Ecological Engineering 37 (2011) 302–308
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Ecological
Engineering
j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e c o l e n
g
In-lake algal bloom removal and submerged vegetation restoration using modified local soils
Gang Pan ∗,Bo Yang,Dan Wang,Hao Chen,Bing-hui Tian,Mu-lan Zhang,Xian-zheng Yuan,Juan Chen
Rearch Center for Eco-environmental Sciences,Chine Academy of Sciences,18Shuangqing Road,Beijing 100085,China
a r t i c l e i n f o Article history:
Received 30September 2009
Received in revid form 2October 2010Accepted 10November 2010
Available online 14 December 2010Keywords:
Eutrophication HAB mitigation
Alternative stable states transition MLS-IER
Macrophytes restoration
a b s t r a c t
A “modified local soil induced ecological restoration”(MLS-IER)technology was developed for the restora-tion of degraded shallow lakes.Modified local soils that mixed with macrophyte eds were ud to flocculate the algal blooms and sink them down to the bottom of the lake.The incread water clarity and the improved diment quality due to the covering of clean modified local soils make it possible for a quick restoration of submerged macrophytes in eutrophic shallow lakes.The MLS-IER technology was tested in the whole bay of Liaoyangyuan (0.1km 2)in Lake Tai (Wuxi,China)in August 2006.The whole bay was fully covered by more than 1cm cyanobacterial bloom since June,which caud massive killing of fish and aquatic vegetations.Some 4tons of chitosan-modified local soils were sprayed over the whole bay and the vere bloom was successfully removed within one day.The cchi depth was incread from 0cm to 30cm,and the chlorophyll-a,total-P,and total-N were all reduced by more than 86%within one day’s time.Four month纺织技术
s after the treatment,submerged macrophytes were successfully restored within the whole bay.Cyanotoxin microcystins RR and LR were reduced by 50%and 40%,respectively,compared to tho outside the bay 4months later.The biodiversity index of zoobenthos and that of phytoplankton inside the bay became higher than that outside the bay,while zooplankton diversity index remained rel-atively unchanged.This field trial study indicated that restoration of submerged macrophytes in shallow lakes could be significantly accelerated by using MLS-IER technology.The long-term ecological respon and the transition mechanism between algal cells and submerged macrophytes in the diment need to be further studied in controlled whole lake experiments.
© 2010 Elvier B.V. All rights rerved.
1.Introduction
甘蓝菜的做法
In recent years,harmful algal blooms (HAB)are occurring with greater frequency and intensity in many shallow lakes.A vere HAB of some 700km 2occurred in Taihu Lake (China)in 2007,caus-ing a drinking water crisis in Wuxi city (Guo,2007).HAB is a global problem,and toxic freshwater has been implicated in human and animal illness and death in over 45countries worldwide (Chorus and Bartram,1999;Huisman et al.,2005).
During the past veral decades much effort has been made around the world to solve this disaster.Some of the existing techniques focus on removing algae from the water through mech-anisms such as floatation,filtration,and pumping/sucking methods (Lam et al.,1995).The methods have advantages of getting rid of HAB and the related nutrients safely but are not suitable for most
∗Corresponding author at:State Key Lab.Environ.Aquatic Chemistry,Rearch Center for Eco-environmental Sciences,Chine Academy of Sciences,18Shuangqing Road,Beijing 100085,China.Tel.:+861062849686.
E-mail address:gpan@rcees.ac (G.Pan).open water columns where the floating algae is not thick enough becau of the low efficiency and high costs.Other in situ control techniques,such as chemical flocculation of algae,or algaecides (Chorus and Bartram,1999),filter-feeding fish and zoonplankton control (Jeppen et al.,2004;Ke et al.,2009),plant allelopathy or bacteria,and clay flocculation (Anderson,1997;Beaulieu et al.,2005;Sengco,2009;Sengco and Anderson,2004),can remove blooms temporarily but can produce a variety of adver effects (change of pH and oxygen levels,adver ecological effects,etc.),and require high dosage and high costs.Although the HAB mitiga-tion techniques mentioned above have some advantages to remove HAB,few of them can control such large-scale HAB safely,quickly and cost-effectively.While long-term remediation involves
basin management and pollution control,short-term respon requires in-lake techniques that can be applied in situ at very large scales,at low cost,with high efficiency and safety relative to public and ecological health.
Nevertheless,removing algae from water is not enough to achieve the goal of restoration of degraded shallow lakes,and rebuilding of submerge vegetation is considered an important and necessary step for the restoration of eutrophic lake (Gulati et al.,
0925-8574/$–e front matter © 2010 Elvier B.V. All rights rerved.doi:10.leng.2010.11.019
G.Pan et al./Ecological Engineering37 (2011) 302–308303
2008).It is well recognized that sudden shifts between alterna-tive stable states occur in lakes(Scheffer et al.,1997,2001,2003; Carpenter et al.,1999).One of the best-studied state shifts is the sudden loss of transparency and vegetation subject to human-induced eutrophication such as increa in nutrient loading(Conley et al.,2009;Jeppen et al.,2007;Schindler et al.,2008).When nutrient loading pass a threshold level,the lake can shift from a macrophyte-dominated to an algae dominated state with sig-nificant algal biomass,high turbidity,poor oxygen conditions and major shift i
nfish species.Restoration of clear water and macro-phyte vegetation could only happen at much lower nutrient levels than existed at the time of the state shift to an algae-dominated state.Meijer(2000)showed that the macrophyte vegetation of Lake Veluwe collapd in the late1960s and early1970s when total phosphorus pasd0.2mg/l,and it took more than a decade to reduce the total-P to below0.1mg/l at which point the lake began to return to macrophyte vegetation dominated state.Although the abrupt shift to an algae state has been widely reported,it is also well understood that return to a macrophyte state is only possible after many years of water quality improvement(Scheffer et al.,2001, 2003).There is no evidence in the literature of a naturally occurring rapid return to macrophyte condition without the help of restora-tion interventions.Despite such interventions,although able to quickly reduce phosphorus(albeit,usually only temporarily)or flocculate/remove an algal bloom,there has been no technology that can produce a sustainable long-term effect that combines both algal bloom control and submerged macrophyte restoration.
Our work responds to this need through the development of a“modified local soil induced ecological restoration”(MLS-IER) technology.This technology combines both in situ removal and in situ conversion of HAB into submerged macrophytes using cheap,easily available,and ecologically friendly materials(such as non-polluted local soils)(ES&T news,2006;Pan et al.,2006a,b;Zou et al.,20
06).The principle of modified local soil(MLS)technology is described in Pan et al.,2006a,b)and in our patent(Pan et al.,2005). Briefly,the technology is bad on the discovery that local soil par-ticles(the soil near the bank of a lake)can be modified by adding a small amount of biodegradable natural polymers or proteins,such as chitosan,to produce a highly effectiveflocculent that quickly flocculates algal biomass and sinks it to the bottom of the lake. The overlying water is rendered transparent enhancement and nutrient concentration reduction.The anoxic diment-water state can be quickly altered by applying an additional layer of MLS that can cover the algalflocs and the originally polluted diment.The technology can be applied mechanically to a very large area with low operational and material costs.The load of MLS can be much less than that of using clays only(Pan et al.,2006a,b;Zou et al., 2006).The small amount of modifier ud in MLS(such as chitosan) must be natural materials rather than commercial chemicals that are ecologically friendly,biodegradable,and able to promote the growth of macrophytes.The short-term physicochemical effect of incread water clarity and the cleaner diment-water condi-tions may create a new favorable environment for the growth of submerged vegetation.By using soils that contain eds of suitable macrophytes,the technology provides a edbed in which the eds germinate and produce new macrophyte growth,consuming the nutrients that are contained in theflocculated algae cells.Pan et al.(2006b)had shown afield test of MLS technology and the successful removal of algal bloom in a35m2enclosure.
However, the scale of the test was too small that it could not address the ecological effect of submerged macrophyte restoration.
In this paper we report on a whole bay(0.1km2)experiment in northern Taihu Lake,in which the MLS-IER technology was employed during an inten HAB situation in the August2006. The objective was to study the efficiency of this technology
in
Fig.1.Experimental location of Liaoyangyuan Bay and sampling sites. emergency treatment of freshwater HABs and to monitor its eco-logical effects in submerged macrophyte restoration triggered by the water and diment quality improvement resulting from this technology.Changes in phosphorus,nitrogen,chlorophyll-a, microcystins,biomass of submerged vegetation,phytoplankton, zooplankton and zoobenthos were continuously monitored for v-eral months inside the bay and compared with tho from control areas outside the bay.
2.Materials and methods
2.1.Experimental location
The experiment was carried out on13August2006in the Liaoyangyuan bay in north Taihu Lake,which is about0.1km2in area and approximately1.6m deep(Fig.1).Three sides of the bay are surrounded by resort hotels with one side of the bay open to Taihu Lake.HAB begins to occur in this area in late May every year. Natural wind-driven circulation tends tofill this bay and accumu-lated continuously with HAB from the Taihu Lake.By August2006, the bay was fully covered with more than1cm of HAB biomass (Fig.2)with accompanyingfish and macrophytes killing,and strong odor that created significa
nt problems for local residents.As part of our experiment,local government built an enclosure at the mouth of the Bay to block further transfer of HAB from Taihu
Lake.
Fig.2.Severe HAB inside the bay before the treatment(photo taken before the treatment on13th August2006).
304G.Pan et al./Ecological Engineering
37 (2011) 302–308
Fig.3.Treatment of HAB in process using MLS-IER technology.
2.2.MLS-IER technology
MLS-IER technology is toflocculate the HABs using modified local soils and sink them down to the bottom of the lake,and the macrophyte eds that are wrapped in the modified soils can grow on the clean layer of MLS that cover the algaeflocs and the pol-luted diment under an improved water transparency conditions. The local soil is collected from the lakeside and a natural poly-mer called chitosan is ud to modify the soil particle surfaces so that the soil particles can combine strongly with HAB cells(Pan et al.,2006b;Zou et al.,2006).The local soil that we ud near the Liaoyangyuan Bay is a kind of sandy soil which mainly con-sists of clays,iron oxides,and sands.It was found that chitosan can greatly enhance the netting and bridging function of many type of solid particles as aflocculent in removal algal cells(Zou et al.,2006).The technology was conducted in thefield as follows: the local soil suspension(containing macrophyte eds)and chi-tosan solution were placed in two storage tanks respectively;the machine which was specifically designed for this technology mixed the two components with lake water in a controlled ratio(usu-ally V local soil suspension/V chit
osan solution/V lake water=1/1/50)and then sprayed the mixture onto the water surface(Fig.3).For shallow lakes(<2m),one t of the apparatus can clear6000–10,000m2 HAB per hour,the average cost for material was0.1US$/m2,and the average dosage/load was40–50g MLS/m2.More details includ-ing the principles of MLS technology is described previously(Pan et al.,2006b;Zou et al.,2006).
2.3.Sampling sites and analysis
To estimate the emergent and long-term effects of the MLS-IER technology,three sampling sites inside the bay and two control sites outside the bay were ttled(Fig.1).Total nitro-gen(TN),total phosphorus(TP),phosphate(PO43−),chlorophyll-a (Chl-a),ammonium nitrogen(NH4+-N),nitrate nitrogen(NO3−
-N),Fig.4.One day after treatment using MLS-IER technology(photo taken on14August 2006).
nitrite nitrogen(NO2−-N),dissolved algae toxins(microcystins RR and LR),biomass of submerged vegetation,phytoplankton,zoo-plankton,and zoobenthos,were monitored after the treatment. Submerged vegetation biomass was sampled over0.25m2.The TN,TP,PO43−,Chl-a,NH4+-N,NO3−-N,NO2−-N and Chl-a were measured in the laboratory as prescribed in Monitoring Analysis Method of Water and Waste Water(Ministry of Environmental Protection of China,2002).Microcystins RR and LR were measured as described in Zhang et al.(2004)and Yan et al.(2004);submerged macrophytes,phytoplankton,zooplankton,and zoobenthos were measured by Nanjing Geography and Limnology Institute of the Chine Academy of Science.
3.Results
3.1.Short-term effect of MLS-IER technology
Ten hours after the treatment using MLS-IER,the HAB layer disappeared in the whole bay(Fig.4).Fig.3shows the effect dur-ing the treatment process.The short-term effect on water quality improvement is prented in Table1.Removal rates for TP,TN, and Chl-a in the sampled water columns were86%,88%,and89%, respectively.The water transparency was improved instantly from virtually zero to above30cm.Fig.5compared the samples before and a few minutes after the treatmen
t.Theflocs which formed between algae cells and chitosan-modified local soils sank quickly to the bottom.As the are quite sticky,a cond application of the MLS was effective to prevent the re-suspension after the treatment.
3.2.Long-term effect of MLS-IER technology
To investigate the long-term effect of MLS-IER technology, changes in water quality,algae toxins of microcystins,submerged
Table1
Short-term effect of the MLS-IER technology.
Mean values(mg/l)Transparency
TN TP PO43−-P NH4+-N NO3−-N NO2−-N Chl-a SD(cm)
Before treatment36.0 1.200.23 1.370.60.15 5.40
After treatment 4.50.170.18 1.310.50.130.630
曲奇饼干英文Removal(%)8886224171389–
G.Pan et al./Ecological Engineering 37 (2011) 302–308
305
Fig.5.Sampling before (a)and a few minutes after the treatment
(b).
Fig.6.TN changes with time inside and outside the bay.
macrophytes,phytoplankton,zooplankton,and zoobenthos were monitored for 4months after treatment.Further monitoring was not possible becau the bay was turned into an artificial park by the local government in early 2007.Figs.6–8show that MLS-IER technology maintained the removal
effect of TN,TP and Chl-a within the monitoring period.TP was effectively reduced from some 1.2mg/l to about 0.14mg/l within veral days and kept drop-ping down to 0.11mg/l over the next 4months in the bay,which was lower than the average TP value of about 0.2mg/l outside the bay (Fig.7).TN was reduced from more than 30mg/l to less than 8mg/l and maintained this level throughout the monitoring period (Fig.6).Fig.9shows that about 1/3of NH 4+-N inside the bay was reduced in the following 4months compared to that of control sites outside the bay.
Two cyanobacterial toxins microcystins RR and LR were moni-tored after the treatment of the HAB.After 4months,more than 50%microcystins RR and 40%microcystins LR were reduced compared to tho outside the Bay (Fig.10
廉吏
).
Fig.7.TP changes with time inside and outside the
bay.Fig.8.Chlorophyll-a changes with time inside and outside the bay.
Changes in phytoplankton,zooplankton,and zoobenthos inside and outside the bay are prented in Tables 2–4,respectively.For phytoplankton,before the treatment,cyanobacteria were domi-nant inside and outside the bay.After the treatment,cyanobacteria decread gradually to 26%and chlorophyta incread from 0.01%to 37%by December inside the bay.However,outside the bay,cyanobacteria only reduced to 38%and chlorophyta incread to 28%(Table 2).Zooplankton composition inside and outside the bay was similar (Table 3).For zoobenthos,Branchiura sowerbyi ,Glyp-totendipes barbipes ,and Propsilocerus akamusi became detectable inside the bay,while they were not detectable outside the bay (Table 4).
Bad on Tables 2–4,the biodiversity index (Table 5)was calcu-lated according to Shannon–Wiener equation:d =−
s i =1
n
i
N
ln
n i
N
Fig.9.NH 4+-N changes with time inside and outside the bay.
306G.Pan et al./Ecological Engineering
37 (2011) 302–308
Fig.10.Microcystins RR and LR changes with time inside and outside the bay.
Table 2
Composition changes of phytoplankton.Position
Time
Composition of phytoplankton (%)Cyanophyta
Chlorophyta Bacillariophyta Cryptophyta Euglenophyta Chrysophyta Xanthophyta Inside bay
August 98.20.01 1.7––––October 66.923.2 3.6 4.4 1.1-0.7December 26.437.415.47.5- 6.7 6.6Outside bay
August 98.10.01 1.8––––October 21.630.825.415.9 3.7 2.9–December
38.6
28.2
16.0
8.1
--9.1
Table 3
Composition changes of zooplankton.Position
Time
勇担当Composition of zooplankton (%)Cladocera
Copepods Rotifera Inside bay
August 50.013.037.0October 37.3 5.157.6December 18.014.867.2Outside bay
August 50.013.037.0October 35.08.057.0December
17.0
20.5出国护照办理流程
62.5
where d is biodiversity index,n i is the number of single species in the sample,and N is the sum of all species in the sample,n i /N is the proportion of each species in the sample.Table 5indicates that phytoplankton biodiversity dropped initially inside the bay one month after the treatment (September),but 4months later it became higher than that of the control sites outside the bay.The zooplankton diversity remained relatively unchanged inside and outside the bay before and after the treatment.The zoobenthos biodiversity inside the bay became much higher than that of the control sites 4months after the treatment.
日下无双Before the treatment there was no submerged vegetation in any of the sampling sites inside and outside the bay.Four months after the treatment,macrophytes (mainly potamogeton crispus )have
Table 5200作文
Comparison of biodiversity index inside and outside the bay.Position
Time
d
Phytoplankton
Zooplankton Zoobenthos Inside bay
August 0.0910.9790.087October 0.9490.8370.633December 1.5620.858 1.011Outside bay
August 0.0910.9790.087October 1.5590.8890.741December
1.439
0.920
0.779
been successfully re-established in the whole bay (Fig.11).The biomass of submerged vegetation incread from zero in August to about 1000g/m 2(wet weight)in December,while submerged vegetation in the control sites outside the bay was still nil during the same period (Table 6).4.Discussion
During the algal blooms,many of the nutrients are enriched in the algal cells.The short-term nutrients
removal efficiency shown in Table 1was largely due to the removal of algal cells.The nutri-ents may be relead back to water either through re-suspension
Table 4
Composition changes of zoobenthos.Position
Time
Composition of zoobenthos (%)Limnodrilus hoffmeisteri
Branchiura sowerbyi Propsilocerus akamusi Chironomus plumosus Tanypus
punctipennis Glyptotendipes barbipes Inside bay
August 1.1––98.30.6–October 0.06––68.231.70.04December 28.8 1.90.258.110.90.1Outside bay
August 1.1––98.30.6–October 53.8––0.945.20.1December
60.9
–
–
3.2
35.9
–
