Atmospheric fluxes of nutrients onto Singapore Strait

Q IWA Publishing 2009 Water Science & Technology—WST | 59.11 | 2009 2287 Atmospheric fluxes of nutrients onto Singapore Strait P. Sundarambal, R. Balasubramanian and P. Tkalich ABSTRACT In view of recurring forest fires in Southeast Asia (SEA) on a large scale and the abundant rainfall in this tropical region, atmospheric fallout of airborne particles i.e. dry atmospheric deposition (DAD) and wet atmospheric deposition (WAD) of nutrients to the ocean surface are thought to be significant. Currently, limited data sets of atmospheric deposition (AD) exist for tropical ecosystems in the region. Furthermore, there is a lack of reliable experimental data on AD of nitrogen (N) & phosphorus (P) in tropical environments. It is therefore imperative to quantify the AD of macro-nutrients, N and P species in order to estimate their impacts on aquatic and terrestrial ecosystems. In this study, field measurements of nitrite, nitrate, ammonium, total N (TN), phosphate and total P (TP) were made, in both airborne particulate matter and precipitation, from January 2006 to July 2006 in Singapore. These measurements were done to characterize and estimate the difference between DAD and WAD fluxes of N & P to coastal waters. The estimated loadings from DAD and WAD (g/m2/year) of TN were 1.011 ^ 0.441 and 7.052 ^ 4.34 and those of TP were 0.187 ^ 0.16 and 0.532 ^ 0.524, respectively. This P. Sundarambal P. Tkalich Tropical Marine Science Institute, National University of Singapore, Singapore 119223, Singapore E-mail: [email protected]; [email protected] P. Sundarambal Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117576, Singapore R. Balasubramanian Division of Environmental Science and Engineering, National University of Singapore, Singapore 117576, Singapore E-mail: [email protected] investigation represents a baseline study to access environmental effects of AD of nutrients on the coastal aquatic ecosystem. Key words | atmospheric deposition, coastal waters, eutrophication, nutrient fluxes, Singapore strait, tropical environment, wet and dry deposition INTRODUCTION The atmosphere is recognized as an important pollutant Potential sources of P include biogenic aerosols (e.g. dead transportation route by which nutrients and particles are microorganisms), which have a small size and thus have delivered to the sea surface. The first step in determining the longer atmospheric residence time (Mahowald et al. 2005), quality of ambient air is to measure its total suspended soil derived dusts and anthropogenic emissions, agricultural particulate matter (TSP). These particles could be either of (mainly fertilizers), and emissions from marine aerosols. natural origin or man-made. The TSP in urban air is an In Europe, America and Asia, the atmospherically depos- aggregate of direct emissions from different sources and ited nutrients have been reported to have increased tenfold those formed through condensation and transformation. in recent decades due to a diverse array of industrial human Important anthropogenic sources that contribute to activities and forest fires (Galloway et al. 2004). Estimates of particulate matter in urban air are emissions from vehicular the atmospheric fluxes of nutrients to the ocean suggest that traffic, industrial and construction activities, fossil-fuel the atmosphere can be a major source in terms of mass burning and natural biomass burning (Balasubramanian (Duce et al. 1991; Prospero et al. 1996), and it plays a major et al. 2003). Anthropogenic activities can provide important role in the oceanic biogeochemical cycling (Jickells 1995; inputs of atmospheric N, for example, from vehicle Paerl 1997). Atmospherically deposited N (AD-N) can reach emissions but with little influence on atmospheric P level. N-sensitive waterways via direct deposition to the water’s doi: 10.2166/wst.2009.262 Downloaded from http://iwaponline.com/wst/article-pdf/59/11/2287/435435/2287.pdf by guest Water Science & Technology—WST | 59.11 | 2009 P. Sundarambal et al. | Atmospheric fluxes of nutrients 2288 surface or by deposition to land surface and subsequent (Peierls & Paerl 1997). Some studies have shown evidence runoff (indirect deposition). Furthermore, there are two that the atmospheric input of phosphate is likely to affect depositional pathways for removing pollutants from the biological productivity in Mediterranean oligotrophic atmosphere: DAD (particulate matter and gases) and WAD waters (Herut et al. 1999; Markaki et al. 2003). The impact (precipitation) (Figure 1). Dry deposition is the process by of nutrient-enriched atmospheric inputs is enhanced under which atmospheric gases and particles are transferred to the oligotrophic conditions. Under nutrient depleted conditions surface as a result of random turbulent air motions. Wet at surface waters, the atmospheric spreading of nutrients deposition is the process where gaseous and particulate over offshore waters is expected to generate a phyto- components are scavenged by the means of rain droplets plankton biomass increase (Ridame & Guieu 2002). The and subsequently transferred to the ground. dry deposition mode is a significant source of nutrients to The atmospheric deposition may introduce a significant surface waters at the yearly scale; however, when nutrient nutrient load to the surface water and aquatic ecosystem. concentrations in surface water are low, nutrients do not Once the atmospheric nutrients enter surface water, the accumulate and are immediately consumed by biota chemical form of the dissolved ion may be altered, thus (Migon et al. 2001), and new production triggered by the changing its solubility, retention in the euphotic zone, and atmospheric nutrients input may not be clearly observable. bioavailability. Thus, AD could contribute a substantial The rapid exhaustion of atmospheric suspended matter fraction of dissolved inorganic N to the euphotic zone. This during atmospheric washout causes high pulses of nutrients new source could possibly support the primary production. associated with washout events (Buat-Menard & Duce However, these estimates have a relatively large uncertainty 1986). The excess nitrogen can deplete essential oxygen due to errors associated with deposition flux calculations levels in the water by eutrophication and has significant and its temporal variability. The coastal and oceanic effects on climate, food production, and ecosystems all over primary production due to atmospherically transported N the world (Duce et al. 2008). and other nutrient sources may promote the major The air in Singapore and the region is episodically biological changes that are now apparent in coastal and polluted by the transboundary smoke haze from the land oceanic waters, including the proliferation of harmful algal and prolonged forest fires in Indonesia and neighboring blooms (HAB) and decline in the water quality and fish countries (Balasubramanian et al. 2003). These haze stock (Jickells 1998). Atmospherically derived dissolved ON episodes could introduce considerable amounts of atmos- has also been shown to stimulate bacterial and algal growth pheric nutrients to aquatic systems through both DAD and WAD. However, no detailed studies to date have yet been conducted in the region on nutrient composition in aerosol particles and precipitation. The main goals of this work were to develop sampling and laboratory methods for measuring nutrients (N & P species) in DAD and WAD, and to estimate annual N and P fluxes on water surface in Singapore Strait. The data obtained from the field measurements are presented and discussed in this paper. MATERIALS AND METHODS Study area Figure 1 | Schematic diagram of atmospheric deposition occurrence onto aquatic ecosystem. Downloaded from http://iwaponline.com/wst/article-pdf/59/11/2287/435435/2287.pdf by guest Singapore is a small urban country with total land area of 700 km2 located at latitudes 18060 N and 18240 N & Figure 2 Water Science & Technology—WST | 59.11 | 2009 P. Sundarambal et al. | Atmospheric fluxes of nutrients 2289 | Map of Southeast Asia, Singapore and sampling locations. longitudes 1038240 E and 1048240 E, 137 km north of the potentially could transport haze from the region to equator (Figure 2). Because of its geographical location, Singapore area, Malacca Straits and Peninsular Malaysia. its climate is characterized by uniform temperature The ambient air temperature is ranging from 21.1 to 35.18C, and pressure, high humidity and abundant rainfall. Mon- the annual average rainfall of 2,136 mm and a resident soon system over the Singapore region is a part of the population of four million (Singapore Department of Asian monsoon system; however, it has some regional Statistics 2005). In general, dry weather is the result of characteristics different from that over the Indian Ocean lack of convection or stable atmosphere which prevents the and Indian subcontinent. Singapore has two seasons, the development of rain-bearing clouds. SW and NE winds Northeast Monsoon (NEM) (November to March) and the occur in the coastal area periodically and the maximum Southwest Monsoon (SWM) season (June to September), wind speeds range from 5 m/s to 10 m/s. and inter-monsoon (IM) periods (April to May and October). During NEM period (Figure 3a), the air mass Sample collection masses might bring air pollution from China, Myanmar, Both the aerosol and rainwater sampling was conducted at Cambodia, Vietnam, Laos and Thailand. During SWM the atmospheric research station (latitudes 18180 N and period (Figure 3b), air masses pass by southern Sumatra, longitudes 1038460 E, 67 m above sea level) located at the Borneo, Surabaya & Java Islands of Indonesia and rooftop of building E2, National University of Singapore Figure 3 | Climatological winds averaged over the years 1980–2006. Downloaded from http://iwaponline.com/wst/article-pdf/59/11/2287/435435/2287.pdf by guest 2290 Water Science & Technology—WST | 59.11 | 2009 P. Sundarambal et al. | Atmospheric fluxes of nutrients (NUS, Figure 2), Singapore. There are no industrial sources in the vicinity of the sampling site. The atmospheric particulates (TSP) for dry deposition measurements were collected by a High Volume air sampler (model 3,800 AFC, HI-Q Environmental Products Company, USA). Air flow was maintained at 40 SCFM (Standard Cubic Feet per Minute) by an automatic air flow control system. Air samples were collected over 24 hours at the sampling location mainly during dry weather conditions randomly during the study period. The TSP samples were collected on 20.3 £ 25.4 cm size Whatman QM-A Quartz air-sampling filters for water soluble ionic and nutrients analysis. The filters were conditioned in a dry box at 40% relative humidity and 258C temperature for 24 hours pre- and postsampling weights to obtain mass collected on the filters. The Sample analysis The sample analysis was done to characterize wet and dry nutrient deposition. The types of atmospheric nutrients were identified for AD calculations: N species such as ammonium (NH4), nitrate (NO3), nitrite (NO2), total nitrogen (TN) and organic nitrogen (ON), and P species such as phosphate (PO4), total phosphorus (TP) and organic phosphorus (OP). The air sampling and the chemical analysis of atmospheric samples were carried out according to standard protocols (APHA 2005). The collected atmospheric samples were analyzed for N species and P species by an analytical procedure developed for DAD and WAD samples in the tropical region (Sundarambal et al. 2007). mass concentration of TSP (mg/m3) was calculated from the Dry deposition filter samples were taken as a fraction, collected mass of particulate (mg) divided by the volume of for example, 1/4 or 1/8th part of total filter area and 20 or air passed through the filter (m3) during sampling period. 50 ml Milli-Q water (Millipore) was added in a tapered Filters were then weighed using a Mettler top-loader balance bottle. It was sonicated for 30– 60 min. The extracts were with the lowest readability of 0.0001 mg. The balance was then filtered using a syringe filter. Rain water samples regularly checked with NIST-traceable standard calibrated were taken after filtration for laboratory analysis. Wet and weights. The particulate filters were stored in a refrigerator dry samples were analyzed for the ionic species by at 48C until extraction for sample analysis. ion chromatography (IC) (Model ICS-2000; Dionex The rainwater samples for wet deposition were collected Corporation) using a cation column and anion column by using an automated wet only rainwater sampler (Ecotech according to our standard laboratory procedure, TN and TP Model 200, Ecotech Pty Ltd, Australia) at the sampling (Karthikeyan et al. 2007; Sundarambal et al. 2007). The location. Rainwater samples were transferred from the dominant ionic species are sulfate, nitrate, and ammonium sampler to pre-cleaned high-density polyethylene (HDPE) among the inorganic ions. bottles after the rain event and immediately filtered using To determine TN, the samples were placed in a bottle 0.45 nylon membrane filters and refrigerated at 48C for with an oxidizing reagent (potassium persulfate – sodium sample analysis. Rainfall, , 1 mm was not taken into hydroxide) and borate buffer solution. The bottles were account, firstly for analytical convenience, and secondly placed in a pressure cooker at 1008C (0.2 –0.27 atm) for because even when the nutrient concentration is high, such 60 min for sample digestion so that all N species could be events yield low or negligible nutrient loads. Daily rainfall converted into nitrate. After the samples were cooled to room amounts and other meteorological were temperature, the digested samples were filtered through a obtained for January 2006 through July 2006 from NUS 0.45 mm filter. A boric acid-sodium hydroxide buffer was weather station (Department of Geography, NUS). The dry added to bring the pH of the sample within the range 7 – 8. deposition (27 aerosol samples) and wet deposition samples If IC was used for TN determination, the digested sample pH (24 rain samples) were collected for the period from January should be adjusted to alkaline condition to avoid the IC 2006 to July 2006. The aerosol and rainwater samples at the columns damage. The sample was then ready for the sampling station (NUS), and seawater samples (n ¼ 11) from determination of total oxidized nitrogen using IC as nitrate. Singapore Strait near Southern Island (SJI, Figure 2) were EDTA standards were used for calibration. parameters also collected during October 2006 haze episode to explore the relation between AD nutrients and phytoplankton. Downloaded from http://iwaponline.com/wst/article-pdf/59/11/2287/435435/2287.pdf by guest Wet and dry samples were analyzed by the IC anion column for PO4 and by the Ascorbic Acid method for TP 2291 Water Science & Technology—WST | 59.11 | 2009 P. Sundarambal et al. | Atmospheric fluxes of nutrients (APHA 2005). The digested sample was used for TP determination as per standard phosphate procedure. OP was quantified by subtracting the PO4 from the TP. The quality of the methods for both N and P species was verified by a known NIST SRM 1648 (urban particulate matter) standard sampling procedure and a standard addition method. The PM10 air samples (n ¼ 10) collected from August 1997 to November 1997 during the smoke haze period were utilized for validation of the developed laboratory methods of nutrient analysis (Sundarambal et al. 2007). RESULTS AND DISCUSSIONS Nutrients in aerosol particles TSP contains airborne particles of all sizes, a fraction of these particles is only inhalable. These are the particles with an aerodynamic diameter of 10 mm and less, generally referred to as PM10; WHO guideline for TSP is 120 mg/m3 (WHO 1997). During the sampling period, the highest TSP was 93.2 mg/m3 while PSI (Pollution Standard Index) was 51. Singapore adopted the USEPA’s Pollution Standards Index (PSI) to report the ambient air quality i.e good Atmospheric flux calculations (0–50), moderate (51 – 100), unhealthy (101– 200), very The atmospheric fluxes of identified nutrient species were estimated as follows. The DAD flux (Fd) (g/m2/year) of each nutrient was calculated from the concentration of the soluble fraction of aerosol nutrient in the air (Ca) and the dry deposition velocity of aerosol nutrient (Vd), (i.e) Fd ¼ CaVd. The WAD flux (Fw) (g/m2/year) of each nutrient was calculated from the precipitation rate (Pr) and the concentration of the nutrient in rainwater (Cr), (i.e) Fw ¼ CrPr. The magnitude of dry deposition rate (Vd) depends on the specific chemical components. Deposition velocities for particulate contaminants are a function of particles’ mass median diameters and meteorological parameters. Physical processes determining the dry deposition velocity include unhealthy (201 –300) or hazardous (. 300). PSI is calculated by measuring the concentrations of CO, SO2, NO2, O3 and PM10. Whenever there is a haze episode, high PM10 concentrations usually contributes to the PSI. It was also observed that measured nutrient concentrations were high when PSI was high. The maximum measured TN, ammonium, nitrate þ nitrite (hereafter denoted as nitratenitrogen), ON, TP, phosphate, OP concentrations (mg/m3) in the aerosol were 5.78, 0.997, 3.54, 2.13, 0.635, 0.355 and 0.339, respectively, when the highest TSP (93.2 mg/m3) was observed. The average N species concentrations in the aerosol phase were 1.31 ^ 0.91 mg/m3 for nitrate-nitrogen, 0.374 ^ 0.27 mg/m3 for ammonium, 0.963 ^ 0.661 mg/m3 gravitational settling, impaction, and diffusion (Jickells & for ON and 2.67 ^ 1.17 mg/m3 for TN. The average P Spokes 2001). Also, it is dependent on climatological and species physical conditions in the troposphere, and on the chemical concentrations in the aerosol phase were 0.156 ^ 0.144 mg/m3 for phosphate, 0.14 ^ 0.122 mg/m3 species, since the species are known to be associated with for OP and 0.296 ^ 0.254 mg/m3 for TP. Figure 4 shows different particle fractions. Duce et al. (1991) proposed a average concentration of nutrients in DAD from January mean Vd value of 0.1 cm/s for sub-micrometre particles, and 2006 to July 2006 and the seawater baseline derived from 2.0 cm/s for aerosols .1 mm in diameter depositing to Tkalich & Sundarambal (2003). Deposition was fairly ocean regions ,1,000 km from land. Dry deposition evenly distributed between nitrate-nitrogen, ammonium, velocities and ON (50%, 14%, and 36%, respectively). The percentage for particles were found to range from 0.0062 cm/s, for particles with a diameter of 0.75 mm, to 5.4 cm/s for those with a diameter of 24 mm (Qi et al. 2005). Owing to the absence of measured deposition rates, the Vd values used in this study follow those reported by Duce et al. 1991 for phosphate, nitrate and ammonium, which are respectively 2.0, 1.2 and 0.6 cm/s and those assumed for both TN & ON, and TP & OP are 1.2 cm/s and 2 cm/s, respectively. These values were used previously in similar flux calculations by Herut et al. (1999). Downloaded from http://iwaponline.com/wst/article-pdf/59/11/2287/435435/2287.pdf by guest Figure 4 | Average concentration of nutrients (N and P species) in atmospheric dry deposition and seawater in Singapore. Figure 5 Water Science & Technology—WST | 59.11 | 2009 P. Sundarambal et al. | Atmospheric fluxes of nutrients 2292 | Representative 4 days air mass back trajectories for starting altitude of 1,000 m, 500 m, and 60 m above ground level (AGL) calculated for the sampling site (a) on 28th July 2006 and (b) on 4th March 2006. The location of hotspots in Sumatra observed on 26th July 2006 is shown on the regional haze map. contribution of phosphate and OP on Singapore Strait were respectively 53 and 47 of TP. The air mass back trajectories were plotted for each sampling period to identify the origin and history of air masses received at the sampling site in Singapore. The backward trajectories were plotted using NOAA HY-SPLIT model (Draxler & Rolph 2003) at altitudes 1,000, 500, and 60 m for the representative periods on 28th July 2006 (SWM, Figure 5a) and 4th March 2006 (NEM, Figure 5b). Archived data of the hot spots count in Sumatra (Singapore’s National Environment Agency, NEA) showed that South Sumatra, the area whereby most of the trajectories passed through (Regional haze map on 26th July 2006 by NEA), had more hot spots than the rest of Sumatra during hazy days. The transport of the smoke haze strongly depends on the prevalent wind direction (Figure 3). The smoke haze particles from fires in the northern ASEAN Nutrients in precipitation The concentrations of N species in precipitation were in the range of 0.725 –5.783 mg/l for TN, 0.39 –5.55 mg/l for nitrate-nitrogen, 0.01– 0.94 mg/l for ammonium and 0.12– 2.66 mg/l for organic N. The results show that WAD was the predominant source of atmospheric nutrients to the Singapore area. Figure 6 shows the average concentrations of WAD from January to July 2006 and the seawater baseline derived from Tkalich & Sundarambal (2003). The dissolved phase in rainwater is regarded here as an approximation of its bioavailable fraction. The particulate fraction in rainwater that enters the marine surface layer partly dissolves, however. There was no DAD regional data published previously and few WAD data for ammonium and nitrate only were published elsewhere (e.g. Ayers & Yeung 1996; Ayers et al. 2000; Asiati et al. 2001). The importance of ON in (Association of Southeast Asian Nations) region were carried over by mild winds, contributing to hazy conditions (NEA, Singapore). The maximum TN concentration of 5.78 mg/m3 and 3.81 mg/m3 was observed respectively in DAD on 28th July 2006 and 4th March 2006. Both values were higher as compared to clear days. This observation is consistent with those made earlier during the previous smoke haze episodes at the same sampling site (Balasubramanian et al. 2003). Downloaded from http://iwaponline.com/wst/article-pdf/59/11/2287/435435/2287.pdf by guest Figure 6 | Average concentration of nutrients (N and P species) in atmospheric wet deposition and seawater in Singapore. Water Science & Technology—WST | 59.11 | 2009 P. Sundarambal et al. | Atmospheric fluxes of nutrients 2293 Table 1 | Comparison of WAD flux (g/m2/year) of ammonium and nitrate in some countries, SEA Country Period NH4 NO3 Reference Malaysia 1993 – 1998 0.718 3.607 Ayers et al. (2000) Indonesia 1992 & 1996 1.38 1.74 Asiati et al. (2001) Hong Kong 1998 – 1991 0.439 2.32 Ayers & Yeung (1996) Singapore 2006 0.631/0.071# 3.76/0.495# Present study Note: # for DAD flux. TN from AD has recently been re-evaluated; it may represent continental, natural and anthropogenic source for P species half of the input of inorganic forms on a regional scale and be (Herut et al. 1999). The WAD flux was higher than the DAD equal to them for global ocean (Cornell et al. 1995). The flux and the total budget shows that the biologically observed ON is 36 to 40% of TN in the present study while available N load to the surface waters is significantly more that published was 41% of TN (Cornell et al. 2003). than ,10 times the biologically available P load to the surface waters (Figure 7). Duce et al. (2008) reported that the ratio of 2030 to 2000 deposition rates increased up to a Atmospheric fluxes of nutrients factor of 2 in SEA, TN deposition constitutes 40% of net In the present study, the atmospheric fluxes of nutrients external N supply. are calculated based on the field measurements from January 2006 to July 2006 in Singapore. The mean DAD fluxes of organic and inorganic P species were estimated as Total AD nutrients fluxes 0.088 ^ 0.077 and 0.098 ^ 0.091 (g/m2/year), respectively. The range and mean of total (WAD þ DAD) fluxes of N The mean WAD fluxes of organic and inorganic P species and P species over the sampling period in Singapore based were 0.068 ^ 0.047 on the present study are shown in Table 2. The maximum (g/m /year), respectively. Table 1 shows the WAD flux annual flux of atmospheric TP was 2.85 (g/m2/year) while of ammonium and nitrate-nitrogen in Singapore were that of TN was 21.9 g/m2/year. The proportion of DAD flux comparable with those published elsewhere in SEA. to total fluxes for N species and P species were in the range The nutrient composition in DAD and WAD indicated of 0.1 to 0.12 and 0.15 to 0.59, respectively. It was observed a dominant anthropogenic source for N species and a that the proportion of DAD to total fluxes for N compounds estimated as 0.498 ^ 0.525 and 2 Figure 7 | Atmospheric deposition flux of nutrients (N and P species) in atmospheric wet deposition and dry deposition during sampling period. Downloaded from http://iwaponline.com/wst/article-pdf/59/11/2287/435435/2287.pdf by guest Table 2 Water Science & Technology—WST | 59.11 | 2009 P. Sundarambal et al. | Atmospheric fluxes of nutrients 2294 | (WAD þ DAD) fluxes (g/m2/year) of inorganic and Total AD nutrient fluxes (g/m2/year) in Singapore organic N species were in the range of 0.97 –15.4 and Nutrients Mean SD Minimum Maximum TN 8.09 5.96 1.33 21.9 NH4 0.70 0.673 0.016 NO3 þ NO2 4.41 3.17 0.955 ON 2.98 2.12 0.363 6.49 The estimated atmospheric nutrient fluxes could contribute TP 0.75 0.740 0.145 2.85 a substantial fraction of dissolved inorganic N to the PO4 0.17 0.138 0.003 0.344 euphotic zone. This investigation represents a baseline OP 0.59 0.602 0.142 2.51 study using which possible environmental effects of “new” 2.19 13.2 0.363 – 6.49, and those of P species were 0.003 – 0.344 and 0.142 – 2.51, respectively. The atmospheric depositions were mainly contributed by nitrate-nitrogen, followed by ON and then ammonium ion (50%, 36%, and 14%, respectively). AD of N & P compounds on the coastal aquatic ecosystem was smaller than that for P compounds. The observed range can be assessed. of seawater phytoplankton was 0.018 – 0.172 mg C/l during 2006 haze event. From the analysis of field measurements of AD and seawater during October 2006 haze, a significant correlation between phytoplankton and AD deposition (Pearson correlation coefficient . 0.6, P-value , 0.05) was found; The field observations of AD nutrients made during the October 2006 haze event will be published elsewhere. A long term monitoring of both AD of nutrients and the corresponding changes in seawater is needed to conclude the exact relationship between phytoplankton and ACKNOWLEDGEMENTS This research is a part of the main author’s PhD research. We would like to thank the Division of Environmental Science and Engineering (ESE) for providing laboratory facilities and financial support, He Jun (ESE) for sample collection, and Tropical Marine Science Institute, National University of Singapore for the technical support. AD nutrients in tropical coastal waters. The transfer of atmospheric nutrients through precipi- REFERENCES tation is a more efficient deposition process for the particulate matter in the marine area as compared to DAD (Bergametti et al. 1992) which is consistent with the observations made in this study. Using the estimated AD nutrient fluxes from this study and water quality model (NEUTRO, Tkalich & Sundarambal 2003; Sundarambal et al. 2007), the simulated results to show the effects of atmospheric nutrient input into Singapore area and surrounding waters will be published elsewhere. 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