Robert C. Ferrier

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.

Modelling stream acidification in afforested catchments: An assessment of the relative effects of acid deposition and afforestation

Abstract A model of the combined long-term effects of acidic deposition and forest growth has been developed and calibrated for an upland site in Scotland. The model is used to perform a series of simulation experiments to assess the relative effects of afforestation and acidic deposition on soil and surface water chemistry. The experiments compare and contrast: (a) the simulated historical effects of increased acidic deposition and forest growth, both individually and in combination; (b) the simulated future effects of various levels of reduction of deposition in combination with the forestry strategies of harvesting with and without replanting. Results indicate that historical acidification of surface waters in areas receiving high levels of acidic deposition has been exacerbated by afforestation practices. Afforestation in the absence of acidic deposition, however, has had a lesser effect on surface water acidification even though the nutrient demands of forest growth have caused significant soil acidification. Comparisons of future forest management strategies in conjunction with likely deposition reductions indicate that, in sensitive areas, replanting of a felled forest without treatment of the soil by addition of base cations, should not be undertaken even if significant deposition reductions are realised.

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.

Evidence that soil carbon pool determines susceptibility of semi-natural ecosystems to elevated nitrogen leaching

Deposition of reactive nitrogen (N) compounds has the potential to cause severe damage to sensitive soils and waters, but the process of ‘nitrogen saturation’ is difficult to demonstrate or predict. This study compares outputs from a simple carbon–nitrogen model with observations of (1) regional- and catchment-scale relationships between surface water nitrate and dissolved organic carbon (DOC), as an indicator of catchment carbon (C) pool; (2) inter-regional variations in soil C/N ratios; and (3) plot scale soil and leachate response to long-term N additions, for a range of UK moorlands. Results suggest that the simple model applied can effectively reproduce observed patterns, and that organic soil C stores provide a critical control on catchment susceptibility to enhanced N leaching, leading to high spatial variability in the extent and severity of current damage within regions of relatively uniform deposition. Results also support the hypothesis that the N richness of organic soils, expressed as C/N ratio, provides an effective indicator of soil susceptibility to enhanced N leaching. The extent to which current C/N is influenced by N deposition, as opposed to factors such as climate and vegetation type, cannot be unequivocally determined on the basis of spatial data. However, N addition experiments at moorland sites have shown a reduction in organic soil C/N. A full understanding of the mechanisms of N-enrichment of soils and waters is essential to the assessment of current sensitivity to, and prediction of future damage from, globally increasing reactive nitrogen deposition.

Changes in acidification of lochs in Galloway, southwestern Scotland, 1979–1988: The MAGIC model used to evaluate the role of afforestation, calculate critical loads, and predict fish status

Abstract Decades of acid deposition in the Galloway area, southwestern Scotland, have resulted in acidification of surface waters and damage to fish. In the period since 1980, however, acidic deposition has decreased substantially. A survey of 50 lochs conducted in 1979 and repeated in 1988 reveals major changes in water chemistry over this 9 year period. Together these two data sets separated in time by 9 years and covering a period of relatively large and rapid change in acid deposition offer a valuable basis for the evaluation of acidification models. Concentrations of SO 4 in the lochs were on the average 42% lower in 1988 relative to 1979. The decline is readily explained by the large and rapid decline in sulphate concentrations in precipitation in the area. Concentrations of non-marine base cations decreased from 155 to 90 μequiv1 −1 and acid neutralising capacity (ANC) increased. The change in ANC was due mostly to decreased concentrations of Al. pH levels showed no systematic change from 1979 to 1988. The regional changes in water chemistry over the period 1979–1988 are corroborated by regular measurements at several of these lochs over this 9 year period. MAGIC (Model for Acidification of Groundwater In Catchments) successfully reproduces the major changes in water chemistry observed over the period 1979–1988. Both calibration to the 1979 data with prediction of 1988, and calibration to the 1988 with reconstruction of 1979 give close fits to the observations. The model provides a means by which the future impact of acidic deposition and afforestation can be evaluated. A fish response function coupled to MAGIC provides the basis for evaluation of past and future fish status in the region. MAGIC predictions under different acid deposition and forestry scenarios indicate that if acidic deposition is held constant at 1988 levels, afforestation causes further acidification of the lochs. Acidic deposition emerges as the major cause of soil and water acidification in the Galloway region, although forestry practices can exacerbate the effects.

Modelling stream acidification in afforested catchments: long-term reconstructions at two sites in central Scotland.

Abstract A conceptual model of the combined effects of afforestation and acidic deposition is applied to two forested sites in central Scotland. Refinements are made to the model inputs specifically to include: increased dry deposition to the forests (in excess of the dry deposition expected for moorland sites) as the forest canopy develops; uptake of ions by the growing forests; and increased evapotranspiration (and thus decreased water yield) as the forests mature. The model is calibrated using a fuzzy optimisation technique which incorporates uncertainty in target variables (stream base cation concentrations and soil exchangeable bases) and uncertainty in selecting values for fixed and adjustable parameters which describe the physico-chemical characteristics of the catchments. Simulated present-day stream and soil chemistry closely match observed values at both sites. The calibrated models indicate that while the patterns of acidification in the two catchments are broadly similar, some differences do exist between the sites in the responses of the soils to acidic deposition and afforestation. It is concluded that the calibrated models provide a tool for: (a) comparison of the relative effects of deposition and afforestation on soil and surface water acidification; (b) assessment of the likely effects of reductions in future deposition combined with future forestry management practices.

Addressing China’s grand challenge of achieving food security while ensuring environmental sustainability

China’s increasingly urbanized and wealthy population is driving a growing and changing demand for food, which might not be met without significant increase in agricultural productivity and sustainable use of natural resources. Given the past relationship between lack of access to affordable food and political instability, food security has to be given a high priority on national political agendas in the context of globalization. The drive for increased food production has had a significant impact on the environment, and the deterioration in ecosystem quality due to historic and current levels of pollution will potentially compromise the food production system in China. We discuss the grand challenges of not only producing more food but also producing it sustainably and without environmental degradation. In addressing these challenges, food production should be considered as part of an environmental system (soil, air, water, and biodiversity) and not independent from it. It is imperative that new ways of meeting the demand for food are developed while safeguarding the natural resources upon which food production is based. We present a holistic approach to both science and policy to ensure future food security while embracing the ambition of achieving environmental sustainability in China. It is a unique opportunity for China to be a role model as a new global player, especially for other emerging economies.

Limitations to the understanding of ion-exchange and solubility controls for acidic Welsh, Scottish and Norwegian sites

Abstract A summary of soilwater and streamwater data from acidic catchments in Wales, Scotland and Norway is presented. It is concluded that insufficient detail has been established to describe quantitatively the ion-exchange and weathering processes in determining streamwater chemistry: such a description is required before reliance can be placed on mathematical models describing short- and long-term changes. The need for manipulative studies is highlighted, emphasis being placed on minimizing perturbation of the system from field conditions. An appeal is made for the use of a standardized method for determining the exchangeable cations. The studies provide overwhelming evidence showing the incorrectness of the commonly used modelling assumption that Al(OH) 3 solubility determines inorganic aluminium levels in the soil and streams. The importance of simple mixing of soil and ground water, in explaining streamwater aluminium-hydrogen ion relationships, is emphasized.

Evidence for enhanced atmospheric sulphate interception by Sitka spruce from evaluation of some Scottish catchment study data

Abstract Recent environmental controversy has focused on the role of forestry practices in stream acidification, with conflicting claims regarding interception mechanisms, altered site hydrology, etc. While it is generally accepted that there are strong correlations between some parameters, for example aluminium in stream water and coniferous afforestation, there is less consensus on the reaction of trees to pollutants with consequences on the crucial production and mobility of anions, especially sulphate. Examination of data from Scottish studies has shown that Sitka spruce is capable of intercepting atmospheric SO 2 , leading to accumulations of excess sulphate in tree foliage. This sulphate is readily soluble and when leached by rainfall produces increases in tree throughfall sulphate concentrations in Sitka spruce compared with other species.

A quality classification for management of Scottish standing waters

The development of a national scheme for the standing waters of Scotland is described. It classifies waters along three gradients – phosphorus, loss of acid neutralising capacity and degree of contamination with toxic suubstances. A series of case studies provide examples of the application of the classification in lake management.