Anthony C. Edwards

A review of water quality concerns in livestock farming areas.

Post-war changes in farming systems and especially the move from mixed arable-livestock farming towards greater specialisation, together with the general intensification of food production have had adverse affects on the environment. Livestock systems have largely become separated into pasture-based (cattle and sheep) and indoor systems (pigs and poultry). This paper reviews water quality issues in livestock farming areas of the UK. The increased losses of nutrients, farm effluents (particularly livestock wastes), pesticides such as sheep-dipping chemicals, bacterial and protozoan contamination of soil and water are some of the main concerns regarding water quality degradation. There has been a general uncoupling of nutrient cycles, and problems relating to nutrient loss are either short-term direct losses or long-term, related to accumulated nutrient surpluses. Results from several field studies indicate that a rational use of manure and mineral fertilisers can help reduce the pollution problems arising from livestock farming practices. Several best management practices are suggested for the control of nutrient loss and minimising release of pathogen and sheep-dip chemicals into agricultural runoff.

Low molecular weight organic acid adsorption in forest soils: effects on soil solution concentrations and biodegradation rates

Low molecular weight (LMW) organic acids are believed to play a key role in many rhizosphere and pedogenic processes; However, their efficiency is likely to depend on their susceptibility to sorption and biodegradation. The sorption characteristics of three organic acids (citrate, oxalate and acetate) and phosphate were examined over the concentration range 0–1000 μM in three coniferous forest soil profiles. Sorption to the soils solid phase could be adequately described by the Langmuir equation with sorption capacity following the horizon series: B>C>E>O. The strength of anion sorption followed the series: phosphate>oxalate≥citrate≫acetate. Calculations indicated that between 50 and 95% (O and E horizons) and >93% (B horizons) of these LMW organic acids entering the soil will become sorbed to the solid phase. The amount of organic acids predicted to be present on the solid phase at typical soil solution concentrations ranged from <1 to 1100 nmol g−1 yielding adsorbed-to-solution ratios (adsorption coefficients) of between <0.1 and 3100. In the case of citrate, sorption to the solid phase significantly reduced its biodegradation potential by 35–99% depending upon the degree and type of sorption surface. The findings of this work are discussed in the context of the quantitative effects of adsorption on organic acids, their ecological functions and role in soil forming processes.

Manuring and fertilization effects on phosphorus accumulation in soils and potential environmental implications

Abstract Phosphorus application as manure to agricultural soils in intensive livestock farming and arable cropping systems often exceeds P offtake by crops. This surplus could lead to P accumulation in soils, making them long-term diffuse sources of P loss to water. We investigated the impact of a range of manuring and fertilization practices in intensive farming systems on the accumulation of P in soils, soil test phosphorus (STP), distribution of organic and inorganic P, P-sorption capacity and degree of soil saturation with P (DSSP). The results from the 10 long-term sites investigated showed increases in both total soil P content and STP values (Olsen-P and Mehlich-3 P), as a result of P surpluses. The net total P accumulation in the soils across the sites ranged from 16 to 232 kg P ha−1 year−1. The effects of long-term P surpluses were a significant reduction in P-retention capacity and increase in DSSP. The sites investigated would attain 25% DSSP in 10–150 years, depending upon the size of P surplus and sorption capacity. A combination of large P surplus and low P-sorption capacity could saturate soils to 25% DSSP within 10–30 years. The values of Olsen (85 mg P kg−1) and Mehlich-3 (305 mg P kg−1) extractable-P predicted for the 25% DSSP are likely to result in environmentally significant P losses.

Catchment microbial dynamics: the emergence of a research agenda:

Parallel policy developments driven in the USA by the Clean Water Act and in Europe by the Water Framework Directive have focused attention on the need for quantitative information on the fluxes of faecal indicator bacteria in catchment systems. Data are required on point and diffuse source loadings, fate and transport of these non-conservative parameters, on the land surface, within soil systems, in groundwater, streams, impoundments and nearshore waters. This new information is needed by regulators to inform Total Maximum Daily Load estimates in the USA and Programmes of Measures in Europe both designed to prevent impairment of water quality at locations where compliance is assessed against health-based standards for drinking, bathing or shellfish harvesting. In the UK, the majority of catchment-scale activity in this field has been undertaken by physical geographers although microbial flux analysis and modelling has received much less attention from the research and policy communities than, for example, the nutrient parameters. This paper charts the policy drivers now operative and assesses the evidence base to support current policy questions. Finally, gaps and priority research questions are identified.

Phosphorus fractions in soil solution: Influence of soil acidity and fertiliser additions

The influence of soil acidity and phosphorus fertilization on phosphorus fractions and dissolved organic carbon (DOC) in soil solution was quantified experimentally in an iron humus podzol. Soil solution was isolated by centrifugation from top- and sub-soil samples. Total dissolved phosphorus (TDP), dissolved reactive phosphorus (DRP), dissolved organic phosphorus (DOP) and DOC increased as soil pH and P status increased. DOP was the fraction present at the highest concentration (0.080–0.464 mg P L−1) for the majority of samples. DOC and DOP concentrations which remained relatively constant down the soil profile were also highly correlated. Soluble organic P compounds may make a significant contribution to plant available soil P particularly for soils with low fertility levels. The relatively high DOP concentrations (ca 0.227 mg P L−1) found throughout the soil profile have important consequences with regards to P leaching and plant nutrition.

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.

Role of proteinaceous amino acids released in root exudates in nutrient acquisition from the rhizosphere

The role of proteinaceous amino acids in rhizosphere nutrient mobilization was assessed both experimentally and theoretically. The degree of adsorption onto the soils solid phase was dependent on both the amino acid species and on soil properties. On addition of amino acids to both soil and freshly precipitated Fe(OH)3, no detectable mobilization of nutrients (K, Na, Ca, Mg, Cu, Mn, Zn, Fe, S, P, Si and Al) was observed, indicating a very low complexation ability of the acidic, neutral and basic amino acids. This was supported by results from a solution equilibria computer model which also predicted low levels of amino acid complexation with solutes present in the soil solution. On comparison with the Fe(OH)3 and equilibria data obtained for the organic acid, citrate, it was concluded that amino acids released into the rhizosphere have a limited role in the direct acquisition of nutrients by plants. The effectiveness of root exudates such as amino acids, phytosiderophores and organic acids in nutrient mobilization from the rhizosphere is discussed with reference to rhizosphere diffusion distances, microbial degradation, rate of complexation and the roots capacity to recapture exudate-metal complexes from the soil.

The prediction and management of water quality in a relatively unpolluted major Scottish catchment: current issues and experimental approaches

Abstract The potential impacts of diffuse pollution from atmospheric deposition and land use on the water quantity and quality of the river Dee in N.E. Scotland are currently being assessed. The importance of headwater regions for supplying a large proportion of catchment runoff with water of a high quality is clearly demonstrated. However, the quality of this water is threatened by the impact of acid deposition in a number of sub-catchments. In some of the more agriculturally developed lowland sub-catchments, there are increasing levels of nitrogen runoff. The catchment attributes, together with hydrochemical data, are being considered in terms of an ongoing research programme established to predict the impact of future environmental and land-use change scenarios.

Factors regulating the spatial and temporal distribution of solute concentrations in a major river system in NE Scotland

Abstract The River Dee in NE Scotland, an oligotrophic soft water system, has a catchment area of approx. 2100 km2, its source in the Cairngorm mountains being approx. 140 km from its outlet to the North Sea at Aberdeen. A comprehensive sampling strategy and analytical programme, commensurate with the size and nature of the Dee system, have been established for major water quality determinands to identify the controls on, and origins of, dissolved species throughout the system at a range of catchment scales and over a range of flow regimes. Fifty-nine sites covering a range of catchment types and scales were therefore sampled bi-weekly for 1 year. At the basin scale, there is a general downstream increase in determinand concentrations. This produces strong linear relationships between many determinands which are unrelated in terms of a common terrestrial process or origin. At the sub-catchment scale, however, specific hydrochemical processes control streamwater chemistry. The Dee basin divides into two distinct geographic regions in terms of land use (upland and lowland) which produce clear differences in water chemistry. Individual sub-catchments can also be grouped in terms of temporal variations in streamwater chemistry. The strength of the relationship between weathering-derived ionic concentrations and flow in the upland sub-catchments has lead to the identification of specific concentration limits in sub-catchments which can be used as characteristics of soil water and groundwater end-members. This provides a basis for the prediction of upland weathering-derived component concentrations for each sub-catchment at a range of flows.

The quality of drinking water from private water supplies in Aberdeenshire, UK

The quality of private water supplies within Aberdeenshire sampled between 1992 and 1998 was analysed with respect to the presence of total coliforms (TC), faecal coliforms (FC), and nitrate. Of the approximately 1750 samples analysed, which included multiple samples from larger supply categories, the individual failure rate was 41%, 30% and 15% for TC, FC and nitrate, respectively. A combined failure rate for these samples was 48%. Failure rates on microbiological grounds displayed a seasonal trend being greater during the latter half of the year. Although this observation is likely to be due to a combination of local and regional scale factors, part of the variability in failure rate was explained by a significant positive relationship with rainfall amount. Concentrations of nitrate tended to display an opposite trend with a greater number of failures occurring during the spring period and no relationship with rainfall was immediately apparent. A relatively small number of samples (< 50) failed simultaneously for both coliforms and nitrate suggesting that the mechanism responsible for the contamination differed. A similar failure rate for samples collected directly from the source (i.e. well) compared with those taken from the potable tap (usually kitchen cold water tap) suggests that it is the groundwater source itself that contributes much of the microbiological and nitrate contamination rather than a storage or supply line contamination mechanism. A more frequent and random sampling of category one F supplies suggested a greater overall failure rate, which has its own implications for deciding an appropriate sampling frequency.