Assessing the influence of different plant species in drainage ditches on mitigation of non-point source pollutants (N, P, and sediments) in the Purple Sichuan Basin

Nitrogen removal performance and mechanism in constructed wetlands under saline conditions: Role of Canna indica inoculated with Piriformospora indica

The phytopromotional root endophytic fungus Piriformospora indica was introduced into the wetland plant Canna indica L. to explore its impact on nitrogen (N) removal in constructed wetlands (CWs) to treat normal and saline (0.9 % NaCl) wastewater. P. indica colonization increased total nitrogen, NH4+-N, and NO3--N removal efficiencies under normal and saline conditions, with NO3--N removal rates significantly increasing by 17.5 % under saline conditions (P<0.05). N removal by plant uptake improved by 26.1 % and 27.7 % under normal and saline conditions due to P. indica-mediated growth-promoting effects. Salt-tolerant denitrifiers and nitrifiers guaranteed the dominant role of microbial degradation in N removal under saline conditions. P. indica inoculation considerably improved the contribution of Nocardioides and Nitrosomnas to dissimilatory/assimilatory nitrate reduction and nitrification genes, respectively. These findings elucidate the mechanisms and potential applications of P. indica-mediated phytoremediation in practical wastewater treatment under varying salty conditions.

Simulation of suspended sediment transport in a floating canopy channel based on random displacement model

In conventional research, the suspended sediment distribution in a channel under the action of floating canopy has been rarely studied. In this study, experiments on sediment transport in flume with fixed suspended vegetation were carried out under different velocity conditions. It was performed to examine the suspended sediment transport and distribution law as impacted by the floating canopy. The vertical distribution formula of velocity impacted by the floating canopy was derived based on improved two-layer theory. Combined with the random displacement model (RDM), a Lagrangian method was developed to simulate the suspended sediment transport under the action of the floating canopy. Compared with the experimental data, the R² of vertical velocity simulation was higher than 0.96, and the vertical distribution of suspended sediment concentration varied significantly (4.64 to 19.83 g/L) following the vertical coordinate. Subsequently, the numerical model of sandy flow with the floating canopy was established by complying with the stratified sediment turbulence diffusion coefficient to predict the suspended sediment transport. Besides, the established numerical model can lay a theory basis for sediment transport in such channels (floating canopy channels).

Phosphorus retention within a relic agricultural ditch in a constructed wetland

Stormwater treatment areas (STAs) are constructed wetlands established to capture phosphorus (P) from agricultural runoff before reaching the Florida Everglades. Retained P is primarily stored in wetland soils and sediments generated through a collection of interrelated physical, chemical, and biological processes. The amount of P and other elements (Al, Ca, Cu, Fe, Mg, Mn, Pb, and Zn) retained in the flocculent (floc) and recently accreted soil (RAS) horizons from a relic agricultural ditch within Cell 4S of STA-1E were compared with the surrounding marsh soils (upstream and downstream sites of the ditch). The amount of P retained in the ditch was significantly greater than the surrounding marsh soils and for all the elements in the floc horizon and five of the nine elements in the RAS horizon, suggesting that different processes or process rates influenced accumulation. Phosphorus species in the floc and RAS sediment horizons were identified and quantified using ³¹ P nuclear magnetic resonance (NMR) spectroscopy and total P determined by microwave plasma-optical emission spectroscopy. In general, P forms were dominated by orthophosphate, sugar phosphates, nucleotides, DNA, and pyrophosphate, with varying relative abundances of species. Total P concentration significantly decreased from upstream to downstream of the ditch by an average of 28 and 35% for floc and RAS soils, respectively. The relatively high P accrual rate within the ditch suggested that relic ditches perpendicular to flow could reduce P transport to downstream soils and sediments and, in turn, help maintain low P levels in overlying water.

Discussing on "source-sink" landscape theory and phytoremediation for non-point source pollution control in China

Water pollution is exacerbated due to irrational human activities in China. Restoring and rebuilding river basin ecosystems are major ecological strategies at present. Controlling the non-point source pollution (NPSP) by reasonable management of land use in the basin and phytoremediation of contaminated waters is the optimum approach. Thus, it is significant to study on the relationship that between landscape change and the aquatic environment, as well as further to analyze on the combined effect of the landscape and water quality. This paper describes the application and development of the "source-sink" landscape theory in China, and the role of the theory in controlling NPSP. From this perspective, a landscape capable of generating NPSP would be a "source" landscape, such as farmland, while another capable of preventing NPSP would be a "sink" landscape, such as forests and wetland. Applying the source-sink landscape theory, it is possible to exert the ecological benefits of the landscape while playing the esthetic value of the landscape. Also, the purification mechanism of plants in contaminated water is discussed. Besides, it is vital that research on water body restoration should focus not only on single discipline but also on integration and coordination between various ones such as ecology, environmental science, and geography to jointly push up researches related to water body phytoremediation. Hopefully, this paper could help to control water pollution from a new perspective, also to improve water environment and benefit human lives.

Nutrient dynamics and retention in a vegetated drainage ditch receiving nutrient-rich sewage at low temperatures

Vegetated agricultural drainage ditches (VDs) are a relatively new best management practice for pesticide and nutrient mitigation that is receiving increasing global interest. However, VDs are seldom used during winter due to considerable deterioration of pollutants reduction efficiencies driven by low-temperature effects. Limited knowledge on the internal loading of nutrient in VDs due to vegetation decomposition calls for further evaluation. Here, we assessed plants growth characteristics and nutrient dynamics in a field-scale VD receiving nutrient-rich sewage and planted with the overwintering plants: Acorus gramineus, Myriophyllum aquaticum and Iris sibirica. Water purification performance showed average TN, NH₄-N, NO₃-N, TP and PO₄-P reduction efficiencies of 44, 46, 43, 52 and 46%, respectively, over the winter period. Maximum reduction rates of TN and TP were 5.31 and 0.34 g^-2 d^-1, respectively. Of the total nutrient removal by plants of 5.37 × 10³ kg N y^-1 and 0.65 × 10³ kg P y^-1 from the VD system, A. gramineus contributed 65.7% and 72.1%, respectively. Nonetheless, substantial amounts of N and P retained within the aboveground biomass were released into the water column as ditch plant shoots decayed to deteriorate the water quality. All three species, A. gramineus, M. aquaticum and I. sibirica demonstrated considerable nutrient accumulation during winter and facilitated nutrient retention in the VD system. Consequently, they can be considered effective overwintering species of choice in VDs for purifying nutrient-rich water and potentially appropriate for vulgarizing elsewhere, particularly throughout the winter season.

Ecological aesthetic assessment of a rebuilt wetland restored from farmland and management implications for National Wetland Parks

While wetlands are usually used as a natural approach to remove biodegradable pollutants in surface water, their purification efficiencies coupled with their aesthetic features are of less concern. The water quality, plant landscape, acoustic environment and odour indicators were investigated in the surface water inlet and outlet of the Fujin National Wetland Park (FNWP), restored from farmlands in Northeast China. Major concentrations of pollutants in the inlet and the outlet subjected to surface flow wetland treatment were monitored, and the removal efficiencies were calculated based on 54 water samples (6 sites×3 seasons×3 replicates). The results showed that the total nitrogen (TN) and organic carbon in surface water decreased significantly after the wetland treatment, while the total phosphorus (TP) did not decrease significantly. The removal efficiencies for TN and BOD5 changed seasonally and reached 69.08% and 60.44%, respectively. An ecological aesthetic index (EAI) was developed based on the trophic state index coupled with plant landscape, acoustic and odour indicators, and the calculated EAI showed that the outlet delivered a more aesthetically harmonious appearance than the inlet in spring and autumn, but not in summer. Based on the current aquatic macrophyte species and documented purification efficiencies in FNWP, we recommend an improved ecological aesthetic management approach that utilizes and arranges diverse native plants from the surrounding wetlands (e.g. Scirpus validus) in addition to local Nelumbo nucifera, Nymphaea tetragona and Myriophyllum spicatum, and conserves the indicative and endangered species (Aldrovanda vesiculosa), from the visual appeal of the waterscape.

Lateral distribution of sediment and phosphorus in a two-stage ditch with partial emergent vegetation on the floodplain

Two-stage channels are effective drainage facilities because they can decrease soil erosion and nutrient loss effectively. The lateral distribution of streamwise velocity in two-stage channels has been substantially studied. However, knowledge about the lateral distribution of sediment and phosphorus in two-stage channels with emergent vegetation on the floodplain are limited. In this work, flume experiments were conducted to investigate the relationship between current and transport of sediment and phosphorus. Results show that lateral distributions of total suspended sediment (TSS), particulate phosphorus (PP), and dissolved phosphorus (DP) are affected by the lateral variation of streamwise velocity, i.e., larger TSS and DP were found in the main channel, while larger PP appeared in the floodplain. Besides, theoretical models for the lateral distribution of TSS and DP were presented. Three models were adopted to predict the depth-averaged streamwise velocity, and corresponding results have been used to predict the TSS and DP. Comparisons indicated that with a high-precision velocity model, the newly presented analytical models can give satisfied predictions of the lateral distributions of TSS and DP.

The biomass accumulation and nutrient storage of five plant species in an in-situ phytoremediation experiment in the Ningxia irrigation area

Phytoremediation has been widely used and is considered an environmentally friendly and efficient method for mitigating nitrogen (N) and phosphorus (P) loads. However, the technique is rarely employed in the Ningxia irrigation area, which suffers from serious N and P pollution. To investigate ways of protecting the aquatic environment in this region, we conducted in-situ experiments along an agricultural ditch in 2014 and 2015. During the pre-experiment in 2014, five single species floating-bed systems (Zizania latifolia, Oryza sativa, Ipomoea aquatica, Lactuca sativa and Typha latifolia) and one multi-species floating-bed system with three replicates were evaluated over about two months. I. aquatica performed best with respect to biomass accumulation and nutrient storage among all plant systems. Multi-species system was not superior to single species systems: 42% and 37% of the N and P storage in the multi-species system were achieved by I. aquatica. In the formal experiment during 2015, I. aquatica was tested again and performed excellently with respect to biomass production (1.06 kg/m²), N (27.58 g/m²) and P (2.34 g/m²) uptake. Thus, this study demonstrated that I. aquatica could be used to reduce N and P loads under saline and alkaline conditions in the Ningxia irrigation area.

Plant-microbial synergism: An effective approach for the remediation of shale-gas fracturing flowback and produced water

Effective and affordable treatment of hydraulic fracturing flowback and produced water (FPW) is a major challenge for the sustainability of unconventional shale-gas exploration and development. We investigated the effectiveness of different combinations of activated sludge (AS), three microbial preparations, and ten plants (ryegrass, water dropwort, typha, reed, iris, canna, water caltrop, rape, water spinach, and Alternanthera philoxeroides) on the treatment performance of FPW. Water quality parameters (NH₄-N, NO₃-N, NO₂-N, COD_cr, and BOD) and the algal toxicity of the treated FPW were used as metrics to assess the treatment efficiency. The results showed that AS had higher treatment efficiency than the prepared microorganisms, and water dropwort was the best plant candidate for boosting performance of AS treatment of FPW. The treated FPW showed improved water quality and microbial diversity. The Shannon-Wiener index increased from 4.76 to 7.98 with FPW treatment. The relative abundance of microbes with a greater resistance to high salt conditions, such as Bacteroidetes, Firmicutes, Chloroflexi, increased substantially in the treated FPW. The combination of water dropwort and AS showed the greatest improvement in water quality, the highest algal density and microbial diversity, thus indicating good potential for this candidate in the treatment of FPW.

Removal of non-point source pollutants from domestic sewage and agricultural runoff by vegetated drainage ditches (VDDs): Design, mechanism, management strategies, and future directions

Domestic wastewater and agricultural runoff are increasingly viewed as major threats to both aquatic and terrestrial ecosystems due to the introduction of non-point source inorganic (e.g., nitrogen, phosphorus and metals) and organic (e.g., pesticides and pharmaceutical residues) pollutants. With rapid economic growth and social change in rural regions, it is important to examine the treatment systems in rural and remote areas for high efficiency, low running costs, and minimal maintenance in order to minimize its influence on water bodies and biodiversity. Recently, the use of vegetated drainage ditches (VDDs) has been employed in treatment of domestic sewage and agricultural runoff, but information on the performance of VDDs for treating these pollutants with various new management practices is still not sufficiently summarized. This paper aims to outline and review current knowledge related to the use of VDDs in mitigating these pollutants from domestic sewage and agricultural runoff. Literature analysis has suggested that further research should be carried out to improve ditch characteristics and management strategies inside ditches in order to ensure their effectiveness. Firstly, the reported major ditch characteristics with the most effect on pollutant removal processes (e.g., plant species, weirs, biofilms, and substrates selection) were summarized. The second focus concerns the function of ditch characteristics in VDDs for pollutant removal and identification of possible removal mechanisms involved. Thirdly, we examined factors to consider for establishing appropriate management strategies within ditches and how these could influence the whole ditch design process. The current review promotes areas where future research is needed and highlights clear and sufficient evidence regarding performance and application of this overlooked ditch system to reduce pollutants.