An Assessment of Ecosystem Health of the Wetlands in the Upper Lake Pontchartrain Basin

G. Shaffer

Project Overview

The swamps surrounding Lake Maurepas are severely stressed. During spring of 2000, a large study was launched in the baldcypress/tupelogum swamps of Lake Maurepas to determine the feasibility of diverting freshwater, sediments, and associated nutrients from the Mississippi River into these swamps via a proposed diversion at Hope Canal. This study was created to assess the health of the Maurepas swamps and experimentally mimic diversion conditions in selected plots by measuring both plant and tree response.

This portion of the study focuses on the response of herbaceous plants to the addition of nutrients under pressure by large herbivores such as white-tailed deer and nutria, and without that pressure (by erecting cages around some plots). We mimicked diversion scenarios by fertilizing caged and un-caged plots at dosages that would mimic a small diversion opened only during spring, a small diversion opened throughout the growing season, and an intermediate diversion opened only during spring. We compared these treatments with unfertilized caged and un-caged control plots and measured changes in vegetative cover and primary production.

In general, the intermediate and small diversions opened throughout the growing season produce significantly greater vegetation than a small diversion opened only through the spring or no diversion. When uncaged, the standing crop stayed at steadily low levels, implicating extensive browsing. It appears that the low herbaceous production for the southern Maurepas swamps as a whole is primarily due to nutrient limitation.

Following this study, a subsequent study began regarding restoration of the Maurepas system.