Dr Robert Grabowski, BSc – Biology, Illinois Wesleyan University, MSc – Marine Biology, University of Maine, Orono
Teaching Assistant
Location: Room 202, Geography Buildingemail: r.c.grabowski@qmul.ac.uk
Phone: 020 7882 2777
Research interests:
Research Interests:
My research focuses on the interaction of physical forces and biological/ecological processes in aquatic and marine environments. I use a combination of field surveys and flume experiments to investigate the causal relationships between hydrodynamics, benthic organisms, and their physical habitat.
PhD Thesis:
The stability of surficial fine sediment deposits in permeable (chalk) streams
Lowland chalk streams in the UK are experiencing increased deposition of fine sediment due to changes in land-use practices, channel modifications, and groundwater abstraction. The fine sediment is linked to benthic habitat degradation, the obstruction of surface-groundwater flow, and the storage of contaminants, such as pesticides and heavy metals. While research has been conducted on the provenance, transport, deposition, and storage of fine sediment in chalk streams, none has expressly investigated erosion. Therefore a key step is missing in our understanding of sediment dynamics in these systems. To help fill this gap in knowledge, a yearlong field survey is being conducted in two reaches in the Frome-Piddle Catchment (Dorset, England) to quantify the stability of surficial fine sediment deposits. In situ sediment stability measurements are paired with sediment cores for analysis of the physical, chemical and biological properties of the sediment. This work will provide information on spatial and temporal variations in sediment stability, as well as the hydrodynamic conditions and sediment properties that influence stability. Due to the ecological, environmental and human health impacts of fine sediment and its associated contaminants, the outcomes of this research will be of interest to sediment researchers and modelers, environmental managers, and policy-makers.
Supervisors:
Dr. Geraldene Wharton (QMUL Geography)
Prof. Roger Wotton (UCL Biology)
Dr. Jenny Schmid-Arraya (QMUL Biology)
Dr. Ian Droppo (Environment Canada)
Rationale and Aims:
Chalk streams have historically supported diverse and productive aquatic communities. Fine sediment deposition is increasing, though, as a result of changes in agricultural practices, urbanisation and groundwater abstraction. Due to their dependence on clear waters and clean gravel beds, these ecosystems are particularly vulnerable to siltation.
While research has been conducted on fine sediment provenance, transport and deposition as well as the ecological impacts of siltation in chalk streams, to date no study has expressly investigated the stability of fine sediment deposits. Therefore a key step is missing in the sediment transport cycle. The aim of my PhD research is to fill this gap by quantifying the stability of surficial fine sediment in chalk streams and identifying the key factors responsible for stability.
 Bere Stream (Dorset) April (l) and July 08 (r) |  |
Sediment cored from beneath a Ranunculus sp. Stand.
Methodology:
I am currently conducting field surveys in chalk streams in the Frome-Piddle Catchment (Dorset, England) over a 2 year period, using paired sediment cores and in situ cohesive strength measurements in areas of fine sediment accumulation. The stabilising role of key sediment properties, such as clay content, organic content and the abundance of extracellular polymeric substances, is being addressed with multivariate analysis of survey data, and further examined in laboratory flume experiments. I am overseeing the construction of a laboratory flume for the Physical Geography Laboratories at Queen Mary, University of London. The facility will allow for the determination of erosion rates and critical shear stresses for natural fine sediment, as well as the experimental manipulation of sediment properties.
This work is being funded by a University of London studentship (R.C. Grabowski), a NERC studentship (G. Davies), and the QMUL Department of Geography.
Additional Projects:
Calibration of the Cohesive Strength Meter
The cohesive strength meter (CSM) is a lightweight, portable device that measures the in situ strength of surficial sediments. It is used extensively in estuarine environments, but it is currently limited to relative stability measurements because of difficulties correlating the forces generated by the jet to horizontal shear stress. Through collaboration with Dr. Ian Droppo (National Water Research Institute, Burlington, ON, Canada), I am developing a calibration factor for the CSM based on artificial sediment mixtures. This work will allow CSM stability measurements to be transformed to horizontal critical shear stresses that can be used in river hydraulics and sediment transport models.
Funding provided by the University of London Central Research Fund, the Royal Society’s Dudley Stamp Memorial fund and the QMUL Department of Geography.
 The 2m annular flume (l) and cohesive strength meter (r) at NWRI. |  |
The Role of Hydrodynamics in External Fertilisation
Our understanding of fertilization kinetics for broadcast spawning marine invertebrates is based largely on laboratory experiments conducted under quiescent conditions. In the ocean, though, moving water is the norm. Through a series of laboratory flume experiments, we are beginning to comprehend how the mechanical properties of gametes and low levels of turbulence affect gamete viability and fertilization success.
 Male (l) and female (r) green sea urchins induced to spawn within a unidirectional seawater flume. Note: The rubberbands keep the urchins from wandering off. |  |
Publications:
Publications:
Peer-Reviewed Journals:
Grabowski, R.C., Windholz, T., and Y. Chen. 2005. Estimating exploitable stock biomass for the Maine green sea urchin (Strongylocentrotus droebachiensis) fishery using a spatial statistics approach. Fishery Bulletin. 103(2): 320-330.
Grabowski, R., and Y. Chen. 2004. Incorporating uncertainty into the estimation of the biological reference points F0.1 and Fmax for the Maine green sea urchin (Strongylocentrotus droebachiensis) fishery. Fisheries Research. 68: 367-371.
Conference Proceedings:
Kregting L.T., Yund P.O., Thomas F.I.M., Grabowski R.C. 2006. Position, distance and hydrodynamic effects on fertilization success of the green sea urchin Strongylocentrotus droebachiensis. Integrative and Comparative Biology. 46 (Suppl. 1): E78
Thomas, F.I.M., Badgley, B.D., Yund, P.O., and R.C. Grabowski. 2005. Linking field measurements of hydrodynamic conditions to the fertilization of the green sea urchin Strongylocentrotus droebachiensis. Integrative and Comparative Biology. 45 (6): 1083.