Wednesday, January 27, 2010

Water Level In Beaver Creek Marsh

Water level in the marsh changes on many time and space scales.  EPA gives a clear definition that shows the importance of water level to a wetland:
Wetlands are areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season. Water saturation largely determines how the soil develops and the types of plant and animal communities living in and on the soil. Wetlands may support both aquatic and terrestrial species. The prolonged presence of water creates conditions that favor the growth of specially adapted plants and promote the development of characteristic wetlands soils.
Water level changes on a daily and seasonal basis depending on rainfall, the tidal cycle at the mouth of the creek, and the amount of sand that blocks the creek on the beach.  Storms can move sand off the beach, while high surf and tides can push water back into the marsh.  Water levels are generally higher in the fall and winter and lower in the spring and summer. 

The mouth of Beaver Creek

Other events can alter water levels.  Large floods can redistribute sediment and organic debris through the marsh, altering drainage patterns by blocking or clearing smaller streams and culverts that drain through the marsh to Beaver Creek.  Beavers can build dams in smaller creeks and culverts, raising water level in areas of the marsh.  Drainage can be increased and water levels lowered by ocean scouring of the creek mouth and by clearing beaver dams and culverts. 

Cows used to graze next to this fence 

Changes in water level are a natural part of the marsh.  How often and where they occur can have an important influence on the types of plants in the marsh.  Looking at the marsh, patches of different species can be seen.  Because of the relationships between species occurrence, soil type, and water level, these patches reflect the varying water levels in space and time.  

Grazing by nutria and beaver can also change vegetation patterns.  Pollen and other plant remains from cores of marsh soil can be analyzed to map the history of marsh formation and spatial change in vegetation and soil.  Dead trees can be seen in the marsh.  These trees show that water level has increased with time and the trees became inundated during their growing season and died.

The historical presence of tsunamis can be detected in marsh cores and drowned forests.  Reading the history of the marsh through vegetation patterns is a wonderful mystery story.  
Posted by michael

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