•We model metabolism of a large lake during four months with a 10min increment.•High-frequency measurements and seasonal duration of experiment are combined.•Magnitude of uncertainty in metabolism is ...clearly displayed.
We used a Bayesian metabolic model for assessing the gross primary production (GPP), ecosystem respiration (ER) and their uncertainties in lake Võrtsjärv, a large eutrophic lake in Estonia (North-eastern Europe). Diel cycle modeling was based on high-frequency (10-min) measurements of irradiance, water temperature and dissolved oxygen during most of the growing season (from May to August 2011). Posterior distribution of production and respiration was successfully simulated with the model and displayed with highly credible intervals (2.5 and 97.5 percentiles). Considering the mean GPP and ER values, the lake was autotrophic from May to June, at equilibrium in July, and heterotrophic in August. However, adding the uncertainty to metabolism estimates revealed that an ambiguous metabolic state (no clear monthly predominance of auto- or hetero-trophy) represented between 12 and 32% of the period. It is thus incautious to conclude about lake metabolic state in these conditions. A comparison with the existing classical model based on dissolved oxygen measurements showed that metabolic dynamics differed between the two approaches. Though the classical model recorded highest ecosystem productivity in midsummer, the Bayesian model predicted that productivity peaked earlier in the season and gradually declined as the irradiance dropped and the water temperature rose. Coupling between GPP and ER during the whole study period was very variable, resulting that, depending on the month, 50–100% of primary production was consumed in the lake. This coupling variability was caused by extensive diel fluctuation of irradiance-dependent production compared to relatively stable water temperature and respiration. The background respiration was high in spring and declined progressively in summer, reflecting lower inputs of allochthonous organic matter to the lake. With a wider use of high-frequency techniques for measuring lake ecological parameters, this kind of performant models that are able to assess lake productivity within small time steps and take into account the uncertainty, will be increasingly needed in the future.
Efficient zooplankton grazing is a prerequisite for establishing a cascading food web control over phytoplankton in a lake. We studied if the top-down impact of fish could reach phytoplankton in a ...lake where the grazing pressure of small-sized zooplankton on filamentous phytoplankton is considered weak. We analysed >30 years of data on plankton, fish catches, hydrochemistry, hydrology, and meteorology from Võrtsjärv, a large and shallow eutrophic lake in Estonia with intensive commercial fisheries. The lake’s unregulated water level has been considered the strongest factor affecting the ecosystem through modifying sediment resuspension, internal loading of nutrients, and underwater light conditions and spawning conditions for fish. We found a negative relationship between phytoplankton biomass and pikeperch biomass indicating a potential top-down cascading effect in the food web. Top-down control of phytoplankton by zooplankton was reflected in a negative relationship between phyto- and zooplankton biomasses. A decrease of the individual weight of crustacean zooplankton with increasing biomass of small fish suggested top-down control of zooplankton by planktivorous fish. In contrast, we could not demonstrate a direct linkage between piscivorous fish and small fish. The top-down food web impact of piscivores, however, was manifested at zooplankton level in a positive correlation of pikeperch biomass with the biomass of dominating cladoceran species
Bosmina coregoni
and the individual weight of copepods. At high biomasses of small fish, ciliate domination over metazooplankton increased and thus enhanced the strength of the microbial food web. According to our results, fishery management measures that increase small plankti- and benthivorous fish biomass have to be avoided as they have a cascading negative effect on the ecosystem health.
Lakes play an important role in the global carbon cycle. Hence, data on seasonal and spatial variations of phytoplankton primary production (PP) is needed to estimate their ecological state. However, ...considerable difficulties arise when investigating the spatial and temporal variations of productivity in inland waters. Traditional in situ sampling approaches cannot provide the necessary data over large lakes or for lakes over large geographic regions. A solution can be to combine modelling with satellite data, by using different satellite products as inputs for a primary production model. The objective of this study is to evaluate and validate a lake primary production model based on satellite products. For that purpose we compared PP(sat) with PP(in situ) in two large, shallow, well mixed, and eutrophic Estonian lakes. A semi-empirical phytoplankton primary production model, derived by us earlier, was used. It allows estimating the values of phytoplankton primary production for lakes over large geographic areas. The primary production model operated well using MERIS products as input data. Our results show that spatial variability in primary production cannot be neglected in large lakes. Combining satellite data with model calculations allows monitoring of the state of lakes in space and time, providing a new perspective for lake primary production studies.
•A semi-empirical bio-optical model was used for lake primary productivity studies.•MERIS products were used as the input parameters.•The model performed well in two large eutrophic lakes.•Satellite data shows significant spatial variability of primary productivity.
Eutrophication and lake depth are of key importance in structuring lake ecosystems. To elucidate the effect of contrasting nutrient concentrations and water levels on the microbial community in fully ...mixed shallow lakes, we manipulated water depth and nutrients in a lake mesocosm experiment in north temperate Estonia and followed the microbial community dynamics over a 6-month period. The experiment was carried out in Lake Võrtsjärv—a large, shallow eutrophic lake. We used two nutrient levels crossed with two water depths, each represented by four replicates. We found treatment effects on the microbial food web structure, with nutrients having a positive and water depth a negative effect on the biomasses of bacterial and heterotrophic nanoflagellates (HNF) (RM-ANOVA,
p
< 0.05). Nutrients affected positively and depth negatively the mean size of individual HNF and ciliate cells (RM-ANOVA;
p
< 0.05). The interactions of depth and nutrients affected positively the biomass of bacterivorous and bacteri-herbivorous ciliates and negatively the biomass of predaceous ciliates (RM-ANOVA;
p
< 0.05). Bacterivorous ciliates had lowest biomass in shallow and nutrient-rich mesocosms, whilst predaceous ciliates had highest biomass here, influencing trophic interactions in the microbial loop. Overall, increased nutrient concentrations and decreased water level resulted in an enhanced bacterial biomass and a decrease in their main grazers. These differences appeared to reflect distinctive regulation mechanisms inside the protozoan community and in the trophic interactions in the microbial loop community.
Generalist invasion in a complex lake food web Kuparinen, Anna; Uusi‐Heikkilä, Silva; Perälä, Tommi ...
Conservation science and practice,
June 2023, Letnik:
5, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Invasive species constitute a threat not only to native populations but also to the structure and functioning of entire food webs. Despite being considered as a global problem, only a small number of ...studies have quantitatively predicted the food web‐level consequences of invasions. Here, we use an allometric trophic network model parameterized using empirical data on species body masses and feeding interactions to predict the effects of a possible invasion of Amur sleeper (Perccottus glenii), on a well‐studied lake ecosystem. We show that the modeled establishment of Amur sleeper decreased the biomasses of top predator fishes by about 10%–19%. These reductions were largely explained by increased larval competition for food and Amur sleeper predation on fish larvae. In contrast, biomasses of less valued fish of lower trophic positions increased by about 0.4%–9% owing to reduced predation pressure by top piscivores. The predicted impact of Amur sleeper establishment on the biomasses of native fish species vastly exceeded the impacts of current‐day fishing pressures.
We study using an allometric trophic network model how an invasive species can alter a lake ecosystem. We show reductions in the highest trophic position fishes, which are the most valued by fishers.
Calcium (Ca) is an essential element for almost all living organisms. Here, we examined global variation and controls of freshwater Ca concentrations, using 440 599 water samples from 43 184 inland ...water sites in 57 countries. We found that the global median Ca concentration was 4.0 mg L
with 20.7% of the water samples showing Ca concentrations ≤ 1.5 mg L
, a threshold considered critical for the survival of many Ca-demanding organisms. Spatially, freshwater Ca concentrations were strongly and proportionally linked to carbonate alkalinity, with the highest Ca and carbonate alkalinity in waters with a pH around 8.0 and decreasing in concentrations towards lower pH. However, on a temporal scale, by analyzing decadal trends in >200 water bodies since the 1980s, we observed a frequent decoupling between carbonate alkalinity and Ca concentrations, which we attributed mainly to the influence of anthropogenic acid deposition. As acid deposition has been ameliorated, in many freshwaters carbonate alkalinity concentrations have increased or remained constant, while Ca concentrations have rapidly declined towards or even below pre-industrial conditions as a consequence of recovery from anthropogenic acidification. Thus, a paradoxical outcome of the successful remediation of acid deposition is a globally widespread freshwater Ca concentration decline towards critically low levels for many aquatic organisms.
The importance of lakes and reservoirs leads to the high need for monitoring lake water quality both at local and global scales. The aim of the study was to test suitability of Sentinel-2 ...Multispectral Imager's (MSI) data for mapping different lake water quality parameters. In situ data of chlorophyll a (Chl a), water color, colored dissolved organic matter (CDOM) and dissolved organic carbon (DOC) from nine small and two large lakes were compared with band ratio algorithms derived from Sentinel-2 Level-1C and atmospherically corrected (Sen2cor) Level-2A images. The height of the 705 nm peak was used for estimating Chl a. The suitability of the commonly used green to red band ratio was tested for estimating the CDOM, DOC and water color. Concurrent reflectance measurements were not available. Therefore, we were not able to validate the performance of Sen2cor atmospheric correction available in the Sentinel-2 Toolbox. The shape and magnitude of water reflectance were consistent with our field measurements from previous years. However, the atmospheric correction reduced the correlation between the band ratio algorithms and water quality parameters indicating the need in better atmospheric correction. We were able to show that there is good correlation between band ratio algorithms calculated from Sentinel-2 MSI data and lake water parameters like Chl a (R2 = 0.83), CDOM (R2 = 0.72) and DOC (R2 = 0.92) concentrations as well as water color (R2 = 0.52). The in situ dataset was limited in number, but covered a reasonably wide range of optical water properties. These preliminary results allow us to assume that Sentinel-2 will be a valuable tool for lake monitoring and research, especially taking into account that the data will be available routinely for many years, the imagery will be frequent, and free of charge.
Abundance and biomass of the microbial loop members bacteria, heterotrophic nanoflagellates (HNF), and ciliates were seasonally measured in the naturally eutrophic and shallow (2.8 mean depth) Lake ...Võrtsjärv, which has a large open surface area (average 270 km²) and highly turbid water (Secchi depth <1 m). Grazing rates (filter feeding rates) on 0.5-, 3-, and 6-μm-diameter particles were measured to estimate pico- and nanoplankton grazing (filter feeding) by micro- and metazooplankton. Among grazers, HNF had a low abundance (<50 cells mL-¹) and, due to their low specific filtering rates, they only grazed a minor fraction of the bacterioplankton (<=4.2% of total grazing). Ciliates were relatively abundant (<=158 cells mL-¹) and, considering their high specific feeding rates, were able to graze more than 100% of the bacterial biomass production in the open part of the lake, whereas the average daily grazing accounted for 9.3% of the bacterial standing stock. Ciliates were potentially important grazers of nanoplanktonic organisms (on average, approximately 20% of the standing stock of 3-μm-size particles was grazed daily). Metazooplankton grazed a minor part of the bacterioplankton, accounting for only 0.1% of standing stock of bacteria. Grazing on nanoplankton (3-6 μm) by metazooplankton was higher (0.4% of standing stock). The hypothesis is proposed that ciliates dominate due to a lack of top-down regulation by predators, and HNF have a low abundance due to strong grazing pressure by ciliates.
Different sources of particulate organic matter (POM) as well as its composition affect the biological food web and hence the self-purification potential and water quality of rivers. We studied the ...effect of a large shallow lake on the POM pool of the water passing through it. Over four years, we analysed monthly the amount and composition of POM and a set of environmental variables in the inflows and in the outflow of Lake Vortsjarv (Estonia). In the inflows, the live pool of POM consisted of phytoplankton--small crypto-, dino-, and chlorophytes. The concentration of chlorophyll a (Chl a), as a proxy of phytoplankton biomass, was positively correlated with temperature and total phosphorus and negatively with dissolved silica, total nitrogen, and discharge. In the outflow, the share of the live component of POM was much larger than in the inflows but was also dominated by phytoplankton represented by grazing resistant filamentous cyanobacteria. Chl a was positively correlated with total phosphorus, temperature, pH, and precipitation, and negatively with dissolved silica, total nitrogen, and discharge in the outflow. The different amounts, composition, and seasonal dynamics of POM in the inflows and in the outflow have potentially substantial impacts on the food web with a predominating classical pathway in the inflows versus a detrital pathway in the outflow. Key words: particulate organic matter, rivers, lakes, algal species, food web.
We assessed feeding of planktivorous fish larvae on ciliate protozooplankton in shallow eutrophic Lake Võrtsjärv, Estonia to determine whether ciliates are an important part of larval fish diet. We ...collected larvae of the most common fish species and examined their gut contents by gut segmentation and epifluorescence microscopy. Ciliates were present in the gut of all fish larvae. Gut segmentation analysis showed clear differences in food composition between gut quarters. The hard-bodied food items were quite evenly distributed in the gut, but the soft-bodied ciliates and rotifers were present only in the first gut quarters. Neglecting differences in prey digestion rate leads to underestimation of diet amount and composition and, especially, to underestimation of the role of protists in food. In Võrtsjärv, ciliates account for ∼ 60% of the total carbon biomass consumed by fish larvae. The food requirement of fish larvae during first feeding stages (May–Jun) would not be met without consumption of ciliates.
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