Subaqueous Soils and Coastal Acidification: A Hydropedology Perspective with Implications for Calcifying Organisms

Abstract

In the coastal zone, biological and biogeochemical processes, influenced by anthropogenic inputs, drive pH variability and contribute to coastal acidification. Spatial patterns of these processes across coastal estuaries are unknown. In this study, we used a hydropedological approach to assess the spatial variability of coastal acidification within two coastal lagoons and embayments in Rhode Island by measuring oyster shell dissolution, pH within the water column, and pore water pH within the upper 5 cm of the underlying subaqueous soils. Sampling and monitoring sites were stratified based on submerged soil-landscape types mapped at the Great Group level as Haplowassents, Sulfiwassents, and Psammowassents. We found that pore water pH varied significantly among soils and with depth. Median pore water pH was significantly greater in sandy, low organic matter content Psammowassents (7.97) than the finer textured, higher soil organic matter content Sulfiwassents (7.35), and the Haplowassents (6.57) that receive groundwater discharge from the surrounding subaerial soils. Juvenile calcifying organisms can experience acidic stress at pH values below 7.6; thus, current pH values within the upper few centimeters of Sulfiwassents and Haplowassents may be low enough to impact recently set juvenile calcifying organisms inhabiting these soils. Consequently, mean shell loss during a 4-wk period was significantly greater in the Sulfiwassents (1.54) than the Psammowassents (0.96%), with the greatest shell loss (18.62%) in one of our Haplowassent sites with groundwater discharge. Our research suggests that measures of pore water pH and shell dissolution may be helpful in developing soil interpretations regarding the effects of coastal acidification on calcifying organisms.