Increasing the accuracy of Nitrogen Dioxide (NO2) pollution mapping using geographically weighted regression (GWR) and geostatistics.

Nitrogen Dioxide (NO2) is known to act as an environmental trigger for many respiratory illnesses. As a pollutant it is difficult to map accurately, as concentrations can vary greatly over small distances. In this study three geostatistical techniques were compared, producing maps of NO2 concentrations in the United Kingdom (UK). The primary data source for each technique was NO2 point data, generated from background automatic monitoring and background diffusion tubes, which are analysed by different laboratories on behalf of local councils and authorities in the UK. The techniques used were simple kriging (SK), ordinary kriging (OK) and simple kriging with a locally varying mean (SKlm). SK and OK make use of the primary variable only. SKlm differs in that it utilises additional data to inform prediction, and hence potentially reduces uncertainty. The secondary data source was Oxides of Nitrogen (NOx) derived from dispersion modelling outputs, at 1km x 1km resolution for the UK. These data were used to define the locally varying mean in SKlm, using two regression approaches: (i) global regression (GR) and (ii) geographically weighted regression (GWR). Based upon summary statistics and cross-validation prediction errors, SKlm using GWR derived local means produced the most accurate predictions. Therefore, using GWR to inform SKlm was beneficial in this study.

Dynamics of critical source areas: does connectivity explain chemistry?

Abstract: Critical source area approaches to catchment management are increasingly being recognised as effective tools to mitigate sediment and nutrient transfers. These approaches often assume hydrological connectivity as a driver for environmental risk, however this assumption has rarely been tested. Using high resolution monitoring, 14 rainfall events of contrasting intensity were examined in detail for spatial and temporal dynamics of overland flow generation at a hydrologically isolated grassland hillslope in Co. Down, Northern Ireland. Interactions between overland flow connectivity and nutrient transfers were studied to test the critical source area hypothesis. While total and soluble phosphorus loads were found to be representative of the size of the overland flow contributing area (P=

Assessing the Legacy of Red Mud Pollution in a Shallow Freshwater Lake: Arsenic Accumulation and Speciation in Macrophytes

Little is known about long-term ecological responses in lakes following red mud pollution. Among red mud contaminants, arsenic (As) is of considerable concern. Determination of the species of As accumulated in aquatic organisms provides important information about the biogeochemical cycling of the element and transfer through the aquatic food-web to higher organisms. We used coupled ion chromatography and inductively coupled plasma mass spectrometry (ICP-MS) to assess As speciation in tissues of five macrophyte taxa in Kinghorn Loch, UK, 30 years following the diversion of red mud pollution from the lake. Toxic inorganic As was the dominant species in the studied macrophytes, with As species concentrations varying with macrophyte taxon and tissue type. The highest As content measured in roots of Persicaria amphibia (L.) Gray (87.2 mg kg-1) greatly exceeded the 3 - 10 mg kg-1 range suggested as a potential phytotoxic level. Accumulation of toxic As species by plants suggested toxicological risk to higher organisms known to utilise macrophytes as a food source.