A Test of Diversity–Productivity Models in Natural,Degraded, and Restored Wet Prairies

Conceptual restoration models depict strong correlations between structure and function, with both decreasing as an ecosystem is degraded and increasing during restoration. We evaluated the “linear” and “asymptotic” models by measuring diversity and annual net primary productivity (NPP) within four states of a southern Wisconsin floodplain: a remnant (unplowed) wet prairie, two degraded sites (soybean field and invaded prairie), and a restored prairie. Neither model fit our data for aboveground (ANPP), belowground (BNPP), or total (TNPP) productivity. ANPP declined as species richness increased (r = 0.998, df = 2), with highest values for soybeans (1,024 g/m²; two species in 30 0.25‐m² plots) and invaded prairie (937 g/m²; nine species, 99% cover of Phalaris arundinacea), intermediate for restored prairie (712 g/m²; 28 species), and lowest for diverse remnant prairie (571 g/m²; 36 species). In contrast, BNPP was lowest for soybeans (225 g/m²) and highest for remnant prairie (571 g/m²). TNPP in restored prairie (990 g/m²) matched that of the remnant (1,147 g/m²) within 7 years, but root:shoot NPP ratios were quite different (0.39 and 0.99, respectively). Overall, results suggest that the relationship between species diversity and productivity can differ with the component measured (ANPP, BNPP, or TNPP) and that diversity does not ensure high productivity. Because measuring ANPP does not fully test ecosystem‐function theory, we recommend assessing BNPP and additional ecosystem processes in future attempts to determine whether adding species will restore more function to degraded ecosystems.     

巢湖叶绿素a浓度的时空分布及其与氮、磷浓度关系

基于巢湖水体2002~2007年水质监测资料,对叶绿素a浓度的分布、动态及与TN、TP的关系进行了统计分析。巢湖叶绿素a浓度与TN、TP的浓度分布存在明显的空间差异,西半湖叶绿素a浓度全年高于20μg/L,TN为1.94~3.84mg/L,TP为0.20~0.42mg/L;东半湖叶绿素a浓度全年小于5.5μg/L,TN为0.95~1.83mg/L,TP为0.08~0.14mg/L。在东半湖,叶绿素a含量与TN呈不明显的正线性关系,当TP浓度较低时,叶绿素a随TP的增加小幅上升,但是当TP>0.15mg/L时,叶绿素a随TP的增加而明显上升;在西半湖,当水体TN<5.8mg/L或者TP<2.0mg/L时,叶绿素a含量与TN、TP关系为正线性关系,当TN在5.8~9.4mg/L或者TP介于0.2~0.3mg/L间时,叶绿素a含量与TN、TP关系为不显著的负线性关系,当TP浓度>0.3mg/L时,叶绿素a含量与TP关系又为正线性关系。西半湖叶绿素a浓度的变化可能是藻类生物活动与沉积物及水体中营养盐的相互作用结果。在治理巢湖富营养化时,应优先控制西半湖的磷元素。     

胶州湾湿地海域水体和表层沉积物环境质量评价

基于2009年对胶州湾湿地48个站点的调查数据,采用内梅罗(Nemerow)指数、富营养指数(EI)和Hakanson潜在生态危害指数法对胶州湾湿地水体和表层沉积物环境质量现状进行了评价.结果表明:对参与评价的pH值、溶解氧、无机氮、活性磷酸盐、CODMn、石油类、Cu、Zn、Pb、Cd、Hg、As、六六六、滴滴涕、大肠菌群、粪大肠菌群等16项指标而言,各调查月份大沽河感潮河段水质处于中污染-重污染水平,潮间带区域水质处于轻污染-中污染水平,浅海区域水质处于轻污染水平.胶州湾湿地不同区域富营养化程度差异明显,其中大沽河感潮河段水体EI值在58.13 ～327.89,富营养化程度严重;潮间带区域水体EI值在1.34 ～19.96,富营养化程度较为严重;浅海区域水体EI值在0.65 ～ 2.10,富营养化程度较轻.胶州湾湿地海域表层沉积物质量基本处于轻污染水平,其中大沽河感潮河段处于轻污染水平,潮间带区域处于轻污染-中污染水平,浅海区域处于较清洁-轻污染水平.胶州湾湿地海域表层沉积物中重金属单项污染参数(Cfi)和污染程度指数(Cd)较低,污染程度处于低级水平,Cu、Zn是表层沉积物中的主要污染因子;重金属潜在的生态危害系数(Eir)和潜在生态危害指数(RI)较小,污染程度属于低生态危害范畴.     

Mountain cheese factory wastewater treatment with the use of a hybrid constructed wetland

This paper describes the activity period of an experimental hybrid wetland system placed in a cold climate region. The aim is to determine the efficiency of the system in reducing TSS, BOD₅, COD and other pollutants. The constructed wetland consists of a fat-removal unit and a basin for the storage and the distribution of the wastewater which precedes three phytoremediation beds: the first two are parallel and they work as submerged vertical flow wetland with gravel medium for an area of 180 m²; the last is a submerged horizontal flow wetland with sand medium and an area of 360 m². The CW was designed to process a total estimated BOD₅ loading rate of about 24 g m⁻² d⁻¹, which was less than half of the average actual loading rate. The wastewater treatment did not meet the required Italian law outflow limits, most likely due to BOD₅ overloading.     

Modeling impacts of Yangtze River water transfer on water ages in Lake Taihu, China

To improve water quality and alleviate eutrophication in Lake Taihu, the third largest freshwater lake in China, a Yangtze River water transfer project was initiated in 2002 to bring water from the Yangtze River to Lake Taihu to dilute and divert pollutants out of the lake. We used a three-dimensional numerical model, Environmental Fluid Dynamics Code, to study the impacts of water transfer on the transport of dissolved substances in the lake by using the concept of water age. In particular, the influences of inflow tributaries and wind forcing on water age were investigated. Model results showed that the effect of water transfer on transport processes in the lake is strongly influenced by hydrodynamic conditions induced by wind and inflow/outflow tributaries. During the simulation year (2005), the water ages in Lake Taihu were highly variable both spatially and temporally, with a mean of approximately 130 days in summer and 230 days in the other seasons. Southeasterly winds—dominant in the summer—could improve the quality of water by reducing the water age in the eastern areas of the lake, which are used as a drinking water source, and in Meiliang Bay, the most polluted bay. In terms of dilution, the most efficient flow rate for transferred water was predicted to be approximately 100 m³/s. The spatial distribution of water ages showed that water transfer may preferentially enhance exchanges in some areas of the lake unless nutrient concentrations in the transferred water are reduced to a reasonable level. This study provides useful information for a better understanding of the complex hydrodynamic and mass transport processes in the lake, which is important for developing and implementing effective ecological restoration strategies in the region.     

Dynamics in the bacterial community-level physiological profiles and hydrological characteristics of constructed wetland mesocosms during start-up

The objective of this work was to study the effect of plant presence (Phragmites australis) and inoculant origin on wetland mesocosm start-up dynamics. Eight mesocosms were studied based on a duplicated 2² factorial design tracking bacterial community and hydrological changes during an 8 month start-up period. The mesocosms were characterized in terms of their hydrological character based on evapotranspiration (ET), porosity, and a dispersion coefficient. The microbiological regime was characterized using a microbial activity measure and community-level physiological profiling (CLPP) employing BIOLOG™ ECO plates. CLPP-related indices such as substrate richness, substrate diversity, over-all community profile, and community divergence are also presented. It was found that mesocosm porosities decreased over time as a result of media-related biofilm development. This biofilm development also contributed to a substantial increase in the dispersion coefficient in the mesocosms over the start-up period. Dispersion coefficients in planted systems reached values of ∼50-55 cm²/min whereas in the unplanted systems values of ∼30-35 cm²/min were observed. Bacterial community divergence in the mesocosms was quantified using a Euclidean-based divergence metric. All mesocosms showed a sharp increase in community divergence until day 75, at which point a steady state was reached. The interstitial communities were also characterized in terms of similarity based on the experimental design treatments. Four stages of mesocosm development were identified that can be described by an initial community state based on the origins of the initial inoculum [days 0-6]; a dynamic period where adjustments and shifts in the bacterial community occurred in all mesocosms [days 7-26]; a period where all interstitial CLPPs were quite similar [days 27-73]; and finally a shift towards unplanted and planted mesocosm CLPP groupings [days 74-232].     

Estimating biogeochemical and biotic interactions between a stream channel and a created riparian wetland: A medium-scale physical model

Straightened channels and altered and drained adjacent riparian wetlands have adversely impacted streams and rivers throughout the US Midwest. This research investigated the biological connection and water quality of a 0.07 ha diversion wetland and adjacent stream at the Olentangy River Wetland Research Park in central Ohio. Before the flowthrough conditions were established, we demonstrated with mark and recapture techniques that the wetland already was a biorefuge for fish under extreme conditions; two species (Centrarchidae) captured in the stream before a total drawdown of the stream were found in the wetland a year later. In addition, water at the bottom remained at around 4 °C over the winter likely due to groundwater input, which possibly provided a warmer shelter for fish. Stream water quality of the lower section, downstream of the wetland outlet, generally improved with hydrologic pulsing in spring after flow-through reconnection due to the trapping of nutrients in the wetland. Mean removal per flood pulse for nitrate-nitrite, total nitrogen (TN), soluble reactive phosphorus (SRP), total phosphorus (TP) were 1.81 g-N m⁻² per pulse, 1.02 g-N m⁻² per pulse, 0.014 g-P m⁻² per pulse, and 0.004 g-P m⁻² per pulse, respectively. The wetland exported 2.8 g-C m⁻² per pulse of organic carbon. A greater attenuation of NO₃⁻ and TP occurred in the marshy outlet channel section of the wetland than the open water section. The diversion wetland successfully removed nitrate and phosphorus during storm pulses in spring. Similar designs should be applied to other locations to examine their function under different climatic and hydrological conditions.     

Hydraulic residence time computation for constructed wetland design

Hydraulic residence time (HRT) is one of the key design parameters controlling the removal efficiency of contaminants and nutrients in stormwater and wastewater wetlands. The paper presents a new approach to the estimation of HRT using the variable residence time (VART) model. The VART model is employed to simulate the major processes (including advection, dispersion, and transient storage of contaminants/nutrients in vegetated zones) affecting HRT and thereby to produce a hydraulic residence time distribution (HRTD) for a design wetland. The HRTD in combination with a moment-based method is then utilized to find a mean design HRT for the design wetland. Methods for estimation of parameters governing the HRTD are proposed. The new approach to HRT computation is demonstrated through a case study for the Tres Rios Demonstration (TRD) Wetlands in Arizona, USA. Modeling results show that the design HRTs for the Hayfield wetland (H1) and the Cobble wetlands (C1 and C2) are 4.04, 4.66, and 2.65 days, respectively. The computed HRTs agree well with those reported by previous studies, confirming the efficacy of the new approach to hydraulic design of constructed wetlands.     

Estimation of nitrogen dynamics in a vertical-flow constructed wetland

The vertical-flow constructed wetland (VFCW) is a promising engineering technique for removal of excess nutrients and certain pollutants from wastewater and stormwater. The aim of this study was to develop a model using the STELLA software for estimating nitrogen (N) dynamics in an artificial VFCW (i.e., a substrate column with six zones) associated with a growing Cyperus alternifolius species under a wetting (wastewater) -to-drying ratio of 1:3. The model was calibrated by our experimental data with a reasonable agreement prior to its applications. Simulations showed that rates of NH₄⁺-N and NO₃⁻-N leaching decreased with increasing zone number (or column depth), although such a decrease was much more profound for NH₄⁺-N. Our simulations further revealed that rate of NH₄⁺-N leaching decreased with time within each zone, whereas rate of NO₃⁻-N leaching increased with time within each zone. Additionally, both the rates of NH₄⁺-N and NO₃⁻-N leaching through zones followed the water flow pattern: breakthrough during wetting period and cessation during drying period. In general, the cumulative amounts of total nitrogen (TN) were in the following order: leaching > denitrification > uptake > settlement. About 54% of the TN from the wastewater flowed out of the VFCW system, 18% of TN lost due to denitrification, 6% of TN was taken up by roots of a single plant (one hill), and the rest of 22% TN from the wastewater was removed from other mechanisms, such as volatilization, adsorption, and deposition. This study suggested that to improve the overall performance of a VFCW for N removal, prevention of N leaching loss was one of the major issues.     

Simulation study on water quality based on sediment release flume experiment in Lake Taihu, China

Sediments have a significant influence on the overlying water, and nutrient release from sediments is an important source for lake eutrophication, particularly in shallow lakes. Sediment resuspension is primarily driven by wind-induced currents. In this research, the correlation between release rate of suspended sediment and flow velocity was studied, and an experiment on hydrodynamic forces was conducted in a rectangle flume using water and sediments collected from three sites in Lake Taihu, a eutrophic lake in China. It was shown that the starting velocities of sediment in Lake Taihu at three different incipient standards gained from the experiment were 15, 30, and 40 cm s⁻¹ and the release rate of suspended sediment could reach up to 643.4, 5377.1, and 13980.5 g m⁻² d⁻¹, respectively. Based on the experiment, a water quantity and quality numerical model of wind-induced current with sediment pollution for Lake Taihu was developed. The model was calibrated and validated by applying it to the study of the water quality of Lake Taihu. The calculated values were generally in good agreement with field observations, which indicated that the developed model could represent the dynamics of sediment resuspension to a certain extent. This study provides a new approach and a practical tool for planning and management policy and operations to protect the water quality and ecosystems of shallow lakes.