Seasonal variations of suspended sediment and diatoms in the Western Scheldt

Seasonal variations of suspended sediment and diatoms in the Western Scheldt

Nederbragt, G.

Stive, M.J.F. (mentor)
De Vries, M.B. (mentor)
Verbeek, H. (mentor)
Winterwerp, H. (mentor)
Van ledden, M. (mentor)

Civil Engineering and Geosciences

2001-09-01

This study focused on the possible relationship between seasonal variations of suspended sediment concentration (SSC) and diatom biomass. In order to determine whether a relationship exists, the effect of other parameters on these seasonal variations was also studied. This was accomplished to prevent the risk of finding a spurious relationship between SSC and diatom biomass. This approach resulted in a literature study and the analysis of data. The literature study was necessary to provide the theoretical background, the data analysis was used for the quantification of the identified relationships. The literature survey showed that SSC variations do not affect diatom biomass in the Western Scheldt. Turbidity, caused by both SSC and organic matter, is too high throughout the year for diatoms to be active during inundation of the flats. Diatom, which are in fact algae, depend on the availability of light for their growth. The role of diatoms on SSC variations is an indirect one. Diatoms do not influence deposition of sediment, but they do play a role in stabilising fresh deposits. When this occurs on a large scale during a period of time, then suspended particles are constantly removed from the water column. A relation scheme was proposed in which all identified parameters and their relationships were summarised. Among the parameters that play a role in the seasonal variation of SSC and diatom biomass are wind, rain, discharge and biological activity. The flats play a role through seasonal changes in accretion and erosion of fine grained sediment. The interaction between SSC and diatoms takes place at the flats. Data acquisition and analysis was used to investigate the contribution of the various parameters to SSC and diatom biomass variations. It showed that wind is an important parameter, probably through the influence on hydrodynamic conditions. This was a result of the analysis of both short term, high frequency measurements and long term, low frequency measurements. The performed regression analyses explained only part of the SSC and diatom biomass variations. This indicates that the parameters on which no information was selected play a role. Also the fact that the analyses were performed on the scale of the entire estuary might contribute. Some indications for this assumption were provided in the analysis of spatial variations of SSC, discharge and chlorophyll a. Future research should aim at combining spatial and temporal scales and the use of other types of data and analysis techniques.

Westerschelde
sediment
turbidity
biomass
algae

http://resolver.tudelft.nl/uuid:203c4bc4-255c-42e2-9346-44f3169d648a

TU Delft, Civil Engineering and geosciences, Hydraulic Engineerning

Student theses

master thesis

(c) 2001 G. Nederbragt