A Lab Notebook

 
Sanford Seminar
Although it was 67 and sunny outside (btw it is now 19 hours after the seminar and it is 32 degrees and snowing heavily here in NJ), I managed to convince myself to attend the Larry Sanford seminar yesterday afternoon. He presented a summary of particle transport dynamics in Chesapeake Bay. He used a LISST (Laser In Situ Scattering and Transmission), ADV (Acoustic Doppler Velocimeter), and a high speed camera to observe settling speeds and measure sediment floc volumes in the Chesapeake. Among the more interesting notes from his lecture was the fact that the sediment load (quantity of sediment suspended in the water) of the Chesapeake has actually declined significantly over the past 100 years. This is due primarily to reforestation in the Chesapeake watershed. Forested lands tend to reduce the amount of sediment runoff into rivers and estuaries while land without vegetation is quite sucseptible to erosion ans subsequent increased river sediment loads. Basically, our forefathers (the founding brothers included) cut down a ton of trees for building/fuel and to clear land for agriculture, during the 18th and 19th centuries. However, as industry moved wetsward, the focus of land use shifted, which in turn allowed for reforestation of the eatsern US forests and clearer waters in the Chesapeake.
Beyond direct environmental issues, Larry expolered the current models used for sediment flocculation. The principle theories are the same for sediment and algal flocculation. However, algal flocs have a much larger unknown quantity in the form of biologic acitvity such as cell division, cellular exudates, microbial degradation among others. Indeed, some of these biologic processes afect sediment flocculation, but for the most part have been ignored by estuarine scientists (the group largely repsonsible for studying inorganic flocs). It was cool though, that Larry mentioned how he thought biology actually played a more significant role in the aggregation/flocculation in estuaries. As he was saying this, I thought, "Bingo", this is what I a studying. He then proceeded to show several equations that have recently been formulated to more accurately model sediment flocculation. The two critical terms he pointed at in the equations were the stickiness coefficient and the floc strength. As regards algal cell aggregation, I am particularly interested in the stickiness coefficient (commonly referred to as "alpha", its greek letter representation used in formulae). After the seminar, he andf I talked a bit with some of the other IMCS faculty. He wasn't quite sure how alpha and floc strength would be different other than due to "age". From what I have read (as related to algal cell aggrgeation dynamics), it has been assumed that the alpha for algae is also used for floc strength. For example, if a bloom of phytoplankton is very sticky and has a high value for alpha, current model equations imply that the resultant flocs will be strong due to the high alpha value. The cool thing about breaking the parameter of alpha into interaction and strength components is that it allows for a more comprehensive model for understanding complex aggregation dynamics where a) batceria can degrade adhesive polymers b) aquatic medium chemistry at the time of formation will be manifest in aggregate properties c) modeling of colloidal or dissolved materials apart from the cell surface can also be included. Dr. Sanford also focuse on the fractal dimensions of aggregates. Aggregates are often described as being fractal because they are often comprised of small units clustered together into larger units. This pattern repeats until some maximum size of aggregation is approached, which can be set by floc strength/stickiness and energy levels (ie turbulence) in the aquatic medium of observation. A completely solid aggregate (without pores or interstitial spaces) would have a theoretical fractal number of 3. A loosely aggregated particle would have a fractal number approaching zero. The fractal number is often invoked in equations that help to determine settling speed. Of course, the principle equation governing the vertical velocity of an object is Stokes Law. Stokes Law is a function of the area of the object (usually expressed as the radius perpendicular to the direction of the object's trajectory), the density of the object, the density of the medium through which the object is passing, and of course gravity. The fractal number can be aplied to a variation of Stokes Law in the exponent that would be used to determine the area of the particle (used as [fractal number]- 1, where a solid aggregate would have an exponent of 2). This ends up working out nicely when one wants model a floc with lots of interstitial space that would permit the free flow of water through a certain portion of the floc. Since lower fractal numbers are indicative of more loosely bound aggregates, a lower fractal number applied to a form of Stokes Law would allow for a slower settling velocity of a more porous aggregate (which would settle much slower than a tightly bound aggregate of the same parent material). From what I have read, most algal cell aggregates have a fractal number somewhere near 1.5 to 2 (closer to 2 than 1.5).
Finally, Sanford left me with a point I should try ot nail down in the nest few weeks; what are the standards for algal cell aggregation. As far as I know, nothing has been established. Everyone is competing to have their method and nomenclature accepted as the standard, but very few folks are listening to each other during this whole process.


also, I ran for 50 minutes in 45F rain at the Livingston Capmpus Ecological Reserve.
- posted by alex @ 11:26