Atmospheric nutrients have recently gained considerable attention as a significant additional source of new nitrogen (N) and phosphorus (P) loading to the ocean. The effect of atmospheric macro nutrients on marine productivity depends on the biological availability of both inorganic and organic N and P forms. During October 2006, the regional smoke haze episodes in Southeast Asia (SEA) that resulted from uncontrolled forest and peat fires in Sumatra and Borneo blanketed large parts of the region. In this work, we determined the chemical composition of nutrients in aerosols and rainwater during hazy and non-hazy days to assess their impacts on aquatic ecosystem in SEA for the first time. We compared atmospheric dry and wet deposition of N and P species in aerosol and rainwater in Singapore between hazy and non-hazy days. Air mass back trajectories showed that large-scale forest and peat fires in Sumatra and Kalimantan were a significant source of atmospheric nutrients to aquatic environments in Singapore and SEA region on hazy days. It was observed that the average concentrations of nutrients increased approximately by a factor of 3 to 8 on hazy days when compared with non-hazy days. The estimated mean dry and wet atmospheric fluxes (mg/m²/day) of total nitrogen (TN) were 12.72 ± 2.12 and 2.49 ± 1.29 during non-hazy days and 132.86 ± 38.39 and 29.43 ± 10.75 during hazy days; the uncertainty estimates are represented as 1 standard deviation (1σ) here and throughout the text. The estimated mean dry and wet deposition fluxes (mg/m²/day) of total phosphorous (TP) were 0.82 ± 0.23 and 0.13 ± 0.03 for non-hazy days and 7.89 ± 0.80 and 1.56 ± 0.65 for hazy days. The occurrences of higher concentrations of nutrients from atmospheric deposition during smoke haze episodes may have adverse consequences on receiving aquatic ecosystems with cascading impacts on water quality

Abstract. Atmospheric deposition of nutrients (N and P species) can intensify anthropogenic eutrophication of coastal waters. It was found that the atmospheric wet and dry depositions of nutrients was remarkable in the Southeast Asian region during the course of smoke haze events, as discussed in a companion paper on field observations (Sundarambal et al., 2010b). The importance of atmospheric deposition of nutrients in terms of their biological responses in the coastal waters of the Singapore region was investigated during hazy days in relation to non-hazy days. The influence of atmospherically-derived, bio-available nutrients (both inorganic and organic nitrogen and phosphorus species) on the coastal water quality between hazy and non-hazy days was studied. A numerical modeling approach was employed to provide qualitative and quantitative understanding of the relative importance of atmospheric and ocean nutrient fluxes in this region. A 3-D eutrophication model, NEUTRO, was used with enhanced features to simulate the spatial distribution and temporal variations of nutrients, plankton and dissolved oxygen due to atmospheric nutrient loadings. The percentage increase of the concentration of coastal water nutrients relative to the baseline due to atmospheric deposition was estimated between hazy and non-hazy days. Model computations showed that atmospheric deposition fluxes of nutrients might account for up to 17 to 88% and 4 to 24% of total mass of nitrite + nitrate-nitrogen in the water column, during hazy days and non-hazy days, respectively. The results obtained from the modeling study could be used for a Correspondence to: R. Balasubramanian (eserbala@nus.edu) better understanding of the energy flow in the coastal zone system, exploring various possible scenarios concerning the atmospheric deposition of nutrients onto the coastal zone and studying their impacts on water quality.

Atmospheric deposition is an important source of nutrients to the ocean, potentially stimulating primary production, but its relative effect on coastal eutrophication remains largely unknown. This paper presents data generated by the 3-D modelling program NEUTRO to assess the proportion of atmospheric nutrient fluxes, allowing a quantification of the relative contribution of atmospheric and ocean fluxes in the Singapore Strait. This work included an assessment of the importance of high concentration episodic inputs of nitrate-nitrogen associated with transport of polluted air onto the surface water. The NEUTRO model features a nutrient-fuelled food web composed of nutrients, plankton, and dissolved oxygen dynamics. Model simulations show that atmospheric deposition fluxes alone might contribute nitrate-nitrogen mass up to 15% into the Singapore Strait. This amount might be a significant contributor toward regional eutrophication when the system is under nutrient-depleted conditions. Model calibrations for temporal and spatial variability of nutrients qualitatively and quantitatively agreed with available measurements.

A recent algal bloom in the East Johor Strait has led to the damage of marine life in the water channel. This has lead to heavy economic losses to the fish farms located along the water channel. There is a desire to study and be able to predict the occurrences of algal blooms so that their effects on the fish industry can be reduced. Many factors such as weather patterns, tidal conditions and nutrient content in the water contribute to the extent of the eutrophication. This paper describes the design of experiments carried out in the East Johor Strait to study the dynamics of algal blooms. Physical and biogeochemical water column sampling were carried out using Acoustic Doppler Current Profilers (AD-CP) and a Conductivity, Temperature and Depth (CTD) probe that could measure various water quality parameters such as Turbidity, Salinity, pH level, Dissolved Oxygen (DO) and Chrolophyll-a concentration. Water samples from 1 m below the surface and 1 m above the channel floor were collected using Niskin Bottles. The water samples were sent to chemistry labs to test for the concentrations of various nutrients such as Ammonium, Nitrite, Nitrate and Phosphorus. Additional sampling was done using an Autonomous Underwater Vehicle (AUV) that was capable of measuring water quality parameters similiar to those measured by the CTD. The collection of the water sample data were meant to coincide with the spring and neap tides. The schedule is important to align with major phases of astronomic tide driving forces, such as flood tide, ebb tide and the transition between the two. Comparison can then be made to attempt to understand the various factors that contribute to algal blooms in the water body. Collected biogeochemical data can be used to improve water quality forecasts as well.

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/m(2)/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 investigation represents a baseline study to access environmental effects of AD of nutrients on the coastal aquatic ecosystem.