Long-term allelopathic control of phytoplankton by the submerged macrophyte Elodea nuttallii

1. It is well known that submerged macrophytes can suppress phytoplankton blooms in lakes and thus promote water quality and biodiversity. One of the possible mechanisms through which submerged macrophytes control phytoplankton is by producing allelochemicals that suppress phytoplankton growth rates. The in situ importance of allelopathy, however, is often questioned because it is assumed that phytoplankton communities can rapidly evolve resistance to allelochemicals. 2. Here, we present the results of two mesocosm experiments in which we evaluated whether the submerged macrophyte Elodea nuttallii is capable of controlling phytoplankton biomass over periods of 4 to 8 weeks. Such a time scale is long relative to the generation time of phytoplankton and is therefore expected to allow the development of resistance through compositional shifts at both population and community levels. 3. Although the mesocosms were inoculated with a diverse phytoplankton inoculum including species that had previously been exposed to Elodea, phytoplankton biomass remained consistently low during the course of the experiments in the treatments with Elodea. As zooplankton grazing and competition for nutrients and light by macrophytes were excluded in our experiments, this suggests that phytoplankton was controlled by allelopathy. 4. Dialysis bag assays, performed at the end of each mesocosm experiment, showed that phytoplankton communities from mesocosms with Elodea were equally sensitive to exudates from Elodea than phytoplankton communities from mesocosms without Elodea.status: publishe

Bottom-up effects on biomass versus top-down effects on identity: a multiple lake fish community manipulation experiment

© 2017, Springer Science+Business Media New York. The extent to which ecosystems are regulated by top-down relative to bottom-up control has been a dominant paradigm in ecology for many decades. For lakes, it has been shown that predation by fish is an important determinant of variation in zooplankton and phytoplankton community characteristics. Effects of fish are expected to not only be a function of total fish biomass, but also of functional composition of the fish community. Previous research on the importance of trophic cascades in lakes has largely focused on the role of zooplanktivorous and piscivorous fish. We conducted a large-scale multiple-lake fish community manipulation experiment to test for the effect of differences in fish functional community composition on the trophic structure of lakes. We examine the effect of top-down and bottom-up factors on phytoplankton and zooplankton biomass as well as on their community composition. We put our data in a broader perspective by comparing our results to data of a survey that also included ponds with low fish densities as well as ponds with very high densities of fish. Our results indicate that the overall food web structure under relative high fish densities is primarily structured by bottom-up factors, whereas community characteristics seem to be primarily regulated by top-down factors. Our results suggest a subtle interplay between bottom-up and top-down factors, in which bottom-up factors dominate in determining quantities while top-down effects are important in determining identities of the communities.status: publishe

I Want to Be a Billionaire:How Do Extrinsic and Intrinsic Values Influence Youngsters’ Well-Being?

Values guide our attitudes and behavior, but to what extent and how do individual values determine our overall well-being? Self-determination theory holds that particular types of values (i.e., intrinsic or extrinsic) matter most, but the person-environment fit perspective argues that any values can be beneficial as long as they align with values prevalent in one’s environment. the evidentiary support for these competing claims is inconclusive. We use the World Value Survey to see how these perspectives do in predicting life satisfaction, happiness, and health in youngsters aged 18 to 30 around the world. Our results generally confirm hypotheses derived from self-determination theory, showing that the type of values held by youngsters and the type of values prevailing in their environments account for significant variation in young peoples’ life satisfaction, happiness, and health. the pattern of evidence suggests that youngsters benefit from attaching greater importance to intrinsic values related to affiliation and community contribution rather than to extrinsic values that relate to financial success and accumulation of power

I Want to Be a Billionaire: How Do Extrinsic and Intrinsic Values Influence Youngsters’ Well-Being?

Values guide our attitudes and behavior, but to what extent and how do individual values determine our overall well-being? Self-determination theory holds that particular types of values (i.e., intrinsic or extrinsic) matter most, but the person-environment fit perspective argues that any values can be beneficial as long as they align with values prevalent in one’s environment. The evidentiary support for these competing claims is inconclusive. We use the World Value Survey to see how these perspectives do in predicting life satisfaction, happiness, and health in youngsters aged 18 to 30 around the world. Our results generally confirm hypotheses derived from self-determination theory, showing that the type of values held by youngsters and the type of values prevailing in their environments account for significant variation in young peoples’ life satisfaction, happiness, and health. The pattern of evidence suggests that youngsters benefit from attaching greater importance to intrinsic values related to affiliation and community contribution rather than to extrinsic values that relate to financial success and accumulation of power.status: publishe

Limnology and trophic status of glacial lakes in the tropical Andes (Cajas National Park, Ecuador)

© 2016 John Wiley & Sons Ltd 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.status: publishe

Limnology and trophic status of glacial lakes in the tropical Andes (Cajas National Park, Ecuador)

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 LtdThe 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 Lt