Advanced

Influence of constructed wetlands on cyanobacterial growth with regards to the effect of nutrient concentrations and water colour

Easdon, Hannah (2020) BIOM02 20201
Degree Projects in Biology
Popular Abstract
Can constructed wetlands be used to fight cyanobacterial blooms?

Cyanobacterial blooms are more than just a nuisance that prevents swimmers from making the most of the warmest months. Cyanobacterial blooms can cause a wide array of problems such as polluting freshwater reservoirs and causing fish die offs, owing to their ability to grow rapidly and release toxins which are harmful to both humans and animals alike. They are often attributed to excess nutrients entering the water from agricultural and urban runoff. Increasing water colour, or brownification, is an increase in dissolved organic carbon (DOC) which also aids in cyanobacterial growth to an extent. Brownification has not only been linked to an increase of cyanobacteria, is... (More)
Can constructed wetlands be used to fight cyanobacterial blooms?

Cyanobacterial blooms are more than just a nuisance that prevents swimmers from making the most of the warmest months. Cyanobacterial blooms can cause a wide array of problems such as polluting freshwater reservoirs and causing fish die offs, owing to their ability to grow rapidly and release toxins which are harmful to both humans and animals alike. They are often attributed to excess nutrients entering the water from agricultural and urban runoff. Increasing water colour, or brownification, is an increase in dissolved organic carbon (DOC) which also aids in cyanobacterial growth to an extent. Brownification has not only been linked to an increase of cyanobacteria, is also thought to increase the toxicity of blooms.

We wanted to investigate if constructed wetlands could be used as a management strategy to reduce the occurrence or intensity of cyanobacterial blooms in lakes and oceans. Wetlands can reduce nutrient concentration, and some research suggests they can also have a positive impact on water colour, though there are few studies focused on brownification in wetlands. Due to the regulating action of the wetland, cyanobacterial growth may be reduced thereby reducing the intensity of cyanobacterial blooms in downstream lakes and oceans.

We collected water from the inflow and outflow of each wetland to observe changes to the water after it has passed through the wetland. Specifically, we measured phosphorus for nutrients, water colour as a proxy to DOC, and cyanobacteria concentration. A culture experiment was carried out to observe how well the cyanobacteria would grow in a mix of wetland and lake water over 14 days. Microcystin, a toxin produced by cyanobacteria, was measured from day 14 in July.

Half of our sampled wetlands reduced cyanobacteria concentrations in some capacity. Three of eight wetlands had a reduction in all cultures by day 14, while one wetland saw a decrease in cyanobacteria in the outflow only. Neither phosphorus nor water colour was correlated to the increase in cyanobacterial concentration over the sampling period. The concentration of cyanobacteria increases in half of the wetlands. Two wetlands experienced a higher concentration of cyanobacteria per biomass, meaning they produced more toxins, while two decreased in toxicity.

Whether or not constructed wetlands can be used to lessen the impact of cyanobacterial blooms is heavily context dependent. It is not as simple as digging a hole anywhere and filling it with water, as convenient as that would be. The efficiency of the wetland depends on where and how it was built. Some blooms may become more toxic simply because the wetland was built to deal with only nutrients and consequently promotes browning. However, the fact that half of our wetlands were able to reduce cyanobacteria is a promising sign. With proper planning and monitoring, constructed wetlands may be able to reduce the impact that cyanobacterial blooms have on the aquatic ecosystem.


Master’s Degree Project in Biology 30 credits 2020
Department of Biology, Lund University

Advisors: Johanna Sjöstedt and Anna Borgström
Department of Aquatic Ecology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Easdon, Hannah
supervisor
organization
course
BIOM02 20201
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
9031387
date added to LUP
2020-10-27 11:53:04
date last changed
2020-10-27 11:53:04
@misc{9031387,
  author       = {Easdon, Hannah},
  language     = {eng},
  note         = {Student Paper},
  title        = {Influence of constructed wetlands on cyanobacterial growth with regards to the effect of nutrient concentrations and water colour},
  year         = {2020},
}