Factors affecting nitrogen loss in experimental wetlands with different hydrologic loads

Constructed or restored wetlands have great potential for reducing nonpoint source contamination of surface and ground waters by agricultural chemical contaminants. The work reported here combines field and experimental studies of factors affecting nitrogen loss in the Des Plaines River Experimental Wetlands, northeastern Illinois, USA. These wetlands receive approximately 5–36 cm/week of pumped river water with significant but seasonally variable loads of nitrate and organic nitrogen. On an annual basis, the wetlands removed 78–95% of the nitrate and 54–75% of the total nitrogen received. At the low hydrologic loading rate, organic nitrogen exports approximately equalled imports. However at the higher hydrologic loading rate, the wetlands exported 22–31% more organic nitrogen than received. Seasonal variation in nitrate and organic nitrogen loads had significant effects on the effectiveness of the wetlands as sinks for total nitrogen. The wetlands were nitrogen sinks during periods of the nitrate loading and nitrogen sources during periods of low nitrate loading. Experimental studies demonstrated the effects of nitrate concentration, temperature, and location on rates of nitrate loss. Results suggest that nitrite loading rates might influence not only nitrate loss rates but also loss rate coefficients.     

Adaptation of wastewater surface flow wetland formulae for application in constructed stormwater wetlands

Over the past 30 years, the use of constructed wetlands for wastewater treatment has been a topic of significant research culminating in a good data base from which simplistic equations have been derived to aid in the design of these facilities to meet long term water quality treatment performance criteria. Over the past decade, the use of treatment wetlands has extended to stormwater and combined sewer overflow (CSO) management applications. Designing constructed wetlands for stormwater and CSO applications have unique challenges stemming from the highly stochastic nature of the hydraulic and pollutant loading on a stormwater wetland compared with wastewater treatment systems. This paper explores the possibility of adapting the simplistic models for wastewater wetlands for interim use in developing design guidelines for stormwater wetland systems. A procedure that takes into account the unsteady intermittent nature of stormwater inflows to these wetlands has been incorporated into one of these simplistic models and a case study presented to demonstrate the application of the procedure.     

Environmental decision support systems: A new approach to support the operation and maintenance of horizontal subsurface flow constructed wetlands

This paper describes the development and operation of an Environmental Decision Support System (EDSS) to improve the operation and maintenance of horizontal subsurface-flow constructed wetlands (EDSS-maintenance). Constructed wetlands (CWs) allow wastewater treatment in a sustainable manner since they involve low energy consumption, low construction and functioning costs and low environmental impact. However, operation and maintenance activities are essential to guarantee reliability in CWs performance. The definition of operation and maintenance protocols depends on several quantitative and qualitative aspects such as wastewater treatment plant configuration, CW design, influent characteristics, sensitivity of the receiving media, etc. Bearing this in mind and considering the limited technical knowledge about CWs, the need for a new tool to support CW performance is clear. In this sense, EDSSs offer a new approach because they can tackle problems of complex and uncertain systems. The EDSS-maintenance provides operation and maintenance manuals specifically defined for every CW. To achieve it, the required knowledge was implemented within a rule-based system, which forms the backbone of the EDSS. Several features presented in this paper demonstrate how the EDSS-maintenance provides a proper platform to support the necessary collaborative work in the ecological engineering problem of horizontal subsurface flow CWs operation and maintenance.     

Assessing the influence of vegetation on reduction of pesticide concentration in experimental surface flow constructed wetlands: Application of the toxic units approach

In summer 2008, an experiment on retention of a mixture of five pesticides in the Lier experimental wetland site (Norway) was performed. Two vegetated cells with hydraulic retention times (HRT) of 280 min and 330 min and one cell without vegetation (HRT of 132 min) of 120 m² surface area each were investigated regarding their ability to reduce peak concentrations, pesticide masses and predicted adverse effects. Discrete water, plant and sediment samples were taken and analysed. The inlet peak concentrations of the pesticides dimethoate, dicamba, trifloxystrobin and tebuconazole ranged from 18 ng/L up to 5904 ng/L. The mean reduction of peak concentration was 72% in the non-vegetated cell and up to 91% in the vegetated cells. Less than 5% of the masses were retained within the wetlands. Uptake and sorption by plants was low (up to 4%), however, higher for the vegetated cell dominated by Phalaris arundinacea L. than for the one with Typha latifolia L. as dominant plant. The toxic units (TU) approach was used to describe the potential reduction of toxicity within the wetland cells. Calculated toxicity of the substances decreased by 79% in the non-vegetated cell and by 95% in the two vegetated cells. Despite the low mass retention, the vegetated wetland system reduced the toxic effects, expressed as toxic units from values of 0.24 to 0.01, i.e. a concentration two orders of magnitude below the acute toxicity threshold, within a distance of 40 m while the non vegetated would need to be about 64 m long for the same efficiency.     

The effects of forest on stream water quality in two coastal plain watersheds of the Chesapeake Bay

Forest had varying effects on stream nutrients in two coastal plain basins of the Delmarva Peninsula, USA. In the Choptank basin, forest was strongly associated with low stream total nitrogen (TN) and nitrate (NO₃⁻) concentrations (r²0.70), and forest placement along first order streams was important in maintaining low stream nitrogen (N) concentrations (r²0.35). In addition, a multiple regression model explained 40% of the stream total phosphorus (TP) variance and indicated that forest directly adjacent to streams (0–100 m) acted as a TP source and forest further away (100–300 m) from streams acted as a TP sink. In contrast, stream nutrients in the nearby Chester basin demonstrated a strong relationship with soil hydrologic properties. Forest had no significant effect on stream N and P because the finer-textured soils, higher stream slopes, and higher runoff potential of the Chester basin appeared to result in less baseflow compared to that in the Choptank basin. This reduced the opportunity for forest to intercept N via plant uptake and denitrification in the high runoff potential soils of the Chester basin. The high percentage of stormflow (40%) coupled with high stream slopes resulted in high soil erosion potential, which may explain the higher TP stream concentrations measured in the Chester compared to that in the Choptank. Differences in the hydrologic pathway appear to explain the different effects of forest on water quality in these two basins.     

Plant-derived phenolic compounds impair the remediation of acid mine drainage using treatment wetlands

The use of wetlands to remediate acid mine drainage has expanded rapidly since the realisation that acid coal mine drainage running into natural sphagnum wetlands undergoes an increase in pH and a precipitation of metals. However, our study suggests that the inclusion of plants in the acid mine drainage treatment system may be questionable, due to inefficiencies caused by exudation of dissolved organic carbon (DOC), and in particular its phenolic constituents. They complex with iron, causing increased solubility, the exact opposite of what is required to facilitate amelioration. The addition of minewater to planted wetland mesocosms initially caused a decline in Fe concentrations, typically from over 1100 to a low of 75 mg L⁻¹. However, it increased higher than 300 mg L⁻¹ after 15 days. The rise in iron occurred concurrently with DOC and phenolic increases; 15-69 and 5-15 mg L⁻¹, respectively, for Eriophorum angustifolium. Removal of DOC by precipitation with calcium lowered the DOC abundance, but without a simultaneous decrease in iron concentration. The concentration of one fraction of the DOC, phenolic compounds, did not decline, and we propose that the Fe was complexed with that phenolic DOC pool. The proposal was confirmed by enzymic depletion of the phenolic compounds using phenol oxidase. Our findings suggest that phenolic complexation represents a potent constraint on wetland-based bioremediation of iron in acid mine drainage.     

ECOBAS — A tool to develop ecosystem models exemplified by the shallow lake model EMMO

The modelling and simulation tool ECOBAS was extended in order to include special features supporting the development of ecological models. The «Graphical Model Editor» allows the connection of at least 2 modules in order to build a whole model to run simulations. With the ECOBAS simulation system the model can be tested extensively in order to find appropriate parameter sets («Parameter analysis» and «Parameter estimation») and to identify critical parameters («Sensitivity analysis»). The «Interaction Analysis» shows the internal dependencies of a model. ECOBAS integrates the steps of ecological modelling and creates well readable and complete documentations within one working step, supports modularization of models and the user is rid of the technical and numerical aspects of modelling. Hence ECOBAS is setting up complete, consistent and syntactical correct models.All new features of the ECOBAS-system will be introduced by applying it on the existing ecosystem model EMMO.     

Test of the first-order removal model for metal retention in a young constructed wetland

The first-order removal model is widely used in constructed wetland design. The suitability of this model was tested to predict metal retention in a young constructed wetland receiving agricultural and urban runoff. During two years, water samples for total and dissolved metal analyses were collected every third day at both the inlet and the outlet. The wetland retained metals best during summer and fall whereas during winter the retention of metals was significantly lower. The first-order removal model predicted Fe and Mn retention in the spring and dissolved Zn retention from spring to fall in both years. During those periods, hydraulic retention times (HRTs) greater than 7 days provided maximum retention for Fe, Mn, and dissolved Zn. However, first-order removal models failed to fit summer, fall and winter data for almost every metal under investigation (Fe, Mn, dissolved Cu, dissolved As) suggesting that HRTs (<1–25 days) did not affect metal retention during these seasons. The metal loading to the wetland was low and the input of metals through internal loading may be more significant consequently decreasing the metal retention. Therefore, the first-order removal model is inadequate to predict metal retention on a seasonal basis. Models used to design constructed wetlands under cold climates must consider seasonal changes that affect biological as well as hydrological variables.     

Mathematical model for the ecosystem response of Lake Ladoga to phosphorus loading

The ecosystem response model described in this paper combines an ecosystem model and a three-dimensional circulation model of Lake Ladoga developed earlier by the authors. The ecosystem model describes the process of Lake Ladoga eutrophication, and its biological submodel describes changes in the phyto- and zooplankton. In the earlier model version, lake circulation was determined using a two-dimensional hydrodynamical model which was not completely adequate. The present model allows calculation of the distributions of phyto- and zooplankton and mineral phosphorus and nitrogen. One of its main advantages is that reliable computations of the ecosystem dynamics over an extended period of time are possible. The response of the ecosystem to different levels of phosphorus pollution loading and to weather conditions is studied.     

Hydroperiods of created and natural vernal pools in central Ohio: A comparison of depth and duration of inundation

Water levels were recorded weekly from six natural vernal pools and 10 created vernal pools at two forested wetland complexes in central Ohio. Vernal pool median water depth and duration of inundation were significantly greater at the created vernal pools than at the natural vernal pools (α = 0.05, P < 0.05). The average period of inundation for created pools was 309 ± 32 days, compared with 250 ± 16 days for natural pools. The created pools produced a range of inundation times, from 163 to 365 days in length, with three pools permanently inundated.     

A management-oriented valuation method to determine ecological water requirement for wetlands in the Yellow River Delta of China

A wide range of human impacts have resulted in changes to wetland water regimes throughout the natural reserve of the Yellow River Delta. Specific local impacts which affect wetland water regimes include hydrological alterations associated with urban and agricultural development. Increasingly, management decisions must be made regarding the amount and timing of water required to maintain the ecosystem's diversity and its ecological characteristics. In this paper, based on the practice in the natural reserve and the important request of Ramsar for the “wise use” of wetlands in which ecological characteristics need to be reserved, a set of management objectives for the wetland natural reserve is proposed. The objectives include protecting the ecosystem and the waterfowl resources in the new wetland, renewing biodiversity and maintaining the function of the ecosystem. By means of a correlation analysis between the wetland biota and water regime, the ecological water requirement for the wetlands is proposed and classified into three classes, i.e., minimum, moderate and perfect water requirement, corresponding to the basic, moderate and perfect management objective, respectively. The results show that the minimum, moderate and perfect water requirements, respectively, are 37.94×10⁸, 49.47×10⁸ and 64.57×10⁸ m³ per year if the water required for sediment flushing is not considered in the wetland natural reserve. If the water required for sediment flushing is included, the amount will be 187.94×10⁸, 199.47×10⁸ and 214.57×10⁸ m³ per year, respectively, which cover 47%, 50% and 54% of the available ecological water quantities observed in the lower Yellow River during the 1950s.     

River phytoplankton prediction model by Artificial Neural Network: Model performance and selection of input variables to predict time-series phytoplankton proliferations in a regulated river system

In this study, a comparison between statistical regression model and Artificial Neural Network (ANN) is given on the effectiveness of ecological model of phytoplankton dynamics in a regulated river. From the results of the study, the effectiveness of ANN over statistical method was proposed. Also feasible direction of increasing ANN models' performance was provided. A hypertrophic river data was used to develop prediction models (chlorophyll a (chl. a) 41.7 ± 56.8 μg L^− 1; n = 406). Higher time-series predictability was found from the ANN model. Failure of statistical methods would be due to the complex nature of ecological data in the regulated river ecosystems. Reduction of ANN model size by decreasing the number of input variables according to the sensitivity analysis did not have effectiveness with respect to the predictability on testing data set (RMSE of the ANN with all 27 variables, 25.7; 47.9 from using 2 highly sensitive variables; 42.9 from using 5 sensitive variables; 33.1 from using 15 variables). Even though the ANN model presented high performance in prediction accuracy, more efficient methods of selecting feasible input information are strongly requested for the prediction of freshwater ecological dynamics.     

A conceptual model for the assessment of depressional wetlands in the prairie pothole region

The U.S. Environmental Protection Agency's (EPA's), Environmental Monitoring and Assessment Program (EMAP) is developing a landscape-level conceptual model to evaluate the condition of depressional (basin-type) wetlands in the prairie pothole region (PPR) of the United States. This effort is underway to determine the current condition of the Nation's wetlands and to track how it is improving or degrading over time, as well as to identify management priorities over major geographic areas. The depressional wetlands in the PPR were selected by EMAP both because of the importance of this region for waterfowl and because of the efforts currently being conducted by federal agencies and academic institutions in this region. The PPR provides nesting habitat for more than 15 species of ducks, and supports as much as half of the total production of dabbling and diving ducks in North America. Wetlands in this area became a vulnerable resource after extensive draineage in the 1800s. We propose a conceptual model that represents a framework for guiding the development of ecological indicators, research activities, and data collection for the evaluation of wetland conditions. In princple, this conceptual model is applicable to wetlands in any part of the world.     

Prevention of Vessel-Source Marine Pollution: A Note on the Challenges and Prospects for Chinese Practice Under International Law

This article examines China's domestic legal regime for the prevention of vessel source pollution. It pays special attention to the recently adopted Regulation on Prevention and Control of Marine Pollution from Vessels. Potential challenges and emerging issues that China has to confront are addressed, including: application of the legislation to disputed sea areas between China and its neighbors, freedom of navigation in the exclusive economic zone, reduction of emission from ships, and prevention of invasive species from ballast water.     

Model-free model elimination: A new step in the model-free dynamic analysis of NMR relaxation data

Model-free analysis is a technique commonly used within the field of NMR spectroscopy to extract atomic resolution, interpretable dynamic information on multiple timescales from the R ₁, R ₂, and steady state NOE. Model-free approaches employ two disparate areas of data analysis, the discipline of mathematical optimisation, specifically the minimisation of a χ² function, and the statistical field of model selection. By searching through a large number of model-free minimisations, which were setup using synthetic relaxation data whereby the true underlying dynamics is known, certain model-free models have been identified to, at times, fail. This has been characterised as either the internal correlation times, τ _e , τ _f , or τ _s , or the global correlation time parameter, local τ _m , heading towards infinity, the result being that the final parameter values are far from the true values. In a number of cases the minimised χ² value of the failed model is significantly lower than that of all other models and, hence, will be the model which is chosen by model selection techniques. If these models are not removed prior to model selection the final model-free results could be far from the truth. By implementing a series of empirical rules involving inequalities these models can be specifically isolated and removed. Model-free analysis should therefore consist of three distinct steps: model-free minimisation, model-free model elimination, and finally model-free model selection. Failure has also been identified to affect the individual Monte Carlo simulations used within error analysis. Each simulation involves an independent randomised relaxation data set and model-free minimisation, thus simulations suffer from exactly the same types of failure as model-free models. Therefore, to prevent these outliers from causing a significant overestimation of the errors the failed Monte Carlo simulations need to be culled prior to calculating the parameter standard deviations.     

A three-layer continuous model of porous media to describe the first phase of skin irritation

Mechanical skin irritation induces vasodilation on the line of scratch and in the neighboring zone. In order to model the effect of an irritation on the microcirculation, the vascular network has been described using a three-layer model. The first and last layer, considered as horizontal two-dimensional porous media, describe irrigation and drainage of the system, respectively. The intermediate layer, described by means of a lumped parameter method, does not permit horizontal fluxes. Hierarchical fluxes are directed from the first to the second layer and then towards the drainage layer in order to take into account physiological flow direction. Irritation is modeled by changing compliance of vessels situated at the entrance of the micro-circulation. The model permits to investigate the influence of change in compliance on flow and pressure behavior at microscopic and macroscopic level.     

A model for the upstream motion of elvers in the Adour River

The aim of this paper is contributing to the study of the exploitation of the European eel (Anguilla anguilla) in the basin of the French river 'Adour'. This exploitation constitutes the basis of the economy of local professional fishermen, who have recently noticed a diminution of the hunting of elvers. In order to design a sustainable exploitation strategy, we must know as much as possible about eel life cycle. For that purpose, we build a model to describe a phase of eels evolution, their migration upstream the river. Our model is based on the biological details of eels behaviour and constitutes a virtual laboratory, useful to test different hypotheses about eels migration.