Martins, Sara Varandas; (2019) Ecohydrology of temporary ponds. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Temporary ponds (TP) comprise a complex ecohydrology and are extremely vulnerable to habitat degradation. These ecosystems contain species rarely found elsewhere but the environments are highly exposed to human and climate change pressures. TP have been recognised as priority habitats for conservation in Europe by the Habitats Directive, and work towards improved knowledge, understanding and conservation has increased since. This thesis focuses on the ecohydrological controls on the cladoceran species and communities in coastal temporary ponds in two geographic regions along a northwest Europe latitudinal gradient: the northwest coast of Ireland and the southwest coast of Portugal. It explores local time-variance in two dune slack ponds at Sheskinmore, Co. Donegal, Ireland, local spatial-variance across 24 ponds at the same site, and regional controls on temporary pond Cladocera ecohydrology at two sites in southwest Portugal (Malhão (MAL) and Vila do Bispo (VB)). The focus of investigation here is the seasonal hydrological balance and dependence of this dynamic on the ecology and biology of the habitats. This research aims to achieve a better understanding of individual, local and regional ecohydrological dynamics of TP’s and characterise the drivers of ecosystem variation within. Results uncover that ponds and slacks of Sheskinmore are highly dependent on rainfall and their vulnerability is confirmed when precipitation levels are not met. Increased variability inter-annually of cladocerans as opposed to intra-annual seasonal variation showed this. Weather changeability is the most important aspect of future climate change but there is a complex interaction between weather variability, local hydroregime and topography of a waterbody, impacting species’ temporal and spatial assemblages varyingly. Spatial dynamics of these dune ponds evaluated that within a rather small area, cladoceran composition differs, mainly according to hydrological categories, which are then linked to proximity of each site to the water table. Water chemistry was not so relevant to the spatial patterns in species. At a regional scale, sediment composition and water chemistry were better predictors of differentiation of the cladoceran composition within the Portuguese ponds, rather than geomorphological differentiations between regions. MAL ponds contained higher cladoceran abundance, whereas VB ponds contained higher cladoceran richness. Regionally, cladoceran communities are shaped by a combination of important factors and explanations vary according to the individual characteristics and to the collective groups of ponds. Results corroborate the importance of hydrology, topology and climatic factors as ecological drivers of ecosystem functioning in TP. This work demonstrates the uniqueness and sensitivity of TPs, therefore supporting the need to conserve these habitats.

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