Browsing by Author "Van Colen, Willem"

Now showing 1 - 3 of 3

Impact of nutrient stress on antioxidant production in three species of microalgae
(2015) León Tamariz, Fabián; Goiris, Koen; Van Colen, Willem; Wilches Arizabala, Isabel Maria; Coomana, Luc de; Muylaert, Koenraad
Microalgae are a novel source of sustainable natural antioxidants with various applications, including food preservation. To optimize antioxidant production in microalgae, we investigated the influence of nutrient limitation on antioxidant content in three species, Phaeodactylum tricornutum, Tetraselmis suecica and Chlorella vulgaris. Microalgae were cultivated in batch culture under nutrient replete, P- and N-limited conditions. Total antioxidant activity of the biomass was measured using Trolox equivalent antioxidant capacity and square wave voltammetry. Additionally, contents of carotenoids, phenolics, tocopherols and ascorbic acid were measured. Nutrient limitation, particularly N-limitation, resulted in low antioxidant content. Both phenolic and carotenoid contents were significantly reduced in nutrient-limited cultures. In contrast tocopherols and ascorbic acid levels were higher in nutrient-limited cultures, particularly under P-limitation. Our results indicate that nutrient stress is not an effective strategy to enhance overall antioxidant content in microalgae, although it may be useful to enhance production of some vitamin antioxidants such as tocopherols or ascorbic acid. © 2014 Elsevier B.V.
Limnology and trophic status of glacial lakes in the tropical Andes (Cajas National Park, Ecuador)
(2017) Van Colen, Willem; Mosquera, Pablo; Vanderstukken, Maarten; Goiris, Koen; Carrasco Espinoza, María Cecilia; Decaestecker, Ellen; Alonso, Miguel; León Tamariz, Fabián; Muylaert, Koenraad
The tropical Andes has a high density of glacial lakes that are situated in the high-altitude páramo (3500–4500 m). Ecological information about such lakes is scant despite the fact that these lakes are an important source of water for drinking, irrigation and electricity generation and feed several major tributaries of the Amazon. In this study, we provide data on a survey of 31 lakes in Cajas National Park (Ecuador). Two of the lakes were monitored monthly during one year. In situ nutrient addition experiments were carried out in three of the lakes. Seasonal monitoring in two lakes revealed a thermal stratification of the water column between October and June, with a small temperature difference between epi- and hypolimnion (2–3 °C). Oxygen depletion of the hypolimnion towards the end of the stratification period indicated that no complete mixing of the water column occurred during stratification. There was no evidence of depletion of nutrients in the epilimnion or accumulation in the hypolimnion during stratification. There were also no clear seasonal changes in chlorophyll-a (Chl-a) concentration nor in phytoplankton community composition in the two lakes. Inputs of dissolved organic carbon (DOC) from the vegetated catchment resulted in high DOC concentrations (median 2.9 mg L−1) compared to temperate mountain lakes. Water transparency was relatively low, with a median extinction coefficient for photosynthetic active radiation of 0.50 m−1 and for UV-B radiation of 10.13 m−1. Although the thermocline was deep and water transparency was low, estimates of the critical depth for photosynthesis were deeper than the mean water depth in all lakes, suggesting that phytoplankton was not light limited. The phytoplankton community was dominated by chlorophytes (e.g. Oocystis), diatoms (small Cyclotella spp.) or small colonial cyanobacteria (Aphanocapsa, Merismopedia). The zooplankton community was either dominated by large cladocerans and cyclopoid copepods, or by the calanoid copepod Boeckella occidentalis. Total concentrations of phosphorus (P) and nitrogen (N) were comparable to those in temperate mountain lakes (4–35 μg P L−1 and 162–758 μg N L−1) while Chl-a concentrations were in the lower range (<1 μg L−1). A large part of the total nutrient pool consists of dissolved organic N and P that appeared to have a low bioavailability to phytoplankton. The median seston N:P ratio of 44, a positive correlation between Chl-a and total P concentration, as well as nutrient addition assays carried out in three lakes all pointed to P limitation of phytoplankton. © 2016 John Wiley & Sons Ltd
Link between cattle and the trophic status of tropical high mountain lakes in páramo grasslands in Ecuador
(2018) Van Colen, Willem; Hampel, Henrietta; Muylaert, Koenraad
The high-altitude páramo grasslands of the Andes Mountains are rich in lakes that represent a source of high-quality water for the region. Páramo grasslands are mainly used for cattle grazing. The aim of this study was to investigate the influence of cattle on the trophic status of páramo lakes. In a survey of 30 lakes in Cajas National Park (NP), a semi-quantitative estimate for cattle abundance in the vicinity of the lakes was the best predictor of the chlorophyll-a concentrations in the lakes. Cattle abundance was also significantly related to phytoplankton community composition, being associated with a shift from chlorophytes to diatoms and dinoflagellates. Lake Culibrillas, a lake situated in the Sangay National Park (Sangay NP), a region with much more intensive cattle farming than Cajas NP exhibited a chlorophyll-a concentration greater than twice as much as the largest concentration measured in the Cajas NP lakes, being characterized by a dinoflagellate bloom. Although chlorophyll-a concentrations increased with cattle abundance, the concentrations in all the study lakes remained low (0.02–1.8 μg/L), indicating that extensive cattle farming does not cause severe eutrophication. The results of this study nevertheless indicate that intensification of livestock farming in páramo grasslands might result in a deterioration of water quality in the páramo lakes.