Emergent Wetland Plants Research Articles

Polynuclear aromatic hydrocarbons (PAHs) differentially influence growth of various emergent wetland species

The growth of emergent wetland plants may be influenced by toxic organic pollutants, which would influence the extent of phytoremediation when used in constructed wetlands. A series of glasshouse experiments were conducted to investigate the influence of polynuclear aromatic hydrocarbons (PAHs) on the growth of various emergent wetland species. The response of species to PAHs varied significantly. A significant interaction (species × PAH treatment) was observed for relative growth rates (RGRs) of Baumea juncea, Baumea articulata, Schoenoplectus validus and Juncus subsecundus in hydroponics with naphthalene, and of B. juncea and J. subsecundus in soils freshly spiked with phenanthrene and pyrene. In hydroponics, biomass of B. articulata significantly increased in the treatments with relatively low addition of naphthalene, whereas that of S. validus significantly increased with all naphthalene additions. In both hydroponics and soils, the growth of B. juncea increased with the PAH (phenanthrene and pyrene) additions, whereas that of J. subsecundus decreased in the treatments with relatively high concentrations of PAHs. The removal of PAHs from soil was not affected significantly by J. subsecundus after 70 days of growth and B. juncea after 150 days of growth. The growth of J. subsecundus was slightly (but not significantly) influenced by the PAH residues in soil. The effect of PAHs on wetland plant growth could be species-specific regardless of PAH types and media. The response of species to PAHs needs to be taken into account when selecting species for wetlands constructed for phytoremediation.

Cadmium Accumulation and Translocation in Four Emergent Wetland Species

Emergent wetland plant species may exhibit different capacity for phytoremediation when used in constructed wetlands. To evaluate cadmium (Cd) remediation capacity of four emergent wetland species (Baumea juncea (R.Br.) Palla, Baumea articulata (R.Br.) S.T. Blake, Schoenoplectus validus (M.Vahl) A. & D.Love, andJuncus subsecundus N.A. Wakef.), a glasshouse experiment was conducted in hydro- ponics to investigate the effects of Cd (0, 5, 10, and 20 mg L �1 )o n plant growth and Cd uptake and translocation as well as uptake of other nutrients after 14 days. The relative growth rates of the three species changed little in various Cd treatments, but was severely inhibited for B. juncea at 20 mg Cd per liter treatment. Hence, the Cd tolerance index (root length in Cd treatment vs. control) was significantly lower in B. juncea compared to other species. Among the species, the highest concentration of Cd was in the roots ofJ. subsecundus ,f ollowed by S. validus, B. articulata ,a ndB. juncea ,w hile the lowest concentration of Cd was in the S. validus shoots. Of all the species, J. subsecundus had the highest bioconcentration factor (BCF) in shoots, whereas S. validus and B. juncea had the lowest BCF in rhizomes and roots, respectively. The translo- cation factor was significantly lower in S. validus compared to the other species. J. subsecundus had a higher Cd accumulation rate than the other species regardless of the Cd supply. The lowest allocation of Cd in shoots was recorded for S. validus and in roots for B. juncea. The concentrations of other elements (P, S, Ca, Fe, Cu, and Zn) in shoots decreased with Cd additions, but the interactions between Cd and other elements in roots varied with the different species. These results indicate that the four wetland species have good tolerance to Cd stress (except B. juncea at high Cd exposure), varying in Cd accumulation and translocation in tissues. These properties need to be taken into account when selecting species for wetlands constructed for phytoremediation.

Understanding the potential effects of water regime and salinity on recruitment of Melaleuca ericifolia Sm.

Although many emergent wetland plants may readily tolerate rapid changes in flooding and drying under freshwater conditions, their tolerance to dynamic water regimes may be compromised by salinity. Melaleuca-dominated woodlands occur naturally in Australia, south-east Asia and New Caledonia. Coastal wetlands dominated by Swamp paperbark ( Melaleuca ericifolia) (Myrtaceae), native to south-east Australia, are commonly degraded as a consequence of altered water regime and salinity. This study simulates the release of M. ericifolia seeds from the aerial canopy under a range of water regime and salinity scenarios to determine conditions limiting sexual recruitment. Plant growth and survival were examined following seed release under two static water regimes (moist and flooded sediment) and two dynamic water regimes (simulated drawdown—“flooded-moist” and simulated re-flooding—“moist-flooded”). All water regimes, excluding the continuously flooded regime, were examined at three salinities: 0.1 dS m −1 (fresh), 8 dS m −1 and 16 dS m −1, over a 50-day period commencing 44 days after the seeds were sown. The flooded treatment was examined at 0.1 dS m −1 only, to confirm that flooding prohibits establishment of M. ericifolia. Seed and seedlings were positively buoyant and establishment was limited to moist soil. Flotation of seedlings in the flooded-moist treatment, however, did not inhibit subsequent establishment upon moist soil, even at the highest salinity of 16 dS m −1. Growth, but not survival, was reduced by salinities of 8 dS m −1 and 16 dS m −1 in the moist treatment. Flotation of seedlings in saline water in the flooded-moist treatment did not reduce growth or survival compared with fresh water. Survival of seedlings in the moist-flooded treatment was lower in the freshwater and 16 dS m −1 treatment compared with the moist treatment, but not at 8 dS m −1. These findings suggest that water regime influences establishment of young M. ericifolia plants more strongly than does salinity, at least up to ∼1/3 seawater and in the short term (<2 months). Seedlings are likely to establish during a drawdown where the soil is exposed at salinities of ≤16 dS m −1. In contrast, premature re-flooding of seedlings, even with fresh water, will compromise survival.

Methane emission from natural wetlands: interplay between emergent macrophytes and soil microbial processes. A mini-review.

According to the Intergovernmental Panel on Climate Change (IPCC) 2007, natural wetlands contribute 20-39 % to the global emission of methane. The range in the estimated percentage of the contribution of these systems to the total release of this greenhouse gas is large due to differences in the nature of the emitting vegetation including the soil microbiota that interfere with the production and consumption of methane. Methane is a dominant end-product of anaerobic mineralization processes. When all electron acceptors except carbon dioxide are used by the microbial community, methanogenesis is the ultimate pathway to mineralize organic carbon compounds. Emergent wetland plants play an important role in the emission of methane to the atmosphere. They produce the carbon necessary for the production of methane, but also facilitate the release of methane by the possession of a system of interconnected internal gas lacunas. Aquatic macrophytes are commonly adapted to oxygen-limited conditions as they prevail in flooded or waterlogged soils. By this system, oxygen is transported to the underground parts of the plants. Part of the oxygen transported downwards is released in the root zone, where it sustains a number of beneficial oxidation processes. Through the pores from which oxygen escapes from the plant into the root zone, methane can enter the plant aerenchyma system and subsequently be emitted into the atmosphere. Part of the oxygen released into the root zone can be used to oxidize methane before it enters the atmosphere. However, the oxygen can also be used to regenerate alternative electron acceptors. The continuous supply of alternative electron acceptors will diminish the role of methanogenesis in the anaerobic mineralization processes in the root zone and therefore repress the production and emission of methane. The role of alternative element cycles in the inhibition of methanogenesis is discussed. The role of the nitrogen cycle in repression of methane production is probably low. In contrast to wetlands particularly created for the purification of nitrogen-rich waste waters, concentrations of inorganic nitrogen compounds are low in the root zones in the growing season due to the nitrogen-consuming behaviour of the plant. Therefore, nitrate hardly competes with other electron acceptors for reduced organic compounds, and repression of methane oxidation by the presence of higher levels of ammonium will not be the case. The role of the iron cycle is likely to be important with respect to the repression of methane production and oxidation. Iron-reducing and iron-oxidizing bacteria are ubiquitous in the rhizosphere of wetland plants. The cycling of iron will be largely dependent on the size of the oxygen release in the root zone, which is likely to be different between different wetland plant species. The role of the sulfur cycle in repression of methane production is important in marine, sulfate-rich ecosystems, but might also play a role in freshwater systems where sufficient sulfate is available. Sulfate-reducing bacteria are omnipresent in freshwater ecosystems, but do not always react immediately to the supply of fresh sulfate. Hence, their role in the repression of methanogenesis is still to be proven in freshwater marshes.

Ecophysiological responses of five emergent-wetland plants to diminished water supply: an experimental microcosm study

Freshwater wetlands are fundamentally tied to hydrology as they are often found along the boundaries between terrestrial uplands and open waters. Although wetland systems are frequently prone to extended periods of flooding and exposure, the degree of water deprivation may intensify during periods of low precipitation or drought. Therefore, the purpose of this study was to evaluate plant–water relations in five emergent macrophytes (Carex alata, Juncus effusus, Peltandra virginica, Saururus cernuus, and Justicia americana) to simulated drought conditions. Weekly evaluations of tissue water content and xylem water potential (free energy of water in xylem tissues) were conducted on plants grown in experimental microcosms over a 9-week period. Plant performance was also evaluated in each species by monitoring the changes in plant biomass, leaf area, and survival. The results indicate that J. effusus and P. virginica performed better in both flooded and moderately dry conditions, and plants that maintained higher water content in water logged soils (i.e., J. americana) were less tolerant to drying conditions. This study also illustrates the importance of periodic water withdrawal on plant performance. In general, plants that were subjected to both flooded and dry conditions responded better physiologically than plants that were either continuously flooded or received extended droughts (≥4 weeks). Therefore, provided the duration of water deficit is not extensive, short periods of water withdrawal can enhance the performance and water relations in some emergent-wetland plant species.

Dynamics of Arsenic Species in Laboratory‐Scale Horizontal Subsurface‐Flow Constructed Wetlands Treating an Artificial Wastewater

AbstractKnowledge regarding the dynamics of arsenic species and their interactions under gradient redox conditions in treatment wetlands is still insufficient. The aim of this investigation was to gain more information on the biotransformation of As and the dynamics of As species in horizontal subsurface‐flow constructed wetlands. Experiments were carried out in laboratory‐scale wetland systems, two planted with Juncus effusus and one unplanted, using an As‐containing artificial wastewater under defined organic C‐ and SO42–‐loading conditions. Immobilization of As was found in all systems under conditions of limited C, mainly due to adsorption and/or co‐precipitation. The removal efficiencies were substantially higher in the planted systems (60–70 %) as compared to the unplanted system (37 % on average). Immobilization under the conditions mentioned above appeared to decrease over time in all systems. At the beginning, the dosage of organic carbon immediately caused intensive microbial dissimilatory sulfate reduction in all systems (in the range of 85–95 %) and highly efficient removal of total arsenic (81–96 % on average). Later on, in this operation period, the intensity of sulfate reduction and simultaneous removal of As decreased, particularly in the planted wetlands (ranging from 30–46 %). One reason could be the re‐oxidation of reduced compounds due to oxygenation of the rhizosphere by the emergent wetland plants (helophytes). A significant amount of reduced As [As(III)] was found in the planted systems (&gt; 75 % of total As) during the period of efficient microbial sulfate reduction, compared to the unplanted system (&gt; 25 % of total As). The immobilization of arsenic was found to behave more stably in the planted beds than in the unplanted bed. Both systems (planted and unplanted) were suitable to treat wastewater containing As, particularly under sulfate reducing conditions. The unplanted system seemed to be more efficient regarding the immobilization of As, but the planted systems showed a better stability of immobilized As.

Lead, zinc and iron (Fe 2+) tolerances in wetland plants and relation to root anatomy and spatial pattern of ROL

Metal (Pb, Zn and Fe 2+) tolerances, root anatomy and profile of radial oxygen loss (ROL) along the root (i.e., spatial pattern of ROL) were studied in 10 emergent wetland plants. The species studied could be classified into three groups. Group I included Alternanthera philoxeroides, Beckmannia syzigachne, Oenanthe javanica and Polypogon fugax, with high ROL along the whole length of root (‘partial barrier’ to ROL). Group II included Cyperus flabelliformis, Cyperus malaccensis, Juncus effusus, Leersia hexandra and Panicum paludosum, ROL of which was remarkably high just behind the root apex, but decreased significantly at relatively basal regions (‘tight barrier’ to ROL). Group III consisted of only Neyraudia reynaudiana, with extremely low ROL along the length of root. The results indicated that metal tolerance in wetland plants was related to root anatomy and spatial pattern of ROL. Co-evolution of metal (Fe and Zn) tolerance and flood tolerance possibly developed in wetland plants since species showing a ‘tight barrier’ to ROL (a common trait of flood-tolerant species) in basal root zones had higher Fe and Zn tolerances than those showing a ‘partial barrier’. Root anatomy such as lignin and suberin deposition contributed to a ‘tight barrier’ in root and conferred to exclusion ability in tolerant species.

Host specificity of Ischnodemus variegatus, an herbivore of West Indian marsh grass (Hymenachne amplexicaulis)

West Indian marsh grass, Hymenachne amplexicaulis Rudge (Nees) (Poaceae), is an emergent wetland plant that is native to South and Central America as well as portions of the Caribbean, but is considered invasive in Florida USA. The neotropical bug, Ischnodemus variegatus (Signoret) (Hemiptera: Lygaeoidea: Blissidae) was observed feeding on H. amplexicaulis in Florida in 2000. To assess whether this insect could be considered as a specialist biological control agent or potential threat to native and cultivated grasses, the host specificity of I. variegatus was studied under laboratory and field conditions. Developmental host range was examined on 57 plant species across seven plant families. Complete development was obtained on H. amplexicaulis (23.4% survivorship), Paspalum repens (0.4%), Panicum anceps (2.2%) and Thalia geniculata (0.3%). Adults survived 1.6 times longer and laid 6.6 times more eggs on H. amplexicaulis than the other species. Oviposition on suboptimal host species was positively related to I. variegatus density under multiple choice conditions. Results from field experiments indicated that H. amplexicaulis had higher densities of I. variegatus than other species. Spill-over to suboptimal hosts occurred in an area where H. amplexicaulis was growing in poor conditions and there was a high density of I. variegatus. Thus, laboratory and field studies demonstrate that I. variegatus had higher performance on H. amplexicaulis compared to any other host, and that suboptimal hosts could be colonized temporarily.

Establishment and Evaluation of the Vegetative Community in A Surface Flow Constructed Wetland Treating Industrial Park Contaminants

A surface flow constructed wetland, designed to curve in a kidney shape in order to increase the length to width ratio to 5:1 was used to treat runoff from an industrial park. A natural wetland system located approximately 200 m downstream of the constructed wetland was selected to act as the vegetative community model for the constructed wetland. The selected model was a riparian, open water marsh dominated by emergent macrophytes. Baseline plant species surveying was conducted. In total, 21 emergent wetland plant species, 40 upland vascular plant species, 17 upland shrub species and 13 upland tree species were identified in the model site. The species from the model site were screened for suitability in the constructed wetland based on the following criteria: (a) phytoremediation potential (especially metal uptake), (b) sedimentation and erosion control, (c) habitat function, (d) public deterrent potential and (e) rate of plant establishment, tolerances and maintenance requirements. Transplantation was chosen as the main vegetation establishment methodology in the constructed wetland. The species woolgrass (Scirpus cyperinus) and soft rush (Juncus effusus) were chosen to dominate the interior berms and littoral edges of the constructed wetland cells. The buffer areas were dominated by meadowsweet (Spiraea alba var. latifolia) and the open water areas were dominated by cowlily (Nuphar variegate) and pickerelweed (Pontederia cordata) species. A diverse, self-sustaining vegetative community was successfully established in the constructed wetland. The transplant success was gauged by mortality census in the spring of 2003. Over all, 138 dead transplants were observed, many of which had died as a direct result of washout. These computes to an overall site establish success rate of about 87.3%. The species, which suffered the highest mortality rates, were the pickerelweed, with approximately 50 dead plants, the meadowsweet with 32 observed dead plants and woolgrass with 27 dead plants.

Growth and resource allocation of Canna indica and Schoenoplectus validus as affected by interspecific competition and nutrient availability

Nutrient availability and interspecific competition may affect emergent wetland plant growth and resource allocation in constructed wetland. A glasshouse study was conducted to investigate the influence of nutrient and mixture between Canna indica Linn and Schoenoplectus validus (Vahl) A. Love & D. Love on their growth and resource allocation in the wetland microcosms, using simulated secondary-treated municipal wastewater effluent with either low (17.5 mg N and 10 mg P l -1 ) or high (35 mg N and 20 mg P l -1 ) nutrient concentrations. After 65 days, the high nutrient treatment stimulated plant growth and resulted in allocation of more resources to the above-ground tissues compared to below-ground ones. The concentrations of N and P in the plant tissues (except P in above- ground tissues) were significantly higher, whereas N and P use efficiencies were significantly lower in the high than the low nutrient treatment. The total biomass for C. indica in mixture increased significantly in the high nutrient treatment, but that for S. validus was significantly lower in mixture than in monoculture. Relative yield (RY) indicated that there was significant inter- specific competition between S. validus and C. in- dica in mixtures, with C. indica being the superior competitor. The growth of S. validus was signif- icantly inhibited by the presence of C. indica in their mixture. Compared with monoculture, S. validus in mixture had significantly higher percentages of root biomass and allocations of N and P to roots, whereas C. indica was not significantly affected by mixture. The results suggested that the growth and resource allocation of C. indica and S. validus could be altered by nutrient availability and interspecific competition in constructed wetlands.

Nutrient Removal from Simulated Wastewater Using Canna indica and Schoenoplectus validus in Mono- and Mixed-Culture in Wetland Microcosms

Emergent wetland plant species may exhibit different nutrient removal efficiencies when grown in monoculture and mixed stands in constructed wetlands for tertiary purification of wastewater. A glasshouse study was conducted to investigate the influence of mono- and mixed-culture between Canna indica Linn and Schoenoplectus validus (Vahl) A. Love & D. Love on their growth in, and nutrient removal from, simulated wastewater in the surface water of vertical-flow wetland microcosms. Plants were grown for 50 days before imposing nutrient treatments that simulated secondary-treated municipal wastewater effluent with either low (17.5 mg N and 10 mg P per litre) or high (35.0 mg N and 20 mg P per litre) nutrient concentrations. Treatment solutions were renewed in weekly intervals. After 65 days of nutrient and plant treatments, the total and above-ground biomass was significantly (P < 0.01) greater in the high compared with the low nutrient treatment, but there were no significant differences in below-ground biomass. Significant (P < 0.01) differences in above-ground and below-ground biomass were observed, but no significant difference in total biomass was detected among plant treatments. The highest below-ground biomass was in monoculture of C. indica, whereas the highest above-ground biomass was in the monoculture of S. validus. The biomass of mixed-culture was intermediate to that in the two monoculture treatments. There was significant interspecific competition between C. indica and S. validus in mixed-culture, with C. indica being the superior competitor. The concentrations of N and P in plant tissues (except P in above-ground tissues) were significantly (P < 0.01) higher in the high than in the low nutrient treatment. The accumulation of N and P in above- and below-ground tissues largely reflected patterns of biomass allocation. No significant difference was observed between the nutrient treatments in nutrient removal efficiencies. Plant uptake was the major nutrient removal pathway in the wetland microcosms. Nutrient removal from simulated wastewater in mixed-culture was not greater than in mono-cultures, due to interspecific competition. The results suggested that plant nutrient uptake was the major removal mechanism at the establishment stands in the constructed wetlands.

Temporary floating island formation maintains wetland plant species richness: The role of the seed bank

In wetlands, fluctuating water levels create opportunities for recruitment of new individuals from seed banks, and drawdown periods often favor the establishment of species adapted for life in shallow water. In this study, floating island formation functioned similarly to drawdowns in water level by creating patches of sediment that were less inundated relative to the surrounding deep water marsh. The disturbance of floating island formation (i.e., mats of sediment and vegetation rising vertically in the water column) also resulted in reduced cover of the dominant rooted, floating-leaved macrophyte, thereby creating temporary gaps for the establishment of other species. To assess how floating island formation influences species richness and composition of wetland plant assemblages relative to surrounding deep water marsh, field surveys of plant percent cover on and off of islands were conducted over 2 years, along with a controlled greenhouse seed bank experiment in which levels of inundation were manipulated. Five plant species were present in deep water marsh compared to 22 in surrounding on floating islands. Plant assemblages on floating islands consisted primarily of emergent species, while floating-leaved perennials dominated the deep water marsh. Species richness and assemblage composition in the greenhouse seed bank experiment differed among water level treatments in a manner consistent with differences observed in field surveys. Assemblages germinating under minimal inundation treatments were more species rich (3.5–4.3 species per sample) and contained more emergent species (>450 individuals m −2) than did those germinating under flooded conditions (2.8–2.9 species per sample and <405 individuals m −2). This study, in addition to being the only reported seed bank study of temporary (i.e., seasonal) floating islands, demonstrates that islands altered levels of inundation favoring the germination of more species-rich, emergent wetland plant assemblages. Because these islands persisted long enough for several species to set seed, their formation may be one mechanism by which the seed bank is replenished and populations of otherwise uncommon species are maintained.

Lake Okeechobee conceptual ecological model

With a surface area of nearly 1,800 square kilometers, Lake Okeechobee is a prominent central feature of the South Florida aquatic ecosystem. The lake provides regional flood protection, supports a prized recreational fishery, provides habitat for migratory waterfowl and regional wading bird populations, and is a source of fresh water for irrigation, drinking, and restoration of downstream ecosystems. The main stressors on Lake Okeechobee are (1) large inputs of phosphorus from agricultural and other anthropogenic land uses in the watershed, (2) unnatural variation in water levels due to channelization of inflows and dike containment, and (3) rapid expansion of non-native plants. Ecological effects are complicated due to three distinct in-lake zones with different water chemistry, physical properties, and biota. A central pelagic zone has turbid, nutrient-rich water and phytoplankton dominance; a shallow south and western near-shore zone has submerged plant or phytoplankton dominance (at low vs. high water levels, respectively); and a western littoral zone is dominated by emergent wetland plants. Changes in water level influence the flow of nutrients between zones, thereby creating a synergistic effect between stressors. Under high water conditions, there is considerable advective transport of nutrients from the pelagic zone into the littoral zone. Under low water conditions, the littoral zone is cut off hydrologically and is a rainfall-driven oligotrophic wetland. Low water also facilitates drying and wildfires in the littoral zone, which in turn has an influence on expansion of non-native plants and recovery of native plants from buried seed banks. All of these factors influence fish, wading birds, and other animals, which depend on littoral and near-shore plant communities for nesting and foraging habitat. This paper describes our current knowledge of these complex processes, the lake’s expected responses to ongoing and planned restoration programs, and key areas of uncertainty requiring future research.

A Comparison of Subcanopy Versus Overhead Application of Constructed Wetland Treated Nursery Runoff on Short and Long Rotation Nursery Crops

Abstract The nursery/greenhouse industry is the fastest growing segment of U.S. agriculture. Consumer demand for excellent product quality requires luxury applications of water and agricultural chemicals. These cultural practices tend to yield significant volumes of runoff rich in nutrients and pesticides. A capture and recycle system at the Nursery/Floral Crops Research and Education Center at Texas A&amp;M University was fitted with 12 gravel filtration sub-surface flow (SSF) and 12 bog-like free-surface flow (FSF) wetland cells. Three cells of each type were planted with Canna x generalis Bailey ‘Cherry Red’, Iris L. x ‘Clyde Redmond’, both species, or no wetland plants. Runoff was continually collected from the nursery and recycled through wetland cells prior to application via overhead impact sprinklers or subcanopy microsprinklers. Short-term (10 wk) differential effects between overhead and subcanopy irrigation during production of Fraxinus pennsylvanica, Pistacia chinensis von Bunge, Quercus virginiana P. Miller, and Taxodium distichum (L.) Richard in 9.4 liter (#3) containers or Ilex vomitoria W. Aiton ‘Nana’ and Catharanthus roseus G. Don in 5.8 liter (#2) containers were limited in magnitude. However, overhead irrigation reduced height and caliper growth or injured the foliage compared to plants irrigated with subcanopy microsprinklers during longer-term (14 months) production in large 87.9 liter (#27) containers. The extent of reduction was species dependent with Pinus elliottii Englemann being minimally impacted, Pyrus calleryana Descaisne ‘Bradford’ intermediate, and Lagerstroemia L. x ‘Basham's Party Pink’ (purportedly a Lagerstroemia indica L. x Lagerstroemia fauriei B. Koehne hybrid) and T. distichum exhibiting more pronounced effects. Damage appeared to be largely a result of high dissolved salt concentrations in irrigation water contacting the foliage. Recycling of runoff through the FSF cells concentrated soluble salts more so than passing the water through the SSF cells. Efficacy of nitrate nitrogen removal varied with species, season, loading rate, and wetland type. However, the constructed wetlands were generally effective under our test conditions at maintaining effluent nitrate levels at ≤10 mg/liter (10 ppm) when loading rates were ≤50 mg/liter (50 ppm). Presence of emergent wetland plants (those with roots imbedded in the substrate and shoots extending above the water surface, rather than floating or submerged plants) in the system was more important for effectively reducing nitrate levels in effluent from SSF than from FSF cells.

MARSH DEVELOPMENT AT RESTORATION SITES ON THE WHITE MOUNTAIN APACHE RESERVATION, ARIZONA1

ABSTRACT: To prioritize sites for riparian restoration, resource managers need to understand how recovery processes vary within landscapes. Complex relationships between watershed conditions and riparian development make it difficult to predict the outcomes of restoration treatments in the semiarid Southwest. Large floods in 1993 scoured riparian areas in the Carrizo watershed on the White Mountain Apache Reservation in east‐central Arizona. We evaluated recovery at three of these sites using repeated photographs and measurements of channel cross sections and stream‐side vegetation along permanent transects. The sites were mapped as lying on the same soil type, had similar streamside vegetative communities, and were similarly treated through livestock exclusion and supplemental seeding. However, the sites and individual reaches within the sites followed strikingly different development paths. Dramatic recovery occurred at a perennial reach where cover of emergent wetland plants increased from 4.7 percent (standard error = 0.8 percent) in October 1995 to 55.5 percent (standard error = 2.7 percent) in September 2001. At several other reaches, geologic and hydro geomorphic characteristics of the sites limited inputs of fine sediment or surface water, resulting in modest or negligible increases in emergent cover. Recovery efforts for highly valued marshlands in this region should prioritize perennial reaches in low gradient valleys where salty sediments are abundant.

Effects of water vapour pressure deficit and stomatal conductance on photosynthesis, internal pressurization and convective flow in three emergent wetland plants

Internal pressurization and convective gas flow in emergent wetland plants is a function of the water vapour pressure deficit (WPD) and stomatal conductance (Gs) separating the external atmosphere from the internal aerenchyma. We have compared the effects of WPD and Gs under a range of light intensities on static pressures and convective flows in Phragmites australis, Typha orientalis and Baumea articulata. The capacity of the three species to generate flows per unit leaf area differed, being greatest in P. australisand lowest in B. articulata. In all three species, decreasing light intensity from full sunlight (2200 μmol m−2 s−1 photosynthetically active photon flux density (PPFD)) to < 200 and < 10 μmol m−2 s−1PPFD caused immediate decreases in photosynthetic assimilation, followed by more gradual decreases in transpiration and Gs. However, internal pressures and flows in the two low light intensities remained similar to values recorded in full sunlight. WPD was more significantly related to pressures and flows in P. australis and T. orientalis than Gs. In B. articulata, pressures increased at low Gs values but flow rates were unaffected, as predicted by earlier models describing pore size effects on pressures and flows. The data suggest that emergent macrophytes can maintain significant internal convection even at low light intensities, and this may be beneficial for nocturnal aeration, particularly in arid climates where the atmospheric humidity at night is low.

Identifying optimum locations for new ponds

Abstract Pond ecological quality is influenced by surrounding land uses. Continued intensification of land use has led to a progressive decline in the ecological quality of the pond stock within Britain. To reverse this trend new ponds need to be carefully designed and sited using a targeted approach. Consequently, this study uses a Geographical Information System (GIS) to identify optimum locations for new ponds within the Chiltern Hills Area of Outstanding Natural Beauty. Multiple regression analysis was used to identify the relationship between macrophyte pond quality indicators and environmental data from 300 ponds to produce models that could predict pond quality. These models were tested at 10 locations in the study area by comparing predicted pond qualities with the actual pond qualities, established by identifying all plants in each pond. Aquatic plants successfully predicted pond quality, while emergent plants and total wetland plant species did not. The regression model for aquatic plants was used in the GIS to identify locations within the study area where new ponds could be located to obtain maximum ecological quality. Six scenarios were tested and the optimum situation identified. The study demonstrated the potential and importance of using GIS in a strategic approach for pond conservation. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Influence of a dominant macrophyte, Juncus effusus, on wetland plant species richness, diversity, and community composition.

Few studies have experimentally investigated the influence of competition for light on structure and composition of wetland vascular plant communities, despite the well-documented high productivity in such systems. Influences of the dominant emergent wetland plant Juncus effusus on the surrounding macrophyte community were evaluated in a shallow freshwater wetland through two consecutive growing seasons. Permanent transects were constructed along diagonals of randomly oriented 1m2 plots centered around isolated, colonizing J. effusus tussocks. Percent areal cover was measured for each species or identifiable taxon group in 400cm2 sub-plots centered 10, 20, 30, and 40cm from the tussock edge, to evaluate species richness, diversity, and dominance indices. Observational studies during the first growing season indicated that plots having larger, more heavily shading tussocks yielded significantly lower cover and species richness in the surrounding plant community than less shaded plots. Shading by J. effusus was reduced experimentally during the second growing season by holding culms in a vertical position in half of the J. effusus-occupied study plots in order to assess directly the influence of shading by J. effusus. Manipulated plots became more diverse and species-rich and developed higher total percent areal cover. Within shaded reference plots, reductions in cover, richness, and diversity were correlated with intensity of shading; each of these measures was lowest in sub-plots centered 10cm from the tussock, where measured light reduction was highest. Neighborhood analyses of biomass, species composition, and light reduction indicated that individual species biomass varied with distance from J. effusus tussocks and shading intensity, an indication of the potential for shifts in community composition as populations of this dominant macrophyte expand to fill a wetland area. A mathematical model is presented to illustrate shading effects of J. effusus as a population grows from isolated, colonizing tussocks to an interacting system of tussocks in an established population of this dominant macrophyte.

Microcosm Study of Bioremediation of Oil-Contaminated Freshwater Wetlands

ABSTRACT Use and transport of petroleum products can result in serious contamination of freshwater habitats via leakage, spills, aerosols, and runoff. Little development of bioremediation strategies has occurred for enhancing degradation of petroleum products in situations involving contamination of freshwater wetland ecosystems. The objective of this study was to investigate different inorganic mineral nutrients for their ability to enhance biodegradation of crude oil in contaminated wetlands on a microcosm scale. Aquaria of 10-gallon capacity, filled with wetland soil and planted with species of emergent wetland plants, were used to simulate natural wetlands. Two levels of water coverage were studied: (1) water level even with soil surface, and (2) water level 10 cm above the soil surface. Six treatments were evaluated in duplicate for each water level: unoiled, no-nutrient control; oiled + no nutrient control; oiled + nitrate addition; oiled + nitrate + phosphate addition; oiled + ammonia addition; and oiled + ammonia + phosphate addition. Thus, 24 aquaria were set up for each sampling event (0, 2, 4, 8, 16, and 32 weeks) totaling 144 aquaria. Nutrients were applied once each week. Nitrate, ammonia, dissolved oxygen, pH, temperature, and conductivity were measured before and after nutrient addition. Biodegradation was tracked by GC/MS analysis of hopane-normalized crude oil components from the sacrificed aquaria over the 32-week experimental period. Results indicated that: (1) the rates of biodegradation of the alkanes and PAHs (polycyclic aromatic hydrocarbons) were higher for all treatments in the high-water level microcosms compared with the low-water level microcosms; (2) the highest rates of alkane and PAH degradation were measured in the high-water level microcosms receiving nitrate and phosphate; (3) the treatments with nitrate and phosphate showed nearly a 90% reduction of alkanes and a 50% reduction of PAHs as compared to nearly a 50% reduction of alkanes and 40% reduction of PAHs by the oil with no nutrients control for the high-water level; (4) the nitrate and phosphate addition treatments, for both water levels, showed good plant growth and the highest plant and root densities as compared to the other treatments. This information is being used in the design of a mesoscale experiment as part of the second phase of this study.

Temperature‐Driven Variation in Substrate Oxygenation and the Balance of Competition and Facilitation

Emergent wetland plants often alleviate the effects of anaerobic soils on root respiration by passively transporting oxygen belowground through continuous air spaces (aerenchyma) in leaves and roots. Oxygen leaked from the roots into the rhizosphere may oxidize minerals in the soil or become available to other plants. Some spatial patterns in marsh plant communities suggest interspecific facilitative interactions, but there is little experimental evidence for interplant facilitation via soil oxygenation. We investigated the capability of the widespread, highly aerenchymous wetland plant, Typa latifolia, to aerate sediments and affect the growth of two non—aerenchymous neighbors, Salix exigua and Myosotis laxa, both in greenhouse experiments and in a natural pothole pond in western Montana. At soil temperatures of 11°—12°C in the greenhouse, mean dissolved oxygen (DO) ranged from 2.75±0.41 to 4.43±1.11 mg/L (mean ± 1 SE) in pots with Typha, whereas in pots without Typha DO content ranged from 0.40 ± 0.06 to 0.65 ± 0.06 mg/L. At soil temperatures of 18°—20°C, DO in the Typha treatment was lower than in the low—temperature experiment and did not differ significantly from DO in the pots without Typha. At substrate temperatures 11°—12°C, all rooted Salix cuttings survived when planted with Typha, whereas non survived when planted alone. At the same substrate temperature, Myosotis transplants grew significantly larger when planted with Typha than when alone, also indicating that facilitation occurred. When grown with Typha at soil temperatures of 18°—20°C, however, Myosotis root mass was significantly less than when grown alone, suggesting that competition occurred. At the pond margins where Typha and Myosotis coexist in water—saturated soils, naturally occurring Myosotis plants adjacent to transplanted Typha had significanlty larger shoot and fruit mass than did control Myosotis without nearby Typha. In this experiment DO levels in soil water and available soil nitrogen did not differ among treatments. These experiments indicate that aerenchymous wetland plants have the potential to facilitate neighbors via soil oxygenation, and that facilitaton and competition may shift in importance with changes in the physical environment.