Natural Resources Conservation Service Assessing Wetland Morphometrics and Conservation Effects Assessment Project Ecosystem Functions in Agricultural CEAP Science Note Landscapes of the Atlantic Coastal Plain September 2015 Using Fine Scale Topographic Information Summary Background • Topography is a known control on Topography is a known control on Light Detection and Ranging multiple ecosystem processes, influencing the movement of water, soil, multiple ecosystem processes, (LiDAR)-based digital elevation and other constituents. influencing the movement of water, models (DEMs; see summary at soil, and other constituents. In the left) enable mapping of landscape • In the Atlantic Coastal Plain, even subtle differences in topography can lead to Atlantic Coastal Plain, even subtle features that were previously substantial variations in these processes, differences in topography can lead difficult if not impossible to including those related to to substantial variations in these distinguish with commonly biogeochemistry (i.e., nutrient cycling), erosion/deposition, and surface and processes, including those related available DEMs produced using groundwater movement. to biogeochemistry (i.e., nutrient stereo-interpretation of aerial cycling), erosion/deposition, and • Traditionally available digital elevation photographs. Fenstermacher et al. models (DEMs) created using aerial surface water and groundwater (2014) highlights the importance of photography have much coarser vertical movement. In turn, these processes LiDAR-based DEMs for mapping accuracies 3.28 – 32.81 feet (1 – 10 m) than those derived from LiDAR ~ 0.50 influence a number of ecosystem Delmarva bays, elliptical feet (~ 15 cm). services which are highly relevant depressional landforms that are in agricultural landscapes including commonly found on the • LiDAR-derived DEMs also have relatively fine horizontal resolutions ~ the provision of clean water, the agriculturally dominated Delmarva 3.28 – 9.84 feet (~ 1 – 3 m). management of climate, mitigation Peninsula, including portions of of flood hazards, availability of Delaware, Maryland, and Virginia • Using LiDAR, a total of 14,969 bays were visually identified, and it was fresh water, and support for soil (Figure 1). Although not all estimated that areas without LiDAR data character and function. In addition, Delmarva bays currently contain contained approximately 2,000 additional the influence of topography on wetlands, it is likely that the vast bays for a total of ~ 17,000 bays within the entire study area. water flux and availability, soil majority did at one time. quality, and nutrient cycling Furthermore, prior converted • Mean bay density was found to be strongly affects crop production. croplands (i.e., historical wetlands approximately 5 bays per mi2 (2 bays per km2) ranging up to ~ 69 bays per mi2. The importance of topography is converted to upland cropland especially evident near the before 1985 and continuously used • Bays had an average area of 6.99 ac (2.83 boundary between wetlands and for agriculture through the present ha) with mean relief within bays of 3.97 feet (1.21 m; median 3.64 feet [1.11 m]). uplands. This boundary was in time) have been found to support large part established by scientists some wetland characteristics and • This study provided regional assessment to identify the area at which water processes (Fenstermacher et al. of wetland landscape morphetric regimes, which are greatly 2011; Denver et al. 2014; Hunt et information to help identify local soil and hydrologic conditions suitable for influenced by elevation, produce al. 2014; McCarty et al. 2014). supporting wetland functions and wetland markedly different plant Before publication of the restoration. communities and soils. However Fenstermacher et al. (2014) study, • For additional information regarding until recently the spatial resolution Delmarva bay wetland studies LiDAR technology and wetland of commonly available topographic focused on a small number of sites conservation applications please see the CEAP Science Note: “Light Detection data were not sufficient for and little was known about the and Ranging (LiDAR) for Improved mapping the subtle changes in larger population of bays, including Mapping of Wetland Resources and topography frequently associated their morphology and spatial Assessment of Wetland Conservation Practices” (Lang and McCarty 2014). with the presence of wetlands, characteristics as well as their especially in landscapes that are current land cover. relatively flat, like the Atlantic Coastal Plain. 1 Figure 1. A LiDAR-based digital elevation model (DEM) for a portion of the Choptank Watershed, including areas within Maryland and Delaware. Three expanded views can be seen to the right. Note the abundance of relatively small circular depressions or Delmarva bays which are present across all land covers including both cropland and forest. The images to the right provide a more detailed look at (A) natural, (B) historical, and (C) restored Delmarva bays. Historical Delmarva bays are often drained by ditches and can be seen in all images. Note that only the northwest portion of the restored wetland (C) has been restored through excavation, while the southeastern portion of the bay was not converted to cropland. This CEAP Science Note Introduction to Delmarva Bays “Grady ponds.” Carolina bays are summarizes the Fenstermacher et often oriented along a northwest – al. (2014) study findings and Delmarva bays are believed to be a southeast major axis (Sharitz & highlights the importance of this geographic subset of the Gibbons 1982; Stolt & Rabenhorst type of morphometric assessment depressional features that have 1987b; Bruland et al. 2003) and for the estimation of ecosystem more broadly been termed Carolina typically have a sandy rim at their services provided by natural, bays. Although the Carolina bays southeast end (Prouty 1952; Thom restored, and historical wetlands of North and South Carolina are the 1970; Stolt and Rabenhorst 1987a; (i.e., prior converted croplands) best known examples, natural Tiner 2003). Bays range in size and assessment of agricultural depressions with a unique elliptical from tens of meters to kilometers in management practice effects. shape are found along the Atlantic length and cover as much as 50% Coastal Plain from New Jersey to of the land area where they are Florida and along the Gulf of most abundant (Prouty 1952). LiDAR Reveals the Density, Mexico. In the Alabama and Although there are a number of Distribution and Morphology Georgia Coastal Plain areas, these theories regarding the origin of of Delmarva Bays depressions are locally known as Carolina and Delmarva bays, 2 available field evidence suggests Peninsula, in areas of Maryland that they were wind blow-outs and Delaware. The Delmarva A stratified random approach based formed during the Pleistocene that Peninsula is located within the on bay density was used to select filled with water and were outer Coastal Plain Physiographic areas for more detailed elongated by wind-driven currents, Province and has a humid morphologic analysis. Using this resulting in their unique shape and subtropical climate with an average approach a total of 1,494 bays were characteristic sandy rim (Grant et annual rainfall of 44 inches selected, manually outlined, and al. 1998; Prouty 1952; Savage (Denver et al. 2004). The landscape their area, perimeter, major and 1982; Stolt and Rabenhorst 1987b; is generally flat (elevation between minor axis, relief and land cover French and Demitroff 2001). 0 and 102 feet [0 and 31 m]) and is were determined using ArcGIS 9.2 Less information is known about dominated by agriculture (48%), (Environmental Systems Research Delmarva bays than Carolina bays. primarily corn and soybean fields, Institute, Redlands, CA). Bays Delmarva bays are generally but also includes forests (33%), and were categorized as having a smaller than Carolina bays, which a smaller amount of urban areas natural, agricultural, residential, are found to the south in North and (7%; Denver et al. 2004). and/or fallow land cover class South Carolina. Delmarva bays are using false-color near-infrared known to be extremely common in Publicly available LiDAR based aerial photography obtained from portions of the Delmarva Peninsula DEMs with a spatial resolution the USDA Geospatial Data including Queen Anne’s, Caroline, between ~ 6.6 and 9.8 feet (2 and 3 Gateway. Additional information and Talbot Counties in Maryland m) and a vertical accuracy of regarding the methods used to map and New Castle and Kent Counties approximately 7.1 inches (18 cm) and characterize Delmarva bays in Delaware. Their common were obtained from the USDA can be found in Fenstermacher et occurrence exerts strong controls Geospatial Data Gateway and the al. (2014). on field and landscape scale Maryland Department of Natural processes in this region (Figure 1). Resources. These data were used to Results and Discussion Delmarva bays that have not been manually identify Delmarva bays A total of 14,969 bays were visually drained for agricultural or urban based on their characteristic identified (Figure 2), and it was development typically contain elliptical shape. Although estimated that areas without LiDAR wetlands. These wetlands can act automated processes are available data contained approximately 2,000 as both recharge wetlands that to identify landscape features with bays for a total of ~ 17,000 bays replenish groundwater and distinct shapes, a manual