Modelling sedimentation processes in a constructed stormwater wetland

Zeolite performance in removal of multicomponent heavy metal contamination from wastewater

Efficient removal of heavy metal pollutants from wastewater by ion-exchange sorbents requires knowledge and understanding of the interplay between the adsorption patterns of the different components. The present study elucidates the simultaneous adsorption characteristics of six toxic heavy metal cations (Cd²⁺, Cr³⁺, Cu²⁺, Ni²⁺, Pb²⁺, and Zn²⁺) by two synthetic (13X and 4 A) and one natural (clinoptilolite) zeolite from solutions containing equimolar mixtures of the six metals. Equilibrium adsorption isotherms and equilibration dynamics were obtained by ICP-OES and complemented by EDXRF. An order of magnitude lower adsorption efficiency was exhibited by clinoptilolite (maximum of 0.12 mmol ions/g zeolite), relative to that obtained by the synthetic zeolites 13X and 4 A (a maximum of 2.9 and 1.65 mmol ions/g zeolite respectively). The strongest affinities to both zeolites were demonstrated by Pb²⁺ and Cr³⁺ (1.5 and 0.85 mmol/g zeolite respectively for 13X, and 0.8 and 0.4 mmol/g zeolite respectively for 4 A adsorbed from the highest solution concentration). The weakest affinities were observed by Cd²⁺ (0.1 mmol/g for both zeolites), Ni²⁺ (0.2 and 0.1 mmol/g for 13X and 4 A respectively), and Zn²⁺ (0.1 mmol/g for both zeolites). Large differences were observed between the two synthetic zeolites in terms of their equilibration dynamics and adsorption isotherms. Pronounced maxima were displayed in the adsorption isotherms for zeolites 13X and 4 A. The decline in adsorption of the weaker adsorbing ions with the increase in total solution concentration was attributed to the thermodynamic equilibrium between the ions adsorbed on the zeolite surface and those in the solution. Regeneration by 3 M KCL eluting solution resulted in considerable reduction in adsorption capacities following each desorption cycle.

Statistically based soil-climate exposure scenarios for aquatic pesticide fate modeling and exposure assessment in the Pampa Region of Argentina

Although pesticides are used intensively in Argentina's Pampa region, the possibility of performing an environmental risk assessment (ERA) remains limited due to the absence of readily available databases to run pesticide fate models and the lack of standardized realistic worst-case scenarios. The aim of the present study was to further advance capacities for performing probabilistic ERAs in the Pampa region by dividing and parameterizing the region into functional soil-climate mapping units (SCU) and defining statistically based, worst-case soil-climate exposure scenarios. Results obtained demonstrate that the SCU selected for a specific modeling exercise should depend on the dissociation constant (K_d ) of the pesticide evaluated and whether short- or long-term pesticide fate modeling and risk assessment are needed. Four regionally representative SCUs were specifically identified for modeling the fate of pesticides with low, high, and intermediate values of K_d . Fate modeling of pesticides with an intermediate K_d requires the use of a different SCU for short- versus long-term pesticide modeling, whereas this distinction is not necessary for pesticides with both low and high K_d . The current definition of realistic, worst-case, soil-climate scenarios represents a crucial step toward better pesticide fate modeling and exposure assessment in Argentina's Pampa region. Integr Environ Assess Manag 2023;19:626-637. © 2022 SETAC.

Sequential Sedimentation-Biofiltration System for the purification of a small urban river (the Sokolowka, Lodz) supplied by stormwater

The study analyses the efficiency of a Sequentional Sedimentation-Biofiltration System (SSBS) built on the Sokolowka river in Lodz (Poland). It was constructed to purify a small urban river whose hydrological regime is dominated by stormwater and meltwater. The SSBS was constructed on a limited area as multi-zone constructed wetlands. The SSBS consists of three zones: sedimentation zone with structures added to improve sedimentation, a geochemical barrier made of limestone deposit and biofiltration zone. The purification processes of total suspended solids (TSS), total phosphorus (TP), total nitrogen (TP) and other nutrients: phosphates (PO₄^3-), ammonium (NH₄⁺) and nitrates (NO₃^-) of the SSBS were analyzed. Chloride (Cl^-) reduction was investigated. Monitoring conducted in the first two hydrological years after construction indicated that the SSBS removed 61.4% of TSS, 37.3% of TP, 30.4% of PO₄^3-, 46.1% of TN, 2.8% of NH4+, 44.8% of NO₃^- and 64.0% of Cl^-. The sedimentation zone played a key role in removing TSS and nutrients. The geochemical barrier and biofiltration zone each significantly improved overall efficiency by 4-10% for TSS, PO₄^3-, TN, NO₃^- and Cl^-. Although the system reduced the concentration of chloride, further studies are needed to determine the circulation of Cl^- in constructed wetlands (CWs), and to assess its impact on purification processes.

Evaluation of factors affecting soil carbon sequestration services of stormwater wet retention ponds in varying climate zones

The carbon sequestration services of stormwater wet retention ponds were investigated in four different climates: U.S., Northern Sweden, Southern Sweden, and Singapore, representing a range of annual mean temperatures, growing season lengths and rainfall depths: geographic factors that were not statistically compared, but have great effect on carbon (C) accumulation. A chronosequence was used to estimate C accumulations rates; C accumulation and decomposition rates were not directly measured. C accumulated significantly over time in vegetated shallow water areas (0-30cm) in the USA (78.4gCm^-2yr^-1), in vegetated temporary inundation zones in Sweden (75.8gCm^-2yr^-1), and in all ponds in Singapore (135gCm^-2yr^-1). Vegetative production appeared to exert a stronger influence on relative C accumulation rates than decomposition. Comparing among the four climatic zones, the effects of increasing rainfall and growing season lengths (vegetative production) outweighed the effects of higher temperature on decomposition rates. Littoral vegetation was a significant source to the soil C pool relative to C sources draining from watersheds. Establishment of vegetation in the shallow water zones of retention ponds is vital to providing a C source to the soil. Thus, the width of littoral shelves containing this vegetation along the perimeter may be increased if C sequestration is a design goal. This assessment establishes that stormwater wet retention ponds can sequester C across different climate zones with generally annual rainfall and lengths of growing season being important general factors for C accumulation.

Ecosystem service provision by stormwater wetlands and ponds - a means for evaluation?

Stormwater control measures (SCMs) such as constructed stormwater ponds and constructed stormwater wetlands (CSWs) are designed to regulate runoff hydrology and quality. However, these created ecosystems also provide a range of other benefits, or ecosystem services, which are often acknowledged but rarely quantified. In this study, additional ecosystem services, including carbon sequestration, biodiversity, and cultural services, were assessed and compared between 20 ponds and 20 CSWs in North Carolina, USA. Carbon sequestration was estimated through the carbon content of pond and wetland sediments across a gradient of system age. Biodiversity was quantified in terms of the richness and Shannon diversity index of vegetative and aquatic macroinvertebrate communities. Cultural services were qualitatively assessed based on the potential for recreational and educational opportunities at each site. Ponds and wetlands were found to support similar levels of macroinvertebrate diversity, though differences community composition arose between the two habitat types. CSWs demonstrated greater potential to provide carbon sequestration, vegetative diversity, and cultural ecosystem services. This assessment provides an initial framework upon which future assessments of ecosystem service provision by SCMs can build.

Risk management of sediment stress: a framework for sediment risk management research

Research related to the ecological risk management of sediment stress in watersheds is placed under a common conceptual framework in order to help promote the timely advance of decision support methods for aquatic resource managers and watershed-level planning. The proposed risk management research program relies heavily on model development and verification, and should be applied under an adaptive management approach. The framework is centered on using best management practices (BMPs), including eco-restoration. It is designed to encourage the development of numerical representations of the performance of these management options, the integration of this information into sediment transport simulation models that account for uncertainty in both input and output, and would use strategic environmental monitoring to guide sediment-related risk management decisions for mixed land use watersheds. The goal of this project was to provide a sound scientific framework based on recent state of the practice in sediment-related risk assessment and management for research and regulatory activities. As a result, shortcomings in the extant data and measurement and modeling tools were identified that can help determine future research direction. The compilation of information is beneficial to the coordination of related work being conducted within and across entities responsible for managing watershed-scale risks to aquatic ecosystems.