Growth,nitrogen and phosphorus removal ability of Vallisneria natans under natural light
In order to explore the optimal control range of water depth for Vallisneria natans type aquiculture,based on the natural distribution water depth of V.natans in the pond,four light intensity gra-dient groups,including 5%(L1),15%(L2),25%(L3),and 35%(L4)of the full sunlight intensity(L1 was the suitable light intensity group,L2,L3,and L4 were the strong light groups),were set up,corresponding to the underwater depth of 1.0-1.1,0.6-0.8,0.4-0.6,and 0.3-0.4 times the transparency of the pond,respectively,to study the growth,antioxidant,and purification ability of V.natans under natural light period and intensity.The results showed that under natural light period,the total biomass of V.natans increased significantly with the increase of light intensity(5%-35%full sunlight range),and the maximum leaf length appeared in L2 group.The content of malondialdehyde(MDA)and superoxide dismutase(SOD)activity in L2,L3,and L4 groups were significantly lower than those in L1 group;the content of dissolved oxygen(DO)and pH values in water in L3 and L4 groups were significantly higher than those in L1 group,while the chlorophyll a(Chl a)content was opposite.The concentrations of ammonium nitro-gen(NH4+-N)and nitrite nitrogen(NO2--N)in each group rapidly decreased to lower levels(<0.30,<0.02 mg/L)within 3 and 2 weeks,respectively;except for group L1,the concentrations of nitrate nitro-gen(NO3--N)and total nitrogen(TN)in other groups continued to decrease at different rates with time until the end of the experiment(<2.50,<3.00 mg/L),which was negatively correlated with light intensi-ty to a certain extent.The activities of glutamate synthase(Fd-GOGAT)and alkaline phosphatase(AKP)in L3 and L4 groups were significantly higher than those in L1 and L2 groups,and the removal rates of orthophosphate(PO43--P)and total phosphorus(TP)in each group were more than 80%,show-ing good removal effects.Research has shown that the water level for V.natans type aquiculture should be controlled within a range of about 0.3 to 0.6 times transparency above V.natans.
light intensityVallisneria natansgrowth statusnitrogen and phosphorus in waterpu-rification capacitygrass-type pond
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