Mapping Soil Pore Water Salinity of Tidal Marsh Habitats Using Electromagnetic Induction in Great Bay Estuary, USA

Abstract

Electromagnetic induction was used to measure apparent conductivity of soil pore water within 15 oligohaline to polyhaline tidal marshes of the Great Bay Estuary in New Hampshire, USA. The instrument was linked to a differential global positioning system via a hand-held field computer to geo-reference data. Apparent conductivity was converted to salinity using a regression derived from field data, and mapped to illustrate spatial salinity gradients throughout the marshes. Plant communities occurring at the study sites included native low marsh, high marsh, and brackish tidal riverbank marsh, as well as communities dominated by native and non-native common reed, Phragmites australis. Results revealed mean salinity values were significantly different between each of the community categories sampled within the Estuary. Due to management concerns over expansion of Phragmites within the Estuary, we mapped the salinity range for this community and provided graphic and numerical estimates of potential Phragmites habitat based on salinity alone (26% of the total acreage surveyed). Electromagnetic induction is an efficient tool for rapid reconnaissance of apparent conductivity and salinity gradients in tidal marsh soils that can be superimposed on aerial imagery to estimate suitable habitat for restoration or invasive control based on salinity ranges.