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MARSHES: Sail Luis Lakes The San Luis Valley is like nowhere else in Colorado-a rift valley lar~er than the state of Connecticut, Ul~ated millions of years a~o when a ~reat block of land slowly dropped while the surrounding San Juan and Sangre de Cristo mountains rose. The "basement floor" of the valley is two to three miles below the surface; in between the floor and the surface is about 10,000 feet of sediment-chock full of water and impervious layers. The southern part of the valley is drained hy the Rio Grande River and its wetland systems. On the other hand, the northern portion of the San AnJcels feed ill (/ playa ill lite Safl Luis LaRes area. flloto iiI' /louid Cooper ~." 'YO' ~.-. ........... "'. . ~. .".' , , / ,~ i13 Luis Valley is a "closed basin": Water flows in and does not flow out again. This closed basin acts like a giant bucket, creating a perennially high water table, a situation ideal for marsh ecosystems. Marsh systems like those found in the San Luis Lakes State Wildlife Area 30 miles northeast of A1amosa are very dynamic wetlands. Their size and the depth of the water that covers them vary with regional weather patterns and C... <<,.~"\ - with the seasons. ) ) San Luis' Valley marshes have standing. 1'\1': water from snowmelt that is ,,\\S'Z: water for part of the "'Zir~- added to an already high year; water can cover 1~~~' water table. Nutrients them as deep as 12-18 \~_ released from the inches, or even up to 3 ';- ~ __ ". decomposition or4feet. Then,bytheend =--~-- ~~ ;:;;:~~~ --.. oflasty~~r's of the summer, most of that . ~ plants fertlhze water may be gone, leaving the marsh's water, and aquatic plants, behind shallow temporary lakes al~ae and insects grow in a rush called playas and a few deep- beginning in April. water lakes. Because of this richness of The seasonal pat- plant and animal life, Colorado's .... tern of a marsh begins in .~ marshes are our most impor- spring, when lowland ~ tant wetlands for migratory '" basins receive an influx of e water birds. Ducks...geese... Billf/Jsh (JI/d SI/Wlll/leed (tlw plauts il/ t/ie waler). Phuto by DO/lid Cooper shorebirds...wading birds...all use marshes as stopovers during migration, as resting and feeding sites and/or as breeding and moulting grounds. As the mud and shallow waters begin to wann in the spring, the first birds are waiting to feed on fairy shrimp and midge larvae-sometimes as soon as early April. Several species of ducks, as well as killdeer and spot- ted sandpipers, depend on this same food source to provide them with the protein they need for e~g laying and to put on fat to fuel their northward migrations. Awcet. IIIlIslralioll by Arm W f)(}IJ(/en