Management procedures required to increase chironomid availability to waders feeding on artificial lagoons remain unclear

Abstract

1. Rehfisch (1994) made various recommendations for how to increase chironomid biomass and its availability to waders in artificial lagoons. We argue that his studies form an insufficient basis for some of these recommendations. 2. He suggested protocols for depth manipulation based on a model predicting biomass in terms of depth and depth squared which was not a meaningful representation of his data. This model should therefore not be used as a guide for managing water levels. 3. He predicted that biomass would peak at a depth of about 117 cm, yet he only studied depths of up to 54 cm. We used data from a large, permanent, brackish lake to illustrate how biomass at shallow depths cannot be used to predict that found at greater depths. 4. His aim of a simple model allowing managers to predict chironomid biomass on the basis of depth in artificial lagoons was unrealistic, owing to wide variation in the biomass-depth relationship within and between sites. 5. The value of his 'inverted sombrero' design for a wader lagoon needs to be demonstrated empirically. He advocated regular drying-out of lagoons followed by immediate refilling, a flooding cycle that may not maximize chironomid biomass.