Ανάπτυξη καμπυλών καταλληλότητας ενδιαιτημάτων ιχθυοπανίδας με σκοπό τον υπολογισμό οικολογικών παροχών

Abstract

Water needs for several anthropogenic uses are growing rapidly. Increasing water demand for human purposes intensify the need for better understanding on the relationships between the biota and the environment since less water mean less space for the riverine organisms. The ability of water to cover uses such us domestic, irrigation, industrial, energy, recreation require humanity to reinforce trade-offs between environmental and all the other water uses. In addition, the growing demands for water have increased the need to build dams, which in many cases alter the seasonal and interannual streamflow variability of rivers (Poff et al. 2007), while they also reduce the available amount of water downstream (Li et al. 2012; Mao et al. 2016). To mitigate the downstream impact of dams, several countries worldwide have established environmental flow rules, to quantify the water required for ecosystem conservation and resource protection (Tharme 2003). When it comes to rivers in Greece, limited work has been carried out regarding the development of adequate ecological flow assessment methods considering local ecological conditions (Muñoz-Mas et al. 2016; Papadaki et al. 2016). Flow regime is often severely impacted by over-abstraction for agriculture and other uses, and some formerly perennial rivers now flow as artificially intermittent courses, with parts of the river stretch being totally desiccated during the summer period (Benejam et al. 2010; Skoulikidis et al. 2011). In this thesis, a worldwide review of the present status of environmental flow methodologies has been carried out. Four major categories of these methodologies (hydrological, hydraulic rating, habitat simulation and holistic), are presented and analyzed. Moreover habitat suitability models for seven Greek endemic fish species have been developed. The habitat requirements are represented by functions known as Habitat Suitability Indices (HSIs), which are curves describing habitat suitability for various target species. Habitat Suitability Curves (HSC) have become by far the most common approach in studies involving the physical habitat simulation (Payne and Allen, 2009). The HSCs werecategorized by Bovee (Bovee, 1986) in three categories according to the methodology of their development. Category I include curves generated from literature and experts' experience. Consequently they do not consider empirical microhabitat data. Category II are the Habitat Use curves, based on frequency analysis of the habitat variables at the fish locations. The last, Category III curves, are also known as preference curves. These curves derived also from observational data on habitat use (i.e. hydraulics in the locations where fish were observed) but weighted (or divided) by the habitat availability (i.e. hydraulics over the surrounding unoccupied locations). For the development of the HSC each fish species was categorized into size classes for the field work and data analyses. These classes were estimated in cm based on simple intervals (e.g. 0-5 cm total length, 5-10. 10-20, etc.). Fish habitat data were collected from mountain areas using specific hydro ecological and water management criteria to ensure the representation of a significant variety of aquatic habitats and the fish species living in the Greek medium sized streams, as well as sites with significant hydrologic alterations from human developments (eg dams and irrigation abstractions). Two techniques were used for their selection snorkelling and electrofishing). In addition hydraulic modeling was combined with the developed habitat models to estimate areas of available habitat in terms of Weighted Suitable Area (WUA), for most of the aforementioned fish species. Weighted Usable Area (WUA) is the most renowned general indicator of habitat quality and quantity and is usually calculated for every of the simulated flows becoming the WUA-flow curve (Boavida et al., 2014). Upon the WUA-flow curve further calculations were made for Environmental Flow Assessment, for instance the comparison of alternative flow regimes and/or scenario analysis with habitat time series (Milhous et al., 1990; Papadaki et al, 2016). In this PhD a threshold index was developed (WUA0.5) mainly because the productive capacity of small areas with optimum habitat is different than the large areas of less than optimum habitat.Hydraulic-habitat models combine the dynamic behavior of river discharge with geomorphological and ecological responses. In this PhD project a Pseudo-two-dimensional (2D) model based on the one-dimensional (1D) HEC-RAS model and a 2D hydrodynamic model (FLOW-R2D) for several flows in respect to summer conditions were applied to several study sites of the upper part of Acheloos river. Comparison of models results was made in terms of water depths and velocities as well as habitat predictions in terms of weighted usable area (WUA). During this PhD project three main publications were made. The main objective of the first one was to assess potential climate change impacts on the generic hydrological patterns and constituent fish habitats in a typical mountain river system of the south-western Balkans focusing on a case-study in the upper part of Acheloos River, Northwestern Greece.The climate change in the Mediterranean area is expected to have significant impacts on the aquatic ecosystems and particular in the mountain rivers and streams that often host important species such as the Salmo farioides, Karaman 1938. These impacts will most possibly affect the habitat availability for various aquatic species resulting to an essential alteration of the water requirements, either for dams or other water abstractions, in order to maintain the essential levels of ecological flow for the rivers. The altered flow regimes under different emission scenarios of the Intergovernmental Panel on Climate Change (IPCC) were estimated using a hydrologicalmodel and based on regional climate simulations over the study area. The most prominent effects of the climate change scenarios depict severe flow reductions that are likely to occur especially during the summer flows, changing the duration and depressing the magnitude of the natural low flow conditions. Weighted Usable Area-flow curves indicated the limitation of suitable habitat for the native trout. Finally, this preliminary application highlighted the potential of science-based hydrological and habitat simulation approaches that are relevant to both biological quality elements (fish) and current EU Water policy to serve as efficient tools for the estimation of possible climate change impacts on the south-western Balkan river ecosystems.In the second publication hydraulic-habitat models (1D and 2D hydrodynamic models) were used for estimating environmental flow requirements in terms of weighted usable area (WUA). In general, 2D models are more promising in habitat studies since they quantify spatial variations and combinations of flow patterns important to stream flora and fauna in a higher detail than the 1D models. Relationships between WUA and discharge for the two models were examined, to compare the similarity as well as the magnitude of predictions over the modelled discharge range. The models predicted differences in the location of maxima and changes in variation of velocity and water depth. Finally, differences in spatial distribution (in terms of suitability indices and WUA) between the Pseudo-2D and the fully 2D modelling results can be considerable on a cell-by-cell basis.In the third publication implemeentation of environmental flows incorporating a hydrologic and a fish habitat simulation method was carried out. The ecological integrity of rivers ultimately depends on flow regime. Flow degradation is especially prominent in Mediterranean systems and assessing environmental flows in modified rivers is difficult, especially in environments with poor hydrologic monitoring and data availability. In many Mediterranean countries, which are characterized by pronounced naturalvariability and low summer flows, water management actions usually focus on prescribing minimum acceptable flows estimated by hydrologic methods. In this study, a comparative assessment of environmental flow estimation methods is developed in a river with poorly monitored flows and limited understanding of past reference conditions. This assessment incorporates both a hydrologic and a fish habitat simulation effort that takes into consideration hydrologic seasonality in a Greek mountainous river. The results of this study indicate that especially in data scarce regions the utilization of biotic indicators through habitat models, may provide valuable information, beyond that achievable with hydrologic methods, for developing regional environmental flow criteria. Despite the widespread use of the method, challenges in transferability of fish habitat simulation provide undefined levels of uncertainty and may require the concurrent use of different assessment tools and site-specific study.5. ConclusionsEstimation of ecological flows is not an easy task. Comparison between different approaches revealed significant differences between hydrological and habitat simulation methodologies. Also, transferability issues of fish data even with small differences in geomorphological and environmental conditions, can be difficult for mountain rivers in the Mediterranean. Although fish are important indicators of instream flow conditions, theremight be confusion in cause of poor application of habitat suitability models when relationships between fish and their habitats are not clear and properly quantified. Water management issues need to be considered by multidisciplinary teams, working with local authorities and administrations towords a holistic approach. Finally, future changes in other anthropogenic stresses on fish habitat, such as increasing water withdrawals, dams or changing land use must also be quantified and analyzed. Thereafter, more research is needed to investigate the effects of flow reduction and flow regime change on the instream environments of mountain rivers. This is especially important in sensitive areas with high-endemicity aquatic ecosystem within restricted freshwater ecoregions such as in the southernwestern Balkans.

Στο πλαίσιο της παρούσας διδακτορικής διατριβής έγινε ενδελεχής επισκόπηση όλων των θεμάτων που σχετίζονται με τις οικολογικές παροχές. Παράλληλα, αναπτύχθηκαν καμπύλες καταλληλότητας ενδιαιτημάτων εφτά ειδών της ελληνικής ιχθυοπανίδας ως τμήμα ενός ευρύτερου μεθοδολογικού πλαισίου εκτίμησης των οικολογικών παροχών κινούμενο προς το πνεύμα της Ευρωπαϊκής Οδηγίας – Πλαίσιο (2000/60/ΕΚ, ΟΠΥ; EC, 2000). Αρχικά έγινε εκτενής ανάλυση και μελέτη της βιβλιογραφίας. Ακολούθησαν δειγματοληψίες κατά την περίοδο Σεπτέμβριος 2013 έως Αύγουστος 2016 για τη συλλογή των δεδομένων, με στόχο την ανάπτυξη των καμπυλών καταλληλότητας ενδιαιτημάτων ιχθυοπανίδας ως προς βασικές παραμέτρους (βάθος, ταχύτητα, υπόστρωμα και κάλυψη) και την ανάπτυξη υδραυλικών μοντέλων ως τμήμα ενός μεθοδολογικού πλαισίου εκτίμησης οικολογικών παροχών σε ελληνικές συνθήκες. Η συλλογή των δεδομένων ιχθυοπανίδας πραγματοποιήθηκε μέσω της παρατήρησης με μάσκα και μέσω της ηλεκτραλιείας. Τα δεδομένα της ιχθυοπανίδας επεξεργάστηκαν στατιστικά και σε επόμενο στάδιο αναπτύχθηκαν αλγόριθμοι (ψευδοκώδικες) σε περιβάλλον R (R Core Team, 2014) με στόχο την ποσοτικοποίηση των σχέσεων μεταξύ της παροχής και των παραμέτρων που προαναφέρθηκαν. Οι αλγόριθμοι αυτοί χρησιμοποιήθηκαν για την ανάπτυξη καμπυλών καταλληλότητας ενδιαιτημάτων δύο τύπων (χρήσης και προτίμησης) και για την εκτίμηση κατάλληλης σταθμισμένης έκτασης (WUA) με ενσωματωμένο ένα κριτήριο βελτιστοποίησης (0.5) της καταλληλότητας της σταθμισμένης κατάλληλης έκτασης (WUA0.5) το οποίο αναπτύχθηκε στο πλαίσιο της διατριβής για την εκτίμηση της διαθεσιμότητας ενδιαιτημάτων ιχθυοπανίδας με υψηλή καταλληλότητα σε διαφορετικές παροχές. Οι περιοχές μελέτης αφορούν κυρίως ορεινά τμήματα ποταμών. Επιλέχθηκαν έχοντας γνώμονα την ήπια ανθρωπογενή παρέμβαση προσεγγίζοντας συνθήκες αναφοράς, τόσο για τη συλλογή των δεδομένων ιχθυοπανίδας όσο και για τα υδραυλικά μοντέλα. Στο πλαίσιο εκπόνησης της διδακτορικής διατριβής πραγματοποιήθηκαν τρεις βασικές εφαρμογές με αντικείμενο την κλιματική μεταβλητότητα και τη συσχέτιση αυτής με ενδιαιτήματα οργανισμών στόχων (ενδείκτες) σε ορεινά ποτάμια, τη σημασία της μονοδιάστατης και δισδιάστατης υδραυλικής προσομοίωσης στην εκτίμηση των οικολογικών παροχών και τέλος τη διερεύνηση διαφορετικών προσεγγίσεων που σχετίζονται με την εκτίμηση των οικολογικών παροχών. Τα αποτελέσματα από την πρώτη εφαρμογή έδειξαν ότι υπό την επίδραση ενδεχόμενων κλιματικών σεναρίων (ειδικά με βάση τα Α2 και Α1Β 2100) της Διακυβερνητικής Επιτροπής για την Αλλαγή του Κλίματος (IPCC - Intergovernmental Panel on Climate Change) θα συμβεί τροποποίηση του υφιστάμενου καθεστώτος ροής. Συγκεκριμένα τα αποτελέσματα έδειξαν μείωση του ρυθμού εμφάνισης πλημμυρικών επεισοδίων τη θερινή περίοδο, η οποία θα επηρεάσει αρνητικά τα ενδιαιτήματα της ενδημικής πέστροφας του Αχελώου περιορίζοντας την υψηλή καταλληλότητα. Τα αποτελέσματα της δεύτερης εφαρμογής έδειξαν ότι η προσομοίωση ταχυτήτων από μονοδιάστατο και δισδιάστατο υδραυλικό μοντέλο επηρεάζει σε μεγαλύτερο βαθμό τα αποτελέσματα της καταλληλότητας ενδιαιτημάτων συγκριτικά με την παράμετρο του βάθους. Τέλος τα αποτελέσματα της τρίτης εφαρμογής δείχνουν υποεκτίμηση των μηνιαίων ελάχιστων παροχών από την υδρολογική μεθοδολογία συγκριτικά με την μεθοδολογία προσομοίωσης ενδιαιτημάτων. Βασικό κίνητρο για την ολοκλήρωση της διδακτορικής διατριβής σε όλη τη διάρκεια αυτής ήταν η εναρμόνιση και η σύνδεση του ερευνητικού χαρακτήρα με την επικαιρότητα και τα πραγματικά ζητήματα με τα οποία σχετίζεται το αντικείμενο των οικολογικών παροχών.