Comparing automated classification and digitization approaches to detect change in eelgrass bed extent during restoration of a large river delta

Northwest Science
By: , and 

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Abstract

Native eelgrass (Zostera marina) is an important contributor to ecosystem services that supplies cover for juvenile fish, supports a variety of invertebrate prey resources for fish and waterbirds, provides substrate for herring roe consumed by numerous fish and birds, helps stabilize sediment, and sequesters organic carbon. Seagrasses are in decline globally, and monitoring changes in their growth and extent is increasingly valuable to determine impacts from large-scale estuarine restoration and inform blue carbon mapping initiatives. Thus, we examined the efficacy of two remote sensing mapping methods with high-resolution (0.5 m pixel size) color near infrared imagery with ground validation to assess change following major tidal marsh restoration. Automated classification of false color aerial imagery and digitized polygons documented a slight decline in eelgrass area directly after restoration followed by an increase two years later. Classification of sparse and low to medium density eelgrass was confounded in areas with algal cover, however large dense patches of eelgrass were well delineated. Automated classification of aerial imagery from unsupervised and supervised methods provided reasonable accuracies of 73% and hand-digitizing polygons from the same imagery yielded similar results. Visual clues for hand digitizing from the high-resolution imagery provided as reliable a map of dense eelgrass extent as automated image classification. We found that automated classification had no advantages over manual digitization particularly because of the limitations of detecting eelgrass with only three bands of imagery and near infrared.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Comparing automated classification and digitization approaches to detect change in eelgrass bed extent during restoration of a large river delta
Series title Northwest Science
DOI 10.3955/046.091.0307
Volume 91
Issue 3
Year Published 2017
Language English
Publisher Northwest Scientific Association
Contributing office(s) Western Ecological Research Center
Description 11 p.
First page 272
Last page 282
Country United States
State Washington
Other Geospatial Nisqually Delta, Puget Sound