Lake States Research Articles

First report of Diplodia corticola causing dieback of white oak (Quercus alba) in Tennessee.

Diplodia corticola is a fungal pathogen causing oak dieback in Quercus (oak) spp. in parts of North America, northern Africa, and Europe (Ferreira et al., 2021; Smahi et al., 2017; Tsopelas et al., 2018). In August 2021, a single mature white oak (Q. alba) exhibiting wilt symptoms, vascular discoloration, and interveinal chlorosis was observed in Cove Lake State Park in Campbell County, Tennessee, U.S.A. Small sections of phloem tissues were cut from the margins of discolored vasculature of a single wilt symptomatic branch with a sterile scalpel and surface sterilized following Parra et al. (2020). Surface sterilized wood chips were plated onto potato dextrose agar amended with antibiotics (PDA++) following Gazis et al. (2018). Three days after plating, we recovered a single fungal isolate from wood chips that when grown in ½ PDA resembled D. corticola, having irregular margins and white aerial mycelia that progressively turned greyish-black 15 days after sub-culturing (Alves et al., 2004). Total genomic DNA was extracted from the isolate following Gazis et al. (2018). The internal transcribed spacer (ITS) was then amplified using the ITS1 and ITS4 primers and the subsequent PCR product was sequenced. Resulting reads were assembled into a consensus sequence and identity was assigned using BLAST on the NCBI nucleotide database. The assembled sequence (accession OM716006) had a 100% identity match with D. corticola type culture CBS 112549 (accession NR_111152). To complete Koch's postulates and identify potential host range, 5 red oaks (Q. rubra; 2-3 yrs old; caliper 14.7 ± 2 mm) and 5 white oaks (Q. alba; 2-3 yrs old; caliper 22.8 ± 2.3 mm) were inoculated with D. corticola (isolate DC_2.5). Trees were inoculated 15 cm above the soil line in a greenhouse with a 3 mm diameter plug of a 10-day old culture of D. corticola grown on PDA following Sitz et al. (2017). As a negative control, 5 red and 5 white oaks were inoculated with a 3 mm diameter plug of PDA. For each species, trees were sampled when seepage was observed from D. corticola inoculated sites (15 days post-inoculation for red and white oaks). At time of sampling, bark adjacent to inoculation sites on each tree was removed and cankers were photographed. Using a sterile scalpel, four wood chips were cut from canker margins and placed onto PDA++. For all trees, canker areas were measured using ImageJ software (Rasband, 2012). Recovered isolate identities were confirmed by extracting total genomic DNA as described above (Gazis et al. 2018) and PCR amplification of the ITS, large ribosomal subunit (LSU), and elongation factor 1-α (ef1-α) following (Ferreira et al., 2021). Diplodia corticola was reisolated from wood chips of D. corticola inoculated red (5/5 trees) and white (5/5 trees) oaks and ITS (accession OM716954), LSU (accession OM716955), and ef1-α (accession OM752198) sequences matched D. corticola type culture 112549 ITS (100% identity), LSU (99.76%-100% identity; accession KF766323), and ef1-α (98%-98.9% identity; accession XM_020275852). All D. corticola inoculated trees exhibited seepage from inoculation sites with streaking present in vasculature. Cankers were significantly larger in D. corticola inoculated red (2.34 ± 1.36 cm; P=0.042) and white (2.96 ± 0.52 cm; P=0.00029) oaks compared to agar inoculated trees. To the best of our knowledge, this is the first report of D. corticola causing decline of oaks in Tennessee.

Planktonic functional diversity changes in synchrony with lake ecosystem state.

Managing ecosystems to effectively preserve function and services requires reliable tools that can infer changes in the stability and dynamics of a system. Conceptually, functional diversity (FD) appears as a sensitive and viable monitoring metric stemming from suggestions that FD is a universally important measure of biodiversity and has a mechanistic influence on ecological processes. It is however unclear whether changes in FD consistently occur prior to state responses or vice versa, with no current work on the temporal relationship between FD and state to support a transition towards trait-based indicators. There is consequently a knowledge gap regarding when functioning changes relative to biodiversity change and where FD change falls in that sequence. We therefore examine the lagged relationship between planktonic FD and abundance-based metrics of system state (e.g. biomass) across five highly monitored lake communities using both correlation and cutting edge non-linear empirical dynamic modelling approaches. Overall, phytoplankton and zooplankton FD display synchrony with lake state but each lake is idiosyncratic in the strength of relationship. It is therefore unlikely that changes in plankton FD are identifiable before changes in more easily collected abundance metrics. These results highlight the power of empirical dynamic modelling in disentangling time lagged relationships in complex multivariate ecosystems, but suggest that FD cannot be generically viable as an early indicator. Individual lakes therefore require consideration of their specific context and any interpretation of FD across systems requires caution. However, FD still retains value as an alternative state measure or a trait representation of biodiversity when considered at the system level.

Planktothrix agardhii versus Planktothrix rubescens: Separation of Ecological Niches and Consequences of Cyanobacterial Dominance in Freshwater.

Cyanobacteria dominate lakes under diverse trophic conditions. Of these, two harmful filamentous cyanobacterial species, namely Planktothrix agardhii and P. rubescens, occupy completely different ecological niches in which they can form dense populations. In the present study, we investigated the effects of environmental conditions on the growth and vertical distribution of these species in lakes of different trophic statuses. Moreover, we underscored certain inconveniences in the assessment of the ecological status of lakes according to the European Union Water Framework Directive. The highest biomass of P. agardhii was recorded in eutrophic lake at a depth of 0.5-1 m, under high light intensity. Meanwhile, the highest biomass of P. rubescens, at which the deep chlorophyll maximum was recorded, was observed in mesotrophic lakes at a depth of 11-12 m, often below the euphotic zone under very low light intensity. P. rubescens, but not P. agardhii, exerted a strong allelopathic effect on the diversity and biomass of phytoplankton. Moreover, both species utilised different dissolved nitrogen fractions for their growth; specifically, P. agardhii used ammonium nitrogen, whilst P. rubescens used nitrate nitrogen. Furthermore, dissolved phosphorus produced a potentially limiting effect on P. rubescens growth. Overall, the tested Polish PMPL, German PSI, and Estonian phytoplankton indices were indeed useful in the assessment of the ecological status of lakes, albeit limited to the eutrophic lake with a high biomass of cyanobacteria (P. agardhii) in the upper water layers. However, problems arose in the proper assessment of lakes with a high biomass of cyanobacteria (P. rubescens) with a deep chlorophyll maximum outside the range of the euphotic zone. In such cases, two of the tested indices, namely the Polish and German indices, allowed sample collection from the euphotic layers, which significantly affected the number of samples included in the calculation. Consequently, the correct calculation of the ecological status of the lake was uncertain. Only the Estonian index allowed for a sample collection from two to three thermal layers of water, including the bloom layer of P. rubescens. Hence, the Estonian index offered the best fit for calculations.

Abiotic factors as a long-term stressor for the vendace fisheries in Lake Ińsko (European Central Plains Ecoregion, Poland)

The population of vendace ( Coregonus albula L., 1758) in many European lakes, especially in Central Europe, have declined recently as a result of lake eutrophication. The aim of the study was to (i) determine many years’ changes in the volume of vendace catches and specific physicochemical parameters of water, (ii) determine correlations between particular physicochemical parameters, and (iii) indicate hydrochemical parameters which show the greatest impact on the volume of vendace catches on the example of Lake Ińsko located in the European Central Plains Ecoregion. Principal Component Analysis (PCA) was applied to indicate the most important hydrochemical variables impact on vendace fisheries. Among them, after redundancy analysis, 6 were taken into account (total nitrogen, N-NO3, N-NO2, total phosphorus, oxygen concentration, temperature). Time series analysis revealed an increasing trend in nutrients concentration in lake. Analyses showed that fish catches were mostly negatively connected to nitrogen and phosphorus concentration. Trend analysis, based on the above-mentioned parameters, can provide prediction of vendace catches for further years with the predictability at the level of around 60% accuracy. The results of this study are very crucial to the vendace fisheries and for formulating fisheries management policies in the future in the changing hydrochemical condition of lakes.

Experimental Evidence from the Field that Naturally Weathered Microplastics Accumulate Cyanobacterial Toxins in Eutrophic Lakes.

Freshwater ecosystems with recurring harmful algal blooms can also be polluted with plastics. Thus the two environmental problems may interact. To test whether microplastics influence the partitioning of microcystins in freshwater lakes, we examined the sorption of four microcystin congeners to different polymers of commercially available plastics (low-density polyethylene, polyethylene terephthalate, polyvinyl chloride, and polypropylene). We conducted three experiments: a batch sorption experiment in the laboratory with pristine microplastics of four different polymers, a second batch sorption experiment in the laboratory to compare pristine and naturally weathered microplastics of a single polymer, and a 2-month sorption experiment in the field with three different polymers experiencing natural weathering in a eutrophic lake. This series of experiments led to a surprising result: microcystins sorbed poorly to all polymers tested under laboratory conditions (<0.01% of the initial amount added), irrespective of weathering, yet in the field experiment, all polymers accumulated microcystins under ambient conditions in a eutrophic lake (range: 0-84.1 ng/g). Furthermore, we found that the sorption capacity for microcystins differed among polymers in the laboratory experiment yet were largely the same in the field. We also found that the affinity for plastic varied among microcystin congeners, namely, more polar congeners demonstrated a greater affinity for plastic than less polar congeners. Our study improves our understanding of the role of polymer and congener type in microplastic-microcystin sorption and provides novel evidence from the field, showing that naturally weathered microplastics in freshwater lakes can accumulate microcystins. Consequently, we caution that microplastics may alter the persistence, transport, and bioavailability of microcystins in freshwaters, which could have implications for human and wildlife health. Environ Toxicol Chem 2022;41:3017-3028. © 2022 SETAC.

Is it possible to optimise the labour and time intensity of diatom analyses for determination of the Polish Diatom Indices (IO, IOJ)?

Diatom-based indices are a recommended approach in the assessment of the ecological status of lakes and rivers, required by the EU Water Framework Directive. To optimise the time-consuming microscopic analyses, we determined the lowest number of diatom valves needed to be identified (‘counted’) in a sample to arrive at a reliable ecological status assessment based on the Polish multimetric diatom indices (diatom index, IO for rivers, and diatom index for lakes, IOJ). We compared the indices calculated with different valve counts. The dataset consisted of diatom counts in 55 samples collected in the rivers Ina and Drawa (Western Pomerania, NW, Poland) and their lakes. Following the method used by the Polish Chief Inspectorate for Environmental Protection (ChIEP), periphyton samples were collected from macrophytes growing in the rivers and lakes, and diatom slides were prepared. Originally, the ecological status was determined based on identifying 400 valves per slide. In the subsequent simulation, 50, 100, 150, 200, 250, 300, 350 and 400 valves per slide were randomly drawn 20 times for each sample and each simulation, and the indices were calculated again. In 87% of our simulations, the ecological status turned out to be identical, regardless of the number of valves identified. However, the standard deviation of the index values was at its highest (> 0.05) with 50 valves, and decreased systematically (below 0.05) for 100 and more valves. Simulated datasets showed logarithmic trend of changes where the compilation and standard deviation was stable above 200 valves identified. Therefore, we recommend simplified methodology for Polish multimetric diatom indices. Reduction of identified valve quantity in a sample to 200 valves would result in over 95% of compliance with classification obtained when 400 valves were identified.

Trophic state assessment of optically diverse lakes using Sentinel-3-derived trophic level index

• The TLI retrieval algorithm with a global OWT classification scheme can achieve higher accuracy. • Using S owt > 0.9 to group training data for each OWT can help build more robust algorithms. • The eutrophic of lakes in Wuhan haven’t decreased during the COVID-19 lockdown period. An accurate estimation of trophic state of lakes with satellite remote sensing is a challenge due to the optical complexity and variability associated with inland waters. Match-up data from 393 sampling stations that has concurrent Sentinel-3 OLCI images were acquired across Wuhan lakes. Trophic Level Index (TLI) algorithms were developed within a global Optical Water Type (OWT) classification system. The performance of algorithms with limited training data gathered by using spectral similarity of highest S owt was not improved compared with that on basis of no classification. In contrast, using spectral similarity of S owt > 0.9 rather than the highest S owt to group more training data with similar traits for each OWT can help build more robust algorithms, which performance is better than that on basis of no classification. Algorithm performance statistics of the test dataset for the stepwise multiple linear regression (SMLR) method were the following: Mean Absolute Error (MAE) = 5.56; Mean Absolute Percentage Error (MAPE) = 11.02 %; Root Mean Square Error (RMSE) = 7.24 and for the back propagation neural network on the basis of the Levenberg-Marquardt-Bayesian regularization algorithm (LMBR-BPNN) method MAE = 4.56; MAPE = 8.33 %; RMSE = 5.98. We detected 8 different OWTs (2,3,4,5,9,10,11,12) in Wuhan lakes and clear spatio-temporal patterns of the trophic state between 2018 and 2020.Our results revealed that the trophic state of Wuhan lakes did not decrease as expected during the COVID-19 lockdown period.

Climatic and hydrological variations on the southwestern Tibetan Plateau during the last 30,000 years inferred from a sediment core of Lake Zabuye

Climate change on the Tibetan Plateau (TP) is governed by the mid-latitude westerlies and Indian summer monsoon (ISM). However, the past hydrological changes on the TP induced by interactions between the westerlies and the ISM remain unclear. A sediment core from Lake Zabuye on the southwestern TP was analyzed to reconstruct climatic and hydrological variability over the last 30 kyr. Stable isotopic compositions (δ13C and δ18O) of authigenic carbonate act as an indicator of hydrological status for closed-basin lakes on the TP. Four major climatic and hydrological stages were identified: (1) last glacial maximum (29.8–18.9 cal kyr BP), the influence of the westerlies dominated, and a cold-wet climate prevailed; (2) last deglaciation (18.9–11.8 cal kyr BP), the influence of the westerlies receded, and a general trend of decreased wetness was interrupted by two pronounced glacial meltwater events recorded at 17.2 and 15.2 cal kyr BP, respectively; (3) early and middle Holocene (11.8–3.8 cal kyr BP), the Holocene climate optimum was attained and sustained under the dominance of ISM circulation; (4) late Holocene (from 3.8 cal kyr BP to the present), the ISM collapsed during the middle to late Holocene, and a hypersaline lacustrine environment was ultimately formed, as inferred from mirabilite deposition and isotopic signals. Our lake record demonstrates an anti-phase relationships between the westerlies and the ISM on the glacial-interglacial timescale over the southwestern TP. We suggest that both North Atlantic climate and tropical ocean temperature are major drivers of climatic variations on the TP.

Two closely related ureotelic fish species of the genus Alcolapia express different levels of ammonium transporters in gills.

Most fish excrete their nitrogenous waste across the gills as ammonia through the activity of the Rhesus glycoprotein ammonium transporters. In contrast, fish of the subgenus Alcolapia (Oreochromis) are the only vertebrates that survive the extreme conditions of the soda lakes of Natron and Magadi in East Africa and have evolved adaptations to the highly alkaline waters including the ability to excrete their nitrogenous waste as urea. Nevertheless, Alcolapia retain the Rhesus glycoprotein genes in their genomes and using two heterologous expression systems, we demonstrate that Alcolapia Rhbg is capable of moving ammonia. Comparing ammonia and urea excretion from two closely related Alcolapia species from the same aquarium, we found that while Alcolapia grahami remains fully ureotelic after many generations in lab conditions, Alcolapia alcalica excretes some of its nitrogenous waste as ammonia. Using in situ hybridisation, we demonstrate robust, localised gene expression of Rhbg, rhcg1 and rhcg2 in the gill tissue in both A. alcalica embryos and adults, similar to that in other ammoniotelic fish. In contrast, the expression of these genes in A. grahami gills is much lower than in A. alcalica, suggesting the rapid evolution of a molecular mechanism underlying the complete ureotelism of A. grahami.

Holocene Lacustrine Abiotic Aragonitic Ooids from the Western Qaidam Basin, Qinghai-Tibetan Plateau

Carbonate ooids are a significant component of shallow water carbonate deposits in the present and geologic past, yet their origin and formation mechanism have been the subject of continuing debate. This study focuses on the well-preserved Holocene aragonitic ooids collected from the west Qaidam Basin, Qinghai-Tibetan Plateau (QTP). The mineralogical and chemical compositions, and stable (δ13C and δ18O), and radiocarbon isotopes of the ooids were analyzed to investigate their formation and develop a depositional model. The ooids formed approximately 5377±61 cal BP, and their cortices were composed of microcrystalline aragonite, with most nuclei being quartz grains. Stable carbon and oxygen isotopes indicate that authigenic aragonite precipitation is driven by evaporation and associated degassing of CO2 under turbulence conditions in a shallow alkaline lakes. Furthermore, eletron microscopy showed no presence of microfossils in ooid cortices or other evidence of microbial activity. Therefore, we propose that aragonite precipitation during ooid formation is most likely induced abiotically by increasing alkalinity due to evapoconcentration of lake waters based on an absence of an efficient carbonate-inducing metabolic pathway. New observations and detailed analyses of aragonitic ooid samples in the Qaidam Basin provide an improved understanding of the origin and formation processes of carbonate ooid in modern environment and the geologic past.

Spatiotemporal Changes in Water Quality Parameters and the Eutrophication in Lake Erhai of Southwest China

To understand the lake status and reasons of eutrophication at Lake Erhai in recent years, water quality, including water temperature (T), pH, dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP) and chlorophyll-a (Chl-a) from 2016 to 2020 was monitored and analyzed. The results showed no obvious thermocline in the vertical direction at Lake Erhai, while Chl-a demonstrated obvious spatiotemporal distribution characteristics in Lake Erhai. Chl-a concentrations increased to a maximum in summer in August with the low TN:TP value, leading to algal blooms, most notably in the southern lakes. Low pH and DO appeared due to the thermocline of Erhai Lake (August 2016). A large area of algae distribution due to the increase of total phosphorus appeared in the northern lake area of Lake Erhai in December 2016, with a tendency of mesotrophic to light eutrophic in summer by the nutritional evaluation of Lake Erhai, especially in the central lake area and the northern lake area. Pearson’s correlation coefficient and principal component analysis showed a significant positive correlation between Chl-a and T (r = 0.34, p ≤ 0.01) and TP (r = 0.31 p ≤ 0.01) in the mesotrophic Lake Erhai, indicating that TP content was one of the triggering factors for the algal blooming. Based on the spatiotemporal changes in water quality parameters and their relationship with eutrophication, scientific agencies should implement management strategies to protect Lake Erhai, supplemental to the costly engineering measurements.

Assessing temporal variability of lake turbidity and trophic state of European lakes using open data repositories

Water turbidity is one of the more important water quality parameters that is strictly linked with the productivity of the lake and is commonly used as an indicator of the trophic state. However, limited field data availability across wide geographic gradients may hinder the conduction of large scale longitudinal studies. In this study, time series of lake turbidity and trophic state index (TSI) between 2002 and 2012 were obtained from the Copernicus Lake Water products to create a large longitudinal dataset of lake variables for 22 European lakes. The dataset was combined with estimates of nutrient concentrations and surface water temperature obtained from the Hydrological Predictions for the Environment (HYPE) and ERA5-Land data repositories, that were used as environmental predictors. Hence, the validity of the lake water quality parameters was tested by a) exploring their spatial and temporal variability and b) identifying associations with the environmental predictors. For this purpose, seasonal Mann-Kendall tests were applied to find significant inter-annual trends of turbidity and TSI for each lake, and generalized additive models (GAMs) were employed to identify the main parameters that shape their temporal dynamics. Although we did not find significant inter-annual changes, our findings highlighted the strong influence of seasonality and surface water temperature in defining the temporal variability patterns in most of the lakes. In addition, the importance of nutrients varied among lakes as several lakes exhibited narrow nutrient gradients reflecting relatively stable nutrient conditions during the examined period. Other lake intrinsic factors, such as local climate and biotic interactions, are important drivers of shaping turbidity and nutrient dynamics. This study highlighted the usefulness of combining lake data from large repositories in conducting large scale spatial studies as a valuable asset for future lake research and management purposes.

Mapping water clarity in North American lakes and reservoirs using Landsat images on the GEE platform with the RGRB model

Lakes and reservoirs provide important ecosystem services that support human welfare and socio-economic activities. However, in many world regions, the ecological integrity of lakes and reservoirs is threatened by human perturbations and climate change. The Secchi disk depth (SDD) is a widely-used proxy representing the trophic status of lakes and reservoirs and can be retrieved from remote sensing data. Despite their potential for large-scale (regional, global) and long-term lake and reservoir water clarity assessment, the transferability of remote sensing-based models has been a major limitation. In this study, we assembled in situ SDD in lakes and reservoirs across North America (NA) from five different sources. We identified a subset of 3235 samples collected within ±7 days of a Landsat satellite overpass. Relationships between various spectral index models calculated from Landsat top-of-atmosphere reflectance and in situ SDD were analyzed. A model based on Landsat blue/green plus blue/red ratios (denoted as RGRB) was selected to retrieve the SDD of all NA lakes and reservoirs. The RGRB model performed well during calibration (R2 = 0.81) and validation (R2 = 0.78, MAPE = 30.85 %). This model also exhibited stable and reliable performances regardless of the Landsat sensors (TM, ETM+, and OLI), despite spectral configuration differences among these sensors. RGRB was implemented to generate SDD maps for all lakes and reservoirs (water surface area ≥1 ha) across NA in 2019. More than 2.9 million lakes and reservoirs were mapped with Landsat OLI images, resulting in an average SDD of 3.84 ± 1.77 m. A strong positive relationship between average SDD and log-transformed water surface area (R2 = 0.80, p < 0.001) indicated that large lakes and reservoirs tend to be more transparent than small ones. Latitudinal variations were found in the water clarity gradient, with maximum SDD recorded at the 35°N–60°N latitude and lower SDD at the 10°N–30°N latitude. This model can be implemented using the Google Earth Engine platform to derive SDD for NA lakes and reservoirs at annual or even seasonal time steps to assess water eutrophication variation in both time and space at the continental scale.

Geochemical characteristics of n-alkanes in sediments from oligotrophic and eutrophic phases of five lakes and potential use as paleoenvironmental proxies

Profiles of n-alkane proxies in sediment cores have been frequently used to detect historical trends in the nutrient status of lakes. However, the results obtained from these proxies are occasionally confusing because the situations in which a given n-alkane proxy might make a valid indication have tended thus far to be elusive. The current study compared geochemical characteristics of n-alkanes in sediments from the oligotrophic (before 1950) and relatively eutrophic phases (after 1980) of five representative lakes in order to assess their suitability and reliability as proxies for lake trophic state. The results from Lakes Liangzi, Changdang, Taibai and Erhai demonstrated that short-chain odd carbon n-alkane abundances were significantly higher (P < 0.05) in sediments deposited after 1980 than in those dating to before 1950, whereas TAR (terrigenous: aquatic ratios) and ACL15–33 (average chain length of C15–C33n-alkanes) were significantly lower (P < 0.05) in the more recent sediments. These results are compatible with generally accepted variation seen in lakes that have undergone eutrophication. In Lake Fuxian, however, short-chain odd carbon n-alkane abundances, TAR and ACL15–33 were all higher in sediments after 1980 than in sediments before 1950, although the variation was only significant (P < 0.05) for ACL15–33. These results, especially the unexpected trends in TAR and ACL15–33, mean these cannot be relied upon as proxies for eutrophication in this lake. The anomaly is likely to be related to the predominantly low phytoplankton productivity and OM input in Lake Fuxian, coupled with the availability of OM from submerged macrophytes in the relatively eutrophic phase. Interestingly and importantly, two new proxies CPI15–20 ((n-C15 + n-C17 + n-C19)/(n-C16 + n-C18 + n-C20) alkanes) and n-C17/n-C16 alkane, which are indicative of OM input from phytoplankton over non-photosynthetic bacteria, were significantly higher (P < 0.05) in post-1980 sediments than in those dating to before 1950 in all five studied lakes. These two are thus shown to be widely applicable for recording lake eutrophication. Their presence in Lake Fuxian can be explicitly attributed to the absence of influence from submerged macrophytes. Moreover, as ratio results of n-alkanes with similar carbon number, these two proxies are less influenced by processes of OM diagenesis due to comparable degradation of n-alkanes in sediments. The combined results suggest that these previously overlooked proxies may be of considerable value to studies of lake trophic history.

Biomarker and Pollen Evidence for Late Pleistocene Pluvials in the Mojave Desert

AbstractThe climate of the southwestern North America has experienced profound changes between wet and dry phases over the past 200 Kyr. To better constrain the timing, magnitude, and paleoenvironmental impacts of these changes in hydroclimate, we conducted a multiproxy biomarker study from samples collected from a new 77 m sediment core (SLAPP‐SRLS17) drilled in Searles Lake, California. Here, we use biomarkers and pollen to reconstruct vegetation, lake conditions, and climate. We find that δD values of long chain n‐alkanes are dominated by glacial to interglacial changes that match nearby Devils Hole calcite δ18O variability, suggesting both archives predominantly reflect precipitation isotopes. However, precipitation isotopes do not simply covary with evidence for wet‐dry changes in vegetation and lake conditions, indicating a partial disconnect between large scale atmospheric circulation tracked by precipitation isotopes and landscape moisture availability. Increased crenarchaeol production and decreased evidence for methane cycling reveal a 10 Kyr interval of a fresh, productive, and well‐mixed lake during Termination II, corroborating evidence for a paleolake highstand from shorelines and spillover deposits in downstream Panamint Basin and Death Valley during the end of the penultimate (Tahoe) glacial (140–130 ka). At the same time brGDGTs yield the lowest temperature estimates (mean months above freezing = 9°C ± 3°C) of the 200 Kyr record. These limnological conditions are not replicated elsewhere in the 200 Kyr record, suggesting that the Heinrich stadial 11 highstand was wetter than the last glacial maximum and Heinrich 1 (18–15 ka).

Study on purification performance of nitrogen and phosphorus in landscape water by enhanced combined ecological floating bed

Taking Hornwort, Hydrilla verticillata, Iris, Calamus and Loosestrife as the research objects, under the static water condition of a university landscape lake in Xi’an, the combined ecological floating bed composite system of emergent plant submerged plant matrix microorganism enhancement was constructed to carry out the simulated hydroponic experiment for the investigation of the absorption to nitrogen and phosphorus in the water and the purification ability of the ecological floating bed composite system. The results showed that: (1) The best group of combined plants in the landscape lake water was calamus + Hydrilla verticillata, and their removal rate on Total nitrogen, Total phosphorus, Chemical oxygen demand, and ammonia nitrogen are 92.72%, 81.26%, 68.55%, 93.69% respectively. (2) Under the composite floating bed matrix system, the optimal substrate group and ratio are ceramsite and vermiculite (1:1), and their removal rates on Total nitrogen, Total phosphorus, Chemical oxygen demand, and ammonia nitrogen are 61.68%, 86.96%, 79.65%, and 78.12% respectively. (3) The best residence time of AM bacteria in the enhanced combination floating bed was 25 days, and the removal efficiency of total nitrogen and total phosphorus was 67.31% and 93.20% respectively.

Influence of the modern climatic setting in the mountains of Central Asia on the state of glaciation, glacier runoff and glacial lake outbursts

The climatic setting of Central Asia in the second half of the 20th century and in the first decade of the 21st century is characterized by a change of horizontal and vertical temperature gradients at the western periphery of the Central Asian Mountain system. The growth of summer air temperatures led to the decrease of mountain glaciations. In the last 45 years the glaciers in selected catchments of Gissar-Alay lost about 16% in area while the glaciers of the Pskem river catchment lost 27% in area. The river regimes, primarily the annual distribution of runoff react to the glacier decrease. The share of glacial runoff is over 25% in years with little precipitation, while it considerably decreases in years with abundant precipitation. One of the negative consequences of the glacier decrease is the formation of lakes in the periglacial area. The state of glacial lakes should be monitored, because they may pose outburst debris flow hazard.

Understanding the changes of optically active substances (OACs) in Hulun Lake in the past 35 years and its indication to the degradation of aquatic ecology

Lake eutrophication and ecological degradation are among the most serious environmental problems in the world and identifying changes in key water quality parameters and associated drivers is critical for lake management. Optically active substances (OACs) are important water quality indicators that affect lake water ecology and evaluate lake eutrophication. Climate change and human activities are important factors driving the changes of OACs in lakes. Understanding how and why OACs varies in long-term trend in response to different influencing factors and its driving mechanism is needed to understand. In this study, based on the Landsat series satellite data, this study investigated the historical changes of OACs in Hulun Lake, quantitatively explained the response relationship of OACs to meteorological, hydrological and human activity elements, and discussed their indicative role in the degradation of water ecology. The results showed that during 1986–2020, OACs had obvious periodic changes; from 1986 to 1999, Chla, CDOM and TSM are relatively stable at lower values; during 2000–2009, the concentration of total suspended matter (TSM) and coloured dissolved organic matter (CDOM) increased, and the concentration of chlorophyll a (Chla) decreased; during 2010–2020 The annual TSM and CDOM concentration decreased, and the Chla concentration increased. The results showed that among the hydrometeorological and anthropogenic variables selected to explain changes in the OAC, gross domestic product (GDP) is the key factor influencing changes in the OACs, explaining 39.3%, 71.8% and 60.6% of the changes in Chla, CDOM and TSM, respectively. Air temperature (AT) can explain 24.0% of the variation in Chla, evapotranspiration (Eva) can explain 19.1% and 5.52% of the variation in CDOM and TSM, and precipitation (P) can explain 13.8% and 7.5% of the variation in Chla and TSM. Water level is an important pathway affecting OACs in Hulun Lake, explaining 50.7% of the variation in CDOM, 48.0% of the variation in TSM and 23.1% of the variation in Chla. Warming and drought in the Hulun Lake basin and human activities ultimately lead to changes in OACs. Finally, a pattern diagram to assess the degree of ecological degradation of lake was proposed. This study has substantial implications to monitor and assess the ecological degradation status of lake and maintain the sustainable development of lakes in cold and arid regions.

Radar altimetry for classifying surface conditions of subarctic lakes during freezing and thawing periods

ABSTRACT Ice cover on subarctic lakes is an important indicator of climate change at local- or regional scales. This study proposes a new approach for classifying altimetry data from Jason-2 and SARAL/Altika satellite missions to characterize surface states of subarctic lakes. It focuses on Great Slave Lake (Canada) during freeze-up and thaw periods. For the first time, parameters from altimetry waveforms were used in an unsupervised clustering to establish distinct clusters from waveforms observed from Jason-2 and SARAL/Altika during the freeze-up and the thaw period. Clusters are assigned to the different surface states (open water, pure ice and leads) based on a priori altimetry and radiometric information. The statistics of these clusters were then used to construct two trained models of supervised classification based upon KNN (K-nearest neighbour) and SVM (support vector machine). The SVM-based model yielded the best results (accuracy of 92% with Jason-2, and 98% with SARAL/Altika). It was used to classify all waveforms considered in the study from the nominal orbits of Jason-2 (2008–2016) and SARAL/Altika (2013–2016). Results were superimposed onto Moderate Resolution Imaging Spectroradiometer (MODIS) products for qualitative visual and semi-quantitative assessments.

Applying the “Goldilocks Rule” to Riparian Buffer Widths for Forested Headwater Streams across the Contiguous U.S.—How Much Is “Just Right”?

Delineating riparian management zones (RMZ) around streams to protect riparian ecological functions is critical during forest management. This study compared the area dedicated to RMZ using the USFS functional-based riparian buffer approach versus individual state-defined riparian buffer allocation strategies along headwater streams across 17 states within the US. The USFS method uses a variable-width riparian buffer that seeks to capture the functions of a riparian area. Our study sought to contrast this USFS method with various state-defined RMZ guidelines. The functional approach delineated the highest percentages of the watershed area around headwater streams in most watersheds, sometimes &gt;20% of forestland, whereas state RMZ guidelines delineated &lt;10% of forestland around headwater streams in many watersheds. Although many state guidelines failed to identify the variable widths of functional riparian areas, some watersheds in the Great Lakes states over-allocated forestland as riparian when compared to a functional riparian delineation. The topographic and forest composition differences observed across the study area were not represented by their respective state RMZ guidelines, and these variables strongly influence the delineation of a functional RMZ.