High-concentrations diel-fluctuations of Plants Protection Products in dry periods

<p>Modern agriculture routinely uses Plant Protection Products (PPPs) to guarantee food security. However, PPPs can reach surface waters where they pose a threat to susceptible non-target organisms. Understanding the contamination sources and flowpaths is of utmost importance to design optimal pollution mitigation strategies. While highest concentration peaks typically occur during rainfalls following PPPs applications, a monitoring campaign in a small Swiss agricultural stream in 2019 detected several compounds in concentrations exceeding the precautionary limit of 100 ng/l by up to 14 times during a dry period. The further exploration of the time series revealed for the first time diel fluctuations of some PPPs. Such peculiar patterns excluded the occurrence of known contamination pathways including spray drift, wind erosion and dry deposition. Despite the availability of an unprecedented high-temporal resolution dataset, we were not able to disentangle the source-flowpath combination driving the observed peculiar dynamics.</p><p>Here we present the results of the follow-up 1-day field campaign aiming to close this knowledge gap. The campaign was carried out on the dry day of August 12<sup>th</sup> 2020 and we collected water samples every 6 hours from the stream at 6 different locations and from 4 outlets of active tile drains.</p><p>The results revealed widespread contamination by the fungicide fluopyram; its transformation product fluopyram-benzamide followed identical dynamics but its concentration was 10 times lower than the parent compound. This result is in line with the high DT50 of fluopyram and its broad use in the catchment. The data showed that diel fluctuations were a reoccurring phenomenon; concentrations were higher in the early morning and lower in the early evening at the most downstream location. However, the fluctuating PPPs showed a concentration peak in the upstream location at midday. We were able to narrow down the contamination sources of napropamide, clothianidin, and oxadixyl; the first is a current herbicide, the second is an insecticide not reapproved since 2020, while the third is an old fungicide banned in Switzerland in 2005, which we measured at approximately 200 ng/l. Finally, the investigated tile drains delivered PPPs at lower concentrations compared to the levels measured in the surface water, with the exception of the herbicide metamitron, which was measured at nearly 20 ng/l only at the outlet of 1 tile drain.</p><p>The presented research suggested that contamination sources can be localized by means of grab samples collected along the stream. However, it was not conclusive on the flowpath delivering PPPs to the stream. We hypothesize that 2 processes may explain the reported patterns: (i) irrigation at the upstream locations in the early morning; (ii) intra-daily exchanges at the interface between surface water and contaminated shallow groundwater. We will complement the study with expert knowledge by local stakeholders, satellite-derived soil moisture indices, high-resolution land use data and regulatory information to establish a methodology to optimally identify critical source areas in dry periods, where mitigation strategies should be put in place.</p>

Agricultural Nitrogen Budget for a Long-Term Row Crop Production System in the Midwest USA

In the Midwestern United States, subsurface drainage (commonly known as tile drains) systems have been extensively used for sustaining agricultural production. However, the tile drains have raised concerns of facilitating the transport of agricultural chemicals from the fields to receiving waters. Data from a long-term field experiment in the Little Vermilion River (LVR) watershed of east-central Illinois, USA, shows that the tile drain systems have contributed to increased nitrate N (NO3-N) to the receiving water body, Georgetown Lake Reservoir, over time. We conducted more than 10 years of research on fate and transport of NO3-N in tile drain water, surface runoff and soil N. Corn (Zea mays L.) and soybean (Glycine max L.) were planted in rotation for this watershed. We evaluated N balance (inputs and outputs) and transfer (runoff and leaching) components from three sites with both surface and subsurface flow stations within this watershed, and N budgets for individual sites were developed. Nitrogen fertilizer application (average 192 kg ha−1 y−1) and soil N mineralization (average 88 kg ha−1 y−1) were the major N inputs for corn and soybean, respectively in this watershed. Plant N uptake was the major N output for both crops during this entire study period. Annual N uptake for the LVR watershed ranged from +39 to +148 (average +93) kg ha−1 and −63 to +5 (average −32) kg ha−1, respectively, for corn and soybeans. This data indicates that most of the soil mineralized N was used during soybean production years, while corn production years added extra N in the soil. Surface runoff from the watershed was negligible, however, subsurface leaching through tile drains removed about 18% of the total rainfall. Average NO3-N concentrations of leaching water at sites A (15 mg L−1) and B (16.5 mg L−1) exceeded maximum contaminant level (MCL; 10 mg L−1) throughout the experiment. However, NO3-N concentrations from site E (6.9 mg L−1) never exceeded MCL possibly because 15–22% lower N was received at this site. We estimated that the average corn grain yield would need to be 28% higher to remove the additional N from this watershed. Our study suggests that N application schemes of the LVR watershed need to be reevaluated for better N management, optimum crop production, and overall environmental sustainability.

Effects of grassland renewal and submerged drains on greenhouse gas exchange at an intensively managed bog peat soil

<p>Intact peatland ecosystems are efficient sinks of atmospheric carbon dioxide (CO<sub>2</sub>). Disturbance, e.g. by drainage to transform peatlands into agricultural land, causes high emissions of the greenhouse gases (GHG) CO<sub>2</sub> and nitrous oxide (N<sub>2</sub>O). Our Project “Gnarrenburger Moor” focuses on the evaluation of the effects of submerged drains on GHG emissions and dissolved solute losses from bog peat under intensive grassland management. Due to installation of the water management system, grassland renewal was necessary at one of our two experimental grassland sites, both being located in Northwest Germany and subjected to similar management in the past. Here, we report on the initial year of the project, which was dominated by the impact of grassland renewal as target groundwater levels were only reached after several months.</p><p>The reference site, representing common region-specific grassland management on peat, is deeply drained by tile drains, while submerged drains were installed at the project site to achieve constantly high water levels of 30 to 40 cm below ground. Both sites are equipped with eddy covariance towers for CO<sub>2</sub> measurements and 6 plots for manually measuring N<sub>2</sub>O and methane (CH<sub>4</sub>) with closed chambers. Water samples for the analysis of phosphorus and nitrogen species are collected from ditches, tile drains and suction plates at 15, 30 and 60 cm depths. Measurements started in March 2019, i.e. approximately one month before the grassland renewal. The mechanical renewal involved mulching of the old grass sward and grading the surface of the site. Due to very dry conditions, growth of grass species was poor and the site was mulched and re-seeded again in July 2019. Target groundwater levels were reached in September 2019.</p><p>During the initial year of our study, grassland renewal substantially dominated the response of the system. From April to November, net ecosystem exchange of the project site was approximately 400 g C m<sup>-2</sup> higher than that of the reference site. When including carbon input and output from organic fertilizer and harvest on the reference site, the project site is still by far (around 140 g C m<sup>-2</sup>) a larger source. When the bare soil and raising groundwater levels coincided between July and September, N<sub>2</sub>O fluxes and dissolved nitrogen and phosphorus concentrations drastically increased at the project site. N<sub>2</sub>O fluxes were partially 100 times higher than at the reference site. The next years will show whether an operational water management system and a fully developed grass sward will turn the project site with submerged drains into a smaller source of GHGs than the reference site.</p>

Impacts of Tile Drainage on Phosphorus Losses from Edge-of-Field Plots in the Lake Champlain Basin of New York

Quantifying the influence of tile drainage on phosphorus (P) transport risk is important where eutrophication is a concern. The objective of this study was to compare P exports from tile-drained (TD) and undrained (UD) edge-of-field plots in northern New York. Four plots (46 by 23 m) were established with tile drainage and surface runoff collection during 2012–2013. Grass sod was terminated in fall 2013 and corn (Zea mays L.) for silage was grown in 2014 and 2015. Runoff, total phosphorus (TP), soluble reactive phosphorus (SRP), and total suspended solids (TSS) exports were measured from April 2014 through June 2015. Mean total runoff was 396% greater for TD, however, surface runoff for TD was reduced by 84% compared to UD. There was no difference in mean cumulative TP export, while SRP and TSS exports were 55% and 158% greater for UD, respectively. A three day rain/snowmelt event resulted in 61% and 84% of cumulative SRP exports for TD and UD, respectively, with over 100% greater TP, SRP and TSS exports for UD. Results indicate that tile drainage substantially reduced surface runoff, TSS and SRP exports while having no impact on TP exports, suggesting tile drains may not increase the overall P export risk.

The effect of nitrogen mitigation measures evaluated by monitoring of nitrogen concentrations and loadings in Danish mini-catchments – 1990–2015

Monitoring of agricultural mini-catchments (AMC) has been part of the Danish national monitoring programme (National Monitoring Programme for Water and Nature) since 1989. Thus, nitrogen (N) concentrations and loads have been monitored in soil water, tile drains, and streams within five AMC. Moreover, extensive monitoring of N concentrations and loads in streams draining 46 mini-catchments has been conducted every year since 1989. This has resulted in two national datasets on trends in flow-weighted N concentrations relative to factors such as groundwater age and management history. We analyzed these datasets and found that the intensively monitored micro-catchments generally showed a strong signal with significant downward trends in flow-weighted N concentrations in monitored soil water (−22% to −68%), tile drains (−38% to −59%), and streams (−19% to −53%). The 46 micro-catchments monitored for N in streams also exhibited downward trends in flow-weighted N concentrations, which can mainly be ascribed to the introduction of mandatory national regulation of N in agriculture in Denmark in the mid-1980s. However, classification of the mini-catchments according to the age of the oxidized groundwater revealed significant differences in N trends between the groups of mini-catchments. Thus, the strongest downward trend in flow-weighted N concentrations was as follows: <1 year (−52%), 1–3 years (−44%), and >3 years (−38%).

EFFECTS OF CONTROLLED DRAINAGE ON SOIL WATER REGIME AND QUALITY IN LITHUANIA

Lithuania remains one of the most extensively drained of the Baltic and Nordiccountries. The overall drained area (ditches plus tile drains) totalled 87% of theagricultural land area. Many nutrients from soil are leached through drainageresulting in polluting streams (drain flow receivers) water. Drain flow is treated asa major determinant of water quality. Therefore, the reduction of nutrients enteringthe drains is very important. Controlled drainage conception, when the outflowheight is increased at the mouth, helps reduce drainage runoff and partially purifywater. The aim of the research was to establish controlled drainage influence on thesoil moisture regime, nitrogen and phosphorus leaching. Investigations werecarried out in sandy loam and loam soils in the Middle Lithuanian Lowland. Basedon studies, several tendencies were observed: when drainage outflow began, theamount of soil moisture in subsoil (50-80 cm layer of the soil) of controlleddrainage plot was higher than in the conventional drainage plot, and highermoisture supplies stayed for a longer period of time. Controlled drainage had nodirect impact on phosphorus and nitrogen concentrations but they were influencedby the leaching quantities of plant usable nutrients. The reason that in many caseslower nitrate nitrogen (54% of all measurements) and phosphorus concentrations(77% of all measurements) were found in the conventional system rather than inthe controlled drainage might be connected to the fact that the latter area containedpredominantly lighter textured soils (sandy loam) making it easier to wash awaythe nutrients unused by plant.