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Green cooling towers, or thermal green-walls, recirculate hot water flowing through a living plant and porous material. Through convective and evaporative heat and mass transfer they can actively cool a building or an industrial heat waste. Thus they can provide an alternative cooling technology. Thermal green-walls use wetland plant species in highly constructed wetlands selected for their heat tolerance. In addition, they offer such co-benefits as carbon capture and control of local microclimates. Optimal heat rejection (HR) requires the plant rhizosphere to be completely inundated at temperatures much higher than the ambient air temperature, potentially inducing thermal physiological stress. To study the viability of specific plants within a HR system, we exposed three macrophytes, Iris versicolor, Scirpus cyperinus and Carex lurida, to hydroponic recirculating water at three different temperatures (25 °C, 35 °C, and 40 °C). We assessed the plant responses over a period of eight weeks by measuring photochemical efficiency, leaf temperature, stomatal conductance, G s and biomass output. Plant biomass was highest at 35 °C (particularly in I. versicolor), even higher than ambient water temperature at 25 °C. We observed a general homeothermic-like response in G s over a 5-week time period, but the response was species-specific with respect to temperature. Results suggests a possible leaf-level physiological acclimation mechanism as well as high maintenance of tissue moisture that allows macrophytes to tolerate hydro-thermal stress, and support their suitability to perform in HR systems at input temperature, T win = 35 °C.

Chlorantraniliprole (CAP), an emergent insecticide commonly replacing banned neonicotinoids, is used worldwide despite the risk of contaminating water bodies. Treatment wetlands (TWs) have shown great potential for mitigating various pesticides in agricultural runoff, but little is known about CAP removal. The aim of this study was to determine the effect of adding biochar to subsurface flow treatment wetlands (SSF TWs) and the performance of three macrophyte species (Phragmites australis subsp. americanus, Scirpus cyperinus and Sporobolus michauxianus) in CAP removal. Removal efficiency was monitored over a one-month period in water-saturated SSF mesocosms fed with synthetic agricultural runoff containing CAP. To reflect temporal changes in agricultural runoff dynamics, two CAP concentrations were used in influent: a peak concentration (4 μg/L) for the first week and a trace concentration (0.4 μg/L) for the three subsequent weeks. Results showed that mesocosms with biochar were very effective in removing CAP mass (90 to 99%) and remained so throughout the experimental period. On the other hand, the level of CAP removal achieved in planted mesocosms without biochar was low (less than 13%). Evapotranspiration contributed significantly to volume reduction, but no general pattern in CAP mass removal efficiency was detected among the planted treatments without biochar. However, planted treatments acted as buffer zones, accumulating CAP and reducing its peak mass in effluent. Evapotranspiration rates of Scirpus and Phragmites were higher than that of Sporobolus, resulting in a greater buffering effect. This study suggests that addition of biochar to SSF TW substrate is a promising approach for CAP mitigation in agricultural runoff, but long-term efficiency remains to be assessed.

As the use of constructed storm water wetlands to treat storm water runoff becomes more frequent, strategies for maintaining or increasing their pollutant removal over time must be examined. One potential strategy is plant harvesting at the water surface to remove nutrients that would otherwise be deposited back into the wetland during senescence. This technical note presents a first look at this strategy from a storm water management perspective. Vegetation was harvested from two storm water wetlands located in Smithfield and Pactolus, North Carolina, to evaluate the ability of five wetland plant species to sequester nitrogen. Biomass samples were collected from the following species of emergent vegetation: Pontederia cordata (Pickerelweed), Saururus cernuus (Lizard Tail), Scirpus cyperinus (Wool Grass), Sagittaria latifolia (Arrowhead), and Schoenoplectus tabernaemontani (Softstem Bulrush). Samples were collected immediately prior to senescence in September and October 2007 and analyzed for nitr...

Thousands of depressional wetlands accidentally formed as a result of pre-1977 contour coal mining in the Appalachian Mountains. Eleven 20-yr old sites were found in a watershed that did not receive acid mine drainage. The purpose of this study was to quantify and model above- and below-ground plant biomass in these created wetlands and to evaluate functional development. Sampling was stratified by weighted average of two plant communities, which corresponded to shallower and deeper water levels, facultative wetland and obligate wetland communities, respectively. In 1994, peak above-ground biomass averaged 473.7 g m−2 in the facultative wetland community and 409.5 g m−2 in the obligate wetland community. Scirpus cyperinus exhibited the highest peak above-ground biomass (51.8% of total biomass) and Typha latifolia ranked second. Canonical correspondence analysis detected positive effects of longer soil exposure to the atmosphere and greater sediment depth on above-ground biomass at the site (wetland ecosystem) level. Within communities, forward stepwise regression identified positive association of above-ground biomass with water soluble reactive P, water soluble NH3, decomposition rate over 507 d, live S. cyperinus tissue P content, and sediment depth. When these results are combined with prior studies conducted at the same 20-yr old sites, it appears that both structural and functional development has been arrested at a somewhat immature state resulting primarily from soil and hydrologic factors.

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.

Pocosins are shrub wetlands of the southeastern coastal plain maintained by fire. Increased herbaceous plant diversity has been reported after wildfire. To test the effect of radiant heating on the seed bank of pocosin-upland ecotones, wet heat treatments were applied to Sphagnum substrate from a Virginia small depression pocosin. The seedling emergence method was used to quantify wetland seedling abundance and richness. Extant vegetation was measured at each seed bank sampling area and the seed bank and vegetation were compared with Sorenson similarity values. No significant seedling abundance, richness, or evenness effects were detected among wet heat and control groups. However, the high wet heat treatment (75 °C) significantly reduced the density of Sphagnum cuspidatum capitula more than 80% relative to the control. Mean seed bank density was 6,209 seedlings/m2 (richness = 11) and was dominated by Scirpus cyperinus (97.8%), contained many early successional species. The seed bank did not cl...

Plant cover, density, and standing crop biomass were measured and compared in a created wetland and an adjacent freshwater marsh (reference wetland) in Charles City County, Virginia. No significant difference was observed between monthly standing crop in the created wetland and the reference wetland. Species composition differed between sites (mean SI < 0.50) with no significant relationship between species composition and distance from adjacent seed source. Dominant species in the created wetland (Eleocharis obtusa, Juncus acuminatus) were dissimilar to those of the reference wetland (Dichanthelium dichotomum var. dichotomum, Scirpus cyperinus). Results suggest that if both standing crop and composition are going to be used to establish short-term goals for a created wetland, these two measures should not be considered interdependent. Further, the high relative importance of perennials within the created wetland does not fit primary succession predictions, indicating that certain wetland perenni...

Constructed wetlands have the potential to be used for treatment of N-rich livestock wastewater. Our objectives were to evaluate both the time effect and increasing N loading rates on soil N distribution and NH + 4 -N concentration in surface-pore water of constructed wetlands. A 5-yr study in North Carolina investigated two wetland systems that treated swine lagoon wastewater. Wetland System 1 was planted to a Schoenoplectus americanus (Pers.) Volkart ex Schinz & R. Keller, S. tabernaemontani (K.C. Gmel.) Palla, Scirpus cyperinus (L.) Kunth, and Juncus effusus L. plant community, and Wetland System 2 was planted to a Typha angustifolia L., T. latifolia L., and Sparganium americanum Nutt. plant community. Nitrogen loading rates were increased annually from 0.6 to 2.7 g m -2 d -1 . Soils were analyzed for total N annually. Surface-pore water was sampled with equilibrators and analyzed for NH + 4 -N. Although the total N accumulation significantly increased with time in both systems, total soil N accumulation by depth did not differ significantly between systems. Distribution profiles in the surface-pore water column showed that NH + 4 -N was transported upward into surface water at N loading rates from 1.2 to 2.7 g m -2 d -1 . As total N loading rates increased annually in both wetland systems, soil pore water had higher levels of NH + 4 -N but N removal efficiency of the wetlands sharply decreased. Accumulation of high levels of NH + 4 -N (>200 mg L -1 ) in soil pore water could negatively affect long-term ability of wetland systems to treat wastewater with high N levels.

Constructed wetland treatment of swine wastewater probably involves substantial denitrification. Our objective was to assess denitrification and denitrification enzyme activity (DEA) in such wetlands in relation to plant communities, N loading, carbon or nitrogen limitations, and water depth. Two wetland cells each 3.6 m wide and 33.5 m long were connected in series. One set of cells was planted with rushes and bulrushes, including soft rush (Juncus effusus L.), softstem bulrush [Schoenoplectus tabernaemontani (K.C. Gmel.) Pallal, American bulrush [Schoenoplectus americanus (Pers.) Volkart ex Schinz & R. Keller], and woolgrass bulrush [Scirpus cyperinus (L.) Kunthl. Another set was planted with bur-reeds and cattails, including American bur-reed (Sparganium americanum Nutt.), broadleaf cattail (Typha latifolia L.), and narrowleaf cattail (Typha angustifolia L.). The sets will be referred to herein as bulrush and cattail wetlands, respectively. Denitrification and DEA were measured via the acetylene inhibition method in intact soil cores and disturbed soil samples that were taken during four years (1994-1997). Although DEA in the disturbed samples was greater than denitrification in the core samples, the measurements were highly correlated (r 2 ≥ 0.82). The DEA was greater in the bulrush wetlands than the cattail wetlands, 0.516 and 0.210 mg N kg -1 soil h -1 , respectively; and it increased with the cumulative applied N. The DEA mean was equivalent to 9.55 kg N ha -1 d -1 in the bulrush wetlands. We hypothesized and confirmed that DEA was generally limited by nitrate rather than carbon. Moreover, we determined that one of the most influential factors in DEA was wetland water depth. In bulrush wetlands, the slope and r 2 values of the control treatment were -0.013 mg N kg -1 soil h -1 mm -1 depth and r 2 = 0.89, respectively. Results of this investigation indicate that DEA can be very significant in constructed wetlands used to treat swine wastewater.

Plant decomposition and litter accumulation are important components of wetland functions, yet they have rarely been evaluated in created wetlands. In this study, eleven 20-yr and six 2-yr-old depressional wetlands, the most common type of created wetlands, were investigated. We measured plant decomposition as mass loss over 507 days for both age classes and litter accumulation as litter (detritus) mass present in the 20-yr-old wetlands. The wetlands were all created via excavation and contained shallow facultative wetland and deeper obligate wetland plant communities that were often dominated by Scirpus cyperinus and Typha latifolia, respectively. In the decomposition study, stems and leaves from each species were harvested from an adjacent 20-yr-old wetland site and placed in separate plastic mesh bags. Bags were deployed in March 1994 and were recovered after 2, 161, 258, 364, and 507 days. In the litter accumulation study, plant litter that accumulated on top of alluvium was harvested in 0.25...

Metal accumulations in sediments and plants of constructed and natural wetlands were compared in two wetlands constructed by the Tennessee Valley Authority (TVA) for the treatment of acid mine drainage and a natural wetland. Load rates and removal efficiencies of most metals were generally greater in the constructed wetlands than in the natural wetland. There were similar sediment and plant metal concentrations between one constructed wetland and the natural wetland and greater metal concentrations in the sediments and plants in the other constructed wetland compared to the natural wetland. Data indicate that Mn, Zn, Cu, Ni, B, and Cr are being accumulated in the plants at all three wetlands, although accumulation of metals by these plants accounts for only a small percentage of the removal of the annual metal load supplied to each wetland.

In many locations nitrogen (N) addition to the environment is of concern because of the existing quality or intended use of groundwater. To address this concern we evaluated the impact of residence time on N removal in constructed wetlands employed to treat domestic wastewater. Constructed subsurface flow (SF) wetlands were installed at two locations for this study. Twelve small, gravel-based, SF wetlands were constructed at the Virginia Tech’s Kentland Research Farm (KRF). Treatments included combinations of two plant species [woolgrass (Scirpus cyperinus) and cattail (Typha latifolia)] and three residence times (2.6, 3.9 and 5.9 days). Twelve larger SF wetlands were constructed at the Powell River Project (PRP) site. Treatments at the PRP site consisted of the same plant species and three residence times (4, 8 and 12 days). The wastewater at both sites was septic tank effluent (STE) from a single family residence. Changes in ammonium (NH+4), nitrate (NO−3), and total Kjeldahl N (TKN) were determined by monitoring influent and effluent quality over a 3-year period. Plant species had little impact on N concentration or removal. Both NH+4 and TKN concentrations in the wetlands decreased exponentially with increased residence time. Removal of NH+4 and TKN ranged from 18.1 to 39.0% and from 31.3 to 45.8%, respectively, for the KRF site and from 44.4 to 73.4% and from 46.2 to 67.5%, respectively, at the PRP site. The NO−3 concentrations in the influent and effluent at both sites were low and no differences in concentrations with residence time was observed. Temperature dependent rate constants (KT), developed from NH+4–N and TKN data collected from the KRF site, was effective in predicting NH+4–N and TKN concentrations as a function of residence time in the wetlands at the PRP site.

The study investigated vegetative and soil properties in four created mitigation wetlands, ranging in age from three to ten years, all created in the Virginia Piedmont. Vegetation attributes included percent cover, richness (S), diversity (H'), floristic quality assessment index (FQAI), prevalence index (PI), and productivity [i.e., peak above-ground biomass (AGB) and below-ground biomass]. Soil attributes included soil organic matter (SOM), gravimetric soil moisture (GSM), pH, and bulk density (D(b)) for the top 10 cm. Species dominance (e.g., Juncus effusus, Scirpus cyperinus, Arthraxon hispidus) led to a lack of differences in vegetative attributes between sites. However, site-based differences were found for GSM, pH, and SOM (P 0.001). Soil attributes were analyzed using Euclidean cluster analysis, resulting in four soil condition (SC) categories where plots were grouped based on common attribute levels (i.e., SC1 SC2 SC3 SC4, trended more to less developed). When vegetation attributes were compared between SC groups, greater SOM, lower D(b), more circumneutral pH, and higher GSM, all indicative of maturation, were associated with higher H' (P 0.05), FQAI (P 0.05), and total and volunteer percent cover (P 0.05), and lower AGB (P 0.001), PI (P 0.05), and seeded percent cover (P 0.05). The outcome of the study shows that site age does not necessarily equate with site development with soil and vegetation developmental rates varying both within and among sites. The inclusion of soil attributes in post-construction monitoring should be required to enhance our understanding and prediction of developmental trajectory of created mitigation wetlands.

As the use of constructed stormwater wetlands to treat stormwater runoff becomes more frequent, strategies for maintaining their pollutant removal over time must be examined. One potential strategy is plant harvesting to remove nutrients that would otherwise be deposited back into the wetland during senescence. Vegetation was harvested in two stormwater wetlands located in Smithfield and Pactolus, North Carolina, in 2007 to evaluate the ability of five wetland plant species to uptake nitrogen. Biomass samples from harvested emergent vegetation for Pontederia cordata (Pickerelweed), Saururus cernuus (Lizard Tail), Scirpus cyperinus (Wool Grass), Sagittaria latifolia (Arrowhead) and Schoenoplectus tabernaemontani (Softstem Bulrush) were collected in October 2007 and analyzed for nutrient content. At the Pactolus wetland Pontederia cordata, Scirpus cyperinus and Schoenoplectus tabernaemontani biomass retained significantly (p

Animal waste management is a national concern that demands effective and affordable methods of treatment. We investigated constructed wetlands from 1993 through 1997 at a swine production facility in North Carolina for their effectiveness in treatment of swine wastewater from an anaerobic lagoon. We used four wetland cells (3.6 U 33.5 m) with two cells connected in series. The cells were constructed by removing topsoil, sealing cell bottoms with 0.30 m of compacted clay, and covering with 0.25 m of loamy sand topsoil. One set of cells was planted with bulrushes (Scirpus americanus, Scirpus cyperinus, and Scirpus validus) and rush (Juncus effusus). The other set of cells was planted with bur–reed (Sparganium americanum)and cattails (Typha angustifolia and Typha latifolia). Wastewater flow and concentrations were measured at the inlet of the first and second cells and at the exit of the second cell for both the bulrush and cattail wetlands. Nitrogen was effectively removed at mean monthly loading rates of 3 to 40 kg N ha –1 day –1 ; removals were generally >75% when loadings were

A woolgrass (Scirpus cyperinus (L.) Kunth) community in Juneau County, Wisconsin was studied by means of belt transects in August, 1951. Species composition and cover values for a total of 35 stand samples were recorded. Units based on a field technique of recording data by samples of physiognomic homogeneity revealed a very definite structure. These types were distinguished: woolgrass-grass, woolgrass-spikerush, and woolgrass-sedge. Analysis showed these types to be related to water depths and allowed development of a hypothesis of the successional trends of these units. The dominance of woolgrass in a community similar in almost all respects to cattail communities was probably due to the pattern of water level fluctuation. The results of this study indicate a close ecologic relationship between cattail and woolgrass.