Plastic debris in lakes and reservoirs.

Plastic debris is thought to be widespread in freshwater ecosystems globally1. However, a lack of comprehensive and comparable data makes rigorous assessment of its distribution challenging2,3. Here we present a standardized cross-national survey that assesses the abundance and type of plastic debris (>250 µm) in freshwater ecosystems. We sample surface waters of 38 lakes and reservoirs, distributed across gradients of geographical position and limnological attributes, with the aim to identify factors associated with an increased observation of plastics. We find plastic debris in all studied lakes and reservoirs, suggesting that these ecosystems play a key role in the plastic-pollution cycle. Our results indicate that two types of lakes are particularly vulnerable to plastic contamination: lakes and reservoirs in densely populated and urbanized areas and large lakes and reservoirs with elevated deposition areas, long water-retention times and high levels of anthropogenic influence. Plastic concentrations vary widely among lakes; in the most polluted, concentrations reach or even exceed those reported in the subtropical oceanic gyres, marine areas collecting large amounts of debris4. Our findings highlight the importance of including lakes and reservoirs when addressing plastic pollution, in the context of pollution management and for the continued provision of lake ecosystem services.

Characterizing and Implementing the Hamamatsu C12880MA Mini-Spectrometer for Near-Surface Reflectance Measurements of Inland Waters.

In recent decades, inland water remote sensing has seen growing interest and very strong development. This includes improved spatial resolution, increased revisiting times, advanced multispectral sensors and recently even hyperspectral sensors. However, inland waters are more challenging than oceanic waters due to their higher complexity of optically active constituents and stronger adjacency effects due to their small size and nearby vegetation and built structures. Thus, bio-optical modeling of inland waters requires higher ground-truthing efforts. Large-scale ground-based sensor networks that are robust, self-sufficient, non-maintenance-intensive and low-cost could assist this otherwise labor-intensive task. Furthermore, most existing sensor systems are rather expensive, precluding their employability. Recently, low-cost mini-spectrometers have become widely available, which could potentially solve this issue. In this study, we analyze the characteristics of such a mini-spectrometer, the Hamamatsu C12880MA, and test it regarding its application in measuring water-leaving radiance near the surface. Overall, the measurements performed in the laboratory and in the field show that the system is very suitable for the targeted application.

Structure Elucidation of the First Sex-Inducing Pheromone of a Diatom.

Diatoms are abundant unicellular microalgae, responsible for ≈20 % of global photosynthetic CO2 fixation. Nevertheless, we know little about fundamental aspects of their biology, such as their sexual reproduction. Pheromone-mediated chemical communication is crucial for successful mating. An attraction pheromone was identified in the diatom Seminavis robusta, but metabolites priming cells for sex and synchronizing search and mating behavior remained elusive. These sex-inducing pheromones (SIP) induce cell cycle arrest and trigger the production of the attraction pheromone. Here we describe the challenging structure elucidation of an S. robusta SIP. Guided by metabolomics, a candidate metabolite was identified and elucidated by labeling experiments, NMR, ESI MSn analyses, and chemical transformations. The use of negative ion mode MS was essential to decipher the unprecedented hydroxyproline and ß-sulfated aspartate-containing cyclic heptapeptide that acts in femtomolar concentrations.