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Phosphous limited community dynamics of steam benthic algae and insects

University of British Columbia

The relationship between external soluble phosphorus (P) concentration and the abundance and taxonomic composition of stream insects was determined in streamside artificial troughs. The response of peak algal biomass (PB) to target P concentrations of 0, 0.5, 2.5, 5, 10, 50 ɥg P 1⁻¹ was also monitored. A log-linear function of P concentration was used to approximate PB and insect abundance. PB measured as chlorophyll a increased with P concentration linearly to 7.4 mg m⁻² at 2.5 ɥg P 11 and reached an asymptote at 9.2 mg m⁻² (2.7X the controls). Adult baetid mayflies showed a significant increase in number after 23 days of P addition; this effect was maintained over 9 weeks of treatment. Numbers of benthic baetids, nemourid and perlodid stoneflies and hydroptilid tricopterans sampled at the end of the experiment significantly increased with P concentration. Adult and benthic insects of these taxa exhibited similar rapid increases in abundance from 0 - 2.5 ɥg P 1⁻¹ and all showed signs of saturation at approximately 1.5 - 3 times the controls at concentrations greater than 2.5 P l1. Increased abundances of insects resulted from greater food availability. There was no detectable difference in the numbers of large Baetid nymphs drifting from the troughs with increasing P concentration. Increased survival of Baetidae nymphs with increasing P level was thought to account for higher numbers of adult and benthic baetids observed with increasing P concentration. Graphical comparisons between the control and treated troughs showed that they were similar in taxonomic composition of insects. Insect taxonomic richness did not change with increasing P concentration. These findings are important to fisheries researchers who are assessing the potential of stream fertilization as a technique to enhance salmonid populations in nutrient deficient streams.

Thesis/Dissertation

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2009-02-25

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http://hdl.handle.net/2429/5065

Zoology

University of British Columbia

UBCV

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