Phosphorus removal in created wetland ponds receiving river overflow

Ecological Engineering 14 (2000) 107 – 126

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Phosphorus removal in created wetland ponds receiving river overflow Robert W. Nairn 1, William J. Mitsch * School of Ci6il Engineering and En6ironmental Science, The Uni6ersity of Oklahoma, 202 West Boyd Street, Room 334, Norman, OK 73019 -0631, USA Received 12 November 1997; received in revised form 12 October 1998; accepted 22 December 1999

Abstract Water quality changes and biogeochemical development were evaluated over 2 years in two newly created freshwater riparian wetland ponds (1 ha each) in an agricultural and urban watershed. Both wetlands received pumped river water and had similar hydrologic regimes. One wetland was planted with 13 species of vegetation typical of Midwestern US marshes; the other received no planted vegetation. Water quality sampling was conducted weekly and detailed hydrologic budgets were developed from data collected twice daily. Hydrologic budgets were dominated by pumped surface flows (mean inflow =1480 m3 day − 1). Two floods accounted for 32% of inflow in 1 year. Both wetlands significantly decreased turbidity (62 to 27 NTU) and increased dissolved oxygen (9 – 11 mg l − 1). Inflow dissolved reactive phosphorus (DRP) and total phosphorus (TP) concentrations (17 93 and 169911 mg P l − 1) were significantly higher (PB0.05) than outflow concentrations (DRP: 5 91 and 6 9 1 mg P l − 1; TP: 69 98 and 74 99 mg P l − 1) for planted and unplanted wetlands, respectively. Phosphorus removal was related to decreases in turbidity and the level of biological activity. Extensive and highly productive algal coverage in both wetlands and the subsequent deposition and decomposition of the algal mat influenced P retention through biological uptake and chemical sorption and coprecipitation. Mean removal rates were 1.0 g P m − 2 year − 1 for DRP and 5.4 g P m − 2 year − 1 for TP and did not differ significantly between wetlands (P B0.05). Approximately 35% of TP mass removal occurred during two floods. A conservative tracer (Cl) indicated limited and negligible effects of dilution on decreases in P concentration. Water flow rate and P concentration did not affect P removal which was loading-limited and seasonal. Initial development of macrophytic vegetation demonstrated no influence on water quality changes. Both wetlands acted as effective P sinks in the initial 2 years of operation. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Created wetlands; Water quality; Nonpoint source pollution; Phosphorus; Pollutant removal; Wetland; Freshwater marsh; Olentangy River; Olentangy River Wetland Research Park Ohio

* Corresponding author. Present address: Environmental Science Graduate Program and School of Natural Resources, The Ohio State University, 2021 Coffey Road, Columbus, OH 43210, USA. E-mail address: [email protected] (W.J. Mitsch) 1 Tel.: + 1-405-325-3354; fax: +1-405-325-4217; e-mail: [email protected] 0925-8574/99/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 8 5 7 4 ( 9 9 ) 0 0 0 2 3 - 3

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1. Introduction Natural wetlands have been known for decades to improve water quality (Grant and Patrick (1970), Odum et al. (1977), reviewed by Johnston (1991)). This inherent water quality enhancement ability has been exploited in recent years through the construction of wetlands to specifically treat concentrated forms of water pollution, including municipal waste water (Ewel, 1976; Odum et al., 1977; Richardson et al., 1978; Kadlec, 1979; Tilton and Kadlec, 1979; Nichols, 1983; Kadlec and Knight, 1996), animal wastes (Hunt et al., 1993; Skarda et al., 1994), septage (Teal and Peterson, 1991), pulp mill wastes (Moore et al., 1994) and mine drainage (Kleinmann et al., 1983; Wieder, 1989; Hedin et al., 1994). Great interest has recently developed in the use of wetlands for agricultural and urban nonpoint source (NPS) pollutant retention (Meyer, 1985; Lowe et al., 1992; Olsen and Marshall, 1992; Baker, 1992; Hammer, 1992a; Mitsch, 1992). However, the ability of these created wetlands to improve nearambient (i.e. non-waste stream) water quality has not been well-documented (Mitsch et al., 1995a). In addition, the loss or alteration of wetland area in the USA must be legally mitigated by the creation, restoration or enhancement of replacement wetlands. The ability of these created and restored ecosystems to perform in a manner functionally equivalent to natural wetlands is not well understood. Relatively little is known regarding the water quality improvement capabilities of these systems. Hydrologic factors are especially important in the ability of both natural and created wetlands to improve water quality. Examinations of the significant role of hydrology in wetland ecosystem function have often been neglected in studies of both natural and created ecosystems (LaBaugh, 1986; Zedler and Weller, 1990; Hammer, 1992b). In most studies of water quality improvement processes in wetlands, water chemistry data have been overemphasised while hydrologic data have received much less attention or are completely disregarded. Riverine and riparian wetlands are particularly important as biogeochemical and ecological

buffers between upland and open water systems (Gilliam, 1994; Patrick, 1995). Prior to human impacts, riparian wetlands connecting many streams and rivers helped to maintain critical biogeochemical balances and landscape continuity. The creation and restoration of riparian wetlands has been identified as especially critical for enhancing the biological, chemical and physical integrity of rivers and streams (Mitsch, 1995). The goal of this research was to investigate the ability of created riparian wetlands to improve the quality of river water in an agricultural and urban watershed. This objective was accomplished by: (1) developing complete hydrologic budgets, (2) combining detailed water quality data with the hydrologic budgets, (3) refining the budgets for dilution effects with a conservative ion, and (4) comparing several performance evaluation methods.

2. Methods

2.1. Study site description The research described in this study was conducted at the Olentangy River Wetland Research Park (ORWRP), located on the Columbus campus of The Ohio State University (approximately 83° 1’ 81’’ W longitude and 40° 1’ 59’’ N latitude; Fig. 1). The ORWRP is designed to be a comprehensive wetland research and education facility (Mitsch et al., 1998). Almost the entire 9 ha site lies in the 100-year floodplain of the Olentangy River, a fourth-order stream in an agricultural and urban watershed. Wetland construction was completed in 1993–1994. A river water intake structure, two pumps, two large (1-ha each) basins, outflow weirs and an experimental outflow swale were installed in phase one of a multi-year effort. Water is drawn from the river by two electrically-driven submersible pumps and delivered to the wetlands in a parallel manner via two 20-cm diameter pipes. Both wetlands receive similar water quantity and quality, but are otherwise hydrologically isolated. The two wetlands were designed and excavated as mirror images of one another. Pumped river water was first introduced

R.W. Nairn, W.J. Mitsch / Ecological Engineering 14 (2000) 107–126

to the wetlands in March 1994 and continued, with several periods of drawdown for construction, maintenance and research, through November 1995. Attempts were made to mimic the hydrologic fluxes and hydroperiods of natural riparian marshes. An ecosystem-scale experiment was begun at the ORWRP in May 1994: Wetland 1 (the western basin) was manually planted with 13 species of hydrophytic vegetation common to the Midwestern USA (Table 1). By 1995, percent cover in wetland 1 was estimated to be approximately 13% (Mitsch et al., 1998), with proportional cover estimates dominated by Scirpus tabernaemontani (82%) and Scirpus flu6iatilis (4%) (Weihe and Mitsch, 1996). Wetland 2 serves as an unplanted control.

2.2. Hydrologic budgets Hydrologic budgets of both marshes were developed for calendar years 1994 and 1995. Cal-

109

culations of hydrologic budgets include data collected by others as part of an intensive twice daily monitoring program at the ORWRP (Nairn et al., 1996). Surface inflows to the two wetlands consisted of controlled pumped inflows and, in 1995 only, two river flooding events (27 June and 8 August, 1995). Surface inflows to each wetland were measured with Data Industrial series 200 non-magnetic in-pipe flow sensors and Data Industrial series 1000 or 1500 flow monitors. For both flood events, flows were estimated from velocity and depth measurements obtained near peak flood flows at the point of river overflow into the wetlands. Flows were assumed to be distributed equally between both wetlands. In 1994, daily precipitation data were obtained from an Ohio State University meteorological station located approximately 3 km southwest of the ORWRP. In 1995, precipitation was recorded with a Unidata model 6506B tipping bucket rain gauge located in the on-site meteorological station. Surface outflows of the two wetlands were controlled by a compound vnotch weir. Outflows were calculated using empirically developed weir equations (US Department of the Interior, 1984). For 1994, monthly evapotranspiration was estimated by the Thornthwaite equation. In 1995, evapotranspiration was estimated by using a combination of empirical pan evaporation (Unidata model 6501-EU Thermistor and a model 6531/6529 evaporation pan/water level monitoring system) and the Thornthwaite equation. Reliable estimates of groundwater dynamics were unavailable for calculation of the hydrologic budgets. However, Koreny et al. (1999) provided details of groundwater and surface water interactions at the ORWRP; estimated monthly seepage ranges from 5 to 10% of total inflows (Wang et al., 1997).

2.3. Water quality sampling and analysis

Fig. 1. Site map showing water quality sampling stations at the ORWRP. Stations are identified in Table 2.

Water samples were collected in polyethylene bottles from 9–13 stations on a weekly basis except during periods of drawdown for mainte-

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Table 1 Number of hydrophytes of several common Midwestern species introduced to the three depth habitats of Wetland 1 on 14 May 1994 and number surviving through the first two growing seasonsa Number surviving May 1994 (planting) Days from planting Deep water (0.6 m) Nelumbo lutea [Willd.] Pers. Nymphaea odorata Ait. Potamogeton pectinatus L. Edges and middle (0.3 m) Scirpus tabernaemontani KC Gmel.b Scirpus flu6iatilis (Torrey) Gray Mud flat (0–0.3 m) Acorus calamus L. Cephalanthus occidentalis L. Juncus effusus L. Pontederia cordata L. Sagittaria latifolia Willd. Saururus cernuas L. Sparganium eurycarpum Engelm. Spartina pectinata Link Total a b

June 1994

August 1994

August 1995

–

32

95

460

132 198 83

2 17 0

0 0 0

0 0 0

1010 184

332 13

312 8

312 8

151 20 190 73 25 30 151 190

65 5 52 58 17 20 37 29

61 1 35 51 16 15 33 28

39 0 24 1 16 5 33 24

2437

679

655

462

Data from Weihe and Mitsch (1996). Formerly known as Scirpus 6alidus Vahl.; also included plants identified as Scirpus acutus

nance. Sampling stations included the intake system, wetlands and outflow swale (Fig. 1 and Table 2). All samples were collected as surface grab samples. One sample was preserved by acidification with 2 ml 36N H2SO4 per l of sample (to pH B2) immediately upon return to the Ecosystem Analytical Laboratory. The other unpreserved sample was split in the laboratory: an equal portion was maintained as an unpreserved, unfiltered sample and an equal portion was filtered through a 0.45 mm filter. In the field, conductivity was determined with a Hach model 17250 conductivity meter. Dissolved oxygen and temperature were determined with a YSI model 51B or Orion model 820 polarigraphic dissolved oxygen meter after appropriate calibration. A Fisher Scientific Accumet 1002 pH meter was used to measure pH. Beginning in August 1994, a Hydrolab H20G multiparameter water quality data transmitter was used to

collect pH, conductivity, dissolved oxygen, temperature and oxidation–reducdon potential measurements. The H20G was calibrated on a biweekly basis and was used in conjunction with a Hydrolab Surveyor 3 data display logger. Turbidity was determined on the day of sampling with a Hach model 18900 ratio turbidimeter. Turbidity standards were always within 10% of the prescribed values. Dissolved reactive phosphorus (DRP) concentrations were analysed on filtered portions of each sample on a Lachat QuikChem IV flow injection analysis (FIA) system by calorimetric determination via the standard ascorbic acid method (APHA, 1989). Total phosphorus (TP) concentrations were determined on acidified portions of each sample via persulfate digestion and the ascorbic acid method (APHA, 1989). Chloride was measured colorimetrically (US EPA, 1983). Approximately 40% of all analyses were conducted for quality assur-

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ance/quality control (QA/QO) reasons. Spike recoveries were always within 20% of the expected value. Blanks were always within 10% of the expected value.

3. Results

3.1. Hydrologic budgets Surface inflows and outflows dominated the hydrologic budget of the Olentangy River wetlands in both 1994 and 1995. Precipitation and evapotranspiration were minor components of the annual budgets. Seepage to groundwater, assumed to be part of the residual component of the budgets, was also minimal (Table 3). The hydrographs of the wetlands were nearly identical to each other in both 1994 and 1995 (Fig. 2). Water was pumped into the wetlands for a total of 245 days in 1994 and 246 days in 1995. Mean daily pumped surface inflows were approximately 1403 m3 day − 1 for both wetlands in 1994 and 1562 and 1550 m3 day − 1 for wetlands 1 and 2, respectively, in 1995, for those days of wetland operation. In 1994, mean daily surface outflows were 989 and 979 m3 day − 1 for wetlands 1 and 2, respectively, calculated for those days of wetland oper-

ation. These calculated outflows are significantly less than pumped inflows (PB 0.05).). In 1995, mean daily surface outflows were 1607 and 1496 m3 day − 1 for wetlands 1 and 2, respectively, and were not significantly different from inflows (P\ 0.05). During 1995, two floods provided approximately 32% of the total volume of water to pass through each wetland. Approximately 86 000 m3 of flood water entered the Olentangy River wetlands during the 27 June flood. The volume of the 8 August event was approximately 36 000 m3. Instantaneous flood inflows were estimated to peak at 321 000 m3 day − 1 on 27 June and 208 000 m3 day − 1 on 8 August.

3.2. Ri6er water quality Summary water quality data for all regularly monitored sampling stations are presented in Table 4. The relationships between river flow and selected water quality parameters are shown in Fig. 3. For most parameters the values measured at the wetland inflows were not significantly different but were highly correlated with those from the river (Table 5). No significant differences were found, with the notable exception of dissolved reactive P. DRP concentrations were significantly higher in the river

Table 2 Water quality sampling stations included in regular weekly monitoring at the ORWRPa

1 2 3 4 5 6 7 8 9 10 11 12 13 a

Station ID

Location

Dates sampled

CP-W DF-I SP-I CB-I B1-I B2-I B1-M BT-E B2-E SW-1 SW-2 FL-E DS-C

Olentangy River (Clinton Park weir) Disc-flo pump inflow Standard pump inflow Combined pump inflow Wetland 1 inflow Wetland2 inflow Wetland 1 middle Wetland 1 outflow Wetland2 outflow Swale inflow Swale middle Swale outflow (final outflow) Urban stream

May 1993–Nov.1995 April 1994–May 1995 April 1994–May 1995 April 1994–May 1995 April 1994–November 1995 April 1994–November 1995 March 1995–November 1995 April 1994–November 1995 April 1994–November 1995 April 1994–Nov 1995 October 1994–November 1995 April 1994–November 1995 April 1994–May 1995

Locations are shown in Fig. 1.

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Table 3 Hydrologic budgets of the two wetlands for 1994 and 1995 represented by summed annual volumesa Wetland 1 annual volume (103 m3) 1994 Inflows Pumped inflow Precipitation

354 344

Wetland 2 annual volume (103 m3)

354 344

10

10

Outflows 270 Surface 263 outflow Evapotranspira 7 tion

270 263

87

87

518 388

515 385

118 12

118 12

Outflows 539 Surface 532 outflow Evapotranspira 7 tion

502 495

Residual 1995 Inflows Pumped inflow Flood inflow Precipitation

Residual

−20

7

7 13

ows tended to be higher than the inflows, although differences were not significant (P\0.05). No difference existed between the two wetlands (P\0.05). Dissolved oxygen (D.O.) concentrations were significantly higher at the wetland outflows than the inflows (PB 0.05). Mean inflow D.O. concentrations were 8.990.43 mg l − 1 and outflow concentrations were 11.1 9 0.36 and 11.8 9 0.64 mg l − 1 for wetlands 1 and 2, respectively. Outflow D.O. concentrations were not significantly different between wetlands (P\ 0.05). Mean conductivity at the inflow was 5999 23 ms − 1 cm − 1 over the course of the entire study. Conductivity was significantly lower at outflow of wetland 2 (PB 0.05) but not at the outflow of wetland 1. Wetland 1 and 2 outflow mean conductivities were 547 9 23 and 530 9 22 ms − 1 cm − 1, respectively and were not significantly different. Wetland outflows demonstrated significantly higher pH than the wetland inflow (PB0.05). Inflow pH was 8.09 0.07 and outflow pH values were pH 8.5790.07 and 8.7090.08 for wetlands 1 and 2, respectively. Wetland 1 and 2 outflow pH values were not significantly different (P \0.05). Turbidity was significantly lower in wetland outflows than inflows (PB 0.05). Mean inflow turbidity was 629 13 NTU. Mean wetland 1

a For precipitation and evapotranspiration, volumes are calculated based on a surface area of 10 000 m2.

(35 95.9 mg P l − 1) than wetland inflows (17 – 19 mg P l − 1).

3.3. Wetland water quality In the inflow, turbidity and total phosphorus were positively correlated (r =0.8), suggesting a relationship between TP and suspended solids (Table 6). Two major anions, chloride and sulfate, were highly correlated (r = 0.91). Conductivity and turbidity were negatively correlated (r= − 0.62), illustrating the effects of dilution on river water quality. Conductivity and both chloride and sulfate, turbidity and TP, and chloride and sulfate were positively correlated as well (Table 6). In the spring and summer months, water temperatures in the wetland outfl-

Fig. 2. Water stage elevations of the two wetlands based on twice daily staff gauge readings for 1994 – 1995. The horizontal lines represent the elevations of the minimum and maximum design water depths.

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Table 4 Summary statistics for regularly monitored water quality parameters at the ORWRP wetlandsa Station

Temperature (°C)

D.O. (mg l−1)

Conductivity (ms cm−1)

pH (s.u.)

CP-W B1-I B2-I B1-M B1-E B2-E SW-1 SW-2 FL-E

16.4 90.97 17.2 90.90 17.5 90.89 18.8 91.36 17.7 91.16 17.9 91.17 17.7 9 1.18 17.2 9 1.43 18.4 91.24

8.99 0.29 8.99 0.44 8.39 0.37 10.69 0.85 11.190.36 11.89 0.64 11.69 0.41 11.690.44 11.39 0.39

599 9 23 603 923 606 9 25 554 9 26 547 923 530 9 22 538 921 535 9 23 530 924

8.190.06 8.090.07 8.090.05 8.59 0.10 8.69 0.07 8.79 0.08 8.79 0.06 8.79 0.06 8.69 0.06

a b

(50) (53) (52) (28) (54) (54) (53) (37) (52)

(47) (53) (49) (26) (50) (52) (52) (36) (52)

(33) (32) (30) (18) (33) (33) (33) (27) (31)

(44) (46) (45) (25) (50) (50) (48) (36) (48)

Turbidity (NTU)b

DRP (mg l−1)

TP (mg l−1)b

55 9 13 (49) 62913 (50) 649 14 (49) 3398 (25) 279 8 (51) 2797 (51) 219 4 (50) 249 6 (32) 289 8 (50)

3995 (47) 17 9 3 (55) 19 9 3 (35) 12 9 2 (26) 5 91 (58) 6 9 1 (58) 8 92 (45) 11 93 (28) 48 9 16 (35)

163912 (58) 169 9 11 (57) 164912 (56) 979 10 (29) 699 8 (58) 7499 (60) 619 6 (58) 799 8 (39) 111919 (59)

Station locations are identified in Fig. 1. Entries are mean 9S.E. (n). DRP, dissolved reactive phosphorus; TP, total phosphorus.

and 2 outflow turbidities were 279 8 and 279 7 NTU, respectively, representing a 56% decrease in concentrations. Both dissolved reactive and total phosphorus concentrations were significantly lower in outflows than inflows of both wetlands (P B0.05). Mean influent total phosphorus concentration was 1699 11 mg P l − 1 (mean9S.E.) over the entire study period. Mean effluent TP concentrations were 69 98 and 74 9 9 mg P l − 1 for wetlands 1 and 2. Dissolved reactive P decreased from 17 9 3 mg P l − 1 to 591 and 691 mg P l − 1 for wetlands 1 and 2, respectively.

4. Discussion

4.1. Hydrologic budgets Total pumped inflows to both wetlands varied with valve settings and river-flow dependent head. Assuming water volumes of 6000 m3 for each wetland, mean theoretical residence times were approximately 6 days for each wetland during normal pumping operations. Nominal residence times ranged from 1 to 25 days during normal pumping based upon calculated daily flows. Approximately 27% of calculated 1994 outflow estimates are problematic due to use of a rectangular weir equation, although elevations of the weir boxes at the ORWRP do not allow free flow. Best estimates were used in the hydrologic budget

calculations. In 1995, mean daily surface outflows were not significantly different from inflows (P\ 0.05) due to the consistent use of the v notch weirs in establishing reliable estimates of outflow. During 1995 flood volumes accounted for approximately 32% of the total volume of water to pass through each wetland. The flood of 27 June was produced by a local precipitation event of approximately 9 cm, while the 8 August flood was in response to a regional precipitation event. Because the June event damaged the pumps, inflows decreased precipitously after flood recession. The pumps continued to function after the August event and wetland levels dropped at a slower rate (Fig. 2). The floods of 27 June and 8 August resulted in massive outflow peaks. As the flood waters receded, outflows decreased precipitously after the June event due to a lack of pumping. High outflow rates after the August event lingered due to continued high rates of pumped inflow. An unusually large volume of water remained in the wetlands and residence times were decreased as outflows remained high.

4.2. Water quality changes DRP concentrations were significantly higher in the river (359 5.9 mg P l − 1) than wetland inflows (17–19 mg P l − 1). River water samples were collected on the surface but the pumps which deliver water to the wetlands draw water from near the

114

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bottom of the river. If the river was not fully mixed, surface waters may not be indicative of the water the wetlands received. However, because the two wetland inflows were not significantly different and to minimize disturbance (in 1995, only wetland 1 contained a boardwalk to facilitate sample collection), it was assumed wetland 1 inflows were representative of both wetland inflows. Wetland 1 inflows were used in all subsequent data analyses. All data were collected during the weekly midday sampling regime. The water temperature followed expected seasonal patterns as it passed through both wetlands. As expected, the shallow water depths, open canopy and the motionless water surface of the wetlands acted to increase river water temperatures in the warmer months. Similar seasonal patterns have been noted in other studies (Kadlec and Knight, 1996). In the summers, supersaturated D.O. concentrations (\20 mg l − 1 at 30°C or \ 250% O2 saturation) at the wetland effluents were not uncommon. Supersaturated D.O. concentrations are not unusual in highly productive ecosystems, especially those dominated by algae. Kuhl and Mann (1951) (as cited in Beyers and Odum

(1993)) found \ 260% O2 saturation in marine mesocosms. Goldman and Horne (1983) report that naturally productive lakes often reach 250% O2 saturation. Cronk and Mitsch (1994) found greater than 200% O2 saturation in a study of aquatic metabolism in restored wetlands at the Des Plaines River Experimental Wetlands. Dissolved oxygen concentrations at the ORWRP have been shown to demonstrate a diurnal pattern indicative of a highly productive water column (Mitsch et al., 1995b). Also, in the first two growing seasons, the warm temperatures and ample nutrients in the waters of both wetlands led to the establishment of diverse algal mats (Deal, 1995; Deal and Kantz, 1996) that were highly productive (Wu and Mitsch, 1998). Outflow pH for both wetlands never decreased below pH 7.5 and was as high as pH 9.8–10 in the warm, mid-summer sampling periods. The high water column productivity illustrated by the significant increases in dissolved oxygen concentrations also increased pH as carbonate solubility equilibria shifted. These high pH values, coupled with temperatures greater than 30°C and high water column productivity, could have a direct effect on phosphorus dynamics via both biological

Fig. 3. Relationships of several water quality parameters in Olentangy River water to log river flow: (a) conductivity, (b) turbidity, (c) DRP, and (d) TP.

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Table 5 Summary statistics and statistical comparison of water quality of the Olentangy River (CP-W) and inflows to wetland 1 (B1-I) and wetland 2 (B2-I)a Summary statistics

Temp. (°C) D.O. (mg l−1) Conductivity (ms−1 cm−1) pH (s.u.) Turbidity (NTU) DRP (mg l−1) TP (mg l−1)

CP-W (mean 9 S.E. (n))

B1-I (mean 9 S.E. (n))

B2-I (mean 9S.E. (n))

16.4 9 0.97 (50) 8.99 0.29 (47) 5999 23 (33) 8.1 90.06 (44) 55 9 13 (49) 359 5.9 (32) 1639 12 (58)

17.2 90.90 (53) 8.990.44 (53) 603 9 23 (32) 8.0 90.07 (46) 62 913 (50) 17 93.4 (55) 169911 (57)

17.5 90.89 (52) 8.3 9 0.37 (49) 606 9 25 (30) 8.0 90.05 (45) 64 915 (49) 19 9 3.4 (35) 164 9 12 (56)

Statistical comparison CP-W vs. B1-I

Temperature D.O. Conductivity pH Turbidity DRP TP

CP-W vs. B2-I

B1-I vs. B2-I

r

p

r

p

r

p

1.00 0.85 0.99 0.51 0.99 0.32 0.85

0.45 0.92 0.84 0.06 0.42 0.01 0.35

0.98 0.77 1.00 0.94 0.98 0.50 0.86

0.41 0.17 0.84 0.07 0.66 0.02 0.53

0.99 0.93 1.00 0.69 1.00 0.67 0.90

0.95 0.30 0.70 0.79 0.73 0.71 0.81

a Statistical comparisons include Pearson product-moment correlation coefficients (r) and P-values obtained by unpaired t-tests assuming unequal variance.

uptake and chemical precipitation and sorption mechanisms. As a rough estimate of total suspended solids, turbidity is representative of the sediment load carried by a sample of water. Upon entering the wetlands, water velocities decreased allowing settleable materials to leave the water column and deposit on the floor of the wetlands. Although on most sampling dates less turbid water exited the wetlands than entered, several apparent exports of turbid waters may be attributable to resuspension by wind or wave action. In shallow lakes and wetlands, resuspension has been determined to be a significant factor in sedimentation dynamics (Jurg, 1993). Also, the 1995 floods brought the common carp, Cyprinus carpio, into the wetlands which resulted in increased water column turbidity due to bioturbation and export of higher turbidity water on several occasions. However, mean

turbidity values after the floods were not significantly different from those before the floods (P \ 0.05).

4.3. Wetland phosphorus dynamics Wetland influent phosphorus concentrations demonstrated a great deal of temporal variability. A seasonal pattern was not readily apparent for total phosphorus concentrations which appeared to be more closely linked to precipitation events and river flow. Influent total phosphorus concentrations peaked at over 500 mg P l − 1 during the large flooding events of the summer of l995 (Fig. 4a). Dissolved reactive phosphorus also demonstrated peak levels during the floods and several times during late fall (Fig. 4b). Dissolved reactive phosphorus consistently represented 10–12% of total phosphorus concentrations throughout the entire wetland system.

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Concentrations of P and suspended sediments are often closely related in NPS pollution and in rivers. Phosphorus readily sorbs to soil and sediments and this pathway is the most prevalent mode of transport (Logan, 1980). Overbeck (1988) reported chat over 90% of the P load carried by streams and rivers is in the particulate inorganic form. Meybeck (1982) estimated that particulate P represents 95% of P naturally carried by rivers, of which 60% is particulate inorganic P. Fennessy et al. (1994) determined sedimentation to be an important P retention mechanism in similar wetland systems. Decreases in total phos-

phorus concentrations are probably linked to sedimentation in the ORWRP wetlands. Total phosphorus concentrations were correlated with turbidity values at the wetland influent and effluents (Fig. 5a). While turbidity may be related to suspended solids, correlation of turbidity with suspended solids is difficult because the size, shape and refractive index of particles affects the light-scattering properties of the suspension (APHA, 1989). Therefore, assuming a direct relationship between turbidity and suspended solids is speculative. Changes in P and turbidity values from wetland inflow to outflow demonstrated a

Table 6 Matrix of Pearson product-moment correlation coefficients for inflows and outflows of wetlands Temperature

D.O.

Conductivity

pH

Turbidity

DRP

TP

Cl

SO4

SiO2

Wetland 1 inflow Temperature 1 D.O. −0.29 Conductivity −0.49 pH 0.12 Turbidity 0.15 DRP 0.14 TP 0.24 Cl −0.05 SO4 0.09 SiO2 0.11

1 0.08 0.16 0.00 −0.24 −0.11 0.20 0.02 0.04

1 0.07 −0.62 −0.24 −0.19 −0.08 0.08 −0.07

1 −0.40 40.03 −0.29 0.20 0.12 −0.12

1 0.06 0.80 −0.32 −0.39 0.49

1 0.14 0.02 0.13 −0.18

1 −0.12 −0.05 0.07

1 0.91 −0.52

1 −0.58

1

Wetland 1 outflow Temperature 1 D.O. 0.03 Conductivity −0.64 pH 0.40 Turbidity 0.01 DRP 0.44 TP −0.13 Cl −0.54 SO4 −0.58 SiO2 0.63

1 −0.17 0.38 −0.09 −0.01 −0.27 −0.07 −0.14 −0.13

1 −0.35 −0.20 −0.49 0.12 0.83 0.93 −0.59

1 −0.43 0.23 −0.51 0.21 0.12 0.02

1 0.01 0.81 −0.39 −0.41 0.33

1 0.12 −0.16 −0.04 0.37

1 −0.20 −0.14 0.18

1 0.93 −0.52

1 −0.59

1

Wetland 2 outflow Temperature 1 D.O. −0.25 Conductivity −0.60 pH 0.16 Turbidity 0.08 DRP 0.33 TP 0.02 Cl −0.43 SO4 −0.52 SiO2 0.57

1 0.09 0.53 −0.27 −0.40 −0.31 0.07 0.03 −0.17

1 −0.15 −0.24 −0.26 −0.01 0.51 0.89 −0.52

1 −0.51 −0.16 −0.44 0.32 0.10 −0.21

1 0.14 0.79 −0.43 −0.42 0.41

1 0.49 −0.27 −0.16 0.59

1 −0.27 −0.17 0.28

1 0.89 −0.54

1 −0.59

1

R.W. Nairn, W.J. Mitsch / Ecological Engineering 14 (2000) 107–126

Fig. 4. Weekly (a) TP and (b) DRP dynamics at the wetland influent and effluents, 1994 – 1995.

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positive yet weak relationship (r =0.50, Fig. 5b). Removal of several outliers (those paired data with retention \200%) decreases the correlation coefficient to r =0.25. Therefore, although total phosphorus and turbidity values do demonstrate a positive relationship, quantitative conclusions regarding rates of P removal via sedimentation are speculative with the limited data available. Although total phosphorus retention may be related to sedimentation, decreases in dissolved reactive phosphorus concentrations in the wetlands are probably related to biological activity. A highly productive algal mat covered the majority of the surface area of both wetlands in 1994 and to a lesser extent in 1995. The potential for substantial P uptake by metabolically active algal mats has been documented. Adey et al. (1993) studied nutrient removal using man-

Fig. 5. Relationship between (a) turbidity and TP in wetland inflow and outflows (note log scales) and (b) change in TP and turbidity within the wetlands.

aged, attached algal production in raceways in Florida. Removal rates of 140 mg TP m − 2 day − 1 were determined with harvesting of biomass (0.34–0.43% P) on a 7–8 day harvest interval. Wu and Mitsch (1998) determined mean P concentrations of 1297 mg P l − 1 dry weight in the algal mat for samples collected during a drawdown at the ORWRP in August 1994. They determined a mean biomass of 235 g dry weight m − 2, resulting in a mean algal standing stock of approximately 0.30 g P m − 2. Inflow– outflow water quality data for the period prior to the drawdown demonstrate a mean mass retention of approximately 0.45 g DRP m − 2 for the wetlands. If it is assumed that algal P uptake occurs only from the water column, and neglecting resuspension of bioavailable P from the sediments, relatively short algal life cycles (which result in cyclic uptake and release of P) and other aspects of intrasystem cycling, algal uptake of DRP may account for 66% of DRP removal over the period of the algal bloom. On a mass basis, assuming maximum algal coverage of 86% of the wetlands (Wu and Mitsch, 1998), the algae in both wetlands contained approximately 5.2 kg P. Both wetlands retained only 2.7 kg P over the time of the bloom, therefore indicating the possibly temporally dynamic role of algal removal mechanisms without harvesting and removal of algal biomass. The highly productive nature of the wetland may have also produced conditions conducive to the direct precipitation of CaCO3. Phosphorus dynamics in wetlands are known to be closely linked to CaCO3 through direct precipitation of Ca–P compounds or coprecipitation and sorption to CaCO3 (Reddy et al., 1993). While not directly measured, chemical mechanisms may have affected P retention in the ORWRP wetlands. These processes, due to the relatively high alkalinity and Ca concentrations of Olentangy River water coupled with a highly productive wetland water column, may represent sustainable P removal mechanisms for the wetlands through the deposition and accumulation of Ca–P compounds.

R.W. Nairn, W.J. Mitsch / Ecological Engineering 14 (2000) 107–126 Table 7 Comparison of four methods of performance evaluation for TP retention by Wetlands 1 and 2 at the ORWRP

Paired retention (%) Mean retention (%) Unadjusted mass removal (g P m−2 year−1) Dilution adjusted mass removal (g P m−2 year−1)

Wetland 1 (mean 9 S.E.)

Wetland 2 (mean 9 S.E.)

59 94 62 5.64 91.33

54 95 58 5.19 91.49

6.6691.68

7.47 9 2.74

4.4. Wetland water quality performance e6aluation A reliable method of water quality improvement performance of created wetlands should be used that allows comparison of systems that vary in size and that receive different levels of pollutant loadings. Traditionally, concentration efficiency (CE%) has been utilised as a measure of performance. Including all available paired data points, mean percent retention of dissolved reactive phosphorus for wetlands 1 and 2 were 43 9 7 and 41 9 8%, respectively. Total phosphorus percent retention was 59 94 and 54 95% for wetlands 1 and 2 (Table 7). Concentration efficiency may also be calculated based on the mean influent and effluent values. Calculated in this way, percent retention for dissolved reactive phosphorus was 71% for wetland 1 and 67% for wetland 2. Total phosphorus retention was 62 and 58% for wetland 1 and 2, respectively (Table 7). Except in the most carefully controlled environments, the use of either method of concentration efficiency (or percent retention) as a measure of performance can be problematic and misleading (Hedin et al., 1994). A system which decreases pollutant concentrations from 10 to 1 mg l − l is calculated to perform as effectively as another system which may decrease concentrations from 1000 to 100 mg l − l (both are 90% efficient). The utility of this method of performance evaluation is dubious when comparing the pollutant removal capabilities of systems of different sizes or of systems which receive different pollutant loadings.

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For wetlands like the ORWRP, which receive waters of highly variable pollutant concentrations and flow rates, comparison of the same system on different days may lead to erroneous conclusions about pollutant removal rates and processes. Evaluation of performance should be conducted in a manner that takes into account pollutant loads and area of the treatment system. Calculation of area or volume adjusted pollutant removal rates may then be made based by matching flow rates and pollutant concentrations. Loads retained may then be calculated and retention apportioned to treatment area or volume. In this study, individual wetland area (10 000 m2) was used.Using this evaluation of performance, and excluding two flood-event outliers, the mean dissolved reactive phosphorus loads to the Olentangy River wetlands were calculated to be approximately 1.2 g P m − 2 year − 1. Total phosphorus loadings were between 8.5 and 10 g P m − 2 year − 1. For dissolved reactive phosphorus, the wetlands retained between 0.8 and 1.1 g P m − 2 year − 1. For total phosphorus, wetland 1 retained approximately 5.649 1.3 g P m − 2 year − 1 yet and wetland 2 retained approximately 5.199 1.5 g P m − 2 year − 1 (Table 7). The calculations above purposely exclude data collected during the two floods in 1995. If included, based on two pairs of water samples collected during or immediately after the floods, the annual total phosphorus removal rates increase to 21 and 24 g P m − 2 year − 1 for wetlands 1 and 2, respectively. These numbers are skewed upward by the massive P loads brought into each wetland by the floods (approximately 20–25 kg P per flood per wetland) directly related to the flood flows (30 000–90 000 m3 day − l). Each of the wetlands was estimated to retain approximately 7–9 kg P during each of the flood events. However, because NPS discharges are temporal and often stormevent driven, the ability of wetlands to function as P sinks during extreme events is crucial to their role in water quality improvement. In 1995, flood event phosphorus mass loading to both wetlands (102 kg over 2 days) was comparable to the summed pumped mass loads (132 kg over 244 days). Mass retention during the two 1-day flood events was 33 kg (35% of the total mass removal) compared to 62 kg (65% of total mass removal) for the 244 days of pumping.

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4.5. Effects of flow rate and phosphorus concentration on performance Pollutant removal processes in wetland ecosystems are dependent on the flow, velocity and retention time of water in the system. Percent retention in the ORWRP wetlands demonstrated no significant trend with pumped inflow rate (r 2 B0.2, Fig. 6a). Extreme inflow rates (\ 3000 m3 day − 1) resulted in some of the highest and lowest percent retention values. Percent retention was highest at normal operating flow rates of about 1000–1500 m3 day − 1. Mass removal on a per day basis did not demonstrate a significant relationship with flow rate (r 2 B0. 1, Fig. 6b). However, a slight positive trend is apparent. Percent retention demonstrates no relationship with inflow TP concentration (Fig. 6c). Mass removal, however, shows a slight positive trend (r 2 =0.41 for wetland 1 and 0.37 for wetland 2), indicating that concentration may be limiting loads at the ORWRP and not flows (Fig. 6d).

Increased P concentrations may result in increased rates of P removal. The successful exploitation of the many physical, chemical and biological processes responsible for pollutant removal in wetlands (e.g. sedimentation, algal and macrophytic uptake, sorption, precipitation) is dependent upon their kinetics in wetland water and soil. These processes occur at rates which rely on the amount of given pollutant in a given volume or area of wetland. Although pollutant concentration is important, a given wetland volume or area is exposed to a mass load, i.e. the product of concentration and flow. At some threshold, pollutant removal may become asymptotic and increased loads may result in increased pollutant export from the system. This situation may occur as soil exchange sites fill, biological uptake is inhibited or water velocities limit physical and chemical retention processes. Phosphorus loadings at the ORWRP wetlands are well below this threshold. The NPS P loadings are such that the rate of removal increases as loading increases (Fig. 7). While regression analy-

Fig. 6. Pumped inflow and concentration vs. TP removal relationships: (a) pumped inflow vs. percent retention, (b) pumped inflow vs. mass removal, (c) inflow concentration vs. percent retention, and (d) inflow concentration vs. mass removal.

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due to retention and burial of inorganic sediments, as indicated by other studies (Nairn, 1996).

4.6. Effects of season on performance

Fig. 7. Empirical TP loading vs. TP removal for the ORWRP wetlands.

sis shows that this relationship is not statistically significant (r 2 B 0.5), the increased rate of removal at increased loadings indicates that these wetlands are on the climbing limb of the theoretical curve. At the present time the rate of P removal in the ORWRP wetlands is loading-limited. The evaluation of P removal capabilities would require sufficient P loads to ensure that removal rates were not limited by absence of P. Although the ORWRP wetlands receive river water and are not considered treatment wetlands, a comparison was made to the first-order phosphorus retention models developed for these systems by Kadlec and Knight (1996) who report first-order areal removal rate constants, k, for 20 emergent marshes. Rate constant values ranged from 2.4 to 23.7 m year − 1 with a mean 9 S.D. of 12.1 96.1 m year − 1. Based upon mean intermediate and outflow sampling point data and mean hydraulic loading rates, a first-order areal removal rate constant of 13.3 m year − 1 is determined for the ORWRP wetlands. Using mean inflow and intermediate data, a k value of 23.6 m year − 1 is determined, near the maximum value reported by Kadlec and Knight (1996). It is interesting to note chat the maximum value reported by Kadlec and Knight (1996) was obtained from data collected at the Des Plaines River Experimental Wetlands, a system similar to the ORWRP in that the wetlands are located in an agricultural and urban watershed and receive pumped river water. Higher values of k may indicate phosphorus retention

Limited cold-weather sampling was conducted due to construction and maintenance activities at the ORWRP. Only 18 of 57 sampling dates on which paired inflow and outflow samples were collected for both wetlands did not occur during the growing season, defined as 15 April–15 October. For the 39 dates sampled during the growing season, percent retention of total phosphorus was 6993 and 639 5% for wetlands 1 and 2, respectively. Area-adjusted mass removals were 1893 and 15 93 mg P m − 2 day − 1. Differences between wetlands were not significant (PB 0.5). For the 18 non-growing season sampling dates in the early spring or late fall, percent retention of total phosphorus was 399 9 and 449 8% for wetlands 1 and 2 and mass removals were 7 95 and 8 9 4 mg P m − 2 day − 1. No significant differences existed between wetlands. Percent retention total phosphorus was significantly different (PB 0.05) between growing season and non-growing season for both wetlands but mass removals were not (P\ 0.05). This limited data set suggests that seasonality is important in the initial P retention function of created wetlands. Kadlec and Knight (1996) found percent P retention to vary little (B 10%) with season in the evaluation of 49 freshwater marshes that received wastewater. However, the mass balance approach for a single wastewater wetland in Ontario (Typha spp. monoculture) found greater P removal in the spring and autumn than in the winter and summer (Kadlec and Knight, 1996).

4.7. Effects of dilution on wetland performance In general, pollutant concentrations decrease in constructed wetlands by two mechanisms: (1) biogeochemical and physical processes occurring in the wetland water column, substrate and vegetation retain pollutants in the system; or (2) dilution results in lower concentration in the outflow than the inflow on a particular sampling day. Although

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surface runoff may cause substantial dilution effects in some systems, the landscape configuration and experimental design of the ORWRP wetlands substantially decreases the possibility of runoff being an important contributory factor. Direct precipitation may also cause dilution effects hampering the proper performance evaluation of wetlands constructed for water quality improvement. However, normal precipitation events would have little influence on water quality improvement performance of the ORWRP wetlands (a 3-cm rain event would add 300 m3 or approximately 5% to the volume of each of the wetlands when water levels were at that of normal operations). Groundwater influxes may also cause dilution, but as indicated by the hydrologic budget calculations, seepage is of limited magnitude in the ORWRP wetlands. In the ORWRP wetlands, the effects of dilution may also be manifested in the matching of inflow and outflow samples. If influent water quality changes in a time period shorter than the retention time of the system, the matching of influent and effluent samples is erroneous. An attempt was made to adjust pollutant for the effects of dilution based on the use of a conservative ion. By definition, the concentration of a conservative ion changes only by dilution or evaporation as it passes through a treatment system (Stauffer, 1985; Bencala et al., 1987; Hedin and Nairn, 1993; Hedin et al., 1994). In this study, chloride was used as a conservative ion to adjust for dilution effects. The biogeochemistry of Cl is relatively inert in wetland ecosystems. Chloride does not significantly enter redox reactions, does not form important solute or salt complexes and is not absorbed onto mineral surfaces (Hem, 1989). Kadlec (1979) used Cl as an inert tracer in his study of nutrient removal from wastewater in a natural wetland. Dilution factors were calculated as the change in the concentration of the conservative ion between sampling points for paired data sets. Chloride concentrations were determined on 38 paired sets of inflow and outflow samples taken from April 1994 through early July 1995. Chloride concentration at the wetland influents ranged from 8 to 76 mg l − l (mean=37 mg l − 1). effluent Cl concentrations ranged from 7 to 98 mg l − 1 for wetland 1

(mean=38 mg l − 1) and from 7 to 75 mg l − 1 for wetland 2 (mean= 38 mg l − 1). Chloride concentrations were not significantly different between wetland inflows and outflows or between wetland outflows. Mean dilution factors were 1.06 for wetland 1 and 1.08 for wetland 2. The magnitude of the dilution factors demonstrates the small role dilution plays in these systems. Dilution factors near unity, as found for the Olentangy River wetlands, indicate essentially no effect of dilution. The sole effect of evapotranspiration most likely resulted in increased Cl concentrations at the outflows. Discounting precipitation, calculated and measured rates of evapotranspiration result in enrichment factors of 1.01–1.03, very near those calculated by Cl concentration changes.

4.8. Comparison to phosphorus remo6al by floodplains Natural riparian areas have displayed a capacity to retain phosphorus, thus preventing detrimental impacts to adjacent waterways. Mitsch et al. (1979) found that an alluvial cypress swamp in Illinois retained approximately 3.48 g P m − 2 year − 1 via sedimentation during flooding. This represented 10 times the amount of P the swamp annually released to the river. Peterjohn and Correll (1984) found that a Maryland riparian forest adjacent to agricultural fields retained 0.29 g P m − 2 year − 1. Lowrance et al. (1984) determined a P retention rate of 0.17 g P m − 2 year − 1 for a forested riparian area under similar land use conditions in Georgia. Chescheir et al. (Chescheir et al., 1991a,b) examined the ability of natural, yet manipulated, wetland buffer areas to treat pumped agricultural drainage waters containing mean total phosphorus concentrations of 250 mg P l − 1. The wetlands effectively removed P. but retention was dependent on hydraulic loading rates. Detenbeck et al. (1993), in a study of 33 lake watersheds in Minnesota, found that wetland type may be important in total P removal capacity at the landscape level. Recent studies of the Cache River Basin of Arkansas provide similar results (Dortch, 1996; Kleiss, 1996). In a phosphorus retention modeling study of forested wetlands of this watershed, Dortch (1996) calculated a

R.W. Nairn, W.J. Mitsch / Ecological Engineering 14 (2000) 107–126

mean first order rate constants of 3 m year − 1, comparable to values reported by Kadlec and Knight for forested wetlands. Mitsch et al. (1995a) investigated the retention of P under different hydrologic loading rates in created riparian wetlands in northeast Illinois at the Des Plaines River Experimental Wetlands. They found that high-flow wetlands (receiving 34 – 97 cm week − 1) removed 1.4 – 2.9 g P m − 2 year − 1 while low-flow wetlands (receiving 7 – 16 cm week − 1) removed 0.4 – 1.71 g P m − 2 year − 1. These data suggest that P retention may increase with loading at these near-ambient concentrations. A study by Niswander and Mitsch (1995) supports the hypothesis that removal rates of systems receiving NPS P loads are often load limited. A replacement wetland in central Ohio received relatively high loadings of approximately 18 g P m − 2 year − 1 yet and retained 2.9 g P m − 2 year − 1. The ORWRP wetlands performed in a similar manner to these published results. Excluding two flood-event outliers, total phosphorus loadings to the ORWRP wetlands were between 8.5 and 10 g P m − 2 year − 1. Wetland 1 retained approximately 5.64+ 1.3 g P m − 2 year − 1 and wetland 2 retained approximately 5.199 1.5 g P m − 2 year − 1. Mineral sediment deposition in these first two growing seasons may result in elevated total phosphorus removals. Further study will determine the sustainability of these removal rates.

5. Conclusions The establishment of a hydrologic regime similar to those of natural riparian marshes assisted in the development of wetland processes affecting water quality. Both unplanted and planted wetlands effectively improved the quality of river water by retaining P and decreasing turbidity. Planted wetland vegetation showed limited demonstrable effects on water quality changes in the first two growing seasons. Both wetlands helped to improve the general quality of the river water, decreasing turbidity and conductivity levels and increasing mean dissolved oxygen. Decreased flow velocities and high rates

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of biological productivity influenced these processes. Both wetlands acted as effective sinks for total and dissolved reactive phosphorus. Phosphorus removal was not significantly different between planted and unplanted wetlands (P \ 0.05). Decreases in P concentrations by dilution were of limited importance. Changes in turbidity and TP in the Olentangy River wetlands support the premise that P retention in wetlands is often linked to removal of suspended solids via sedimentation. Extensive and highly productive algal coverage in both wetlands and the subsequent deposition and decomposition of the algal mat may have had a substantial influence on P retention through biological uptake and chemical sorption and coprecipitation with CaCO3. Over the limited range of flows used in this study, P removal rates were not generally affected by hydrologic loading rates or P concentrations. Phosphorus removal capabilities of the Olentangy River wetlands appear to be loading-limited. Under extreme P loading conditions, the wetlands retained greater amounts of P. Floods are extremely significant events in evaluation of overall water quality improvement. Phosphorus retention for each wetland during each of the floods was estimated to be approximately 8 or 32 kg P for both wetlands over both floods (35% of the total mass removal). Some cold-weather sampling and analysis indicated potentially important seasonal impacts on P removal performance. Evaluation of water quality improvement in created riparian wetlands by use of input–output budgets is beneficial and indicative of the important role of these systems in the landscape. However, ‘black-box’ studies are of limited utility in the understanding of ecosystem function and assist little with future ecosystem design. The elucidation of removal mechanisms and rates is necessary to fully assess and optimize the capabilities of wetlands for NPS pollution control. Created riparian wetlands, placed at the appropriate location in the landscape in order to maintain an adequate hydrologic regime, can help restore the quality of rivers and streams. Created wetlands represent an opportunity to ameliorate some of the detrimental influences of humankind on aquatic systems and provide additional

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benefits, e.g. habitat creation. The self-designing ecological and biogeochemical diversity and unique landscape position of wetlands allow them to be a suitable and practical application of ecological engineering. Returning water to its prominent role in the landscape through the creation and restoration of riparian wetlands holds promise as a tool for attaining an ecologically sustainable future.

Acknowledgements This paper is number 00-003 of Olentangy River Wetland Research Park.

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