Observations on the recent history of Lough Neagh and its drainage basin

The present study traces the recent development of Lough Neagh from the microfossil record of the lake sediment. The history of vegetational change in the catchment area is discussed on the basis of pollen analytical information and by reference to primary and secondary documentary historical sources. Changes in the history of the lake itself are inferred from changes in the relative composition of diatom assemblages in the sediment and from changes in the calculated influx of diatoms to the sediment. The accumulation of sediment in the lake basin is discussed and radiometric data (14C, 137Cs, 210Pb) are used to construct a sediment chronology from which accumulation rates are calculated. It is shown that the rate has increased from about 0.08 cm a-1 (where a is the symbol for year) in A.D. 1700 to about 0.8 cm a-1 today. Four major stages in the recent development of the lake are indicated: a pre-disturbance stage ( > 2000 B.C. to ca. a.d. 1700), a stage of accelerated mineral inwash (from ca. A.D. 1700); and two stages of cultural eutrophication (from ca. 1915 and from ca. 1960 respectively). The eutrophication stages are characterized by increased sediment accumulation rates, increased diatom influx rates, and the emergence of Stephanodiscus as the most important diatom genus.