Sediment accumulation rates and relative sea-level rise in lagoons

Abstract

Sediment accumulation and relative sea-level rise rates are compiled for 22 United States lagoons to determine their accretionary status. The lagoons reviewed exhibit a range of accretionary differences (accumulation minus relative sea-level rise rate) varying between two end members: (1) a “surplus” lagoon in which accretion exceeds the relative sea-level rise rate, e.g., by 4.0 mm/yr for short-term (decades) differences in Atchafalaya Bay, and (2) a “deficit” lagoon in which relative sea-level rise exceeds the accretion rate, e.g., by −4.3 mm/yr for short-term differences in Matagorda Bay. The majority of lagoons have a near balance (±1.6 mm/yr) in which the rate of accretion nearly equals relative sea-level rise. The accretionary status reveals a lagoon continuum that emphasizes the way in which lagoons may be examined in a conceptual model as resultants of accretion and submergence. Short-term accretionary differences reflect the direction of long-term (millennia) differences, a trend suggesting that processes of the Holocene are continuing to the present day. Marked accretionary differences, as in Galveston Bay and Mobile Bay, indicate human intervention in the long-term trends. Although lagoons are commonly viewed as sediment sinks destined to be filled in a few millennia, the majority of lagoons reviewed have a near balance of accretion and relative sea-level rise rates and thus can persist.