Evidence details

The evidence record you selected is shown below.
Click 'Duplicate evidence' to create an editable copy of this record.

Study

Citation

Zoe S. Dewson, Alexander B. W. James, Russell G. Death (2007). Invertebrate community responses to experimentally reduced discharge in small streams of different water quality. J. N. Am. Benthol. Soc..

Study description

Water abstraction can alter invertebrate community composition by changing the availability or suitability of habitat for invertebrates. The consequences of water abstraction for the physical habitat and invertebrate communities of small permanent streams are not clear. Therefore, we used whole-channel flow manipulations to imitate real water abstractions. We used weirs and diversions to reduce discharge by .85% in 3 small New Zealand streams (mean discharges: 11–84 L/s), ranging in water quality from pristine to moderately polluted. We sampled benthic invertebrates and periphyton at control and impact sites on each stream before and during 2 mo of artificially reduced discharge during summer 2005, and then we left the diversions in operation throughout the following year and sampled invertebrates again after 9 and 12 mo of flow reduction. During the experiment, wetted width decreased by 24 to 34% at impact sites. Water velocity and depth also decreased at impact sites, but only small changes to conductivity, pH, dissolved O2, and temperature were observed. At the pristine site, density of invertebrates and percentage of Ephemeroptera, Plecoptera, Trichoptera (EPT) individuals decreased in response to reduced flows. Only taxonomic richness decreased at the mildly polluted stream, and reduced discharge had no effect on the invertebrate community at the stream with the poorest water quality. Overall community structure also changed in response to flow reduction at all but the poorest-water-quality stream. Alterations to community composition involved changes in the density of common taxa and collection of fewer rare taxa per sample. Our results indicate that the impacts of water abstraction on invertebrate communities differ between streams that vary in water quality, probably because of the relative sensitivities of invertebrate communities to changes in the physical habitat of these streams. Here I am recording the results for the pristine stream.

Response

Cause term/trajectory

Hydrology - surface flow (volume) (Decrease)

Cause description

They used weirs and diversions to remove water from the natural channels of 3 small streams for 1 mo . After this time, they removed the weirs and restored natural flow patterns to the streams until the following summer.

Effect term/trajectory

EPT taxa - richness (Decrease)

Effect description

percentage of Ephemeroptera, Plecoptera, Trichoptera (EPT) individuals

Response measure type

F statistic/ratio

Statistical significance

yes, values significant at p . 0.05

Documentation

p 760

Response measure description

BACIP design. Analyzed data from each stream separately because invertebrate communities differed substantially between the streams. 3-factor (control–impact [CI], before–after [BA], and time) analysis of variance. here I am recording the results for the 'pristine' stream only.

Design

Source data

Field

Study type

Manipulation

Study design

BACIP

Number of independent control or reference sampling units

2

Number of indendent impact or treatment sampling units

2

Sample size used in analysis

F 1,3

Design description

Here I am recording the results for the pristine stream only.

Context

Climate

Temperate

Country

New Zealand

Habitat

Stream/river

Spatial extent

Reach/section

Temporal extent

Months

Context description

Study done on 3 streams in the Wairarapa region of the lower North Island, New Zealand