LATE-QUATERNARY ENVIRONMENTAL CHANGE ON THE MONTE VISTA NATIONAL WILDLIFE REFUGE, COLORADO, USA

Analyses of soils, wetland peats, pollen, and tree rings were used to reconstruct environments of the Monte Vista National Wildlife Refuge (MVNWR) of southern Colorado. A late-Pleistocene flood deposit was bracketed to between ~11,530 and ~14,050 BP using housed faunal remains of mammoth, bison, horse, beaver, and wolf as a maximum age and overlying peats as a minimum age. The post-LGM timing of the flood coincides with several regional and global climatic cool/wet events including the Younger Dryas. The flood deposits are capped by three distinct layers of peat that reflect changing water tables and environments. The lowest layer is evaporite silt and represents a fluctuating water table ~11,530 BP resulting in seasonally dry playas. Lunette dunes on the downwind side of the wetland system support this interpretation. Woody peats represent boggy conditions with saturated sediments and a high biomass ~11,390 BP. Overlying organic silts represent a rising of the water table and a marshy environment with standing water where windblown silts were layered with organics at the bottom between ~9,120 BP and ~8,740 BP. Picea, Abies, Juniperus, and total pollen count concentrations reflect these patterns, as do changes in species composition from Abies to Pinus suggesting timberline ascension and warming. These data align with other regional studies and suggest that warmer conditions result in aridity, and thus, have implications for future climate change. As climate warms, water scarcity in this already arid region will increase. Spring creek is a small, artesian fed creek that used to run through the MVNWR. The Refuge lost Spring Creek water rights because Alamosa Water Courts argue that wetland recharge in this area is from the Monte Vista Canal (MVC) built in the 1880’s to divert water from the Rio Grande for agriculture. Environmental data were used to ascertain whether the original source of these wetlands is Spring Creek as the MVNWR asserts or the MVC as the Alamosa Water Courts suggest. An historical map from the 1873 Wheeler Expedition shows wetlands at the locality and dendrochronology data suggest a Juniper grove started growing before the MVC was installed. Further, thirteen carbon 14 ages from peat samples suggest the water table was higher and standing water was present before the 1880's. These three data sets support the MVNWR's claim that there were wetlands here before installation of the MVC and provide supporting documentation for the refuge to attain needed water rights to fulfill their mission of protecting migrating birds.