Study

The effect of water level management on the soils and vegetation of two coastal Louisiana marshes

  • Published source details Flynn K.M., Mendelssohn I.A. & Wilsey B.J. (1999) The effect of water level management on the soils and vegetation of two coastal Louisiana marshes. Wetlands Ecology and Management, 7, 193-218.

Actions

This study is summarised as evidence for the following.

Action Category

Actively manage water level: brackish/salt marshes

Action Link
Marsh and Swamp Conservation

Use prescribed fire to maintain or restore disturbance: brackish/salt marshes

Action Link
Marsh and Swamp Conservation
  1. Actively manage water level: brackish/salt marshes

    A replicated, paired, site comparison study in 1989 in two brackish marshes in Louisiana, USA (Flynn et al. 1999) found that actively managing water levels within impoundments had mixed effects on the density and biomass of dominant saltmeadow cordgrass Spartina patens in each marsh. In Fina LaTerre marsh, saltmeadow cordgrass was always significantly less abundant in an impounded area than an area open to natural tidal exchange. This was true for density (impounded: 81; open: 99 stems/m2) and above-ground biomass (impounded: 897; open: 1,357 g/m2). In Rockefeller marsh, saltmeadow cordgrass abundance increased over the growing season. From August to November, it had a similar density in impounded and open marshes (impounded: 94–136 stems/m2; open: 107–117 stems/m2) and greater biomass in impounded marshes (impounded: 1,960–2,750 g/m2; open: 420–1,200 g/m2). The study suggests that the different responses in each marsh could be related to the design of the tidal control structures, distance of each marsh from the coast and soil chemistry. Methods: In 1989, and in each of two brackish marshes, vegetation was surveyed in an impounded area where water levels were managed (drawn down in spring/summer every 1–4 years, then reflooded in autumn/winter) and a nearby unmanaged area open to tidal exchange. Some parts of one marsh were also burned. Throughout the year, vegetation was cut from 0.1-m2 plots (7–19 plots/area/sampling date). Then, live cordgrass plants were counted, dried and weighed.

    (Summarised by: Nigel Taylor)

  2. Use prescribed fire to maintain or restore disturbance: brackish/salt marshes

    A replicated, paired, site comparison study in 1989 in two brackish marshes in Louisiana, USA (Flynn et al. 1999) found that a single prescribed burn typically had no significant effect on density or biomass of saltmeadow cordgrass Spartina patens. Between two and eight months after intervention, burned and unburned plots contained a statistically similar density of cordgrass stems (data not reported) and similar cordgrass biomass in five of six statistically tested comparisons (for which burned: 420–2,750 g/m2; unburned: 680–2,480 g/m2). In the other comparison, cordgrass biomass was lower in burned plots (1,970 g/m2) than in unburned plots (2,650 g/m2). Methods: Vegetation was sampled in May, August, October and November 1989, from 1–10 plots/marsh burned in March and 1–10 plots/marsh not burned that year. It is not clear whether the marshes had been burned before 1989, but burning is a traditional management technique in the area. Each sample involved cutting vegetation from one 0.1-m2 quadrat/plot then counting stems, and drying and weighing cordgrass plants.

    (Summarised by: Nigel Taylor)

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