Nicole Kowalski

Sinking rates of microplastics and potential implications of their alteration by physical, biological, and chemical factors

To follow the pathways of microplastics in aquatic environments, profound knowledge about the behaviour of microplastics is necessary. Therefore, sinking experiments were conducted with diverse polymer particles using fluids with different salinity. Particles ranged from 0.3 and 3.6mm with sinking rates between 6 and 91×10(-3)ms(-1). The sinking velocity was not solely related to particle density, size and fluid density but also to the particles shape leading to considerable deviation from calculated theoretical values. Thus, experimental studies are indispensable to get basic knowledge about the sinking behaviour and to gain representative datasets for model approaches estimating the distribution of microplastics in aquatic systems. The sinking behaviour may be altered considerably by weathering and biofouling demanding further studies with aged and fouled plastic particles. Furthermore, assumptions are made about the influence of sinking fouled microplastics on the marine carbon pump by transferring organic carbon to deeper water depths.

Regional Differences of Hydrographical and Sedimentological Properties in the Beibu Gulf, South China Sea

ABSTRACT Bauer, A.; Radziejewska, T.; Liang, K.; Kowalski, N.; Dellwig, O.; Bosselmann, K.; Stark, A.; Xia, Z.; Harff, J.; Böttcher, M.E.; Schulz-Bull, D.E., and Waniek, J.J., 2013. Regional differences of hydrographical and sedimentological properties in the Beibu Gulf, South China Sea. In: Harff, J., Leipe, T., Waniek, J.J., and Zhou, D. (eds.), Depositional Environments and Multiple Forcing Factors at the South China Seas Northern Shelf, Journal of Coastal Research, Special Issue, No. 66, pp. 49–71. Coconut Creek (Florida), ISSN 0749-0208. Analyzing the Beibu Gulfs hydrography and sediment properties is crucial for the understanding of naturally and anthropogenically induced matter and energy fluxes in the South China Seas north-western coastal regions. For this reason, the present study combines hydrographical (T, S, σt, chlorophyll, nutrients, suspended particulate matter) and sedimentological (grain size, pore water properties, phosphate speciation, foraminifera, plant pigment contents) investigations. On the basis of hydrographical profiles (temperature, salinity and σt) taken at 25 stations, four ecological zones are identified in the study area for the sampling period in September/October 2009. These zones are mainly influenced by riverine input and tidal mixing, water mass transport through the Qiongzhou Strait which also affects the gulfs circulation, and South China Sea waters in the southern Beibu Gulf. The zonation extends from the coastal areas in the northern Beibu Gulf and west of Hainan Island across the central regions to the southern part of the gulf. The study demonstrates that the hydrographical peculiarities of the different zones influence not only the biogeochemical features (chlorophyll, nutrients, suspended particulate matter) of the water column but also the deposition of sediments and their biological (plant pigment contents and foraminifera) and geochemical (pore water properties) characteristics. Both, the near-shore area and the zone in the vicinity of the Qiongzhou Strait show relatively high chlorophyll concentrations and therefore give evidence of enhanced primary production in the entire water column. Whereas the grain size and the foraminifera in the surface sediments follow the hydrodynamically controlled sedimentation conditions, plant pigment contents in the surface sediments additionally follow the productivity pattern in the water column. Depending on the depositional environments with their respective sedimentology and organic matter contents, the geochemical sediment properties reflect the primary production within the water column as well.