Benthic secondary production and biomass of insects emerging from a northern German temperate stream

• 1 Secondary production and emergence of aquatic insects were examined in the outlet of Lake Belau, Northern Germany, by means of benthic samples and emergence traps.
• 2 At three stream sections annual larval secondary production varied between 4.9 and 10.8 gDM (dry mass) m^‐2 year^‐1. Insects contributed with 3.4, 8.9, and 8.7% to the total macroinvertebrate production that varied between 56.5 and 215.1 gDM m^‐2 year^‐1. Emerged biomass was between 1.0 and 2.0 gDM m^‐2 year^‐1. At all three stream sections Diptera dominated with a larval production of 3.0–l6.1 gDM m^‐2 year^‐1, followed by Trichoptera with 1.0–2.1 and Ephemeroptera with up to 0.9 gDM m^‐2 year^‐1.
• 3 Average larval production amounted to 9.0 gDM m^‐2 year^‐1 and emerged biomass to 1.7 gDM m^‐2 year^‐1. Larvae of insects amounted to 7.0% of total macroinvertebrate production.
• 4 The ratio of annual emerged biomass to secondary production (E/P) varied among individual taxa. At the stream sections the ratio ranged from 15.9% to 20.1% with an average of 18.3% for the stream.
• 5 Relative constancy of the E/P ratio suggests that the determination of emerged biomass can be used as a method for estimating the secondary production of aquatic insects. The composition of functional feeding groups clearly differs between emerged biomass and total macroinvertebrate production. Therefore, the method does not allow conclusions on the level of production of the whole benthic community. However, composition of functional feeding groups at emergence roughly reflects composition of these groups in the benthic insect community.