Agricultural Drainage Ditches Research Articles

Bacterial diversity in agricultural drainage ditches shifts with increasing urea-N concentrations.

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 (0.5mg N L-1) during the mesocosm experiment. The results of our study suggests that urea-N concentrations >0.07mg 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.

Effects of Nitrogen Input and Aeration on Greenhouse Gas Emissions and Pollutants in Agricultural Drainage Ditches

Understanding the patterns of greenhouse gas emissions and the changes in pollution load in terrestrial freshwater systems is crucial for accurately assessing the global carbon cycle and overall greenhouse gas emissions. However, current research often focuses on wetlands and rivers, with few studies on agricultural drainage ditches, which are an important part of the agricultural ecosystem. Investigating the greenhouse gas emission patterns and pollution load changes in agricultural drainage ditches can help accurately assess the greenhouse effect of agricultural systems and improve fertilization measures in farmlands. This study explored the effects of nitrogen input and aeration on the pollution load and greenhouse gas emission processes in paddy field drainage ditches. The results showed that aeration significantly reduced the concentration of ammonium nitrogen (NH4+) in the water, decreased the emissions of nitrous oxide (N2O) and methane (CH4), and slightly increased the emission of carbon dioxide (CO2), resulting in an overall reduction of the global warming potential (GWP) by 34.02%. Nitrogen input significantly increased the concentration of ammonium nitrogen in the water, slightly reduced the emissions of N2O and CH4, and increased the CO2 emissions by 46.60%, thereby increasing the GWP by 15.24%. The drainage ditches reduced the pollution load in both the water and sediment, with the overall GWP downstream being 9.34% lower than upstream.

Agricultural practices and ditch size drive microbial community assembly and mediate N- and P-transformation in multistage drainage networks of paddy fields: Insights from a large-scale irrigation district in eastern China

Agricultural drainage ditches (ADDs) are ubiquitous and regarded as active zones for biogeochemical reactions and microbe-mediated pollutant removal. However, little is known about the microbial distribution and community assembly in ADDs. Here, a typical large-scale irrigation district, including five orders of farmland drainage systems (namely field, sublateral, head, branch, and trunk ditches that could efficiently remove excess water from paddy fields to downstream water bodies), was selected to investigate the ecological processes of microbial communities and N- and P-transformation processes in multistage ditches. We found that scale effects drove distinct environmental gradients and microbial community dissimilarities and that the five ordered ditches were grouped into three clusters (field vs. sublateral vs. head, branch, and trunk ditches). Specifically, the microbial communities in the field ditches located adjacent to the paddy fields were strongly selected by agricultural fertilization and irrigation drainage, enriching salt-tolerant microbes with high nitrification and inorganic P solubilization capabilities. In comparison, the sublateral ditches showed the highest removal performance for total nitrogen (13.28–55.80%) and total phosphorus (9.06–65.07%) during the growth of rice, which was mainly attributed to the enrichment of versatile microbiota (e.g., C39, Nitrospira, and Novosphingobium) as a result of the increased stochastic processes driven by the low redox potential. Notably, the specific gene (i.e., hzsB) for anaerobic ammonium oxidation in sublateral ditches was 1–2 orders of magnitude higher than in adjacent ditches, further contributing to N loss. As field water was discharged into the large-sized head, branch, and trunk ditches, the nutrient levels decreased sharply. At the same time, deterministic processes gained more importance (∼82%), leading to the flourishing of Synechococcus and increasing the potential risk of eutrophication. Overall, the microbial communities in multistage ADDs were co-shaped by agricultural practices and ditch size, which further governed the N and P removal performance. These results provide unique insights into microbiota assembly patterns and dynamics in multistage ADDs and important ecological knowledge for controlling agricultural non-point source pollutants by managing of small-sized ditches.

Spatiotemporal patterns and main driving factors of drainage water quality of an arid irrigation district with shallow groundwater table.

Drainage water quality is a crucial factor reflecting the regime of agricultural non-point source pollution in irrigation districts and is closely related to land use, soil texture, cropping pattern, fertilization, and irrigation and drainage conditions. However, the response of drainage water quality to various natural and anthropogenic factors needs further exploration in irrigation districts affected by shallow groundwater table. Spatiotemporal patterns of chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), and ammonium nitrogen (NH4-N) were monitored and analyzed in ten agricultural drainage ditches in the arid region of China from 2011 to 2019. Spatially, water pollution in agricultural drainage ditches with small water quantity can be significantly exacerbated by urban sewage, whereas a large amount of agricultural drainage can effectively dilute the pollution of urban sewage. Severe soil salinization in the cropland increases the risk of water pollution due to easier losses of soil nutrient and organic matter. Soil salinization is a key factor in the crop distribution pattern based on the crop salt tolerance, and the maize/wheat field with a higher fertilizer application rate generally results in poorer drainage water quality. Temporally, for the agricultural drainage ditches, the monthly and annual COD, TP, TN, and NH4-N concentrations fluctuate inversely with drainage water quantity and are positively correlated with fertilizer application, among which the monthly COD concentration in drainage water has larger variation in severe salinized areas. There exist critical annual and monthly drainage amounts, above which the probabilities of higher concentrations of COD, TP, TN, and NH4-N reduce greatly.

Investigating Microbial Triggers of Nitrous Oxide Emissions in Agriculturally Influenced Aquatic Ecosystems

The agricultural sector in Canada is responsible for approximately 9% of greenhouse gas (GHG) emissions in Canada, accounting for 54 MT of carbon dioxide (CO2), as well as 31% of methane (CH4) and 75% of national nitrous oxide (N2O) emissions in 2021 (Environment and Climate Change Canada 2021). However, these estimates do not include the indirect GHG emissions that occur in agriculturally impacted waterways. Ontario is home to over 45 000 kilometers of agricultural drainage ditches, with tile drains directly connecting terrestrial and aquatic environments. Microbial biogeochemical cycles in the causeways experience fluxes of nutrients leading to hotspots for GHG at the sediment-water interfaces. Along with fluxes of nutrients, the causeways are regularly disturbed by anthropogenic effects (e.g., dredging, removal of vegetative buffers) and increasing frequency of storm events. Previous studies have used static chambers to evaluate GHG emissions from aquatic systems (Mu et al. 2022, Xiao et al. 2016). However, this approach can be time consuming and labour intensive and is impractical in aquatic systems due potential extensive underestimation of fluxes from diffusion. To resolve driving factors contributing to GHG in these systems a detailed study investigating the activity of the microbial community is warranted. In this study we hypothesize microbial activity within the sediment will correlate with N2O emissions. To test the response of the microbial community a combination of molecular approaches (i.e., qPCR and Ion torrent) targeting archaeal and bacterial nitrifiers and denitrifies was used. These functional responses were evaluated with respect to N2O emissions, which were measured in the field at the time of sampling using Unisense N2O probes. In this study, N2O sensor response was calibrated to a functional gene index for rapid risk assessment of GHG hotspots.

Importance of Dense Aquatic Vegetation in Seasonal Phosphate and Particle Transport in an Agricultural Headwater Stream

AbstractAgricultural headwater streams and ditches commonly host dense stands of aquatic vegetation that grow and decay over seasons and exert physical and biological controls on the transport of nutrients from cropland to larger rivers. This study examined changes in the transport of phosphorus (P) in an agricultural drainage ditch in the Maumee River Basin (Ohio, USA) by conducting constant rate injections of a novel tracer mixture (conservative salt [Cl as NaCl], dissolved P [KH2PO4], and a fluorescent fine particle) in spring, summer, and fall. We quantified transport behavior for solutes and particles using a traditional transient storage modeling framework consisting of mobile and immobile storage zones connected by a first‐order exchange rate constant. Transient storage was greatest during the spring, when thicker vegetation caused more pooling and flow stagnation, and decreased through fall, as vegetation thinned. Soluble P uptake lengths were 8.7 times longer in fall than spring, likely due to declines in biological uptake rates with colder temperatures and immobile zone storage with thinning vegetation. Particle capture lengths also decreased by a factor of 4.3 from fall to spring. With the increasing eutrophication of Lake Erie and waterbodies around the world that lie downstream from agricultural landscapes, it is beneficial to understand nutrient transport across watersheds, including small agricultural streams. This study highlights the physical and biological roles that aquatic vegetation plays in small agricultural streams by creating seasonally variable immobile zones that slow the flow of nutrients, providing surface area for biofilms, and capturing particles that bind nutrients.

Characteristics of Nitrogen in Overlying Water and Sediment of Typical Agricultural Drainage Ditches during Different Periods in a Freezing-Thaw Area of China

In the Sanjiang Plain, agricultural drainage ditches effectively alleviate agricultural non-point source nitrogen pollution. However, limited information is known about the characteristics of bidirectional trans-ports of nitrogen between sediment and overlying and pore water in different patterns of ditches undergoing seasonal freezing-thawing cycles. It is vital to better understand nitrogen interception and purification by ecological ditches. In order to clarify the interception of ecological ditches on internal and external nitrogen, overlying water and sediment samples of two typical agricultural ditches were collected and analyzed in Sanjiang Plain during the growing seasons of 2015–2017. The results indicated that the N-NO3− in overlying water, which was higher than N-NH4+, was the dominant inorganic nitrogen, whilst, in the sediment, N-NH4+ was much higher than N-NO3−, which should be attributed to the soil’s adsorption of N-NH4+. In contrast to the dryland ditch, the paddy ditch had a more significant amount of inorganic nitrogen both in overlying water and sediment, which means that the non-point source nitrogen pollution caused by paddy fields was more severe than that of drylands. Compared with dryland ditches, N-NH4+ in the sediment of pad ditches seemed to be much easier to migrate to a deeper layer, which may cause a greater risk of nitrogen pollution to groundwater. Both in the overlying water and the sediment of ditches, nitrogen content fluctuated during different periods, and inter-annual variation was noticeable, which results means that estimation or prediction of the non-point source pollution output needs to extend the monitoring period and increase sampling frequency to reduce the great uncertainty. The findings may provide a foundation for forecasting agricultural nitrogen pollution and guide best management practices (BMPs) of non-point source nitrogen pollution control in seasonally frozen areas.

Natural sources and controlling factors of urea-nitrogen concentrations in agricultural drainage ditches.

Agricultural drainage ditches accumulate high urea-nitrogen (N) concentrations even in the absence of urea fertilizer applications to adjacent crop fields. The accumulated urea, and other bioavailable forms of dissolved organic nitrogen (DON), can be flushed downstream during substantial rainfall events altering downstream water quality and phytoplankton communities. Sources of urea-N supporting its accumulation in agricultural drainage ditches are poorly understood. A ditch flooding event was simulated using mesocosms with N treatment solutions and monitored for changes in N concentrations, physicochemical properties, dissolved organic matter (DOM) composition, and N cycling enzymes. N concentrations were also monitored in field ditches after two rainfall events. Urea-N concentrations were higher with DON enrichment, but the treatment effects were temporary. The DOM released from the mesocosm sediments was dominated by terrestrial-derived, high molecular weight material. The lack of microbial-derived DOM and evidence from the bacterial gene abundances in the mesocosms suggests that urea-N accumulation after rainfall may not be associated with fresh biological inputs. The urea-N concentrations after spring rainfall and flooding with DON substrates indicated the urea from fertilizers may only temporarily affect urea-N concentrations in drainage ditches. Because urea-N concentrations increased with a high degree of DOM humification, sources of urea may derive from the slow decomposition of complex DOM structures. This study provides further insights of sources contributing to high urea-N concentrations and the types of DOM released from drainage ditches to nearby surface waters after hydrological events.

Core and conditionally rare taxa as indicators of agricultural drainage ditch and stream health and function

BackgroundThe freshwater microbiome regulates aquatic ecological functionality, nutrient cycling, pathogenicity, and has the capacity to dissipate and regulate pollutants. Agricultural drainage ditches are ubiquitous in regions where field drainage is necessary for crop productivity, and as such, are first-line receptors of agricultural drainage and runoff. How bacterial communities in these systems respond to environmental and anthropogenic stressors are not well understood. In this study, we carried out a three year study in an agriculturally dominated river basin in eastern Ontario, Canada to explore the spatial and temporal dynamics of the core and conditionally rare taxa (CRT) of the instream bacterial communities using a 16S rRNA gene amplicon sequencing approach. Water samples were collected from nine stream and drainage ditch sites that represented the influence of a range of upstream land uses.ResultsThe cross-site core and CRT accounted for 5.6% of the total number of amplicon sequence variants (ASVs), yet represented, on average, over 60% of the heterogeneity of the overall bacterial community; hence, well reflected the spatial and temporal microbial dynamics in the water courses. The contribution of core microbiome to the overall community heterogeneity represented the community stability across all sampling sites. CRT was primarily composed of functional taxa involved in nitrogen (N) cycling and was linked to nutrient loading, water levels, and flow, particularly in the smaller agricultural drainage ditches. Both the core and the CRT were sensitive responders to changes in hydrological conditions.ConclusionsWe demonstrate that core and CRT can be considered as holistic tools to explore the temporal and spatial variations of the aquatic microbial community and can be used as sensitive indicators of the health and function of agriculturally dominated water courses. This approach also reduces computational complexity in relation to analyzing the entire microbial community for such purposes.

Organic Micropollutants from an Agricultural Drainage Ditch Contaminate a Shrimp Farm in Sinaloa (Mexico)

Organic Micropollutants from an Agricultural Drainage Ditch Contaminate a Shrimp Farm in Sinaloa (Mexico)

Nitrate-dependent anaerobic methane oxidation (N-DAMO) as a bioremediation strategy for waters affected by agricultural runoff.

Agricultural drainage ditches are subjected to high anthropogenic nitrogen input leading to eutrophication and greenhouse gas emissions. Nitrate-dependent anaerobic methane oxidation (N-DAMO) could be a promising remediation strategy to remove methane (CH4) and nitrate (NO3-) simultaneously. Therefore, we aimed to evaluate the potential of N-DAMO to remove excess NO3- and decrease CH4 release from agricultural drainage ditches. Microcosm experiments were conducted using sediment and surface water collected from three different sites: a sandy-clay ditch (SCD), a freshwater-fed peatland ditch (FPD), and a brackish peatland ditch (BPD). The microcosms were inoculated with an N-DAMO enrichment culture dominated by Candidatus Methanoperedens and Candidatus Methylomirabilis and supplemented with 13CH4 and 15NO3-. A significant decrease in CH4 and NO3- concentration was only observed in the BPD sediment. In freshwater sediments (FPD and SCD) the effect of N-DAMO inoculation on CH4 and NO3- removal was negligible, likely because N-DAMO microorganisms were outcompeted by heterotrophic denitrifiers consuming NO3- much faster. Overall, our results suggest that bioaugmentation with N-DAMO might be a potential strategy for decreasing NO3- concentrations and CH4 emission in brackish ecosystems with increasing agricultural activities where the native microbial community is incapable of efficient denitrification.

A CSM-Based Procedure for Identifying Segments of Agricultural Drainage Ditches to Be Prioritized in Maintenance Work

Highlights Maintenance of agricultural ditches is important to secure food production. To reduce costs, ditch segments in most need of maintenance should be prioritized. CSM measurements can help prioritize maintenance of agricultural ditch segments. Abstract. Productive agricultural land is vital for food production. To help secure the productivity of drained agricultural soils, diches need to be intermittently maintained. Maintenance work is costly, however, so ditch segments in most need of maintenance should be prioritized. Here, we present a procedure for identifying drainage ditch segments likely to need maintenance based on susceptibility to soil erosion by water flowing in the ditch, evaluated using a cohesive strength meter (CSM). An important part of the procedure is to relate the pressure of the CSM jets to pressures acting on the soil. The relationship between CSM jet pressure and pressures at the soil surface was established based on measurements made with a pressure sensor plate and was applied to obtain several values for pressure at the surface, which were used in turn to estimate critical shear stress for erosion. The results showed that the CSM-based method was able to identify differences in critical shear stress for erosion for different field soils. This information can be useful in identifying drainage ditch segments that should be prioritized for maintenance work. Keywords: Drainage data acquisition, Drainage maintenance, Drainage performance evaluation, Soil erosion.

Effects of Aeration on Pollution Load and Greenhouse Gas Emissions from Agricultural Drainage Ditches

Human activities input a large amount of carbon and nitrogen nutrients into water, resulting in inland freshwater becoming an important source of greenhouse gas (GHG) emissions. Agricultural drainage ditches are the main transport route of non-point source pollution. Understanding the rules for how greenhouse gas emissions from drainage ditches impact the environment can help to accurately estimate the greenhouse effect of agricultural systems. However, current research mainly focuses on the effect of different measures on the migration and transformation process of pollutants in drainage ditches. The process of greenhouse gas emissions when the non-point source of pollution is transported by drainage ditches is still unclear. In this study, the influence of aeration on the pollution load and GHG emission process of a drainage ditch in a paddy field was explored. The following conclusions were drawn: Aeration reduced the content of nitrate nitrogen in the water but had no significant effect on the content of ammonium nitrogen and it reduced the chemical oxygen demand (COD) of water by 24.9%. Aeration increased the potential of hydrogen (PH), dissolved oxygen (DO) and oxidation–reduction potential (ORP) of water and reduced the total organic carbon content, microbial carbon content and soluble carbon content of the soil in the sediment. Aeration reduced the N2O and CH4 emission fluxes and increased the CO2 emission fluxes in the drainage ditch, but it reduced the greenhouse effect generated by the drainage ditch by 33.7%. This study shows that aeration can reduce both the pollution load and the greenhouse gas emission flux in drainage ditches.

Assessing GHG cycling in agricultural and riparian soils using a uniform reactive transport modeling approach

Agricultural drainage ditches are necessary for regulating moisture contents in fields for crop production, and moreover, they can provide and regulate important ecosystem services. Drainage ditches and their associated riparian zones can be significant sources of enhanced N2O, CH4 and CO2 emissions, since they receive nutrient laden runoff and drainage from adjacent fields, while providing moisture conditions suitable for the production of greenhouse gases (GHGs). In this study, a uniform reactive transport model with up-scaled rate parameters was used to assess the dynamics of GHG cycling and biogeochemical processes in a crop field and riparian soils adjacent to a drainage ditch (i.e., located on the shoulder and midslope of the ditch) in eastern Ontario, Canada. Simulations adequately reproduced observed spatial variations in pore gas GHG concentrations in the cropped field and the monitoring locations near the drainage ditch. Spatial variations can be attributed to differences in environmental factors (i.e., soil moisture content and temperature), soil nutrient supply (i.e., NH4+, NO3–), and organic C availability. Simulation results also showed that at this site, GHG emissions did not vary significantly between monitoring locations, suggesting that the ditch slopes are not significant GHG emission hotspots. Both major rainfall events and warmer summer temperatures led to the development of hot moments for CO2 and N2O emissions and corresponding soil gas concentrations. Although the uniform model was successful in reproducing long-term trends in observed data, the model was not able to fully capture in-season temporal variability of fluxes and concentrations related to acute precipitation events (i.e., hot moments). Nevertheless, the modeling approach presented shows promise for future studies comparing the effect of management styles for agricultural soils and drainage ditch zones on GHG emissions and uptake.

Inhibition of sediment internal phosphorus release in agricultural drainage ditches by ceria nanoparticle capping.

In this study, ceria nanoparticles (CNPs) were introduced as an in-situ capping agent to inhibit the release of phosphorus (P) from sediments of agricultural drainage ditches. High-resolution dialysis (HR-Peeper) and diffusive gradients in thin film (DGT) techniques were used to measure the concentrations of P and iron (Fe) in the overlying water and sediments. The results showed that the CNP capping not only decreased the soluble reactive P (SRP) in the overlying water by 55.36% but also decreased the SRP in the pore water by 30.06%. More importantly, after the CNP capping, the flux of SRP from the pore water to the overlying water decreased by 34.12%, indicating that CNP capping can effectively inhibit the release of P from sediments to the overlying water. In addition, 38.38% of DGT-labile P was immobilized using CNP capping. Furthermore, the results of P speciation showed that CNP capping led to the change of P species from easily released NH4Cl-extractable P (NH4Cl-P) and Na2S2O4/NaHCO3-extractable P (BD-P) to more stable HCl-extractable P (HCl-P) and residual P (Res-P). These results show that CNP capping can further decrease the release of P from sediments to the overlying water. The present study shows that CNP is a feasible and effective capping material to inhibit the release of P from sediments of agricultural drainage ditches.

Assessing the Influences of Land Use Change on Groundwater Hydrochemistry in an Oasis-Desert Region of Central Asia

Land use change greatly affects groundwater hydrochemical cycling and thereby food and ecosystem security in arid regions. Spatiotemporal distribution of groundwater hydrochemistry is vital to understand groundwater water-salt migration processes in the context of land use change, while it is not well known in the oasis-desert region of arid inland basins. Here, to investigate the influences of land use change on groundwater hydrochemistry and suggest sustainable management, 67 water samples were obtained in the Luntai Oasis, a typical oasis desert of Central Asia. Stable isotopes and chemical components of samples were analyzed. Piper and Gibbs plots were used to elaborate the chemical type and major mechanisms controlling water chemistry, respectively. The results showed that cultivated land area has markedly expanded in the Luntai Oasis over the last 20 years (increasing by 121.8%). Groundwater seasonal dynamics and groundwater–surface water interaction were altered dramatically by farmland expansion and groundwater exploitation. Specifically, the spatial heterogeneity and seasonal variability of groundwater hydrochemistry were significant. Compared with the desert area, the δ18O and TDS of river water and shallow groundwater in the oasis cropland exhibited lower values but greater seasonal variation. Higher TDS was observed in autumn for river water, and in spring for shallow groundwater. The chemical evolution of phreatic water was mainly controlled by the evaporation-crystallization process and rock dominance, with a chemical type of Cl-SO4-Na-Mg. Significant spatiotemporal heterogeneity of groundwater hydrochemistry demonstrated the influence of climatic, hydrogeological, land use, and anthropogenic conditions. Groundwater overexploitation would cause phreatic water leakage into confined water, promoting groundwater quality deterioration due to fresh saltwater mixing. Improving agricultural drainage ditches in conjunction with restricting farmland expansion and groundwater extraction is an effective way to alleviate groundwater environment deterioration and maintain oasis-desert ecosystems in arid regions.

Feasibility of using Mg/Al-based layered double hydroxides as an inactivating agent to interrupt phosphorus release from contaminated agricultural drainage ditch sediments

This study aimed to evaluate the feasibility of using Mg/Al-based layered double hydroxides (Mg/Al-LDHs) treatment to prevent phosphorus release from sediments of agricultural drainage ditches. A high-resolution diffusive gradient film technique and a high-resolution peeper technique were used to measure the phosphorus and iron concentrations in the overlying water and sediment profiles at sub-millimeter vertical resolution. Results demonstrated that Mg/Al-LDHs effectively reduced the concentrations of soluble reactive P (SRP) (about 69%) in the overlying water and the concentrations of SRP (about 37.42%) and labile P (about 36.72%) in the pore water. The highly positive correlation (p < 0.01) between SRP and soluble Fe, labile P and labile Fe in the sediment profiles provided high-resolution evidence for the simultaneous release of iron and phosphorus in sediments. Furthermore, Mg/Al-LDHs inactivated mobile P (NH4Cl-P and BD-P) in the uppermost sediment (0–50 mm) and then transformed the mobile P to more stable P (NaOH-rP, HCl-P, and Res-P) (about 81% of total extractable P). An inactivation layer with low phosphorus concentrations was observed in the upper sediment. In brief, the addition of Mg/Al-LDHs to the sediment surface of agricultural drainage ditches was effective in reducing SRP concentrations in the overlying water while effectively hindering the release of sediment internal phosphorus from the pore water to the overlying water.

Vegetation and Residence Time Interact to Influence Metabolism and Net Nutrient Uptake in Experimental Agricultural Drainage Systems

Agricultural drainage networks within the Lower Mississippi River Basin (LMRB) have potential to attenuate nutrient loading to downstream aquatic ecosystems through best management practices. Nutrient uptake (nitrogen, phosphorus), gross primary production (GPP), ecosystem respiration (ER), and denitrification rates were estimated using a combination of sensor measurements and hourly discrete samples for dissolved nutrients and gases at three hydraulic residence times (2, 4, and 6 h) in three vegetated and three unvegetated ditches. We also measured vegetation and soil nutrient content. GPP and ER were significantly higher in vegetated drainages and increasing hydraulic residence time increased respiration rates. Shorter hydraulic residence times were associated with increased uptake rates for both N and P, and vegetation increased N uptake rates in all hydraulic residence time (HRT) treatments. Vegetation and sediment assimilated N and P over the course of the experiment. Overall, our experimental results demonstrate the strong role of emergent vegetation in nutrient retention and removal processes in agricultural drainage ditch networks.

Production and outmigration of young-of-year northern pike Esox lucius from natural and modified waterways connected to Lower Green Bay, Wisconsin.

Production and outmigration of young-of-year (YOY) northern pike from natal sites in Lower Green Bay, WI, USA, were documented over three consecutive years (2013-2015). We tested the hypothesis that spawning success and outmigration characteristics of YOY northern pike would vary among natural and anthropogenically modified habitats. Sixteen focal study locations were surveyed, including a restored natural wetland, agricultural drainage ditches, a flooded forested wetland and several unimpounded tributaries. We collected 1469 YOY northern pike with most individuals (N= 1163) originating from a flooded forested wetland on the east shore. Most sites produced YOY in all years (range N= 2-1145 individuals among study years). Outmigration ranged between 1 and 40 days during 2013-2015. Greater production and extended outmigration times occurred at most sites in 2014 (range 17-40 days) when the region experienced a late spring with heavy precipitation. In contrast, the lowest production and shortest outmigration period occurred at most sites in 2015 (range 14-23 days) when environmental conditions reflected regional averages. Outmigration began nearly 3 weeks earlier in 2015 (5/8) than in other study years (8 June 2013 and 25 May 2014). Total length (TL) of outmigrating northern pike ranged between 17 and 138 mm. Total length of YOY was significantly different among sites in 2013 and 2014, with the smallest fish (17 mm TL) outmigrating from agricultural ditches in both years. There were no significant variations in size among sites in 2015 (range 21-95 mm TL). Our results indicate significant variation in YOY northern pike outmigration characteristics within Lower Green Bay that may reflect the interplay between adult spawning site selection and annual weather patterns. Our findings highlight the importance of quantifying overlooked habitats in regions of mixed development.

The Effects of Ditch Management in Agroecosystems on Embryonic and Tadpole Survival, Growth, and Development of Northern Leopard Frogs (Lithobates pipiens).

Agricultural drainage ditches help remove excess water from fields and provide habitat for wildlife. Drainage ditch management, which includes various forms of vegetation clearing and sediment dredging, can variably affect the ecological function of these systems. To determine whether ditch conditions following dredging/vegetation clearing management affected the survival, growth, and development of embryos and tadpoles of northern leopard frogs (Lithobates pipiens), we conducted three field studies using in situ cages over 2years. We measured nutrients, pesticides, and other water quality properties in vegetated/unmanaged (i.e., no clearing or dredging) and newly cleared/dredged (i.e., treeless, then dredged), clay-bottomed drainage ditches in a river basin in Eastern Ontario, Canada. Nutrients, atrazine, and total neonicotinoid concentrations were generally lower at the cleared/dredged sites, whereas glyphosate was at higher concentrations. In contrast, water-quality variables measured in situ, particularly temperature, dissolved oxygen, and turbidity, tended to be higher in the cleared/dredged sites. Total phosphorous and total organic carbon concentrations at all sites were above the recommended limits for amphibian assays. No significant differences were detected in the survival, hatching success, or development of embryos among the ditch management treatments, but premature hatching was observed at one vegetated/unmanaged site where high specific conductivity may have been formative. We found the cleared/dredged sites supported earlier tadpole growth and development, likely as a result of the higher water temperatures. Increased temperature may have offset other growth/development stressors, such as those related to water chemistry. However, the long-term consequences of these differences on amphibian populations requires further study.