The Role Of Periphyton In Shallow Lakes Restoration

Shallow lakes can have two alternative stable states over a wide range of nutrient concentration: a macrophyte-dominated clear-water state and a phytoplankton--dominated turbid-water state.Periphyton communities play a key role in primary productivity,nutrient cycling,and food web interactions in the littoral zone of shallow lakes.However,Periphyton communities have received relatively little attention in lake restoration.The experiments were conducted from December 2013 to November 2014 in Lake Donghu.The primary physicals,chemistry,benthic algae biomass and composition were determined,and these characteristics were compared between 2004 and 2014 to explore the role of periphyton in the submerged macrophytes restoration.At the same time,the contents of total phosphorus and forms of periphyton were mearsured.The water quality of Moshan(Site C)belonged to class II to class IV based on TN and TP levels during the survey,and class IV to class V in Shuiguohu(Site A),Wuhan University(Site B)and Jiunvdun(Site D).There were seasonal fluctuation in concentration of Chlorophyll a(Chl a),ash free dry mass(AFDM),and significant correlation between them(r = 0.639,P < 0.05).Regression analysis showed that there is no correlation between water total phosphorus(TP)and benthic algae Chl a.A total of 156 taxa(including variations)of 22 genera belonged to Bacillariophyta were observed.Benthic diatom communities in Site A,B and D were similarly,and relatively stable in the seasonal changes throughout the year,and Melosira varians and Fragilaria capucina var.capitellata were the predominant species.However,the diatom communities in Site C were changed: the dominant species were Achnanthidium minutissimum and Fragilaria capucina var.capitellata.The result of Redundancy Analysis(RDA)indicated that water temperature was the most important factor in Site A/B/D.The trends of diatom indices(TDI,IPS and IBD)were basically consistent.The values of diatom indices all indicated that the water quality of Site C belonged to good or high level,while that of Site A/B were moderate to poor quality.There was significant relationship(r = 0.887,p < 0.01)between the periphyton total phorphorus(TP)and AFDM.The concentrations of Fe-P was greater when periphyton TP was greater.The IP made the most part of TP(54~85%),while Fe-P and Ca-P were 32~64% and 9~46%,respectively.Fe-P was the absolutely dominant form in spring at all sites,while it was the dominant form at Site D in the whole year.At Site A/B/C,the ratios of Ca-P were higher than Fe-P in autumn.The data showed that benthic algae played a key role in short-term phorphorus retention in eutrophication lakes.In comparison to 2004,the results showed that,the decline of sewage and better water treatment has led to some water quality improvements in Lake Donghu.In addition,the water level reduction(0.46 m)was the ultimate force which accelerated the system to a macrophyte-filamentous green algae dominant state.And more species of epiphytic diatoms were found in 2014 at all sites.But the submerged macrophytes covered only about 30 % area of the littoral zone while the rest areas were blanketed by thick benthic algae mats.In a lake lacking submerged plants,abundance of filamentous green algae may act as a buffer against water degradagion.