Investigating the distinct ecohydrological characteristics of Mediterranean intermittent and ephemeral streams and considerations for their management

Borg Galea, Alexander (2024). Investigating the distinct ecohydrological characteristics of Mediterranean intermittent and ephemeral streams and considerations for their management. University of Birmingham. Ph.D.

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Abstract

Even though intermittent rivers and ephemeral streams (IRES) in the Mediterranean are the major surface water bodies, most hydrologically transient catchment areas that are unmonitored, lacking gauges and habitat surveys, and/or not generally included in environmental restoration plans. When they are gauged, the monitoring stations are in most cases sparsely distributed and do not capture the spatial variability of flows and water cessation dynamics within the stream network. It is important that monitoring methodologies capture the spatio-temporal variability of different hydrological states and their influence on the various biophysical dynamics occurring along the stream continuum. A monitoring framework was employed in this thesis, and through various studies, selected dynamics within Mediterranean IRES were explored. The thesis presents a conceptual framework (Chapter 2) identifying the many process cascades and links that influence the variables governing the functioning of Mediterranean IRES and proposes alternative approaches to ‘traditional’ gauged data for the monitoring of the various complex stream dynamics. Using 30-minute interval water level and in-stream temperature readings from six dataloggers deployed in six case study areas and precipitation records from weather stations, Chapter 3 interpreted hydrological and thermal response patterns following precipitation events in catchments and sub-catchments with different drainage area size, ecohydrological and land cover typologies. The fourth chapter explored the potential of using vegetation indices (VIs) derived from visible RGB consumer-grade cameras installed on uncrewed aerial vehicles (UAVs) to analyse the relationships between streambed water presence and riparian vegetation health. The fifth chapter presents a novel ecosystem-service based assessment to provide decision makers an affordable and easy-to-use tool to prioritise and conserve Mediterranean IRES. UAVs combined with structure from motion photogrammetry techniques and GIS applications were used to extract and measure catchment and stream features that drive the provision of ecosystem services of fifteen different transient catchment areas. The findings illustrate the potential of UAVs and water level dataloggers in ameliorating the understanding of the processes occurring within Mediterranean IRES. Results show that: (1) water level response times to precipitation depend on the size of the catchment, seasonality of rain events, and land cover characteristics; (2) streambed temperature responses to precipitation episodes are influenced by the hydrological regime, were the presence groundwater springs contribute to more stable temperature variations, and the catchment land cover characteristics; (3) reflectance values from visible VIs respond to different in-stream water levels; and (4) larger catchment areas and flow regimes characterised by intermittent flows have the potential to provide more ecosystem services, whereby smaller drainage areas with predominantly urban land uses have the reduced ability to provide ecosystem services. Although Mediterranean IRES share common elements, different catchments possess diverse attributes that are fundamental in influencing the biophysical response processes. The evolution of tools capable of monitoring ecohydrological dynamics at centimetre resolutions and elevated spatio-temporal scales should pave the way for the improved identification, categorisation, and understanding of different catchment dynamics to better inform the management of Mediterranean IRES.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):