Remote Sensing and Spatial Analysis of Watershed and Estuarine Processes for Conservation Planning in Elkhorn Slough, Monterey County, California

Abstract

The Elkhorn Slough watershed, located on the coast of Monterey Bay in Central California, is a significant Pacific Coast estuarine system. It has become a nexus of remote sensing research due to partnerships with multiple nearby institutions, and innovative approaches in the research area have addressed several management issues in the watershed. Historical ecological research with archival aerial photographs identified significant trends in marshland conversion to other habitat types, mainly from hydrological modifications but also from off-farm sedimentation. Research addressing nutrient and sediment runoff demonstrate the potential to correlate estuarine disturbance and response to watershed inputs or properties. Spectral indices from HyMap hyperspectral imaging of salt marsh vegetation were correlated with water nutrient enrichment. Also the current extent of sedimentation in the salt marsh was linked to historical land cover and physical watershed variables. Repeat multibeam bathymetry surveys identify regions of the slough with high erosion rates from tidal scour and point to causes of salt marsh conversion. Despite challenges associated with these applications, remote sensing and GIS analyses, especially salt marsh vegetation change detection and bathymetric change detection, inform current restoration planning efforts described in the Elkhorn Slough Tidal Wetland Strategic Plan. Multiple committees and working groups have formed a consensus on the need to address the problem of tidal scour partly due to the availability of high quality, high resolution spatial data. In addition GIS-based watershed management continues to improve estuarine conditions, as agencies, land trusts and private landowners have reduced nutrient and sediment inputs through restoration and erosion control.