•  
  •  
 

EFFECTS OF HYDROLOGICAL HETEROGENEITY AND MAINTENANCE DRAWDOWNS ON ALGAL DYNAMICS IN A FRESHWATER RESERVOIR SYSTEM (LAKE SINCLAIR, GEORGIA, USA)**

Abstract

As human-made environments, reservoir systems face the unique challenges of frequently regulated flow rates and periodic drawdown events. The effects of reservoir drawdowns on phytoplankton communities are specifically understudied. Lake Sinclair (Georgia, USA) is a reservoir providing critical recreation, drinking water, and hydropower benefits. The lake’s irregular boundary and morphology create both deep-water basins and shallow coves — the latter being more susceptible to algal blooms and to exposure during drawdown events. To understand the effect of drawdowns on algal communities in Lake Sinclair, monthly monitoring of surface water (<1 m) was conducted in 2020, measuring algal composition and physicochemical baselines of deep basins and shallow coves. In 2025, these parameters were reexamined both before and after a winter drawdown, incorporating upstream and downstream sites. In summer 2020, algal biomass did not vary over time (ANOVA, p = 0.22) but was 4.0-fold higher in shallow vs deep sites (p = 0.01). PCA revealed lower variability in community composition among deep sites, with differences from shallow sites driven by elevated green algae. Preliminary 2025 data using linear mixed effect models show that during the drawdown, downstream chlorophyll a significantly increased (p < 0.01), but upstream levels did not (p = 0.31). Diatom percentage increased by 34% downstream, yet only 12% upstream, indicating community assemblage changes beyond seasonal shifts. Additional analysis including spatial assessments and predictive modeling will aim to understand post-drawdown resilience and local drivers of algal blooms. This study will inform directions for future monitoring and management efforts.

Acknowledgements

GCSU Aquatic Sciences Center (Funding and Equipment), GCSU Deparment of Biological and Environmental Sciences (Equipment), Georgia Power (Site Access)

This document is currently not available here.

Share

COinS