The Development of a GIS Methodology to Identify Oxbows and Former Stream Meanders from LiDAR-Derived Digital Elevation Models

Abstract

Anthropogenic development of floodplains and alteration to natural hydrological regimes have resulted in extensive loss of off-channel habitat. Interest has grown in restoring these habitats as an effective conservation strategy for numerous aquatic species. This study developed a process to reproducibly identify areas of former stream meanders to assist future off-channel restoration site selections. Three watersheds in Iowa and Minnesota where off-channel restorations are currently being conducted to aid the conservation of the Topeka Shiner (Notropis topeka) were selected as the study area. Floodplain depressions were identified with LiDAR-derived digital elevation models, and their morphologic and topographic characteristics were described. Classification tree models were developed to distinguish relic streams and oxbows from other landscape features. All models demonstrated a strong ability to distinguish between target and non-target features with area under the receiver operator curve (AUC) values ≥ 0.82 and correct classification rates ≥ 0.88. Solidity, concavity, and mean height above channel metrics were among the first splits in all trees. To compensate for the noise associated with the final model designation, features were ranked by their conditional probability. The results of this study will provide conservation managers with an improved process to identify candidate restoration sites.

Multipurpose Oxbows as a Nitrate Export Reduction Practice in the Agricultural Midwest

“…Oxbows recommended for restoration have nearly completely filled in with sediment and no longer have the storage capacity to retain tile water. Zambory et al (2019) developed a GIS procedure to locate potential oxbow restoration sites and found several hundred potential sites in the Boone River watershed alone. Restoration deepens the oxbow down to the current adjacent streambed elevation to ensure connection to groundwater, allowing the oxbow to hold ample water to sustain fish populations year‐round.…”

“…Due to their proximity to streams, oxbows, whether naturally occurring or restored, are a type of wetland that is ideally suited to process nitrate‐rich water exiting agricultural fields via natural pathways or artificial tile systems. Thus, restoration of former oxbows (Zambory et al, 2019), particularly where they can intercept tile drainage, has great potential as a nitrate export reduction practice in the agricultural Midwest.…”

Applying a Hybrid Modeling Approach to Evaluate Potential Pesticide Effects and Mitigation Effectiveness for an Endangered Fish in Simulated Oxbow Habitats

“…We applied a hybrid model for the endangered Topeka shiner to assess potential population‐level impacts of pesticide exposures in an oxbow habitat. The food web composition and the habitat definition were adapted to represent off‐channel habitats (oxbow lakes) in Iowa, which have been recognized as important habitats of the species and where restoration efforts are underway (Bybel et al 2019; Simpson et al 2019; Zambory et al 2019). Because these existing and restored oxbow habitats are located in agricultural landscapes, the ecological risks posed by exposure to pesticides to resident populations, including listed species, should be considered.…”

“…One such species is the Topeka shiner ( Notropis topeka ), a small minnow found in the central United States that was first listed as endangered under the Endangered Species Act in 1998 (Tabor 1998). Habitat restoration efforts are under way in parts of its range, focusing on the restoration of the oxbows that provide suitable habitat for the Topeka shiner (Fischer et al 2018; Bybel et al 2019; Simpson et al 2019; Zambory et al 2019). However, oxbows and similar off‐channel habitats may be vulnerable to pesticide runoff from agricultural fields.…”

Spatial distribution and ecological relationships of stream fishes in Iowa's Driftless Area

“…Landscape scale environmental factors often govern instream processes (Meyer et al, 1988;Benda et al, 1998) and can accurately predict species distributions (Hopkins & Burr, 2009;. Therefore, applying watershed-level relationships observed here to map predicted suitable habitats with GIS-derived data may allow for simpler and more efficient means to prioritize site selection for conservation projects or future sampling efforts Zambory et al, 2019). .…”