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In situ simulation of sea‐level rise impacts on coastal wetlands using a flow‐through mesocosm approach

The impact of sea level rise (SLR) on coastal wetlands is dependent on the net effects of increased inundation and saltwater intrusion. The need for accurate projections of SLR impacts has motivated several experimental mesocosm studies aimed at detailed investigations on wetland biogeochemical cycling. However, the degree with which they accurately reproduce field conditions remains unknown because they have primarily been laboratory based using relatively small sediment volumes (10–200 L) treated over short time periods. As a first step towards addressing these issues, we present a novel mesocosm device and portable methodology for long‐term SLR simulation via in situ saltwater additions to relatively large sediment volumes (approximately 1,000 L). The device (chamber) consists of two interlocking polycarbonate cylinders with an internal diameter of 1.4 m. Each cylinder has holes drilled in the side to facilitate water exchange. The outer cylinder (collar) can be rotated to one of two possible positions. The first position produces alignment of the inner cylinder holes with the collar holes, whereas the second position offsets the holes to eliminate water exchange and contain salt additions (doses). Our device design and dosing scheme produced higher porewater salinities in the sediments of treatment mesocosms relative to control mesocosm sediments. In addition, we observed low incidence of elevated porewater salinity outside of the chamber walls and no measurable salt contamination of control plots. Widespread SLR simulations in a variety of geographical settings, whether with our proposed design or some other design, would likely help reduce some of the general uncertainties regarding the sensitivity of coastal wetlands to SLR and saltwater intrusion.