Part IV Applications of Wetland Plant Studies L1372 - Chapter 9 04/19/2001 9:20 AM Page 323 © 2001 by CRC Press LLC 9 Wetland Plants in Restored and Constructed Wetlands Around the world, wetland area has diminished due to ever-increasing human pressures. Our increased understanding and appreciation of wetland functions and values have spurred legislation to protect wetlands as well as popular interest in wetland preservation. Today, in an effort to stem the rate of wetland loss, wetlands are being restored or new wet- lands are being created in many parts of the world. In the U.S., although wetlands continue to be lost to development, agriculture, and other landscape alterations, many of these losses are compensated by the construction of new wetlands. In addition, hundreds of wet- lands have been built to treat wastewater of a variety of types. These treatment wetlands are an application of the natural water-cleansing functions of wetlands. A number of terms concerning wetland restoration and creation are in use (Table 9.1). In this chapter, we use the term restored wetlands to refer to wetlands that are reinstated where they once were. Within our definition of restored wetlands, we include those that are enhanced by, for example, the removal of an invasive species or the introduction of a desir- able plant or animal species. Entirely new wetlands, built where there were previously TABLE 9.1 Definitions of Some of the Terms Related to Restored and Constructed Wetlands Constructed Any wetland that is made by humans rather than naturally occurring; refers to new wetlands built on a site where there were previously no wetlands; it can also refer to treatment wetlands Restored Includes enhancing an existing wetland by removing an invasive species, restoring some aspect such as the hydrology or topography of an existing wetland, building a wetland where one existed previously, and building a wetland in an area where wetlands probably were, such as in a riparian zone Enhanced The enhancement of an existing wetland by removing invasive species or restor- ing past animal or plant species or other aspects of the wetland (we include enhanced wetlands in restored wetlands) Created A new wetland, made on a site where there were not wetlands in the past Mitigation Wetlands constructed to replace wetlands that have been destroyed; may be created, preserved, or restored wetlands Replacement The same as mitigation wetlands Treatment Built to treat a specific wastewater problem such as domestic sewage, nonpoint source pollution, mine drainage, or animal farm wastewater Artificial Can refer to a created or treatment wetland, not widely used L1372 - Chapter 9 04/19/2001 9:20 AM Page 325 © 2001 by CRC Press LLC none, are called created or constructed wetlands. Wetlands created, restored, or preserved to compensate for the loss of natural wetlands due to agriculture and development are called mitigation or replacement wetlands. We use the term treatment wetlands to refer to wetlands built to improve water quality. While we discuss some aspects of these wetlands in general terms, we concentrate on the plants and plant communities. We discuss the development of wetland plant commu- nities in newly created and restored wetlands and the role of plants in treatment wetlands. I. Wetland Restoration and Creation The restoration and creation of wetlands challenge our knowledge of ecosystem ecology. Can humans restore or create peatlands, swamps, marshes, and other wetland types? Can we duplicate the many complex functions of natural wetlands? Is it possible to re-create in a short period of time ecosystems that have taken centuries or longer to develop? Some types of wetlands, such as freshwater marshes, are easier to restore than rare wetland types with specialized plant species, such as peatlands, sedge meadows, and wetlands fringing olig- otrophic rivers and lakes (Galatowitsch and van der Valk 1996; Weiher et al. 1996). Because natural wetlands are in constant flux, due to periodic disturbance or climatic variability, the goal of wetland restoration or creation can be a shifting target (Clewell and Lea 1990). The most important aspect of restoring or creating wetlands is restoring or providing for the natural hydrology. There must be sufficient water flow to maintain hydric soils and hydrophytic vegetation. A key challenge is to reinstate the correct hydroperiod and allow for the hydrologic variability that occurs in natural wetlands. Restoring hydrology may involve providing or removing control structures in order to re-establish water flow or flooding regimes. In agricultural land, tile drains may need to be removed or broken. In some cases, fill material has to be removed. In tidal marsh restoration, the tidal regime and elevation are vital parameters because they determine the extent, duration, and timing of submergence (U.S. National Research Council 1992). Beyond hydrological remediation, steps to ensure sediment restoration may also be necessary. For example, the input of sed- iments from upland may need to be controlled, sediment dams in streams may need to be removed, and protective beaches or sand spits may need to be restored. Water quality is also important; controlling contaminant loadings is a vital step in many restoration efforts (Wilcox and Whillans 1999). Wetland restoration includes a variety of activities. The restoration could involve diverting or eliminating a source of pollution, repairing damage caused by nearby devel- opment, reintroducing desirable species, reducing the population of exotics, or restoring wetlands where they existed previously (Wheeler 1995). Clewell and Lea (1990) described three levels of restoration for forested wetlands that apply to all wetland types: • Enhancing an existing wetland to accelerate succession (or slow it down), or to provide suitable habitat for an endangered species • Restoring a wetland so that its former hydrology is in place; this may be all that is necessary for its plant community to return • Creating a wetland that resembles a locally indigenous wetland community in species composition and physiognomy on sites that have been altered The success of wetland restoration depends, in part, on the degree of disturbance at the project site and the condition of the surrounding landscape at the beginning of the project. Success is more likely in areas with little or short-term disturbance and where the landscape L1372 - Chapter 9 04/19/2001 9:20 AM Page 326 © 2001 by CRC Press LLC is generally in its natural condition. The most difficult wetlands to restore are those in very degraded sites, such as the salt marshes of southern California and the Hackensack River Meadowlands of New Jersey (U.S. National Research Council 1992). Wetlands in urban- ized areas or in many developing countries are also difficult to restore due to intense human pressures (Helfield and Diamond 1997; Walters 1997, 2000a, b; see Case Study 9.A, Integrating Wetland Restoration with Human Uses of Wetland Resources). To determine the success of restoration, a monitoring plan is usually part of the project. Deciding whether or not a restoration project has been successful is often based on the structure of the plant community or on an ecosystem function such as primary productiv- ity. In some cases, the presence or absence of indicator species can reveal whether a project is successful (see Case Study 9.B, Restoring the Habitat of an Endangered Bird in Southern California). Monitoring often includes comparing the restored wetland to nearby natural reference wetlands. Parameters that are compared include species diversity, plant produc- tivity, stem density, sediment texture, sediment nutrient content, invertebrate populations, and wildlife use (Langis et al. 1991; Zedler 1993; Havens et al. 1995; Boyer and Zedler 1998; Walters 2000b). Throughout the monitoring period, it is important that the restoration plan remain flexible in order to respond to problems. A management strategy that adapts to problems and allows for changes is essential in many cases (Zedler 1993; Pastorok et al. 1997; Thom 1997). The necessary length of the monitoring period varies with the type of wetland and the goals of the project. In many cases, success is assumed if the new wetland’s community structure resembles that of reference wetlands. However, the establishment of food webs, the movement of carbon and energy, nutrient recycling, and other wetland functions may never be restored, or may take many years to develop (McKee and Faulkner 2000). For salt marshes, estimates of the time required for the success of plant community restoration vary from 3 to 10 years or even longer (Broome et al. 1988). Because of wide year-to-year variability, Zedler (1993) suggests that salt marsh restoration requires 20 years of monitor- ing along with a large data base from natural reference wetlands against which to com- pare. Forested wetlands may require much longer monitoring periods because of the long establishment time for trees. Given the correct hydrological conditions, restored mangrove forests may resemble natural communities within about 20 years of planting (Ellison 2000b). Mitsch and Wilson (1996) suggest that restored wetlands of all types should be given enough time for wetland functions to become established. They state that monitor- ing should continue for 15 to 20 years or even longer for specific types of wetlands (e.g., forested, coastal, and peatlands). A. The Development of Plant Communities in Restored and Created Wetlands Whether plants are carefully chosen and planted, arise from the seed bank, or arrive through natural dispersal mechanisms, the new wetland plant community is determined, to a large extent, by the environmental conditions found in the wetland. While some wet- land restoration efforts include planting and managing for specific species, others have relied on volunteer plant species to colonize the site. Propagules arrive via wind, water, or animals. In some restored sites, wetland species already exist in the seed bank. 1. Environmental Conditions One way to look at the assembly of wetland plant communities is as a series of filters, or environmental sieves, that strain species so that only the final assemblage remains (see Chapter 7, Section III.A.3, The Environmental Sieve Model; van der Valk 1981). Knowledge L1372 - Chapter 9 04/19/2001 9:20 AM Page 327 © 2001 by CRC Press LLC of each of the filters and how to manipulate them aids in restoring the desired community. Filters in wetlands include water levels, soil fertility, disturbance, salinity, competition, herbivory, and the accumulation of sediments that may bury seeds and propagules. Different wetland types may be more influenced by some filters than others. For example, species distribution in estuarine wetlands is heavily influenced by salinity, while plants in deltaic wetlands may be influenced most by the accumulation of sediments (Keddy 1999). Organisms possess life-history traits that allow them to pass through different filters. A systematic method of predicting how a set of species might respond to a particular filter would be helpful in many cases (Shipley et al. 1989; Keddy 1999). Screening studies pro- vide data that enable the researcher to predict how a set of species might respond to a par- ticular filter. In order to screen wetland plants, a large number of species would need to be exposed to a certain filter or a set of filters. For example, in a salt marsh or mangrove, salin- ity levels provide a suitable filter to test, since the number of salt-tolerant plants is rela- tively low. In wetlands where there are multiple filters, screening might be more complex but still feasible, particularly if one or two filters, such as climate or water regime, can be used to filter out a large number of potential plant species (Keddy 1999). FIGURE 9.1 Growth parameters of salt-tolerant species from Otago, New Zealand salt marshes: 1 = salinity for maximum growth, 2 = half-growth salinity, 3 = salinity for death of plant parts, 4 = cessation of growth. The species are arranged in order based on cessation of growth. Asterisks indicate significant (p = 0.05) salt requirements for max- imum growth. The thickness of the horizontal lines indicates the highest rates of growth and the vertical line, sea- water salinity. (From Partridge, T.R. and Wilson, J.B. 1987. New Zealand Journal of Botany 25: 559–566. Reprinted with permission.) L1372 - Chapter 9 04/19/2001 9:20 AM Page 328 © 2001 by CRC Press LLC Partridge and Wilson (1987) performed a screening experiment with 31 of the most fre- quently encountered species in the salt marshes of Otago, New Zealand. They measured the effects of salinity on survival and growth and found considerable differences among species (Figure 9.1). Most could not grow in seawater, which has a salinity of 35 ppt, although a small number could grow in hypersaline conditions of up to 75 ppt. Some species required some salt for maximum growth (e.g., Suaeda novae-zelandiae), although none required salt to survive. Most of the species grew best in fresh water. Similar knowl- edge of the salt tolerance, water level requirements, or other adaptations of a wide variety of plants would allow wetland restorationists to choose appropriate species for the envi- ronmental conditions of their site. 2. Self-Design and Designer Approaches The designer approach and self-design are two general approaches to introducing vegeta- tion to restored or constructed wetlands. The designer approach involves introducing and maintaining chosen plant species (and sometimes animals). In this approach, the wetland restorationist needs an understanding of the life history of the species involved, including their dispersal, germination, and establishment requirements (Middleton 1999). In the sec- ond approach, called ‘self-design,’ the self-organization capacity of natural systems is emphasized (Mitsch and Wilson 1996). In this approach, species may arrive as volunteers through wind, water, or animal dispersal. Species might also be introduced to the wetland, but their ultimate survival depends on the ecosystem’s conditions, which filter out species not adapted to the conditions at hand. The assemblage of plants, microbes, and animals that is best adapted to the existing conditions will persist, while all other species will dis- appear from the system or not become established. Although the introduction of plants is often required in order to comply with a mitiga- tion or restoration plan, it may not always be ecologically necessary. When specific plants are chosen and carefully planted, their establishment and survival are ultimately a func- tion of the abiotic filters in the wetland. When volunteer species arrive, as long as they are not invasives or otherwise undesirable, their presence is usually welcome in restored wet- lands in which the self-design principle is at work. The self-design approach may, in some instances, be more sustainable than the close maintenance required in the designer approach (Mitsch et al. 1998). However, when a restoration site has a poor seed bank and limited possibilities for seed or propagule dispersal, planting may result in a more rapidly vegetated wetland (Middleton 1999). If the goal is to enhance the population of a specific species or set of species, wetland managers must ensure those species’ survival and inter- vene with adaptive management approaches when necessary (Zedler 1993; 2000b). The extent and rate of revegetation by natural dispersal can be unpredictable and depend on many interacting (and little understood) variables, including the availability of upstream or upwind seed sources, soil temperature and moisture regimes, streamflow regimes, slopes, soil fertility, and disturbance patterns (Goldner 1984; Day et al. 1988). In general, where there are nearby natural wetlands, more recovery of local flora might be expected, especially for species that are dispersed by wind or waterfowl. Species with poor dispersal capabilities may have to be reintroduced during restoration (Leck 1989; van der Valk and Pederson 1989; Reinartz and Warne 1993; Keddy 1999). Some studies have shown that when initial conditions are suitable in constructed and restored wetlands, plant species arrive and new plant communities form, often without any human intervention (but see Case Study 9.C, Vegetation Patterns in Restored Prairie Potholes). In four constructed freshwater marshes in Illinois (from 1.9 to 3.4 ha in size; Figure 9.2) plant diversity increased with time (Fennessy et al. 1994a). During the first 4 © 2001 by CRC Press LLC years of the wetlands’ existence, the number of wetland taxa (obligate and facultative wet- land species) increased from 2 to 19 in the first marsh, from 14 to 28 in the second, from 13 to 17 in the third, and from 12 to 22 in the last. Only one species was introduced, and it was only planted in the first marsh; all of the others arrived as volunteers. In two 1-ha constructed marshes in Ohio, an experiment to test the effects of planting on species diversity began in 1994, when one of the marshes was planted with 13 species while the second was left unplanted. By the beginning of the fourth growing season, the plant cover in the unplanted wetland (58%) slightly exceeded the plant cover in the planted wet- land (51%; Mitsch et al. 1998). By the end of the 1998 growing season, the number of wet- land plants (obligate and facultative wetland species) in the planted wetland had increased from the 13 introduced species to 55 species. The number of species in the unplanted wet- land increased from 0 to 45 species. The planted wetland has more species because many of the original planted species have become established there (Bouchard and Mitsch 1999). In both the Ohio and Illinois studies, rivers adjacent to the study site were the main source of water for the constructed wetlands. Riverine wetlands may be more likely to revegetate naturally than isolated wetlands because the river water carries seeds and propagules from upstream wetlands (Middleton 1999). Early introduction of a diversity of wetland plants may enhance the ultimate diversity of vegetation in constructed and restored wetlands. Reinartz and Warne (1993) examined the colonization of 5 constructed freshwater marshes that were seeded with 22 native species. They compared these to 11 unseeded constructed marshes. The diversity of native wetland species increased with wetland age, wetland size, and with proximity to the near- est established wetland. After 3 years, the unseeded wetlands had an average of 22 species. In contrast, the 5 seeded wetlands had an average of 42 species; 17 of the 22 planted species became established. Typha latifolia and T. angustifolia became the most dominant species in FIGURE 9.2 An aerial photograph of four constructed marshes at the Des Plaines River Wetlands Demonstration Project in Illinois. The marshes were built for research purposes. The water source, the Des Plaines River, has relatively high levels of suspended solids and nutrients from agricultural sources. Researchers tested the capacity of the marshes to ameliorate water quality and they examined wetland plant community development. (Sanville and Mitsch 1994; photo courtesy of D. Hey, Wetlands Research, Inc.) © 2001 by CRC Press LLC the unseeded wetlands; their cover increased from 15 to 55% during the 3-year study. The extent of the Typha cover was lower in the seeded sites with an average of 22% cover in the second year. Cover by the seeded species accounted for the difference in the Typha cover. 3. Seed Banks in Restored Wetlands Seed banks may be present in restored wetlands from prior periods of wetland plant growth. The seeds of most herbaceous wetland species are capable of persisting more than a year in soil, and some persist for many years. Persistent species often have small seeds that respond positively to light, increased aeration, and/or alternating temperature. Herbaceous species dominate wetland seed banks, with graminoids usually constituting over half of the seed bank (Leck 1989). In restoration projects, seed banks have been used to restore or establish native vege- tation. Seed banks can be used only if suitable conditions can be established and main- tained for the germination of the preferred species. Seed banks may not be the entire answer for the restoration of native vegetation because the desired species may not be rep- resented or because the seeds of unwanted species are present (van der Valk and Pederson 1989). Seed banks in forested wetlands typically do not reflect the woody plant commu- nity. Rather, seeds are often from herbaceous species from nearby open areas. One cannot rely on the seed bank in forested wetland restoration projects, including mangrove forests (Leck 1989; Buckley et al. 1997; Walters 2000b). The following are recommendations regarding the use of seed banks in restored wetlands: • Before a management plan that relies on a seed bank is implemented, it is impor- tant to test the seed bank to determine the presence of viable seeds and the com- munity composition (van der Valk and Pederson 1989). However, results of seed bank tests do not always reflect the species composition of the restored plant community. The hydrologic regime or soil organic matter of the restored site may allow for the germination of some species, but not others (van der Valk 1981; Wilson et al. 1993; ter Heerdt and Drost 1994). • Relict seed banks can be used in the restoration of native vegetation, but their utility decreases with time because many seeds lose their viability. Sites where native vegetation has only recently been eliminated make the best candidates for restoration projects using the seed bank (van der Valk and Pederson 1989; Wienhold and van der Valk 1989; Galatowitsch and van der Valk 1994, 1995, 1996). • Historical records of plant distribution at the site are useful because the seeds of desired species will be present where they had the densest growth in the past (Leck and Simpson 1987; Welling et al. 1988a). • A period of drawndown conditions in which mudflats are exposed may enhance germination rates (van der Valk and Davis 1978; Siegley et al. 1988; Leck 1989; Willis and Mitsch 1995). However, if the purpose is to establish a maximum num- ber of emergent seedlings, a 1-year drawdown may be sufficient. In a 2-year seed bank study in a Canadian marsh, recruitment of emergents occurred primarily during the first year. Many of the first-year seedlings died during the second year of drawndown conditions (Welling et al. 1988b). • Knowledge of the desired plants’ life history is necessary. If only certain species within the seed bank are desirable, then it is essential to know the conditions L1372 - Chapter 9 04/19/2001 9:20 AM Page 331 © 2001 by CRC Press LLC required for germination (e.g., frost, aerobic conditions) as well as the plant’s optimal hydroperiod (van der Valk 1981; van der Valk and Pederson 1989). • The seed bank should not be covered with other sediments. For instance, 1 cm of sand can substantially reduce germination (Leck 1989). • In general, germination rates in sand or sites with finely textured or highly organic soils are lower and these substrates should be avoided where possible (Leck 1989). • The seeds of woody species are not common (as compared to herbaceous species), even in swamp seed banks, so for the restoration of forested or shrub wetlands, planting is necessary (Leck 1989). Donor seed banks from other sites can be used in restoration projects, but they should be tested for species composition. Donor soils should be collected and carefully preserved in order to avoid a loss in seed viability. They should be used at the beginning of the grow- ing season when germination would naturally occur (van der Valk and Pederson 1989). The uppermost portion of the soil contains the highest concentration of seeds and should be preserved. van der Valk and Pederson (1989) recommend that donor soils be collected to a depth no greater than 25 cm. If the soil layer is too thick, the seed bank is diluted and lower germination rates result (Putwain and Gillham 1990). Donor seed banks can enable the rapid development of diverse native vegetation and impede the establishment of unwanted species (van der Valk and Pederson 1989). B. Planting Recommendations for Restoration and Creation Projects The goal of many restoration projects is to produce a sustainable, diverse plant community with high percentages of desirable species that will attract wildlife. In some cases, partic- ularly where the new wetland is close to natural ones, plants will arrive via natural dis- persal mechanisms (Mitsch et al. 1998). When a specific community is desired, such as in the restoration of rare communities or a specific habitat type, or when natural dispersal may be unlikely, wetland restorationists must choose species for the site. The edaphic and hydrologic conditions of a site should be assessed in order to choose the right species and the best planting techniques (Imbert et al. 2000). Nichols (1991) suggests asking the fol- lowing questions when considering species for restoration or construction projects: • Does the species have the desired properties needed in the restoration? Does the plant provide good waterfowl food, desirable fish habitat, and aesthetic value? Is it able to withstand wind or waves? • Does the species have weedy tendencies? Will it become a nuisance? • Does the species have the potential to grow and reproduce well enough to main- tain and increase its population? • How large an initial population is needed to ensure a viable stand, taking into account losses from herbivores, pathogens, poor reproductive success, wind and wave action, and adverse climatic conditions? • Is the physical and chemical habitat suitable for the desired species? Even if the species formerly grew in the area, the habitat might have been altered to the extent that it is no longer suitable. Planting techniques have been developed for many species and the nursery or other plant source should always be consulted for planting instructions. The instructions may be L1372 - Chapter 9 04/19/2001 9:20 AM Page 332 © 2001 by CRC Press LLC quite specific and should be followed to ensure success. For example, the instructions for propagating Spartina alterniflora indicate that seeds should be harvested by hand or machine as near as possible to maturity or just prior to release from the plant. The seeds are threshed after being stored at 1º to 4ºC for about 1 month. After threshing, the seeds are stored in covered containers filled with water with a salinity of 35 ppt at 2º to 4 ºC. Seeds are broadcast from mid-April to mid-June, depending on the latitude. The seeds are incor- porated into the substrate to a depth of 2 to 3 cm and the density of planting is 100 seeds m -2 . Seeding is only feasible in the upper half of the intertidal zone (Broome et al. 1988). The timing of planting in both temperate and tropical latitudes is crucial. Mangrove seedlings, for example, may be best planted at the onset of the rainy season (July/August) to avoid drought. However, if the shoreline is poorly sheltered, planting may be done ear- lier (February/March) when the mean sea level is at a minimum (Imbert et al. 2000). In general, when seeds are used, they may be broadcast or packed in mud balls before sowing. Whole plants or vegetative propagules can be placed directly in the sediments, or weighted with mesh bags and gravel and sown from the water surface. To plant emer- gents, it may be necessary to decrease the water level in order to expose the sediments and allow seeds to germinate (Nichols 1991). Some wetland types pose unique challenges. For instance, in the restoration of sedge meadows, it is difficult to establish the dominant sedges, such as Carex, whose seeds are short-lived and do not usually remain viable within seed banks (Reinartz and Warne 1993; van der Valk et al. 1999). To maximize the probability that Carex will become established, the use of fresh seeds is necessary, preferably seeds produced earlier in the same growing season. The soil moisture must be kept as high as possible and the soil’s organic matter content should be as high as that found in natural sedge meadows (van der Valk et al. 1999). Wetland restoration often includes the careful choice of native plants; however, inva- sives may become established. Fast-growing species such as Phragmites australis (common reed), Lythrum salicaria (purple loosestrife), and Typha species may dominate sites that were intended for other vegetation. Typha is frequently found in freshwater marshes; it often outcompetes other species and creates dense monocultures with little variety in food or habitat. Extensive stands of Typha have become established in several freshwater marsh restoration projects (Reinartz and Warne 1993; Fennessy et al. 1994a; Bouchard and Mitsch 1999). Weiher and others (1996) performed a 5-year mesocosm study using seeds from 20 wet- land species under a range of environmental conditions. Although all of the species germi- nated, only six species were found in large numbers after 5 years. By the end of the study, most of the mesocosms were dominated by Lythrum salicaria while the other eudicot species were extirpated. L. salicaria establishment and dominance were minimal only under low fertility conditions and when the mesocosms were flooded in the spring and early summer to a depth of 5 cm. The growth of Typha angustifolia was poor on coarse substrates (particle size >4 mm). To inhibit the establishment of these fast-growing species, adverse conditions such as those noted in this study might be included in the restoration plan. II. Treatment Wetlands Because of their capacity to enhance water quality, hundreds of wetlands have been con- structed around the world to treat liquid wastes in a number of forms, including domestic sewage (Figure 9.3; Hammer 1989; Kadlec and Knight 1996), livestock wastewater (Figures 9.4 and 9.5; Hammer 1994; Cronk 1996), nonpoint source pollution (Figure 9.2 Hammer L1372 - Chapter 9 04/19/2001 9:20 AM Page 333 © 2001 by CRC Press LLC [...]... NRCS 199 1 Hammer 199 3 NRCS 199 1, Biddlestone et al 199 1 NRCS 199 1, Hammer 199 3 NRCS 199 1, Hammer 199 3 Manna grass NRCS 199 1 Tanner 199 6 Tanner 199 6 Tanner 199 6 Tanner 199 6 Hornwort Naiad Pondweed Water weed Wild celery Hammer 199 3 Hammer 199 3 Hammer 199 3 Hammer 199 4 Hammer 199 4 Big duckweed Duckweed Water hyacinth Water lettuce Water fern Koles et al 198 7 Koles et al 198 7 Tanner 199 6 Tanner 199 6 Tanner...L1372 - Chapter 9 04/ 19/ 2001 9: 20 AM Page 334 199 2; Mitsch and Cronk 199 2), landfill leachate (Mulamoottil et al 199 9), stormwater runoff (Figure 9. 6; Livingston 198 9; Strecker et al 199 2), mine drainage (Wieder 198 9; Fennessy and Mitsch 198 9; Hedin et al 199 4; Nairn et al 2000), and other industrial discharges (Kadlec and Knight 199 6; Odum et al 2000) In addition, many riparian wetlands have been... Floating-Leaved Nelumbo lutea Nymphoides spp Nymphaea spp Common Name Arrowhead Bulrush Canna lily Cattail Elephant ear Giant cutgrass Iris Maidencane Pickerelweed Plantain Common reed Rush Sedges Water chestnut Wild rice Source NRCS 199 1, Hammer 199 3 NRCS 199 1, Hammer 199 3, Surrency 199 3 NRCS 199 1, Tanner 199 6 NRCS 199 1, Hammer 199 3 NRCS 199 1 NRCS 199 1, Surrency 199 3 NRCS 199 1, Hammer 199 3 NRCS 199 1 NRCS... habitat and make wastewater treatment wetlands aesthetically pleasing (Knight 199 7) For these reasons, vegetated treatment wetlands are more efficient at removing BOD, SS, nitrogen, and phosphorus than unvegetated wetlands (Table 9. 2; Radoux 198 2; Gersberg et al 198 6; Karnchanawong and Sanjitt 199 5; Ansola et al 199 5; Tanner et al 199 5a, b; Sikora et al 199 5; Zhu and Sikora 199 5; Heritage et al 199 5; Drizo... root, and rhizome Data for herbaceous species from authors 5 and 7–12 compiled in Greenway 199 7; data for tree species from authors 1–4 compiled in Reddy and DeBusk 198 7; additional data from Peverly 198 5, Reddy and DeBusk 198 7, and Greenway 199 7 1Schlesinger 10Gumbricht 197 8; 2Reynolds et al 197 9; 3Brown 198 1; 4DeBusk 198 4; 5Hocking 198 5; 6Peverly 198 5; 7Reddy and DeBusk 198 7; 8Breen 199 0; 9Tripathi... 4–64 Tanner et al 199 5a, b Karnchanawong and Sanjitt 199 5 81–100 84–100 97 99 95 98 58–78 25–66 79 97 81 91 34 96 3–57 54 95 55–71 67 91 22–34 11–56 99 45–75 85 95 45–75 Heritage et al 199 5 Drizo et al 199 7 Note: In some of the studies, several species were planted together, and for these only one set of results is given In others, species were planted separately and separate results for each species... nutrients Greenway ( 199 7) analyzed eight common wetland plant emergents and floating-leaved species from both high-nutrient load treatment wetlands and from control wetlands Plant phosphorus levels in the treatment wetlands averaged 2 mg P g-1 dry weight more than in the control wetlands Nitrogen levels averaged 7 mg N g-1 more than in control wetlands (calculated from data in Greenway 199 7) Plants near... stream load (Peverly 198 5) © 2001 by CRC Press LLC L1372 - Chapter 9 04/ 19/ 2001 9: 20 AM Page 348 The rates at which nitrogen and phosphorus accumulate in the substrate range between 0.1 and 4.7 g N m-2 yr-1 and between 0.005 and 0.22 g P m-2 yr-1 in moderate to cold climates, and up to 10.0 g N m-2 yr-1 and 0.5 g P m-2 yr-1 in warm, highly productive areas (as reviewed by Nichols 198 3) 4 Vegetation as... 199 6 American water lily Gentian Water lily Hammer 199 3 Hammer 199 3 Hammer 199 3 Note: The species from Tanner 199 6 have been used in New Zealand; some are of Asian origin The species from Biddlestone et al 199 1 and Koles et al 198 7 have been used in Europe The remaining species have been used in the U.S (NRCS 199 1 = U.S Natural Resources Conservation Service 199 1) © 2001 by CRC Press LLC L1372 - Chapter. .. LLC 9: 20 AM Plastic-lined beds, gravel substrate Location 04/ 19/ 2001 Wetland Type Surface flow Constructed marshes L1372 - Chapter 9 TABLE 9. 2 The Percent Removal of Wastewater Contaminants in Unplanted and Planted Treatment Wetlands L1372 - Chapter 9 04/ 19/ 2001 9: 20 AM Page 343 2 Physical Effects of Vegetation The presence of macrophyte stands reduces water velocity and allows for the filtering and . 58–78 34 96 Heritage et al. S. tabernaemontani 92 97 84–100 25–66 3–57 199 5 Baumea articulata 98 –100 97 99 79 97 54 95 Cyperus 97 99 95 98 81 91 55–71 involucratus Unplanted 87 95 67 91 22–34. (Figures 9. 4 and 9. 5; Hammer 199 4; Cronk 199 6), nonpoint source pollution (Figure 9. 2 Hammer L1372 - Chapter 9 04/ 19/ 2001 9: 20 AM Page 333 © 2001 by CRC Press LLC 199 2; Mitsch and Cronk 199 2), landfill. wetlands (Table 9. 2; Radoux 198 2; Gersberg et al. 198 6; Karnchanawong and Sanjitt 199 5; Ansola et al. 199 5; Tanner et al. 199 5a, b; Sikora et al. 199 5; Zhu and Sikora 199 5; Heritage et al. 199 5;