Acidification of coastal zone subaqueous soils (coastal acidification) is a complex process driven by a range of anthropogenic activities such as increased CO₂ concentrations, nutrient enrichment, hypoxia/anoxia, and anaerobic sulfide mineralization. Understanding these complexities is critical to developing an understanding of the impact of coastal acidification on our natural resources. We examined coastal acidity of the water column and subaqueous soils within two coastal lagoons and two embayments in Rhode Island. We examined contrasting soils within each estuary to determine whether coastal acidity was of concern for biological development (oysters) and if it varied among soil types. Our data clearly show that  the water column and substrate vary significantly among soil types within both lagoons and embayments. At some locations pH values were at or below 7.6, suggesting that at these locations calcifying organisms may be stressed or undergoing dissolution because of coastal acidification.