Polyhumic Lake Research Articles

Nowe stanowisko Botrychium lunaria (Ophioglossaceae) w Krakowie na tle danych historycznych

A detailed study of vascular plants in the Tobolinka Nature Reserve (Augustów Forest, NE Poland) was carried out in July 2016 and February 2020. The reserve covers a very small area, and the diversity of its plant communities is very low due to the high acidity of its habitats (extremely poor fen surrounding a small polyhumic lake; wet and mesic pine forest). Only 48 species were recorded, including five species red-listed nationally (e.g. Goodyera repens, Scheuchzeria palustris).

Complex Analysis of the Plankton Community of two Brown-Water Bog Lakes in the European Part of Russia

The composition and vertical distribution of plankton of two polyhumic bog lakes on the territory of the Volga-Kama State Natural Biosphere Reserve were studied. It was found that the anaerobic conditions were formed in the water column at a depth deeper than 2 m due to stratification and lack of light. Phyto- and zooplankton (including ciliates) prevailed in the upper aerobic layers of water, heterotrophic bacteria and green sulfur bacteria (Chlorobiaceae) – in the anaerobic zone. Rotifers dominated the metazooplankton in the whole water column (>95% of the biomass); prevailing genera were Asplanchna, Polyarthra, and Bipalpus. Heterotrophic organisms formed 70 ± 10% of the plankton biomass in both lakes. A high proportion of ciliates (on average 3%, maximum up to 18%) and heterotrophic bacteria (on average 49 ± 25%) was also revealed. The invasive species algae Gonyostomum semen (Raphidophyta) was first registered in the lakes of the Republic of Tatarstan. It formed 28-80% of the phytoplankton biomass in the studied lakes. It was found that at least one of the ciliate species (Frontonia cf. leucas) is able to feed on G. semen cells in situ.

Phosphorus thresholds for bloom-forming cyanobacterial taxa in boreal lakes

Cyanobacteria may limit recreational use of waters and have negative impacts on ecosystem services. The aim of this study was to determine phosphorus (P) thresholds for cyanobacterial taxa, which form toxin-producing blooms (mass occurrences) in boreal lakes. These thresholds help to set robust P reduction targets for restoration measures. We used long-term (> 40 years) June–August data from > 2000 Finnish lakes to evaluate the total P (TP) thresholds for the most important bloom-forming cyanobacterial genera and selected Microcystis and Dolichospermum species. The analyses were carried out separately for oligohumic, mesohumic and polyhumic lakes. TP threshold values varied between 10 and 61 µg l−1. The values were lower in oligohumic (water colour < 30 mg Pt l−1) than mesohumic (water colour 30–90 mg Pt l−1) lakes. The highest TP threshold (50 µg l−1) was observed for Microcystis in polyhumic lakes, and the lowest (10 µg l−1) for Planktothrix in oligohumic lakes.

Eutrophication and browning influence Daphnia nutritional ecology

ABSTRACTClimate change and land-use practices can enhance lake eutrophication and browning, which influence phytoplankton composition by decreasing the availability of food high in nutritional quality (algae) and increasing the abundance of low-quality food (terrestrial detritus, bacteria) for herbivorous zooplankton. Nutritionally valuable algae for zooplankton are rich in essential biomolecules such as amino acids, polyunsaturated fatty acids (PUFAs), sterols, and phosphorus. We performed laboratory experiments and showed a stronger positive relationship between zooplankton (Daphnia) cumulative offspring number and availability of high-quality algae (Cryptophytes: Rhodomonas/Cryptomonas; and Chrysophytes: Mallomonas) than with intermediate-quality (Chlorophytes: Acutodesmus) or poor-quality (Dinoflagellates: Peridinium) algae. The higher cumulative offspring number of Daphnia was a result of higher amounts of total ω-3 and ω-6 PUFA, proteins, sterols, and amino acids in the algal diets. The experiments also showed that even a small addition of high-quality algae (Rhodomonas) to intermediate-quality (Acutodesmus) or low-quality (bacteria, heterotrophic nanoflagellates, or terrestrial organic matter) diets can enhance the Daphnia cumulative offspring production. Our carbon mass balance calculation for a eutrophic clearwater lake and an oligotrophic polyhumic lake showed that the abundance of high-quality phytoplankton (cryptophytes, chrysophytes, diatoms) among total particulate organic carbon was minor (8.7% [SD 2.4%] and 6.5% [7.0%]). We modeled Daphnia diets (i.e., resource assimilation) using a fatty acid mixing model. Our analyses showed that Daphnia were able to locate high-quality algae (cryptophytes, chrysophytes, and diatoms) more effectively during cyanobacteria blooms in a eutrophic lake (55% [SD 12%]) than in a polyhumic lake (25% [10%]). Nevertheless, our results show that intense eutrophication and browning diminish assimilation of high quality algae, limiting Daphnia biomass production.

Recent changes in chironomid communities and hypolimnetic oxygen conditions relate to organic carbon in subarctic ecotonal lakes

A key question in aquatic elemental cycling is related to the influence of bottom water oxygen conditions in regulating the burial and release of carbon under climate warming. In this study, we used head capsules of Chironomidae larvae to assess community and diversity change between the past (estimated as Pre-Industrial Period) and present and to reconstruct changes in hypolimnetic oxygen conditions from 30 subarctic ecotonal lakes (northeastern Lapland) using the top-bottom paleolimnological approach applying surface sediment (topmost 0–2 cm) and reference (4–5 cm) samples. Subsequently, we tested the findings against dissolved organic carbon (DOC) concentration of the sites. We found that the benthic communities were statistically dissimilar between the past and the present with largest changes occurring in the more transparent oligo-mesohumic lakes. However, murky polyhumic lakes displayed uniformly a decrease in diversity. The chironomid-inferred oxygen values showed a general decrease toward the present with largest shifts in low-DOC lakes, whereas no significant changes were found in the hypolimnetic oxygen conditions of high-DOC lakes, which were often located in wetland areas. These finding suggest that lakes associated with constant organic carbon inputs are more resilient toward climate-induced reductions in hypolimnetic oxygen.

Late Holocene changes in the humic state of a boreal lake and their associations with organic matter transport and climate dynamics

An important factor in the ontogeny of boreal lakes is the development of their humic state through terrigenous input of organic matter (carbon) that affects strongly the functioning and structure of these ecosystems. The long-term dynamics and role of humic substances for these systems in relation to climate are not clear. In this study, a boreal lake from southern Finland was investigated using paleolimnological methods, including diatom, chironomid and geochemical analyses, for Late Holocene changes in the humic state. The aim was to examine the relationship between sediment biogeochemistry and climate variation. Consistent trends were found in diatom-inferred total lake-water organic carbon (TOC) and in the ratio of humic/oligohumic chironomids. Sediment geochemistry provided further evidence for the limnological development of the lake and related long-term climate trends in the region. The results indicated three distinct phases with differing humic state; the beginning of the record at ca. 4,500 cal year BP was characterized by extremely humic conditions coinciding with warm and dry climatic conditions, a meso-oligohumic period between ca. 3,000–500 cal year BP with increasing allochthonous organic matter transport and cooler and wetter climate, and recent period with polyhumic (TOC >10 mg L−1) lake status and warming climate. This study shows that instead of straightforward linear development, boreal lakes evolve through dynamic humic stages related to climate and lake-catchment coupling processes. As the changes in the humic state are ultimately climate-driven, the ongoing climate change probably has a major influence on boreal lakes through direct and indirect effects on organic carbon transport, utilization and accumulation.

Distribution of fullerenes (nC60) between sediment and water in freshwaters

Depending on environmental conditions, fullerenes (nC60) have the potential to settle to the bottom sediments. In this study the distribution of nC60 was investigated in the labile zone between sediment and water. Three freshwater–sediment systems representing oligohumic, mesohumic, and polyhumic lakes with varying sediment composition and structure were used to investigate the target of fullerenes. The largest portion of water suspended fullerenes was found in the sediment, but a part re-suspended relatively quickly to water-stabile particles associated with natural particles. Rapid initial re-suspending was followed by a slower one offering a continuous pathway to the water phase. Re-suspending was highest from the sediment with a high amount of amorphous matter, small particles and a highly aliphatic character, amounting to 9±1% of the initial amount of fullerenes, whereas it was 4±1% in aromatic sediments with larger particles and less amorphous matter. These results indicate that bottom sediments can retain fullerenes but a portion may remain mobile depending on sediment character. Re-suspended fullerenes may again be available to aquatic species—this knowledge should thus be taken into account in the environmental risk assessment of fullerenes.

Erratum to: Development of bog-like vegetation during terrestrialization of polyhumic lakes in north-eastern Poland is not accompanied by ecosystem ombrotrophication

The aim of the present study was to use the analysis of surface water chemistry to understand vegetation succession pathways in terrestrializing polyhumic lakes. We hypothesized that Sphagnum mire development was accompanied by a decrease in the mineral content in water. A total of 111 vegetation plots along 23 transects were analysed in 11 lakes and adjacent peat lands in the Wigry National Park (NE Poland). The vegetation of the lake-mire systems forms distinct zones: (1) nymphaeid-, bladderwort- and bryophyte-dominated aquatic vegetation; (2) sedge-dominated edge of the Sphagnumcarpet; (3) quaking, extremely poor fen with various Cyperaceae; (4) non-quaking, Eriophorum vaginatum-dominated bog-like vegetation and (5) pine woodland. Surface water corrected conductivity (ECcorr.), pH, COD-KMnO4 and Ca2+, Mg2+, Fetot. and SiO2 were measured along the transects. The environmental gradients best explaining the observed pattern were pH (with the highest values in the lake and the lowest in the bog-like vegetation) and COD-KMnO4 (showing an inverse direction). At least in some Sphagnum-mires conditions were more minerotrophic than in the lakes. The process of humic lake overgrowing by Sphagnum-mires in NE Poland results in pine woodlands on mineralised peat. The climate conditions in NE Poland, combined with evapotranspiration accelerated by encroaching trees, do not seem to support the development of ombrotrophic bogs.

Development of bog-like vegetation during terrestrialization of polyhumic lakes in north-eastern Poland is not accompanied by ecosystem ombrotrophication

Development of bog-like vegetation during terrestrialization of polyhumic lakes in north-eastern Poland is not accompanied by ecosystem ombrotrophication

Methane-oxidizing and photoautotrophic bacteria are major producers in a humic lake with a large anoxic hypolimnion

Heterotrophic processes are considered to prevail in lakes with high terrestrial loading and a high content of dissolved organic carbon. However, previous studies have shown abundant methanotrophic bacteria (MOB) and photoautotrophic green sulphur bacteria (GSB) in some boreal lakes. We used genetic and lipid biomarkers to follow the seasonal succession of the abundance and carbon biomass of the major bacterial groups in Lake Mekkojarvi, a small Finnish polyhumic lake with a large anoxic hypolimnion. Biomarkers were based on length heterogeneity analysis of 16S rRNA gene amplification by polymerase chain reaction (PCR) (LH-PCR) and on phospholipid fatty acid (PLFA) analysis. Representative strains closely affiliated to the dominant bacterial groups in the lake were cultured and their characteristic PLFA biomarkers were selected. According to these bio- markers, the relative abundance and biomass of the anaerobic photo autotrophic bacteria (e.g. GSB) were extremely high in the pelagial during summer stratification (on average 47% of the bacterial rRNA genes and 77% of the total particulate organic carbon). Type I MOB were especially abundant during autumn mixing, forming on average 32% — but occasionally up to 73% — of the carbon bio- mass. Heterotrophic bacteria affiliated to Actinobacteria and Poly nucleobacter spp. together con- tributed 1 to 8% of the seasonal carbon biomass in the lake, although their genetic biomarkers were much more common. The results indicate that a significant proportion of the bacterial biomass was formed through methanotrophic and photoautotrophic production, both being comparable with the summer primary production rates of phytoplankton. These findings challenge the current model of the heterotrophic microbial pathway as the principal basis for microbial mobilisation of carbon and energy in freshwater food webs in oxygen-stratified lakes.

The disintegration of populations of underwater plants in soft water lakes enriched with acidic organic matter

The characteristics of habitats, individuals and populations of four submerged macrophytes, &lt;em&gt;Lobelia dortmanna &lt;/em&gt;L., &lt;em&gt;Isoetes lacustris &lt;/em&gt;L., &lt;em&gt;Sphagnum denticulatum &lt;/em&gt;Brid. and &lt;em&gt;Fontinalis antipyretica &lt;/em&gt;Hedw., were studied in 12 soft water oligohumic lakes which had no inflow of allochtonic DOM and the DOC concentration in the water was &amp;lt;4.0 mg C dm&lt;sup&gt;-3&lt;/sup&gt; and 13 humic lakes enriched with allochthonous dissolved organic matter (DOM) from drained peat bogs and ranging in DOC water concentration from 4.1 to 44.0 mg C dm&lt;sup&gt;-3&lt;/sup&gt;. The analyses of population disintegration were conducted basing on characteristics of individuals (size, habitat, fertility) and populations (aggregation density index, settlement index of the population area). The settlement index of the population area for &lt;em&gt;Lobelia&lt;/em&gt;, &lt;em&gt;Fontinalis&lt;/em&gt;, &lt;em&gt;Isoetes&lt;/em&gt;, &lt;em&gt;Sphagnum&lt;/em&gt; decreased from 8.4 to 6.2 g d.w. m&lt;sup&gt;-2&lt;/sup&gt;, 4.6 to 0.01 g d.w. m&lt;sup&gt;-2&lt;/sup&gt;, 85.4 to &amp;lt;0.001 g d.w. m&lt;sup&gt;-2&lt;/sup&gt; and 39.3 to 7.2 g d.w. m&lt;sup&gt;-2&lt;/sup&gt;, respectively. Similar trends were observed in aggregation density. The general pattern of the disintegration of populations of these species was always similar. It was independent of the source macrophytes drew resources from or their susceptibility to environmental changes. Individuals began to be eliminated from the deep and central parts of the population area. The remainder of the populations, which persist in the shallowest, best-illuminated part of the area, are themselves endangered by disturbances caused by wavy motion. The only populations of submerged macrophytes which can survive in polyhumic lakes under such conditions are those which are resistant to disturbances common in the shallow littoral (&lt;em&gt;Lobelia dortmanna&lt;/em&gt;, &lt;em&gt;Fontinalis antipyretica&lt;/em&gt;).

Diel dynamics of vertical changes of chlorophyll and bacteriochlorophyll in small humic lakes

Abstract The diel variability of algal and bacterial chlorophyll and the physicochemical parameters (temperature, pH, dissolved oxygen, conductivity, transparency) in the vertical profile of three mid-forest humic lakes in Drawa National Park (northwest Poland) were analyzed in summer. The euphotic zone consisted of the smaller part of the water column in poly- and mesohumic lakes but almost the whole water column of the oligohumic lake. The 24-hour dynamics of chlorophyll a and bacteriochlorophyll d+e in poly- and mesohumic lake was significantly smaller than that in the polyhumic lake. The maximum concentrations of chlorophyll a and bacteriochlorophyll d+e were observed near the bottom border or below the euphotic zone in waters with oxygen deficits and containing sulfur hydrogen. The main producers of chlorophyll in meso- and oligohumic lake were green anaerobic sulphuric bacteria.

Climate induced thermocline change has an effect on the methyl mercury cycle in small boreal lakes

We conducted a whole-lake experiment by manipulating the stratification pattern (thermocline depth) of a small polyhumic, boreal lake (Halsjärvi) in southern Finland and studying the impacts on lake mercury chemistry. The experimental lake was compared to a nearby reference site (Valkea–Kotinen Lake). During the first phase of the experiment the thermocline of Halsjärvi was lowered in order to simulate the estimated increase in wind speed and in total lake heat content (high-change climate scenario). The rate of methyl mercury (MeHg) production during summer stagnation (May–August) was calculated from water profiles before the treatment (2004), during treatment (2005, 2006) and after treatment (2007). We also calculated fluxes of MeHg from the epilimnion and from the hypolimnion to the sediments using sediment traps. Experimental mixing with a submerged propeller caused a 1.5–2 m deepening of the thermocline and oxycline. Methyl mercury production occurred mostly in the oxygen free layers in both lakes. In the experimental lake there was no net increase in MeHg during the experiment and following year; whereas the reference lake showed net production for all years. We conclude that the new exposed epilimnetic sediments caused by a lowering of the thermocline were a major sink for MeHg in the epilimnion. The results demonstrate that in-lake MeHg production can be manipulated in small lakes with anoxic hypolimnia during summer. The climate change induced changes in small boreal lakes most probably affect methyl mercury production and depend on the lake characteristics and stratification pattern. The results support the hypothesis that possible oxygen related changes caused by climate change are more important than possible temperature changes in small polyhumic lakes with regularly occurring oxygen deficiency in the hypolimnion.

The structure of phosphorus compounds in mid-forest humic lakes

The structure of phosphorus compounds in mid-forest humic lakes This study presents the vertical distribution of phosphorus fractions in three postglacial mid-forest humic lakes: oligohumic, mesohumic, and polyhumic. Total phosphorus concentrations were similar in these humic lakes (mean 76 μg 1-1 P). The greatest share of phosphorus was in mineral fractions, while a lesser share was in organic, especially soluble, fractions. Concentrations of mineral forms (phosphates and polyphosphates) were the lowest at the time of maximum development of phytoplankton, especially of bacterioplankton near the bottom of the oligohumic lake. An exceptionally high participation of soluble polyphosphates was found in the polyhumic lake near the surface.

Vertical diversity of bacteria in an oxygen-stratified humic lake, evaluated using DNA and phospholipid analyses

Microbes play a particularly important role in the food web in lakes with high dissolved organic carbon content. The bacterial community of a polyhumic lake, Mekkojarvi, was studied using DNA techniques and phospholipid fatty acid (PLFA) analysis during the mid-summer period of water column strati- fication. According to the 16S rRNA gene clone libraries and length heterogeneity analysis (LH-PCR), heterotrophic bacteria dominated only in the oxic epilimnion, in which various Actinobacteria (mostly cluster acI-B) and Betaproteobacteria (especially Poly- nucleobacter subcluster PnecC) were common. Se- quences assigned to heterotrophic, methylotrophic, photoautotrophic, and chemoautotrophic genera were all abundant in the oxic-anoxic boundary layer. Methylobacter and Methylophilus were dominant genera among methylotrophic bacteria. Sequences assigned to the photoautotrophic green sulfur bac- terium Chlorobium sp. dominated in the anoxic water column, in which the microbial PLFA biomass was 6 times higher than in the oxic surface layer. All PLFA- profiles were dominated by 16 monounsaturated fatty acids typical of Gram-negative bacteria, whereas iso- and anteiso-branched PLFAs typical of Actinobacteria were present only in minor proportions. The high bio- mass of the potentially autotrophic meta- and hypolim- netic bacteria may form an important carbon source for the whole lake after spring and autumn overturns; thus, the role of these bacteria in the seasonal energy mobilization deserves more study in oxygen-stratified humic lakes and ponds.

Could bacterivorous zooplankton affect lake pelagic methanotrophic activity?

We tested the hypothesis that grazing by bacterivorous zooplankton might suppress methanotrophic ac- tivity in small stratifi ed, humic lakes. During two series of replicated laboratory experiments, densities of methane- oxidising bacteria (MOB) in water from a small, polyhumic lake were measured in the presence of different densi- ties (range 0-200 individuals l -1 ) of a large bacterivorous cladoceran, Daphnia longispina. Grazing by Daphnia and by nanofl agellates reduced the proportion of MOB in the microbial community and the methanotrophic activity decreased signifi cantly at higher Daphnia densities. Thus, the hypothesis arising from previous fi eld observations was supported experimentally, but fi eld studies are required to quantify the infl uence of grazers on methanotrophic activity and CH4 effl uxes of lakes.

Contributions of Different Organic Carbon Sources to Daphnia in the Pelagic Foodweb of a Small Polyhumic Lake: Results from Mesocosm DI13C-Additions

Freshwater ecosystems derive organic carbon from both allochthonous and autochthonous sources. We studied the relative contributions of different carbon sources to zooplankton in a small, polyhumic, steeply stratified lake, using six replicate surface-to-sediment enclosures established during summer and autumn 2004. We added 13C-enriched bicarbonate to the epilimnion of half the enclosures for three weeks during each season and monitored carbon stable isotope ratios of DIC, DOC, POC and Daphnia, along with physical, chemical and biological variables. During summer, 13C-enriched DIC (δ13C up to 44 ± 7.2‰) was soon taken up by phytoplankton (δ13C up to −5.1 ± 13.6‰) and was transmitted to Daphnia (δ13C up to −1.7 ± 7.2‰), demonstrating consumption of phytoplankton. In contrast, during autumn, 13C-enriched DIC (δ13C up to 56.3 ± 9.8‰) was not transmitted to Daphnia, whose δ13C became progressively lower (δ13C down to −45.6 ± 3.3‰) concomitant with decreasing methane concentration. Outputs from a model suggested phytoplankton contributed 64–84% of Daphnia diet during summer, whereas a calculated pelagic carbon mass balance indicated only 30–40% could have come from phytoplankton. Although autumn primary production was negligible, zooplankton biomass persisted at the summer level. The model suggested methanotrophic bacteria contributed 64–87% of Daphnia diet during autumn, although the calculated carbon mass balance indicated a contribution of 37–112%. Thus methanotrophic bacteria could supply virtually all the carbon requirement of Daphnia during autumn in this lake. The strongly 13C-depleted Daphnia values, together with the outputs from the models and the calculated carbon mass balance showed that methanotrophic bacteria can be a greater carbon source for Daphnia in lakes than previously suspected.

Oxidation, efflux, and isotopic fractionation of methane during autumnal turnover in a polyhumic, boreal lake

We studied the oxidation and efflux of methane (CH4) in a small, polyhumic lake, Mekkojärvi (southern Finland), during 6 weeks in autumn when the stability of the water mass first weakened, temporarily restabilized, and finally mixed completely. During the summer stratification period, CH4 had accumulated in the anoxic hypolimnion to high concentrations (&gt;150 mmol m−3). Gradual mixing of the water column during the autumn allowed access to both oxygen and CH4 by aerobic methane‐oxidizing bacteria (MOB) deeper in the water column. Thus the bulk (∼83–88%) of the CH4 accumulated in the hypolimnion was subsequently consumed by MOB while only 12–17% was lost from the lake to the atmosphere at a rate varying between 0.05 and 8.8 mmol m−2 d−1. Phospholipid fatty acid (PLFA) analyses revealed that type I methanotrophs (MOB I) were responsible for this CH4 oxidation. The stable carbon isotope ratio of CH4 in the water column (δ13C‐CH4) ranged from −81.2‰ close to the bottom to −45.1‰ at the surface. At CH4 concentrations &gt;1 mmol m−3 the δ13C‐CH4 isotopic value was linearly related to the specific oxidation rate. The carbon isotopic fractionation factor α for aerobic CH4 oxidation calculated from the results (1.037) is within the range of maximum values reported in literature. Our results show that in stratified boreal lakes the greatest MOB activity and effluxes of CH4 both occur during autumnal mixing. Owing to their great abundance and areal cover, small water bodies should not be neglected in global analyses of the CH4 cycle.

Seasonal variations of dominant phytoplankton in humic forest lakes

Abstract This work presents the community composition, abundance and seasonal dominance of phytoplankton taxa in three hydrochemically different, mid-forest humic lakes. The largest number of taxa was observed in the oligohumic lake (76), with smaller numbers seen in the mesohumic (42) and polyhumic lakes (37), which were characterized by higher contents of dissolved humic substances carbon (DHSC). Along an increasing gradient of DHSC in a pool of dissolved organic carbon (DOC) the autotrophic algae were seen to disappear, being replaced by taxa with features of facultative heterotrophs and flagellated algae that are able to move in the water column.

Weak coupling between community composition and functioning of aquatic bacteria

We performed a batch culture experiment with a factorial design in which sterile water from four lakes and bacterial assemblages (size‐fractionated lake water) from the same lakes were set up in all possible combinations. The functional performance (biomass yield, respiration, growth rates, and growth efficiency) of bacterial communities growing in the cultures depended primarily on the type of the medium and to a much lesser extent on the origin of the bacterial assemblage. Functional changes were only partly paralleled by changes in community composition, as indicated by terminal restriction fragment length polymorphism analysis. Similar bacterial communities developed in different cultures as a result of receiving either the same medium or the same inoculum, indicating that bacterial communities are comprised of populations of generalists that can grow under most conditions as well as populations with the life strategy of specialists. However, bacteria originating from a slightly acidic polyhumic lake failed to grow, grew unsteadily, or exhibited an extended lag phase when exposed to media originating from other lakes, indicating that the bacterial community in the polyhumic lake was not able to adapt rapidly to changes in environmental conditions.