Effects of plant and influent C:N:P ratio on microbial diversity in pilot-scale constructed wetlands

Microbial processes within the rhizosphere of constructed wetlands are crucial to wastewater treatment, but the relation between microbial community diversity in rhizosphere, plant growth and water quality are unclear at present. The effects of plant growth, water C:N:P ratio and their interaction on microbial diversity in the rhizosphere were studied in synthetic wastewater in planted and unplanted wetlands during three different seasons. The physiological profile of microbial community-level in each wetland was assessed using substrate utilization patterns gathered via BIOLOG? ECO plates. Plant had a significant effect on AWCD parameter, since the planted wetlands usually had a higher the total microbial activity than the unplanted over the study period. The Shannon, Simpson and McIntosh indices in the planted wetlands were apparently higher than those in the unplanted wetlands under any C:N:P ratio influent condition especially in summer. It was also shown that the unplanted wetlands have a greater shift of the interstitial microbial community than the planted at different seasons, since plant rhizospheres produce a more ecologically stable system in order to resist against shifts in microbial community composition in response to C:N:P ratio change in wastewater. Principal component analysis and clustering analysis indicated that influent C:N:P ratio would induce similar microbial species in the planted wetlands and detach them from the unplanted wetlands.     

The effect of phosphorus enrichment on the nutrient status of a northern Everglades slough

The response of wetlands to elevated nutrient loads typically has been examined in the context of using wetlands for nutrient removal. However, concern over the degradation of natural wetlands following anthropogenic disturbance continues to increase. Most research has focussed on the response of emergent wetlands, with an emphasis on the role of macrophytes. In this study, 21 1.8 m² enclosures (mesocosms) were placed in a pristine open-water (slough) wetland and subjected to 7 inorganic phosphorus (P) loads; 0, 0.4, 0.8, 1.6, 3.2, 6.4, and 12.8 g/m²/y. This study demonstrated that while the rate of specific P accumulation was a function of the loading rate, the duration of loading is a critical factor in the ultimate P concentration in the biota and soil. Thus, time is an important consideration when determining response to enrichment. Phosphorus added to the slough was removed rapidly by the initially abundant metaphyton (unattached floating and suspended periphyton) and epipelon (benthic periphyton), which concentrated P 10- to 50-fold above background periphyton concentrations. Metaphyton concentrated P more rapidly than epipelon; however, both assemblages stabilized P concentrations between 2.6–3.0 g/kg. Water lily responded to elevated P loads with increased leaf size and nutrient accumulation. After 2-y, water lily P concentrations in the highest loaded mesocosms were similar to those observed in periphyton. Soil and porewater nutrients were slower to respond to P enrichment. Soil P concentrations were unchanged by P enrichment except for the highest loaded mesocosms. After 1-y of P loading, mesocosms receiving 12.8 g/m²/y had soil P concentrations almost 2-fold higher than background concentrations. Porewater P concentrations also showed little change throughout the experiment, with the exception of load 12.8 g/m²/y, which increased dramatically after the 1st year. During the 2nd year, average porewater P concentrations in this highest load were over 50-fold higher than background concentrations. Nitrogen concentrations in periphyton and water lily also generally increased in response to increased P loads. The high affinity of periphyton and water lily for P, combined with their subsequent influence on N uptake, suggests that these components can play an important role in wetland nutrient cycling. The disappearance of these communities may result in a reduction in the nutrient assimilative capacity of wetlands.     

人工湿地处理炼油废水的生态效益研究

来自茂名石化公司的炼油废水含有较高浓度的污染物 ,超过广东省规定的排放标准 ,未经处理不能直接排放。 4种草本植物 ,香根草、芦苇、宽叶香蒲和蒲草被用来测试建植人工湿地的效果以及所建植的人工湿地处理炼油废水的效果。在为期 2个月的处理过程中 ,人工湿地在前期对炼油废水的净化效率很高 ,它们对第一批高浓度废水中氨氮、COD、BOD和油的去除率分别是 97.7%、78.2 %、91 .4%和 95 .3% ,对第一批低浓度污水分别是 97.1 %、71 .5 %、73.7%和 89.8%。但是 ,随着时间的推移 ,湿地的净化效果会有一定程度的下降 ,然后逐渐趋于稳定。湿地对氨氮、COD、BOD和油类的去除效率始终表现为氨氮 >油类 >BOD>COD,但植物对它们的净去除量却是 COD>BOD>氨氮和油类。湿地建植之初 ,植物的净化功能很弱 ,但随植物的生长和生物量的增加而逐渐增强。然而 ,不同植物种对废水的净化率很接近 ,基本上无显著性差异。被测试的 4种植物在污水湿地中的生长表现都好过在清水湿地中的 ,但香根草、芦苇和宽叶香蒲在高浓度废水的分蘖数比在低浓度的废水少些 ,而蒲草相反 ,表明高浓度污水相对于低浓度污水而言已经对前面 3个种产生了伤害 ,却仍促进蒲草生长。在清水培养阶段 ,香根草产生分蘖的速度是 4个种中最低的 ;进入污水培养阶     

Horizontal subsurface flow constructed wetlands for tertiary treatment of dairy wastewater

The aim of this work was to evaluate the efficiency of horizontal subsurface flow constructed wetlands (HSFCWs) planted with Typha domingensis and Phragmites australis in the final treatment of dairy wastewater. Ten microcosms-scale reactors simulating HSFCWs were arranged outdoors under a semi-transparent plastic roof. Five replicates were planted with T. domingensis and five with P. australis. In both cases, light expanded clay aggregate (LECA) 10/20 was used as a substrate. Real effluent with previous treatment was used. In order to evaluate contaminant removal efficiencies in each reactor, pH, electrical conductivity, suspended solids, ammonium, nitrate, nitrite, total phosphorus, and chemical oxygen demand (COD) were analyzed before and after treatment. HSFCWs planted with T. domingensis and P. australis were efficient for the final treatment of dairy wastewater. Removal efficiencies obtained in microcosms planted with both macrophytes were over 96% for ammonium and nitrite. Nitrate removal efficiency was 39%. COD decreased along the experiment near 75% for both treatments. High removal percentages for suspended solids (78.4–81.1%) were also achieved. However, systems planted with T. domingensis were significantly more efficient for total phosphorus removal (88.5%) than those planted with P. australis (71.6%).     

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.     

潜流人工湿地中植物对氮磷净化影响效应的研究

采用潜流人工湿地系统,配制以NH⁺₄-N、NO^-₃-N和PO^3-₄-P为主要成分的模拟污水,通过间歇运行方式,考察了芦苇和小叶章的生长情况、生理生态学特性及其对污水中N、P净化效能的影响,并研究了植物对湿地系统pH变化、NO^-₃-N和NH⁺₄-N净化效率的影响。结果表明,当水力停留时间为7d时,小叶章和芦苇湿地对TN的去除率分别为65.1%和99.6%,去除负荷分别为1.66g · m^-3 · d^-1和2.53g · m^-3 · d^-1。小叶章和芦苇对去除TN的贡献率分别为14.7%、61.7%,对去除TP的贡献率分别为11.7%和12.9%;芦苇植株内N、P浓度分别为29.2mg/g和3.41mg/g。芦苇湿地的净化效能高于小叶章湿地。湿地系统中pH值先升高后降低的拐点可作为氨氧化反应结束的指示参数。     

Isoprene emission and primary metabolism in Phragmites australis grown under different phosphorus levels

Aquatic plants are generally used for wastewater purification and phytoremediation, but some of them also emit large amounts of isoprene, the most abundant biogenic volatile organic compound. Since isoprenoid biosynthesis requires high amounts of phosphorylated intermediates, the emission may also be controlled by inorganic phosphorus concentration (Pi) in leaves. We carried out experiments to determine the emission of isoprene from Phragmites australis plants used in reconstructed wetlands to phytoremediate elevated levels of phosphorus contributed by urban wastes. Four groups of plants were grown hydroponically in water containing different levels of KH(2)PO(4). High levels of phosphorus in the water resulted in high Pi in the leaves. High Pi stimulated photosynthesis at intercellular CO(2) concentrations lower and higher than ambient, implying higher ribulose 1,5-bisphosphate carboxylase (Rubisco) activity and higher ribulose 1,5-bisphosphate regeneration rates, respectively. However, isoprene emission was substantially lower at high Pi than at low Pi, and was not associated to photosynthesis rates at high Pi. This surprising result suggests that isoprene is limited by processes other than photosynthetic intermediate availability or by energetic (ATP) requirements under high Pi levels. Irrespective of the mechanism responsible for the observed reduction of isoprene emission, our results show that Phragmites plants may effectively remove phosphorus from water without concurrently increase isoprene emission, at least on a leaf area basis. Thus, Phragmites used in reconstructed wetlands for phytoremediation of urban wastes rich of phosphates will not contribute high loads of hydrocarbons which may influence air quality over urban and peri-urban areas.     

Nitrogen and phosphorus removal from wastewater by subsurface wetlands planted with Iris pseudacorus

Subsurface horizontal flow constructed wetlands are being evaluated for nitrogen (N) and phosphorus (P) removal from wastewater in this study through different gravel sizes, plant densities (Iris pseudacorus), effects of retention times (1 to 10 days) on N and P removal in continuously fed gravel wetland. The inlet and outlet samples were analyzed for TKN, NH₄-N, and NO₃-N, as standard methods. The planted wetland reactor with fine (SG) and coarse (BG) gravels removed 49.4% and 31.4% TKN, respectively, while unplanted reactors removed 43.4% and 26.8% TKN. Also, the efficiencies for NH₄-N were 36.7–43% and 21.6–25.4% for SG and BG planted reactors, respectively. The efficiencies for NO₃-N were 53.5–62.5% and 21.6–25.4% for SG and BG planted reactors, respectively. Roles of plants in SG reactors for O-PO₄ were 5–12% and 3–8% in BG. Also, the roles of plants in the reactors for TP were 9% and 7.4%. The minimum effective detention time for the removal of NO₃-N was 4–5 days. The subsurface constructed wetlands planted with I. pseudacorus can be an appropriate alternative in wastewater treatment natural system in small communities.     

闽江河口不同河段芦苇湿地土壤碳氮磷生态化学计量学特征

为了阐明不同河段湿地土壤生态化学计量学特征及其指示意义,对闽江河口不同河段芦苇湿地土壤碳、氮、磷含量进行了测定与分析。结果表明:上游段芦苇湿地0—60 cm土壤C/N、C/P和N/P分别为36.5—51.3、43.0—93.6和0.8—2.3,平均值分别为44.1、66.9和1.6;中游段湿地0—60 cm土壤C/N、C/P和N/P分别为15.8—21.7、28.0—72.2和1.6—4.2,平均值分别为17.6、45.7和2.6;下游段湿地0—60 cm土壤C/N、C/P和N/P分别为13.5—19.8、63.6—125.4和4.2—6.3,平均值分别为16.4、90.5和5.5;不同河段湿地的3种比值表现为不同的变化趋势,土壤C/N为上游段湿地>中游段湿地>下游段湿地,C/P为下游段湿地>上游段湿地>中游段湿地,N/P为下游段湿地>中游段湿地>上游段湿地;单一河段湿地不同土壤剖面C/N、C/P和N/P的变异性小于不同河段湿地之间的变异性;土壤水分含量和粉粒含量是影响不同河段湿地土壤C/N、C/P、N/P变化的最为关键的因子;不同河段湿地土壤C/N和N/P对厌氧碳分解过程具有良好的指示作用。     

Contaminant Removal of Domestic Wastewater by Constructed Wetlands： Effects of Plant Species

A comparative study of the efficiency of contaminant removal between five emergent plant species and between vegetated and unvegetated wetlands was conducted in small-scale （2.0 m×1.0 m×0.7 m, lengthxwidthxdepth） constructed wetlands for domestic wastewater treatment in order to evaluate the decontaminated effects of different wetland plants. There was generally a significant difference in the removal of total nitrogen （TN） and total phosphorus （TP）, but no significant difference in the removal of organic matter between vegetated and unvegetated wetlands. Wetlands planted with Canna indica Linn., Pennisetum purpureum Schum., and Phragmites communis Trin. had generally higher removal rates for TN and TP than wetlands planted with other species. Plant growth and fine root （root diameter ≤ 3 mm） biomass were related to removal efficiency. Fine root biomass rather than the mass of the entire root system played an important role in wastewater treatment. Removal efficiency varied with season and plant growth. Wetlands vegetated by P. purpureum significantly outperformed wetlands with other plants in May and June, whereas wetlands vegetated by P. communis and C. indica demonstrated higher removal efficiency from August to December. These findings suggest that abundance of fine roots is an important factor to consider in selecting for highly effective wetland plants. It also suggested that a plant community consisting of multiple plant species with different seasonal growth patterns and root characteristics may be able to enhance wetland performance.     

Response of Periphytic Algae to Gradients in Nitrogen and Phosphorus in Streamside Mesocosms

In this study we manipulated both nitrogen and phosphorus concentrations in stream mesocosms to develop quantitative relationships between periphytic algal growth rates and peak biomass with inorganic N and P concentrations. Stream water from Harts Run, a 2nd order stream in a pristine catchment, was constantly added to 36 stream-side stream mesocosms in low volumes and then recirculated to reduce nutrient concentrations. Clay tiles were colonized with periphyton in the mesocosms. Nutrients were added to create P and N concentrations ranging from less than Harts Run concentrations to 128 μg SRP l⁻¹ and 1024 μg NO₃-N l⁻¹. Algae and water were sampled every 3 days during colonization until periphyton communities reached peak biomass and then sloughed. Nutrient depletion was substantial in the mesocosms. Algae accumulated in all streams, even streams in which no nutrients were added. Nutrient limitation of algal growth and peak biomass accrual was observed in both low P and low N conditions. The Monod model best explained relationships between P and N concentrations and algal growth and peak biomass. Algal growth was 90% of maximum rates or higher in nutrient concentrations 16 μg SRP l⁻¹ and 86 μg DIN l⁻¹. These saturating concentrations for growth rates were 3–5 times lower than concentrations needed to produce maximum biomass. Modified Monod models using both DIN and SRP were developed to explain algal growth rates and peak biomass, which respectively explained 44 and 70% of the variance in algal response.     

Effect of artificial aeration and macrophyte species on nitrogen cycling and gas flux in constructed wetlands

Constructed wetlands (CWs) are efficient at removing excessive nutrients from wastewaters. However, this removal often results in the flux of important greenhouse gases (GHG), such as nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) that could mitigate the environmental benefits of CWs. We studied the efficiency of artificial aeration and 2 different macrophyte species (Phragmites australis, Typha angustifolia) on the removal and transformations of nitrogen and GHG gas flux using CW mesocosms supplied with 60 L m^?2 d^?1 of wastewater. Removal of total nitrogen (TN) and dissolved organic nitrogen (DON) was generally high in all beds but resulted in a net production of oxidized nitrogen (NO_y) in aerated CW mesocosms as compared to ammonium (NH₄⁺) in non-aerated units. Aerated units emitted less N₂O when planted with P. australis or left unplanted. Aerated beds and planted mesocosms had lower CH₄ fluxes than non-aerated units and unplanted beds, respectively. Our study suggests that planted systems with artificial aeration have the overall best performances in that they lead to a reduction of GHG flux and promote the release of NO_y over NH₄⁺ in their effluents.     

Does Wet Prairie Vegetation Retain More Nitrogen with or withoutPhalaris arundinaceainvasion?

Elevated nitrogen (N) levels accelerate expansion of Phalaris arundinacea L. (reed canary grass), a highly aggressive invader that displaces native vegetation and forms monotypes. Hence, Phalaris is commonly presumed to have high nutrient uptake that contributes to higher N retention in a wetland. We compared the capability of wet prairie vegetation with and without invading Phalaris under low-N and high-N treatments to (1) accumulate N in plant tissues, (2) retain N in soil and (3) remove N from water flowing through mesocosms. With high-N treatment, above-ground biomass increased by > 90% (P < 0.0004; yrs. 1–2) and percent total N in above-ground tissues increased by > 46% (P = 0.0005; yrs. 1–2). Consequently, there was ~3 times as much total N accumulation in above-ground tissue (calculated from biomass and percent total N in tissues) with high-N treatment vs. low-N treatment (P < 0.0001; yrs. 1–2). Without invading Phalaris, wet prairie vegetation produced over 49% more above-ground biomass (P ￡ 0.022; yrs. 1–2) and accumulated over 38% more N in its above-ground tissues (P = 0.009; yrs. 1–2), compared to invaded mesocosms. The high-N treatment increased concentrations of soil ammonium (NH4–N) up to 157% (P = 0.0001) and soil nitrate (NO3–N) up to 549% (P < 0.001). After N treatments began, we found no differences in total N or NO3–N in soils (P > 0.05) or in concentrations of NH4–N or NO3–N released in the discharged water (P > 0.1) from wet prairie mesocosms with and without invading Phalaris. Soil NH4–N did not differ between the wet prairie mesocosms with and without Phalaris invasions on five dates (P > 0.05); the one exception was in August 2004 (27% greater with invasion; P = 0.02). Our results from wet prairie mesocosms do not support the presumption that Phalaris retains more N than native plant assemblages.     

Removal of phosphates by pilot vertical-flow constructed wetlands using a mixture of sand and dolomite as substrate

This study evaluates the performance of a mixture of river sand and dolomite (10:1, w/w) used as substrate in vertical-flow constructed wetlands in removal of phosphates. Two duplicate pilot-scale artificial wetlands (total 4 units) were set up outdoors, planted with Phragmites australis and fed with a synthetic sewage solution, corresponding to medium strength municipal wastewater. The wetlands were fed with two batch (intermittent) operational modes and their effluent was monitored for the presence of soluble phosphates over a period of 3 months. Laboratory (batch) incubation experiments were also carried out separately to ascertain the phosphate adsorption capacity of the two materials (i.e. sand and dolomite). The wetlands were capable to remove more than 45% of initially applied phosphates. Phosphorus accumulation in the wetlands body at the end of the operation period was in the range of 6.5–18%, as compared with the unused media. The Ca Mehlich-III extractable content was also increased, indicating that the removal of phosphates would be mainly attributed to the sorption of orthophosphate ions onto calcium carbonates and/or to the precipitation of orthophosphate ions with calcium ions as the respective insoluble calcium phosphates.     

Use of horizontal subsurface flow constructed wetlands to treat reverse osmosis concentrate of rolling wastewater

According to the characteristics of the reverse osmosis concentrate (ROC) generated from iron and steel company, we used three sets of parallel horizontal subsurface flow (HSF) constructed wetlands (CWs) with different plants and substrate layouts to treat the high-salinity wastewater. The plant growth and removal efficiencies under saline condition were evaluated. The evaluation was based entirely on routinely collected water quality data and the physical and chemical characteristics of the plants (Phragmites australis, Typha latifolia, Iris wilsonii, and Scirpus planiculmis). The principal parameters of concern in the effluent were chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The results showed that the CWs were able to remove COD, TN, and TP from ROC. S. planiculmis was not suitable for the treatment of high-saline wastewater. The sequence of metals accumulated in CW plants was K>Ca>Na>Mg>Zn>Cu. More than 70% of metals were accumulated in the aboveground of P. australis. The CW filled with gravel and manganese ore and planted with P. australis and T. latifolia had the best performance of pollutant removal, with average removal of 49.96%, 39.45%, and 72.01% for COD, TN, and TP, respectively. The effluent water quality met the regulation in China. These results suggested that HSF CW planted with P. australis and T. latifolia can be applied for ROC pollutants removal.     

Fate of Pseudomonas putida after release into lake water mesocosms: Different survival mechanisms in response to environmental conditions

To study the fate of Pseudomonas putida DSM 3931 in an aquatic environment, cultures of the strain were released into lake water mesocosms. P. putida, bearing the TOL-plasmid, was released as a representative xenobiotic-degrading microorganism. The release was carried out in mesocosms with unamended lake water and in lake water with added culture medium to compare the survival of the strain due to the influence of different organic load. As a comparison, the survival of P. putida was followed in microcosms with sterile lake water. Survival and fate of the strain were determined by means of immunofluorescence with highly specific monoclonal antibodies and growth on selective agar medium for up to ten weeks after release. Addition of medium had a pronounced influence on survival in mesocosms. In mesocosms without added medium, the number of P. putida cells decreased within ten days by over 2 orders of magnitude. In mesocosms with medium, cell numbers increased in the first two days by an order of magnitude and were, after ten days, in the same range as at the time of introduction. Over time, cell numbers decreased but remained detectable in both types of mesocosms for up to ten weeks after release. In mesocosms with unamended lake water, the major fraction of the cells was attached to particles after two days. In mesocosms with medium, large aggregates of P. putida cells formed which included algae. The observed decrease in cell numbers in mesocosms was attributed mainly to grazing. Sedimentation was an additional factor contributing to loss of cells out of the water column, which especially affected aggregate-forming cells in mesocosms with medium in the long run (beyond two weeks). These studies demonstrate that experimental tools on a mesoscale are crucial in order to understand the complex processes microorganisms are subjected to after release into a natural environment, and that single cell detection, such as immunofluorescence, is essential to understand mechanisms of survival and elimination.Correspondence to: M.G. Höfle     

九段沙芦苇湿地生态系统N、P、K的循环特征

对九段沙(上沙、中沙、下沙)芦苇湿地土壤、植物中N、P、K含量进行了测定,研究其分布规律.结果表明:水平分布上,湿地土壤全量养分与速效性养分含量均是中沙最低,并以中沙为中心向两端递增,速效性养分的这种变化尤为显著.垂直分布上,土壤全N和全K含量的分布规律一致,为上层＞下层＞中层;全P含量分布为中层＞上层＞下层.速效N含量分布为上层＞中层＞下层;速效P含量上层土壤最高,中、下层土壤含量因湿地类型而异;速效K含量多以中层土壤最低,上、下层土壤含量变化不稳定,以不同湿地而异.不同芦苇湿地的土壤速效性养分含量差异显著大于全量养分的差异,0～60 cm深度土壤的全量养分和速效性养分含量排序均为K＞N＞P.中沙湿地植物中养分含量最低,与土壤中营养元素总体水平分布一致;多数芦苇湿地植物中营养元素含量排序为N＞K＞P,与土壤养分含量排序不一致.不同芦苇湿地的吸收系数排序均为N＞P＞K;芦苇湿地利用系数排序为P＞K＞N;循环系数排序为N＞K＞P.     

Algal responses to experimental nutrient addition in the littoral community of a subtropical lake

1. An in situ experiment was performed in the littoral zone of a large, subtropical lake to quantify effects of phosphorus (P) and nitrogen (N) on algal biomass, productivity, nutrient content and phosphate uptake kinetics. 2. We hypothesized that resident periphyton rapidly sequester added nutrients from the water column, but once a certain threshold is reached, nutrients remain in the water and permit a shift to a phytoplankton-dominated community. 3. Three duplicate sets of 1.2-m diameter mesocosms were treated with 10, 20 or 50 μg P L^??1 in combination with 100, 200 or 500 μg N L^??1, respectively. The nutrients were added thrice weekly for 14 days, after which the treatment doses were doubled for an additional 9 days. The cumulative amounts of P and N added over the course of the study were 700 and 7000 μg L^??1, respectively. Two untreated mesocosms and two open reference sites were used as controls. 4. The total P concentration in the water column of nutrient-treated mesocosms remained low, even after prolonged high dosing. However, there was a two-fold increase in the P content of surface algal mats and epiphyton. This indicates that some of the added P was sequestered by those components of the community. In contrast, metaphyton and epipelon displayed little or no increase in their P content. Large quantities of added P could not be accounted for in the periphyton community, and may reflect unmeasured losses to the sediments or other pools. 5. Nitrogen also was depleted from the water column, but there were no significant increases in periphyton N content. Much of the added N could not be accounted for in mass balances, and may have been lost from the mesocosms through volatilization or other biochemical processes. 6. Chlorophyll-a in epiphyton increased significantly after 14 days in the highest nutrient treatment, where there also was a proliferation of Spirogyra on day 28. 7. On day 28, water column samples from the highest nutrient treatment also displayed a significantly higher rate of carbon uptake, and a significantly higher concentration of midday dissolved oxygen. 8. The hypothesis that phytoplankton become dominant at high nutrient loading rates was not supported. However, there were dramatic changes in community structure (increased dominance by epiphytic Spirogyra) and function (increased productivity and dissolved oxygen) in response to nutrient additions.     

Nutrient removal in constructed microcosm wetlands for treating polluted river water in northern China

River water pollution is increasingly widespread in northern China and can lead to problems with the drinking water for the residents if not properly treated. Constructed wetlands are a promising solution and have become increasingly popular in China. In this study the nutrient removal and plant uptake in constructed microcosm wetlands vegetated with Typha orientalis, Phragmites australis, Scirpus validus and Iris pseudacorus for treating simulated polluted river water in northern China were investigated. The performance of the treatment systems from April to November was assessed. The maximum TN, NH₄-N and TP removal efficiencies were 68%, 93% and 67%, respectively. And the maximum nutrient uptake by plants constituted 51.89% of the N removal and 34.17% of the P removal throughout the trial. S. validus and I. pseudacorus have a higher nutrient uptake capacity and are preferred species from a treatment perspective in constructed wetland in northern China.     

Comparison of created and natural freshwater emergent wetlands in Connecticut (USA)

Five three- to four-year old created palustrine/emergent wetland sites were compared with five nearby natural wetlands of comparable size and type. Hydrologic, soil and vegetation data were compiled over a nearly two-year period (1988-90). Created sites, which were located along major highways, exhibited more open water, greater water depth, and greater fluctuation in water depth than natural wetlands. Typical wetland soils exhibiting mottling and organic accumulation were wanting in created sites as compared with natural sites. Typha latifolia (common cattail) was the characteristic emergent vegetation at created sites, whereas a more diverse mosaic of emergent wetland species was often associated with Typha at the natural sites. Species richness was slightly higher in created (22–45) vs. natural (20–39) wetlands, but the mean difference (33 vs. 30) was not significant. Nearly half (44%) of the 54 wetland taxa found at the various study sites were more frequently recorded at created than natural wetlands. The presence of mycorrhizae in roots of Typha angustifolia (narrow-leaved cattail) and Phragmites australis (common reed) was greater at created than natural wetlands, which may be related to differential nutrient availability. Wildlife use at all sites ranged from occasional to rare, with more sightings of different species in the natural (39) than created (29) wetlands. The presence of P. australis and introduced Lythrum salicaria (purple loosestrife) may pose a threat to future species richness at the created sites. One created site has permanent flow-through hydrology, and its vegetation and wildlife somewhat mimic a natural wetland; however, the presence of P. australis and its potential spread pose an uncertain future for this site. This study suggests the possibility of creating small palustrine/emergent wetlands having certain functions associated with natural wetlands, such as flood water storage, sediment accretion and wildlife habitat. It is premature to evaluate fully the outcome of these wetland creation efforts. A decade or more is needed, emphasizing the importance of long term monitoring and the need to establish demonstration areas.