No abstract

612 lakes in Northern Ireland between 1 and 100 hectares surface area were sampled in the summers of 1988-1990 . Water analyses for major ions and nutrients are presented in summary form and demonstrate the wide range of lake chemistry in the region. Altitude was the main determinant of water chemistry, which varied from near rain water to greater than 100 mg Ca 1 -1 faithfully reflecting the underlying geology, even in regions of diverse geology . `Rainfall' lakes were commonly depleted of potassium but enriched in calcium and bicarbonate compared to average rainfall composition in the area . Major ion chemistry in general plotted as expected on a diagram of Na/(Na + Ca) ratio against total dissolved solids, with major deviations only found in lakes on an offshore island or which were known to be polluted .Nutrient enrichment was widespread, 27% of lakes contained more than 100 pg TP 1 -1 enriched lakes were commonest in lowland areas but also occurred in upland lakes with afforested catchments .

Effects of bait digging on distribution and population recovery of Arenicola marina, Hydrobia ulvae and Macoma balthica have been investigated on trial plots at Blackness. Forth estuary (Scotland). A. marina rapidly recolonised the basins created by digging, but had reduced populations on the dug mounds. Its populations were dislocated for over 3 rno after digging. H. ulvae and M. balthica showed enhanced populations on the mounds for up to 2 wk, but were otherwise unaffected by digging. Factors influencing the mode of population recovery are discussed; it is suggested that enhanced basin populations of recolonising A. marina are due substantially to above-surface migration of worms into areas with increased levels of organic matter.