Remote Sensing Tools for Assessing Wetland Condition and Soil Moisture Status in Agricultural Landscapes

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1 Remote Sensing Tools for Assessing Wetland Condition and Soil Moisture Status in Agricultural Landscapes Cathleen J. Hapeman US Department of Agriculture Agricultural Research Service

2 Importance of Wetlands Provide valuable ecosystem services to society Pollutant regulation Natural hazard mitigation Climate regulation Food and fiber Biodiversity Aesthetics and recreation

3 Wetland Loss However, over 60% of historic wetlands lost in the Chesapeake Bay watershed Existing wetlands are at high risk for future loss and most CB wetlands are forested Forested wetlands continue to sustain high levels of loss Risk Based on Historic Population/Construction Data and 1980s NWI Wetland Density Credit: US FWS NWI: A Strategy for the 21 st Century

4 Conserving Wetlands and Maximizing Their Benefits Therefore, tools are needed to map wetlands and monitor key wetland functional drivers: Hydroperiod Surface water flow pathways This will allow us to conserve existing wetlands, restore wetlands successfully, and promote wetland ecosystem services

5 Assessing Restoration Success USDA has spent billions of dollars to restore wetlands But it is often difficult to assess restoration effectiveness in forests, especially in areas with saturated soil conditions This information is needed to demonstrate restoration effectiveness, to aid in adaptive management, and to ensure future allocation of funds Road flooded (lower photo) subsequent to the plugging of a ditch (upper photo)

6 Key Hydrologic Drivers Hydroperiod Duration and frequency of inundation and soil saturation at a specified depth The most important abiotic factor controlling wetland extent and function Flow Pathways Where water is coming from and where it is going Governs interaction of landscape components Water quality and biotic dispersal

7 Remote Detection of Hydrology Aerial photographs were traditionally used to map wetlands, hydroperiod, and flow pathways, but their utility is limited This is especially true in forested areas Forested wetlands are the most common type of wetland in the US Three recently-available remote sensing technologies which improve our ability to characterize wetlands and estimate wetland functions Synthetic Aperture Radar (SAR), LiDAR, and Landsat time series

8 Synthetic Aperture Radar (SAR) (Jensen, J. 2000; Remote Sensing of the Environment) Active sensors; transmit microwave energy Very sensitive to inundation and soil moisture Energy can be transmitted through the plant canopy Hydroperiod can be detected below a plant canopy Collects data regardless of solar illumination and weather (e.g., rain)

9 SAR Map of Wetland Restoration Effects SAR was used to map inundation and soil moisture change, as well as wetland acreage and functional gains resulting primarily from wetland restoration % change Hydroperiod Post-Pre/Pre Wetland Restoration Percent Change with Restoration

10 Wetland Acreage Gains Post-Restoration Wetland Gains ~30% increase in forested wetland area with restoration

11 Amphibian Habitat Gains Post Restoration 13 times the habitat was available post restoration

12 Carbon accumulates in areas of low relief After LiDAR Before LiDAR Why LiDAR DEMs? LiDAR makes analysis of relatively small but critical variations in topography possible. Subtle variations in topography often lead to significant variations in ecosystem function.

13 Delmarva Bay Delmarva Bay Darker circular areas are Delmarva bays a type of depressional wetland

14 To restore and replace what has been lost need to know what was lost 17,000 Delmarva are on the Delmarva Peninsula, earlier estimates were 1,500 2,500 ~75% of bays are found on cropland or mixed cropland/natural land cover Size of bays increased with decreasing latitude, possibly due to a reduction in winddriven erosion in northernmost bays Fenstermacher, D., Rabenhorst, M., Lang, M., and McCarty, G., and Needelman, B. (2014) Distribution, Morphometry, and Land Use of Delmarva Bays. Wetlands. Vol. 34(6):

15 Wetland-Stream Connectivity Different types of connectivity, but surface water connectivity is most commonly assessed W-S connections influence downstream condition and function. Many groups have sought to estimate W-S connectivity. organic rich wetland water Outlet of Natural Wetland into Agricultural Ditch

16 LiDAR for Enhanced Assessment of Connectivity LiDAR based maps demonstrated ~15% greater connectivity between wetlands and streams than high resolution National Hydrography Dataset (NHD) High resolution NHD only represented ~66% of all perennial and intermittent stream length LiDAR stream maps are more accurate and complete than NHD and identify significantly more wetlands as connected to streams via surface water Lang, M., McCarty, G., McDonough, O., Oesterling, R., and Wilen, W. (2012) Enhanced Detection of Wetland-Stream Connectivity Using LiDAR. Wetlands. Vol. 32:

17 Landsat Time-Series Images Landsat, a series of moderate resolution multispectral satellite sensors, provides a 40+ year historic record that is continued today Landsat-8 (launched 2013) Invaluable historic record Image processing advancements have made mapping of hydroperiod possible in multiple wetland types, including forested wetlands

18 Percent Inundation Soil organic carbon > 3 times higher in wetlands with longer hydroperiod

19 Hydroperiod Restored Wetland Historical Wetland MD Study Site SIP Value (%) DE

20 Hydroperiod Restored Wetland MD Study Site SIP Value (%) DE

21 Hydroperiod Map Applications Remotely sensed images can best support positive environmental outcomes when combined with field data within a decision support system Parameterize, calibrate and validate process-based water quality models (e.g., Soil and Water Assessment Tool) Create wetland functional classifications to augment traditional wetland status and trends (i.e., Natural Resources Inventory) surveys

22 Future Prospects Data Availability Price Hardware Capabilities Software Capabilities Development of Methods = Increased Use of SAR, LiDAR, and Landsat Time Series Data to Aid Natural Resource Management

23 The strong potential of remotely-sensed data for improving environmental management paired with the rapid increase in availability of such datasets highlights the critical role that this information source will play in future conservation efforts. For further information please contact ( ) This work was supported by the USDA Conservation Effects Assessment Project and the US Environmental Protection Agency.