Soil Properties in Native, Reconstructed, and Farmed Prairie Potholes: A Chronosequence Study of Restoration Timeframes

Restoration Notes have been a distinguishing feature of Ecological Restoration for more than 25 years. This section is geared toward introducing innovative research, tools, technologies, programs, and ideas, as well as providing short-term research results and updates on ongoing efforts. Please direct submissions and inquiries to the editorial staff (ERjournal@aesop.rutgers.edu).

The Des Moines Lobe landform region of Iowa is the southernmost extent of the prairie pothole region (PPR) and was glaciated as recently as 12,000 years ago by the Wisconsin glaciation (Ruhe 1969, Prior 1991). The PPR primarily consists of hummocky topography that formed during ice melt of the Wisconsin ice sheet and contains many thousands of small, shallow, and poorly drained closed depressions, “potholes” (Sloan 1972, Miller et al. 2009). Prior to European settlement, the PPR landscape was composed of an extensive prairie ecosystem interspersed with many wetlands and marshes. However, in the late 1880s to early 1900s, artificial drainage was introduced in the region, and many of these pothole areas were drained for agricultural purposes. Artificial subsurface drainage (tiling) is a common practice of installing perforated tile approximately 1.2 m below the soil surface in order to remove excess soil water from poorly drained or wet areas (Singh et al. 2006). Due to water quality, soil conservation, and wildlife habitat concerns, many farmed wetlands on the Des Moines Lobe are undergoing restoration attempts: this is a process of preserving, restoring, and enhancing wetlands to a state that is similar to that of native wetlands (Ewing et al. 2012). Compared to native wetlands that have never been drained, the introduction of tiling alters the factors of soil formation. Drained wetlands experience faster soil warming, altered carbon (C), nitrate nitrogen (N), phosphorus (P), and iron (Fe) cycling (Gambrell and Patrick Jr. 1978), and altered respiration rates (Davidson and Janssens 2006).

Native and reconstructed wetlands are ecologically vital habitat for birds and animals (LaGrange and Dinsmore 1989, Leibowitz and Vining 2003) and the dispersal and life history traits of many aquatic organisms (Mushet et al. 2015). There are several cases of restoration efforts that have been unsatisfactory in terms of hydrologic or soil quality (Zedler 2000). Some restorations have even left soil properties, including soil organic matter (SOM), N, and bulk density, more altered than they were before restoration attempts (Ballantine et al. 2012). However, soil properties are difficult to evaluate in terms of restoration success due to a lack of data on restoration rates and poor soil characterization prior to restoration efforts; this lack reduces our ability to detect change. In order to assess the success of long-term wetland restoration, a realistic timeframe for restoration must be established for each soil property of interest.

Evaluating long-term trends in ecosystem services may be accomplished by using chronosequences. Chronosequences are time series of sites that vary by age with otherwise similar characteristics (Schilling and Jacobson 2010). Chronosequences resolve the issue of poor monitoring data by allowing data collection of many different restoration ages at the same relative time (Stevens and Walker 1970). Meyer et al. (2008) successfully used a chronosequence to compare soil restoration in river valley wetlands, and Ballantine and Schneider (2009) evaluated long-term wetland soil restoration using a chronosequence. The objective of this study was to use a chronosequence approach to determine the restoration timeframes of soil properties within closed depressions located on the Des Moines Lobe of Iowa. Our approach utilized a range of restoration ages, comparing current farmed potholes to decadal-long wetland restorations and native wetlands, in order to assess how long it may take for soil properties of reconstructed wetland sites to resemble those of native systems.

The area of interest for this study was prairie pothole wetlands (wetlands in closed depressions) on the Des Moines Lobe of Iowa. In all, 21 wetlands were selected for extensive soil analysis and were split into three groups based on land use and drainage (Figure 1). The three groups included native wetlands that have never been artificially drained and are currently in native vegetation (n = 5...