Abstract:For an experimental field site at the River Leith, United Kingdom, the spatial and temporal distribution of nitrate was observed along the upwelling flow path from groundwater to surface water. The study was carried out during baseflow conditions for two successive years. For two contrasting stream reaches, the physical and chemical characteristics of streambed sediment cores were analysed together with observations of hydraulic head, dissolved oxygen, redox and nitrogen speciation using an array of nested streambed piezometers.Pressure head gradients in the streambed piezometers showed that upwelling flows dominated the exchange between groundwater and surface water throughout the observation period. Infiltration of surface water into the streambed was not evident at depths below 10 cm. Pore water collected from sediment cores and streambed piezometers showed spatially variable redox conditions and nitrogen speciation within up to 100 cm depth in the streambed. In particular, nitrate concentrations along upwelling flow paths appeared to follow two opposite trends, with both decreasing and increasing nitrate concentrations being observed at different points in the experimental reach. The observed changes of nitrate concentrations in the upwelling groundwater are restricted to the loose superficial sediments that overlay the sandstone bedrock and do not appear to coincide with surface water-groundwater mixing in the streambed. The magnitude of variation in nitrate concentration along the upwelling flow path to the streambed appears to be governed by the sediment structure and characteristics in the two contrasting field sites.The results suggest that changes in redox status and pore water nitrate concentrations in the hyporheic may occur at depths greater than surface water infiltration into the streambed and may call for new conceptual understanding of hyporheic nutrient transformations.

Abstract. A unique long-term dataset from the UK National Ammonia Monitoring Network (NAMN) is used here to assess spatial, seasonal and long-term variability in atmospheric ammonia (NH 3 : 1998(NH 3 : -2014) and particulate ammonium (NH + 4 : 1999-2014) across the UK. Extensive spatial heterogeneity in NH 3 concentrations is observed, with lowest annual mean concentrations at remote sites (< 0.2 µg m −3 ) and highest in the areas with intensive agriculture (up to 22 µg m −3 ), while NH + 4 concentrations show less spatial variability (e.g. range of 0.14 to 1.8 µg m −3 annual mean in 2005). Temporally, NH 3 concentrations are influenced by environmental conditions and local emission sources. In particular, peak NH 3 concentrations are observed in summer at background sites (defined by 5 km grid average NH 3 emissions < 1 kg N ha −1 yr −1 ) and in areas dominated by sheep farming, driven by increased volatilization of NH 3 in warmer summer temperatures. In areas where cattle, pig and poultry farming is dominant, the largest NH 3 concentrations are in spring and autumn, matching periods of manure application to fields. By contrast, peak concentrations of NH + 4 aerosol occur in spring, associated with long-range transboundary sources. An estimated decrease in NH 3 emissions by 16 % between 1998 and 2014 was reported by the UK National Atmospheric Emissions Inventory. Annually averaged NH 3 data from NAMN sites operational over the same period (n = 59) show an indicative downward trend, although the reduction in NH 3 concentrations is smaller and nonsignificant: Mann-Kendall (MK), −6.3 %; linear regression (LR), −3.1 %. In areas dominated by pig and poultry farming, a significant reduction in NH 3 concentrations between 1998 and 2014 (MK: −22 %; LR: −21 %, annually averaged NH 3 ) is consistent with, but not as large as the decrease in estimated NH 3 emissions from this sector over the same period (−39 %). By contrast, in cattle-dominated areas there is a slight upward trend (non-significant) in NH 3 concentrations (MK: +12 %; LR: +3.6 %, annually averaged NH 3 ), despite the estimated decline in NH 3 emissions from this sector since 1998 (−11 %). At background and sheep-dominated sites, NH 3 concentrations increased over the monitoring period. These increases (non-significant) at background (MK: +17 %; LR: +13 %, annually averaged data) and sheep-dominated sites (MK: +15 %; LR: +19 %, annually averaged data) would be consistent with the concomitant reduction in SO 2 emissions over the same period, leading to a longer atmospheric lifetime of NH 3 , thereby increasing NH 3 concentrations in remote areas. The observations for NH 3 concentrations not decreasing as fast as estimated emission trends are consistent with a larger downward trend in annual particulate NH + 4 concentrations (1999-2014: MK: −47 %; LR: −49 %, p < 0.01, n = 23), associated with a lower formation of particulate NH

A yeast (Saccharomyces cerevisiae) DNA repair reporter assay termed the GreenScreen assay (GSA) is described. This is a novel, cost-effective genotoxicity screen, developed to provide a pre-regulatory screening assay for use by the pharmaceutical industry and in other applications where significant numbers of compounds need to be tested. It provides a higher throughput and a lower compound consumption than existing eukaryotic genotoxicity assays and is sensitive to a broad spectrum of mutagens and, importantly, clastogens. We describe a simple, robust assay protocol and a validation study. The end-point of the test reflects the typically eukaryotic chromosomes and DNA metabolizing enzymes of yeast. The capacity for metabolic activation (MA) in yeast is limited compared with the mammalian liver or its extracts, but the assay does detect a subset of compounds that would require MA in existing genotoxicity tests. The GSA detects a different spectrum of compounds to bacterial genotoxicity assays and thus, together with an in silico structure-activity relationship (SAR) screen, and possibly a high throughput bacterial screen, would provide an effective preview of the regulatory battery of genotoxicity tests.

We evaluate different frequencies of riverine nutrient concentration measurement to interpret diffuse pollution in agricultural catchments. We focus on three nutrient fractions, nitrate-nitrogen (NO3-N), total reactive phosphorus (TRP) and total phosphorus (TP) observed using conventional remote laboratory-based, low-frequency sampling and automated, in situ high-frequency monitoring. We demonstrate the value of low-frequency routine nutrient monitoring in providing long-term data on changes in surface water and groundwater nutrient concentrations. By contrast, automated high-frequency nutrient observations provide insight into the fine temporal structure of nutrient dynamics in response to a full spectrum of flow dynamics. We found good agreement between concurrent in situ and laboratory-based determinations for nitrate-nitrogen (Pearson's R = 0.93, p < 0.01). For phosphorus fractions: TP (R = 0.84, p < 0.01) and TRP (R = 0.79, p < 0.01) the relationships were poorer due to the underestimation of P fractions observed in situ and storage-related changes of grab samples. A detailed comparison between concurrent nutrient data obtained by the hourly in situ automated monitoring and weekly-to-fortnightly grab sampling reveals a significant information loss at the extreme range of nutrient concentration for low-frequency sampling.

No abstract