Size Classes Research Articles

Lessons learned during a 12-year monitoring project with the endangered Magdalena River turtle (Podocnemis lewyana): hunting pressure, habitat degradation, and methodological considerations

Turtle species in the Family Podocnemididae, including the Colombian endemic and critically endangered Magdalena River Turtle Podocnemis lewyana, characteristically present low recapture rates that preclude estimation of population parameters using maximum likelihood modeling. In our 12-year monitoring project with this species, we evaluated changes in relative abundances, proportions of sex/size classes, and individual body sizes and body conditions in a population in four channels in the middle Magdalena River drainage. We also inspected for associations between trends in changes in these variables and differences in hunting pressure and habitat degradation. To inspect for temporal and spatial demographic dynamics, we estimated variation in relative abundances using the Catch Per Unit Effort index, the total number of turtles captured over an entire 5-day sampling period using ten baited funnel traps. Relative abundances and the proportions of sex/size classes were different between sites and years. We found a significant decline in the proportion of females and juveniles over time, along with evidence that the females still present were smaller in body size. Our results support the hypothesis that hunting eliminates adult females from these sites, perhaps also translating into a reduction in recruitment. The lack of evidence of generalized declines in body condition of all size classes suggests that habitat degradation might contribute less to the population declines in this region. Our results also illustrate that even when recapture rates are low, monitoring turtles via standardized trapping may yield insights into the population’s conservation status that other relative abundance indices cannot.

Assimilating Size Diversity: Population Balance Equations Applied to the Modeling of Microplastic Transport.

Modeling of microplastic (MP) transport in the aquatic environment is complicated by the diverse properties of the plastic particles. Traditional modeling methods such as Lagrangian particle tracking and Eulerian discrete class (DC) methods have limitations as they are not best placed to account for the diverse characteristics of individual particles, namely, size, density, and shape, which are crucial for determining the transport of MPs. In this work, we address the issue of particle size diversity by using the population balance equations (PBE) method. In addition to the advection-diffusion terms, the PBE transport equation involves a deposition sink term. Seven size classes of MPs are modeled in the DC method, which is compared to the PBE method. The evolution of particle size distribution is compared between the two methods using a simplified test case of a schematized estuary with tidal forcing and river discharge. This work successfully demonstrates the applicability and appropriateness of the PBE model in modeling the transport of MPs to track the dynamic and complete size distribution at a reduced computational cost in comparison to the DC model. With the PBE method, it is possible to address other diversities of the MPs such as the shape and density.

Microfiber pollution: Assessment, emission estimation, and time-series-based forecast of microfibers from domestic washing machine laundering and mitigation measures.

Microfibers are thread-like structures shorter than 5 mm and have natural, semisynthetic, or synthetic origins. These micropollutants are ubiquitous and are emerging in the environment, living organisms, and food sources. Textile laundering is a prominent source of microfibers, but limited research has been conducted on microfiber pollution from domestic washing machines in emerging economies such as India, where consumption and production rates are exorbitantly high. This study aimed to assess the abundance and size distribution of microfibers from the effluent of a semiautomatic domestic washing machine using three categories of "not-new" textiles: cotton, blended, and synthetic under "with" and "without" detergent conditions. Although most Indians still rely on hand washing, this study focused on washing machines due to their increasing use in India driven by improving socioeconomic factors. This study also developed annual emission estimation and forecasting models for India to understand pollution trends. The results revealed that microfibers were highly abundant in washing machine effluent, with a mean abundance of cotton, blended, and synthetic in "with detergent" conditions of 6476.67, 3766.67, and 8645/L, respectively, whereas in "without detergent," it was lower. All identified microfibers were divided into five size classes. The study also found that powdered detergent increased the abundance and emission of tiny fibers. The overall annual emissions estimate was 1.23 × 1011 microfibers, with cotton, synthetic, and blended categories accounting for 2.11 × 1010, 1.40 × 1010, and 6.15 × 109 microfibers, respectively. Time-series-based future estimates (autoregressive integrated moving average [ARIMA] and error-trend-seasonality [ETS]) showed an alarming increase in microfiber emissions, with forecasted annual emission reaching 1.90 × 1011 by 2030. Synthetic and cotton textiles are the most significant contributors to microfiber pollution. This study emphasized the urgent need to address the issue of microfiber pollution caused by washing machine laundering in developing countries, such as India, where sociodemographic factors intensify the problem. Integr Environ Assess Manag 2024;20:2116-2127. © 2024 SETAC.

Diet, feeding, and niche overlap of west coast steenbras (Lithognathus aureti) and silver kob (Argyrosomus inodorus) in the northern Benguela.

In this study, we described and compared the diet, monthly feeding intensity, and condition of west coast steenbras (Lithognathus aureti) and silver kob (Argyrosomus inodorus) caught at a unique habitat in the northern Benguela. Stomach contents of 179 west coast steenbras and 114 silver kob caught from October 2020 to September 2022 were investigated. The peak in feeding intensity of west coast steenbras appeared to be opportunistic during winter and summer periods depending on food availability. The fish condition, however, peaked at the beginning (October) and at the end (April) of the austral summer spawning period, with the hepatosomatic index (HSI) at 1.5% and the condition factor (CF) at 0.022%. Seven prey taxa were found in the diet of west coast steenbras (bivalves, bony fishes, other mollusks, algae, crustaceans, cnidaria, and polychaetas) and six taxa in the diet of silver kob (bivalves, crustaceans, bony fishes, algae, starfish, and zooplankton), indicating generalist feeding behavior in both the species. The bivalves were the most important prey items in the diet of west coast steenbras (95.9% index of relative importance [IRI]). The most important prey items in the diet of silver kob were crustaceans (83.1% IRI) and bony fishes (16.0% IRI). Crustaceans were most important in the diet of small-to-medium-sized silver kob, whereas bony fishes were most important in the diet of larger silver kob(>75 cm), with significant differences of IRI% by size class. Schoener's index of niche overlap indicated a relatively low overall niche overlap (0.11) between west coast steenbras and silver kob. This allows them to coexist as their feeding habits allow them to occupy unique niches in the coastal reef and sandy habitat and reduce competition for resources.

Heterarchical modelling of comminution for rotary mills: part II—particle crushing with segregation and mixing

In granular media, the crushing of individual particles is influenced by the number of contacts with neighbouring particles. This well-known phenomenon of “cushioning” shields the individual particles from crushing when the number of contacts is high. However, in open systems that involve extensive granular flow and bulk motion, like those found in industrial mills, the neighbouring particles continually exchange positions due to segregation and mixing, thereby altering the number of neighbouring contacts and their sizes, affecting the crushing of individual particles. Therefore, a critical challenge for properly modelling comminution in such systems lies in tracking the fluxes of the various particle size classes. Here, we explore the physics that governs the mechanisms of segregation and mixing within the multiscale heterarchical modelling paradigm. Building upon the framework developed in Part I, which integrated the heterarchical aspects of the physics of crushing along streamlines, we further account for segregation and mixing, and demonstrate their impact on the comminution efficiency of autogenous grinding mills. In particular, segregation is shown to greatly enhance the extent of particle crushing within the mill. Accordingly, we posit that this mechanism cannot be ignored. In summary, the new model sheds light on previously obscured dynamics within industrial mills, as well as enables the field to predict the time evolution of the particle size distribution at any point in the mill domain. This modelling capability opens the doors to new developments for estimating and improving milling efficiencies.Graphical

Impact of Increment Coring on Growth and Mortality across Various Size Classes of Khasi Pine (Pinus kesiya) in Northern Thailand

Impact of Increment Coring on Growth and Mortality across Various Size Classes of Khasi Pine (Pinus kesiya) in Northern Thailand

Diversity, stand and population structure of riparian woody species in two contrasting land use types in the distal Okavango Delta, Northwestern Botswana

AbstractLand use change threatens the integrity of riparian woodland vegetation. The aim of this study was to investigate the diversity and population structure of riparian plant species in protected and communal areas. A total of 71 transects were sampled from each of the protected and communal areas. Total species richness recorded was 36 and 38 in communal and protected areas, respectively. Species diversity was significantly (p < 0.05) higher in the protected than communal areas. Vachellia tortilis (communal areas) and Croton megalobotrys (both areas) showed a reverse J shaped pattern with more individuals in the lower diameter size classes than in the large ones. Dichrostachys cinerea (both areas), Ziziphus mucronata (communal areas), Combretum imberbe (protected areas), C. hereroense (protected areas), Berchemia discolor (protected areas) and Vachellia erioloba (communal areas) showed a reverse-J distribution pattern, but with missing size classes. Philenoptera violacea (protected areas) was characterized by a bell-shaped distribution with more individuals in the middle size classes than in the lower and upper ones while Combretum hereroense, C. imberbe and B. discolor were characterized by irregular population structure in communal areas. Croton megalobotrys, D. cinerea, C. imberbe, C. hereroense, Z. mucronata, B. discolor and S. erubescens had higher Important Value Indices (IVIs) in protected than communal areas. Comparatively, Vachellia tortilis, P. violacea and V. erioloba had higher IVIs in communal than protected areas. We recommended that species with J-shaped population structure and those with only one size class be protected to enable them to attain healthy population structures.

Effect of Grinding and Successive Sieving on the Distribution of Active Biological Compounds in the Obtained Fractions of Blackthorn Berries

The current study evaluated the effect of powder fractionation based on particle size on the chemical composition of macronutrients such as proteins and sugars, on the phytochemical properties (total content of polyphenolic compounds, vitamin C, and antioxidant activity), on preservation capacity (water activity), powder functional properties (water absorption capacity and water solubility index), and physicochemical properties (particle size distribution and moisture content) of blackthorn berry (Prunus spinosa) powders. The fruits were separated from the plant material and seeds, dried, and then ground using an universal mill for dry materials. Eight fractions were obtained after sieving on sieves with different mesh sizes, such as 1 mm, 0.8 mm, 0.630 mm, 0.450 mm, 0.315 mm, 0.200 mm, and 0.125 mm. The grinding/sieving procedure was effective in separating Prunus spinosa powder into sufficiently different size classes. The maximal moisture content and water activity were 5.61% and 0.250, respectively, showed good preservation from a microbiological point of view, and ensured the prevention of oxidation of biologically active compounds of blackthorn berry powders. For samples with reduced particle sizes, the powder functional properties were greatly improved. The total phenolic content, carbohydrates, and antioxidant activity showed significantly different values for some particle size classes compared to the un-sieved sample. A considerable content of vitamin C was presented in the fraction with large particle sizes, precisely because they did not undergo intense degradation processes. Therefore, the technique of grinding and successive sieving proved effective in enhancing the physicochemical and functional characteristics of powdered blackthorn berries, particularly for smaller particles.

Separation of microplastics from deep-sea sediment using an affordable, simple to use, and easily accessible density separation device

Microplastics accumulate in the environment but methods to extract particles from sediment for quantification and identification often lack accuracy and reproducibility. Existing methods vary greatly and many do not achieve adequate microplastic separation. During method development for extraction procedures, spike-recovery experiments (positive controls) are essential to ensure accurate and reproducible results from each sample matrix. Furthermore, the large variability in grain size and organic matter can affect the extraction of microplastics from the matrix. Scientists have used density separation to separate microplastics from matrices for decades, but apparatuses are often made of plastic, need to be custom made, and require multiple sample transfers from one apparatus to another. This study presents an affordable, easily accessible, and simple to use Density Separation Device (DSD) to remove plastics from deep-sea sediments. Eight polymers were spiked into replicates of environmental sediment, including six fragments: high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), nylon (PA6), and crumb rubber (CR) and two fibers: cellulose acetate (CA) and polyester (PEST). Two size classes of polymers were used: 100 μm to 300 μm and > 300 μm. Using a sodium polytungstate solution at a density of 1.9 g/mL and reflectance FTIR microscopy for particle identification, mean recoveries of all fragments exceeded 78% (CR: 92.7% ± 30.8%, PP: 78.4% ± 34.0%, HDPE: 93.8% ± 13.5%, PS: 86.9% ± 25.7%, PA6: 98.4% ± 63.2%, PVC: 100.0% ± 12.4%). Fiber recovery was much lower (PEST: 28.1% ± 28.1% and CA: 25.9% ± 17.3%) because they aggregated, passed through sieves vertically, or were obscured under other particles. The fragment recovery success, accessibility (available online, all parts under $200) and ease of use of this DSD should facilitate widespread use, thus helping to standardize sample preparation methods for microplastic metrology.

Internal friction and flowability of clay powder depend on particle moisture, size and normal stress

This work investigates the impact of changes in the moisture content of bulk materials. The regularity of moisture change in bulk materials was evaluated for three different particle size classes of clay powders. The research measures the angle of internal friction and flowability under four different normal loads, reflecting the varying pressures during bulk material storage. The influence of moisture change in bulk materials was most pronounced for the smallest particle size fraction, where even a very small moisture change in the order of tenths of a percent steeply affected flowability due to internal friction. After increasing the moisture content by a few percent, a steady state of flow occurred. Critical value was determined when water in the bulk material caused liquefaction. For larger particle size fractions, the impact of moisture change was evident only at higher values (12.5%), with no liquefaction occurring even at 30% moisture. The change in normal load, on the other hand, affected particles of larger size fractions, resulting in improved flow properties.

Diet variation and trophic impact of weakfish, Cynoscion regalis, within multiple marine habitats of the eastern United States.

Weakfish (Cynoscion regalis) is not federally managed but feeds on species of management and ecological interest. We examined the trophic ecology of weakfish in Chesapeake Bay and the coastal and offshore waters of the eastern United States. For these areas, we determined the dominant prey of weakfish; identified how much diet variation was explained by the factors: season, size class, and year; and quantified prey biomass removed by weakfish from 2007 to 2019. In general, diet composition was mostly dominated by Engraulidae, Osteichthyes (bony fishes), and Mysidacea, and significantly varied by season and size class in Chesapeake Bay and coastal waters, although this was less dramatic in Chesapeake Bay. The total amount of variance explained by the three factors was 23.1% (Chesapeake Bay) and 14.7% (coastal waters), with year not being a significant factor in explaining weakfish diet variation for these areas. Weakfish total prey biomass removal occurred primarily in coastal waters in the fall and small size class (annual mean: approximately 41,038 t; maximum: approximately 63,793 t). Highly opportunistic feeders, weakfish cannibalism also played an essential part of their diet. These results have implications for fisheries and ecosystem management of weakfish when considering ecological interactions in regulatory approaches, such as recruitment and cannibalism, competition with federally managed fishes, and the natural mortality of their prey.

Prevalence of injuries in a Caiman crocodilus chiapasius (Bocourt 1876) population from the South Pacific coast of Mexico

ABSTRACT Crocodilians injuries are indicators of their health and social interactions. We analyzed the prevalence and distribution of injuries in spectacled caiman (Caiman crocodilus chiapasius) from the Biosphere Reserve of La Encrucijada (BRLE) in relation to the habitat, size, and sex of individuals. We collected data on injuries in caimans captured during nocturnal surveys (2014–2022) in the estuary and swamps of the BRLE. We determined the sex of each caiman, measured their snout–vent length, and registered the type of injury and body region where injuries were detected. From all records, 102 of 301 caimans (33.9%) presented injuries and they were more likely to be injured in the estuary than in the swamps, probably due to the presence of a larger sympatric crocodile species in the estuary (Crocodylus acutus). Sex had no effect on the proportion of injured individuals, but larger caimans have a higher probability of being injured than smaller ones, explained by an ontogenetic change in the individuals’ behaviors. Habitat, sex, and size class of individuals do not influence the number of injuries on different body regions. The tail was the most injured body region (17.6% of individuals), followed by the abdomen (13.0%), back (12.6%), head (9.6%), and extremities (4.0%).

A method for estimating biomass of age-0 fish in case of protracted spawning leading to multiple larval cohorts in the population

We propose a new method for estimating the density and biomass of fish larvae and early juveniles when spawning is extended over time and the egg production in spawning groups varies widely with time. As a proof of concept, the method is applied to catch data for age–0 polar cod (Boreogadus saida), collected by the ichthyoplankton survey in the Kara Sea in 2019. The biomass among different size classes of age–0 fish was calculated based on the selectivity of a Bongo net with 500-μm mesh size. The age of larvae and juveniles in each group and average length at hatch (5.5 mm) were determined used for assessing average growth rate (0.18 mm/day) and hatching date for each age–0 fish assemblage. By fitting the population curve to the samples of age–0 polar cod collected in a small area sequentially over ten days, the instantaneous rate of natural mortality was estimated as ∼ 0.05 day-1. Changes in abundance and biomass over time were modeled by the Baranov's equation and power growth function. The average biomass for the time step of interest was calculated by projecting each cohort abundance to a selected point in time and taking a weighted average of all cohort biomasses.

Microplastics in sea surface waters in the Southern Bight of the North Sea

Microplastic pollution in the marine environment is of concern, with evidence of harmful effects on marine biota and ecosystems. There is still a knowledge gap of the mass of plastics supplied to the ocean and plastics observed in the ocean, indicating a missing sink. Therefore, baseline and monitoring data are needed to inform policy and regulatory measures. The goal of this study was to collect harmonised data of microplastics from the surface of the ocean using the Neuston Microplastic Catamaran. This study shows that the surface water of the coastal ocean in the North Sea holds/sustains high concentrations of microplastic, which exceed previously recorded measurements from the North-East Atlantic and Scottish Waters, indicating that the total stock of plastics might be much higher than previously determined. Microplastics were detected in all samples with concentrations ranging from 857 to 25,462 items km−2. The majority of microplastics analysed were fragments of polyethylene, polypropylene, and polystyrene in the size range of 1,000–5,000 µm. Mesoplastics (>5,000 µm) mainly in the form of filaments were found with concentrations ranging from 0 to 2,139 items km−2, and macroplastics (>5,000 µm) in the form of fragments and filaments were also found with concentrations ranging from 0 to 1,078 items km−2. These fragments and filaments likely originate from the break-up of common macrolitter items in the environment, such as plastic bags, bottles, and fishing gears, which are commonly comprised of similar polymers to those found in the present study. Our findings demonstrate that litters of all size classes are abundant in surface water, highlighting that it is a key compartment for the transport of marine litter and should be monitored to better our understanding of the fate and danger of plastic contamination in our ocean.

Understanding national brand customer erosion: exploring socio-demographic and weight of purchase factors

Purpose The purpose of this study is to explore brand customer erosion at both the category and brand levels while considering consumer socio-demographic characteristics and weight of purchase factors. Design/methodology/approach Data from 3,563 buyers encompassing 20,601 purchases were collected from a prominent household data panel. Findings Brand customer erosion varies depending on socio-demographic factors (householder age, family size, life cycle and social class) and weight of purchase; variations are evident depending on the specific brand. Originality/value The paper makes a substantial contribution to the established fields of marketing and consumer behavior literature by opening a new line of research. It does so by demonstrating, the impact of socio-demographic factors on customer erosion. Simultaneously, it presents results that contradict the limited existing research on the influence of weight of purchase on brand customer erosion.

Microplastics in bulk atmospheric deposition along the coastal region of Victoria Land, Antarctica

The increasing global concern over microplastic pollution has driven a surge in research efforts aimed at detecting microplastics across various ecosystems. Airborne microplastics (MPs) have been identified in remote environments worldwide, including Antarctica. However, data on bulk atmospheric deposition remain scarce. From January to December 2020, atmospheric deposition was directly collected using passive samplers placed in eight sites across Victoria Land. Using Raman Microspectroscopy, MPs were identified in six out of the seven samples collected (one sample was lost due to the extreme weather conditions). The average daily MP deposition for Victoria Land was 1.7 ± 1.1 MPs m−2 d−1, with values ranging from 0.76 to 3.44 MPs m−2 d−1. The majority (53 %) of MPs found in the atmospheric deposition were in the size class of 5–10 μm, and the main shape of MPs was fragments (95 %). The predominant plastic type was polypropylene (31 %), followed by polyethylene (19 %) and polycarbonate (12 %). Polystyrene, polyester, styrene and polyethylene terephthalate each accounted for ~6 %. Microplastics identified in the coastal sites may have local origins, potentially associated with scientific activities at research stations. Conversely, a backward trajectories analysis suggested a potential contribution of atmospheric transport to microplastic deposition at Larsen Glacier and Tourmaline Plateau, the two most remote sites of the study area, where the highest MP concentrations were detected. Our findings present the first evidence of microplastics in the Antarctic atmospheric deposition directly collected via passive samplers, highlighting the need for continued monitoring and research to assess the environmental impact of MPs, particularly in sensitive and remote ecosystems like Antarctica.

Body length determines flow refuging for rainbow trout (Oncorhynchus mykiss) behind wing dams.

Complex hydrodynamics abound in natural streams, yet the selective pressures these impose upon different size classes of fish are not well understood. Attached vortices are produced by relatively large objects that block freestream flow, which fish routinely utilize for flow refuging. To test how flow refuging and the potential harvesting of energy (as seen in Kármán gaiting) vary across size classes in rainbow trout (Oncorhynchus mykiss; fingerling, 8 cm; parr, 14 cm; adult, 22 cm; n=4 per size class), we used a water flume (4100 l; freestream flow at 65 cm s-1) and created vortices using 45deg wing dams of varying size (small, 15 cm; medium, 31 cm; large, 48 cm). We monitored microhabitat selection and swimming kinematics of individual trout and measured the flow field in the wake of wing dams using time-resolved particle image velocimetry (PIV). Trout of each size class preferentially swam in vortices rather than the freestream, but the capacity to flow refuge varied according to the ratio of vortex width to fish length (WV:LF). Consistent refuging behavior was exhibited when WV:LF≥1.5. All size classes exhibited increased wavelength and Strouhal number and decreased tailbeat frequency within vortices compared with freestream, suggesting that swimming in vortices requires less power output. In 17% of the trials, fish preferentially swam in a manner that suggests energy harvesting from the shear layer. Our results can inform efforts toward riparian restoration and fishway design to improve salmonid conservation.

Species assemblages and their drivers differ between trees and lianas in a seasonal evergreen forest in Thailand

AbstractDespite a long tradition in ecology of studying tree species assembly and its potential drivers in tropical forest communities, little information exists with respect to lianas (woody climbers), the second most abundant life form of woody plants in tropical forests. Lianas influence forest diversity and stability and provide critical resources for forest fauna. Using a unique dataset of a 30‐ha plot in Thailand, where tree and liana individuals were fully mapped, we investigated the degree to which local species assemblages of trees and lianas of different size classes (i.e., seedlings, established individuals, and large individuals) are related to local environmental conditions. We asked (1) What are the spatial patterns and environmental drivers of local tree and liana species assemblages? (2) How do such patterns and drivers differ among size classes? (3) Which species associate with these assemblages? Local assemblages of established trees showed substantial structuring by environmental variables, whereas we found only weakly structured assemblages of tree seedlings, large trees, and lianas of all size classes. Our results indicated that the biotic and abiotic drivers of local species assemblages differed strongly between tree and liana communities and across size classes. Species assemblages of trees were mainly driven by soil nutrients, leading to patchy assemblages associated with high base saturation (Alfisols) and assemblages associated with lower levels of base saturation and higher aluminum (Ultisols), whereas tree seedling assemblages were only weakly structured by riparian zones. In contrast, species assemblages of established and large lianas were primarily associated with forest canopy structure, separating low‐canopy forests from high‐canopy forests, whereas soil nutrients were the only factors associated with liana seedling assemblages. The weak environmental structuring of tree seedlings and large trees suggests that other mechanisms, such as stochastic disturbances, competition for space, or animal seed dispersal, may play an important role in structuring tree communities in this seasonal tropical forest. The weak patterns observed in liana communities across all life stages raise questions about the underlying mechanisms of liana community assembly, and further research should focus on liana niches, their dispersal mechanisms, and host tree relations.

Responses of C4 grasses to aridity reflect species‐specific strategies in a semiarid savanna

AbstractThe C4 Poaceae are a diverse group in terms of both evolutionary lineage and biochemistry. There is a distinct pattern in the distribution of C4 grass groups with aridity; however, the mechanistic basis for this distribution is not well understood. Additionally, few studies have investigated the functional strategies of co‐occurring C4 grass species for dealing with aridity in their natural environments. We explored the coordination of leaf‐level gas exchange, water use, and morphology among five co‐occurring semiarid C4 grasses belonging to divergent clades, biochemical subtypes, and size classes at three sites along a natural aridity gradient. More specifically, we measured predawn and midday water potential, stomatal conductance, water use efficiency, and photosynthesis. Leaf tissue was also collected for the analysis of stable isotopes of carbon and oxygen as well as for measurement of specific leaf area (SLA) and leaf width. Species differences in responsiveness of stomata to changes in vapor pressure deficit (VPD) were also assessed. It was expected that NAD‐me species would maintain higher rates of photosynthesis, higher water use efficiency, and have more responsive stomata than other co‐occurring species based on observed biogeographic patterns and past greenhouse studies. We found that Aristidoideae and Chloridoideae NAD‐me‐type grasses had greater stomatal sensitivity to VPD, consistent with a more isohydric strategy. However, midgrasses had both greater apparent water access and water use efficiency, regardless of subtype or lineage. PCK‐type species had less responsive stomata and maintained lower levels of photosynthesis with increasing aridity. There were strong interspecific differences in δ13C, leaf width, and SLA; however, these were not significantly correlated with water use efficiency. C4 grasses in our study did not fit discretely into functional groups as defined by lineage, biochemistry, or size class. Interspecific differences, evolutionary legacy, and biochemical pathway are likely to interact to determine water use and photosynthetic strategies of these plants. Control of water loss via highly responsive stomata may form the basis for dominance of certain C4 grass groups in arid environments. These findings build on our understanding of contrasting strategies of C4 grasses for dealing with aridity in their natural environments.

Small microplastics have much higher mass concentrations than large microplastics at the surface of nine major European rivers.

Understanding the fates and impacts of microplastics requires information on their sizes, polymer types, concentrations, and spatial and temporal distributions. Here, we focused on large (LMPs, 500µm to 5mm) and small (SMPs, 25 to 500µm) microplastics sampled with the exact same protocol in nine of the major European rivers during the seven months of the Tara Microplastic Expedition. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC-MS) analyses were used to determine the microplastics contents by number and mass. The median LMP concentration was 6.7 particles m-3, which was lower than those in other regions of the world (America and Asia). The SMP mass concentration was much higher to the LMP concentrations, with SMP/LMP ratios up to 1000 in some rivers. We did not observe a systematic positive effect of urban areas for the two size classes or polymers; this could be explained by the fact that the transport of microplastic is highly heterogeneous in rivers. We believe that this study has important implications for predictive models of plastics distribution and fate in aquatic environments.