Small Mountain Stream Research Articles

A new, apparently lotic species of Relictorygmus from the Northern Cape Kamiesberg, South Africa (Coleoptera, Hydrophilidae, Cylominae)

Relictorygmus Seidel, Minoshima, Arriaga-Varela & Fikáček, 2018, the only known African genus of the hydrophilid subfamily Cylominae, currently includes two lentic species from the far southwestern Cape of South Africa. Here Relictorygmus riparius sp. nov. is described, based on specimens collected from wet moss beside a small mountain stream in the Kamiesberg, Northern Cape Province, South Africa, almost 500 km from previously known taxa and the first lotic member of the genus. The new species is compared with the two previously described Relictorygmus, R. trevornoahi Seidel, Minoshima, Arriaga-Varela & Fikáček, 2018 and R. repentinus (Hebauer, 2002) and notes are provided on its ecology at the type locality. This unexpected find suggests that other cylomines may remain undetected in southern Africa, particularly since they can easily be mistaken for species of the morphologically similar, but distantly related, Coelostoma Brullé, 1835.

Response of a small, forested stream to a large input of sediment

In small headwater channels coupled to hillslopes, episodic supplies of sediment from events like landslides can dominate local channel morphodynamics and impact ecosystem health. In this study we investigate the response of a small mountain stream in British Columbia to a sediment input event that was up to 150 times the volume of sediment transported in an average flood year caused by the upstream installation of a road bridge. Using four years of repeated UAV surveys, bedload tracers, and other field monitoring techniques, we examined the spatial and temporal changes in sediment storage along the reach, identified changes to channel morphology, and characterized the interaction between the channel bed and the supplied sediment. Historical monitoring of the reach allowed for a comparison of the response to nearly 20 years of information about bedload transport and morphologic change. We observed that most of the change within the reach occurred during the first flood after bridge installation. The supplied sediment mostly moved across the bed surface with little interaction, as tracers installed in the bed had lower than expected rates of mobility. A narrow, steep segment of the channel proximal to the bridge installation stored little sediment, whereas a wider, less steep segment further downstream absorbed much of the change. This effect was exacerbated by a logjam that formed during the first flood after bridge installation. Despite the relative magnitude of the sediment transport event, there was little change to the channel pattern, with the added sediment increasing the relief of the already existing morphologic units. This suggests river managers should focus their restoration attention on segments likely to respond to a disturbance and that the pool-riffle channel morphology can persist across a wide range of sediment-supply conditions.

Analysis of the driving factors of the change of erosion-deposition in the Minjiang Estuary, Southeast China

Understanding the evolution and driving factors of sedimentation and erosion at the mouths of small and medium-sized mountain streams during various periods is essential for regional spatial utilization, development, and sustainable economic growth. This is particularly important when considering the combined impact of climate change and human activities. This paper presents an analysis of the changes in sedimentation and erosion of mouth isobaths and underwater deltas over different periods using nautical chart data (1950-2019) and analyzes the factors driving changes in sedimentation and erosion during different periods from 1950 to 2020 based on the runoff-sediment discharge of the Minjiang River (MR) and extreme climate factors such as typhoons, especially the driving factors that caused a sudden change in the sedimentation and erosion process between 1998 and 2005. The results indicate that runoff-sediment characteristics are crucial in driving sedimentation and erosion changes. In the past 70 years, the underwater delta of the MRE has mainly experienced four stages: deposition (1950-1992) -erosion (1993-1998) -deposition (1998-2011) -erosion (2011-2019). Taking the impoundment operation of the Shuikou Reservoir in 1993 as the node, the sediment load of the Minjiang River into the sea began to decrease sharply, and then the estuary quickly showed a state of erosion. The change of sediment flux into the sea is the main driving factor for the evolution of erosion and deposition in the Minjiang River Estuary (MRE). The critical value of the erosion-deposition transition is about 570.3 × 104 t/yr. After the estuary entered a state of erosion in 1993-1998, significant siltation suddenly occurred in 1998-2005. The reason for the siltation in this period may be related to the frequent transit typhoons and flood events in 1998-2005. Therefore, the change of river sediment supply into the sea is the main driving factor controlling the erosion and deposition evolution of the Minjiang River estuary on a long time scale of more than 10 years, which reflects the influence of large-scale human activities on the river and estuary area in the past half century. Extreme climate events are the incentive to adjust the estuary landform in the short term. Extreme climate events will not fundamentally change the process of estuarine geomorphological evolution under the background of sediment supply reduction.

Effects of Environmental Factors on the Distribution and Diversity of Aquatic Oligochaetes

The aim of our study was to detect the actual distribution of oligochaete species and to identify their ecological differentiation with respect to environmental factors: altitude, temperature, oxygen concentration, conductivity, total organic carbon, and waterbody type. Although widespread, differentiation of oligochaete communities in four waterbody types and altitudinal groups can be observed through alpha and beta diversity. Their differences were analyzed using MANOVA, while the ecological preferences of species were presented with logistic Gaussian regression analyses. The highest number of the species of Oligochaeta was recorded in oligochaete communities in medium and large rivers. Total beta diversity decreased with the decreasing of waterbody size, the increasing of size of the substrate particles, river flow velocity, as well as altitude. Communities from small mountain rivers and streams and large and medium rivers with coarser substrate differed from other oligochaete communities. When coarser substrate was prevalent in smaller and medium rivers, a domination of a certain family was observed: Lumbriculidae (>800 m a.s.l.), Propappidae and Enchytraeidae (500–800 m), and Naididae (<500 m a.s.l.). Common species of Oligochaeta, with significantly overlapping ranges in running waters in Serbia, still show a clear grouping with respect to preference for certain types of waterbodies.

Assessment of the viable effects of structural reconstruction of habitats in a mountain stream: A long-term study

The Carpathians are biodiversity hotspots in Europe. However, transformations resulting from human activity have affected stream catchments where forest management is carried out. Numerous anti-rubble weirs and other low-head barriers disrupt the continuity of many streams. New requirements for human interference in stream channels were formulated. Measures are urgently needed to restore the ecological continuity and mosaicism of semi-natural habitats in mountain streams. Recently, small streams have been restored in mountainous areas. To assess the viable effects of stream restoration, analyses of in-stream habitats and fish communities, which are excellent bioindicators, were performed. This study aimed to assess the effects of structural reconstruction of habitats in a mountain stream (Eastern Carpathians, Poland). The analyses were based on a long-term assessment of fish responses to barrier removal and habitat changes following stream restoration measures. The research was conducted from 2009 to 2022. Our study indicates numerous positive and viable effects of using boulder ramps as technical solutions for restoring small mountain streams. Restored ecological continuity and in-stream habitats provide fish with adequate feeding grounds, spawning grounds, and fry-growth places. On the other hand, we indicated that the assessment of the effects of mountain stream restoration should be carried out over a long-term period, in three stages after the completion of work: early, medium, and late. This may allow for the most reliable assessment of the effects of restoration measures and the early detection of the need for corrections. It is also necessary to monitor possible changes that may occur in new hydrotechnical objects, such as boulder ramps, due to natural hydro-morphodynamic processes in the stream bed.

Context‐specific positive effects of woody riparian vegetation on aquatic invertebrates in rural and urban landscapes

Abstract Woody riparian vegetation (WRV) benefits benthic macroinvertebrates in running waters. However, while some functions are provided by WRV irrespective of surrounding and catchment land use, others are context‐specific. In recent large‐scale studies, effects of WRV on macroinvertebrates were therefore small compared to catchment land use, raising the question about the relevance of WRV for restoration. Model‐based recursive partitioning was used to identify context‐dependent effects of WRV on the macroinvertebrates' ecological status in small (catchment area 10–100 km2) lowland (n = 361) and mountain (n = 748) streams. WRV cover was quantified from orthophotos along the near (500 m) and far (5000 m) upstream river network and used to predict the site's ecological status. Agricultural, urban and woodland cover at the local and catchment scales along with hydromorphology were considered as partitioning variables. In rural agricultural landscapes, the effect of WRV on the ecological status was large, indicating that establishing near‐upstream WRV can improve the ecological status by as much as two of the five classes according to the EU Water Framework Directive. Even in urban landscapes, effects of far‐upstream WRV were large if catchments had a moderate share of agricultural land use in addition. The beneficial effects of WRV were only limited in purely urban catchments or in a multiple stressor context. Synthesis and applications. While woody riparian vegetation (WRV) can even improve the ecological status in urban settings, it is especially relevant for river management in rural agricultural catchments, where developing WRV potentially are effective measures to achieve good ecological status.

Modelling the Effects of Dam Reservoir Backwater Fluctuations on the Hydrodynamics of a Small Mountain Stream

The water depth and flow velocity of a river may be temporarily disturbed by the water level fluctuations connected with the operation of artificial dam reservoirs located downstream (so-called backwater fluctuations (BF)). In this research, we use the two-dimensional hydrodynamic model iRIC MFlow_02 to quantify the effects of BF on the lowermost section (ca. 1.5-km length) of a small (channel width ≤ 20 m) mountain stream, the Smolnik Stream, which flows into the Rożnów Dam Reservoir, in Southern Poland. To reproduce the hydrological conditions generally observed in the stream, six scenarios were simulated, considering three steady flow discharges at the inlet, with recurrence intervals of 1 year (1.8 m3 s−1, small flood), 2 years (24.5 m3 s−1; medium flood), and 20 years (89.5 m3 s−1; large flood), and two reservoir levels at the outlet: 265 m a.s.l. (normal reservoir water level) and 270 m a.s.l. (maximum reservoir water level). In these simulations, sediment transport and morphodynamics are not considered. The average modelled water depth was increased by backwater fluctuation in the channel, from 28% (from 1.62 m vs. 2.07 m) during a small flood, up to 59% (from 3.46 m to 5.50 m) during a large flood. Contrastingly, the average modelled flow velocity was decreased in the channel (from −8% 0.52 m s−1 vs. 0.47 m s−1) during a small flood to −78% (0.49 m s−1 vs. 0.11 m s−1) during a large flood. Our results demonstrate that backwater fluctuations substantially disturb the hydrodynamics of the studied stream, which is interpreted as a triggering factor of the previously documented alterations in its sedimentology, morphology, and riparian vegetation pattern.

Fire and ice: Winter flooding in a Southern Rocky Mountain stream after a wildfire

We observed a low-discharge flooding phenomenon on Little Beaver Creek, a tributary to the Cache la Poudre River in the Southern Rocky Mountains of Colorado, USA. Ice ranging in thickness from a few centimeters to 0.5 m occupied a large volume of the channel, forcing flows out of its banks. On two occasions, multiple consecutive days of uncharacteristically warm weather caused a spike in snowmelt, and bankfull stage was surpassed 60 days before peak runoff. The flow events occurred in late winter, six months after a wildfire had burned a large portion of the watershed at medium-to-high severity. Ash and other organic materials were mobilized during the overbank flows, and we observed evidence of recent ash deposition in the floodplain and high ash concentrations in the channel. During the same time period, camera footage captured the formation and collapse of a large accumulation of ice and snow at a log jam. Because climate change projections and recent observations indicate higher variability in weather patterns, wildfire regime, and precipitation events, winter flooding associated with ice, although not widely documented in small mountain streams, may become more common. Flooding and subsequent deposition of ash and other sediment can disrupt fluvial processes, impair the local biotic community, cause property damage, and impact drinking water sources.

Geo-historical database of flood impacts in Alpine catchments (HIFAVa database, Arve River, France, 1850–2015)

Abstract. In France, flooding is the most common and damaging natural hazard (CCR, 2021). Global warming is expected to exacerbate flood risk and could be more pronounced in the European Alps which are experiencing a high warming rate, likely to lead to heavier rainfall events. Alpine valleys are densely populated, potentially increasing exposure and vulnerability to flood hazard. The study of historical records is highly relevant to understand long-term flood occurrence and related socio-economic impacts in relation to changes in the flood risk components (i.e. hazard, exposure and vulnerability). To this aim we introduce the newly constituted database of Historical Impacts of Floods in the Arve Valley (HIFAVa) located in the French northern Alps starting in 1850. This quite unique database reports historical impacts related to impact events occurrences in a well-documented Alpine catchment that encompasses both hydrological and socio-economical diversity. After a complete description of the database (collection, content and structure), we explore the distribution of the recorded impacts with respect to their characteristics and evolution in both time and space. The analysis reveals that small mountain streams and particularly glacial streams caused more impacts (67 %) than the main river. While an increase in heavy rainfall and ice melt are expected to enhance flood hazard in small Alpine catchments, this finding calls for greater attention to flood risk assessment and management in small catchments. The analysis also reveals an increasing occurrence of impacts from 1920 onwards, for which possible factors are discussed. Further work is, however, needed to conclude on the respective contribution of the source effect, the increase in flood hazard, or the exposure of goods and people.

Passive Restoration of a Small Mountain Stream in Eastern Oregon

In this study, I documented the results of 11 years of passive restoration of a small mountain stream in northeastern Oregon. Removal of the main stressors on the system, grazing and agricultural practices, resulted in a strong recovery of the riparian vegetation over the middle two-thirds of the reach. Cover of trees and shrubs tripled, tree density increased sevenfold, and stream shading fourfold over the period 2007 through 2018. Average maximum daily stream temperature declined by 2.1 to 2.8 °C, and average maximum diurnal temperature range narrowed by 3.7 to 4.6 °C. Recolonizing American beavers (Castor canadensis) played an essential role in improving the condition of the streambed over 18% of the reach. Their dams and ponds initiated the process of streambed aggradation and transformed the single-thread, incised channel into a multi-thread configuration within beaver complexes. Vegetation expansion was much stronger in impounded than in un-impounded parts of the stream. Passive restoration was not effective in two sections, together comprising one-third of the reach. In the upper part of the stream, recovery stalled because of continued (unauthorized) trespass grazing during late summer and fall. The channelized lower section of the stream was too severely modified for measurable recovery to occur. I concluded that 11 years of passive restoration improved the functionality of the stream from 24% to 32%, and within beaver complexes, up to 57% of its pre-disturbance condition.

Revision of larvae of the dobsonfly genus Platyneuromus van der Weele (Megaloptera, Corydalidae, Corydalinae)

Platyneuromus van der Weele (Megaloptera, Corydalidae, Corydalinae) is a dobsonfly genus endemic to Mexico and Central America with three valid species. Its larvae or hellgrammites are exclusively aquatic, feed on aquatic invertebrates or – sometimes – small vertebrates, and inhabit lotic ecosystems, from small mountain streams to large tropical rivers, typically clean and well oxygenated. Until the present study only Platyneuromus soror (Hagen) had its larva described. Recently, dobsonfly larvae were collected in Agua Azul waterfalls, Chiapas, Mexico, a previously recorded site for the geographically restricted Platyneuromus reflexus Glorioso & Flint. Herein, we associate those larvae to the latter species through DNA barcoding comparison with adults from the site. We describe the larva of P. reflexus for the first time, as well as the larva of Platyneuromus sp. A, a probable undescribed species from mountainous areas of western Mexico; both are compared with the previously described P. soror. We also provide a key for the identification of known larvae of this poorly known dobsonfly genus.

Assessment of the naturalness and anthropogenic transformation of the habitats of small mountain streams in different climate zones

The study compares the quality of the habitats of mountain streams in sections without visible human integration and those permanently transformed by human activity between mountain areas in different climate zones. Three mountain streams with small catchments (10–20 km2) characterized by different natural conditions were selected for the research. The selected streams are Bystrzanka (Beskid Niski, Polish Carpathians), Peshok (Darjeeling Himalaya in India), and Fanshen (Hengduan Shan in China). Field studies were carried out using the British River Habitat Survey (RHS) method. Habitat quality was analyzed based on the following indicators: Habitat Quality Assessment (HQA) and Habitat Modification Score (HMS). The obtained results indicated that sections of mountain streams located in upper catchment areas show greater habitat naturalness in relation to stream sections in lower areas. This results from the greater variety and number of natural hydromorphological elements in streams and the close vicinity of channels. In both upper and lower stream sections, regardless of the degree of naturalness and anthropopressure, the same RHS attributes have the greatest impact on the HQA and HMS values. Similar regularities in the degree of naturalness and anthropogenic modifications of the habitat between the upper and lower reaches of streams can be also expected in other mountain areas, apart from areas not affected by human activities.

The influence of lithology on stream metabolism in headwater systems

AbstractPhysical disturbances in streams have important effects on rates of gross primary production (GPP) and ecosystem respiration (ER). Underlying lithology can control sediment size, amount, and evolution in the stream, influencing substrate stability and in turn benthic organisms. We assessed patterns of disturbance and recovery for metabolic processes of GPP and ER associated with periods of increased flow and suspended sediment flux between December and April in two streams in the Oregon Coast Range with differing lithologies (basalt and sandstone). The results of whole‐stream metabolism modelling indicate that the two study streams have varying patterns of response and recovery rates after storm events. Both streams were heterotrophic during the entirety of the study period with changes in heterotrophy driven by changes in ER. Poststorm GPP decreased in both streams, but the basalt basin had greater proportional decreases and recovered slower than the sandstone basin. This result was unexpected and appeared to be associated with lower light availability in the basalt basin driven by increased turbidity during storm events; the coarser basalt substrate weathers into smaller size fractions than the finer sandstone substrate, remaining in suspension over longer periods and limiting light availability to benthic primary producers. The rates of ER in the sandstone basin did not change from prestorm to poststorm, whereas rates of ER in the basalt basin had varying responses. Overall, our results indicated that the underlying lithology of small mountain streams can drive variability in GPP by controlling sediment size and light availability during storms events.

Indirect Estimation of Flow and Suspended-sediment Concentration and Load in Small Mountain Streams: an Exploratory Study in Ribeira Seca Stream, Madeira Island

The aim of this study was to assess the applicability of indirect techniques for streamflow and suspended sediment concentration estimation and their use in the calculation of suspended sediment transport rate in the small mountain watersheds of Madeira Island, Portugal. Emphasis was given to the application of salt dilution gauging to the indirect determination of the flow rate and the use of water turbidity data to estimate the concentration of suspended sediments. The field and laboratory work carried out are briefly described, and the main experimental results and the field data from the short measurement campaign performed in the Ribeira Seca stream in Faial, on the north side of the island, are presented and discussed. Whilst the measurement campaign carried out was temporally and spatially limited, it was pioneering for Madeira and allowed to verify the applicability of the indirect hydrometric and sedimentometric techniques used in this exploratory study.

КОМПОНОВОЧНО-КОНСТРУКТИВНЫЕ РЕШЕНИЯ ФИЛЬТРУЮЩИХ ВОДОЗАБОРОВ ИЗ МЕЛКОВОДНЫХ ВОДОТОКОВ ДЛЯ СИСТЕМ КАПЕЛЬНОГО ОРОШЕНИЯ

Purpose: development of layout and design schemes for low-flow water intakes, arranged on shallow river and stream watercourses for supplying water to drip irrigation systems. Agricultural development of terraces and floodplains of small foothill and mountain streams actualizes the development of facilities for water intake from them for the purpose of irrigating land. Morphological and hydrographic features, including shallow low-water depths, high flow rates, flow rates variability, saturation with sediments, the presence of underflow and overflow runoff, etc., make water intake from such watercourses difficult and specific. These circumstances predetermine the relevance of water intake structures development corresponding to the specified conditions. Materials and Methods. When developing the layout and design schemes of low-flow water intakes from shallow watercourses, the technologies of exploratory design of engineering systems and structures were used. Results. With regard to the morphometric, hydrological and other conditions of shallow foothill and mountain streams, a water intake with a bottom water intake was adopted for development. The water intake part of headworks is designed in the form of a toe drain, which has under-flow and overflow intake parts that allow water intake from the channel and off-channel water streams. The toe is made of two or three layers of sand and gravel material. Drainage pipes or pipe filters are used as a drainage element. Depending on the conditions of the watercourse, water intakes with transverse, longitudinal and pocket-coastal placement of water intakes are proposed. Conclusion. The layout and design schemes of filtering water intakes from shallow watercourses based on the use of overflow, underflow and combined structures of multilayer drainage water intakes with stream (transverse and longitudinal) and off-channel (pocket-coastal) placement have been proposed and developed.

Study of ancient monuments in namangan region

During the years of independence, the study of archeological monuments in the Namangan region has begun. The services of archaeologists in this regard are invaluable. Archaeological excavations in recent years have revealed that Namangan region has also been extensively developed by primitive farmers. Especially in the foothills, where small mountain streams flow, created conditions and opportunities for the emergence and development of sedentary agriculture. The ruins of these small rivers, such as Govasay in Chust, Tergachi on the banks of the Kosonsoy, and other ancient villages, are typical of this period.

A new fossil species of Trentepohlia (Diptera, Limoniidae) from the Dominican Miocene

We present the description of a new species of Limoniidae Rondani, 1856. Trentepohlia (Paramongoma) miocenica Mederos & Wang n. sp. is described from resinites (little or poorly polymerized amber) of Yanigua Formation, in the Eastern District of Dominican Republic, well differentiated from the other species from the fossil record of Hispaniola to date, Trentepohlia (Paramongoma) agriPodenas & Poinar, 1999. A key to the five fossil species of the subgenus ParamongomaBrunetti, 1911 described to date is also offered. Since the biology of the immature stages of Paramongoma are associated with aquatic microhabitats (such as phytotelmata and small mountain streams), the occurrence of such microhabitats can therefore be hypothesized in the area then occupied by the Hispaniolan paleo-island. The records of extant species of the subgenus Paramongoma from several islands of the Lesser and Greater Antilles, as well as presence of the suitable ecological conditions, offers the possibility of finding living species of TrentepohliaBigot, 1854 at Hispaniola, which is currently the only large island in the Caribbean without records of the genus.

Do changes in temperature affect EU Water Framework Directive compliant assessment results of central European streams?

BackgroundBenthic invertebrate communities are an integral and longstanding component of stream biomonitoring. However, multiple stressors driven by global change threaten benthic invertebrate communities. In particular, climate warming is expected to disrupt freshwater ecosystems. While an increasing number of studies have shown changes in benthic invertebrate community composition in response to climate warming, the effect on stream assessments has rarely been investigated. As several community composition metrics are also used in stream assessments, we predicted that climate warming would worsen stream assessment results. Therefore, we used a comprehensive data set of 2865 benthic invertebrate samples taken between 2000 and 2014 from small central European low mountain streams. We examined the effects of changes in temperature on common community and stream assessment metrics. We used 31 metrics covering composition, richness, tolerance and function of communities, of which many are used in various stream assessment schemes.ResultsAgainst our expectations, we identified a decreasing air temperature trend of − 0.18 °C over 15 years. This trend was accompanied by significant changes in community composition, for example, increases in species richness and decreases in the community temperature index (CTI). Further, we identified slight concomitant improvements of various globally used stream quality assessment metrics, such as a decreasing saprobic index and an increasing BMWP.ConclusionsWhile temperature increased by + 0.9 °C during the past 30 years (1985–2014), our 15-year study period (2000–2014) showed a decrease by − 0.18 °C. Therefore, we regard the concomitant improvement in several assessment metrics as a recovery from prior increasing temperatures. In turn, we assume that increases in water temperature will lead to opposite effects and therefore cause declining assessment results. Water managers should be aware of this linkage that in turn could provide a chance to mitigate the effects of global warming by, for example, planting trees along the rivers and the removal of artificial barriers to increase current velocity to minimize a warming effect.

Continuous riverine biodiversity changes in a 10‐years‐post‐restoration‐study—Impacts and pitfalls

AbstractEvaluating river restoration effects over several years is the exception rather than the rule. The benthic invertebrate fauna of three small mountain streams was investigated yearly from 2010 to 2019 following remeandering measures. Additionally, upstream near‐natural reaches were studied following a Before‐After‐Control‐Impact (BACI) design. Species richness and Ephemeroptera, Plecoptera and Trichoptera richness decreased strongly immediately after restoration but had positive effect sizes in the following 6 years. Abundances increased in all sites after restoration. These patterns were consistent also in the upstream near‐natural reaches, except for the decrease in richness in the second year, indicating that other factors beside the restoration affected the sites. A large flood event coincided with the implementation of the restoration measures depleting also the near‐natural sites. The similarity between paired reaches showed a sharp decline in the first year after restoration, followed by a direct increase, which indicates fast recolonization from the upstream reaches. Community composition analysis showed a shift of all communities with the time axis, underlining a substantial effect of external factors. Generalized linear mixed effects models exhibited that the percentage of tree cover and riparian vegetation had significant effects on changes in richness and abundance. Clear‐cut logging in the floodplains to restore natural floodplain forest supposedly increased water temperatures because many cold‐adapted upstream species were replaced by species naturally inhabiting more downstream reaches. The results emphasize that multiannual samples and a BACI design are necessary to understand restored systems. Furthermore, floodplain restoration and natural hydrology often shape benthic invertebrate communities more than pure instream restoration measures.

The Significance of Log and Boulder Steps for Diversification of Fluvial Sediments Characteristics in a Stream Channel in a Small Forest Catchment in the Polish Carpathians

The study presents the diversification of sediments deposited on log (LS), boulder (BS) and mixed-type (LBS) steps located in the channel of a stream in a small forest mountain catchment in the Polish Carpathians. The topic of sediment diversification in a stream channel is an important issue not only from the perspective of sediment transport process and shaping fluvial systems in forested catchments caused by woody or rock debris but also in the context of functioning of local ecosystems. We aimed to test the following hypothesis: the morphodynamic features of a stream channel and the type of steps therein significantly affect the diversification of the size and shape of mineral deposits and play an important role in the process of sediments transport and processing in the channels of small mountain streams. In order to verify the above hypothesis, sediments were sampled directly from the stream channel (Ch) in its longitudinal profile as well as upstream and downstream of steps (LS, BS and LBS) in the channel. The diversification of features of sediment grain size was analysed taking into account step type and sediment location in the longitudinal profile of the stream channel. The research was conducted separately for fine-grained sandstone (A) and coarse-grained sandstone (B). In addition, the basic sedimentological indicators and the shape parameter of the gravels, as described by the Zingg method, were determined. In order to determine the transport predisposition of the sediments in a specific load, an analysis of sediment distribution was performed on the C/M (C—first percentile and M—median) diagram. The PCA (Principal component analysis) analysis showed that the step type significantly affects the processing as well as the size and shape diversification of mineral deposits, which confirms our hypothesis. Therefore, this study is a contribution to the current knowledge on fluvial processes occurring in stream channels in small forest mountain catchments.