SEDIMENTARY ALGAL PIGMENTS IN LAKES AS AN INDICATOR OF CHANGES IN TROPHIC STATUS

Across the US, increased lake trophic status has become an ecological and environmental concern since it created significant undesirable effects on lacustrine ecosystems and consequently human health and recreation. Harmful Algal Blooms (HABs), which are a common result of eutrophication, lead to conditions of hypoxia that affect biodiversity and cyanobacteria within HABs release harmful toxins that can cause respiratory distress and neurological issues. To determine historical shifts in trophic status in aquatic systems, we can look at the long-term accumulation of chlorophyll-a and its derivatives in lake core samples as a proxy to algal bloom events. We analyzed sediments in 4cm intervals across core sections by isolating photosynthetic pigments from two Florida lakes (Lake Washington and Blue Cypress Lake). The percentage of pheophytin, a chlorophyll derivative found in cyanobacteria, proportionally describes the percentage of native chlorophyll (%NC) as the pigments are acidified. Productivity can be calculated using UV-Vis spectrophotometry to measure the change in absorbance after acidification with HNO₃. The pigment data from each lake will be compared with pre-existing non-source specific proxy data (TC:TN, TP, TN, δ¹³C_TOC) of primary productivity to determine how trophic status has changed across each core interval. The study of pheo-pigments offers a specific understanding of lacustrine primary productivity that, when combined with other core proxy data, details a better understanding of the contributions algal and bacterial biomass have on lake productivity.