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. However, it was shown for alkalinity prediction that rainfall exerts a significant dilution effect and should be incorporated into the model in addition to flow path-weighted sediments Ca% and Mg%. The results also strongly suggest that in catchments with substantial rough moorland land-use neutralization of organic acids consumes alkalinity and this fact should be considered in any future development of the model.

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. Predictive model forms were linear. Attempts to predict minimum values for Ca and alkalinity also were less satisfactory. This probably is due to variations in hydrological response times to individual precipitation events across the catchment.

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. In the Dee network, the spatial distribution of sodium dominance reflects the distribution of soil parent material geology, but land use also influences the equations. It is postulated that road density, via winter road salting, influences the sodium dominance calibration in lowland agricultural areas. Although road salting can also be problematic in some upland areas, the index still can provide clear indication of the likely severity of acid flush events in remote upland streams. In the Etherow catchment, sodium dominance varies markedly, sometimes over relatively small distances, reflecting soil type distribution, the occurrence of ground-water inputs to streams, and the influence of water in tributaries above the sampling point.

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. EC50 values expressed in terms of concentration, varied significantly with K2SO4 molarity for all metals. However, when EC50 values were expressed in terms of free ion activity they were not significantly different for Pb and Zn, supporting the free ion activity model. Conversely, EC50 values expressed as free Cu activity did vary significantly with K2SO4 molarity, possibly due to a greater degree of adsorption of Cu onto inactive sites on the cell surfaces than for Zn and Pb. Linear regression analysis of bioluminescence on free ion activity revealed significant correlations for each metal above the toxicity threshold. In conclusion, lux-marked E. coli is suitable for investigating the toxicity of metal ions and complexes in non saline systems although cell surface adsorption effects could be important for some metals, e.g. Cu.

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. River water chloride concentrations increased significantly from west to east. In depth investigation of the relationship with distance from the coast revealed the significant difference in spatial distribution of river water chloride concentrations between upland and lowland/agricultural areas, suggesting the possible importance of agricultural practices to streamwater chloride concentrations. Thirty of the sample sites are independent and have been used to develop a simple model for prediction of streamwater Cl- concentration throughout the catchment. The model has been validated using data from the remaining sub-catchments. The model shows that mean Cl- concentration may be reliably predicted from distance from the coast and the percentage of improved grassland and arable land cover in each sub-catchment (r2 = 0.98). It is postulated that the land use effects may be partly due to the evolved link between landuse and catchment altitude characteristics, rather than just the direct effect of applied potassium chloride fertiliser on agricultural land. It was noted that there was insufficient forestry within the River Dee Catchment to reliably include % forest cover in the model.

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. Nitrate accounted for most of the variability in TN; largest concentrations were observed in the Southern Uplands and smallest concentrations were observed in the Highlands. Nitrate concentrations were positively correlated with the percentage cover of improved grasslands and brown forest soils and negatively correlated with the percentage cover of peat. Concentrations of DON also varied between regions, but to a lesser extent than those of NO3. Largest concentrations occurred in SW Scotland and smallest concentrations in the Cairngorms. Although a significant positive correlation between DON and DOC was observed, stream water DON content was not related to the percentage cover of peat in the catchment, as was the case for DOC. The average DOC:DON ratio was narrower for streams in the Southern Uplands than for those in the Cairngorms and Highlands. Nitrate and DON displayed contrasting seasonal trends; NO3 concentrations were larger in the winter while DON concentrations were larger in the summer. Only a small proportion, < 8% and < 7%, of TN was PN and NH4, respectively, the majority of N was present as either NO3 or DON. Nitrate was the dominant fraction (58-65%) in all regions except the Highlands where DON accounted for 57% of TN. However, the relative importance of the DON component increased in the summer in all regions. This study has demonstrated that the DON fraction is an important component of the total N transported by streams from upland catchments in Scotland. Thus, assessments of anthropogenic impacts on N losses from upland ecosystems need to consider not only the dissolved inorganic species but also DON.

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. Fifty-nine subcatchments, chosen to reflect the variety of soils, parent materials and land use patterns across this major river system were sampled bi-weekly for 1 year. The distribution of aluminium was closely linked to factors of parent material and organic soil cover. Strong spatial and temporal relationships were observed between pH and all fractions of aluminium. Significant episodic peaks in aluminium occurred, these being especially pronounced when a storm event followed a period of dry weather. A weathering rate index utilizing the Na dominance of base cations was found to be a predictor of potential streamwater toxicity implied through Ca/inorganic aluminium ratios. It was demonstrated that Al was mobilized from acid headwater streams, whilst concentrations in the main stem remained much lower.

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). This probably reflects the importance of the riparian zone as an area where hydrological inputs to stream systems occur via flow paths in the soil and groundwater zones. Thus, evolution of drainage water chemistry appears to retain the geochemical characteristics of the riparian area as it enters the channel network. In more intensively managed catchments, riparian land use is a further influential factor, which can be incorporated into models to improve predictions for certain base cations. The utility in providing simple hydrochemical models, based on readily available data sets, to assist environmental managers in planning land use in catchment systems is discussed.

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. Nevertheless, environmental pollution management and abatement policy planning will continue to require application of the critical loads concept or something very similar, both in existing and novel areas of application, for the sustainable management of soil and water resources in the long term.

Evaluation of cycling patterns of dissolved oxygen in a tropical lake as an indicator of biodegradable organic pollution.

Dissolved oxygen cycling patterns in a tropical lake (Weija Lake) were shown to be useful as a potential indicator of biodegradable organic pollution, by dosing with liquid malt to give an additional organic burden of 2.5 and 5.0 mg l-1 TOC, and monitoring the DO values continuously for 140 h. These loadings were added to water columns (in tubes) suspended from a raft in a lake in south-east Ghana. The addition of organic pollution burden to the lake water produced two main effects: the mean DO value was lowered, and the amplitude of the DO cycle decreased as organic loading increased from 2.5 to 5.0 mg l-1 TOC. There was also an indication of heterotrophic respiration associated with organic inputs for the 5.0 mg l-1 added TOC suggesting a P/R ratio of well below 1.0. Taking the results of a DO cycling computer model together with those from the lake raft experiments, it can be concluded that dissolved oxygen cycles can be a good indicator of biodegradable organic pollution load.

An empirical map of critical loads of acidity for soils in Great Britain.

The method used to produce a critical load map of acidity for soils in Great Britain is described. Critical loads were assigned to the dominant soil in each 1 km grid square of the UK national grid. Mineral soils were assigned a critical load based on mineralogy and chemistry, using approaches appropriate to UK conditions. Critical loads for peat soils are based primarily on a maximum acceptable reduction of peat pH, and results from laboratory equilibration studies. The map shows that soils with small critical loads (<0.5 kmol(c) ha(-1) year(-1)) i.e. highly sensitive to acidic deposition, dominate in the north and west of Britain; the south and east are dominated by soils with large critical loads, with small areas of more sensitive soils associated with sandy soil-forming materials. A modified critical load map illustrates the potential impact of agricultural liming on soil critical loads.

The sensitivity of surface waters of Great Britain to acidification predicted from catchment characteristics.

Using a combination of soil, land use and geological information, a map of Great Britain has been derived which indicates the sensitivity of surface waters to acidification. For the geological information, a slightly modified version of an available map was used which indicated the sensitivity of groundwaters to acidification. For soils, 1-km databases of soil information for England and Wales and for Scotland were employed to map the soil sensitivity as determined by buffering capacity. The derived soils map was modified to take account of agricultural liming in arable and managed grassland areas using the ITE Land Classification. The final map of surface water sensitivity was obtained by using a geographic information system overlay procedure which enabled each combination of soil and geology sensitivity to be uniquely defined. The final sensitivity classification was based upon expert knowledge and the experience of a similar sensitivity mapping exercise for Wales.

Redistribution of zinc from sewage sludge applied to a range of contrasting soils.

An incubation study has been performed to investigate the rates of redistribution of 65Zn from spiked sewage sludge into different soil fractions. The labeled zinc in soils amended with sludge was fractionated by operationally defined procedures at three different times (1, 7 and 30 days after incubation) into exchangeable, organically bound, amorphous iron oxide-bound, crystalline iron oxide-bound and residual fractions. The rates of redistribution of zinc from sewage sludge mainly depended on soil pH. In acid soils, most of the sludge-derived zinc (70-80%) went to the exchangeable pools, and was retained in this form at high concentration for at least a month. The effect of the time during digestion of the incorporation of a 65Zn spike into sludge was also studied. Although the results were significantly effected by spike timing, the effects of the latter on subsequent zinc fractionation results were minor compared with the effect of soil pH.

Changes in sulphate retention, soil chemistry and drainage water quality along an upland soil transect.

Soils sampled along an altitudinal transect in an upland area of North East Scotland have been used to investigate downslope changes in the capacity of soils to retain sulphate. Simulated laboratory experiments involving the leaching of reconstituted cores with 'rainfall' containing low (1.85 mg litre(-1) and high (51.90 mg litre(-1) concentrations of sulphate indicate that soils developed on upper slopes have a limited capacity to adsorb sulphate, whereas soils on lower slopes have a much greater sulphate adsorption capacity. Soil drainage water, produced from 'sensitive' upper slope soils may therefore be significantly modified by physico-chemical reactions in lower slopes before reaching watercourses.

A review of the export of carbon in river water: fluxes and processes.

This review summarizes data on exports of carbon from a large number of temperate and boreal catchments in North America, Europe and New Zealand. Organic carbon losses, usually dominated by dissolved organic matter, show relatively little variation, most catchments exporting between 10 and 100 kg C ha(-1) yr(-1). Inorganic carbon exports occur at a similar rate. However, a lack of information on the flux of particulate organic carbon and dissolved CO2 is highlighted, particularly for rivers in Europe. Processes regulating the flux of organic carbon to streams and its subsequent fate in-stream are reviewed, along with the effects of land use and acidification on these processes. The size of the global riverine flux of carbon in relation to the global carbon cycle and the possible effects of environmental change on the export of carbon in rivers are considered.

Assessment by laboratory simulation of approaches to amelioration of peat acidification.

The effects of different liming materials (CaCO(3), Ca(OH)(2), CaHPO(4), and dolomite) on soil and drainage-water chemistry have been investigated for upland acidic peats by using a soil-core-simulation experiment. Intact cores from three depths (0-30, 0-60, and 0-90 mm) were subjected to ten years of simulated rainfall. Drainage water was periodically analysed for Ca(2+), Mg(2+), Na(+), K(+) NH(4)(+), TOC, Cl(-), SO(4)(2-), NO(3)(-), PO(4)(3-), and pH, and at the end of the experiment the cores were destructively sampled and analysed. Temporal changes in soil and drainage-water chemistry are used to evaluate the advantages and disadvantages of using different liming materials for the amelioration of soil and drainage-water chemistry.

Automated determination of sulphite and sulphur dioxide by cool flame molecular emission spectrometry after reduction to hydrogen sulphide with sodium tetrahydroborate III.

An automated method for the determination of sulphite and sulphur dioxide by cool flame molecular emission spectrometry is described. The method is based on the reduction of both compounds to hydrogen sulphide with sodium tetrahydroborate III. The sample which is mixed with NaBH(4) is acidified with 6M hydrochloric acid and carried by a continuous-flow stream into a gas-liquid separator where the evolved hydrogen sulphide is swept by nitrogen into a cool, hydrogen-nitrogen-entrained air flame. The intensity of the blue diatomic S(2) emission generated is measured at 384 nm. The proposed method has a detection limit for sulphite of 0.029 mug/ml and relative standard deviations of 1.2 and 1.5% for 1 and 5 mug/ml respectively. The calibration graph is linear up to 24 mug/ml sulphite and samples can be analysed at a rate of about 40/hr. The method has been applied to the determination of SO(2) in air and sulphite in wines.

Determination of dissolved organic phosphorus in soil solutions by an improved automated photo-oxidation procedure.

An improved automated photo-oxidation procedure to determine dissolved organic phosphorus in soil solutions is described. Organically combined phosphorus is converted quantitatively to orthophosphate under UV radiation and an excess of dissolved oxygen. The orthophosphate is determined spectrophotometrically using the Murphy and Riley procedure, modified by increasing the concentration of ascorbic acid. Fluoride was added to the system to overcome potential interference when working with soil solution. The limit of detection was 0.64 mug/l. PO(4)(-3) -P and calibration was linear over the range studied (5-1000 mug/l. PO(4)(-3) -P).

Predicting stream-water quality using catchment and soil chemical characteristics.

The distribution and chemistry of soils in 10 upland catchments in NE Scotland have been used to develop a means of predicting minimum, maximum and mean concentrations of calcium and hydrogen ions in streams. The approach is based on the control of stream-water chemistry by soil chemical properties. Stream-water chemistry was monitored over a two-year period. Each catchment was surveyed and soils sampled to characterize the chemistry of the main soil units. Stream-water chemical parameters are related to the chemical characteristics of the upper and lower soil horizons in the catchments. The contribution of each soil unit is assessed using randomly generated flow paths. Soil chemistry is weighted according to the distribution of soils in the immediate vicinity of the stream. In this paper the approach is largely confined to the prediction of minimum, maximum and mean concentrations of calcium ions in stream waters. In the longer term, the approach may have the potential to predict what effects changes in soil chemistry and management practice (drainage, ploughing) will have on water quality in upland catchments.

Factors influencing nitrogen retention in forest soils.

Leaching and agitation experiments with soil organic horizons showed that nitrogen pollutant concentration, temperature, contact time and neutral soluble salts influence the fate of enhanced ammonium and nitrate inputs to the soil and the leaching of inorganic and organic nitrogen. Soils investigated included L, F and H horizons under Sitka spruce, the L and F horizons under Scots pine and Japanese larch and L and O horizons under Calluna. Effects attributable to species were also observed. The results are discussed in the light of their relevance to being incorporated into models of the effects of excess nitrogen inputs to forest soils, and in view of current concern that forest ecosystems in areas of high nitrogen deposition may become nitrogen saturated.