Rapid assessment o f water eutrophic state in tien yen ha coi bay by estimating chlorophyll a concentration using geostatistical interpolations and modis data

VNU Jo u rn al of Scicncc, E arth Scicnces 28 (2012) 181-189 Rapid assessment of water eutrophic state in Tien Yen-Ha Coi Bay by estimating Chlorophyll-a concentration using geostatistical interpolations and MODIS data Nguyen Thi Thu Ha’’*, Pham Thi Tuyet^, Mai Trong Nhuan', Nguyen Van Vuong', ^Faculty o f Geology, VNU University o f Science, 334 Nguyen Trai, Hanoi, Vietnam ^ VNƯ Sea and Island Research Center R eceived 25 July 2012; received in revised form A ugust 2012 Abstract E uữophication is a natural process of enrichm ent o f water by nutrients, how ever in many case is considered as one of the major factors of water pollution affecting coastal ecosystem Selection and application o f suitable indicator and m ethod to assess sea euừophication is utm ost im portant This study aim s at clarifying w ater euứophic state m Tien Y en - Ha Coi B ay using geostatistical methods of 40 in situ sites data and auxiliary information from MODIS/Terra image Resultant predicted chlorophyll-a concenừation distribution map in Tien Yen - Ha Coi Bay produced by cokriging and euừophic possibility map com puted by indicator kriging identified clearly that the bay is classified as natural euừophic waters B y this study, M ODIS offers the possibility to support auxiliary information for assessment euữophic state m large water areas Cokrigm g and indicator kriging was proved to be effective for rapid environm ental quality assessm ent and coastal w ater m anagem ent Keywords: Eutrophications, cokriging, indicator kriging, estim ation map, probability map Introduction fish kills; a loss of ecosystem integrity, aquaculture production, fish stocks and amenity Eutrophication o f coastal w aters has been value; and changes in biodiversity [5] considered one o f the m ajor threats to the health Therefore, identifying the m ost efficient w ay to o f marine ecosystem s The different processes diagnose the euữophic state o f coastal waters is and effects o f coastal eutrophication are well indispensable known and docum ented [1-4] The m ain cause environm ent and preserve ecosystem health o f euừophication in coastal w aters is nutrient over-enrichm ent (nitrogen, phosphorus harm ful algal bloom s, to protect coastal H ow ever euừophication o f coastal waters has been considered for a long time and many related researches have been carried-out w orldwide, one im portant question is still to be answered: “H ow should prim ary production o f eutrophication be m easured or estim ated?” Such question requires thorough scientific and silica) leading to: an increase in the frequency of task shellfish contamination, anoxic and hypoxic events and * Corresponding author Tel: 84-1222275688 E-mail: hantt_kdc@vnu.edu.vn 181 182 N T T H a et a l / V N U Journal o f Science, Earth Sciences 28 (2012) Ĩ - Ì obtained results were considered as a first baseline for coastal w ater environmental analysis and m anagem ent o f Tien Yen - Ha Coi Bay on eutrophication assessm ent a n a ly se s as w ell as c o o rd in a tio n , n e w m e th o d s and approaches in assessm ent o f coastal water euữophic state need be developed and demonstrated C hlorophyll-a (Chl-a) concentration is an effective m easure o f the ừophic status o f sea and land waters, because it is re la te d s o n g ly to abundance an d M aterials an d M eth o d s a q u a tic p h y to p la n k to n b io m a ss E s tim a tin g C h l-a The study area concentration is one o f the m ost traditional and significant applications o f rem ote sensing for evaluating aquatic ecosystem s and m onitoring eutrophication [6-10] This study develops a m ethod for rapid assessm ent o f w ater eutrophic Tien Yen - H a Coi Bay IS adjacent to China - Vietnam border and connected to the South China Sea by five channels (Fig 1) The most state in Tien Yen - Ha Coi Bay by using various geostatistical interpolations o f in situ Chl-a concenfrations and auxiliary inform ation from M ODIS/T eư a im age Resultant probability map o f w ater eutrophic state and potential based on Chl-a concentrations o f this study helps delim iting zones o f high and low rem arkable feature o f the bay IS its shallowness: eufrophication Since no other data o f similar nature is available at the present time, the such as tide, waves, and near-shore currents the sea depth generally ranges from to m A nother feature is that the bay has a strong dium al tide regim e with maxim um am plitude o f m [11] Therefore, aquatic ecosystem and environm ent o f the bay are dom inated m ainly by oceanographic factors 21.67'’N tida! 10 20 km 1_I I I I I I I I Figure Location o f T ien Y en - H a Coi B ay and positions o f 40 sam pling points for w ater sampling 183 N T T Ha et a i / V N U lournal o f Science, Earth Sciences 28 (2012) Í S Ì - Ĩ A decline in the environm ental and M O D IS d a ta ecological systems in Tien Yen - Ha Coi Bay has been reported, including loss o f seagrass T h e T e a sp a c e c ft p a sse s o v e r T ie n Y en meadows, phytoplankton abundance and water - H a C o i B a y a t a b o u t 3:20 G M T (1 :2 local contam ination [12] tim e ) environm ental threats One on of serious the bay water each day T h is tim e IS su itab le for ac q u irin g s a te llite im a g e ry to c o m p a re w ith in environm ent is euữophication process: its state situ and cause Therefore, assessing w ater eutrophic image data acquired on the same date as the state in Tien w ater sampling (6 July 2010), which were indispensable Yen - Ha task to Coi Bay IS an protect the bay environm ent and preserve ecosystem health w ater quality IB calibrated at-aperture radiances for the 36 bands a n d g e o -lo c a te d fo r W S G -8 N o f th e Ư T M sy stem , Waĩer sam pling and analysis M O D IS/Teưa level w e re c o n c e n tra tio n u se d to A c c o rd in g e stim a te to Ha and C h l-a K o ik e (2011) [14], it was identified that dark-object Sea water in Tien Yen - Ha Coi Bay was subừaction (DOS) by Chavez (1988) [15] was a sampled at 40 points using a speed-board on suitable atm ospheric correction method for the July 2010 with a Global Positioning System M ODIS data o f Tien Yen - (GPS) receiver to locate the points These T h e re fo re , th is stu d y u se d o b ta in e d re fle c ta n c e points, shown after DOS as data for cross-estimation in Fig 1, were selected to Ha Coi Bay investigate the environm ental conditions all over the bay The samples were taken at 50 cm w ater depth using Van D om w ater sampler, filled in liter cleaned bottles at the constant tem perature of "c storage and transported to a laboratory W ater sampling was can ied out w ithin 10 hours before/after time o f image acquiring on July 2011 Speed-boat was used for fast data collection Concentration determ ined by measurem ent of G eostatistical methods Co-Kriging C o-K riging (CK) is a form o f kriging that involves multiple variables It is considered a ‘hybrid’ Kriging technique (i.e non-stationary geostatistical m ethod) In fact, the method is a m ultivariate extension o f Kriging that allows Chl-a standard m ethod in water was Specfa-ophotometric [13] Firstly, water inclusion of more readily available and inexpensive attributes in the prediction process [16] CK uses auxiliary variables and takes into samples were filtered by a pre-w ashed 47m m account glass fiber filter and then exừacted into 90% between variables to improve spatial prediction, acetone w hich The Chl-a and phaeophytin additional requires an coưelated estimation information of cross- concentrations in the extract were determ ined variograms W ith CK the estimated value at an by specữophotom eter at 750 nm and 664 nm unsam pled location is a linear weighted sum o f before acidification, and 750 nm and 665 nm all o f the variables being exam ined (i.e two or after acidification Descriptive statistics o f the more) For two variables, the m odels are: resultant Chl-a concenừations o f the 40 samples z ^ { x ) = ụ ^ {x ) + s^{x) (1) z , { x ) = ụ, {x ) + e,{x) (2) are summarized in Table 184 N T T Ha et a i Ị V N U jou rnal o f Science, Earth Sciences 28 (2 012) 181-189 W here ỊẦ^ and are unknow n mean values E[l{u-, z J ( « ) ) ] = P r a ỗ (constants) and and £ị^ are random eưors {Ziu) Z ị k A t an u n s a m p le d lo c a tio n , Uo, estim a tio n m u s t u se in d ic a to r k rig in g and th e in d ic a to r e stim a to r, / (uo; Zk), a cc o rd in g to: (7 ) = ;= w h e re I(uj, Z re p re s e n ts th e v a lu e s o f th e in d ic a to r at m e a su re d lo c a tio n s Up j = ,2 , ,/i, an d X,j(Zk) is th e w e ig h tin g facto r o f I(uj, ZfJ in e stim a tin g f (uo; Z Results and Discussion The atm ospheric coưection m ethods, DOS, were applied to the M ODIS 36 bands data to obtain surface reflectance (R ự s(Ẵ ))o ĩ the Tien Yen - Ha Coi Bay w ater surface entire Table summarizes descriptive statistics o f obtained Rrs(Ằ)dX two bands: visible green band (band 12, at 551 nm) and blue band (band 9, at 443 nm), The expected value o f I(u; Z t), conditional to n surrounding data, can be expressed as: using M O D IS/T eưa image at km pixel size with total num ber o f pixels is 392 Table i Descriptive statistics w ater samples datasets o f Chl-a concenừations (mg/m^) and obtained reflectance o f bands and 11 M O D IS/Teưa Image after DOS Item Param eter Num ber o f data Average M edian M axim um M inim um Standard deviation Range Chl-a (m g/m ’) 40 12.5 12.7 16.5 8.1 1.8 8.4 ^ (4 ) (M ODIS band 9) 392 0.045 0.043 0.090 0.025 0.011 0.066 /?„(551) (M OD IS band 12) 392 0,047 0.047 0.095 0.014 0.015 0.081 185 N T T Ha et a i / V N U Journal o f Science, Earth Sciences (2012) -Ì Experim ental Fig shows a strong relationship between covariance produced from C hl-a concentrations o f w ater samples and ratio th e se tw o d a ta se ts w a s a p p ro x im a te d b est by o f tw o 12: the exponential model with a nugget effect o f R„(551), versus band 9: R^,(443) (correlation 12 m g / m \ a sill o f 16.6 m g / m \ an d a ran g e o f reflectances coefficient r = at 0.78) M ODIS This band relationship 17 km (Fig 3A) check prediction validation, a scattergram that represents the from M O D IS/Terra image data (R,,(551)/R,,(443)) with spatial estim ation concentrations o f CK the confirm ed a high possibility o f cokriging in Chl-a accuracy To a cross- re la tio n s h ip b e tw e e n th e in situ ^C h ỉa an d Cchia th e p re d ic te d data was CK v a lu e produced (Fig - v alu e u sin g th e 3B) The re su lta n t m ean e o r o f th e p re d ic tio n is clo se to (0.005 mg/m^) and the RM SE is relatively low (0 9 m g /n v '), w h ic h co n firm s th e high o -s c a p a b ility o f C K T h e re s u lta n t C K d istrib u tio n o f Chl-a concentration and the kriging variance map are depicted in Fig and The kriging variances are negligible over the entire bay Only a small zone outside the bay, where no in situ data was collected, has a relatively high variance, but its value is under 10% o f the estim ated (^Chia Figure R elationship between Chl-a concentration o f w ater sam ple and ratio o f two reflectances at M ODIS band 12 (551 nm) versus band (443 nm) c 10 ãã Model + Averfl8ôd Such variance trend also supports the correctness o f the CK estimation Predicted 10- 0istar>ce(0^r«e) h 10 Measured 10' Figure (A) Covariance and exponential model (curve) o f the in 5/7uChl-a concentrations andR„(551)/R„(443) ( B) Scattergram for cross-validation o f cokriging prediction The 45-degree line is superim posed 186 N T T Ha et al / V N U Journal o f Science, Earth Sciences (20 12 ) Ĩ Ĩ - Prediction Chl-adừtribution map produced by CK in local estuaries at the m ouths o f the Ha Coi and D am Ha Rivers and along the coast from The spatial distribution of Chl-a M ong Cai to Hai Ha The middle bay also concenứations within Tien Y en - H a Coi Bay was predicted by CK interpolation (Fig 4) contains high C hl-a from 13.8 to 14.3 mg/m^ Basing on the map, Chl-a concentrations on confrary, the concentrations become low toward July 2010 ranged from 8.1 to 16.5m g/m ^ the west near Cai B au Island with a minimum which are to 7.5 tim es o f the eutrophic level, o f 8.1mg/m^ in the channels connected with the 2.21 mg/m^of Simboura et al [17] Generally, outer sea from Cai Chien to Hai Ha districts On the concentrations o f Chl-a over 14.3 mg/m^ occur 21.55»N ÍOS.DO-E C h l-a (n ig /m ^ ■ i 15.15- 16.50 14.32- 15.15 H i H i ) - 13.81 13.29- 13.49 12.97- 13,29 i S 12.45- 12.97 11.62- 12.45 10.27 -1 1.6 - 10.27 107.45‘F 21.15-’N Figure Spatial distribution of Chl-a concenứations produced by cokriging 21.55-'N I08.00“E Variance of C hl-a (mg/in')^ WÊÊ ■ 1.77 l.2 t 1.46 H I 1.00 1.21 I Ẽ M Ổ.83 1.00 -O.s:^ -0 0 -0 0.38 - 0.49 107.45«E I _ £ 21.15‘N Figure Kriging variance for representing uncertainty of estimation o f Chl-a concenữations by cokriging 187 N T T Ha et al / V N U journal o f Science, Earth Sciences 28 (2 Ì ) Ĩ - Ĩ Those spatial characteristics of Chl-a am ounts of re-suspended material, the accum ulation and concentrations conform ed to the hydrodynamic prevent system in the bay that is generated by the phytoplankton interaction o f regional surface cuưents, tides becom e low in such high-energy zones and waves The local river estuaries and central bay are shielded by the islands (Van Nuoc, Cai Chien, and Chl-a growth of concentrations Water eutrophic state probability map Thuc) and the tortuous CSTT[18] defined 10 mg/m^ o f Chl-a as the therefore the hydro-energy Environm ental Quality Standard (EQS) for related to currents and waves is w eak there coastal waters If the C hl-a concenừation o f a Under such conditions, phytoplankton, the main w ater body frequently exceeds this criterion in source o f high Chl-a concentrations, accumulate summer, it is regarded as having a eutrophic and condition Based on this criterion, the waters o f coastline, and grow channels V inh Thus, which In and contrast, the in largely the connection m ovable waters affected directly by the outer sea, the hydro­ Tien Yen - Ha Coi Bay w ere considered to be euưophic energy is strong These waters contain abundant 21.55"N 108,00*E P{u;\ồ) ■ ■ 0.97 - 1.00 ■ ■ 0.94 - 0.97 m 0.89-0.94 B | 0.84-0.89 s 0.68-0.84 ggsi 0.56- 0.68 0.42-0.56 0.23 - 0.42 0.00-0.23 Cai Bau 107.45-E Figure Probability map o f w ater euừophic state and potential in T ien Y en - Ha Coi Bay by IK Figure shows probability of w ater the bay w ith outer sea which located between euừophic state and potential in Tien Y en - Ha Van N uoc and Cai Chien islands However, Coi Bay by using IK and threshold o f 10 undesirable eutrophication disturbances, such as m g/m ^ A high probability o f euừophication algae bloom s, generated in the water with (P(u;10) ranges from 0.97 to 1) was determ ined concentration o f C hi-a over lOOmg/m^ [19] in the bay w ater entire except for the zones in have not been observed in Tien Yen - Ha Coi front o f Tien Yen Estuary or channel connected Bay This bay m ay be eutrophic by natural 188 N T T Ha et al / V N U jou rn al o f Science, Earth Sciences (2 01 2) 181-189 processes rather than by anthropogenic causes References such as waste water, thereby m aintaining a high ecological quality sim ilar to other coastal areas [1] Anderson, D M., Gilbert p M., and Burkholder J M., “Harmful Algal Blooms and Euừophication: Nutrient Sourccs, Composition, and Consequences.” Estuaries 25 (4b) (2002) 704^726 [2] Diaz, R J., Nestlerode J., and Diaz M L., 2004 “A global perspective on the effects of eufrophication and hypoxia on aquatic biota” InG L Rupp and M D White, eds Proceedings of the 7th International Symposium on Fish Physiology, Toxicology, and Water Quality, Tallinn, Estonia, May 12-15, 2003 Athens, Georgia: U.S Environmental Protection Agency, Ecosystcms Research Division (EPA 600/R-04/049) [3] Lu, S and Hodgkiss I J., “Harmful algal bloom causative collected from Hong Kong waters.” Nydrobioỉogia.5l2(ì-3) (2004) 231-238 [4] Spokes, L J and JickcHs T D., “Is the atmosphere really an important source of reactive niừogen to coastal waters?” ContinentalShelf Research 25 (2005) 20222035 [5] Shafique N A., Fulk F A., Autrcy B c , and Flotemersch J E., Hyperspcctral Remote Sensing of Water Quality Parameters for Large Rivers in the Ohio River Basin, Ohio River Basin Consortium for Research and Education, Marietta, OH, November 5-7, (2003) pp 216 - [20] Conclusions This study dem onsfrates usefulness o f two geostatistical auxiliary methods, inform ation CK and IK, for coastal and w ater euừophication assessm ent by considering the relationship between in situ data and M ODIS image reflectance, analyzing the excess o f Chla concentration against the environm ental standard A case study for Tien Yen - Ha Coi Bay clarified that Chl-a concentrations in seawater exceeded high eufrophic level [17] and the bay can be m arked as natural eufrophic waters Another superiority o f the com bination between geostaitistical m ethods and rem ote sensing data was to provide rapidly database for good understanding o f the spatial variation and distribution of Chl-a concenừation Consequently, that is easy to delineate high and low risk areas o f eufrophic state and potential for regional water management Acknowledgement We are grateful to Projects coded QGTD 10.31 TRIG-A and 105.09.82.09 N AFO STED by the V ietnam ese National Scientific G rant for their support o f the fieldw ork and sample analysis Thanks also to N A SA for providing the M ODIS data 221 [6] Matthews A M., Duncan A G., Davison R G., An assessment o f validation techniques for estimating chlorophyil-a concentration from airborne multispectral imagery International Journal o f Remote Sensing, 22(2001) 429-447 [7] Cauwer V D., Ruddick K., Park Y J., Nechad B., Kyramarios M., Optical remote sensing in support of euừophication Monitoring in the southern North Sea EARSeL eProceedingSy 3(2004)208-221 [8] Zimba p V and Gitelson A., 2006 Remote estimation o f chlorophyll concentration in hyper-eutrophic aquatic systems: Model tuning and accuracy optimization Aquaculture, 256; 272-286 [9] Schalles J techniques F., to Optical remote sensing estimate phytoplankton chlorophyll-a concentrations in coastal waters with varying suspended matter and CDOM concentrations In: Richardson L L and LeDew N T T Ha et al / VhJU Journal o f Science, Earth Sciences (2 012) Ĩ - Ì 189 E.F (Eds.), Remote sensing of Aquatic Coastal F.cosystem Processes: Science and Management Application, spnnger, Netherlands, (2009) 2778 [15] rh av ez J p s Jr., An improved dark-object subtraction technique for atmospheric scattering coưection of multispectral data Remote Sensing of Environment, 24 (1988) 459-479 [10] Ibrahim A N, Mabuchi Y., Murakami M., Remote sensing aigorilhms for monitoring eutrophi cation in Ishizuchi stonn water reservoir in Kochi Prefecture, Japan Hydrological Sciences Journal, 50 (2009) 525542 [16] McBratney A.B., Odch I.O.A., Bishop T.F.A., Dunbar M.S and Shatar T.M., An overview of pedometric techniques for use in soil survey Geoderma, 97 (2000) 293-327 [11] NOAA, lUCN, VASI, Khuôn khổ quàn lý tổng hợp vùng bờ Quảng Ninh - Hải Phòng Báo cáo tổng kết Dự án Hà Nội, 2009, 44p [12] ƯNEP (United Nations Environmental Programme), 2004 Scagrass in the South China Sea Technical document of Project: “Reversing Environmental Degradation Trends in the South China Sea and G ulf of Thailand’’, UNEP, Bangkok [13] APHA, 1998 Standard Methods for the Examination of Water and Wastewater, 20th ed Amcncan Public Health Association, Washington DC [14] Ha N T T., Koike K., Integrating satellite imagery and geostatistics o f point samples for monitoring spatio-temporal changes of total suspended solids in bay waters: application to Tien Yen - Ha Coi Bay (Northern Vietnam) Frontiers o f Earth Science, (201 1) 305-316 [17] Simboura N., Panayotidis p., Papathanassiou E., A synthesis of the biological quality elements for the implementation of the European Water Framework Directive in the Mediteưanean ecoregion: The case of Saronikos Gulf Ecological Indicators, (2005) 253-266 [18] CSTT, 1997 Comprehensive studies for the purposes of Article & 8.5 of DIR91/271 EEC, the Urban Waste Water Treatment Directive, 2nd edition, Ireland [19] Cannizzaroa J p., Cardcra K L., Chena F R., Heilb c A., Vargoa G A., A novel technique for detection of the toxic dinoflagcllate, Karcnia brevis, in the G ulf of Mcxico from remotely sensed ocean color data Continental Shelf Research, 28 (2008) 137-158 [20] Hoang V T and Pham V H., 2010 Biodiversity in coastal zones of Tien Yen - Dam Ha, Quang Ninh Province and Conservation Proceeding of the 2nd National Confcrcncc on Biodiversity, Hanoi 17 October 2010, pp: 6174  ... Vietnam border and connected to the South China Sea by five channels (Fig 1) The most state in Tien Yen - Ha Coi Bay by using various geostatistical interpolations o f in situ Chl -a concenfrations... imagery and geostatistics o f point samples for monitoring spatio-temporal changes of total suspended solids in bay waters: application to Tien Yen - Ha Coi Bay (Northern Vietnam) Frontiers o f. .. understanding o f the spatial variation and distribution of Chl -a concenừation Consequently, that is easy to delineate high and low risk areas o f eufrophic state and potential for regional water management