Showing papers by "Chris Soulsby published in 1999"

Hydrogeochemsitry of montane springs and their influence on streams in the Cairngorm mountains, Scotland

Abstract: . Springs are important groundwater discharge points on the high altitude (>800m) plateaux of the Cairngorm mountains, Scotland and form important wetland habitats within what is often a dry, sub-arctic landscape. The hydrogeochemistry of a typical spring in the Allt a'Mharcaidh catchment was examined between 1995-98 in order to characterise its chemical composition, identify the dominant controls on its chemical evolution and estimate groundwater residence time using 18O isotopes. Spring water, sustained by groundwater flow in shallow drift deposits and fractured bedrock, was moderately acidic (mean pH 5.89), with a very low alkalinity (mean 18 μeq l-1) and the ionic composition was dominated by sea-salts derived from atmospheric sources. Geochemical modelling using NETPATH, predicted that the dissolution of plagioclase mainly controls the release of Si, non-marine Na, Ca, K and Al into spring water. Hydrological conditions influenced seasonal variations in spring chemistry, with snowmelt associated with more rapid groundwater flows and lower weathering rates than summer discharges. Downstream of the spring, the chemistry of surface water was fundamentally different as a result of drainage from larger catchment areas, with increased soil and drift cover, and higher evaporation rates. Thus, the hydrogeochemical influence of springs on surface waters appears to be localized. Mean δ18O values in spring water were lower and more damped than those in precipitation. Nevertheless, a sinusoidal seasonal pattern was observed and used to estimate mean residence times of groundwater of around 2 years. Thus, in the high altitude plateau of the Cairngorms, shallow, coarse drift deposits from significant aquifers. At lower altitudes, deeper drift deposits, combined with larger catchment areas, increase mean groundwater residence times to >5 years. At high altitudes, the shallow, permeable nature of the drifts dictates that groundwater is vulnerable to impacts of environmental changes that could be usefully monitored at spring sites.

Modelling the evolution of minewater pollution at Polkemmet Colliery, Almond catchment, Scotland

Abstract: Polluted discharges from abandoned mines are a major cause of freshwater pollution in central Scotland, often contributing high Fe, SO 4 2- and acidity to receiving streams. The Central coalfield has been extensively mined for over a century and Polkemmet was the last colliery to close in 1985. Recent monitoring indicates that the rate of groundwater recovery is approximately 0.15 to 0.2 m per week. Without intervention, this trend would result in complete recovery by 2000 and probable discharge into the River Almond. Geochemical modelling indicates that pyrite oxidation, calcite dissolution and goethite precipitation are primarily responsible for the evolution of groundwater chemistry currently observed at Polkemmet. Predictive modelling using PHREEQE suggests that unregulated minewater discharges will have marked effects in the River Almond, with goethite being initially precipitated at a rate of up to 36 kg/day, dissolved sulphate concentrations ranging between 170 and 800 mg/l and pH being depressed to 6.5. Combined active lime flocculation and passive aerobic wetlands may be the most effective means of treating the predicted minewater discharges. Keywords: abandoned mines, hydrochemistry, surface water, underground mining, water quality

Inter‐Basin Water Transfers and Drought Management in the Kielder/Derwent System

Abstract: During the dry years between 1989 and 1994, inter-basin water transfers from the Kielder system augmented flows in the River Derwent, and these flows substituted compensation releases from Derwent reservoir to retain storage for supply and recreational purposes. The paper discusses the use of the Kielder transfers together with their impact upon (a) flow regime, (b) water quality, and (c) instream ecology of the River Derwent. Also, implications of the increasing use of water transfers in the UK are critically evaluated from the perspective of sustainability.

Seasonal hydrology of oxygen-18 in the Allt a' Mharcaidh, Scotland : implications for water movement and residence times

Abstract: The seasonal variation of oxygen-18 has been observed in precipitation, groundwater and streamwater in the Allt a' Mharcaidh catchment, Cairngorm mountains, Scotland. Precipitation showed strong seasonal variation in its isotopic signature over the 1995-1998 study period. As anticipated, such variation was substantially damped in groundwater and surface water. Nevertheless, 18 O proved a useful tracer, indicating the influence of spring snowmelt events and summer rainfall on stream waters. Detailed examination of the seasonal variation in δ 18 O levels in various catchment waters provided an insight into mixing processes and a first approximation of mean residence times. Preliminary estimates for the latter are 5 years for shallow and deeper groundwater respectively. These longer-term data sets demonstrate the ability of the catchment to effectively mix new precipitation with resident soil and groundwater over the hydrological year. This implies that the influence of groundwater on the hydrology and hydrochemistry upland catchments has been underestimated.