Chapter 19: Non-tidal Wetlands

Transcription

1 Chapter 19: Non-tidal Wetlands by J. Pojar INTRODUCTION SHALLOW OPEN WATERS MARSH FEN SWAMP BOG LITERATURE CITED

2 INTRODUCTION Most people are familiar with the terms marsh, swamp, and bog, but only relatively recently have these well-known landscape units been grouped together under the single term wetlands. We have no single, correct, ecologically sound definition for wetlands, primarily because they are so diverse and because the transition to uplands is often gradual. A functional definition of wetlands stresses that saturation with water is the dominant factor determining the nature of soil development and the type of plant and animal communities living in the soil and on its surface (Cowardin et al. 1979). The common denominator of most wetlands is soil or substrate that is at least periodically saturated with or covered by water. Thus, the National Wetland Working Group of Canada defined wetlands as lands having the water table at, near, or above the land surface or which are saturated for a long enough period to promote wetland or aquatic processes as indicated by hydric soils, hydrophilic vegetation and various kinds of biological activity which are adapted to the wet environment (Tarnocai 1980). We have adopted a simpler definition suitable for most of British Columbia after Runka and Lewis (1981): Wetlands are lands that are wet enough or inundated frequently enough to develop and support a distinctive natural vegetative cover that is in strong contrast to the adjacent matrix of better drained lands. Wetland classes recognized in Canada include shallow open waters, marsh, fen, swamp, and bog (Zoltai et al. 1975; Tarnocai 1980; National Wetlands Working Group 1988). SHALLOW OPEN WATERS This wetland class is composed of permanent, shallow (less than 2 m at the midsummer levels), standing water that lacks extensive emergent plant cover. Vegetation can be absent, or emergent plants (plants rooted in bottom materials and extending upwards above the water surface) can cover up to 10% of the surface. Shallow open waters often include various submerged and floating aquatic macrophytes. Submerged aquatic plants include species of Myriophyllum (water milfoil), Utricularia (bladderwort), Isoetes (quillwort), Elodea canadensis (Canadian waterweed), Ceratophyllum demersum (coontail), Ranunculus aquatilis (white waterbuttercup), Ruppia maritima (ditch-grass), and Subularia aquatica (awlwort). Floating aquatics include both free-floating species (Lemna [duckweed] spp., Spirodela polyrhiza [great duckweed], Azolla mexicana [Mexican mosquito fern]) and floating species rooted in bottom materials (e.g., Nuphar variegatum [yellow waterlily], Nymphaea tetragona [pygmy waterlily], Calla palustris [water-arum], several species of Sparganium [bur-reed], Callitriche [water-starwort], and Polygonum [smartweed], and numerous species of Potamogeton [pondweed]). 276

3 Water chemistry is the key factor determining the different types of shallow open water; conditions range from soft fresh through hard fresh to saline water. Bottom substrate is another important determinant, especially of the type and abundance of rooted vegetation. This class of wetland (which includes what are often termed ponds and sloughs) is especially common throughout the Interior Plateau and the Great Plains regions. MARSH Marshes are wetlands that are permanently or seasonally inundated with nutrientrich water, and that support extensive cover of emergent herbaceous vegetation rooting in mineral-rich substrate. The water level of marshes varies seasonally and from marsh to marsh. Marshes that dry by late summer expose matted vegetation and unvegetated mudflats or saltflats, but saturation persists near the surface. The substrate ranges from dominantly mineral materials to shallow, well-decomposed peat derived primarily from marsh vegetation. The substrate is strongly influenced by water chemistry, which in turn reflects basin geology and regional climate. Emergent vegetation covers more than 10% of the surface in marshes. Some typical emergent species in British Columbia are Typha latifolia (cattail), Scirpus lacustris (great bulrush), S. paludosus (alkali bulrush), Carex aquatilis (water sedge), C. rostrata (beaked sedge), C. lasiocarpa (slender sedge), Juncus balticus (wire rush), Equisetum fluviatile (swamp horsetail), Menyanthes trifoliata (buckbean), and Potentilla palustris (marsh cinquefoil). Marshes are especially common on the Interior Plateau, where geology and climate have combined to produce numerous poorly drained basins with nutrient-rich water. Some of the Interior marshes are even highly alkaline or saline. In contrast, ecological conditions in northeastern and north coastal British Columbia (where poorly drained basins are even more abundant) have generally resulted in the formation of organic substrates, and dominantly bog and fen rather than marsh formation. FEN Fens are wetlands composed of accumulations of well to poorly decomposed, nonsphagnic peats. Most fens have more than 40 cm of peat accumulation. Fen waters come mostly from groundwater and runoff from adjacent mineral uplands. As a result, fens are less acid and more mineral-rich than are bogs. Fen peat is well to moderately decomposed. Associated soils are Mesisols and Humisols. Fen vegetation can be dominated by graminoids (grasses, sedges, rushes), low shrubs, or trees, often underlain by mosses. Typical fen shrubs include Betula glandulosa (scrub birch), B. pumila (swamp birch), willows (Salix barclayi, S. glauca, S. maccalliana, S. pedicellaris, among others), Spiraea douglasii (hardhack), Myrica gale (sweet gale), Alnus tenuifolia (mountain alder), Cornus stolonifera (red-osier dogwood), and Potentilla fruticosa (shrubby cinquefoil). Common herbs include Carex 277

4 rostrata, C. aquatilis, C. disperma (soft-leaved sedge), C. sitchensis (Sitka sedge), C. lasiocarpa, Trichophorum cespitosum (tufted clubrush), Deschampsia cespitosa (tufted hairgrass), Calamagrostis canadensis (bluejoint), Equisetum arvense (common horsetail), E. fluviatile, Platanthera dilatata (white bog-orchid), and Amerorchis rotundifolia (round-leaved orchis). Characteristic trees are white and/or black spruce and tamarack, which is common only in the Boreal White and Black Spruce zone (BWBS) of northeastern British Columbia. Fens typically have an abundance of brown mosses such as Tomenthypnum nitens (golden fuzzy fen moss) and species of Calliergon and Drepanocladus, as well as Mnium, Plagiomnium and Rhizomnium (leafy mosses), and Aulacomnium palustre (glow moss). Hummock-forming Sphagnum mosses are uncommon, except in fens that are transitional to bogs. SWAMP Swamps are wooded wetlands dominated by 25% or greater cover of trees or tall shrubs, and characterized by periodic flooding and nearly permanent subsurface water flow through various mixtures of mineral sediments and peat. Swamps are, like fens, rich in minerals and nutrients, but the characteristic water movement through swamps tends to make them better aerated than fens. Swamp waters thus have sufficient levels of dissolved oxygen to support either tall shrubs or trees. Some typical swamp types are: western redcedar, Sitka spruce, or red alder swamps on the coast, usually with Lysichiton americanum (skunk cabbage); Engelmann, white, and/or black spruce types in the Interior; and tall deciduous shrub types, usually dominated by Salix spp., but often also with Betula glandulosa or Alnus tenuifolia or Malus fusca (Pacific crab apple). The substrate of swamps ranges from mineral material with surface enrichment with organic matter, through mixtures (often interlayered) of mineral and organic matter, to organic accumulations (usually woody and highly humified) of 50 cm or more. Associated soils are Gleysols, Humisols, and Mesisols. BOG Bogs are wetlands covered or filled with poorly to moderately decomposed Sphagnum-derived peats. Bog surfaces are often raised or level with their immediate surroundings, and thus are little affected by nutrient-rich groundwater from the surrounding mineral soils. Precipitation, a relatively poor source of dissolved ions, is the major source of water to the upper peat. Hence, the upper peat layer of bogs is strongly acid and low in nutrients. Peat materials in bogs derive primarily from Sphagnum moss and forest materials (decaying wood and litter); typical bog peat is sometimes underlain by more decomposed fen peat. Bog soils are usually Fibrisols, Mesisols, or Humisols; Organic Cryosols occur in some of the bogs of the BWBS in the Fort Nelson Lowland. 278

5 Bog vegetation in the Interior typically has a dominant surface cover of Sphagnum mosses with variable amounts of poorly growing or stunted black spruce, low or dwarf ericaceous shrubs (especially Ledum groenlandicum [Labrador tea] and Oxycoccus oxycoccos [bog cranberry]), Carex spp. and Eriophorum spp. (cotton-grasses), and lichens. Coastal bogs may or may not have a continuous matrix of Sphagnum moss. Typical tree species are shore pine and yellow-cedar, and Trichophorum caespitosum characterizes the herb layer along with various species of Carex and Eriophorum. Bogs are especially abundant in the BWBS on the flat, poorly drained terrain of the Great Plains and on the outer coastal lowlands, in the hypermaritime subzones of the Coastal Western Hemlock zone. 279

6 LITERATURE CITED Cowardin, L.M., V. Carter, F.C. Golet, and E.T. Laroe Classification of wetlands and deepwater habitats of the United States. U.S. Dep. Int., Fish and Wildl. Serv., Publ. No. FWS/OBS-79/31. Washington, D.C. National Wetlands Working Group Wetlands of Canada. Environ. Can., Ecol. Land Class. Series No. 24. Ottawa, Ont. 452 p. Runka, G.G. and T. Lewis Preliminary wetland manager s manual, Cariboo Resource Management Region. B.C. Min. Environ., APD Tech. Pap. 5. Victoria, B.C. Tarnocai, C Canadian wetland registry. In Proceedings of a workshop on Canadian wetlands. C.D.A. Rubec and F.C. Pollett (editors). Environ. Can., Ecol. Land Class. Series No. 12. Ottawa, Ont., pp Zoltai, S.C., F.C. Pollett, J.K. Jeglum, and G.D. Adams Developing a wetland classification for Canada. In Forest soils and forest land management. B. Bernier and C.H. Winget (editors). Proc. 4th N. Amer. For. Soils Conf. Les Presses de l Universite Laval, Quebec City, Que., pp