The depth distribution of biomass, average weight and number
of
earthworm individuals in the VF were shown in Fig. 1, while
the earthworm enzymatic activities in the upper and under layers
were presented in Fig. 2. As the depth, the biomass, average weight,
number and AKP activity of the earthworms tended to decrease
(one-way ANOVA, P > 0.05), while the protein content and activi-
ties of POD and CAT had an increasing tendency (one-way ANOVA,
P > 0.05). The results implied that the earthworm growth property
in the upper layer was better than that in the under layer. The
possible reason was that organic matter content in the VF sludge
samples decreased with the depth, causing that the organic food
for earthworm growth was less in the under layer [6]. Additionally,
there were large standard deviations in mean values of earthworm
biomasses, average weights and numbers at the four depths of VF.
The reason was that the mean values of average weights and num-
bers of earthworm individuals was based on the data during the
whole experimental period at the four depths, and the data varied
considerably with the operation time, as were shown in Fig. S1 of
SD. Xing et al. [1] suggested that temperature variation might be
an important factor to cause the changes in the average weight and
number of earthworm individuals.