Biofilm development and extracellular enzyme activities on wood in billabongs of south-eastern Australia

Murray-Darling Freshwater Research Centre

MDFRC item.

1. The accrual of organic matter, chlorophyll a and bacteria, and the activities of various extracellular enzymes were studied during biofilm formation on River Red Gum (Eucalyptus camaldulensis) wood submerged in two temperate Australian billabongs for 24 weeks over summer and winter of 1989–90.2. Peak organic matter content of the biofilm ranged from 0.7 to 3.3mg AFDW cm−2, chlorophyll a content from 1.3 to 4. 2μg cm−2 and bacterial abundance from 18 × 106 to 94 × 106 cells cm−2. Most variation in organic matter content, chlorophyll a content and bacterial abundance in the biofilms couid be attributed to the duration of immersion (28–48% of variation) and to the interaction between site and submergence period (11–12%). Differences between sites and between seasons were less important in explaining total variation.3. Alkaline phosphatase, aminopeptidase and [3-D-glucosidase activities, determined per unit substratum surface area, were up to 138 ± 26 nmol cm−2h−1, 113 ± 1 nmol cm−2h−1 and 9.3 ± 2.2 nmol cm−2h−1, respectively. Activities of these three enzymes determined per unit organic biomass were up to 203 ± 25, 157 ± 13, and 16 ± 2.1 nmol mg1 AFDW h−1 respectively. Enzyme activities expressed on an area- or biomass-specific basis responded differently to the effects of season, site and duration of substratum exposure.4. Few consistent relationships could be established between the activity of a given enzyme system and the activity of other enzymes, nor with the various biomass parameters, such as total organic matter content, chlorophyll a content or bacterial abundance.5. We suggest that submerged wood of the River Red Gum is an important site for biofilm development in lentic systems in south-eastern Australia, and thus as a food resource for grazing invertebrates and for transformations of various nutrients and organic matter.