The relationship between epilithic diatom assemblages and water chemistry in Scottish streams

During the late 1970s and early 1980s it became apparent that a large number of lochs and streams draining base-poor catchments in various parts of Scotland had been acidified, and had impoverished fish and invertebrate communities. The Scottish Acid Waters Baseline Study was therefore initiated in 1986 with the aim of surveying the current distribution and extent of acid rivers and streams in Scotland, and to provide a baseline of chemical and biological data against which future changes may be assessed. The survey involved a three-year sampling program of stream-water chemistry, benthic invertebrates and epilithic diatoms. This report presents results from the diatom component of this study, and detailed description of the chemistry and diatom data from the survey sites. In addition to documenting the diatom dataset, this interim report also examines the relationship between the diatom assemblages and environmental factors, and develops a predictive model for the bio-monitoring of stream-water pH. I should like to thank members of the Scottish RPBs for collecting diatom samples and Ross Doughty of the Clyde River Purification Board for collating and transferring water chemistry data. The project was funded by a Department of the Environment grant to Prof. R.W. Battarbee

Experimental Diatom Dissolution and the Quantification of Microfossil Preservation in Sediments

Four laboratory experiments on fresh, modern diatoms collected from lakes in the Northern Great Plains of North America were carried out to assess the effects of dissolution on diatom abundance and composition. Marked differences in mean dissolution susceptibility exist between species, despite sometimes significant intra- specific variation between heterovalves. Twenty-four taxa were ranked according to susceptibility to dissolution using an exponential decay model of valve abundance. This dissolution ranking was used to derive two weighted indices of sample preservation. A third index (F) was based on a simple binary classification of valve morphology into dissolved and pristine categories, as distinguished by light microscopy (LM). When compared against rank indices and a measure of species diversity, this diatom dissolution index was found to be the best predictor of the progress of dissolution as estimated by total valve abundance or biogenic silica (BiSi) loss. Strong empirical relationships between F index values and diatom abundance (r2 = 0.84, n = 32) and BiSi (r2 = 0.89, n = 32) were developed and applied to a diatom sequence from a short core from Devils Lake, North Dakota, and compared to diatom-inferred and observed salinity at this site. The F index is a simple, effective diagnostic tool to assess important aspects of diatom preservation. The index can provide insight into Si cycling and record changes in conditions pertinent to diatom dissolution, and has a role in validation of transfer functions or other inferences derived from compositional data

The role of the North Atlantic Oscillation in controlling U.K. butterfly population size and phenology

Copyright @ 2012 The Authors. This article can be accessed from the links below.This article has been made available through the Brunel Open Access Publishing Fund.1. The North Atlantic Oscillation (NAO) exerts considerable control on U.K. weather. This study investigates the impact of the NAO on butterfly abundance and phenology using 34 years of data from the U.K. Butterfly Monitoring Scheme (UKBMS). 2. The study uses a multi-species indicator to show that the NAO does not affect overall U.K. butterfly population size. However, the abundance of bivoltine butterfly species, which have longer flight seasons, were found to be more likely to respond positively to the NAO compared with univoltine species, which show little or a negative response. 3. A positive winter NAO index is associated with warmer weather and earlier flight dates for Anthocharis cardamines (Lepidoptera: Pieridae), Melanargia galathea (Lepidoptera: Nymphalidae), Aphantopus hyperantus (Lepidoptera: Nymphalidae), Pyronia tithonus (Lepidoptera: Nymphalidae), Lasiommata megera (Lepidoptera: Nymphalidae) and Polyommatus icarus (Lepidoptera: Lycaenidae). In bivoltine species, the NAO affects the phenology of the first generation, the timing of which indirectly controls the timing of the second generation. 4. The NAO influences the timing of U.K. butterfly flight seasons more strongly than it influences population size.This study was supported by a multi-agency consortium led by the U.K. Department for Environment, Food and Rural Affairs (Defra), including the Countryside Council for Wales, the Joint Nature Conservation Committee, the Forestry Commission, Natural England, the Natural Environment Research Council, the Northern Ireland Environment Agency and Scottish Natural Heritage. This article is made available through the Brunel Open Access Publishing Fund

Ultrahigh resolution total organic carbon analysis using Fourier Transform Near Infrarred Reflectance Spectroscopy (FT-NIRS)

[1] Fourier transform near infrared reflectance spectroscopy (FT-NIRS) is a cheap, rapid, and nondestructive method for analyzing organic sediment components. Here, we examine the robustness of a within lake FT-NIRS calibration using a data set of almost 400 core samples from Lake Suigetsu, Japan, as a means to rapidly reconstruct % total organic carbon (TOC). We evaluate the best spectra pretreatment, examine different statistical approaches, and provide recommendations for the optimum number of calibration samples required for accurate predictions. Results show that the most robust method is based on first-order derivatives of all spectra modeled with partial least squares regression. We construct a TOC model training set using 247 samples and a validation test set using 135 samples (for test set R2 = 0.951, RMSE = 0.280) to determine TOC and illustrate the use of the model in an ultrahigh resolution (e.g., 1 mm/annual) study of a long sediment core from a climatically sensitive archive.Emma J. Pearson and Steve Juggins, Jonathan Tyle

Biases in the estimation of transfer function prediction errors

In the quest for more precise sea-surface temperature reconstructions from microfossil assemblages, large modern training sets and new transfer function methods have been developed. Realistic estimates of the predictive power of a transfer function can only be calculated from an independent test set. If the test set is not fully independent, the error estimate will be artificially low. We show that the modern analogue technique using a similarity index (SIMMAX) and the revised analogue method ( RAM), both derived from the modern analogue technique, achieve apparently lower root mean square error of prediction (RMSEP) by failing to ensure statistical independence of samples during cross validation. We also show that when cross validation is used to select the best artificial neural network or modern analogue model, the RMSEP based on cross validation is lower than that for a fully independent test set