The Inhibitory Effect Of Submerged Macrophytes On Sediment Resuspension Induced By Fish Disturbance

Submerged macrophytes and fishes are important part of shallow lakes. The activities of demersal fish lead to suspension of sediment. Submerged macrophytes, as the primary producer of shallow lakes, play an important role in the element cycling and energy flow in lake ecosystems. It can absorb the nutrient to improve water quality. The bottom-dwelling submerged macrophyte has more roots and the biomass mainly concentrate in the sediment, so the inhibiting effect may be stronger. However the canopy-forming submerged macrophyte has less roots and the biomass distribute in water column, so the inhibiting effect may be weaker. By constructing mesocosms, we studied the inhibiting effect of different species and coverage of submerged macrophytes on sediment resuspension and water quality, in order to provide some theoretical basis for shallow lake restoration.The experiment was operated in field stations of Dong shan from June to September in2013. The first experiment studied the inhibiting effect of different species of submerged macrophytes on sediment resuspension induced by crucian carp. We set up seven biomass densities of meadow-forming Vallisneria spinulosa and canopy-forming Elodea nuttallii in the experiment. We add two fish in each experiment. Results showed that:(1)The concentration of suspended solids and total nitrogen in water column increased after fish released; the biomass of phytoplankton also increased;(2)The resuspension rate was145.18g dw/m2/d in the treatment without plants,14.68g dw/m2/d～23.37g dw/m2/d in the treatment of E. nuttallii, and14.24g dw/m2/d～119.21g dw/m2/d in the treatment of V. spinulosa;(3)The resuspension rate had significant negative correlation with the biomass of V. spinulosa, while no significant relation with E. nuttallii;(4) the biomass of V. spinulosa increase379.06g～1387.68g, while E. nuttallii increase975.41g～1547.88g.Another experiment was carried on to study the inhibiting effect of different coverage of submerged macrophytes on sediment resuspension. We set up treatments with different coverage of V. spinulosa, i.e0,25,50,75,100%. the biomass of all treatments except0%was300g. Results showed that:(1) The concentration of total nitrogen and phosphorus in water column increased after fish released;(2) the concentration of the suspended solids in75%and100%treatment was significantly lower than0%treatment;(3) The biomass of phytoplankton also increased significantly, but was lowest in75%treatment;(4)V. spinulosa obtained a significant growth;(5) The resuspension rate had significant negative correlation with the coverage and biomass of V. spinulosa.The study showed that submerged macrophytes reduced the sediment resuspension. The inhibitory effect had significant negative correlation with the biomass of V. spinulosa and little relationship with E. nuttallii. The inhibitory effect was different in the different coverage treatments, which was strongest when the coverage were>75%. Therefore, one should take into account the effect of the type and biomass of submerged macrophytes when restoring eutrophic shallow lakes.