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Papers by Timothy Milligan

Agu Fall Meeting Abstracts, Dec 1, 2006

To date most of the research on the resuspension of cohesive sediments has focused on erosion rat... more To date most of the research on the resuspension of cohesive sediments has focused on erosion rate and cumulative mass eroded under varying stress conditions. Much less attention has been paid to size sorting during and after resuspension events. Three separate cruises in the Gulf of Lions France, during October 2004 and February and April 2005 were undertaken with the goal of understanding the effect of grain size on the size-specific erodibility of bottom sediments. Bottom cores with an undisturbed sediment-water interface were collected along a transect off the mouth of the Tet river. The cores were exposed to increasing shear stresses onboard the vessel shortly after collection by using a Gust microcosm erosion device. In addition to determining erosion rates, samples of the suspensate were collected during the erosion experiments and were analyzed for disaggregated inorganic grain size (DIGS) using a Coulter Counter Multisizer IIe. Size specific mobility plots were generated by dividing the DIGS distribution of the sediment suspended for each increasing erosion step (Cai,. the concentration of size class i in suspension) by the DIGS distribution of the site specific bottom sediment before erosion (Cbi, the concentration of size class i in the bed). If all grain sizes that make up the bottom sediment are eroded equally from the bed then Cai/Cbi =1. Values > 1 indicate that the suspended sediment is enriched in the size class and values < 1 indicate that that size class is enriched in the bed. Results show that non-cohesive, sandy sediments sort under increasing bottom shear stress with increasingly coarser grains being suspended as stress increases. In cohesive, muddy sediments a wide range of sizes are eroded at equal rates. Effectively, a muddy sand can be winnowed of its fine grain fraction during erosion while sandy muds or muds cannot. This difference in the sortability of cohesive and non- cohesive sediment during erosion may prove to be the dynamic control on the position and maintenance of the sand-mud transition.

... 306 Chapter Extracellular Enzymes Associated with Microbial Flocs from 307 14 Activated Sludg... more ... 306 Chapter Extracellular Enzymes Associated with Microbial Flocs from 307 14 Activated Sludge of Wastewater Treatment Systems Gill G. Geesey ... Chapter Surface Thermodynamics and Hydrophobic Properties of Microbial 406 19 Flocs BQ Liao, Gary G. Leppard, D. Grant ...

In October 2000, an 80-year flood event in the Po River resulted in the rapid formation of a fine... more In October 2000, an 80-year flood event in the Po River resulted in the rapid formation of a fine-grained sediment deposit extending up to 20km from the river mouth. Immediately following this event, and for a subsequent period of two years, box cores were collected on a grid of stations off of the Po Delta to observe the evolution of the flood deposit. Using process based parameterization of the disaggregated inorganic grain size, the evolution of the surficial sediment on the Po Shelf since the 2000 flood has been examined in terms of aggregation dynamics. A key parameter is floc limit, the diameter at which the amount of single grain and floc settled material in the sediment are equal. It depends primarily on the degree of flocculation in suspension. Over the period of observation floc limit is high and relatively constant near the river mouth but it is lower and varies with time and distance at stations away from the mouth. In general this pattern indicates that sediment is depo...

Handbook of Environmental Chemistry, 2005

Sedimentation rates were measured on gravity cores collected near finfish cages in Lime Kiln Bay,... more Sedimentation rates were measured on gravity cores collected near finfish cages in Lime Kiln Bay, N.B. in the Western Bay of Fundy using the radionuclide tracers 210Pb and 137Cs. Sediment cores collected close to aquaculture sites that have undergone extensive salmon fish farm activity over the past 20 years exhibit elevated levels of Zn and Cu in the upper 50 cm of

Estuarine and Coastal Modeling (2001), 2002

ABSTRACT The textural and geochemical properties of surficial sediment were characterized on near... more ABSTRACT The textural and geochemical properties of surficial sediment were characterized on nearshore cross-shelf transects spanning the sand-mud transition (SMT) off the Tronto and Pescara rivers, Apennine Margin (Adriatic Sea), Italy. Measured parameters were geometric mean diameter (GMD), specific surface area (SSA), mud fraction (

ABSTRACT A LISST-100 in situ laser particle sizer was deployed together with a digital floc camer... more ABSTRACT A LISST-100 in situ laser particle sizer was deployed together with a digital floc camera (DFC) in estuarine and continental shelf settings on several occasions. The LISST-100 can measure particle sizes in the range 2.5-500mu m, whereas the DFC can detect particles larger than 125mu m; the two instruments thus overlap in the 125-500mu m size range. The particle sizes from the two instruments are compared. At a first glance, the LISST-100 underestimates the floc median diameter (D50) by a factor of 2-4 when compared to the DFC. However, when the data from the two instruments are "trimmed", so that only particles in the overlapping size ranges are considered, the two instruments yield nearly identical values for D50. Thus, the LISST-100 and the DFC both appear to detect particles in their overlapping size ranges correctly. Since the DFC only detects particles larger than 125mu m, it will usually overestimate D50, whereas the LISST-100 will usually underestimate D50. Using the two instruments in conjunction, floc size spectra from 2.5mu m and up can be measured, hence better estimates of the D50 can be obtained.

Coastal and Estuarine Studies, 1993

Flocculation in Natural and Engineered Environmental Systems, 2004

Page 22. 1 Methods for Analyzing Floc Properties Steven N. Liss, Timothy G. Milligan, Ian G. Drop... more Page 22. 1 Methods for Analyzing Floc Properties Steven N. Liss, Timothy G. Milligan, Ian G. Droppo, and Gary G. Leppard 1.1 ... Accordingly, the size-porosity function was expressed as: (1.8) Mikkelsen and Perjrup69 presented a method for determining effective floc density and ...