Abstract
Algal blooms occur frequently in lakes and oceans and the causes and consequences of those are often studied. In this study, we focus on a less well known type of algal bloom by the freshwater raphidophyte Gonyostomum semen. This species’ abundance and occurrence is increasing, especially in brown water lakes, the most abundant lake type in the boreal zone. The aim of the study was to investigate which environmental factors are associated with G. semen by statistical evaluation of field data of 95 Swedish lakes over five years. Although we found G. semen to be associated with dark waters it was, contrary to our expectations, mainly high concentrations of iron, and only to a lesser extent high TOC (total organic carbon) concentrations, that were associated with blooms of G. semen. In addition, high phosphorus concentrations and low pH also appear to facilitate G. semen blooms. We suggest that browning of lakes caused by increased iron concentrations may decrease net heterotrophy by fostering heavy algal blooms, i.e. the opposite to commonly assumed effects of increased DOM (dissolved organic matter).
Highlights
Algal blooms are important threats to the ecosystems and ecosystem services, not all types of algal blooms have received the same attention, neither by the public nor by the scientific community
To characterize the physical and chemical environment of the lakes, the following parameters from the database were used: latitude (Xcoord), longitude (Ycoord), surface water temperature (Temp), pH, conductivity measured at 25 °C (Cond), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), alkalinity (Alk), sulphate (SO4), chloride (Cl), ammonium-nitrogen (NH4), total nitrogen (TotN), total phosphorus (TotP), water color measured as absorbance of 0.45 μm filtered water in a 5 cm cuvette (AbsF420), silicon (Si), turbidity (Turb), total organic carbon (TOC), iron (Fe), and manganese (Mn)
We focused here on lakes in Sweden where these blooms have become more frequent over time and hypothesized that this could be linked to the observed increase in water color in Swedish lakes and with the quantity and quality of dissolved organic matter (DOM)
Summary
Algal blooms are important threats to the ecosystems and ecosystem services, not all types of algal blooms have received the same attention, neither by the public nor by the scientific community. Studies have focused on the correlation between G. semen and the DOM concentrations and light conditions of lakes[2,10], but little work has been invested in the potential link to the composition of the DOM or to increases in essential micronutrients such as iron. The results show, as expected, that high abundances of G. semen were associated with high water color This association appeared to be linked to high concentrations of iron in those lakes rather than high concentrations of total organic carbon (TOC) or any other aspect of the composition of the DOM. High abundance of G. semen was linked to high concentration of phosphorus and low pH as shown in previous studies[2,10]
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