Temperate Streams Research Articles

Effects of micro-topography on N2O emission from sediments in temperate streams

Denitrification is a major biological source or sink of N2O, an important greenhouse gas, which is a multi-step respiratory process that converts nitrate (NO3−) to gaseous forms of nitrogen (N2 or N2O). In aquatic ecosystems, the residence time and flow length within the streambed can modulate denitrification, which is highly affected by micro-topography of streambed. For the reason, various restoration projects targeting streams and rivers incorporate the installment of dune-shaped streambed, but its role in ecosystem functions and key controlling variables are still elusive. In this study, N2O fluxes according to streambed micro-topography were measured at four locations in two streams with dune-shaped streambeds in Korea. We found that micro-topographical variations influenced N2O fluxes, chemical properties, and denitrifier abundances, but that this effect was highly constrained by carbon availability. In sites with relatively higher DOC, N2O fluxes increased along the flow direction, and the highest flux of each site (19.1 ± 5.67 μg N2O-N m−2 h−1 and 16.2 ± 0.896 μg N2O-N m−2 h−1, respectively) was observed in the slope on the back side of the dune, followed by decreases afterward. In contrast, streams with low DOC concentration did not exhibit micro-topographical variations. This study suggests that the presence of small dunes in streams can substantially enhance N2O fluxes when carbon availability was appropriate. The variations of N2O flux highlight the importance of micro-topography and DOC concentration of sediment for the accurate estimation of uncertainty of N2O flux. This has further implication for stream restoration where installment or management of dune-shaped streambed is of importance in the removal of inorganic N in water.

Environmental filtering and limiting similarity as main forces driving diatom community structure in Mediterranean and continental temporary and perennial streams

Climatic extreme events such as droughts (unpredictable), dry periods (predictable) or even flush floods, threaten freshwater ecosystems worldwide. The filtering mechanisms of these events and their strength on communities, however, can be different among regions. While time-for-adaptation theory defines whether or not water scarcity can be considered as disturbance, the stress-dominance theory predicts an increase in importance of environmental filtering and a decrease in the role of biotic interactions in communities with increasing environmental stress. Here, we tested whether environmental filtering (leading to trait convergence) or limiting similarity (leading to trait divergence) is the main assembly rule shaping the structure and trait composition of benthic diatom assemblages in Mediterranean (Portuguese) and continental (Hungarian) temporary and perennial streams. We assumed that the trait composition of diatom assemblages in the two stream types would be less different in the Mediterranean than in the continental region (addressed to time-for-adaptation theory). We also hypothesized that trait composition would be shaped by environmental filtering in the Hungarian streams while by biotic interactions in Portuguese streams (addressed to stress-dominance theory). Our results supported our first hypothesis since traits, which associated primarily to temporary streams were found only in the continental region. Our findings, however, only partially proved the stress-dominance hypothesis. In the continental region, where drying up of streams were induced by unpredictable droughts, biotic interactions were the main assembly rules shaping community structure. In contrast, environmental filtering was nearly as important as limiting similarity in structuring trait composition in the Mediterranean region during the predictable dry phase with no superficial flow. These analyses also highlighted that drought events (both predictable and unpredictable ones) have a complex and strong influence on benthic diatom assemblages resulting even in irreversible changes in trait composition and thereby in ecosystem functioning.

Ecosystem services of temporary streams differ between wet and dry phases in regions with contrasting climates and economies

Abstract Temporary streams are dynamic ecosystems in which mosaics of flowing, ponded and dry habitats support high biodiversity of both aquatic and terrestrial species. Species interact within habitats to perform or facilitate processes that vary in response to changing habitat availability. A natural capital approach recognizes that, through such processes, the ‘natural assets’ of all ecosystems deliver services that benefit people. The ecosystem services of temporary streams remain largely unexplored, in particular those provided during ponded and dry phases. In addition, recent characterizations have focused on dryland systems, and it remains unclear how service provision varies among different climatic regions, or between developed and developing economies. We use evidence from interdisciplinary literature to examine the ecosystem services delivered by temporary streams, including the regulating, provisioning and cultural services provided across the continuum from flowing to dry conditions. We focus on service provision during dry phases and wet–dry transitions, across regions with contrasting climates and economic development. Provision of individual services in temporary streams may be reduced, enhanced or changed by surface water loss. Services enhanced by dry phases include provision of higher‐quality subsurface drinking water and unique opportunities for recreation. Shifts between dry and wet phases enable groundwater recharge that mitigates water scarcity, and grant dry‐phase access to sediments deposited during flowing phases. However, the accessibility and thus perceived value of these and other services varies considerably among regions. In addition, accessing provisioning services requires careful management to promote sustainable resource use and avoid ecological degradation. We highlight the need for environmental managers to recognize temporary streams as aquatic–terrestrial ecosystems, and to take actions promoting their diversity within functional socio‐ecological systems that deliver unique service bundles characterized by variability and differing availability in space and time. A free Plain Language Summary can be found within the Supporting Information of this article.

Connectivity of Ephemeral and Intermittent Streams in a Subtropical Atlantic Forest Headwater Catchment

Stream network extension and contraction depend on landscape features and the characteristics of precipitation events. Although this dependency is widely recognized, the interaction among overland-flow generation processes, drainage active length, and frequency in temporary streams remains less understood. We studied a forest headwater catchment with wide variation in soil depth to investigate the runoff generation processes that lead to the occurrence of ephemeral and intermittent flow and connectivity between hillslope and outlet. We used low-cost equipment to monitor the variation in the length of the active drainage network and to measure the water table development. The flow in the channels can develop even under light rainfall conditions, while the connectivity is controlled by antecedent wetness, total precipitation, and active contribution area thresholds. Runoff permanence and fragmentation were related to soil depth variation; flow being usually more disconnected due to deeper water tables in deeper soil locations. Our findings emphasized the impact of soil structure on runoff generation in hillslopes and can be useful in the management of the most active areas and their impact on the quality of available water.

Local and regional environmental factors drive the spatial distribution of phototrophic biofilm assemblages in Mediterranean streams

Temporary streams are submitted to high seasonal hydrological variations which induce habitat fragmentation. Global change promotes longer non-flow periods, affecting hydrological continuity and the distribution of biological assemblages in river networks. We aimed to investigate the effects of hydrological discontinuity on phototrophic biofilm assemblages in a Mediterranean stream, at both network and habitat scales. At the network scale during basal flow conditions, mostly nitrate and DOC concentrations were associated to the taxonomical and trait distribution of algae and cyanobacterial assemblages. Cyanobacteria dominated at the upstream and downstream sites of the network, while green algae and diatoms were abundant in its middle part. At the habitat scale, hydrological discontinuity promoted large changes in biofilm composition between riffles and pools, where pools were inhabited preferentially by green algae and riffle habitats by cyanobacteria. Our findings emphasize the myriad of factors affecting the spatial distribution of phototrophic biofilms, which become more heterogeneous according to water flow interruption. Under the predicted climate change scenarios, spatial heterogeneity in temporary streams may increase, which will lead to change phototrophic biofilm assemblages.

Understanding effects of small dams on benthic metabolism and primary production in temperate forested streams

Dams can alter the chemical and physical conditions of downstream environments by increasing stream temperatures, altering nutrient limitation, reducing flow variability, and reducing fine sediment deposition. However, little is known about how fundamental stream ecosystem processes like productivity and respiration respond to dams. Nutrient diffusing substrates were installed in three dam streams and three control streams to evaluate the effect of dams on benthic gross primary productivity (GPP), respiration (R), and chlorophyll α production. Dam streams were an average of 5.6 °C warmer than control streams but GPP, R and chlorophyll α were not different between control and dam streams. Phosphorus enrichment increased heterotrophic R relative to controls (~1.8×) but not autotrophic GPP, R or chlorophyll α. Stream nutrient concentrations and nutrient limitation of heterotrophic R were similar in dam and control streams, suggesting that the dams had limited effects on nutrient transport downstream. Autotrophic GPP, R and chlorophyll α were limited by light and varied within and across streams, potentially masking our ability to detect differences caused solely by dams. Dams may alter stream ecosystem func- tion but consideration of other factors associated with and independent of dams is critical for predicting ecosystem responses to dams.

A new species of Cypris (Crustacea: Ostracoda) from the Iberian Peninsula and the Balearic Islands, with comments on the first ostracod named using the Linnean system.

The genus Cypris, considered the oldest ostracod generic name erected using the Linnean system, comprises a reduced number of large-bodied species, mostly found in Africa and Asia. Only six of them are known to occur in Europe. Here we describe a new species, Cypris pretusi sp. nov., collected in small temporary streams and ponds along the Eastern Iberian Peninsula and Minorca (Balearic Islands). The new species is very close to the type species of the genus, Cypris pubera O.F. Müller, 1776, but differs from it in having a set of smaller subequal spines on the posterior edge of the valves, by the absence of conspicuous spines along the front edge, and by the beak-like frontal shape of its carapace in dorsal view, similar to Cypris decaryi Gauthier, 1933. Soft parts are very similar to the type species, but it differs in having shorter swimming setae on the second antennae. Molecular analyses of the COX1 region support its status as a species distinct from C. pubera and closer to Cypris bispinosa Lucas, 1849, also providing evidence for a separation of C. pubera s.l. in two clades, one of which is here considered to correspond to Cypris triaculeata Daday, 1892. We discuss the relationships of C. pretusi sp. nov. to other members of the genus and its possible origin from nearby biogeographic regions (probably Africa or Asia) and provide a key to species of Cypris found in Europe. We also discuss the relationship between Monoculus concha pedata (= M. conchaceus), the first ostracod named by Linnæus, and Cypris pubera, the type species of the genus, described by Müller in 1776 and considered by him the same species as the one first named by Linnæus.

Calculation of the Height of Capillary Rise of Water in Soils

Rain and melt water will form temporary accumulations of surface water on the surface. When they seep into the ground, temporary streams of leaky filter water are formed. If a limited section of water-resistant soil layer or the roof of an underground structure is encountered in the path of these waters, a temporary aquifer-the upper layer of ground water-may form above them. In temporary and permanent aquifers, the soil pores are completely filled with gravitational water, the degree of water saturation is equal to one, and there is pressure under the surface of underground water. Above this surface is a zone of capillary moisture, while the level of capillary rise is determined by the granulometric composition of the soil and ranges from tens of centimeters in sand to several meters in dusty and clay soils. Capillary water rises in the ground on free canals formed by mutually communicating pores, or is kept in them in limbo.The lifting of the liquid in the capillary continues until the gravity acting on the column of the liquid in the capillary becomes equal to the resulting force. Capillary water penetrates from the ground into the walls and rises to a height of up to 2 meters. The normal moisture content of the brick walls is 0.02...0,03, and in the case of unprotected contact with moist soil is increased to 0.15...0.25. On the inside of the walls there is a damp, mildew. Evaporating water increases humidity in the room, and the salts released when it evaporates from salt solutions lead to peeling paint, destruction of plaster and wall material.

ПІДВИЩЕННЯ ЕФЕКТИВНОСТІ УПРАВЛІННЯ ПРОЕКТОМ НА ОСНОВІ ВИКОРИСТАННЯ ON-LINE КОМПЛЕКСУ WRIKE

The article proposes to consider the problems of interaction of the members of virtual teams. Virtual team is a team whose members can be located in different offices, cities, countries. In modern business conditions, IT companies often choose such type of organization. The authors have analyzed the researches and articles and made the following conclusions. There are several problems in such a team: psychological, communication and control problems. Each issue is the topic of a separate article. Moreover, the authors have chosen to consider the issues of communication of team members. Authors have analyzed and tested various software products carried out to assist the manager in organizing the work. As a result, the Wrike online software, which solves a whole range of tasks for project management and teamwork, namely: work planning, appointment of the person responsible for the task, file storage, accounting of work resources, fast communication within the team, has been chosen. Wrike allows to organize a multi-level hierarchy of projects and a hierarchy within projects in the form of folders and tasks, providing tools for creating folders, projects, and tasks. In addition, each component listed above may have several important attributes, namely, the contractor, status (new, in progress, completed, pending, rejected) The issue of access to project components is solved by providing a security tool. Either an individual person, a group, or public can access each part of the project. The availability of tools that visually depict the execution of tasks in time, namely, the classic Gantt chart and the usual table rendering, is an important moment of using the product. When working with a temporary stream, you can use various filters. The authors have tested and analyzed the software product and revealed its strengths and weaknesses, as well as the ability to be used in business processes.

Drought and Ecological Flows in the Lower Guadiana River Basin (Southwest Iberian Peninsula)

Drought temporal characterization is a fundamental instrument in water resource management and planning of basins with dry-summer Mediterranean climate and with a significant seasonal and interannual variability of precipitation regime. This is the case for the Lower Guadiana Basin, where the river is the border between Spain and Portugal (Algarve-Baixo Alentejo-Andalucía Euroregion). For this transboundary basin, a description and evaluation of hydrological drought events was made using the Standardized Precipitation Index (SPI) with monthly precipitation time series of Spanish and Portuguese climatic stations in the study area. The results showed the occurrence of global cycles of about 25–30 years with predominance of moderate and severe drought events. It was observed that the current requirements of ecological flows in strategic water bodies were not satisfied in some months of October to April of years characterized by severe drought events occurring in the period from 1946 to 2015. Therefore, the characterization of the ecological status of the temporary streams that were predominant in this basin should be a priority in the next hydrologic plans in order to identify the relationships between actual flow regimes and habitat attributes, thereby improving environmental flows assessments, which will enable integrated water resource management.

Agricultural and urban delivered nitrate pollution input to Mediterranean temporary freshwaters

Nitrate dual stable isotopes (δ15NNO3 and δ18ONO3) have proven to be a powerful technique to trace nitrate sources and transformations in freshwater systems worldwide. However, most studies have focused on perennial systems, and less is known about intermittent ones. The impacts of intensive agricultural practices and wastewaters in Doñana (SW Spain), an iconic Mediterranean temporary wetland protected as a UNESCO World Heritage Site, were quantified using stable isotope mixing models in a Bayesian framework under different denitrification scenarios. We aimed to identify the main nitrate sources and transformation processes in surface waters of interconnected temporary streams, ponds and marshes, and link them with the main human pressures in the watershed (e.g. intensive fruticulture, urban wastewaters). We measured nitrate (NO3−) concentrations and stable isotopes (δ15NNO3 and δ18ONO3) in water samples collected during different periods over two years (2015–2016). Most sites showed coupled increases of nitrate isotopic values (δ15NNO3 and δ18ONO3), which were higher than reference values of any possible sources (e.g. synthetic/organic fertilizers and wastewaters), indicating fractionations typical of denitrification processes. The main nitrate sources to the watershed were linked to agricultural practices and the use of synthetic fertilizers, but further investigations in other transformation processes that occur simultaneously should be evaluated. These results highlight an important nitrate removal capacity (i.e. denitrification) of the system, which may positively contribute to natural resilience against eutrophication. However, given the high intra and interannual hydrological fluctuations of Mediterranean aquatic systems, future studies on the relative contribution of nitrate sources and processes should increase spatio-temporal resolution of water sampling, and include measurements of groundwater and interstitial water as well as surface water.

Relative expression analysis of light-harvesting genes in the freshwater alga Lympha mucosa (Batrachospermales, Rhodophyta).

Members of the freshwater red algal order Batrachospermales are often described as shade‐adapted. Nevertheless, recent ecophysiological studies have demonstrated species‐level differences in acclimation to a range of irradiances. Lympha mucosa occurs in open and shaded portions of temperate streams and is abundant during summer months, suggesting it tolerates high and low irradiances. Specimens of L. mucosa were collected from open (sun‐acclimated) or shaded (shade‐acclimated) sites and exposed to low (<20 μmol photons · m−2 · s−1) or high (220 μmol photon · m−2 · s−1) light for 72 h to examine mechanisms of photoacclimation at the transcriptional level. High‐throughput sequence data were used to design specific primers for genes involved with light harvesting and these were quantified with qPCR. The greatest significant difference in transcript abundances was observed in the psaA gene (Photosystem I P700 apoprotein), and site‐type had an effect on these responses. Shade‐acclimated thalli were 22‐fold down‐regulated at high light, whereas sun‐acclimated thalli were only 5‐fold down‐regulated. Another gene involved with Photosystem I (petF ferredoxin) was down‐regulated at high light, but only individuals from the shaded site were significantly different (4‐fold). In thalli from both sites, cpeA (Phycoerythrin alpha chain) was down‐regulated at high light. Although not statistically significant, patterns consistent with previous physiological and transcriptomic studies were uncovered, namely the inverse response of transcriptional activity in genes that encode phycobiliproteins. In support of previous ecophysiological studies of freshwater red algae, these data indicate significant transcriptional changes involving Photosystem I and phycobiliprotein synthesis are required to tolerate and grow at various irradiances.

ПЕРСПЕКТИВИ ВІДКЛАДІВ НАДЗАПЛАВНИХ ТЕРАС ДНІСТРА НА ЗОЛОТУ МІНЕРАЛІЗАЦІЮ

The article clarifies the stratigraphic binding and origin of silicon nodules, which served as the main raw material for the manufacture of tools for mammoth hunters of the Mezhyrich Late Paleolithic site. In archaeological publications, these nodules are often mentioned to be confined to the "Vyrzhikovsky layer" (the Albian layer of the Lower Cretaceous), which was formed under continental conditions and consists of sand-clay (kaolin, in particular) deposits. The analysis of the necessary conditions and possible mechanisms for the formation of silicon nodules indicates the erroneousness of such ideas. Most likely, the source of silicon raw materials was the marine deposits of the Cenomanian (Upper Cretaceous), or, in accordance with the modern stratigraphic division of the Mesozoic-Cenozoic sequence, deposits of the Burim suite (upper Albian – lower Cenomanian). The paleogeographic setting, sedimentological conditions and lithological composition of the "Vyrzhikovsky layer" did not ensure the formation of silicon nodules in it in the form of inclusions. The latter are diagenetic in origin and could only form in the thickness of carbonate rocks, free of clay minerals. The region of Kaniv dislocations was the optimal region from the silicon production point of view, which was determined: firstly, by the tectonic dislocation of the sedimentary sequence, which contributed to the removal of deposits containing silicon nodules in the thickness of younger rocks; secondly,the erosion activity of temporary streams, which brought these deposits to the level of the denudation cut-off. The most convenient place for collecting flints was not the outcrop of bedrock in ravines but the cones of their removal, which overlook the floodplains of the Dnipro and Ros'. The possibility of collecting flint in the immediate vicinity of the Mezhirich site, in the ravines and gullies between the Ros and Rosava rivers, does not find confirmation, since the chalk deposits here lie much lower than the local erosion base and are not exposed by ravines. Therefore, the leading role in the formation of the raw material supply of the Late Paleolithic site of Mezhirich was played by the region adjacent to the Kaniv mountains of the alluvial-proluvial plain.Despite long-term geological study of the Dniester River basin, we still have no clear evidences about gold-bearing potentiality of this area as well as origin of gold. The leading role of geological, geochemical and mineralogical criteria is proved for defining the prospects of substantial gold deposits finding within the Dniester river basin. Gold was found here in the crystalline basement and in the sedimentary cover rocks. Study of mineralogy and lithology of the terraces above the flood-plain and typomorphic peculiarities of native gold shows that palaeogeographic conditions and alimentation zones of debris vary at the different tectonic stages of this area development. Gold-bearing potential of the Pliocene-Quaternary sediments in the Dniester River basin is related to the Pliocene (VI-IX terraces above the flood-plain) and Quaternary (I-V terraces above the flood-plain) terraces complex of the Dniester river, as well as this river and its inflows recent alluvia. Our study of the Mid-flow part of the Dniester river basin allow to conclude that native gold was found in geologocal strata of all ages, from Proterozoic up to the recent alluvium. This fact points the necessity of further prospecting to find the mother lodes of gold. Our field study, samples analyses made as well as publications observation allow highlighting the principal directions of further prospecting and evaluation works. The main among that are: 1) comprehensive study of river Dniester alluvia and its terraces complex (previously VI–VII terraces), that will allow to specify their material composition, to assess real gold-bearing potential and to define the history of denudation areas changes; 2) lithogeochemical prospecting of primary and secondary dispersion haloes to clear the principal gold-bearing regularities; 3) definition of prospect plots within the area described; 4) modern analytical approach study of typomorphic peculiarities of native gold from alluvia and terrace deposits to define its ore formational affinity and mineral type.

ПРО ВІК І ПОХОДЖЕННЯ КРЕМ'ЯНОЇ СИРОВИНИ ІНВЕНТАРЮ ГЕОАРХЕОЛОГІЧНОЇ ПАМ'ЯТКИ МЕЖИРІЧ (КАНІВСЬКЕ ПРИДНІПРОВ'Я)

The article clarifies the stratigraphic binding and origin of silicon nodules, which served as the main raw material for the manufacture of tools for mammoth hunters of the Mezhyrich Late Paleolithic site. In archaeological publications, these nodules are often mentioned to be confined to the "Vyrzhikovsky layer" (the Albian layer of the Lower Cretaceous), which was formed under continental conditions and consists of sand-clay (kaolin, in particular) deposits. The analysis of the necessary conditions and possible mechanisms for the formation of silicon nodules indicates the erroneousness of such ideas. Most likely, the source of silicon raw materials was the marine deposits of the Cenomanian (Upper Cretaceous), or, in accordance with the modern stratigraphic division of the Mesozoic-Cenozoic sequence, deposits of the Burim suite (upper Albian – lower Cenomanian). The paleogeographic setting, sedimentological conditions and lithological composition of the "Vyrzhikovsky layer" did not ensure the formation of silicon nodules in it in the form of inclusions. The latter are diagenetic in origin and could only form in the thickness of carbonate rocks, free of clay minerals. The region of Kaniv dislocations was the optimal region from the silicon production point of view, which was determined: firstly, by the tectonic dislocation of the sedimentary sequence, which contributed to the removal of deposits containing silicon nodules in the thickness of younger rocks; secondly,the erosion activity of temporary streams, which brought these deposits to the level of the denudation cut-off. The most convenient place for collecting flints was not the outcrop of bedrock in ravines but the cones of their removal, which overlook the floodplains of the Dnipro and Ros'. The possibility of collecting flint in the immediate vicinity of the Mezhirich site, in the ravines and gullies between the Ros and Rosava rivers, does not find confirmation, since the chalk deposits here lie much lower than the local erosion base and are not exposed by ravines. Therefore, the leading role in the formation of the raw material supply of the Late Paleolithic site of Mezhirich was played by the region adjacent to the Kaniv mountains of the alluvial-proluvial plain.

Sediment Properties Drive Spatial Variability of Potential Methane Production and Oxidation in Small Streams

AbstractEmissions of the potent greenhouse gas methane (CH4) from streams and rivers are a significant component of global freshwater methane emissions. The distribution of CH4 production and oxidation within stream sections and in vertical sediment profiles is not well understood, and the environmental controls on CH4 production and emission in such systems create a significant challenge for assessing larger‐scale dynamics. Here we investigate factors driving the spatial variability of sediment potential methane production (PMP) and potential methane oxidation (PMO) in a temperate stream network in Germany. PMP was highly variable, ranging from 5 × 10−4 to 28.58 μg CH4 gDW−1 d−1 and PMO ranged from 0.43 μg CH4 gDW−1 d−1 to 14.41 μg CH4 gDW−1 d−1. Important drivers of spatial variability of PMP and PMO in the sediments of the stream main‐stem were related to fine sediment fraction and organic carbon content. At smaller spatial scale, that is, in a sub‐catchment stream section, the drivers were more complex and included sediment nitrogen and organic carbon content, as well as porewater dissolved organic carbon, dissolved organic matter quality, and metal concentrations. As with reservoirs and impounded rivers, fine sediment deposition and organic carbon content were found to be key controls on the spatial variability of CH4 production and oxidation. These findings enhance our understanding of CH4 dynamics, improve the potential for identifying CH4 production hotspots in small streams, and provide a potential means for upscaling emission rates in larger‐scale assessments.

Does biofilm origin matter? Biofilm responses to non‐flow period in permanent and temporary streams

Abstract In some regions, climate change is increasing the variability of rainfall and the frequency of extreme events such as drought. Consequently, non‐flow periods have grown in length and frequency, both in temporary and in formerly permanent streams. Water abstraction for human use may further prolong these dry periods. We analysed the resistance and resilience of biofilms from permanent and temporary streams to non‐flow conditions. This was achieved by exposing cobbles (collected from permanent and temporary streams) with intact biofilm to 31 days of non‐flow, followed by 20 days of stream flow in artificial stream channels. Biofilm resistance and resilience were assessed at a structural (algal biomass, pigment composition, and algae and cyanobacteria composition) and functional level (photosynthetic efficiency and community metabolism). Algal taxa in biofilms from permanent and temporary streams differed throughout the experiment. Biofilms from permanent streams were less resistant to non‐flow than those from temporary streams at structural level. Permanent stream biofilms also presented lower resilience at a structural level, but responded similarly to temporary stream biofilms at a functional level. Our investigation shows how the non‐flow period disturbed permanent stream biofilms, and suggests that temporary stream biofilms will have greater adaptive capacity as hydroperiod becomes shorter due to climate change.

Influence of landscape and hydrological factors on stream–air temperature relationships at regional scale

AbstractIdentifying the main controlling factors of the stream temperature (Tw) variability is important to target streams sensitive to climate and other drivers of change. The thermal sensitivity (TS), based on relationship between air temperature (Ta) and Tw, of a given stream can be used for quantifying the streams sensitivity to future climate change. This study aims to compare TS for a wide range of temperate streams located within a large French catchment (110,000 km2) using 4 years of hourly data (2008–2012) and to cluster stations sharing similar thermal variabilities and thereby identify environmental key drivers that modify TS at the regional scale. Two successive classifications were carried out: (a) first based on Ta–Tw relationship metrics including TS and (b) second to establish a link between a selection of environmental variables and clusters of stations. Based on weekly Ta–Tw relationships, the first classification identified four thermal regimes with differing annual Tw in terms of magnitude and amplitudes in comparison with Ta. The second classification, based on classification and regression tree method, succeeded to link each thermal regime to different environmental controlling factors. Streams influenced by both groundwater inflows and shading are the most moderated with the lowest TS and an annual amplitude of Tw around half of the annual amplitude of Ta. Inversely, stations located on large streams with a high distance from source and not (or slightly) influenced by groundwater inflows nor shading showed the highest TS, and so, they are very climate sensitive. These findings have implications for guiding river basin managers and other stakeholders in implementing thermal moderation measures in the context of a warming climate and global change.

Habitat-specific effects of interstitial space between stream substrate particles on the colonization of aquatic organisms

We examined the effects of interstitial space between stream substrate particles on the colonization of aquatic organisms using three types of substrates (gravel, a cobble, and a cobble on gravel) in a riffle and pool of a temperate stream. Significantly greater abundance, wet weight, diversity (H′), taxonomic richness, and evenness of aquatic organisms were found in the riffle than in the pool, and the interstitial space substrate (i.e., a cobble on gravel) had significantly greater abundance, wet weight, and taxonomic richness of aquatic organisms than did the cobble substrate. Of the 13 families observed in the experiments, larval net-spinning caddisfly (Hydropsychidae) dominated the riffle in terms of the abundance and wet weight; chironomid larvae dominated both the riffle and the pool in terms of abundance. Simple main effect tests indicated significant effects of substrate on the abundance and wet weight of larval caddisfly in the riffle, and post hoc tests on substrate in each habitat indicated that the abundance and wet weight of larval caddisfly on interstitial space substrate were significantly greater than those on cobble substrate in the riffle. Our results suggest the importance of interstitial space between stream substrates in riffles to ensure higher colonization rates of aquatic organisms such as larval net-spinning caddisflies characterized as filter feeders.

Development and Application of Predictive Models of Surface Water Extent to Identify Aquatic Refuges in Eastern Australian Temporary Stream Networks

AbstractMany organisms living in temporary streams rely on remnant surface water to survive during extended dry periods and recolonize newly established habitats when flow resumes. However, research on the spatiotemporal variations in surface water extent for entire river networks is scarce. In this study, we first present a new field method for rapid surface water assessment. Next, we develop predictive models relating observed water extent to environmental attributes at a large number of surveyed stream segments (n = 241) in eastern Australian coastal catchments. We use the models to predict daily variations in surface water dynamics throughout entire river networks over the period of 1911–2017, based on available long‐term environmental attributes influencing hydrological processes. We find descriptors of surface water extent can be accurately predicted based on robust internal and external validations. Environmental predictor variables representing water gaining processes were more important in predicting surface water extent than variables representing water losses. Simulated long‐term variations in surface water extent were highly dynamic through space and time, particularly in inland streams, which were predicted to be the driest on average. Total stream length with surface water ranged from 8,974 to 13,742 km across the study period. Our study presents a novel and practical approach to quantifying and predicting variations in surface water extent, with potential applicability to other parts of the world. The simulated surface water extent through space and time can be used to identify and prioritize potential aquatic refuge areas that sustain aquatic biodiversity in river networks during extended dry periods.

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.