The rivers of North East Scotland: physicochemical characteristics

Abstract

Multivariate analysis of spatial variation in 15 physicochemical characteristics grouped the seven major north-east rivers into two sets — highland and lowland rivers. The highland rivers formed a continuum that could be further divided into rivers with low concentrations of dissolved materials including the Spey and Dee (full highland rivers), and a more variable group with higher concentrations of dissolved materials including the Don, Deveron and Lossie (intermediate highland rivers) emphasising the diversity of river types classically described as highland. The Lossie was differentiated from the other intermediate highland rivers by lower oxygen concentration and pH. The major differences in physicochemistry between rivers were consistent with differences in catchment geology, soil type, climate, and land use. The large amounts of dissolved material and high nutrient status of the lowland Ythan and Ugie rivers reflected the high proportion of their catchments under agriculture, and the acidity of the Lossie reflected the high proportion of its catchment under forest. The small amounts of dissolved material in the Spey and Dee were attributable to the high proportion of slow weathering acidic rocks and acid soils in their catchments, and to the high volume flows of these rivers relative to the others. The amounts of dissolved material were greater in summer during low base flows and were accomparied by an increase in phosphate concentration in the lowland rivers. Oxygen saturation increased in summer in the Ythan and the Don, presumably as a result of greater photosynthetic activity. Marked declines in silica were thought to result from significant diatom growth in the highland and intermediate highland rivers, particularly the Don, during summer.