Evaluating the effects of land-use change and future climate change on vulnerability of coastal landscapes to saltwater intrusion

Abinash Bhattachan,Marcelo Ardón,Steven M Anderson,Ryan E Emanuel,Matthew G Stillwagon,Justin P Wright,Emily S Bernhardt,Emily A Ury,Todd K Bendor,Donald R Zak,Julian D Olden

doi:10.1525/elementa.316

Abstract

The exposure of freshwater-dependent coastal ecosystems to saltwater is a present-day impact of climate and land-use changes in many coastal regions, with the potential to harm freshwater and terrestrial biota, alter biogeochemical cycles and reduce agricultural yields. Land-use activities associated with artificial drainage infrastructure (canals, ditches, and drains) could exacerbate saltwater exposure. However, studies assessing the effects of artificial drainage on the vulnerability of coastal landscapes to saltwater exposure are lacking. We examined the extent to which artificial drainage infrastructure has altered the potential for saltwater intrusion in the coastal plain of eastern North Carolina. Regional spatial analyses demonstrate that artificial drainages not only lower the overall elevation in coastal landscapes, but they also alter the routing and concentration of hydrological flows. Together, these factors have the potential to increase the total proportion of the landscape vulnerable to saltwater intrusion, not only in areas adjacent to drainage infrastructure but also in places where no artificial drainages exist due to large scale effects of flow rerouting. Among all land cover types in eastern North Carolina, wetlands are most vulnerable to saltwater exposure. Droughts and coastal storms associated with climate change potentially exacerbate vulnerability to saltwater facilitated by artificial drainage.

Highlights

Global sea level is rising, but the consequences of sea level rise for freshwater dependent ecosystems depends on topography, hydrology and land use among other factors (IPCC, 2013)
To identify the pixels that contain artificial drainages, the original digital elevation model (DEM) was processed through a range filter, which generated a raster where each output pixels contained the difference between maximum elevation and m inimum elevation for a 3-by-3 pixel neighborhood around the Bhattachan et al: Evaluating the effects of land-use change and future climate change on vulnerability of coastal landscapes to saltwater intrusion
For all four of the samples, we found that median Saltwater Intrusion Vulnerability Index (SIVI) values are lower (p < 0.01) for the pre-development DEM (North pre: 0.42, North post: 0.60; East pre: 1.84, East post: 2.25; West pre: 0.62, West post: 0.75; South pre: 0.46, South post: 0.65), elevation, flow accumulation and SIVI are significantly different without artificial drainages (Table 2) and that the difference in median SIVI values is highest in East sample

Summary

Introduction

Global sea level is rising, but the consequences of sea level rise for freshwater dependent ecosystems depends on topography, hydrology and land use among other factors (IPCC, 2013). In coastal plain regions, which are characterized by low topographic relief, freshwater-dependent ecosystems such as swamp forests and freshwater marshes are susceptible to saltwater exposure through the landward movement of marine salts via surface or ground water connections (Herbert et al 2015, White and Kaplan 2017). Such exposure is one category of saltwater intrusion, a term often limited to studies of groundwater salinization in coastal regions. The projected increases in drought severity and long-term sea level rise will act in concert with these land-use changes to extend the upstream and upland reach of saltwater with deleterious effects on vegetation, soil biogeochemistry and water quality (e.g., Anderson and Lockaby, 2012; Ardon et al, 2013; Helton et al, 2014)

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