Search

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 x 103 kg N y(-1) and 0.65 x 10(3) 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. (c) 2020 Elsevier B.V. All rights reserved.

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.

Watermilfoil (Myriophyllum) is one of the world's most troublesome invasive aquatic weeds. Although current management practices may inhibit its expansion, it also impacts not only the quality of water but habitat deterioration. Therefore, the need for developing highly efficient and low-cost biotechnologies with resource recovery into the agriculture field as a complementary management strategy cannot be overstated. Here, we reviewe the scientific/grey literature to offer readers a precise and panoramic view of the invasive watermilfoil ecology, regional problems, impacts, ecosystem services, and management. In this regard, an in-depth review aimed to assess the potential for reducing non-point source inorganic and organic pollutants using invasive watermilfoil, with the sustainable approaches, while offering other services and mitigating ecological trade-offs is presented. Global distributions, growth, and current progress on the management and utilization of invasive watermilfoil biomass are summarized to develop the aim, which is to convey challenges during the implementation of large-scale weed use. In short, pollutant assimilation in plant and bacterial communities linked to this weed considerably contribute to the reduction and degradation of pollutants from both natural and artificial systems. Although several considerations in recycling and reusing biomass need to be considered, the potential reuse of the harvested material for livestock feed, compost and direct use in farming systems offer an additional strategy to achieve sustainable ecosystem restoration. Further research and development may focus on a more detailed economic modeling approach that integrates the costs (worker's wage, harvesting, transportation, and energy consumption), legal and regulatory barriers, health risks and ecosystem service benefits (biodiversity improvement, and pollutant removal) to holistically evaluate the economic, environmental, and societal value of reusing and recycling this waste material.

Seasonal rainfall events reinforce the link between terrestrial and fluvial domains and are crucial for assessing hydrological control over riverine nutrient dynamics and pollutant source behaviors, especially in a semi-arid watershed. Taking the Qingshuihe river basin, a semi-arid mountainous basin in China, as an example, this paper investigated storm effects on riverine nitrogen (N) and phosphorus (P) dynamics (i.e. concentration, load, and composition changes) through continuous sampling of four storm events of the 2019 rainy season, including one small storm, two moderate storms, and a large storm. Pollutant sources and transport pathways were then examined over the storm sequence via hysteresis analysis. The results revealed a strong linkage between N/P dynamics and hydrological processes. Storm runoff caused a 6-fold increase in particulate-P (PP) and a 4-fold increase in ammonia-N (NH4-N) fluxes through four storms (most sensitive nutrients to storms). On average, PP shared 86% of P exports, and nitrate-N (NO3-N) contributed 79% of N exports. PP and NH4-N were delivered primarily from overland sources and transported by surface runoff. Nonetheless, mobilization of channel sediment reserves was also an important way of PP supply during storms. The results suggested groundwater as the principal NO3-N source in the watershed, and subsurface flow was important for NO3-N and total dissolved-P (TDP) delivery during storms. The large storm (>20 mm) often registered the highest N/P load exports. However, there were other influencing factors/processes on stormflow N/P dynamics in the semi-arid watershed, which complicate/override the effects of different storm magnitudes. Total suspended solids (TSS)/PP source availability and inter- and intra-storm export trends influenced P behaviors through storms. Moreover, impacts of mobilization processes on NO3-N behavior appeared over the storm sequence. These findings enhance our understanding of storm events induced N/P exports in water-scarce regions and provide references for water quality predictions and control in flood seasons.

Agricultural runoff impacts rivers and lakes on a global scale, while in developing countries (e.g., China), rural domestic wastewater is often an additional source of pollution. Scholars and policy makers are now promoting the use of agricultural vegetated ditches (VDs) as a potential supplemental management practices for nutrients and pesticide reduction from agricultural sources; however, information on the efficacy of these systems for the treatment of rural wastewater loaded with nutrients and heavy metal(loid)s (HMLs) removal and standing stock (SS) in aquatic plants growing there is rare or unknown. These shortcomings in our understanding of these systems must be addressed if they are going to serve further as an effective tool for purifying rural domestic sewage laden with concentrations of HMLs. To address this knowledge gap, the present study deals with SS of ten HMLs in ten plant species growing in a VD receiving raw rural domestic wastewater, with the intention to revealing an appropriate period for ditch plant harvesting to maximize HM removal. Mean reduction efficiencies amount to TN (60.6%), NH4-N (63.3%), NO3-N (48.1%), TP (58.5%) and PO4-P (51.9%), with favorable treatment performance during the summer season. Concentrations of nutrients typically declined gradually with distance along the length of the VD. Furthermore, the annual average reduction amounted to Ni (50.6%), Cu (56.1%), Cr (63.3%), Zn (79.3%), Cd (67.5%), Pb (80.1%), As (60.3%), Fe (52.6%), Al (19.8%), and Mn (24.3%). Plant uptake and sediment retention were the major contributors for nutrient mitigation within the vegetated ditches, with subsequent bacterial interaction and transformation of pollutants. Accumulation of HMLs varied among species and plant parts. Overall, SSs of most HMLs in plant species were greater in either stems or roots than leaves, with maximum values recorded in SSs of Al, Fe, and Mn. Based on the seasonal fluctuation of the accumulated HMLs in different plant species, the approach of harvesting plant biomass in order to effectively target HMLs in August or early September is recommended. Overall, reported results suggest that VD is an effective ecosystem to mitigate HMLs and nutrients from raw rural domestic wastewater in a similar way as constructed wetlands, noting the potential incorporation into local best management practices.

Discharge of phosphorus (e.g., PO4-P) and nitrogen (NO3-N) from the wastewater treatment facility (WWTF) effluent even at low occurrence (e.g., μg PO4-P L−1) could lead to eutrophication of receiving environments. Zhangjiakou city will host the international winter multi-sport event in 2022, which would probably yield a large amount of domestic WW and their associated contaminants in the water systems. To reveal the feasibility of an integrated surface flow constructed wetland (ISFCW) system for the purification of WWTF effluent, a field-scale ISFCW system was applied and operated in Zhangjiakou city. The ISFCW system consisted of a vegetated sedimentation pond (VSP) section followed by a biogeochemical barrier (BGB), and an SFCW. The purification performance of each purification component was monitored weekly over twelve months in terms of nutrient (N and P) removal. With the application of the ISFCW system, a total of 48.7, 59.4, 50.0, 54.9, and 60.2 % removal of TN, NH4-N, NO3-N, TP, and PO4-P was achieved in the summer period. Further analysis demonstrated that the contributions of VSP, BGB and FTW to all analyzed nutrient removal were 3–78 %. The key removal processes appeared to be biological and physicochemical pathways, and the integration of the VSP, BGB and SFCW enhanced the purification capacity of the system. Overall, the ISFCW system was effective at reducing nutrients from WWTF effluent and could consequently be used locally and in other similar mountain-river systems. Additional optimization of operating conditions could result in an enhanced reduction of nutrients.

Hybrid accidental urban wetlands (HAUWs) are expected to be a potential low-cost and highly efficient alternative means of minimizing pollutant loads from municipal areas as compared to the single-stage system being used. These unexpected HAUWs are created not through deliberate restoration, but as a result of water infrastructure decisions by local government. However, information on the long-term purification efficiency of large-scale HAUW improving eutrophic urban rivers is largely unexplored. An in-situ HAUW system consisting of a rubber dam, detention pond, accidental urban wetland, and overflow weir was evaluated at the field-scale for the purification of a eutrophic urban river in Zhangjiakou City, Hebei Province. The results for seven months of operation demonstrated that the effluent TP and NH4-N in the HAUW system could comply with the Grade III of Chinese National Surface Water Quality Standards. Average removal efficiencies for TN, NH4-N, NO3-N, TP, and PO4-P in the summer–autumn period of 52.6, 65,8, 56.6, 51.4, 58.2 and 88.3%, respectively, were recorded. These removal efficiencies were 59.4, 61.5, 65.6, 57.1, 59.4 and 65.7% higher than the respective values in the spring period. Furthermore, removal rates of nutrients were highly sensitive to temperature and showed seasonal trends. Further analysis showed that, with the application of the HAUW system, a total of 92.1, 69.5, 57.3, 37.8, 33.2, 12.4, 14.5, 7.3, 3.4% removal of Al, Mn, Cd, Pb, Zn, Ni, Fe, Ni, and As was achieved. Mean removal rates of TN, NH4-N, NO3-N, TP, TDP, PO4-P in the summer–autumn period were 2- 5 times higher than in those recorded in the early spring period. These results suggest that a variety of contaminant elimination mechanisms were offered by the HAUW, including enhanced hydraulic resistance, sedimentation, plant assimilation, microbial biofilm growth on roots’ surface and the HAUW design. Overall, this study demonstrated that the monitored HAUW could be another feature of the urban landscape that could help minimize pollutant loading to surface urban water bodies. This function is especially true in warm periods, in a similar way as natural wetlands or purposely built constructed wetlands. Nonetheless, managing these accidental treatment systems to maximize pollutant dissipation in the long-term would necessitate appropriate management strategies.

Due to lack of ditch maintenance, many ditches in the upper reaches of the Yangtze River are strongly affected by nutrient over-enrichment. Accordingly, we conducted surveys of nutrient concentrations in ditchwater and sediment in the hilly area of the central Sichuan Basin to investigate the spatiotemporal variations of nutrient concentrations and to promote the restoration of ditches for ecological functions. The results showed that the mean total nitrogen, particulate nitrogen, nitrate nitrogen, ammonia nitrogen, and total phosphorus values in ditchwater were 4.80, 1.09, 0.94, 1.09, and 0.18 mg/L, respectively. The mean concentrations of total nitrogen, nitrate nitrogen, ammonia nitrogen, and total phosphorus in ditch sediment were 1.58 g/kg, 2.62 mg/kg, 1.54 mg/kg, and 6.95 g/kg, respectively. Higher total nitrogen concentrations in ditchwater occurred in western areas, while higher total phosphorus concentrations occurred in central areas. Seasonally, we measured higher nitrogen and phosphorus concentrations in ditchwater close to agricultural areas during the rainy season, while the opposite effect was true for residential areas. Although nutrient concentrations in ditchwater could be affected by both surrounding land uses and ditch water levels, land use was critical. Moreover, nitrogen and phosphorus concentrations were significantly higher in the ditchwater near residential areas when compared to paddy or sloping cropland ditches. However, we found no significant differences between the nutrient contents of sediments in ditches surrounded by different land uses. Our results indicate that water pollution control initiatives in residential areas would be the most critical factor in combating ditchwater and sediment pollution in this region. Therefore, efforts to restore the ecological functions of drainage ditches should take into account rural township sewage management, fertilizer reduction, and especially ditch vegetation restoration.

A trapezoidal constructed ditch (TCD) of 300 m length and 2.2 m width was designed and built in the downstream section of the upper Yangtze River for in situ treatment of primary domestic sewage. The removal efficiencies of TN, NH4-N, NO3-N, TP and PO4-P from the TCD were approximately 61, 63, 48, 58 and 51%, respectively. The concentrations of TN, NH4-N, NO3-N, TP and PO4-P showed a decreasing trend with increasing distance downstream. Plant assimilation and sediment retention were the key mechanisms for N and P removal within the TCD, with subsequent microbial uptake and transformation of the nutrients. The TCD outlet showed significantly higher dissolved oxygen (DO) concentrations and lower values of electrical conductivity and total dissolved solids compared to the influent. Results of this study highlight the potential of TCD to mitigate nutrients from primary domestic sewage transported downstream and could be incorporated into local best management practices.

Pollution of freshwaters poses a major threat to water quality and human health and thus, nutrients have been targeted for mitigation. One such control measure is floating treatment wetlands (FTWs), which are designed to employ vigorous macrophytes above the water surface and extensive plant root system below the water surface to increase plant uptake of nutrients. The efficacy of FTWs in purifying different water systems has been widely studied and reviewed, but most studies have been performed in warm periods when FTW macrophytes are actively growing. In low-temperature conditions, the metabolic processes of macrophytes and microbial activity are usually weakened or reduced by the winter months and are not actively assimilating pollutants. These circumstances hamper the purification ability of FTWs to perform as designed. Furthermore, decayed macrophytes could release pollutants into the water column. Hence, this paper aimed to systematically summarize strategies for use of enhanced FTWs in eutrophic water improvement at low temperature and identify future directions to be addressed in intensifying FTW performance in low-temperature conditions. Low-temperature FTW show variable nutrient removal efficiencies ranging from 22% to 98%. Current amendments to enhance FTW purification performance, ranging from direct strategies for internal components to indirect enhancement of external operation environments encourage the FTW efficacy to some extent. However, the sustainability and sufficiency of water purification efficiency remain a great challenge. Keeping in mind the need for optimizing the FTW components and dealing with high organic and inorganic chemicals, future research should be carried out at the large field-scale and focus on macrophyte- benthos- microorganism synergistic enhancement, breeding of cold-tolerant macrophytes, and combination of FTWs with many strategies, as well as rational design and operational approaches under cold conditions.

Ditches are subjected to a large input of nutrients, trace metals, and arsenic and the enhancement of sedimentation due to human activities. However, the influence of different types of land uses on the distribution and associated environmental risk of metals and arsenic in the Red purple Sichuan Basin remains largely unclear, which is needed for water management. This study was carried out to characterize metal/metalloid status in ditch sediments from different land uses. A total of 68 surface sediment samples (0–5 cm) were collected from open ditches distributed in different land use types, i.e., cultivated ditches (CD), barren land ditches (BLD), roadside ditches (RSD), and residential ditches (RD), within the Sichuan Basin. Mean concentrations of Cr, Ni, Cu, Zn, Cd, Pb, and Mn in both RD and RSD were above the soil background values of Sichuan Basin, but Cd in ditch sediments of the basin posed considerable ecological risk to the environment. Overall, metals/metalloid (except Pb) decreased in the following order of RD > RSD > BLD > CD. Of the different land use types in the hilly region, residential and roadside land uses were likely to adverse effects on aquatic life. Multivariate statistical analysis showed that Mn, As, Cu, Ni, Zn, Fe, and Al were mainly influenced by natural weathering (erosion), while Pb might come from heavy vehicular traffic. The degree of contamination (Md), enrichment factor (EF), and the geo-accumulation index (Igeo) showed that Cd causes strong sediment pollution in the basin. Sediment quality guidelines SQG-Q values displayed that metals and arsenic created medium-low potential of adverse biological effects. These results provide baseline information on the metals and arsenic pollution in the Sichuan Basin. Awareness of land use type contributions to metals and arsenic requires that these man-made ditches be considered for their mitigation of pollutants in this region.

Three different types of ditches, each 300 m in length, were employed in this study. One vegetated constructed ditch (VCD), three natural vegetated soil ditches (NVSD), and three constructed ditches left unvegetated (UCD) as controls were investigated using simple in/out mass balances and uptake by plant species with a potential for phytoremediation and their mechanisms. Significant differences in the ditches were observed, suggesting the importance of plant species in nutrient mitigation. The removal rates of TN (total nitrogen) and TP (total phosphorus) were 64.28 and 58.02, 31.16 and 27.49, and 3.91 and 2.97%, respectively, in the VCD, NVSD, and UCD. Canna indica (45.12 g m−2) and Oenanthe javanica (21.48 g m−2) had the highest total N and P storage in the VCD and NVSD. Furthermore, species C. indica possessed the highest annual N and P uptake in the VCD (216.59 kg N/ha/yr and 30.73 kg P/ha/yr). In the NVSD, species O. javanica had the greatest annual N and P uptake (96.66 kg N/ha/yr and 7.94 kg P/ha/yr). Both VCD and NVSD were found to have a reasonably good outcome compared to UCD. Retention of nutrients by ditch sediments was probably the major attenuation mechanism, with subsequent plant uptake and microbial nitrification–denitrification of the nutrients as secondary removal mechanisms. Results of this study highlight the importance of taking actions for establishment of appropriate plant species inside the ditches in order to enhance its direct and indirect roles and maximize purification rate in aquatic environments.

Eco-ditches are being explored to maximize their capability of capturing pollutants and mitigate any harmful side effects in rivers. In this study, mesocosm plastic drum sediment and field experiments were set up to screen 18 plant species found in ditches and identify those with potential for high biomass production and nutrients removal. Terrestrial plants grown in the mesocosm system were shown to be able to acclimate to aquatic conditions and to survive in primary domestic sewage. About 73-95% increase in plant biomass was recorded. Removal efficiencies for total nitrogen, total phosphorus, and ammonium-nitrogen from the sewage of 72-99%, 64-99%, and 75-100%, respectively, were recorded. Furthermore, complete removal of the applied nitrate-nitrogen load was achieved in mesocosm systems. Findings also show that all species, but especially Acorus calamus, Canna indica, Canna lily, Cyperus alternifolius, Colocasia gigantea, Eichhornia crassipes, Iris sibirica, and Typha latifolia had the highest efficiencies for nitrogen and phosphorous removal. The N and P mass balance analysis demonstrated that plant uptake and sediment N and P accumulation accounted for 41-86% and 18-49% of the total influent TN and TP loads, respectively. In addition, the amounts of nitrogen and phosphorous uptake by these plant species were influenced significantly by biomass. The field-culture experiment further identified Canna indica followed by Cyperus alternifolius as the most promising for high biomass production and nutrients uptake. Therefore, these plants may be recommended for extensive use in treating highly eutrophicated rivers. Outcomes of this work can be useful for model design specifications in eco-ditch mitigation of sewage pollution.

The contributions of drainage ditches to the accelerated eutrophication of rivers have rarely been assessed, especially for the Three Gorges Reservoir (TGR) drainage ditches. Forty drainage ditches in the TGR from multiple land use types were extensively investigated for ten parameters of water quality. The results showed that the concentrations of total nitrogen (TN) and total phosphorus (TP) in the TGR drainage ditches were generally far higher than the internationally recognized eutrophication threshold. Based on this study, both ditch water and sediments from residential land and roadside land had the highest concentrations of nutrients. Possible sources of these nutrients include sewage water and septic tank overflow. Forestland had significantly lower concentrations of nutrients. Residential ditches had higher values of electrical conductivity (EC) and total dissolved solid (TDS) values and lower dissolved oxygen (DO) concentrations. Forestland had lower values of EC and TDS values and higher DO concentrations. The results indicate that the nutrients that have accumulated in the sediments have significant impacts on the water quality in adjacent ditches. A long-term plan must be developed to more strictly control the external loading of nutrients from surrounding land. Action plans to promote the growth of wetland plants in drainage ditches are important for increasing agrochemical retention in the TGR drainage ditches. TGR drainage ditches from residential zones must be actively managed by cleaning and sediment removal to control the risk of nutrients being released into the reservoir.

We evaluate the long-term performance of a vegetated drainage ditch (VDD) treating domestic sewage with respect to heavy metal/metalloid (HM/M) accumulation in sediments, plants and water. VDD sediment contained significantly higher macro and trace elements compared to an agricultural ditch (AD) sediment. However, concentrations of HM/Ms in VDD sediment were below the ranges considered toxic to plants. Most HM/Ms were efficiently removed in the VDD, whereby removal efficiencies varied between 11% for Al and 89% for K. Accumulation of HM/Ms varied among species and plant parts, although sequestration by plants represents only a small proportion (1%) of the inflow load. Accumulation of Al, As, Cd, Pb, Cr, Fe and Ni in VDD plants were mostly distributed in the roots, indicating an exclusive strategy for metal tolerance. The opposite was found for Zn, Cu, K, Ca, P, K, Na, N and Mg, which were accumulated either in the stems or leaves. Overall, concentrations of metals in sediment showed significant positive correlations with those in ditch plants. None of the studied species were identified as metal hyper-accumulators (i.e.10,000mgkg

Ecological ditches have demonstrated the ability to filter and control nutrient transport to rivers. Few studies, however, have examined the internal loading of nitrogen (N) and phosphorus (P) in these systems due to vegetation decomposition. Most often, this concept is overlooked during evaluation of the nutrient removal rate of the ditches. Thus, the litter bag technique was used to analyze nutrient release to surface water during these processes. Mesocosm and field experiments were conducted to assess the growth characteristics and consequent nutrient accumulation by six ditch plant species. Of the six, Canna indica had the highest aboveground accumulation of N and P. About 85–95 % increase in the aboveground biomass was recorded at the end of the experimental period. The removal efficiencies of TN, TP, and NH4-N from the sewage reached up to 72–99.4, 64–98.7, and 75 %–100, respectively. Complete removal of all NO3-N was achieved. The amounts of N and P uptake by plant species were closely related to the biomass of plants. During the decaying process, N and P concentrations in the aboveground biomass decreased. These lost nutrients were eventually shifted to the system, which led to a deterioration of the water quality. Therefore, harvesting of aboveground biomass from inside the ditch is an appropriate intervention to prevent the release of N and P in the dormant season. The finding is important for planning an efficient eco-ditch system and predicting the influence of nutrient loading in the eco-ditches upon senescence of ditch plants.

In order to assess the impact of four land use changes on metal concentrations in the hilly Sichuan Basin of China, 71 surface water samples were collected in July and November 2014. Samples from residential ditch water were found to have higher metal concentrations than those in other types of ditches, while the lowest occurred in barren land ditch water. However, the selected metals were below the Chinese surface water quality standards and WHO (2011). The pollution index of four determined land use types was also below the critical pollution index, suggesting there were low levels of pollution in Sichuan Basin. Arsenic was the most important pollutant of concern. Results indicate steps should be taken to control and reduce the risk of metals released from residential ditch water.