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Offwell Wetland Survey

Area B - Marsh Zone

areab.jpg (120932 bytes)

In the marsh zone, the standing water levels vary across the area and the sediment is not permanently covered by water. Water levels rise and fall according to the amount of rainfall and run-off entering the wetland. In many places there is no standing water, although the underlying sediment is water-logged and anaerobic. In areas with standing water, the depth is rarely more than 10cm and usually as little as 1cm.

This area supports a much greater variety of plant species (32) than the swamp area (17). However, there is a good deal of overlap of species between the two areas. Species characteristic of this area include Willow, Alder, Soft Rush, Yellow Iris, Branched Bur-reed, Greater Reedmace, Water Mint and Wood Clubrush amongst many others. Isolated local mounds of trapped sediment which raise the substrate above standing water levels are a feature of the area. These allow a few plants belonging to species normally characteristic of much drier areas to survive. (This includes species such as Bramble and Silver Birch.) 

The invertebrate animals inhabiting this area include a variety of spiders such as the Garden Spider (Araneus diadematus), many different hoverflies, wasps and ichneumon flies. Dragonflies such as Southern Hawkers (Aeschna cyanea) and the Golden-ringed Dragonfly (Cordulegaster boltonii) patrol the area and damselflies and snails are common. In the spring, toads and common frogs abound as they come to spawn in the open water and swamp areas of the wetlands. Grass snakes can often be observed and roe deer come to lie up in the day time.  

Marsh plant adaptations

Plant Species List for Area B 

Salicaceae

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Salix caprea agg. Goat Willow
Betulaceae

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Alnus glutinosa (L.) Gaertn. Alder
Betula pendula Roth Silver Birch
Ranunculaceae

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Ranunculus lingua L. Greater Spearwort
Saxifragaceae

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Chrysosplenium oppositifolium L. Opposite-Leaved Golden Saxifrage
Rosaceae

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Filipendula ulmaria (L.) Maxim. Meadowsweet
Rubus fruticosus agg. Bramble
Onagraceae

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Circaea lutetiana L. Enchanter's Nightshade
Epilobium palustre L. Marsh Willowherb
Umbelliferae

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Angelica sylvestris L. Angelica
Oenanthe crocata L. Hemlock Water Dropwort
Polygonaceae

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Persicaria hydropiper (L.) Spach Water-Pepper
Reynoutria japonica Houtt. Japanese Knotweed
Rumex conglomeratus  Murray Clustered Dock
Callitrichaceae

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Callitriche stagnalis Scop. Common Water-Starwort
Menyanthaceae

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Menyanthes trifoliata L. Bogbean
Labiateae

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Mentha aquatica L. Water Mint
Rubiaceae

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Galium palustre agg. Marsh Bedstraw
Solanaceae

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Solanum dulcamara L. Bittersweet/Woody Nightshade
Scrophulariaceae

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Scrophularia auriculata L. Water Figwort
Compositae

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Cirsium palustre (L.) Scop. Marsh Thistle
Pulicularia dysenterica (L.) Bernh. Fleabane
Alismataceae

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Alisma plantago-aquatica L. Water-plantain
Graminae

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Glyceria fluitans (L.) R. Br. Floating Sweet Grass
Juncaceae

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Juncus effusus L. Soft Rush
Juncus acutiflorus Ehrh. ex Hoffm. Sharp-flowered Rush
Cyperaceae

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Carex paniculata L. Greater Tussock Sedge
Carex pendula Huds. Pendulous Sedge
Scirpus sylvaticus L. Wood Club-rush
Iridaceae

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Iris pseudacorus L. Yellow Iris
Lemnaceae

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Lemna minor L. Common Duckweed
Sparganiaceae

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Sparganium erectum L. Branched Bur-reed
Typhaceae

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Typha latifolia L. Greater Reedmace
Ferns

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Athyrium felix-femina (L.) Roth. Lady Fern
Mosses

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Brachythecium rivulare B., S. & G.
Dicranum scoparium Hedw.
Eurhynchium praelongum (Hedw.)Br. Eur.
Hypnum cupressiforme Hedw.
Thuidium tamarascinum (Hedw.)B., S. & G

 

These species lists are not exhaustive. They represent  initial collections and identifications carried out in early autumn. Many species of flowering plants may already have flowered and died back at this time and would therefore have been missed. These lists will be updated periodically.



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Wetland Survey Contents

 

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