Evaluation of a tidal flat sediment nourishment as estuarine management measure
The tidal flats in the Eastern Scheldt tidal basin (The Netherlands) are eroding as a result of the construction of the storm surge barrier. These intertidal areas are important foraging grounds for birds and therefore it is important to mitigate the negative effects of erosion. As a pilot, a small part (20 ha) of the Galgeplaat tidal flat in the middle of the Eastern Scheldt was nourished with 130,000 m3 of sediment in 2008. This paper investigates this tidal flat nourishment using a large set of morphological and ecological monitoring data from 2008 to 2012. The nourishment proved effective in mitigating the negative effects of tidal flat erosion. The elevated tidal flat provides a foraging area for birds that is available for a longer period. The nourished area was relatively stable, giving time for the recovery of benthic macrofauna such that birds can benefit from the longer exposure time. Therefore, we conclude that sediment nourishments are an effective management measure to counteract the negative consequences of tidal flat erosion in the Eastern Scheldt, and have potential for other estuaries worldwide.
Monitoring tidal flat dynamics affected by human activities along an eroded coast in the Yellow River Delta, China
The coast of the northern Yellow River Delta (YRD) has experienced significant erosion since 1976 due to avulsion and consequent lack of sediment supply. Moreover, massive reclamation activity, expansion of the oil industry, and sea-level rise have jointly contributed to the rapid change of tidal flats over recent decades. Therefore, accurate reporting of the coast spatial extent and stability status is urgently required. We presented a method using remotely sensed waterlines to map tidal flats and monitor their spatiotemporal dynamics. The empirical results show that the area of the intertidal zone west of Tiao River Mouth (TRM) appeared to be decreasing. Despite intense hydrodynamic force, the intertidal zone to the east of TRM has expanded due to law prohibiting land reclamation in nature reserve. However, this trend weakened due to the expansion of oil industry after 2007. The movement of the mean high-tide line is the main cause for the increase–decrease patterns of the intertidal zone area. To achieve and maintain land equilibrium in this area, we suggest that a 554-m buffer must be preserved for mean high-tide line retreat. Unfortunately, the shrink crisis of the tidal flats has been extremely severe. Future reclamation and oil projects must be supplemented by studies that evaluate the complexities and dynamics of tidal flats so as to prevent the loss of this unique ecosystem.
Computer simulations and theory of oceanographic fluorescence lidar signals: effect of sea surface structure.
A 3-D computer simulation model has been developed using geometrical optics suitable for analyzing the effect of sea surface structure on oceanographic fluorescence lidar signals. Depth-resolved and depth-integrated signals reveal a considerable dependence on the surface structure. The results obtained by simulation are confirmed by a theoretical approach based on the transformation of solid angles by curved boundaries. Using statistical assumptions about the distribution of curvatures of the ocean surface, a general expression for this influence is found.