Search

Sediment transport to the sea by rivers is crucial for the stability of estuaries and coasts. The Yangtze River, the largest river in China, like many large rivers worldwide, is experiencing a decrease in sediment load reaching the coast. However, the tidal flat around Qidong Cape, located at the entrance of the North Branch of the Yangtze Estuary, is undergoing extensive siltation. The source of this sediment is unclear. In this study, a sediment core was collected and the geochemical characteristics of rare earth elements (REE) were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The results indicate the following: (1) The average content of REE is 178.57 μg/g, and the average ratio between LREE and HREE is 8.66, which is comparable to sediments from the South Yellow Sea. The chondrite-normalized and UCC-normalized patterns resemble those of the Yangtze River and the South Yellow Sea, indicating a negative gradient, a weak Ce-negative anomaly, and a distinct Eu-negative anomaly. (2) The continental shelf deposits in eastern China are primarily derived from sediment flux delivered by rivers. The sediments in the South Yellow Sea mainly originate from the Yangtze River and the Yellow River, exhibiting characteristics of a mixed source due to long-term geological processes, namely geochemical processes. The REEs in the tidal flat around Qidong Cape inherit the source area's characteristics and originate from the weathering of upper continental rock in mainland China. Moreover, the tidal flat around Qidong Cape is influenced by both runoff and tidal actions, leading to strong land–sea interactions and reducing the environment, explaining the Eu-negative anomaly. (3) Hydrodynamic forces in the North Branch of the Yangtze River have shifted from runoff to tidal dominance since the 1930s. However, marine hydrodynamics outside the estuary have remained unchanged. Consequently, the Subei coastal current plays a key role in sediment transport and diffusion. Sediments from the south wing of the Radiative Sand Ridge in the South Yellow Sea are transported southward by the Subei coastal current, and under tidal influence, suspended sediment is deposited in the tidal flat around Qidong Cape. Therefore, the sediment source has gradually shifted from the Yangtze River to the South Yellow Sea. [ABSTRACT FROM AUTHOR]

The youngest uplifted marine terrace at Kahutara Point on Māhia Peninsula, New Zealand, is undergoing rapid retreat (backwear) despite being fronted by a wide contemporary shore platform that attenuates wave energy. In this paper, wave energy and water level were recorded across the shore platform, and these data were used to model (a) how frequently waves reach the terrace riser and potentially erode it and (b) how frequently waves overtop the terrace. Analyses of wave data across shore normal transects show that under quiescent and storm conditions >90% of the energy delivered to the back beach and terrace riser is at infragravity frequencies (i.e., <0.05 Hz). Significant wave heights are reduced in a landward direction for both gravity (Hm0H) and infragravity (Hm0L) wave frequencies, with 50%–80% of Hm0H and 20%–50% of Hm0L reduced between seaward and landward sensors. Wave energy during quiescent conditions is strongly attenuated at the seaward margin whereas under storm conditions, proportionally more energy is delivered to the marine terrace riser. The development of a simple inundation model at Māhia reveals that the northern flank of Kahutara Point is more vulnerable to wave inundation, with 17 storms overtopping the youngest marine terrace between 1980 and 2020. Furthermore, despite there being no evidence of a 1‐in‐100 year storm event occurring at Māhia since 1980, there has been an increase in storminess since 2013. Changes in storm frequency may have offset decreases in wave energy (from energy attenuation) with increased platform width associated with marine terrace retreat. [ABSTRACT FROM AUTHOR]

Sedimentation is an important stressor of coastal ecosystems; yet, there is little research into specific mechanisms by which populations are affected by additional sediment loads resulting from anthropogenic-driven processes. This study explored the potential impact of the proposed disposal of over 7 million [m.sup.3] of dredge spoil on a nearby fishery for the blackfoot abalone Haliotis iris. The range of sediment deposition predicted by models to occur on reefs inhabited by H. iris as a result of the dispersal of sediment from the disposal site was used to design controlled experiments between July and September 2011 to test the likely effects of sedimentation on: (a) behaviour and mortality of juvenile H. iris and (b) photosynthetic vitality of crustose coralline algae (CCA) that form nursery habitats for H. iris obtained from Brinns Point (45, 40.3'S, 170, 39.4'E). We observed no direct effects on the health or mortality of H. iris juveniles or the photosynthetic vitality of habitat forming CCA. H. iris did, however, avoid sediments by moving from predation refugia beneath cobbles to vertical surfaces on cobble edges significantly more often in sediment treatments compared to sediment-free controls. Deposited sediments were also found to inhibit righting response, key behaviour in allowing H. iris to reattach to the substratum following dislodgement. Results of this study suggest that indirect mortality from reductions in available refugia from predation and inability to recover from dislodgement could be significant. These results highlight the importance of understanding indirect impacts of stressors on key ecological processes in order to predict ecological responses., Introduction Sedimentation is one of the most important stressors of coastal ecosystems, and there is significant concern about increased coastal sedimentation worldwide and the associated consequences of these changes on [...]