Soil Phosphorus Characteristics of Created and Natural Wetlands in the Atchafalaya Delta, LA

Abstract

Quantitative comparisons of created and natural wetlands are typically confounded by differences in wetland age, with created wetlands generally younger than their natural counterparts. Observed differences may be attributed to either age differences or to the inability to create wetland functions. The objective of this study was to determine if created dredge-material wetlands and comparably aged wetlands formed by natural deposition in the Atchafalaya Delta have similar sediment phosphorus compositions. Sediment cores were collected on five occasions from elevational strata (low, mid and high) in created and natural wetlands belonging to three age classes (<1–3 years old, 5–10 years old, and 15–20 years old). Sediment phosphorus fractions were determined by sequential chemical extraction.When compared to similarly aged natural wetland sediments: (1) old, created wetland sediments had similar mean phosphorus contents at mid and low elevations, but had lower mean contents at high elevations; and (2) intermediate aged, created wetland sediments had greater phosphorus contents on a per weight basis, but mean contents were lower on a per area basis. At all elevations, the young created wetland had lower phosphorus contents than all other wetlands.Results suggest that dredge sediment used to form the created wetlands in the Atchafalaya Delta is lower in phosphorus than the suspended sediment which forms the natural wetlands. Also, the created wetlands develop natural phosphorus characteristics through time due to sediment deposition during river flooding. In the Atchafalaya Delta, if created wetlands provide the natural flooding cycle, then they begin to develop natural phosphorus characteristics between 10 and 20 years after formation.