CHLOROPHYLL A AND MICROCYSTIN VARIATIONS ACROSS WETLANDS LOCATED IN MINERAL AND PEAT SOILS IN SOUTH SWEDEN

Abstract

Concentrations of chlorophyll a (Chl-a) and cyanobacterial toxins such as microcystin are used as indicators of phytoplankton biomass, water quality and ecological status in surface waters such as wetlands. Although rewetting wetlands for biodiversity restoration is on the political agenda, little is known on how physical characteristics of the wetlands will affect water quality and in turn Chl-a and microcystin concentrations. In this study, it was examined the influence of physical characteristics (i.e. soil type, age, depth) and water quality (i.e. nutrient content, dissolved organic carbon-DOC, light-extinction or pH) on Chl-a and microcystin variations among 41 wetlands in south Sweden. In addition, it was assessed if detected levels of Chl-a and microcystin can pose an impact on ecosystem integrity and the quality for drinking water. Phytoplankton pigments were quantified using spectrophotometric analysis, and microcystin concentrations using ELISA assay. Relationships between variables were investigated through statistical analysis. Results show that the mean Chl-a was higher (25±21 μg/L) in young wetlands (<4 years) than in old wetlands (>4 years; 5±2 μg/L), and especially if the wetlands were located in peat soils. Detected levels of Chl-a were above the threshold for eutrophic state (10 μg/L) in 24% of the wetlands studied and all of them were young (<4 years). Phycocyanin (marker for cyanobacteria) was positively correlated with microcystin, indicating that the highest microcystin concentrations occurred in wetlands with higher phycocyanin concentrations. However, detected levels of microcystin were always below the threshold for human health risk (ie. 1 μg/L; World Health Organization). Wetlands located in peat soils had higher levels of nutrients (Total Nitrogen, NO3 ⁻ , PO43⁻) and DOC, and lower pH and dissolved oxygen (DO), suggesting that the poor water quality in wetlands located in peat soils contributed to the higher Chl-a and microcystin of these wetlands. Altogether, this preliminary study shows that young wetlands in peat soils tend to have a lower water quality (nutrient content and phytoplankton descriptors) than old wetlands or those located in mineral soils, independently of the year of its formation. This research highlights the merit of monitoring phytoplankton in wetlands and indicates that the management of wetlands could benefit from controlling which type of soil and age of the wetlands.