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Development of vegetation in a constructed wetland receiving irrigation return flows
Agriculture, Ecosystems and Environment 121 (2007) 401–406 www.elsevier.com/locate/agee
Development of vegetation in a constructed wetland receiving irrigation return flows Andrew M. Ray *, Richard S. Inouye Center for Ecological Research and Education and the Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007, USA Received 5 March 2006; received in revised form 23 November 2006; accepted 28 November 2006 Available online 16 January 2007
Abstract The Fairview Constructed Wetland, a complex of replicated wet meadow (primary filter) and shallow marsh (shallow wetland) cells, was built in southeast Idaho in 1999 and planted with seven native plant species. The development of aboveground biomass and root mass and the accumulation of litter for each cell and for each species are described here. Establishment patterns varied among species and wetlands. Juncus balticus and Carex nebrascensis contributed disproportionately to the biomass in the primary filter cells. In these wetlands, aboveground biomass increased from an overall average of 443 in 2000 to 560 g/m2 in 2003, while root mass increased from 387 to 1108 g/m2. Litter mass increased from 230 in 2001 to 829 g/m2 in 2003. In the shallow wetlands, average aboveground biomass increased from 82 in 2000 to 391 g/ m2 in 2003, while root mass increased from 108 to 574 g/m2 over this same period. From 2001 to 2003, litter mass increased from 68 to 214 g/ m2. All measures of biomass and litter in the shallow wetlands were less than the corresponding values in the primary filter cells over the same time period. Still, biomass measures differed among shallow wetlands and some of this variation was explained by the differences in each wetland’s hydrograph. # 2006 Elsevier B.V. All rights reserved. Keywords: Constructed wetlands; Aboveground biomass; Root mass; Litter accumulation; Semi-arid west; Idaho
1. Introduction The effectiveness of wetlands at sequestering nutrients is vastly disproportionate to their size. Using several watersheds, Weller et al. (1996) demonstrated the importance of natural wetlands in watersheds and determined that 1 ha of riparian wetland could sequester more phosphorus than was released by 35 ha of agricultural land. Kovacic et al. (2000) demonstrated that 37% of total nitrogen and 22% of dissolved phosphorus could be removed from source waters with small constructed wetlands having watershed:wetland ratios ranging from 17 to 32. As a result of these and other studies, the USDA NRCS (2000) has identified constructed * Corresponding author at: Department of Biological Sciences, Box 8007, Idaho State University, Pocatello, ID 83209-8007, USA. Tel.: +1 208 282 4831; fax: +1 208 282 4570. E-mail address: [email protected] (A.M. Ray). 0167-8809/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2006.11.018
wetlands as a viable conservation strategy for treating wastewaters associated with the following agricultural practices: confined animal operations, row cropping, dairies, and silage storage. The importance of vegetation in treatment wetlands has been demonstrated repeatedly and is often documented by comparing the performance of vegetated and unvegetated treatment cells (e.g. Gearheart et al., 1989). Wetland plants improve water quality by reducing water velocity, thereby allowing suspended particles to settle (Brueske and Barrett, 1994), and by the direct uptake of nutrients (e.g. Reddy and De Busk, 1985). Despite these roles, the more important and indirect role of wetland vegetation is to provide support for microbial populations. Plants in treatment wetlands have been shown to influence microbial processes by increasing oxygen concentrations in the rhizosphere (Allen et al., 2002), releasing exudates like carbohydrates and amino acids (Brix, 1997; Coleman et al., 2001), providing
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additional surfaces for growth and proliferation of microbial populations (Wetzel, 1990), and increasing air spaces in the soil medium (Tanner and Sukias, 1995). Despite the recognition that constructed wetlands and their associated vegetative and microbial communities can successfully treat agricultural runoff, few studies have characterized the development of vegetation in constructed wetlands receiving agricultural runoff (Hoagland et al., 2001). Luckeydoo et al. (2002) described the early development of vascular vegetation in three Ohio wetlands receiving surface and subsurface runoff from agricultural fields. Hoagland et al. (2001) described the biomass accumulation and nutrient uptake by vegetation in a constructed wetland in Illinois receiving agricultural drainage waters. The development of aboveground (AG) biomass and root mass and the accumulation of litter in experimental wetland cells that received irrigation return flows are described here. Changes in biomass and litter were documented for seven species planted in 1999 and summarized from 2000 to 2003.
2. Methods 2.1. Study location The Fairview Constructed Wetland (FCW), located on the west side of American Falls Reservoir in southeastern Idaho, received water from about 48.5 ha of furrow-irrigated cropland. Mean annual precipitation for this region has been approximately 30 cm/year and summer temperatures in this region often exceed 37 8C (NCDC, 2001). As a result of the restricted irrigation season, discontinuous supply of water, limited precipitation, and hot summer temperatures, plants in the FCW experienced extended periods with no standing water and, during much of that time, with very little available soil moisture. FCW included five treatment components including a sediment pond, primary filter cells, shallow wetland cells, a deep-water wetland, and a final filter cell. The primary filter consisted of eight 5 m 30 m wetland cells planted in June 1999. Four cells (1, 4, 5, 8) were planted as monocultures of Carex nebrascensis Dewey and four cells (2, 3, 6, and 7) were planted as mixtures of C. nebrascensis, Eleocharis palustris (L.) Roemer & J.A. Schultes, Juncus balticus Willd., and Scheonoplectus maritimus (L.) Lye. In the mixed species cells, each species was planted in 2-m strips along the first 24 m of each cell, and in 1-m and 0.5-m strips along the remaining 6 m of each cell. Rigid plastic material, buried to a depth of 20 cm and extending approximately 25 cm above the ground, separated the cells. Water entered the cells through separate gates in a common pipe that ran along the north side of the cells and emptied from each cell into a separate pipe along the end of each cell. Water depth in the wetland cells averaged 15–20 cm when full. Cell, as used here, referred to individual 5 m 30 m
experimental wetland cells that make up the primary filter and patch referred to the 2-m strips of vegetation planted as a single species in mixed vegetation cells (i.e. cells 2, 3, 6, and 7). Fairview Constructed Wetland also included four 10 m 60 m wetlands, hereafter referred to as shallow wetlands, planted with emergent marsh vegetation and having water levels that varied between 20 and 50 cm. Two shallow wetlands were planted with a predominance of Typha latifolia L. and two were planted predominantly with Schoenoplectus acutus (Muhl. ex Bigelow) A.&D. Lo¨ve var. acutus; both planting designs included these two species and Schoenoplectus pungens (Vahl) Palla. Water levels in each primary filter cell and each shallow wetland were monitored at 10 min intervals with mini-Troll pressure/level sensors (In-situ Inc., Laramie, WY, USA) during the 2003 field season. Water level monitors were located 1 m from the outlet of primary filter cells and 2 m from the outlet of each shallow wetland. Although water levels in each wetland were monitored over the irrigation season, individual wetlands were, on occasion, drained to facilitate regular or irregular maintenance and monitoring activities or to purposefully manipulate floods for other research (see Ray and Inouye, 2006). Waters leaving the irrigated fields and entering the initial component, the settling (sediment) pond, had concentrations of total suspended solids (TSS) that ranged from 7 to 837 mg/l, nitrate + nitrite (NO3 + NO2 ) from 0.03 to 3 mg/l, and soluble phosphorus (P) from 0.05 to 2 mg/l. Concentrations of these same constituents leaving the sediment pond and entering the primary filters ranged from 5 to 101 mg/l TSS, 2 to 521 mg/l NO3 + NO2 , and 14 to 89 mg/l soluble P. The shallow wetlands, located third in the series of treatment wetlands at FCW, showed much less variation and documented concentrations of TSS, NO3 + NO2 , and soluble P ranged from 2 to 14 mg/l, 5 to 300 mg/l, and 19 to 70 mg/l, respectively. Mean concentrations of TSS, NO3 + NO2 and soluble P in waters leaving the shallow wetlands were 4.1 mg/l, 16, and 21 mg/l, respectively. 2.2. Vascular vegetation biomass sampling AG biomass from a random subset of 25 cm 25 cm quadrats was sampled along permanent transects in each wetland cell from 2000 to 2003. Vegetation and litter in each quadrat were clipped at ground level. AG biomass was sorted to species, and both biomass and litter were weighed separately after drying. In this paper, ‘‘litter’’ referred to all accumulated standing and fallen litter sampled in each quadrat. Roots were sampled by inserting a 6-cm diameter soil core 17 cm deep in the center of each quadrat. The 17cm deep core likely provided a conservative estimate of the total belowground mass for the species described here (Ratliff and Westfall, 1988; Manning et al., 1989; Edwards, 1991; Pullin and Hammer, 1991). As used here, ‘‘roots’’
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referred to all belowground structures (roots and rhizomes) collected from the sampling described above. Root material was separated from the soil, dried, and weighed. No attempt was made to sort roots by species. The same quadrats were not sampled in consecutive years. Biomass samples were taken within a 3-week period extending from mid September to mid October each year. In primary filter cells, sampling was conducted along two transects that ran the 30 m length of each cell, placed 1 m from the sides of each cell. In 2000, 2001, and 2003, six quadrats were sampled in each of the four cells that were planted as monocultures of C. nebrascensis; in 2002 six quadrats in cells 1 and 8 and three in cells 4 and 5 were sampled to better characterize the variability within replicates. Quadrats sampled from mixed species primary filter cells were stratified so that representative samples were harvested in each of the 2 m vegetative patches located in the first 24 m of each wetland cell. This provided three measures of production for each of four plant species per mixed vegetation treatment cell. Shallow wetlands planted primarily with S. acutus were sampled by randomly placing one quadrat along each of 24 permanent transects oriented perpendicular to the long axis of the wetland. Transects were established at varied distances from the isolated patches planted in different species to characterize the movement of plant species relative the original planted interface. Shallow wetlands cells planted predominantly with T. latifolia were sampled by harvesting one randomly spaced quadrat along each of 22 permanent transects. However, the vegetation was sampled less exhaustively in the portions planted as monocultures of T. latifolia. In this portion of the wetland, transects were placed following a roughly systematic design at 5 m intervals. The portions of the cells that were planted with alternating strips of different plant species were sampled by arbitrarily placing transects along the edges of alternating strips to denote dynamics along the planted interface (as in S. acutus dominated shallow wetlands). 2.3. Statistical analysis Univariate analyses were used to detect differences in total AG biomass, AG biomass of the planted species, litter mass, and total root mass among species (specieslevel comparisons). Plant species was used as a treatment factor and wetland as a blocking factor. Students t-tests or two-sample t-tests of ranked data were used when variances differed to compare estimates of production for C. nebrascensis patches from monoculture (cells 1, 4, 5, and 8) and mixed plantings (cells 2, 3, 6, and 7) cells (Zar, 1999). To detect annual differences in total AG biomass, AG biomass of the planted species, litter mass, and root mass for each species (within species comparisons), repeated measures ANOVA (RM-ANOVA) was used. Annual sampling date (e.g. 2000, 2001, 2002, and
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2003 for total AG biomass) was used as the within-subject factor and the wetland cell, the unit of replication for all analyses, was used as the between-subjects factor. Since all measurements were repeated on individual cells, nonsignificant sphericity using RM-ANOVA was ensured. When sphericity was non-significant, univariate analysis was used with year and cell as treatment factors. All biomass data were natural log transformed (i.e. ln[measure + 1]) prior to analysis. Where significant cell effects were identified using univariate analysis, Pearson correlation was used to examine the relationship between mean relative flood length and biomass measures. Relative flood length was calculated by dividing the flood duration for each wetland (in days) by the wetland with the shortest flood duration.
3. Results 3.1. Primary filter cells From 2000 to 2003, AG biomass in the primary filter cells increased from an overall average of 443 to 560 g/m2, while root mass increased from 387 to 1108 g/m2. From 2001 (when litter produced in the previous year was first present) to 2003, litter mass increased from 230 to 829 g/m2. Mean total AG biomass (all species in harvested sample) in monoculture cells did not vary among years (P = 0.052). In these cells, the percent of AG biomass contributed by C. nebrascensis ranged from 68 in 2000 to 97% in 2003. C. nebrascensis AG biomass in monoculture cells varied among years (P = 0.003) and cells (P = 0.026). In monoculture cells, litter (P = 0.001) and root mass (P = 0.001) differed among years. Litter mass increased more than threefold and root mass increased more than five from 2001 to 2003 (Table 1). In mixed culture cells, total AG biomass in patches of C. nebrascensis varied among years (P = 0.011) and nearly doubled from 2000 to 2003. By 2003, C. nebrascensis represented 90% of the total AG biomass in these patches. Root biomass (P = 0.008) and litter mass (P < 0.001) varied among years; both measures were greatest in 2003 (Table 1). In contrast, E. palustris AG biomass did not differ among years (P = 0.118). Still, litter mass in patches planted with E. palustris more than doubled from 2001 to 2003 and root mass experienced a four-fold increase from 2000 to 2003. From 2000 to 2002 mean total AG biomass in patches planted with J. balticus exhibited limited variation and exceeded 750 g/m2 each year (Table 1). By 2003, mean total AG biomass in these patches fell to 363 g/m2, but annual differences in total AG biomass and J. balticus AG biomass were not significant (P = 0.074 and P = 0.167). Similar to patches planted with C. nebrascensis, J. balticus AG biomass represented most (95% for all years) of the biomass in patches where it was originally planted. Litter
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Table 1 Mass of shoots (total and planted species only), roots, and litter reported in g/m2 for patches in primary filter cells planted with each of four species Species
Year
Shoots
Roots
Litter
Total
Planted species
Carex nebrascensis (mono)
2000 2001 2002 2003
365.8 520.1 516.0 677.3
249.2 317.9 437.7 657.9
281.4 822.6 1011.7 1582.1
– 251.7 453.9 819.9
Carex nebrascensis (mixed)
2000 2001 2002 2003
419.7 413.9 665.4 751.6
294.2 314.0 530.1 679.4
360.4 1070.8 1448.0 1728.9
– 246.9 337.2 808.6
Eleocharis palustris
2000 2001 2002 2003
279.2 98.2 354.9 430.7
50.8 5.2 19.8 55.4
229.3 171.5 674.1 920.7
– 234.6 374.0 558.4
Juncus balticus
2000 2001 2002 2003
757.6 829.4 795.6 363.0
701.0 788.4 742.3 338.8
674.3 925.2 1487.2 1587.1
– 198.2 864.1 1456.8
Schoenoplectus maritimus
2000 2001 2002 2003
395.6 153.0 395.6 581.6
33.3 2.3 96.4 123.8
387.5 386.2 650.5 1322.1
– 217.1 264.4 500.0
There were no differences in total AG biomass, C. nebrascensis biomass, or root biomass between C. nebrascensis monoculture cells and C. nebrascensis patches in mixed species cells in any of the four sample years. 3.2. Shallow wetlands
Carex nebrascensis values are shown separately for monoculture cells and mixed species cells. Dashed lines indicate no data.
mass in J. balticus patches differed among years (P < 0.001) and increased 7 from 2001 to 2002; root biomass did not differ among years (P = 0.079). Mean total AG biomass in patches of S. maritimus differed among years (P = 0.021), but S. maritimus contributed on an average only 21% (124 g/ m2) of that total AG biomass in patches where it was planted. In these same patches, C. nebrascensis and J. balticus represented 36 and 27% of the total AG biomass. As early as 2000, C. nebrascensis and J. balticus patches had significantly greater AG biomass than E. palustris and S. maritimus in primary filter cells planted with mixtures of species. In that same year there were no differences in total AG biomass or root biomass among patches planted with different species (Table 1). Differences in total AG biomass were detected among patches planted with different species in 2001 (P = 0.001), 2002 (P = 0.006), and in 2003 (P = 0.002). In each year those differences were the result of greater AG biomass in patches planted with C. nebrascensis or J. balticus. AG biomass of planted species, rather than all species, showed similar patterns, with significant species differences in 2001, 2002, and 2003 (P < 0.001 for all years). Root mass varied among species in 2001 (P = 0.005) and 2002 (P = 0.016). Litter mass varied among patches in 2002 (P = 0.006) and 2003 (P < 0.001) only; J. balticus patches had nearly 3 as much litter as patches planted with E. palustris or S. maritimus (Table 1).
From 2000 to 2003 the mean AG biomass of the patches sampled in the shallow wetland cells increased from 81.9 to 390.8 g/m2, while root mass increased from 108.4 to 573.6 g/m2. From 2001 to 2003, litter mass increased from 67.9 to 214.3 g/m2. Although the biomass of all three planted species increased over the four years of monitoring (Table 2), the proportion of total AG biomass that was contributed by these species never reached values approaching those for C. nebrascensis or J. balticus of primary filter cells. In 2003 S. acutus contributed 63% of the AG biomass where it was planted, S. pungens contributed only 39% where it was planted, and T. latifolia contributed 50%. In patches planted with S. acutus there were significant increases in root mass (P < 0.001), but not in AG biomass or litter mass from 2000 to 2003. S. pungens patches experienced no significant changes in the AG biomass of S. pungens, root mass, or in litter mass. For patches planted with T. latifolia there were significant increases in total AG biomass (P = 0.016), biomass of T. latifolia (P = 0.007), and litter (P = 0.002) over the 4-year period of record. In these patches, average root mass experienced a six-fold change from 2000 to 2003 (Table 2), but difference among years or cells was not significant. Total AG biomass, AG biomass of planted species, root mass, and litter mass did not differ among patches planted with the three species in any of the sample years. However, there were differences among the four shallow wetland cells for litter in 2001 (P = 0.032) and in 2003 (P = 0.034). To examine the effects of flooding on measures of production for each species, two flood events (see Fig. 1 for Table 2 Mass of shoots (total and planted species only), roots, and litter reported in g/m2 for areas in shallow wetlands planted with each of the three species Species
Year
Shoots Total
Planted species
Roots
Litter
Schoenoplectus acutus
2000 2001 2002 2003
56.5 208.9 249.3 424.9
16.6 71.5 132.8 269.0
101.6 407.9 557.1 903.8
– 82.1 153.9 224.9
Schoenoplectus pungens
2000 2001 2002 2003
72.2 112.7 162.5 375.0
21.9 35.4 43.3 106.9
152.2 143.6 320.2 354.4
– 52.5 165.5 243.9
Typha latifolia
2000 2001 2002 2003
117.1 197.0 277.3 372.7
16.2 42.4 110.2 185.7
71.5 189.6 471.1 462.5
– 69.1 132.5 174.2
Dashed lines indicate no data.
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Fig. 1. Hydrograph for each shallow wetland during a representative flooding in June 2003. For this flood, waters entered the wetlands within a window of 4 h, yet total flood duration differed among wetlands by over 38 h.
an example of one flood; mean flood duration calculated from all four wetlands for event 1 and 2 were 5.1 and 4.8 days, respectively) were summarized during the 2003 irrigation season. S. acutus root mass was positively correlated with mean flood duration (R = 0.986, P = 0.014). We found no significant relationships between mean flood duration and measures of standing stock biomass for S. pungens and T. latifolia. Shallow wetland B was flooded for the shortest duration and shallow wetland C was flooded the longest amount time for the focal flood events (see Fig. 1). In both cases the rank order of wetland mean flood duration was the same as the rank order of S. acutus and S. pungens AG biomass; wetlands that were flooded longer also had higher AG biomass and this was true for both species of Scheonoplectus.
4. Discussion 4.1. Primary filter biomass Introduced vegetation in the eight experimental wetland cells that make up the primary filters underwent rapid development, however, establishment patterns differed considerably for the four species that were planted in these cells. By 2001, just two full growing seasons after planting, mean total root mass exceeded AG biomass for all species. Invasion of planted patches occurred soon after planting and continued through 2003. Patches originally planted with either E. palustris or S. maritimus were quickly invaded by C. nebrascensis and J. balticus. By 2003, 34% of the AG biomass in patches originally planted with E. palustris was C. nebrascensis and 39% was J. balticus and similar levels of invasion were noted in patches originally planted with S. maritimus. Under the conditions present at FCW, it is likely that S. maritimus and E. palustris will be outcompeted by the other species, further diminishing their presence in the wetlands. Invasion also occurred in patches planted with J.
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balticus and C. nebrascensis even though these species established rapidly after planting. J. balticus was more successful at invading patches planted with C. nebrascensis than the reverse and J. balticus was not restricted to regions of C. nebrascensis patches where the species shared a border. Instead, J. balticus was present and established throughout patches of C. nebrascensis. The long-term dataset from FCW also suggests these species are complementary; patches containing both species are more productive than patches where species are growing alone (Ray, 2005). Aboveground biomass, litter mass, and total root mass generally increased with time; however, the patterns of development differed by species. AG biomass of C. nebrascensis at FCW was similar but mean litter mass was less than the 1155 g/m2 reported for this same species elsewhere (Ratliff and Westfall, 1988). Annual changes in C. nebrascensis, contrasted with those of the other three species. J. balticus reached a maximum in AG biomass in 2001 and had its lowest biomass in 2003. Both E. palustris and S. maritimus had lowest AG biomass in 2001, two years after planting. AG biomass of E. palustris in 2003 was nearly identical to those measured in 2000. Total root mass in the primary filter cells exceeded total AG biomass in all species patches. Root:shoot ratios for all species exceeded 2 by 2003. Patches originally planted with J. balticus had the highest root to shoot ratio at 4.4. Total root mass for C. nebrascensis and J. balticus were less than values reported elsewhere. Manning et al. (1989) documented total belowground biomass of 3382 for C. nebrascensis and 2545 g/m2 for J. balticus. Ratliff and Westfall (1988) documented belowground biomass as >6000 g/m2 for populations of C. nebrascensis in California. Belowground biomass of C. nebrascensis is thought to reach its seasonal maximum at the close of the growing season during shoot senescence (Ratliff and Westfall, 1988). Therefore, the September sampling estimates reported here likely coincided with this species’ seasonal maximum, but were simply below the root masses reported for established populations elsewhere. 4.2. Shallow wetland biomass From 2000 to 2003 total AG biomass in the shallow wetlands increased nearly five-fold, to 382 g/m2, and belowground biomass increased more than five-fold, to 574 g/m2. Mean litter mass in 2003 was 214 g/m2 averaged across all species. These values are similar to those reported by Hoagland et al. (2001) for a constructed wetland treating agricultural tile drainage in Illinois four years after establishment. There, total AG biomass was 570 g/m2 and litter mass in October was 100 g/m2, down from a maximum of 400 g/m2 earlier that season; root mass in this wetland had a seasonal maximum of 2300 g/m2 (Hoagland et al., 2001). From the description of their focal
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wetland, the dominant plant species were different than those at FCW, however, similarities in wetland age provided an opportunity to compare measures of production. Root to shoot ratios for vegetation growing in the patches originally planted with S. acutus, S. pungens, and T. latifolia were 2.1, 0.9, and 1.2. These values are relatively low compared with those calculated in the primary filter cells. However, establishment of vegetation in the shallow wetlands has been slower and this measure may further characterize the sluggish pattern of establishment witnessed in shallow wetlands at FCW. Aboveground biomass of T. latifolia was greatest in wetland C (>300 g/m2 in 2003). This value is considerably lower than the biomass reported in natural wetlands elsewhere. For example, Dickerman and Wetzel (1985) reported AG biomass averaging 1076 g/m2 over a 2-year study in Michigan. Similarly, Boyd (1971) found AG biomass patterns of T. latifolia stands ranged from 530 to 1132 g/m2 in five wetlands in South Carolina. T. latifolia AG biomass and litter mass in a 1 ha shallow marsh located approximately 10 km from FCW and managed as part of the Sterling Wildlife Management Area, was 920 and 1060 g/ m2, respectively (Ray, 2005). Unlike the primary filter comparisons, shallow wetland (block) effects were detected in comparisons of biomass and litter among years and species. In 2003, total root biomass was positively correlated with flood duration and this relationship suggested that biomass differences among wetlands are at least partially the result of differences in the hydrographs of the four shallow wetlands (Fig. 1). Biomass development and litter accumulation were greatest in patches planted with C. nebrascensis and J. balticus. Both species are common to riparian corridors and montane meadows, and are widely used in wetland construction and restoration efforts in the Western U.S. Flows at FCW were tied to sporadic irrigation events and resulted in prolonged periods of flooding and drying. This hydrologic regime may have selected for species better adapted to extended periods of drawdown (C. nebrascensis and J. balticus) over other emergent species commonly used in treatment wetlands elsewhere. Acknowledgements Support for this research was provided by the Center for Ecological Research and Education, the Idaho State Board of Education, the NSF-Idaho EPSCOR Program, and the National Science Foundation under award number EPS0447689. We thank landowners Neil and Marita Poulson for their support and assistance with the Fairview Constructed Wetland. Edward Buhler, Ryan Dunham, Aaron Inouye, Martha Inouye, Amy Jenkins, Scott Owen, Linda Qvarnemark, and Heather Ray provided much needed assistance in the field and in the lab.
References Allen, W.C., Hook, P.B., Biederman, J.A., Stein, O.R., 2002. Temperature and wetland plant species effects on wastewater treatment and root zone oxidation. J. Environ. Qual. 31, 1010–1016. Boyd, C.E., 1971. Further studies on productivity, nutrient and pigment relationships in Typha latifolia populations. Bull. Torrey Bot. Club 98, 144–150. Brix, H., 1997. Do macrophytes play a role in constructed treatment wetlands? Water Sci. Technol. 35, 11–17. Brueske, C.C., Barrett, G.W., 1994. Effects of vegetation and hydrologic load on sedimentation patterns in experimental wetland ecosystems. Ecol. Eng. 3, 429–447. Coleman, J., Hench, K., Garbutt, K., Sexstone, A., Bissonnette, G., Skousen, J., 2001. Treatment of domestic wastewater by three plant species in constructed wetlands. Water Air Soil Pollut. 128, 283–295. Dickerman, J.A., Wetzel, R.G., 1985. Clonal growth in Typha latifolia: population dynamics and demography of the ramets. J. Ecol. 73, 535–552. Edwards, G.S., 1991. Root distribution of soft-stem bulrush (Scirpus validus) in a constructed wetland. Eco. Eng. 1, 239–243. Gearheart, R.A., Klopp, F., Allen, G., 1989. Constructed free surface wetlands to treat and receive wastewater: pilot project to full scale. In: Hammer, D.A. (Ed.), Constructed Wetlands for Wastewater Treatment Municipal, Industrial, and Agricultural. Lewis Publishers, Chelsea, pp. 121–137. Hoagland, C.R., Gentry, L.E., David, M.B., Kovacik, D.A., 2001. Plant nutrient uptake and biomass accumulation in a constructed wetland. J. Freshwater Ecol. 16, 527–540. Kovacic, D.A., David, M.B., Gentry, L.E., Starks, K.M., Cooke, R.A., 2000. Effectiveness of constructed wetlands in reducing nitrogen and phosphorus export from agricultural tile drainage. J. Environ. Qual. 29, 1262–1274. Luckeydoo, L.M., Fausey, N.R., Brown, L.C., Davis, C.B., 2002. Early development of vascular vegetation of constructed wetlands in northwest Ohio receiving agricultural waters. Agric. Ecosyst. Environ. 88, 89–94. Manning, M.E., Swanson, S.R., Svejcar, T., Trent, J., 1989. Rooting characteristics of four intermountain meadow community types. J. Range Manage. 42, 309–312. NCDC (National Climatic Data Center), 2001. Climatic data for Aberdeen, Idaho. http://www.weather.com/weather/climatology/USIDO50. Pullin, B.P., Hammer, D.A., 1991. Aquatic plants improve wastewater treatment. Water Environ. Technol. 3, 36–40. Ratliff, R.D., Westfall, S.E., 1988. Biomass trends in a Nebraska sedge meadow, Sierra National Forest, California. Aquat. Bot. 30, 109–124. Ray, A.M., 2005. Physical, chemical, and biological interactions in wetlands: a case study using Fairview Constructed Wetland in southeastern Idaho. Ph.D. Dissertation, Idaho State University, Pocatello, Idaho, USA. Ray, A.M., Inouye, R.S., 2006. Effects of water-level fluctuations on the arbuscular mycorrhizal colonization in Typha latifolia L. Aquat. Bot. 84, 210–216. Reddy, K.R., De Busk, W.F., 1985. Nutrient removal potential of selected aquatic macrophytes. J. Environ. Qual. 14, 459–462. Tanner, C.C., Sukias, J.P., 1995. Accumulation of organic solids in gravelbed constructed wetlands. Water Sci. Technol. 32, 229–239. United States Department of Agriculture Natural Resource Conservation Service, 2000. Conservation Practice Standard, Constructed Wetlands, CODE 656, National Handbook of Conservation Standards. http:// www.nrcs.usda.gov/Technical/Standards/nhcp.html. Weller, C.M., Watzin, M.C., Wang, D., 1996. Role of wetlands in reducing phosphorus loading to surface water in eight watersheds in the Lake Champlain Basin. Environ. Manage. 20, 731–739. Wetzel, R.G., 1990. Land-water interfaces: metabolic and limnological regulators (Edgardo Baldi Memorial Lecture). Ver. Int. Ver. Limnol. 24, 6–24. Zar, J.H., 1999. Biostatistical Analysis. Prentice Hall, Upper Saddle River.
Development of vegetation in a constructed wetland receiving irrigation return flows Andrew M. Ray *, Richard S. Inouye Center for Ecological Research and Education and the Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007, USA Received 5 March 2006; received in revised form 23 November 2006; accepted 28 November 2006 Available online 16 January 2007
Abstract The Fairview Constructed Wetland, a complex of replicated wet meadow (primary filter) and shallow marsh (shallow wetland) cells, was built in southeast Idaho in 1999 and planted with seven native plant species. The development of aboveground biomass and root mass and the accumulation of litter for each cell and for each species are described here. Establishment patterns varied among species and wetlands. Juncus balticus and Carex nebrascensis contributed disproportionately to the biomass in the primary filter cells. In these wetlands, aboveground biomass increased from an overall average of 443 in 2000 to 560 g/m2 in 2003, while root mass increased from 387 to 1108 g/m2. Litter mass increased from 230 in 2001 to 829 g/m2 in 2003. In the shallow wetlands, average aboveground biomass increased from 82 in 2000 to 391 g/ m2 in 2003, while root mass increased from 108 to 574 g/m2 over this same period. From 2001 to 2003, litter mass increased from 68 to 214 g/ m2. All measures of biomass and litter in the shallow wetlands were less than the corresponding values in the primary filter cells over the same time period. Still, biomass measures differed among shallow wetlands and some of this variation was explained by the differences in each wetland’s hydrograph. # 2006 Elsevier B.V. All rights reserved. Keywords: Constructed wetlands; Aboveground biomass; Root mass; Litter accumulation; Semi-arid west; Idaho
1. Introduction The effectiveness of wetlands at sequestering nutrients is vastly disproportionate to their size. Using several watersheds, Weller et al. (1996) demonstrated the importance of natural wetlands in watersheds and determined that 1 ha of riparian wetland could sequester more phosphorus than was released by 35 ha of agricultural land. Kovacic et al. (2000) demonstrated that 37% of total nitrogen and 22% of dissolved phosphorus could be removed from source waters with small constructed wetlands having watershed:wetland ratios ranging from 17 to 32. As a result of these and other studies, the USDA NRCS (2000) has identified constructed * Corresponding author at: Department of Biological Sciences, Box 8007, Idaho State University, Pocatello, ID 83209-8007, USA. Tel.: +1 208 282 4831; fax: +1 208 282 4570. E-mail address: [email protected] (A.M. Ray). 0167-8809/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2006.11.018
wetlands as a viable conservation strategy for treating wastewaters associated with the following agricultural practices: confined animal operations, row cropping, dairies, and silage storage. The importance of vegetation in treatment wetlands has been demonstrated repeatedly and is often documented by comparing the performance of vegetated and unvegetated treatment cells (e.g. Gearheart et al., 1989). Wetland plants improve water quality by reducing water velocity, thereby allowing suspended particles to settle (Brueske and Barrett, 1994), and by the direct uptake of nutrients (e.g. Reddy and De Busk, 1985). Despite these roles, the more important and indirect role of wetland vegetation is to provide support for microbial populations. Plants in treatment wetlands have been shown to influence microbial processes by increasing oxygen concentrations in the rhizosphere (Allen et al., 2002), releasing exudates like carbohydrates and amino acids (Brix, 1997; Coleman et al., 2001), providing
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additional surfaces for growth and proliferation of microbial populations (Wetzel, 1990), and increasing air spaces in the soil medium (Tanner and Sukias, 1995). Despite the recognition that constructed wetlands and their associated vegetative and microbial communities can successfully treat agricultural runoff, few studies have characterized the development of vegetation in constructed wetlands receiving agricultural runoff (Hoagland et al., 2001). Luckeydoo et al. (2002) described the early development of vascular vegetation in three Ohio wetlands receiving surface and subsurface runoff from agricultural fields. Hoagland et al. (2001) described the biomass accumulation and nutrient uptake by vegetation in a constructed wetland in Illinois receiving agricultural drainage waters. The development of aboveground (AG) biomass and root mass and the accumulation of litter in experimental wetland cells that received irrigation return flows are described here. Changes in biomass and litter were documented for seven species planted in 1999 and summarized from 2000 to 2003.
2. Methods 2.1. Study location The Fairview Constructed Wetland (FCW), located on the west side of American Falls Reservoir in southeastern Idaho, received water from about 48.5 ha of furrow-irrigated cropland. Mean annual precipitation for this region has been approximately 30 cm/year and summer temperatures in this region often exceed 37 8C (NCDC, 2001). As a result of the restricted irrigation season, discontinuous supply of water, limited precipitation, and hot summer temperatures, plants in the FCW experienced extended periods with no standing water and, during much of that time, with very little available soil moisture. FCW included five treatment components including a sediment pond, primary filter cells, shallow wetland cells, a deep-water wetland, and a final filter cell. The primary filter consisted of eight 5 m 30 m wetland cells planted in June 1999. Four cells (1, 4, 5, 8) were planted as monocultures of Carex nebrascensis Dewey and four cells (2, 3, 6, and 7) were planted as mixtures of C. nebrascensis, Eleocharis palustris (L.) Roemer & J.A. Schultes, Juncus balticus Willd., and Scheonoplectus maritimus (L.) Lye. In the mixed species cells, each species was planted in 2-m strips along the first 24 m of each cell, and in 1-m and 0.5-m strips along the remaining 6 m of each cell. Rigid plastic material, buried to a depth of 20 cm and extending approximately 25 cm above the ground, separated the cells. Water entered the cells through separate gates in a common pipe that ran along the north side of the cells and emptied from each cell into a separate pipe along the end of each cell. Water depth in the wetland cells averaged 15–20 cm when full. Cell, as used here, referred to individual 5 m 30 m
experimental wetland cells that make up the primary filter and patch referred to the 2-m strips of vegetation planted as a single species in mixed vegetation cells (i.e. cells 2, 3, 6, and 7). Fairview Constructed Wetland also included four 10 m 60 m wetlands, hereafter referred to as shallow wetlands, planted with emergent marsh vegetation and having water levels that varied between 20 and 50 cm. Two shallow wetlands were planted with a predominance of Typha latifolia L. and two were planted predominantly with Schoenoplectus acutus (Muhl. ex Bigelow) A.&D. Lo¨ve var. acutus; both planting designs included these two species and Schoenoplectus pungens (Vahl) Palla. Water levels in each primary filter cell and each shallow wetland were monitored at 10 min intervals with mini-Troll pressure/level sensors (In-situ Inc., Laramie, WY, USA) during the 2003 field season. Water level monitors were located 1 m from the outlet of primary filter cells and 2 m from the outlet of each shallow wetland. Although water levels in each wetland were monitored over the irrigation season, individual wetlands were, on occasion, drained to facilitate regular or irregular maintenance and monitoring activities or to purposefully manipulate floods for other research (see Ray and Inouye, 2006). Waters leaving the irrigated fields and entering the initial component, the settling (sediment) pond, had concentrations of total suspended solids (TSS) that ranged from 7 to 837 mg/l, nitrate + nitrite (NO3 + NO2 ) from 0.03 to 3 mg/l, and soluble phosphorus (P) from 0.05 to 2 mg/l. Concentrations of these same constituents leaving the sediment pond and entering the primary filters ranged from 5 to 101 mg/l TSS, 2 to 521 mg/l NO3 + NO2 , and 14 to 89 mg/l soluble P. The shallow wetlands, located third in the series of treatment wetlands at FCW, showed much less variation and documented concentrations of TSS, NO3 + NO2 , and soluble P ranged from 2 to 14 mg/l, 5 to 300 mg/l, and 19 to 70 mg/l, respectively. Mean concentrations of TSS, NO3 + NO2 and soluble P in waters leaving the shallow wetlands were 4.1 mg/l, 16, and 21 mg/l, respectively. 2.2. Vascular vegetation biomass sampling AG biomass from a random subset of 25 cm 25 cm quadrats was sampled along permanent transects in each wetland cell from 2000 to 2003. Vegetation and litter in each quadrat were clipped at ground level. AG biomass was sorted to species, and both biomass and litter were weighed separately after drying. In this paper, ‘‘litter’’ referred to all accumulated standing and fallen litter sampled in each quadrat. Roots were sampled by inserting a 6-cm diameter soil core 17 cm deep in the center of each quadrat. The 17cm deep core likely provided a conservative estimate of the total belowground mass for the species described here (Ratliff and Westfall, 1988; Manning et al., 1989; Edwards, 1991; Pullin and Hammer, 1991). As used here, ‘‘roots’’
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referred to all belowground structures (roots and rhizomes) collected from the sampling described above. Root material was separated from the soil, dried, and weighed. No attempt was made to sort roots by species. The same quadrats were not sampled in consecutive years. Biomass samples were taken within a 3-week period extending from mid September to mid October each year. In primary filter cells, sampling was conducted along two transects that ran the 30 m length of each cell, placed 1 m from the sides of each cell. In 2000, 2001, and 2003, six quadrats were sampled in each of the four cells that were planted as monocultures of C. nebrascensis; in 2002 six quadrats in cells 1 and 8 and three in cells 4 and 5 were sampled to better characterize the variability within replicates. Quadrats sampled from mixed species primary filter cells were stratified so that representative samples were harvested in each of the 2 m vegetative patches located in the first 24 m of each wetland cell. This provided three measures of production for each of four plant species per mixed vegetation treatment cell. Shallow wetlands planted primarily with S. acutus were sampled by randomly placing one quadrat along each of 24 permanent transects oriented perpendicular to the long axis of the wetland. Transects were established at varied distances from the isolated patches planted in different species to characterize the movement of plant species relative the original planted interface. Shallow wetlands cells planted predominantly with T. latifolia were sampled by harvesting one randomly spaced quadrat along each of 22 permanent transects. However, the vegetation was sampled less exhaustively in the portions planted as monocultures of T. latifolia. In this portion of the wetland, transects were placed following a roughly systematic design at 5 m intervals. The portions of the cells that were planted with alternating strips of different plant species were sampled by arbitrarily placing transects along the edges of alternating strips to denote dynamics along the planted interface (as in S. acutus dominated shallow wetlands). 2.3. Statistical analysis Univariate analyses were used to detect differences in total AG biomass, AG biomass of the planted species, litter mass, and total root mass among species (specieslevel comparisons). Plant species was used as a treatment factor and wetland as a blocking factor. Students t-tests or two-sample t-tests of ranked data were used when variances differed to compare estimates of production for C. nebrascensis patches from monoculture (cells 1, 4, 5, and 8) and mixed plantings (cells 2, 3, 6, and 7) cells (Zar, 1999). To detect annual differences in total AG biomass, AG biomass of the planted species, litter mass, and root mass for each species (within species comparisons), repeated measures ANOVA (RM-ANOVA) was used. Annual sampling date (e.g. 2000, 2001, 2002, and
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2003 for total AG biomass) was used as the within-subject factor and the wetland cell, the unit of replication for all analyses, was used as the between-subjects factor. Since all measurements were repeated on individual cells, nonsignificant sphericity using RM-ANOVA was ensured. When sphericity was non-significant, univariate analysis was used with year and cell as treatment factors. All biomass data were natural log transformed (i.e. ln[measure + 1]) prior to analysis. Where significant cell effects were identified using univariate analysis, Pearson correlation was used to examine the relationship between mean relative flood length and biomass measures. Relative flood length was calculated by dividing the flood duration for each wetland (in days) by the wetland with the shortest flood duration.
3. Results 3.1. Primary filter cells From 2000 to 2003, AG biomass in the primary filter cells increased from an overall average of 443 to 560 g/m2, while root mass increased from 387 to 1108 g/m2. From 2001 (when litter produced in the previous year was first present) to 2003, litter mass increased from 230 to 829 g/m2. Mean total AG biomass (all species in harvested sample) in monoculture cells did not vary among years (P = 0.052). In these cells, the percent of AG biomass contributed by C. nebrascensis ranged from 68 in 2000 to 97% in 2003. C. nebrascensis AG biomass in monoculture cells varied among years (P = 0.003) and cells (P = 0.026). In monoculture cells, litter (P = 0.001) and root mass (P = 0.001) differed among years. Litter mass increased more than threefold and root mass increased more than five from 2001 to 2003 (Table 1). In mixed culture cells, total AG biomass in patches of C. nebrascensis varied among years (P = 0.011) and nearly doubled from 2000 to 2003. By 2003, C. nebrascensis represented 90% of the total AG biomass in these patches. Root biomass (P = 0.008) and litter mass (P < 0.001) varied among years; both measures were greatest in 2003 (Table 1). In contrast, E. palustris AG biomass did not differ among years (P = 0.118). Still, litter mass in patches planted with E. palustris more than doubled from 2001 to 2003 and root mass experienced a four-fold increase from 2000 to 2003. From 2000 to 2002 mean total AG biomass in patches planted with J. balticus exhibited limited variation and exceeded 750 g/m2 each year (Table 1). By 2003, mean total AG biomass in these patches fell to 363 g/m2, but annual differences in total AG biomass and J. balticus AG biomass were not significant (P = 0.074 and P = 0.167). Similar to patches planted with C. nebrascensis, J. balticus AG biomass represented most (95% for all years) of the biomass in patches where it was originally planted. Litter
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Table 1 Mass of shoots (total and planted species only), roots, and litter reported in g/m2 for patches in primary filter cells planted with each of four species Species
Year
Shoots
Roots
Litter
Total
Planted species
Carex nebrascensis (mono)
2000 2001 2002 2003
365.8 520.1 516.0 677.3
249.2 317.9 437.7 657.9
281.4 822.6 1011.7 1582.1
– 251.7 453.9 819.9
Carex nebrascensis (mixed)
2000 2001 2002 2003
419.7 413.9 665.4 751.6
294.2 314.0 530.1 679.4
360.4 1070.8 1448.0 1728.9
– 246.9 337.2 808.6
Eleocharis palustris
2000 2001 2002 2003
279.2 98.2 354.9 430.7
50.8 5.2 19.8 55.4
229.3 171.5 674.1 920.7
– 234.6 374.0 558.4
Juncus balticus
2000 2001 2002 2003
757.6 829.4 795.6 363.0
701.0 788.4 742.3 338.8
674.3 925.2 1487.2 1587.1
– 198.2 864.1 1456.8
Schoenoplectus maritimus
2000 2001 2002 2003
395.6 153.0 395.6 581.6
33.3 2.3 96.4 123.8
387.5 386.2 650.5 1322.1
– 217.1 264.4 500.0
There were no differences in total AG biomass, C. nebrascensis biomass, or root biomass between C. nebrascensis monoculture cells and C. nebrascensis patches in mixed species cells in any of the four sample years. 3.2. Shallow wetlands
Carex nebrascensis values are shown separately for monoculture cells and mixed species cells. Dashed lines indicate no data.
mass in J. balticus patches differed among years (P < 0.001) and increased 7 from 2001 to 2002; root biomass did not differ among years (P = 0.079). Mean total AG biomass in patches of S. maritimus differed among years (P = 0.021), but S. maritimus contributed on an average only 21% (124 g/ m2) of that total AG biomass in patches where it was planted. In these same patches, C. nebrascensis and J. balticus represented 36 and 27% of the total AG biomass. As early as 2000, C. nebrascensis and J. balticus patches had significantly greater AG biomass than E. palustris and S. maritimus in primary filter cells planted with mixtures of species. In that same year there were no differences in total AG biomass or root biomass among patches planted with different species (Table 1). Differences in total AG biomass were detected among patches planted with different species in 2001 (P = 0.001), 2002 (P = 0.006), and in 2003 (P = 0.002). In each year those differences were the result of greater AG biomass in patches planted with C. nebrascensis or J. balticus. AG biomass of planted species, rather than all species, showed similar patterns, with significant species differences in 2001, 2002, and 2003 (P < 0.001 for all years). Root mass varied among species in 2001 (P = 0.005) and 2002 (P = 0.016). Litter mass varied among patches in 2002 (P = 0.006) and 2003 (P < 0.001) only; J. balticus patches had nearly 3 as much litter as patches planted with E. palustris or S. maritimus (Table 1).
From 2000 to 2003 the mean AG biomass of the patches sampled in the shallow wetland cells increased from 81.9 to 390.8 g/m2, while root mass increased from 108.4 to 573.6 g/m2. From 2001 to 2003, litter mass increased from 67.9 to 214.3 g/m2. Although the biomass of all three planted species increased over the four years of monitoring (Table 2), the proportion of total AG biomass that was contributed by these species never reached values approaching those for C. nebrascensis or J. balticus of primary filter cells. In 2003 S. acutus contributed 63% of the AG biomass where it was planted, S. pungens contributed only 39% where it was planted, and T. latifolia contributed 50%. In patches planted with S. acutus there were significant increases in root mass (P < 0.001), but not in AG biomass or litter mass from 2000 to 2003. S. pungens patches experienced no significant changes in the AG biomass of S. pungens, root mass, or in litter mass. For patches planted with T. latifolia there were significant increases in total AG biomass (P = 0.016), biomass of T. latifolia (P = 0.007), and litter (P = 0.002) over the 4-year period of record. In these patches, average root mass experienced a six-fold change from 2000 to 2003 (Table 2), but difference among years or cells was not significant. Total AG biomass, AG biomass of planted species, root mass, and litter mass did not differ among patches planted with the three species in any of the sample years. However, there were differences among the four shallow wetland cells for litter in 2001 (P = 0.032) and in 2003 (P = 0.034). To examine the effects of flooding on measures of production for each species, two flood events (see Fig. 1 for Table 2 Mass of shoots (total and planted species only), roots, and litter reported in g/m2 for areas in shallow wetlands planted with each of the three species Species
Year
Shoots Total
Planted species
Roots
Litter
Schoenoplectus acutus
2000 2001 2002 2003
56.5 208.9 249.3 424.9
16.6 71.5 132.8 269.0
101.6 407.9 557.1 903.8
– 82.1 153.9 224.9
Schoenoplectus pungens
2000 2001 2002 2003
72.2 112.7 162.5 375.0
21.9 35.4 43.3 106.9
152.2 143.6 320.2 354.4
– 52.5 165.5 243.9
Typha latifolia
2000 2001 2002 2003
117.1 197.0 277.3 372.7
16.2 42.4 110.2 185.7
71.5 189.6 471.1 462.5
– 69.1 132.5 174.2
Dashed lines indicate no data.
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Fig. 1. Hydrograph for each shallow wetland during a representative flooding in June 2003. For this flood, waters entered the wetlands within a window of 4 h, yet total flood duration differed among wetlands by over 38 h.
an example of one flood; mean flood duration calculated from all four wetlands for event 1 and 2 were 5.1 and 4.8 days, respectively) were summarized during the 2003 irrigation season. S. acutus root mass was positively correlated with mean flood duration (R = 0.986, P = 0.014). We found no significant relationships between mean flood duration and measures of standing stock biomass for S. pungens and T. latifolia. Shallow wetland B was flooded for the shortest duration and shallow wetland C was flooded the longest amount time for the focal flood events (see Fig. 1). In both cases the rank order of wetland mean flood duration was the same as the rank order of S. acutus and S. pungens AG biomass; wetlands that were flooded longer also had higher AG biomass and this was true for both species of Scheonoplectus.
4. Discussion 4.1. Primary filter biomass Introduced vegetation in the eight experimental wetland cells that make up the primary filters underwent rapid development, however, establishment patterns differed considerably for the four species that were planted in these cells. By 2001, just two full growing seasons after planting, mean total root mass exceeded AG biomass for all species. Invasion of planted patches occurred soon after planting and continued through 2003. Patches originally planted with either E. palustris or S. maritimus were quickly invaded by C. nebrascensis and J. balticus. By 2003, 34% of the AG biomass in patches originally planted with E. palustris was C. nebrascensis and 39% was J. balticus and similar levels of invasion were noted in patches originally planted with S. maritimus. Under the conditions present at FCW, it is likely that S. maritimus and E. palustris will be outcompeted by the other species, further diminishing their presence in the wetlands. Invasion also occurred in patches planted with J.
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balticus and C. nebrascensis even though these species established rapidly after planting. J. balticus was more successful at invading patches planted with C. nebrascensis than the reverse and J. balticus was not restricted to regions of C. nebrascensis patches where the species shared a border. Instead, J. balticus was present and established throughout patches of C. nebrascensis. The long-term dataset from FCW also suggests these species are complementary; patches containing both species are more productive than patches where species are growing alone (Ray, 2005). Aboveground biomass, litter mass, and total root mass generally increased with time; however, the patterns of development differed by species. AG biomass of C. nebrascensis at FCW was similar but mean litter mass was less than the 1155 g/m2 reported for this same species elsewhere (Ratliff and Westfall, 1988). Annual changes in C. nebrascensis, contrasted with those of the other three species. J. balticus reached a maximum in AG biomass in 2001 and had its lowest biomass in 2003. Both E. palustris and S. maritimus had lowest AG biomass in 2001, two years after planting. AG biomass of E. palustris in 2003 was nearly identical to those measured in 2000. Total root mass in the primary filter cells exceeded total AG biomass in all species patches. Root:shoot ratios for all species exceeded 2 by 2003. Patches originally planted with J. balticus had the highest root to shoot ratio at 4.4. Total root mass for C. nebrascensis and J. balticus were less than values reported elsewhere. Manning et al. (1989) documented total belowground biomass of 3382 for C. nebrascensis and 2545 g/m2 for J. balticus. Ratliff and Westfall (1988) documented belowground biomass as >6000 g/m2 for populations of C. nebrascensis in California. Belowground biomass of C. nebrascensis is thought to reach its seasonal maximum at the close of the growing season during shoot senescence (Ratliff and Westfall, 1988). Therefore, the September sampling estimates reported here likely coincided with this species’ seasonal maximum, but were simply below the root masses reported for established populations elsewhere. 4.2. Shallow wetland biomass From 2000 to 2003 total AG biomass in the shallow wetlands increased nearly five-fold, to 382 g/m2, and belowground biomass increased more than five-fold, to 574 g/m2. Mean litter mass in 2003 was 214 g/m2 averaged across all species. These values are similar to those reported by Hoagland et al. (2001) for a constructed wetland treating agricultural tile drainage in Illinois four years after establishment. There, total AG biomass was 570 g/m2 and litter mass in October was 100 g/m2, down from a maximum of 400 g/m2 earlier that season; root mass in this wetland had a seasonal maximum of 2300 g/m2 (Hoagland et al., 2001). From the description of their focal
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wetland, the dominant plant species were different than those at FCW, however, similarities in wetland age provided an opportunity to compare measures of production. Root to shoot ratios for vegetation growing in the patches originally planted with S. acutus, S. pungens, and T. latifolia were 2.1, 0.9, and 1.2. These values are relatively low compared with those calculated in the primary filter cells. However, establishment of vegetation in the shallow wetlands has been slower and this measure may further characterize the sluggish pattern of establishment witnessed in shallow wetlands at FCW. Aboveground biomass of T. latifolia was greatest in wetland C (>300 g/m2 in 2003). This value is considerably lower than the biomass reported in natural wetlands elsewhere. For example, Dickerman and Wetzel (1985) reported AG biomass averaging 1076 g/m2 over a 2-year study in Michigan. Similarly, Boyd (1971) found AG biomass patterns of T. latifolia stands ranged from 530 to 1132 g/m2 in five wetlands in South Carolina. T. latifolia AG biomass and litter mass in a 1 ha shallow marsh located approximately 10 km from FCW and managed as part of the Sterling Wildlife Management Area, was 920 and 1060 g/ m2, respectively (Ray, 2005). Unlike the primary filter comparisons, shallow wetland (block) effects were detected in comparisons of biomass and litter among years and species. In 2003, total root biomass was positively correlated with flood duration and this relationship suggested that biomass differences among wetlands are at least partially the result of differences in the hydrographs of the four shallow wetlands (Fig. 1). Biomass development and litter accumulation were greatest in patches planted with C. nebrascensis and J. balticus. Both species are common to riparian corridors and montane meadows, and are widely used in wetland construction and restoration efforts in the Western U.S. Flows at FCW were tied to sporadic irrigation events and resulted in prolonged periods of flooding and drying. This hydrologic regime may have selected for species better adapted to extended periods of drawdown (C. nebrascensis and J. balticus) over other emergent species commonly used in treatment wetlands elsewhere. Acknowledgements Support for this research was provided by the Center for Ecological Research and Education, the Idaho State Board of Education, the NSF-Idaho EPSCOR Program, and the National Science Foundation under award number EPS0447689. We thank landowners Neil and Marita Poulson for their support and assistance with the Fairview Constructed Wetland. Edward Buhler, Ryan Dunham, Aaron Inouye, Martha Inouye, Amy Jenkins, Scott Owen, Linda Qvarnemark, and Heather Ray provided much needed assistance in the field and in the lab.
References Allen, W.C., Hook, P.B., Biederman, J.A., Stein, O.R., 2002. Temperature and wetland plant species effects on wastewater treatment and root zone oxidation. J. Environ. Qual. 31, 1010–1016. Boyd, C.E., 1971. Further studies on productivity, nutrient and pigment relationships in Typha latifolia populations. Bull. Torrey Bot. Club 98, 144–150. Brix, H., 1997. Do macrophytes play a role in constructed treatment wetlands? Water Sci. Technol. 35, 11–17. Brueske, C.C., Barrett, G.W., 1994. Effects of vegetation and hydrologic load on sedimentation patterns in experimental wetland ecosystems. Ecol. Eng. 3, 429–447. Coleman, J., Hench, K., Garbutt, K., Sexstone, A., Bissonnette, G., Skousen, J., 2001. Treatment of domestic wastewater by three plant species in constructed wetlands. Water Air Soil Pollut. 128, 283–295. Dickerman, J.A., Wetzel, R.G., 1985. Clonal growth in Typha latifolia: population dynamics and demography of the ramets. J. Ecol. 73, 535–552. Edwards, G.S., 1991. Root distribution of soft-stem bulrush (Scirpus validus) in a constructed wetland. Eco. Eng. 1, 239–243. Gearheart, R.A., Klopp, F., Allen, G., 1989. Constructed free surface wetlands to treat and receive wastewater: pilot project to full scale. In: Hammer, D.A. (Ed.), Constructed Wetlands for Wastewater Treatment Municipal, Industrial, and Agricultural. Lewis Publishers, Chelsea, pp. 121–137. Hoagland, C.R., Gentry, L.E., David, M.B., Kovacik, D.A., 2001. Plant nutrient uptake and biomass accumulation in a constructed wetland. J. Freshwater Ecol. 16, 527–540. Kovacic, D.A., David, M.B., Gentry, L.E., Starks, K.M., Cooke, R.A., 2000. Effectiveness of constructed wetlands in reducing nitrogen and phosphorus export from agricultural tile drainage. J. Environ. Qual. 29, 1262–1274. Luckeydoo, L.M., Fausey, N.R., Brown, L.C., Davis, C.B., 2002. Early development of vascular vegetation of constructed wetlands in northwest Ohio receiving agricultural waters. Agric. Ecosyst. Environ. 88, 89–94. Manning, M.E., Swanson, S.R., Svejcar, T., Trent, J., 1989. Rooting characteristics of four intermountain meadow community types. J. Range Manage. 42, 309–312. NCDC (National Climatic Data Center), 2001. Climatic data for Aberdeen, Idaho. http://www.weather.com/weather/climatology/USIDO50. Pullin, B.P., Hammer, D.A., 1991. Aquatic plants improve wastewater treatment. Water Environ. Technol. 3, 36–40. Ratliff, R.D., Westfall, S.E., 1988. Biomass trends in a Nebraska sedge meadow, Sierra National Forest, California. Aquat. Bot. 30, 109–124. Ray, A.M., 2005. Physical, chemical, and biological interactions in wetlands: a case study using Fairview Constructed Wetland in southeastern Idaho. Ph.D. Dissertation, Idaho State University, Pocatello, Idaho, USA. Ray, A.M., Inouye, R.S., 2006. Effects of water-level fluctuations on the arbuscular mycorrhizal colonization in Typha latifolia L. Aquat. Bot. 84, 210–216. Reddy, K.R., De Busk, W.F., 1985. Nutrient removal potential of selected aquatic macrophytes. J. Environ. Qual. 14, 459–462. Tanner, C.C., Sukias, J.P., 1995. Accumulation of organic solids in gravelbed constructed wetlands. Water Sci. Technol. 32, 229–239. United States Department of Agriculture Natural Resource Conservation Service, 2000. Conservation Practice Standard, Constructed Wetlands, CODE 656, National Handbook of Conservation Standards. http:// www.nrcs.usda.gov/Technical/Standards/nhcp.html. Weller, C.M., Watzin, M.C., Wang, D., 1996. Role of wetlands in reducing phosphorus loading to surface water in eight watersheds in the Lake Champlain Basin. Environ. Manage. 20, 731–739. Wetzel, R.G., 1990. Land-water interfaces: metabolic and limnological regulators (Edgardo Baldi Memorial Lecture). Ver. Int. Ver. Limnol. 24, 6–24. Zar, J.H., 1999. Biostatistical Analysis. Prentice Hall, Upper Saddle River.