Rapid, Episodic Change In Gulf Coast Estuaries during the Holocene

A study of five Gulf Coast estuaries (Calcasieu Lake, Sabine Lake, Galveston Bay, Matagorda Bay and Corpus Christi Bay) was aimed at examining their response to changes in the rate of sea-level rise and climate changes during the Holocene, changes that were similar in magnitude to those that could occur by the end of this century. Our results show that estuarine response has been one of rapid landward shifts in bayhead deltas, at times greater than 10 km/century. Flooding events were most pronounced during the early Holocene, when the average rate of sea-level rise was 4.0 mm/yr. Two flooding events at ~9800 to ~9500 cal yrs BP and at ~8400 to ~8000 cal yrs BP occurred contemporaneously in all estuaries and are attributed to rapid, episodic sea-level rise. More localized flooding events are attributed to flooding of low gradient fluvial terraces and to a combination of rapid sea-level rise and climate variability that resulted in reductions in sediment supply to some estuaries. Even during the late Holocene, when the average rate of sea-level rise decreased to between 1.5 and 0.7 mm/yr, flooding events continued to occur, most likely in response to climate change and reduced sediment supply.

The changes that occurred during the early Holocene provide a sobering perspective on changes that could occur by the end of this century. The problem is exacerbated by human influence, which has resulted in increased rates of coastal subsidence and alteration of sediment input to these estuaries.