Using Macrophytes in Urban Stream Rehabilitation: A Cautionary Tale

Abstract

Native macrophytes were transplanted into a small urban stream as part of a rehabilitation program, that also meandered the previously channeled stream, naturalized stream banks, and planted native riparian vegetation. Transplanted macrophytes minimized spread of introduced macrophytes and were viewed beneficially by residents, as was the stream rehabilitation. We transplanted the native macrophyte Myriophyllum triphyllum into five larger streams dominated by exotic macrophytes-some of which were weeded prior to transplanting-to see whether Myriophyllum could prevent regrowth of weeded plants.Transplanted Myriophyllum plants were washed away in two streams, reflecting high shear stresses there. Myriophyllum cover in the other streams decreased as weeded plants regrew. Our attempt at eliminating exotic macrophytes in patches in large streams was unsuccessful. Furthermore, council authorities weeded other experimental sections following complaints from residents of excess macrophyte growth. This problem highlighted conflicting multiple values placed on urban streams by managers and the public. A repeat survey of residents living near the original rehabilitated stream showed that many respondents were now critical of excessive plant growth-both in-stream and riparian. A recurring comment made concerned the apparent lack of maintenance to the stream, giving it an untidy appearance. Difficulties with propagating and transplanting native macrophytes into larger streams, coupled with a negative perception of native vegetation (both in-stream and riparian) if it looks unmanaged, suggest that planting macrophytes or riparian plants as part of urban stream rehabilitation programs may be more problematic than realized.

Experimental Tests of Priority Effects and Light Availability on Relative Performance of Myriophyllum spicatum and Elodea nuttallii Propagules in Artificial Stream Channels

“…The limited number of studies in flowing systems that address the usefulness of native establishment priority as a management technique have yielded mixed results. Native macrophytes can be successfully established in degraded or newly-created stream reaches [ 32 , 44 ], but this process can be difficult and expensive, and new plantings are subject to being washed away [ 45 ]. Establishing natives has been shown to limit the spread of invasive macrophytes in restored stream reaches with little weed pressure [ 21 ], but not in streams where invasive macrophytes have been weeded but not removed entirely [ 45 ].…”

Use of native macrophytes for recovery of the habitat structure and complexity of a lowland stream affected by river engineering works: Implications for management

“…Plantation and propagation techniques have been developed for the rehabilitation of lakes, where recolonization is sought in order to improve water quality and environmental heterogeneity (Qiu et al, ; Zhou et al, ; Paice, Chambers, & Robson, ). Although these techniques have been tested on lowland streams, they have been hardly studied and their success has been questioned (Delmail et al, ; Larned, Suren, Flanagan, Biggs, & Riis, ; Riis et al, ; Suren, ). Due to the fact that aquatic plants constitute a key element of the ecological integrity of these ecosystems, their inclusion in rehabilitation projects is relevant (Riis et al, ).…”

Macrophytes respond to reach‐scale river restorations

“…For example, planting native macrophytes in a restored New Zealand urban stream was followed by enhanced growth and dominance of the native plants over alien plants (Larned et al. 2006), although this technique has not been without difficulty (Suren 2009). In Danish lowland streams, Pedersen, Baattrup‐Pedersen & Madsen (2006) showed that restored reaches had macrophyte communities similar to those of naturally meandering reaches, but their communities were different from those of channelized reaches.…”