Mapping intertidal eelgrass (Zostera marina L.) in three coastal estuaries of the Pacific Northwest USA using false colour near-infrared aerial photography

Abstract

This study describes a hybrid technique of digitally classifying aerial photography used for mapping the intertidal habitat of eelgrass (Zostera marina L.) in Pacific Northwest USA estuaries. The large tidal range (2–3 m) in this region exposes most of this seagrass community at low tide, permitting the use of false colour near-infrared film that provides good contrast in imaging vegetated intertidal habitats. Three Oregon coastal estuaries in the USA were surveyed in 2004 or 2005 at photoscales of 1:10 000 or 1:20 000. Spatial resolution was 0.25 m and the minimum mapping unit was 2.5 × 2.5 m. Spatial accuracy was within 1.5 m. Comparison of the image classification and ground survey results yielded overall classification accuracies of 83% to 97%. This appears to be an effective technique for mapping intertidal eelgrass distributions in turbid coastal estuaries with large tidal ranges.

Acknowledgements

The aerial photography was conducted by Bergman Photographic Services, Inc. (Portland, OR). The DTM of Yaquina estuary used in the desktop orthorectification of the 2004 aerial photographs was developed by Photogrammetric Digital Services (Eugene, OR) from our 1998 aerial photosurvey. Dr Stephen Rumrill and Dr Derek Sowers (South Slough National Estuarine Research Reserve, Charleston, OR) provided assistance in the ground survey of Coos estuary. The ground survey in Yaquina estuary was conducted with the assistance of Dynamac, Inc. (Newport, OR). Technical advice was provided by Dr Thomas Mumford and Helen Berry (Department of Natural Resources, Olympia, WA), Dr William Pickles (Lawrence Livermore National Laboratory, CA), Professor Donald Potts (University of California, Santa Cruz), Dr Ralph Garono (Earth Design Consultants, Inc., Corvallis, OR), Jeff Weber (Department of Land Conservation and Development, Portland, OR), Jeff Robinson (Humboldt Bay Harbor, Recreation and Conservation District, CA) and Dr Denis White and Dr Mary Kentula (US EPA Western Ecology Division, Corvallis, OR). We also thank Bryan Coleman (CSC, Inc., Newport, OR) and Dr Henry Lee II, Christina Folger, Chris Mochon-Collura and Chris Eide (US EPA Pacific Coastal Ecology Branch, Newport, OR) for their assistance.