Lowland River Research Articles

Understanding the temporal dynamics of a lowland river fish community at a hazardous intake and floodgate to inform safe operation

Entrainment and mortality of freshwater fish at hazardous pumping station intakes used for Flood Risk Management (FRM) are of global concern. Although upstream and downstream passage of diadromous fish has received considerable attention, the ecological behaviours of river-resident fish at these structures and how to protect these species from entrainment is poorly-understood. At a lowland flood-relief pumping station and floodgate situated off-channel (River Foss) to the main-river Yorkshire Ouse (York, England), multi-beam sonar (Dual-Frequency Identification Sonar: DIDSON) was used over a pluriannual (three years) period to investigate diel movements of river-resident fish in response to the variations in temperature, hydrology and pump and floodgate operation, and to determine fish-friendly management options. Diel lateral movements of thousands of river-resident fish between the main-river, floodgate operated channel (River Foss) and off-channel pump forebay were predominantly during the crepuscular period and daytime, proposing important considerations for when managers should operate pumps and associated flood infrastructure. Seasonal diel movements increased throughout winter during a baseline year (no pump operation) and overwintering behaviour was influenced by cooling river temperatures. A Generalized Linear Mixed Model (GLMM) revealed fish entered the off-channel forebay when river levels were stable and not when they were rising or falling, suggesting hydrological stability was important for the ecological function of this fish community. Two years of impact data (pumps operated) then revealed pump operations severely disrupted the ecological functions of local fish populations, which was also uniquely quantified over two independent 24h periods during which temporal fish counts were reduced by 85%. A trial period where the floodgate was lowered ahead of dawn significantly reduced fish immigration into the hazardous forebay when compared to two different hydrological periods. Modifying when the floodgate and pumps operate, including lowering the floodgate ahead of fish immigration at dawn, and starting pumps during the night (but not day), are therefore promising non-engineered management options to prevent immigration of fish into the hazardous off-channel pump forebay and to reduce entrainment and mortality risk during pump operation.

The concept for innovative Comprehensive Assessment of Lowland Rivers.

Current river assessment methods focus on evaluating a single aspect (e.g. the physical and chemical quality of the water or its hydromorphological state) and usually do not integrate various factors. The lack of an interdisciplinary method makes it difficult to correctly assess the condition of a river as a complex ecosystem significantly influenced by humans. This study aimed to develop a novel Comprehensive Assessment of Lowland Rivers (CALR) method. It is designed to integrate and evaluate all-natural and anthropopressure-related elements that influence a river. The CALR method was developed using the Analytic Hierarchy Process (AHP). The application of the AHP allowed the assessment factors to be determined and given weights to define the importance of each assessment element. As a result of AHP analyses, the following ranks were determined for the six main parts of the CALR method: hydrodynamic assessment (0.212), hydromorphological assessment (0.194), macrophyte assessment (0.192), water quality assessment (0.171), hydrological assessment (0.152) hydrotechnical structures assessment (0.081). In the comprehensive assessment of lowland rivers, each of the six elements listed above is rated on a scale of 1-5 (where 5 means very good and 1 bad) and multiplied by an appropriate weighting. After summing up the obtained results, a final value is obtained, classifying the river. CALR can be successfully applied to all lowland rivers thanks to its relatively simple methodology. The widespread use of the CALR method may facilitate the assessment process and enable the comparison of the condition of lowland rivers worldwide. The research conducted in this article is one of the first attempts to develop a comprehensive method for evaluating rivers that considers all aspects.

Distribution and encounter rates of the river dolphin (Inia geoffrensis boliviensis) in the central Bolivian Amazon

The ecology and conservation status of river dolphins (Inia sp.) distributed in the lowland rivers of Bolivia are poorly understood and only recently have basic studies been conducted to investigate their population size, taxonomic status, distribution, behaviour, environmental threats and ecology in this region. This paper examines the distribution and encounter rates of the bufeo (Inia sp.) in the middle reach of the Bolivian Amazon and was conducted in the Mamoré River and four of its tributaries during the low water season. Methods were employed which can be replicated during future surveys of Bolivian river dolphins and the results can be compared with those from surveys of Inia throughout its range. Sixty-two hours were spent surveying for dolphins, with 68% of the effort in Mamoré River and 32% in its tributaries. The Inia encounter rates reported here (1.6-5.8 dolphins km21) are the highest recorded anywhere in its broad geographic range; and indicate the importance of continuing and expanding surveys in this area. The mean group size was greatest in the Tijamuchi River (3.3±2.96) and smallest in the Yacuma River (1.8±0.75) and the maximum group size was 14. The high bufeo encounter rates in the central Bolivian Amazon can be taken as a reflection of the general environmental status of the region; however, a growing human population, associated with an increase in boat traffic and fishing activity, poses a future threat to bufeos and their aquatic habitats.

Calculation of Seasonal Erosion on the Oka River Riverbanks Using Geodetic Modeling

Abstract—Directed erosion of riverbanks stands out among the dangerous geomorphological processes on large lowland rivers. In the middle reaches of the Oka river, horizontal channel deformations make a significant contribution to regional lithodynamics and the reduction in the area of floodplain lands. We carried out field geological and geomorphological studies in the valley of this large tributary of the Volga, which revealed the complex facies architecture of the floodplain. The forecast for riverbank erosion near the city of Ryazan has recently declined due to the unstable water regime of the Oka river. For a detailed assessment of the consequences of destabilization of the coastal slopes, their surface was surveyed using a total station and aerial photography from a UAV. Regular observations of erosion by the seasons of the hydrological year allowed us to obtain actual data on the redistribution of soils along the height of the slope. We have found that erosion in summer low water is three times weaker than during high water. The predominance of collapses of the uppermost (0.0–2.0 m from the day surface) part of the erosion fronts was also revealed. The article also discusses possible reasons for the mobilization of the geological filling of the river bank, arising from local differences in the Pleistocene-Holocene evolution of the morpholithic system of the Oka river floodplain and the fixation of geological information in it.

Downstream Controls on Coastal Plain River Avulsions: A Global Study

AbstractThe avulsion frequency of coastal‐plain rivers is primarily governed by the rate at which channels become superelevated over neighboring plains, which is itself controlled by multiple factors. Notably, the importance of wave and tidal processes, the rates of relative sea‐level (RSL) change, and the bathymetry of the receiving basin are thought to affect channel morphodynamics and channel‐mouth progradation, thereby controlling streambed aggradation and influencing the avulsion frequency and drainage density of coastal plains and deltas. This work tests the significance of these downstream factors on the avulsion histories of 57 Holocene lowland river systems. A quantitative analysis is performed of relationships between variables that quantify downstream controls and estimations of avulsion frequency, based on the number of avulsion events, active or abandoned channel paths, and delta lobes; measures of spatiotemporal avulsion “density” are also derived by normalizing these metrics by the size of study areas and the number of distinct drainage systems. Relationships between avulsion‐frequency metrics and descriptors of process regime indicate that wave and tidal processes may stabilize coastal channel systems, but also that their influence may be modest. No consistent relationship is seen between avulsion‐frequency proxies and the offshore bathymetric gradient, which in the studied examples does not scale with the rate of shoreline progradation. No evident trend exists between measures of avulsion frequency and estimated rates of either eustatic or RSL fluctuations. Overall, the considered variables do not leave a clear statistical signature in Holocene avulsion histories, suggesting that upstream or intrabasinal factors may represent more important controls.

Effect of ecoregion and river type on neotropical Chironomidae (Diptera) from humid mountain to semiarid lowland

Introduction: Chironomidae (Diptera) is the most widespread and abundant aquatic insect family in freshwater ecosystems. Chironomids are considered good indicators of water quality but are seldom identified at the genus level in broad spatial scale studies. Objective: To identify environmental conditions associated with chironomids in an altitudinal gradient. Methods: We compared ecoregions, river types, and seasons, for chironomids in neotropical streams and rivers (18 river sites; 2014-2018; Yungas rainforest and Western Chaco dry forest, Argentina). We used non-metric multidimensional scaling, dissimilarity, envfit analysis and rank-abundance curves. Results: Chironomic “assemblages” matched both ecoregions and river types. However, ecoregions presented a better fit with species composition. The stenothermal taxa of Orthocladiinae were dominant at high elevations and the eurythermal Chironominae in lowland rivers. Altitude, water temperature and conductivity were important. Seasonal differences were smaller than ecoregional differences. Conclusions: Ecoregions, altitude, water temperature and conductivity correlated with chironomid communities. Orthocladiinae were dominant at high elevations and Chironominae in lowland rivers.

Intercomparing LSTM and RNN to a Conceptual Hydrological Model for a Low-Land River with a Focus on the Flow Duration Curve

Machine learning (ML) algorithms slowly establish acceptance for the purpose of streamflow modelling within the hydrological community. Yet, generally valid statements about the modelling behavior of the ML models remain vague due to the uniqueness of catchment areas. We compared two ML models, RNN and LSTM, to the conceptual hydrological model Hydrologiska Byråns Vattenbalansavdelning (HBV) within the low-land Ems catchment in Germany. Furthermore, we implemented a simple routing routine in the ML models and used simulated upstream streamflow as forcing data to test whether the individual model errors accumulate. The ML models have a superior model performance compared to the HBV model for a wide range of statistical performance indices. Yet, the ML models show a performance decline for low-flows in two of the sub-catchments. Signature indices sampling the flow duration curve reveal that the ML models in our study provide a good representation of the water balance, whereas the HBV model instead has its strength in the reproduction of streamflow dynamics. Regarding the applied routing routine in the ML models, there are no strong indications of an increasing error rising upstream to downstream throughout the sub-catchments.

PREDICTING RETENTION EFFECTS OF A RIPARIAN ZONE IN AN AGRICULTURAL LANDSCAPE: IMPLICATION FOR EUTROPHICATION CONTROL OF THE TISZA RIVER, SERBIA

We explored the long-term influence of land use in the riparian zone on the water quality of the Tisza River, as a model of a non-wadeable lowland river located in a temperate, predominantly agricultural landscape. The analysis was based on a comparison of water quality variables between three river sites having contrasting, but constant land use patterns (in 500 m upstream radius) during the study period (2006-2019). While the first river site was characterized primarily by forests, the second and the third were dominated by urban and agricultural areas respectively. The variables which showed a significant difference between the pairs of sampling sites were oxygen saturation, nitrite nitrogen, total nitrogen, and orthophosphates. In contrast to urban and agricultural land, riparian forests showed a positive long-term influence on the river water quality. Natural and seminatural forests and shrubs had a favorable long-term influence on nutrient concentrations and oxygen regime of the Tisza River. However, the retention effects of orthophosphates and nitrite/nitrate content here were relatively low, demonstrating the limited performance of riparian buffers as a main or only management option in the Pannonian landscape, as the agricultural hotspot of Central and Eastern Europe. In conclusion, the riparian buffer assessment design applied in this study may be successfully used in pre-restoration monitoring, prior to the construction of buffer strips.

Benthic metabolism and nutrient uptake vary with geomorphology and season in a lowland river

Meandering rivers are characterized by geomorphic units like cut banks, point bars, and thalwegs. These units arise from interactions between hydrological and geomorphological forces. However, the individual contributions of geomorphic units to whole-river metabolism or nutrient processing are unclear because these quantifications are often done at larger spatial scales. We used closed recirculating chambers to measure benthic gross primary production (GPP), respiration (R), N uptake or release, and P uptake or release at bimonthly intervals over 1 y at different geomorphic units in the Mulde River, Germany. We compared GPP, R, and nutrient processing among a cut bank, a point bar, and the thalweg at a natural meander. We also compared the cut bank of this natural meander with a cut bank fixed by riprap at a human-altered meander. In the natural meander, GPP, R, and nutrient processing rates were higher at the point bar than the cut bank or thalweg. These differences are likely related to larger sediment grain sizes that provide a more stable substrate for microbial communities. A strong interaction between geomorphic units and time for GPP and NH4+ fluxes suggested that differences in nutrient processing rates among geomorphic units were restricted to specific times during the year. Specifically, we found that the nutrient processing rates differed among geomorphic units during the summer, but not winter. Furthermore, in June and August 2017, R was 2 to 3× lower at the cut bank stabilized by riprap than at the natural cut bank. Our results demonstrate that rivers are composed of functionally distinct geomorphic units susceptible to human-induced hydromorphological degradation. However, strong interactions between space and time and large within-geomorphic unit variability propose that local drivers influence ecosystem function, suggesting that we need additional research to resolve these drivers at the scales of geomorphic units.

Longitudinal Changes in Diverse Assemblages of Water Mites (Hydrachnidia) along a Lowland River in Croatia

Water mites are the most diverse freshwater group of Acari and despite growing research interest in the ecology of this group, the environmental influences along longitudinal river gradients on their assemblages are still not fully understood. The objective of this study was to determine how physico-chemical water properties and hydromorphological alterations affect the composition and distribution of water mite assemblages along a longitudinal river gradient. Macroinvertebrate samples were collected from 20 study sites distributed longitudinally along the entire 106 km course of a lowland river (Bednja River) in the Pannonian Lowlands ecoregion of Croatia. At each site, 20 samples were collected with regard to microhabitat composition (+400 samples in total). In parallel with the sampling of macroinvertebrates at each site, the physico-chemical water properties were measured and the degree of hydromorphological alteration was assessed (European Standard EN 15843:2010). Both the number of taxa and water mite abundance were found to increase significantly with increasing distance from the source. However, the assemblages from the upper reaches and those from the lower reaches shared very few species, emphasizing the importance of species-level identification. Water mite species richness and diversity were not reduced with increased levels of variables associated with organic enrichment and eutrophication pressures. Similarly, hydromorphological alteration did not reduce either water mite abundance or species richness and was positively correlated with both. Furthermore, a correspondence analysis on water mite microhabitat preferences revealed that 32% of all species were positively associated with artificial microhabitats (technolithal). These positive associations may be the result of reduced competitive pressure from other larger invertebrates, as well as a possible preference for higher velocity, which usually occurs on smooth technolithal surfaces. A total of 22 different species of water mites were found during this study, 8 of which (or 36% of all species found) were recorded for the first time in Croatia.

Features Of A Long-Term Heat Flux Formation Of The Large Russian Arctic Rivers And Its Transformations In Estuaries Under The Influence Of Climate-Induced And Dam-Induced Effects

The heat flux of the large rivers flowing into the Arctic seas of Russia plays an essential role in the thermal and ice regime of the lower reaches of these rivers and the southern part of the Arctic seas. However, estimates of the total value of heat flux and its spatial-temporal distribution require clarification. In this research, we analyzed monthly, and yearly water temperature data from 55 gauges and water flow data from 35 gauges in the lower reaches of the rivers of the Russian Arctic northerner of 60 N. These rivers are: Onega, Northern Dvina, Mezen, Pechora, Ob, Nadym, Pur, Taz, Yenisei, Khatanga, Anabar, Olenek, Lena, Yana, Indigirka, Alazeya, Kolyma and their main tributaries. The collected data series covers 1930-2018, focusing more on 1960–2018. We used Spearman trend tests and Mann-Whitney U-test to clarify changes in the thermal regime of study rivers. Our estimations showed that heat flux did not significantly increase in the past three decades on most rivers except Yenisei and Yana lowlands. Water temperatures on rivers monotonically increased after 1960, especially in May and June, but without statistical significance. The role of dams in the water temperature regime is observed for nearly 500 km lower dams, but it is not observed in their lowlands and mouths. We also identified the decrease in water temperatures and heat flux in river lowlands, estuaries and deltas up to 25% for Yenisei lowlands.

A multi-spatiotemporal scale strategy to evaluate factors controlling pebble mobility and its interactions with bedforms in a lowland gravel-bed river

This work analysed the factors controling the spatiotemporal variability in bedload mobility in a low-energy gravel-bed meandering river, with a particular focus on interactions between bedload transport distance and bedforms (bar-riffle-pool units). We first addressed the influence of pre-existing morphology, especially bars, on event transport distance, and examined to what extent the maintenance of bedforms requires hydrological events that can move bedload over distances at least equivalent to the length of two successive identical geomorphic units. Specifically, we tracked the displacement of passive integrated transponder (PIT)-tag particles 10 years after their injection, and applied bedload formulae to reconstruct the event transport distance for a 32-year study period. The results showed that event bedload distances for bed surface median size sediments (D50) could not exceed an active channel width, roughly equivalent to 0.3 times the median distance between riffles and between pools. This has two main implications; first, trapping by bars is rare, or perhaps even absent, at the scale of competent events for most particles located at a distance greater than an active channel width from a bar; second, because no event is able to transport bedload over distances at least equal to the length of one riffle-pool unit, maintenance of bedforms must arise from successive minor changes. Furthermore, our data reveal important variability in bedload velocity at the decadal scale according to the year of injection, type of geomorphic unit of injection, and method of injection. This highlights the long-term effects in low-energy rivers of location, timing, and method of injection on velocity estimate. Lastly, we inferred the long-term bedload velocity from PIT-tag data and applied it to bedload formulae. The resulting velocity of 0.95–1.3 km century-1 is considered an overestimate because the slowdown of tracers seeded at the bed surface due to their progressive mixing in the active layer and their trapping in bars is still ongoing.

Great cormorant (Phalacrocorax carbo sinensis) predation on adult anadromous brown trout (Salmo trutta)

AbstractThe increase in abundance of great cormorants (Phalacrocorax carbo sinensis) over the last decades has caused concern for the sustainability of fish populations. Cormorants are opportunistic piscivorous birds that eat fish from a wide range of species and sizes, in marine, lacustrine and riverine habitats. It has been documented that juvenile salmonids are under significant predation pressure by great cormorants, although knowledge on the predation of adult salmonids by cormorants is limited. In this study, adult anadromous brown trout (Salmo trutta) were tagged over multiple years with PIT tags during their spawning migration in a Danish lowland river. Two nearby cormorant colonies were subsequently scanned for PIT tags to estimate predation rate. It was estimated that by minimum 15.4% of tagged adult sea trout were predated by cormorants. The majority of the individuals were predated in the river, and females were more likely to be predated than males. Moreover, length had a significant effect on predation probability: individuals between 35 and 43 cm had the highest likelihood to be predated, while smaller and larger individuals were less likely to be predated. Our findings challenge the assumption that cormorants do not prey on reproductively mature salmonids. Furthermore, predation of mature individuals may have implications for the recruitment and sustainability of the population.

Channel abandonment alters trophic characteristics of highland rivers

The Qinghai-Tibet Plateau (QTP) serves as a collection of unique ecosystems featured as oligotrophic and hypometabolic conditions, and is particularly vulnerable to threats posed by anthropogenic and natural disturbances. Active fluvial processes on the QTP, especially the lateral migration of rivers and channel abandonment accompanied by variations in the hydrological connectivity, and changes in river geomorphology, intensively modify this highland river-floodplain system. However, little is known about how these processes alter the trophic characteristics of highland river system on earth. In this study, we conducted field investigations on a typical meandering river, the Quanji River (QR), located in the northeastern QTP by sampling macroinvertebrates, surveying trophic sources, and measuring a range of environmental conditions. Based on the collected data, we identified four biotopes for the QR through hierarchical clustering, established the representative food web for each biotope through the allometric diet breadth model, and estimated the biomass storage and flux within food web for each biotope through the biomass balance model. Our results show that the identified biotopes differed markedly in hydrological connectivity. Biotopes 1 and 2, which were in the main river channel represented the condition of high connectivity, Biotope 3 in the open channel represented the median connectivity, while Biotope 4 in the semi-open/closed channel represented the low connectivity. In contrast to the unimodal pattern commonly observed in lowland rivers, indices for the highland QR, including the taxa richness, trophic group richness, biomass flux, biomass transfer efficiency, and trophic stability demonstrated a single-valley response pattern to the hydrological connectivity. We argue that the intermediate disturbance hypothesis still works on highland river ecosystems, whereas the optimal disturbance occurs in the low connectivity rather than median connectivity. We attribute this skewness to the low resistance and resilience of highland macroinvertebrate community in the face of hydrodynamic disturbances brought by flood events, and the biological disturbances from the predation by endemic migratory fish (Gymnocypris przewalskii) in QR. This study reveals that lateral migration and channel abandonment play important roles in highland river systems in the QTP in the context of biological and energetic perspectives and suggests that management strategies for highland rivers should be made different from those of lowland rivers.

Ecohydrological metrics derived from multispectral images to characterize surface water in an intermittent river

Accurately describing the hydrology of intermittent rivers is a critical step in improving our understanding and management of freshwater ecosystems. Traditional approaches such as using gauged discharge data provide little information once flow ceases and no insight into the location, morphology, or persistence of river pools. However, multispectral images can be used to describe surface water, characterize hydrology, and provide insight into ecological functioning. A multispectral approach is highly cost-effective and well suited to remote intermittent rivers with little or no gauging infrastructure. Here, we develop an algorithm to extract hydrological attributes (i.e., pool area, length, perimeter, and mean width) from multispectral imagery (Sentinel-2) and use these attributes to create a suite of ecologically relevant hydrological metrics. We describechanges in attributes and metrics in a large lowland intermittent river as it transitions from wet to dry over a four-year period. We also describe temporal changes in attributes and metrics among five river sections with contrasting hydrological persistence and fragmentation.Our algorithm successfully identified surface water in the main channel and the adjacent floodplain, the centerline of pools, and their upstream and downstream ends. Metrics proved effective at describing seasonal patterns in hydrology; revealing how the size, complexity, and elongation of surface water features (e.g., pools) decreased as the study river transitioned from wet to dry and how fragmentation increased. Metrics also successfully differentiated the river sections with varied hydrological persistence. Ecohydrological metrics derived from multispectral imagery have the potential to provide meaningful insights into riverine morphology, resilience, and ecological functioning. Our spatial approach represents a significant advancement in the ability to characterize and manage intermittent rivers, which are increasingly threatened by water resource development and a drying climate.

Taxonomic and functional responses of macroinvertebrate communities to dam construction in a non-wadeable river

Damming and impoundment are among the main flow-related alterations in rivers worldwide. However, compared to the highland river sections where the impacts associated with dams have been largely studied, still scarce evidence is available in scientific literature for large, lowland rivers. In this study, the ecological effects of a hydropower dam in the Po River (Italy) on the taxonomic and functional responses of benthic macroinvertebrates were examined by comparing one station upstream of the dam with one downstream station over a six-year period. Weak and not significant differences were observed for taxon richness, abundance and community composition. By contrast, community-level proportion of macroinvertebrates associated with water velocity increased during medium and high flow condition and decreased during low flow condition in downstream stations. Such differences were also mirrored by the Flow-T index, that is a biomonitoring index recently developed to assess hydraulic conditions in rivers. Results of this study support the adoption of stressor-specific metrics in river biomonitoring.

Seasonal decomposition of different types of rivers in Slovakia: Implications for water management and agriculture

This study conducts an analysis of the seasonal decomposition of various river types in Slovakia in order to enhance the understanding of hydrological time series analysis and its potential implications for water management and agriculture. A comprehensive statistical methodology including decomposition of time series and correlation analysis was applied to the data collected from multiple river gauging stations across Slovakia. The results of the study indicate distinct seasonal variations in the hydrological characteristics of different river types, with a clear differentiation between lowland and mountain rivers. These findings have crucial implications for water management and agriculture as they suggest that a deeper understanding of seasonal patterns in river flow can lead to more efficient and effective utilization of water resources. Overall, this study highlights the significance of hydrological time series analysis in gaining a better comprehension of water resources and their management in Slovakia.

Kinematic parameters of flow constrained by combined dams with through part of tetrahedra in compression region

Every major river in the world consists of mountainous, foothills, and flat areas characterized by different flow regimes. The foothill areas differ in slopes i = 0.001 ÷ 0.004, flow kinetics Fr > 0.15, and the size of sediments. The riverbed is unstable, and the banks are prone to erosion. The construction of coastal protection structures requires solving complex issues related to their design. The analysis showed that most of the studies, including ours, were carried out for the conditions of lowland rivers. This work aims to establish the flow features of the foothill sections of a combined dam with a through part of tetrahedra when the ratio of the through part ℓs to the total length of the dam ℓd is greater than or equal to 0.5, i.e., ℓs/ℓd. ≥ 0.5 The presence of a satellite flow behind the through part, a weakly perturbed core, and the presence of two zones of intense turbulent mixing was experimentally established, and the universality of the velocity distribution, which obeys the theoretical dependence of Schlichting-Abramovich, was confirmed. It is once again confirmed that the dependence is on the slope of the bottom, the Froude number, the degree of constraint, and the formation of "calm" and "critical" flow modes. The nature of the level changes along the length of the compression region in the core, and the satellite flow differ from each other, and the alignments occur in the vertical compression alignment. The problem is implemented for the "calm" mode using an integral relation characterizing the law of conservation of momentum in the flow, the equation of conservation of flow, and the differential equation of uneven motion recorded for the satellite flow behind the through part of the combined dam. The presence of a satellite flow, two zones of intense turbulent mixing, and the different nature of the leveled regime of the main and satellite flows are taken into account. A comparison of theoretical solutions with experimental ones shows their similarity.

Mikrobiološke i osnovne agrohemijske osobine fluvisola duž sliva Zapadne Morave

The most common type of soil in the valleys of large lowland rivers is Fluvisol or Alluvial soil. In order to determine the biogenity of this type of soil along the Western Morava basin, the representation of the total microflora, fungi, actinomycetes, ammonifiers, Azotobacter sp. and oligonitrophiles was examined. The samples were taken from soils used in the most common two different ways (plough fields and meadows). For that were used standard microbiological methods of inoculation a certain decimal dilution on appropriate nutrient media. No correlation was established between the number of examined groups of microorganisms and the way of land use, nor was there a correlation with chemical properties, primarily with pH and organic matter content. A good representation of Azotobacter sp., as an indicator of soil fertility, was found. Agrochemical analyses showed an acidic to neutral reaction, a low to medium percentage of organic matter, a very low to very high content of easily available phosphorus and easily available potassium.

River Corridor Sources Dominate CO2 Emissions From a Lowland River Network

AbstractRivers and streams are control points for CO2 emission to the air (fCO2), with emission rates often exceeding internal metabolism (net ecosystem production, NEP). The difference is usually attributed to CO2‐supersaturated groundwater inputs from upland soil respiration and rock weathering, but this implies a terrestrial‐to‐aquatic C transfer greater than estimated by terrestrial mass balance. One explanation is that riparian zones—rich in organic and inorganic C but mostly neglected in terrestrial mass balances—contribute disproportionately to fCO2. To test this hypothesis, we measured fCO2, NEP, and the lateral CO2 contributions from both terrestrial uplands (TER) and riparian wetlands (RIP) for seven reaches in a lowland river network in Florida, USA. NEP contributed about half of fCO2, but the remaining CO2 emission was generally much larger than measured TER. The relative importance of RIP versus TER varied markedly between contrasting hydrogeologic settings: RIP contributed 49% of fCO2 where geologic confinement forced lateral drainage through riparian soils, but only 12% where unconfined karst allowed deeper groundwater flowpaths that bypassed riparian zones. On a land area basis, the narrow riparian corridor yielded far more CO2 than the terrestrial uplands (33.1 vs. 1.4 g‐C m−2 yr−1), resulting in river corridors (i.e., stream channel plus adjacent wetlands, NEP + RIP) sourcing 87% of fCO2 to streams. Our findings imply that true terrestrial CO2 subsidies to streams may be smaller than previously estimated by aquatic mass balance and highlight the importance of explicitly integrating riparian zones into the conceptual model for terrestrial‐to‐aquatic C transfer.