- Email: [email protected]
Responses of wetland plants to ammonia and water level
Ecological Engineering 18 (2002) 257– 264
www.elsevier.com/locate/ecoleng
Responses of wetland plants to ammonia and water level Ernest Clarke a,1, Andrew H. Baldwin a,b,* a
Marine – Estuarine –En6ironmental Sciences Program, Uni6ersity of Maryland, College Park, MD 20742, USA b Department of Biological Resources Engineering, Uni6ersity of Maryland, College Park, MD 20742, USA Received 29 September 2000; received in revised form 15 February 2001; accepted 16 February 2001
Abstract Constructed wetland systems receiving animal wastewater may enhance water quality when designed, operated, and maintained properly. In the case of wetlands designed to treat animal waste, system effectiveness may be limited by high ammonia concentrations and inundation, conditions that can adversely affect macrophytic vegetation. We conducted a 4-month greenhouse experiment to assess the impact of ammonia concentration and water level on plants commonly used in constructed wetlands for treating animal waste. We examined the effects of ammonia concentration (0, 50, 100, 200 and 400 mg/l) on the growth and biomass production of Juncus effusus, Sagittaria latifolia, Schoenoplectus tabernaemontani, Typha angustifolia, and Typha latifolia. We also explored interactions between ammonia concentration (0, 50, 100, 200 and 400 mg/l) and water level (flooded and nonflooded conditions) for S. tabernaemontani and T. latifolia. We found that ammonia levels in excess of 200 mg/l inhibited growth for J. effusus, S. latifolia, and T. latifolia after a period of weeks, and levels in excess of 100 mg/l similarly inhibited growth for S. tabernaemontani. Ammonia levels in the range studied had an ambiguous effect on T. angustifolia. Affected species demonstrated similar fertilization/inhibition responses to increased ammonia, but important differences were noted between species. Flooded conditions of 10 cm did not significantly increase ammonia toxicity to S. tabernaemontani or T. latifolia. Our results emphasize the need for careful consideration of the species used in treatment wetlands, and suggest that management of ammonia concentration may enhance plant growth and system function. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Ammonia toxicity; Constructed wetlands; Wastewater treatment; Juncus effusus; Sagittaria latifolia; Schoenoplectus tabernaemontani; Typha angustifolia; Typha latifolia
1. Introduction * Corresponding author. Present address: Department of Biological Resources Engineering, University of Maryland, College Park, MD 20742, USA. Tel.: + 1-301-4011198; Fax: +1-301-3149023. E-mail address: [email protected] (A.H. Baldwin). 1 Present address: National Audubon Society, Starr Ranch Sanctuary, 100 Bell Canyon Road, Trabuco Canyon, CA 92679, USA.
Macrophytic vegetation plays a critical role in constructed wetlands used to treat wastewater from dairy operations and other concentrated animal production facilities (Kadlec and Knight, 1996). Constructed wetland systems are designed to utilize water quality improvement processes occurring in natural wetlands, including high pri-
0925-8574/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 8 5 7 4 ( 0 1 ) 0 0 0 8 0 - 5
258
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
mary productivity, low flow conditions, and oxygen transfer to anaerobic sediments (Brix, 1993; Kadlec and Knight, 1996). Several of these processes are strongly linked to functional characteristics of macrophytes: plants uptake nutrients directly, oxygenate the soil, reduce water flow, and provide surfaces for microbial colonization (Surrency, 1993; Brix, 1994). However, the extreme conditions found in animal wastewater treatment systems may exceed the tolerance of aquatic plants (Surrency, 1993), limiting both plant survivorship and treatment potential. In particular, plant survivorship in constructed wetlands decreases when partially aerated soil conditions are not maintained (Kadlec and Knight, 1996), and when high ammonia concentrations are typical (Surrency, 1993). Kadlec and Knight (1996) summarized nutrient levels for several natural wetland systems including a marsh, a cypress dome, a bog, and a fen, and report that all have ammonia concentrations below 2 mg/l. Ammonia concentrations in municipal wastewater are typically higher than in natural systems, ranging from 12 to 50 mg/l (Metcalf & Eddy, Inc., 1991). Ammonia concentrations in constructed wetlands treating animal wastes are higher still, often exceeding 100 mg/l and ranging as high as 400 to 500 mg/l (Hammer, 1992; Kadlec and Knight, 1996). Concentrations in this range may exceed what plants need to maximize biomass, and additionally may inhibit plant growth. While ammonia has been shown to be toxic to a variety of plant species (Hageman, 1984; Wang, 1991; Dijk and Eck, 1995; Magalha˜ es et al., 1995), few studies have examined ammonia toxicity to wetland plants at concentrations similar to those found in animal waste (Hill et al., 1997). In an observational study, Surrency (1993) noted that Typha latifolia L. was stressed by ammonia concentrations that averaged 160– 170 mg/l, while Schoenoplectus tabernaemontani (K.C. Gmel.) Palla tolerated the extreme conditions. Hill et al. (1997) exposed five wetland plant species to ammonia concentrations between 20.5 and 82.4 mg/l in a field-scale experiment, and found that only Schoenoplectus acutus var. acutus (Muhl. ex Bigelow) A. & D. L¦ve was negatively affected in
this concentration range. In a 2-year mesocosm study, Humenik et al. (1999) found Juncus effusus L. and S. tabernaemontani to be unaffected by ammonia concentrations of 175 mg/l, and tolerant of concentrations of 350 mg/l. To examine the effects of elevated ammonia and inundation on wetland plants, we conducted a greenhouse study exposing five species to combinations of ammonia and water level. For the study, ammonia was defined as NH3 + NH4OH + NH+ 4 (Ponnamperuma, 1972). The impacts of ammonia levels of 0, 50, 100, 200, and 400 mg/l were examined for three species: J. effusus, Sagittaria latifolia Willd., and Typha angustifolia L. Interactions between these ammonia concentrations and water levels were examined for two species: S. tabernaemontani and T. latifolia. Ammonia and water level effects on growth rate and biomass production were evaluated over a 4-month study.
2. Materials and methods
2.1. Plant material We purchased J. effusus, S. latifolia, S. tabernaemontani, T. angustifolia and T. latifolia plants in June 1998 from Environmental Concern, Inc., St. Michaels, MD. T. angustifolia was purchased as bare-root plants, while the other four species were purchased in quart-sized containers. Plants were transferred to 3-gallon pots filled with topsoil and allowed to establish in tap water until the experimental treatments were applied on 22 July 1998.
2.2. Experimental set-up We constructed 15 wetland tanks measuring approximately 2.0 m× 0.4 m× 0.4 m deep in a greenhouse at the United States Department of Agriculture, Natural Resources Conservation Service, National Plant Materials Center on the Beltsville Agricultural Research Center, Prince George’s County, MD. The tanks were arranged in three experimental blocks to accommodate the five ammonia treatments (0, 50, 100, 200, and 400 mg/l ammonia) and two water level treatments
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
(flooded and nonflooded) planned for the study. One pot of each species was randomly assigned to each tank to examine ammonia effects, for a total of five plants per tank and 75 plants for the experiment. Additional pots of S. tabernaemontani and T. latifolia were added to each tank to examine ammonia and water level interactions, raising the total number of plants to 105 for the study. Beginning in September, supplemental lighting was utilized to extend the photoperiod to a 14 h light/8 h dark cycle.
2.3. Ammonia and water le6el treatments We randomly assigned the ammonia treatments to tanks within each block. Treatment solutions were prepared with reagent-grade ammonium chloride (Fisher Scientific, Fair Lawn, NJ, USA) and tap water, and 40 gallons of solution was initially added to each tank. Water level treatments were randomly assigned to S. tabernaemontani and T. latifolia plants within tanks. Nonflooded plants were elevated to maintain water level at the surface of the soil. Flooded conditions were reached by submerging plants to a depth of 10 cm below the water surface.
2.4. Water monitoring We monitored pH, ammonia concentration, and water level biweekly to detect and correct deviations from desired treatment levels. Deviations in these parameters were expected due to such factors as nutrient uptake, evapotranspiration, nitrification, and ammonia volatilization. We measured pH using an Orion (Orion, Beverly, MA, USA) portable pH/ISE Meter (Model 290A) and a Triode pH electrode (Model 91-57), and found that pH generally remained between 6.0 and 7.0 for all the tanks over the study duration. Ammonia concentration was determined with an Orion portable pH/ISE Meter (Model 290A) and an Orion Ammonia Electrode (Model 95-12), and solution was added when concentrations deviated from desired treatment levels. Over the duration of the study, mean ammonia concentrations were
259
0.139 0.04, 38.119 1.21, 90.339 1.12, 180.739 1.57, and 393.919 3.65 mg/l for treatments of 0, 50, 100, 200, and 400 mg/l ammonia, respectively. Water level was monitored visually, and treatments were maintained by adding solution until plants were flooded as planned.
2.5. Growth measurements Plants were first censused on 22 July 1998, immediately before application of ammonia and water level treatments. The numbers of stems per pot were counted for the five study species, and the numbers of ramets per pot was recorded for T. angustifolia and T. latifolia. The length of all leaves in each pot was measured for all species, providing total leaf length per plant as an indicator of above-ground biomass. Plant censuses were conducted in this manner three times following the initial census, breaking the experiment up into three roughly equal periods.
2.6. Har6est Above-ground biomass was harvested on 6 and 13 November 1998. Plant material was clipped at the ground surface, placed in labeled bags, and dried at 42°C and 12% humidity in a controlledenvironment chamber for \96 h. Dried specimens were weighed and used to construct linear relationships between leaf length and final biomass (SigmaPlot Version 4.01; SPSS, Chicago, IL). All regression slope coefficients were significantly different from zero (PB 0.0001), and adjusted r 2 values ranged from 0.95 to 0.98. Regression equations were used to estimate biomass from leaf length data for the pre-harvest monitoring events. Relative growth rate (RGR) per plant per period was calculated using the equation: RGR =
ln W2 − ln W1 t2 − t1
(1)
where W1 and W2 are nondestructive estimates of biomass for times t1 (beginning of period) and t2 (end of period), respectively (Beadle, 1982).
260
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
2.7. Data analysis A one-way analysis of variance (ANOVA) was conducted for J. effusus, S. latifolia, and T. angustifolia. In this analysis, final biomass was the dependent variable, and ammonia concentration was the independent variable. A two-way ANOVA was conducted on final biomass data for S. tabernaemontani and T. latifolia. Final biomass was again the dependent variable, and ammonia concentration and water level were the independent variables. Repeated measures analysis of variance (RMANOVA) was used to analyze RGR data for each species. All analyses were conducted with SAS Version 6.12 (SAS Institute, Cary, NC). Variance homogeneity and normality of observations were examined for each species, and variances were partitioned in a mixed model in the case of heterogeneous variances. To further visualize the effects of ammonia concentration on plant growth, nonlinear regression was used (SigmaPlot Version 4.01; SPSS, Chicago, IL). For each species, the best fit curve for the data was selected for the purpose of
prediction, recognizing that higher order terms may have no biological significance (Sokal and Rohlf, 1994).
3. Results
3.1. Effects of ammonia on biomass production Ammonia significantly affected final biomass for J. effusus (ANOVA P= 0.0238), S. tabernaemontani (ANOVA PB 0.0001), and T. latifolia (ANOVA PB 0.0001). Final biomass for T. angustifolia was not statistically affected by ammonia over the range of concentrations studied (ANOVA P= 0.2550). S. latifolia was not included in statistical analysis performed on final biomass data because all plants of that species senesced before the final harvest. However, S. latifolia was included in the RGR analysis. Biomass response curves varied among the species (Fig. 1). J. effusus final biomass data were fit with a quadratic response curve, while S. tabernaemontani, and T. latifolia were fit with log-nor-
Fig. 1. Relationship between total dry biomass and ammonia concentration for wetland plant species exposed to five ammonia levels for 4 months in the greenhouse. No response curve is displayed for T. angustifolia because this species was not statistically affected by ammonia over the concentration range studied.
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
261
mal curves. J. effusus reached maximum biomass at approximately 110 mg/l ammonia, S. tabernaemontani at 45 mg/l ammonia, and T. latifolia at 84 mg/l ammonia. J. effusus had lowest biomass at 400 mg/l ammonia, S. tabernaemontani at 0 mg/l ammonia, and T. latifolia at 0 mg/l ammonia. While the specifics of the response curves varied, the overall effect of increasing ammonia on final biomass was similar for these three species: biomass initially increased as ammonia concentration was increased, but eventually the higher concentrations reduced biomass production.
3.2. Effects of ammonia on relati6e growth rate Ammonia concentration significantly affected the RGR for J. effusus (RMANOVA P = 0.0010), S. latifolia (RMANOVA PB 0.0001), S. tabernaemontani (RMANOVA P B0.0001), and T. latifolia (RMANOVA P B0.0001), and did not affect the RGR for T. angustifolia (RMANOVA P = 0.8483; Fig. 2). Minimum RGR generally occurred in the 400 mg/l treatment for J. effusus, and in the 0 mg/l treatment for S. latifolia, S. tabernaemontani, and T. latifolia. Ammonia levels in excess of 200 mg/l reduced the RGR for J. effusus, S. latifolia, and T. latifolia, and levels in excess of 100 mg/l reduced RGR for S. tabernaemontani. RGR varied significantly over time for all five species (RMANOVA P B0.0001), with plants generally growing at slower rates as the study progressed.
3.3. Effects of ammonia and water le6el There was no significant impact of water level on biomass production for S. tabernaemontani (ANOVA P =0.9435) or T. latifolia (ANOVA P= 0.3067). There was also no significant interaction between ammonia concentration and water level for either species. As seen in Fig. 3, the final biomass of S. tabernaemontani was, at times, higher in the nonflooded pots (as in the 100 and 200 mg/l ammonia treatment groups), and at other times higher in the flooded pots (as in the 50 and 400 mg/l ammonia treatment groups). However, at ammonia concentrations of 100 mg/l or greater, biomass was always greater in nonflooded
Fig. 2. Relative growth rates of wetland plant species during 4 months growth at five ammonia levels in the greenhouse. Each period represents approximately 1.3 months. Period 3 data is lacking for S. latifolia because plants of this species senesced before that period’s end. Error bars represent 91S.E.
pots of T. latifolia, with the gap between the water level treatment groups increasing with increasing ammonia concentration (Fig. 3). This explains the low interaction P value for this species (ANOVA P=0.0692).
4. Discussion Ammonia significantly affected biomass production and relative growth rate for J. effusus, S. tabernaemontani, and T. latifolia. Ammonia concentrations above 100 mg/l reduced RGR for S. tabernaemontani after a period of weeks. Concentrations above 200 mg/l similarly reduced RGR for J. effusus and T. latifolia. Shorter periods of elevated ammonia did not appear to affect growth for the three species. A comparison of the biomass response curves for these plants illus-
262
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
trates both similarities and differences in ammonia effects (Fig. 1). Convex response curves resulted for each species, demonstrating that ammonia stimulates biomass production at low to moderate concentrations and inhibits biomass production at higher levels. Similar response curves have been demonstrated for ecosystems exposed to perturbations, particularly when the causal factor is a required component of the responding factor (Odum et al., 1979). While the biomass curves share this convex shape, striking differences exist between species curves (Fig. 1). First, the species maximized biomass at different ammonia levels, with J. effusus peaking at 110 mg/l, T. latifolia at 84 mg/l, and S. tabernaemontani at 45 mg/l. Second, T. latifolia produced more than twice the biomass of the other two species for most of the ammonia range studied. Third, the scale of the stimulation and inhibition varied, with T. latifolia exhibiting
Fig. 3. Total dry biomass of wetland plant species after 4 months growth at five ammonia levels and two water depths in the greenhouse. Error bars represent 9 1S.E.
the greatest relative response, followed by S. tabernaemontani and then by J. effusus. These findings indicate that T. latifolia and S. tabernaemontani exhibit a ‘competitive’ strategy, while J. effusus exhibits a ‘stress-tolerant’ strategy sensu Grime (1977). The observed differences in biomass response curves may affect vegetation dynamics in a constructed wetland system, as well as management techniques. While J. effusus was less inhibited by elevated ammonia concentration than T. latifolia or S. tabernaemontani, the higher productivity of these species may lead to the eventual displacement of J. effusus from a constructed wetland containing all three species. This hypothesis supports the concept of a trade off between stress tolerance and competitive ability noted elsewhere (Grace and Wetxel, 1981; Bertness, 1991), and could be explored in competition studies conducted along an ammonia concentration gradient. With regard to management, if biomass harvesting were planned in order to enhance nutrient removal in a constructed wetland, T. latifolia would be a better choice than J. effusus or S. tabernaemontani due to higher productivity. Biomass production and growth for T. angustifolia were not significantly affected by ammonia concentration. Lack of a treatment effect may be due to high ammonia tolerance of this species, or to experimental variability. Further trials with greater replication are needed to evaluate the response of T. angustifolia to elevated ammonia. Growth for S. latifolia was significantly affected by ammonia, with RGR reduced by ammonia concentrations above 200 mg/l. Ammonia effects on biomass production of this species went unmeasured because, despite the use of supplemental lighting to extend photoperiod, S. latifolia had senesced by the end of the experiment. Our observed decreases in RGR for this species may have been due to this senescence effect. The results of our study generally agree with the findings of Humenik et al. (1999) and Hill et al. (1997). Humenik et al. reported that J. effusus and S. tabernaemontani were tolerant of ammonia concentrations up to 175 mg/l. We observed a similar tolerance for J. effusus, with RGR only moderately affected by ammonia concentrations
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
up to 200 mg/l. While we found S. tabernaemontani growth to be negatively affected by concentrations of as low as 45 mg/l, reductions were not great up to 200 mg/l. Hill et al. (1997) reported that S. latifolia and T. latifolia were unaffected by ammonia concentrations up to 82.4 mg/l. Our study extends the tolerance range of these two species, as we found their growth only moderately affected by ammonia concentrations up to 200 mg/l. Our results differ from observations made by Surrency (1993), who reported that ammonia concentrations averaging 160– 170 mg/l did not affect S. tabernaemontani, but did stress T. latifolia. We observed both species to be somewhat tolerant of ammonia concentrations in this range. Moreover, T. latifolia appeared to be more tolerant of elevated ammonia than S. tabernaemontani (Fig. 1). Flooded conditions of 10 cm did not significantly increase ammonia toxicity to S. tabernaemontani or T. latifolia relative to nonflooded but water-logged conditions. We were surprised that flooding did not reduce growth and biomass production, because the adverse effects of flooding have been documented for wetland plants (for example, McKee and Mendelssohn, 1989; Ernst, 1990; Gough and Grace, 1998). In future studies, we recommend that nonflooded plants be raised 10 cm above the water surface, and therefore exposed to more aerobic conditions. In conclusion, our findings suggest that the effectiveness of wetlands built to treat ammonialaden wastewater can be enhanced through selection of plant species tolerant of the ammonia level in influent water. If vegetation harvesting is planned, species with higher growth rates are better choices, but these may also be less tolerant of elevated ammonia concentrations than slower growing species. Water level may not be important in modifying the effect of ammonia in certain species, but more research is needed on the role of water level in constructed wetlands.
Acknowledgements The authors thank Dr Larry W. Douglas and Dr E´ ric LeBlanc for providing assistance with
263
statistics. They also thank John Adornato, Joann Alexander, Carroll M. Barrack, Laurie Clarke, Ellen DeRico, Mike Egnotovich, Troy Hershberger, Kathy Kamminga, Kimberly Monahan, Frank Pendleton, Jennifer Schaafsma, and Rebecca Stack for their help in the greenhouse. This research was supported by the Maryland Department of Natural Resources and the United States Environmental Protection Agency. Finally, the authors thank Jennifer Kujawski, Kathy Davis, and the USDA National Plant Materials Center for providing technical assistance and greenhouse space.
References Beadle, C.L., 1982. Plant growth analysis. In: Coombs, J., Hall, D.O. (Eds.), Techniques in Bioproductivity and Photosynthesis. Pergamon Press, New York City, NY, pp. 20 – 24. Bertness, M.D., 1991. Zonation of Spartina patens and Spartina alterniflora in a New England salt marsh. Ecology 72, 138 – 148. Brix, H., 1993. Wastewater treatment in constructed wetlands: system design, removal processes, and treatment performance. In: Moshiri, G.A. (Ed.), Constructed Wetlands for Water Quality Improvement. Lewis Publishers, Boca Raton, FL, pp. 9 – 22. Brix, H., 1994. Functions of macrophytes in constructed wetlands. Water Sci. Technol. 29, 71 – 78. Dijk, E., Eck, N., 1995. Ammonium toxicity and nitrate response of axenically grown Dactylorhiza incarnata seedlings. New Phytol. 131, 361 – 367. Ernst, W.H.O., 1990. Ecophysiology of plants in waterlogged and flooded environments. Aquat. Botany 38, 73 – 90. Gough, L., Grace, J.B., 1998. Effects of flooding, salinity and herbivory on coastal plant communities, Louisiana, United States. Oecologia 117, 527 – 535. Grace, J.B., Wetxel, R.G., 1981. Habitat partitioning and competitive displacement in cattails (Typha): experimental field studies. Am. Nat. 118, 463 – 474. Grime, J.P., 1977. Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory. Am. Nat. 111, 1169 – 1194. Hageman, R.H., 1984. Ammonium versus nitrate nutrition of higher plants. In: Nitrogen in Crop Production. ASACSSA-SSSA, Madison, WI, pp. 67 – 82. Hammer, D.A., 1992. Designing constructed wetlands systems to treat agricultural nonpoint source pollution. Ecol. Eng. 1, 49 – 82. Hill, D.T., Payne, V.W.E., Rogers, J.W., Kown, S.R., 1997. Ammonia effects on the biomass production of five constructed wetland plant species. Bioresour. Technol. 62, 109 – 113.
264
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
Humenik, F.J., Szogi, A.A., Hunt, P.G., Broome, S., Rice, M., 1999. Wastewater utilization: a place for managed wetlands. Asian – Australas. J. Anim. Sci. 12, 629 – 632. Kadlec, R.H., Knight, R.L., 1996. Treatment Wetlands. Lewis Publishers, Boca Raton, FL. Magalha˜ es, J.R., Machado, A.T., Huber, D.M., 1995. Similarities in response of maize genotypes to water logging and ammonium toxicity. J. Plant Nutr. 18, 2339 –2346. McKee, K.L., Mendelssohn, I.A., 1989. Response of a freshwater marsh plant community to increased salinity and increased water level. Aquat. Botany 34, 301 – 316. Metcalf & Eddy, Inc., 1991. In: Tchobanoglous, Burton, F.L. (Rev.). Wastewater Engineering, Treatment, Disposal, and Reuse, third ed. McGraw-Hill, New York City, NY.
Odum, E.P., Finn, J.T., Franz, E.H., 1979. Perturbation theory and the subsidy – stress gradient. Bioscience 29, 349 – 352. Ponnamperuma, F.N., 1972. The chemistry of submerged soils. Adv. Agron. 24, 29 – 96. Sokal, R.R., Rohlf, J.F., 1994. Biometry: The Principles and Practice Of Statistics in Biological Research, Third ed. WH Freeman and Co., New York City, NY. Surrency, D., 1993. Evaluation of aquatic plants for constructed wetlands. In: Moshiri, G.A. (Ed.), Constructed Wetlands for Water Quality Improvement. Lewis Publishers, Boca Raton, FL, pp. 349– 357. Wang, W., 1991. Ammonia toxicity to macrophytes (common duckweed and rice) using static and renewal methods. Environ. Toxicol. Chem. 10, 1173 – 1177.
www.elsevier.com/locate/ecoleng
Responses of wetland plants to ammonia and water level Ernest Clarke a,1, Andrew H. Baldwin a,b,* a
Marine – Estuarine –En6ironmental Sciences Program, Uni6ersity of Maryland, College Park, MD 20742, USA b Department of Biological Resources Engineering, Uni6ersity of Maryland, College Park, MD 20742, USA Received 29 September 2000; received in revised form 15 February 2001; accepted 16 February 2001
Abstract Constructed wetland systems receiving animal wastewater may enhance water quality when designed, operated, and maintained properly. In the case of wetlands designed to treat animal waste, system effectiveness may be limited by high ammonia concentrations and inundation, conditions that can adversely affect macrophytic vegetation. We conducted a 4-month greenhouse experiment to assess the impact of ammonia concentration and water level on plants commonly used in constructed wetlands for treating animal waste. We examined the effects of ammonia concentration (0, 50, 100, 200 and 400 mg/l) on the growth and biomass production of Juncus effusus, Sagittaria latifolia, Schoenoplectus tabernaemontani, Typha angustifolia, and Typha latifolia. We also explored interactions between ammonia concentration (0, 50, 100, 200 and 400 mg/l) and water level (flooded and nonflooded conditions) for S. tabernaemontani and T. latifolia. We found that ammonia levels in excess of 200 mg/l inhibited growth for J. effusus, S. latifolia, and T. latifolia after a period of weeks, and levels in excess of 100 mg/l similarly inhibited growth for S. tabernaemontani. Ammonia levels in the range studied had an ambiguous effect on T. angustifolia. Affected species demonstrated similar fertilization/inhibition responses to increased ammonia, but important differences were noted between species. Flooded conditions of 10 cm did not significantly increase ammonia toxicity to S. tabernaemontani or T. latifolia. Our results emphasize the need for careful consideration of the species used in treatment wetlands, and suggest that management of ammonia concentration may enhance plant growth and system function. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Ammonia toxicity; Constructed wetlands; Wastewater treatment; Juncus effusus; Sagittaria latifolia; Schoenoplectus tabernaemontani; Typha angustifolia; Typha latifolia
1. Introduction * Corresponding author. Present address: Department of Biological Resources Engineering, University of Maryland, College Park, MD 20742, USA. Tel.: + 1-301-4011198; Fax: +1-301-3149023. E-mail address: [email protected] (A.H. Baldwin). 1 Present address: National Audubon Society, Starr Ranch Sanctuary, 100 Bell Canyon Road, Trabuco Canyon, CA 92679, USA.
Macrophytic vegetation plays a critical role in constructed wetlands used to treat wastewater from dairy operations and other concentrated animal production facilities (Kadlec and Knight, 1996). Constructed wetland systems are designed to utilize water quality improvement processes occurring in natural wetlands, including high pri-
0925-8574/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 8 5 7 4 ( 0 1 ) 0 0 0 8 0 - 5
258
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
mary productivity, low flow conditions, and oxygen transfer to anaerobic sediments (Brix, 1993; Kadlec and Knight, 1996). Several of these processes are strongly linked to functional characteristics of macrophytes: plants uptake nutrients directly, oxygenate the soil, reduce water flow, and provide surfaces for microbial colonization (Surrency, 1993; Brix, 1994). However, the extreme conditions found in animal wastewater treatment systems may exceed the tolerance of aquatic plants (Surrency, 1993), limiting both plant survivorship and treatment potential. In particular, plant survivorship in constructed wetlands decreases when partially aerated soil conditions are not maintained (Kadlec and Knight, 1996), and when high ammonia concentrations are typical (Surrency, 1993). Kadlec and Knight (1996) summarized nutrient levels for several natural wetland systems including a marsh, a cypress dome, a bog, and a fen, and report that all have ammonia concentrations below 2 mg/l. Ammonia concentrations in municipal wastewater are typically higher than in natural systems, ranging from 12 to 50 mg/l (Metcalf & Eddy, Inc., 1991). Ammonia concentrations in constructed wetlands treating animal wastes are higher still, often exceeding 100 mg/l and ranging as high as 400 to 500 mg/l (Hammer, 1992; Kadlec and Knight, 1996). Concentrations in this range may exceed what plants need to maximize biomass, and additionally may inhibit plant growth. While ammonia has been shown to be toxic to a variety of plant species (Hageman, 1984; Wang, 1991; Dijk and Eck, 1995; Magalha˜ es et al., 1995), few studies have examined ammonia toxicity to wetland plants at concentrations similar to those found in animal waste (Hill et al., 1997). In an observational study, Surrency (1993) noted that Typha latifolia L. was stressed by ammonia concentrations that averaged 160– 170 mg/l, while Schoenoplectus tabernaemontani (K.C. Gmel.) Palla tolerated the extreme conditions. Hill et al. (1997) exposed five wetland plant species to ammonia concentrations between 20.5 and 82.4 mg/l in a field-scale experiment, and found that only Schoenoplectus acutus var. acutus (Muhl. ex Bigelow) A. & D. L¦ve was negatively affected in
this concentration range. In a 2-year mesocosm study, Humenik et al. (1999) found Juncus effusus L. and S. tabernaemontani to be unaffected by ammonia concentrations of 175 mg/l, and tolerant of concentrations of 350 mg/l. To examine the effects of elevated ammonia and inundation on wetland plants, we conducted a greenhouse study exposing five species to combinations of ammonia and water level. For the study, ammonia was defined as NH3 + NH4OH + NH+ 4 (Ponnamperuma, 1972). The impacts of ammonia levels of 0, 50, 100, 200, and 400 mg/l were examined for three species: J. effusus, Sagittaria latifolia Willd., and Typha angustifolia L. Interactions between these ammonia concentrations and water levels were examined for two species: S. tabernaemontani and T. latifolia. Ammonia and water level effects on growth rate and biomass production were evaluated over a 4-month study.
2. Materials and methods
2.1. Plant material We purchased J. effusus, S. latifolia, S. tabernaemontani, T. angustifolia and T. latifolia plants in June 1998 from Environmental Concern, Inc., St. Michaels, MD. T. angustifolia was purchased as bare-root plants, while the other four species were purchased in quart-sized containers. Plants were transferred to 3-gallon pots filled with topsoil and allowed to establish in tap water until the experimental treatments were applied on 22 July 1998.
2.2. Experimental set-up We constructed 15 wetland tanks measuring approximately 2.0 m× 0.4 m× 0.4 m deep in a greenhouse at the United States Department of Agriculture, Natural Resources Conservation Service, National Plant Materials Center on the Beltsville Agricultural Research Center, Prince George’s County, MD. The tanks were arranged in three experimental blocks to accommodate the five ammonia treatments (0, 50, 100, 200, and 400 mg/l ammonia) and two water level treatments
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
(flooded and nonflooded) planned for the study. One pot of each species was randomly assigned to each tank to examine ammonia effects, for a total of five plants per tank and 75 plants for the experiment. Additional pots of S. tabernaemontani and T. latifolia were added to each tank to examine ammonia and water level interactions, raising the total number of plants to 105 for the study. Beginning in September, supplemental lighting was utilized to extend the photoperiod to a 14 h light/8 h dark cycle.
2.3. Ammonia and water le6el treatments We randomly assigned the ammonia treatments to tanks within each block. Treatment solutions were prepared with reagent-grade ammonium chloride (Fisher Scientific, Fair Lawn, NJ, USA) and tap water, and 40 gallons of solution was initially added to each tank. Water level treatments were randomly assigned to S. tabernaemontani and T. latifolia plants within tanks. Nonflooded plants were elevated to maintain water level at the surface of the soil. Flooded conditions were reached by submerging plants to a depth of 10 cm below the water surface.
2.4. Water monitoring We monitored pH, ammonia concentration, and water level biweekly to detect and correct deviations from desired treatment levels. Deviations in these parameters were expected due to such factors as nutrient uptake, evapotranspiration, nitrification, and ammonia volatilization. We measured pH using an Orion (Orion, Beverly, MA, USA) portable pH/ISE Meter (Model 290A) and a Triode pH electrode (Model 91-57), and found that pH generally remained between 6.0 and 7.0 for all the tanks over the study duration. Ammonia concentration was determined with an Orion portable pH/ISE Meter (Model 290A) and an Orion Ammonia Electrode (Model 95-12), and solution was added when concentrations deviated from desired treatment levels. Over the duration of the study, mean ammonia concentrations were
259
0.139 0.04, 38.119 1.21, 90.339 1.12, 180.739 1.57, and 393.919 3.65 mg/l for treatments of 0, 50, 100, 200, and 400 mg/l ammonia, respectively. Water level was monitored visually, and treatments were maintained by adding solution until plants were flooded as planned.
2.5. Growth measurements Plants were first censused on 22 July 1998, immediately before application of ammonia and water level treatments. The numbers of stems per pot were counted for the five study species, and the numbers of ramets per pot was recorded for T. angustifolia and T. latifolia. The length of all leaves in each pot was measured for all species, providing total leaf length per plant as an indicator of above-ground biomass. Plant censuses were conducted in this manner three times following the initial census, breaking the experiment up into three roughly equal periods.
2.6. Har6est Above-ground biomass was harvested on 6 and 13 November 1998. Plant material was clipped at the ground surface, placed in labeled bags, and dried at 42°C and 12% humidity in a controlledenvironment chamber for \96 h. Dried specimens were weighed and used to construct linear relationships between leaf length and final biomass (SigmaPlot Version 4.01; SPSS, Chicago, IL). All regression slope coefficients were significantly different from zero (PB 0.0001), and adjusted r 2 values ranged from 0.95 to 0.98. Regression equations were used to estimate biomass from leaf length data for the pre-harvest monitoring events. Relative growth rate (RGR) per plant per period was calculated using the equation: RGR =
ln W2 − ln W1 t2 − t1
(1)
where W1 and W2 are nondestructive estimates of biomass for times t1 (beginning of period) and t2 (end of period), respectively (Beadle, 1982).
260
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
2.7. Data analysis A one-way analysis of variance (ANOVA) was conducted for J. effusus, S. latifolia, and T. angustifolia. In this analysis, final biomass was the dependent variable, and ammonia concentration was the independent variable. A two-way ANOVA was conducted on final biomass data for S. tabernaemontani and T. latifolia. Final biomass was again the dependent variable, and ammonia concentration and water level were the independent variables. Repeated measures analysis of variance (RMANOVA) was used to analyze RGR data for each species. All analyses were conducted with SAS Version 6.12 (SAS Institute, Cary, NC). Variance homogeneity and normality of observations were examined for each species, and variances were partitioned in a mixed model in the case of heterogeneous variances. To further visualize the effects of ammonia concentration on plant growth, nonlinear regression was used (SigmaPlot Version 4.01; SPSS, Chicago, IL). For each species, the best fit curve for the data was selected for the purpose of
prediction, recognizing that higher order terms may have no biological significance (Sokal and Rohlf, 1994).
3. Results
3.1. Effects of ammonia on biomass production Ammonia significantly affected final biomass for J. effusus (ANOVA P= 0.0238), S. tabernaemontani (ANOVA PB 0.0001), and T. latifolia (ANOVA PB 0.0001). Final biomass for T. angustifolia was not statistically affected by ammonia over the range of concentrations studied (ANOVA P= 0.2550). S. latifolia was not included in statistical analysis performed on final biomass data because all plants of that species senesced before the final harvest. However, S. latifolia was included in the RGR analysis. Biomass response curves varied among the species (Fig. 1). J. effusus final biomass data were fit with a quadratic response curve, while S. tabernaemontani, and T. latifolia were fit with log-nor-
Fig. 1. Relationship between total dry biomass and ammonia concentration for wetland plant species exposed to five ammonia levels for 4 months in the greenhouse. No response curve is displayed for T. angustifolia because this species was not statistically affected by ammonia over the concentration range studied.
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
261
mal curves. J. effusus reached maximum biomass at approximately 110 mg/l ammonia, S. tabernaemontani at 45 mg/l ammonia, and T. latifolia at 84 mg/l ammonia. J. effusus had lowest biomass at 400 mg/l ammonia, S. tabernaemontani at 0 mg/l ammonia, and T. latifolia at 0 mg/l ammonia. While the specifics of the response curves varied, the overall effect of increasing ammonia on final biomass was similar for these three species: biomass initially increased as ammonia concentration was increased, but eventually the higher concentrations reduced biomass production.
3.2. Effects of ammonia on relati6e growth rate Ammonia concentration significantly affected the RGR for J. effusus (RMANOVA P = 0.0010), S. latifolia (RMANOVA PB 0.0001), S. tabernaemontani (RMANOVA P B0.0001), and T. latifolia (RMANOVA P B0.0001), and did not affect the RGR for T. angustifolia (RMANOVA P = 0.8483; Fig. 2). Minimum RGR generally occurred in the 400 mg/l treatment for J. effusus, and in the 0 mg/l treatment for S. latifolia, S. tabernaemontani, and T. latifolia. Ammonia levels in excess of 200 mg/l reduced the RGR for J. effusus, S. latifolia, and T. latifolia, and levels in excess of 100 mg/l reduced RGR for S. tabernaemontani. RGR varied significantly over time for all five species (RMANOVA P B0.0001), with plants generally growing at slower rates as the study progressed.
3.3. Effects of ammonia and water le6el There was no significant impact of water level on biomass production for S. tabernaemontani (ANOVA P =0.9435) or T. latifolia (ANOVA P= 0.3067). There was also no significant interaction between ammonia concentration and water level for either species. As seen in Fig. 3, the final biomass of S. tabernaemontani was, at times, higher in the nonflooded pots (as in the 100 and 200 mg/l ammonia treatment groups), and at other times higher in the flooded pots (as in the 50 and 400 mg/l ammonia treatment groups). However, at ammonia concentrations of 100 mg/l or greater, biomass was always greater in nonflooded
Fig. 2. Relative growth rates of wetland plant species during 4 months growth at five ammonia levels in the greenhouse. Each period represents approximately 1.3 months. Period 3 data is lacking for S. latifolia because plants of this species senesced before that period’s end. Error bars represent 91S.E.
pots of T. latifolia, with the gap between the water level treatment groups increasing with increasing ammonia concentration (Fig. 3). This explains the low interaction P value for this species (ANOVA P=0.0692).
4. Discussion Ammonia significantly affected biomass production and relative growth rate for J. effusus, S. tabernaemontani, and T. latifolia. Ammonia concentrations above 100 mg/l reduced RGR for S. tabernaemontani after a period of weeks. Concentrations above 200 mg/l similarly reduced RGR for J. effusus and T. latifolia. Shorter periods of elevated ammonia did not appear to affect growth for the three species. A comparison of the biomass response curves for these plants illus-
262
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
trates both similarities and differences in ammonia effects (Fig. 1). Convex response curves resulted for each species, demonstrating that ammonia stimulates biomass production at low to moderate concentrations and inhibits biomass production at higher levels. Similar response curves have been demonstrated for ecosystems exposed to perturbations, particularly when the causal factor is a required component of the responding factor (Odum et al., 1979). While the biomass curves share this convex shape, striking differences exist between species curves (Fig. 1). First, the species maximized biomass at different ammonia levels, with J. effusus peaking at 110 mg/l, T. latifolia at 84 mg/l, and S. tabernaemontani at 45 mg/l. Second, T. latifolia produced more than twice the biomass of the other two species for most of the ammonia range studied. Third, the scale of the stimulation and inhibition varied, with T. latifolia exhibiting
Fig. 3. Total dry biomass of wetland plant species after 4 months growth at five ammonia levels and two water depths in the greenhouse. Error bars represent 9 1S.E.
the greatest relative response, followed by S. tabernaemontani and then by J. effusus. These findings indicate that T. latifolia and S. tabernaemontani exhibit a ‘competitive’ strategy, while J. effusus exhibits a ‘stress-tolerant’ strategy sensu Grime (1977). The observed differences in biomass response curves may affect vegetation dynamics in a constructed wetland system, as well as management techniques. While J. effusus was less inhibited by elevated ammonia concentration than T. latifolia or S. tabernaemontani, the higher productivity of these species may lead to the eventual displacement of J. effusus from a constructed wetland containing all three species. This hypothesis supports the concept of a trade off between stress tolerance and competitive ability noted elsewhere (Grace and Wetxel, 1981; Bertness, 1991), and could be explored in competition studies conducted along an ammonia concentration gradient. With regard to management, if biomass harvesting were planned in order to enhance nutrient removal in a constructed wetland, T. latifolia would be a better choice than J. effusus or S. tabernaemontani due to higher productivity. Biomass production and growth for T. angustifolia were not significantly affected by ammonia concentration. Lack of a treatment effect may be due to high ammonia tolerance of this species, or to experimental variability. Further trials with greater replication are needed to evaluate the response of T. angustifolia to elevated ammonia. Growth for S. latifolia was significantly affected by ammonia, with RGR reduced by ammonia concentrations above 200 mg/l. Ammonia effects on biomass production of this species went unmeasured because, despite the use of supplemental lighting to extend photoperiod, S. latifolia had senesced by the end of the experiment. Our observed decreases in RGR for this species may have been due to this senescence effect. The results of our study generally agree with the findings of Humenik et al. (1999) and Hill et al. (1997). Humenik et al. reported that J. effusus and S. tabernaemontani were tolerant of ammonia concentrations up to 175 mg/l. We observed a similar tolerance for J. effusus, with RGR only moderately affected by ammonia concentrations
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
up to 200 mg/l. While we found S. tabernaemontani growth to be negatively affected by concentrations of as low as 45 mg/l, reductions were not great up to 200 mg/l. Hill et al. (1997) reported that S. latifolia and T. latifolia were unaffected by ammonia concentrations up to 82.4 mg/l. Our study extends the tolerance range of these two species, as we found their growth only moderately affected by ammonia concentrations up to 200 mg/l. Our results differ from observations made by Surrency (1993), who reported that ammonia concentrations averaging 160– 170 mg/l did not affect S. tabernaemontani, but did stress T. latifolia. We observed both species to be somewhat tolerant of ammonia concentrations in this range. Moreover, T. latifolia appeared to be more tolerant of elevated ammonia than S. tabernaemontani (Fig. 1). Flooded conditions of 10 cm did not significantly increase ammonia toxicity to S. tabernaemontani or T. latifolia relative to nonflooded but water-logged conditions. We were surprised that flooding did not reduce growth and biomass production, because the adverse effects of flooding have been documented for wetland plants (for example, McKee and Mendelssohn, 1989; Ernst, 1990; Gough and Grace, 1998). In future studies, we recommend that nonflooded plants be raised 10 cm above the water surface, and therefore exposed to more aerobic conditions. In conclusion, our findings suggest that the effectiveness of wetlands built to treat ammonialaden wastewater can be enhanced through selection of plant species tolerant of the ammonia level in influent water. If vegetation harvesting is planned, species with higher growth rates are better choices, but these may also be less tolerant of elevated ammonia concentrations than slower growing species. Water level may not be important in modifying the effect of ammonia in certain species, but more research is needed on the role of water level in constructed wetlands.
Acknowledgements The authors thank Dr Larry W. Douglas and Dr E´ ric LeBlanc for providing assistance with
263
statistics. They also thank John Adornato, Joann Alexander, Carroll M. Barrack, Laurie Clarke, Ellen DeRico, Mike Egnotovich, Troy Hershberger, Kathy Kamminga, Kimberly Monahan, Frank Pendleton, Jennifer Schaafsma, and Rebecca Stack for their help in the greenhouse. This research was supported by the Maryland Department of Natural Resources and the United States Environmental Protection Agency. Finally, the authors thank Jennifer Kujawski, Kathy Davis, and the USDA National Plant Materials Center for providing technical assistance and greenhouse space.
References Beadle, C.L., 1982. Plant growth analysis. In: Coombs, J., Hall, D.O. (Eds.), Techniques in Bioproductivity and Photosynthesis. Pergamon Press, New York City, NY, pp. 20 – 24. Bertness, M.D., 1991. Zonation of Spartina patens and Spartina alterniflora in a New England salt marsh. Ecology 72, 138 – 148. Brix, H., 1993. Wastewater treatment in constructed wetlands: system design, removal processes, and treatment performance. In: Moshiri, G.A. (Ed.), Constructed Wetlands for Water Quality Improvement. Lewis Publishers, Boca Raton, FL, pp. 9 – 22. Brix, H., 1994. Functions of macrophytes in constructed wetlands. Water Sci. Technol. 29, 71 – 78. Dijk, E., Eck, N., 1995. Ammonium toxicity and nitrate response of axenically grown Dactylorhiza incarnata seedlings. New Phytol. 131, 361 – 367. Ernst, W.H.O., 1990. Ecophysiology of plants in waterlogged and flooded environments. Aquat. Botany 38, 73 – 90. Gough, L., Grace, J.B., 1998. Effects of flooding, salinity and herbivory on coastal plant communities, Louisiana, United States. Oecologia 117, 527 – 535. Grace, J.B., Wetxel, R.G., 1981. Habitat partitioning and competitive displacement in cattails (Typha): experimental field studies. Am. Nat. 118, 463 – 474. Grime, J.P., 1977. Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory. Am. Nat. 111, 1169 – 1194. Hageman, R.H., 1984. Ammonium versus nitrate nutrition of higher plants. In: Nitrogen in Crop Production. ASACSSA-SSSA, Madison, WI, pp. 67 – 82. Hammer, D.A., 1992. Designing constructed wetlands systems to treat agricultural nonpoint source pollution. Ecol. Eng. 1, 49 – 82. Hill, D.T., Payne, V.W.E., Rogers, J.W., Kown, S.R., 1997. Ammonia effects on the biomass production of five constructed wetland plant species. Bioresour. Technol. 62, 109 – 113.
264
E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264
Humenik, F.J., Szogi, A.A., Hunt, P.G., Broome, S., Rice, M., 1999. Wastewater utilization: a place for managed wetlands. Asian – Australas. J. Anim. Sci. 12, 629 – 632. Kadlec, R.H., Knight, R.L., 1996. Treatment Wetlands. Lewis Publishers, Boca Raton, FL. Magalha˜ es, J.R., Machado, A.T., Huber, D.M., 1995. Similarities in response of maize genotypes to water logging and ammonium toxicity. J. Plant Nutr. 18, 2339 –2346. McKee, K.L., Mendelssohn, I.A., 1989. Response of a freshwater marsh plant community to increased salinity and increased water level. Aquat. Botany 34, 301 – 316. Metcalf & Eddy, Inc., 1991. In: Tchobanoglous, Burton, F.L. (Rev.). Wastewater Engineering, Treatment, Disposal, and Reuse, third ed. McGraw-Hill, New York City, NY.
Odum, E.P., Finn, J.T., Franz, E.H., 1979. Perturbation theory and the subsidy – stress gradient. Bioscience 29, 349 – 352. Ponnamperuma, F.N., 1972. The chemistry of submerged soils. Adv. Agron. 24, 29 – 96. Sokal, R.R., Rohlf, J.F., 1994. Biometry: The Principles and Practice Of Statistics in Biological Research, Third ed. WH Freeman and Co., New York City, NY. Surrency, D., 1993. Evaluation of aquatic plants for constructed wetlands. In: Moshiri, G.A. (Ed.), Constructed Wetlands for Water Quality Improvement. Lewis Publishers, Boca Raton, FL, pp. 349– 357. Wang, W., 1991. Ammonia toxicity to macrophytes (common duckweed and rice) using static and renewal methods. Environ. Toxicol. Chem. 10, 1173 – 1177.