Most of Iowa\u27s wetlands have been drained, tiled, and cultivated. This project looked at how carbon sequestration has been affected and what might be done to help improve the situation. Researchers collected GPS coordinates of all the sites samples so that in the future someone can return to the sites and determine the amount of change in organic carbon or other properties that have occurred over time

Fenton, Thomas E.

Moran, Louis P.

Most of Iowa's wetlands have been drained, tiled, and cultivated. This project looked at how carbon sequestration has been affected and what might be done to help improve the situation. Researchers collected GPS coordinates of all the sites samples so that in the future someone can return to the sites and determine the amount of change in organic carbon or other properties that have occurred over time.</p

Fenton, Thomas

Moran, Louis

Digital Repository @ Iowa State University (ISU)

COMPETITIVELeopold Center GRANT REPORT L E O P O L D C E N T E R	 01-47FOR SUSTAINABLE AGRICULTURE Soil carbon quality and interactions in Iowa wetlands Abstract: Most of Iowa’s wetlands have been drained, tiled, and cultivated. This project looked at how carbon sequestration has been affected and what might be done to help improve the situation. Researchers collected GPS coordinates of all the sites samples so that in the future someone can return to the sites and determine the amount of change in organic carbon or other properties that have occurred over time. Background Corn and soybeans are grown on most of Iowa’s former wetlands. However, there is increasing recognition of the economic and environmental value of wetlands and some of these areas are being returned to their original condition, particularly on the Des Moines Lobe in north central Iowa. Hydrology, the extent and nature of hydric soils (those containing an abundance of mois­ture), and vegetation are important factors in the proper functioning and maintenance of wetland ecosystems. Wetlands serve many purposes: trapping sediment and water, im­proving groundwater quality, sinks for car­bon, habitats for wildlife, and soaking up con­taminants from adjacent sites. Restoration of previously cultivated landscapes can increase carbon (C) sequestration. A common restora­tion tactic is removal or blockage of drainage tiles to help reinstate the natural hydrology of the area. The objectives of this project were to: •	 Identify the sources of microbial biomass variability in restored wetland complexes and estimate the relative contribution of each, •	 Describe the relationship between micro­bial biomass C with total C by vegetative zones, •	 Assess soil variability in mollic epipedons (dark-colored surface horizons) along re­stored prairie-wetland hillslopes, •	 Determine carbon status of restored prai-rie-wetland hillslopes for long-term moni­toring of carbon changes in central Iowa, •	 Quantify water table depths, duration, and variability in restored prairie-wetland hillslopes on the Des Moines Lobe, and •	 Relate soil morphology to hydrology of restored prairie-wetland hillslopes on the Des Moines Lobe. Approach and methods Three restored wetland sites were chosen on the Des Moines Lobe in Boone, Hamilton, and Story counties. Three low-relief hillslopes with closed depressions were randomly se­lected using photos and soil survey maps. Transects from the upland summit position to the closed depression were established. Each transect was delineated according to changes in dominance of vegetation and slope position. Slope positions were summit, shoulder, backslope, footslope, and toeslope. Soil cores were taken from an average depth of 200 cm at points along the landscape with visible changes in vegetation and slope position. Soil samples were selected from the cores and analyzed in the laboratory. Elevation and GIS coordinates were measured at each sampling point. Moni­toring wells were established at each sampling point. Water levels were checked biweekly to monthly from March 2000 to the end of the project. The time covered by the sampling included a wet year and a dry year. Principal Investigator: T. E. FentonCo-investigator: L. P. MoranAgronomy Iowa State University Budget: $27,500 for year one $26,025 for year two Drainage and cultiva­tion (as well as erosion on sloping soils) have greatly reduced the organic carbon content (organic matter) of Iowa soils, especially in the surface horizons. Conversion of areas to wetlands increases the organic matter content of soils and improves the positive contribu­tions of wetlands to our environment. Leopold Center Progress Reports 33 Results and discussion Four group classifications were used to de­scribe the variability in soils, vegetation, and slope position on the hillslopes. Group I soils included upland prairie soils on summit and shoulder slopes with moderately good and somewhat poor drainage. Group II soils were upland prairie soils on backslopes with poor drainage. Group III soils encompassed wet prairies or sedge wetlands on footslopes with poor drainage. Group IV soils occurred in pond depressions on toeslopes with poor and very poor drainage. Groups II and IV in prai-rie-wetland hill slopes are hydric based on the positive correlation between soil morphology and hydrology. The shallowest water table depths occurred from March to May, the onset of the growing season, and the deepest water table depths occurred from August to October, near the end of the growing season. Wetland depressions were ponded between three to 12 months per year. Wet prairies and sedge wetland zones were ponded for up to three months. In gen­eral, mean and shallowest water table depths paralleled surface typography and mollic epipedon thickness on summits and backslopes at all research sites, reflecting the recharge and throughflow hydrologic nature of these areas. Mean and shallowest water table depths did not parallel the surface typography and mollic epipedon thickness in soils on wet prairie and sedge wetland zones bordering pond depres­sions. Recharge is the dominant process in uplands resulting in leached soils. Group III and IV soils contained the highest amounts of total and organic C as a result of increased moisture conditions, enhanced anaerobiosis, and the high vegetative biomass production. The total and organic C amounts can be used as reference points for future monitoring influence of restoration practices on C balance. Total and organic C varied considerably for each soil group on each hillslope, among each hillslope in each wet­land complex, and among each wetland com­plex. Soils on upland prairie-backslopes produced the highest microbial biomass C for each depth interval. The highest microbial biomass C was from 0-15 cm in all vegetative-slope areas. The greatest variability in microbial biomass C occurred on the upland prairie backslopes. Soils in the sedge wetland had the lowest percentage microbial biomass C, suggesting the presence of more stable organic fractions due to past erosion/deposition in these areas. The vegetative zone accounted for 52 percent of the total variability in total C, whereas soil depth accounted for 74 percent of the total variability in biomass C. Microbial biomass C was significantly linked with total C for each vegetative-slope element. Particle size distri­bution was significantly correlated with mi­crobial biomass and total C in the sedge wet­land zones. Conclusions 1.	 The variability in soils, vegetation, and slope among test sites could be character­ized by four soil groups, ranked I-IV. 2.	 As expected, soil morphology correlated with hydrology, except for one transect in which ditching influenced the hydrology of summit soils. 3.	 Recharge and subsequent leaching was confirmed as the dominant process on uplands. 4.	 Sources of predictable soil systematic vari­ability in exchangeable K, Mehlich P, total C and organic C were site, hillslope, slope position, and soil depth. In general, hillslope and soil depth accounted for most of the variability in each ecogroup. Volume 12 (2003) 34 5.	 Site, hillslope, vegetation, slope position, and soil depth should be considered when assessing restored prairie-wetland hillslopes. 6.	 The total and organic C amounts can be used as reference points for future moni­toring influence of restoration practices on C balance. 7.	 Restoration, using microbial biomass and total C as indicators, is positively influ­encing the soil quality in these restored wetlands. Impact of results This project assessed the influence of restora­tion practices on soil quality, hydrology, and morphology on cultivated hillsides in Iowa. The project also touched on the importance of understanding the sources of soil variability in restoration. Monitoring of water tables for longer periods (more than two years) is needed to truly integrate and understand the hydrol­ogy of these landscapes. Data collected from this study will be used as a reference point in tracking the changes in soil properties over time. Additional information is needed to de­termine rates of soil and vegetation changes. These data will assist the Department of Natu­ral Resources and other researchers in future wetland or prairie assessments. Education and outreach Three papers have been submitted to the Soil Science Society of America Journal. Three poster presentations were given on the project at three American Society of Agronomy an­nual meetings. Another poster was presented at the International Conference on Nitrogen Around the World and Its Effects. For more information contact T. E. Fenton, Agronomy, Iowa State University, Ames, Iowa 50011; (515) 294-2414, e-mail tefenton@iastate.edu Leopold Center Progress Reports 35 

English

Soil carbon quality and interactions in Iowa wetlands

https://dr.lib.iastate.edu/bitstreams/3fdc8a46-e45b-466d-81d8-28b90c2a8510/download

Soil carbon quality and interactions in Iowa wetlands

Abstract

Similar works

Full text

Available Versions

Digital Repository @ Iowa State University (ISU)