Source dependent behaviour of lead and organic matter in the Glomma estuary, SE Norway: evidence from isotope ratios

Concentrations and isotope ratios of lead, organic carbon and nitrogen suggest that the Hvaler basin, SE Norway is more strongly influenced by inputs of atmospheric lead to the coastal current than by discharges from the river Glomma, while the Glomma estuary is affected by lead from the river Glomma. This difference was more pronounced in the early 1900s than in the 1970s. Simultaneously, the shallow Glomma estuary has experienced an increased marine influence in the sedimentary organic matter, interpreted to reflect an increased primary production caused by elevated nutrient input to the estuary. The inner part of the Glomma estuary is over the year dominated by terrestrial organic matter with low δ13C ratio while during spring snow melt the river bottom is resuspended and locally derived lead, atmospheric lead and organic matter deposited over the winter months are washed out into the estuary. Later the river plume withdraws to the inner estuary and atmospheric lead and marine organic matter becomes dominant in the outer part of the estuary. Anthropogenic lead enters the estuary as ‘dissolved’, and it is concluded that this lead is carried through the estuary associated to small particles, which settles in the outer estuary. Marine organic matter seems to be superior to terrestrial organic matter in this process of trapping river borne anthropogenic lead by coagulation and aggregation.