The contribution of a surge event to infilling in a barrier‐enclosed estuary: Insights from field observations

The sediment discharge from the Yangtze River Basin has a stepwise decreasing trend in recent years. The impounding of the Three Gorges Reservoir exacerbated this decreasing trend and affected the change of the suspended sediment concentration (SSC) in the Yangtze River Estuary through the transmission effect. The SSC data of the Yangtze River Estuary during 1959–2012 showed that: (1) The SSC in the South Branch of the Yangtze River in the estuary and in the off-shore sea area displayed decreasing trends and decreased less towards the sea. At the same time, the difference in decreasing magnitude between SSC and sediment discharge became bigger towards the sea. (2) For the North Branch the preferential flow did not change much but the SSC tended to decrease, which was mainly caused by the decrease of SSC in the South Branch and China East Sea. (3) Due to the decreased runoff and the relatively strengthened tide, the peak area of the SSC in the bar shoal section in 2003–2012 moved inward for about 1/6 longitude unit compared with that in 1984–2002, and the inward-moving distance was in the order of flood season > annual average > dry season. (4) In the inlet of the South Passage, the SSC decreased mainly because the increase caused by resuspension and shore-groove exchange was less than the decrease caused by the sharp SSC decrease in the basin and the sea areas. The reverse was true in the middle section, where the SSC showed an increasing trend. (5) In the inlet of the North Passage, under the combined influence of decreased flow split and sediment split ratios, the decreased SSC in the basin and the sea area and decreased amount of resuspension, the SSC displayed a decreasing trend. In the middle section, because the increased amount caused by sediment going over the dyke was markedly more than the decreased amount caused by external environments, the SSC tended to increase. Holistically, the sharp decrease in sediment discharge caused synchronized SSC decreases in the Yangtze River Estuary. But there were still areas, where the SSC displayed increasing trends, indicating synchronicity and difference in the response of SSC to the sharp decrease in sediment discharge from the basin.

Global climate change and human activities jointly drive the long‐term changes of suspended sediment concentration (SSC) in the ocean, including high turbidity coastal seas such as the semienclosed Bohai Sea. In the past few decades, SSC in the Bohai Sea has exhibited a significant decreasing trend according to satellite observations. In this study, a regional numerical model is employed to carry out sensitivity experiments to quantify the relative contributions of several controlling factors to this multidecadal SSC decline in the Bohai Sea. The model results suggest that reduction in wind speed (by 20% over the past 40 years) can cause the largest decrease (8 mg L −1 , 32%, with values close to satellite remote sensing data) in SSC averaged over the Bohai Sea, associated with a decrease (17%) of wave‐induced bottom shear stress. The coastline and bathymetry changes, due mainly to sediment discharge of the Yellow River, cause large SSC changes at local scales. Since 1976 when the Yellow River mouth was relocated from Bohai Bay to Laizhou Bay, sediment deposition led to significant shoaling in the new estuarine area. This can increase the bottom shear stress by over 50% and the local SSC by more than 30 mg L −1 and an increase (2 mg L −1 , 8%) in SSC over the Bohai Sea. The quantification of contributions from different controlling factors can help to predict long‐term SSC changes in the Bohai Sea, and the method of this study can be applied to other coastal regions where such quantifications are still lacking.

Hydraulic evolution of high-density turbidity currents from the Brushy Canyon Formation, Eddy County, New Mexico inferred by comparison to settling and sorting experiments

Asian rivers are significant contributors to the world’s coastal sediment flux and the Western Pacific Coast (WPC) receives most of them. In recent years, Natural changes and human activities constantly change the suspended sediment concentration (SSC) in waters of the WPC; resulting in significant changes in coastal and marine systems, consequently altering the global biogeochemical cycle. However, monitoring these changes is difficult, confounded by the lack of observational data and unavailability of globally SSC algorithms. Here, based on the platform of Google Earth Engine, we retrieved the SSC in the waters where stretching 10 nautical miles from the WPC using multi-source imagery from Landsat-TM/ETM+/OLI sensors (from 1984-2022) to obtain its long-term dynamics using 3 different SSC algorithms. The results indicate that the 3 retrieve algorithms obtained satisfactory results in temporal-spatial variation trend of SSC. We discovered that some estuaries in the WPC show significant decreasing changes. For example, the spatial distribution of SSC in the Pearl River Estuary (PRE) represented a trend of high along the west coast and low along the east coast. Over the past 39 years, the SSC showed a relatively evident decreasing trend in most PRE regions; In the Yangtze Estuary (YRE), the SSC in the outer estuaries was generally significantly higher than that in the inner and SSC demonstrated an overall declining pattern in time; For the Yellow River Estuary, the highest of SSC is located a peripheral zone in front of the estuary, and also showed an overall decreasing trend in time.

Spatiotemporal variations of sediments transported along rivers play a crucial role in a wide spectrum of uses, such as navigation, recreation, habitats or river environmental protection. The advancement in technology has made it possible to use various indirect techniques to study and evaluate the transport of suspended sediment in fluvial environments. To investigate large-scale phenomena, remote sensing is becoming a largely utilized approach, as it allows to combine spatially distributed and local information. The systematic change of suspended sediment concentration (SSC) and dynamic processes controlling sediment transport at a given local scale are often not well known, and generally investigated using reach-specific field information. In this work, SSC maps were created by combining satellite images with local monitoring in situ SSC data, using the Zhijiang-Chenglingji reach of the Changjiang River (China) as a case study, and analyzing how SSC dynamics changed over the period 2016–2023, considering both low- and high-flow events. Multiple relationships between measured SSC and reflectance were selected from the literature and tested. Results show that a combination of Sentinel-2 bands 3,4, and 5 represents the best-performing statistical model (R 2 = 0.73) in mapping SSC spatiotemporal variations over an extent of dozens of kilometers. Despite the uncertainties connected to the small amount of data available and the differences between SSC data measured over the vertical and surface reflectance, this application shows the potential of remote sensing in mapping SSC at a large spatial scale, overcoming the limitations of localized field sampling, eventually suggesting a relatively simple approach that could assist water managers in mapping large-scale dynamics of SSC for applications such as navigation, habitat preservation, and hydropower production.

Min, J. E., Choi, J. K., Yang, H., Lee, S., Ryu, J. H. 2014. Monitoring changes in suspended sediment concentration on the southwestern coast of Korea. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 133–138, ISSN 0749-0208. Concentrations and distribution patterns of suspended sediment (SS) are key indicators of marine environmental change, particularly in coastal areas, which gives good information on the deposition and migration of sediments from land. In this study we analyzed 632 scenes (79 days × 8 scenes) of Geostationary Ocean Color Imager (GOCI) data in order to investigate SS variations relating to tides, tidal currents, bottom morphology, river discharge, and so on. We also compared them to the numerical model of tidal currents for the Yellow Sea. The study area, the coastline of Mokpo, is characterized by shallow water depths (<50 m), a relatively large tidal rang...

Long-term measurements of near-bottom currents and suspended sediment concentration on the outer Texas-Louisiana continental shelf

River deltas are reliant on upstream fluvial sediment delivery for their survival. The ultimate sediment delivery to deltas and the changing bed dynamics of river channels are strongly dependent on climate and anthropogenic changes within the entire river basin that control the increase (due to e.g. increased erosion, climate change) or decrease (due to e.g. sand mining, dam construction) of sediment supply. In the case of the Rhine-Meuse basin, suspended sediment delivery to the delta apex at Lobith has decreased since the 1950s. Therefore, we investigated changes in suspended sediment concentrations (SSC) and suspended sediment loads (SSL) over time along the main Rhine branch and its major tributaries (the Aare, Main, Mosel and Neckar) to determine the cause of the decline. We hypothesis and mathematically demonstrate that the spatial pattern in the temporal change can explain and determine specific mechanisms that are causing the decline. Using collated SSC data of varying frequency from 1997-2014, we explored the suspended sediment transport within and along branches using the rating curve method &amp;amp; discharge-suspended sediment relations for a total of 26 measurements stations in the basin. These were compared with bed level data from Ylla-Arb&amp;#243;s et al. (2021), to examine the interaction of SSC with bed dynamics. A clear spatial trend emerged: the decrease in SSC strongly increases in an upstream direction. In the Alpine Rhine SSC has increased. There is negligible change in the upper basin/impounded section of the Rhine. However, SSC decreases emerge after the confluences with the Main and Mosel branches and this decrease becomes stronger moving towards the delta. We find that contrary to many other river basins which are showing declining fluvial sediment delivery to deltas due to upstream dams or sediment management activities, in the Rhine-Meuse basin &amp;#160;the cause is actually the changing retention of channels and differing erosion rates from the river bed. Since the 19th century there have been activities to straighten and narrow the Rhine river to embank and fix the river course for navigation. This created high amounts of incision in the river bed in the early 20th century, but as proven by Ylla-Arb&amp;#243;s et al. (2021) and others, this incision is now decreasing. These changes in suspended sediment supply from the river bed can be correlated to the changing supply at the delta apex. Since the 1980s efforts have been made to stabilize bed erosion and this &amp;#8216;fixing&amp;#8217; of the river beds has led ultimately to a declining suspended sediment supply to the delta apex. This suggests that response to human interventions is not only relevant at a centurial timescale but is likely to be a defining feature of sediment supply for the coming century. &amp;#160; &amp;#160;

As a key component of global change, dam‐induced sediment reduction occurs in large rivers worldwide, which has profound implications on the fluvial systems. However, the systematic change of suspended sediment concentration (SSC) and its dynamic processes are not well known. We summarize typical SSC changes and propose a new sediment modeling framework for heavily dammed fluvial systems with the Changjiang (Yangtze River) as a background. We find that the fluvial SSC has declined by an order of magnitude, i.e., from ∼1.0 to ∼0.1 kg/m3, and even to ∼0.01 kg/m3 locally. The SSC distribution pattern along the mainstream has changed remarkably, with the sediment source/sink being partially reversed. Downstream of the Three Gorges Dam, the SSC recovery capacity gradually decreases with the sediment erosion quantity accumulated over time, and the SSC contribution rate of a linked large lake (Dongting) will change from negative (ca. −39%) to positive (ca. 17%), in the coming decades.

Huang, Y.-G.; Yang, H.-F.; Yang, S.-L.; Wang, Y.-P.; Dai, Z.-J.; Shi, B.-W., and Wu, Q.-Y., 2021. Decadal decreases of suspended sediment concentrations within the Yangtze River Estuary: A response to human impacts. Journal of Coastal Research, 37(4), 852–863. Coconut Creek (Florida), ISSN 0749-0208.Changes in suspended sediment concentration (SSC) in an estuary have environmental, ecological, and social-economic implications. Under human impact, annual suspended sediment discharges into the Yangtze River Estuary (YRE) display a downward trend, greatly influencing SSCs in the YRE. In this study, statistical analysis of SSCs measured in surficial water at 10 stations in the YRE indicates variations in decadal decreases in SSC, proven to be related to dam construction and soil conservation measures in the past decades. The degree of decrease varies temporospatially, with greater reduction in the annual surficial SSCs in the inner estuary than those in the outer estuary, and with the reduction rate in the former being greater in the dry season than the flood season, primarily because of the pronounced increase in water discharge during the dry season. In the outer estuary, the reduction rate in flood seasons is greater than in dry seasons because of the greater reduction in sediment discharge during the flood season. This study finds that SSC trends can be a useful reference for related studies of the YRE.

A major threat to freshwater taxon diversity is the alteration of natural catchment Land use into agriculture, industry or urban areas and the associated eutrophication of the water. In order to stop freshwater biodiversity loss, it is essential to quantify the relationships between freshwater diversity and catchment Land use and water nutrient concentrations. A literature survey was carried out on biodiversity data from rivers and streams. Fish and macroinvertebrates were selected as focal groups as they are widely used as indicator species of river and stream health. Only published data were selected that (a) compared data found at impaired sites with a pristine reference situation (either in time or space), (b) clearly defined the stressors studied (Land use cover and/or nutrient concentrations), and (c) clearly defined biodiversity (number of native species, species lists or IBI‐scores). The number of native taxa found in each study was transferred in an index of relative taxon richness (RTR) ranging from 0 (severely altered) to 100 (pristine reference conditions). Only those taxa were included that were (at least) present in the most pristine situation. This made it possible to combine, compare and analyse results from different studies. Catchment Land use was expressed as the percentage of non‐natural Land use (agriculture, industry, housing or mining). As a measure of nutrients, the concentrations of NO3, NH4, PO4, total N and total P in the river and stream water were used. Over 240 published articles have been studied, but only 22 met the criteria described above and could be used for further analysis. This study showed that altered catchment Land use has a major effect on freshwater biodiversity and that the rate of species loss is serious; on average every 10% of lost natural catchment Land use cover leads to a loss of almost 6% (±0.83) of the native freshwater fish and macroinvertebrate species. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Salmonid populations were sampled in 36 streams, at altitudes between 10m and 200m, in counties Cork and Kerry, south-western Ireland. The catchment land use ranged from open moorland and rough pasture/improved grassland to afforested sites with varying levels of catchment afforestation, mostly coniferous but with some patches of mixed coniferous and deciduous trees. The main geology types within the region were slate, Old Red Sandstone and limestone. Study sites were electrofished, and the density, biomass, age structure and condition of salmonid populations were assessed. A range of in-stream riparian and catchment environmental variables were measured, and the data were analysed using stepwise multiple regression to identify the most influential environmental factors affecting trout metrics following principle component analysis. The majority of salmonids were trout (86%), and mean trout density ranged from 0.662 fish mto 0.984 fish m-2 for all sites, irrespective of catchment geology. Trout condition did not differ significantly with level of catchment afforestation or geology, with the exception of limestone with high catchment afforestation. At sites with underlying limestone, trout condition decreased with increased catchment afforestation. River habitat structure was identified as the most important variable influencing trout density and biomass, irrespective of geology and water chemistry.

Damutu Bay in eastern Zhejiang, China has abundant tidal flat resources for years of silt deposition in the wide open seas, making it an ideal place for mudflat reclamation. In this study we set up a two-dimensional hydrodynamic and sediment transport model based on Mike 21 FM to investigate changes in suspended sediment concentration (SSC) after reclaiming to 1 m and 3 m depth contours in the seas. The model results are compared temporally and spatially to field observations in December, 2011 and August, 2012 of water levels, current velocities, and SSC, and indicate a strong data-model agreement. This study shows the sensitivity of the system to changes in SSC and suggests that a large-scale tidal flat reclamation could reduce SSC by 15∼20% on average in Damutu seas which would influence physical and biological processes particularly in the intertidal areas around the bay.

Spatiotemporal variations in suspended sediments over the inner shelf of the East China Sea with the effect of oceanic fronts

This paper presents an analysis of the factors contributing to the longitudinal increase in suspended sediment along the Lena River delta branches. Satellite images (Landsat 5-9) from 2000 to 2022 during the open channel period from June to September were captured for the suspended sediment concentration modeling. This period coincides with the water discharge in the Lena River ranging from 17,400 to 78,100 m³/s. The ERA5-Land reanalysis, monitoring observations at the Samoilovsky Island research station and remote sensing data were employed to estimate the factors influencing suspended sediment concentration changes. These factors included air temperature, precipitation, wind speed, solar radiation flux, permafrost temperature, water discharge and suspended sediment concentration in the top of the delta top, and the intensity of bank retreat. The results of the correlation analysis indicated that the observed increase in suspended sediment concentration was attributable to a combination of meteorological factors (temperature, precipitation, wind speed, and solar radiation flux) and the intensity of riverbank erosion associated with thermal processes. The longitudinal increase in in suspended sediment concentration (on average for the study period by 2-4% along the delta length) can be explained by an average daily air temperature and permafrost temperature increase. The analysis demonstrated that temperature factors exert a predominant influence on riverbanks comprising the Ice Complex. here was a significant correlation between the rates of riverbank degradation and the concentration of suspended sediment.