title: Stream Insect Production as a Function of Alkalinity and Detritus Processing
Creators: name: Osborn, Thomas G.
Publisher: name: Utah State University
Year: 1981

description: The study was conducted to determine if aquatic insect production was significantly different between high and low alkalinity mountain streams and if any differences were associated with food availability factors. The major objectives included determining: (1) if annual production differences occur between high and low alkalinity streams; (2) if processing rates of terrestrial detritus differs between high and low alkalinity streams; (3) if detrital processing rates are related to stream insect productivities; (4) if primary productivity varies between high and low alkalinity streams; (5) if toxic effects or micronutrient limitations exist in high or low alkalinity streams that could limit insect survivals. A high alkalinity stream was defined as one having over 150 milligrams per liter average total alkalinity. Six study sites on four high alkalinity streams were located in the Wasatch National Forest near Logan in northern Utah. Six study sites on four low alkalinity streams were located in the Shoshone National Forest near Yellowstone National Park in northern Wyoming. Sites from each region were shown to not differ significantly for all physical parameters tested.
The mean annual production of 22 of the 29 invertebrate taxa analyzed were significantly higher in the high alkalinity streams, while 2 taxa were significantly more productive in the low alkalinity streams. The mean annual production of all taxa summed was significantly higher in the high alkalinity streams. All high alkalinity sites had significantly higher production than any low alkalinity site.
Alder leaf packs left open to allow invertebrate activity had a significantly higher rate of weight loss in the high alkalinity stream. Alder leaf packs placed inside fine mesh bags to exclude invertebrate activity showed no significant differences in weight loss when the experiments were terminated. The patterns of weight loss for these mesh packs did differ between the two stream types. In the high alkalinity stream, the leaves had a early rapid weight loss phase followed by a period of reduced weight loss. In the low alkalinity stream, the leaves experienced little weight loss during the early phase of the study but lost weight rapidly during the latter phase.
The survivorships of all taxa tested did not differ significantly between high and low alkalinity water.
Estimates of detrital inputs based on drift measurements and standing crops of detritus collected with invertebrate samples showed no significant differences between regions.
The following conclusions resulted from the study. The high alkalinity streams had a significantly much higher production of aquatic invertebrates than did the low alkalinity streams. The high alkalinity streams also had significantly higher standing crops of attached algae and faster processing of alder leaves. Algae and processed allochthonous detritus are two major food sources for many aquatic invertebrates. It is concluded that a major reason for the great difference in invertebrate production between the physically similar high and low alkalinity streams in this study was the availability difference of these two food sources. The insects in the high alkalinity streams had much more of both food types available to them so a much higher annal production of aquatic invertebrates was supported.