Outcomes of submerged macrophyte restoration in a shallow impounded, eutrophic river

Published source details Paice R.L., Chambers J.M. & Robson B.J. (2016) Outcomes of submerged macrophyte restoration in a shallow impounded, eutrophic river. Hydrobiologia, 778, 179-192.
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Summary

Action: Directly plant aquatic plants

A replicated, before-and-after study in 2011–2012 in a turbid, impounded river in Western Australia (Paice et al. 2016) found that all tapegrass Vallisneria australis planted within cages survived for at least two months, that tapegrass cover increased over five months, and that the planted/caged areas were colonized by other macrophytes. After two months, 100% of planted tapegrass individuals were still alive. Tapegrass cover increased significantly over time, from 1% at planting to 87% five months later. The planted/caged areas were also colonized by curled pondweed Potamogeton crispus (two of five cages; 7–22% cover after 2–5 months) and hornwort Ceratophyllum demersum (number of cages not clearly reported; 1–4% cover after 3–5 months). The leaves of both tapegrass and pondweed were colonized by algae (0.3–0.5 g algae/g leaf after four months). Methods: In October 2011, tapegrass was planted within five 48-m² cages, situated on bare sediment in the lower Vasse River. There were 48 plants/cage (30 individual ramets/plant), tied onto eight steel mesh grids. The cages, built of steel mesh (50–75 mm) plus bird netting (20 mm), protected the plants from waterbirds and large fish. Macrophyte basal cover was visually estimated monthly until March 2012. Biomass samples were collected in February 2012 and dried before weighing. Note that the study evaluates the combined effect of planting and installing cages on non-planted vegetation.

Action: Exclude wild vertebrates using physical barriers

A replicated, randomized, controlled, before-and-after study in 2011–2012 in a turbid, impounded river in Western Australia (Paice et al. 2016) reported that excluding waterbirds and large fish (along with planting tapegrass Vallisneria australis) increased the abundance of curled pondweed Potamogeton crispus. Statistical significance was not assessed. The experiment was set up in October 2011. Curled pondweed colonized two of five caged/planted areas, reaching 7–22% cover in these areas between December and March. In contrast, curled pondweed was recorded in only one of five uncaged/unplanted areas and only in December (cover not reported). Methods: The study used ten 48-m² patches of bare sediment in the lower Vasse River. Five random patches were protected with steel cages (50–75 mm mesh) and bird netting (20 mm mesh), and planted with tapegrass (48 plants, tied onto steel mesh grids). The other five patches were neither protected with cages nor planted. Tapegrass basal cover was visually estimated monthly until March 2012. Note that the study evaluates the combined effect of installing cages and planting on non-planted pondweed.

Action: Use fences or barriers to protect planted areas

A replicated, before-and-after study in 2011–2012 in a turbid, impounded river in Western Australia (Paice et al. 2016) reported that protection with cages was essential to the survival of planted macrophytes. Over five months after planting within cages, basal cover of tapegrass Vallisneria australis increased from 1% to 87%. When cages were removed six months after planting, all vegetation was completely destroyed by waterbirds within four days. Methods: In October 2011, five 48-m² patches of bare sediment in the lower Vasse River were protected with steel cages (50–75 mm mesh) and bird netting (20 mm mesh), and planted with tapegrass (48 plants, tied onto steel mesh grids). The cages were removed in March 2012, at the end of the planting experiment.