Ditch Maintenance Research Articles

Microplastic Transport and Accumulation in Rural Waterbodies: Insights from a Small Catchment in East China.

Microplastic (MP) pollution in agricultural ecosystems is an emerging environmental concern, with limited knowledge of its transport and accumulation in rural waterbodies. This study investigates the distribution and sources of MP in drainage ditches influenced by pond connectivity, land use, and soil properties within a small catchment in Nanjing, East China. Sediment was collected from ditches in 18 sites across forest, agricultural, horticultural, and urban areas. Using laser-directed infrared spectroscopy (LDIR), 922 MP particles were identified. Six materials were dominant: fluororubber (FR), polyethylene terephthalate (PET), polyurethane (PU), acrylonitrile (ACR), chlorinated polyethylene (CPE), and polyethylene (PE). MP concentrations varied by land use and pond connectivity, with ditches above ponds exhibiting higher counts (1700 particles/kg) than those below (1050 particles/kg), indicating that ponds act as MP sinks. The analysis revealed site-specific MP sources, with FR linked to road runoff and PET associated with agricultural practices. Correlations between MP shape and soil properties showed that more compact and filled shapes were more commonly associated with coarser soils. PE particle size was negatively correlated with organic matter. This study highlights the need for targeted strategies to reduce MP pollution in rural landscapes, such as reducing plastic use, ditch maintenance, and improved road runoff management.

Comparative Analysis of Different Mobile LiDAR Mapping Systems for Ditch Line Characterization

Maintenance of roadside ditches is important to avoid localized flooding and premature failure of pavements. Scheduling effective preventative maintenance requires a reasonably detailed mapping of the ditch profile to identify areas in need of excavation to remove long-term sediment accumulation. This study utilizes high-resolution, high-quality point clouds collected by mobile LiDAR mapping systems (MLMS) for mapping roadside ditches and performing hydrological analyses. The performance of alternative MLMS units, including an unmanned aerial vehicle, an unmanned ground vehicle, a portable backpack system along with its vehicle-mounted version, a medium-grade wheel-based system, and a high-grade wheel-based system, is evaluated. Point clouds from all the MLMS units are in agreement within the ±3 cm range for solid surfaces and ±7 cm range for vegetated areas along the vertical direction. The portable backpack system that could be carried by a surveyor or mounted on a vehicle is found to be the most cost-effective method for mapping roadside ditches, followed by the medium-grade wheel-based system. Furthermore, a framework for ditch line characterization is proposed and tested using datasets acquired by the medium-grade wheel-based and vehicle-mounted portable systems over a state highway. An existing ground-filtering approach—cloth simulation—is modified to handle variations in point density of mobile LiDAR data. Hydrological analyses, including flow direction and flow accumulation, are applied to extract the drainage network from the digital terrain model (DTM). Cross-sectional/longitudinal profiles of the ditch are automatically extracted from the LiDAR data and visualized in 3D point clouds and 2D images. The slope derived from the LiDAR data turned out to be very close to the highway cross slope design standards of 2% on driving lanes, 4% on shoulders, and a 6-by-1 slope for ditch lines.

Evaluation of soil hydrophysical parameters along a semiurban small river: Soil ecosystem services for enhancing water retention in urban and suburban green areas

Urban green areas are subjected to distinct environmental conditions, and plants are exposed to numerous adverse factors. Urban areas are characterised by extensive hardened surfaces, paved or covered by asphalt, which are practically impermeable to water. Appropriate maintenance of ditches and rivers—an issue that has been neglected in recent times—is key for increasing the water-holding capacity of urban soils. Various human activities also adversely affect rainwater retention in urban soils; the transformation of the landscape by urban development changes hydrographic conditions quite radically. This study investigates the hydrophysical conditions and evaluates the variability in water retention capacity of urban (a designed river park), suburban, and rural soils in and around Kraków, Poland. This evaluation is based on hydrophysical measurements in the topsoil and in soil layers below 100 cm. Based on the distribution of water-retention parameters, we found that during the period of investigation, the soil water content at the urban site was comparable to that at rural farmlands. The factors most decisive for water retention in the soil were the soil bulk density and hydraulic conductivity. Multivariate analysis of variance showed that soil compactness influences water retention in urban soil and also the permanent wilting point (PWP, pF = 4.2). These results can inform the evaluation of periodic water supply shortages in urban water-soil systems. Subsequent studies should focus on effective ways to improve water retention in urban soil. Water storage in soils will be an important ecosystem service in many cities where the water table is lowered due to drought and/or the urban heat island effect.

New Insights Into Legacy Phosphorus From Fractionation of Streambed Sediment

AbstractStreambed and lake sediment was studied in Sävjaån, a eutrophic mesoscale catchment (722 km2) in central Sweden. Triplicate sediment cores from five lakes and nine streams, ranging from headwater to fourth order, were sampled. The sediment was analyzed with a sequential extraction method, where six different phosphorus (P) fractions were measured. The results showed that streambed sediments store considerable amounts of P and in some cases have comparable P contents (g/kg DW) to lake sediment. Land use, soil type, and drainage area (location in the catchment) had a significant effect on the different P fractions found in surficial sediments. Sediment from lakes and forested headwater streams generally had high proportions of organic P and iron bound P. In larger streams located in agricultural areas on clay soils closer to the catchment outlet, with dense sediment and a relatively low proportion of organic matter, P was to a larger extent bound to calcium. Streambed sediment may be an important catchment scale P store and should be considered when modeling catchment P dynamics. The large stores of streambed legacy P should also be considered when performing ditch maintenance to avoid unnecessary mobilization of bioavailable P.

Forest ditch maintenance impoverishes the fauna of aquatic invertebrates: Opportunities for mitigation

One of the main factors causing biodiversity loss in wetlands is drainage, nevertheless, even drained areas may provide habitat for aquatic fauna in the form of drainage ditches. Assemblages in ditches are regularly disturbed by ditch maintenance, but the extent of these disturbances and mitigation possibilities are poorly documented. We conducted an experimental study in three commercially managed forest plots in eastern Estonia, aiming to find out how ditch network maintenance (DNM) affects the diversity and assemblages of aquatic macroinvertebrates in ditches and remnant pools, and whether this effect can be alleviated by constructing mitigation waterbodies. For comparison we also collected data from natural pools in three undrained forest plots. Before DNM, ditches supported greater number of higher taxa compared to remnant and natural pools and more strictly aquatic taxa, whereas natural pools in undrained plots supported more Trichoptera shredders. After DNM, the diversity in remnant pools decreased. Moreover, majority of the pools dried out, which resulted in further reduction of the richness and abundance of macroinvertebrates. In ditches the diversity dropped immediately after DNM, but recovered in two to three years. Nevertheless, plot-scale richness and abundance did not completely recover. Assemblage shift in ditches took place right after DNM and remained distinct after the four year survey period. Mitigation pools provided habitat for several taxa (especially Odonata) uncommon in other waterbodies in drained and undrained plots. Our results show that DNM in forests substantially impoverishes habitat availability and reduces the abundance and diversity of aquatic macroinvertebrates. We recommend retaining uncleaned sections in ditches and constructing mitigation pools as tools for supporting wetland biodiversity in drained forests.

MAPPING ROADWAY DRAINAGE DITCHES USING MOBILE LIDAR

Abstract. Roadside ditches serve an important role for draining storm water. Over time vegetation growth, natural sediment deposits, and other debris can change grade of ditches. Effectively monitoring and identifying these changes to prioritize ditch maintenance is important from both a pavement preservation perspective and prevention of localized flooding. This study evaluates the performance of two mobile LiDAR systems for mapping the cross-section of roadside ditches in the presence of vegetation. The geometric quality of data collected by two different wheel-based LiDAR systems were investigated. The mapped ditches were reported and visualized in 2D images as well as 3D point clouds. The cross-sections of man-made drainage ditches were extracted and the quality of mapped ditches was assessed against Real-Time Kinematic Global Navigation Satellite Systems (RTK-GNSS) survey. The overall point cloud accuracy was 4 cm for the medium-grade system, and 1 cm for the high-grade system. The mapping accuracy is 2 cm (medium-grade system) and 1 cm (high-grade system) for solid surface. For rough mowed areas and areas with significant vegetation, the vertical accuracy was found to be 7 cm and 11 cm, respectively, for both wheel-based systems.

Understanding Ditch Maintenance Decisions of Local Highway Agencies for Improved Water Resources across New York State

Networks of roadside ditches criss-cross the landscape, and have played a significant but previously unrecognized role in flooding and water pollution. This study surveyed town and county highway professionals across New York State (NYS) to determine their ditch management practices. There was a 41% response rate from the 999 highway staff surveyed, representing 54 of the 57 counties statewide. 36.8% of the agencies reported using full scraping or reshaping without reseeding as their primary method of ditch management and half scraped their ditches on average once every 1 to 4 years. It is estimated that one-third to one-half of the roadside ditches across upstate NYS are therefore in fair to poor condition. This translates to thousands of miles of exposed substrate vulnerable to storms, acting as a source of sediment and pollution. Limited resources including time, labor, equipment, and money were the primary reasons given for the practices used. Additional challenges identified included interactions with landowners over rights-of-way, farm-field drainage, and increasing frequency of downpours. A comprehensive, state-wide program will be necessary to actualize ditch improvement. It will require a complete toolbox of strategies, from financial support and training to regulatory mandates and penalties, and needs to include a ditch inventory system. Incentives in the form of grants and shared services should be offered by state agencies working collaboratively with local governments. Valuing highway department managers as water stewards and supporting the improved management of roadside ditches can provide an important new mechanism for protecting NYS’s water resources.

Effects of forest management and harvesting intensity on the timber supply from Finnish forests in a changing climate

We studied the potential effects of management and harvesting intensity on the timber supply from Finnish forests in a changing climate and, consequently, the possibilities of meeting the increasing wood demand of the growing forest-based bioeconomy. The study employed data from the 11th National Forest Inventory of Finland. Plots located on forest land assigned to timber production were used to develop two even-flow harvesting scenarios with annual timber harvesting targets of 60 and 80 million m3. Calculations were done for a 90-year simulation period under the current and changing climates using recent-generation (Coupled Model Intercomparison Project Phase 5) global climate model projections under three representative concentration pathways forcing scenarios (RCP2.6, RCP4.5, and RCP8.5). Intensified management used improved seed and seedling stock in artificial regeneration. It also used fertilization on subxeric pine-dominated and mesic spruce-dominated stands and ditch maintenance on 40% of drained peatlands, when the growing stock characteristics fulfilled a set of predetermined criteria. Our results showed that, with intensified management, it is possible to harvest 80 million m3·year−1 of timber under mild (RCP2.6) and moderate (RCP4.5) climate change without decreasing the growing stock volume at the country level during the 90-year simulation period. This is not possible under severe climate change (RCP8.5) due to the rapid decline in forest growth, particularly in the south after about 30 years.

Amphibians in drained forest landscapes: Conservation opportunities for commercial forests and protected sites

Forest drainage has led to the loss of a considerable number of wetlands, especially in the northern hemisphere. In order to find ways to mitigate the loss of biodiversity in drained forests, we investigated two distinct conservation measures: (i) leaving drained peatlands for natural succession, i.e. protecting without active restoration, and (ii) constructing a variety of mitigation pools during ditch maintenance work in commercial forests. We tested the effectiveness of these conservation approaches for wetland biota, selecting brown frogs (Rana arvalis, R. temporaria) as our focal species. We found that ditches do not substitute natural floods as breeding habitats for brown frogs in protected peatlands. One of the main reasons was the reduction of sun exposure due to drainage-induced forest growth. However, secondary wetlands formed on ditches impounded by Eurasian beaver (Castor fiber) offered high quality reproduction sites for brown frogs. In commercial forests, the number of natural pools decreased due to ditch maintenance work, but the colonisation rate of brown frogs increased in cleaned ditches. The reproduction site selection of the two frog species differed – R. arvalis bred mainly in natural and constructed pools, while R. temporaria bred more frequently in ditches. Among mitigation pools, those with a shallow littoral zone were primarily used for breeding. Thus, the conservation measures are effective only if certain key assumptions are met. The success could stand on the considering of the habitat requirements of target species before creating mitigation habitats or presence of a restoration agent (like beaver) in protected sites modified by human activities.

Models for diameter and height growth of Scots pine, Norway spruce and pubescent birch in drained peatland sites in Finland

The aim of this study was to develop individual-tree diameter and height growth models for Scots pine, Norway spruce, and pubescent birch growing in drained peatlands in Finland. Trees growing in peatland sites have growth patterns that deviate from that of trees growing in mineral soil sites. Five-year growth was explained by tree diameter, different tree and stand level competition measures, management operations and site characteristics. The drainage status of the site was influencing growth directly or in interaction with other variables. Site quality had a direct impact but was also commonly related to current site drainage status (need for ditch maintenance). Recent thinning increased growth of all species and former PK fertilization increased growth of pine and birch. Temperature sum was a significant predictor in all models and altitude for spruce and birch. The data were a subsample of the 7th National Forest Inventory (NFI) sample plots representing northern and southern Finland and followed by repeated measurements for 15–20 yrs. Growth levels predicted by the models were calibrated using NFI11 data to remove bias originating from the sample of the modelling data. The mixed linear models technique was used in model estimation. The models will be incorporated into the MOTTI stand simulator to replace the current peatlands growth models.

Nutrient distribution and risk assessment in drainage ditches with different surrounding land uses

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.

States of maintenance: Power, politics, and Egypt’s irrigation infrastructure

Egypt’s irrigation infrastructure comprises a vast network of dams, canals, offtakes, and ditches, which direct water from the Nile throughout the Nile Valley and Delta to millions of farmers who rely on that water to cultivate their land. In this paper, I focus on the vital work of maintenance, which keeps this infrastructure functioning and the water flowing. Yet rather than taking maintenance as an inherent good, I look critically at what exactly is being maintained. I contrast two forms of canal maintenance: first, the work that Egypt’s Ministry of Water Resources and Irrigation conducts, mostly during an annual maintenance period; second, the maintenance that farmers conduct on an everyday basis. State-led maintenance, I argue, is as much about reasserting state authority over the irrigation system as it is about fixing problems within the system. The unsung maintenance of irrigation ditches by farmers, on the other hand, is not only about cleaning ditches but also building communal relations among farmers that are key to the delivery of the water on which they depend. Focusing attention on the decision-making processes around maintenance reveals the variegated outcomes of this work and how it maintains not only the material but also social order.

Community occupancy of herpetofauna in roadside ditches in a managed pine landscape

Aquatic habitat types embedded in managed forest can contribute ecological services and suitable conditions for numerous species despite departing from historical baselines. Although prevalent in the Atlantic Coastal Plain, roadside ditches adjacent to pine plantations have had few surveys of vertebrate diversity and little is known about local and landscape level effects of silvicultural activities on species assemblages. Our goal was to investigate richness and occupancy of amphibians and reptiles in an intensively managed forest landscape with a history of silvicultural alterations of aquatic habitat types, including ditching, draining, and periodic maintenance of ditches for optimizing loblolly pine (Pinus taeda) growth. We selected 15 roadside ditches that were maintained 3–17years earlier and were embedded in a matrix of pine plantations in eastern North Carolina, USA. We conducted repeated, visual encounter surveys of roadside ditches during 2012–2013 and detected 25 species of amphibians and reptiles 447 times including five species of statewide conservation concern. We used a Bayesian, hierarchical, community occupancy model with group-specific hyper-parameters to estimate occupancy probabilities and species richness while accounting for imperfect detection. With our model, we examined effects of time since ditch maintenance, amount of nearby mature forest, and amount of adjacent wetlands on species richness and occupancy. We predicted species would respond positively to an intermediate period of time since ditch maintenance and positively to landscape covariates related to mature forest and wetlands. Our model estimated species richness of anurans from 0.9 to 7.4 species/ditch segment, snakes and lizards from 0.8 to 9.0 species/ditch segment, and turtles from 0.9 to 5.1 species/ditch segment. Contrary to our predictions, occupancy of herpetofauna showed no evidence of a relationship to time since ditch maintenance, and landscape metrics only influenced occupancy of one turtle species. Detection probabilities were influenced by season for several anurans, snakes, and lizards, but not turtles. Our results indicate that aquatic habitat types embedded in managed forests that were hydrologically and structurally altered for silviculture can support local occupancy of a relatively diverse herpetofaunal community and that temporal proximity to ditch maintenance had little effect on occupancy or richness.

The contrasting effects of short‐ and long‐term habitat drainage on the population dynamics of freshwater turtles in a human‐dominated landscape

Summary Most studies on the effect of drought on the biodiversity of freshwater systems have focussed on natural droughts. We sought to assess the effects of artificial drainage on the population dynamics of the European pond turtle (Emys orbicularis). We investigated whether the probability of survival and emigration/immigration was affected by short‐term drawdown (for a few months over winter) or long‐term habitat drainage (a full year of drying out) in this long‐lived species of low dispersal ability. The study was replicated in two different areas using a Capture–Recapture monitoring programme over 5 years. In the two areas, we marked 1412 and 282 individuals, respectively. Short‐term drawdown had no impact on the vital rates of this species, while long‐term drainage promoted greater mobility among the ponds in both areas. This increase in movement might reduce survival, due to road mortality, or result in turtles leaving the study area. Moreover, as the transition probability between ponds was higher when ponds were close together and directly connected, for instance by a ditch, the construction and maintenance of ditches might reduce the effects of drainage. To implement effective conservation plans, studies that aim to assess the effect of human disturbance should monitor population dynamics and vital rates to allow a more complete picture of the real impacts.

Evaluating Geomorphic Change in Constructed Two‐Stage Ditches

AbstractStraight, trapezoidal‐shaped surface drainage channels efficiently drain the soil profile, but their deviations from natural fluvial conditions drive the need for frequent maintenance. Ecological and socioeconomic impacts of drainage ditch maintenance activities can be significant, leading to harmful algal blooms and increased sedimentation. We developed a two‐stage ditch design that is more consistent with fluvial form and process. The approach has potential to enhance ecological services while meeting drainage needs essential for agricultural production. We studied geomorphic change of the inset channel, benches and banks of seven two‐stage ditches in Ohio, Indiana, and Michigan. Three to 10 years after construction, inset channel changes reflected natural adjustments, but not all ditches had reached their quasi‐equilibrium state. Ditches had experienced both degradation and aggradation on the benches at a rate of 0.5‐13 mm/yr. Aggradation on the benches was not likely to threaten tile drain outlets. Localized scour was observed on the banks at some sites, but at all but one site changes were not statistically significant. Except for the removal of woody vegetation, none of the ditches required routine maintenance since construction. Two‐stage ditches can be a stable, viable option for drainage ditch management if designed and installed properly on the landscape.

Managing ditches for agroecological engineering of landscape. A review

Agriculture must now feed the planet with the lowest environmental impact. Landscape management is a means to protect natural resources from the adverse impacts. In particular, the adequate management of ditches could improve crop quality. Here, we review ditch design and maintenance. We found the following major points: (1) ditch networks have been primarily designed for waterlogging control and erosion prevention. Nonetheless, when properly managed, farm ditches provide other important ecosystem services, namely groundwater recharge, flood attenuation, water purification, or biodiversity conservation. (2) All ditch ecosystem services depend on many geochemical, geophysical, and biological processes, whose occurrence and intensity vary largely with ditch characteristics. (3) The major ruling characteristics are vegetative cover; ditch morphology; slope orientation; reach connections such as piped sections and weirs, soil, sediment and litter properties, biota, and biofilms; and network topology. (4) Ditch maintenance is an efficient engineering tool to optimize ecosystem services because several ditch characteristics change widely with ditch maintenance. For instance, maintenance operations, dredging, chemical weeding, and burning improve waterlogging and soil erosion control, but they are negative for biodiversity conservation. Mowing has low adverse effects on biodiversity conservation and water purification when mowing is performed at an adequate season. The effects of burning have been poorly investigated.

A tool for assessing the status of drainage ditches and the need for remedial measures

Poor maintenance of drainage systems has been identified as one of Swedish agriculture's weak points, as impaired land drainage can lead to major environmental problems. Drain maintenance work is receiving increasing attention in work conducted within the European Union Water Framework Directive. Moreover, the functionality and maintenance of agricultural ditches will need to be improved to cope with predicted higher pressures on water infrastructure in a future climate. In Sweden, ditch maintenance work is mandatory, but must be carried out with great consideration for the environment. There is currently no simple method available in Sweden for assessing the comprehensive status of open drainage ditches and determining whether remedial measures are needed. This study tested an on-site method, Minnesota Agricultural Ditch Research Assessment for Stability, for evaluating the status of drains and the need for improvements. The study also included an evaluation of physical ditch properties that can be assessed visually on-site and the processes they represent. The results showed that it is viable to evaluate ditch properties such as bank stability, erosion and deposition susceptibility visually on-site. However, more intensive surveys are needed to identify the processes affecting bank stability. For assessing how improvement of drain status affects bank stability and hydraulic properties, Hydrologic Engineering Centre's River Analysis System simulations can be a useful tool when complemented with updated cross-section measurements and existing documentation.

Anuran assemblages associated with roadside ditches in a managed pine landscape

Abstract Managed forests support a diverse assemblage of herpetofauna. However, less is known about how aquatic features embedded in intensively managed landscapes, particularly modified aquatic habitat types, influence biodiversity. Further, whether additional anthropogenic disturbances to modified aquatic habitats affect occupancy of amphibians has not been studied, but has important ramifications for ongoing policy debates regarding water quality regulations in the United States. We examined species diversity and occupancy of anuran assemblages in an intensively managed forest landscape with a history of ditching, draining, and periodic maintenance of ditches. During 2012–2013, we conducted repeated aural surveys for calling male frogs and toads across 16 roadside ditch segments that were maintained from 3 to 17 years earlier. Across 12 survey events, we detected 15 species of frogs and toads 555 times. We used a community occupancy model to estimate occupancy for multiple anurans and to examine associations between species occupancy for roadside ditches and the time since drainage ditch maintenance, amount of nearby mature forest cover, and metrics describing adjacent depressional wetlands. We predicted a quadratic relationship between both species richness and probability of occupancy for individual species with time since ditch maintenance because we hypothesized anurans would respond positively to intermediate vegetation structure and canopy cover when selecting calling and oviposition sites. Based on previous studies, we also predicted positive relationships between anuran occupancy and diversity with proportion of the surrounding landscape in mature forest or in depressional wetlands, and negative relationship with increasing distance to nearest wetland. Contrary to our prediction, we did not find evidence of a positive response (95% credible intervals included 0) by the community or individual species to time since ditch maintenance or the forest or wetland covariates, but we did observe a diverse assemblage of frogs and toads associated with roadside ditches in managed pine forest. Estimated richness ranged from 5.5 to 11.5 species/site and probabilities of occurrence ranged from 0.01 to 1.00 by species and site. Detection probabilities by species within a season ranged from 0 to 0.93 and were positively influenced by rainfall for several species and differed across months for many species. Our results indicate that reconfigured aquatic habitat types embedded in managed forests can support local and regional occupancy of anurans, but the current anuran community likely differs from what occurred historically.

The role of emergent vegetation in structuring aquatic insect communities in peatland drainage ditches

Availability of macrophyte habitat is recognized as an important driver of aquatic insect communities in peatland drainage ditches; however, eutrophication can lead to the decline of submerged vegetation. While emergent vegetation is able to persist in eutrophicated ditches, vegetation removal, carried out during ditch maintenance, can reduce the availability of this habitat. In this study, we applied the landscape filtering approach to determine whether the absence of emergent vegetation is a habitat filter which structures aquatic insect communities in peatland drainage ditches under different trophic conditions. To this end, a field study was carried out in one mesotrophic (Naardermeer) and one eutrophic (Wormer and Jisperveld) peatland in the province of North Holland, The Netherlands. We assigned life history strategies to insect species and applied linear mixed models and redundancy analyses to taxonomic and functional aquatic insect community data. Our results indicate that while differences between peatlands primarily determine the species pool within each wetland, emergent vegetation acted as a secondary filter by structuring functional community composition within ditches. The eutrophic peatland was dominated by insects adapted to abiotic extremes, while species with good dispersal abilities were strongly related to emergent vegetation cover. This study demonstrates the applicability of life history strategies to provide insight into the filtering of species due to availability of emergent macrophyte habitat. To ensure greater diversity of insect communities in ditch habitats, it is recommended that some vegetation be spared during maintenance to leave patches from which insect recolonization can occur.

An easy to use calculation method for weir operations in controlled drainage systems

If operated appropriately, drainage systems may serve as vast reservoirs to retain or release water and solutes. This paper describes the hydraulic principles ruling the unsteady reaction of groundwater levels as related to drainage control operations. A set of governing equations suited to be implemented in computer codes was deduced focusing on non steady-state drainage, weir hydraulics, and effects of ditch maintenance. Based upon a simplified layout, two easy to handle computer codes were developed (MATLAB/Octave and Excel versions) enabling local engineers to assess system performance. Controlled drainage systems may be used to reduce leaching of agrochemicals from agricultural land and are valuable tools for preventive flood control. Controlled drainage may further support effective field operations necessary for crop production.