- Email: [email protected]
Laboratory analyses of nutrient release processes from Haihe River sediment
International Journal of Sediment Research 27 (2012) 61-72
Laboratory analyses of nutrient release processes from Haihe River sediment Min WU1, Xue-ming SUN2, Sui-liang HUANG1,3, Xian-qiang TANG4, and Miklas SCHOLZ5
Abstract Sediment samples were collected from the heavily contaminated Haihe River to conduct static nutrient release experiments with tap water, and to evaluate the effect of dredging depths, salinity and light on the corresponding release processes. The study is significant because it helps decision-makers to assess the likely impact of dredging (e.g. eutrophication) on contaminated freshwater and brackish rivers. The concentrations of total nitrogen and inorganic phosphorus were approximately 950 mg/kg and 760 mg/kg, respectively. The typical organic matter concentration was 8.6%. Data obtained from the nutrient leaching experiments indicated that 5cm-dredging of sediment reduced the water column total phosphorus, total dissolved phosphorus and ammonia-nitrogen concentrations insignificantly. In contrast, dredging 10cm surface sediment could improve the water quality. Higher salinity values benefited the release of nitrogen and phosphorus from sediment. In contrast to indoor experiments, concentrations of total phosphorus, total dissolved phosphorus and ammonia-nitrogen were higher for the outdoor experiments. Key Words: Aquatic sediment and water interaction, Water quality management, Nitrogen, Phosphorus, Salinity, Dredging, Water depth, Light, Haihe River, China
1 Introduction 1.1 Background Water management of rivers, lakes and other watercourse has become an increasing problem due to an increase in eutrophication (McDowell et al., 2003). Excessive discharge of nitrogen and phosphorus to water bodies leads to the degradation of their quality, thus hindering various water uses. Studies showed that nutrients including nitrogen and phosphorus may be adsorbed to the sediment accumulated on the bottom of rivers or lakes. These sediment may accumulate over long periods and can act as new pollutant sources if disturbed to the overlying water (Lijklema et al., 1993; Abrams and Jarrell, 1995). For freshwater bodies, contaminated sediments are regarded as the most important sources of nutrients leading subsequently to eutrophication (Wu et al., 2005; Li et al., 2007). Nutrient release processes have a significant impact on the water quality and may result in continuous eutrophication of lakes and rivers, 1
Ph.D candidate, 2 Graduate student, 4 Dr., Key Laboratory of Pollution Processes and Environmental Criteria of Ministry of Education, Nankai University, Tianjin, China. E-mail: [email protected], xmsun@mail. nankai.edu.cn, [email protected] 3 Prof., Key Laboratory of Pollution Processes and Environmental Criteria of Ministry of Education, Nankai University, Tianjin, China. Numerical Simulation Group for Water Environment, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin, China. Corresponding author: Tel: +86 22 23503423; Fax: +86 23503423; E-mail address: [email protected] 5 Prof., Civil Engineering Research Centre, School of Computing, Science and Engineering, The University of Salford, Salford M5 4WT, England, United Kindom, E-mail: [email protected] Note: The original manuscript of this paper was received in Mar. 2011. The revised version was received in Aug. 2011. Discussion open until Mar. 2013. International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 61 -
even when external nutrient sources are under control (Abrams and Jarrell, 1995; Tian and Zhou, 2007; Xie et al., 2003). As observed for non-point source (i.e. diffuse) pollution, internal or within-system pollution has numerous release mechanisms including advection, ion exchange, molecular diffusion, biologically mediated changes and uncertainties associated with different release durations, approaches and intensities (Hu et al., 2001; Kim et al., 2003; Scholz, 2006). The characteristics of sediment and the overlying water quality will affect the nutrient release processes. A better understanding of the pollutant release mechanisms and characteristics under different environmental factors is therefore helpful to prevent or reduce the pollutant release from sediment into the overlying water body. 1.2 Representative case study The cost-effective restoration of large, polluted and urban rivers within developing countries is a major challenge. For example, the mainstream of the Haihe River is the largest river in Tianjin (north China) with a length of 73 km (Wang et al., 2003). The river stretches from San Cha Kou (catchments of three primary tributaries) to the Bohai Sea, and flows through downtown Tianjin. The corresponding Haihe River basin provides water for 130 million people. The land use is dominated by large residential and agricultural areas, which are responsible for high nutrient concentrations within the river. With the rapid development of urbanization and the intensive use of water resources, the river becomes increasingly subject to water shortage and water quality deterioration stresses (Liu et al., 2001; Liu et al., 2007). This process has been accelerated by the construction of sluices to prevent sea water intrusion. The reduced exchange of water resulted in virtually stagnant river water and the accumulation of polluted sediment. Relatively low heavy metal and toxic organic compound pollution has been recorded in the past (Ding et al., 2005; Yang et al., 2005; Liu et al., 2007). In contrast, measured ammonia-nitrogen (NH4-N), total nitrogen (TN) and total phosphorus (TP) concentrations were in the ranges between 0.5 and 1.5 mg l-1, 2.1 and 5.38 mg l-1, and 0.4 and 1.2 mg l-1, respectively (Wen et al., 2008). These nutrient data indicate that the mainstream of the Haihe River is heavily eutrophicated. Considering the economic and environmental importance of the mainstream of the Haihe River to the city of Tianjin, much effort and cost have been invested to control the pollution loads by a series of environmental protection programs such as the domestic wastewater discharge scheme and enforcement of the water pollution control law in China, but eutrophication remains one of the most important water quality problem of the mainstream of the Haihe River. Water quantity shortage and water quality deterioration in Tianjin is serious, and become the mainly limiting factors for the economic growth and social advancement. Therefore, Tianjin government aimed to restore the Haihe River as the most promising and reliable drinking water source. Now, the entire external non point pollution source has been eliminated, and sediment was the predominant pollution contributor to Haihe River water quality. In light of the above considerations, several funding agencies including the Tianjin Scientific Commission agreed to collect sediment data to ascertain the extent of the problem and to assess the nutrient release potential of the within river bed material. In comparison to other rivers in China and the wider region, the mainstream of the Haihe River has a low light transmittance and significantly different salinities at different reaches. Only the reach downstream of Erdao sluice is saline water (Xiong et al., 2005). To date, moreover, few or none publications reported nutrient sediment releasing characteristics under different light conditions and salinity levels. Although dredging surface active sediment is one of the most effective methods to manage polluted rivers (Su et al., 2010), the most optimal dredging depths and environmental boundary conditions for the mainstream of the Haihe River and other representative polluted rivers are still subject to discussion. 1.3 Rationale, significance and aim The rationale of the present study was to contribute to the understanding of the interaction between contaminated bed material and aquatic environment by assessing the behavior of real sediment samples taken from a representative and important river. As Haihe River will be restored to be important and reliable drinking water source for Tianjin City, therefore, it is significant to use tap water instead of original river water to conduct sediment nutrient releasing simulation experiments. The study is significant because it helps decision-makers to assess the potential invest of effort and cost that will be used to restored the Haihe River to planned standard. Moreover, exploring the effect of light conditions - 62 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
and salinity levels on nutrient release from Haihe River sediment will publish the first hand material and give some hint for the future river restoration practices. Taking wrong decisions may lead to avoidable eutrophication and waste of physical and financial resources. The discussion of various scenarios is presented with the help of a case study supported by laboratory-scale experiments under controlled and natural conditions to assess the influence of different degrees of freedom on the data variability. The aim was therefore to make nutrient release processes within the mainstream of the Haihe River clear and to assess the role played by polluted sediment on its overall water quality, and evaluate the impact of light, salinity and dredging depths on nutrient release rates. 2 Materials and methods 2.1 Sampling In June 2006, heavily polluted Haihe River sediment was collected from Niwo ferry and relatively clean sediment was obtained from the corresponding bank of the river. Niwo ferry is located in the middle of the studied river reach (39º03´03´´ N, 117º21´30´´ E, Fig. 1). The corresponding river width and depth were approximately 100 m and 1.90 m, respectively. All sediment samples were used to conduct static nutrient release experiments. Samples of sediment were collected by mechanical grab-style samplers and embankment samples were obtained by clean spades. All the sediment were transported to the laboratory immediately in sealed plastic bags that were put in iceboxes under ćto keep original before conducting experiment. Sediment was divided into two parts: one part was used for simulation experiments, and the other part was used for analyzing the physical and chemical sediment properties. Sediment belonging to the latter part was naturally air-dried, and a standard sieve analysis method (Das, 1990) was applied. Four different sieves with 20, 60, 100 and 200 meshes were used to determine mass fractions for the following corresponding grain size diameter ranges: larger than 0.247 mm, 0.147-0.247 mm, 0.074-0.147 mm and 0.0385-0.074 mm, respectively. These ranges match up with medium sand, fine sand, very fine sand and silt according to the China Soil Partition Method (Wang and Kang, 1991).
Fig. 1 Map of the Haihe River showing the sampling sites of the sediment International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 63 -
Furthermore, organic matter, total phosphorus and total nitrogen were analyzed according to the Chinese Soil Physical and Chemical Standard Methods (Bao, 2000). 2.2 Experimental design and operation The authors adopted various conditions for comparing nutrient release to assess the impact of the key environmental boundary conditions such as light, salinity and dredging depths that are of relevance to the decision-makers. Five analogous 2 L cylinders (10 cm in diameter and 50 cm in height), numbered cylinder 1, 2, 3, 4 and 5, were used for the nutrient-release experiments (Fig. 2). Fully mixed river bank sediment of 5-cm depth was placed into cylinder 1. In cylinder 2 a 5-cm deep river bank sediment sample, representing the bottom layer, was topped by a 5-cm thick bed material obtained from the ferry. Cylinders 3, 4 and 5 were each filled with 10-cm deep sediment obtained from the ferry. All cylinders were designed to assess the effect of dredging depths (i.e. 10cm, 5cm and 0cm), light and salinity (0.25‰ or 3.00‰, controlled by the addition of sodium chloride) on nutrient release from Haihe River sediment. The chosen salinity concentrations are representative of the likely salinity values along the assessed river stretch characterized by freshwater (sometimes supplemented by saline water if river levels are low) upstream and saline water (approximately 2.84‰ at Erdao Sluice) downstream (see also above).
Fig. 2 Design and operation of the experimental set-up to assess nutrient release from sediment. Sa, salinity
As Haihe River water in the studied river reach subjected little sunshine. Indoor and outdoor locations for the cylinders were chosen to obtain a better comparison between rather controlled indoor and less controlled outdoor conditions. For example, the outside light and temperature vary in wider ranges, but are realistic. Temperature measurements were always undertaken at 12:00. All experiments were conducted in parallel. Tap water was aerated for 48 hours to remove chlorine, and then added carefully to each cylinder (up to 2.5 cm below the top rim of each cylinder), which were filled with sediment previously (see above). Clean tap water instead of contaminated river water was used to assume the potential sediment releasing characteristics while river water quality is up to the required standard that used for drinking water source. Water samples were collected 10 cm below the water surface using the siphoning principle, which reduced the possibility of disturbing sediment. Furthermore, liquid that was lost from the open cylinders due to periodic water sampling and natural evaporation got recharged on a daily basis or more frequently if appropriate (see below). The static pressure head was therefore comparable throughout the experiment. Moreover, tap water instead of contaminated river water was used as recharge water because it is likely to have a neglectable influence on the nutrient balance. Experiments were conducted with tap water rather than river water and in a static rather than a turbulent flow-through environment to reduce the degrees of freedom (i.e. variability). Moreover, the nutrient loads within the sediment were much higher than those within the river water. - 64 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
2.3 Sediment and overlying water quality All experimental systems were operated between 21 September and 21 October 2007. Overlying water was sampled daily during the first three days, and then at intervals of between three and five days. After each sampling equivalent water was immediately recharged, the following water quality parameters were analyzed to evaluate the effect of sediment dredging, light and salinity on the nutrient release from Haihe River sediment: Ammonia-nitrogen analyzed by the phenol-hypochlorite method (Wetzel and Likens, 2000); total dissolved phosphorus and total phosphorus analyzed by the persulphate digestion and acid-molybdenumblue colorimetric method (Wetzel and Likens, 2000); phosphorus fractions including exchangeable phosphorus (Ex-P), iron/aluminum bounded phosphorus (Fe/Al-P) and calcium bounded phosphorus (Ca-P) analyzed by the modified sequential extraction method (Ruban et al., 1999, 2001). 3 Results and discussion 3.1 Sediment characteristics The particle size distributions of the selected sediment samples are shown in Table 1. The combined sand fractions (0.074-0.247 mm; sum of the medium, fine and very fine sands) dominated both the ferry (93.7%) and bank (99.3%) sediment samples. The clay fractions were of minor importance, accounting only for 6.3% and 0.7% of the total ferry and bank sediment, respectively.
Sediment source Within river River bank
Table 1 Distribution (%) of sediment particles Medium sand Fine sand Very fine sand 15.1 23.0 55.6 18.6 35.6 45.1
Clay 6.3 0.7
Table 2 summarizes the results of the nutrient analysis of the above sediment samples. Readily available phosphorus, which includes the exchangeable phosphorus and iron and/or aluminum bound phosphorus, comprises 30.2% of the total inorganic phosphorus contained within the within-river sediment, which is more than the corresponding value for the bank sediment (only 6.79%). Calcium-bound phosphorus is the dominant fraction of inorganic phosphorus for both sediments. Previous studies indicated that calcium-bound phosphorus is a relatively stable fraction, and is attributed to the permanent burial of phosphorus within sediment (Gonsiorczyk et al., 1998; Kozerski and Kleeberg, 1998). Table 2 Sediment compositions Sediment Ex-P Fe/Al-P Ca-P IN-P TN OM source (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (%) Within river 38.84 190.08 529.33 758.39 947.00 8.60 River bank 6.035 18.01 330.33 354.38 364.23 3.42 Ex-P, exchangeable phosphorus; Fe/Al-P, ferrous and/or aluminum bound phosphorus; Ca-P, Cadmium bound phosphorus; IN-P, inorganic phosphorus; TN, total nitrogen; OM, organic matter.
Generally speaking, the organic matter, total phosphorus and total nitrogen concentrations within the river sediment are significantly (p<0.05) higher than those for the corresponding bank sediment. The total phosphorus and total nitrogen concentrations determined for the Haihe River sediment greatly exceeded the recommended concentrations (550 mg/kg and 600mg/kg for total nitrogen and total phosphorus, respectively), which are considered to be a significant risk to the river ecology (Yue et al., 2007; Liu et al., 2007). It follows that highly polluted Haihe River sediment pose a serious ecological risk to the success of future restoration efforts. 3.2 Effect of dredging depths on phosphorus and nitrogen release Figure 3 shows the concentration variations for total phosphorus, total dissolved phosphorus and ammonia-nitrogen in the overlying water for different dredging depths. The variation of total phosphorus concentration with time is similar to that of dissolved phosphorus with time. For cylinders with dredging 10cm sediment, the concentrations of total phosphorus and total dissolved phosphorus were relatively low during the entire experimental period, but the concentrations for dredging 5cm sediment and dredging International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 65 -
0cm sediment were different. Statistic results in Table 3 indicated that dredging 10cm surface sediment can significantly improve the column water quality, which was different from that reported 5cm for Suzhou River in Shanghai (Xing et al., 2006). Regional environmental conditions, pollution history and river characteristics (e.g. low flow velocity of Haihe River) etc may be the possible reasons.
Fig. 3 Concentration variations for (a) total phosphorus (TP); (b) total dissolved phosphorus (TDP); and (c), ammonia-nitrogen (NH4-N) in water overlying sediment subject to various dredging modes
During the first three days of the experiment, the concentrations of total phosphorus and total dissolved phosphorus were relatively low. However, they increased linearly three days later, and kept stable after twenty days. Wen et al. (2008) found that under static outdoor conditions, total phosphorus concentrations resulting from the release of Haihe river sediment increased when the tap water was used as overlying water; while total phosphorus concentrations decreased when the river water was used as overlying water. Findings indicate that sediment dredging can effectively reduce phosphorus pollution. The ranking order for phosphorus content within the water column of the experimental cylinders subject to the dredging depths was as follows: 0cm > 5cm> 10cm. Similar to phosphorus, the ammonia-nitrogen concentrations were relatively low during the experiment. The concentrations were different for the cylinders containing not dredged samples compared to those cylinders with dredging 5cm sediment. The concentration of ammonia-nitrogen reached 1.4 mg l-1 at the third day of the experiment. This was the highest value for cylinders with dredging 5cm sediment during the entire experimental period, while the corresponding concentration for cylinders with not dredged sediment increased gradually until the 12th day. Approximately twenty days later, regardless of the dredging mode, ammonia-nitrogen concentrations remained low and stable. In general, sediment dredging reduced ammonia-nitrogen and phosphorus concentrations within the overlying water. - 66 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
The properties of sediment will affect the nutrient release processes. According to Table 2, the content of exchangeable phosphorus and iron and/or aluminum bound phosphorus was high for the within-river sediment (38.84 mg/kg and 190.08 mg/kg for exchangeable phosphorus and iron/aluminum phosphorus, respectively (Table 2)). These phosphorus fractions leached out easily from sediment into the water column. This observation helps to explain the relatively high phosphorus concentrations measured within the 0cm dredged and 5cm dredged sediment, as well as similar observations with respect to total phosphorus and total dissolved phosphorus. Because the phosphorus content was low within the bank sediment, total phosphorus and total dissolved phosphorus release rates from this sediment was much less than those obtained from the within river bed material. Without disturbance of the water column, a concentration gradient existed between the interstitial water and the overlying water, which was mostly affected by the intensity of nutrient release. Moreover, microorganism activity also impacted indirectly on the release process (Table 2). The organic matter content was relatively high within the mostly anaerobic river sediment, which was assessed for cylinders that were packed with 5cm dredged and 0cm dredged material. During the mineralization process of organic matter within the sediment, the generation of ammonia-nitrogen consumes dissolved oxygen (provided by algae and the air) and encourages the nitrification-denitrification processes under partly anaerobic environments (Vymazal, 2007). This leads to a gradual reduction of ammonia-nitrogen concentrations within the water column as observed for the cylinders containing 5cm and 0cm dredged sediment towards the end of the experiment (Fig. 3). 3.3 Effect of salinity on phosphorus and nitrogen release Figure 4 illustrates the relationships between total phosphorus, total dissolved phosphorus and ammonianitrogen concentrations and time at salinity values of 3.00‰ and 0.25‰. A similar behavior for all three nutrient parameters at both salinities was observed. The concentrations of total phosphorus and total dissolved phosphorus increased gradually with time and kept stable twenty days later, while the concentration of ammonia-nitrogen showed different tendencies with time; it increased during the first twelve days and subsequently decreased to the lowest value of 0.15 mg l-1. During the entire experimental period, the concentrations of total phosphorus and total dissolved phosphorus within the cylinders with 3.00‰ salinity were significantly higher than those of the cylinders with 0.25‰ salinity. During the first twelve days, the concentration of ammonia-nitrogen within the cylinders containing liquid with 3.00 ‰ salinity was higher than the corresponding one for cylinders subjected to a salinity of 0.25 ‰. Thereafter, the concentrations for both treatments began to decrease. Nitrogen and phosphorus diffusion were affected by both microbial activity within the sediment and external environmental factors (Wang et al., 2008). Both chloride and salinity affect the survival rate of microorganisms. Moreover, salinity plays an important role in the migration and transformation of ammonia-nitrogen, and thus influences the ammonia-nitrogen transfer rate between sediment and water interfaces (Liu et al., 2002). The addition of sodium chloride increased salinity, chloride ion concentration, competition between chloride and phosphate ions, competition between sodium ion and ammonia ion, and reduced the nitrogen and phosphorus adsorption capacity of the sediment, thus causing high nitrogen and phosphorus concentrations to occur in the overlying water column. In addition, salinity can affect microbial nitrification directly. The same phenomenon was also observed in Wen et al’s experiment (Wen et al., 2008). The transformation of ammonia into nitrate performs better for environments with low in comparison to high salinity values. A decrease of the nitrification and denitrification processes can be observed with an increase of salinity (Boatman and Murray, 1982; Rysgsaard et al., 1999; Seitzinger et al., 1991). This explains the observation that total phosphorus, total dissolved phosphorus and ammonia-nitrogen concentrations within the cylinders containing 3.00 ‰ salinity were higher than those of the cylinders associated with only 0.25 ‰ salinity (Table 3). 3.4 Effect of light on phosphorus and nitrogen release Figure 5 shows fluctuations of total phosphorus, total dissolved phosphorus and ammonia-nitrogen within the overlying water at different light conditions. During the first three days, total phosphorus and total dissolved phosphorus concentrations for the outdoor set-up were higher than those for the indoor experiment. However, this tendency reversed between the 3rd and 12th day of the experiment, and International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 67 -
concentrations of the indoor system were slightly higher than those of the outdoor set-up. From the 12th day until the end of the experiment, this observation remained the same and a difference in concentration gradient was obvious. The differences between the two conditions were virtually negligible until five days for total dissolved phosphorus and ammonia-nitrogen and twelve days for total phosphorus. In general, the phosphorus concentrations in the overlying water for the outdoor cylinders were lower than those of the indoor ones during the entire experimental period. Light conditions significantly (p<0.05) influenced phosphorus release from sediment (Table 3).
Fig. 4 Concentration variations for (a) total phosphorus (TP); (b) total dissolved phosphorus (TDP); and (c), ammonia-nitrogen (NH4-N) in water overlying sediment subject to 0.25‰ and 3.00‰ salinity Table 3 Parameter
Impact of dredging depths, light and salinity on the release of nutrients from sediment Dredging depths Light condition Salinity 10cm
5cm
0cm
Indoor
Outdoor
0.25‰
3.00‰
0.10 b 0.12 b 0.12 b 0.08 a 0.12 a 0.322 b 0.02 a TP ±0.01 ±0.07 ±0.09 ±0.09 ±0.04 ±0.09 ±0.06 0.06 b 0.08 b 0.08 b 0.03 a 0.08 0.01 a 0.27 b TDP ±0.00 ±0.05 ±0.07 ±0.07 ±0.01 ±0.07a ±0.17 0.57 a, b 1.13 b 1.13 b 0.48 a 1.13 a 1.78 b 0.31 a NH4-N ±0.20 ±0.45 ±0.95 ±0.95 ±0.52 ±0.95 ±1.20 TP, total phosphorus; TDP, total dissolved phosphorus; NH4-N, ammonia-nitrogen; the means marked by the same letters are not significantly different according to least significant difference multiple range test at p=0.05. - 68 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
Fig. 5 Concentration variations for (a) total phosphorus (TP); (b) total dissolved phosphorus (TDP); and (c), ammonia-nitrogen (NH4-N) in water overlying sediment subject to indoor and outdoor light conditions
Ammonia-nitrogen release patterns were a little different in comparison to phosphorus. During the first three days of the experiment, the ammonia-nitrogen concentrations for the outdoor set-up were slightly higher than those for the indoor set-up. However, between the 3rd and 20th day, the ammonia concentrations for the indoor setup were higher (but not significantly different) than those for the outdoor experiment, and an increase of the concentration gradient was noted. Twenty days later, the ammonia-nitrogen concentrations for both set-ups were stable at a concentration of approximately 0.15 mg l-1. According to Table 3, the effect of light conditions on ammonia release became apparent when the ammonia concentrations for the indoor cylinders were higher than those for the outdoor set-up. During the entire experimental period, the outdoor cylinders received natural light and the mean water temperatures for the outdoor set-up were 1.8oC higher than the corresponding ones for the indoor set-up. The temperature ranges for the inside and outside set-up were between 23.1ºC and 25.2ºC (mean of 24.3 ºC), and between 24.7ºC and 27.3ºC (mean of 26.1 ºC), respectively. However, the temperature difference was not significant. These favorable environmental boundary conditions encouraged microbial activity, and resulted therefore in higher phosphorus and nitrogen concentrations for the outdoor compared to the indoor cylinders. Five days later, suspended matter was visible in the outdoor cylinders and the color of the water body changed from virtually transparent to green due to the growth of algae. As the experiment progressed, various blue-green algae continued to grow and the water color became even much greener. International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 69 -
The consumption of phosphorus and nitrogen by algae can lead to a reduction of the total phosphorus, total dissolved phosphorus and ammonia-nitrogen concentrations in the overlying water (Spears et al., 2008). The phosphorus and nitrogen concentrations within the outdoor cylinders were much lower than those within the indoor ones. This can partly be explained by large amounts of algae being attached to the sediment and walls of the cylinders, escaping bulk water sample collection. This finding is in contrast to reports published by Yao et al. (2004). However, Spear et al. (2008) found out that ammonia-nitrogen and total phosphorus within water columns were all significantly higher under dark in comparison to light conditions. Light conditions affected the release of phosphorus. The phosphorus concentration within the water column decreased with the increase of light availability (Fig. 5). Moreover, Spear et al. (2008) confirmed that better light conditions in long-term incubation experiments can alter the transport of nutrients across the sediment-water interface and lead to the decrease of the phosphorus concentrations as a result of direct uptake by algae. The growth of algae positively correlated with an increase in illumination intensity, and a substantial mass of nutrients was utilized by algae, which confirms findings reported in the literature (Axler and Reuter, 1996; Barlow-Bush et al., 2006). Moreover, nitrogen and phosphorus released from sediment was the main nutrient source for benthic algae, which are also called “biological barriers” due to their nutrient capture effect (Jarvie et al., 2002). 4 Conclusions and further research Phosphorus, nitrogen and organic matter contents were relatively high within the mainstream of the Haihe River sediment, which is heavily polluted and should therefore be considered as a potential risk to the river ecology. The exchangeable phosphorus content within the river sediment contributed to less than 6% of the total inorganic phosphorus. The ion/aluminum phosphorus fraction was approximately 25%. The calcium-phosphorus fraction was dominant (>70%) within the sediment. Sediment dredging had a significant impact on the nutrient release rate from Haihe River sediment. Dredging 5cm surface sediment slightly improved the overlying water quality while dredging 10cm sediment can greatly enhance the overlying water quality. An increase in salinity promotes nutrient release from sediment. Decision-makers should therefore encourage dredging at least 10cm of contaminated surface sediment, particularly for saline waters to reduce the risk of eutrophication. Furthermore, light conditions also indirectly affected nutrient release processes. Compared to the indoor system, natural light exposure to the outdoor cylinders facilitated algae growth, and therefore reduced nitrogen and phosphorus concentrations within the free water column, and indirectly restrained the release of nutrients from sediment. However, the data set is too sparse to perform detailed biochemical process modeling. Nevertheless, future research could assess the suitability of soft modeling techniques (Rustum et al., 2008) to predict nutrient release rates from disturbed sediment. Acknowledgements This work was financed by NSFC (Grant No. 51079068), NSF of Tianjin (Grant No. 09ZCGYSF00400) and the National Key-Projects of Water Pollution Control and Prevention (Grant Nos. 2008ZX0734-005-001 and 2009ZX07209-001). M. Scholz is a Visiting Projessor at Nankai University. Bilateral collaboration is financially supported by The Royal Society. References Abrams M. M. and Jarrell W. M. 1995, Soil-phosphorus as a potential non-point source for elevated stream phosphorus levels. J. Environm. Qual., Vol. 24, No. 1, pp. 132–138. Axler R. P. and Reuter J. E. 1996, Nitrate uptake by phytoplankton and periphyton. Whole-lake enrichments and mesocosm-15N experiments in an oligotrophic lake. Limnology and Oceanography, Vol. 41, No. 4, pp. 659–671. Bao S. D. 2000, Soil and Agricultural Chemistry Analysis. Chinese Agriculture Publishing House, Beijing, China. Barlow-Bush L., Baulch H. M., and Taylor W. D. 2006, Phosphate uptake by seston in the Grand River, southern Ontario. Aquatic Sciences, Vol. 68, No. 2, pp. 1615–1621. Boatman C. D. and Murray J. W. 1982, Modeling exchangeable NH4+ adsorption in marine sediments. Process and controls of adsorption. Limnology and Oceanography, Vol. 27, No. 1, pp. 99–110. Das B. M. 1990, Principles of Geotechnical Engineering, second ed. PWS-KENT, Boston, MA. - 70 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
Gonsiorczyk T., Casper P., and Koschel R. 1998, Phosphorus binding forms in the sediment of an oligotrophic and an eutrophic hardwater Lake of the Baltic District (Germany). Water Science and Technology, Vol. 37, No. 3, pp. 51–58. Ding H., Li X. G.; Liu H., Wang J., Shen W. R., Sun Y. C., and Shao X. L. 2005, Persistent organochlorine residues in sediments of Haihe River and Dagu Drainage River in Tianjin, China. Journal of Environmental Sciences, Vol. 17, No. 5, pp. 731–735. Hu X. F., Gao X. J., and Chen Z. L. 2001, Preliminary study on nitrogen and phosphorus release from the creek sediments, Outskirts of Shanghai. Shanghai Environm. Sci., Vol. 20, No. 2, pp. 66–70 (in Chinese). Jarvie H. P., Neal C., Warwick A., White J., Neal M., Wickham H. D., Hill L. K., and Andrews M. C. 2002, Phosphorus uptake into algal biofilms in a lowland chalk river. Science Total Environment, Vol. 282, No. 1–3, pp. 353–373. Kim L. H., Choi E., and Stenstrom M. K. 2003, Sediment characteristics, phosphorus types and phosphorus release rates between river and lake sediments. Chemosphere, Vol. 50, No. 1, pp. 53–61. Kozerski H. P. and Kleeberg A. 1998, The Sediments and the Benthic-pelagic Exchange in the Shallow Lake Muggelsee (Berlin, Germany). International Review Hydrobiology, Vol. 83, No. 1, pp. 77–112. Li D. P., Huang Y., and Li W. G. 2007, Study on Remediation of City River Water Body by Technology of Aerating Sediments. China Wat. Wastewat., Vol. 23, No. 5, pp. 22–25 (in Chinese). Lijklema L., Koelmans A.A., and Portielje R. 1993, Water quality impacts of sediment pollution and the role of early diagenesis.Water Science and Technology, Vol. 28, No. 2, pp. 1–12. Liu C., Wang Z. Y., He Y., and Cheng D. S. 2007, Evaluation of Water and Sediment Qualities at River Mouths in the Haihe River System. International Journal of Sediment Research, Vol. 22, No. 4, pp. 318–326. Liu G. H., Fu B. J., and Yang P. 2001, Quality of aquatic environment at Haihe River and the pollutant fluxes flowing into Sea. Chinese J Environm Sci., Vol. 22, No. 4, pp. 46–50 (in Chinese). Liu P. F., Chen Z. L., and Liu J. 2002, Study on effects of salinity and pH on NH4+ release in East Chongming Tidal flat sediment. Shanghai Environm. Sci., Vol. 21, No. 5, pp. 28–32 (in Chinese). McDowell R. W., Sharpley A. N., and Folmar G. 2003, Modification of phosphorus export from an eastern USA catchment by fluvial sediment and phosphorus inputs. Agriculture Ecosystems of Environment, Vol. 99, No. 1-3, pp. 187–199. Ruban V., Brigault S., Demare D., and Philippe A. M. 1999, An investigation of the origin and mobility of phosphorus in freshwater sediments from Bort-Les-Orgues Reservoir, France. Journal of Environmental Moniting, Vol. 1, No. 4, pp. 403–407. Ruban V., lópez-Sánchez J. F., Pardo P., Rauret G., Muntau H., and Quevauviller P. 2001, Development of a harmonized phosphorus extraction procedure and certification of a sediment reference material. Journal of Environmental Moniting, Vol. 3, No. 1, pp. 121–125. Rustum R., Adeloye A. J., and Scholz M. 2008, Applying Kohonen Self-Organizing Map as a software sensor to predict biochemical oxygen demand. Water Environment Research, Vol. 80, No. 1, pp. 32–40. Rysgsaard S., Thastum P., Dalsgaard T. 1999, Effects of salinity on adsorption capacity, nitrification and denitrification in Danish Estuarine Sediments. Estuarine, Vol. 22, No. 1, pp. 22–30. Seitzinger S. P., Gardener W. S., and Spratt A. K. 1991, The effect of salinity on ammonium sorption in aquatic sediments. Implications for Benthic Nutrient Recycling. Estuaries, Vol. 14, No. 2, pp. 167–174. Spears B. M., Carvalho L., Perkins R., and Paterson D. M. 2008, Effects of Light on Sediment Nutrient Flux and Water Column Nutrient Stoichiometry in a Shallow Lake. Water Research, Vol. 42, No. 4-5, pp. 977–986. Scholz M. 2006, Wetland Systems to Control Urban Runoff. Elsevier, Amsterdam, The Netherlands. Su C. C., Shun C. W., and Chun H. W. 2010, Sediment removal efficiency of siphon dredging with wedge-type suction head and float tank. International Journal of Sediment Research, Vol. 25, No. 2, pp. 149–160. Tian J. R. and Zhou P. J. 2007, Phosphorus fractions of floodplain sediments and phosphorus exchange on the sediment–water interface in the lower reaches of the Han River in China. Ecological Engineering, Vol. 30, No. 2, pp. 264–270. Xing Y. N., Ruan X. H., and Zhao Z. H. 2006, Effects of depth of sediment dredging in Urban Rivers on release of nitrogen and phosphorus. Journal of Hohai University (Natural Sciences)., Vol. 34, No. 4, pp. 378–382. Vymazal J. 2007, Removal of nutrients in various types of constructed wetlands. Science of the Total Environment, Vol. 380, No. 1-3, pp. 48–65. Wang Y. Z. and Kang Z. C. 1991, Study on the relationship between deposit density and particle size distribution of debris flow. J. Mountain Res., Vol. 9, No. 3, pp. 165–170 (in Chinese). Wang D. Q., Chen Z. L., and Xu S. Y. 2008, Study on the exchange flux of the DIN Through the sediment-water Interface in the Yangtze Estuary. Mar. Sci., Vol. 32, No. 2, pp. 10–15 (in Chinese). Wang H., Yang N. Y., and Shen Y. W. 2003, Safety assessment on several organic pollutants of the Haihe River Valley. Res. Environm. Sci., Vol. 16, No. 6, pp. 35–37 (in Chinese). Wetzel R. G. and Likens G. E. 2000, Limnological Analyses, third ed. Springer, NY, USA. International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 71 -
Wen W., Sun X. M., Sun S. J., and Huang S. L. 2008, Release of phosphorus and nitrogen from Haihe River sediments. J. Agro-Environm. Sci., Vol. 27, No. 1, pp. 295–300 (in Chinese). Wu Y. H., Hu J., and Jin X. D. 2005, Chem ical characteristics of nitrogen and phosphorus in the sediments of the typical bays in Dianchi Lake and calculation of their dredging layers. Environm. Sci., Vol. 26, No. 4, pp. 75–82 (in Chinese). Xie L. Q., Xie P., and Tang H. J. 2003, Enhancement of dissolved phosphorus release from sediment to lake water by microcystis blooms - an enclosure experiment in a Hyper-eutrophic, Subtropical Chinese Lake. Environmental Pollution, Vol. 122, No. 3, pp. 391–399. Xiong D. Q., Du X. M., Tang W. H., Huang M. X., Gu Q. B., Guo L. J., and Li F. S. 2005, Nitrogen distribution in the water of the Haihe River Mainstream and Estuary Seawater and its relationship with water dissolved oxygen levels. Res. Environm. Sci., Vol. 18, No. 3, pp. 1–4. Yue W. Z., Huang X. P., and Sun C. C. 2007, Distribution and pollution of nitrogen and phosphorus in surface sediments from the Pearl River Estuary. Oceanologia et Limnologia Sinica, Vol. 38, No. 2, pp. 111–117 (in Chinese). Yang R. Q., Lu A. H., Shi J. B., and Jiang G. B. 2005, The levels and distribution of oragochlorine pesticides (OCPs) in sediments from Haihe River, China. Chemosphere, Vol. 61, No. 3, pp. 347–354. Yao Y., Jin X. C., and Jiang X. 2004, Study on effects of light on phosphorus release and phosphorus form change in lake sediments. Res. Environm. Sci., 17 (suppl), pp. 30–33 (in Chinese).
- 72 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
Laboratory analyses of nutrient release processes from Haihe River sediment Min WU1, Xue-ming SUN2, Sui-liang HUANG1,3, Xian-qiang TANG4, and Miklas SCHOLZ5
Abstract Sediment samples were collected from the heavily contaminated Haihe River to conduct static nutrient release experiments with tap water, and to evaluate the effect of dredging depths, salinity and light on the corresponding release processes. The study is significant because it helps decision-makers to assess the likely impact of dredging (e.g. eutrophication) on contaminated freshwater and brackish rivers. The concentrations of total nitrogen and inorganic phosphorus were approximately 950 mg/kg and 760 mg/kg, respectively. The typical organic matter concentration was 8.6%. Data obtained from the nutrient leaching experiments indicated that 5cm-dredging of sediment reduced the water column total phosphorus, total dissolved phosphorus and ammonia-nitrogen concentrations insignificantly. In contrast, dredging 10cm surface sediment could improve the water quality. Higher salinity values benefited the release of nitrogen and phosphorus from sediment. In contrast to indoor experiments, concentrations of total phosphorus, total dissolved phosphorus and ammonia-nitrogen were higher for the outdoor experiments. Key Words: Aquatic sediment and water interaction, Water quality management, Nitrogen, Phosphorus, Salinity, Dredging, Water depth, Light, Haihe River, China
1 Introduction 1.1 Background Water management of rivers, lakes and other watercourse has become an increasing problem due to an increase in eutrophication (McDowell et al., 2003). Excessive discharge of nitrogen and phosphorus to water bodies leads to the degradation of their quality, thus hindering various water uses. Studies showed that nutrients including nitrogen and phosphorus may be adsorbed to the sediment accumulated on the bottom of rivers or lakes. These sediment may accumulate over long periods and can act as new pollutant sources if disturbed to the overlying water (Lijklema et al., 1993; Abrams and Jarrell, 1995). For freshwater bodies, contaminated sediments are regarded as the most important sources of nutrients leading subsequently to eutrophication (Wu et al., 2005; Li et al., 2007). Nutrient release processes have a significant impact on the water quality and may result in continuous eutrophication of lakes and rivers, 1
Ph.D candidate, 2 Graduate student, 4 Dr., Key Laboratory of Pollution Processes and Environmental Criteria of Ministry of Education, Nankai University, Tianjin, China. E-mail: [email protected], xmsun@mail. nankai.edu.cn, [email protected] 3 Prof., Key Laboratory of Pollution Processes and Environmental Criteria of Ministry of Education, Nankai University, Tianjin, China. Numerical Simulation Group for Water Environment, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin, China. Corresponding author: Tel: +86 22 23503423; Fax: +86 23503423; E-mail address: [email protected] 5 Prof., Civil Engineering Research Centre, School of Computing, Science and Engineering, The University of Salford, Salford M5 4WT, England, United Kindom, E-mail: [email protected] Note: The original manuscript of this paper was received in Mar. 2011. The revised version was received in Aug. 2011. Discussion open until Mar. 2013. International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 61 -
even when external nutrient sources are under control (Abrams and Jarrell, 1995; Tian and Zhou, 2007; Xie et al., 2003). As observed for non-point source (i.e. diffuse) pollution, internal or within-system pollution has numerous release mechanisms including advection, ion exchange, molecular diffusion, biologically mediated changes and uncertainties associated with different release durations, approaches and intensities (Hu et al., 2001; Kim et al., 2003; Scholz, 2006). The characteristics of sediment and the overlying water quality will affect the nutrient release processes. A better understanding of the pollutant release mechanisms and characteristics under different environmental factors is therefore helpful to prevent or reduce the pollutant release from sediment into the overlying water body. 1.2 Representative case study The cost-effective restoration of large, polluted and urban rivers within developing countries is a major challenge. For example, the mainstream of the Haihe River is the largest river in Tianjin (north China) with a length of 73 km (Wang et al., 2003). The river stretches from San Cha Kou (catchments of three primary tributaries) to the Bohai Sea, and flows through downtown Tianjin. The corresponding Haihe River basin provides water for 130 million people. The land use is dominated by large residential and agricultural areas, which are responsible for high nutrient concentrations within the river. With the rapid development of urbanization and the intensive use of water resources, the river becomes increasingly subject to water shortage and water quality deterioration stresses (Liu et al., 2001; Liu et al., 2007). This process has been accelerated by the construction of sluices to prevent sea water intrusion. The reduced exchange of water resulted in virtually stagnant river water and the accumulation of polluted sediment. Relatively low heavy metal and toxic organic compound pollution has been recorded in the past (Ding et al., 2005; Yang et al., 2005; Liu et al., 2007). In contrast, measured ammonia-nitrogen (NH4-N), total nitrogen (TN) and total phosphorus (TP) concentrations were in the ranges between 0.5 and 1.5 mg l-1, 2.1 and 5.38 mg l-1, and 0.4 and 1.2 mg l-1, respectively (Wen et al., 2008). These nutrient data indicate that the mainstream of the Haihe River is heavily eutrophicated. Considering the economic and environmental importance of the mainstream of the Haihe River to the city of Tianjin, much effort and cost have been invested to control the pollution loads by a series of environmental protection programs such as the domestic wastewater discharge scheme and enforcement of the water pollution control law in China, but eutrophication remains one of the most important water quality problem of the mainstream of the Haihe River. Water quantity shortage and water quality deterioration in Tianjin is serious, and become the mainly limiting factors for the economic growth and social advancement. Therefore, Tianjin government aimed to restore the Haihe River as the most promising and reliable drinking water source. Now, the entire external non point pollution source has been eliminated, and sediment was the predominant pollution contributor to Haihe River water quality. In light of the above considerations, several funding agencies including the Tianjin Scientific Commission agreed to collect sediment data to ascertain the extent of the problem and to assess the nutrient release potential of the within river bed material. In comparison to other rivers in China and the wider region, the mainstream of the Haihe River has a low light transmittance and significantly different salinities at different reaches. Only the reach downstream of Erdao sluice is saline water (Xiong et al., 2005). To date, moreover, few or none publications reported nutrient sediment releasing characteristics under different light conditions and salinity levels. Although dredging surface active sediment is one of the most effective methods to manage polluted rivers (Su et al., 2010), the most optimal dredging depths and environmental boundary conditions for the mainstream of the Haihe River and other representative polluted rivers are still subject to discussion. 1.3 Rationale, significance and aim The rationale of the present study was to contribute to the understanding of the interaction between contaminated bed material and aquatic environment by assessing the behavior of real sediment samples taken from a representative and important river. As Haihe River will be restored to be important and reliable drinking water source for Tianjin City, therefore, it is significant to use tap water instead of original river water to conduct sediment nutrient releasing simulation experiments. The study is significant because it helps decision-makers to assess the potential invest of effort and cost that will be used to restored the Haihe River to planned standard. Moreover, exploring the effect of light conditions - 62 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
and salinity levels on nutrient release from Haihe River sediment will publish the first hand material and give some hint for the future river restoration practices. Taking wrong decisions may lead to avoidable eutrophication and waste of physical and financial resources. The discussion of various scenarios is presented with the help of a case study supported by laboratory-scale experiments under controlled and natural conditions to assess the influence of different degrees of freedom on the data variability. The aim was therefore to make nutrient release processes within the mainstream of the Haihe River clear and to assess the role played by polluted sediment on its overall water quality, and evaluate the impact of light, salinity and dredging depths on nutrient release rates. 2 Materials and methods 2.1 Sampling In June 2006, heavily polluted Haihe River sediment was collected from Niwo ferry and relatively clean sediment was obtained from the corresponding bank of the river. Niwo ferry is located in the middle of the studied river reach (39º03´03´´ N, 117º21´30´´ E, Fig. 1). The corresponding river width and depth were approximately 100 m and 1.90 m, respectively. All sediment samples were used to conduct static nutrient release experiments. Samples of sediment were collected by mechanical grab-style samplers and embankment samples were obtained by clean spades. All the sediment were transported to the laboratory immediately in sealed plastic bags that were put in iceboxes under ćto keep original before conducting experiment. Sediment was divided into two parts: one part was used for simulation experiments, and the other part was used for analyzing the physical and chemical sediment properties. Sediment belonging to the latter part was naturally air-dried, and a standard sieve analysis method (Das, 1990) was applied. Four different sieves with 20, 60, 100 and 200 meshes were used to determine mass fractions for the following corresponding grain size diameter ranges: larger than 0.247 mm, 0.147-0.247 mm, 0.074-0.147 mm and 0.0385-0.074 mm, respectively. These ranges match up with medium sand, fine sand, very fine sand and silt according to the China Soil Partition Method (Wang and Kang, 1991).
Fig. 1 Map of the Haihe River showing the sampling sites of the sediment International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 63 -
Furthermore, organic matter, total phosphorus and total nitrogen were analyzed according to the Chinese Soil Physical and Chemical Standard Methods (Bao, 2000). 2.2 Experimental design and operation The authors adopted various conditions for comparing nutrient release to assess the impact of the key environmental boundary conditions such as light, salinity and dredging depths that are of relevance to the decision-makers. Five analogous 2 L cylinders (10 cm in diameter and 50 cm in height), numbered cylinder 1, 2, 3, 4 and 5, were used for the nutrient-release experiments (Fig. 2). Fully mixed river bank sediment of 5-cm depth was placed into cylinder 1. In cylinder 2 a 5-cm deep river bank sediment sample, representing the bottom layer, was topped by a 5-cm thick bed material obtained from the ferry. Cylinders 3, 4 and 5 were each filled with 10-cm deep sediment obtained from the ferry. All cylinders were designed to assess the effect of dredging depths (i.e. 10cm, 5cm and 0cm), light and salinity (0.25‰ or 3.00‰, controlled by the addition of sodium chloride) on nutrient release from Haihe River sediment. The chosen salinity concentrations are representative of the likely salinity values along the assessed river stretch characterized by freshwater (sometimes supplemented by saline water if river levels are low) upstream and saline water (approximately 2.84‰ at Erdao Sluice) downstream (see also above).
Fig. 2 Design and operation of the experimental set-up to assess nutrient release from sediment. Sa, salinity
As Haihe River water in the studied river reach subjected little sunshine. Indoor and outdoor locations for the cylinders were chosen to obtain a better comparison between rather controlled indoor and less controlled outdoor conditions. For example, the outside light and temperature vary in wider ranges, but are realistic. Temperature measurements were always undertaken at 12:00. All experiments were conducted in parallel. Tap water was aerated for 48 hours to remove chlorine, and then added carefully to each cylinder (up to 2.5 cm below the top rim of each cylinder), which were filled with sediment previously (see above). Clean tap water instead of contaminated river water was used to assume the potential sediment releasing characteristics while river water quality is up to the required standard that used for drinking water source. Water samples were collected 10 cm below the water surface using the siphoning principle, which reduced the possibility of disturbing sediment. Furthermore, liquid that was lost from the open cylinders due to periodic water sampling and natural evaporation got recharged on a daily basis or more frequently if appropriate (see below). The static pressure head was therefore comparable throughout the experiment. Moreover, tap water instead of contaminated river water was used as recharge water because it is likely to have a neglectable influence on the nutrient balance. Experiments were conducted with tap water rather than river water and in a static rather than a turbulent flow-through environment to reduce the degrees of freedom (i.e. variability). Moreover, the nutrient loads within the sediment were much higher than those within the river water. - 64 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
2.3 Sediment and overlying water quality All experimental systems were operated between 21 September and 21 October 2007. Overlying water was sampled daily during the first three days, and then at intervals of between three and five days. After each sampling equivalent water was immediately recharged, the following water quality parameters were analyzed to evaluate the effect of sediment dredging, light and salinity on the nutrient release from Haihe River sediment: Ammonia-nitrogen analyzed by the phenol-hypochlorite method (Wetzel and Likens, 2000); total dissolved phosphorus and total phosphorus analyzed by the persulphate digestion and acid-molybdenumblue colorimetric method (Wetzel and Likens, 2000); phosphorus fractions including exchangeable phosphorus (Ex-P), iron/aluminum bounded phosphorus (Fe/Al-P) and calcium bounded phosphorus (Ca-P) analyzed by the modified sequential extraction method (Ruban et al., 1999, 2001). 3 Results and discussion 3.1 Sediment characteristics The particle size distributions of the selected sediment samples are shown in Table 1. The combined sand fractions (0.074-0.247 mm; sum of the medium, fine and very fine sands) dominated both the ferry (93.7%) and bank (99.3%) sediment samples. The clay fractions were of minor importance, accounting only for 6.3% and 0.7% of the total ferry and bank sediment, respectively.
Sediment source Within river River bank
Table 1 Distribution (%) of sediment particles Medium sand Fine sand Very fine sand 15.1 23.0 55.6 18.6 35.6 45.1
Clay 6.3 0.7
Table 2 summarizes the results of the nutrient analysis of the above sediment samples. Readily available phosphorus, which includes the exchangeable phosphorus and iron and/or aluminum bound phosphorus, comprises 30.2% of the total inorganic phosphorus contained within the within-river sediment, which is more than the corresponding value for the bank sediment (only 6.79%). Calcium-bound phosphorus is the dominant fraction of inorganic phosphorus for both sediments. Previous studies indicated that calcium-bound phosphorus is a relatively stable fraction, and is attributed to the permanent burial of phosphorus within sediment (Gonsiorczyk et al., 1998; Kozerski and Kleeberg, 1998). Table 2 Sediment compositions Sediment Ex-P Fe/Al-P Ca-P IN-P TN OM source (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (%) Within river 38.84 190.08 529.33 758.39 947.00 8.60 River bank 6.035 18.01 330.33 354.38 364.23 3.42 Ex-P, exchangeable phosphorus; Fe/Al-P, ferrous and/or aluminum bound phosphorus; Ca-P, Cadmium bound phosphorus; IN-P, inorganic phosphorus; TN, total nitrogen; OM, organic matter.
Generally speaking, the organic matter, total phosphorus and total nitrogen concentrations within the river sediment are significantly (p<0.05) higher than those for the corresponding bank sediment. The total phosphorus and total nitrogen concentrations determined for the Haihe River sediment greatly exceeded the recommended concentrations (550 mg/kg and 600mg/kg for total nitrogen and total phosphorus, respectively), which are considered to be a significant risk to the river ecology (Yue et al., 2007; Liu et al., 2007). It follows that highly polluted Haihe River sediment pose a serious ecological risk to the success of future restoration efforts. 3.2 Effect of dredging depths on phosphorus and nitrogen release Figure 3 shows the concentration variations for total phosphorus, total dissolved phosphorus and ammonia-nitrogen in the overlying water for different dredging depths. The variation of total phosphorus concentration with time is similar to that of dissolved phosphorus with time. For cylinders with dredging 10cm sediment, the concentrations of total phosphorus and total dissolved phosphorus were relatively low during the entire experimental period, but the concentrations for dredging 5cm sediment and dredging International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 65 -
0cm sediment were different. Statistic results in Table 3 indicated that dredging 10cm surface sediment can significantly improve the column water quality, which was different from that reported 5cm for Suzhou River in Shanghai (Xing et al., 2006). Regional environmental conditions, pollution history and river characteristics (e.g. low flow velocity of Haihe River) etc may be the possible reasons.
Fig. 3 Concentration variations for (a) total phosphorus (TP); (b) total dissolved phosphorus (TDP); and (c), ammonia-nitrogen (NH4-N) in water overlying sediment subject to various dredging modes
During the first three days of the experiment, the concentrations of total phosphorus and total dissolved phosphorus were relatively low. However, they increased linearly three days later, and kept stable after twenty days. Wen et al. (2008) found that under static outdoor conditions, total phosphorus concentrations resulting from the release of Haihe river sediment increased when the tap water was used as overlying water; while total phosphorus concentrations decreased when the river water was used as overlying water. Findings indicate that sediment dredging can effectively reduce phosphorus pollution. The ranking order for phosphorus content within the water column of the experimental cylinders subject to the dredging depths was as follows: 0cm > 5cm> 10cm. Similar to phosphorus, the ammonia-nitrogen concentrations were relatively low during the experiment. The concentrations were different for the cylinders containing not dredged samples compared to those cylinders with dredging 5cm sediment. The concentration of ammonia-nitrogen reached 1.4 mg l-1 at the third day of the experiment. This was the highest value for cylinders with dredging 5cm sediment during the entire experimental period, while the corresponding concentration for cylinders with not dredged sediment increased gradually until the 12th day. Approximately twenty days later, regardless of the dredging mode, ammonia-nitrogen concentrations remained low and stable. In general, sediment dredging reduced ammonia-nitrogen and phosphorus concentrations within the overlying water. - 66 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
The properties of sediment will affect the nutrient release processes. According to Table 2, the content of exchangeable phosphorus and iron and/or aluminum bound phosphorus was high for the within-river sediment (38.84 mg/kg and 190.08 mg/kg for exchangeable phosphorus and iron/aluminum phosphorus, respectively (Table 2)). These phosphorus fractions leached out easily from sediment into the water column. This observation helps to explain the relatively high phosphorus concentrations measured within the 0cm dredged and 5cm dredged sediment, as well as similar observations with respect to total phosphorus and total dissolved phosphorus. Because the phosphorus content was low within the bank sediment, total phosphorus and total dissolved phosphorus release rates from this sediment was much less than those obtained from the within river bed material. Without disturbance of the water column, a concentration gradient existed between the interstitial water and the overlying water, which was mostly affected by the intensity of nutrient release. Moreover, microorganism activity also impacted indirectly on the release process (Table 2). The organic matter content was relatively high within the mostly anaerobic river sediment, which was assessed for cylinders that were packed with 5cm dredged and 0cm dredged material. During the mineralization process of organic matter within the sediment, the generation of ammonia-nitrogen consumes dissolved oxygen (provided by algae and the air) and encourages the nitrification-denitrification processes under partly anaerobic environments (Vymazal, 2007). This leads to a gradual reduction of ammonia-nitrogen concentrations within the water column as observed for the cylinders containing 5cm and 0cm dredged sediment towards the end of the experiment (Fig. 3). 3.3 Effect of salinity on phosphorus and nitrogen release Figure 4 illustrates the relationships between total phosphorus, total dissolved phosphorus and ammonianitrogen concentrations and time at salinity values of 3.00‰ and 0.25‰. A similar behavior for all three nutrient parameters at both salinities was observed. The concentrations of total phosphorus and total dissolved phosphorus increased gradually with time and kept stable twenty days later, while the concentration of ammonia-nitrogen showed different tendencies with time; it increased during the first twelve days and subsequently decreased to the lowest value of 0.15 mg l-1. During the entire experimental period, the concentrations of total phosphorus and total dissolved phosphorus within the cylinders with 3.00‰ salinity were significantly higher than those of the cylinders with 0.25‰ salinity. During the first twelve days, the concentration of ammonia-nitrogen within the cylinders containing liquid with 3.00 ‰ salinity was higher than the corresponding one for cylinders subjected to a salinity of 0.25 ‰. Thereafter, the concentrations for both treatments began to decrease. Nitrogen and phosphorus diffusion were affected by both microbial activity within the sediment and external environmental factors (Wang et al., 2008). Both chloride and salinity affect the survival rate of microorganisms. Moreover, salinity plays an important role in the migration and transformation of ammonia-nitrogen, and thus influences the ammonia-nitrogen transfer rate between sediment and water interfaces (Liu et al., 2002). The addition of sodium chloride increased salinity, chloride ion concentration, competition between chloride and phosphate ions, competition between sodium ion and ammonia ion, and reduced the nitrogen and phosphorus adsorption capacity of the sediment, thus causing high nitrogen and phosphorus concentrations to occur in the overlying water column. In addition, salinity can affect microbial nitrification directly. The same phenomenon was also observed in Wen et al’s experiment (Wen et al., 2008). The transformation of ammonia into nitrate performs better for environments with low in comparison to high salinity values. A decrease of the nitrification and denitrification processes can be observed with an increase of salinity (Boatman and Murray, 1982; Rysgsaard et al., 1999; Seitzinger et al., 1991). This explains the observation that total phosphorus, total dissolved phosphorus and ammonia-nitrogen concentrations within the cylinders containing 3.00 ‰ salinity were higher than those of the cylinders associated with only 0.25 ‰ salinity (Table 3). 3.4 Effect of light on phosphorus and nitrogen release Figure 5 shows fluctuations of total phosphorus, total dissolved phosphorus and ammonia-nitrogen within the overlying water at different light conditions. During the first three days, total phosphorus and total dissolved phosphorus concentrations for the outdoor set-up were higher than those for the indoor experiment. However, this tendency reversed between the 3rd and 12th day of the experiment, and International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 67 -
concentrations of the indoor system were slightly higher than those of the outdoor set-up. From the 12th day until the end of the experiment, this observation remained the same and a difference in concentration gradient was obvious. The differences between the two conditions were virtually negligible until five days for total dissolved phosphorus and ammonia-nitrogen and twelve days for total phosphorus. In general, the phosphorus concentrations in the overlying water for the outdoor cylinders were lower than those of the indoor ones during the entire experimental period. Light conditions significantly (p<0.05) influenced phosphorus release from sediment (Table 3).
Fig. 4 Concentration variations for (a) total phosphorus (TP); (b) total dissolved phosphorus (TDP); and (c), ammonia-nitrogen (NH4-N) in water overlying sediment subject to 0.25‰ and 3.00‰ salinity Table 3 Parameter
Impact of dredging depths, light and salinity on the release of nutrients from sediment Dredging depths Light condition Salinity 10cm
5cm
0cm
Indoor
Outdoor
0.25‰
3.00‰
0.10 b 0.12 b 0.12 b 0.08 a 0.12 a 0.322 b 0.02 a TP ±0.01 ±0.07 ±0.09 ±0.09 ±0.04 ±0.09 ±0.06 0.06 b 0.08 b 0.08 b 0.03 a 0.08 0.01 a 0.27 b TDP ±0.00 ±0.05 ±0.07 ±0.07 ±0.01 ±0.07a ±0.17 0.57 a, b 1.13 b 1.13 b 0.48 a 1.13 a 1.78 b 0.31 a NH4-N ±0.20 ±0.45 ±0.95 ±0.95 ±0.52 ±0.95 ±1.20 TP, total phosphorus; TDP, total dissolved phosphorus; NH4-N, ammonia-nitrogen; the means marked by the same letters are not significantly different according to least significant difference multiple range test at p=0.05. - 68 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
Fig. 5 Concentration variations for (a) total phosphorus (TP); (b) total dissolved phosphorus (TDP); and (c), ammonia-nitrogen (NH4-N) in water overlying sediment subject to indoor and outdoor light conditions
Ammonia-nitrogen release patterns were a little different in comparison to phosphorus. During the first three days of the experiment, the ammonia-nitrogen concentrations for the outdoor set-up were slightly higher than those for the indoor set-up. However, between the 3rd and 20th day, the ammonia concentrations for the indoor setup were higher (but not significantly different) than those for the outdoor experiment, and an increase of the concentration gradient was noted. Twenty days later, the ammonia-nitrogen concentrations for both set-ups were stable at a concentration of approximately 0.15 mg l-1. According to Table 3, the effect of light conditions on ammonia release became apparent when the ammonia concentrations for the indoor cylinders were higher than those for the outdoor set-up. During the entire experimental period, the outdoor cylinders received natural light and the mean water temperatures for the outdoor set-up were 1.8oC higher than the corresponding ones for the indoor set-up. The temperature ranges for the inside and outside set-up were between 23.1ºC and 25.2ºC (mean of 24.3 ºC), and between 24.7ºC and 27.3ºC (mean of 26.1 ºC), respectively. However, the temperature difference was not significant. These favorable environmental boundary conditions encouraged microbial activity, and resulted therefore in higher phosphorus and nitrogen concentrations for the outdoor compared to the indoor cylinders. Five days later, suspended matter was visible in the outdoor cylinders and the color of the water body changed from virtually transparent to green due to the growth of algae. As the experiment progressed, various blue-green algae continued to grow and the water color became even much greener. International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 69 -
The consumption of phosphorus and nitrogen by algae can lead to a reduction of the total phosphorus, total dissolved phosphorus and ammonia-nitrogen concentrations in the overlying water (Spears et al., 2008). The phosphorus and nitrogen concentrations within the outdoor cylinders were much lower than those within the indoor ones. This can partly be explained by large amounts of algae being attached to the sediment and walls of the cylinders, escaping bulk water sample collection. This finding is in contrast to reports published by Yao et al. (2004). However, Spear et al. (2008) found out that ammonia-nitrogen and total phosphorus within water columns were all significantly higher under dark in comparison to light conditions. Light conditions affected the release of phosphorus. The phosphorus concentration within the water column decreased with the increase of light availability (Fig. 5). Moreover, Spear et al. (2008) confirmed that better light conditions in long-term incubation experiments can alter the transport of nutrients across the sediment-water interface and lead to the decrease of the phosphorus concentrations as a result of direct uptake by algae. The growth of algae positively correlated with an increase in illumination intensity, and a substantial mass of nutrients was utilized by algae, which confirms findings reported in the literature (Axler and Reuter, 1996; Barlow-Bush et al., 2006). Moreover, nitrogen and phosphorus released from sediment was the main nutrient source for benthic algae, which are also called “biological barriers” due to their nutrient capture effect (Jarvie et al., 2002). 4 Conclusions and further research Phosphorus, nitrogen and organic matter contents were relatively high within the mainstream of the Haihe River sediment, which is heavily polluted and should therefore be considered as a potential risk to the river ecology. The exchangeable phosphorus content within the river sediment contributed to less than 6% of the total inorganic phosphorus. The ion/aluminum phosphorus fraction was approximately 25%. The calcium-phosphorus fraction was dominant (>70%) within the sediment. Sediment dredging had a significant impact on the nutrient release rate from Haihe River sediment. Dredging 5cm surface sediment slightly improved the overlying water quality while dredging 10cm sediment can greatly enhance the overlying water quality. An increase in salinity promotes nutrient release from sediment. Decision-makers should therefore encourage dredging at least 10cm of contaminated surface sediment, particularly for saline waters to reduce the risk of eutrophication. Furthermore, light conditions also indirectly affected nutrient release processes. Compared to the indoor system, natural light exposure to the outdoor cylinders facilitated algae growth, and therefore reduced nitrogen and phosphorus concentrations within the free water column, and indirectly restrained the release of nutrients from sediment. However, the data set is too sparse to perform detailed biochemical process modeling. Nevertheless, future research could assess the suitability of soft modeling techniques (Rustum et al., 2008) to predict nutrient release rates from disturbed sediment. Acknowledgements This work was financed by NSFC (Grant No. 51079068), NSF of Tianjin (Grant No. 09ZCGYSF00400) and the National Key-Projects of Water Pollution Control and Prevention (Grant Nos. 2008ZX0734-005-001 and 2009ZX07209-001). M. Scholz is a Visiting Projessor at Nankai University. Bilateral collaboration is financially supported by The Royal Society. References Abrams M. M. and Jarrell W. M. 1995, Soil-phosphorus as a potential non-point source for elevated stream phosphorus levels. J. Environm. Qual., Vol. 24, No. 1, pp. 132–138. Axler R. P. and Reuter J. E. 1996, Nitrate uptake by phytoplankton and periphyton. Whole-lake enrichments and mesocosm-15N experiments in an oligotrophic lake. Limnology and Oceanography, Vol. 41, No. 4, pp. 659–671. Bao S. D. 2000, Soil and Agricultural Chemistry Analysis. Chinese Agriculture Publishing House, Beijing, China. Barlow-Bush L., Baulch H. M., and Taylor W. D. 2006, Phosphate uptake by seston in the Grand River, southern Ontario. Aquatic Sciences, Vol. 68, No. 2, pp. 1615–1621. Boatman C. D. and Murray J. W. 1982, Modeling exchangeable NH4+ adsorption in marine sediments. Process and controls of adsorption. Limnology and Oceanography, Vol. 27, No. 1, pp. 99–110. Das B. M. 1990, Principles of Geotechnical Engineering, second ed. PWS-KENT, Boston, MA. - 70 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
Gonsiorczyk T., Casper P., and Koschel R. 1998, Phosphorus binding forms in the sediment of an oligotrophic and an eutrophic hardwater Lake of the Baltic District (Germany). Water Science and Technology, Vol. 37, No. 3, pp. 51–58. Ding H., Li X. G.; Liu H., Wang J., Shen W. R., Sun Y. C., and Shao X. L. 2005, Persistent organochlorine residues in sediments of Haihe River and Dagu Drainage River in Tianjin, China. Journal of Environmental Sciences, Vol. 17, No. 5, pp. 731–735. Hu X. F., Gao X. J., and Chen Z. L. 2001, Preliminary study on nitrogen and phosphorus release from the creek sediments, Outskirts of Shanghai. Shanghai Environm. Sci., Vol. 20, No. 2, pp. 66–70 (in Chinese). Jarvie H. P., Neal C., Warwick A., White J., Neal M., Wickham H. D., Hill L. K., and Andrews M. C. 2002, Phosphorus uptake into algal biofilms in a lowland chalk river. Science Total Environment, Vol. 282, No. 1–3, pp. 353–373. Kim L. H., Choi E., and Stenstrom M. K. 2003, Sediment characteristics, phosphorus types and phosphorus release rates between river and lake sediments. Chemosphere, Vol. 50, No. 1, pp. 53–61. Kozerski H. P. and Kleeberg A. 1998, The Sediments and the Benthic-pelagic Exchange in the Shallow Lake Muggelsee (Berlin, Germany). International Review Hydrobiology, Vol. 83, No. 1, pp. 77–112. Li D. P., Huang Y., and Li W. G. 2007, Study on Remediation of City River Water Body by Technology of Aerating Sediments. China Wat. Wastewat., Vol. 23, No. 5, pp. 22–25 (in Chinese). Lijklema L., Koelmans A.A., and Portielje R. 1993, Water quality impacts of sediment pollution and the role of early diagenesis.Water Science and Technology, Vol. 28, No. 2, pp. 1–12. Liu C., Wang Z. Y., He Y., and Cheng D. S. 2007, Evaluation of Water and Sediment Qualities at River Mouths in the Haihe River System. International Journal of Sediment Research, Vol. 22, No. 4, pp. 318–326. Liu G. H., Fu B. J., and Yang P. 2001, Quality of aquatic environment at Haihe River and the pollutant fluxes flowing into Sea. Chinese J Environm Sci., Vol. 22, No. 4, pp. 46–50 (in Chinese). Liu P. F., Chen Z. L., and Liu J. 2002, Study on effects of salinity and pH on NH4+ release in East Chongming Tidal flat sediment. Shanghai Environm. Sci., Vol. 21, No. 5, pp. 28–32 (in Chinese). McDowell R. W., Sharpley A. N., and Folmar G. 2003, Modification of phosphorus export from an eastern USA catchment by fluvial sediment and phosphorus inputs. Agriculture Ecosystems of Environment, Vol. 99, No. 1-3, pp. 187–199. Ruban V., Brigault S., Demare D., and Philippe A. M. 1999, An investigation of the origin and mobility of phosphorus in freshwater sediments from Bort-Les-Orgues Reservoir, France. Journal of Environmental Moniting, Vol. 1, No. 4, pp. 403–407. Ruban V., lópez-Sánchez J. F., Pardo P., Rauret G., Muntau H., and Quevauviller P. 2001, Development of a harmonized phosphorus extraction procedure and certification of a sediment reference material. Journal of Environmental Moniting, Vol. 3, No. 1, pp. 121–125. Rustum R., Adeloye A. J., and Scholz M. 2008, Applying Kohonen Self-Organizing Map as a software sensor to predict biochemical oxygen demand. Water Environment Research, Vol. 80, No. 1, pp. 32–40. Rysgsaard S., Thastum P., Dalsgaard T. 1999, Effects of salinity on adsorption capacity, nitrification and denitrification in Danish Estuarine Sediments. Estuarine, Vol. 22, No. 1, pp. 22–30. Seitzinger S. P., Gardener W. S., and Spratt A. K. 1991, The effect of salinity on ammonium sorption in aquatic sediments. Implications for Benthic Nutrient Recycling. Estuaries, Vol. 14, No. 2, pp. 167–174. Spears B. M., Carvalho L., Perkins R., and Paterson D. M. 2008, Effects of Light on Sediment Nutrient Flux and Water Column Nutrient Stoichiometry in a Shallow Lake. Water Research, Vol. 42, No. 4-5, pp. 977–986. Scholz M. 2006, Wetland Systems to Control Urban Runoff. Elsevier, Amsterdam, The Netherlands. Su C. C., Shun C. W., and Chun H. W. 2010, Sediment removal efficiency of siphon dredging with wedge-type suction head and float tank. International Journal of Sediment Research, Vol. 25, No. 2, pp. 149–160. Tian J. R. and Zhou P. J. 2007, Phosphorus fractions of floodplain sediments and phosphorus exchange on the sediment–water interface in the lower reaches of the Han River in China. Ecological Engineering, Vol. 30, No. 2, pp. 264–270. Xing Y. N., Ruan X. H., and Zhao Z. H. 2006, Effects of depth of sediment dredging in Urban Rivers on release of nitrogen and phosphorus. Journal of Hohai University (Natural Sciences)., Vol. 34, No. 4, pp. 378–382. Vymazal J. 2007, Removal of nutrients in various types of constructed wetlands. Science of the Total Environment, Vol. 380, No. 1-3, pp. 48–65. Wang Y. Z. and Kang Z. C. 1991, Study on the relationship between deposit density and particle size distribution of debris flow. J. Mountain Res., Vol. 9, No. 3, pp. 165–170 (in Chinese). Wang D. Q., Chen Z. L., and Xu S. Y. 2008, Study on the exchange flux of the DIN Through the sediment-water Interface in the Yangtze Estuary. Mar. Sci., Vol. 32, No. 2, pp. 10–15 (in Chinese). Wang H., Yang N. Y., and Shen Y. W. 2003, Safety assessment on several organic pollutants of the Haihe River Valley. Res. Environm. Sci., Vol. 16, No. 6, pp. 35–37 (in Chinese). Wetzel R. G. and Likens G. E. 2000, Limnological Analyses, third ed. Springer, NY, USA. International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72
- 71 -
Wen W., Sun X. M., Sun S. J., and Huang S. L. 2008, Release of phosphorus and nitrogen from Haihe River sediments. J. Agro-Environm. Sci., Vol. 27, No. 1, pp. 295–300 (in Chinese). Wu Y. H., Hu J., and Jin X. D. 2005, Chem ical characteristics of nitrogen and phosphorus in the sediments of the typical bays in Dianchi Lake and calculation of their dredging layers. Environm. Sci., Vol. 26, No. 4, pp. 75–82 (in Chinese). Xie L. Q., Xie P., and Tang H. J. 2003, Enhancement of dissolved phosphorus release from sediment to lake water by microcystis blooms - an enclosure experiment in a Hyper-eutrophic, Subtropical Chinese Lake. Environmental Pollution, Vol. 122, No. 3, pp. 391–399. Xiong D. Q., Du X. M., Tang W. H., Huang M. X., Gu Q. B., Guo L. J., and Li F. S. 2005, Nitrogen distribution in the water of the Haihe River Mainstream and Estuary Seawater and its relationship with water dissolved oxygen levels. Res. Environm. Sci., Vol. 18, No. 3, pp. 1–4. Yue W. Z., Huang X. P., and Sun C. C. 2007, Distribution and pollution of nitrogen and phosphorus in surface sediments from the Pearl River Estuary. Oceanologia et Limnologia Sinica, Vol. 38, No. 2, pp. 111–117 (in Chinese). Yang R. Q., Lu A. H., Shi J. B., and Jiang G. B. 2005, The levels and distribution of oragochlorine pesticides (OCPs) in sediments from Haihe River, China. Chemosphere, Vol. 61, No. 3, pp. 347–354. Yao Y., Jin X. C., and Jiang X. 2004, Study on effects of light on phosphorus release and phosphorus form change in lake sediments. Res. Environm. Sci., 17 (suppl), pp. 30–33 (in Chinese).
- 72 -
International Journal of Sediment Research, Vol. 27, No. 1, 2012, pp. 61–72