Selection of aquatic microbiota exposed to the herbicides flufenacet and metazachlor.

Herbicides are important, ubiquitous environmental contaminants, but little is known about their interaction with bacterial aquatic communities. Here, we sampled a protected natural freshwater habitat and characterised its microbiome in interaction with herbicides. We evolved the freshwater microbiomes in a microcosm assay of exposure (28 days) to flufenacet and metazachlor at environmental concentrations of 0.5, 5 and 50 µg L-1 . Inhibitory effects of herbicides were exemplarily assessed in cultured bacteria from the same pond (Pseudomonas alcaligenes, Paenibacillus amylolyticus and Microbacterium hominis). Findings were compared to long-term concentrations as provided by local authorities. Here, environmental concentrations reached up to 11 µg L-1 (flufenacet) and 76 µg L-1 (metazachlor). Bacteria were inhibited at minimum inhibitory concentrations far above these values; however, concentrations of 50 µg L-1 of flufenacet resulted in measurable growth impairment. While most herbicide-exposed microcosm assays did not differ from controls, Acidobacteria were selected at high environmental concentrations of herbicides. Alpha-diversity (e.g., taxonomic richness on phylum level) was reduced when aquatic microbiomes were exposed to 50 µg metazachlor or flufenacet. One environmental strain of P. alcaligenes showed resistance to high concentrations of flufenacet (50 g L-1 ). In total, this study reveals that ecologic imbalance due to herbicide use significantly impacts aquatic microbiomes.

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.

Two hundred years of zooplankton vertical migration research.

Vertical migration is a geographically and taxonomically widespread behaviour among zooplankton that spans across diel and seasonal timescales. The shorter-term diel vertical migration (DVM) has a periodicity of up to 1 day and was first described by the French naturalist Georges Cuvier in 1817. In 1888, the German marine biologist Carl Chun described the longer-term seasonal vertical migration (SVM), which has a periodicity of ca. 1 year. The proximate control and adaptive significance of DVM have been extensively studied and are well understood. DVM is generally a behaviour controlled by ambient irradiance, which allows herbivorous zooplankton to feed in food-rich shallower waters during the night when light-dependent (visual) predation risk is minimal and take refuge in deeper, darker waters during daytime. However, DVMs of herbivorous zooplankton are followed by their predators, producing complex predator-prey patterns that may be traced across multiple trophic levels. In contrast to DVM, SVM research is relatively young and its causes and consequences are less well understood. During periods of seasonal environmental deterioration, SVM allows zooplankton to evacuate shallower waters seasonally and take refuge in deeper waters often in a state of dormancy. Both DVM and SVM play a significant role in the vertical transport of organic carbon to deeper waters (biological carbon sequestration), and hence in the buffering of global climate change. Although many animal migrations are expected to change under future climate scenarios, little is known about the potential implications of global climate change on zooplankton vertical migrations and its impact on the biological carbon sequestration process. Further, the combined influence of DVM and SVM in determining zooplankton fitness and maintenance of their horizontal (geographic) distributions is not well understood. The contrasting spatial (deep versus shallow) and temporal (diel versus seasonal) scales over which these two migrations occur lead to challenges in studying them at higher spatial, temporal and biological resolution and coverage. Extending the largely population-based vertical migration knowledge base to individual-based studies will be an important way forward. While tracking individual zooplankton in their natural habitats remains a major challenge, conducting trophic-scale, high-resolution, year-round studies that utilise emerging field sampling and observation techniques, molecular genetic tools and computational hardware and software will be the best solution to improve our understanding of zooplankton vertical migrations.

Influences of pesticides, nutrients, and local environmental variables on phytoplankton communities in lentic small water bodies in a German lowland agricultural area.

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.