Results from an intensive measurement programme for suspended particulate matter in a region of the Irish Sea between Anglesey and the Isle of Man

Abstract

Suspended particulate matter (SPM) plays an important role in the transport of metals and other contaminants in the marine environment. To varying degrees dissolved metals are scavenged by suspended particles and this can have a significant impact on the transport and dispersion of the metal. In contaminated areas, such as the Irish Sea, the SPM becomes increasingly important in understanding the transport and fate of contaminants. Despite its importance, measurements of SPM in the Irish Sea are sparse. This paper presents measured SPM concentrations from a long-term sampling campaign from 25 sites in an area of the Irish Sea between Anglesey and the Isle of Man which were sampled over 14 months (July 1998–August 1999) at 5 and 30 m depth. In total 585 measurements were made. A transmissometer was also deployed on some occasions to look at the depth dependence of SPM. Results showed an average SPM concentration of 2.14 mg l −1 with a maximum value of 6.28 mg l −1 and a minimum of 0.30 mg l −1. The strongest relationship found was between the SPM and the spring-neap tidal cycle, which outweighed any seasonal variation. Spatially, the SPM was highest in the south and east of the region sampled and is probably due to higher tidal velocities and greater availability of fine sediment in these areas. There was no evidence of SPM varying with depth in the water column.