This study examined fine particulate organic matter (FPOM) turnover by one group of collectors, larval Chironomidae (Diptera), in Southern Appalachian headwater streams. Despite the high abundance of chironomids amongst collector macroinvertebrates in these streams (up to 50% of total abundance), and known reliance on detrital material, their importance to stream FPOM dynamics has not been well quantified. We estimated rates of collector-chironomid consumption and secondary production in two similar headwater streams in four seasons and two years and then used these rates to obtain estimates of assimilation efficiency (AE) and FPOM turnover. An ecosystem-level experimental manipulation of detrital inputs in one study stream allowed for a unique concurrent evaluation of turnover in reference, resource-limited, and resource-recovery systems.
Results/Conclusions:
Seasonality had a significant effect on larval gut passage time (GPT), with faster GPT at higher temperatures (p < 0.001). Mean GPT ranged from 39 min. (summer) to 68 min. (winter). Mean annual FPOM turnover was extremely reduced (5.5 kg AFDM/stream, 12% of mean annual FPOM export) in a resource-limited stream versus 46 – 53 kg AFDM/stream (20 – 74% of export) in the reference stream. Following four years of resource-recovery, turnover was 24 kg AFDM/stream (16% of export). Based on measures of secondary production and consumption, assimilation efficiency was estimated to be very low (1.7 – 2.5%). Chironomids in this study turned over a large portion of FPOM available to them, suggesting that turnover by the entire collector community in forested headwater systems may be much higher than previously predicted.
