Humic Rich Lake Research Articles

QPCR-based eDNA workflow for humic-rich lake sediments: Combined use of sedimentary DNA (sedDNA) and Indigenous Knowledge in reconstructing historical fish records

Lake sediment serves as a natural archive of historical biological information. The use of sedimentary DNA (sedDNA), a form of environmental DNA (eDNA) shed by aquatic organisms and preserved in sediment, has been instrumental in reconstructing past faunal composition in aquatic communities. However, the low abundance of fish sedDNA and the often humic-rich nature of lake sediments create methodological challenges for the accurate detection of target sedDNA using quantitative polymerase chain reaction (qPCR)-based approaches. Herein, we present a consolidated qPCR-based eDNA workflow to reconstruct past and current fish fauna in Cowpar Lake located in the Oil Sands region in Alberta (Canada), which were then validated using Indigenous Knowledge from Chipewyan Prairie First Nation community members. The present study highlights the importance of combining column- and precipitation-based PCR inhibitor clean-up, nucleic acid concentration, incorporating endogenous chloroplast DNA as a sample integrity control. Robust qPCR-based eDNA assays were also useful in preventing the false-negative detection of low copies of target fish DNA. The presence of Northern pike (1905 to 2019) and Cisco (1919 to 1942) in Cowpar Lake was confirmed based on detected sedDNA from sediment core. The reconstructed fish records from sedDNA-inferred data aligned with the Indigenous accounts of natural and human-mediated changes in land use around the lake. Overall, the present study addresses common methodological concerns in processing lake sediment samples for fish eDNA detection and demonstrates the great potential of combined eDNA-inferred data and Indigenous Knowledge in reconstructing historical fish records in aquatic communities.

Natural versus anthropogenic controls on the dissolved organic matter chemistry in lakes across China: Insights from optical and molecular level analyses

Dissolved organic matter (DOM) plays an essential role in the global carbon biogeochemical cycle for aquatic ecosystems. The complexity of DOM compounds contributes to the accurate monitoring of its sources and compositions from large-scale patterns to microscopic molecular groups. Here, this study demonstrates the diverse sources and compositions for humic-rich lakes and protein-rich lakes for large-scale regions across China with the linkage to optical components and molecular high-resolution mass spectrometry properties. The total fluorescence intensity of colored DOM (CDOM) for humic-rich lake regions (0.176 Raman unit; R.U.) is significantly (p<0.05) higher than that of the protein-rich lake region (0.084 R.U.). The combined percentages of CDOM absorption variance explained by the anthropogenic and climatic variables across the five lake regions of Northeastern lake region (NLR), Yungui Plateau lake region (YGR), Inner Mongolia-Xinjiang lake region (MXR), Eastern lake region (ELR), and Tibetan-Qinghai Plateau lake region (TQR) were 86.25%, 82.57%, 80.23%, 88.55%, and 87.72% respectively. The averaged relative intensity percentages of CHOS and CHONS formulas from humic-rich lakes (90.831‰, 10.561‰) were significantly higher than that from the protein-like lakes (47.484‰, 5.638‰), respectively. The more complex molecular composition with higher aromaticity occurred in the humic-rich lakes than in the protein-rich lakes. The increasing anthropogenic effects would significantly enhance the sources, transformation, and biodegradation of terrestrial DOM and link to the greenhouse gas emission and the carbon cycle in inland waters.

The role of humic substances in sediment phosphorus release in northern lakes

In northern lakes, which are often stained and productive, the impacts of dissolved organic carbon (DOC) on sediment phosphorus (P) release are largely unexplored. Here we elucidated the factors behind experimentally-derived sediment release rates of P by diffusion (DF) in four Finnish lakes with a range of colour. Next, we extended our analysis to a larger set of northern lakes for further insights regarding possible implications of organic substances on sediment P release.The significant correlation between pore-water soluble reactive P and dissolved iron, and a positive effect of iron-bound sedimentary P (Fe-P) on DF supports the classic paradigm of redox-dependent P release in the four Finnish lakes studied. Nevertheless, the P release from Fe-P may be inhibited by humic substances, as we observed lower Fe-P and negative DF in two humic rich lakes (high DOC). The analysis of a larger set of northern lakes supported the negative effect of humic substances on P release rate (RR) determined by in situ P increases. In this dataset, DOC correlated positively with water colour and negatively with RR. Furthermore, multiple stepwise regression analysis selected sediment total P and organic matter content in sediments (LOI) as the best predictors of RR, similar to a previously published model by Nürnberg (1988). While the model predictions (RRpred) were correlated to RR in the present study, they tended to overestimate RR that was determined in closed experimental systems. The inhibiting effects of humic substances on RR may be manifested in both internal P loading and primary production.

Photoreactivity and bacterioplankton availibility of aliphatic versus aromatic aminoacids and a protein

In batch culture experiments with natural bac- erial assemblages collected from a humic-rich lake (Lake Neusiedl, Austria), labile organic nitrogen containing model substrates (alanine (Ala), an aliphatic amino acid, tryptophan (Trp), an aromatic amino acid, and bovine serum albumin (BSA), as protein) were added to 0.2 µm filtered lake water prior to exposure (for 9 h) to surface levels of the full range of solar radiation or being held in the dark. These organic nitro- gen species were chosen to investigate compound-specific differences in the photochemical transformation of labile dissolved organic matter (DOM) and its subsequent availabil- ity to bacteria. 'Photocoloring' or humification in the Trp- amended water exposed to natural solar radiation and signif- icant dissolved organic carbon (DOC) loss (120 µM C over 9 h exposure) resulted, after inoculation of the natural bacterial assemblage, in a lower maximum bacterial abundance in the previously solar radiation-exposed treatments as compared to the dark control. In contrast, the absorbance characteristics of solar-irradiated Ala- and BSA-amended water were almost identical to the unamended control and to the Ala- and BSA- amended treatments kept in the dark. Also, no significant dif- ference in the maximum bacterial abundance of the solar radiation-exposed Ala- and BSA-amended treatments was detectable as compared to the corresponding dark controls. Our data indicate that Trp is a potential source of solar radia- tion-mediated humification in Lake Neusiedl.

Direct Analysis of Lignin Phenols in Freshwater Dissolved Organic Matter.

A novel approach for the analysis of dissolved lignin in freshwaters is presented. Lignin concentrations in natural water samples are low, and a lignin extraction is usually required to obtain sufficient material for analysis. In this study, the alkaline CuO oxidation, which liberates a set of lignin-derived phenols, is performed directly on 15 mL of water sample in a microwave digestion system, hence reducing the required sample amount and preparation time considerably. These features make the method particularly suitable to study diagenetic changes of dissolved lignin in small-scale laboratory or field experiments. Phenol separation and quantification by gas chromatography tandem mass spectrometry lead to method detection limits between 22.7 and 1260 ng/L for single phenols, which corresponds to minimum lignin concentrations in the range of 8.5 μg/L (Σ8), offering applications for wetland, river, and lake waters with high terrestrial dissolved organic matter inputs. As a general method improvement, we present the addition of EDTA during phenol workup. EDTA binds remaining copper, thereby speeding up sample flow through the solid phase sorbent during phenol extraction and, furthermore, prevents substantial phenol losses, which occur if a water sample contains nitrate. Three natural water samples, a fresh leaf leachate and two humic-rich lake waters, were analyzed by the direct method presented here and in comparison with the established C18 extraction approach. Results show a similar reproducibility of both methods but reveal lower absolute lignin phenol yields in the humic-rich lake water samples upon C18 extraction.

Widespread release of dissolved organic carbon from anoxic boreal lake sediments

Sediments in boreal lakes are important components of the carbon cycle because they receive and store large amounts of organic carbon (OC) and at the same time are a source of greenhouse gases. Under anoxic conditions, sediment OC can be lost through dissolution from the solid phase and subsequent diffusion to the water column. Although this process may have implications for sediment OC budgets, it has yet to be studied systematically. We combined laboratory sediment incubation experiments from 4 boreal lakes in central Sweden that differed widely in their biogeochemical conditions with data from the Swedish monitoring program covering >100 lakes to analyze the frequency of occurrence of sediment DOC loss in boreal lakes and identify lake characteristics and the conditions related to high DOC fluxes from anoxic sediments. We found DOC diffusion from anoxic sediments in all the anoxic sediment incubations but at different mean rates (0.7–3.7 mmol m−2 d−1). Similarly, 16 of 17 of the monitoring lakes that developed anoxic bottom water exhibited an increase in bottom-water DOC concentration, corresponding to a mean (and standard deviation) DOC diffusion flux from anoxic sediment of 11.1 (35.4) mmol m−2 d−1. The observed variability between lakes was related to particularly large DOC fluxes in humic-rich lakes, which we attribute to their low pH and high share of terrestrial OC favoring the formation of OC-iron aggregates. Accordingly, increasing pH might facilitate the dissolution of sediment OC because high dissolved OC fluxes from anoxic sediments were accompanied by high microbial iron and sulfate reduction, resulting in concomitant pH increase.

Differential Sensitivity of a Coccal Green Algal and a Cyanobacterial Species to Dissolved Natural Organic Matter (NOM) (8 pp)

and Aim. In non-eutrophicated freshwaters, humic substances (HS) pose chemical stresses on aquatic organisms and, hence, separating sensitive from less sensitive or even tolerant species. One of the stresses, identified so far, is the reduction of photosynthetic oxygen production and reduction in growth in freshwater macrophytes and algae. In a previous paper, it has been shown that even closely related coccal green algae responded differently upon identical stress by HS, which is consistent with the hypothesis above. Due to their much simpler cellular ultrastructure, cyanobacteria are supposed to be more sensitive to HS exposure than eukaryote should be. One coccal green algal species (Desmodesmus communis) and one cyanobacterium (Chroococcus minutus) were exposed to four natural organic matter (NOM) isolates. One NOM has been isolated from a brown water lake (Schwarzer See) in Brandenburg State; three were obtained from a comprehensive Scandinavian NOM research project and originated from Norway (Birkenes), Finland (Hietajärvi), and Sweden (Svartberget). Cultures of D. communis and C. minutus were obtained from the Culture Collection of Algae, Göttingen, and maintained in a common medium. The cultures were non-axenic. The algae and cyanobacteria were exposed under identical conditions to environmentally realistic NOM concentrations. Cell numbers were counted microscopically in Neugebauer cuvettes in triplicates. To avoid limitation by nutrient depletion, the experiments were terminated after 14 to 15 days. Until culture day 12, no growth limitation has been observed in the controls. All NOM isolates modulated the growth of the algae and cyanobacteria. During the early culture days, there was a slight growth promotion with the coccal green alga and to a much lesser degree with the cyanobacterium. Yet, the major effect were significant reductions in cell yield in both primary producer cultures. C. minutus was much more affected than D. communis. This applies particularly to the three tested Scandinavian NOM isolates, which were effective at concentrations even below 1 mg L-1 DOC. The growth promoting effect may be due to an increase in bioavailability of some trace nutrients in the presence of NOM, the release of some growth promoting substances by microbial or photochemical processing of the NOM, and/or a hormetic effect. The growth reducing effect can be explained as a herbicide-like mode of action that affects the photosystem II most prevalent by blocking the electron transport chain, absorption of electrons, or production of an internal oxidative stress after processing the bioconcentrated HS. Furthermore, it may be postulated that also photo-toxicity of these HS in the algal cells contributes to the overall toxicity; however, experimental evidence is lacking so far. Upon exposure to HS, cyanobacteria appear to be much more sensitive than coccal green algae and respond in growth reduction. This high sensitivity of cyanobacteria to HS may explain phytoplankton patterns in the field. Eutrophic, humic-rich lakes do not support the cyanobacterial blooms characteristic of eutrophic, but humic-poor lakes. In the humic-rich systems, raphidophytes or, less frequent, specific coccal greens are more common. Obviously, cyanobacteria appear to be unable to make advantage of their accessory pigments (phycocyanin) to exploit the reddish light prevailing in humic-rich lakes. . At present, no effective structure can be figured out which may be responsible for the adverse effect on the cyanobacterial species. It is reserved to future research whether or not HS may be applied more specifically (for instance, with elevated moieties of the effective structures) as a natural geochemical to combat cyanobacterial blooms.

UV-light induced mineralization of organic matter bound chlorine in Lake Bjän, Sweden––a laboratory study

Surface water and aqueous solutions of isolated organic matter from a humic rich lake in southern Sweden were exposed to artificial UV radiation to investigate the UV light induced influence on organic matter bound chlorine in natural systems. It was found that the photodegradation of organic matter bound chlorine was more pronounced than the photodegradation of organic carbon. After 120 h of irradiation of the isolated organic matter, only 35% of the initial organochlorine was still in the solution compared to about 70% of the dissolved organic carbon (DOC). A similar result was obtained for unfractionated surface water. Furthermore, our results indicate that the loss of organic chlorine was mainly due to a mineralization of organic chlorine into chloride ions. The total decrease of organic chlorine after 120 h was 32 μg Cl org l −1, of which the major part disappeared in the initial irradiation phase. A similar increase was observed in the chloride concentration (34 μg Cl − l −1).

The Humic Lake Acidification Experiment (HUMEX): Main physico-chemical results after five years of artificial acidification

The HUMEX-project is a whole catchment manipulation experiment where the effects of the addition of H 2SO 4 and NH 4NO 3 to a humic-rich lake, Lake Skjervatjern, and its catchment were studied. The lake was physically divided into an experimental lake (Basin A) and a control lake (Basin B). Two years after the division, Basin A and its catchment were artificially acidified. Hydrological data, meteorology, precipitation, and runoff chemistry collected during a 2-y preacidification period and during 5 y of acidification were evaluated. Randomized intervention analysis (RIA) was used to evaluate statistical significant differences between runoff chemistry from the two basins before and after the acidification. RIA showed significantly higher concentrations of SO 4 2−, H +, NH 4 +, NO 3 −, Al n+, Ca 2+, Mg 2+, total reactive Al (RAL), and labile Al (LAL) in Basin A after treatment compared with the control basin. After the treatment, the acid neutralizing capacity (ANC) in Basin A was significantly lower than in Basin B. However, the average ANC is substantially higher in the control basin after acidification compared with the two years before acidification, while unchanged in the manipulated catchment. The main reason for this is the long lasting effect of Na leakage after seasalt-episodes. No significant changes were observed regarding the amount of total organic carbon (TOC), water color, or UV-absorbency after the treatment, but the anion deficiency (A −) was significantly lower in the treated basin. This indicates that the organic acids are more protonated in the treated basin compared with the control basin. After a cold winter in 1993/94, an extreme NH 4 + increase was observed in runoff water from Basin A. This increase was accompanied by increases in water color and UV-absorbency, but without any increase in TOC.

Methylmercury in some swedish surface waters

AbstractThree lakes and catchment runoff in the Lake Gårdsjön watershed on the Swedish west coast have been sampled for methylmercury during one year. The analyses indicated that high outputs of methylmercury were present during autumn in flushing water systems with short retention time, whereas smaller outputs and variations occurred in lake waters with longer retention time.Thus, methylmercury concentration were measured as 0.16 to 0.41 ng/L (humic rich lake), 0.12 to 0.26 ng/L (limed lake), &lt;0.1 ng/L (acid clearwater lake with long retention time) and 0.13 to 0.28 ng/L (acid runoff from a forest).A flux estimate from one forested catchment (3.6 ha) gave a yearly output of 5.2 mg and the specific output was estimated as 144 ± 70 mg/km2/y.The measured methylmercury concentration in this study accounted for only 6 to 13% of the total dissolved organic bound mercury in the water samples.