Influence of sea salt on stream water chemistry in an upland afforested catchment

Abstract

The chemistry of bulk precipitation and stream water was monitored in an acidic afforested catchment at Llyn Brianne in upland Wales between 1985 and 1990. Throughfall, stemflow and soil water chemistry were also monitored between 1988 and 1989. Marine-derived solutes dominated the ionic composition of precipitation and stream water, which had mean C1 concentrations of 11 3 pequiv. 1-' and 245 pequiv. 1-', respectively. The higher concentrations in stream water reflect occult and dry deposition on the forest canopy and the effect of interception and transpiration losses. Chloride variations in stream water (1 12-454pequiv. 1-') were damped compared with bulk precipitation (28-762 pequiv. l-') due to the mixing of event ('new') water with pre-event ('old') water in the catchment soils. A storm episode monitored in the catchment in April 1989 was associated with high sea salt inputs and C1 concentrations in throughfall (1466pequiv. I-') and storm runoff were exceptionally high (392pequiv. 1-l). The C1 signal in stream water during the episode was consistent with an event ('new') water contribution to the storm response. However, a short-term hydrochemical budget estimated that although C1 outputs from the catchment during the event (1.17 kg ha-') were equivalent to 8% of inputs in throughfall and stemflow, the storm runoff was equivalent to 32% of effective precipitation. This indicates that pre-event ('old') water was the dominant source ( > 75%) of storm runoff. Although sea salt inputs during the event had a marked impact on stream water chemistry, the anomalously high levels of acidity sometimes associated with sea salt events were not observed in this particular study.

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

“…This may suggest that Al 3+ levels and streamwater acidity can be exacerbated following such periods of high sea-salt deposition as observed elsewhere in the UK uplands (e.g. Langan, 1989;Soulsby, 1995b;Jarvie et al, 2001;Bridcut et al, 2004). Such studies have shown that Na concentrations enhance ion exchange reactions which displace Al 3+ from soil cation exchange sites which are then mobilized to surface waters with Cl as the accompanying anion (Soulsby and Reynolds, 1992).…”

Hydrochemical heterogeneity in an upland catchment: further characterisation of the spatial, temporal and depth variations in soils, streams and groundwaters of the Plynlimon forested catchment, Wales

“…Silicate weathering, considered to be the dominant process of weathering in the soils, is modified to a large degree by ion-exchange reactions involving H + and sea-salt inputs (Soulsby, 1995b). Inputs of many trace elements, including trace metals Sr and Ba, are important indicators of weathering reactions but the fine-grained nature of the host minerals makes it difficult to ascertain specific reactions.…”

Near-stream soil water–groundwater coupling in the headwaters of the Afon Hafren, Wales: Implications for surface water quality

“…Deeper flow paths in the lower soils were considered to be an important influence on stream water chemistry. Soulsby (1995) identified storms where runoff generation was dominated by the displacement of 'old' pre-event water. These results were consistent with earlier work by Robson and Neal (1990) but the source of this pre-event water was thought to be in the deeper soil horizons (Robson et al, 1993).…”