WETLAND SEDIMENTARY RECORD AS AN INDICATOR OF THE LAND USE AT A FORMER INDUSTRIAL SITE

Wetland sediments can provide useful temporal information about the land-use history and climate. Similarly sediments that have accumulated in wetlands located on former industrial sites can provide detailed information about the land use history at the site. This information can be combined with other information such as historical aerial photos to provide a more comprehensive understanding of the activities that occurred through time on the site.

We studied sediment in a wetland that is located on a former industrial site. The site includes a former brick factory (1920-1980) as well as several landfills located in the pits that provided the clay for the bricks. The landfills contain demolition debris and municipal waste and were active in the late 1950's to the early 1960's. The wetlands are located in the lowest part of the site and occur in areas excavated for clay in the early 1920's. Water enters the wetland from a small stream that drains the site and some adjacent sports fields. The wetland discharges into a stream offsite. Leachate from the landfills discharges from numerous seeps along the small stream before flowing into the wetland. Parts of the wetland have accumulated over 1.5 m of sediment and preserve evidence for 80 years of activity at the site.

Sediment cores from the wetland were analyzed for grain size and composition, magnetic susceptibility, LOI, and metal content. The basal part of the sequence is a matrix-supported conglomerate which grades up into silts and clays with variable susceptibility, and increasing organic and metal content. This corresponds to the early period of clay excavation (1920's-1940's). At 55cm below the surface, a 10cm organic rich layer represents low sedimentation rates in a wetland environment (1950's). This layer is overlain by alternating silt and clay layers with variable susceptibility, metal, and organic content. This layer grades up into an organic rich wetland soil, heavily iron stained from leachate produced from the landfill. These layers where deposited during and after the existence of the landfill (since the late 1950's). The sedimentary sequence preserved in the wetland provides useful temporal information about the land-use at the site. Other data shows that the wetland operates as a metal sink and effectively remediates the leachate from the landfills.