The Loch Eil project: Chlorophyll a and nutrients in the water column of Loch Eil

Abstract

Monthly measurements of temperature, salinity, chlorophyll a, phosphate, nitrate, and ammonia were made at three stations in Loch Eil and one station in the Lynn of Lome, on the west coast of Scotland, during 1976 and early 1977. Dissolved inorganic phosphate ranged from < 0.03 to 0.91 μg-at.PO 4-P/l, dissolved inorganic nitrate from < 0.05 to 8.4 μg-at.NO 3-N/l, ammonia from < 0.1 to 2.8 μg-at.NH 4-N/l, and chlorophyll a from 0.02 to 5.46 mg/m 3. The main freshwater input to Loch Eil is at the seaward end of its mouth. This gives unusual hydrographie characteristics with an increased proportion of freshwater in the water column. Compared with Loch Creran, of similar dimensions and freshwater input, Loch Eil has a lower standing crop of phytoplankton, higher light attenuation from humic compounds, and a deeper surface mixed layer. There were no significant differences between stations in Loch Eil except for chlorophyll a at 15 m depth and below which decreased with distance from-the mouth. Many of the changes in the water column of Loch Eil appear linked to changes in rainfall which affect water column stability and loch circulation.