Effects of the herbicides metazachlor and flufenacet on phytoplankton communities - A microcosm assay.

Agrochemicals are the main pollutants in freshwater ecosystems. Metazachlor and flufenacet are two common herbicides applied in fall (i.e., August-October) to agricultural fields in Northern Germany. High concentrations of these herbicides are often found in adjacent aquatic ecosystems. Phytoplankton are one of the highly susceptible non-targeted aquatic organismal groups for herbicides and effects on phytoplankton may initiate a chain of consequences in meta communities through trophic interactions. Few studies have focused on responses of the phytoplankton community for metazachlor and, no studies have focused on flufenacet. We studied the effects of metazachlor and flufenacet on the phytoplankton community by conducting a microcosm experiment exposing natural fall phytoplankton communities to environmentally realistic concentrations as 0 (control), 0.5, 5 and 50 µg L-1 of metazachlor and flufenacet treatments over a 4-week period. We measured changes in density, composition (i.e., in phyla and species level), taxonomic diversity indices, and functional features of phytoplankton communities as a response to herbicides. A reduction in the density of Chlorophyta species (e.g., Koliella longiseta, Selenastrum bibraianum) and Cyanobacteria species (e.g., Merismopedia tenuissima and Aphanocapsa elegans) was observed in herbicide treatments compared to controls. The phytoplankton community shifted towards a high density of species from Bacillariophyta (e.g., Nitzschia fonticola and Cyclotella meneghiniana), Miozoa (i.e., Peridinium willei), and Euglenozoa (i.e., Trachelomonas volvocina) in herbicide treatments compared to controls. Metazachlor and flufenacet showed significant negative effects on taxonomic diversity indices (e.g., species richness, the Shannon-Wiener index) and functional features (e.g., functional dispersion and redundancy) of the phytoplankton communities, with increasing herbicide concentrations. Our study provides insights into direct, selective, and irrecoverable effects of metazachlor and flufenacet on phytoplankton communities in the short-term. The comprehensive understanding of these effects of environmentally realistic herbicide concentrations on aquatic biota is essential for a sustainable management of aquatic ecosystems in agricultural areas.

Chromosomal and Nuclear Alterations in the Root Tip Cells of Vicia faba Induced by Sodium Chloride.

Despite the well-known toxic effect of chloride sodium (NaCl), only few studies analyze its genotoxic effect on crops. Micronucleus assay is an efficient tool for the measure of chromosomal DNA damages. Based on this test, the effects of salt on micronucleus induction, and on chromosome and nucleus changes, were investigated in Vicia faba root tips treated with NaCl (electrical conductivity = 25 dS/m) during 24 hours. V. faba meristematic cells showed a significant increase in the number of micronuclei compared with the control. Micronucleus size varied from small to large and appeared at different stages of mitosis. Moreover, different chromosomal aberrations like breaks, bridges, rings, vagrant, and lagging chromosomes, were observed in the metaphase, the anaphase, and the telophase. In addition, nuclear alterations in the interphase were characterized by the presence of binucleated cells, strap nuclei with lesions, hyperchromasia, buds, and nuclei with irregular shapes and lesions.

Simulation of streamflow and sediment with the soil and water assessment tool in a data scarce catchment in the three gorges region, china.

The Three Gorges Region in China is currently subject to a large-scale land use change, which was induced by the construction of the Three Gorges Dam on the Yangtze River. The relocation of towns, villages, and agricultural areas is expected to affect the water balance and increase erosion rates and sediment yields in the affected catchments. Hydrologic and water quality models are frequently used to assess the impact of land use changes on water resources. In this study, the eco-hydrological Soil and Water Assessment Tool (SWAT) model is applied to the Xiangxi Catchment in the Three Gorges Region. This paper presents the calibration and validation of streamflow and sediment loads at Xingshan gauging station. The calibration of daily streamflow resulted in a satisfactory fit of simulated and observed data, which is indicated by Nash-Sutcliffe efficiency (NSE) values of 0.69 and 0.67 for the calibration (1981-1986) and validation (1988-1993) periods, respectively. In contrast, the model was not able to simulate the monthly average sediment loads correctly, as indicated by very low NSE values of 0.47 (calibration) and 0.08 (validation). This might be due to inadequate representation of spatial rainfall variability by the available climate stations, insufficient input data, uncertainties in the model structure, or uncertainties in the observed sediment loads. The discussion of these possible reasons for the incorrect prediction of sediment loads by SWAT reveals the need for further research in the field of hydrological and water quality modeling in China.

Examining characteristics and sampling methods of phosphor dynamics in lowland catchments.

Despite over two decades since the EU Water Framework Directive have passed, achieving the desired water quality in German surface waters remains challenging, regardless of efforts to reduce phosphorus inputs and associated environmental impacts. This study aims at analyzing the characteristics governing the concentrations of four key water quality parameters (total phosphorus, orthophosphate, particulate phosphate, and suspended solids) in two lowland catchments: the 50 km2 catchment of the Kielstau, Germany, and its 7 km2 tributary, the Moorau, which are dominated by agricultural land use. To this end, different sampling methods, particularly high-resolution precipitation event-based sampling and daily mixed samples, are conducted and evaluated, and their effectiveness is compared. The identification of sources and characteristics that affect phosphorus and suspended sediment dynamics, both in general and specifically during heavy precipitation events, is one focus of the study. Over a 15-year period, increasing concentrations of these parameters were observed in daily mixed samples, exhibiting distinct seasonal patterns-higher in summer and lower in winter-consistent with lowland catchment behavior. Particularly during heavy precipitation events, the smaller catchment exhibits a more complex and less predictable response to chemical concentrations compared with the dilution effect observed in the larger catchment. The results underline the complexity of phosphorus dynamics in small catchments and emphasize the importance of event-based sampling for capturing short-term concentration peaks for all four parameters, particularly beneficial regarding measuring suspended solids. While daily mixed samples capture average phosphorus concentrations, event-based sampling is crucial for detecting short-term spikes, providing a more comprehensive understanding of phosphorus dynamics.

Assessment of seasonal and spatial water quality variation in a cascading lake system in Chennai, India.

Water quality and scarcity are among the most severe problems humans have been facing in the last decades. India, as a fast-developing country, is not an exception. The surface water quality has deteriorated due to anthropogenic activities. Another factor which impacts the water quality is the heavy rainfall during monsoon season. To maintain the quality and the sustainability of water resources, there is the need to study how human activities impact water quality. We hypothesized that the water quality can be impacted by the spatial land use types and by the seasonality. In the present study, seasonal and spatial water quality regarding physical, chemical, and biological parameters from a lake cascading system was assessed monthly from July to December 2019. Land use/cover data was produced by Impact Observatory, Microsoft, and Esri based on the 10-m Sentinel-2 images. Redundancy analysis was applied to investigate the relationship between land use/cover data and water quality in the riparian of 500 and 1000 m to the lakes. Our results showed clear temporal and spatial variation of water quality in 2019, with better water quality in rainy season (Oct.-Dec.) and downstream lakes while relatively worse water quality was recorded in dry season (Jul.-Sep.) and upstream lakes. The water quality variation was explained 27.8 % and 42.7 % by the land use types within 500 m and 1000 m buffer widths, respectively. The outlet of the catchment showed exceptional results due to the impact of a dumpsite. Our findings indicate that the water quality is highly impacted by human-induced land use/cover. The land use/cover types, such as crops, woodland and urban area, show negative impacts and relate to the high level of nutrient concentrations. In opposite, grass land shows positive effects and leads to better water quality. Our study confirms that the lake water quality is distinguished in both spatial and seasonal aspects. Monsoon season improves the water quality.

Effects of sampling strategy in rivers on load estimation for Nitrate-Nitrogen and total Phosphorus in a lowland agricultural area.

The transport of nutrients into water bodies is one of the main causes of water eutrophication. It is therefore important to estimate the loads of nutrients. Discharge and nutrient concentrations are the fundamental elements to estimate the loads of nutrients, the latter can be affected by sampling strategies. As conducting sampling campaign and laboratory analysis are both expensive, it is necessary to find the best effective sampling strategy. The aim of this paper is to show how autocorrelation and standard statistical methods can be used to test the effects of different sampling strategies on the nutrient load estimation and to find the optimal sampling strategy. The data set in this study is from the 50 km² Kielstau catchment, a UNESCO demo site for ecohydrology in Northern Germany and consists of 14 years daily values of climate, hydrology, and water quality from 2006 to 2019. We calculated the autocorrelation (AC) of discharge (Q), precipitation, Nitrate-Nitrogen (NO3-N) and total Phosphorus (Ptot). Then we tested the effects of sampling intervals from 7 to 56 days (1-8 weeks) on the nutrient loads. Our results showed a high AC of Q and NO3-N for a long period, but the AC of Ptot and precipitation decreased very fast. An increase of the sampling interval (less frequent) increased the error of estimating the concentrations and loads. Consequently, we recommend that (1) the optimal sampling strategy for nutrient load estimation in an agriculture-dominant catchment should be continuously monitoring discharge combined with periodic grabbed samples; (2) the sampling frequency for NO3-N is suggested to be monthly (every 28 days) and for Ptot weekly (every 7 days). The information will help those tasked with catchment monitoring to design appropriate sampling strategy to ensure adequate data for nutrients load estimation in lowland rivers.

Using integrated models to analyze and predict the variance of diatom community composition in an agricultural area.

With the growing demand of assessing the ecological status, there is the need to fully understand the relationship between the planktic diversity and the environmental factors. Species richness and Shannon index have been widely used to describe the biodiversity of a community. Besides, we introduced the first ordination value from non-metric multidimensional scaling (NMDS) as a new index to represent the community similarity variance. In this study, we hypothesized that the variation of diatom community in rivers in an agricultural area was influenced by hydro-chemical variables. We collected daily mixed water samples using ISCO auto water samplers for diatoms and for water-chemistry analysis at the outlet of a lowland river for a consecutive year. An integrated modeling was adopted including random forest (RF) to decide the importance of the environmental factors influencing diatoms, generalized linear models (GLMs) combined with 10-folder cross validation to analyze and predict the diatom variation. The hierarchical analysis highlighted antecedent precipitation index (API) as the controlling hydrological variable while water temperature, Si2+ and PO4-P as the main chemical controlling factors in our study area. The generalized linear models performed better prediction for Shannon index (R2 = 0.44) and NMDS (R2 = 0.51) than diatom abundance (R2 = 0.25) and species richness (R2 = 0.25). Our findings confirmed that Shannon index and the NMDS as an index showed good performance in explaining the relationship between stream biota and its environmental factors and in predicting the diatom community development based on the hydro-chemical predictors. Our study showed and highlighted the important hydro-chemical factors in the agricultural rivers, which could contribute to the further understanding of predicting diatom community development and could be implemented in the future water management protocol.

Multiple pesticides in lentic small water bodies: Exposure, ecotoxicological risk, and contamination origin.

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.

Salinity decreases cadmium accumulation in Vicia faba.

The study investigates the effect of cadmium (Cd), salinity (NaCl), and combined stress on rhizosphere pH, growth parameters, membrane leakage, and genotoxicity in Vicia faba. Germinated seeds were exposed for 48 h to 0.01 mM Cd(NO3)2 (Cd), 50 mM NaCl (S50), 150 mM NaCl (S150), and Cd-NaCl (CdS50 and CdS150). An accumulation of Cd and Na was found essentially in Vicia roots under each single stress factor associated with variations in rhizosphere pH. Additional NaCl in metallic solution significantly dropped the rhizosphere pH and decreased Cd concentrations in roots by 2.3 and 3.8 times for CdS50 and CdS150, respectively. Growth parameters (root length and fresh and dry matters), mitotic activity, and micronucleus formation were not influenced by Cd and low concentration of NaCl when applied separately or together, while 150 mM of NaCl, alone or combined with Cd, affected negatively all the studied parameters, as well as chromosome and nucleus stability. V. faba seems to reduce the transport of Cd in saline conditions and therefore salinity (50 mM) may act as a protection against Cd accumulation.

Lentic small water bodies: Variability of pesticide transport and transformation patterns.

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.

Dynamic water quality evaluation based on fuzzy matter-element model and functional data analysis, a case study in Poyang Lake.

Comprehensively evaluating water quality with a single method alone is challenging because water quality evaluation involves complex, uncertain, and fuzzy processes. Moreover, water quality evaluation is limited by finite water quality monitoring that can only represent water quality conditions at certain time points. Thus, the present study proposed a dynamic fuzzy matter-element model (D-FME) to comprehensively and continuously evaluate water quality status. D-FME was first constructed by introducing functional data analysis (FDA) theory into a fuzzy matter-element model and then validated using monthly water quality data for the Poyang Lake outlet (Hukou) from 2011 to 2012. Results showed that the finite water quality indicators were represented as dynamic functional curves despite missing values and irregular sampling time. The water quality rank feature curve was integrated by the D-FME model and revealed comprehensive and continuous variations in water quality. The water quality in Hukou showed remarkable seasonal variations, with the best water quality in summer and worst water quality in winter. These trends were significantly correlated with water level fluctuations (R = -0.71, p < 0.01). Moreover, the extension weight curves of key indicators indicated that total nitrogen and total phosphorus were the most important pollutants that influence the water quality of the Poyang Lake outlet. The proposed D-FME model can obtain scientific and intuitive results. Moreover, the D-FME model is not restricted to water quality evaluation and can be readily applied to other areas with similar problems.