Online

Leduc, Meagan R.

Geology

2020

M.S.

In shallow lake systems, phosphorus (P) availability to cyanobacteria populations is often controlled by the release (internal loading) or sequestration of sediment P. This study provides novel insight into the feedbacks between the water column and benthic P pools across multiple time scales and explain how these dynamics influence chemical partitioning of P in lake sediment. Phosphorus partitioning in seasonal sediment core time series collected from a shallow eutrophic bay of Lake Champlain were quantified with SEDEX and enzyme hydrolysis selective extraction schemes. Time series extraction data were interpreted with concurrent water column physical and biogeochemical monitoring data to examine the relationship between water column dynamics and P partitioning of near-surface sediments in this intensively monitored system. Nonmetric multidimensional scaling analysis (NMDS) indicates that both sediment and water column time series cluster seasonally, linking water column variables such as pH, thermal stratification, and dissolved oxygen concentrations to the behavior of sediment P pools over the course of a year. Iron (FeP), exchangeable (Ex-P), calcium carbonate bound P (Ca-P) pools, and enzyme labile P were highly dynamic, especially in spring and summer. The SEDEX concentration data indicated that the sediment was mainly composed of inorganic bound P (De-P), but FeP and Ex-P pools proportionally varied most between sampling dates. Remarkably, while highly dynamic on an intra-annual timescale, the sediment ultimately returned to similar P concentration and chemical partitioning by late fall. The hysteretic nature of this interaction between water column dynamics and sediment P inventory/partitioning was clearly driven by systematic seasonal changes in water column physical, chemical, and ecological conditions governed by northern Vermont's climate and the physical configuration of the bay and its watershed. This study provides novel insight into the unique challenges associated with improving water quality in lake systems impacted by internal loading of legacy P.