Heavy metal in water and aquatic organisms from different intertidal ecosystems,Persian Gulf

Intertidal ecosystems are being damaged by anthropogenic activities, particularly in the developing countries. In this study, the load of heavy metals was determined in water, fish, shrimp, and crab collected from four intertidal ecosystems, including coral reef, rocky shore, mangrove forest, and muddy habitat along the Persian Gulf coasts. Generally, the sequence of metal accumulation in the water of coral reef and mangrove forest was Ni > Pb > V > Cd > As > Hg, whereas in muddy habitats and rocky shores, the sequence was Ni > Pb > V > Cd > Hg > As and Ni > V > Pb > As > Hg > Cd, respectively. Water of the coral reef had the highest level of Ni (97.44 μg l^?1), Pb (3.92 μg l^?1), V (10.42 μg l^?1), Cd (3.92 μg l^?1), As (1.87 μg l^?1), and Hg (0.74 μg l^?1). For the most part, the highest concentrations of the studied metals were found in the liver and the gills of Johnius belangerii and the hepatopancreas of Portunus pelagicus and Metapenaus affinis collected from the coral reef ecosystem.     

Seaweeds as bioindicators of heavy metals off a hot spot area on the Egyptian Mediterranean Coast during 2008–2010

Concentrations of Cu, Zn, Cd, Pb, Ni, Co, Fe, Mn, and Hg were measured successively in water, sediments, and six macroalgal species belonging to three algal classes during 3 years (2008–2010) from Abu Qir Bay, Alexandria, Egypt: Chlorophyceae (Enteromorpha compressa, Ulva fasciata), Phaeophyceae (Padina boryana), and Rhodophyceae (Jania rubens, Hypnea musciformis, Pterocladia capillacea). The study aimed to assess the bioaccumulation potential of the seaweeds, as well as to evaluate the extent of heavy metal contamination in the selected study site. Metals were analyzed using atomic absorption spectrophotometry coupled with MH-10 hydride system. The obtained data showed that the highest mean concentrations of Cu, Zn, Fe, and Mn were recorded in E. compressa; Cd, Ni, and Hg exhibited their highest mean concentrations in P. boryana, while Pb and Co were found in J. rubens. Abundance of the heavy metals in the algal species was as follow: Fe?>?Mn?>?Zn?>?Pb?>?Ni?>?Co?>?Cu?>?Cd?>?Hg. E. compressa showed the maximum metal pollution index (MPI) which was 11.55. Bioconcentration factor (BCF) for the metals in algae was relatively high with a maximum value for Mn. The Tomlinson pollution load index (PLI) values for the recorded algal species were low, which ranged between 1.00 in P. boryana and 2.72 in E. compressa. Enrichment factors for sediments were low fluctuating between 0.43 for Hg to 2.33 for Mn. Accordingly, the green alga E. compressa, brown alga P. boryana, and red alga J. rubens can be nominated as bioindicators. Based on MPI and PLI indices, Abu Qir Bay in the present study is considered as low-contaminated area.     

<Emphasis Type="Italic">Synechococcus</Emphasis> production and grazing loss rates in nearshore tropical waters

Temporal variation of Synechococcus, its production (μ) and grazing loss (g) rates were studied for 2 years at nearshore stations, i.e. Port Dickson and Port Klang along the Straits of Malacca. Synechococcus abundance at Port Dickson (0.3–2.3 × 10⁵ cell ml^?1) was always higher than at Port Klang (0.3–7.1 × 10⁴ cell ml^?1) (p < 0.001). μ ranged up to 0.98 day^?1 (0.51 ± 0.29 day^?1), while g ranged from 0.02 to 0.31 day^?1 (0.15 ± 0.07 day^?1) at Port Klang. At Port Dickson, μ and g averaged 0.47 ± 0.13 day^?1 (0.29–0.82 day^?1) and 0.31 ± 0.14 day^?1 (0.13–0.63 day^?1), respectively. Synechococcus abundance did not correlate with temperature (p > 0.25), but nutrient and light availability were important factors for their distribution. The relationship was modelled as log Synechococcus = 0.37Secchi ? 0.01DIN + 4.52 where light availability (as Secchi disc depth) was a more important determinant. From a two-factorial experiment, nutrients were not significant for Synechococcus growth as in situ nutrient concentrations exceeded the threshold for saturated growth. However, light availability was important and elevated Synechococcus growth rates especially at Port Dickson (F = 5.94, p < 0.05). As for grazing loss rates, they were independent of either nutrients or light intensity (p > 0.30). In nearshore tropical waters, an estimated 69 % of Synechococcus production could be grazed.     

Study of harmful algal blooms in a eutrophic pond, Bangladesh

The purpose of this research was to analyze the underlying mechanisms and contributing factors related to the seasonal dynamic of harmful algal blooms in a shallow eutrophic pond, Bangladesh during September 2005–July 2006. Two conspicuous events were noted simultaneously throughout the study period: high concentration of phosphate–phosphorus (>3.03; SD 1.29 mg l^???1) and permanent cyanobacterial blooms {>3,981.88 × 10³ cells l^???1 (SD 508.73)}. Cyanobacterial blooms were characterized by three abundance phases, each of which was associated with different ecological processes. High nitrate–nitrogen (>2.35; SD 0.83 mg l^???1), for example, was associated with high cyanobacterial abundance, while low nitrate–nitrogen (0.36; SD 0.2 mg l^???1) was recorded during moderate abundance phase. Extremely low NO₃–N/PO₄–P ratio (>3.55, SD 2.31) was recorded, and all blooming taxa were negatively correlated with this ratio. Cyanobacterial blooms were positively correlated with temperature (r?=?0.345) and pH (0.833; p?=?0.05) and negatively correlated with transparency (r?=???0.956; p?=?0.01). Although Anabaena showed similar relationship with water quality parameters as cyanobacteria, the co-dominant Microcystis exhibited negative relationship with temperature (r?=???0.386) and nitrate–nitrogen (r?=???0.172). This was attributed to excessive growth of Anabaena that suppressed Microcystis’s growth. Planktothrix was the third most dominant taxa, while Euglena was regarded as opportunistic.     

Bioaccumulation and toxicity of arsenic in cyanobacteria cultures separated from a eutrophic reservoir

The bioaccumulation and toxicity of arsenate (arsenic (As)(V)) was studied using three cultures of cyanobacterial species—Oscillatoria tenuisa, Anabaena affinis, and Microcystis aeruginosa—that were isolated from a eutrophic reservoir. The As(V) uptake depended on the cyanobacterial species, the growth phase of the cyanobacteria, the duration of exposure, and the initial concentration of As(V). The specific growth rates of the three cultures immediately following the logarithmic phase were 0.033–0.041 L/day when the initial concentration of As(V) was 50 mg/L. These rates were 2.3–3.6 times less than those in the original culture medium without As(V). The rate of intake of As(V) in the logarithmic phase cultures greatly exceeded that in the stationary cultures. The accumulation of As(V) by the three cultures increased rapidly within 1 week from the initial value of 3.23?×?10^?2–5.40?×?10^?2 to 5.06?×?10^?1–6.73?×?10^?1 ng/cell in the logarithmic phase. The effective concentrations (EC₅₀) of As(V) for inhibiting the growth of the three cyanobacterial species growth of at 72 h followed the order Oscillatoria tenuisa (3.8 mg/L)?>?A. affinis (2.6 mg/L)?>?M. aeruginosa (1.2 mg/L). The cyanobacterial species that was most sensitive to As(V) was M. aeruginosa. Preliminary results from SEM-map studies suggest most of the As(V) in Microcystis aeruginosa accumulated in the cytoplasm (intercellular), while in O. tenuisa and A. affinis, a large proportion of As(V) bound to the cell wall (extracellular). These differences were understood with reference to the variation among the metabolic properties and morphological characteristics of the cyanobacterial species.     

Impact of transport and industrial emissions on the ambient air quality of Lahore City, Pakistan

This study was monitored to determine the changes in the micromineral and macromineral composition of common sole (Solea solea), striped red mullet (Mullus surmuletus), and whiting (Merlangius merlangus) throughout the year. Macromineral concentrations in edible parts of fish species were 444–1,559 mg/kg for Na, 1,975–5,130 mg/kg for K, 228–658 mg/kg for Mg, 187–1,105 mg/kg for Ca, and 2,341–7,341 for P, respectively. The highest mercury contents were found in the autumn months. While the highest protein and lowest fat values were found in the summer, the highest ash contents were found in the spring. Mercury content was found to be over the legislative limits in autumn samples for common sole and in summer for striped red mullet. Lead and cadmium contents of striped red mullet were found to be over the legislative limits throughout year.     

Atmospheric arsenic (As) study at five characteristic sampling sites in Taiwan

The main purpose for this study is to observe the seasonal and monthly variations for arsenic (As) in total suspended particulates (TSP) concentration and dry deposition at five characteristic sampling sites during the years 2009 and 2010 in central Taiwan. The results show that the highest and lowest monthly average As concentrations in TSP occurred in January and May at Bei-shi (suburban/coastal) and Quan-xing (industrial) sampling sites. In addition, the results show that the highest and lowest monthly average As dry deposition occurred in October and May at Chang-hua (downtown) and Gao-mei (wetland) sampling sites. This study reflected that the mean highest As concentrations in TSP and mean highest As dry deposition occurred at Quan-xing (industrial). However, the mean lowest As concentrations in TSP and mean lowest As dry deposition also occurred at Gao-mei (wetland). Regarding seasonal variation, the results show that the As average seasonal concentration order in TSP was winter > spring > fall > summer, respectively, at Chang-hua (downtown) and He-mei (residential) sampling sites. Finally, the order of As average seasonal dry deposition was fall > winter > spring > summer, respectively, at Chang-hua (downtown), He-mei (residential), and Gao-mei (wetland) sampling sites.     

Bovine calves as ideal bio-indicators for fluoridated drinking water and endemic osteo-dental fluorosis

Relative susceptibility to fluoride (F) toxicosis in the form of osteo-dental fluorosis was observed in an observational survey of 2,747 mature and 887 immature domestic animals of diverse species living in areas with naturally fluoridated (>1.5 ppm F) drinking water. These animals included buffaloes (Bubalus bubalis), cattle (Bos taurus), camels (Camelus dromedarius), donkeys (Equus asinus), horses (Equus caballus), goats (Capra hircus), and sheep (Ovis aries). Of these mature and immature animals, 899 (32.7 %) and 322 (36.3 %) showed evidence of dental fluorosis with varying grades, respectively. Their incisor teeth were stained with light to deep brownish color. On clinical examination, 31.2 % mature and 10.7 % immature animals revealed periosteal exostoses, intermittent lameness, and stiffness of tendons in the legs as signs of skeletal fluorosis. The maximum susceptibility to fluoride toxicosis was found in bovines (buffaloes and cattle) followed by equines (donkeys and horses), flocks (goats and sheep), and camelids (camels). The bovine calves were found to be more sensitive and highly susceptible to F toxicosis and revealed the maximum prevalence (92.2 %) of dental fluorosis. This indicates that bovine calves are less tolerant and give early sign of F poisoning (dental fluorosis) and therefore, they can be considered as bio-indicators for fluoridated water as well as for endemicity of osteo-dental fluorosis. Causes for variation in susceptibility to F toxicosis (fluorosis) in various species of domestic animal are also discussed.     

Bioaccumulation of heavy metals in fish tissues of a freshwater lake of Bhopal

Contamination of heavy metals, namely, lead, cadmium, zinc, nickel, copper, chromium and mercury was evaluated in the samples of water and tissues of Labeo rohita and Ctenopharyngodon idella of Upper Lake of Bhopal collected during summer, rainy and winter seasons of 2005–2006. Different organs of the fishes accumulated varying quantities of different heavy metals. In L. rohita, accumulation of heavy metals was in the sequence liver > kidney > gills > muscles, and in C. idella, it was gills > liver > kidney > muscles. Zn was the highest accumulating metal in fish, whilst Hg was the lowest and was well corroborated with those of water. The values of heavy metals were so far well within the maximum permissible standard value of heavy metals for drinking water and for fish culture as prescribed by various national and international agencies.     

Assessing genetic structure, diversity of bacterial aerosol from aeration system in an oxidation ditch wastewater treatment plant by culture methods and bio-molecular tools

Airborne bacteria emissions from oxidation ditch with rotating aeration brushes were investigated in a municipal wastewater treatment plant in Beijing, China. Microbial samples were collected at different distances from the rotating brushes, different heights above the water surface, and different operation state over a 3-month period (April, May, and June) in order to estimate the seasonal variation and site-related distribution characteristics of the microorganisms present. The concentration of bacterial aerosol was analyzed by culture methods, while their dominant species, genetic structure and diversity were assayed using bio-molecular tools. Results showed that total microbial concentrations were highest in June and lowest in April. The mechanical rotation caused remarkable variation in concentration and diversity of culturable airborne bacteria before and after the rotating brushes. The highest concentration was observed near the rotating brushes (931?±?129–3,952?±?730 CFU/m³), with concentration decreasing as distance and height increased. Bacterial community polymerase chain reaction and denaturing gradient gel electrophoresis indicated that diversity decreased gradually with increasing height above the water surface but remained relatively constant at the same height. All dominant bacteria identified by DNA sequence analysis belonged to Firmicutes. Pathogenic species such as Moraxella nonliquefaciens and Flavobacterium odoratum were isolated from the bioaerosols. Due to the serious health risks involved, exposure of sewage workers to airborne microorganisms caused by brush aerators should be monitored and controlled.     

The statistical investigation on airborne fungi and pollen grains of atmosphere in Izmir-Turkey

This study aims to investigate the differences in the concentrations of airborne fungi and pollens between the towns located in the province of Izmir and to determine the factors contributing to these differences. Five stations in each of four towns (Buca, Konak, Bornova, and Karsiyaka) were randomly selected as the research areas. Fungus (cfu/m³) and pollen counts (cm²/pollen count) in the air samples collected from each station between June 2003 and May 2004 were measured. The results revealed that whereas Karsiyaka had the highest fungus concentration (521.33 ± 777.1), Buca and Bornova had the lowest concentration (482.67 ± 308.44). The mean fungus concentration in the province of İzmir was 501.5 ± 486.7. Pollen concentration was the highest in Konak (486.67 ± 839.06) and the lowest in Bornova (369.83 ± 551.13). Fungus and pollen concentrations revealed no difference between the towns (p > 0.05). The relationship between pollen-fungus concentrations and temperature-dust-humidity-sulphurdioxide was investigated but it was found statistically insignificant (p > 0.05). As a result of regression analysis, it was determined that correlation of atmospheric parameters had no effects on pollen and fungus concentrations (p > 0.05).     

广州市大气VOCs污染特征及O3生成潜势分析

利用手工及自动监测数据,结合最大增量反应活性(MIR)系数法,对广州市大气挥发性有机物(VOCs)污染特征及臭氧生成潜势(OFP)进行了研究。结果表明：广州市大气VOCs总体积分数为73.85×10^-9,其中,丙烷、甲醛、乙酸乙酯的体积分数最高,分别为5.59×10^-9、4.87×10^-9、4.25×10^-9。组成特征分析结果显示,含氧挥发性有机物(OVOCs)和烷烃为主要污染物种类,分别贡献了总VOCs的34.32%和32.34%。在空间分布上,各站点VOCs体积分数自南向北不断降低,番禺市桥站(南部,76.16×10^-9)>公园前站(中部,75.58×10^-9)>花都梯面站(北部,69.80×10^-9)。广州市大气中甲醛和乙醛的比值为1.22,表明本地排放对广州市醛酮类化合物的贡献较大;乙苯和间/对-二甲苯的比值为0.35,表明广州市气团老化程度低,VOCs主要受本地排放影响;甲苯和苯的比值显示,公园前站苯系物主要受机...     

Levels of polycyclic aromatic hydrocarbons (PAHs) in the Densu River Basin of Ghana

The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) in Densu River Basin in Ghana were measured using gas chromatograph. Surface water samples were collected from nine stations, namely, Potroase, Koforidua Intake, Suhyien, Mangoase, Asuboi, Nsawam Bridge, Afuaman, Ashalaga, and Weija Intake in the Densu Basin. Total PAH concentrations varied from 13.0 to 80.0 ??g/mL in the Densu River, with a mean value of 37.1 ??g/mL. The two- to three-ring PAHs (low-molecular-weight PAHs) were found to be dominant in the Densu River Basin. Total PAH concentrations showed the following pattern: Koforidua Intake (80.0 ??g/mL) > Asuboi (50.8 ??g/mL) > Afuaman (47.9 ??g/mL) > Weija Intake (45.0 ??g/mL) > Suhyien (27.6 ??g/mL) > Nsawam (23.5 ??g/mL) > Ashalaja (22.9 ??g/mL) > Potroase (23.3 ??g/mL) > Mangoase (13.0 ??g/mL). According to the Agency for Toxic Substances and Disease Registry (ATSDR), background levels of PAHs in drinking water supplies in the USA range from 0.004 to 0.024 ??g/mL. PAH levels from all sites exceeded the range set by ATSDR. B[a]P contributed the highest carcinogenic exposure equivalent (0.3 ??g/mL), followed by B[a]A (0.132 ??g/mL) and B[b]F (0.08 ??g/mL), contributing 52.6%, 23.2%, and 4.6%, respectively, of the total carcinogenicity of surface water PAH in the Densu River Basin. The carcinogenic potency was estimated to be 0.57 ??g/mL. The presence of PAHs was an indication of the water sources being contaminated, with potential health implications.     

Effect of wastewater irrigation on vegetables in relation to bioaccumulation of heavy metals and biochemical changes

The present study was conducted to determine the heavy metal contamination in soil with accumulation in edible parts of plants and their subsequent changes in biochemical constituents due to wastewater irrigation. Though the wastewater contains low levels of the heavy metals (Fe, Mn, Pb, Cd, and Cr), the soil and plant samples show higher values due to accumulation. The trend of metal accumulation in wastewater-irrigated soil is in the order: Fe > Pb > Mn > Cr > Cd. Of the three species Colocasia esculentum, Brassica nigra, and Raphanus sativus that are grown, the order of total heavy metal accumulation in roots is Raphanus sativus > Colocasia esculentum, while in shoots the order is Brassica nigra > Colocasia esculentum > Raphanus sativus. The enrichment factor (EF) of the heavy metals in contaminated soil is in the sequence of Cd (3) > Mn (2.7) > Cr (1.62) > Pb (1.46) > Fe (1.44), while in plants EF varies depending upon the species and plant part. C. esculentum and R. sativus show a higher EF for Cr and Cd. All plants show a high transfer factor (TF > 1) for Cd signifying a high mobility of Cd from soil to plant whereas the TF values for Pb are very low as it is not bioavailable. Results of the biochemical parameters show decrease in total chlorophyll and total amino acid levels in plants and an increase in amounts of soluble sugars, total protein, ascorbic acid, and phenol except B. nigra for protein in plants grown in soil irrigated with wastewater as compared to control site.     

Monsoon-induced changes in the size-fractionated phytoplankton biomass and production rate in the estuarine and coastal waters of southwest coast of India

Changes in the autotrophic pico- (0.2–2 μm), nano- (2–20 μm), and microplankton (>20 μm) biomass (chlorophyll a) and primary production were measured in the estuarine and coastal waters off Cochin, southwest coast of India during the onset and establishment of a monsoon. During this period, the estuary was dominated by nutrient-rich freshwater, whereas the coastal waters were characterized with higher salinity values (>30 psu) and less nutrients. The average surface chlorophyll a concentrations and primary production rates were higher in the estuary (average 13.7 mg m^???3 and 432 mgC m^???3 day^???1) as compared to the coastal waters (5.3 mg m^???3 and 224 mgC m^???3 day^???1). The nanoplankton community formed the major fraction of chlorophyll a and primary production, both in the estuary (average 85 ± SD 8.3% and 81.2 ± SD 3.2%) and the coastal waters (average 73.2 ± SD 17.2% and 81.9 ± 15.7%). Nanoplankton had the maximum photosynthetic efficiency in the coastal waters (average 4.8 ± SD 3.9 mgC mgChl a m^???3 h^???1), whereas in the estuary, the microplankton had higher photosynthetic efficiency (average 7.4 ± 7 mgC mgChl a m^???3 h^???1). The heavy cloud cover and increased water column turbidity not only limit the growth of large-sized phytoplankton in the Cochin estuary and coastal waters but also support the proliferation of nanoplankton community during the monsoon season, even though large variation in nanoplankton chlorophyll a and production exists between these two areas.     

Origination and assessment of metal pollution in Qarechay River bed sediments

In the present investigation, bulk and chemical partitioning of elements (Cu, Mn, Ni, Zn, Fe, Ca) together with organic matter as a loss in ignition in the Qarechay River bed sediments have been studied. The concentration of metals in Qarechay River bed sediments is governed by the geological units of the study area. The study of anthropogenic portion shows that a small proportion of elemental concentration belongs to this phase. However, Mn has a large portion of anthropogenic sources (43 %). Also, Mn has a share of 13.6 % in sulfide fractions. This result indicates that Mn is a highly mobile element and can easily enter the water column. The presence of Mn in sulfide fraction might be indicative of initial stages of conversion of oxidation state into reduction in Qarechay River. Share of metals in anthropogenic portion is in the following order: Mn (43 %)?>?Cu (19 %)?>?Zn (10 %)?>?Ni (3 %)?>?Fe (0 %). Organic metallic bonds are not significantly present in the study area. Geochemical index (I _geo), pollution index (I _poll), enrichment factor (EF), and pollution load index (PLI) values are indicative of a clean environment throughout the river course. These values are in well agreement with results of chemical partitioning data. Eventually, based on the results of chemical partitioning, regional standard of elements for Qarechay River bed sediments has been established.     

Density assessment and mapping of microorganisms around a biocomposting plant in Sanandaj,Iran

Exposure to microorganisms can cause various diseases or exacerbate the excitatory responses, inflammation, dry cough and shortness of breath, reduced lung function, chronic obstructive pulmonary disease, and allergic response or allergic immune. The aim of the present study was to investigate the density of microorganisms around the air of processing facilities of a biocomposting plant. Each experiment was carried out according to ASTM E884-82 (2001) method. The samples were collected from inhaled air in four locations of the plant, which had a high traffic of workers and employees, including screen, conveyor belt, aerated compost pile, and static compost pile. The sampling was repeated five times for each location selected. The wind speed and its direction were measured using an anemometer. Temperature and humidity were also recorded at the time of sampling. The multistage impactor used for sampling was equipped with a solidified medium (agar) and a pump (with a flow rate of 28.3 l/m) for passing air through the media. It was found that the mean density of total bacteria was >1.7 × 10³ cfu/m³ in the study area. Moreover, the mean densities of fungi, intestinal bacteria (Klebsiella), and Staphylococcus aureus were 5.9 × 10³, 3.3 × 10³, and 4.1 × 10³ cfu/m³, respectively. In conclusion, according to the findings, the density of bacteria and fungi per cubic meter of air in the samples collected around the processing facilities of the biocomposting plant in Sanandaj City was higher than the microbial standard for inhaled air.     

Blood mercury concentration among residents of a historic mercury mine and possible effects on renal function: a cross-sectional study in southwestern China

This cross-sectional study aimed to investigate blood mercury (B-Hg) concentration of residents living in the vicinity of Chatian mercury mine (CMM) in southwestern China and to assess the possible effects on renal function. It evaluates the effects of gender and age (children, <18 years; adults, 18–60 years; elderly, >60 years) on the B-Hg and serum creatinine (SCR) and serum urea nitrogen (SUN) levels. In the CMM, elevated levels were found for B-Hg, SCR, and SUN with mean values at 6.09 μg/L, 74.21 μmol/L, and 13.26 mmol/L, which were significantly higher than those in the control area, respectively. Moreover, the coefficients between paired results for B-Hg and SCR and SUN levels were positive at statistical significance (B-Hg vs. SCR, r?=?0.45, p?<?0.01; B-Hg vs. SUN, r?=?0.20, p?<?0.05). The aforementioned results revealed that mercury exposure can cause human renal function impairment. B-Hg, SCR, and SUN can also be useful biomarkers to assess the extent of mercury exposure among residents in areas with extensive mining activities. Furthermore, data analysis revealed that there was a tendency for higher B-Hg, SCR, and SUN levels in females than in males, and the levels of B-Hg, SCR, and SUN increased among the older residents. We conclude that females and the elderly in the mining area were more susceptible to mercury exposure, and therefore, they deserve further research.     

Short-term variability of water quality and its implications on phytoplankton production in a tropical estuary (Cochin backwaters—India)

Changes in the phytoplankton biomass (chlorophyll a), production rate, and species composition were studied over two seasons using the time series measurements in the northern limb of the Cochin estuary in relation to the prevailing hydrological conditions. The present study showed the significant seasonal variation in water temperature (F = 69.4, P < 0.01), salinity (F = 341.93, P < 0.01), dissolved inorganic phosphorous (F = 17.71, P < 0.01), and silica (F = 898.1, P < 0.01) compared to nitrogen (F = 1.646, P > 0.05). The uneven input of ammonia (3.4–224.8 μM) from upstream (Periyar River) leads to the inconsistency in the N/P ratio (range 6.8–262). A distinct seasonality was observed in Si/N (F = 382.9, P < 0.01) and Si/P (F = 290.3, P < 0.01) ratios compared to the N/P ratio (F = 1.646, P > 0.05). The substantial increase in chlorophyll a (average, 34.8 ± 10 mg m^???3) and primary production (average, 1,304 ± 694 mg C m^???3 day^???1) indicated the mesotrophic condition of the study area during the premonsoon (PRM) and it was attributed to the large increase in the population of nanoplankton (size < 20 μ ) such as Skeletonema costatum, Thalassiosira subtilis, Nitzschia closterium, and Navicula directa. In contrast, during the post monsoon (PM), low chlorophyll a concentration (average, 9.3 ± 9.2 mg m^???3) and primary production (average, 124 ± 219 mg C m^???3 day^???1) showed heterotrophic condition. It can be stated that favorable environmental conditions (optimum nutrients and light intensity) prevailing during the PRM have enhanced the abundance of the nanoplankton community in the estuary, whereas during the PM, the light limitation due to high turbidity can reduce the nanoplankton growth and abundance, even though high nutrient level exists.