Evaluating the isotopic composition and preservation of photosynthetic pigments in Lake Michigan

This study was designed to quantify the range of variability in the isotopic composition of photosynthetic pigments with depth in a freshwater setting and preservation in the underlying sediments below. Large volume filtration samples were collected from Lake Michigan at six depths at EPA site Mi27M, specifically targeting the deep chlorophyll layer (DCL: Chlorphyll a concentration max between 40 and 42m depth), and sediment cores were taken at the same site (EPA Mi27M, 110m water depth). Analysis of δ15N of bulk biomass/sediment as well as of the extracted chlorophylls/chlorophyll derivatives at each depth and in the core samples will reveal how the average primary producer community changes through the water column. This sample suite will also allow us to evaluate whether or not there are preservation biases or isotopic effects that occur through the water column, and ultimately in the sediments. This work has broad applications to understanding the nitrogen cycle and primary production in modern systems, and applying derived proxies to ancient settings.