Backfilling canals to restore wetlands: empirical results in coastal Louisiana

Published source details Turner R.E., Lee J. & Neill C. (1994) Backfilling canals to restore wetlands: empirical results in coastal Louisiana. Wetlands Ecology and Management, 3.
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This study is summarised as evidence for the following.

	Action	Category
	Plug/dam canals or trenches: brackish/salt marshes Action Link
	Backfill canals or trenches: brackish/salt marshes Action Link

Plug/dam canals or trenches: brackish/salt marshes

A replicated, site comparison study in 1990 of 23 backfilled canals predominantly in brackish and saline marshes in Louisiana, USA (Turner et al. 1994) found that plugging had no significant effect on marsh vegetation coverage alongside the canals. After 6–11 years, coverage of emergent marsh vegetation on former spoil areas alongside canals did not significantly differ between plugged canals and open canals. However, there was a trend towards lower coverage alongside plugged than open canals. Methods: In 1990, aerial photographs were taken of 23 canals. All canals had been backfilled with adjacent spoil between 1979 and 1984. The mouths of some canals (number not reported) had also been plugged with earth or seashell dams at one end, to maintain water levels and reduce saltwater inputs. The area of the former spoil heaps covered by marsh vegetation was determined from the photographs. This study selected canals from the same master set of 33 used in (1). The study does not separate results for freshwater, brackish and saline marshes, but most canals (approximately 80%) were in brackish or saline marshes.

(Summarised by: Nigel Taylor)
Backfill canals or trenches: brackish/salt marshes

A replicated study in 1983–1990 of 30 backfilled canals predominantly in brackish and saline marshes in Louisiana, USA (Turner et al. 1994) reported that they developed some coverage of marsh vegetation, but mainly alongside rather than within the channels. Between 6 and 60 months after backfilling, coverage of emergent marsh vegetation was 47% on former spoil areas alongside the channels, but only 5% within the channels. Upland vegetation occurred alongside the channels, with 28% coverage, in patches where spoil had not been completely levelled. Similar coverage was recorded 6–11 years after backfilling (marsh alongside canal: 51%; marsh within canal: 5%; upland vegetation alongside canal: 26%; statistical significance of changes not assessed). Methods: The area of marsh vegetation alongside and within 30 backfilled canals was estimated from aerial photographs taken in 1983, 1984 and 1990. This study selected canals from the same master set of 33 used in (1) and (4). The canals were originally dug by the oil and gas industry. They were backfilled with adjacent spoil between 1979 and 1984, reducing the water depth. Some canals were also plugged at one end with earth or shell dams. The study does not separate results for freshwater, brackish and saline marshes, but most canals (approximately 80%) were in brackish or saline marshes.

(Summarised by: Nigel Taylor)