Tomales Bay Watershed Wetlands Mapping and Assessment Project: Final Report

Parsons, Lorraine; Donovan, Chelsea; Ryan, Amelia

Brief Description: This is the Final Report of the Tomales Bay watershed Wetlands MApping and Assessment Project. Full Description: Beginning in 2000, the Seashore initiated an enhanced wetlands mapping project with funding from the NPS’s Water Resources Division and the NPS’s Inventory & Monitoring Program. During phase one of the project, an accuracy assessment of existing USFWS National Wetlands Inventory Data (NWI) was conducted. Seashore staff reviewed the NWI map, looking for errors of omission in the NWI GIS data using the same Minimum Mapping Unit (MMU) and other criteria as was used by the NWI photo interpreters. Based on field evaluation of wetland vegetation polygons from a recent vegetation map and a reinterpretation of 1982 1:58000 color IR aerial photographs, the Seashore determined that at least 53 percent of the wetlands in the study area were not delineated on the NWI data. During phase two of the project on 2001, the Seashore started to work on identifying high priority areas within the park for wetlands inventory. These high priority subwatersheds or systems consisted of areas that either have a high potential for degradation because of land use practices such as ranching and/or that support important biological resources such as special status plants and wildlife species. For example, Abbot’s Lagoon, which has dairy and beef cattle grazing in portions of the watershed, supports several special status species populations, including Sonoma alopecurus (Alopecurus aequalis var. sonomensis). As part of phase two, a detailed inventory of wetlands in the 3,750-acre Abbotts Lagoon watershed was conducted, as well as an inventory of some of the wetlands in the Seashore’s pastoral or beef and dairy cattle zones. Using GPS and heads-up digitizing, field crews mapped, classified, and conducted a detailed botanical inventory of all the wetlands in these subwatersheds. More than 911 acres within 230 wetlands units (polygons) were inventoried and mapped.