An analysis of the long-term variation in stream water quality for three upland catchments at Loch Dee (Galloway, S.W. Scotland) under contrasting land management

Abstract

A long term record of water chemistry, consisting of twenty years of weekly spot samples, from three sub-catchments draining into a loch and the loch outflow in Galloway, S.W. Scotland have been analysed. The analysis undertaken consisted of a three component statistical trend model. The technique allows the identification of long-term, seasonal and short-term trends, as well as differentiation between base flow and high flow responses. The land usage in the three sub-catchments is moorland, forest and forest plus lime. The results show that, since the mid1980s, there has been a gradual decline in stream-water sulphate of the same order as reductions in the deposition of non-marine sulphate. Superimposed on this trend are somewhat random but considerable perturbations to this decline, caused by sea-salt deposition. There is no evidence of changes in surface water nitrate concentrations. The influence of different land management is evident in the sulphate, nitrate and pH data, whilst variations in calcium concentrations are also a product of differences in hydrological routing and the impact of sea-salt episodes.

Acidic episodes retard the biological recovery of upland British streams from chronic acidification

“…This is generally similar to deposition in Galloway but more than in the NW Highlands, and these patterns contribute to marked regional variations in critical load exceedance: only small areas of the Highlands receive more deposition than can be buffered, while less than half of Galloway and one‐third of Welsh freshwaters are now exceeded on the steady‐state criterion of ANC <20 μEq L −1 (Hall et al , 2004). Sulphate, ANC and, to a lesser extent, pH in Welsh and Galloway streams confirm that the chemical reversal of acidification is well under way – at least for average conditions (Evans et al , 2001; Harriman et al , 2001; Langan & Hirst, 2004; Reynolds et al , 2004).…”

Influence of forestry, environmental change and climatic variability on the hydrology, hydrochemistry and residence times of upland catchments

“…Nevertheless, the minimal influence on the mass flow curves implies that partial catchment felling, rapid re-growth of grasses and heather (Calluna), together (in the case of B10) with brash (slash) of felled branches from the felling being left on site, retained some degree of interception and resulted in limited effects on annual runoff amounts. The long-term hydrochemistry data sets show the effects of forestry on stream water quality in a wider framework of climatic variability and environmental change (Langan and Hirst, 2004). Although forest operations represent a potential disturbance to catchment functioning, the nature of this disturbance takes place in the wider context of other more stochastic (e.g.…”

“…In Scotland, where much of the UK's commercial forestry has been planted, experimental catchments have been established at Balqhuidder (e.g. Johnson and Whitehead, 1993;Jakeman et al, 1993) and Loch Ard (Harriman and Morrison, 1982), together with Loch Dee and other sites in Galloway (Langan and Hirst, 2004). In the case of Balqhuidder, these studies have focused on water balance issues, and at the other sites on the acidification and chemical recovery of surface waters (Harriman et al, 2003).…”

Forest land cover continues to exacerbate freshwater acidification despite decline in sulphate emissions

“…These reductions have led many authors suggest that the impact of forestry on acid waters will decline (Nisbet et al, 1995;Neal et al, 2004;Gagkas et al, 2007). Conversely, studies looking at the long-term recovery of forest ecosystems have continued to raise the issue of an ongoing impact of forests on freshwaters (Helliwell et al, 2001;Harriman et al, 2003;Langan and Hirst, 2004;Neal et al, 2010;Feeley et al, 2010) and despite evidence for recovery at many UK acid waters monitoring sites, three of the five sites with forested catchments show no evidence of recovery and one shows ongoing deterioration (Davies et al, 2005). Part of the difficulty in assessing the impact of forests on acidification is the lack of datasets designed specifically to address diffuse pollution.…”