Barriers to the recovery of aquatic insect communities in urban streams

Abstract

1. Worldwide, increasing numbers of stream restoration projects are being initiated to rehabilitate waterways modified by urbanisation. However, many of these projects have limited success in restoring stream communities. Prompted by this, we investigated previously unrecognised barriers to aquatic insect colonisation in urban streams. 2. To investigate whether the availability of suitable substrata for oviposition limited the longitudinal distribution of caddisflies, large boulders were added to the upstream reaches of one stream. Prior to the addition, more egg masses were observed downstream and this longitudinal pattern persisted subsequently. 3. Malaise trapping revealed that adult caddisfly diversity and abundance was greater downstream than upstream. Furthermore, in a previous study the authors found larval caddisflies reflected the longitudinal distribution of adults. 4. The only obvious potential obstructions between reaches were roads beneath which the stream flowed through culverted crossings. Malaise trapping was used to examine the effect of road culverts and bridges on caddisfly dispersal. Numbers of caddisflies caught declined upstream and about 2.5 · more individuals were taken in traps immediately below than above five culverts. 4. Bridges, which had a more open structure than culverts, had no significant effect on the size of catches made above and below them. 5. Road culverts could act as partial barriers to upstream flight, with consequences for larval recruitment in urban streams. We recommend that urban planners and designers of restoration projects consider possible synergistic effects of poor oviposition habitat and barriers to aquatic insect dispersal, which may be critical for the colonisation of urban headwater streams and for the maintenance of stream insect populations.

Assessing the local effects of riparian restoration on urban streams

“…stormwater drains) and by increased run-off related to land clearance and development (Paul & Meyer 2001;Roy et al 2006). Silt may have the potential to smother and displace macroinvertebrate communities through decreasing habitat heterogeneity (ANZECC 2000; Larson et al 2001;Blakely et al 2006). Our results were consistent with this; invertebrate communities in the open reaches were dominated by species that are known to be associated with fine sediments, including chironomids and snails.…”

“…Increased 'flashiness' of flows and flooding regimes in urban streams can modify channel and bank stability and increase fine sediment supply loads (Osborne & Kovacic 1993;Fitzpatrick et al 2009). Consequently, many urban streams have been converted from meandering streams into deeper and straighter channels with a loss of boulders and cobbles and increases in fine particulate substrates such as silt (Paul & Meyer 2001;Blakely et al 2006;Miltner et al 2004).…”

Effects of urban stream burial on organic matter dynamics and reach scale nitrate retention

“…For example, Meyer et al (2005) found that stream burial decreased macroinvertebrate and taxonomic richness in a buried stream in Georgia (USA). Others have reported that stream burial can hinder the in-stream migration of macroinvertebrates and fish (Dedecker et al 2006;Foster and Keller 2011;Poplar-Jeffers et al 2009) as well as the longitudinal dispersal of emerging adult insects (Blakely et al 2006). To our knowledge, however, there are no published reports of the effect of stream burial on other important ecosystem services provided by streams, such as nutrient removal.…”

Do culverts impact the movements of the endangered white-clawed crayfish?

“…The use of culverts for stream crossings, or as flood-control structures, is widespread, with the majority of studies focusing almost exclusively on the impacts of these structures on the movement of fish (Richter et al, 1997;Kemp and Williams, 2009;Tonkin et al, 2012), with little consideration of other aquatic species. Nevertheless, these structures can have significant impacts on non-fish species (Richter et al, 1997;Acosta and Perry, 2001;Blakely et al, 2006;Jones and Bergey, 2007;Foster and Keller, 2011). Connectivity of crayfish populations within rivers is probably achieved through a combination of downstream drift of very young juveniles, together with active upstream and downstream movement by larger juveniles and adults (Robinson et al, 2000).…”