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The simulation of drainage sources in irrigation areas at the watershed scale is of great significance for understanding the characteristics and drainage status of irrigation districts under various water-saving irrigation and climatic conditions. In this study, our focus was on the irrigation areas located on the south bank of the Yellow River in Hangjin Banner. We aimed to analyze and simulate the flow rate and overall drainage volume in the drainage ditch by developing a soil and water assessment tool (SWAT) model. The measured drainage data were utilized to calibrate and validate the model to explore the structure and sources of drainage in the selected study area. The results indicated that the average annual drainage volume of the study area was 4355.65 × 104 m³, and the primary source of drainage was subsurface drainage, which accounted for approximately 68% of the total drainage. Subsurface flow was the second-largest source, contributing approximately 31%, while surface drainage accounted for a negligible proportion, contributing merely 1% to the drainage. Concerning the proportion of drainage relative to the total drainage in each irrigation area, the Balahey irrigation area accounted for approximately 20%, the Jianshe irrigation area for approximately 45%, and the Dugui irrigation area for approximately 35%. Moreover, the model parameters were optimized using SWAT-CUP software to obtain the R 2, NSE , Re , and RMSE values of 0.65, 0.60, −8.54%, and 384.65 × 104 m3, respectively, for the model calibration period, and the corresponding values were 0.63, 0.56, −7.82%, and 389.65 × 104 m3, respectively, for the validation period. The traceability simulation results for irrigation drainage are of crucial importance for the efficient utilization of water resources in this study area. [ABSTRACT FROM AUTHOR]

The planting of fruit trees on sloping land can bring significant benefits to the local economy, but it also causes different degrees of soil and water erosion problems. In this study, we investigated the differences in nutrient migration in slope ditch runoff. In 39 scouring tests, a grass ditch reduced the loss of carbon (C), nitrogen (N), and phosphorus (P) by intercepting runoff. There was a positive correlation between runoff and the loss rate of N and P. The flow affected the retention time of runoff in the ditch, and then changed the dissolved organic carbon (DOC) loss rate in the runoff. The concentration of N and P did not affect the N and P loss rate, but did affect the total amount of N and P lost and the DOC loss rate in the runoff. The addition of organic fertilizer significantly increased the N loss rate in the runoff, and the change rule of the P and DOC loss rate was similar; thus, co-migration might have occurred. To sum up, the importance of the four factors on the migration and loss of C, N, and P in ditch runoff was as follows: organic fertilizer (100%) > fertilizer concentration (74.8%) > ditch type (12.6%) > initial flow (10%). [ABSTRACT FROM AUTHOR]

China's lowland rural rivers are facing severe eutrophication problems due to excessive phosphorus (P) from anthropogenic activities. However, quantifying P dynamics in a lowland rural river is challenging due to its complex interaction with surrounding areas. A P dynamic model (River-P) was specifically designed for lowland rural rivers to address this challenge. This model was coupled with the Environmental Fluid Dynamics Code (EFDC) and the Phosphorus Dynamic Model for lowland Polder systems (PDP) to characterize P dynamics under the impact of dredging in a lowland rural river. Based on a two-year (2020–2021) dataset from a representative lowland rural river in the Lake Taihu Basin, China, the coupled model was calibrated and achieved a model performance (R 2>0.59, RMSE<0.04 mg/L) for total P (TP) concentrations. Our research in the study river revealed that (1) the time scale for the effectiveness of sediment dredging for P control was ∼300 days, with an increase in P retention capacity by 74.8 kg/year and a decrease in TP concentrations of 23% after dredging. (2) Dredging significantly reduced P release from sediment by 98%, while increased P resuspension and settling capacities by 16% and 46%, respectively. (3) The sediment-water interface (SWI) plays a critical role in P transfer within the river, as resuspension accounts for 16% of TP imports, and settling accounts for 47% of TP exports. Given the large P retention capacity of lowland rural rivers, drainage ditches and ponds with macrophytes are promising approaches to enhance P retention capacity. Our study provides valuable insights for local environmental departments, allowing a comprehensive understanding of P dynamics in lowland rural rivers. This enable the evaluation of the efficacy of sediment dredging in P control and the implementation of corresponding P control measures. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel zippered cover with capillary barrier effects (CCBE) was proposed. • The hydraulic performance of the novel CCBE was compared with the traditional one. • Relevant influencing factors related to zippered CCBE were revealed. • The zippered CCBE extent the applicability from arid region to semi-humid region. The huge amount of leachate generated in landfills causes persistent pollution to soil and groundwater. Landfill cover is vital for reducing leachate generation through reducing rainwater infiltration. Yet, the traditional cover with capillary barrier effects (CCBE) is only applicable in reducing rainwater percolation at its base in arid or semi-arid region. To solve this problem, a novel capillary barrier cover is proposed, which adds multiple gravel-segments to the traditional CCBE to form the zipper-shape interface between fine- and coarse-grained soils. Hydraulic response of this zippered CCBE is numerically investigated considering different gravel-segment sizes, drainage-ditch widths and climate conditions. It is found that the zippered CCBE has a lower water percolation than the traditional one by up to 57 %. It is because the capillary barrier effects along the right side-wall of gravel-segment leads to water accumulation and hence water percolation near its base, facilitating reducing water percolation using drainage ditch below the gravel-segment. Moreover, water percolation increases when the gravel-segment height exceeds 0.3 times thickness of fine-grained soil or the gravel-segment width increases, due to reduction of water storage in fine-grained soil. Under the recorded annual precipitation of 1235 mm in the semi-humid region in China, the annual percolation of the traditional and zippered CCBEs are 84 mm/year and 36 mm/year, respectively. Thus, the zippered CCBE might extent the applicability of the traditional CCBE from arid or semi-arid region to semi-humid region. [ABSTRACT FROM AUTHOR]

Agricultural intensification is debated as one of the major drivers for the decline of insect biodiversity. Agri-environmental schemes (AES) are a common measure to promote biodiversity in agriculture by granting compensational payments to farmers for environmentally friendly practices. In this study we examined the effect of buffer strips of at least 5 m width, adjacent to small watercourses and drainage ditches, on insect biomass and insect species richness in agricultural landscapes. We selected ten arable fields in each of four regions in lower and upper Bavaria, Southern Germany. 25 out of 40 sites had a buffer strip between arable crops and watercourse. Insects were sampled at three time periods (May/June, June/July and August/September) for two weeks each. In each period two samples were collected (one per week). On each site Malaise traps were set up in 5 and 80 m distance to the embankment of the watercourse. Half of the samples was then subjected to metabarcoding and the other half was classified into different insect groups by morphological identification and the number of the individuals for each group was counted. For hoverflies (Syrphidae), individuals were identified at species-level. Data on vegetation structure (cover of grasses and herbs) in the studied riparian buffer strips was collected and correlated with number of species, abundances and biomass of flying insects. The five taxonomic orders with the highest species richness and individual numbers were: Diptera, Hymenoptera, Coleoptera, Lepidoptera and Hemiptera. Diptera dominated hereby with 34% of all species and 81% of all individuals. On average, mixed models indicated 31% higher insect biomass, 15% higher species richness and 29% higher individual numbers of flying insects in buffer strips at 5 m distance to the watercourse compared to sites with no buffer strip. The effect was even stronger for butterflies (32% higher species species richness, 70% more individuals) and hoverflies (24% higher species richness, 51% more individuals). In the presence of a buffer strip significantly higher numbers were found for total individuals, Diptera, Hymenoptera and Coleoptera. In 80 m distance to the watercourse, the samples of flying insects were not significantly influenced by a riparian buffer strip. This study highlights the importance of buffer strips in agricultural regions and their multifunctional potential in fostering biodiversity additionally to their acknowledged use for water protection. Ideally, buffer strips are rich in herbs and inflorescences and are therefore beneficial for the insect fauna by serving as valuable habitat with high potential connectivity at landscape level. • 31% higher biomass on average of flying insects in riparian buffer strips compared to agriculturally used fields. • 15% higher species richness on average of flying insects in riparian buffer strips compared to agriculturally used fields. • 29% higher individual numbers on average of flying insects in riparian buffer strips compared to agriculturally used fields. [ABSTRACT FROM AUTHOR]

Recent studies indicate that greenhouse gas (GHG) emissions from agricultural drainage ditches can be significant on a per-unit area basis, but spatiotemporal investigations are still limited. Additionally, the impact of dredging – a common management in such environments – on ditch GHG emissions is largely unknown. This study presents year-round GHG emissions from nine ditches on a dairy farm in the center of the Netherlands, where each year, approximately half of the ditches are dredged in alternating cycles. We measured monthly diffusive fluxes of carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2 O), along with ebullitive CH 4 emissions, supplemented by diel flux measurements (i.e., 24-h measurements) conducted in summer and winter. Our findings indicate that while diffusive GHG fluxes exhibited low spatiotemporal variation, ebullitive CH 4 emissions were significantly higher during warmer periods and marginally elevated at ditch intersections. CH 4 ebullition was the dominant pathway of ditch GHG emissions, accounting for 58% of the total annual emissions, followed by CO 2 (39%), and N 2 O (3%). Approximately 80% of the total CH 4 emissions occurred through ebullition during spring and summer. The average CH 4 emission factor estimated for our ditches (574 kg ha−1 year−1) is ∼40% higher than the Tier-1 value suggested by the IPCC for ditches on mineral soils (416 kg ha−1 year−1). Based on two 24-h measurement campaigns, we concluded that neglecting nighttime diffusive CO 2 and CH 4 emissions may lead to inaccurate estimates of annual ditch GHG emissions, with ∼12% underestimation in this study. Although dredging led to subtle increases in water-to-atmosphere GHG emissions immediately after the activity, it reduced overall annual GHG emissions by ∼35%. This study highlights the importance of CH 4 ebullition and of capturing diel cycles of diffusive emissions to accurately assess ditch GHG emissions and underscores the importance of considering seasonal variations and dredging practices when budgeting ditch GHG emissions. • GHG emissions were monthly measured in agricultural ditches that are frequently dredged. • CH 4 ebullition comprised 58% of annual emissions, peaking in warmer months. • Dredging decreased annual GHG emissions by ∼35% but triggered short-term GHG emission spikes. • Ignoring summer nighttime diffusive emissions may underestimate annual CO 2 and CH 4 emissions. [ABSTRACT FROM AUTHOR]

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) have garnered significant scientific attention due to their heightened toxicity and mobility compared to their parent PAHs. This study investigated the occurrence of 11 OPAHs and 16 PAHs within agricultural ditch sediment of Guangzhou City, China. The ΣPAH and ΣOPAH concentrations ranged from 63.8–3955 ng/g and 16.5–522 ng/g, respectively. Notably, concentrations were elevated during the rainy season, attributed to intensified atmospheric deposition and surface runoff during the rainy season. Spatially, Pearson correlation and path analysis disclosed a linkage between OPAHs and high-molecular-weight PAHs and adjacent agricultural practices, whereas low-molecular-weight PAHs were associated with human and industrial operations. This disparity was linked to the restricted mobility of high-molecular-weight PAHs, rendering them particularly susceptible to proximal sources. Diagnostic ratios and principal component analysis-multiple linear regression (PCA-MLR) implicated fossil fuel combustion and vehicle emissions as major contributor to the sedimentary OPAHs and PAHs. Further correlations between estimated source contributions and water quality, strengthened by spatial interpolation, clearly identified agricultural activities, and atmospheric deposition associated with traffic emissions and fossil fuel combustion as primary contributor to sedimentary OPAHs and PAHs. Secondary sources encompassed coal combustion, road runoff, and wastewater from both industrial and shipping activities. The risk quotients (RQ s) for PAH and OPAH mixtures indicated moderate to high ecological hazards. This study demonstrated the importance of employing the integrated approach, combining PCA-MLR, diagnostic ratios, and correlation of source contributions with water quality in precisely delineating the origins of OPAHs and PAHs in agricultural ditch sediment. [Display omitted] ● This is the first study on the occurrence of OPAHs in agricultural ditch sediment. ● Sedimentary PAH and OPAH concentrations exhibited significant temporal variations. ● PAH and OPAH distribution were related to agricultural and industrial activities. ● PCA-MLR and water quality analysis improved source apportionment accuracy. ● Traffic-related aerial deposition and agriculture are main OPAH and PAH sources. [ABSTRACT FROM AUTHOR]