Water Health Assessment And Biological Regulation Of Submereged Macrophytes In A Macrophytic Sub-lake Of Baiyangdian Lake

Baiyangdian Lake is the largest freshwater lake in North China.It plays an important role in maintaining regional ecological security.In recent years,due to human disturbance,the ecological environment in Baiyangdian Lake has been destroyed to a certain extent.Taking the Shihoudian sub-lake(a macrophytic sub-lake)for example,the overgrowth of submerged macrophytes has occurred in this sub-lake.Although the submerged macrophytes play important roles in maintaining clean water of lake,the overgrownth of submerged macrophytes has caused insufficient underwater light and indirectly affect community distribution of other aquatic organisms.Otherwise,the respiration of submerged macrophytes consumes a lot of oxygen,and the decomposition of plant residues causes secondary pollution to the water.At present,the water environment in Shihoudian sub-lake shows a tendency of good water quality in spring and summer,and poor water quality in autumn and winter.Therefore,this study proposed the ecological restoration concept which using biological methods to regulate the submerged macrophytes.It is intended to control or inhibit the overgrowth of submerged plants based on the interaction of aquatic organisms,so as to achieve the purpose of improving water quality and promoting the restoration of ecological health of the water.In this paper,we first used biological assessment method to evaluate the health of the Shihoudian sub-lake,and then the biological regulation method was used to study the effects of omnivorous fish(Carassius auratus)and three snails(Radix swinhoei,Cipangopaludina chinensis,and Bellamya limnophila)on the growth of dominant submerged macrophytes under simulated experimental conditions.The main findings are as follows:1)Useing phytoplankton to assess water body health suatus during the overgrown period of submerged macrophytesA total of 68 species(51 genera)of phytoplankton were identified over a total cuhtured period,belonging to six major functional group,i.e,Chlorophyta(30 species).Bacillariophyta(16 species),Cyanophyta(16 species),Euglenophyta(3 species),Pyrrophyta(1 species),and Cryptophyta(1 species),with phytoplankton biomass of5.68×10~6 cells/L?17.24×10~6 cells/L(average 9.13×10~6 cells/L)and phytoplankton abundance of 1.42?8.71 mg/L(average 4.61 mg/L).Redundancy Analysis analysis indicated that transparency,total dissolved solids,conductivity and p H were the most important environmental factors determining the spatial distribution of phytoplankton species composition in summer.The water quality of Shihoudian sub-lake was?-meso-polluted to oligo-polluted judging from the phytoplankton diversity evaluation results.Submerged macrophytes that grow in large quantities absorb nutrients and release allelochemicals,reducing the abundance and biomass of phytoplankton.Compared with Algal Regions and non-overgrown period of Baiyangdian Lake,the characteristics of phytoplankton community in the overgrown period of submerged macrophytes display a large difference.This study provides support for ecological restoration and functional enhancement of macrophyte-dominated sub-lake.2)Analysing effects of omnivorous fish crucian carp on the dominant submerged macrophyteThe results showed that under crucian carp stress conditions,both Vallisneria natans and Myriophyllum spicatum showed a decreased in the underground part(root length,root dry weight,and root proportion).The root dry weight and root proportion of Vallisneria natans and Myriophyllum spicatum were significantly lower than the control group without crucian carp stress.For the aerial part,in the medium-density group of Carassius auratus treatment group,it was the most beneficial group to the growth of Vallisneria natans and Myriophyllum spicatum.In addition,the stocking density of crucian carp had a significant effect on the interspecific competition between Vallisneria natans and Myriophyllum spicatum.Compared with the control group without crucian carp,Vallisneria natans had the stronger competitive advantage in the low density group and the medium density group.3)Analysing effects of snails on the dominant submerged macrophyteThe nutrient content of the water increased with each kind of snails and the total nitrogen content increased significantly.All three kinds of snails are good for submerged macrophyte.But with the density of snails exceeds a certain value,this effect decreases.Compared with the medium density group,the total dry weight of Myriophyllum spicatum and Potamogeton pectinatus is lower in high density group.In the control group without snails,it is better for Myriophyllum spicatum and Potamogeton pectinatus in individual plant than mixing plant.