Scirpus Robustus Research Articles

Metal concentrations in wetland plant tissues influences transfer to terrestrial food webs.

Wetland plants tolerate potentially hazardous metals through a variety of strategies, including exclusion or accumulation. Whether plants sequester metals and where they store them in their tissues is important for understanding the potential role of plants as remediators or vectors of metals to terrestrial food webs. Here we evaluate metal sequestration in Great Salt Lake wetlands for one invasive (Phragmites australis; phragmites) and three native plant species, i.e. threesquare bulrush (Schoenoplectus americanus), hardstem bulrush (Schoenoplectus acutus), alkali bulrush (Bolboschoenus maritimus), and their terrestrial invertebrates. We observed higher concentrations of arsenic and copper than other metals in plant tissues, although high lead concentrations were observed in phragmites. All plants acted as excluders of arsenic and selenium, retaining the bulk of the metal mass in belowground tissues. In contrast, lead, copper, and cadmium were transferred to above ground tissues of hardstem bulrush and phragmites. The aboveground translocation facilitated the movement of these metals into invertebrates, with the highest concentrations in most cases found in predators. Though our results highlight the potential for metal remediation via wetland plant growth and removal, care should be taken to ensure that remediation efforts do not lead to bioaccumulation.

Effects of a Surfactant Seed Coating on Alkali Bulrush Germination and Biomass

Great Salt Lake (GSL) wetlands provide vital ecosystem services, including habitat for migratory birds. Alkali bulrush (Bolboschoenus maritimus) plays an important role in providing these services, but invasion by Phragmites australis has reduced the extent of alkali bulrush stands in GSL wetlands. Restoring alkali bulrush is a primary goal for GSL managers following Phragmites removal. However, rising temperatures and changing precipitation patterns with climate change, as well increasing human water demands upstream, may alter the hydropattern of GSL wetlands, thus lowering soil moisture availability and potentially inhibiting alkali bulrush germination and seedling establishment. Surfactant seed coatings have been effective in aiding the germination of seeds in upland restoration sites by reducing soil water repellency, but have not been tested in wetlands. We tested whether the addition of a surfactant seed coating to alkali bulrush seeds improved germination at four water levels in a greenhouse. Water level and seed coating were significantly associated with improved germination. In a second experiment, we tested the effect of the seed coating at a low and high dose and staggered water level drawdowns on seedling height and biomass over six weeks. Seed coating and time of water level drop were not significantly associated with differences in seedling height. The water level decrease may not have been extreme enough to negatively affect seedlings. More research is needed to determine if a surfactant seed coating enhances alkali bulrush germination and growth under less favorable water availability conditions.

Seed Dormancy Break and Germination for Restoration of Three Globally Important Wetland Bulrushes

Limited knowledge of seed dormancy break, germination requirements, and intraspecific variation of these traits hinders revegetation of many species targeted for restoration. We evaluated the importance of cold stratification and chemical scarification for breaking seed dormancy and the impact of soaking in water on germination for three globally distributed bulrush species. These species, Bolboschoenus maritimus (alkali bulrush), Schoenoplectus acutus (hardstem bulrush), and S. americanus (threesquare bulrush), form critical habitat in Great Salt Lake wetlands. For B. maritimus and S. acutus , we also evaluated variation in response to seed dormancy breaking treatments among geographically-distant seed sources. We found that both 180 days of cold, moist stratification or 48 hours of bleach scarification were effective for breaking seed dormancy for most seed sources of B. maritimus . For S. acutus , longer stratification lengths may result in consistently higher germination percentages, but 30 days of stratification may be of sufficient length for some source sites. For S. americanus , stratification improved germination in one experiment, but 20–60 percent of viable seed did not germinate in each experiment potentially due to a poor understanding of germination requirements. Soaking seeds in water under greenhouse conditions, improved the germination of all species when done after dormancy breaking treatments. Importantly, response to dormancy breaking treatment varied among source sites; intraspecific variation may account for unpredictable responses to dormancy breaking treatments. These findings can assist practitioners in crafting strategies to effectively break dormancy and germinate seeds of B. maritimus, S. acutus , and S. americanus .

Integrated Mosquito Management in Experimental Constructed Wetlands: Efficacy of Small-Stature Macrophytes and Fluctuating Hydroperiod

The impact of small-stature alkali bulrush (Bolboschoenus maritimus) and two hydroperiod treatments (early season raised water level or ambient water level) on mosquito production and water quality was studied in replicate 0.09 ha free water surface (FWS) treatment wetlands. Following reconfiguration of a 1-ha constructed wetland into a system with six replicate wetlands, bulrush was planted on 0.5-m centers in three 5-m wide bands in each wetland in summer, 2012. Open water and the low density of emergent vegetation effectively limited mosquito production from the bands of B. maritimus in each wetland during summer and autumn of year one. After the autumnal senescence of the bulrush culms, water levels were raised in half of the wetlands during winter and early spring to enhance sinking of dead bulrush biomass to reduce harborage for mosquitoes. Macrophyte coverage continued to increase in both hydroperiod treatments during year two, but non-bulrush species proliferated and eventually overgrew B. maritimus. Immature mosquito abundance in dipper samples from wetlands in the raised water level treatment was greater than from wetlands in the constant water level treatment. During spring of year two, adult mosquito production was associated with volunteer vegetation in the center of the test cells and averaged 6–18 mosquitoes m−2·day−1, approximately twice that of the other treatment. Hydrological regime did not significantly affect water quality performance (removal of nitrogen, phosphorus and chemical oxygen demand) in the wetlands. Alkali bulrush can persist in shallow water (depth < 0.2 m), but did not persist in deeper zones (mean depth > 0.4 m) of the wetlands and after comparatively large stature grasses and cattails colonized the wetlands. Raised planting beds interspersed with zones of deeper water are recommended to facilitate persistence of alkali bulrush and to limit proliferation of superior competitors.

Viability, dormancy, germination, and intraspecific variation of Bolboschoenus maritimus (alkali bulrush) seeds

Bolboschoenus maritimus (alkali bulrush) is a globally distributed, clonal wetland plant. In the Great Salt Lake (GSL) Basin, USA, the focal region for this study, this species forms large, monotypic stands that provide critical wetland habitat for millions of migratory birds. I conducted a series of seed trait studies with B. maritimus seeds sourced from five GSL Basin populations. Seed viability was high (87–98%) and varied little among the five source populations. Chemical scarification with 3% bleach for 24 or 48h broke dormancy in seeds from all five source populations; there was substantial intraspecific variation (up to two-fold differences in germination) in response to scarification. The conditions suitable for germination included high light, summer temperatures (32/15°C or 35/18°C), and flooding. Results of this study suggest conditions under which recruitment from seed may play a role in B. maritimus patch dynamics. Furthermore, study results can be used to improve restoration of this important habitat species through the development of more effective seed revegetation following invasive Phragmites australis removal in GSL wetlands.

Effects of nutrients on mosquitoes and an emergent macrophyte, Schoenoplectus maritimus, for use in treatment wetlands.

Schoenoplectus maritimus (alkali bulrush) has desirable attributes, such as a short growth habit (height of mature stands < 1.5 m) and annual senescence, for a potential alternative to tall (height > 3 m) emergent macrophytes in shallow constructed treatment wetlands treating ammonium-dominated wastewater. The effects of different ammonium nitrogen (NH4-N) levels on alkali bulrush growth and its ability to take up nutrients from the wastewater, as well as on mosquito production, across the range of NH4-N found in constructed wetlands of southern California are unknown. We evaluated the effects of enrichment with NH4-N on mosquito production and on the nutrient uptake and growth of alkali bulrush in two studies. Overall, significantly greater numbers (> 50%) of immature mosquitoes (mainly Culex tarsalis) were found in mesocosms enriched with NH4-N than in mesocosms receiving ambient (<0.3 mg/liter) NH4-N. High NH4-N enrichment (up to 60 mg/liter) did not adversely impact the height and stem density of S. maritimus, although a significant decrease in biomass was observed at the highest enrichment level. Nitrogen uptake by alkali bulrush increased directly with NH4-N enrichment, whereas carbon was conserved in the above-ground biomass across the enrichment gradient. Alkali bulrush is recommended for use as part of integrated mosquito management programs for moderately enriched, multipurpose, constructed treatment wetlands that improve water quality as well as provide wetland habitat for waterfowl.

Small-stature emergent macrophytes and crepuscular sprinkler disturbance reduce mosquito abundance in wetland mesocosms

The impact of emergent macrophyte species and crepuscular sprinkler disturbance on mosquito abundance over a 2-year period was measured in wetland mesocosms. Mosquito oviposition and abundance of immature mosquitoes and aquatic invertebrates were monitored in monotypic plots of small-stature (height of mature stands <1.5 m) alkali bulrush (Schoenoplectus maritimus) and large-stature (height of mature stands > 2 m) California bulrush (Schoenoplectus californicus) without or with daily sprinkler showers to deter mosquito egg laying. Relative to wetlands without operational sprinklers, oviposition by culicine mosquitoes was reduced by > 99% and immature mosquito abundance was reduced by > 90% by crepuscular sprinkler applications. Mosquito abundance or distribution in wetlands did not differ between the two bulrush species subjected to the sprinkler treatment. Alkali bulrush wetlands without daily sprinkler treatments contained more egg rafts but significantly fewer mosquito larvae than did California bulrush wetlands. Predaceous damselfly naiads were 3-5 times more abundant in alkali bulrush than in California bulrush. Stem density, rate of spread, and autumnal mortality of alkali bulrush were higher than for California bulrush. Replacement of large emergent macrophytes by smaller species may enhance the efficacy of integrated mosquito management programs to reduce mosquito-transmitted disease cycles associated with multipurpose constructed wetlands used worldwide for water reclamation and habitat restoration.

Microhabitat Selection, Demography and Correlates of Home Range Size for the King Rail (Rallus elegans)

Abstract. Animal movements and habitat selection within the home range, or microhabitat selection, can provide insights into habitat requirements, such as foraging and area requirements. The King Rail (Rallus elegans) is a wetland bird of high conservation concern in the United States, but little is known about its movements, habitats, or demography. King Rails (n = 34) were captured during the 2010–2011 breeding seasons in the coastal marshes of southwest Louisiana and southeast Texas. Radio telemetry and direct habitat surveys of King Rail locations were conducted to estimate home ranges and microhabitat selection. Within home ranges, King Rails selected for greater plant species richness and comparatively greater coverage of Phragmites australis, Typha spp., and Schoenoplectus robustus. King Rails were found closer to open water compared to random locations placed 50 m from King Rail locations. Home ranges (n = 22) varied from 0.8–32.8 ha and differed greatly among sites. Home range size did not vary b...

The Response of Photosystem II to Soil Salinity and Nutrients in Wetland Plant Species of the Northwestern Gulf of Mexico

Abstract Madrid, E.N.; Armitage, A.R., and Quigg, A., 2012. The response of photosystem II to soil salinity and nutrients in wetland plant species of the Northwestern Gulf of Mexico. The photosynthetic response of many wetland plant species to soil salinity and nutrients has been described in the laboratory, but less is known about the cumulative effect of these abiotic factors in the natural environment. In this investigation we correlated field measurements of chlorophyll fluorescence with simultaneous measurements of soil nitrogen and phosphorus content, soil salinity, and relative leaf nitrogen content in Spartina alterniflora (Loisel), Spartina patens ((Aiton) Muhl), Schoenoplectus californicus ((C.A. Mey.) Steud.) and Schoenoplectus robustus ((Pursh) M.T. Strong), common in brackish and salt marshes of the northwestern Gulf of Mexico. The relationship between chlorophyll fluorescence and soil N ∶ P ratio was not significant in S. alterniflora, nonlinear in S. patens and S. robustus, and significant ...

Ecological re-engineering of a freshwater impoundment for salt marsh restoration in a hypertidal system

The purpose of this paper was to examine the vegetative, sedimentary, nekton and hydrologic response to ecological re-engineering of a freshwater impoundment in the Upper Bay of Fundy. The dyke was breached in five locations and one channel initiated to connect the river to the borrow pit behind the dyke. This triggered significant self-organization within the restoration site. Existing channels (e.g. borrow pit) were incorporated within the newly excavated and developing creek system, increasing the hydraulic connectivity within the marsh and increasing fish habitat. Vegetation colonization, primarily by Spartina alterniflora, was rapid with almost 100% coverage by the end of the third year. Species associated with high marsh communities such as Juncus gerardii, Scirpus robustus, Ranunculus cymbalaria and Puccinellia maritima were present in increasing abundance post-restoration at the restoration site. The constructed channel eroded downward 2.3 m and the head of the channel retreated 35 m in response to the increased tidal prism. In the year immediately following the breach (2006), the surface of the marsh was unconsolidated and rates of change in surface elevation measured at RSET stations ranged from −0.7 (±0.1) to 1.7 (±0.2) cm yr −1 (±1SE). Measurements between years are highly variable. By year 3 the rate of surface elevation change decreased to a more moderate but variable mean of 0.3 (±0.6) cm yr −1 with the marker horizons recording mean accretion rates of 0.7 cm yr −1. This implies subsurface consolidation as the sediments dewatered or organic matter decomposed and vegetation became more established. Fish density decreased after restoration, however, remained higher than at the reference site for most years.

Vegetation Changes and Partitioning of Selenium in 4-Year-Old Constructed Wetlands Treating Agricultural Drainage

The knowledge of selenium (Se) partitioning in treatment wetlands and wetland vegetation management are essential for long-term effective operation of constructed wetlands treating Se-laden agricultural tile-drainage in central California. In this field study, samples from different compartments of treatment wetlands were collected and the vegetation change in each wetland cell was examined four years after the wetland's inception. The results showed that saltgrass (Distichlis spicata) and rabbitfoot grass (Polypogon monspeliensis) were less competitive than cattail (Typha latifolia) and saltmarsh bulrush (Scirpus robustus). Over 90% of the wetland cell originally vegetated with saltgrass or rabbitfoot grass was occupied by invasive plants—i.e., when invasive species were not controlled in the wetlands. More Se was likely found in sediments from vegetated regions, compared to the unvegetated areas of the wetland cell. Particularly, rhizosphere sediments accumulated about 4-fold more Se than non-rhizosphere sediments. Among the total Se retained in the wetland, 90% of the total Se was partitioned in the top 10-cm layer of sediment. The Se accumulation in plant materials accounted for about 2% of the total Se mass retained in each wetland cell. This field study demonstrated that wetland plants play significant roles in the treatment of Se-laden agricultural drainage.

Intraspecific Variation in Growth of Marsh Macrophytes in Response to Salinity and Soil Type: Implications for Wetland Restoration

Genetic diversity within plant populations can influence plant community structure along environmental gradients. In wetland habitats, salinity and soil type are factors that can vary along gradients and therefore affect plant growth. To test for intraspecific growth variation in response to these factors, a greenhouse study was conducted using common plants that occur in northern Gulf of Mexico brackish and salt marshes. Individual plants of Distichlis spicata, Phragmites australis, Schoenoplectus californicus, and Schoenoplectus robustus were collected from several locations along the coast in Louisiana, USA. Plant identity, based on collection location, was used as a measure of intraspecific variability. Prepared soil mixtures were organic, silt, or clay, and salinity treatments were 0 or 18 psu. Significant intraspecific variation in stem number, total stem height, or biomass was found in all species. Within species, response to soil type varied, but increased salinity significantly decreased growth in all individuals. Findings indicate that inclusion of multiple genets within species is an important consideration for marsh restoration projects that include vegetation plantings. This strategy will facilitate establishment of plant communities that have the flexibility to adapt to changing environmental conditions and, therefore, are capable of persisting over time.

Diet and Body Mass of Wintering Ducks in Adjacent Brackish and Freshwater Habitats

Field-collected and hunter-donated ducks obtained during September-January of 1997–98 and 1998–99 were used to determine if food habits and body mass of Northern Pintails (Anas acuta) and Mallards (A. platyrhynchos) wintering in Suisun Marsh (Suisun), California, a managed estuarine brackish marsh, differed from values in the adjacent Sacramento-San Joaquin River Delta (the Delta), a freshwater region of grain fields flooded after harvest. Ducks in Suisun fed primarily on seeds of Sea Purslane (Sesuvium verrucosum), followed by Alkali Bulrush (Schoenoplectus maritimus) and Wild Millet (Echinochloa crusgalli), together forming 73–90% (aggregate % dry mass) of the diets. Ducks in the Delta fed primarily on seeds of Smartweed (Polygonum spp.), followed by corn (Zea mays) and tomato seeds (Lycopersicon esculentum), together forming 62–88% of the diets. Pintails and Mallards collected in Suisun each had similar (5 of 11 seasonal comparisons) or greater (6 of the 11 comparisons) body mass compared to their conspecifics collected from the Delta (90% confidence interval analyses), despite a composite diet in the Delta having about 39% greater metabolizable energy content (ME) and 24% greater protein content than in Suisun. Therefore, diet quality alone was not a predictor of body mass in these two areas. Other factors must have been involved, such as greater food abundance and density, lower waterfowl abundance and density, or lower daily energy costs in Suisun. Direct measurement of these factors should explain the apparent inconsistencies in body mass relative to food quality in these brackish and freshwater habitats.

Home Range, Habitat Selection, and Movements of California Black Rails at Tidal Marshes at San Francisco Bay, California

Little is known about the movements and habitat selection of California Black Rails (Laterallus jamaicensis coturniculus) in coastal California. We captured 130 Black Rails, of which we radio-marked 48, in tidal marshes in San Francisco Bay during 2005 and 2006. Our objective was to examine their home ranges, movements, and habitat selection to improve the species' conservation. The mean fixed-kernel home range was 0.59 ha, the mean core area was 0.14 ha. Home ranges and core areas did not differ by year or site. Males had significantly larger home ranges and core areas than did females. All sites combined, Black Rails used areas with ≥94% total vegetative cover, with perennial pickleweed (Sarcocornia pacifica) the dominant plant. The rails' habitat selection varied by year and site but not by sex. A multivariate analysis of variance indicated that Black Rails selected areas with pickleweed taller and denser than average, greater cover and height of alkali bulrush (Bolboschoenus maritimus) and common saltgrass (Distichlis spicata), more stems between 20 and 30 cm above the ground, maximum vegetation height, and shorter distance to refugia. On average, Black Rails moved 27.6 ±1.8 (SE) m daily and 38.4 ± 5.5 m during extreme high tides. Understanding the California Black Rail's movements, home range, and habitat use is critical for management to benefit the species.

Grit Ingestion and Size-related Consumption of Tubers by Graylag Geese

In herbivorous birds the processing rate of food is constrained by gizzard capacity. To enhance digestive processes, many species ingest grit to grind the food. Grit ingestion, however, may further limit the capacity of the gizzard. Graylag Geese (Anser anser) wintering in SW Spain fed mainly on Alkali Bulrush (Scirpus maritimus) tubers, showing a preference for small tubers. This preference may be due to a faster disintegration of small tubers than larger ones inside the gizzard. As larger tubers are likely coarser than smaller tubers, more grit would be necessary to process larger tubers. However, the ingestion of more grit to grind large tubers would be at the expense of ingesting additional tubers because of gizzard capacity limitations. Under these circumstances, there may be an inverse relationship between tuber size and amount of grit ingested to optimize food ingestion. Indeed, we found such a relationship. Grit facilitated the disintegration of tubers. This suggests that relying on some amount of grit to facilitate the grinding of food should outweigh the loss of gizzard capacity to the amount of food ingested.

True Metabolizable Energy for Seeds of Common Moist‐Soil Plant Species

Abstract: Understanding the true metabolizable energy (TME) value of food is important for constructing bioenergetic models. We estimated gross energy, nutrient composition, and TME values for the seeds of 3 native and 1 invasive exotic wetland plant that occur in the diet of waterfowl. True metabolizable energy values were 0.50 ± 0.080 kcal/g for spike rush (Eleocharis palustris), 0.65 ± 0.080 kcal/g for alkali bulrush (Schoenoplectus maritimus), 1.31 ± 0.090 kcal/g for perennial pepperweed (Lepidium latifolium), and 2.52 ± 0.080 kcal/g for lamb's quarters (Chenopodium album). The TME value for 3 of 4 species, including the invasive species, was low relative to the TME value of other seeds consumed by waterfowl.

Growth of tissue culture–regenerated salt marsh monocots in a simulated marsh field plot: Implication for wetland creation and restoration

Phenotypically and genetically variable salt marsh plants are needed for wetland creation and restoration efforts. Selected tissue culture regenerants of five salt marsh monocots, Spartina patens, Spartina alterniflora, Juncus gerardi, Juncus roemerianus, and Scirpus robustus, were planted in a simulated marsh field plot that was flood-irrigated with 10 ppt salt water to compare their phenotypic variation for potential use in wetland projects. Plant growth was evaluated after one growing season. Phenotypic variation among regenerants was found in S. alterniflora, S. patens and J. gerardi, indicating the occurrence of somaclonal variation. In S. alterniflora, significant differences occurred among regenerants in stem density. In J. gerardi, significant differences occurred in height and clone circumference. In S. patens, two of the nine regenerants exhibited higher biomass and stem density than some of the other regenerants. By using the random amplified polymorphic DNA (RAPD) technique, genome DNA variation in S. patens regenerants was detected. Genetic variation not only occurred among phenotypically different regenerants, but also among those phenotypically similar for the characteristics measured. Tissue culture–regenerated plants often have desirable genetic characteristics and adaptability as a result of somaclonal variation and may enable a species to perform its ecological functions in created or restored wetlands where ideal environments cannot be achieved. Thus, some previously unrestorable sites may be restorable or marginal marshes made more productive.

Clonal variation in response to salinity and flooding stress in four marsh macrophytes of the northern gulf of Mexico, USA

Intraspecific variation in stress tolerance can be an important factor influencing plant population structure in coastal wetland habitats. We studied clones of four species of emergent marsh macrophytes native to the northern coast of the Gulf of Mexico in Louisiana, USA, to examine variation in response to salinity and flooding stress under controlled greenhouse conditions. Clones of Distichlis spicata, Phragmites australis, Schoenoplectus californicus, and Schoenoplectus robustus were collected across the coastal zone of Louisiana. After vegetative propagation through at least three generations to remove acclimation to field conditions, four to six clones of each species were selected for use in the experiment. Treatments consisted of three salinity levels and two water depths, and species were assigned to either a brackish marsh ( P. australis, S. californicus) or salt marsh ( D. spicata, S. robustus) group for treatment application. Treatment effects on plant growth (stem number, total height, and mean height, and aboveground and belowground biomass) were examined, and physicochemical characteristics within treatments (redox potential, and interstitial water pH, salinity, temperature, and nutrients) were monitored. Clonal variation in growth was indicated in all species, and was more pronounced in D. spicata and P. australis than in S. californicus and S. robustus. Distichlis spicata and P. australis clones were assigned to relative categories of low, intermediate, and high tolerance to the imposed stressors. Similar generalizations on clonal stress tolerance were not possible for the two Schoenoplectus species. Overall species response to imposed stressors was also identified through non-statistical comparisons. Phragmites australis was more tolerant than S. californicus of increased salinity. Distichlis spicata was more tolerant of increased salinity but less tolerant of increased water depth than was S. robustus. Our results suggest that information on species and clone variations in growth and tolerance to salinity and flooding stressors can be used to select a variety of plant materials suitable for wetland restoration projects.

Plant regeneration via somatic embryogenesis in the brackish wetland monocot Scirpus robustus

A tissue culture and plant regeneration protocol for salt marsh bulrush, Scirpus robustus, was developed. Callus was induced from seedling mesocotyl on Murashige and Skoog (MS) medium plus 1 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D). Thirty-one percent of the calli became embryogenic upon transfer to MS medium supplemented with 0.25 mg/l 2,4-D. Limited plant regeneration via somatic embryogenesis was obtained after transferring the embryogenic callus to MS medium without growth regulators (MS0). The addition of 6-benzylaminopurine (BA) to the medium effectively increased the number of regenerated shoots and more shoots were regenerated on 3 mg/l BA medium (HBA) than on 0.1 mg/l BA medium (LBA). Transfer of the plants regenerated from BA-supplemented medium to MS0 medium further enhanced the development of the plants, which subsequently grew vigorously in potting soil in the greenhouse. Having a tissue culture and regeneration protocol for S. robustus makes it possible to take advantage of somaclonal variation for selecting lines of this species with characteristics desirable for wetland creation and restoration.

Selenium removal and mass balance in a constructed flow-through wetland system.

A field study on the removal of Se from agricultural subsurface drainage was conducted from May 1997 to February 2001 in the Tulare Lake Drainage District (TLDD) of San Joaquin Valley, California. A flow-through wetland system was constructed consisting of ten 15- x 76-m unlined cells that were continuously flooded and planted with either a monotype or combination of plants, including sturdy bulrush [Schoenoplectus robustus (Pursh) M.T. Strong], baltic rush (Juncus balticus Willd.), smooth cordgrass (Spartina alterniflora Loisel.), rabbitsfoot grass [Polypogon monspeliensis (L.) Desf.], salt-grass lDistichlis spicata (L.) Greene], cattail (Typha latifolia L.), tule [Schoenoplectus acutus (Muhl. ex Bigelow) A. Löve & D. Löve], and widgeon grass (Ruppia maritima L.). One cell had no vegetation planted. The objectives of this research were to evaluate Se removal efficiency of each wetland cell and to carry out a mass balance on Se. The inflow drainage water to the cells had average annual Se concentrations of 19 to 22 microg L(-1) dominated by selenate [Se(VI), 95%]. Average weekly water residence time varied from about 3 to 15 d for Cells 1 through 7 (target 7 d), 19 to 33 d for Cells 8 and 9 (target 21 d), and 13 to 18 d for Cell 10 (target 14 d). Average weekly Se concentration ratios of outflow to inflow ranged from 0.45 to 0.79 and mass ratio (concentration x water volume) from 0.24 to 0.52 for year 2000, that is, 21 to 55% reduction in Se concentration and 48 to 76% Se removal in mass by the wetland, respectively. The nonvegetated cell showed the least Se removal both in concentration and in mass. The global mass balance showed that on the average about 59% of the total inflow Se was retained within the cells and Se outputs were outflow (35%), seepage (4%), and volatilization (2%). Independent measurements of the Se retained in the cells totaled 53% of the total Se inflow: 33% in the surface (0-20 cm) sediment, 18% in the organic detrital layer above the sediment, 2% in the fallen litter, < 1% in the standing plants, and < 1% in the surface water. Thus, about 6% of the total Se inflow was unaccounted for in the internal compartments.