Description: Particulate inorganic matter (PIM) is a key component in estuarine and coastal systems and plays a critical role in trace metal cycling. Better understanding of coastal dynamics and biogeochemistry requires improved quantification of PIM in terms of its concentration, size distribution, and mineral species composition. The angular pattern of light scattering contains detailed information about the size and composition of particles. These volume scattering functions(VSFs) were measured in Mobile Bay, Alabama, USA, a dynamic, PIM dominated coastal environment. From measured VSFs, we determined through inversion the particle size distributions (PSDs) of major components of PIM, amorphous silica and clay minerals. An innovation here is the extension of our reported PSDs significantly into the submicron range. The PSDs of autochthonous amorphous silica exhibit two unique features: a peak centered at about 0.8 μm between 0.2 and 4 μm and a very broad shoulder essentially extending from 4 μm to 〉100 μm. With an active and steady particle source from blooming diatoms, the shapes of amorphous silica PSDs for sizes 〈 10 μm varied little across the study area, but showed more particles of sizes 〉 10 μm inside the bay, likely due to wind-induced resuspension of larger frustules that have settled. Compared to autochthonous amorphous silica, the allochthonous clay minerals are denser and exhibit relatively narrower PSDs with peaks located between 1 and 4 μm. Preferential settling of larger mineral particles as well as the smaller but denser illite component further narrowed the size distributions of clay minerals as they were being transported outside the bay. The derived PSDs also indicated a very dynamic situation in Mobile Bay relative to the cold weather front that passed through during the experiment. With northerly winds of speeds up to 15 m s-1, both amorphous silica and clay minerals showed a dramatic increase in concentration and broadening in size distribution outside the exit of the barrier islands, indicative of wind-induced resuspension and subsequent advection of particles out of Mobile Bay. While collectively recognized as the PIM, amorphous silica and clay minerals, as shown in this study, possess very different size distributions. Considering how differences in PSDs and the associated particle areas will effect differences in sorption/desorption properties of these components, the results also demonstrate the potential of applying VSF-inversion in studying biogeochemistry in the estuarine-coastal ocean system.

Description: The Wadden Sea is a transition area between land, rivers, and the North Sea. It is of great ecological importance for a wide range of fish species that use it in the course of their life cycle for various purposes. It is a highly dynamic environment and is subject to strong seasonal patterns and annual variations in abiotic conditions. The Sylt-Rømø Bight (SRB) is a semi-enclosed tidal basin in the northern Wadden Sea between the islands of Sylt (Germany) and Rømø (Denmark). Monthly monitoring data of juvenile fish taken in the SRB from 2007 to 2019 were analyzed to determine the changes in species composition in comparison to previous monitoring programs (1989–1995). The long-term trends, common patterns, and potential effects of environmental parameters (sea surface temperature (SST), salinity, chlorophyll a, and the North Atlantic Oscillation (NAO) winter indices) were determined. In total, 55 species were recorded and only 22 of these together accounted for more than 95% of the total abundance for the entire monitoring. Results showed a changed species composition as we did not find two boreal, one Lusitanian, and one circum-temperate species recorded in the previous programs. Instead, one boreal, six Lusitanian, and one Atlantic species were observed for the first time. The fish community was dominated by high seasonal fluctuations of abundance with either dome-shaped, increasing, or decreasing trends. Dynamic Factor Analysis (DFA) partitioned the fish community into three seasonal assemblages based on SST preferences. Redundancy Analysis (RDA) revealed that environmental parameters explained 29 % of the variations in the fish community. These variances were partly a result of the spring immigration of Lusitanian species and the emigration of boreal species and vice versa in autumn. The absence of four previously reported species and the addition of eight new species support the hypothesis that warm-adapted species are increasing in the Wadden Sea. The inclusion of these seasonal variations into conservation and management practices is critical to the sustainable management of marine and coastal ecosystems covering spawning, nursery, and feeding grounds.