A comparison of factors controlling sedimentation rates and wetland loss in fluvial–deltaic systems, Texas Gulf coast

Submergence of coastal marshes in areas where rates of relative sea-level rise exceed rates of marsh sedimentation, or vertical accretion, is a global problem that requires detailed examination of the principal processes that establish, maintain, and degrade these biologically productive environments. Using a simple 210Pb-dating model, we measured sedimentation rates in cores from the Trinity, Lavaca–Navidad, and Nueces bayhead fluvial–deltaic systems in Texas where more than 2000 ha of wetlands have been lost since the 1950s. Long-term average rates of fluvial–deltaic aggradation decrease southwestward from 0.514±0.008 cm year−1 in the Trinity, 0.328±0.022 cm year−1 in the Lavaca–Navidad, to 0.262±0.034 cm year−1 in the Nueces. The relative magnitudes of sedimentation and wetland loss correlate with several parameters that define the differing fluvial–deltaic settings, including size of coastal drainage basin, average annual rainfall, suspended sediment load, thickness of Holocene mud in the valley fill, and rates of relative sea-level rise. There is some evidence that upstream reservoirs have reduced wetland sedimentation rates, which are now about one-half the local rates of relative sea-level rise. The extant conditions indicate that fluvial–deltaic marshes in these valleys will continue to be lost as a result of submergence and erosion.