Sand Net Device to Control the Meanders of a Coastal River: The Case of the Authie Estuary (France)

The Authie estuary is characterized by an important southern sand spit and a northern shoreline subject to strong erosion due to the meandering of the coastal river. In order to reduce this erosion, a new soft coastal defence, namely the sand net device (SND), has been implemented inside the Authie estuary. It consists of several nets assembled in an inverted V creating a porous structure and thus trapping sand as shoreline protection. However up to now, little proof has been provided on the explicit influence of this SND on the hydrodynamic pattern and associated morphodynamics. In this paper, field surveys of morphological developments combined with numerical modelling (Telemac-2D/3D) analyze the influence of the SND into flow pattern and morphodynamics. In situ monitoring clearly points out sedimentation around the SND and a deepening of the main channel. Modelling results show that, without SND, erosion is observed around its location. With a SND implemented, the velocity has been reduced and created a deviation in its direction by a circulation around the SND location. The impact area of the structure is around 500 m in both directions, upstream and downstream part.

Distribution and fractionation of rare earth elements in suspended particulate matter in a coastal river, Southeast China

Background In the river system, the geochemistry of rare earth elements (REEs, a series of elements from La to Lu) in suspended particulate matter (SPM) is generally controlled by rock weathering processes and hydrochemical characteristics, as well as being affected by anthropogenic activities. However, the variations of geochemical characteristics and behaviors of REEs in SPM with a salinity gradient from the inland river to the estuary have been short of a systematic understanding. Methods The REE concentrations, Post Archean Australia Shale (PAAS)-normalized REE, La/Yb, La/Sm, and Sm/Yb ratios of SPM were investigated in the Jiulongjiang River, which is a coastal river mainly flowing through granite rocks in Southeast China. The correlation relationships between physicochemical parameters (including water pH, total dissolved solids (TDS), HCO3– concentrations, and the concentrations of major elements of SPM) and PAAS-normalized REE ratios of SPM were analyzed to determine the factors that affect the REE concentration and fractionation of SPM in the different regions of Jiulongjiang River, including the main stream and tributary of Beixi River, Xixi River, Nanxi River, and estuary. Additionally, the Ce, Eu, and Gd anomalies of SPM were estimated. Results The average ∑REE concentration of SPM (352 mg/kg) in the granite rock basin was twice higher than the mean value (175 mg/kg) of the world’s rivers. The PAAS-normalized REE ratios of SPM in the main rivers including Beixi River (main stream), Xixi River, and Nanxi River were near due to the same lithologic distribution. In the tributary of Beixi River, the input of low-weathered carbonate minerals which contain very few REE caused the lower REE concentrations of SPM. The PAAS-normalized REE ratios of SPM in the estuary were significantly lower than those in the main rivers, which was mainly attributed to the significant REE removal with the increment of salinity. The enrichment of LREE relative to HREE in SPM increased with decreasing water pH in the main rivers. In the estuary, the preferential removal of dissolved LREE occurred compared to HREE with the increment of salinity. The negative Ce and Eu anomalies of SPM occurred in both the main rivers and estuary region and rare Gd pollution was present in the basin. Additionally, human activities caused the increment of REE concentrations and more negative Ce anomaly at some specific sites, such as dam effect and agricultural pollution. Conclusions The REE concentrations and fractionations of SPM in river water mainly depend on lithologic distribution and riverine pH, while they are affected by salinity in the estuary.

Influence of wastewater discharges on benthic macroinvertebrate communities in a cantabrian-atlantic coastal river

This paper studies the effect of wastewater discharges on benthic macroinvertebrates in the Furnia River (Pontevedra, NW Spain). Semiquantitative surveys were carried out in spring 2008 and 2017 in three different locations, upstream and downstream of a sewage treatment plant built in 2013. Different indexes were calculated based on benthic macroinvertebrate assemblages: abundance, richness, Shannon-Wiener, EPT, IASPT, IBMWP and several physicochemical variables were measured concurrently. Although the indexes values decreased slightly along the water course, the results indicate an optimal water quality of the Furnia River, supporting a very diverse community of aquatic macroinvertebrates.

Impact of Precipitation and Flow Rate Changes on the Water Quality of a Coastal River

This paper aims to investigate the effects of natural variables, including precipitation and flow rate, on the quality of the Zarjoub River in Guilan province, Iran. The new hydrological insight in this study is a lack of national research focused on the dual effects of rainfall and flow rate on river water quality in coastal areas along the Anzali Wetland. To investigate the effect of precipitation and flow rate on river water quality, nine water quality variables were monitored during the 10-year period. In this article, (a) the existence of trends and the best fitted models of water quality parameters and the discharge and precipitation were analysed using statistical techniques and (b) the relationships between concentration of constituents with the discharge and precipitation on the up-stream and middle station were also examined. Box plots, for explaining the distribution of a data collection, were used. The results showed the existence of trend of water quality parameters with river flow and rainfall. As presented in Section 3, with increasing precipitation and flow rate, concentration of all constituents, except pH and SO₄2, decreased. On the contrary, the maximum amount of water quality elements was observed in low precipitations; therefore, the maximum concentration occurred in less than 15 mm precipitation. Simple regression was used to evaluate the discharge concentration and precipitation concentration. According to the correlation coefficient (r), the relationship between concentration and precipitation is weaker than (0.238) discharge concentration (0.699). The results further showed climate change and river water quality to be related.

Severe Weather Disasters in China Linked to Long-Term Solar Activity During the Last 2000 Years

Historical records truthfully document human life and environment associated with climate changes. We quantify official historical records of China dating back last two thousand years to examine the disasters due to anomalous temperatures of cold or hot, irregular precipitations of wet or drought, and floods in inland/coastal or Northern/Southern areas in four seasons that possibly linked to solar activities during 1-1825 CE (Common Era). Statistical results show that extreme cold weather occurs particularly in the Winter and Spring during low solar activity (LSA) periods. Irregularities precipitations, including heavy rain/hail/snow and severe drought are significantly frequent during LSA periods, while floods on inland and coastal river basins tend to occur more frequently in LSA and high solar activity (HSA) periods, respectively. The two disasters frequently happen in Summer and Autumn, which suggests that the irregular precipitations could cause the floods. The disasters occur significantly in the Nouthern China, which suggests that the climate boundary of the Qinling–Huaihe Line along at about 33°N plays an important role. In total, the disasters due to the anomalously cold temperatures, irregular precipitations, and floods tend to occur during the LSA periods.