Earthquakes, catastrophic sediment additions and the response of urban stream communities

Figures & data

Figure 1 Total lengths of the Avon and Heathcote rivers and their permanent flowing surface tributaries divided into four categories of siltation.

Figure 2 Mean (± 1 SE) substrate characteristics for 16 sites in the Avon and Heathcote rivers.

Sites were allocated to one of four categories of siltation (n = 4), statistically significant differences are shown with statistical values in text. **Indicates statistically significant differences at P < 0.01. Statistical values are shown in text. The absence of error bars indicates no variability.

Table 1 Physical and chemical characteristics of 16 sites on the Avon and Heathcote rivers within four sediment categories (no silt, lightly silted, medium siltation and heavily silted) in September 2011.

	No silt	Light	Medium	Heavy	F	P
pH	6.6–7.7	6.7–7	7.1–7.4	7.1–7.7	–	–
Conductivity (µS25 cm^−1)	162 (4)	219 (40)	212 (40)	265 (116)	0.440	ns
DO (mg/L)	9.1 (0.4)	6.9 (0.4)	9.2 (0.4)	9.7 (0.3)	5.249	<0.05
Temperature (°C)	11.9 (0.4)	11.9 (0.8)	11.2 (0.2)	13.3 (1.2)	1.415	ns
Width (m)	3.5 (0.6)	3.4 (1.2)	2.6 (1.2)	2.4 (0.2)	0.300	ns
Discharge (m^3 s^−1)	0.12 (0.04)	0.16 (0.05)	0.19 (0.2)	0.04 (0.04)	0.396	ns
Channel stability^a	61 (5)	66 (7)	70 (2)	77 (3)	2.034	ns
Riparian condition^b	82 (3)	81 (4)	71 (8)	82 (3)	1.031	ns

Values are mean (± 1 SE, n = 4), except pH which shows a range.

^aChannel stability score derived from Pfankuch (1975).

^bRiparian condition derived from Harding et al. (2009).

Statistics are results of one-way ANOVA.

Figure 3 Mean (± 1 SE) benthic invertebrate indices for 16 sites in the Avon and Heathcote rivers.

Sites were allocated to one of four categories of siltation (n = 4). **Indicates statistically significant differences at P < 0.01; * indicates statistically significant differences at P < 0.05. Statistical values are shown in text.

Figure 4 Mean (± 1 SE) fish indices for 16 sites in the Avon and Heathcote rivers.

Sites were allocated to one of four categories of siltation (n = 4). **Indicates statistically significant differences at P < 0.01. Statistical values are shown in text. The absence of an error bar indicates no variability.

Pfankuch DJ 1975. Stream reach inventory and channel stability evaluation. Missoula, MT, US Department of Agriculture & Forest Service, Northern Region.

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Harding JS, Clapcott JE, Quinn JM, Hayes JW, Joy MK, Storey RG et al. 2009. Stream habitat assessment protocols for wadeable rivers and streams of New Zealand. Christchurch, University of Canterbury. 133 p.

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