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Queen Mary University of London (2016)

Linkages between Saline Lakes and their Riparian zone over climate change

Sanders Philip

Titre : Linkages between Saline Lakes and their Riparian zone over climate change

Auteur : Sanders Philip

Université de soutenance : Queen Mary University of London

Grade : Doctor of Philosophy (PhD) 2016

Résumé
Research on resource transfer across ecosystem boundaries (i.e. allochthonous material ; a subsidy) has been recognised since the 1920s and recognition of allochthonous inputs has been a part of food web theory since its inception. Nonetheless, only in recent decades have subsidies between ecosystems become a feature of large scale food web studies. Measures of subsidy links are usually restricted to studies on either marine or freshwater, the latter being the focus of most attention. In a recent meta-analysis of cross ecosystem boundary subsidies, two thirds of the 32 data sets used focused on freshwater ecosystems and one third on marine ; none involved saline lakes. As a percentage of total global water volume saline lakes are almost equal to that of freshwater, yet there is a paucity of research carried out on linkage between saline lakes and their catchments. Two typical characteristics of saline lakes suggest that linkage between the aquatic and the terrestrial ecosystem is important. The first is that the communities in the aquatic ecosystem are generally made up of fewer actors of specialised species that occur in high abundances. The second is that saline lakes are usually found in arid landscapes which are depauperate in terrestrial production. It is well understood that specialised species with narrow niche widths will have a negative response to environmental change. In arid lake systems salinity is likely to be a function of lake volume, which is affected by the balance between evaporation and precipitation. Arid regions, particularly around the tropics, are susceptible to intensive perturbation caused by climate change. Very few studies on cross-ecosystem subsidies highlight the risk of perturbation to the stability of links in the light of climate change. This project aims to further our knowledge of resource subsidy between saline lakes and their arid catchment over climate change, which can be split into three main objectives. 1. To use stable isotope analysis to investigate the relative strength and temporal patterns of aquatic subsidy to terrestrial consumers caused by the probable strongest link, the emerging chironomids. It is predicted that the strength of subsidy will change, following a lag, to any patterns of emergence that may exist through the chironomid life cycle. Therefore, temporal fluxes in the adult chironomid emergence rates and seasonal changes will be reflected in the isotopic signatures of consumers. 2. The extent to which the aquatic subsidy impacts into Lake Bogoria will be measured and weather that impact expands and retracts in response to the cyclical behaviour of the chironomids. Bayesian mixing models and metrics will be employed, beyond the traditional ratio methods, to give further insight into landscape subsidy dynamics. 3. Past salinity will be inferred through a transfer model created from the diversity of sub-fossilised chironomid head capsules in lake sediment extracted through coring methods. The density of sub-fossilised head capsules linked to the changes in salinity will be compared to contemporary larval densities. Contemporary larval densities will be measures across different salinity regimes provided by the three partially split lake basins and during different water levels as a result of seasonal changes to precipitation.

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