A New Spatiotemporal Risk Index for Heavy Metals: Application in Cyprus

The main aim of this research was to improve risk mapping of heavy metals by accounting for erosion effects. A new spatiotemporal index, namely G2met, is introduced, incorporating the Hakanson index, the G2 model and the Gavrilovic model. The G2met index is expressed in terms of monthly time series of risk maps for each heavy metal and totally. The rich in heavy metals and vulnerable to erosion, island of Cyprus, was selected as a study area, which though was limited to the southern part of the island, where all required data were available. Concentration of major heavy metals was extracted by sampling soil from a grid of 5350 sites. Rainfall, vegetation, soil, land use, topographic, and hydrologic data were collected or calculated from existing European or global databases (WorldClim, BioBar, ESDAC, CORINE, ASTER GDEM, and USGS). A large number of regional-scale risk maps were produced (500-m ell size), i.e. one for each heavy metal and totally per month and annually. Also, choropleth maps per heavy metal are potentially available, in terms of statistics per river basin. The G2met maps provide different patterns in comparison to those depicted by the Hakanson index alone.JRC.H.5-Land Resources Managemen

Renovation and Reuse of Waste Electrical and Electronic Equipment in the Direction of Eco-Design

Nowadays there is a higher need of strict and broader legislation in waste electrical and electronic equipment (WEEE) recycling industry to reduce environmental effects of WEEE. Environmental challenges include pollution, exhaustion of natural resources, waste management and reduction of landfills. High speed in technological development in many sectors puts many products in great challenge of obsoleting almost immediately after their purchase. In particular, this is the fate for electrical and electronic equipment (EEE). They are forever-improving and incorporate state of the art innovations. This provide many benefits; however, at the same time, its expansion results in rapidly growing waste stream of WEEE. WEEE contains a combination of all these situations, including for example, batteries, plastics of quality, precious metals and toxic soldering metals. The reuse and renovation of WEEE are therefore very critical because of its significant ecological environmental impacts. Sustainable development is not a static situation, but a state of dynamic balance between human and environmental system. The current chapter explores sustainability planning and strategies such as eco-design, and design for dismantling and recycling, and what they mean for electronic products. It examines the incentives, methods and tools for sustainable electronic product design, with particular emphasis on reuse, recycling, selection of sustainable materials and processes, and lack of resources

The impact of the covid-19 pandemic on theworking conditions, employment, career development and well-being of refugee researchers

The ongoing ‘refugee crisis’ of the past years has led to the migration of refugee researchers (RRs) to European countries. Due to the COVID-19 pandemic, RRs often had to work from home and/or to continue their social, cultural and economic integration process under new conditions. An online survey carried out to explore the impact of the pandemic on the refugee researchers showed that RRs found it difficult to adapt their everyday working life to the ‘home’ setting. The majority have had neither a suitable work environment at home nor the appropriate technology. Although they stated that they are rather pleased with the measures taken by the public authorities, they expressed concern about their vulnerability due to their precarious contracts and the bureaucratic asylum procedures, as the pandemic has had a negative impact on these major issues. The majority of RRs working in academia seem not to have been affected at all as far as their income is concerned, while the majority of those employed in other sectors became unemployed during the pandemic (58%). Recommendations are provided to the public authorities and policy makers to assist RRs to mitigate the consequences of the pandemic on their life

Impact of Hydrological Modellers’ Decisions and Attitude on the Performance of a Calibrated Conceptual Catchment Model: Results from a ‘Modelling Contest’

In this study, 17 hydrologists with different experience in hydrological modelling applied the same conceptual catchment model (HBV) to a Greek catchment, using identical data and model code. Calibration was performed manually. Subsequently, the modellers were asked for their experience, their calibration strategy, and whether they enjoyed the exercise. The exercise revealed that there is considerable modellers’ uncertainty even among the experienced modellers. It seemed to be equally important whether the modellers followed a good calibration strategy, and whether they enjoyed modelling. The exercise confirmed previous studies about the benefit of model ensembles: Different combinations of the simulation results (median, mean) outperformed the individual model simulations, while filtering the simulations even improved the quality of the model ensembles. Modellers’ experience, decisions, and attitude, therefore, have an impact on the hydrological model application and should be considered as part of hydrological modelling uncertainty

Trends in flow intermittence for European rivers

Intermittent rivers are prevalent in many countries across Europe, but little is known about the temporal evolution of intermittence and its relationship with climate variability. Trend analysis of the annual and seasonal number of zero-flow days, the maximum duration of dry spells and the mean date of the zero-flow events is performed on a database of 452 rivers with varying degrees of intermittence between 1970 and 2010. The relationships between flow intermittence and climate are investigated using the standardized precipitation evapotranspiration index (SPEI) and climate indices describing large-scale atmospheric circulation. The results indicate a strong spatial variability of the seasonal patterns of intermittence and the annual and seasonal number of zero-flow days, highlighting the controls exerted by local catchment properties. Most of the detected trends indicate an increasing number of zero-flow days, which also tend to occur earlier in the year, particularly in southern Europe. The SPEI is found to be strongly related to the annual and seasonal zero-flow day occurrence in more than half of the stations for different accumulation times between 12 and 24 months. Conversely, there is a weaker dependence of river intermittence with large-scale circulation indices. Overall, these results suggest increased water stress in intermittent rivers that may affect their biota and biochemistry and also reduce available water resources

EUSEDcollab: a network of data from European catchments to monitor net soil erosion by water

As a network of researchers we release an open-access database (EUSEDcollab) of water discharge and suspended sediment yield time series records collected in small to medium sized catchments in Europe. EUSEDcollab is compiled to overcome the scarcity of open-access data at relevant spatial scales for studies on runoff, soil loss by water erosion and sediment delivery. Multi-source measurement data from numerous researchers and institutions were harmonised into a common time series and metadata structure. Data reuse is facilitated through accompanying metadata descriptors providing background technical information for each monitoring station setup. Across ten European countries, EUSEDcollab covers over 1600 catchment years of data from 245 catchments at event (11 catchments), daily (22 catchments) and monthly (212 catchments) temporal resolution, and is unique in its focus on small to medium catchment drainage areas (median=43km2, min=0.04km2, max=817km2) with applicability for soil erosion research. We release this database with the aim of uniting people, knowledge and data through the European Union Soil Observatory (EUSO)

Operating Small Hydropower Plants in Greece under Intermittent Flow Uncertainty: The Case of Tsiknias River (Lesvos)

In arid and semi-arid parts of the world, river exploitation is intensive, involving water storage for irrigation or hydropower generation. In Greece, 100 small hydropower plants (SHPs) take advantage of less than 10% of the hydropower potential of low flow streams (<2 m3/s), a very small amount in relation to the 70% of the European Union. The energy policy of complete decarbonization of the country by 2023 on a national scale opens the road for new investments in SHP projects, especially in intermittent-flow streams of the Greek islands. Simulated flows by the Modello Idrologico SemiDistribuito in continuo (MISDc model) are used to construct the annual flow duration curve (FDC) to study and assess the hydropower potential of an intermittent stream (Tsiknias river, Lesvos, Greece). For Tsiknias River, but also for six other intermittent-flow rivers of Crete island, the capacity factor (CF), which represents the mean annual power of the hydropower plant, should remain >75% to exploit the river’s potential. The FDC and CF are essential in designing SHP projects in intermittent-flow streams with long no-flow periods. The development of public participatory approaches and a closer cooperation among policy makers and stakeholders should work to promote hydropower exploitation and accelerate licensing procedures

A Descriptive Study of the Schooling and Higher Education Reforms in Response to the Refugees’ Influx into Greece

Since 2015, a large number of migrants (refugees and asylum seekers) from the Middle East, Asia, and Africa have arrived in Greece and continued their onward journey to western European countries where they settled. As various European Union (EU) countries have later blocked the flow of migrants from Greece to their final destination, thousands of them have been trapped in Greece, confined in overcrowded, temporary camps (known as “hot spots„) and awaiting the processing of their asylum application. The current article examines the response of the Greek educational institutes (primary, secondary and tertiary levels) to the recent migrant influx, with ultimate goals to integrate, educate, and assist them. The number of refugees and asylum seekers living in Greece is estimated to be 58,000 (2018 data) with 22,500 children among them. Their schooling inclusion follows the plan 111, “Refugee Education Host Structures (REHSs)„, as initiated by the Greek Ministry of Education in 2017. Students’ leakage range is still high (10⁻40% at elementary school and 45⁻56% at high School). The disruption in their life results in the lack of regular attendance. Greek universities responded to the challenge of the refugee influx, especially the University of the Aegean (UAeg), which is located on the eastern Mediterranean migration route. The UAeg’s response plan focuses on four areas: (a) to provide education to refugees; (b) to conduct research on the refugee phenomenon and migration processes; (c) to increase local citizens’ awareness and improve social inclusion toward the migrants; and (d) to develop technologies to improve daily life in the refugee camps. These actions are significant toward the social inclusion and cohesion of refugees and the further improvement of their daily life

Assessing the Economic Damage of Potential Flooding Zones by Combining Cadaster and Land Use Data in the Larnaca Region, Cyprus

Precipitation changes caused by climate change are a phenomenon that may have far more serious consequences in urban areas than previously thought. Preventing the flood extent in rural and urban areas is crucial for the protection of human well-being and private and public land, and for the prevention of human casualties. Modeling potential floods and studying historic ones are key parameters to prevent damages from this natural disaster. European Union Directive 2007/60/EK obligated Member States to compile flood risk maps, showing the potential flood’s extent and depth. Using Cyprus river flood risk maps of the region of Larnaca, Corine land cover data, and open-access cadaster data, this study attempts to assess the economic damage. Cadaster data of buildings such as floor number and basement existence are incorporated in the damage functions used for flood recurrence intervals of 20, 100, and 500 years return periods. The study found that in the 500 year return flood period, 562 buildings would be potentially affected. The flood risk areas in the region of Larnaca consist of mainly urban (48%) and cultivation zones (50%), both economically important. The results suggest that economic damage assessment based on the applied data, combined with flood risk maps, can provide valuable information to disaster responders

Modeling hydrological and geochemical processes of a temporary river system

The Mediterranean region is characterized by a variety of microclimates ranging from humid, to semi-arid. Temporary rivers are the dominant surface water bodies under such climatic conditions. Temporary rivers are natural water bodies that experience a recurrent dry phase of varying duration and spatial extent (Uys and O'Keeffe, 1997). During dry periods, there is lack of water due to droughts, extensive evapotranspiration, infiltration, transmission losses, direct water abstraction (high irrigation demand), and overexploitation of groundwater. During the wet period, episodic events and especially the first flush is very important and determines river morphology and water quality (Hooke and Mant, 2002). Geomorphologically, these basins have steep slopes, braided channel morphology, fast travel time and expanded deltas. Temporary rivers are rarely monitored (due to their restricted economic importance), and if they are, the monitoring frequency is lower than what would be required to observed changes due to in-stream biogeochemical processes.Organic matter and nutrients accumulate in the riverbed of the delta at the onset of the dry season, creating hot spots (areas with high reactivity relative to their adjacent environment. The accumulated material is remobilized during the first flood event, transporting into the sea significant quantities of dissolved and suspended matter (hot moment- short periods of time that exhibit disproportionately high reaction rates relative to longer intervening time periods) (McClain et al., 2003). To date, research focused mostly on the geomorphology (Burge L.M., 2004; Anderson D.E., 2005; Kirkby et al., 2005) and the understanding of the flood events of temporary rivers (Belmonte-Camarasa and Beltran-Segura, 2001; De Vera M.R., 1984; Greenbaum and Bergman, 2006). The role of soil moisture and temperature variation on sediment processes that affect Nitrogen (N) and Phosphorous (P) cycles has not been studied adequately. This is an important gap of knowledge since the availability of nutrient and moisture are the principal factors that control the structural and functional characteristics of river communities, including their spatial distribution along the river (Jacobson et al., 2000; D'Odorico et al., 2004). At the same time, river sediments exhibit diurnal temperature fluctuations up to 40°C (Tzoraki et al., 2005). These variations affect microbial activities (including solubilization of organic carbon, mineralization and nitrification rates, carbon respiration rates and microbial decomposition of plant biomass (Zaman and Chang, 2004)) which in turn influence nutrient dynamics. The impact of diurnal temperature variation on in-stream biogeochemical processes has not been studied yet. Temporary rivers dominate the geoenvironment of Greece. The watershed area of temporary rivers that drain into the sea cover approximately 42.5 % of the total area of Greece (Tzoraki et al., 2004). Most of the tributaries of large rivers in Greece can also be characterised as temporary rivers as they become completely dry during the summer. In addition, mountainous tributaries of large rivers exhibit Hortonian characteristics (due to prevalent karstic geology, high catchment slopes, low infiltration soils and shallow depth to bedrock) and their hydrologic response is very flashy and temporary in nature. Temporary rivers have not been studied in Greece at all (Tzoraki et al., 2004). The objective of this research was to assess the importance of predominant in-stream biogeochemical processes that affect nitrogen and phosphorous cycles of a typical Mediterranean temporary river. Hydrologic, sediment and water quality data collected in the field, together with field and laboratory experiments were used to identify and assess the potential impact of in-stream processes on nutrient dynamics of temporary rivers. Krathis River, a temporary river basin with a catchment area of 149 km² located in northern Peloponnesus, Greece, was selected as the study site. It is a mountainous basin (mean altitude 1092 m, mean slope 33%) comprised of neogene and quaternary sediments (60%) limestone (22%) and flysch (18%). The annual average precipitation for the catchment is 845 mm and the potential evapotranspiration 850 mm. There are 111 springs within the watershed located mostly in the karst. Forests cover 75.4% of the watershed, while the cultivated areas cover 24.4% (Amaxidis and Skoulikidis, 2005). The main characteristic of Krathis River is a very high slope gradient (high slopes up to 27% and almost flat 3% in the northern part) that makes the hydrologic response very flushy. The channel morphology is narrow (a few meters wide) with large gravel bed in the high slope portions and it widens (100 meters wide) with graded sand and gravel before it enters the sea. The northern part of the river dries out (occasionally) in the summer due to the combined action of draughts and water abstraction for irrigation. In addition, the channel is partially inundated throughout the year due to the 10fold expansion in size of the channel width. The northern part of Krathis River has all the characteristics of a temporary river. The main channel is wide and has low slopes, the inundated area continuously expands and contracts (changing the sediment moisture in the river bed), and has high sediment accumulation (due to change in channel slope) which is subject to the first flush from the fall rain events. The study site (river reach) is located in the northern end of Krathis River and has a length of 300 m (the reach was selected to have a length 5 times the width of the riparian corridor). No point sources or tributary streams enter the study reach. Three intensive field campaigns (June and November of 2003 and June of 2004) were conducted aimed at gaining better understanding of the hydrologic and water quality regime of the river. A series of field techniques were applied in the study reach in order to understand its hydrologic regime (multilevel wells, infiltration tests and pumping tests). Surface sediment samples (Hot Spots) (from the upper oxidized zone) were collected to estimate the physicochemical properties of the riverbed and to study the main nutrients processes. Analysis of nitrogen and phosphorous cycles indicated that mineralization, nutrient release from and sorption to the sediments were the significant processes occurring at the site. Laboratory experiments were conducted to assess the capacities and rates of these processes. In these experiments, it was important to study nutrient-sediment (hot spots) interaction since these were the most mobile fraction of the river sediments. These processes were studied in the context of soil moisture and temperature variability. The field and laboratory studies provided the necessary information for the development of a conceptual understanding of the hydrologic and biogeochemical mechanisms and in-stream processes that affect the fate and transport of nitrogen and phosphorous. This work illustrated that temporary rivers had high variability in spatial and temporal characteristics. The inundated area in the study site varied from 20-100%. Krathis River exhibited high annual flow variability ranging from 0.05 to 13 mV. There was a significant amount of sediments with fine composition that created “hot spot” areas in the river reach that were flushed out in the fall carrying a significant load of nutrient and suspended matter to the coastal zone. In addition, transmission losses contributed significantly to lowering the amount of water during the dry months. Another problem is the challenge to mathematically model a temporary river. The geomorphology of temporary rivers in the Mediterranean region is outside the traditional geologic norms that watershed models are based on. For instance, a large number of temporary rivers are located in karst areas. Karstic aquifers discharge in springs that feed the temporary rivers with base flow. Karstic base flow which cannot be modelled by traditional watershed models, comprise an important component of river hydrology (White, 2002) and should be included in the hydrologic models. Previous studies were focused mainly on the simulation of fracture and conduit flow in karst aquifers and not on the baseflow contribution of the springs in river hydrograph (Jaquet et al., 2004; Manda and Gross, 2006). A new framework for hydrologic analysis in watersheds where karst formations predominate was developed. Such watersheds could not be simulated in the past because watersheds models could not simulate flushy hydrologic response with runoff coefficients of 0.77 while maintaining flow in the river during the summer even though there was no rain event for periods up to 4 months. To overcome this problem, a new physically based conceptual model that simulated karstic flows throughout the year was developed and it was coupled with the watershed model HSPF. The karstic model simulated not only the recession limb of the spring hydrograph during the dry period (Aquilina et al., 2006; Kiraly L., 2003), but also spring discharges during and after rain and snow melt events using a daily time step. The advantages of using the new approach were twofold: it provided the analytical tool to conduct scenarios concerning climate change (precipitation and temperature variations affecting the rate of snow melt and thus the river base flow) as well as a tool for analyzing the karstic system (understand how the system works, the area of the contributing karst which extends outside the boundaries of the river watershed, the upper and lower reservoirs). The annual average runoff coefficient that was simulated by the watershed model (by subtracting from the river flow the flow from the karst) was recalculated to be 0.42 which is a typical value for Mediterranean catchments. With the new framework, the combined karstic and conventional catchment models were capable of simulating the hydrology (flushy hydrographs with karstic spring flows, steep slopes and high elevation differences) and water quality of Krathis river successfully. The statistics of the performance of the combined models were very good. This framework can be used in simulating karstic, temporary river basins. Existing water quality models such as QUAL2E, WASP, BASINS, HSPF, ETD don't take under consideration the expansion and contraction dynamic of the temporary rivers, the wet and dry period of the riverbed and the dependence of biogeochemical processes on soil moisture and temperature. In order to simulate the biogeochemical processes that dominate in the temporary rivers, the creation of a new model that works at reach scale was necessary. The RSTM (Reach-Scale TempQsim Biogeochemical Model) is a generalized model that can describe the hydrologic, sediment transport and biogeochemical processes of temporary rivers at the reach scale. The model takes under account the expansion-contraction of the inundated area of the river. The RSTM is capable of simulating the processes temporally during the wet and dry period and spatially where the river corridor is expanded and contracted. The RSTM consists of a Hydrologic submodel, a Sediment Transport submodel and a Water Quality submodel. The innovation parts of this PhD dissertation are: (1) A new framework for hydrologic analysis in watersheds, where karst formations predominate was developed. The karst model was developed. (2) Processes of nitrogen and phosphorous were studied in stream in temporary rivers (3) The role of moisture and temperature variation on sediment processes that affect Nitrogen (N) and Phosphorous (P) cycles has been studied. (4) Studies carried out in sediments samples from four temporary rivers in order to assess the affect of moisture and temperature variation in the river water quality. (5) A new model was developed, the Reach Scale tempQsim Model (RSTM) that can describe the hydrologic, sediment transport and biogeochemical processes of temporary rivers at the reach scale.Τα ημίξηρα περιβάλλοντα καλύπτουν περίπου 35% της γήινης χερσαίας επιφάνειας (Wilcox and Newman, 2005). Στην Ευρώπη, ο ημίξηρος χαρακτήρας του Μεσογειακού κλίματος εγκυμονεί κινδύνους, τόσο ξηρασίας από την έλλειψη γεγονότων βροχής κατά τους θερινούς μήνες, όσο και της ερημοποίησης και έκπλυσης του εδάφους από τα πρώτα γεγονότα βροχής. Ένα ιδιάζον χαρακτηριστικό του ημίξηρου κλίματος είναι η ύπαρξη ποταμών διαλείπουσας ροής, δηλαδή ποταμών, που η ροή λαμβάνει χώρα για κάποια χρονικά διαστήματα κατά τα διάρκεια του έτους (Uys and Keeffe, 1997). Επειδή τα ποτάμια διαλείπουσας ροής αφορούν ένα πολύ μεγάλο ποσοστό της Μεσογείου και της χώρας μας και δεδομένου ότι λόγω των κλιματικών αλλαγών και της επικείμενης ξηρασίας απειλούνται με λειψυδρία πολλές χώρες της υδρογείου και συνεπώς, και μεσογειακές χώρες κρίθηκε απαραίτητη και αναγκαία η μελέτη των περιβαλλοντικών αυτών συστημάτων. Η μελέτη αυτών των συστημάτων είναι περιορισμένη και κυρίως είχε εστιαστεί στην μορφολογία τους και στην κατανόηση των πλημμυρικών φαινομένων. Δεν έχει μέχρι σήμερα μελετηθεί και δεν έχει γίνει ακόμα κατανοητό, πώς συμπεριφέρνονται οι λεκάνες απορροής ποταμών διαλείπουσας ροής στις αλλαγές της θερμοκρασίας και της υγρασίας (ραγδαίες βροχοπτώσεις και μεγάλες περίοδοι ξηρασίας) και αν το ρυπαντικό φορτίο που δέχονται (λιπάσματα, απόβλητα, λύματα, σκουπίδια κ.λπ.) επηρεάζεται από τους παράγοντες αυτούς. Η παρούσα διδακτορική διατριβή εστιάζεται στη μελέτη των υδρολογικών και βιογεωχημικών διεργασιών των ποτάμιων συστημάτων διαλείπουσας ροής της Μεσογείου. Λόγω της εναλλαγής υγρής και ξηρής περιόδου τα ποτάμια αυτά παρουσιάζουν έντονη χωρική διαφοροποίηση, διότι η υγρή κοίτη του ποταμού διαπλατύνεται κατά την υγρή περίοδο και συρρικνώνεται κατά την ξηρή. Συνήθως, με την πρώτη βροχή παρατηρείται το φαινόμενο της πρώτης πλημμύρας (first flush), όπου το νερό προκαλεί διάβρωση της κοίτης και κατά συνέπεια μεταφέρει μεγάλο όγκο φερτών υλικών και ρύπων στον κάτω ρου και στην παράκτια ζώνη. Η εναλλαγή ξηρών και υγρών περιόδων δεν επηρεάζει μόνο τη μεταφορά ιζημάτων και ρύπων, αλλά ολόκληρο το βιογεωχημικό κύκλο. Οι πλημμύρες επηρεάζουν έμμεσα τον κύκλο των θρεπτικών, διότι είναι η κύρια αιτία εναπόθεσης νέου ιζήματος και διαμόρφωσης ενός μωσαϊκού ιζημάτων, τόσο από άποψη κοκκομετρίας, όσο και ορυκτολογικής σύστασης. Η σύσταση και η κοκκομετρία των ιζημάτων επηρεάζει τόσο το ρυθμό απονιτροποίησης, όσο και άλλες διεργασίες. Ο ρόλος της υγρασίας και της θερμοκρασίας των ιζημάτων, που επηρεάζουν τους κύκλους του αζώτου και του φωσφόρου, δεν έχει μελετηθεί ικανοποιητικά. Αυτό είναι ένα σημαντικό κενό, κυρίως λόγω του ότι τα θρεπτικά και το διαθέσιμο περιεχόμενο σε υγρασία των ιζημάτων ρυθμίζουν τη δομή και τη λειτουργία των βιοκοινωνιών και των ενδιαιτημάτων τους. Οι ιδιαίτερες βιογεωχημικές διεργασίες, που λαμβάνουν χώρα (in stream) σε ποτάμια διαλείπουσας ροής δεν είναι πλήρως κατανοητές. Παρά το μεγάλο αριθμό μοντέλων ποιότητας νερού, δεν υπάρχει προηγούμενη εμπειρία από την εφαρμογή ενός μοντέλου σε ποτάμι διαλείπουσας ροής. Η προσομοίωση ποταμού διαλείπουσας ροής δεν είναι εφικτή, εξαιτίας των περιορισμών με τους οποίους περιγράφονται στα διαθέσιμα μοντέλα οι υδρολογικές διεργασίες και οι διεργασίες στα ιζήματα της κοίτης του ποταμού. Συνεπώς, πρέπει να τροποποιηθούν τα διαθέσιμα υδρολογικά μοντέλα ή να δημιουργηθούν νέα, που θα λαμβάνουν υπόψη τα ειδικά υδρολογικά χαρακτηριστικά των ποταμών διαλείπουσας ροής, δίνοντας ιδιαίτερη βαρύτητα στο φαινόμενο του πρώτου πλημμυρικού επεισοδίου βροχής, καθώς και στις βιογεωχημικές διεργασίες, που λαμβάνουν χώρα στα ιζήματα κατά τη διάρκεια της ξηρής περιόδου. Περιοχή μελέτης αποτέλεσε ο Κράθης ποταμός στη βόρεια Πελοπόννησο, διότι παρουσιάζει όλα τα χαρακτηριστικά ενός ποταμού διαλείπουσας ροής. Το κύριο χαρακτηριστικό του είναι οι μεγάλες κλίσεις (υψηλές κλίσεις μέχρι και 27% ανάντη και σχεδόν επίπεδος 3% κλίση στο βόρειο τμήμα, κατάντη) που δίνουν ένα χειμαρρώδη χαρακτήρα στην υδραυλική του συμπεριφορά. Η διατομή της κοίτης του ποταμού είναι πολύ στενή, λίγα μόλις μέτρα πλάτους, με μεγάλες πέτρες και λιθάρια ανάντη, ενώ πριν την εκβολή του στη θάλασσα το πλάτος φθάνει τα 100 μέτρα πλάτος. Κατά μήκος του κυρίου κλάδου παρατηρείται μεγάλη διαφορά υψομέτρου. Το βόρειο τμήμα του ποταμού ξηραίνεται (περιστασιακά) το καλοκαίρι λόγω της συνδυαστικής δράσης της ξηρασίας-ανυδρίας και των αντλήσεων για την κάλυψη των αρδευτικών αναγκών. Επίσης το τμήμα αυτό, κατά τη διάρκεια του χρόνου πλημμυρίζει, εν μέρει, με αποτέλεσμα το πλάτος του να απλώνεται και 10 φορές περισσότερο από το μέσο πλάτος της κοίτης. Το βόρειο αυτό τμήμα του Κράθη έχει όλα τα χαρακτηριστικά ενός ποταμού διαλείπουσας ροής. Η κοίτη έχει μεγάλο πλάτος και πολύ μικρές κλίσεις και η πλημμυρική επιφάνειά της διαρκώς επιμηκύνεται και διαπλατύνεται (μεταβάλλοντας το ποσοστό υγρασίας στην κοίτη), ενώ παρουσιάζει μεγάλη συγκέντρωση ιζημάτων (λόγω της απότομης μεταβολής της κλίσης), τα οποία αποτελούν ουσιαστικά τα προϊόντα της διάβρωσης της first flush. Οι κύριοι στόχοι της παρούσας διατριβής είναι: • Η εφαρμογή και αξιολόγηση υδρολογικού μοντέλου λεκάνης απορροής για την προσομοίωση ποταμού διαλείπουσας ροής, περίπτωση Κράθη ποταμού. • Η μελέτη των βιογεωχημικών διεργασιών του αζώτου (Ν) και του φωσφόρου (Ρ) στα ιζήματα, τόσο στο πεδίο, όσο και στο εργαστήριο σε συνάρτηση με τη θερμοκρασία και της υγρασία. • Η αξιολόγηση της σημασίας των βιογεωχημικών διεργασιών στην επιβάρυνση του ποταμού, του υπόγειου υδροφόρου στρώματος και του παράκτιου συστήματος, • Η δημιουργία γενικευμένου μοντέλου ποταμού διαλείπουσας ροής, που θα καλύψει τα κενά των υπαρχόντων μοντέλων. • Η σύγκριση των πειραματικών αποτελεσμάτων των διεργασιών στα ιζήματα του Κράθη ποταμού με τα αποτελέσματα από τρία επιπλέων ποτάμια διαλείπουσας ροής της Μεσογείου, για να μελετηθεί η επίδραση των διεργασιών στη χημεία των ποταμών αυτών. Η μελέτη εστιάστηκε στο κατώτερο πεδινό τμήμα του ποταμού, όπου πραγματοποιήθηκαν μελέτες πεδίου (διάνοιξη γεωτρήσεων, υδρολογικές μελέτες, μετρήσεις υδραυλικών παραμέτρων) και περαιτέρω μελέτες των ιζημάτων στο εργαστήριο (φυσικοχημικός χαρακτηρισμός των ιζημάτων και πειράματα μελέτης των διεργασιών των θρεπτικών). Λόγω της έλλειψης δεδομένων και για να δημιουργηθεί μια πλήρη εικόνα των εισροών μέσα στο τμήμα ποταμού μελετήθηκε ολόκληρη η λεκάνη απορροής, όσον αφορά στα υδρολογικά, γεωχημικά και από άποψη διάβρωσης και ρύπανσης χαρακτηριστικά της. Στόχος ήταν να προσδιοριστούν οι παράμετροι εκείνες που καθορίζουν το χαρακτήρα της διαλείπουσας ροής του Κράθη ποταμού, όπως η τιμή της επιφανειακής απορροής, οι κλίσεις κ.α. Όσον αφορά στο μεγαλύτερο μέρος της λεκάνης απορροής του Κράθη (πλην του κατώτερου τμήματος μελέτης) έγινε προσομοίωση της υδρολογίας, της μεταφοράς ιζημάτων και των θρεπτικών με το υδρολογικό μοντέλο HSPF σε συνδυασμό με το καρστικό μοντέλο (που αναπτύχθηκε στα πλαίσια αυτής της διατριβής). Το καρστικό μοντέλο λαμβάνει υπόψη την ύπαρξη δυο υπόγειων ταμιευτήρων, ενός ανώτερου γρήγορης απόκρισης και ενός κατώτερου αργής απόκρισης και υπολογίζει τις εκφορτίσεις των πηγών στη λεκάνη απορροής του ποταμού με ημερήσιο χρονικό βήμα. Επίσης, πραγματοποιήθηκαν μελέτες στο πεδίο και στο εργαστήριο για να προσδιοριστούν οι παράμετροι του μοντέλου όπως είναι η ταχύτητα διήθησης, το πορώδες, η υγρασία, η μηχανική σύσταση των εδαφών κ.λπ. Με το μοντέλο HSPF προσδιορίστηκαν οι εισροές στο τμήμα μελέτης και με τις χημικές αναλύσεις, τόσο κατά τη διάρκεια γεγονότος βροχής, όσο και κατά την περίοδο χαμηλής ροής και την ανάλυση των κύκλων αζώτου και φωσφόρου καθορίστηκε η σπουδαιότητα των διεργασιών σε επίπεδο τμήματος ποταμού. Από την ανάλυση έγινε κατανοητό ποιες διεργασίες παίζουν σημαντικό ρόλο, ποιες όχι και ποιες χρήζουν περαιτέρω μελέτης στο εργαστήριο. Στη συνέχεια, διεξήχθησαν στο εργαστήριο πειράματα διαλείποντος έργου (batch) (κινητικά και ισορροπίας) για τη μελέτη των κύριων γεωχημικών διεργασιών: ανοργανοποίηση, εκχύλιση και προσρόφηση. Από τις χημικές αναλύσεις και την επίλυση των εξισώσεων ισοζυγίου για άζωτο και φώσφορο υπολογίστηκαν τα φορτία των θρεπτικών που δημιουργούνται (εισέρχονται ή μετασχηματίζονται) του τμήματος του Κράθη ποταμού και που εμπλουτίζουν τον υπόγειο υδροφορέα και το παρόχθιο περιβάλλον ή καταλήγουν λόγω των ραγδαίων βροχοπτώσεων στη θάλασσα. Δημιουργήθηκε το μοντέλο Reach Scale tempQsim (RSTM), που περιγράφει τις κύριες υδρολογικές και βιογεωχημικές διεργασίες που λαμβάνουν χώρα στο τμήμα μελέτης ποταμού. Το μοντέλο αυτό λειτουργεί σε κλίμακα τμήματος ποταμού και περιλαμβάνει διεργασίες, όπως διαπλάτυνση - συρρίκνωση της κοίτης, περιοχές της κοίτης upwelling-downwelling και διεργασίες (προσρόφηση, εκρόφηση, ανοργανοποίηση θρεπτικών κ.α.), που λαμβάνουν χώρα όχι μόνο στη στήλη του νερού αλλά και στη στήλη του ιζήματος. Το μοντέλο λαμβάνει υπόψη τη μεταβολή του ρυθμού των διεργασιών σε συνάρτηση με τη θερμοκρασία, την κύρια παράμετρο σε περιβάλλοντα διαλείπουσας ροής. Συμπεριλαμβάνει, επίσης, την επίδραση της υγρασίας των ιζημάτων στους ρυθμούς των αντιδράσεων, καθώς κατά τη διάρκεια της ξηρής περιόδου τα ιζήματα της κοίτης από υπερκορεσμένα μειώνουν βαθμιαία το ποσοστό υγρασίας μέχρι και 20%. Τέλος, έγινε αναγωγή των στοιχείων πεδίου από συγκεκριμένες θέσεις στο πεδίο και των ρυθμών ταχυτήτων που υπολογίστηκαν από εργαστηριακές μελέτες σε κλίμακα τμήματος ποταμού, τα οποία εισήχθησαν στο μοντέλο RSTM, προκειμένου να προσομοιωθούν οι υδρολογικές και γεωχημικές διεργασίες της κοίτης του Κράθη ποταμού (διεργασίες θρεπτικών, first flush, expansion - contraction) κατά τη διάρκεια των δυο ετών παρακολούθησης της λεκάνης. Για να ολοκληρωθεί ο προσδιορισμός και η κατανόηση της επίδρασης των κύκλων υγρασίας και ξηρασίας στις διεργασίες των ιζημάτων, που προέρχονται από ποτάμια διαλείπουσας ροής και για