Gradient analysis of the vegetation in a brackish marsh in Bellingham Bay, Washington

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Abstract
The islands in the delta of the Nooksack River support a brackish marsh with maximum salinity of 5.18 parts per thousand (ppt). On high tides, the marsh is flooded with water from the river rather than from Bellingham Bay. Marsh species were distributed according to combinations of elevation, length of tidal submergence, sand and silt content of the soil, and soil moisture. Two broad marsh zones were recognized. The Scirpus americanns marsh occurs below 274 cm above mean lower low water (MLLW), where it is submerged on nearly all high tides. It has over 70 submergence days per year. Soils are sandy but poorly drained, and aerial biomass is low. The Carex lyngbyei marsh occupies sites above 274 cm. This zone has fewer than 50 submergence days per year. These sites have siltier soils, better soil-moisture values, and greater biomass.