Humic Lake Research Articles

The role of visual and physiological refuges in humic lakes: Effects of oxygen, light quantity, and spectral composition on daytime depth of chaoborids

To clarify the effect of brownification on the functioning of lake ecosystems, the utilization of daytime refuges by chaoborids was examined in two lakes having different water color. It was hypothesized that with high water color, oxygen concentration plays a smaller role for the behavior of chaoborids than with lower water color. It was also expected that the depth distribution of chaoborids is associated with light intensity at 680–700 nm. This could decrease their visibility to predators. In Lake Iso Valkjärvi with 50 mg L−1 Pt water color, chaoborids occurred below 5 m depth, where the oxygen concentration was 0.4 mg L−1. Supporting the first hypothesis, in Lake Majajärvi with 340 mg L−1 Pt color, the leading edge of the population was at 3 m with 3.5 mg L−1 oxygen concentration. In Majajärvi, chaoborids remained in a layer where planktivorous fish could feed, explained by the low light intensity that decreased the potential predation pressure of fish. In Iso Valkjärvi with higher light intensity, chaoborids inhabited only the layers where oxygen concentration was too low for fish. Supporting the second hypothesis, the intensity of 693 nm light in the two lakes was similar at the depth of the leading edge of the chaoborid population. This wavelength represents the wavelengths that chaoborids reflect most effectively and is beyond the sensitivity peak of their main predator perch. The results suggested that combined effects of oxygen and water color are potential explanatory mechanisms of the observed patterns in the behavior of chaoborids. The results thus suggested that along the worldwide brownification of lakes, the role of oxygen as a regulator of invertebrate predators may change. Because invertebrate predators are important components of lake food webs, such effects may be reflected to the whole ecosystem and further studies on the subject are encouraged.

Effects of multiple stressors on cyanobacteria abundance vary with lake type.

Blooms of cyanobacteria are a current threat to global water security that is expected to increase in the future because of increasing nutrient enrichment, increasing temperature and extreme precipitation in combination with prolonged drought. However, the responses to multiple stressors, such as those above, are often complex and there is contradictory evidence as to how they may interact. Here we used broad scale data from 494lakes in central and northern Europe, to assess how cyanobacteria respond to nutrients (phosphorus), temperature and water retention time in different types of lakes. Eight lake types were examined based on factorial combinations of major factors that determine phytoplankton composition and sensitivity to nutrients: alkalinity (low and medium-high), colour (clear and humic) and mixing intensity (polymictic and stratified). In line with expectations, cyanobacteria increased with temperature and retention time in five of the eight lake types. Temperature effects were greatest in lake types situated at higher latitudes, suggesting that lakes currently not at risk could be affected by warming in the future. However, the sensitivity of cyanobacteria to temperature, retention time and phosphorus varied among lake types highlighting the complex responses of lakes to multiple stressors. For example, in polymictic, medium-high alkalinity, humic lakes cyanobacteria biovolume was positively explained by retention time and a synergy between TP and temperature, while in polymictic, medium-high alkalinity, clear lakes only retention time was identified as an explanatory variable. These results show that, although climate change will need to be accounted for when managing the risk of cyanobacteria in lakes, a "one-size fits-all" approach is not appropriate. When forecasting the response of cyanobacteria to future environmental change, including changes caused by climate and local management, it will be important to take this differential sensitivity of lakes into account.

Browning-related oxygen depletion in an oligotrophic lake

ABSTRACTIn recent decades, terrestrial dissolved organic matter (DOM) has increased in many northeastern North American and European lakes and is contributing to long-term browning. We used a long-term dataset (1988–2014) to study the consequences of browning-related decreased water transparency on dissolved oxygen dynamics in 2 small temperate lakes in Pennsylvania, USA, that differ in their dissolved organic carbon concentrations. The oligotrophic (“clearer”) lake has low productivity and historically oxygenated deep waters. The mesotrophic–slightly dystrophic (“browner”) lake also has relatively low productivity but historically anoxic deep waters. We examined whether browning coincided with changes in summer dissolved oxygen dynamics, with a focus on deep-water oxygen depletion. In the clearer lake, we found that minimum oxygen concentrations decreased by ∼4.4 mg L−1 over the 27-year period, and these changes were strongly associated with both decreased water transparency and increased water column stability. We also found a shallowing of the maximum dissolved oxygen depth by ∼4.5 m and anoxic conditions established in more recent years. In the browner lake, the metrics we used did not detect any significant changes in dissolved oxygen, supporting the prediction that vertical temperature and oxygen patterns in clearer lakes may be more sensitive to increasing DOM than darker lakes. Anoxia is traditionally considered to be a consequence of anthropogenic nutrient loading and, more recently, a warming climate. We show that browning is another type of environmental change that may similarly result in anoxia in oligotrophic lakes.

Coupled UV-exposure and microbial decomposition improves measures of organic matter degradation and light models in humic lake

Increasing terrestrial input of colored dissolved organic matter (CDOM) to temperate softwater lakes has reduced transparency, distribution of pristine rosette plants and overall biodiversity in recent decades. We examined microbial and UV-induced reduction of absorption by CDOM and dissolved organic carbon pools (DOC) in humic water from a groundwater-fed softwater lake as well as groundwater received from surrounding heathland and coniferous forest. An experimental setup that mimics naturally coupled continuous UV-exposure and microbial degradation was introduced and compared with experiments applying a single initial or no UV-exposure. We found that decreases of CDOM and DOC concentrations were negligible in groundwater and very small in lake water over 30 days in the absence of UV-exposure. Initial UV-exposure increased degradation rates, but further degradation ceased after 20 days preventing determination of the natural time course of degradation. Coupled continuous UV-exposure and microbial degradation showed high and constant degradation of CDOM (340 nm) over 30 days removing 87% of the initial absorption in heathland groundwater, and 20% in forest groundwater and lake water. Declines in DOC concentrations over 30 days were 34%, 28% and 13% of the initial levels in heathland groundwater, forest groundwater and lake water, respectively. Model estimates showed that a shift in land use from a forest dominated to a heathland dominated catchment could increase lake transparency from 0.6 to 2.5 m. and expand plant-covered area from 3 to 35%. The main time delay to a new steady state of better light climate would be degradation of soil organic pools and exchange of groundwater magazines, while the delay in the lake water after a complete shift to inflow of CDOM-poorer groundwater would last only 1–2 years. Consequently, changes in CDOM levels in groundwater input should have relatively rapid and marked influence on light conditions and plant distribution in shallow softwater lakes.

Microplastics: New substrates for heterotrophic activity contribute to altering organic matter cycles in aquatic ecosystems

Heterotrophic microbes with the capability to process considerable amounts of organic matter can colonize microplastic particles (MP) in aquatic ecosystems. Weather colonization of microorganisms on MP will alter ecological niche and functioning of microbial communities remains still unanswered. Therefore, we compared the functional diversity of biofilms on microplastics when incubated in three lakes in northeastern Germany differing in trophy and limnological features. For all lakes, we compared heterotrophic activities of MP biofilms with those of microorganisms in the surrounding water by using Biolog® EcoPlates and assessed their oxygen consumption in microcosm assays with and without MP. The present study found that the total biofilm biomass was higher in the oligo-mesotrophic and dystrophic lakes than in the eutrophic lake. In all lakes, functional diversity profiles of MP biofilms consistently differed from those in the surrounding water. However, solely in the oligo-mesotrophic lake MP biofilms had a higher functional richness compared to the ambient water. These results demonstrate that the functionality and hence the ecological role of MP-associated microbial communities are context-dependent, i.e. different environments lead to substantial changes in biomass build up and heterotrophic activities of MP biofilms. We propose that MP surfaces act as new niches for aquatic microorganisms and that the constantly increasing MP pollution has the potential to globally impact carbon dynamics of pelagic environments by altering heterotrophic activities.

Pipes or chimneys? For carbon cycling in small boreal lakes, precipitation matters most

AbstractAre small lakes passive pipes transporting terrigenous organic carbon (dissolved organic carbon [DOC]), or chimneys for CO2 release in the landscape? Using a unique combination of 30‐yr measurements, sediment dating and modeling of a small humic lake and its catchment in southeast Norway, we calculated lateral DOC fluxes and in‐lake retention. Concentrations and fluxes rose significantly, driven by declining sulfur deposition and increased precipitation. In‐lake retention (% of inputs) declined because of higher discharge and lower residence times. DOC removal rates were not sensitive to residence time. Modeled in‐lake DOC removal was driven primarily by microbial metabolism and, secondarily, by flocculation, suggesting that the likely fate of lake‐retained DOC is CO2 evasion to the atmosphere. Precipitation was the overriding landscape control on DOC fluxes and retention. In a wetter climate, small northern lakes will, on balance, function more as pipes than chimneys, with increasing lateral DOC fluxes but little change in CO2 production.

Assessing sedimentation in a temperate dystrophic lake in the NE Atlantic seaboard region

Organic materials deposited in lacustrine environments can be derived from both aquatic and terrestrial ecosystems, and can serve as valuable indicators of catchment and in-lake ecological changes over time. However, spatial and temporal variation in the deposition of these materials within a lake basin will influence the interpretation of these sediment deposits. In this study, materials deposited in suspended sediment traps and basin sediments in Lough Feeagh, a temperate coastal humic lake, show variations in organic matter, total organic carbon and nitrogen loads, algal pigment concentrations and diatom assemblages. Sediment trap samples from three locations along with adjacent surface sediment cores show a clear north–south (inlet to outlet) gradient. C/N ratios reflected a mixture of algal and land-derived organic matter with a major peat influence, and comparisons between sediment trap and surface sediment assemblages revealed pigment and diatom assemblages influenced by lake-basin position and water depth. While some coherency between trap and sediment samples was apparent a more complicated biological response is demonstrated along with reduced water clarity in recent years thus highlighting the implications of increased allochthonous imputs for biological and biogeochemical processes in oligo-humic aquatic systems.

Mercury in fish from Norwegian lakes: The complex influence of aqueous organic carbon

Mercury (Hg) concentrations in water and biota are often positively correlated to organic matter (OM), typically measured as total or dissolved organic carbon (TOC/DOC). However, recent evidence suggests that higher OM concentrations inhibit bioaccumulation of Hg. Here, we test how TOC impacts the Hg accumulation in fish in a synoptic study of Methyl-Hg (MeHg) in water and total Hg (THg) in perch (Perca fluviatilis) in 34 boreal lakes in southern Norway. We found that aqueous MeHg (r2 = 0.49, p < 0.0001) and THg (r2 = 0.69, p < 0.0001), and fish THg (r2 = 0.26, p < 0.01) were all positively related with TOC. However, we found declining MeHg bioaccumulation factors (BAFMeHg) for fish with increasing TOC concentrations. The significant correlation between fish THg concentrations and aqueous TOC suggests that elevated fish Hg levels in boreal regions are associated with humic lakes. The declining BAFMeHg with increasing TOC suggest that increased OM promotes increased aqueous Hg concentrations, but lowers relative MeHg bioaccumulation. A mechanistic understanding of the response from OM on BAFMeHg might be found in the metal-complexation properties of OM, where OM complexation of metals reduces their bioavailability. Hence, suggesting that MeHg bioaccumulation becomes less effective at higher TOC, which is particularly relevant when assessing potential responses of fish Hg to predicted future changes in OM inputs to boreal ecosystems. Increased browning of waters may affect fish Hg in opposite directions: an increase of food web exposure to aqueous Hg, and reduced bioavailability of Hg species. However, the negative relationship between BAFMeHg and TOC is challenging to interpret, and carries a great deal of uncertainty, since this relationship may be driven by the underlying correlation between TOC and MeHg (i.e. spurious correlations). Our results suggest that the trade-off between Hg exposure and accumulation will have important implications for the effects of lake browning on Hg transport, bioavailability, and trophodynamics.

Restoration of a Dystrophic Lake: The Case of Efoulan Lake in Yaounde Cameroon

Restoration of a Dystrophic Lake: The Case of Efoulan Lake in Yaounde Cameroon

Vertical distribution of expansive, bloom-forming algaeGonyostomum semenvs.plankton community and water chemistry in four small humic lakes

One of the features ofGonyostomum semen, a bloom-forming and expansive flagellate, is uneven distribution in the vertical water column often observed in humic lakes. In this paper, we analysed vertical distribution of the algae in four small (0.9–2.5 ha) and humic (DOC: 7.4–16.5 mg dm−3) lakes with similar morphometric features with the aim to test the hypothesis that vertical distribution ofG. semenmay be shaped by zooplankton structure and abundance. In addition, we wanted to check whether high biomass of this flagellate has any influence on the chemical composition as well as on planktonic bacteria abundance of the water column. The results of the study showed that vertical distribution of the algae during the day varied among all studied lakes. Our most important finding was that (a) the abundance and structure of zooplankton community (especially in case of large bodied daphnidsDaphnia pulicaria, D. longispinaand copepodEudiaptomus graciloides) may shapeG. semenvertical distribution in studied lakes; (b) highG. semenbiomass may decrease the content of ammonium ions in the water column by intense uptake, but has low effect on other water chemical parameters. The results of the study contribute to the understanding of the factors influencing this expansive algae behaviour as well as it shows interesting aspects ofG. semeninfluence on some components of the lake ecosystem.

Influence of environmental factors on vertical distribution of zooplankton communities in humic lakes

The influence of vertical environmental gradients on zooplankton communities was studied in five humic lakes with the high availability of food resources (phytoplankton and bacterioplankton) and low fish pressure. The factors that inhibit the development of large zooplankton in humic lakes are currently widely debated. We have found that relatively productive humic lakes do not offer many niches for zooplankton because of the sharp thermal gradient which results in a shallow layer of oxygenated waters. The results of this study indicated that different taxonomic groups of zooplankton are determined by a different set of environmental variables. This phenomenon explains very low species richness of zooplankton and a possibility of their coexistence in the narrow oxygenated layer. We concluded that due to sharp thermal gradient in humic lakes biomass of herbivores may be reduced which could promote development of phytoplankton.

Low biodegradability of dissolved organic matter and trace metals from subarctic waters

The heterotrophic mineralization of dissolved organic matter (DOM) controls the CO2 flux from the inland waters to the atmosphere, especially in the boreal waters, although the mechanisms of this process and the fate of trace metals associated with DOM remain poorly understood. We studied the interaction of culturable aquatic (Pseudomonas saponiphila) and soil (Pseudomonas aureofaciens) Gammaproteobacteria with seven different organic substrates collected in subarctic settings. These included peat leachate, pine crown throughfall, fen, humic lake, stream, river, and oligotrophic lake with variable dissolved organic carbon (DOC) concentrations (from 4 to 60mgL−1). The highest removal of DOC over 4days of reaction was observed in the presence of P. aureofaciens (33±5%, 43±3% and 53±7% of the initial amount in fen water, humic lake and stream, respectively). P. saponiphila degraded only 5% of DOC in fen water but did not affect all other substrates. Trace elements (TE) were essentially controlled by short-term (0−1h) adsorption on the surface of cells. Regardless of the nature of organic substrate and the identity of bacteria, the degree of adsorption ranged from 20 to 60% for iron (Fe3+), 15 to 55% for aluminum (Al), 10 to 60% for manganese (Mn), 10 to 70% for nickel (Ni), 20 to 70% for copper (Cu), 10 to 60% for yttrium (Y), 30 to 80% for rare earth elements (REE), and 15 to 50% for uranium (UVI). Rapid adsorption of organic and organo-mineral colloids on bacterial cell surfaces is novel and potentially important process, which deserves special investigation. The long-term removal of dissolved Fe and Al was generally consistent with solution supersaturation degree with respect to Fe and Al hydroxides, calculated by visual Minteq model. Overall, the biomass-normalized biodegradability of various allochthonous substrates by culturable bacteria is much lower than that of boreal DOM by natural microbial consortia.

Temperature Dependence of Apparent Respiratory Quotients and Oxygen Penetration Depth in Contrasting Lake Sediments

AbstractLake sediments constitute an important compartment in the carbon cycle of lakes, by burying carbon over geological timescales and by production and emission of greenhouse gases. The degradation of organic carbon (OC) in lake sediments is linked to both temperature and oxygen (O2), but the interactive nature of this regulation has not been studied in lake sediments in a quantitative way. We present the first systematic investigation of the effects of temperature on the apparent respiratory quotient (RQ, i.e., the molar ratio between carbon dioxide (CO2) production and O2 consumption) in two contrasting lake sediments. Laboratory incubations of sediment cores of a humic lake and an eutrophic lake across a 1–21°C temperature gradient over 157 days revealed that both CO2 production and O2 consumption were positively, exponentially, and similarly dependent on temperature. The apparent RQ differed significantly between the lake sediments (0.63 ± 0.26 and 0.99 ± 0.28 in the humic and the eutrophic lake, respectively; mean ± SD) and was significantly and positively related to temperature. The O2 penetration depth into the sediment varied by a factor of 2 over the 1–21°C temperature range and was significantly, negatively, and similarly related to temperature in both lake sediments. Accordingly, increasing temperature may influence the overall extent of OC degradation in lake sediments by limiting O2 supply to aerobic microbial respiration to the topmost sediment layer, resulting in a concomitant shift to less effective anaerobic degradation pathways. This suggests that temperature may represent a key controlling factor of the OC burial efficiency in lake sediments.

Influence of littoral periphyton on whole-lake metabolism relates to littoral vegetation in humic lakes.

The role of littoral habitats in lake metabolism has been underrated, especially in humic lakes, based on an assumption of low benthic primary production (PP) due to low light penetration into water. This assumption has been challenged by recent recognition of littoral epiphyton dominance of whole-lake PP in a small highly humic lake and of epiphyton as an important basal food source for humic lake biota. However, as these studies have mostly concerned single lakes, there is a need to test their wider generality. We studied the whole-lake PP and community respiration (CR) in eight small humic lakes in southern Finland during July 2015 using 14 C incorporation to measure pelagic PP and the changes in dissolved inorganic carbon in light and dark insitu incubations to measure CR and littoral PP by epiphyton. Changes in O2 concentration in both pelagic and littoral surface water were measured periodically from each lake and, additionally, continuously with a data logger from one lake during the study period. The results revealed that the littoral dominated whole-lake net primary production (NPP) in five of the eight lakes, which was supported by observed O2 supersaturation in the littoral surface water in most of the lakes. Calculated pelagic:littoral ratios by area correlated negatively with both littoral NPP and littoral contribution to whole-lake NPP. Moreover, there was a significant positive relationship between littoral proportion of whole-lake NPP and the fraction of lake surface area covered by littoral aquatic vegetation. This demonstrates that increased aquatic littoral vegetation cover increases the overall importance of the littoral to whole-lake PP in highly humic lakes. Littoral NPP also correlated strongly with littoral O2 saturation, and the continuously measured O2 revealed substantial temporal variation in O2 saturation, particularly in the littoral zone. Whole-lake gross primary production:community respiration (GPP:CR) ratios revealed that accounting for littoral metabolism produced a marked shift towards lake metabolic balance, although all the eight lakes remained net heterotrophic. This study emphasizes that littoral metabolism needs to be accounted for when estimating whole-lake C fluxes in all lakes, even in highly colored humic waters.

Direct and context‐dependent effects of light, temperature, and phytoplankton shape bacterial community composition

AbstractSpecies interactions, environmental conditions, and stochastic processes work in concert to bring about changes in community structure. However, the relative importance of specific factors and how their combined influence affects community composition remain largely unclear. We conducted a multi‐factorial experiment to (1) disentangle the direct and interaction‐mediated effects of environmental conditions and (2) augment our understanding of how environmental context modulates species interactions. We focus on a planktonic system where interactions with phytoplankton effect changes in the composition of bacterial communities. Further, light and temperature conditions can influence bacteria directly as well as through their interactions with phytoplankton. Epilimnetic bacteria from two humic lakes were combined with phytoplankton assemblages from each lake (home or away) or a no‐phytoplankton control and incubated for 5 d under all combinations of light (surface, ~25% surface irradiance) and temperature (five levels from 10° to 25°C). Observed light effects were primarily direct, while phytoplankton and temperature effects on bacterial community composition were highly interdependent. The influence of temperature on aquatic bacteria was consistently mediated by phytoplankton and most pronounced for bacteria incubated with “away” phytoplankton treatments, likely due to the availability of novel phytoplankton‐derived resources. The effects of phytoplankton on bacterial community composition were generally increased at higher temperatures. Incorporating mechanisms underlying the observed interdependent effects of species interactions and environmental conditions into modeling frameworks may improve our ability to forecast ecological responses to environmental change.

Patterns and drivers of deep chlorophyll maxima structure in 100 lakes: The relative importance of light and thermal stratification

AbstractThe vertical distribution of chlorophyll in stratified lakes and reservoirs frequently exhibits a maximum peak deep in the water column, referred to as the deep chlorophyll maximum (DCM). DCMs are ecologically important hot spots of primary production and nutrient cycling, and their location can determine vertical habitat gradients for primary consumers. Consequently, the drivers of DCM structure regulate many characteristics of aquatic food webs and biogeochemistry. Previous studies have identified light and thermal stratification as important drivers of summer DCM depth, but their relative importance across a broad range of lakes is not well resolved. We analyzed profiles of chlorophyll fluorescence, temperature, and light during summer stratification from 100 lakes in the Global Lake Ecological Observatory Network (GLEON) and quantified two characteristics of DCM structure: depth and thickness. While DCMs do form in oligotrophic lakes, we found that they can also form in eutrophic to dystrophic lakes. Using a random forest algorithm, we assessed the relative importance of variables associated with light attenuation vs. thermal stratification for predicting DCM structure in lakes that spanned broad gradients of morphometry and transparency. Our analyses revealed that light attenuation was a more important predictor of DCM depth than thermal stratification and that DCMs deepen with increasing lake clarity. DCM thickness was best predicted by lake size with larger lakes having thicker DCMs. Additionally, our analysis demonstrates that the relative importance of light and thermal stratification on DCM structure is not uniform across a diversity of lake types.

High rates and close diel coupling of primary production and ecosystem respiration in small, oligotrophic lakes

Studies on small, shallow lakes are few and have traditionally focused on humic lakes, whereas transparent, oligotrophic lakes dominated by submerged macrophytes have been overlooked. This may have given rise to a skewed perception of shallow lakes as being well mixed, turbid and dominated by ecosystem respiration relative to primary production. Mixing patterns and ecosystem metabolism in five oligotrophic shallow lakes dominated by charophytes were investigated in order to determine gross primary production, ecosystem respiration, their regulation and mutual coupling in this very common lake type. Although lakes were very shallow (<0.5 m), high charophyte biomass caused strong daytime stratification followed by nocturnal mixing. Despite the nutrient-poor water, volumetric rates of production and respiration during spring–summer were high compared to most medium to large lakes. This intensive metabolism is likely a result of the high charophyte biomass and the shallow mixed surface layer. Areal rates of production and respiration were also high compared to values from other aquatic systems. Strong coupling between daily rates of production and respiration suggested that the majority of organic substrates for ecosystem respiration were produced within the lakes. Net ecosystem production was slightly positive during the growth season. This study highlights the role of submerged macrophytes as primary drivers of temperature dynamics, stratification-mixing as well as high metabolism in small, shallow lakes with dense vegetation.

Epiphytic bacteria make an important contribution to heterotrophic bacterial production in a humic boreal lake

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 79:247-257 (2017) - DOI: https://doi.org/10.3354/ame01835 Epiphytic bacteria make an important contribution to heterotrophic bacterial production in a humic boreal lake Jussi Vesterinen1,*, Shawn P. Devlin1,2, Jari Syväranta1,3, Roger I. Jones1 1University of Jyväskylä, Department of Biological and Environmental Science, PO Box 35, 40014 University of Jyväskylä, Finland 2Flathead Lake Biological Station, University of Montana, Polson, MT 59860, USA 3University of Eastern Finland, Department of Environmental and Biological Sciences, PO Box 111, 80101 Joensuu, Finland *Corresponding author: jussi.p.vesterinen@jyu.fi ABSTRACT: Bacterial production (BP) in lakes has generally only been measured in the pelagic zone without accounting for littoral BP, and studies of BP at the whole-lake scale are very scarce. In the dystrophic humic lakes, which are common throughout the boreal region, low light penetration through water has been assumed to seriously limit available habitats for littoral organisms. However, many highly humic boreal lakes have extensive partly submerged vegetation around the lake perimeter which can provide well-lit substrata for highly productive epiphyton. We measured epiphytic BP on the littoral vegetation and pelagic BP in a small highly humic boreal lake in Finland during an open-water season and extrapolated the BP rates to the whole lake. Pelagic BP dominated the combined BP over the study period, but the epiphytic BP contributed an average of 24% to overall BP over the sampling period and was almost equal to pelagic BP in July. According to these results, a substantial component of BP has been previously overlooked in the lake when BP has been measured only from the pelagic. Our study demonstrates that the role of the littoral zone in BP in highly humic lakes has previously been understated, and needs to be taken into account in assessments of whole-lake carbon cycling and metabolism. KEY WORDS: Littoral · Periphyton · Pelagic · Autotrophic · Heterotrophic Full text in pdf format PreviousNextCite this article as: Vesterinen J, Devlin SP, Syväranta J, Jones RI (2017) Epiphytic bacteria make an important contribution to heterotrophic bacterial production in a humic boreal lake. Aquat Microb Ecol 79:247-257. https://doi.org/10.3354/ame01835 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 79, No. 3. Online publication date: July 05, 2017 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2017 Inter-Research.

Autochthonous and allochthonous organic matter in trophic chain of lake ecosystems

This work presents analysis of mass–balance model simulating biotic flows of energy in pelagial of the large lakes of Russia (Ladoga, Onego, and Baikal) and small lake in northern part of the Karelia. The model had been developed on the basis of software package Stella and intended to predict an annual production of phytoplankton, bacterio plankton and consumers (non predatory and predatory zooplankton, planktivorous and piscivorous fishes). The input (independent) abiotic parameters of the model were latitude, mean lake depth, total phosphorus content and water color. The model analyzed an involvement of the autochthonous and allochthonous organic matter in the total energy flow through trophic chain. It was underlined that bacteria are important component of the planktonic community linking the dissolved organic matter (DOM) with organisms of the trophic chain. In high humic and oligotrophic boreal lakes the plankton respiration exceeds the primary production, therefore allochthonous DOM transformed to bacterial production replaces photosynthetic production in consumer feeding. The efficiency of bacterial growth (the ratio of bacterial production to consumed energy) depends on the ratio between autochthonous and allochthonous DOM. It had been shown that efficiency of bacterial growth in lakes with high primary production was higher than in oligotrophic waters with dominated allochthonous DOM. The author discussed different–type organic matter contribution to hydrobiont production depending on total phosphorus and humic matter content. Bacterioplankton consuming allochthonous DOM is additional energy source for zooplankton. For prediction of the total biological productivity it was recommended to take into account also production of heterotrophic bacterioplankton which is involved in utilization of allochthonous DOM.

Using oxygen stable isotopes to quantify ecosystem metabolism in northern lakes

In remote regions of the world, whole lake metabolic estimates are scarce, largely because long incubations, intensive sampling and deployment of monitoring equipment are impractical. The oxygen isotope (δ18O) mass balance approach represents a simple and efficient alternative to measure whole-lake gross primary production (GPP) and respiration (R) from a single point sample, yet this option has not been extensively explored in habitats such as remote northern lakes. Here, we explored the applicability of the method using a sensitivity analysis on simulated data, showing that in large, heterotrophic (i.e., R > GPP) lakes, model outputs are sensitive to input terms for isotopic fractionation and air–water gas exchange. Despite these sensitivities, field applications of the δ18O method generated promising results that were generally consistent with parallel, free-water diel DO metabolic modelling, but greater than in vitro incubation measurements. The isotopic approach captured both wide-ranging metabolic conditions in in situ experimental mesocosms, and the seasonal trends in GPP and R in a shallow, dystrophic lake. In a clearer, deeper heterotrophic lake, the isotope approach integrated a fraction of metalimnetic metabolism missed by diel DO metabolic estimates. Overall, metalimnetic contributions to surface δ18O–DO dynamics had the greatest impact on model outputs, but with accurate information on air–water gas exchange, mixing depth, and the vertical DO and light regime of a given system, these effects can be accounted for and the isotopic approach can yield well constrained, spatio-temporally integrated rates of GPP and R. The approach is clearly suitable for use in oligo- and mesotrophic lakes, especially in remote regions where sampling is logistically difficult.