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–En�ironmental Sciences Program, Uni�ersity of Maryland, College Park, MD 20742, USA

b Department of Biological Resources Engineering, Uni�ersity 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, andmaintained properly. In the case of wetlands designed to treat animal waste, system effectiveness may be limited byhigh ammonia concentrations and inundation, conditions that can adversely affect macrophytic vegetation. Weconducted a 4-month greenhouse experiment to assess the impact of ammonia concentration and water level on plantscommonly 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 betweenammonia 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 speciesdemonstrated similar fertilization/inhibition responses to increased ammonia, but important differences were notedbetween species. Flooded conditions of 10 cm did not significantly increase ammonia toxicity to S. tabernaemontanior T. latifolia. Our results emphasize the need for careful consideration of the species used in treatment wetlands, andsuggest that management of ammonia concentration may enhance plant growth and system function. © 2002 ElsevierScience B.V. All rights reserved.

Keywords: Ammonia toxicity; Constructed wetlands; Wastewater treatment; Juncus effusus ; Sagittaria latifolia ; Schoenoplectustabernaemontani ; Typha angustifolia ; Typha latifolia

1. Introduction

Macrophytic vegetation plays a critical role inconstructed wetlands used to treat wastewaterfrom dairy operations and other concentrated ani-mal production facilities (Kadlec and Knight,1996). Constructed wetland systems are designedto utilize water quality improvement processesoccurring in natural wetlands, including high pri-

* Corresponding author. Present address: Department ofBiological 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, CA92679, USA.

0925-8574/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.

PII: S 0925 -8574 (01 )00080 -5

mailto:[email protected]

E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264258

mary productivity, low flow conditions, and oxy-gen transfer to anaerobic sediments (Brix, 1993;Kadlec and Knight, 1996). Several of these pro-cesses are strongly linked to functional character-istics of macrophytes: plants uptake nutrientsdirectly, oxygenate the soil, reduce water flow,and provide surfaces for microbial colonization(Surrency, 1993; Brix, 1994). However, the ex-treme conditions found in animal wastewatertreatment systems may exceed the tolerance ofaquatic plants (Surrency, 1993), limiting bothplant survivorship and treatment potential. Inparticular, plant survivorship in constructed wet-lands decreases when partially aerated soil condi-tions are not maintained (Kadlec and Knight,1996), and when high ammonia concentrationsare typical (Surrency, 1993).

Kadlec and Knight (1996) summarized nutrientlevels for several natural wetland systems includ-ing a marsh, a cypress dome, a bog, and a fen,and report that all have ammonia concentrationsbelow 2 mg/l. Ammonia concentrations in munic-ipal wastewater are typically higher than in natu-ral systems, ranging from 12 to 50 mg/l (Metcalf& Eddy, Inc., 1991). Ammonia concentrations inconstructed wetlands treating animal wastes arehigher still, often exceeding 100 mg/l and rangingas high as 400 to 500 mg/l (Hammer, 1992;Kadlec and Knight, 1996). Concentrations in thisrange may exceed what plants need to maximizebiomass, and additionally may inhibit plantgrowth.

While ammonia has been shown to be toxic toa variety of plant species (Hageman, 1984; Wang,1991; Dijk and Eck, 1995; Magalhaes et al., 1995),few studies have examined ammonia toxicity towetland plants at concentrations similar to thosefound in animal waste (Hill et al., 1997). In anobservational study, Surrency (1993) noted thatTypha latifolia L. was stressed by ammonia con-centrations that averaged 160–170 mg/l, whileSchoenoplectus tabernaemontani (K.C. Gmel.)Palla tolerated the extreme conditions. Hill et al.(1997) exposed five wetland plant species to am-monia concentrations between 20.5 and 82.4 mg/lin a field-scale experiment, and found that onlySchoenoplectus acutus var. acutus (Muhl. exBigelow) A. & D. L�ve was negatively affected in

this concentration range. In a 2-year mesocosmstudy, Humenik et al. (1999) found Juncus effususL. and S. tabernaemontani to be unaffected byammonia concentrations of 175 mg/l, and tolerantof concentrations of 350 mg/l.

To examine the effects of elevated ammoniaand inundation on wetland plants, we conducteda greenhouse study exposing five species to combi-nations of ammonia and water level. For thestudy, ammonia was defined as NH3+NH4OH+NH4

+ (Ponnamperuma, 1972). The impacts of am-monia levels of 0, 50, 100, 200, and 400 mg/l wereexamined for three species: J. effusus, Sagittarialatifolia Willd., and Typha angustifolia L. Interac-tions between these ammonia concentrations andwater levels were examined for two species: S.tabernaemontani and T. latifolia. Ammonia andwater level effects on growth rate and biomassproduction were evaluated over a 4-month study.

2. Materials and methods

2.1. Plant material

We purchased J. effusus, S. latifolia, S. taber-naemontani, T. angustifolia and T. latifolia plantsin June 1998 from Environmental Concern, Inc.,St. Michaels, MD. T. angustifolia was purchasedas bare-root plants, while the other four specieswere purchased in quart-sized containers. Plantswere transferred to 3-gallon pots filled with top-soil and allowed to establish in tap water until theexperimental treatments were applied on 22 July1998.

2.2. Experimental set-up

We constructed 15 wetland tanks measuringapproximately 2.0 m×0.4 m×0.4 m deep in agreenhouse at the United States Department ofAgriculture, Natural Resources Conservation Ser-vice, National Plant Materials Center on theBeltsville Agricultural Research Center, PrinceGeorge’s County, MD. The tanks were arrangedin three experimental blocks to accommodate thefive ammonia treatments (0, 50, 100, 200, and 400mg/l ammonia) and two water level treatments

E. Clarke, A.H. Baldwin / Ecological Engineering 18 (2002) 257–264 259

(flooded and nonflooded) planned for the study.One pot of each species was randomly assigned toeach tank to examine ammonia effects, for a totalof five plants per tank and 75 plants for theexperiment. Additional pots of S. tabernaemontaniand T. latifolia were added to each tank to exam-ine ammonia and water level interactions, raisingthe total number of plants to 105 for the study.Beginning in September, supplemental lightingwas utilized to extend the photoperiod to a 14 hlight/8 h dark cycle.

2.3. Ammonia and water le�el treatments

We randomly assigned the ammonia treatmentsto tanks within each block. Treatment solutionswere prepared with reagent-grade ammoniumchloride (Fisher Scientific, Fair Lawn, NJ, USA)and tap water, and 40 gallons of solution wasinitially added to each tank. Water level treat-ments were randomly assigned to S. tabernaemon-tani and T. latifolia plants within tanks.Nonflooded plants were elevated to maintain wa-ter level at the surface of the soil. Flooded condi-tions were reached by submerging plants to adepth of 10 cm below the water surface.

2.4. Water monitoring

We monitored pH, ammonia concentration,and water level biweekly to detect and correctdeviations from desired treatment levels. Devia-tions in these parameters were expected due tosuch factors as nutrient uptake, evapotranspira-tion, 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), andfound that pH generally remained between 6.0and 7.0 for all the tanks over the study duration.Ammonia concentration was determined with anOrion portable pH/ISE Meter (Model 290A) andan Orion Ammonia Electrode (Model 95-12), andsolution was added when concentrations deviatedfrom desired treatment levels. Over the durationof the study, mean ammonia concentrations were

0.13�0.04, 38.11�1.21, 90.33�1.12, 180.73�1.57, and 393.91�3.65 mg/l for treatments of 0,50, 100, 200, and 400 mg/l ammonia, respectively.Water level was monitored visually, and treat-ments were maintained by adding solution untilplants were flooded as planned.

2.5. Growth measurements

Plants were first censused on 22 July 1998,immediately before application of ammonia andwater level treatments. The numbers of stems perpot were counted for the five study species, andthe numbers of ramets per pot was recorded forT. angustifolia and T. latifolia. The length of allleaves in each pot was measured for all species,providing total leaf length per plant as an indica-tor of above-ground biomass. Plant censuses wereconducted in this manner three times followingthe initial census, breaking the experiment up intothree roughly equal periods.

2.6. Har�est

Above-ground biomass was harvested on 6 and13 November 1998. Plant material was clipped atthe ground surface, placed in labeled bags, anddried at 42°C and 12% humidity in a controlled-environment chamber for �96 h. Dried speci-mens were weighed and used to construct linearrelationships between leaf length and finalbiomass (SigmaPlot Version 4.01; SPSS, Chicago,IL). All regression slope coefficients were signifi-cantly different from zero (P�0.0001), and ad-justed r2 values ranged from 0.95 to 0.98.Regression equations were used to estimatebiomass from leaf length data for the pre-harvestmonitoring events. Relative growth rate (RGR)per plant per period was calculated using theequation:

RGR=ln W2− ln W1

t2− t1

(1)

where W1 and W2 are nondestructive estimates ofbiomass for times t1 (beginning of period) and t2

(end of period), respectively (Beadle, 1982).


2.7. Data analysis

A one-way analysis of variance (ANOVA) wasconducted for J. effusus, S. latifolia, and T. angus-tifolia. In this analysis, final biomass was thedependent variable, and ammonia concentrationwas the independent variable. A two-wayANOVA was conducted on final biomass data forS. tabernaemontani and T. latifolia. Final biomasswas again the dependent variable, and ammoniaconcentration and water level were the indepen-dent variables. Repeated measures analysis ofvariance (RMANOVA) was used to analyze RGRdata for each species. All analyses were conductedwith SAS Version 6.12 (SAS Institute, Cary, NC).Variance homogeneity and normality of observa-tions were examined for each species, and vari-ances were partitioned in a mixed model in thecase of heterogeneous variances.

To further visualize the effects of ammoniaconcentration on plant growth, nonlinear regres-sion was used (SigmaPlot Version 4.01; SPSS,Chicago, IL). For each species, the best fit curvefor the data was selected for the purpose of

prediction, recognizing that higher order termsmay have no biological significance (Sokal andRohlf, 1994).

3. Results

3.1. Effects of ammonia on biomass production

Ammonia significantly affected final biomassfor J. effusus (ANOVA P=0.0238), S. tabernae-montani (ANOVA P�0.0001), and T. latifolia(ANOVA P�0.0001). Final biomass for T. an-gustifolia was not statistically affected by ammo-nia over the range of concentrations studied(ANOVA P=0.2550). S. latifolia was not in-cluded in statistical analysis performed on finalbiomass data because all plants of that speciessenesced before the final harvest. However, S.latifolia was included in the RGR analysis.

Biomass response curves varied among the spe-cies (Fig. 1). J. effusus final biomass data were fitwith a quadratic response curve, while S. taber-naemontani, 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 levelsfor 4 months in the greenhouse. No response curve is displayed for T. angustifolia because this species was not statistically affectedby ammonia over the concentration range studied.


mal curves. J. effusus reached maximum biomassat approximately 110 mg/l ammonia, S. tabernae-montani at 45 mg/l ammonia, and T. latifolia at 84mg/l ammonia. J. effusus had lowest biomass at400 mg/l ammonia, S. tabernaemontani at 0 mg/lammonia, and T. latifolia at 0 mg/l ammonia.While the specifics of the response curves varied,the overall effect of increasing ammonia on finalbiomass was similar for these three species:biomass initially increased as ammonia concentra-tion was increased, but eventually the higher con-centrations reduced biomass production.

3.2. Effects of ammonia on relati�e growth rate

Ammonia concentration significantly affectedthe RGR for J. effusus (RMANOVA P=0.0010),S. latifolia (RMANOVA P�0.0001), S. taber-naemontani (RMANOVA P�0.0001), and T. lat-ifolia (RMANOVA P�0.0001), and did notaffect the RGR for T. angustifolia (RMANOVAP=0.8483; Fig. 2). Minimum RGR generally oc-curred 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 levelsin excess of 200 mg/l reduced the RGR for J.effusus, S. latifolia, and T. latifolia, and levels inexcess of 100 mg/l reduced RGR for S. tabernae-montani. RGR varied significantly over time forall five species (RMANOVA P�0.0001), withplants generally growing at slower rates as thestudy progressed.

3.3. Effects of ammonia and water le�el

There was no significant impact of water levelon biomass production for S. tabernaemontani(ANOVA P=0.9435) or T. latifolia (ANOVAP=0.3067). There was also no significant interac-tion between ammonia concentration and waterlevel for either species. As seen in Fig. 3, the finalbiomass of S. tabernaemontani was, at times,higher in the nonflooded pots (as in the 100 and200 mg/l ammonia treatment groups), and atother times higher in the flooded pots (as in the 50and 400 mg/l ammonia treatment groups). How-ever, at ammonia concentrations of 100 mg/l orgreater, biomass was always greater in nonflooded

Fig. 2. Relative growth rates of wetland plant species during 4months growth at five ammonia levels in the greenhouse. Eachperiod represents approximately 1.3 months. Period 3 data islacking for S. latifolia because plants of this species senescedbefore that period’s end. Error bars represent �1S.E.

pots of T. latifolia, with the gap between thewater level treatment groups increasing with in-creasing ammonia concentration (Fig. 3). Thisexplains the low interaction P value for this spe-cies (ANOVA P=0.0692).

4. Discussion

Ammonia significantly affected biomass pro-duction and relative growth rate for J. effusus, S.tabernaemontani, and T. latifolia. Ammonia con-centrations above 100 mg/l reduced RGR for S.tabernaemontani after a period of weeks. Concen-trations above 200 mg/l similarly reduced RGRfor J. effusus and T. latifolia. Shorter periods ofelevated ammonia did not appear to affect growthfor the three species. A comparison of thebiomass response curves for these plants illus-


trates both similarities and differences in ammo-nia effects (Fig. 1). Convex response curves re-sulted for each species, demonstrating thatammonia stimulates biomass production at low tomoderate concentrations and inhibits biomassproduction at higher levels. Similar responsecurves have been demonstrated for ecosystemsexposed to perturbations, particularly when thecausal factor is a required component of theresponding factor (Odum et al., 1979).

While the biomass curves share this convexshape, striking differences exist between speciescurves (Fig. 1). First, the species maximizedbiomass at different ammonia levels, with J. ef-fusus 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 ofthe other two species for most of the ammoniarange studied. Third, the scale of the stimulationand inhibition varied, with T. latifolia exhibiting

the greatest relative response, followed by S.tabernaemontani and then by J. effusus. Thesefindings indicate that T. latifolia and S. tabernae-montani exhibit a ‘competitive’ strategy, while J.effusus exhibits a ‘stress-tolerant’ strategy sensuGrime (1977).

The observed differences in biomass responsecurves may affect vegetation dynamics in a con-structed wetland system, as well as managementtechniques. While J. effusus was less inhibited byelevated ammonia concentration than T. latifoliaor S. tabernaemontani, the higher productivity ofthese species may lead to the eventual displace-ment of J. effusus from a constructed wetlandcontaining all three species. This hypothesis sup-ports the concept of a trade off between stresstolerance and competitive ability noted elsewhere(Grace and Wetxel, 1981; Bertness, 1991), andcould be explored in competition studies con-ducted along an ammonia concentration gradient.With regard to management, if biomass harvest-ing were planned in order to enhance nutrientremoval in a constructed wetland, T. latifoliawould be a better choice than J. effusus or S.tabernaemontani due to higher productivity.

Biomass production and growth for T. angusti-folia were not significantly affected by ammoniaconcentration. Lack of a treatment effect may bedue to high ammonia tolerance of this species, orto experimental variability. Further trials withgreater replication are needed to evaluate theresponse of T. angustifolia to elevated ammonia.

Growth for S. latifolia was significantly affectedby ammonia, with RGR reduced by ammoniaconcentrations above 200 mg/l. Ammonia effectson biomass production of this species went un-measured because, despite the use of supplementallighting to extend photoperiod, S. latifolia hadsenesced by the end of the experiment. Our ob-served decreases in RGR for this species mayhave been due to this senescence effect.

The results of our study generally agree withthe findings of Humenik et al. (1999) and Hill etal. (1997). Humenik et al. reported that J. effususand S. tabernaemontani were tolerant of ammoniaconcentrations up to 175 mg/l. We observed asimilar tolerance for J. effusus, with RGR onlymoderately affected by ammonia concentrations

Fig. 3. Total dry biomass of wetland plant species after 4months growth at five ammonia levels and two water depths inthe greenhouse. Error bars represent �1S.E.


up to 200 mg/l. While we found S. tabernaemon-tani growth to be negatively affected by concen-trations of as low as 45 mg/l, reductions were notgreat up to 200 mg/l. Hill et al. (1997) reportedthat S. latifolia and T. latifolia were unaffected byammonia concentrations up to 82.4 mg/l. Ourstudy extends the tolerance range of these twospecies, as we found their growth only moderatelyaffected by ammonia concentrations up to 200mg/l.

Our results differ from observations made bySurrency (1993), who reported that ammonia con-centrations averaging 160–170 mg/l did not affectS. tabernaemontani, but did stress T. latifolia. Weobserved both species to be somewhat tolerant ofammonia concentrations in this range. Moreover,T. latifolia appeared to be more tolerant of ele-vated ammonia than S. tabernaemontani (Fig. 1).

Flooded conditions of 10 cm did not signifi-cantly increase ammonia toxicity to S. tabernae-montani or T. latifolia relative to nonflooded butwater-logged conditions. We were surprised thatflooding did not reduce growth and biomass pro-duction, because the adverse effects of floodinghave been documented for wetland plants (forexample, McKee and Mendelssohn, 1989; Ernst,1990; Gough and Grace, 1998). In future studies,we recommend that nonflooded plants be raised10 cm above the water surface, and thereforeexposed to more aerobic conditions.

In conclusion, our findings suggest that theeffectiveness of wetlands built to treat ammonia-laden wastewater can be enhanced through selec-tion of plant species tolerant of the ammonia levelin influent water. If vegetation harvesting isplanned, species with higher growth rates arebetter choices, but these may also be less tolerantof elevated ammonia concentrations than slowergrowing species. Water level may not be impor-tant in modifying the effect of ammonia in certainspecies, but more research is needed on the role ofwater level in constructed wetlands.

Acknowledgements

The authors thank Dr Larry W. Douglas andDr Eric LeBlanc for providing assistance with

statistics. They also thank John Adornato, JoannAlexander, Carroll M. Barrack, Laurie Clarke,Ellen DeRico, Mike Egnotovich, Troy Hersh-berger, Kathy Kamminga, Kimberly Monahan,Frank Pendleton, Jennifer Schaafsma, and Re-becca Stack for their help in the greenhouse. Thisresearch was supported by the Maryland Depart-ment of Natural Resources and the United StatesEnvironmental Protection Agency. Finally, theauthors thank Jennifer Kujawski, Kathy Davis,and the USDA National Plant Materials Centerfor providing technical assistance and greenhousespace.

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