Channel Migration of the Meandering River Fan: A Case Study of the Okavango Delta

Okavango delta is a typical distributive fluvial system, which is composed of a series of sand island-river-swamp networks. River migration in the Okavango delta is analyzed by using satellite images from Google Earth and Alaska Satellite Facility (ASF). Four configuration characterization parameters are selected to depict and measure the meandering river. These four parameters are sinuosity index (S), curvature (C), the difference of along-current deflection angle (Δθ) and expansion coefficient (Km). In the fan, the channel migration is mainly asymmetric. According to geomorphic elements and associated features, Okavango Delta can be subdivided into three zones: axial zone, median zone and distal zone. Under the influence of slope, climate and vegetation, different migration modes are developed in different zones. As the river moves downstream, the sinuosity index of the river on the Okavango Delta decreases downstream. Based on the characteristics of different zones, the sedimentary facies model of a single source distributive fluvial system of a meandering river is proposed. The models of channel migration and sedimentary facies have wide application. This research will not only provide a basis for the prediction of future river channels but will also provide important theoretical guidance for the study of the sedimentary morphology of underground reservoirs.

Impact of river channel lateral migration on microbial communities across a discontinuous permafrost floodplain

Permafrost soils store approximately twice the amount of carbon currently present in Earth’s atmosphere and are acutely impacted by climate change due to the polar amplification of increasing global temperature. Many organic-rich permafrost sediments are located on large river floodplains, where river channel migration periodically erodes and re-deposits the upper tens of meters of sediment. Channel migration exerts a first-order control on the geographic distribution of permafrost and floodplain stratigraphy and thus may affect microbial habitats. To examine how river channel migration in discontinuous permafrost environments affects microbial community composition, we used amplicon sequencing of the 16S rRNA gene on sediment samples from floodplain cores and exposed riverbanks along the Koyukuk River, a large tributary of the Yukon River in west-central Alaska. Microbial communities are sensitive to permafrost thaw: communities found in deep samples thawed by the river closely resembled near-surface active layer communities in non-metric multidimensional scaling analyses but did not resemble floodplain permafrost communities at the same depth. Microbial communities also displayed lower diversity and evenness in permafrost than in both the active layer and permafrost-free point bars recently deposited by river channel migration. Taxonomic assignments based on 16S and quantitative PCR for the methyl-coenzyme M reductase functional gene demonstrated that methanogens and methanotrophs are abundant in older permafrost-bearing deposits, but not in younger, non-permafrost point bar deposits. The results suggested that river migration, which regulates the distribution of permafrost, also modulates the distribution of microbes potentially capable of producing and consuming methane on the Koyukuk River floodplain. Importance Arctic lowlands contain large quantities of soil organic carbon that is currently sequestered in permafrost. With rising temperatures, permafrost thaw may allow this carbon to be consumed by microbial communities and released to the atmosphere as carbon dioxide or methane. We used gene sequencing to determine the microbial communities present in the floodplain of a river running through discontinuous permafrost. We found the river’s lateral movement across its floodplain influences the occurrence of certain microbial communities—in particular, methane-cycling microbes were present on the older, permafrost-bearing eroding riverbank but absent on the newly deposited river bars. Riverbank sediment had microbial communities more similar to the floodplain active layer than permafrost samples from the same depth. Therefore, spatial patterns of river migration influence the distribution of microbial taxa relevant to the warming Arctic climate.

The benefits of merging passive and active tracking approaches: new insights into riverine migration by salmonid smolts

The process of smolting is a critical phase in the life-cycle of anadromous salmonids and it has been associated with substantial rates of mortality. Survival during freshwater and marine migration is known to have population level effects, thus an understanding of the patterns of mortality has the potential to yield important insights into population bottlenecks. Despite important advancements in tracking techniques, the specifics of mortality events in anadromous salmonids during their initial migration to sea remains somewhat elusive. Here, we develop a framework combining spatial and temporal detections of smolt riverine migration from two tracking techniques, which enable inferences to be made about mortality locations, causes, and rates. We embed this framework into a fine-scale behaviour study of migration and social structure. In this study, we demonstrate that during their initial riverine transitional phase, smolts were particularly vulnerable to predators. Specifically, avian predation appeared to be the main cause of mortality (42%), although piscine predation events were not trivial (14%). Our results suggested some direct and indirect tagging-induced mortality (e.g., through increased predation vulnerability), which highlights the importance of determining tagging mortality in a telemetry study to ensure adequate interpretation of migration success. There is evidence that predation induced selection on smolt morphology. Unsuccessful river salmon migrants with a phenotype comprising a shorter head and jaw and smaller eye had a higher probability of mortality in the later parts of riverine migration where avian and aquatic predation mortality dominated. In contrast, mortality earlier in river migration was independent of phenotype, most likely a result of tagging effects. Successfully river migrants were found to be interacting with each other, often in a pair or as a trio, indicating that a few individuals of Atlantic salmon and sea trout formed notable intra- and interspecific social associations. However, the heterogeneity of the social associations of successful migrants did not support the assumption that social network features attributed any clear specific benefits of reduced predation risk. Overall, by estimating migration loss and its variability, our study framework should help to guide management actions to mitigate the widespread population declines these species are currently facing.

The Braided River: Migration and the Personal Essay, Diane Comer (2019)

Review of: The Braided River: Migration and the Personal Essay, Diane Comer (2019) Dunedin: Otago University Press, 304 pp., ISBN 978 1 98853 153 3 (pbk), NZ$35

National-scale assessment of river migration at critical bridge infrastructure in the Philippines using Google Earth Engine

<p>River migration represents a geomorphic hazard at sites of critical bridge infrastructure, particularly in rivers where migration rates are high, as in the tropics. In the Philippines, where exposure to flooding and geomorphic risk are considerable, the recent expansion of infrastructural developments warrants quantification of river migration in the vicinity of bridge assets. We analysed publicly available bridge inventory data from the Philippines Department of Public Works and Highways (DPWH) and leveraged freely available satellite imagery in Google Earth Engine (GEE) to assess river migration. Specifically, we extracted active river channel masks of the bankfull extent (including the wetted channel and unvegetated, alluvial deposits) from Landsat products (Landsat 5, 7 and 8) using multi-spectral indices, before identifying river planform adjustments over decadal and engineering (30-year) timescales. For 74 bridges, we calculated similarity coefficients (Jaccard index) to indicate planform (dis)similarity and quantified changes in river channel width using RivWidthCloud.</p><p>Monitoring revealed the diversity of river planform adjustment at bridges in the Philippines (including channel migration, contraction, expansion and avulsion). The mean Jaccard index over decadal (0.65) and engineering (0.50) timescales indicated considerable planform adjustment throughout the national-scale inventory. However, planform adjustment and morphological behaviour varied between bridges. Some inventoried bridges were characterised by substantial planform adjustment and river migration, with maximum active channel contraction and expansion over decadal timescales equal to approximately 25% of the active channel width. This represents considerable lateral adjustment and when left unmanaged could pose a substantial geomorphic hazard. However, for other inventoried bridges the planform remained approximately stable and changes in channel width were limited. We suggest that multi-temporal analysis from satellite remote sensing offers a low-cost approach for monitoring the relative risk of river migration at critical bridge infrastructure; the approach can be extended to include other critical infrastructure adjacent to rivers (e.g., road, rail pipelines) and extended elsewhere to other dynamic riverine settings.</p>

Wireless logging of extracellular neuronal activity in the telencephalon of free-swimming salmonids

Background Salmonids return to the river where they were born in a phenomenon known as mother-river migration. The underpinning of migration has been extensively examined, particularly regarding the behavioral correlations of external environmental cues such as the scent of the mother-river and geomagnetic compass. However, neuronal underpinning remains elusive, as there have been no biologging techniques suited to monitor neuronal activity in the brain of large free-swimming fish. In this study, we developed a wireless biologging system to record extracellular neuronal activity in the brains of free-swimming salmonids. Results Using this system, we recorded multiple neuronal activities from the telencephalon of trout swimming in a rectangular water tank. As proof of principle, we examined the activity statistics for extracellular spike waveforms and timing. We found cells firing maximally in response to a specific head direction, similar to the head direction cells found in the rodent brain. The results of our study suggest that the recorded signals originate from neurons. Conclusions We anticipate that our biologging system will facilitate a more detailed investigation into the neural underpinning of fish movement using internally generated information, including responses to external cues.

Guo Pu Crosses the River: Migration Anecdotes in Jinshu Biographical Narratives

In the early fourth century CE, after the escalation of a series of succession disputes among the imperial Sima clan, the Jin dynasty collapsed and its capital city of Luoyang 洛陽 was destroyed. However, the end of the dynasty did not cause the Sima clan to fall from power entirely. Instead, the Jin dynasty was reestablished in the new capital of Jiankang 建康, the city known today as Nanjing. The earlier incarnation of the Jin would come to be known as the Western Jin dynasty, while the restored Jin dynasty is referred to as the Eastern Jin. The impact of this cataclysm on the inhabitants of Luoyang and the surrounding regions is difficult to quantify, and even harder to understand in more personal terms. We know that many of those who did not perish fled to the southeast, crossing the Yangzi River to resettle in the new capital. Later texts refer to this period as “The disorder of the Yongjia Reign” (Yongjia zhi luan 永嘉之亂). This epithet uses the imperial reign name given to the period between 307 and 313, even though the disasters did not neatly begin and end with those years. Although the Yongjia troubles are addressed throughout surviving historiographic material, there is no work of history dedicated to documenting the ensuing exodus from Luoyang to Jiankang.