Supporting the development of scientific understanding when constructing an evolving explanation

We explore how students developed an integrated understanding of scientific ideas and how they applied their understandings in new situations. We examine the incremental development of 7th grade students’ scientific ideas across four iterations of a scientific explanation related to a freshwater system. We demonstrate that knowing how to make use of scientific ideas to explain phenomena needs to be learned just as developing integrated understanding of scientific ideas needs to be learned. Students participated in an open-ended, long-term project-based learning unit, constructing one explanation over time to address, “How healthy is our stream for freshwater organisms and how do our actions on land potentially impact the water quality of the stream?” The explanation developed over several weeks as new data were collected and analyzed. Students discussed evidence by revisiting scientific ideas and including new scientific ideas. This research investigates two questions: (1) As students engage in writing a scientific explanation over time, to what extent do they develop integrated understanding of appropriate scientific ideas? and (2) When writing about new evidence, do these earlier experiences of writing explanations enable students to make use of new scientific ideas in more sophisticated ways? In other words, do earlier experiences allow students to know how to make use of their ideas in these new situations? The results indicated statistically significant effects. Through various iterations of the explanation students included richer discussion using appropriate scientific ideas. Students were also able to make better use of new knowledge in new situations.

2-Methylisoborneol (2-MIB) Excretion by Pseudanabaena yagii under Low Temperature

Outbreaks of 2-methylisoborneol (2-MIB) contamination in drinking water sources cause inconvenient odor issues in the water distribution system. In this study, microscopy-based isolation with physiological and molecular phylogenetic characterization were performed to investigate and characterize the 2-MIB odor producers that caused an odor problem in the freshwater system of the North Han River in the autumn of 2018. A benthic cyanobacterium was isolated from 2-MIB odor-issue freshwater samples and was found to be phylogenetically affiliated with Pseudanabaena yagii (99.66% sequence similarity), which was recorded in South Korea for the first time. The 2-MIB synthesis gene sequences from the odor-issue freshwater samples showed 100% similarity with those in the P. yagii strains. Protein sequences of 2-MIB synthase observed in the genome of the isolated strain showed structural and functional characteristics similar to those observed in other Pseudanabaena species. The 2-MIB production rate increased slowly during mat formation on the vessel wall; however, it rapidly increased after the temperature dropped. The 2-MIB gene was continuously expressed regardless of the temperature changes. These results suggest that the 2-MIB odor issue in the North Han River might be caused by the release of 2-MIB from the mat-forming P. yagii species in a low-temperature freshwater environment.

Microplastic Pollution in Urban Lake Phewa, Nepal: The First Report on Abundance and Composition in Surface Water of Lake in Different Seasons

Microplastics are man-made pollutants which have been detected in surface water and groundwater. Research on microplastic concentration in aquatic environment is an emerging field for developing countries. Nepal despite having rich water resources no information regarding microplastic in freshwater system is available. Therefore, this study investigate the presence and abundance of microplastic in lake surface water of Phewa Lake, the second largest lake of the country. A total of 16 sampling locations were selected for surface water sample to cover the area of 5.72 km2. The average concentration of microplastic for surface water was 2.96±1.83 particles/L for winter season and 1.51 ±0.62 particles/L for rainy season. Significance difference in microplastic concentration were observed in two different seasons. Fibers was the commonly found microplastic type in lake water and transparent as the dominant color for the two seasons. Almost all the detected microplastic were found to be <1 mm in size. Polymer identification was not possible due to small size of microplastic and unavailability of advanced technique. Phewa Lake, the heart of Pokhara is an important tourist destination so proper waste disposal plan can only maintain the lake’s beauty from further deterioration.

A Preliminary Study on Microplastic Occurrences in Surface Waters of Ousudu Lake, Pondicherry, India.

Microplastics (MP) in both freshwater and marine ecosystem is the next issue that has been recently the fore. However, freshwaters are the potential source and pathway to transport MPs to the marine environment. There is a lack of understanding about the presence and analysis of MP in the freshwater system in India, one of the leading global plastic producers and consumers responsible for 5.6 million tonnes of waste every year. The present attempt is the first in Ousudu Lake, Puducherry, Tamil Nadu, to study the MPs occurrence and examine its properties in the surface water of the largest lake and an important wetland. The concentration range of MP in Ousudu Lake was 0.0039 particles/m2. Fibre was dominant, homogenous with the size fraction of ≤100µm comprised of total MPs collected in Lake. Raman spectroscopy identified plastics with polyethylene as a homogenous component. This study indicated that the presence of MP in water might influence the environment.

Ostracods, Charophytes, and Pollen from the Baynunah Formation

Ostracods, charophytes and pollen were retrieved from sediments of the Baynunah Formation. Autoecological characteristics of the ostracods and the charophytes, together with detailed observations on the taphonomy of ostracod valves, provide a reconstruction of the depositional environments of the Baynunah freshwater system. These microfossil assemblages indicate the presence of a large floodplain with a slow-flowing river with high suspended sediment load, as well as a system of shallow, possibly isolated, water bodies with clear waters and submerged meadows of macroalgae. The water bodies were characterized by fluctuating salinities that could be linked to phases of evaporation-desiccation and regeneration of the freshwater environment, i.e. alternation of humid and dry periods. Pollen remains indicate associations of herbaceous plants typical of open woodland to grassland habitats, with halophytes growing close to the water bodies.

Joint assimilation of GRACE satellite and in-situ discharge observations into a global hydrological model

&lt;p&gt;Global hydrological models simulate water storages and fluxes of the water cycle which is important for e.g. water management decisions and drought/flood predictions. However, the models include many uncertainties due to the model inputs (e.g. climate forcing data), model parameters, and model structure resulting in disagreements with observations. To reduce these uncertainties, the models are typically calibrated against in-situ discharge observations or GRACE-derived total water storage anomalies (TWSA) are integrated into the model by data assimilation.&lt;/p&gt;&lt;p&gt;In this study, we introduce a framework for jointly assimilating multiple observations into the WaterGAP 2.2d model over the Mississippi River Basin for 2003-2018. We do not only assimilate GRACE-derived TWSA but also in-situ discharge observations from gauge stations. In addition, we vary the number as well as the location of the considered discharge stations to derive information about e.g. the influence of assimilating down- or upstream stations.&lt;/p&gt;&lt;p&gt;Our results show a strong influence of the GRACE data and that the assimilation of multiple discharge stations resembles the results of a traditional calibration approach. We expect the most downstream stations to have a larger impact on the assimilation results than the more upstream stations (as the downstream stations already include the information of the upstream stations). The gained insights of this study show a great potential to better assess and understand the global freshwater system and become even more relevant in view of the Surface Water and Ocean Topography (SWOT) satellite. SWOT will be launched in 2022 and is expected to allow the derivation of discharge observations globally for rivers wider than 50-100m.&lt;/p&gt;