Effects Of Sediment Phosphorus Immobilization On The Growth Of Submerged Plants

Submerged plants are one of the primary producers of lake ecosystems.Submerged plants are important to maintain the stability of clear-water states in shallow lake ecosystems.Submerged plants can not only use stems and leaves to absorb nutrients from water,but also use roots to absorb nutrients from sediments.Myriolhyllum spicatum,Hydrilla verticillata,and Vallisneria denseserrulata are common submerged plants in lakes in China.All three submerged plants are often used in lake ecological restoration projects.In the mid-to-late period of ecological restoration,submerged plants grow excessively,forming a dense underwater canopy,reducing the light transmittance in the water.The release of internal phosphorus from sediments is one of the main reasons delaying the recovering lakes from the eutrophication.Adding lanthanum-modified bentonite in sediments can effectively control the release of phosphorus release form sediments,enhance the adsorption capacity of phosphorus in sediments and improve the transparency of lakes.However,the effects of the lanthanum-modified bentonite on submerged macrophytes are not well studied,and relevant works have important implication for lake restoration practices.First,in this study,Myriolhyllum spicatum is selected as the research object.Myriophyllum spicatum was planted in two different nutrient sediments(low nutrient sediment and high nutrient sediment)to explore the effect of sediment fertility on its growth and morphological characteristics.Secondly,two kinds of treatments were set up with and without Phoslock~?in the sediments to explore the effect on the growth and morphological characteristics of Myriophyllum spicatum.In addition,Hydrilla verticillata and Vallisneria denseserrulata were studied under two different overlying water nutrient levels and sediment treatments with and without lanthanum-modified bentonite to explore the effect on the plants by both water and sediments.The research results showed that:(1)The growth of submerged plants increased with the increase of sediment nutrients.The biomass of Myriophyllum spicatum in the high-nutrient group was 166.79 g/m~2,which was significantly higher than the low-nutrient group(65.67 g/m~2).(2)The addition of Phoslock~?in the sediments effectively reduced the bioavailable phosphorus contents in the sediments.In low-nutrient overlaying water,BD-P content is 0.577 mg/g in control(without Phoslock~?)group,but Phoslock~?group BD-P content is only 0.159 mg/g.And Org-P content is 0.098 mg/g in control(without Phoslock~?)group,but Phoslock~?group Org-P content is only 0.069 mg/g.In high-nutrient overlaying water,BD-P content is 0.503 mg/g in control(without Phoslock~?)group,but Phoslock~?group BD-P content is only 0.169 mg/g.And Org-P content is 0.110mg/g in control(without Phoslock~?)group,but Phoslock~?group Org-P content is only 0.066 mg/g.(3)The addition of Phoslock~?inhibited the growth of submerged plants and changed biomass distribution of submerged plants aboveground and underground,the biomass aboveground was reduced and that belowground was increased.The biomass of Myriophyllum spicatum in Phoslock~?group is 370.72 g/m~2,which was significantly lower than that in the control(without Phoslock~?)group at 481.57 g/m~2.In low-nutrient overlaying water,the biomass of Hydrilla verticillata in Phoslock~?group is 1169.67 g/m~2,which was significantly lower than that in the control(without Phoslock~?)group at 2403.31g/m~2.And the biomass of Vallisneria denseserrulata in Phoslock~?group is 809.83 g/m~2,which was significantly lower than that in the control(without Phoslock~?)group at 1128.32 g/m~2.In high-nutrient overlaying water,the biomass of Hydrilla verticillata in Phoslock~?group is 2039.23g/m~2,which was significantly lower than that in the control(without Phoslock~?)group at 2641.06g/m~2.And the biomass of Vallisneria denseserrulata in Phoslock~?group is959.17g/m~2,which was significantly lower than that in the control(without Phoslock~?)group at1254.42 g/m~2.(4)In low-nutrient overlaying water,the effect size of Hydrilla verticillata is-0.9475,and in high-nutrient overlying water the effect size is-0.2520.Then,in low-nutrient overlaying water,the effect size of Vallisneria denseserrulata is-0.5294,and in high-nutrient overlying water the effect size is-0.2323.Overall,the inhibitory effect of adding Phoslock~?in sediments to the growth of submerged plants is more significant when the overlying water nutrient are low.The results of this experiment provide a scientific theoretical basis for better determination of how to use lanthanum-modified bentonite in the process of lake ecological restoration.