Evaluation of Benthic Macroinvertebrate Biomass Methodology. Part 1. Laboratory Analytical Methods

摘要

Evaluation of analytical methods employed for wet weight (live or preserved samples) of benthic marcoinvertebrates reveals that centrifugation at 140 x gravity for one minute yields constant biomass estimates. Duration of specimen exposure in ethanol, formalin, and formol (formalin -ethanol combinations) causes significant body weight loss within 48 hr. Formalin and formol cause less body weight loss than ethanol. However, as all preservatives tested cause body weight loss, preservation time of samples collected for comparative purposes should be treated uniformly. Constant dry weights are attained by oven drying at 103 deg C at a minimum of four hours or vacuum oven drying (15 inches of mercury pressure) at 103 deg C a minimum of one hour. Although requiring more time in preparation than oven drying and inalterably changing specimen body shape, freeze drying (10 microns pressure - 55 C, 24 hr) provides constant dry weights and is advantageous for long term sample storage by minimizing curatorial attention.