Analysis of the water quality dynamics of Lake Vomb; Interactions between water quality profile and cyanobacterial bloom in a eutrophic lake in Sweden

Abstract

Lake Vomb, located in Sk˚ane, Sweden, provides water for groundwater
infiltration, used for the drinking water supply of several municipalities,
including Malm¨o. The lake is in a bad ecological condition
with intense algae blooms during summer. Cyanobacteria dominate
mentioned blooms in 2021 posing the threat of releasing cyanotoxins.
The goal of this work is to asses the water quality dynamics to support
the lake management. An approach to predict algae blooms and
oxygen depletion to return the lake into a good ecological state and
secure a long-term drinking water supply is investigated.
To assess the water quality, the profiles of the parameters pH, dissolved
oxygen, and the water temperature was analysed for possible correlations
with the abundance of algae represented by the chlorophyll-a
concentration. Meteorological effects on the water quality dynamics
were assessed. The availability of essential nutrients was evaluated by
inspecting the phosphorous and nitrogen concentrations in the in- and
outflow of the lake.
The pH value at the water surface showed the strongest correlation
with the chlorophyll-a concentration during the summer. Besides seasonal
patterns, wind and temperature fluctuations indicate a correlation
with oxygen depletion. The possibility of phosphorous release
supporting the algae bloom was found, but more measurements are
needed to find the cause and possible preventative measures.
Random forest was used to predict the risk of high chlorophyll-a concentrations
and oxygen depletion. The model shows potential, but
more input data is needed to make significant predictions. Future
research could focus on the regulation of phosphorous release and implementation
of the phosphorous dynamic into the prediction model.

Popular Abstract

Analysis of the water quality dynamics of a eutrophic lake in Sweden
Eutrophication is a global problem that can lead to excessive proliferation
of algae, including toxin-producing cyanobacteria. Bad eutrophic water
conditions can jeopardise the drinking water quality and the utility of surface
waters for recreational use.
This case study examines Lake Vomb, located in Skane, Sweden. The
lake provides water for groundwater infiltration, used for the drinking water
supply of Malm¨o. The lake is in a bad ecological condition with intense
algae blooms during summer.
The results show an effect of temperature on the water quality parameters,
pH and dissolved oxygen concentration. The deeper measuring locations
are more affected by oxygen depletion whereas more remote locations
have the highest occurrence of thermoclines. The pH value at the water
surface showed the strongest correlation with chlorophyll-a concentration
during the summer. The possibility of phosphorous release supporting the
algae bloom was found, but more measurements are needed to find its cause.
The random forest prediction models with the targets of chlorophyll-a and
oxygen depletion show potential, but more input data is needed to make
relevant predictions.
Eutrophication and excessive algae blooms requires the lake management
to take measures. Finding factors triggering algae bloom is necessary to
make a real time prediction on water conditions which is a useful tool to
find suitable solutions to return the lake into a good ecological state.
Predicting water conditions and algae blooms can facilitate the lake management’s
decision-making on solutions to improve the water quality and
ensure a long term usage of the surface water.
The findings of this work can be used to support lake management.
Measurements can be improved to facilitate further attempts at real-time
predictions and assessing possible solutions. The parameter profiles were
tested for correlations with the chlorophyll-a concentration and meteorological
data. The availability of essential nutrients was evaluated by looking at
the phosphorous and nitrogen concentrations in the in- and outflow of the
lake. A categorized Random Forest model was used to predict the risk of
high chlorophyll-a concentrations and oxygen depletion.

• author: Coenen, Wiebke
• supervisor: Kenneth M Persson; Jing Li
• organization: Division of Water Resources Engineering
• course: VVRM01 20221
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Vombsj¨on, Lake profile, Cyanobacteria, Drinking water, Random Forest
• publication/series: TVVR 5000
• report number: TVVR22/5012
• ISSN: 1101-9824
• language: English
• additional info: Examinor:Catherine Paul
• id: 9097674
• date added to LUP: 2022-08-30 08:59:17
• date last changed: 2022-08-30 08:59:17