Biomedical subjects

Colin Neal

Publications and source records attributed to Colin Neal.

24 records · Page 2Linked to original sources

PubMed2002

Patterns in nutrient concentrations and biological quality indices across the upper Thames river basin, UK.

This paper examines the nutrient chemistry and biological quality indices [Mean Trophic Rank (MTR) and Trophic Diatom Index (TDI)] for rivers within the upper Thames basin. The predominant sources of nitrogen within the rivers monitored were diffuse and agricultural in nature. However, phosphorus showed both diffuse and point source signals. MTR surveys undertaken both upstream and downstream of major STWs indicate that these rivers are 'at risk' of eutrophication or 'badly damaged'. MTR surveys also indicate increased trophic status downstream of STWs, whereas TDI does not indicate such a consistent pattern. Phosphorus treatment at selected major sewage treatment works in the upper Thames basin resulted in significant reductions in in-stream P concentrations and reductions in fluxes by a half to two thirds. However, the effects of P-reduction on in-stream ecology (measured as MTR and TDI) were more difficult to ascribe, owing to: (1) the high variability in river flow rates experienced since P-reduction was introduced; (2) lag effects related to P stores in river bed sediments; and (3) diffuse and smaller point source inputs upstream. The results of this study indicate that control of upstream sources of phosphorus may prove critical in improving the biological quality status of UK lowland rivers, including ecological responses to P-source controls on the major sewage treatment works downstream. Upstream sources include both diffuse (agricultural) sources and small point source inputs which, at present, are not classified as 'qualifying discharges' under the Urban Wastewater Treatment Directive (UWWTD) and are thus not subject to phosphorus control measures. These results are of relevance for integrated, sustainable management and protection of European freshwater resources, particularly in terms of new ecological targets for water quality management under the new Water Framework Directive.

Cities↗

PubMed2002

Phosphorus-calcium carbonate saturation relationships in a lowland chalk river impacted by sewage inputs and phosphorus remediation: an assessment of phosphorus self-cleansing mechanisms in natural waters.

The relationship between calcium carbonate saturation and phosphorus concentrations for seven sites on the upper reaches of the River Kennet are examined. The findings are related to issues of groundwater supplies and the introduction of phosphorus treatment of effluent from the Marlborough sewage treatment works (STW) at part of the way along the study reach. Being supplied from a Cretaceous Chalk aquifer, the Kennet is mainly of a calcium-bicarbonate type and has a relatively constant composition of many major water quality determinands. Typically, the waters average a pH of approximately eight (range approx. 7.5-8.5) during the day with the lowest values occurring at the upstream site. Dissolved carbon dioxide varies from approximately 5 to 35 times atmospheric pressure during the late morning with the highest values occurring at the upstream site. However, in-stream biological activity gives rise to marked diurnal fluctuations in pH and dissolved carbon dioxide concentrations and during the summer months, by mid to late afternoon, pH is at its maximum and dissolved carbon dioxide is at its lowest: this is shown by continuous measurements at one of the river sites. Alkalinity and calcium concentrations remain relatively constant at approximately 4,700 microEq/l (range 3,500-6,000 microEq/l) and 120 mg/l (range 85-150 mg/l), respectively, and the waters are oversaturated with respect to calcium carbonate (calcite) typically by a factor of six (range 2-25). Along the reach, soluble reactive phosphate (SRP) increases from the first to the second site with the introduction of sewage supplies from the Marlborough STW, and then declines further downstream as sewage dilution and uptake by the river bed/aquatic plants increases. The differences in concentration decrease after phosphorus removal from Marlborough STW. Despite this change, there is no clear indication of any calcite solubility control except perhaps at times of extreme baseflow during the growing season when within-stream photosynthesis is maximal and within-stream residence times are longer. A comparison of river and groundwater data shows that the groundwaters have similar alkalinities and calcium concentrations. However, the groundwaters have (a) higher carbon dioxide saturations (a factor of 2-5 times the value for the river), (b) lower pHs (0.5-1.5 units), (c) lower SRP concentrations (a quarter or less of the river values) and (d) waters near calcite saturation (unlike the surface waters which are oversaturated). The findings indicate a river system dominated by the input carbon dioxide laden groundwaters in approximate equilibrium with calcite attenuated by within-channel biological and physical processes. Within the river: (a) the waters degas carbon dioxide increasing the pH, producing oversaturated conditions; and (b) oscillating pH-dissolved carbon dioxide levels occur between day and night due to changing balances between photosynthesis and respiration. It seems that lowering the phosphorus levels have not resulted in calcite precipitation within the water column and that no significant within-stream self-cleansing mechanisms are occurring that might be predicted from theory: other components in the water such as dissolved organic carbon may inhibit calcite nucleation. However, the low SRP levels in the groundwater coupled with calcite saturation, may well indicate that phosphorous concentrations within the groundwater are regulated by such processes: the number of calcite nucleating sites are orders of magnitude higher and the calcite inhibitors may be less prevalent.

Calcium Carbonate↗

PubMed2002

Calcite saturation in eastern UK rivers.

Calcite saturation in eastern UK rivers is assessed in relation to the potential kinetic inhibition of calcite precipitation. Two well established inhibitors are considered: soluble reactive phosphorus (SRP, i.e. inorganic monomeric phosphorus); and dissolved organic carbon (DOC). The rivers show a range of calcite saturation levels from approximately 1hundredth to approximately 100-fold. The greatest range occurs for the northernmost river considered, the Tweed, where the waters range from highly unsaturated to highly oversaturated. The lowest range occurs for the most southerly rivers (the Great Ouse and the Thames) where the waters are consistently oversaturated with respect to calcite. The contrasting patterns relate to a greater diversity of water quality within the northern regions. Thus, during the winter, the main waters are derived from the upland areas with acidic soils and low weathering rates. During the summer baseflow periods, groundwater inputs are more important and high photosynthesis results in particularly high pHs and calcite oversaturation. In contrast, for the southern rivers, the main source of water during both the summer baseflow and the winter highflow periods comes from calcium carbonate rich aquifer sources. Statistical analysis of pH vs. the logarithm of the calcite saturation index for each river indicates strong linear features with individual gradients of approximately 1. This linearity results from an autocorrelation (the logarithm of the saturation index is calculated from the pH) and this indicates that calcite solubility controls are not operative in any of the rivers examined. A comparison of calcite saturation levels and SRP and DOC concentrations show a pattern inconsistent with kinetic hindrance, although some structure is observed, probably due to the mixing reactions between point and diffuse sources of water with contrasting chemistry.

Journal Article↗

PubMed2002

Interception and attenuation of atmospheric pollution in a lowland ash forested site, Old Pond Close, Northamptonshire, UK.

A study of interception of chemicals at an ash plantation forest in southern-central England shows the modification of acidic pollution as it passes from precipitation, through the vegetation cover and the soil to generate surface runoff. Precipitation is highly acidic (pH 3.7-4.8, alkalinity -16 to -200 microEq/l) and it is enriched in the strong acid anions associated with acidification (sulfate and nitrate) as well as ammonium and the trace elements aluminium and zinc. The concentration of both sea-salt and pollutant components varies considerably over time and this is linked to washout from the atmosphere during precipitation events as marked by an inverse relationship between concentration and volume of catch. The catchment is also supplied by sea-salt and pollutant additions as dry deposition: gaseous inputs of SO(x) may also increase sulfate deposition. Through the vegetation, much of the acidity is neutralised and, particularly during the growth period, calcium, magnesium and potassium is cycled, while sodium and nitrate are partially removed. Within the catchment, weathering ensures that further base cation production occurs leading to enhanced neutralisation of acidity and the generation of positive alkalinities. As a result, surface runoff becomes buffered with alkalinity approximately 490 microEq/l and pH approximately 7.9. Thus, although the acidification input from the atmosphere is high, this does not translate to acidic runoff due to within-canopy and within-soil processes.

Acid Rain↗

PubMed2002

Phosphorus sources, speciation and dynamics in the lowland eutrophic River Kennet, UK.

This paper examines the behaviour of phosphorus (P) in a lowland chalk (Cretaceous-age) stream, the upper River Kennet in southern England, which has been subject to P remediation by tertiary treatment at the major sewage treatment works in the area. The effects of treatment are examined in relation to boron, a conservative tracer of sewage effluent and in terms of the relative contributions of soluble reactive phosphorus (SRP) loads from point and diffuse sources, and in-stream SRP loads. These results indicate a baseline reduction in in-stream SRP concentrations immediately following P-treatment of approximately 72%. Subsequent high flows result in a greater contribution of diffuse inputs and increases in SRP levels relative to the initial post-treatment period. The dynamics of SRP and particulate phosphorus (PP) are examined under a wide range of river flow conditions. Given the flashy nature of near-surface runoff in the River Kennet, sub-weekly (daily automated) sampling was used to examine the dynamics in SRP and PP concentrations in response to storm events. Simple empirical models linking weekly SRP concentrations with flow were developed. The empirical models were successfully applied to the daily data, to partition TP measurements and provide an estimate of daily SRP and PP concentrations. Mass balance studies were used to examine net gains and losses along the experimental river reach and indicate large net losses (up to 60%) during the extreme low flows and high SRP concentrations prior to P-treatment, which may be linked to extensive epiphytic growth. Phosphorus dynamics and response to P-treatment are discussed in relation to hydrological controls in permeable chalk catchments and wider implications for eutrophication management are examined.

Calcium Carbonate↗

PubMed2002

Diurnal and longer term patterns in carbon dioxide and calcite saturation for the River Kennet, south-eastern England.

Continuous pH, dissolved oxygen and temperature information for three sites on the upper portion of the River Kennet, a tributary of the Thames in southern England is presented. A thermodynamic model is developed which links this information to weekly water quality data allowing the estimation of dissolved carbon dioxide and calcite saturation levels within the river on a continuous basis. The results show a dynamic and variable system along the length of the river. Marked diurnal patterns are observed for pH, dissolved oxygen, dissolved carbon dioxide and calcite saturation and the highest fluctuations occur during the summer months. There is also a marked gradient downstream in average pH (7.5-8.0) and dissolved carbon dioxide (30-10 times atmospheric pressure). Dissolved oxygen levels average approximately 100% saturation across all sites, and the diurnal pattern occurring during the summer months declines downstream. The waters are permanently oversaturated with respect to calcite and the diurnal patterns of change are maximal during the summer months. The results are discussed in relation to: (a) the balance between photosynthesis and respiratory processes; (b) the relative interchanges between the sediment/plant interface with the water column; and (c) the rates of degassing of carbon dioxide and oxygen between the river surface and the atmosphere.

Calcium Carbonate↗