Abstract
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.
Highlights
The question of processes of erosion, transport and accumulation of mineral sediments in mountain river and stream channels is the focus of research for numerous researchers [1,2,3,4]
Among important factors involved in the differentiation of mineral material features is the occurrence of steps formed along a stream channel out of woody debris (LS) [6] and rock debris (BS) [11,12], which become the places of deposition of mineral sediments [13], large woody debris (LWD), fine woody debris (FWD) [14] and particulate organic matter (POM) [15]
Morphodynamic features of stream channels in small forest mountain catchments determine the type of sources of mineral material supply to the fluvial system by which these features affect the characteristics of alluvial deposits
Summary
The question of processes of erosion, transport and accumulation of mineral sediments in mountain river and stream channels is the focus of research for numerous researchers [1,2,3,4]. In forest mountain catchments, woody debris in the form of dead trees or their fragments is supplied to stream channels by windblow, rubble and mud downflow, landslides, avalanches, forest management activities or the activity of beavers [18,19]. It plays an important role in bedload transport [20]. Log steps increase channel roughness and reduce flow velocity [6], which means that the transported sediments of different fractions are introduced into the fluvial system gradually, mainly during high flows [22]
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