PEAT FOR PETE'S SAKE: HYDRIC SOILS AND RECORDS OF HOLOCENE PALEOENVIRONMENT FROM SMALL WETLANDS IN EASTERN COLORADO

Analyses of hydric soils found in “pocket fens” (small, groundwater fed peatlands) and marshes (mineral substrate) on the western Great Plains indicate they contain high-resolution (sub-decadal) records of Holocene paleoenvironment. Earlier research on sediment cores from lakes and boreal bogs indicate that organic matter content and bulk density provide a temperature proxy and calcium carbonate content provides a relative effective moisture proxy in lake sediments. My interest was to test these relationships between climate variables and the organic matter and calcium carbonate content of the sediments from fens and marshes in eastern Colorado to determine the validity of these characteristics as paleoenvironmental proxies. To this end, I compared historic climate records from stations in Denver and Pueblo with sediments from a small marsh located 25 km east of Denver and a small fen located 20 km east of Pueblo. High-resolution geochronologies for the upper 40 cm of sediment in both wetlands are provided by close interval (2 cm) Lead-210 dates.

Correlation of organic matter, calcium carbonate and bulk density with warm season mean minimum temperature are significant in both fen and marsh sediments, implicating the importance of later frosts to both wetland productivity and vegetation cover relating to sediment availability for transport and deposition in the wetlands. Sediment-climate relationships are complex; when sediments dating from the last 20 to 50 years are included, correlations are not significant, suggesting that other environmental factors, such as the influence on productivity from aerosol related diffuse radiation fertilization or other non-linear environmental phenomena have overwhelmed the relationship between wetland productivity and temperature during this period. This divergence between temperature and productivity is also seen in tree-ring records of the past 50 years.

These results can be extrapolated into the past, and data from pocket fens and marshes suggest that they contain sensitive records of climate fluctuations, including the Medieval Climate Anomaly and the Little Ice Age. Due to the heterogeneity of the sediments contained within pocket fens, new methods of data analysis and display have been developed to compensate for sediment differences within and between fens.