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Spatial Variability and the Assessment of Forest Streams. Swedish University of Agricultural Sciences Deparment of Environmental Assessment Institution Report 2005:9,

Bishop, Kevin


Watercourses are a valued part of the Swedish environment. One environmental sub goal concerning watercourses is that no more than 15% of Swedish water courses should be acidified. Initial efforts to assess fulfillment of that goal revealed that Sweden has little chemical or biological data on streams in relation to the number of streams. Most of those streams are also small, and the existing data is heavily biased towards larger watercourses. Having identified the problem, this study seeks to summarize what is known about spatial variability in the chemistry of streams, with an emphasis on the smaller streams, and suggest how to move towards a more adequate assessment of streams. Two specific approaches were examined. One is the use of monitoring data from small lakes to supplement stream data. The other is the use of synoptic surveys (landscape-scale “snapshots”) to define the spatial variability of headwater streamwater chemistry on catchments smaller than 20 km2, the effective cutoff for current monitoring of water courses. The major findings of this project were: • Small lakes can be useful source of information on stream chemistry at the point in the landscape where a lake exists, provided that procedures are developed to account for spatial and temporal differences between what a lake and stream sample represent. • Perennial streams generally exist when 1 km of catchment area has accumulated. Monitoring data is collected on streams with catchment areas greater than 20 km2, mostly on much larger catchment areas. The vast majority of stream length in Sweden has catchment areas 1 - 20 km2. • Differences between the chemistry of nearby streams are much greater for headwaters (1-20 km2 catchment areas) than downstream. Thus we know very little about the distribution of water chemistry and aquatic habitats in headwaters • Headwaters tend to be more acid and sensitive to acidification than downstream. • It is not clear about obligations for assessment of headwaters under the Water Framework Directive, but reason to believe headwaters have great ecological significance. Many human actions and management decisions concern headwaters. • There is a temporal dimension to spatial patterns. Headwaters become more acid at high flow, but many features of the spatial variability are consistent between high and low flow, with DOC an important exception. Persistence of spatial patterns is the basis for predicting high flow conditions from the situation at low flow. • Map information not currently able to improve the understanding of landscape scale patterns on its own. It is possible that GIS can be used in a stochastic approach where one tries to predict the distribution of headwater chemistry relative to downstream. Based on these findings, we suggest: 1. Augmenting the national register of watercourses to include streams on the 1:100 000 Blue map 2. Developing routines for using lake chemistry as surrogates for stream chemistry 3. Surveying headwater chemistry in representative basins from across Sweden to create a basis for predicting the variability and systematic offsets in chemistry upstream from where routine monitoring data are collected. Both agricultural and forested catchments should be considered

Publicerad i

Rapport / Sveriges lantbruksuniversitet, Miljöanalys
2005, nummer: 9
Utgivare: SLU Inst f miljöanalys