A modified stratification index method to assess reservoir water quality trends.

Harmful algal blooms (HABs) have been a harm to reservoir health for decades and it is believed that as climate changes and temperatures rise, frequency and severity of HABs are likely to increase as well. Understanding the relationships between physical factors in a reservoir and bloom trends could be key for keeping rising blooms at bay. A modified stability index based on temperature dependent water density at multiple depths was adapted into a code to process high frequency reservoir monitoring data. Metrics and visual tools were developed to use this stability index to objectively analyze how stratification - including intensity, start date, and turnover point - and water quality characteristics are changing, and how they are likely to change in the coming decades. This code was then used to analyze the relationships between physical and environmental reservoir characteristics, a generated stratification index, and algal bloom behavior for several United States Army Corps of Engineers (USACE) reservoirs, with specific focus on Shenango reservoir. Surface temperature, maximum temperature difference, and depth were found to correspond with strength of stratification. The calculated stratification index showed significant strength of correlation to algae when compared to other commonly collected reservoir parameters. Bettering our understanding of when stratification is occurring within reservoirs, as well as when blooms are occurring, will lead to more informed management decisions and better HAB control. For Shenango reservoir, it was determined that a hydrodynamic management strategy that maintains stability (horizontal flushing, epilimnetic withdrawals) during peak periods, while removing epilimnetic biomass and reducing nutrient availability, would be the most practical management strategy for bloom reduction.

A critical review of operational strategies for the management of harmful algal blooms (HABs) in inland reservoirs.

Occurrences of freshwater harmful algal blooms (HABs) are increasing on a global scale, largely in part due to increased nutrient input and changing climate patterns. While reservoir management strategies that can influence phytoplankton are known, there is no published guideline or protocol for the management of harmful algal blooms. There is a need to establish what factors are the predominant drivers of blooms, and how common reservoir management strategies specifically influence each factor. The following literature review seeks to establish the benefits and drawbacks of operational management strategies that currently exist. The main focus is altering hydrodynamic conditions (hypolimnetic withdrawals, surface flushing, pulsed inflow, artificial mixing), in order to induce environmental changes within the reservoir itself. Since excess nutrients are one of the biggest contributors to worsening bloom conditions, internal nutrient dynamics and reduction are also discussed. Additionally, we review the predominant seasonal factors (stratification, light, temperature, and wind) that affect likelihood of bloom occurrence and duration. The ultimate objective of this review is to increase understanding of the relationships between HAB drivers and reservoir operations in order to inform the development of data, modeling, and management strategies for the prevention and mitigation of blooms.