Study On The Environment Factors Of The Restoration Of Submerged Macrophyte Population In The Restored Sites Of Honghu Lake From The Enclosure Studies

Hong Hu is the largest lake in Hubei Province and a gem among the lakes in the middle and lower reaches of the Yangtze River.However,in recent decades,due to factors such as climate change and human interference,the water quality of Hong Hu has gradually deteriorated,and biodiversity has become almost scarce.Submerged plants are the primary productivity of aquatic ecosystems,and the distribution area of submerged plants in the lake has gradually decreased and tended to disappear.The implementation of the"returning farmland to lake"project is based on the ecological restoration and protection of Hong Hu,and based on this,to restore the submerged vegetation of Hong Hu.This study was conducted in three lake areas with different habitat backgrounds in the"returning farmland to lake"area,namely:the Yangchai Hu area(29.751~oN,113.319~oE),all embankments were demolished),the Bagua Zhou area(29.759~oN,113.310~oE),part of the embankments were demolished),and the Guandun Cun area(29.759~oN,113.362~oE),the embankments were functionally removed,but mostly intact).As a natural lake,Hong Hu should have accumulated a large number of submerged plant underground reproductive organs in its sediment;grazing(mixed)animals enclosed in Hong Hu in the past should be the main factor affecting the growth of submerged plants in the"returning farmland to lake"area.In addition,the environmental factors affecting the recovery and growth of submerged plants are different in different habitat backgrounds.Therefore,water plant diversity and underground reproductive organ inventory surveys were conducted in three areas,and in-situ enclosed controlled experiments were conducted to explore the environmental factors affecting the recovery and growth of submerged plants in the"returning farmland to lake"area of Hong Hu,in order to provide scientific basis for the restoration of the submerged plant community in this area.This study explored the environmental factors affecting the recovery and growth of submerged plants in the"returning farmland to lake"area.A survey of submerged plant reproductive organ inventories and aquatic vegetation communities was conducted,and controlled experiments were conducted on 11 species of submerged plants with 5 growth types(the experimental materials used in the three experiments were different)after removing the effects of fish through experimental enclosure.The experimental materials were divided into the following five growth types:1)Potamogeton lucens,Potamogeton Maackianus,and Potamogeton Malaianus,2)Elodea nuttallii,Hydrilla verticillata,and Egeria densa,3)Vallisneria denseserrulata,Vallisneria spinulosa,and Vallisneria natans,4)Ceratophyllum demersum,and 5)Myriophyllum spicatum.The main results are as follows:(1).The Yangchai Hu area is open around,connected to the open water area.Four kinds of submerged plants were found in the inventory of reproductive organs,but the density was low,all less than 200 ind/m~2.After 30 days of the experiment,nine types of submerged plants,including Potamogeton lucens,Potamogeton Maackianus,Potamogeton Malaianus,Vallisneria spinulosa,and Vallisneria natans,had died both inside and outside the enclosure.Within the enclosure,only Vallisneria denseserrulata,Elodea nuttallii,Hydrilla verticillata,and Egeria densa survived.Additionally,during the experiment,the Hong Hu experienced extreme floods,and the water level rose sharply in a short time(an average of about 120 cm),which was one of the important reasons for the death of submerged plants.The quarterly survey of aquatic plants showed that there were no submerged plants outside the enclosure,and the cover of the water chestnut(Trapa bispinosa R.)was as high as 100%from summer to autumn.Therefore,this area is not suitable for the recovery of submerged plants.(2).In the area surrounding Bagua Zhou,there are many embankments.Only two types of submerged plants,Chara Linn.and Potamogeton crispus L.,were found in the seedbank,with a density of 75 ind/m~2 for Potamogeton crispus L.In the experiment,three types of submerged plants were selected,and on the 7th day of the experiment,the growth indicators of the submerged plants inside the enclosure were significantly higher than those outside.After 30 days,only the Vallisneria denseserrulata survived inside the Bagua Zhou enclosure,and all other plants had died.In addition,the quarterly survey of aquatic plants found that there were emergent plants,such as the lotus(Nelumbo nucifera G.)and the reed(Phragmites australis T.),in this area.Although these plants have a certain mitigating effect on wind and wave stress,the competition for ecological niches between emergent plants and submerged plants is very obvious.Therefore,this area is not suitable for the restoration of submerged plants.(3).In Guandun Cun,the water level is shallow,and the wind and waves are small.After 30 days of the experiment,there was no significant difference in the growth indicators of the Myriophyllum spicatum between inside and outside the enclosure.However,there was a significant difference in the growth indicators of Hydrilla verticillate inside and outside the enclosure(P>0.05),and the growth indicators of Vallisneria denseserrulata were significantly different inside and outside the enclosure,but the height of the inside Vallisneria denseserrulata was higher than the initial value of the experimental materials.The quarterly survey of aquatic plants showed that there were a large number of submerged plants inside the enclosure,and the Ceratophyllum demersum became the dominant species,with a plant cover of more than 30%.This area has the potential to restore submerged vegetation.In summary,the main reasons why the submerged vegetation cannot recover naturally in the Hong Hu retreat embankment and lake area are as follows:(1)the population cannot be naturally renewed due to the depletion of the seedbank;(2)the low water transparency,water level fluctuations,and shading effect of emergent plants all restrict the growth of submerged plants.Based on the above research results,the following restoration suggestions are proposed for the submerged vegetation in this lake area:(1)artificial supplementation of the seedbank is necessary;(2)artificial planting should be assisted,and the planting area should be selected in areas with relatively shallow water;(3)during planting,the phenological period of submerged plants should be taken into account,and the shading effect of emergent plants should be avoided.The implementation should be gradually advanced in zones,with priority given to the restoration of submerged vegetation in Guandun cun.