Presentation at River Watch Spring Workshop, Kathryn, North Dakota, 2013

Veselina Valkov is a PhD student in the Environmental Conservation Science program at North Dakota State University. She holds a Master of Science degree in Ecology and Environment Protection from the Technical University-Varna, Bulgaria. She worked for the Institute of Oceanology - Bulgarian Academy of Science and focused on phytoplankton ecology. Veselina’s current research address the impacts of artificial aeration on phytoplankton distribution and diversity in a eutrophic lake.


Phone: 701-231-7051



Presentation at River Watch Spring Workshop, Kathryn, North Dakota, 2013

The effect of artificial aeration on phytoplankton growth in a small eutrophic lake in North Dakota

Fellow: Veselina A. Valkov

Advisor: Dr. Wei Lin, Associate Professor, Department of Civil Engineering North Dakota State University

Degree Progress: PhD in the Environmental Conservation Science


Eutrophication is a process by which lakes and reservoirs become more productive as a result of increased concentrations of nutrient, especially nitrogen (N) and phosphorus (P). Eutrophication occurs naturally; however, human activities that cause increased nutrient release accelerate eutrophication. This process is defined as cultural eutrophication. The high concentrations of N and P stimulate growth and blooms of phytoplankton, periphyton, and macrophytes. The common consequences of water quality changes related to eutrophication, and particularly to an increase of phytoplankton growth, include a decrease of water transparency, increase of diurnal dissolved oxygen (DO) variation, anoxic condition in water bottom layer, and shifts of phytoplankton composition to bloom-forming species of certain classes, such as Cyanobacteria. Species such as Aphanizomenon sp., Anabaena sp. and Microcystis sp. are among the most common Cyanobacteria in eutrophic lakes and reservoirs. As reported in the “North Dakota 2012 Integrated Section 305(b) Water Quality Assessment Report”, 45% of assessed lakes and reservoirs are eutrophic making eutrophication a serious water quality concern in North Dakota.

Artificial aeration is one of the methods used as a management technique to increase DO concentration in the water column and to prevent thermal stratification. On one hand, the introduced air become dissolved in the water, and on the other hand, lake circulation caused by artificial aeration reduces, or prevents the stratification and increases natural mixing of oxygen rich surface waters with oxygen poor bottom water. Improved DO concentrations in turn prevent fish kill and loss of suitable habitats for aquatic biota. Recently, artificial aeration has been an adopted method to control algal and especially Cyanobacteria blooms.

The remediation of water quality problems, including reduction of Cyanobacteria blooms, using an aeration system requires an understanding of the factors favoring Cyanobacteria dominance in lakes. The two most competitive advantages of Cyanobacteria are their ability to regulate buoyancy and the capability of some species to fix atmosphere nitrogen N2. Buoyancy regulation of many Cyanobacteria through the production of gas vesicles is an ecologically important mechanism enabling them to adjust their vertical position in the water column. The rate of sinking and upward movement, however, depends on colony size and cell density of the species. In addition to buoyancy regulation, nitrogen fixation influences the growth of Cyanobacteria such as Aphanizomenon sp. and Anabaena sp. In fact, the N2-fixation capability provides N2-fixing species with a competitive advantage over the other phytoplankton species when the nitrogen concentrations in water are limited.

The aim of this study is to examine the effects of artificial destratification on Cyanobacteria growth through changing the nutrient availability.

Project Objectives:

The purpose of this research is to determine variation of phytoplankton species in response to physical and chemical environmental variables. More specifically this research aims to evaluate the effect of artificial aeration on the change in dominance of certain phytoplankton species. The sampling plan was developed using a spatial and temporal design during the summer 2010, 2011 and 2012.


To investigate the effect of artificial aeration on phytoplankton biomass and population structure, water samples were taken periodically in the growing seasons of 2010, 2011 and 2012 from desigated sites in an artificially-aerated eutrophic lake located in LaMore County, ND. Changes in phytoplankton biomass were estimated by photosynthetic pigment, chlorophyll a (Chla). The relative abundance phytoplankton population was detected through species identification. In addition, field measurements of water temperature, DO, pH, conductivity and nutrient (nitrogen and phosphorus) concentrations water samples were also taken to identify how a change in nutrient concentration impact the seasonality of phytoplankton.

During 2010, 2011 and 2012, eight classes of phytoplankton were identified. Although, Cyanobacteria were expected to thrive at a low Total dissolved Inorganic nitrogen(TDIN):Soluble Reactive Phosphorus(SRP) ratio, they did not dominate in 2010. Instead, in June 2010 and 2011, diatoms out competed the other microalgae. The mixing from aeration influenced turbulence that maintained diatoms in suspension in water. The Chla gradient in mid-summer suggested that the mixing from artificial aeration was sufficient to maintain phytoplankton population homogeneously suspended in the water column.

In July 2011, however diatoms were succeeded by the Cyanobacteria nitrogen-fixing species, Aphanizomenon sp. and Anabaena sp. The dominant species Aphanizomenon sp., formed flattened aggregates 1-20 cm in length and diameter, and each comprised of tens to hundreds of filaments. When the aeration was stopped on July 13, 2011 the water column become stratified. This change influenced nutrient availability, which affected phytoplankton growth. During the stagnation period, the nutrient rich bottom waters were separated from the surface layer and nutrient were no longer available for phytoplankton growth. Aphanizomenon sp. and Anabaena sp. are nitrogen fixers, however, and have compete advantage when the nitrogen concentration is limited. Therefore, the phosphorus limitation was likely the control factor of their growth. In 2011, SRP decreased from 0.17 to 0.06 mg/l. In addition, the Aphanizomenon sp. flake-like aggregated devolving into separate filaments, which indicated that population maybe stressed. In 2011, the Cyanobacteria bloom collapsed and phytoplankton population shifted to the slow-growing Dinophyceae species: Peridinium sp. and Ceratium sp.

In 2012, the dominant growth of Aphanizomenon sp. and Anabaena sp. was observed at the end of June. At the same time measurements of water temperature and DO indicated that the artificial aeration system was not working properly. The Apanizomenon sp. decreased rapidly until mid-July. In the mid-summer another nitrogen-fixing species, Anabaena sp. developed and was visible to the naked eye, but Aulacoseira sp. (diatom) dominated over the phytoplankton species.

Further data processing and analyses are ongoing.


The long-term goal of this research is to apply knowledge on the variation of phytoplankton population distribution and diversity contributes to a better understanding of ecological status of eutrophic lakes. Understanding the effect of artificial destratification on nutrient availability and its impact on the physiology of Cyanobacteria species is considered necessary for the development of artificial destratification as a remediation technique to control problematic Cyanobacteria blooms..

Relevant Publications:

Veselina Valkov “Temporal-spatial distribution (dynamics) of phytoplankton and diversity in relation to lake physical and chemical condition” poster at presentation at ECS Poster Session and Recruiting Fair, Fargo, North Dakota 2011/2012
Veselina Valkov “Temporal-spatial distribution (dynamics) of phytoplankton and diversity in relation to lake physical and chemical condition “presentation at International Student Prairie Conference Winnipeg, Canada 2010 and Fargo, North Dakota 2011
Veselina Valkov “Temporal-spatial distribution (dynamics) of phytoplankton and diversity in relation to lake physical and chemical condition “presentation at ND AWWA Young Professional Poster Competition Fargo, North Dakota, 2010 and Bismarck, 2011
Veselina Valkov “The effect of artificial aeration on phytoplankton growth in a small eutrophic lake in North Dakota” presentation at River Watch Spring Workshop, Kathryn, North Dakota, 2013

Dr. Wei Lin


Advisor: Dr. Wei Lin

Assistant Professor of Civil Engineering

North Dakota State University