Macrophytes in Urban Stream Rehabilitation: Establishment, Ecological Effects, and Public Perception

Abstract

Efforts to rehabilitate degraded urban streams generally focus on improving physical habitat and rarely include reestablishing biota such as macrophytes. Our objectives in this study were to propagate and transplant native macrophytes into a South Island, New Zealand, urban stream undergoing rehabilitation, assess macrophyte survival and growth, and determine whether native macrophytes suppress non-native macrophytes and/or enhance stream invertebrate communities. Effects of native macrophytes on invertebrates and non-native macrophytes were assessed after transplanting patches of native macrophytes into a 230-m-long stream section. A 100-m-long section upstream was left unplanted for subsequent comparisons. Following the study, a survey was conducted to gauge public opinion about the rehabilitation project and determine whether macrophytes were prominent in perceptions of stream health. In the first growing season, native macrophyte cover in the planted stream section increased from 1.5 to 20%, and then decreased during winter. Regrowth from rhizomes led to rapid aboveground growth during the second year, when cover reached 51%. Non-native macrophytes colonized the stream the first year, but native macrophytes appeared to limit the spread of non-natives, which were absent in the planted section by the second spring. Native macrophyte establishment did not enhance invertebrate communities as predicted; few invertebrate metrics differed significantly between the planted and unplanted sections. Pollution-and sediment-tolerant invertebrate taxa were abundant in both sections, suggesting that invertebrate colonization was limited by water quality or sedimentation, not macrophyte composition. Survey respondents considered the stream to be visually and ecologically improved after rehabilitation, and macrophyte establishment was generally considered positive or neutral.

Transplanting macrophytes to rehabilitate streams: experience and recommendations

“…The propagation technique used in our study and in New Zealand (Larned et al 2006) seems to be a success as all plant beds established in the trays. Propagation reduces the risk of losing biomass after planting because a well-developed root system has better anchoring strength.…”

“…Generally, the three basic physical conditions needed for sustainable macrophyte growth are shallow water (\1 m), water velocity(\0.4 m s -1 ) during plant establishment, and unshaded conditions. From our experience we have found that newly created headwater stream reaches and larger stream reaches with initially low plant cover (\10%) re very suitable for establishment of new macrophyte beds (Larned et al 2006;this study). On the other hand, stream reaches with high plant cover and those with high flow variability are less suitable for macrophyte transplantation projects (Suren 2008).…”

“…Undertaking transplanting in streams necessitates a comprehensive knowledge of the autecology of macrophyte species and the function of different macrophyte communities in relation to the physical and chemical conditions of the streams. To support the use of transplanting in rehabilitation works we here give some general recommendations of how to plan and undertake the transplanting procedure based on previous studies in New Zealand (Larned et al 2006;Suren 2008) and on results from this study. The recommendations are divided into four parts: (1) selecting suitable streams, (2) selecting and obtaining suitable plant species, (3) propagation technique and (4) transplanting technique.…”

“…Larned et al 2006 and Suren 2008 investigated the success of planting macrophytes for restoring the ecological status of urban streams in New Zealand. They got ambiguous results for propagating and transplanting success and to achieve rehabilitation goals.…”

Linkages between cultural and scientific indicators of river and stream health

“…Community-led monitoring programmes involve, educate and empower local communities. Examples of community-scientific monitoring in New Zealand include the Stream Health Monitoring and Assessment Kit (Biggs et al 1998), the national wetland indicators monitoring handbook (Clarkson et al 2002) Larned et al 2006). Identifying synergies between Māori-community monitoring, and scientific and community-scientific approaches may provide a platform to integrate multiple stakeholder views into resource management and policy development.…”