Application of City Wetland Park on Protection of Urban Rivers

Frontier of Environmental Science September 2015, Volume 4, Issue 3, PP.77-85

Application of City Wetland Park on Protection of Urban Rivers Xianfei Huanga, b, Jiwei Hua†, Fanxin Qina a

Guizhou Provincial Key Laboratory for Ecological Environment, Guizhou Normal University, Guiyang 550001, P. R. China

b

College of forestry, Guizhou University, Guiyang 550025, P. R. China

â€

Corresponding author: jwhu@gznu.edu.cn

Abstract With the rapid development of urbanization and the lack of sustainable regulation policies, large cities have become a critical pollution source to urban rivers. To elucidate the pollution status of the Nanming River, an urban river in Guiyang City, SW China, water samples were collected along the river from the upstream (through the urbanization area) to the downstream locations. Pollution levels of heavy metals, NH4+ and total phosphorus (TP) were investigated, and dissolved organic matter (DOM) was analyzed with fluorescence spectrophotometer. The results reveal that Huangjindadao, a local famous scenic spot, is a notable pollution source to the Nanming River, and the Huaxi National City Wetland Park plays an important role in protection of the water quality of this river. Analysis of 3DEEM characteristics of DOM indicated that the main pollution sources of DOM in this water body was municipal waste water. Protein-like compounds and humic acid with high molecular weight was the main components of DOM in this river. Organic compounds with low molecular weight represented a very small portion of the DOM in water of the Nanming River, especially in the downstream part of this river.

Keywords: Pollution; Heavy Metals; Dissolved Organic Matter; Urbanization; Nanming River

1 INTRODUCTION Cities are always built near rivers since rivers can provide humans with water for drinking, washing, irrigation of crops, transportation by boat or raft, and even for security from invaders. However, with rapid development of urbanization and the lack of sustainable regulation policies, cities have become a fatal pollution source to urban rivers. Large amount of contaminants have been discharged into urban rivers including nutrients (mainly nitrogen and phosphorus), heavy metals (mainly Pb, Cd, Hg, As and Cu), organic compounds, and so on. Input of nutrients into a water body may lead to the eutrophication problem which will cause algae bloom and great increase of phytoplankton in a water body [1]. Following that, the specific fish and some other aquatic animal populations will be threatened, drinking water will become taste-and-odor, and other undesirable effects will appear. In addition, pollution of heavy metals in aquatic systems has become a hot topic for several decades since these contaminants cannot be degraded through physicochemical or biological ways and they could be concentrated, accumulated and magnified through aquatic food chain [2].

Previous studies reveal that organic matter (OM, including dissolved organic matter (DOM)) plays important roles in transformation, migration and even remediation of environmental pollutants in aquatic systems, consequently affecting bioavailability and toxicity of organic and inorganic contaminants [3-5]. DOM consists of a complex and heterogeneous mixture of compounds including humic substances (humic acids and fulvic acids) and compounds with smaller molecules such as polysaccharides, amino acids, proteins and lipids, together with their degradation products[6-7]. It has been reported that DOM is one of the largest active pools of organic carbon on earth, and represents a critical component of the global carbon cycle and plays significant roles in aquatic food webs regulating the bioavailability of dissolved nutrients [8-9]. With the depletion of the dissolved oxygen (DO) content in the sedimentary environment as a result of microbiological activity, OM is an electron donor causing sulfate reduction in - 77 http://www.ivypub.org/fes

anaerobic sediments. The generated sulfide is an important ligand, which can form stable metal sulfide precipitates in sediments, and thereby governs the behavior of divalent metals. Therefore, DOM can be considered as one of the most important parameters in aquatic environments [10].

Fluorescence technique is fast, specific, sensitive and precise method for study of DOM in different aquatic environments, such as fluvial water, lake water, marine sediment pore water, estuarine water and sea water [8, 11-13].

3-dimensional excitation–emission fluorescence matrix has been successfully used to probe the chemical structure of DOM because they can distinguish different classes of DOM with different origins [5]. The organic components in natural waters commonly studied with fluorescence spectroscopy include humic substances, derived from the breakdown of plant materials by biological and chemical processes in the terrestrial and aquatic environments, and amino acids in proteins and peptides mainly from municipal sewage [14-15]. For example, Her et al. have investigated the composition of DOM with a group of methods including high performance liquid chromatography (HPLC) – size exclusion chromatography (SEC), ultraviolet–visible spectroscopy, fluorescence, and DOC measurement [16]. They suggested that the maxima locations of excitation/emission wavelengths were 278/353 nm for protein-like substances and 337/423 nm for fulvic-like substances.

The Nanming River, which originates from Huaxi Reservoir and flows through three districts of Guiyang City (Huaxi, Nanming and Yunyan districts), is the source river of the Qingshui River which flows into the Wujiang (a main tributary of the Yangtze River, China). The main part of the Nanming River flows through Guiyang City, the capital of Guizhou Province. The water quality of this river has deteriorated dramatically during the past two decades.

In the past several years, local governments have taken measures to reduce the pollution level of the Nanming River and to restore its ecology stability. One of these measures was to build a city wetland park, namely “The Huaxi National City Wetland Park”. Several years have passed, and the water of the Nanming River has become a little clear. However, it is still a puzzle whether this measure have some significant contribution in protection of the water quality of the Nanming River.

The main objectives of the present research were: (a) to study pollution status of the Nanming River based on analysis of heavy metals, DO, chemical oxygen demand (COD), biochemical oxygen demand (BOD), NH4+ and total phosphorus (TP); (b) to investigate excitation–emission fluorescence matrix characteristics of DOM in the water of the Nanming River and to analyze the potential pollution sources of DOM for this water body; and (c) to reveal the fate of this urban river and explore possible regulation and protection policies for urban rivers.

FIG. 1. MAP PRESENTING THE LOCATIONS OF THE SAMPLING SITES ALONG THE NANMING RIVER.

2 MATERIALS AND METHODS 2.1 Sampling and Preparation Sampling was undertaken along the Nanming River on 30 May 2013. Surface water samples were collected at 10 sites (Figure 1), which were selected with consideration of potential pollution sources, along the river from the - 78 http://www.ivypub.org/fes

upstream (through the urbanization area) to the downstream locations. The water sample collected at sampling site 1 was suggested to present the natural baseline of contaminants of the Nanming River. From the site 2 to site 3, the river flows through the Huaxi Park. From sites 3 to 5, the river flows through the Huaxi National City Wetland Park.

From sites 6 to 10, the river flows through the main part of Guiyang City. 2.5 L of water sample was taken in polyethylene bottles at each site and transported to the laboratory within 10 hours. All of the water samples were maintained at 4 oC in the dark and analyzed within 24 hours.

2.2 Physicochemical Analysis Temperature (T), pH value and DO of water samples were determined on spot with a multi-parameter meter (YSI6600V2). COD, NH4+ and TP were analyzed with chemical methods in the laboratory. BOD was determined by incubation of samples for 5 days at 20 °C. For analysis of Pb, Cd and Cu, 200 mL of water samples were digested with 2 mL mixed solution of conc. nitrate acid (HNO3) and conc. perchloric acid HClO4 (V:V = 4:1), and their concentrations were analyzed with an atomic absorption spectroscopy (WFX-210). For analysis of Hg and As, 8 mL of water sample was taken into a 10-mL volumetric flask, and 0.5 ml of reducing agent solution (10% thiourea solution) was added into each flask, then flasks were diluted to volume with deionized water. Concentrations of Hg and As were determined using an atomic fluorescence spectrometer (AF-640) from Beijing Beifen Ruili Instrument Corporation, China. All chemicals used in the present study were analar grade, and deionized water used in all experiments was prepared with a water purification system (Nex Power 2000) from Human Co., Korea.

2.3 Fluorescence Analysis All samples were filtered (0.22 um) before analyzing DOM. 3-dimensional excitation–emission fluorescence matrixes (3DEEM) of DOM in water samples were measured with a fluorescence spectrophotometer (Cary Eclipse from Varian Corporation, USA) with a xenon lamp as the excitation source. Excitation–emission matrix (EEM) was obtained with subsequent scanning emission spectra from 250 to 650 nm at 2 nm increments by varying the excitation wavelength from 200 to 400 nm at 10 nm increments. For the samples collected from sites 1 to 7, the slit was 20 nm for excitation and 10 nm for emission. For the water samples collected from sites 8 to 10, the slit was 10 nm for excitation and 10 nm for emission since the fluorescence intensity was too high (higher than 1000 a.u.) if 20 nm was applied for emission. The scanning speed was 1200 nm/min, and the spectra were zeroed with deionized water.

3 RESULTS AND DISCUSSION 3.1 Physicochemical Parameters Physicochemical parameters of water samples are listed in Table 1. The temperature of water in the Nanming River increased gradually from 17.9 oC to 22.0 oC from site 1 to site 7. This result reveals that the urbanization has a direct impact on the temperature of water in this urban river as a consequence of “heat island effect”, probably. The pH values ranged from 7.5 to 8.2, and it was also found that there was no significant change along the river suggesting that the urbanization have only slight effect on the pH values of this urban river. The concentration of DO was not stable as pH values. At site 1, the concentration of DO was relatively high, and the value was up to 8.29 mg/L. This value, probably, reflects the background of DO since the water was discharged from Huaxi Reservoir directly. Then the concentration of DO decreased at sites 2 (7.16 mg/L) and 3 (6.16 mg/L). This could be attribute to the pollution caused from Huangjindadao, which was a local famous scenic spot located between site 1 and site 2 (lots of local people, usually, do out-door activities here, typically for barbecuing. Waste water containing high concentration of organic matter are discharge into the river directly), and Huaxi District located between sampling site 2 and site 3. At sites 4 and 5, the concentration of DO was higher than 7.0 mg/L again. This, probably, benefit from the Huaxi National City Wetland Park, which is located between sampling sites 3 and 5. Therefore, we inferred that the Huaxi National City Wetland Park plays an important role in protecting the water quality of the Nanming River. The highest concentration of DO appeared at site 6. We inferred that two main factors might account for this: one is attributed to the work of the Huaxi National City Wetland Park mentioned above; and the other one might be attributed to that substantial oxygen was brought into the water with the import of the Chengliang stream and the - 79 http://www.ivypub.org/fes

Mati stream. At the following sites, the concentration of DO decreased generally, and this could be attributed to the pollution caused effluents from the Nanming and Yunyan districts. COD showed a high concentration at site 2 (113.8 mg/L) and site 8 (197 mg/L). High concentration of COD at site 2 was another implication that the local famous scenic spot Huangjindadao causing severe pollution to the river. High concentration of COD at site 8 was probably caused by the Xiaoche Stream. Concentrations of NH4, TP and BOD presented a similar distribution model.

Their concentrations were relatively low in the water samples collected from upstream 6 sampling sites and relatively high in the water samples collected from the downstream 4 sites.

TABLE 1 PHYSICOCHEMICAL PARAMETERS AND CONCENTRATIONS OF HEAVY METALS IN THE WATER SAMPLES

Sam. No.

T ( C)

pH

1 2 3 4 5 6 7 8 9 10

17.9 18.1 18.4 18.5 20.0 20.4 22.0 21.1 21.4 21.9

8.2 7.9 7.6 7.7 7.7 7.8 7.7 7.7 7.8 7.5

o

DO

COD

NH4+

TP

Pb

Cd

(mg/L) 8.29 7.16 6.16 7.34 7.09 10.8 6.06 6.25 5.26 3.25

79.7 113.8 42.7 17.4 21.3 25.3 37.9 197.6 37.2 26.9

0.47 0.73 0.86 0.62 0.84 1.14 2.43 3.48 6.46 5.44

0.03 0.02 0.10 0.09 0.11 0.11 0.48 0.71 0.52 0.69

7.83 0.17 0.02 5.33 8.16 20.84 ＊ — 5.17 0.37 2.38

0.04 0.02 0.24 0.95 1.71 — 0.27 0.07 0.23 0.12

Hg (ug/L) 0.41 0.70 1.02 0.54 0.59 0.54 0.50 0.37 0.74 0.47

As

Cu

0.97 1.26 1.73 1.64 1.73 2.17 2.48 2.29 3.93 2.64

2.54 2.15 2.11 1.93 1.90 2.61 4.07 1.45 3.44 2.46

＊

Note: —, means the lack of data.

3.2 Pollution Status of Heavy Metals As listed in Table 1, concentration of each heavy metal varied along the water flowing direction. Concentrations of Pb, Cd, Hg and Cu fluctuated randomly. This phenomenon was probably caused by many factors, such as pollution sources (especially for point pollution sources), physicochemical property of certain elements, and special context of the water body. The main reason may be that there were some point pollution sources along the river. In addition, these elements were easily deposited with other suspended particulate solids. Concentrations of arsenic in the water samples collected from the upstream 5 sampling sites were lower than those in the water samples from the downstream 5 sampling sites, and it was also found that concentration of arsenic increased slightly along the river flow direction. Therefore, our interpretations are as follows: (a) the pollution of this element was mainly caused by urban effluents; (b) this element could not be deposited easily with suspended particulate solids as Pb, Cd, Hg and Cu in this water body.

TABLE 2 LIMIT VALUE OF EACH HEAVY METAL BY ENVIRONMENTAL QUALITY STANDARDS FOR SURFACE WATER (GB 3838-2002)

Heavy metal Pb Cd Hg As Cu

Class I (ug/L) ≤10 ≤1 ≤ 0.05 ≤ 50 ≤ 10

Class II (ug/L) ≤ 10 ≤5 ≤ 0.05 ≤ 50 ≤ 1000

Class III (ug/L) ≤ 50 ≤5 ≤ 0. 1 ≤ 50 ≤1000

Class IV (ug/L) ≤ 50 ≤5 ≤1 ≤ 100 ≤1000

Class V (ug/L) ≤ 100 ≤ 10 ≤1 ≤ 100 ≤1000

Table 2 presents the permit values for different heavy metal according to environmental quality standards for surface water (GB 3838-2002). Concentrations of Pb for each sampling site lower than 10 ug/L and met the permit value of Class I according to environmental quality standards for surface water (GB 3838-2002) with the exception of that for site 6 (20.84 ug/L). Concentrations of Cd lower than 1 ug/L and met the permit value of Class I with the exception of that for site 5 (1.71 ug/L). All concentrations of As and Cu for each sampling site lower than their permit value limited by class I. Concentrations of Hg, excepting that for sampling site 3 (1.02 ug/L), higher than 0.1 ug/L and lower than 1.0 ug/L. Therefore, the water quality of the naming river belongs to Class IV, and even belongs to Class V at site sampling 3. It is obvious that this urban river had not been polluted by heavy metals Pb, Cd, As and Cu. - 80 http://www.ivypub.org/fes

However, special attention should focus on Hg pollution.

3.3 Pearson Correlation Analysis and Principal Component Analysis To present some in-depth information, principal component analysis (PCA) and the Pearson correlation analysis were carried out. PCA is a mathematical method that can convert a set of observations of possibly correlated variables into a set of values of linearly uncorrelated variables, and correlation analysis is an analytical technique by which the relationship between two items could be measured [17]. The Pearson's correlation coefficients between physicochemical parameters and heavy metals are listed in Table 3, and the results from PCA analysis are presented in Figure 2.

TABLE 3 PEARSON CORRELATION COEFFICIENTS BETWEEN DETERMINED ITEMS

T pH DO COD NH4+ TP Pb Cd Hg As Cu

T 1 -0.523 -0.451 -0.064 0.769** 0.858** 0.088 -0.062 -0.324 0.804** 0.469

pH

DO

COD

NH4+

TP

Pb

Cd

Hg

As

Cu

1 0.552 0.239 -0.371 -0.497 0.214 -0.225 -0.233 -0.423 0.092

1 -0.020 -0.690* -0.682* 0.795* 0.254 -0.103 -0.469 -0.128

1 0.030 0.282 -0.192 -0.482 -0.296 -0.167 -0.420

1 0.857** -0.338 -0.326 -0.092 0.898** 0.360

1 -0.257 -0.332 -0.350 0.723* 0.213

1 0.535 -0.426 -0.154 0.003

1 0.021 -0.131 -0.249

1 0.073 0.033

1 0.510

1

**Significant at 0.01 level, *Significant at 0.05 levels

3.4 Pearson Correlation between Studied Items It was found that the temperature of water in the Nanming River showed close relationships with NH4+ (R=0.769, p<0.01), TP (R=0.858, p<0.01), BOD (R=0.705, p<0.05), and arsenic (R=0.804, p<0.01). As mentioned above, the impact of a city on temperature of an urban river was mainly caused by “heat island effect”. Therefore, the temperature of water in this river was increased along the time and distance of it flowing into the Guiyang City. It was also notable that close relationships existed between NH4+ and TP (R=0.857, p<0.01), and between NH4+ and BOD (R=0.972, p<0.01), and between NH4+ and arsenic (R=0.898, p<0.01), and between TP and BOD (R=0.777, p<0.01), and between TP and arsenic (R=0.723, p<0.05), and between BOD and arsenic (R=0.920, p<0.01).

Therefore, we inferred that these items (NH4+, TP, BOD and arsenic) shared similar pollution sources and underwent similar migration experience in the Nanming River.

Negative Pearson correlation coefficients were observed between DO and NH4+ (R=-0.690, p<0.05), and between DO and TP (R=-0.682, p<0.05). These correlation coefficients probably implied that an increase in DO may lead to the decrease in NH4+ and TP. We suggested that the increase in DO accelerated the growth and respiration of aquatic microphyte, and then accelerated bio-absorption of NH4+ and TP. However, Pb showed a close relationship with DO ((R=0.795, p<0.01)). This, probably, reveals that DO is a critical factor that influences behavior of Pb in aquatic systems. We suggested that DO increase would change physicochemical properties of Pb in aquatic system, and then increase solubility of Pb in the surface water. The other items including pH, COD, Cd, Hg and Cu showed no close relationship with any concerned items in the presented study.

3.5 Principal Component Analysis Three principal components were extracted through the PCA analysis accounting for 83.48% of the total variance, and these components could reflect the majority of information from the original data. Temperature, NH4+, TP, BOD and arsenic presented high positive loading scores to Component 1. This result is in accordance with the Pearson correlation analysis, and once again indicated that the impact of Guiyang City on the temperature of water in the Nanming River was mainly caused by “heat island effect”, and indicated that NH4+, TP, BOD and arsenic in this - 81 http://www.ivypub.org/fes

river were mainly caused by the urban sewage. DO and pH showed negative loading scores to Component 1. With the inflow of the municipal sewage, concentration of OM in the surface water increased sharply. Consequently, the aquatic organisms increased. Then, DO was exhausted and a large amount of organic acid appeared due to activity of the aquatic organisms. COD and Pb presented positive loading scores to Component 2, and Hg and Cu presented negative loading scores to this component. In combination with the above analysis, we inferred that Component 2 was associated with OM content. COD and pH showed positive loading scores to Component 3, and Cd presented negative loading scores to it. We suggested that this component was connected with potential point sources (may be drainage outlets). Municipal sewage increased COD and pH value. Then, enhanced COD (OM) may combine with Cd2+ and deposit in the sediments leading to the reduction of Cd in the surface water.

FIG. 2 PLOTS OF PHYSICOCHEMICAL PARAMETERS AND HEAVY METALS’ LOADING SCORES ON EACH OBTAINED COMPONENTS: (A) 3D PLOT FOR ALL OF THE THREE OBTAINED COMPONENTS, (B) COMPONENTS 1 AND 2, (C) COMPONENTS 1 AND 3, AND (D) COMPONENTS 2 AND 3.

3.6 3DEEM characteristics of DOM The excitation–emission fluorescence characteristics of DOM in water samples collected from the Nanming River are presented in Figure 3. Two peaks (peaks A and B) were observed in the 3DEEMs of water samples, and a third peak (Peaks C) appeared only in 3DEEMs for the water samples collected from sites 1 to 7. Thus, the 3DEEMs showed at least three groups of fluorophores with different chemicals and spectroscopic behavior existed in the water samples from sites 1 to 7. Only two groups of fluorophores presented enough concentration (could be observed in the contour plots of excitation-emission fluorescence matrix) in water samples collected from 8 to 10. It was also found that the λex and λem at maximum intensity (λex-max and λem-max) of the fluorophores for peaks B and C appeared in the same domain of each 3DEEM. However, the λex-max and λem-max of the fluorophores for Peak A varied from site to site.

In combination with the circumstance of each sampling site and previous studies [15, 18], we inferred that Peak A was associated with the groups of fluorophores that are commonly named visible humic-like according to the λex-max/λem[12, 19-20] . One group was humic acid max (320-360/420-460 nm). Peak B was referred to two groups of compounds (hydrophobic acid fraction, HPOA) with large molecular weight according to the λex-max/λem-max (237-260/400-500 nm). The other group was associated with protein-like compounds (hydrophobic base fraction, HPOB) according to the λex-max/λem-max (225-237/340-381 nm). In the present study, we suggest that Peak C was associated with humic acid, which are easily adsorbed by aquatic organisms (high bioavailability), with low molecular weight. At site 1, the water quality was good (water sample collected here could reflect the water quality of Huaxi reservoir to some extent), and aquatic organisms are not so abundant to remove all compounds which could be adsorbed by these organisms. From sites 2 to 6, a large amount of pollutants from Huangjindadao and city of Huaxi District were brought into the river. As shown in Table 1 and Figure 3, temperature, COD, NH4, TP, BOD, heavy metals and DOM increased in this part. Responsible for this, the growth of aquatic organisms increased and a large amount of aquatic organisms appeared in the water. Protein-like compounds were decomposed and small organic compounds, - 82 http://www.ivypub.org/fes

which are easily adsorbed by aquatic organisms, were produced quickly.

FIG. 3. CONTOUR PLOTS OF EXCITATION-EMISSION FLUORESCENCE MATRIX FOR WATER SAMPLES FROM DIFFERENT SITE.

As shown in Figure 3, the 位ex-max and 位em-max for Peak A changed obviously. In the 3DEEMs for the water samples collected from sites 2, 3 and 5, the 位ex-max and 位em-max for Peak A were shorter than those for the water - 83 http://www.ivypub.org/fes

samples collected from the other sites. However, the λex-max and λem-max for Peak A presented no observed change in the 3DEEMs for the water samples collected from site 7 to 10. It is believed that a large amount of pollutants were brought into the Nanming River with urban sewage. Protein-like compounds and humic substances (associated with Peak B) were also the main components of DOM in the water samples from sites 6 to 10, although the number of micro-organisms in water might increase significantly. Then, organic matter (connected with Peak C), which are easily adsorbed by aquatic organisms, were reduced sharply due to the activities of micro-organisms. This might be one of the reasons why Peak C disappeared in the 3DEEMs for the water samples collected from sites 8 to 10.

4 CONCLUSIONS Based on the present study, the following conclusion could be drawn. (a) Guiyang City causes significant pollution to the Naming River, especially for NH4, TP and BOD; (b) Pb, Cd, Hg and Cu were easily precipitated in the sediments, and arsenic might exist and be accumulated in the surface water. (c) The Huaxi National Wetland Park plays an important role in protection of the water quality of the Nanming River, and we inferred that most of the pollutants caused by Huangjindadao, Huaxi Park and Huaxi District were removed in this wetland system; (d) 3DEEM characteristics indicated that the main pollution source of DOM in the Nanming River was caused by urban sewage; (e) The main component of DOM in the Nanming River was protein-like compounds and humic acid with large molecular weight, and DOM with lower molecular weight could be absorbed by aquatic organisms. However, the last point deserves a further study with some more advanced analytic techniques.

The present study implicates that the main components of DOM in an urban river with no pollution from chemical industries, as the Nanming River, might be protein-like compounds and humic acid with large molecular weights. It is advisable to build wetland parks along urban rivers in consideration of water quality, and it is unadvisable to develop scenic spots, which may cause severe pollution to water system, such as Huangjindadao near urban rivers.

ACKNOWLEDGMENT This work was financially supported by the Science and Technology Department of Guizhou Province (Project number: [2011] 2179) and the Environmental Protection Department of Guizhou Province (Project number: [2011] 8).

REFERENCES [1]

Jaing, C.H., Wu, D., Hu, J.W., Liu, F., Huang, X.F., Li, C.X., Jin, M., 2011, Application of chemical fractionation and X-ray powder diffraction to study phosphorus speciation in sediments from Lake Hongfeng, China. Chinese Science Bulletin, 56(20): 2098-2108

[2]

Huang, X.F., Hu, J.W., Li, C.X., Deng, J.J., Long, J., Qin F.X., 2009, Heavy-metal pollution and potential ecological risk assessment of sediments from Baihua Lake, Guizhou, P.R. China. International Journal of Environmental Health Research, 19(6): 405-419

[3]

Fu, P.Q., Wu, F.C., Liu, C.Q., Wang, F.Y., Li, W., Yue L.X., Guo, Q.J., 2007, Fluorescence characterization of dissolved organic matter in an urban river and its complexation with Hg(II). Applied Geochemistry, 22, 1668-1679

[4]

Guéguen, C., Burns, D.C., McDonald A., Ring, B., 2012, Structural and optical characterization of dissolved organic matter from the lower Athabasca River, Canada. Chemosphere, 87, 932-937

[5]

Patel-Sorrentino, N., Mounier S., Benaim, J.Y., 2002, Excitation-emission fluorescence matrix to study pH influence on organic matter fluorescence in the Amazon basin rivers. Water Research, 36, 2571-2581

[6]

Marin, P., Beiras, R., 2002, Adsorption of different types of dissolved organic matter to marine phytoplankton and implications for phytoplankton growth and Pb bioavailability. Journal of Plankton Research, 33, 1396-1409

[7]

Florence, V., Leticia Cotrim da, C., Léon, S., Jean V., Jean-Marie, S., 2009, Spatio-temporal variations of fluorescence properties of dissolved organic matter along the River Têt (Pyrénées-Orientales, France). Chemistry and Ecology, 25, 435-452

[8]

Guéguen, C., Guo, L.D., Wang, D.L., Tanaka N., Hung, C.C., 2006, Chemical characteristics and origin of dissolved organic matter in the Yukon River. Biogeochemistry, 77, 139-155

[9]

Hedges, J.I., Keil R.G., Benner, R., 1997, What happens to terrestrial organic matter in the ocean? Organic Geochemistry, 27, 195-212

- 84 http://www.ivypub.org/fes

[10] Frimmel, F.H., 1998, Characterization of natural organic matter as major constituents in aquatic systems, Journal of Contaminant Hydrology, 35, 201-216 [11] Raymond P.A., Bauer, J.E., 2001, Riverine export of aged terrestrial organic matter to the North Atlantic Ocean. Nature, 409, 497-500 [12] Kelton, N., Molot, L.A., Dillon, P.J., 2007, Spectrofluorometric properties of dissolved organic matter from Central and Southern Ontario streams and the influence of iron and irradiation, water research. 41, 638-646 [13] McCarren, J., Becker, J.W., Repeta, D.J., Shi, Y.M., Young, C.R., Malmstrom, R.R., Chisholma, S.W., DeLonga, E.F., 2010, Microbial community transcriptomes reveal microbes and metabolic pathways associated with dissolved organic matter turnover in the sea. PANS, 107, 16420-16427 [14] Elkins, K.M., Nelson, D.J., 2001, Fluorescence and FT-IR spectroscopic studies of Suwannee river fulvic acid complexation with aluminium, terbium and calcium. Journal of Inorganic Biochemistry, 87, 81-96 [15] Stedmon, C.A., Markager S., Bro, R., 2003, Tracing dissolved organic matter in aquatic environments using a new approach to fluorescence spectroscopy. Marine Chemistry, 82, 239-254 [16] Her, N., Amy, G., McKnight, D., Sohn, J., Yoon, Y., 2003, Characterization of DOM as a function of MW by fluorescence EEM and HPLC-SEC using UVA, DOC, and fluorescence detection. Water Research, 37, 4295-4303 [17] Fu, L.Y., Hu, J.W., Shen, W., Huang, X.F., Luo, J., Jia M., Zhang, J.P., 2014 Occurrence and implications of SEM-AVS for surface sediments from Baihua Lake, China. Soil and Sediment Contamination: An International Journal, 23, 287-312 [18] Hudson, N., Baker, A., Reynolds, D., 2007, Fluorescence analysis of dissolved organic matter in natural, waste and polluted watersâ&#x20AC;&#x201D;a review. River Research and Applications, 23, 631-649 [19] Marhaba, T.F., Lippincott, R.L., 2000, Application of fluorescence technique for rapid identification of DOM fractions in source waters. Journal of Environmental Engineering, 126, 1039-1044 [20] Marhaba, T.F., Van, D., Lippincott, R.L., 2000, Rapid identification of dissolved organic matter fractions in water by spectral fluorescent signatures. Water Research, 37, 3543-3550

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