Journal of Conference Abstracts

Changes in Soil and Stream-Water Chemistry over 25 Years at a Site of the UK Environmental Change Network (ECN)

John K. Adamson (J.Adamson@ITE.AC.UK)

Institute of Terrestrial Ecology, Merlewood Research Station,
Grange-over-Sands, Cumbria, LA11 6JU, U.K.

This paper illustrates the usage of long-term data for determining the relationship between anthropogenic changes in atmospheric chemistry and ecosystem processes affecting soil and stream water chemistry. Data evaluated were collected within the Environmental Change Network (ECN), which is the UK's integrated environmental monitoring programme launched in 1992. It aims to collect, store, analyse and interpret long-term data on a set of key variables which drive and respond to environmental change at a range of terrestrial and freshwater sites. The network is a cooperative venture between many Government bodies which provide support mainly by funding monitoring at particular sites. Standard measurements are made at all sites based on detailed protocols (Sykes & Lane, 1996) intended to minimise experimental variation between sites and over time. There are eleven terrestrial sites in ECN which range from arable land in southern England to moorland in north-east Scotland. Of the 38 freshwater sites, 22 are rivers and 16 are lakes.

Moor House National Nature Reserve (NNR), together with the neighbouring Upper Teesdale NNR, form a UNESCO Biosphere Reserve. The site was selected as a founding ECN sites where both terrestrial and freshwater monitoring take place, in part because of the wealth of past research. The site lies in the Northern Pennine Uplands of England and ranges in altitude from 290 to 848 m. Although it has important communities of arctic/alpine species, much of the gently sloping ground is blanket peatland which has formed because of the cool wet climate (Pigott, 1956; Eddy et al., 1969). To assess changes prior to the establishment of ECN, two studies have been undertaken where historic data have been compared with recent data.

Soil profiles from the site, first sampled between 1963 and 1973, were re-sampled in 1991. One hundred horizons from 32 profiles were analysed for pH and seven other variables in addition to pH, using the same laboratory methods on both sampling occasions. Organic and A horizons show a consistent increase in acidity between samplings. Although Dystrochrepts and Cryorthents have increased in acidity throughout their depth, Placaquads and Cryaquods have decreased in acidity at depth, probably because of poor water transmission downwards into these horizons. Correlations with other determinands suggest that the dominant process in the soils is leaching of basic cations and their replacement on exchange sites by protons and probably aluminium ions. A cause of the increase in soil acidity is likely to be the deposition of atmospherically transported pollutants (Adamson et al. 1996).

Precipitation, soil solution, and drainage water were collected from the Trout Beck catchment between 1993 and 1995. Two tributaries of the main stream were also sampled. Inputs of N in precipitation exceeded outputs in stream water, organic N represented a small proportion of N inputs and inputs of inorganic N averaged 10.2 kg ha^-1 yr^-1. Soil solution from 10 cm depth in the peat was dominated by organic N whereas at 50 cm NH₄⁺ slightly exceeded organic N. Nitrate was rarely detected at either depth except during a period of exceptionally warm and dry weather in 1995. In the streams, the output fluxes of organic N (5.7 and 6.5 kg ha^-1 yr^-1) were much larger than those of inorganic N (0.6 to 2.2 kg ha^-1 yr^-1). Inorganic N in streams was largely NO₃^- but the smallest stream had the largest concentrations of NH₄⁺, suggesting that N transformations take place in the stream bank mineral soils or within the stream channel. One of the tributaries was first sampled for inorganic N over a period of one year between 1962 and 1963. Inorganic N input at that time was 6.8 kg ha^-1 yr^-1 and output was 2.9 kg ha^-1 yr^-1 indicating that while inputs have risen, outputs have tended to decline. At these N deposition levels it appears that stream water N status is controlled by decomposition rates in the peat.

References

Adamson, J. K. et al. Soil Use Manag., 12, 55-61 (1996).

Eddy, A. et al. Vegetatio, 16, 239-284 (1969).

Pigott, C. D. J. Ecol. 44, 545-586 (1956).

Sykes, J. M. & Lane, A. M. J. (eds.) The United Kingdom Environmental Change Network: Protocols for Standard Measurements at Terrestrial Sites. The Stationery Office, London (1996).