Concentrations of suspended chlorophyll a in the Humber rivers

Concentrations of chlorophyll a have been determined at weekly intervals for all of the major rivers feeding the Humber Estuary since September 1993, as part of the LOIS monitoring programme. Highest concentrations generally occurred in the two southern rivers, the R. Trent and the R. Don, and also in the larger of the northern rivers, the R. Ouse and its main feeder, the R. Ure. High concentrations also developed on occasions in some of the other northern rivers, especially during the summer of 1995 when the unusually dry conditions led to low flows and extended retention times. Heavy pollution levels in the R. Aire and the R. Calder, a major tributary of the Aire, were probably responsible for the consistently low concentrations recorded in these rivers.