洱海底泥红壤改性对水质和水生植物的影响

Effects of Red Soil-Modified Sediment on Water Quality and Submerged Macrophytes:An in Situ Experiment in Erhai Lake

鉴于湖泊内源污染不断加重,出现了较多以铝(Al)、铁(Fe)、钙(Ca)、镧(La)盐等化学絮凝材料为主的湖泊底质环境改善方法,但大规模应用受长期控磷效率、生物毒性和使用成本等因素限制;天然粘土、红土和石英砂等材料由于廉价无污染、环境友好等特性,其用于改善湖泊水体环境和控制底泥磷释放越来越受到重视。2014年8月至2015年7月,在洱海近岸水域设置围隔开展原位试验,采用洱海本地无污染红壤对底质进行浅层覆盖改性,探究此方法对水质及沉水植物的影响。试验设置3个不同处理组,分别为对照组(CK)、红壤覆盖组(S)以及红壤覆盖+沉水植物组(MS),每组处理4个重复,逐月监测各围隔内水质和沉水植物生长情况。结果表明,采用红壤对底泥进行改性,可以短期提高水体透明度,为沉水植物生长创造良好条件,促进移栽沉水植物的生长与建群,在某些时段可以改善水质(透明度最高达2.2 m),但红壤覆盖措施并没有长期显著降低水体中的总氮、总磷和藻类的含量(P>0.05)。全年水生植物保持在7种左右,群落主要由黑藻(Hydrilla verticillat)、篦齿眼子菜(Potamogeton pectinatus)、单果眼子菜(P.acutifolius)、金鱼藻(Ceratophyllum demersum)、狐尾藻(Myriophyllum spicatum)、苦草(Vallisneria natans)和微齿眼子菜(P.maackianus)组成,生物量也在不断增加,最高达18000 g/m^2,群落稳定后的优势种为黑藻。研究结果可以为富营养化湖泊生态修复短期水质危机处理提供借鉴,为沉水植物群落恢复提供可探索的方向。

Recently,many types of geomaterials have been used to improve the sediment environment with the aim of controlling nutrient release from fertile sediments.However,the use of geomaterials on a large scale is limited by cost,toxicity and the effectiveness of long term phosphorus control.In this study,an in situ experiment was carried out in Erhai Lake from August 2014to July 2015,using unpolluted local red soil to cover the sediment within experimental enclosures(3min diameter,4min height).The effects on water quality and submerged macrophytes were examined and compared.The test area was at the north of Erhai Lake where excessive deposition of sediments high in nitrogen and phosphorus was occurring.The water depth at location was 1.5-3.0mand water quality was GradeⅢ.Three treatment groups were set,each with 4replicates:red soil cap(S),red soil cap with submerged macrophytes(MS)and a control(CK).Before the test,aquatic plants in the enclosure were cleaned and the sediment in each enclosure for the S and MS treatments was capped with 5cm of red soil.The Macrophytic,Vallisneria natans,was transplanted in the MS enclosures to study the effect of submerged vegetation.Water quality within the en-closure and growth of submerged macrophytes were measured monthly.Results show that the use of red soil modified sediment quickly increased clarity,creating conditions that promoted macrophyte colonization and growth,and improved water quality,particularly water clarity(Secchi depth up to 2.2m).However,the red soil cap did not significantly reduce the concentration of total nitrogen or total phosphorus,or reduce phytoplankton biomass during the experimental period(P>0.05).The annual aquatic plants colonizing the enclosures included about 7species,including Hydrilla verticillate,Potamogeton pectinatus,P.acutifolius,Ceratophyllum demersum,Myriophyllum spicatum,Vallisneria natans and P.maackianus.The biomass of the aquatic community increased continuously,up to 1.8kg/m^2.After the plant community stabilized,the dominant species was Hydrilla verticillate.Our findings provide a reference for treatment of short-term water quality crises in eutrophic lakes and a research direction for restoration of sub-merged plant communities.