RELATIONSHIP BETWEEN VEGETATION AND SOIL FORMATION IN A RAPIDLY SUBMERGING COASTAL MARSH

Purposes of this study were to determine the relative importance of organic matter and mineral matter to marsh vertical accretion and to determine if insufficient vertical accretion was a factor in land loss in a Terrebonne Basin (Louisiana, USA) marsh. Cs-137 dating indicated that vertical accretion (0.98 cm yr-1) was extremely rapid relative to other marshes, but insufficient to counter submergence (1.38 cm yr-1). Mineral and organic matter accumulation were similar to that in other marshes. Variation in vertical accretion was accounted for by variation in organic matter accumulation rather than mineral matter accumulation; thus, inadequate vertical accretion resulted from inadequate organic matter accumulation. Inadequate organic matter accumulation (593 g m-2 yr-1) was attributed to inadequate plant production resulting primarily from flooding stresses; inadequate mineral matter accumulation (1629 g m-2 yr-1) was attributed to inadequate mineral matter availability. These data suggest that this marsh is threatened by a positive feedback loop of plant flooding stress and inadequate vertical accretion. Inadequate plant growth limits vertical accretion, which further increases flooding and decreases plant production. Thus plant production, which has previously been considered only in the context of trophic dynamics, also partly determines the degree of submergence some coastal and estuarine marshes will tolerate.