable for the situation. Data were drawn from old topographic maps and aerophotos and from field observations. The main conclusion from this study is that the coasts of Thrace, and the North Aegean Sea, in their major stretch are retreating and submegning slowly(transgressive); most of them are formed by terrestrial deposits (river, torrents, etc) and are plain (open) coasts, according to Valentin classification. Even stretches of the Nestos River delta retreated by 100-150 m during the last forty years. The retrogression of the Thrace coasts is attributed mainly to engineering interference in the drainage system inland (construction of dams and irrigation canals, rearrangement or diversion of the river courses, embankment at rivers, etc.). All these works reduced drastically the sediments supply to the sea through the drainage system resulting in the erosion of the coasts. Technical interference near or on the shoreline like port construction, summer resorts, breakwaters, etc. also changed the dynamic equilibrium of the sediment transport along the shoreline, resulting in erosion at some stretches and deposition at others. There are but a few places where the coast is in equilibrium or even advancing e.g. estuaries and deltas of small torrents,the Mangana coast, the Mandra-Porto Lagos coast, etc.