Microbial–organic coupling mediates groundwater ammonium dynamics under seasonal hydrological fluctuations

Microplastics have emerged as pervasive contaminants in freshwater ecosystems, significantly affecting aquatic biodiversity. This chapter explores how microplastics act as seasonal ecological disruptors, with particular emphasis on color and size variations and their differential impacts on zooplankton diversity in river systems. Seasonal fluctuations in hydrology, temperature and nutrient dynamics alter microplastic distribution and bioavailability, thereby influencing zooplankton feeding behavior, reproduction and community composition. Evidence suggests that smaller particles (<100 µm) and visually attractive colors (e.g., blue and red) are preferentially ingested, leading to physiological stress and trophic transfer. The chapter synthesizes current research, identifies knowledge gaps and proposes future directions for ecological risk assessment and management strategies.

Microplastics have emerged as pervasive contaminants in freshwater ecosystems, significantly affecting aquatic biodiversity. This chapter explores how microplastics act as seasonal ecological disruptors, with particular emphasis on color and size variations and their differential impacts on zooplankton diversity in river systems. Seasonal fluctuations in hydrology, temperature and nutrient dynamics alter microplastic distribution and bioavailability, thereby influencing zooplankton feeding behavior, reproduction and community composition. Evidence suggests that smaller particles (<100 µm) and visually attractive colors (e.g., blue and red) are preferentially ingested, leading to physiological stress and trophic transfer. The chapter synthesizes current research, identifies knowledge gaps and proposes future directions for ecological risk assessment and management strategies.

Low‐order boreal streams are particularly sensitive interfaces where dissolved organic matter (DOM) is transported from soils to inland waters. Disentangling the relative influence of key environmental factors suspected to influence stream water DOM composition is highly relevant to predicting the reactivity and fate of terrestrial DOM entering inland waters. Here we examined changes to DOM composition using absorbance and fluorescence, from 17 boreal streams ranging from first to fourth orders, over 14 months, including the rarely studied winter season, and two snowmelt periods (n = 836). We also analyzed soil pore water samples from three forest soil lysimeters to a depth of 70 cm (n = 60). Of five identified fluorescing parallel factor analysis components, two (C4 and C5) expressed a clear mire wetland or forest signature, providing distinct molecular markers of dominant land cover. In fact, land cover alone explained 49% of the variability in DOM composition. In contrast, seasonal fluctuations in hydrology only contributed to minor shifts (8%) in the composition of stream water DOM, while in‐stream transformations to DOM composition were undetectable. These findings suggest that low‐order boreal streams act as a passive pipe, since in‐stream processing of DOM is restricted by short water residence times (6 h to 2 days). In addition, we demonstrated the sensitivity of optical approaches to distinguish between key terrestrial sources of DOM in the boreal landscape. By distinguishing the proportional leverage of key environmental controls on headwater stream DOM composition, we are better equipped to predict where and when key DOM transformations occur in the aquatic conduit.

Seasonally flooded landscape connectivity and implications for fish in the Napo Moist Forest: A high-resolution mapping approach

The reproductive success of the American alligator in the Everglades is constrained primarily by egg mortality, due to flooding by seasonally fluctuating water levels. The timing of nesting is positively correlated with spring air temperatures, and nesting during the summer rainy season places eggs at risk to flooding. Water level at the time of nesting is positively correlated with the elevation at which eggs are deposited above the marsh bottom, which involves nest size, egg placement, and site elevation. Alli- gators respond and to some extent accommodate to higher water levels at the time of nesting. The percent of nests lost to flooding depended on clutch elevation and on the maximum water depth during the incubation period. Clutch elevation frequencies were normally distributed. Regression models permit estimation of the extent of nest flooding over a 30-yr period. Flooding has increased in recent years, coincident with the institution of water management in the southern Everglades. Prior to water manage- ment, the increment of water level rise during the incubation period was predictably correlated with water level at the time of nest construction. This predictability disappeared during the current period of water management, thereby altering the pattern of environmental variation. These results suggest that conser- vation of alligators in the Everglades, and by extension of the Everglades wetland ecosystem, depends on restoration of more predictable hydrological fluctuations. A primary factor regulating tropical and sub- tropical wetlands is the seasonal fluctuation of water depth caused by variation in rainfall and

Floodplain lakes and associated wetlands in tropical dry climates are controlled by pronounced and severe seasonal hydrologic fluctuations. We examined the plant community response to a bimodal flooding pattern in the Zapatosa Floodplain Lake Complex (ZFLC), Northern Colombia. We measured floristic and quantitative change in four sampling periods emphasizing seasonal differences in plant abundance and life-form structure. Of 79 species identified in the lake complex, 52 were used to characterize eight community types via classification and ordination procedures. Results showed that community structure does not change significantly during the flooding/receding stages. But maximum drawdown phase significantly disrupts the aquatic community structure and the exposed shorelines become colonized by ruderal terrestrial plants. Early rainfalls at the beginning of the wet season are emphasized as an important feature of plant regeneration and community development. The general strategy of the ZFLC vegetation can be framed into the flood pulse concept of river-floodplain systems. Thus, plant communities are mainly responding to disturbances and destruction events imposed by extreme water level fluctuations.

Community assembly processes generate shifts in species abundances that influence ecosystem cycling of carbon and nutrients, yet our understanding of assembly remains largely separate from ecosystem-level functioning. Here, we investigate relationships between assembly and changes in microbial metabolism across space and time in hyporheic microbial communities. We pair sampling of two habitat types (i.e., attached and planktonic) through seasonal and sub-hourly hydrologic fluctuation with null modeling and temporally explicit multivariate statistics. We demonstrate that multiple selective pressures—imposed by sediment and porewater physicochemistry—integrate to generate changes in microbial community composition at distinct timescales among habitat types. These changes in composition are reflective of contrasting associations of Betaproteobacteria and Thaumarchaeota with ecological selection and with seasonal changes in microbial metabolism. We present a conceptual model based on our results in which metabolism increases when oscillating selective pressures oppose temporally stable selective pressures. Our conceptual model is pertinent to both macrobial and microbial systems experiencing multiple selective pressures and presents an avenue for assimilating community assembly processes into predictions of ecosystem-level functioning.

Grindelia rheophila (Asteraceae, Astereae), the first known rheophytic gumweed species is proposed, described, and illustrated here. Unlike most species of the genus, which are adapted to almost permanently dry environments, this new species thrives in dynamic riverine habitats with fast-flowing water. Grindelia rheophila is characterized by the erect to decumbent growth form, long linear-elliptic leaves, and a pappus with hemipaleaceous and bristle elements, which differentiate it from the morphologically similar G. buphthalmoides, G. pulchella and G. scorzonerifolia. The new species is known only at the northern headwaters of the Ibicuí river basin along the edge of the South Brazilian plateau in the state of Rio Grande do Sul, Brazil, where it grows along rocky flood-prone margins of the watercourse, as rapids and waterfalls are influenced by seasonal hydrological fluctuations. We highlight the vulnerability of rheophile ecosystems to anthropogenic threats, particularly dam construction and climate-driven extreme weather events, justifying the recognition of the new species as Critically Endangered (CR A2ac+3c+4ac; B1a,b(i,ii,iii,iv),c(iii)). A watercolor illustration, habitat photographs, a distribution map, and an identification key for Brazilian Grindelia are also provided.

Seasonal hydrological fluctuations strongly influence riparian habitats in the middle Yangtze River, yet the relationships of inundation duration with soil properties and riparian vegetation remain insufficiently understood in representative riparian sections. Here, field surveys and laboratory analyses were conducted to examine (1) inundation–soil associations and (2) soil–vegetation relationships. Soil moisture (W), pH, particle-size composition, soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) were measured, and vegetation parameters were compared among inundation-duration zones. Partial redundancy analysis (pRDA) was used to evaluate the relationships between environmental factors and vegetation parameters after controlling for elevation and shoreline distance. Vegetation occurrence, coverage, and diversity decreased with increasing inundation duration, and no vascular plants were recorded in the severe-inundation zone. After accounting for topographic factors, TN and gravel were the main soil variables associated with vegetation variation. Overall, inundation duration was closely associated with soil variation, whereas vegetation variation was mainly associated with selected soil environmental factors. These findings provide site-based evidence for riparian ecological restoration in representative riparian sections of the middle Yangtze River.

Community assembly processes generate shifts in species abundances that influence ecosystem cycling of carbon and nutrients, yet our understanding of assembly remains largely separate from ecosystem-level functioning. Here, we investigate relationships between assembly and changes in microbial metabolism across space and time in hyporheic microbial communities. We pair sampling of two habitat types (i.e., attached and planktonic) through seasonal and sub-hourly hydrologic fluctuation with null modeling and temporally-explicit multivariate statistics. We demonstrate that multiple selective pressures—imposed by sediment and porewater physicochemistry—integrate to generate changes in microbial community composition at distinct timescales among habitat types. These changes in composition are reflective of contrasting associations of Betaproteobacteria and Thaumarchaeota with ecological selection and with seasonal changes in microbial metabolism. We present a conceptual model based on our results in which metabolism increases when oscillating selective pressures oppose temporally-stable selective pressures. Our conceptual model is pertinent to both macrobial and microbial systems experiencing multiple selective pressures and presents an avenue for assimilating community assembly processes into predictions of ecosystem-level functioning.

Evolving fluvial architecture during a marine transgression: Upper Buntsandstein, Triassic, central Spain

The occurrence of myxomycetes is reported for the first time in the Brazilian Pantanal and on Attalea phalerata (acuri palm). The records are based on sporocarp collections made in the municipality of Poconé, State of Mato Grosso, in an area characterized by seasonal hydrological fluctuations and naturally open areas. We report six species: Arcyria obvelata, Perichaena depressa, and P. vermicularis (Trichiaceae); and Physarum album, P. compressum, and P. polycephalum (Physaraceae), all of which represent new records for the Pantanal and a new substrate, A. phalerata.

Wetlands in tropical wet-dry climates are governed by distinct and extreme seasonal hydrologic fluctuations. In this study, we investigated the plant community response to seasonal flooding and drought in Palo Verde Marsh, Costa Rica. Climate change models for the region predict reduced rainfall and a drier wet season which would likely alter seasonal hydrologic cycles and prompt vegetation change. We quantified compositional change following disturbance emphasizing seasonal differences in plant life-form abundance across life history stages via standing vegetation, seed bank, and seedling recruitment measurements. Whereas the dry season standing vegetation was dominated by emergent species, aquatic species (floating-rooted, free-floating, and submerged life forms) were more dominant during the wet season. Seed bank and seedling recruitment measurements indicated that many species are resilient with life history traits that enable them to respond rapidly to extreme hydrologic filters. Interestingly, species richness was highest during seasonal flooding. Our results highlight the importance of early-wet season rainfall for plant regeneration and community change. Our findings also indicate that a drier future would likely have a large impact upon wetland plant communities with a decrease in species richness and an increase in the abundance of drought-tolerant emergent species.

Hydrologic alterations within the Everglades have degraded American alligator (Alligator mississippiensis) habitat, reduced prey base, and increased physiological stress. Alligator body condition declined across many management areas from 2000 through 2014, prompting us to investigate the relationship between their intraspecific isotopic niche dynamics and body condition. Alligators within the estuary had a larger niche driven by a wider range in stable carbon isotope ratios than those sampled in freshwater habitats. Spatially, model predictability was higher at the smaller scale, reflecting the variability in basal sources and biochemistry among capture sites. Male niches were often larger than those of females, driven by wider ranges of δ13C values, suggesting that they differ in their proportional use of habitats and or resources. However, the similar ranges of δ15N values indicated both sexes foraged within the same trophic level. Furthermore, while not significantly different, large alligators often had a larger niche with elevated δ15N values compared to medium-sized alligators. Although alligators utilize similar stable carbon and nitrogen isotope pools through time, there was considerable temporal variability. These temporal variations in alligators’ isotopic niche were likely influenced by seasonal hydrologic fluctuations within each site, with their niches often being larger in the spring captures than the fall captures. Alligators’ body condition estimates were correlated with intraspecific niche characteristics, including the mean centroid distance between sexes and the interaction between male and female niche size and overlap, within a site, capture period, and year. The variability in intraspecific niche dynamics, landscape heterogeneity, and dynamic hydrology are considerations for designing sustainable management strategies to conserve and enhance alligator populations within the Everglades landscape.

Severe drought changes the soil bacterial community in wetland ecosystem: Evidence from the largest freshwater lake wetland in China