Search for: All records

Abstract. The natural wetlands of coastal Louisiana areexperiencing rapid subsidence rates averaging 9±1 mm yr−1. Recentmeasurements based on GPS data and CRMS surface elevation tables (SETs) haveshown that most of the subsidence is shallow and occurs in the uppermost 5meters. Sources of subsidence and the origin of their spatial variabilityare strongly debated. Here we use CRMS SETs together with historic maps ofcoastal Louisiana to explore two hypotheses: (i) shallow subsidence is aresult of accommodation created by (long-term) deep subsidence processes andself-weight consolidation, and (ii) changes in marsh hydrology (groundwaterand surface water flows) have led to a recent increase in shallowsubsidence. First, we find that, although self-weight consolidation would result ingenerally high observed shallow subsidence rates, it does not explain therates nor the spatial variability of the CRMS SET data. Second, based onhistoric maps, we find that shallow subsidence rates are significantlyhigher for CRMS sites where shipping canals have reduced their distance tothe marsh edge. This is potentially a result from increased sedimentdeposition, but CRMS data also show altered groundwater levels near themarsh edge. We find some indication that prolonged periods of low watercould have led to increases in effective stresses that explain some of therapid rates of shallow subsidence observed along Louisiana's coastline.