was supported by Nivala et al. (2007) who found that direct aeration of the Jones County wetland provided the system with a much better degree of internal mixing in comparison to conventional non-aerated wetlands. However, phosphorus adsorption and precipitation throughout the experiments was not estimated in this study to avoid destruction of the experimental filter composition and the air diffuser.
The mean SRP and TP removal rates were higher in wetland E containing PHPB in comparison to wetland F without PHPB (Fig. 3). However, the difference was not statistically significant. After the introduction of intermittent artificial aeration, the presence of PHPB greatly stimulated phosphorus removal; e.g. the SRP and TP mean removal rates increased both by 0.04 g/m2 day for the aerated.
wetland C containing PHPB in comparison to the non-aerated wetland E containing PHPB (Fig. 3).Substrate with a higher porosity allows for more oxygen transfer and biomass accumulation inside the wetland (Yang et al. 2001). Considering this study,the high porosity of PHPB (81% compared to 46% for shale) and the intermittent artificial aeration improved COD, nitrogen and phosphorus removal. Moreover, the interactive effect between bottom aeration and PHPB presence resulted in the highest phosphorus removal observed in wetland C with mean removal rates of 0.25 and 0.31 g/m2 day for SRP and TP,respectively (Fig. 3).
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常弘： 冬季满堂河小流域人工湿地对污染物消减研究
Fig. 3 a Soluble reactive phosphorus (SRP), and b total phosphorus (TP) removal in different constructed wetlands during the Typha latifolia L. (cattail) growing season between June and November 2006. Max, Min, Mean and SD represent the maximal, minimal, mean values and standard deviation of the removal rate. Box charts with different letters are signifi-cantly (p<0.05) different from each other according to Duncan’s multiple range tests.
3.4 Aboveground Biomass Production of Plants and Nutrient Accumulation
According to Tables 4 and 5, T. latifolia has a high aboveground biomass production. The total dry weight of harvested biomass was between 845 and 1400 g per wetland. Based on the experimental wetland surface, calculated cattail biomass yield in this study was between 4.31
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and 7.14 kg/m2, which were much higher than the yield of 2.8 kg/m2 reported by Ciria et al. (2005). However, these results should be viewed with some caution considering that the wetlands were relatively small and that ‘edge effects’ may have influenced the results (Ciria et al. 2005; Scholz 2006). Total dry matter was lower in the aerated wetlands A and B in comparison to the non-aerated wetland F (Tables 4 and 5). Intermittent artificial aeration reduced cattail biomass development. However, the presence of PHPB caused an increase of 155 and 385 g dry matter yield for the aerated wetlands C and D in comparison to the non-aerated wetland E (Tables 4 and 5).
The total phosphorus content was similar for leaves and stems. However, the total nitrogen content was much higher for the leaves compared to the stems (Tables 4 and 5). Similar findings were also reported by Vymazal (2007) and Li et al. (2008). For example,the corresponding plant material for total phosphorus and total nitrogen were between 1 and 4 mg/g and between 10 to 15 mg/g, respectively (Li et al. 2008).
Statistical analysis indicated that the nutrient content of the aboveground cattail stems and leaves was significantly higher in the aerated wetlands A and B than in the non-aerated wetland F (Tables 4 and 5). The combined effect of intermittent artificial aeration and PHPB encourages the uptake of nutrients into the aboveground plant tissue. Compared to wetland F, as much as 2.19 and 2.32 times the TP,and 1.99 and 3.24 times the TN were assimilated into cattail stems and leaves, respectively, in wetland C(Tables 4 and 5).
Wetland plants are known to take up nutrients.However, the total uptake is often insignificant compared to the corresponding wastewater inflow load (Brix 1994, 1997). However, other researchers reported that plants play an important role in nutrient removal (Huett et al. 2005; Vymazal 2007). The aboveground biomass nitrogen accumulation was in the range between 0.6 and 88 g/m2(Johnston 1991; Mitsch and Gosselink 2000; Vymazal 1995). Moreover, the nitrogen uptake was even 250 g/m2 for the water hyacinth Eichhornia crassipes (Vymazal 1995). The phosphorus uptake capacity of wetland plants is reported to be lower than the one for nitrogen (Brix 1994). The aboveground phosphorus removal isusually in the range between 0.1 and 45 g/m2(Johnston 1991; Reddy and DeBusk 1987; Vymazal 1995). In this study, the aboveground nitrogen and phosphorus removal rates were between 21.45 and 79.93 g/m2 and between 14.78 and 41.56 g/m2, respectively. These figures are well within reported ranges. The
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常弘： 冬季满堂河小流域人工湿地对污染物消减研究
combination between bottom aeration and PHPB presence led to the highest nutrient accumulation measured in wetland C; additional nitrogen and phosphorus of 58.48 and 26.78 g/m2, respectively, were measured if compared to wetland F (Tables 4 and 5).
Table 4 Aboveground total phosphorus (TP) biomass production of Typha latifolia L. (cattail) and nutrient removal by plant harvesting in November 2006.
The total dry weight and total removal was the sum of the dry weight and nutrient removal of the aboveground stems and leaves,respectively. Values (mean±SD, triplicate samples) marked with different letters are significantly (p<0.05) different from each other according to the Duncan’s multiple range tests.
Table 5 Aboveground total nitrogen (TN) biomass production of Typha latifolia L. (cattail) and nutrient removal by plant harvesting in November 2006
The total dry weight and total removal was the sum of the dry weight and nutrient removal of the aboveground stems and leaves,respectively. Values (mean±SD, triplicate samples) marked with different letters are significantly (p<0.05) different from each other according to the Duncan’s multiple range tests.
Assuming that plant uptake and subsequent storage of nitrogen and phosphorus only occurred from the water column during the running period, a mass balance calculation indicated that plant uptake con-tributed to 4.02%, 3.94%, 8.80%, 8.19%, 6.53% and 2.98% removal of nitrogen, and 35.53%, 42.54%,74.87%, 69.42%, 59.11% and 34.70% removal of phosphorus in the planted wetlands A, B, C, D, E and F, respectively. Previous treatment of eutrophic lake
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water in China indicated that wetland plant accumu-lation accounted for between 5.1% and 26.2% of the TN removal, and between 40.5% and 80.9% of the TP removal (Li et al. 2008). In the present study, findings suggested that plant uptake played an important role in nitrogen and phosphorus removal in eutrophic Jinhe River water treatment.Moreover, aboveground biomass nutrient accumulation was improved by both intermittent artificial aeration and the presence of PHPB. This combination of treatment resulted in the greatest improvement of the water quality.
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