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Globally, there are millions of kilometres of drainage ditches which have the potential to emit the powerful greenhouse gas methane (CH 4 ), but these emissions are not reported in budgets of inland waters or drained lands. Here, we synthesise data to show that ditches spanning a global latitudinal gradient and across different land uses emit large quantities of CH 4 to the atmosphere. Area-specific emissions are comparable to those from lakes, streams, reservoirs, and wetlands. While it is generally assumed that drainage negates terrestrial CH 4 emissions, we find that CH 4 emissions from ditches can, on average, offset ∼10% of this reduction. Using global areas of drained land we show that ditches contribute 3.5 Tg CH 4 yr −1 (0.6–10.5 Tg CH 4 yr −1 ); equivalent to 0.2%–3% of global anthropogenic CH 4 emissions. A positive relationship between CH 4 emissions and temperature was found, and emissions were highest from eutrophic ditches. We advocate the inclusion of ditch emissions in national GHG inventories, as neglecting them can lead to incorrect conclusions concerning the impact of drainage-based land management on CH 4 budgets.

Denitrification, as the main nitrogen (N) removal process in farmland drainage ditches in coastal areas, is significantly affected by saline-alkali conditions. To elucidate the effects of saline-alkali conditions on denitrification, incubation experiments with five salt and salt-alkali gradients and three nitrogen addition levels were conducted in a saline-alkali soil followed by determination of denitrification rates and the associated functional genes (i.e., nirK / nirS and nosZ Clade I) via N 2 /Ar technique in combination with q PCR. The results showed that denitrification rates were significantly decreased by 23.83–50.08%, 20.64–57.31% and 6.12–54.61% with salt gradient increasing from 1 to 3‰, 8‰, and 15‰ under 0.05‰, 0.10‰ and 0.15‰ urea addition conditions, respectively. Similarly, denitrification rates were significantly decreased by 44.57–63.24% with an increase of the salt-alkali gradient from 0.5 to 8‰. The abundance of nosZ decreased sharply in the saline condition, while a high salt level significantly decreased the abundance of nirK and nirS . In addition, the increase of nitrogen concentration attenuated the reduction of nirK , nirS and nosZ gene abundance. Partial least squares regression (PLSR) models demonstrated that salinity, dissolved oxygen (DO) in the overlying water, N concentration, and denitrifying gene abundance were key determinants of the denitrification rate in the saline environment, while pH was an additional determinant in the saline-alkali environment. Taken together, our results suggest that salinity and high pH levels decreased the denitrification rates by significantly inhibiting the abundance of the denitrifying genes nirK , nirS, and nosZ , whereas increasing nitrogen concentration could alleviate this effect. Our study provides helpful information on better understanding of reactive N removal and fertilizer application in the coastal areas.

Urea-based fertilizers applied to crop fields can enter the surface waters of adjacent agricultural drainage ditches and contribute to the nitrogen (N) loading in nearby watersheds. Management practices applied in drainage ditches promote N removal by the bacterial communities, but little is known about the impacts of excess urea fertilizer from crop fields on the bacterial diversity in these ditches. In 2017, sediments from drainage ditches next to corn and soybean fields were sampled to determine if fertilizer application and high urea-N concentrations alters bacterial diversity and urease gene abundances. A mesocosm experiment was paired with a field study to determine which bacterial groups respond to high urea-N concentrations. The bacterial diversity in the ditch next to corn fields was significantly different from the other site. The bacterial orders of Rhizobiales, Bacteroidales, Acidobacteriales, Burkholderiales, and Anaerolineales were most abundant in the ditch next to corn and increased after the addition of urea-N (0.5 mg N L−1) during the mesocosm experiment. The results of our study suggests that urea-N concentrations >0.07 mg N L−1, which are higher than concentrations associated with downstream harmful algal blooms, can lead to shifts in the bacterial communities of agricultural drainage ditches.

Aquatic macroinvertebrates in drainage ditches may alter rates of nutrient cycling and decomposition of organic matter but have not been accounted for in studies of ditch biogeochemistry. We collected sediment cores from four pairs of field (intermittent) and collection (perennial) ditches on Maryland’s Eastern Shore monthly from March 2011 to February 2012 to determine how taxonomic and functional group composition varies among different ditch types. We identified 138 taxa and assigned them to functional groups according to trophic position and modes of burrowing. There was no difference in mean abundance of invertebrates (5821 ind./m 2 ) between seasons or types of ditches, and species richness peaked in winter (20 taxa/site) compared to other seasons (15 taxa/site), but did not vary between ditch types. Assemblage composition differed between field and collection ditches, but functional group composition did not. Field ditches flow intermittently which may limit the assemblage to early colonists and taxa adapted to survive desiccation. The benthic macroinvertebrate assemblage was dominated by the collector–gatherer functional feeding group (83.6%) and burrowing taxa (97.1%). Bioturbation by burrowing macroinvertebrates is likely an important process contributing to ecosystem-scale functions of drainage ditches, including regulation of biogeochemical processes occurring at the sediment–water interface.

Draining and extracting peat alters the conditions that control CO2 and CH4 emissions. Carbon (C) emissions from peatlands undergoing horticultural peat extraction are not well constrained due to a lack of measurements. We determine the effect that production duration (years of extraction) has on the CO2 and CH4 emissions from an actively extracted peatland over 3 years of measurements (2018–2020). We studied five sectors identified by the year when extraction began (1987, 2007, 2010, 2013, 2016). Greater average CO2 and CH4 emissions were measured from the drainage ditches (CO2: 2.05 ± 0.12 g C m-2 d-1; CH4: 72.0 ± 18.0 mg C m-2 d-1) compared to the field surface (CO2: 0.9 ± 0.06 g C m-2 d-1; CH4: 9.2 ± 4.0 mg C m-2 d-1) regardless of sector. For peat fields, CO2 fluxes were highest in the youngest sector, which opened in 2016 (1.5 ± 0.2 g C m-2 d-1). The four older sectors all had similar mean CO2 fluxes (∼ 0.65 g C m-2 d-1) that were statistically different from the mean 2016 CO2 flux. A spatial effect on CO2 fluxes was observed solely within the 2016 sector, where CO2 emissions were highest from the centre of the peat field and declined towards the drainage ditches. These observations occur due to operators contouring surfaces to facilitate drainage. The domed shape and subsequent peat removal resulted in a difference in surface peat age hence different humification and lability. In addition, 14C dating confirmed that the peat contained within the 2016 sector was younger than peat within the 2007 sector and that peat age is younger toward the centre of the field in both sectors. Humification indices derived from mid-infrared spectrometry (MIRS) (1630/1090 cm-1) indicated that peat humification increases with increasing years of extraction. Laboratory incubation experiments showed that CO2 production potentials of surface peat samples from the 2016 sector increased toward the centre of the field and were greater than for samples taken from the 1987 and 2007 sectors. Our results indicate that peatlands under extraction are a net source of C, where emissions are high in the first few years after opening a field for extraction and then decline to about half the initial value and remain at this level for several decades, and the ditches remain a 2 to 3 times greater source than the fields but represent <3.5 % of the total area of a field.

Drainage ditches play a key role in the conservation of fragmented landscapes by providing refuge sites and secondary habitats for many terrestrial and aquatic organisms across various taxa. Species richness of ditches can exceed that of adjacent natural habitats, but here, we looked further and assessed the role of drainage ditches in shaping the community structure of true bugs aiming to better estimate ditches’ conservation value from the point of their species and trait composition. We tested the effects of the ditch substrate (saline, sandy or fen), landscape matrix (agrarian or grassland) and vegetation (species richness of all plants and invasive plants, and abundance of woody plants) on the true bug communities of 60 drainage ditches in the lowland of East-Central Europe. We found that substrate and landscape matrix contributed the most in determining true bug communities. Based on species composition, different substrates and landscape matrix types had distinct communities, but the trait composition showed differentiation according to the landscape matrix in saline habitats only. The trait composition in true bug communities was more diverse in grassland ditches than in agrarian ones, which hosted more habitat generalists associated with invasive vegetation. We concluded that a pronounced gradient in habitat stress, originating in substrate salinity and aridity, causes the differentiation of the true bug communities based on their trait composition. Additionally, intense habitat stress increases the number of habitat specialists and the conservation value of a drainage ditch.

Energy utilization efficiency (EUE) for Movable boards ditch opener (MB) and for conventional ditch opener (CD) were compared using three operating depths for MB(30, 40 and 50cm), three angles between its movable boards, three foot wings widths and two soil types (cultivated an uncultivated soils). For CD there was one angle between its boards (65°), they were permanently fastened, one share width (35cm), one operating depth in the uncultivated soil only (25cm), could not penetrate such soil, and three operating depths in the cultivated soil.The results showed that EUE for MB increased as the operating depth increased in the cultivated and uncultivated soil whereas, for CD it increased in the cultivated soil only whereas, it could not penetrate the uncultivated soil more than 25 cm. However, the rate of increase was almost the same for both implements in the cultivated soil, EUE for CD increased from 5.57 to 7.93m3MJ−1 (2.36m3MJ−1) whereas, for MB, it increased from 9.64 to 11.78m3MJ−1 (2.14m3MJ−1). EUE for MB also increased with angle between its boards and the width of the wings of its foot while for CD did not occurred because it boards were permanently fastened to the machine frame at angle of 65° and it was provided with share rather than wings. EUE for MB was higher in the cultivated soil comparing with uncultivated soil.EUE for MB was higher than that for CD for all operating depths, angle between the boards and the width of the wings of the foot and in both soil types. The results showed that MB surpassed CD in field performance in addition to that it can penetrate the soil to the required depth whether it was cultivated or uncultivated soil. It also can produced different cross-section width ditches whereas, CD can produce one cross-section width ditches.

This study trialled a convolutional neural net (CNN)-based approach to mapping peat ditches from aerial imagery. Peat ditches were dug in the last century to improve peat moorland for agriculture and forestry at the expense of habitat health and carbon sequestration. Both the quantitative assessment of drained areas and restoration efforts to re-wet peatlands through ditch blocking would benefit from an automated method of mapping, as current efforts involve time-consuming field and desk-based efforts. The availability of LiDAR is still limited in many parts of the UK and beyond; hence, there is a need for an optical data-based approach. We employed a U-net-based CNN to segment peat ditches from aerial imagery. An accuracy of 79% was achieved on a field-based validation dataset indicating ditches were correctly segmented most of the time. The algorithm, when applied to an 802 km2 area of the Flow Country, an area of national significance for carbon storage, mapped a total of 27,905 drainage ditch features. The CNN-based approach has the potential to be scaled up nationally with further training and could streamline the mapping aspects of restoration efforts considerably.

In agriculture‐dominated watersheds where natural drainage is poor, agricultural ditches (narrow engineered channels) and tile drains (perforated pipes) are widely employed to enhance surface and subsurface drainage, respectively. Despite their relatively small scale, these features exert substantial control over the hydro‐biogeochemical function of watersheds and their effects need to be represented in the models. We introduce a novel strategy to incorporate the effects of artificial agricultural drainage into a fully distributed basin‐scale integrated surface‐subsurface hydrology models. In our approach, narrow agriculture ditches for surface drainage are resolved efficiently using ditch‐aligned computational meshes that are hydrologically conditioned to ensure connectivity in the stream/ditch network. For tile drainage in the subsurface, we use the physically based Hooghoudt's drainage equation as a subgrid model and route the water drained through tiles to the nearest ditch. Without site‐specific calibration, this model reproduced observed streamflow in the Portage River Watershed (>1,000 km2) as recorded by a USGS gauge with good accuracy (normalized KGE = 0.81) and outperformed a calibrated SWAT model (normalized KGE = 0.68). Numerical experiments confirm that artificial drainage reduces surface inundations and effectively controls the water table. At the watershed scale, artificial drainage increases baseflow but has little effect on watershed discharges above the 90th percentile. The strong physical underpinnings and reduced need for calibration allow us to study the impacts of artificial drainage on distributed hydrological response in terms of fluxes and states and provide a platform for investigating watershed‐scale nutrient transport. Key Points Novel strategy is developed to incorporate effects of artificial drainage into fully distributed basin‐scale integrated hydrology model Without site‐specific calibration, our model reproduced observed streamflow well and outperformed calibrated SWAT model Numerical experiments reveal the effects of surface and surface drainage on various hydrological states and fluxes