Hierarchical climate-driven dynamics of the active channel length in temporary streams

Looking across a landscape, river networks appear deceptively static. However, flowing streams expand and contract following ever-changing hydrological conditions of the surrounding environment. Despite the ecological and biogeochemical value of rivers with discontinuous flow, deciphering the temporary nature of streams and quantifying their extent remains challenging. Using a unique observational dataset spanning diverse geomorphoclimatic settings, we demonstrate the existence of a general hierarchical structuring of river network dynamics. Specifically, temporary stream activation follows a fixed and repeatable sequence, in which the least persistent sections activate only when the most persistent ones are already flowing. This hierarchical phenomenon not only facilitates monitoring activities, but enables the development of a general mathematical framework that elucidates how climate drives temporal variations in the active stream length. As the climate gets drier, the average fraction of the flowing network decreases while its relative variability increases. Our study provides a novel conceptual basis for characterizing temporary streams and quantifying their ecological and biogeochemical impacts.

Characterizing temporary stream dynamics: the Stream Length Duration Curve

<p>Temporary streams (i.e. streams that temporarily cease to flow) are becoming a hot research topic in hydrology. These streams provide an invaluable contribution to riverine ecosystems, as they host a variety of habitats (from lotic to lentic and terrestrial) which sustain high biodiversity. Temporary streams can be found in different regions of the world and are characterized by strongly heterogeneous flow patterns, from flashy streams that flow only after rainfall events to rivers that episodically experience droughts. Many recent studies investigated temporary streams, originating interesting observational datasets about event-based or seasonal network dynamics. Empirical or conceptual models are usually employed for assessing the main physical drivers of network dynamics in each specific study site.<br>In this contribution, we develop and apply novel theoretical tools to understand how the local statistical properties of each reach of the network affect the catchment-scale variability of the active length. In particular, the Stream Length Duration Curve (SLDC) is proposed to efficiently summarize catchment-scale dynamics of the active length, providing an objective way to quantify network dynamics. The concept of SLDC is applied to a number of Italian headwater catchments, where data about temporal changes in the configuration of the flowing stream are available, providing a clue for the characterization of emergent temporal and spatial patterns of network dynamics. The Stream Length Duration Curve can facilitate comparisons across different catchments an time periods, possibly enabling and objective classification of temporary streams. </p>

Placoneis cattiensis sp. nov.—a new, diatom (Bacillariophyceae: Cymbellales) soil species from Cát Tiên National Park (Vietnam)

A new species from the genus Placoneis (Bacillariophyceae: Cymbellales) is described on the basis molecular and morphological data. Placoneis cattiensis Glushchenko, Kezlya, Kulikovskiy & Kociolek sp. nov. is described from soil collected from the bottom of a dry, temporary stream in the forest of Сát Tiên National Park in Vietnam. On the basis of molecular data our new species appears to be more closely related to two strains of Placoneis previously identified as P. elginensis. However, P. cattiensis shows lower statistical support with two strains of P. elginensis on the basis ML. Additionally, P. cattiensis is distinguished from P. elginensis on the basis of morphological features such as the shape of the valve, breadth and density of areolae and striae. Comparisons of P. cattiensis with other similar species are given.

Microplastic of polystyrene in soil and water: fluxes study from industrial site

<p>In the paper the experience of investigation of polystyrene content in soil and its distribution from industrial enterprise, where expanded polystyrene foam insulation is produced more than 40 years, is presented. Polystyrene belongs to the one of the most widely produced and used polymer. Once being in the environment, this type of plastic breaks easily and crumbles, and is dispersed by wind and water. Moreover, the danger of environmental pollution by polystyrene may be very serious because of hexabromocyclododecane that can be present in polystyrene as flame retardant additive.  Unfortunately, the level of study of environmental pollution with polystyrene and his behavior in soil and water is very poor.</p><p>Methodological approaches of sampling and polystyrene identification are shown. Since the enterprise is located on the elevated area close (500-700 m) to a small river with temporary stream, the direct flow of pollutants into the floodplain is possible. Therefore, soil and technogenic deposits at industrial site as well as soil and groundwater within floodplain were collected for study.</p><p>In order to identify plastic in solid samples, multiple stages were applied including visual detection, drying, sieving (using mesh widths from 1 to 5 mm), flotation (with heating for the fractions with the size of 1-2 mm and less than 1 mm), and natural organic matter removal. Method of water filtration was used.</p><p>Polystyrene was revealed in all solid (12) and liquid (4) samples. High amounts of polystyrene particles with a size less than 5 mm were recorded in technogenic deposits (up to 16700 units/kg) and in soils (up to 1700 units/kg). Particles of microplastic (less than 1 mm) were detected not only in surface layer of soil (0-5 cm) but at the depth of 10-15 cm. Discharges of small granules (less than 1 mm) of raw materials (expanded polystyrene) into environment and its distribution with runoff away from its sources were revealed.</p><p>Necessity of further investigation of plastic and microplastic pollution in terrestrial ecosystems in impact zones, including estimates of plastic volume discharges from industrial area with waste, surface runoff and via runoff collector, in order to prevent aquatic ecosystem pollution is discussed.</p>

Spatiotemporal changes in the hydrological state of temporary streams in a pre-alpine headwater catchment

<p>Temporary streams are common in headwater catchments and serve as important ecological and hydrological links between these catchments and downstream perennial rivers. However, our understanding of temporary streams in headwater catchments is limited due to a lack of high spatiotemporal resolution data of the three main hydrological states of these streams: dry streambed, standing water and flowing water. In this study, we used a custom designed multi-sensor monitoring system to collect high spatiotemporal resolution state data of the temporary streams in the 0.12 km<sup>2</sup> upper Studibach catchment, a pre-alpine headwater catchment in Alptal, Switzerland. The monitoring system was installed at 30 locations in the stream network. The state data was used to determine: (1) the temporary stream regime for every monitoring location based on the permanence of each hydrological state, (2) the state change thresholds (antecedent soil moisture, precipitation amount and intensity, and discharge at the outlet) for every monitoring location, and (3) the state change patterns in the stream network during precipitation events. The temporary stream regimes, and the state change thresholds and patterns were compared to topographic, land cover and channel characteristics to determine if these factors can explain the variability in temporary stream dynamics. The results show that there are four different landscape areas with distinctive temporary stream dynamics in the catchment, and that a steep forested section with coarse streambed material often disconnects the flowing parts of the upper and lower stream network.</p>

Murciélago gris de saco (Balantiopteryx plicata) atrapado en una red de araña de seda dorada (Nephila sp.) en Oaxaca

ResumenEn esta nota se reporta la observación de un murciélago Balantiopteryx plicata, atrapado en una red de la araña Nephila sp. en una selva baja caducifolia en Pinotepa Nacional, Oaxaca. La hora y condiciones en que el murciélago fue encontrado indican que el ejemplar no fue atacado por la araña y posiblemente moriría de inanición, deshidratación e insolación si no hubiese sido liberado. Esta observación es el primer registro en México de un murciélago atrapado en una telaraña.Palabras clave: Balantiopteryx plicata, depredación, Emballonuridae, Nephila sp., Pinotepa Nacional, Oaxaca, red de seda de araña.AbstractWe report the observation of a bat (Balantiopteryx plicata) trapped in a spider web (Nephila sp.), which was found alongside a temporary stream in a low tropical deciduous forest, in Pinotepa Nacional, Oaxaca. The bat was found in good condition, which indicates that the specimen was not attacked by the spider and it had no signs of dehydration and insolation, when it was released. This observation is the first record of a bat trapped in a spider web in Mexico.Key words: Balantiopteryx plicata, Emballonuridae, Nephila sp., Pinotepa Nacional-Oaxaca, predation, spider silk.

A Low-Cost, Multi-Sensor System to Monitor Temporary Stream Dynamics in Mountainous Headwater Catchments

While temporary streams account for more than half of the global discharge, high spatiotemporal resolution data on the three main hydrological states (dry streambed, standing water, and flowing water) of temporary stream remains sparse. This study presents a low-cost, multi-sensor system to monitor the hydrological state of temporary streams in mountainous headwaters. The monitoring system consists of an Arduino microcontroller board combined with an SD-card data logger shield, and four sensors: an electrical resistance (ER) sensor, temperature sensor, float switch sensor, and flow sensor. The monitoring system was tested in a small mountainous headwater catchment, where it was installed on multiple locations in the stream network, during two field seasons (2016 and 2017). Time-lapse cameras were installed at all monitoring system locations to evaluate the sensor performance. The field tests showed that the monitoring system was power efficient (running for nine months on four AA batteries at a five-minute logging interval) and able to reliably log data (<1% failed data logs). Of the sensors, the ER sensor (99.9% correct state data and 90.9% correctly timed state changes) and flow sensor (99.9% correct state data and 90.5% correctly timed state changes) performed best (2017 performance results). A setup of the monitoring system with these sensors can provide long-term, high spatiotemporal resolution data on the hydrological state of temporary streams, which will help to improve our understanding of the hydrological functioning of these important systems.