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AcknowledgementsAcknowledgementsWe thank Mike Winterbourn, Angus McIntosh, Hamish Greig, Leanne O’Brien and membersof the Freshwater Ecology Research Group, University of Canterbury, for their helpful discussions.Thanks also to Fiona Blakely and Hamish Greig who helped in the field and Matt Walters whohelped with graphics. TJB received a summer scholarship, provided by Rachel Barker and theChristchurch City Council.
ReferencesReferencesBlakely, T.J., J.S. Harding & A.R. M cIntosh. 2003. Im pacts of urbanisation on Okeover Stream,
C hristchurch. Chr istchurch City Counci l Repor t. Universi ty of Canterbury: C hristchurch.Dendy, A. 1900. The p lants and anim als of Canterbury. In: Association, N.Z.N., (eds), Canterbury
– old and new, 1850-1900: a souvenir of the jubilee. Christchurch, New Zealand: Whi tcombe& Tombs, pp 178-197.
Paul , M.J. and J.L. M eyer. 2001. Streams in the urban landscape. Annual Review of Ecologyand System atics. 32 : 333-365.
Ryan, P.A. 1991. Environmental effects of sediment on N ew Zealand streams: a review. NewZ ealand Journal of M arine and Freshwater Research 25: 207-221.
i . To determine habitat, water quality and macroinvertebrate communities in the 1200 m long Okeover Stream.ii. To explore factors limiting macroinvertebrate recovery in this stream.
Historically, Christchurch was a mosaic of swampland and meandering spring-fed streams(Dendy 1990). Its waterways have been subjected to three broad impacts, typical of urbanstreams (as discussed in Paul and Meyer 2001):
i. Pollutants (e.g., chemicals and sediments from stormwaters)ii. Altered hydrological regimes (e.g., decreased water table, exaggerated flooding)iii. Changes in riparian and in-stream habitat (e.g., channelisation, removal of riparianvegetation, reduced in-stream habitat complexity/diversity)
IntroductionIntroduction
Study objectivesStudy objectives
For sampling methods see Blakely et al. 2003.
Water chemistry and physical conditions in November and December 2002, changed very l ittlefrom headwaters to downstream. pH was circum-neutral, turbidity low, and water temperatureand dissolved oxygen relatively constant in all s ites.
Are habitat and water quality responsible forAre habitat and water quality responsible forthe longitudinal change in the macroinvertebratethe longitudinal change in the macroinvertebrate
community?community?
Sedimentation can reduce macroinvertebrate abundance and diversity in urban streams (Ryan1991); however, we found no difference in the amount of sediment on stone surfaces amongsites. In contrast, there was significantly more periphyton biomass (Chlorophyll-a) upstream.
However, the periphyton gradient does not fully explain the pattern observed in themacroninvertebrate fauna along Okeover Stream.
1 2 3 4 5 60
2
4
6
8
10
12
1 2 3 4 5 60
2
4
6
8
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16
Downstream Downstream
2 3 4 5 60.000
0.001
0.002
0.003
0.004
0.005
0.006
2 3 4 5 60.0
0.2
0.4
0.6
0.8
1.0
1.2
F4, 20= 7.52, p= 0.001F4, 20= 2.67, p= 0.06
Downstream Downstream
Riparian plantings reduces runoffand increases in-stream shading.
Changes in weedmanagementpractices haveallowed macrophytegrowth, which hascreated habitat forstream animals andincreased water flow.
Substrate additionshave improved flowconditions, creatingpool-riffle sequencesand increasing in-stream habitat diversity.
Okeover Stream flows through the University of CanterburyOkeover Stream flows through the University of Canterburycampus and is approximately 1200 m long. Restoration effortscampus and is approximately 1200 m long. Restoration efforts
began in 1998.began in 1998.
Main FindingsMain Findings•We found a distinct longitudinal change in the macroinvertebrate community, which could not be explained by water and habitat quality alone.•Upon further investigation, oviposition substrates were found to be in short supply throughout Okeover Stream, and we found marked decreases in egg masses upstream.•This distribution pattern was mirrored by adult caddisfl ies, with fewer encountered upstream. Thus, the lack of adults in upstream reaches may have a much greater effect on larval recruitment than the shortage of oviposition substrata.
What is the current macroinvertebrate community?What is the current macroinvertebrate community?
Invertebrate densities were highly variable among sites. The headwaters were almost entirely dominatedby oligochaete worms (>95 %), but a more diverse community, including amphipods, snails, dipteransand caddisfl ies, appeared downstream.
What might be causing this longitudinal change in macroinvertebrates?
Taxonomic richness generally increased downstream and a similar trend was shown by caddisfly species,which were present in very low numbers at site 2, and increased to seven taxa downstream.
1 2 3 4 5 60
20
40
60
80
100
TrichopteraDipteraGastropodaOligochaetaAmphipodaOther
Downstream
1 2 3 4 5 60
5
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15
20
25
Total taxonomic richnessTotal caddisfly taxa
1 2 3 4 5 60
4000
8000
12000
16000
20000
Downstream Downstream
Are oviposition substrates limiting larvalAre oviposition substrates limiting larvalrecruitment?recruitment?
Upstream reaches had more boulders suitable for egg mass deposition, but had significantlyfewer hydrobiosid caddisfly egg masses on them (F3, 32= 15.52, P= 0.001).
To investigate why this might be, boulders were added to the stream channel to provide suitableoviposition substrates for egg-laying hydrobiosid females.
Substrate addition increased the number of caddisfly egg masses. However, upstream reachesstil l had significantly fewer egg masses, than reaches downstream (F3, 16= 16.14, P<0.001).Similarly, more hydrobiosid adults were captured downstream (F3, 8= 41.87, P<0.001).
I. Substrates suitable for caddisfly oviposition were counted.
II. All caddisfly egg ma sses werecounted
I. Five boulders were added at each site,and egg masses counted on these
II. Adult caddisflies were collected in Malaise traps
Survey of natural substratesSurvey of natural substra tes
Substrate addit ionsSubstrate addi tions
3 4 5 60
2
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6
8
10
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14
16
0
2
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6
8
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14
0
2 0
4 0
6 0
8 0
0
5
10
15
20
25
Egg massesBoulders
Downstream
Downstream
AdultsEgg masses
3 4 5 6
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