Saara Olsen's research while affiliated with Aarhus University and other places

Publications (11)

Article
Full-text available
Nature Ecology & Evolution - online Abstract There is a pressing need to apply stability and resilience theory to environmental management to restore degraded ecosystems effectively and to mitigate the effects of impending environmental change. Lakes represent excellent model case studies in this respect and have been used widely to demonstrate th...
Article
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The ongoing global climate change involves not only increased temperatures but may also produce more frequent extreme events, such as severe rainfall that could trigger a pulse of nutrients to lakes. In shallow lakes, this may affect primary producers through a number of direct and indirect mechanisms. We conducted a six-month mesocosm experiment t...
Article
1. Shallow lakes may play an important role for the nitrogen (N) balance in drainage basins by processing, transferring and retaining N inputs. An increase in the frequency of storm-induced short-term N pulses and increased water temperatures are both likely outcomes of climate change, potentially affecting the N processing in lakes. 2. An experime...
Article
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Losses of phosphorus (P) and nitrogen (N) have important influences on in-lake concentrations and nutrient loading to downstream ecosystems. We performed a series of mesocosm experiments along a latitudinal gradient from Sweden to Greece to investigate the factors influencing N and P loss under different climatic conditions. In six countries, a sta...
Article
Full-text available
Losses of phosphorus (P) and nitrogen (N) have important influences on in-lake concentrations and nutrient loading to downstream ecosystems. We performed a series of mesocosm experiments along a latitudinal gradient from Sweden to Greece to investigate the factors influencing N and P loss under different climatic conditions. In six countries, a sta...
Article
Full-text available
Losses of phosphorus (P) and nitrogen (N) have important influences on in-lake concentrations and nutrient loading to downstream ecosystems. We performed a series of mesocosm experiments along a latitudinal gradient from Sweden to Greece to investigate the factors influencing N and P loss under different climatic conditions. In six countries, a sta...
Article
1. Excess loading of phosphorus (P) and nitrogen (N) triggers a shift in the trophic structure of shallow lakes from a clear-water, macrophyte-dominated state to an algal-dominated turbid state. However, the role of N in the shift is debated, and experimental evidence is, with a few exceptions, based on short-term studies (days to a few months). 2....
Article
Full-text available
1. Excess loading of phosphorus (P) and nitrogen (N) triggers a shift in the trophic structure of shallow lakes from a clear-water, macrophyte-dominated state to an algal-dominated turbid state. However , the role of N in the shift is debated, and experimental evidence is, with a few exceptions, based on short-term studies (days to a few months)....
Article
1. To help improve our understanding of the nitrogen cycle in lakes, particularly in the context of climate change, we analysed total nitrogen (TN) and nitrate (NO � 3 -N) data from six mesocosm experiments (in Denmark, U.K., China and Turkey) covering different climatic regions. We assessed the effects of nitrogen (N) and phosphorus (P) loading, t...
Article
1. To help improve our understanding of the nitrogen cycle in lakes, particularly in the context of climate change, we analysed total nitrogen (TN) and nitrate (NO À 3 -N) data from six mesocosm experi-ments (in Denmark, U.K., China and Turkey) covering different climatic regions. We assessed the effects of nitrogen (N) and phosphorus (P) loading,...

Citations

... Thus, the combination of the four scenarios and the three diagnostic indicators provide a well-defined set of characteristics which can be used to identify either the presence or the absence of alternative equilibria in a given dataset. In this way, we avoid the dangers of a conjunction fallacy 39 where the assertion that the real-world dataset does not contain alternative equilibria is based on the fact that there is no strong evidence of its presence, rather than a pattern that confirms its absence. ...
... For dissolved nutrients (dissolved organic carbon, orthophosphate, nitrate, ammonium and silicate), water samples were filtered through pre-combusted (500°C) Whatman® glass microfiber filters grade GF/C (1.2 μm pore size). Although GF/F filters (0.6-0.7 μm pore size) are generally recommended in dissolved nutrient analyses (Wetzel and Likens, 2000), GF/C have also been commonly used, without considerable impact (Olsen et al., 2017;Trochine et al., 2017). Dissolved organic carbon (DOC) was measured in a TOC-L analyzer (Shimadzu Corporation, Japan). ...
... both the water and the sediment, and to harvest light as close to the water surface as possible, whereas phytoplankton have first access to light, but rely on nutrients from the water column (Hansson 1988). If nutrient concentrations in the water increases, phytoplankton, as well as filamentous algae, generally become more abundant (Cao et al. 2017), reducing light penetration through the water column and subsequently primary production at the sediment surface becomes light-limited (Hansson 1988(Hansson , 1989. Hence, there is an ever-ongoing competition among different life-forms of primary producers which to a large extent determines water clarity (Scheffer 1990;Moss 2012). ...
... We cultured the plants at three different water temperatures (20, 24, and 28°C) and four distinct nutrient conditions (nutrient-poor and nutrient-rich sediments, with and without external nutrient loading) in a full-factorial design. Nutrient conditions were experimentally manipulated in the water column, the sediment, or both, because nutrient enrichment in eutrophic water bodies can result from external loading into the water column ( Coppens et al., 2016), internal loading from the sediment ( Fisher et al., 2005;Immers et al., 2015), or a combination thereof. We also monitored nutrient availability for the plants, and the development of competing primary producers (e.g. ...
... There were 12 treatments in total and four replicates for each treatment, and all treatments were randomly assigned to the 48 mesocosms. Doses of 0.5 mg L −1 N (NaNO 3 ) and 0.05 mg L −1 P (KH 2 PO 4 ) were added weekly to the selected mesocosms to simulate eutrophication (E), similar to those used in previous studies (Coppens et al., 2016;Jeppesen et al., 2007). W and H treatments were achieved by a computer-controlled temperature system with two digital temperature sensors (DS18B20, Risym, China) and a heating element (600 W in power) in each mesocosm. ...
... Increase in temperature influences internal nutrient loading and enhances sediment phosphorus release promoting plant growth. Lower precipitation and high evaporation leading to reduced water levels and improved light conditions at lake bottoms also stimulate macrophyte growth (Coppens et al. 2015;Short et al. 2016). The climatic variations along with overexploitation and habitat may be some of the major reasons for declining natural fish production and diminishing fish diversity in this wetland. ...
... In addition, periphyton is considered to have distinct roles in the alternative equilibrium states along the trophic gradient. On the one hand, phototrophic periphyton maintains a clear state in lakes due to its capacity for nutrient retention (Genkai-Kato et al. 2012); on the other hand, submerged macrophytes can be shaded by epiphyton, keeping shallow lakes in a turbid state for a long time (Olsen et al. 2015). Furthermore, periphyton may change its ecological role in response to climate change. ...
... For example, the pot experiments conducted in the ponds near natural conditions showed that high ammonium in winter and spring had a negative impact on the leaf length and leaf dry weight of V. natans, while it has a weak or even no impact on the number of plants and root dry weight; moreover, the tolerance of submersed macrophytes in summer and autumn is higher than that in winter and spring (Yu et al., 2015(Yu et al., , 2017. The 11-month mesocosm experiment showed that longterm high nitrogen exposure had a negative impact on the growth of submersed macrophytes (Olsen et al., 2015). Thus, the effect of ammonium is related to exposure duration, and the sensitivity of submersed macrophytes to ammonium is also changeable in different growth periods (Ochieng et al., 2021). ...
... In lake management, a reduction of P availability with the aim to decrease phytoplankton biomass is therefore often the first measure introduced to combat and reverse cultural eutrophication. discussed (Sterner, 2008;Conley et al., 2009;Moss et al., 2013;Olsen et al., 2015a). Worldwide, huge amounts are invested in reducing nutrient loading to aquatic ecosystems, and targeting eutrophication efficiently and cost effectively is of utmost importance (Schindler & Hecky, 2009). ...
... In addition to the challenges with achieving a sufficiently low critical turbidity threshold, macrophyte reestablishment in shallow lakes can also be impeded due to factors that include the following: 1) lack of viable propagules, 2) grazing by wildfowl or herbivorous fish, 3) persistently high-nitrogen conditions, 4) unsuitable substrate, 5) high plant costs, and 6) inadequate availability of plants (Bakker et al., 2013;Barko & Smart, 1986;Olsen et al., 2015). ...