Secondary production in a southern Illinois headwater stream: relationships between organic matter standing stocks and macroinvertebrate productivity

Abstract

We quantified macroinvertebrate production and organic matter standing stocks in riffle/run and pool habitats for 2 y in 2 reaches of Big Creek, a 3rd-order stream in southern Illinois, USA. Habitat-weighted secondary production was 24.9 and 26.2 g ash-free dry mass (AFDM) m−2 y−1 in the upper and lower reaches, respectively, in year 1 of the study and 17.6 and 15.1 AFDM m−2 y−1 in year 2. Annual production to biomass (P/B) ratios of the macroinvertebrate assemblages ranged from 7 to 10. Collector-gatherers, which were dominated by nontanypodine Chironomidae and Oligochaeta, accounted for >60% of total habitat-weighted production in both reaches, and consumption estimates based on production efficiencies indicated they consumed high proportions of available organic matter resources ≤250 µm. Macroinvertebrate production in Big Creek was strongly correlated with organic matter standing stocks, and our subsequent analyses of production and organic matter resources across several low-order North American streams suggested standing stocks of small wood, a relatively refractory component of organic matter, are an important component of the relationship between macroinvertebrate production and organic matter. However, the apparent influence of small wood on production may be related to associated physical characteristics of these streams, such as pH and canopy cover. Secondary production estimates in our data set were a function of both adjusted total organic matter exclusive of wood and wood standing stocks. Although production–organic matter relationships may be obscured by other factors at the local level, our results indicate that patterns of macroinvertebrate production across large geographic scales may be driven largely by the availability of detrital resources.