Effects of anthropogenic nitrogen deposition on soil nitrogen mineralization and immobilization in grassland soil under semiarid climatic conditions.

Earlier studies by the authors on English soils under grassland strongly supported their hypothesis that soil/plant systems have naturally evolved to conserve nitrogen (N) by having a close match between the dynamics of mineral-N production in soils and the dynamics of plant N requirements. Thus, maximum mineral-N production in soils occurred in spring when plant N requirements were greatest and were very low in mid to late summer. Low temperature and a high C:N ratio of senescing material helped to conserve N in winter, but mobile N was associated with pollution inputs.

A critical re-evaluation of controls on spatial and seasonal variations in nitrate concentrations in river waters throughout the River Derwent catchment in North Yorkshire, UK.

Since mean nitrate concentration along single river channels increases significantly with percent arable land use upstream of sampling points and autumn/early winter flushes in nitrate concentration are widespread, it is generally concluded that farmers contribute most of the nitrate. For the River Derwent in North Yorkshire, the correlation between nitrate concentration and percent arable land use is much poorer when tributary data are included in the equation, because of greater variations in dilution by water draining upland areas and in other N input sources. For the whole river system therefore, percent upland moorland/rough grazing land cover is an appreciably better predictor than percent arable land use for nitrate concentration.

Disruption of the naturally evolved N conservation strategy in soil under grassland at a sports field in York, UK.

Water- and KCl-extractable ammonium-N and nitrate-N concentrations have been monitored at approximately monthly intervals over a year in soils from 0-10 and 10-20 cm depths under permanent grass at a sports field in York, UK. Measurements were made on both fresh, field-moist soils and after the same soils had been incubated for 7 days at ambient outdoor temperatures, to assess seasonal changes in the capacity of the soils to produce mineral-N species in the absence of plant uptake and other effects. Water extracts allowed potential mobility of N species to be assessed.

A critical re-evaluation of the prediction of alkalinity and base cation chemistry from BGS sediment composition data.

The model of Begum et al. (2010) that predicts alkalinity and Ca and Mg concentrations in river water from available sediment composition data has been critically re-evaluated using an independent validation data set. The results support the hypothesis that readily available stream water sediment elemental composition data are useful for prediction of mean and minimum concentrations of alkalinity and Ca and Mg in river water throughout the River Derwent catchment in North Yorkshire without requiring land-use data inputs as stream water sediment composition reflects all aspects of the riparian zone soil system, including land-use.

Regulatory ecotoxicity testing of engineered nanoparticles: are the results relevant to the natural environment?

Engineered nanoparticles (ENPs) will be released to the environment during use or following the disposal of ENP-containing products and concerns have been raised over the risks of ENPs to the environment. Many studies have explored the toxicity of ENPs to aquatic organisms but these studies have usually been performed with little understanding of the ENPs' behaviour in the test media and the relationship between behaviour in the media to behaviour in natural waters. This study evaluated and compared the aggregation behaviour of four model gold nanoparticle (NP) types (coated with neutral, negative, positive and amphoteric cappings) in standard ecotoxicity test media and natural waters.

Does plant uptake or low soil mineral-N production limit mineral-N losses to surface waters and groundwater from soils under grass in summer?

Summer minima and autumn/winter maxima in nitrate concentrations in rivers are reputedly due to high plant uptake of nitrate from soils in summer. A novel alternative hypothesis is tested here for soils under grass. By summer, residual readily mineralizable plant litter from the previous autumn/winter is negligible and fresh litter input low.

Can sediment data be used to predict alkalinity and base cation chemistry of surface waters?

We hypothesise that stream sediment elemental composition can predict mean and minimum concentrations of alkalinity, Ca and Mg in the river water throughout a river network. We tested this hypothesis for the River Derwent catchment in North Yorkshire, England, by using 6 years of water chemistry data from the Environment Agency and a digital elevation model to flow path-weight British Geological Survey (BGS) sediment element concentration data. The predictive models for mean concentrations were excellent for Ca and alkalinity, but less good for Mg, and did not require land use data inputs as stream water sediment composition seems to reflect all aspects of the riparian zone soil system.

Spatial and temporal trends in nitrate concentrations in the River Derwent, North Yorkshire, and its need for NVZ status.

Long-term spatial and temporal variations in nitrate-N concentrations along the River Derwent have been examined using Environment Agency data to investigate the relative importance of impacts of atmospheric N deposition, land use, and changes in management. Where moorland and rough grazing dominate upstream of Forge Valley and Malton, over the 20 years since 1988 mean nitrate-N concentrations were initially increasing significantly, but are now levelling off, with peaks at ca. 4.

The importance of ammonium mobility in nitrogen-impacted unfertilized grasslands: a critical reassessment.

The physico-chemical absorption characteristics of ammonium-N for 10 soils from 5 profiles in York, UK, show its high potential mobility in N deposition-impacted, unfertilized, permanent grassland soils. Substantial proportions of ammonium-N inputs were retained in the solution phase, indicating that ammonium translocation plays an important role in the N cycling in, and losses from, such soils. This conclusion was further supported by measuring the ammonium-N leaching from intact plant/soil microcosms.

A reappraisal of the terrestrial nitrogen cycle: what can we learn by extracting concepts from Gaia theory?

Although soil scientists and most environmental scientists are acutely aware of the interactions between the cycling of carbon and nitrogen, for conceptual convenience when portraying the nitrogen cycle in text books the N cycle tends to be considered in isolation from its interactions with the cycling of other elements and water, usually as a snap shot at the current time; the origins of dinitrogen are rarely considered, for example. The authors suggest that Lovelock's Gaia hypothesis provides a useful and stimulating framework for consideration of the terrestrial nitrogen cycle. If it is used, it suggests that urbanization and management of sewage, and intensive animal rearing are probably bigger global issues than nitrogen deposition from fossil fuel combustion, and that plant evolution may be driven by the requirement of locally sustainable and near optimal soil mineral N supply dynamics.

Does road salting induce or ameliorate DOC mobilisation from roadside soils to surface waters in the long term?

Soils down slope of roads have been affected over decades by road salting in the UK uplands. Salt additions to fresh soil facilitate dispersal of organic matter so there is a potential risk of release of DON and DOC to nearby rivers where these run parallel to roads. Over time, however, salting enhances soil pH of naturally acid soils, and thus organic matter degradation through to CO2, thereby, lowering soil organic matter content.

Extent and causes of 3D spatial variations in potential N mineralization and the risk of ammonium and nitrate leaching from an N-impacted permanent grassland near York, UK.

Changes in the dynamics of inorganic N species transformations with depth have been investigated for seven soil profiles from a nitrogen-impacted ancient grassland on a nature reserve outside York in the UK, using incubation experiments. In five of the profiles, both ammonification and nitrification are occurring below the rooting zone, probably partly in response to the low C:N ratio in the soils. This contributes to elevated nitrate concentrations found in an adjacent stream.

Effect of long-term changes in soil chemistry induced by road salt applications on N-transformations in roadside soils.

Of several impacts of road salting on roadside soils, the potential disruption of the nitrogen cycle has been largely ignored. Therefore the fates of low-level ammonium-N and nitrate-N inputs to roadside soils impacted by salting over an extended period (decades) in the field have been studied. The use of road salts disrupts the proportional contributions of nitrate-N and ammonium-N to the mineral inorganic fraction of roadside soils.

Evaluating alternative river management options in the tidal Ouse using the QUESTS1D model.

The tidal Ouse forms a significant part of the Humber river system in Eastern England, which provides the largest UK fresh water source to the North Sea and a valuable habitat for fish. However it suffers from dissolved oxygen (DO) sag in summer, exacerbated by the industrial effluent discharged at Selby. A one-dimensional water quality model, QUESTS1D, as utilized by the Environment Agency (EA) has been used to evaluate the effectiveness of management options based on exploiting spatial distribution of the assimilative capacity of the river as an alternative to implementing more stringent effluent consents.

Sequential element extraction of soils from abandoned farms: an investigation of the partitioning of anthropogenic element inputs from historic land use.

Enhanced soil element concentrations may serve as indicators not only of modern pollution, but also of former historic and/or pre-historic human activity. However, there is little consensus over the most appropriate means of extraction for identifying chemical signatures of modern and archaeological pollution. This study addressed this question by using a 5-step sequential extraction to examine the partitioning of elements within the soil.

Predicting Gran alkalinity and calcium concentrations in river waters over a national scale using a novel modification to the G-BASH model.

Monthly stream water calcium and Gran alkalinity concentration data from 11 sub-catchments of the Nether Beck in the English Lake District have been used to appraise the transferability of the Scottish, River Dee-based G-BASH model. Readily available riparian zone geochemistry and flow paths were used initially to predict minimum and mean stream water concentrations at the Nether Beck, based on calibration equations from the River Dee catchment data. Predicted values significantly exceeded observed values.

Assessment of the spatial heterogeneity of weathering rates in upland catchments using the sodium dominance index and its significance in integrated catchment management.

The sodium dominance index was developed to quantify weathering rates and critical loads in Scotland, where atmospheric aerosols of maritime origin dominate over biogeochemical weathering in providing base cation inputs to catchment soils and drainage waters. High sodium dominance in river or lake water indicates low weathering rate. Here, this concept is evaluated using intensive temporal and spatial sampling strategies in two substantial catchments, one in Scotland and the other in central England, with particular reference to detection of groundwater inputs, and to possible problems from road salting in the calibration.

A novel modelling approach for spatial and temporal variations in nitrate concentrations in an N-impacted UK small upland river basin.

Monthly data for 11 moorland streams displaying marked seasonality and spatial variation in nitrate concentrations have been used with readily available catchment characteristics to develop a method for predicting stream water nitrate concentrations throughout an upland river network in the Lake District, UK. Over a 12-month period, a simple asymmetric truncated cosine function of day number is used to describe seasonality effects on stream water nitrate concentrations. This is then adjusted to compensate for differences in seasonality effects with catchment elevation.

Arsenic accumulation and metabolism in rice (Oryza sativa L.).

The use of arsenic (As) contaminated groundwater for irrigation of crops has resulted in elevated concentrations of arsenic in agricultural soils in Bangladesh, West Bengal (India), and elsewhere. Paddy rice (Oryza sativa L.) is the main agricultural crop grown in the arsenic-affected areas of Bangladesh.

Catchment characteristics controlling the mobilization and potential toxicity of aluminium fractions in the catchment of the River Dee, northeast Scotland.

Elevated streamwater concentrations of aluminium have been associated with the onset of acidification, both by natural and anthropogenic means. This has important implications for river water quality. Concentrations of total, labile-inorganic and non-labile-organic fractions of aluminium were determined across the River Dee catchment, northeast Scotland.

Riparian zone influence on stream water chemistry at different spatial scales: a GIS-based modelling approach, an example for the Dee, NE Scotland.

A geographical information system (GIS-ARC/INFO) was used to collate existing spatial data sets on catchment characteristics to predict stream water quality using simple empirical models. The study, based on the river Dee catchment in NE Scotland, found that geological maps and associated geochemical information provided a suitable framework for predicting chemical parameters associated with acidification sensitivity (including alkalinity and base cation concentrations). In particular, it was found that in relatively undisturbed catchments, the parent material and geochemistry of the riparian zone, when combined with a simple hydrological flow path model, could be used to accurately predict stream water chemistry at a range of flows (Q95 to > Q5) and spatial scales (1-1000 km2).

Toxicological response of a bioluminescent microbial assay to Zn, Pb and Cu in an artificial soil solution: relationship with total metal concentrations and free ion activities.

The relationship between toxicological response and both total concentrations and free ion activities of Pb, Cu and Zn in an artificial soil solution has been investigated using lux-marked Escherichia coli HB101 (pUCD607) as a bioassay. SO4(2-) (as K2SO4) was added as an inorganic complexing agent up to 0.01 M representing the range of ionic strengths found in soil solutions and giving a wide range of free metal ion activities.

The nitrogen composition of streams in upland Scotland: some regional and seasonal differences.

The nitrogen (N) composition of streams draining four upland regions of Scotland was compared in samples collected monthly between April 1997 and April 1998. Stream samples were analysed for total N (TN), particulate N (PN), nitrate (NO3), ammonium (NH4), dissolved organic N (DON) and dissolved organic carbon (DOC). Concentrations of TN were small, generally less than 1 mg l(-1) , dominated by dissolved forms of N, and varied significantly between upland regions.

A model for predicting chloride concentrations in river water in a relatively unpolluted catchment in north-east Scotland.

The River Dee is an oligotrophic soft water system, in the NE of Scotland, with a catchment area of approximately 2100 km2. The river rises in the Cairngorm Mountains and enters the North Sea at Aberdeen, approximately 140 km from its source. Water chemical quality data was collected every 2 weeks over 12 months for 59 sites distributed throughout the catchment.

The critical loads concept: milestone or millstone for the new millennium?

The significance of the introduction of the critical loads concept in the closing decades of the 20th century is considered critically, both in the context of its potential in planning pollution abatement strategies over a range of regional spatial and temporal scales and in terms of its more general impact upon atmospheric pollution effects research. Based upon perceived strengths and shortcomings of the concept and of the ways in which it has thus far been applied, a brief assessment is made also of its possible role in the opening decade of the new millennium. It is concluded that the validity of some of the fundamental underpinning concepts and of the data being used for their application could, and should, be questioned.