Environmental
Chemistry U6220
Part II:
The St. Lawrence Estuary is a very large estuarine system that links the St. Lawrence and Saguenay Rivers to the Gulf of St. Lawrence and North Atlantic Ocean. In the 1940s to 1970s, a substantial industrial amount of mercury (Hg) was released into the upstream region of the Saguenay River. This contaminant redistributed into mostly the Saguenay Fjord but also the St. Lawrence Estuary. Using the data provided in the table linked, please estimate the year of maximum input.
1) Graph [Hg] in all cores with respect to core depth (all on the same graph)
2) Using the sedimentation rates provided, please do the same thing as a function of sediment age.
3) Estimate the year of maximum input for all cores and comment on the consistency/inconsistency of the data. Why should you observe the patterns you are observing in term of time of contamination and amount of contamination at the different stations.
Lignin is a structural organic molecule found in higher (vascular) plants' woody and non-woody tissues. It is the second-most abundant naturally occurring biopolymer in the biosphere after cellulose and is a primary constituent of the cell wall of vascular plants (it actually forms a complex structural association with cellulose and is mostly found in nature as lignocellulose). In woody and non-woody tissues, this polymer generates a 3-D composite structure that decreases permeation of both water and destructive enzymes across the cell wall (have you ever tried to chew a piece of wood to get nourishment out of it? Same thing goes for microorganisms). Lignin also imparts rigidity to the plant itself and creates an outstanding resistance to impacts, compression and bending. This type of compound provides a unique stability to the lignified plant tissues and thus acts as an ideal multifunctional structural material. Lignin has been extensively studied in two highly applied fields of research: wood chemistry and agronomy. Both these fields regard lignin components of the cell wall structure as "undesired" compounds that reduce the optimum conversion of the polysaccharide fractions (mostly cellulose) of lignocellulose to useful end-products, namely livestock biomass in agronomy and pulp and paper in the wood industry. Geochemists are a third group of scientists who have shown a particular interest in lignin research and, in contrast to the above-mentioned two fields, find many applications for this compound assigning it, in some instances, a higher value that its polysaccharide lignocellulosic counterpart. The following exercise is just one example of such type of research.
4) Graph the lignin concentration for Stations Sag05, Cap Eternite, and Sta23 vs. time along the sedimentary profile. How can you explain the distribution of lignin vs. depth (age) in these three different sedimentary systems?
5) Then use the second set of data ("Transport") and represent the concentrations in terms of distance from the source of these compounds (the source is at "0" km and is a little upstream from "St. Fulgence" on the map below).
6) Find the transport constants (k) for both Hg and lignin. To do this, use the concentration data provided in the "Transport" sheet and transform the formal exponential equation (Cd = C0 x e-kd) into a linear relationship that provides k.
7) What does it mean for the distribution of Hg and lignin? Do these data and their analysis confirm/infirm your initial hypothesis (conceptual model) developed in Part I?
8) Please read the following article (Hg in St. Lawrence) and reassess your initial explanation of the behavior of Hg and lignin.
Note: Please find a template for a double x-axes in the linked Excel spreadsheet “double-axis”