A RELATIVE ELEVATION MODEL FOR A SUBSIDING COASTAL FORESTED WETLAND RECEIVING WASTE-WATER EFFLUENT

This paper describes a wetland elevation/sediment accretion model for a subsiding forested wetland located within the coastal zone of Louisi ana, USA. We designed the model to determine if the addition of second arily treated municipal wastewater to the wetland could stimulate orga nic matter production and deposition to the point that sediment accret ion would balance relative sea level rise (deep subsidence plus eustat ic sea level rise (ESLR)). We also used the model to simulate the effe ct of predicted increases in ESLR on wetland stability and to determin e the amount of additional mineral sediment that would be required to compensate for relative sea level rise. The model utilizes a cohort ap proach to simulate sediment dynamics (organic and mineral matter accre tion, decomposition, compaction, and below-ground productivity) and yi elds total sediment height as an output. Sediment height is balanced w ith ESLR and deep subsidence, both forcing functions, to calculate wet land elevation relative to mean water levels. The model also simulates primary production (roots, leaves, wood, and floating aquatic vegetat ion) and mineral matter deposition, both of which are feedback functio ns of elevation. Simulated wetland elevation was more sensitive to the uncertainty surrounding estimates of deep subsidence and future ESLR rates than in other processes that affect wetland elevation and could be influenced by wastewater (i.e. rates of decomposition and primary p roductivity). The model projected that, although the addition of waste water effluent would increase long term accretion rates from 0.35 to 0 .46 cm year(-1), it would not be enough to offset the current rate of relative sea level rise. A series of mineral input simulations reveale d that, given no increase in ESLR rates, an additional 3000 g m(-2) ye ar(-1) of mineral sediments would be required to maintain a stable ele vation. (C) 1998 Elsevier Science B.V. All rights reserved.