Results
Water
quality parameters
Shading reduced water temperature (S0, 18.12±0.60 °C; S1, 16.38±0.50 °C)
and DO concentration (S0, 11.42±0.18 mg L-1; S1,
7.85±0.24 mg L-1), but increased conductivity (S0,
371.18±3.77 µs cm-1; S1, 387.33±3.16 µs
cm-1), TN (S0, 1.80±0.07 mg/L mg
L-1; S1, 2.63±0.07mg L-1), and TP
concentration (S0, 0.033±0.01 mg L-1; S1, 0.045±0.01
mg L-1) (Table S3 and S4). TN concentration and
conductivity were found to increase with snail biomass (Table S3 and
S4). Nutrient loading treatment increased conductivity. Shading,
nutrient loading and snail biomass also interactively affected DO
concentration and conductivity (Table S3 and S4).
Effect of treatments on
submerged plant growth
Nutrient loading did not affect the biomass of both submerged plants
(Table 1). Shading decreased P. crispus shoot biomass and shoot
number, but increased P. crispus internode length (Figure1A and
Figure2A, B). Shading and snail biomass interactively affected the shoot
biomass of P. crispus (Table 1, Figure1A). In the full light
treatment, shoot biomass and number of P. crispus showed a
humped-shape response to snail biomass, but shoot biomass declined with
snail biomass in the shading treatment (Figure1A). No changes in N
content and C: N ratio of P. crispus could be detected in any of
the treatments (Table 1 and Figure3B, C). The P content of P.
crispus decreased and C:P ratio
increased under shading (Table 1 and Figure3C, E). Plant C content
decreased with snail biomass during shaded conditions (Table 1 and
Figure3A). Nutrient loading and snail biomass interactively affected C:P
and N:P ratios of P. crispus , and the two treatments together
with shading affected the P content and C:P ratio of P. crispus(Table 1).
Effect of treatments onperiphyton and phytoplankton
biomass
Nutrient loading did not affect periphyton biomass. Shading
significantly increased biomass of periphyton and phytoplankton.
Periphyton biomass decreased with snail biomass under both full light
and shaded conditions, while phytoplankton increased with increasing
snail biomass only during shading (Table 1 and Figure1C, D).