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A nature reserve managed by Northumberland Wildlife Trust. The area contains calaminarian grassland which is on the river Tyne floodplain; these types of grassland are rare habitats only found in areas where there are high concentrations of heavy metals.
Northumberland Wildlife Trust: Link

"Close House Riverside is one of a series of sites in the Tyne and Allen river system where alluvial deposits, contaminated by heavy metals derived from the North Pennine Orefield upstream, support an unusual community of metal-tolerant plants.This site, on the tidal reach of the River Tyne, is the lowest point at which this metalliferous habitat is represented and furthest from the sources of metal contamination. The unusual plant community is less well developed here than at other sites further upstream, perhaps reflecting the dilution of metal content by uncontaminated sediment, but this site is nevertheless important as part of the sequence of sites along the river system. These metalliferous deposits form soils hostile to plant growth due to the toxic effects of the constituent metals. The unusual community at this site includes alpine penny-cress (Thlaspi alpestre), thrift (Armeria maritime) and mountain pansy (Viola lutea) with meadow oat-grass (Avenula pratensis), harebell (Campanula rotundifolia), common bird’s-foot trefoil (Lotus corniculatus) and wood sage (Teucrium scorodonia). The dominant species are however grasses, including common bent (Agrostis capillaries) and red fescue (Festuca rubra) in areas of metal contamination, and false oat-grass (Arrhenatherum elatius), cock’s-foot (Dactylis glomerata) and Yorkshire fog (Holcus lanatus) elsewhere. Woodland developed on the river deposits includes willows (Salix spp.), alder (Alnus glutinosa), downy birch (Betula pubescens), ash (Fraxinus excelsior) and sycamore (Acer pseudoplatanus). The ground flora is diverse and includes narrow-lipped helleborine (Epipactis leptochila) which is characteristic of woodlands on metal-contaminated sites in the Tyne system, hemlock water-dropwort (Oenanthe crocata), yellow loosestrife (Lysimachia vulgaris), butterbur (Petasites hybridus) and giant bellflower (Campanula latifolia)."
SSSI Notification (1988): Archive Link