Chapter 21 The Role of Vegetation in Phosphorus Removal by Cold Climate Constructed Wetland: The Effects of Aeration and Growing Season

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1 Chapter 21 The Role of Vegetation in Phosphorus Removal by Cold Climate Constructed Wetland: The Effects of Aeration and Growing Season Aleksandra Drizo 1 (*ü ), Eric Seitz 1, Eamon Twohig 1, David Weber 2, Simon Bird 1, and Donald Ross 1 Abstract The objective of this study was to evaluate the effectiveness and contribution of Schoenoplectus fluviatilis (Torr.) (river bulrush) to phosphorus (P) removal from dairy-farm effluent in a cold climate constructed wetland. After 3 years of operation (1,73 days), both nonaerated wetland cell 3 (C3) and aerated cell 4 (C4) exhibited a sharp decline in dissolved reactive phosphorus (DRP) storage, indicating wetlands saturation. The quantities of DRP stored during the three growing seasons (433 days) represented only 1.%(C3) and 17.7%(C4) of the total amount of DRP (435.6 ± 2.3 g m 2, 97.2 kg) added to each cell (C3 and C4) over the entire 3-year period. However, of the total DRP retained by both wetland cells during 1,73 days of operation, the quantities stored during the three growing seasons (433 days) represented 5.3%(C3) and 36.5%(C4) of the total DRP retention. This indicated that vegetation had an important role in the overall DRP storage regardless of supplemental aeration. Overall, nonaerated C3 DRP mass removal efficiency during the 3-year period of investigation was low, averaging 19.9%. Aerated C4 DRP mass removal efficiency was 2.4-fold higher, averaging 48.4%. Belowground (BG) biomass had significantly higher (p <.1) P content than aboveground (AG) biomass, throughout the 3-year period of investigation. Keywords Aeration, agricultural effluent, cold climate, phosphorus removal, Schoenoplectus fl uviatilis 1 University of Vermont, Department of Plant and Soil Science, Hills Agricultural Building, 15 Carrigan Drive, Burlington, VT 545, USA 2 Vermont Agency of Agriculture Food & Markets. 116 State Street, Drawer 2 Montpelier, VT , USA (*ü ) Corresponding author: adrizo@uvm.edu J. Vymazal (ed.), Wastewater Treatment, Plant Dynamics and Management 237 in Constructed and Natural Wetlands. Springer Science + Business Media B.V. 28 Vymazal_Ch21.indd 237 3/31/28 7:29:13 PM

2 238 A. Drizo et al Introduction Constructed wetlands (CW) have been used to treat a variety of wastewaters for over 2 decades (Reddy & Smith, 1987; Hammer, 1989; Kadlec & Knight, 1996; Vymazal et al., 1998; Vymazal, 26; Cooper, 26). Vymazal (26) recently provided a comprehensive review of CW technology evolution over time. It has been well documented that CW provide sustainable removal of organic material and suspended solids (Kadlec et al., 2; Brix et al., 26). However, phosphorus (P) removal by CW has been generally low regardless of the type of wastewater treated, especially in cold climates (Kadlec, 1999; Schaafsma et al., 2; Luderitz & Gerlach, 22; Picard et al., 25; Weber et al., 26). According to Kadlec (1999) and Kadlec and Knight (1996), P removal via wetland substrate represents only short-term storage, lasting up to a few months. Kadlec (1999) estimated that P removal through vegetation uptake can last for 1 6 years, and the only long-term, sustainable P storage occurs via the biogeochemical cycle and accretion. The contribution of wetland vegetation to pollutant removal through filtration and sedimentation, stabilization of bed surface, light attenuation, and additional surface area for the attachment of microorganisms has long been established (Brix, 1997). The role of vegetation in providing insulation and thermal protection against ice formations in cold climate CW has also been demonstrated (Allen et al., 22; Munoz et al., 26). Oxygen release from plant roots, nutrient content and plant growth in CW were well researched (Brix, 1997; Tanner, 21; Allen et al., 22). Despite a relatively large pool of data, there is some discrepancy about the quantities of nutrient uptake and exact contribution of emergent macrophytes to P removal, especially in cold climates (Serodes & Normand, 1999; Luderitz & Gerlach, 22; Gottschall et al., 27). In their review of CW for animal wastewater treatment, Hunt and Poach (21) noted that Scirpus, Typha and Juncus are the most common plant genera used in the USA. However, there is not enough information about the exact contribution of various plant species to P removal from high strength wastewaters in full-scale systems (Tanner, 21). Agricultural effluents have higher nutrient concentrations, making it difficult to achieve efficient P removal, especially in cold climate wetlands. In addition, vegetation-growing season in these wetlands (average 15 days) is much shorter than in warmer climates. In this chapter, we evaluated the effectiveness of Schoenoplectus fluviatilis (Torr.) (river bulrush) and its contribution to P removal from dairy-farm effluent in a cold climate CW. The effects of plant-growing seasons (first, second and third growing season) and supplemental aeration on P storage and mass removal were also assessed. Vymazal_Ch21.indd 238 3/31/28 7:29:13 PM

3 21 The Role of Vegetation in Phosphorus Removal by Cold Climate Constructed Wetland Site Location and Methods Site Location The Constructed Wetlands Research Center (CWRC) was established at the University of Vermont (UVM) Paul Miller Dairy Farm in the fall of 23. A CW system, consisting of four horizontal subsurface flow wetland cells (1 4) designed to treat dairy effluent (barnyard runoff and milking operations wastewater) represents the main feature of the CWRC. The system has been recently described (Munoz et al., 26; Drizo et al., 26; Weber et al., 26). Each cell is 12 m wide, 18.5 m long and.6 m deep with total surface area and total volume of 223 m 2 and 134 m 3, respectively. The first third of each cell from the influent side has been filled with coarse gravel while the remaining two thirds were filled with smaller particle size gravel (2 and 1 cm diameter, respectively) resulting in a total porosity of approximately 38.7%. Munoz et al. (26) presented a detailed schematic of the UVM CW, including the pretreatment settling pit and a series of holding tanks. Each CW cell has been equipped with an aeration system patented by Wallace (21) and designed by North American Wetland Engineering LLC, (Forest Lake, MN). However, aeration was activated for only two CW cells at a time, in order to test the effect of oxygenation on pollutant treatment performance (Munoz et al., 26; Drizo et al., 26). All wetland cells were vegetated with river bulrush (Schoenoplectus fluviatilis (Torr.) ). The design of cell 1 and 2 changed several times over a 3-year period of system operation (Drizo et al., 26); therefore, this data represents a focused study on only two wetland cells: nonaerated C3 and aerated C Methods Sample locations were selected to be representative of the wetland inlet and outlet areas. Three quadrants were positioned within each of the inlet and outlet areas of C3 and C4. Quadrants covered an area of.23 m 2. Plant aboveground (AG) and belowground (BG) biomass were collected from six quadrants per cell during each sampling period (September 24, 25 and 26). For each sampling event, plant samples were taken from a different location within designated cell inlet or outlet sampling areas. Samples were separated by AG and BG biomass and cut into shorter lengths (.2 m). They were then brought to the CWRC Laboratory, where they were weighed, dried at 55 C and ground in a Wiley mill to pass a 1 mm screen. Root samples were milled at the Geology Laboratory (UVM). Total nutrient concentration was determined by microwave-assisted nitric acid digestion (CEM Corp. Matthews, NC) following EPA Vymazal_Ch21.indd 239 3/31/28 7:29:13 PM

4 24 A. Drizo et al. Method SW , with analysis by an inductively coupled plasma atomic emission spectrophotometer (ICP-AES; Perkin-Elmer Corp., Norwalk, CT). Monitoring of the CW performance began in January 24 and sampling continues on a weekly basis (Drizo et al., 26). Dissolved reactive phosphorus (DRP) concentration is determined using the molybdate-reactive P method (APHA et al., 1998) Results and Discussion The Effects of Wetland Age, Plants-Growing Season and Aeration Phosphorus Storage Nonaerated wetland cell 3 (C3) received ± 2.2 g DRP m 2 (total kg) in the first year (346 days) of operation (23/24). Of this, ± 1.91 g DRP m 2 (14.3 kg) was added during a 147 days growing-season period (Fig. 21.1A). The wetland retained a total of ±.82 g DRP m 2 (8.83 kg), over the entire year, of which 3.1 ±.83 g m 2 (6.69 kg) was stored during the growing season (147 days). In the second year (354 days) of operation (24/25), C3 received a 2.5-fold increase of DRP (212.6 ±.8 g m 2, total kg) over the previous year (Fig. 21.1B, A) due to serious malfunctioning of the inlet flow distribution system which occurred in February 25 and lasted for 97 days (Drizo et al., 26). Consequently, there was no increase in DRP storage by the wetland in this period: C3 stored ± 1.22 g m 2 (9.3 kg), which was similar to the amount stored in the first year (Fig. 21.1B, A). Although the amount of DRP added during the second growing season (76.8 ± 1.37 g DRP m 2, kg) was similar to the total added over the entire previous season (14.3 kg), the wetland stored 2.5-fold lower amount of DRP (11.77 ±.7 g DRP m 2, 2.62 kg) due to hydraulic and organic overloading (Fig. 21.1B, A). In the third year (372 days) of operation (25/26), C3 received ± 2.1 g DRP m 2 (3.38 kg). The amount of DRP retained during this period was 7.8-fold lower (5.33 ±.3 g m 2, 1.19 kg) than the DRP storage documented in the previous year (Fig. 21.1C, B). The decrease in C3 DRP storage during the third growing season followed a similar pattern of declining efficiency as observed between the first two growing seasons. Although the amount of DRP added during this period (147 days) was similar (74.8 ± 1.7 g m 2, kg) to the previous growing season, the amount of DRP stored decreased 6.84-fold, from ±.7 to only 1.72 ±.3 g m 2 (.38 kg) (Fig. 21.1B, C). An exponential decrease in DRP storage occurred after only 3 years of operation, indicating that the wetlands saturated in a shorter period than suggested by Kadlec (1999), who stated 5 6 years as the approximate time it takes for wetland vegetation to reach maturation. We attribute this rapid decrease in DRP storage to the hydraulic and organic overloading of the system (Drizo et al., 26). Vymazal_Ch21.indd 24 3/31/28 7:29:13 PM

5 2.1 Regulation of Gene Expression in Plants 241 Cumulative DRP (g m -2 time -1 ) a IN OUT RETAINED Entire period (346 days) b c Entire period (372 days) 1st year of operation (23 / 24) CELL 3, NON-AERATED 1st growing season (147 days) 354 days 2nd year of operation (24 / 25) 2nd growing season (14 days) 3rd year of operation (25 / 26) 3rd growing season (147 days) IN OUT RETAINED Entire period (346 days) d e f 354 days Entire period (372 days) 1st year of operation (23 / 24) CELL 4, AERATED 1st growing season (147 days) 2nd year of operation (24 / 25) 2nd growing season (14 days) 3rd year of operation (25 / 26) 3rd growing season (147 days) Fig Cumulative DRP added and retained (g m 2 time 1 ) by nonaerated cell 3 and aerated cell 4, during each year of operation and each growing season. Nonaerated cell 3, first year of operation (A), second year of operation (B) and third year of operation (C); Aerated cell 4 first year of operation (D), second year (E) and third year (F) The amount of DRP load to the aerated cell 4 (C4) was almost equal to the load into nonaerated C3 during the investigated periods (Fig. 21.1D, A). In the entire first year (346 days) of operation (23/24), C4 received ± 4.39 g DRP m 2 (total 19.5 kg) and retained 1.3-fold more DRP (52.27 ± 1.33 g m 2, kg) than the amount retained by the C3 during the same period. In the first growing season, C4 received ±.79 g DRP m 2 (11.78 kg) and stored ±.29 g m 2 (6.14 kg), which was nearly equal to the amount of DRP stored by C3 during the same period (3.1 ±.8 g m 2, 6.69 kg). These results indicate that the presence of aeration did not have a significant effect on the amount of DRP stored by plant biomass during this first year of investigation. Vymazal_Ch21.indd 241 3/31/28 7:29:13 PM

6 242 A. Drizo et al. The amount of DRP added to aerated C4 during the second year (354 days) of operation (24/25) was equal to the amount added to nonaerated C3 (212.6 ± 3.4 g m 2, total kg) during the same time period. The amount of DRP stored in C4 during this period ( ± 1.13 g m 2, 2.96 kg) was 2.3-fold higher than the amount stored in the previous year of operation (Fig. 21.1E, D) and 2.9-fold higher than the amount stored by C3 in the same year of operation. Contrary to the decline in DRP retention of nonaerated C3 observed between growing seasons 1 and 2, the amount of DRP stored by aerated C4 during the second growing season (36.35 ±.46 g m 2, 8.11 kg) was 1.3-fold higher than the amount stored during the first growing season (6.14 kg). The amount of DRP stored by C4 during this 147- day period was 3.-fold higher than the amount stored by a nonaerated C3 during the same growing season (Fig. 21.1E, B). In the third year (372 days) of operation (25/26), C4 received the same amount of DRP ( ± 2.1 g DRP m 2, 3.38 kg) as nonaerated C3 (Fig. 21.1F). C4 stored 3.-fold less DRP than in the previous year (39.12 ± 2.19 g m 2, total 8.72 kg), showing the same pattern of exponential decrease as observed in C3. However, the amount of DRP stored (8.72 kg) during this entire 372-day period was still 7.3-fold higher than the amount stored by the nonaerated C3 (1.19 kg). During the third growing season, C4 stored 2.8-fold less DRP (12.76 ± 1.1 g DRP m 2, 2.8 kg) than in the previous growing season, exhibiting a similar pattern of DRP storage decline as observed in C3. However, the amount of DRP stored during this 147-day growing season (2.8 kg) was 7.4-fold higher than the amount stored by nonaerated C3 (.38 kg), indicating the beneficial effect of aeration on the wetlands overall phosphorus storage. In total, nonaerated and aerated wetland cells 3 and 4 received ± 2.3 g DRP m 2 (97.2 kg) each, during the entire 3-year period (1,73 days) of investigation (Fig. 21.2). The amount of DRP added during three growing seasons (433 days) was 2.-fold lower ( ± 1.66 in C3 and ± 3.86 g DRP m 2 in C4, or and 45.6 kg, respectively) than the total DRP load over 3 years, corresponding to a 2.5-fold shorter period of loading (Fig. 21.2). Of the total amount of DRP stored by nonaerated C3 (86.47 ± 2.1 g DRP m 2, kg) over the 1,73-day period, ± 1.2 g DRP m 2 (9.7 kg) was stored during the three growing seasons (Fig. 21.2A). Supplemental aeration in C4 resulted in a 2.4-fold increase of DRP storage (21 ± 1.55 g DRP m 2, kg) during the entire 3-year period, as compared to the DRP retention of the nonaerated C3 (Fig. 21.2B). Aeration also had positive effect on C4 DRP storage during the three growing seasons, which was 1.8-fold higher (76.67 ± 3.83 g m 2, 17.1 kg) than the amount stored by C3. The quantities of DRP stored during the three growing seasons within cells 3 and 4 represented 1. and 17.7%, respectively, of the total amount of DRP added to these cells over the entire 1,72 days. Our results are similar to those reported by Tanner (21), who found that after three growth seasons, P accumulation by Schoenoplectus tabernaemontani (C.C. Gmelin) Palla (soft-steam bulrush) contributed to only 6 13% of the total P removal by a dairy-treatment wetland in New Zealand. However, DRP storage by Schoenoplectus fluviatilis (Torr.) (river bulrush) found in nonaerated cell 3 is 2.-fold higher than P storage observed in Typha (5%) Vymazal_Ch21.indd 242 3/31/28 7:29:13 PM

7 21 The Role of Vegetation in Phosphorus Removal by Cold Climate Constructed Wetland 243 DRP (g m -2 time -1 ) NW - CELL 3, NON-AERATED Entire period (173 days) IN OUT RETAINED 3 Growing seasons (433 days) 1 DRP (g m -2 time -1 ) a SW - CELL 4, AERATED Entire period (173 days) IN OUT RETAINED 3 Growing seasons (433 days) 1 5 b Fig Cumulative DRP added and retained by cell 3 (A) and cell 4 (B) during the entire 3-year period of investigation and the three growing seasons after 8 years of operation, recently reported for a free surface flow wetland treating dairy-effluent wastewater (Gottschall et al., 27). When looking at the total DRP retained by wetland cells 3 and 4 during the entire 3 years of operation (1,73 days), the quantities stored during the three growing seasons (433 days) represented 5.3% and 36.5%, respectively, indicating a potentially important role of vegetation in the overall DRP storage, regardless of supplemental aeration. Our results are similar to the observations made by DiPietro (24), who investigated the effects of forced aeration on root architecture, plant biomass, and wastewater treatment of three wetland species (Scirpus atrovirens Willd., Iris versicolor L., and Schoenoplectus fluviatilis (Torr.) M.T. Strong. DiPietro (24) did not observe any statistically significant difference in Schoenoplectus fluviatilis root architecture, plant biomass or nutrients storage Vymazal_Ch21.indd 243 3/31/28 7:29:13 PM

8 244 A. Drizo et al. between the aerated and nonaerated treatment. However, the positive effects of supplemental aeration on organic matter degradation, total suspended solids, nitrogen removal and plant growth development in cold climates have been reported by other authors (Jamieson et al., 23; Ouellet-Plamondon et al., 26). Munoz et al. (26) showed evidence that supplemental aeration prevents clogging and preferential flows. Higher DRP storage in aerated cell 4 could have been attributed to the increased organic matter decomposition, suspended solids removal and better contact time between wastewater and the wetland substrate Phosphorus Mass Removal DRP mass removal efficiency decreased exponentially with wetlands age in both nonaerated cell 3 and aerated cell 4 (Fig. 21.3). Overall, nonaerated C3 DRP mass removal efficiency during the 3-year period of investigation was low, averaging 19.9%. In the first year of operation (23/24), DRP mass removal efficiency was 45.9% ± 1.%; it decreased 2.3-fold during the second year of operation (24/25), falling from 45.91% to 19.54% ±.4%. C3 DRP treatment efficiency in the third year of operation (25/26) was only 3.9% ±.2%, 5.-fold lower than in the second year and 11.8-fold lower than the efficiency achieved in the first year of operation. Nonaerated C3 DRP mass removal efficiencies during the first, second, and third growing seasons followed the same trend of exponential decrease, representing 34.8% ± 1.1%, 5.5% ±.7% and 1.3% ± 1.2% of the total DRP load added each year, respectively. However, it is worth noting that 75.8%, 28.3% and 32.3% of the overall DRP retained during the first, second and third years of operation, respectively, was retained during the growing season, indicating positive effects of vegetation to the overall DRP mass removal efficiency (Fig. 21.3A). Aerated C4 DRP mass removal efficiency averaged 48.4% over the 3 years, 2.4-fold higher than the efficiency of nonaerated C3 during the same period. In the first year of operation (23/24) C4 overall DRP mass removal efficiency was 61.2% ± 1.8%; the efficiency achieved in the second year of operation (24/25) was only slightly lower (55.8% ± 1.8%) than during the previous year of operation. However, in the third year of operation (25/26) DRP efficiency fell to 28.7% ± 1.2%, 2.-fold lower than the efficiency achieved in the second year and 1.9-fold lower than the efficiency achieved in the first year of operation. DRP removal efficiency between the first and second growing seasons decreased 1.9-fold (from 32.3% ± 1.2% to 17.1% ±.4%), followed by a 1.7-fold decline to 9.8% ±.8% during the third growing season (Fig. 21.3B). The positive effect of vegetation on the overall DRP mass removal was also observed in the aerated cell 4: the quantities of DRP retained during the first, second and third growing seasons represented 52.7%, 3.6% and 32.6% of the overall DRP retained during the entire 1,72 days of operation. The decline in overall DRP reduction performance was most prominent during the third year of operation, in both nonaerated and aerated wetland cells. Although a decrease in phosphorus treatment performance is expected to occur as the wetland ages (Kern & Idler, 1999; Kadlec, 1999; Hunt & Poach, 21; Schaafsma et al., 2, Gottschall et al., 27), in the case of our system, it occurred at an early stage Vymazal_Ch21.indd 244 3/31/28 7:29:14 PM

9 21 The Role of Vegetation in Phosphorus Removal by Cold Climate Constructed Wetland st year 2nd year 3rd year 1st growing season 2nd growing season 3rd year of operation Entire year of operation 23/24 CELL 3, NON-AERATED Storage during growing season 4 24 DRP removal efficiency (%) a 24/ /26 26 CELL 4, AERATED Entire year of operation Storage during growing season 23/24 24/ / b Fig DRP mass removal during each of the 3 years of operation and each of the three growing seasons. (A) nonaerated cell 3; (B) aerated cell 4 of operation (within the first 3 years). Such rapid decrease in treatment performance has been attributed to the high hydraulic loading rate (1.44 ±.1 cm day 1 ) which was nearly twice as high as those recommended for dairy-wastewater treatment wetlands in North America (5.5 cm day 1 ) (Drizo et al., 26) The Effects of Wetland Age and Aeration on Phosphorus Uptake and Biomass Development At the end of the first growing season (24), the P content in the nonaerated wetland C3 AG biomass inlet and outlet areas was 4.5 ±.48 and 4.95 ± 1.5 g P kg 1, respectively, averaging 4.5 ±.64 g P kg 1 ; P content in the BG biomass inlet and Vymazal_Ch21.indd 245 3/31/28 7:29:14 PM

10 246 A. Drizo et al. outlet wetland areas was 5. ±.84 and 7.3 ± 1.27 g P kg 1, respectively, averaging 6.15 ±.92 g P kg 1 (Fig. 21.4A). Phosphorus content in both AG and BG biomass decreased between the first and second growing seasons. At the end of the second growing season (25), P content in the AG biomass wetland inlet and outlet areas was 1.36 ±.26 and 1.42 ±.38 g P kg 1, respectively, being in average 3.-fold lower than at the end of the first season (1.39 ±.4 g P kg 1 ). P contents in the BG biomass inlet and outlet wetland areas were 6.42 ±.97 and 6.36 ± 1.16 g P kg 1, respectively, averaging 6.4 ±.4 g P kg 1 and being slightly higher than at the end of the first season (Fig. 21.4B). P content (g kg 1 ) a b c INLET AREA OUTLET AREA AVERAGE AG Biomass INLET AREA OUTLET AREA AVERAGE AG Biomass INLET AREA OUTLET AREA AVERAGE AG Biomass 1st year (23 / 24) BG Biomass 2nd year (24 / 25) BG Biomass 3rd year (25 / 2 6) BG Biomass d e f INLET AREA OUTLET AREA AVERAGE AG Biomass INLET AREA OUTLET AREA AVERAGE AG Biomass INLET AREA OUTLET AREA AVERAGE AG Biomass 1st year (23 / 24) BG Biomass 2nd year (24 / 25) BG Biomass 3rd year (25 / 26) BG Biomass Fig Phosphorus content in nonaerated cell 3 and aerated cell 4 aboveground and belowground biomass at the end of the first (A, D), second (B, E) and third (C, F) growing seasons Vymazal_Ch21.indd 246 3/31/28 7:29:14 PM

11 21 The Role of Vegetation in Phosphorus Removal by Cold Climate Constructed Wetland 247 When compared to the second growing season, P content of C3 AG biomass during the third growing season showed a slight increase; however, third growing season biomass P content was still significantly lower (p <.1) than that determined at the end of the first season. Average P content of the AG biomass wetland inlet and outlet areas at the end of the third growing season (26) was 2.-fold higher (2.67 ±.77 g P kg 1 ) than the P content in the second growing season (Fig. 21.4B, A); P content in the AG biomass outlet wetland area was 1.6 ±.11 g P kg 1, averaging 2.14 ±.44 g P kg 1 between inlet and outlet areas (Fig. 21.4C). P contents in the BG biomass inlet and outlet wetland areas were 4.51 ±.78 and 3.71 ±.35 g P kg 1, respectively, averaging 4.11 ± 1.6 g P kg 1 ; average BG biomass P content at the end of this season was 1.6-fold and 1.5-fold lower than the BG biomass P contents found at the end of the first and second growing seasons (Fig. 21.4). At the end of the first growing season, P content in the AG biomass of aerated wetland C4 inlet and outlet areas was 4.3 ±.42 and 4.15 ±.76 g P kg 1, respectively, averaging 4.22 ±.11 g P kg 1. P content in the BG biomass inlet and outlet wetland areas was 7. ± 1.15 and 7.6 ±.82 g P kg 1, averaging 7.3 ±.42 g P kg 1 (Fig. 21.4D). The AG and BG biomass P contents in this wetland were not significantly different from that found in the nonaerated C3, indicating that supplemental aeration did not have any significant effect on the P content plant biomass during this first growing season. The P content in the AG biomass wetland inlet and outlet areas at the end of the second growing season (25) was 1.3 ±.32 and 1.44 ±.12 g P kg 1, averaging 1.37 ±.1 g P kg 1. Second season AG biomass P content was significantly lower (p <.1) than the AG biomass P content measured at the end of the first season. Similarly, second season P contents in the BG biomass inlet and outlet wetland areas was 4.6 ±.67 and 5.18 ±.98 g P kg 1, averaging 4.9 ±.41 g P kg 1, which was 1.5-fold lower than at the end of the first season (Fig. 21.4E, D) and 1.3-fold lower than in the nonaerated cell 3 during the same time period (Fig. 21.4E, B). Phosphorus content of the AG biomass wetland inlet and outlet areas at the end of the third growing season (26) was 1.74 ±.42 and 2.25 ±.58 g P kg 1, respectively, averaging 2. ±.5 g P kg 1. P content in the BG biomass inlet and outlet wetland areas was 4.65 ± 1.4 and 4.51 ±.98 g P kg 1, respectively, and averaged 4.58 ± 1.16 g P kg 1. Average BG biomass P content at the end of this season was 1.6-fold lower than the P content measured at the end of the first growing season but nearly equal to the P content observed at the end of the second season (Fig. 21.4). Throughout the 3-year period of investigation, BG biomass P content was significantly higher (p <.1) than in the AG biomass (Fig. 21.4). These results confirm findings by Tanner (21) and Gottschall et al. (27), who observed nutrients allocation from the AG to BG biomass towards the end of a growing season (Tanner, 21; Gottschall et al., 27). A significant drop in AG plant biomass was observed during the 3-year study period, indicating a potential decline in plant health and nutrients uptake. Vymazal_Ch21.indd 247 3/31/28 7:29:14 PM

12 248 A. Drizo et al Conclusions Supplemental aeration had a positive effect on the overall DRP mass removal efficiency, contributing to a 2.4-fold increase (from 19.9% in nonaerated C3 to 48.4% in aerated C4). However, after 3 years of operation, both C3 and C4 wetland cells exhibited a sharp decline in DRP storage, indicating wetlands saturation regardless of supplemental aeration. Hydraulic and organic overloading greatly impacted DRP mass removal and may have adversely affected plant contribution to wetland treatment. The quantities of DRP stored during the three growing seasons occurring within this study represented only 1.% C3 and 17.7% C4 of the total amount of DRP added throughout the entire 3-year study period, initially suggesting that plant contribution to P removal was minimal. However, when considering that the DRP quantities stored only during the three growing seasons represented 5.3% C3 and 36.5% C4 of the total DRP retention measured over the entire study period, such results indicate that vegetation had an important role in the overall DRP storage, regardless of supplemental aeration. There was no significant difference in the AG or BG P content between C3 and C4 wetland cells. BG biomass had a significantly higher (p <.1) P content than AG biomass, throughout the 3-year period of investigation. A significant drop in AG plant biomass was observed during the 3-year study period indicating a potential decline in plant health, and therefore, effectiveness. Future research should focus on in-series multistage CW designs that can improve the systems DRP retention of nutrient-rich agriculture-wastewater runoff. Acknowledgements The financial support from Senator Jeffords Office, USDA-CSREES Special Research Grant is greatly appreciated. We also wish to thank Dr. Donald Foss for his efforts in establishing the CWRC and Joel Tilley for conducting plant mineral analyses. References APHA, AWWA, and WEF (1998). In A.D. Eaton, L.S. Clesceri, & A.E. Greenberg (Eds.), Standard methods for the examination of water and waste water, 19th ed. Washington DC: American Public Health Association. Allen, W.C., Hook, P.B., Biederman, J.A., & Stein, O.R. (22). Temperature and wetland plant species effects on wastewater treatment and root zone oxidation. Journal of Environmental Quality, 31, Brix, H. (1997). Do macrophytes play a role in constructed treatment wetlands?. Water Science and Technology, 35(5), Brix, H., Schierup, H.-H., & Arias, C. (26). Twenty years experience with constructed wetland systems in Denmark what did we learn? In Proceedings Of the 1th International Conference Constructed Wetlands for Water Pollution Control (pp ). MAOTDR: Lisbon, Portugal. Cooper, P. (27). The Constructed Wetland Association UK database of constructed wetland systems. Water Science & Technology 56(3), 1 6. DiPietro, T. (24). Wastewater strength and forced aeration impacts on root architecture, plant biomass, and wastewater treatment of three plant species using laboratory-scale wetland cells. MS Thesis, University of Vermont, Burlington. Vymazal_Ch21.indd 248 3/31/28 7:29:14 PM

13 21 The Role of Vegetation in Phosphorus Removal by Cold Climate Constructed Wetland 249 Drizo, A., Twohig, E., Weber, D., Bird, S., & Ross, D. (26). Constructed wetlands for dairy effluent treatment in Vermont: 36 months of operation. In Proceedings of the 1th International Conference Constructed Wetlands for Water Pollution Control (pp ). MAOTDR: Lisbon, Portugal. Gottschall, N., Boutin, C., Crolla, A., Kinsley, C., & Champagne, P. (27). The role of plants in the removal of nutrients at a constructed wetland treating agricultural (dairy) wastewater, Ontario, Canada. Ecological Engineering, 29, Hammer, D.A. (1989) (ed). Constructed Wetlands for Waste Water Treatment: Municipal, Industrial and Agricultural. Lewis Publishers. Boca Raton, Florida. Hunt, P.G., & Poach, M.E. (21). State of the art for animal wastewater treatment in constructed wetlands. Water Science and Technology, 44 (11 12), Jamieson, T.S., Stratton, G.W., Gordon, R., & Madani, A. (23). The use of aeration to enhance ammonia nitrogen removal in constructed wetlands. Canadian Biosystems Engineering, 45, Kadlec, R.H. (1999). The limits of phosphorus removal in wetlands. Wetlands Ecology and Management, 7, Kadlec, R.H., & Knight, R. (1996). Treatment Wetlands. Lewis Publishers, Chelsea, MI. Kadlec, R.H., Knight, R., Vymazal, J., Brix, H., Cooper, P., & Haberl, R. (2). Constructed Wetlands for Pollution Control. Published by International Water Association, London, UK. Kern, J., & Idler, C. (1999). Treatment of domestic and agricultural wastewater by reed bed systems. Ecological Engineering, 12, Knight, R.L., Payne, V.W.E., Borer, R.E., Clarke, R.A., & Pries, J.H. (2). Constructed wetlands for livestock wastewater management. Ecological Engineering, 15, Luderitz, V., & Gerlach, F. (22). Phosphorus removal in different constructed wetlands. Acta Biotechnologica, 22, Munoz, P., Drizo, A., & Hessoin, C. (26). Flow patterns of dairy farm wastewater constructed wetlands in a cold climate. Water Research, in press. Ouellet-Plamondon, C., Chazarenc, C., Comeau, Y., & Brisson, J. (26). Artificial aeration to increase pollutant removal efficiency of constructed wetlands in cold climate. Ecological Engineering, 27, Picard, C.R., Lauchlan, F.H., & Steer, D. (25). The interacting effects of temperature and plant community type on nutrient removal in wetland microcosms. Bioresource Technology, 96, Reddy, K.R., & Smith, W.H. (1987). Aquatic plants for water treatment and resource recovery. Orlando, FL: Magnolia. Schaafsma, J.A., Baldwin, A.H., & Streb, C.A. (2). An evaluation of a constructed wetland to treat wastewater from a dairy farm in Maryland, USA. Ecological Engineering, 14, Serodes, J.B., & Normand, D. (1999). Phosphorus removal in agricultural wastewater by a recently constructed wetland. Canadian Journal of Civil Engineering, 26, Smith, E., Gordon, R., Madani, A., & Stratton, G. (25). Cold climate hydrological flow characteristics of constructed wetlands. Canadian Biosystems Engineering, 47, 1 7. Tanner, C.C., Clayton, J.S., & Upsell, M.P. (1995). Effect of loading rate and planting on treatment of dairy farm wastewaters in constructed wetlands-ii. Removal of nitrogen and phosphorus. Water Research, 29, Tanner, C.C. (21) Growth and nutrient dynamics of soft-stem bulrush in constructed wetlands treating nutrient-rich wastewaters. Wetlands Ecology and Management 9, Vymazal, J. (26). Constructed wetlands with emergent macrophytes: from experiments to a high quality treatment technology. In Proceedings of the 1th International Conference on Constructed Wetlands for Water Pollution Control (pp. 3 27). MAOTDR: Lisbon, Portugal. Vymazal, J., Brix, H., Cooper, P.F., Green, M.B., & Haberl, R. (1998). Constructed wetlands for wastewater treatment in Europe. Leiden, The Netherlands: Backhuys. Wallace, S., Parkin, G., & Cross, C. (21). Cold Climate Wetlands: Design & Performance. Water Sci Tech. 44(11 12), Weber, D., Drizo, A., Twohig, E., Bird, S., & Ross, D. (27). Upgrading Constructed Wetlands Phosphorus Reduction from a Dairy Effluent using EAF Steel Slag Filters. Water Science and Technology 56(3), Vymazal_Ch21.indd 249 3/31/28 7:29:14 PM

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