Bennion, Helen; (1993) A diatom-phosphorus transfer function for eutrophic ponds in south-east England. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The aim of this thesis is to establish whether the ponds in south-east England can be used for palaeolimnological research, and whether a nutrient "transfer function" can be generated from, a training set of surface sediment diatom assemblages and contemporary water chemistry. The study area covers the region within a 60 mile radius of central London. A preliminary water chemistry survey of 123 randomly chosen ponds was undertaken. Following Principal Components Analysis (PCA) which identified total phosphorus (TP) and conductivity as important environmental gradients, a subset of 31 ponds was selected along these gradients to form a training set. These sites were monitored on a monthly basis over a 15 month period for pH, conductivity, alkalinity, and nutrient chemistry, and major ionic chemistry was monitored quarterly. Surface sediments were sampled at each site for diatom analysis. Canonical Correspondence Analysis (CCA) was performed on the training set. Annual mean TP and winter mean soluble reactive phosphorus (SRP) were the most significant environmental variables in explaining the diatom species distributions. Weighted averaging (WA) regression and calibration techniques were subsequently used to generate transfer functions, enabling annual mean TP and winter mean SRP to be inferred from 102 common diatom taxa. For annual mean TP and winter mean SRP, the correlation coefficients between inferred and measured concentrations were r 2 = 0.79 and r 2 = 0.82 respectively (where n = 30). The WA models were successfully applied to diatom assemblages in cores from two sites. Eleven Acre Lake, Buckinghamshire, and Marsworth Reservoir, Hertfordshire. In contrast to most natural lakes, many of the ponds have poor sediment records due to disturbance or their recent origin. However, in some cases the record is complete and the WA technique can be used to reconstruct phosphorus (P) concentrations with good statistical confidence over a large range of values (annual mean TP 25-646 [mu]g 1-1; winter mean SRP 3-558 [mu]g 1-1). This method can provide estimates of pre-enrichment P concentrations and an indication of the onset and development of eutrophication for any site with a suitable sediment record in south-east England, and with modifications to the training set, for natural lakes in the United Kingdom.

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