Sequential inorganic chemical analysis of a core from Slapton Ley, Devon, UK

Analysis of the upper 40 cm of a sediment core from Slapton Ley, a coastal lake in SW England was based on the fractionation procedure devised by Engstrom (Engstrom & Wright, 1984). This allows separation of the sediment into authigenic, biogenic and allogenic components. Lead-210 dating of the same core enabled trends in both concentration (mg g–1 dry mass) and influx (mg cm–2 a–1) to be evaluated, and to be compared with events over the past two hundred years in the Ley and its catchment. The results show that before ca. 1950 AD, Slapton Ley was a shallow, clear, eutrophic lake, into which, in the mid-C19th, calcareous material was introduced by a phase of lime-kiln operation, road construction and lake level control. Since 1950, erosion of detrital material from the catchment has increased, as has the input of both allogenic and authigenic phosphorus, and biogenic silica. These changes reflect the intensification of agriculture post-1945, and the construction of Slapton sewage treatment works in 1953. A major peak in authigenic nitrogen, 6 cm below the present sediment surface, is correlated with the severe 1976 drought in the UK. The ecosystem of the Ley appears to have been triggered by this event into its present hypertrophic state