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 process within the entire study area discharge wetlands that receive was selected due to the complex (Fenstermacher et al. 2014). groundwater during different times morphology of many Delmarva Previous estimates based on aerial of the year and in accordance with bays which have been photography are an order of large or prolonged weather events. superimposed upon each other, magnitude less, including an Where Delmarva bays are bisected by ditches, or otherwise estimate of 1,500 – 2,500 (Stolt and abundant, they constitute the modified. Bays with a continuous Rabenhorst 1987b) and an estimate majority of wetlands and provide elliptical perimeter were identified of 10,000 to 20,000 for the entire important habitat to a as a single feature. Where the rims Atlantic Coast (Richardson and disproportionately high number of of overlapped bays were Gibbons 1993). Mean bay density rare and endangered species sufficiently distinct they were was found to be approximately 5 (Sharitz 2003; Olivero and Zankel recognized and counted as separate bays per mi2 (2 bays per km2) but 2000; Sharitz and Gibbons 1982). features. Man-made depressions, was as high as ~ 69 bays per mi2 (27 such as ponds or reservoirs, which per km2) accounting for over 50% of Assessment Approach typically have a linear side for an land area (Fenstermacher et al. earthen dam, were excluded from 2014). Bays had a mean area of 6.99 Study Area the study. When LiDAR-derived ac (2.83 ha; median 3.58 ac [1.45 The Fenstermacher et al. (2014) DEMs were not available for sites, ha]), with 80% between 1.14 and study was conducted on the ~ their density was assumed to be 14.04 ac (0.46 and 5.68 ha). 6,000 mi2 (15,540 km2) Delmarva similar to adjacent areas.

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Figure 2. The abundance and distribution of Delmarva bays within the Delmarva Peninsula study area. Each dot represents one Delmarva bay. A total of 14,969 bays were manually identified using a LiDAR-based digital elevation model (DEM). Areas where LiDAR data were not available are marked in gray. Note that bays are concentrated in the northern portion of the Peninsula and are less likely to be found near large streams and the shoreline.

Mean relief within bays was 3.97 2.02 m). Delmarva bays had an (Fenstermacher et al. 2014). Overall feet (1.21 m; median 3.64 feet [1.11 average major to minor axis ratio of Delmarva bays were found to be m]) with 80% falling within the 1.32 (median 1.26), with 80% falling smaller, shallower, and rounder than range of 1.81 to 6.63 feet (0.55 to within the range of 1.08 to 1.65 Carolina bays, which have been 4

found to have a mean area of 113.67 The Importance of Landscape- Wetland restoration has proven to ac (46 ha) (Bennett and Nelson Scale Wetland Assessment be difficult, partly because 1991), relief of 5.94 feet (1.81 m) wetlands are regionally and locally (Prouty 1952; Thom 1970), and Although successful wetland distinct (Zedler and Callaway major-minor axis ratio of 1.51 restoration is generally considered 1999), and restoration of wetland (Melton and Scriever 1933). to provide net benefits to society, hydrology is considered to be one Fenstermacher et al. (2014) the large investment that USDA of the most difficult and critical hypothesized that the difference has made in wetland restoration components of restoration. Lang et between Delmarva and Carolina bay and increasing societal need for al. (2012) found relief to be well morphologies may be due to the wetland ecosystem services correlated with patterns of relatively colder temperatures of the highlight the importance of inundation on the Delmarva Pleistocene during the development environmental research and Peninsula and developed a LiDAR- of the higher latitude Delmarva bays. monitoring. These efforts are based technique to map elevation Frozen water would have been more needed to better understand the driven controls on wetland common with the Delmarva bays and effects and effectiveness of distribution and hydroperiod. The could have inhibited development of conservation practices, such as link between hydroperiod and thus bay morphology due to wind driven wetland restoration, and to develop relief and the distribution of plant waves, therefore limiting the size wetland restoration and agricultural and animal species is well known and elliptical shape of these features. management practices that result in (e.g., Pechmann et al. 1989; Corti This hypothesis is supported by the greater societal benefits. et al. 1996; Snodgrass et al. 2000). relatively large size of bays found in the southern portion of the Delmarva Fenstermacher et al. (2014) Current wetland restoration relative to the northern Delmarva. demonstrates the significant and practices seek to mimic more growing importance of remote natural variation in relief, making The vast majority of Delmarva sensing for supporting these them generally shallower and bays have been influenced by efforts, both through the adding micro-topography. The human development, mainly extrapolation of field scale Fenstermacher et al. (2014) study agriculture, with only 29% (4,930 information and greater provides a guideline as to out of the estimated 17,000 total; understanding of landscape scale variations in depressional wetland Fenstermacher et al. 2014) located processes that would have been relief that are naturally occurring, within areas of natural vegetation. costly and difficult to ascertain on thus supporting the stated goal of Many of these have been drained the ground. The functions that the USDA NRCS Wetland and all have likely been affected by occur within individual or groups Restoration (657) Practice Standard regional declines in groundwater of wetlands are unique to their to “restore wetland function, value, due to irrigation, human placement on the landscape habitat, diversity and capacity to a consumption, and other uses. (Bedford 1999; Simenstad et al. close approximation of the pre- Delmarva bays found entirely 2006). Therefore the landscape disturbance conditions.” The ability within natural land covers had perspective that remote sensing to locate and restore former significantly greater (p < 0.001) provides is critical to ensuring the depressional wetlands with relief (4.17 feet or 1.27 m) than optimum provision of wetland sufficient relief to support wetland those in agriculture (3.54 feet or ecosystem services through hydrology without the need for 1.08 m; Fenstermacher et al. 2014). restoration at the individual excavation could be advantageous This reduction in relief within wetland and watershed scale. The for the management of greenhouse cropland bays may have been use of remotely sensed data can gases and thus climate via carbon caused by erosion and also provide temporal context. The sequestration, since wetland sedimentation following tillage or importance of this historic excavation on the Delmarva resulted from the preferential perspective was emphasized by Peninsula was found to lower soil selection of shallower bays with Bedford (1999): “By definition organic carbon levels relative to better drainage for agricultural [wetland restoration] seeks to even historical wetlands and this development. The average area of replace what has been lost. By topsoil was found to be used in Delmarva bays found in natural definition then, it should be berms or other areas where and agricultural landscapes was not undertaken with knowledge of oxidation and loss of carbon to the shown to be significantly different what has been lost.” atmosphere was more likely (Fenstermacher et al. 2014). (Fenstermacher 2011).

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In conjunction with relief, most wetland restorations have a depression size (i.e., volume) is depressional shape or morphometry also key to supporting wetland although additional wetland types, processes. McDonough et al. including flats, and riparian (2014) found wetland area to be wetland do occur there. correlated with flow in adjacent streams when depressional Information regarding the wetlands were connected to those distribution, density, and streams via surface flows. Wetland morphology of Delmarva bays volume relative to landscape produced by Fenstermacher et al. position (e.g., catchment area) is (2014) is currently being analyzed considered to be critical to the to estimate the historical and establishment of wetland current storage of surface water hydroperiod and therefore within Delmarva bays, as well as restoration success (Bedford 1999). the contribution of USDA wetland Restored depressional wetlands restoration practices to enhanced have been found to generally be wetland volume storage. This study smaller than natural depressional was made possible by nationally wetlands (Galatowitsch and van der available land cover maps Valk 1996 [Prairie Pothole produced using remotely sensed Region]; McDonough et al. 2014 data and LiDAR-derived DEMs. [Delmarva Peninsula]; Mid- Atlantic CEAP-Wetlands The wetland morphometric data unpublished). Thus larger wetland (Fenstermacher et al., 2014) also restorations may be needed to support the extrapolation of results enhance the ability of restored from a number of other studies wetlands to maintain surface water supported by the Wetland flows and likely to mitigate floods. Component of the National Even when depressional wetlands Conservation Effects Assessment are not directly connected to Project, including studies streams via surface water flow, documenting plant and amphibian their size and arrangement has been biodiversity and abundance found to be critical for supporting (Yepsen et al. 2014; Mitchell in flow in adjacent streams review), carbon storage, quality, (McLaughlin et al. 2014). Remote- and movement (Fenstermacher sensing based studies such as 2011; McDonough et al. in Fenstermacher et al. (2014) provide review), and nutrient dynamics the context necessary to better (Denver et al. 2014; Hunt et al. approximate historical conditions, a 2014) within natural, restored and USDA NRCS Wetland Restoration historical wetlands in the Mid- (657) Practice Standard goal, and Atlantic Region. Indeed, remotely wetland hydrology, a critical factor sensed data greatly adds to wetland in restoration success. insights obtained on the ground and via modeling. CEAP team Fenstermacher et al. (2014) members are currently working to provides insights regarding where better incorporate remotely sensed local soil and hydrologic conditions data into process-based modeling, may be suitable for supporting thus supporting the CEAP National wetland function. These specific Assessment for Cropland and sites are more likely to be well Wetlands. suited for wetland restoration. This restoration information is especially critical considering the fact that on the Delmarva peninsula

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References French, H. M. and M. Demitroff. 2001. Melton, F. A. and W. Scriever. 1933. Cold-Climate Origin of the The Carolina "Bays": are they Bedford, B.L. 1999. Cumulative Enclosed Depressions and meteorite scars? The Journal of effects of wetland landscapes: links Wetlands (`Spungs') of the Pine Geology, 41:52-66. to wetland restoration in the United Barrens, Southern New Jersey, Olivero, A. and M. Zankel. 2000. States and southern Canada. USA. Permafrost and periglacial Delmarva bay density analysis. The Wetlands 19(4): 775-788. processes. 12:337-350. Nature Conservancy. Bennett, S.H. and J.B. Nelson. 1991. Galatowitsch, S. M., and A.G. van der http://gis.tnc.org/data/MapbookWe Distribution and status of Carolina Valk. 1996. Characteristics of bsite/map_page.php?map_id=11. Bays in South Carolina. SC recently restored wetlands in the Pechmann, J. H., D.E. Scott, J.W. Wildlife and Marine Resources prairie pothole region. Wetlands, Gibbons, J.W. and R.D. Semlitsch, Department, Columbia, SC. 16(1):75-83. 1989. Influence of wetland Nongame and Heritage Trust Grant, J. A., M. J. Brooks, and B. E. hydroperiod on diversity and Publication No. 1. Taylor. 1998. New constraints on abundance of metamorphosing Bruland, G.L., M.F. Hanchey, and C.J. the evolution of Carolina Bays juvenile amphibians. Wetlands Richardson. 2003. Effects of from ground-penetrating radar. Ecology and Management, 1(1):3- agriculture and wetland restoration Geomorphology, 22:325-345. 11. on hydrology, soils, and water Hunt, P., J. Miller, T. Ducey, M. Lang, Prouty, W. F. 1952. Carolina Bays and quality of a Carolina Bay complex. A. Szogi, and G. McCarty. 2014. their origin. Geological Society of Wetlands Ecology and Denitrification in Natural, America Bulletin, 63:167-224. Management 11:141-156. Restored, and Converted Wetlands Richardson, C.J., and J.W. Gibbons. Corti, D., S.L. Kohler, and R.E. of the Delmarva Region of the US. 1993. Pocosins, Carolina Bays, and Sparks. 1996. Effects of Ecological Engineering. 71:438- mountain bogs. In S. G. Boyce, et hydroperiod and predation on a 447. al., (eds.) Biodiversity of the Mississippi River floodplain Lang, M. and McCarty, G. 2014. Light Southeastern United States: invertebrate community. Detection and Ranging for lowland terrestrial communities. Oecologia, 109(1):154-165. Improved Mapping of Wetland ed. John Wiley, New York. Denver, J., S. Ator, M. Lang, T. Resources. USDA NRCS Savage, H., Jr. 1982. The mysterious Fisher, A. Gustafson, R. Fox, J. Conservation Effects Assessment Carolina Bays. University of South Clune, and G. McCarty, G. 2014. Project Science Note. September Carolina Press, Columbia, SC. Nitrate Fate and Transport through 2014:1-7. Sharitz, R. R. 2003. Carolina Bay Current and Former Depressional Lang, M., G. McCarty, R. Oesterling, wetlands: Unique habitats of the Wetlands in an Agricultural and I.-Y Yeo. 2012. Topographic southeastern United States. Landscape, Choptank Watershed, Metrics for Improved Mapping of Wetlands, 23:550-562. Maryland, USA. Journal of Soil Forested Wetlands. Wetlands. Vol. Sharitz, R. R. and J. W. Gibbons. and Water Conservation. Vol. 33:141-155. 1982. The ecology of southeastern 69:1-16. McCarty, G., C. Hapeman, C. Rice, D. shrub bogs (pocosins) and Carolina Denver, J.M., S.W. Ator, L.M. Hively, L. McConnell, A. Sadeghi, Bays: a community profile. Debrewer, M.J. Ferrari, J.R. M. Lang, D. Whitall, K. Bialek, FWS/OBS-82/04. US Fish and Barbaro, T.C. Hancock, Tracy C., and P. Downey. 2014. Metolachlor Wildlife Service, Division of M.J. Brayton, and M. R. Nardi. Metabolite (MESA) Reveals Biological Services, Washington, 2004. Water quality in the Agricultural Nitrate-N Fate and DC. Delmarva Peninsula, Delaware, Transport in Choptank River Simenstad, C., D. Reed, and M. Ford. Maryland, and Virginia, 1999– Watershed. Science of the Total 2006. When is restoration not?: 2001: Reston, Va., U.S. Geological Environment. Vol. 473-474: 473- Incorporating landscape-scale Survey Circular 1228, 36 pp. 482. processes to restore self-sustaining Fenstermacher, D. 2011. Carbon McDonough, O., M. Lang, and M. ecosystems in coastal wetland Storage and Potential Carbon Palmer. 2014. The Impact of restoration. Ecological Sequestration in Depressional Agricultural Wetland Restoration Engineering, 26(1):27-39. Wetlands of the Mid-Atlantic on Surface Hydrologic Snodgrass, J. W., M.J. Komoroski, Region. Thesis submitted to the Connectivity Between A.L. Bryan, and J. Burger. 2000. University of Maryland Depressional Wetlands and Relationships among isolated Department of Environmental Adjacent Streams. Wetlands. doi wetland size, hydroperiod, and Science and Technology. 10.1007/s13157-014-0591-5. amphibian species richness: Fenstermacher, D., M. Rabenhorst, M. McLaughlin, D., D. Kaplan, and M. implications for wetland Lang, G. McCarty, and B. Cohen. 2014. A significant nexus: regulations. Conservation Biology, Needelman. 2014. Distribution, Geographically isolated wetlands 14(2):414-419. Morphometry, and Land Use of influence landscape hydrology. Stolt, M.H., and M.C. Rabenhorst. Delmarva Bays. Wetlands. DOI: Water Resources Research, 50(9): 1987a. Carolina Bays on the 10.1007/s13157-014-0583-5. 7153-7166. eastern shore of Maryland: I. soil 7

characterization and classification. Soil Science Society of America Journal 51:394–398 Stolt, M. H. and M. C. Rabenhorst. The Conservation Effects Assessment 1987b. Carolina Bays on the Project (CEAP) is a multi-agency effort eastern shore of Maryland: II. to build the science base for distribution and origin. Soil conservation. Project findings help to Science Society of America guide USDA conservation policy and Journal, 51:399-405. program development and help farmers Thom, B. G. 1970. Carolina Bays in and ranchers make informed Horry and Marion Counties, South conservation choices. Carolina. Geological Society of America Bulletin, 81:783-813. One of CEAP’s objectives is to quantify Tiner, R. W. 2003. Geographically the environmental benefits of isolated wetlands of the United conservation practices for reporting at States. Wetlands, 23:494-516. the national and regional levels. Because Yepsen, M., A. Baldwin, D. Whigham, wetlands are affected by conservation E. McFarland, M. LaForgia, and actions taken on a variety of landscapes, M. Lang. 2014. Agricultural the wetlands national assessment Wetland Restorations Achieve complements the national assessments Diverse Native Wetland Plant for cropland, wildlife, and grazing lands. Communities but Differ from The wetlands national assessment works Undisturbed Wetlands. through numerous partnerships to Agriculture, Ecosystems and support relevant assessments and Environment. Vol. 197:11-20. focuses on regional scientific priorities. Zedler, J.B., and J.C. Callaway. 1999. Tracking wetland restoration: do This analysis was conducted by Daniel mitigation sites follow desired Fenstermacher, former UMD graduate trajectories? Restoration Ecology. student; supervised by Dr. Martin 7, 69–73. Rabenhorst, UMD. The Science Note was written by Dr. Megan Lang, UMD, Daniel Fenstermacher; Drs. Martin C. Rabenhorst and Brian Needelman at UMD, and Dr. Greg McCarty, USDA Agricultural Research Service Hydrology and Remote Sensing Lab, Beltsville, MD.

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