A report about the intertidal salt marshes and mudflats in the estuary of the River Ythan in Aberdeenshire. An estuary is the lower part of a river valley where it meets the sea. It is partly filled with sediment deposited by the slow flowing river. The tides inundate an estuary twice a day creating a mix of salt and sea water described as brackish. Salt marshes can form by the slow rise and fall of the tides. Salt-tolerant plants colonise the mud, trapping material round them so that the level of the mud flats rise. Taller plants can then take hold.

First broadcast:
17 October 2007

Students could create a series of annotated diagrams showing the formation of salt marsh. They should highlight the aspects that encourage deposition - slow river flow, accretion of sediment around vegetation and vegetation's role in both trapping sediment and buffering land from wave action. Use this clip to inform discussion of salt marsh land use, considering the high productivity of salt marsh land, its value to flood defence and arguments for its conservation.