Small Forest Lakes Research Articles

Sedimentary phosphorus burial in three contrasting boreal lakes in Finland

AbstractPermanent phosphorus (P) burial in sediment regulates lake trophic state over long timescales, but the controls on P burial are only partially understood. A diversity of biogeochemical settings may be found in lake sediments, which may have a strong impact on the processes controlling P burial from one location to another. Here, we investigate early diagenesis of P in three contrasting lakes in Southwest Finland. Eutrophic Lake Köyliönjärvi and mesotrophic Lake Pyhäjärvi have a history of nutrient loadings from agriculture, while Lake Vähäjärvi is an oligotrophic small forest lake, leading to potentially contrasting sediment biogeochemical dynamics. We combined porewater data and solid-phase sediment geochemical data to identify P phases in each system and investigate the dominant processes controlling P burial. Porewater profiles showed opposite gradients between the oligotrophic and the mesotrophic/eutrophic systems, implying net diffusive fluxes into and out of the sediments, respectively. Furthermore, sediment P data showed contrasting P speciation. Reactive P is buried in all systems, but the role of reducible iron (Fe) oxides in P retention is greater in mesotrophic/eutrophic lakes. In the oligotrophic system, aluminium (Al) oxides controlled P sorption into the sediment after diffusion from lake water. Evidence for vivianite formation was found only in the mesotrophic Lake Pyhäjärvi sediment, where 42–47% of total P was released in a Fe(II)-P specific extraction from the deeper part of the sediment column and vivianite crystals could be isolated from sediment samples.

Две данных грамоты преподобному Евфросину Псковскому на земли под монастырь 1450-х – 1465 гг. (новые открытия)

The article reports on the discovery of new texts of Pskov charateic charters of the XV – beginning of the XVI century, originating from the patrimonial archive of the Three-Holy Eleazar Monastery. They were preserved in the form of lists around 1732. The discovery was made by the author during the work on the identification and scientific description of the available composition of documents of the XVI–XVIII centuries. in the collection of the Ancient Repository of the Pskov Museum. The study showed that the Copy Notebook found as part of the book binding includes lists with 21 letters. Among them are complete documents and their fragments. This publication presents the experience of studying two acts from the Copy Book of the Three-Holy Monastery. These are certificates No. 6 and No. 11 in order in the collection. They are remarkable in that they are directly related to the history of the monastery's creation, since in the middle of the XV century they were given to the Most Reverend Euphrosyne on the land for the monastery he had built. The plots of land were located in the Krivovitsky rural district of the Belsky ambush of Pskov County between the Tolva River and a small forest lake. Transferred from the previous owners "to oderen", that is, to full unconditional ownership, they created the core of the patrimony and remained with the current monastery, despite the later secularization of 1764. The same lands are part of the modern borders of the restored monastery. Temples, monastic cells, a cemetery, a refectory, a cow village, a hotel and all other buildings necessary for a statutory life are located on them. The new letters of the era of the Veche Pskov are a valuable source for the study of the ancient Pskov script, the ancient topography of the Pskov land, church history and monastic land ownership.

Three Decades of Changing Nutrient Stoichiometry from Source to Sea on the Swedish West Coast

European ecosystems have been subject to extensive shifts in anthropogenic disturbance, primarily through atmospheric deposition, climate change, and land management. These changes have altered the macronutrient composition of aquatic systems, with widespread increases in organic carbon (C), and declines in nitrogen (N) and phosphorus (P). Less well known is how these disturbances have affected nutrient stoichiometry, which may be a more useful metric to evaluate the health of aquatic ecosystems than individual nutrient concentrations. The Swedish west coast has historically experienced moderate to high levels of atmospheric deposition of sulfate and N, and eutrophication. In addition, coastal waters have been darkening with damaging effects on marine flora and fauna. Here, we present three decades of macronutrient data from twenty lakes and watercourses along the Swedish west coast, extending from headwaters to river mouths, across a range of land covers, and with catchments ranging 0.037–40,000 km2. We find a high degree of consistency between these diverse sites, with widespread increasing trends in organic C, and declines in inorganic N and total P. These trends in individual macronutrients translate into large stoichiometric changes, with a doubling in C:P, and increases in C:N and N:P by 50% and 30%, showing that freshwaters are moving further away from the Redfield Ratio, and becoming even more C rich, and depleted in N and P. Although recovery from atmospheric deposition is linked to some of these changes, land cover also appears to have an effect; lakes buffer against C increases, and decreases in inorganic N have been greatest under arable land cover. Our analysis also detects coherently declining P concentrations in small forest lakes; so called (and unexplained) “oligotrophication.” Taken together, our findings show that freshwater macronutrient concentrations and stoichiometry have undergone substantial shifts during the last three decades, and these shifts can potentially explain some of the detrimental changes that adjacent coastal ecosystems are undergoing. Our findings are relevant for all European and North American waters that have experienced historically high levels of atmospheric deposition, and provide a starting point for understanding and mitigating against the trajectories of long-term change in aquatic systems.

Boulder cenotaphs of Eastern Fennoscandia: the question of one kind of the orthodox funeral rite in the late middle ages

The paper is devoted to the little-studied funeral practice of the Orthodox communities of the White Sea region and Russian Lapland in the absence of a body. The research was based on the results of the authors work in the last two decades. On the island of Kildin in the Barents Sea, on Lake Sredne Kuito in North Karelia and on a small forest lake near the town of Kovdor three original, similar monuments groups of stone structures of unknown purpose have been recorded. The originality and controversiality of these objects requires their systematic study, introduction into scientific circulation and interpretation. Archaeologists, as a rule, carry out only a primary fixation of objects, but excavations do not always allow to determine clearly the purpose of stone piles. Based on the experience of working with such facilities in Karelia and on the Kola Peninsula, it can be argued that they were not intended for economic purposes. A number of common features make it possible to attribute these structures to a group of monuments associated with the Orthodox funeral tradition. This is the orientation of the stone constructions west east, the general location beyond the water, on the periphery of cemeteries, visual similarity with grave mounds of earth or wooden houses of the dead. Presumably they were ground cenotaphs for the drowned a house for the soul in the absence of a body. The spread of the tradition of their creation can be limited to the area of culture of the Russians and Karelians of the Pomerania of the European North. They are tentatively dated to the period of the Late Middle Ages Modern Times and are considered as part of the Orthodox culture of the population of Eastern Fennoscandia. Understanding the idea of these objects is impossible without information on the ethnography of Slavic and Finno-Ugric ethnic groups about the division of the dead into those who died a natural or unnatural death.

Quantitative landscape reconstruction and erosion history during the past 1,100\xa0years in the Skogaryd Research Catchment, southern Sweden

A sediment sequence from a small forest lake in southwestern Sweden was investigated to explore the effects of forestry and land-use on catchment erosion and delivery of organic and minerogenic matter to the lake. Catchment-scale vegetation changes during the last 1,100 years were reconstructed quantitatively at 50-year resolution using pollen analysis and the Landscape reconstruction algorithm (LRA). Variations in terrestrial organic matter input to lake sediments were assessed by total organic carbon (TOC) content and carbon to nitrogen (C/N) ratios. Changes in minerogenic matter were analysed using X-ray fluorescence (XRF) scanning. The results show that Skogaryd was not intensively used for agriculture throughout the past 1,100 years, but its land-use changes were very sensitive to societal changes. Between ca. ad 950 and 1350, local land-use was characterized by small-scale agricultural activities associated with the Medieval expansion, and enhanced soil erosion was recorded by increased K, Ti and Rb deposition. Around ad 1350 much of the farmland was abandoned, most likely in response to outbreaks of plague. The abandonment of farmland caused increased coniferous woodland cover and lower soil erosion. From the 16th century land-use expanded and gradually intensified, concurrent with a population increase documented in the study area between ca. ad 1600 and 1850. Intensive exploitation of the forest led to soil erosion and increased terrestrial organic and minerogenic matter export to the lake. These processes peaked with the artificial drainage of a nearby wetland for agricultural purposes. During the 20th century, modern forestry management started with the plantation of conifers, and soil erosion declined.

Changes in the functional features of macrophyte communities and driving factors across a 70-year period

Functional homogenisation occurs across many areas and organism groups, thereby seriously affecting biodiversity loss and ecosystem functioning. In this study, we examined how functional features of aquatic macrophytes have changed during a 70-year period at community and species levels in a boreal lake district. At the community level, we examined if aquatic macrophyte communities showed different spatial patterns in functional composition and functional richness in relation to main environmental drivers between the time periods. We also observed each species in functional space to assess if species with certain sets of traits have become more common or rare in the 70-year study period. We found changes in the relationship between functional community composition and the environment. The aquatic macrophyte communities showed different patterns in functional composition between the two time periods, and the main environmental drivers for these changes were partly different. Temporal changes in functional richness were only partially linked to concomitant changes in the environment, while stable factors were more important. Species’ functional traits were not associated with commonness or rarity patterns. Our findings revealed that functional homogenisation has not occurred across these boreal lakes, ranging from small oligotrophic forest lakes to larger lakes affected by human impacts.

Carbon dioxide efflux and ecosystem metabolism of small forest lakes

Small lakes are numerous in the landscape and closely connected to the terrestrial environment, which strongly influences the system scale carbon cycling. However, despite their importance in large-scale carbon budgets, small lakes remain understudied compared to large lakes. We investigated oxygen and carbon dynamics in four small Danish forest lakes over a year. Continuous pH measurements were used to establish a high-frequency time series of CO2 partial pressure and 1169 direct measurements of air–water CO2 flux were performed using floating chambers. Net ecosystem oxygen production (NEP) was derived from free-water oxygen measurements in order to quantify the contribution of in-lake aerobic metabolism to the air–water CO2 flux. We found that the forest lakes, on average, were tenfold CO2 supersaturated. The two most intensively studied lakes had mean CO2 effluxes of 36.3 mol m−2 year−1. The CO2 effluxes exceeded NEP during all months implying that the CO2 generated by aerobic respiration alone could not account for the observed CO2 efflux. The observed discrepancy is likely promoted by a hydrologic CO2 input and/or anaerobic sediment processes generating CO2 without a concurrent consumption of O2. A broad-scale national analysis showed that the CO2 efflux increased as lake size decreased despite lower gas exchange velocity. Small lakes also showed higher excess CO2 efflux compared to O2 influx. Overall, small lakes and forest lakes in particular have high CO2 effluxes and high CO2 supersaturation. However, the contribution of hydrological inputs and anaerobic sediment processes to the net CO2 efflux remains elusive.

Taxonomic Structure and Ecology of Phytoplankton in Small Forest Lakes in the Zone of Technogenesis of Sulphide Deposits (Southern Urals)

Long-term data (2009–2017) on the taxonomic structure of phytoplankton in small forest lakes of the Southern Ural region in the territory of the sulfide copper–zinc deposits and in the zone of impact of a copper smelting plant have been systematized. Patterns of changes in the species richness of phytoplankton towards a considerable decrease in the taxonomic diversity of phytoplankton have been determined in the gradient of increasing acidity, concentrations of heavy metals, and sulfate ion content. The species richness of golden algae increases in oligoacidic conditions of forest lakes in the buffer zones of technogenesis. The relationships between the structural parameters of phytoplankton and abiotic factors are analyzed.

Technical note: A simple and cost-efficient automated floating chamber for continuous measurements of carbon dioxide gas flux on lakes

Abstract. Freshwaters emit significant amounts of CO2 on a global scale. However, emissions remain poorly constrained from the diverse range of aquatic systems. The drivers and regulators of CO2 gas flux from standing waters require further investigation to improve knowledge on both global-scale estimates and system-scale carbon balances. Often, lake–atmosphere gas fluxes are estimated from empirical models of gas transfer velocity and air–water concentration gradient. Direct quantification of the gas flux circumvents the uncertainty associated with the use of empirical models from contrasting systems. Existing methods to measure CO2 gas flux are often expensive (e.g. eddy covariance) or require a high workload in order to overcome the limitations of single point measurements using floating chambers. We added a small air pump, a timer and an exterior tube to ventilate the floating chamber headspace and passively regulate excess air pressure. By automating evacuation of the chamber headspace, continuous measurements of lake CO2 gas flux can be obtained with minimal effort. We present the chamber modifications and an example of operation from a small forest lake. The modified floating chamber performed well in the field and enabled continuous measurements of CO2 gas flux with 40 min intervals. Combining the direct measurements of gas flux with measurements of air and waterside CO2 partial pressure also enabled calculation of gas exchange velocity. Building and using the floating chamber is straightforward. However, because an air pump is used to restart measurements by thinning the chamber headspace with atmospheric air, the duration of the air pump pause–pulse cycle is critical and should be adjusted depending on system characteristics. This may result in shorter deployment duration, but this restriction can be circumvented by providing a stronger power source. The simple design makes modifications of the chamber dimensions and technical additions for particular applications and systems easy. This should make this approach to measuring gas flux flexible and appropriate in a wide range of different systems.

Пищевые взаимоотношения обыкновенного сига (COREGONUS LAVARETUS) и речного окуня (PERCA FLUVIATILIS) в малом лесном озере

Пищевые взаимоотношения обыкновенного сига (COREGONUS LAVARETUS) и речного окуня (PERCA FLUVIATILIS) в малом лесном озере

Contribution of different bacterial dispersal sources to lakes: Population and community effects in different seasons.

The diversity and composition of lake bacterial communities are driven by the interplay between local contemporary environmental conditions and dispersal of cells from the surroundings, i.e. the metacommunity. Still, a conceptual understanding of the relative importance of the two types of factors is lacking. For instance, it is unknown which sources of dispersal are most important and under which circumstances. Here, we investigated the seasonal variation in the importance of dispersal from different sources (mixing, precipitation, surface runoff and sediment resuspension) for lake bacterioplankton community and population dynamics. For that purpose, two small forest lakes and their dispersal sources were sampled over a period of 10 months. The influence of dispersal on communities and populations was determined by 454 sequencing of the 16S rRNA gene and SourceTracker analysis. On the community level direct effects of dispersal were questionable from all sources. Instead we found that the community of the preceding sampling occasion, representing growth of resident bacteria, was of great importance. On the population level, however, dispersal of individual taxa from the inlet could be occasionally important even under low water flow. The effect of sediment resuspension and precipitation appeared small.

Spatial variability of organic matter molecular composition and elemental geochemistry in surface sediments of a small boreal Swedish lake

Abstract. The composition of sediment organic matter (OM) exerts a strong control on biogeochemical processes in lakes, such as those involved in the fate of carbon, nutrients and trace metals. While between-lake spatial variability of OM quality is increasingly investigated, we explored in this study how the molecular composition of sediment OM varies spatially within a single lake and related this variability to physical parameters and elemental geochemistry. Surface sediment samples (0–10 cm) from 42 locations in Härsvatten – a small boreal forest lake with a complex basin morphometry – were analyzed for OM molecular composition using pyrolysis gas chromatography mass spectrometry for the contents of 23 major and trace elements and biogenic silica. We identified 162 organic compounds belonging to different biochemical classes of OM (e.g., carbohydrates, lignin and lipids). Close relationships were found between the spatial patterns of sediment OM molecular composition and elemental geochemistry. Differences in the source types of OM (i.e., terrestrial, aquatic plant and algal) were linked to the individual basin morphometries and chemical status of the lake. The variability in OM molecular composition was further driven by the degradation status of these different source pools, which appeared to be related to sedimentary physicochemical parameters (e.g., redox conditions) and to the molecular structure of the organic compounds. Given the high spatial variation in OM molecular composition within Härsvatten and its close relationship with elemental geochemistry, the potential for large spatial variability across lakes should be considered when studying biogeochemical processes involved in the cycling of carbon, nutrients and trace elements or when assessing lake budgets.

Land Use Affects Carbon Sources to the Pelagic Food Web in a Small Boreal Lake.

Small humic forest lakes often have high contributions of methane-derived carbon in their food webs but little is known about the temporal stability of this carbon pathway and how it responds to environmental changes on longer time scales. We reconstructed past variations in the contribution of methanogenic carbon in the pelagic food web of a small boreal lake in Finland by analyzing the stable carbon isotopic composition (δ13C values) of chitinous fossils of planktivorous invertebrates in sediments from the lake. The δ13C values of zooplankton remains show several marked shifts (approx. 10 ‰), consistent with changes in the proportional contribution of carbon from methane-oxidizing bacteria in zooplankton diets. The results indicate that the lake only recently (1950s) obtained its present state with a high contribution of methanogenic carbon to the pelagic food web. A comparison with historical and palaeobotanical evidence indicates that this most recent shift coincided with agricultural land-use changes and forestation of the lake catchment and implies that earlier shifts may also have been related to changes in forest and land use. Our study demonstrates the sensitivity of the carbon cycle in small forest lakes to external forcing and that the effects of past changes in local land use on lacustrine carbon cycling have to be taken into account when defining environmental and ecological reference conditions in boreal headwater lakes.

Formation of macroinvertebrates communities in duckweed (Lemnaceae) and artificial surface-floating substrate: Results of the experiment under natural conditions

Macroinvertebrate communities which were formed in isolates with free-floating duckweed plants of the species Spirodella polyrhiza (L.) Schleid, Lemna minor L., Wolffia arrhiza (L.) Horkel ex Wimm, mixtures of these species, and an isolate with crushed styrofoam were studied in comparison to the control aggregation of floating plants in a small forest lake located in the Usman pine forest (Voronezh oblast, Russia) during the vegetation season of 2011. The seasonal dynamics of the biomass of Lemnaceae in isolates differed significantly from the control aggregation. The isolation negatively affected the growth of Lemnaceae, but had a positive effect on the development of the macroinvertebrate communities. Statistically significant differences in the abundance, biomass, and the number of species in phytophilic communities were not found between experimental isolates and in comparison to the control. Differences in the species composition of macroinvertebrate communities of surface-floating substrates were determined to a greater degree by characteristics of a waterbody than of the substrate.

Large-eddy simulation of stratified turbulent flows over heterogeneous landscapes

Large-eddy simulation (LES) runs are performed to calculate flows over heterogeneous surfaces imitating small forest lakes. Regularities in the turbulent exchange of heat and momentum over such objects are examined. A weak sensitivity of turbulence characteristics over a “lake” to thermal stratification is noted. Problems of the representativeness of field eddy covariance measurements of turbulent fluxes over such objects are discussed.

An evaluation of gillnet CPUE as an index of perch density in small forest lakes

Gillnets are commonly used for monitoring fish communities and assessing the ecological quality in European lakes. However, the relationship between gillnet CPUE and fish abundance is not linear and depends on several factors affecting the catchability of gillnets. We investigated the effects of high water colour, naturally anoxic hypolimnion, water temperature and sex ratio on the catchability of perch Perca fluviatilis in gillnets. Data were collected during 10 years in nine forest lakes in southern Finland. Such lakes are very common in Finland. The density and size structure of perch populations were estimated by mark and recapture method during spring and standard gillnet fishing (CEN, 2005. Water quality Sampling of Fish with Multimesh Gillnets. European Committee for Standardization, Brussels (EN 14757)) in late summer. Perch CPUE was positively but non-linearly dependent on the perch density. Catchability increased with water colour, water temperature, and the volume of the anoxic hypolimnion. The sex ratio was also important because late summer gillnetting overestimates the proportion of female perch. If the factors that affect the catchability of perch in gillnets are taken into account, gillnet CPUE using standard methods can be used as rough index of fish density in small forest lakes.

Phototrophic microflora of dystrophic Lake Sęczek, Masuria, Poland

Abstract Microflora of cyanobacteria and algae of small forest dystrophic Lake Sęczek located in the Masurian Lake District, NE Poland, was investigated in 2012 and 2013. A total of 16 genera with 7 species of cyanobacteria and 56 genera with 74 species, 6 varietas and forms of algae were determined. Most of them represented commonly occurring microorganisms of slightly acidic waters, but some of them are considered rare, i.e. the oscillatorian cyanobacterium Katagnymene accurata Geitler (for the first time found in Poland), and green algae Coenochloris sphagnicola Hindák, Mucidosphaerium sphagnale (Hindák) C. Bock, Pröschold et Krienitz, Closterium navicula (Bréb.) Lütkem., and Cosmarium cf. aphaerosporum var. corribense (W. et G.S. West) Krieger et Gerloff., which are described in more detail. As regards the species diversity, the plankton of the lake was rather species-poor in contrast to the algal communities in the Sphagnum littoral.

Hydromycoflora fungi of small forest lakes "Suchary" in the Wigry National Park

One hundred and fifteen species of fungi were found in the small forest lakes "Suchary" in the Wigry National Park. The following fungi were recorded for the first time from Poland: <i>Blastociadella simplex, Rhizoclosmatium globosum, R. hyalinum, Rhopalophlyctis sarcoptoides, Condylospora spumigena, Gyoerffyella myrmecophagiforms, Helicon pluriseptatum</i> and <i>Kontospora halophila</i>.

Importance of maternal size on the reproductive success of perch,Perca fluviatilis, in small forest lakes: implications for fisheries management

Abstract Abundance, sex ratio and size structure of perch,Perca fluviatilisL., populations were studied in two forest lakes. The influence of maternal size on the amount and quality of eggs and larvae was investigated, and the effect of the spawning stock’s length structure on population egg and fry production was evaluated. The importance of large females was essential for the reproduction of perch. Large perch spawned more and bigger eggs that had higher hatching percentage resulting in considerably higher fry production. Larvae of large females were heavier and survived longer with bare yolk sac reserves. The relation between egg dry weight and female length differed between the study lakes suggesting varying maternal influence in different environments. Decrease in the share of large individuals in a perch population can substantially reduce the amount and quality of larvae produced. The results can be applied to improve the sustainability of perch fisheries.

Short- and long-term patterns of 137Cs in fish and other aquatic organisms of small forest lakes in southern Finland since the Chernobyl accident

We summarize the patterns of 137Cs activity concentrations and transfer into fish and other biota in four small forest lakes in southern Finland during a twenty-year period following the Chernobyl accident in April 1986. The results from summer 1986 showed fastest accumulation of 137Cs into planktivorous fishes, i.e. along the shortest food chains. Since 1987, the highest annual mean values of 137Cs have been recorded in fish occupying the highest trophic levels, for perch ( Perca fluviatilis) 13,600 Bq/kg (ww) and for pike ( Esox lucius) 20,700 Bq/kg (ww). At the same time, activity concentrations of 137Cs in crustacean zooplankton and Asellus aquaticus have ranged between 1000 and 19,500 Bq/kg (dw). In 2006, 5–28% of the 1987 137Cs activity concentration levels were still present in perch and pike. Since 1989 their 137Cs activity concentrations in oligohumic seepage lakes have remained significantly higher than in polyhumic drainage lakes due to the increased transfer of 137Cs into fish in the seepage lakes with lower electrolyte concentrations, longer water retention times and lower sedimentation rate.