No description available.

No description available.

Escalating demands for sustainable water resources management, anthropogenic disturbances (e.g. channelisation and impoundment) and changing environmental conditions (for example floods and droughts) has led to an increased need to understand the influence of 'flow variability' on in-stream ecological communities. In this thesis, the importance of hydrological variability in structuring macroinvertebrate communities is explored at a range of spatial and temporal scales for rivers across England and Wales. At the reach scale (individual river reach), the influence of flow velocity variability on the seasonal distribution of benthic macroinvertebrate communities is examined. At the mesoscale (regional), hydrological regime variability and macroinvertebrate community data (species- and family-level) for fourteen rivers (all located within the Environment Agency, Anglian northern region) are examined over an eleven-year period (1990-2000). At the macroscale (national), the hydrological regime and family-level macroinvertebrate community data for 83 rivers across England and Wales are explored for an eleven-year period (1990-2000) to identify macroscale ecological responses using a range of 'ecologically-relevant' hydrological variables (up to 201 indices).

An exquisitely preserved biota is preserved in the Pragian Rhynie cherts an ancient hot spring deposit located in NE Scotland. This biota inhabited the subaerial and subaqueous niches that developed on the distal parts of the outwash apron created by the silica depositing hot springs. A key element of the subaqueous biota preserved in the cherts is the charophyte alga<i> Palaeonitella cranii</i> (Kidston & Lang) Pia. With ecorticate thalli that give rise to whorls of furcating branchlets and anteridia that are attached to the branchlet furcations by a pedicel <i>P. cranii</i> has a body which is remarkably similar to that of the extant Nitelleae tribe of charophytes. <i>Palaenitella</i> has non-calcified gryogonites composed of 6 sinistrally spiralling cells to which are attached a single tier of 6 coronula cells, a form that has affinities with the extant Chareae tribe. <i>Palaeonitella</i> may, therefore, be an early ancestor of the Chareae, one that retains the body plan of the more basal Nitelleae. Overall, the preservation of biota in the Rhynie cherts is of a very high standard, but there are variations. Hiatuses in silica deposition may be recorded by the development of shrinkage textures, the experimental shrinkage of the <i>Psilotum nudum,</i> an extant analogue for the rhyniophytes, suggests that this texture records a hiatus that lasted a few weeks at most. Composite cherts mark the presence of longer hiatuses in silica deposition. In some cases silification was virtually instantaneous, indicating the presence of a silica gel. An abundance of organic matter in the small shallow freshwater pools was sufficient to lower the pH of silica-saturated waters with low salinity levels, enabling a silica gel to form instead of the precipitates of opal-A lepispheres that form more commonly.

No description available.

If humanity is to make the best of this planet then it is crucial that we develop the capacity to implement the most effective environmental management practices. Essential is a holistic approach to management, as is advocated by integrated catchment management (ICM), which proposes that catchment management issues will be best dealt with when interventions are planned together at the catchment scale and all stakeholder interests are given consideration during decision making. The issue of weir modification is a good example of a problem that would benefit from these principles. Many stakeholder interests are affected by weir modification, and if effective and fair weir modification decisions are to be made, all must be used to evaluate alternative weir modification options. So that decision makers can make the most of the synergies and avoid the conflicts that can occur between interventions, they need to know how multiple weir modifications interact. To do this decision makers must be able to manage and utilise a large amount of information and use it to help them make effective decisions. The objective of the research presented in this thesis is to develop an approach to the management of weirs in the Don Catchment that is holistic both a spatial sense and in terms of the assessment of alternative management options. An evaluatory framework for weir modifications is formulated by adapting published typologies of river ecosystem services (ESs). The prediction of how catchment interventions affect sociocultural ESs is recognized as a particularly challenging to the application of this framework because their qualitative and subjective nature makes them hard to predict. Bayesian Networks (BNs) are identified as a potential solution as they use probabilities to describe the relationships between variables. A BN was built to predict how weir modification affected weir danger and weir fun for canoeists by utilising the knowledge of canoeing groups. It is concluded that despite a number of caveats, BNs offer a potentially important method for allowing sociocultural ESs to be predicted in decision making processes. The consideration ofthe complex interdependencies multiple weir modifications can have is recognised as another of the challenges facing weir management decision making. A spatially explicit modelling approach is developed that can account for the interactive effect multiple weir modifications have on river connectivity for several river species in the Don Catchment. Expert judgement and hydrological modelling are used to discriminate between different levels of habitat quality for European eel (Anguilla anguilla) and Atlantic salmon (Safrna safar). Several strategies to increase connectivity in the Don Catchment were explored. It was found that each had its own set of winners and losers, indicating trade-offs between species need to be considered when planning connectivity enhancements. The modelling approach shows the interdependent effects of weir modifications are vet: important in determining habitat accessibility, particularly the cumulative effect of multiple fish passes.

Most consumers maintain body tissue Carbon:Nitrogen:Phosphorus within narrow constraints, despite ratios often varying markedly among basal resources. Elemental quality may be a major factor governing resource selection by, and production of, consumers. Elemental imbalances between resources and consumers could constrain the flux of matter through food webs. Here the aim was to characterise and quantify the distribution and flux of C, N and P in a headwater stream food web. The stream water was nutrient rich (TP=208 μg L-1; TON=7 mg L-1), resulting in low C:N and C:P of basal resources. Nevertheless, elemental imbalances were evident between consumers and basal resources, particularly for organisms feeding on detritus. Although taxonomic differences existed, detritivores were typically depleted in N and P compared to taxonomically related species. Detritus comprised 97% of the biomass entering the food web, resulting in excess consumption of C and, therefore, stoichiometric imbalances. 75% of the tree canopy was removed from the heavily shaded experimental reach, resulting in a significant increase in benthic algae and a subsequent reduction in elemental imbalance and an increase in secondary production. It appears that stoichiometric constraints on secondary production were relaxed by increasing the availability of high quality resources in this detritus based food web. Most previous studies have calculated imbalances based on diet assumed from trophic level or functional feeding groups; however, the results presented here from gut contents analysis highlight the potentially erroneous interpretation of assumed measures of imbalance. Furthermore, static measures of elemental imbalances, i.e. the difference in elemental quality between consumers and their resources, do not give an adequate measure of these constraints. The dynamic measures explored here, give an assessment of relative rates of supply (rate of consumption) and demand (from metabolism). Such dynamic measures are crucial to understanding the role of ecological stoichiometry in determining key ecosystem processes.

No description available.

Phosphorus is often considered the limiting nutrient in rivers, and reducing concentrations has long been a key policy focus. However, experience has shown that many phosphorus mitigation schemes fail to achieve any improvements in ecological status. The primary aim of this thesis is to identify target phosphorus concentrations that need to be attained to improve river ecology. In-stream flume mesocosms were deployed on three UK rivers of varying levels of nutrient enrichment. Phosphorus concentrations were simultaneously increased and decreased (by iron-dosing) to provide a concentration gradient over which periphyton accrual was examined. This identified whether rivers were phosphorus limited, and allowed a phosphorus-limiting threshold to be quantified. The effects of nitrogen, and combined phosphorus and nitrogen addition were also examined. The River Lambourn study simultaneously manipulated light intensity and nutrient concentrations, demonstrating shading to have benefits in improving periphyton quality as a food resource and in reducing periphyton accrual. The near-pristine River Rede showed that increase in river phosphorus concentration had no effect on periphyton growth rate, but that there was a 3.5-fold increase in growth rate when phosphorus and nitrogen were added simultaneously, demonstrating the presence of sequential nutrient co-limitation. By repeating a 2005 study on the River Frome, the 2012 study proved that phosphorus-limiting thresholds change in response to changing river nutrient concentrations. Examination of changes in community structure by the trophic diatom index and flow cytometry provide evidence for a lower ecological threshold in rivers of ca. 30 μg l-1. A fast repetition rate fluorometer was used to assess phytoplankton stress across the Thames catchment throughout an algal bloom and data was examined alongside water quality data. Bloom development and collapse was primarily controlled by residence time and, secondarily, phosphorus concentration. This thesis has challenged traditional beliefs that phosphorus is the limiting nutrient in freshwater ecosystems and has provided insights on how to best meet the requirements of the Water Framework Directive and improve ecological status.

Στόχος της διπλωματικής εργασίας αυτής είναι η εκτίμηση των περιβαλλοντικών συνθηκών που επικρατούν στο πεδίο ανάμειξης γλυκού και αλμυρού νερού στις εκβολές του ποταμού Γλαύκου με βάση μετρήσεις φυσικοχημικών παραμέτρων. Ιδιαίτερη έμφαση δόθηκε στην μέτρηση της χλωροφύλλης, χρησιμοποιήθηκε το όργανο IDS Sublogger/Chealsea. Οι μετρήσεις έγιναν σε προφίλ σε αυξανόμενη απόσταση από τις εκβολές του ποταμού και σε διαφορετικές ημερομηνίες έτσι ώστε να καλυφθούν κυρίως η ξηρή και η υγρή περίοδος, αλλά και οι υπόλοιπες εποχές. Οι μετρήσεις συγκεκριμένα έγιναν στις πιο κάτω ημερομηνίες: 23/6/2012, 13/10/2012, 14/10/2012, 14/11/2012, 1/12/2012, 1/2/2013, 28/3/2013, 19/4/2013 και 27/5/2013. Σχεδιάστηκαν τα διαγράμματα που δείχνουν τις μεταβολές της συγκέντρωσης της χλωροφύλλης με το βάθος του νερού και έγινε η περιγραφή των διαγραμμάτων αυτών. Από την περιγραφή των διαγραμμάτων αυτών προέκυψαν τα πιο κάτω: 1. Σε ορισμένες περιόδους το επιφανειακό στρώμα νερού χαρακτηρίζεται από αυξημένες συγκεντρώσεις χλωροφύλλης συγκριτικά με τα υποεπιφανειακά στρώματα νερού. 2. Σε ορισμένες περιόδους του έτους παρατηρούνται χαρακτηριστικά μέγιστα χλωροφύλλης σε βαθύτερα στρώματα νερού. 3. Τα πιο πάνω μέγιστα είναι περισσότερο έντονα σε μικρή απόσταση από την εκβολή, γεγονός που δείχνει την επίδραση του γλυκού νερού στην κατανομή της χλωροφύλλης. Για να ερμηνευθούν τα αποτελέσματα καθώς και οι γεωγραφικές τους μεταβολές έγιναν μετρήσεις αγωγιμότητας, θερμοκρασίας και pH με την χρήση του οργάνου 600 XML V2. H αξιολόγηση των αποτελεσμάτων των πιο πάνω παραμέτρων έδειξε ότι: τα μέγιστα της χλωροφύλλης συνδέονται με μειώσεις της αγωγιμότητας, γεγονός που δείχνει την εξάρτηση της από την παρουσία γλυκού νερού. Για την εξαγωγή συμπερασμάτων που αφορούν στην ποιότητα των νερών στην περιοχή εργασίας με βάση τις τιμές της χλωροφύλλης, έγινε επεξεργασία των αποτελεσμάτων (simple statistics) όπου προσδιορίστηκαν οι μέσες τιμές, τα μέγιστα και ελάχιστα τους καθώς και η σταθερή απόκλιση από τη μέση τιμή. Η σύγκριση των μέσων τιμών χλωροφύλλης με το εύρος τιμών που χρησιμοποιούνται διεθνώς για τον χαρακτηρισμό των νερών σε ευτροφικά, μεσοτροφικά, και ολιγοτροφικά έδωσε τα πιο κάτω αποτελέσματα: Τον Ιούνιο 2012 η μέση τιμή χλωροφύλλης ήταν 5,76 μg/l ευτροφικό Τον Οκτώβριο 2012 η μέση τιμή χλωροφύλλης ήταν 0,69 μg/l μεσοτροφικό Το Νοέμβριο 2012 η μέση τιμή χλωροφύλλης ήταν 1,89 μg/l μεσοτροφικό Τον Δεκέμβριο 2012 η μέση τιμή χλωροφύλλης ήταν 1,84 μg/l μεσοτροφικό Τον Φεβρουάριο 2013 η μέση τιμή χλωροφύλλης ήταν 3,01 μg/l ευτροφικό Τον Μάρτιο 2013 η μέση τιμή χλωροφύλλης ήταν 3,26 μg/l ευτροφικό Τον Απρίλιο 2013 η μέση τιμή χλωροφύλλης ήταν 4,37 μg/l ευτροφικό Τον Μάϊο 2013 η μέση τιμή χλωροφύλλης ήταν 1,60 μg/l μεσοτροφικό Για την μελέτη των διαχρονικών μεταβολών των τιμών της χλωροφύλλης σχεδιάστηκαν τα διαγράμματα που δείχνουν τις μεταβολές των μέσων και μέγιστων στις διάφορες περιόδους μετρήσεων. Από τα διαγράμματα αυτά προκύπτουν αυξημένες τιμές τον Ιούνιο 2012, Φεβρουάριο 2013, Μάρτιο 2013 και Απρίλιο 2013, ενώ οι τιμές της χλωροφύλλης τον Οκτώβριο 2012, Νοέμβριο2012, Δεκέμβριο 2012 και Μάϊο 2013 ήταν χαμηλότερες. Τα αποτελέσματα αξιολογήθηκαν επιπροσθέτως σε συνάρτηση με μετεωρολογικά και άλλα στοιχεία της περιοχής / The aim of this study is to assess the environmental conditions prevailing in the field of mixing freshwater and saltwater at Glafkos outlet based on the measurements of physicochemical parameters. Particular emphasis was given to the measurement of chlorophyll-a. The instrument used was the IDS Sublogger / Chealsea. The measurements were made in profiles at increasing distance from the outlet of Glafkos river and on different dates in order to cover mainly the dry and wet season, as well as the remaining seasons. The measurements were made specifically in the following dates: 23/06/2012, 13/10/2012, 14/10/2012, 14/11/2012, 01/12/2012, 02/01/2013, 03/28/2013 , 04.19.2013 and 05.27.2013. The vertical variability of chlorophyll-a values in the sea column showed the following: 1. At certain times the surface layer of the seawater was characterized by increased concentrations of chlorophyll-a compared to subsurface water layers. 2. At certain periods of year, chlorophyll-a showed distinct peaks in the subsurface seawater. 3. The above mentioned peaks were more distinct at short distance from the river’s outlet, which shows the influence of freshwater in the distribution of chlorophyll. To interpret the results and the geographical variations, conductivity, temperature and pH were measured with the use of the probe YSI 600 XML V2. The results assessment of the above parameters showed that: the peaks of chlorophyll-a associated with decreases of conductivity, indicates its dependence on the presence of freshwater. To draw conclusions regarding the quality of seawater in the study area based on the variability of chlorophyll-a values, simple statistics was applied on the data. The mean, maximum and minimum values, as well as the standard deviation from the mean values were determined. The comparison of the average values of chlorophyll-a with the values used internationally to characterize water eutrophic, mesotrophic and oligotrophic gave the following results: In June 2012, the average chlorophyll was 5.76 μg/l showing eutrophic aquatic environment In October 2012, the average chlorophyll of 0.69 μg/l showing mesotrophic aquatic environment In November 2012, the average chlorophyll was 1.89 μg/l showing mesotrophic aquatic environment In December 2012, the average chlorophyll was 1.84 μg/l showing mesotrophic aquatic environment In February 2013, the average chlorophyll was 3.01 μg/l showing eutrophic aquatic environment In March 2013, the average chlorophyll was 3.26 μg/l showing eutrophic aquatic environment In April 2013, the average chlorophyll was 4.37 μg/l showing eutrophic aquatic environment In May 2013, the average chlorophyll was 1.60 μg/l showing mesotrophic aquatic environment In order to study the time variability of chlorophyll-a, diagrams were drawn showing the variations of the average and maximum values in different measurement periods. From these diagrams increased values were observed in June 2012, February 2013, March 2013 and April 2013, while chlorophyll-a values, in October 2012, November 2012, December 2012 and May 2013 were lower. The results are evaluated also in relation to the meteorological data and other elements of the area.