removal of nitrogen and phosphorus from fluctuating ...

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Fresenius Environmental Bulletin

REMOVAL OF NITROGEN AND PHOSPHORUS FROM FLUCTUATING DEGRADED RIVERINE WETLAND WATER USING SPHAGNUM FLOATING BED Huai Li1,2, Zifang Chi2,4, Baixing Yan1,*, Vladimir Chakov3, Victoria Kuptsov3 1

Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, 130102, P.R.China 2 State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090, P.R.China 3 Institute of Water & Ecology Problems, Far Eastern Branch, Russian Academy of Sciences, Khabarovsk, 680000, Russia 4 Key Lab of Groundwater Resources and Environment, Ministry of Education, Jilin University, Changchun, 130021, P.R. China

wetland; fluctuating water level; removal

ABSTRACT Riverside wetland in the lower reaches of Songhua River has suffered intense damage resulting in rapid degeneration of the water purification system related to human destruction and water pollution. Violent fluctuations in water levels may lead to worsening water quality effects and destruction of plant growth. Ecological floating beds provide an effective way to overcome the problems, yet limited information regarding Sphagnum purification has been obtained in the open waterenvironment. The ability of Sphagnum survival and its correlation to nutrients enrichment in violently fluctuating riverside wetland water as applied to the ecological floating bed are investigated in this study. Ecological floating beds, with Sphagnum fallax and Sphagnum squarossum, were chosen for nitrogen (N) and phosphorus (P) enrichment. The results indicated that changes of water quality (high N low P, low N high P) resulting from water level fluctuations in test areas were beneficial for the survival of Sphagnum species, especially in flood periods that high carbon content of water could effectively stimulate the growth of Sphagnum species. Following four months of field tests, the amounts of N and P enrichment in Sphagnum squarossum were 2.29 and 0.82 mg/g dry weight, respectively, while in Sphagnum fallax were 1.98 and 0.64 mg/g dry weight. N enrichment was superior to P for both Sphagnum moss types. The release of nutrients, especially P, can be controlled effectively by harvesting Sphagnum species in early winter. This study could be useful for improved understanding of water restoration in violent fluctuating degraded riverine wetland by eutrophic Sphagnum mosses.

INTRODUCTION Sphagnum is not only a key organism community in the wetland ecosystem, but also significantly contributes to carbon sequestration in the process of swamp formation as it accumulates carbon (CO2) from the atmosphere in the form of peat deposits[1]. Sphagnum also acts as an effective organic moisturizing material and absorbent of toxic chemical by its anatomicalstructure. Hence, nutrientrich sphagnum may be employed to remove nitrogen (N) and phosphorus (P) pollutants, thus restoring the damaged wetland ecosystem[2,3]. Freshwater wetlands in China are only visible in the flood plain areas that are mainly located in nature reserves. Human destruction and water pollution has produced significant damage to riverside wetlands in the lower reaches of Songhua River causing water purification function to degenerate rapidly. Urgent need persists for proper eco-remediation technology to ameliorate the damage and provide restoration and environmental protection. Sphagnum has been cultivated in many countries such as Canada, Finland, Chile, Germany, Japan, South Korea, etc. The cultivation in those countries occurred under specific water level [4] conditions differing from China where riverine wetlands experience extreme fluctuations. Water level fluctuations may affect water quality while acting to destroy plant growth [5].The ecological floating bed has been widely applied to the open water environment for addressing potentially damaging effects of, for example, agricultural runoff [6], eutrophic lake waters [7], urban stormwater [8,9], river water [10]etc. Advantages of the

KEYWORDS: Sphagnum moss; ecological floating bed; degraded

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TABLE 1 Water quality standards of China (only relevant water constituents shown)

ecological floating bed include low cost, simple maintenance and water level fluctuation adaptability[11]. Limited information exists related to the efficiency of Sphagnum purification in degraded riverside wetland water environments through the application of ecological floating bed. Sphagnum’s ability to survive and provide enrichment for nutrients in extreme fluctuating riverside wetland water was investigated by utilizing ecological floating beds with two dominant eutrophic Sphagnum species, Sphagnum fallax and Sphagnum squarossum. Objectives of this study were to (1) evaluate N and P uptake by two dominant Sphagnum species and select promising Sphagnum species, (2) investigate effects of water level and water quality fluctuation on the survivability and enrichment of Sphagnum, (3) provide optimal management strategies such as biomass harvest to nutrient removal.

Parameters/standard value (mg/L) pH COD≤ TN≤ TP≤

GB 3838-2002 IV V 6-9 6-9 30 40 1.5 2.0 0.3 0.4

System configuration and operation strategy. Five ecological floating beds were designed uniformly as follows. Sphagnum moss was transplanted into polyethylene barrels with punching around the bottom and then fixed in the plastic foam board. Following construction with Sphagnum fallax (I) and Sphagnum squarossum (II, III, IV, V) the ecological floating beds were submerged in water to a depth of 1.5 cm. Sphagnum fallax was transplanted from area A in Xingkai Lake (45.35049 oN ， 132.35049oE) while Sphagnum squarossum was transplanted from area B (45.34889 oN, 132.29316 o E). The perennial water area was selected to study water purification of the degraded wetland river area (Fujin test area). Enrichment ability of N and P nutrients was assessed after the four month term of the experiment from June 2014 to October, 2014.

MATERIALS AND METHODS Studied sites. The study was conducted in a degraded wetland area in the city of Fujin (47.23481oN, 131.96415oE). The lower reach of the Songhua River in China runs a total length of 267 km through the areas of the Sanjian Plain from Jiamusi to Tongjiang. Fujin is located on the southern bank of the lower reaches of the Songhua River and within the Sanjiang Plain area. The wetland study area is typical and representative of this location (Fig.1). Water quality of the lower reaches of Songhua River is poor in dry, normal and wet seasons and meets the national quality standard of China (Environment Quality Standard of Surface Water in China, GB 3838-2002) for class IV and V surface water, respectively (Table 1), while the wetland landscape of transient flood and perennial water were formed due to seasonal fluctuation of water levels[12].

Analytical procedure. Sphagnum fallax, Sphagnum squarossum and water samples were collected from Xingkai Lake in June, 2014, while samples from Fujin test area were got in July, September and October, 2014, respectively. Furthermore, water levels were measured at different sample collection time. Fresh weight of plant samples was tested on the collected day and samples by air drying were grinded for testing their TN and TP concentrations. Water quality parameters (TN, TP and COD) were quantified using automatic chemical analyzer (Smartchem 200, AMS/Westco, Italy).

RESULTS AND DISCUSSION The biodiversity of Sphagnum. Various Sphagnum species from transplantation areas A and B in Xingkai Lake were identified. Sphagnum squarossum, Sphagnum flexuosum and Sphagnum fallax were found in low-lying water and high water level conditions of transplantation area A [13], while

FIGURE 1 General view of the study sites 3016

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Sphagnum squarossum and Sphagnum auriculatum were found in transplantation area B. Sphagnum flexuosum and Sphagnum fallax were the special species of transplantation area A, while Sphagnum auriculatum was the special species of transplantation area B. Sphagnum fallax and Sphagnum squarossum were dominant species of area A and B in Xingkai Lake, which belonged to entrophic species. Nutrient removal from the polluted water was then possible by transplanting the entrophic Sphagnum species in the local region.

transplanting were as follows: pH 7.34, COD 217 mg/L, TN 2.35 mg/L, TP 0.29 mg/L. Carbon (C) and P contents were relatively lower than the transplantation areas in Xingkai Lake though pH was approximately neutral, indicating effective N and P nutrients removal from polluted water by a selfadjustment and adaptability process of the eutrophic Sphagnum species. Spatial and temporal variations of water quality and water level. Spatial and temporal variations of water quality and water level in test areas are presented in Table 2. Results indicate the water level patterns from June to October 2014 ranged from medium water level, high water level and low water level in the Fujin test areas. C, N and P concentrations rose significantly when peak water level, 130 cm, was reached in July, presenting water quality with low N and high P, potentially caused by pollutants diffusion in the flooding period. Water quality with high N and low P was constant, with the exception of in July, and then water level and COD content in different time was positively correlated. Water quality for Fujin test areas including high N and low P, and low N and high P with pH remaining neutral was beneficial for survival of Sphagnum species at site A (high N and low P) and site B (low N and high P) during the entire experimental phase as demonstrated above. Water quality with high C levels caused by pollutant diffusion in the flooding period also benefitted the growth of Sphagnum species. Biomass of the whole plant also increased gradually with variability of urban stormwater ponds water quality as driven by dynamic hydrologic conditions and the associated input of pollutants[15].

Characteristic of Sphagnum and its transplantation environment. Physical and chemical characteristics were analyzed before and after Sphagnum transplantation. TN and TP contents of Sphagnum fallax were 7.08±0.35 and 2.04±0.05 mg/g dry weight, respectively, while that of Sphagnum squarossum were 5.27±0.24 and 1.77±0.08 mg/g dry weight, respectively. Water quality parameters from transplantation area A were as follows: pH 6.33, COD 500 mg/L, TN 5.45 mg/L, TP 0.43 mg/L, while from transplantation area B were: pH 6.21, COD 447 mg/L, TN 0.36 mg/L, TP 1.14 mg/L. The results suggested that N contents of Sphagnum fallax and Sphagnum squarossum were more than 1 mg/g dry weight, and higher than P contents in both Sphagnum moss samples, indicating that Sphagnum fallax and Sphagnum squarossum exhibited efficient enrichment characteristics for N and P. The two species were deemed suitable for the partial acid (pH < 6.5) environment [14] with Sphagnum fallax more suitable for the high N and low P environment and Sphagnum squarossum more suitable for the low N and high P environment. Water quality parameters of the Funjin test area when

TABLE 2 Temporal and spatial variation of water quality and water level in test area

COD (mg/L) TN (mg/L) TP (mg/L) pH water level (cm)

June 217 2.35 0.29 7.34 40-45

July 459 2.60 3.02 7.49 130

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September 156 2.44 0.14 7.82 18-31

October 53.28 5.28 0.59 7.0 0-5

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to re-release of nutrients into the environment with weaker growth and senescenceat lower temperatures in northeast China(< 10℃). Vegetation decay resulting from seasonal transition from summer to winter may have contributed a surplus of organic matter to the processing system [16]. Kadlec confirms this with a report that plant storage of N and P is temporary and as plant tissues degrade and die, nutrients re-release into the treatment system [17]. N and P removal and storage, thus was temporary as the plant served as a medium for nutrients removal. Contents of N and P in Sphagnum moss, as presented in Fig.3(a) and Fig.3(b), also exhibit a reduction trend after the rise in different Sphagnum squarossum floating beds (II, III, IV, V) tested from June to October. The contents of N and P in Sphagnum moss increased to 6.23~10.11 and 2.30~2.93 mg/g dry weight in September from 5.27± 0.24 and 1.77±0.08 mg/g dry weight in June with average increase ranges were 7.56 and 2.59 mg/g dry weight. The contents of N and P enrichment in plants, thus increased by 2.29 and 0.82 mg/g dry weight. A downward trend also similarly appeared for contents of N and P in the Sphagnum squarossum floating bed in October, with reduction of P content in Sphagnum far exceeding that of N as P content in Sphagnum was less than that of the early transplant (1.77 ±0.08 mg/g dry weight). Harvesting Sphagnum before October then may effectively control re-release of nutrients, especially P. Meuleman et al. [18]suggested that TN and TP removal efficiency could be increased by harvesting above-ground biomass in September instead of winter when most nutrients transfer to the rhizome/root system.Plant harvest promoted removal of nutrients, especially P, from internal wetland cycling processes[19,20]. Wang et al.[15] also suggested that above-ground biomass harvest in June was beneficial to maximum P removal or in September to prevent P release due to senescence. Biomass harvest could then simultaneously provide economic returns for animal, human and industrial production, such as animal feeds, human food, biomass material, and nanomaterials [21-24]. The effect of N and P enrichment in Sphagnum squarossum was superior to that of Sphagnum fallax, and N enrichment for both was better than P enrichment. Potential explanations may be that N/P of Sphagnum fallax was higher at 3.46 than of Sphagnum squarossum at 2.97, and higher than 1 before Sphagnum transplantation. Water quality of high N and low P in test areas obtained during the

Content（mg/g dry weight）

10 8 6

TN

4

TP

2 0 June

September

October

FIGURE 2 Enrichment of N, P in Sphagnum Fallax at different time

FIGURE 3 Enrichment of N and P at different Sphagnum Squarossum floating bed N and P enrichment of different Sphagnum moss. The capacity of N, P enrichment in Sphagnum fallax and Sphagnum squarossum is presented in Fig. 2 and Fig.3. Results indicated that contents of N and P were 7.08 ±0.35 and 2.04±0.05 mg/g dry weight in the early transplant of Sphagnum fallax (floating bed I) in June 2014. Following four months with water quality fluctuation (high N and low P, low N and high P), the highest contents of N and P in the Sphagnum fallax floating bed were 9.06 ± 0.55 and 2.68± 0.03 mg/g dry weight in September, respectively. The contents of N and P enrichment in plants, thus increased by 1.98 and 0.64 mg/g dry weight (Fig.2). N and P content in the Sphagnum moss declined remarkably in October possibly due 3018

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tests (except July), may then also have been more beneficial to the growth of Sphagnum fallax with the ability of insufficiency enrichment was caused by relatively low C content (Table 2) which was consistent with the results from Limpens [25]. C concentration was the key to the growth of Sphagnum fallax with high N and low P. The growth environment of Sphagnum squarossum before transplantation consisted briefly high C, low N and high P in July, contributing to conditions of exuberant growth for Sphagnum squarossum. The amount of N accumulation and N/P ratio were positively correlated in Sphagnum squarossum of different floating beds (II, III, IV, V) in September (Fig. 4). Results indicated that increasing N content could promote N enrichment of Sphagnum species. Significant changes could be observed when the N/P ratio was higher than the value (2.97) of Sphagnum squarossum before transplantation. This study proposed and confirmed the possibility of N and P removal from polluted water by transplanting eutrophic Sphagnum and discussed added benefits to landscape of building a floating bed vegetation zone.

squarossum were superior to those with Sphagnum fallax, and N accumulation was better than P for both. Sphagnum harvest could effectively control the rerelease of nutrients, especially the P release, in the Sphagnum body. This study supports increased understanding of N and P removal through eutrophic Sphagnum mosses application and application of the ecological floating bed for pollutant removal in degraded extreme fluctuating riverine wetland.

ACKNOWLEDGEMENTS This work was financially supported by National Natural Science Foundation of China (41401548), Jilin Provincial Research Foundation for Basic Research, China (20150520151JH) , and Open Project of State Key Laboratory of Urban Water Resource and Environment，Harbin Institute of Technology (NO.ES201510, and NO.HC201622).

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FIGURE 4 Relationship between N enrichment and N/P

CONCLUSIONS N and P pollutant removal from polluted water was proven possible by transplanting eutrophic Sphagnum with both practical value and landscape effects. Sphagnum floating beds exhibited adaptability for water quality and water level fluctuations in degraded riverine wetland water. Water quality fluctuations with high N and low P, then low N and high P in test areas were beneficial to the survival of Sphagnum fallax (high N and low P) and Sphagnum squarossum (low N and high P). Water quality with high carbon levels in flood periods was beneficial for the growth of Sphagnum. The effects of N and P enrichment with Sphagnum 3019

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Received: Accepted:

30.9.2016 24.3.2017

CORRESPONDING AUTHOR

Baixing Yan Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, 130102, P.R.China email: [email protected]

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