Effects of pulsed riverine versus non-pulsed wastewater inputs of freshwater on plant community structure in a semi-arid salt marsh

Published source details Forbes M.G., Alexander H.D. & Dunton K.H. (2008) Effects of pulsed riverine versus non-pulsed wastewater inputs of freshwater on plant community structure in a semi-arid salt marsh. Wetlands, 28, 984-994.
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This study is summarised as evidence for the following.

	Action	Category
	Actively manage water level: brackish/salt marshes Action Link

Actively manage water level: brackish/salt marshes

A before-and-after, site comparison study in 1996–2006 of four brackish/salt marshes in a delta in Texas, USA (Forbes et al. 2008) reported that adding treated wastewater to compensate for reduced natural freshwater inputs changed the overall plant community composition, and increased plant species richness. Unless specified, statistical significance was not assessed. Over the first four years after intervention, the overall plant community composition changed in the marsh directly affected by water additions, but was relatively stable in downstream marshes (data reported as a graphical analysis). In the marsh directly receiving water additions, sea marigold Borrichia frutescens cover significantly increased (before: <1–5%; after four years: 55%) whilst pickleweed Salicornia virginica cover significantly decreased (before: 83–88%; after: 34%). Meanwhile, in the downstream marshes, sea marigold cover did not significantly increase (before: 7–44%; after: 5–26%) whilst pickleweed cover did not significantly decrease (before: 28–54%; after: 28–56%). Plant species richness increased in the marsh directly receiving water additions (before: 1.6–2.1 species/1.25 m²; after four years: 3.4 species/1.25 m²) – but only to a similar level as the downstream marshes (before: 1.6–4.3; after four years: 3.1–4.4). Methods: Every day from October 1998, treated wastewater was discharged into one marsh in the Nueces Delta (via holding ponds), to compensate for reduced freshwater inputs and hypersalinity linked to upstream dams. Three downstream marshes, less affected by the wastewater inputs, provided comparisons. Plant species and their cover were surveyed before (June 1996–November 1997) and after (spring 1999–2002) water additions, along 11 transects/marsh/survey.

(Summarised by: Nigel Taylor)