Background
The separation of runoff components within a model simulation is of great importance for a successful implementation of management measures. Diatoms could be a promising indicator for tile ...drainage flow due to their diverse preferences to different aquatic habitats. In this study, we collected diatom samples of 9 sites (4 tile drainage, TD, and 5 river sites, Ri) in a German lowland catchment at a weekly or biweekly time step from March to July 2013 with the aim of testing the suitability of diatoms for tile drainage flow, which is typical for lowland catchment.
Results
Planothidium lanceolatum
,
Ulnaria biceps
, and
Navicula gregaria
dominated in TD sites with relative abundances of 22.2, 21.5, and 10.9%, respectively. For Ri sites, the most abundant species was
Navicula lanceolata
(20.5%), followed by
Ulnaria biceps
(12.9%),
Cyclotella meneghiniana
(9.5%), and
Planothidium lanceolatum
(9.3%). Compared with Ri sites, TD had a lower diatom density, biomass, species richness, and percentage of Aquatic/Riparian diatoms (AqRi%). However, the proportion of Riparian diatoms (RiZo%) increased at TD. Indicator value method (IndVal) revealed that the two groups (Ri and TD) were characterized by different indicator species. Fifteen taxa, including
Cocconeis placentula
,
Cyclotella meneghiniana
,
N. lanceolata
, and
U. biceps
, were significant indicators for Ri sites.
Planothidium lanceolatum
,
Achnanthidium minutissimum
, and
Navicula gregaria
were significant indicators for TD sites.
Conclusion
A pronounced variation was found in the species lists of diatom community between Ri and TD water body types associated with different indicator species. With respect to hydrograph separation, these findings highlight the suitability of diatoms as an indicator for tile drainage flow. However, spatial and temporal variations of diatoms should be considered in future surveys.
The frequent detection of residues from pesticides in various natural water types has raised public awareness. This study investigated the pesticide transformation in soil and their loss to shallow ...groundwater in a small agricultural catchment in Northern Germany. The pesticide Flufenacet and its transformation product Flufenacet ESA were examined in Luvisol and Colluvic Gleyosol under field conditions during two consecutive years. In the second year, a fluorescent tracer experiment applying Uranine and Sulforhodamine - B was carried out to gain additional insights into leaching and formation of transformation products in soil during and after a drought. We found preferential flow in response to low precipitation as an important transport pathway for Flufenacet in dry soil, as a Flufenacet concentration (1.57 μg L−1) was detected in shallow groundwater within 10 days after application. Leaching of Flufenacet to shallow groundwater by preferential flow posed greater risks during the dry than during the wet period. In contrast, Flufenacet ESA was detected in all groundwater samples. During the dry period, we detected no formation of TP510 (tracer transformation product) in the immediate topsoil. A fraction of both tracers remained there, suggesting also long-term residues of pesticides in the topsoil caused by limited living conditions for microorganisms under dry conditions. Newly formed transformation products of Uranine and Flufenacet were mainly trapped in upper soil if capillary flow was marginal. Formation of TP510 could be related to a soil water optimum and a soil temperature threshold. The occurrence of increased TP510 amounts in soil after drought was concurrent with the main peak of Flufenacet ESA in shallow groundwater. This suggested similar retention and transformation processes of fluorescent tracers and organic pesticides inside the soil. This study contributed to an extended understanding of the leaching and transformation of organic pollutants in agricultural soil under real field conditions.
Temporal occurrence of pesticides and fluorescent tracers in antecedent dry soil. Display omitted
•Leaching of pesticides to shallow groundwater poses a risk for drinking water.•Pesticides were measured in agricultural soil and in shallow groundwater.•Transport and transformation of pesticides and fluorescent tracers were similar.•During dry conditions transformation was limited but preferential flow significant.•During wet conditions Flufenacet ESA constantly developed and reached groundwater.
Drainage ponds have the potential to serve as long-term interface measures primarily for flood control, and mass retention. They are often considered as promising supplements for the mitigation of ...drainage pipe loads to improve the water quality in agricultural landscapes. In this study, a highly dynamic drainage pond system with non-steady inflows and groundwater interaction was modified and investigated regarding its potential for pesticide and transformation product (TP) retention. For this purpose, two 104-day monitoring campaigns were conducted before and after pond modification. Field experiments with fluorescent tracers, Uranine and Sulforhodamine-B, proved that structural modifications improved the hydraulic functionality of the ponds. The effective volume (Ɛ) increased from 20% to almost 100% in the modified pond and the mean hydraulic residence time (τ) was ten times longer. After a dry period, pesticide retention was high during slow refilling of the ponds, still TP loads posed a risk by infiltration into shallow groundwater due to the permeable ground. During wet periods, short nominal detention times together with high inflows led to rare high retention rates through peak attenuation. Moderate inflows resulted in extremely variable retention values, owing to the small pond storage capacity. Along with this, the total retention efficiency after modification reached up to 38% for mobile, 29% for sorptive pesticides, and 32% for mobile TPs. To achieve the best performances for ponds as natural landscape elements, they should be analysed for their hydrological functionality as a prerequisite and then modified for delayed pesticide and TP transport. Then, dynamic drainage ponds can utilize their full potential regarding mitigation of pesticide and TP loads in agricultural catchments.
Pesticide and transformation product retention efficiency of a modified drainage pond system. Display omitted
•Pesticide load balances were assessed for a drainage pond system in permeable strata.•Tracers revealed flow shortcuts and documented the efficiency of pond modification.•Transformation products were continuously detected in surface- and groundwater.•During low inflows, a large fraction of incoming mobile solutes reached groundwater.•During high inflows, a filled-up pond system attenuated load peaks.
Agrochemicals such as pesticides and nutrients are concurrent chemical stressors in freshwater aquatic ecosystems surrounded by agricultural areas. Lentic small water bodies (LSWB) are ecologically ...significant habitats especially for maintaining biodiversity but highly understudied. Phytoplankton are ideal indicator species for stress responses. Functional features of the phytoplankton are important in revealing the processes that determine the structure of the communities. In this study, we investigated the effects of pesticides, nutrients, and local environmental variables on the species composition and functional features of phytoplankton communities in LSWB. We studied pesticide toxicity of ninety-four pesticides, three nutrients (NH4-N, NO3-N and PO4-P) and local environment variables (precipitation, water level change, temperature, dissolved oxygen concentration, electrical conductivity, pH) in five LSWB over twelve weeks during the spring pesticide application period. We explored respective changes in species composition of phytoplankton community and functional features. Redundancy analysis and variance partitioning analysis were applied to correlate phytoplankton community compositions with the pesticide toxicity (as maximum toxicity in toxic units), nutrients and local environment variables. We used multiple linear regression models to identify the main environmental variables driving the functional features of phytoplankton communities. Pesticide toxicity, nutrients and local environmental variables significantly (p < 0.001) contributed to shaping phytoplankton community composition individually. Local environment variables showed the highest pure contribution for driving phytoplankton composition (12%), followed by nutrients (8%) and pesticide toxicity (2%). Functional features (represented by functional diversity and functional redundancy) of the phytoplankton community were significantly affected by pesticide toxicity and nutrients concentrations. The functional richness and functional evenness were negatively affected by PO4-P concentrations. Pesticide toxicity was positively correlated with functional redundancy indices. Our findings emphasized the relative importance of concurrent multiple stressors (e.g., pesticides and nutrients) on phytoplankton community structure, directing potential effects on metacommunity structures in aquatic ecosystems subjected to agricultural runoff.
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•Pesticides and nutrients are concurrent stressors in lentic small water bodies.•Pesticide toxicity and nutrients affect phytoplankton community composition.•Functional diversity reduced with increasing nutrient concentrations.•Functional redundancy increased with increasing pesticide toxicity.
Lentic small water bodies (LSWB) are a highly valuable landscape element with important ecosystem services and benefits for humans and the environment. However, data about their pesticide ...contamination dynamic and the associated ecotoxicological effects are scarce. To overcome these knowledge gaps, five LSWBs located in agricultural fields in Northern Germany were studied during the spring pesticide application period (April to July 2018) and the concentrations of 94 pesticides were measured in weekly intervals. The goals of this study were to observe the trends of pesticide contamination during the application period, assess the ecotoxicity of the contamination, and assign the findings to temporal and spatial origins. Samples contained pesticide concentrations between 0.12 and 4.83 μg L−1 as sums. High detection frequencies (81% of samples) and concentrations (max 1.2 μg L−1) were observed for metazachlor transformation products. Contamination from multiple pesticides was detected with up to 25 compounds per sample and a maximum of 37 compounds per LSWB during the entire sampling period. High toxicities for algae and macrophytes were recorded using toxic units (TU) of −0.2 to −3.5. TUs for invertebrates were generally lower than for algae/macrophytes (−2.7 to −5.2) but were also recorded at levels with ecological impacts. Pesticide detections were separated into four categories to assign them to different temporal and spatial origins. Pesticides from the spring (5–11%) and the previous autumn (0–36%) application periods were detected in the LSWB. Some pesticides could be related to the application of the previous crop on the same field (0–39%), but most of the compounds (44–85%) were not related to the crop management in the last two years on the respective LSWB fields. The relevance of different input pathways is still unknown. Particularly, the effect of long-distance transport needs to be clarified to protect aquatic biota in LSWBs.
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•Five lentic small water bodies were sampled in spring 2018 to assess their pesticide exposure.•Up to 25 compounds/sample and 35 compounds/site during the sampling period were observed.•TUmax/TUsum indicate ecological impacts for algae and macrophytes.•Most findings (44–85%) were not related to the crop management of the previous 2 years.
The protection of the globally widespread lentic small water bodies (LSWB) must be based on detailed knowledge about their hydrological connectivity and water balance. The study aimed to identify and ...quantify water balance components as well as surface‐groundwater interaction of two LSWB in a characteristic lowland region with a combination of different methods. This includes the collection of hydrological data and the use of bromide and water stable isotopes (δ2H and δ18O) as tracers. With their help, mixing models were established, and daily water balances were assessed. The results show a strong bidirectional interaction of both LSWB systems with shallow groundwater. Bromide and stable isotope tracers allowed for the identification of the most relevant in‐ and outflow sources and pathways. Thereby, isotope data revealed isotopic enrichment typical for open‐water bodies and only minor precipitation inputs mainly relevant at the end of the dry season. Water balance calculations suggested accentuated seasonal dynamics that were strongly influenced by shallow groundwater, which represented large inputs into both LSWB. By that, different phases could be identified, with high inflow rates in winter and spring and decreasing fluxes in summer. In one LSWB, a drainage system was found to have a major impact next to the shallow groundwater interaction. The findings of this research provide detailed insights into the influence and importance of shallow groundwater for LSWB in lowland regions. This impacts the diffuse input of agricultural pollutants into these ecologically important landscape features.
The study provides a detailed insight into the hydrology of lentic small water bodies (LSWB) by combining different methods. The multi‐method approach allowed various inflow and outflow pathways of the LSWB to be identified and quantified. The high‐resolution results indicate strong bidirectional interaction with shallow groundwater, show groundwater origins and highlight the high seasonal dynamic of LSWB.
This study aims to assess the environmental fate of the commonly used herbicides flufenacet and metazachlor in the Northern German Lowlands with the ecohydrological Soil and Water Assessment Tool ...(SWAT model) and to test the sensitivity of pesticide‐related input parameters on the modeled transport dynamics. The river discharge of the Kielstau watershed was calibrated (Nash‐Sutcliffe efficiency NSE, 0.83; r2 = 0.84) and validated (NSE, 0.76; r2 = 0.77) for a daily time step. The environmental fate of metazachlor (NSE, 0.68; r2 = 0.62) and flufenacet (NSE, 0.13; r2 = 0.51) was simulated adequately. In comparison to metazachlor, the simulated flufenacet concentration and loads show a lower model efficiency due to the weaker simulation of the stream flow. The in‐stream herbicide loads were less than 0.01% of the applied amount in the observed time period and thus not in conflict with European Environmental Legislation. The sensitivity analysis showed that, besides the accurate simulation of stream flow, the parameterization of the temporal and spatial distribution of the herbicide application throughout the watershed is the key factor for appropriate modeling results, whereas the physicochemical properties of the pesticides play a minor role in the modeling process.
Caption: Pesticides in a tile drained landscape.
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•hydrological conditions are key factor for total drainage loads.•wet weather conditions lead to 10-fold increase in drainage ...loss.•timing and frequency of pesticide peaks are controlled by sorption properties.•leaching of flufenacet is not only controlled by high amounts of precipitation.•highest loss of pendimethalin and diflufenican during high discharges in winter.
The input of harmful substances into surface waters are of major concern since their side effects may negatively affect the chemical state of surface waters. This study investigated the drainage loss of pesticides into surface waters in a small agricultural catchment in Northern Germany. The pesticides flufenacet, diflufenican, and pendimethalin were monitored at a daily resolution for 154 days in 2016 (dry period) and 111 days in 2017 (wet period) for two consecutive years at both field- (10 ha) and catchment-scale (100 ha). Highly contrasting weather conditions led to extremely high differences in loads between both monitoring periods. Regarding both scales and campaigns, flufenacet was released often in considerably higher amounts and faster than diflufenican and pendimethalin. The very mobile pesticide, flufenacet, is not exclusively leached during high precipitation events but also continuously discharged from soils to the drainage system during low precipitation. Pendimethalin had the lowest recovery rate in comparison to its application amount and showed a lower total loss rate than the less sorptive pesticide diflufenican. Pendimethalin and diflufenican showed high retarded loads caused by increased drainage discharge and sediment transport during late winter induced by freezing and thawing processes in the upper soil. Hence, leaching of the pesticides was controlled by the sorption properties of the investigated compounds and, to a large extent, by hydrological boundary conditions, which were highly variable from an (inter-) annual perspective. Our study identified antecedent and prevailing precipitation and soil moisture conditions as the key impact of pesticide leaching to the drainage system in the long-term.
The research of the environmental fate of pesticides has demonstrated that applied compounds are altered in their molecular structure over time and are distributed within the environment. To assess ...the risk for contamination by transformation products (TP) of the herbicides flufenacet and metazachlor, the following four water body types were sampled in a small-scale catchment of 50 km
2
in 2015/2016: tile drainage water, stream water, shallow groundwater, and drinking water of private wells. The TP were omnipresent in every type of water body, more frequently and in concentrations up to 10 times higher than their parent compounds. Especially metazachlor sulfonic acid, metazachlor oxalic acid, and flufenacet oxalic acid were detected in almost every drainage and stream sample. The transformation process leads to more mobile and more persistent molecules resulting in higher detection frequencies and concentrations, which can even occur a year or more after the application of the parent compound. The vulnerability of shallow groundwater and private drinking water wells to leaching compounds is proved by numerous positives of metazachlor-TP with maximum concentrations of 0.7 μg L
−1
(drinking water) and 20 μg L
−1
(shallow groundwater) of metazachlor sulfonic acid. Rainfall events during the application period cause high discharge of the parent compound and lower release of TP. Later rainfall events lead to high displacement of TP. For an integrated risk assessment of water bodies, the environmental behavior of pesticide-TP has to be included into regular state-of-the-art water quality monitoring.
Lentic small water bodies have a high ecological potential as they fulfill several ecosystem services such as the retention of water and pollutants. They serve as a hot spot of biodiversity. Due to ...their location in or adjacent to agricultural fields, they can be influenced by inputs of pesticides and their transformation products. Since small water bodies have rarely been part of monitorings/campaigns up to now, their current exposure and processes guiding the pesticide input are not understood, yet. This study presents results of a sampling campaign of 10 lentic small water bodies from 2015 to 2016. They were sampled once after the spring application for a pesticide target screening, before autumn application and three times after rainfall events following the application. The autumn sampling focused on the herbicides metazachlor, flufenacet and their transformation products - oxalic acid and - sulfonic acid as representatives for common pesticides in the study region. The concentrations were associated with rainfall before and after application, characteristics of the site and the water bodies, physicochemical parameters and the applied amount of pesticides. The key results of the pesticide screening in spring indicate positive detections of pesticides which have not been applied for years to the single fields. The autumn sampling showed frequent occurrences of the transformation products, which are formed in soil, from 39% to 94% of all samples (n=71). Discharge patterns were observed for metazachlor with highest concentrations in the first sample after application and then decreasing, but not for flufenacet. The concentrations of the transformation products increased over time and revealed highest values mainly in the last sample. Besides rainfall patterns right after application, the spatial and temporal dissemination of the pesticides to the water bodies seems to play a major role to understand the exposure of lentic small water bodies.
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•Transformation products of applied in the previous year were clearly detected in the following year.•Parent compounds were measured in the year of application only.•Consistent concentration patterns were observed for metazachlor and for the transformation products but not for flufenacet.•Positives of a pesticide probably present a snapshot, they may originate from former applications at larger distance.•Subsurface inputs are a crucial entry path for pesticides into lentic small water bodies and are not well understood, yet.
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