Modeling of Sea-Level Rise and Deforestation in Submerging Coastal Ultisols of Chesapeake Bay

Global warming and the predicted adverse environmental implications in coastal areas haw prompted the use of a quantitative pedological approach to model the history of relative sea-level rise and the subsequent lateral migration of marshes (deforestation) during the pedogenic transformation of Ultisols (forest soils) to Histosols (marsh soils). The modeling was based on the transgressing soil-landscape concept and data collected from sampling units along two marsh transects in Dorchester County, Maryland. In low-relief submerging environments, coastal marshes accrete vertically and migrate laterally over adjacent Ultisols to keep pace with sea-level rise. The marsh substrate is organic in nature overlying what once were upland forest soils. The history of relative sea-level rise was a two-step linear function illustrating acceleration in the last two centuries. During the last 150 yr, the Pb-210-based rare of relative sea-level rise averaged 2.4 +/- 0.7 min yr(-1). Before the last few hundred years, the long-term C-14-based rate of relative sea-level rise was 0.82 +/- 0.15 mm yr(-1). The race of lateral migration of coastal marshes (deforestation) showed similar acceleration following the history of relative sea-level rise. During the last 150 yr, the average rate of lateral migration of marshes (deforestation) ranged from 3.51 +/- 2.0 to 6.78 +/- 7.4 m yr(-1). Before the last 150 yr, the average long-term rate of lateral migration of marshes (deforestation) ranged between 0.18 +/- 0.07 and 1.27 +/- 1.2 m yr(-1). Within a given region where sea-level rise and tidal range remain constant, the rate of lateral migration of marshes is a function of site characteristics and the slope of the adjacent uplands. The predicted rate of lateral migration of marshes in the next century ranges from 3.2 to 33 in yr(-1), averaging 14 +/- 11 in yr(-1). Assuming that the present rate of relative sea-level rise remains constant, the time needed to complete the pedogenic transformation of Ultisols to Histosols is 180 +/- 35 yr. The most conservative future scenario of sea-level rise has reduced this time by 63%. The projected sequestration of C, total N, and pyrite in the newly formed coastal marshes during the next 100 yr average 231 +/- 124, 11.7 +/- 6.30, and 6.63 +/- 3.57 Mg ha(-1), respectively. These projections are half the nutrient sequestration potential of existing coastal marshes.