Shade effects on stream periphyton and invertebrates: An experiment in streamside channels

Abstract

The effects of shade on periphyton and invertebrates were investigated by comparisons in 12 replicate channels beside a pasture stream where shade cloth reduced the photosynthetically available radiation (PAR) by 0, 60, 90, and 98%. Periphytic productivity decreased with increasing shade. Periphyton chlorophyll a was consistently low (< 30 mg m -2 ) under 98 and 90% shade and usually low at 60% shade, whereas blooms were common during summer in the unshaded channels. More periphytic taxa occurred in the open than shaded channels and the relative concentration of the photoprotective pigment beta-carotene decreased with increasing shade. Nitrate uptake rates by periphyton, measured in separate chamber studies, decreased progressively as shade increased from 60% through 90% to 98%, and were more strongly correlated with gross primary productivity than periphyton chlorophyll a and particulate carbon levels. Total invertebrate and chironomid densities declined significantly as shade increased from 60 to 90% and invertebrate taxa richness declined markedly between 90 and 98% shade. Most collector-browsing invertebrates (other than chironomids) had similar densities under 0-90% shade and only declined at 98%. This suggests a weak coupling of these invertebrates with local M96078

Effect of substrate stability and canopy cover on stream invertebrate communities

“…The artificial cover in this study significantly reduced periphyton biomass as in similar shading experiments (Towns 1981;Quinn et al 1997). The cover reduced periphyton biomass well below that of substrates in the stream further up the catchment under full canopy forest (Zimmermann 2001).…”

“…Bond & Downes (2000) found no reduction in Hydropsychidae density with increasing scour disturbance and Reice (1984Reice ( ,1985 found no change in diversity with increasing substrate disturbance. Similarly, studies investigating the effect of reduced periphyton biomass under artificial covers have found invertebrate abundance and species richness were reduced by the lower levels of periphyton created by the cover (Towns 1981;Quinn et al 1997). However, this was not the case in our study, and despite the much lower periphyton levels under the cover there was no effect of this reduction on either total invertebrate abundance or species richness.…”

Land‐water interactions at Whatawhata, New Zealand: Introduction and synthesis

“…Advantage was taken of the marked change in shade that occur as a small stream passed 574 New Zealand Journal of Marine and Freshwater Research, 1997, Vol. 31 Quinn et al 1997b).…”

“…Two papers Quinn et al 1997b) describe research conducted in 12 flowthrough stream mesocosms constructed on the banks of one of our study streams (Fig. 4).…”

“…Mesocosms allow a component of the ecosystem to be manipulated so that the effects on other stream components can be understood. Quinn et al (1997b) manipulated light input and the effects on periphyton, nitrogen uptake, photosynthetic activity, and invertebrates were determined. That paper concludes the degree of light input was a key driver of ecosystem metabolism, trophic level interactions, and community structure and, therefore, can explain many of the differences observed in the land-use comparison study of Quinn et al (1997a).…”