Lake Cycle Research Articles

Life-cycles of a lava lake: Ambrym volcano, Vanuatu

Eighteen years of heat flux data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) are used to investigate cycles of lava lake activity at Ambrym volcano in Vanuatu. Lava lakes are dynamic manifestations of open-vent volcanic behaviour and time-series analysis of this behaviour reveals the timing and magnitude of magmatic processes. Pulsatory fluctuations in heat flux of > 50 MW over periods of 30 to >100 days during lava lake activity are interpreted to represent episodes of magma replenishment. These are periodically interrupted by rapid falls in heat flux (50–100 MW over <5 days) or variations in the relative heat flux from lava lakes in different vents of the volcano, which are interpreted to represent changes to the shallow plumbing system feeding lava lake activity. Sudden lava lake drainage and flank eruptions can interrupt or terminate lava lake cycles. Heat flux patterns preceding such events do not show an obvious consistent pattern, suggesting that different magmatic processes may initiate these potentially hazardous surges in eruption intensity. Comparison with the dynamics of other lava lakes reveals similarities in long-term behaviour, despite differences in lava lake size, surface motion or degassing. Collectively this suggests fundamental similarities in the processes that sustain open-vent behaviour, including, the stability of magma supply, conduit-plumbing/geometry and local strain-state.

Trophic resources use pathways between two coexisting freshwater shrimp (Palaemon argentinus and Macrobrachium borellii)

Context A better understanding of the use of different trophic pathways as a mechanism for adjusting interactions between coexisting omnivorous decapod species may help define the extent of their influence on energy flows in freshwater ecosystems. Aims Analyse the patterns of use of the benthic and littoral pathways by Macrobrachium borellii and Palaemon argentinus during a hydrological cycle in lakes of the middle Paraná River. Methods The study was conducted during one high-water (HW) and one low-water (LW) period in three lakes permanently connected to the middle Paraná River. We calculated the relative contributions of potential basal resources (benthic and littoral) to each species for each lake and hydrological period using mixing models. Key results It was observed that M. borellii feeds more in the littoral pathway and P. argentinus in the benthic pathway, especially in low water where we observed that the partitioning of resources was more pronounced. Conclusion The more aggessive species, M. borelli, during HW period quickly utilises the bioavailable material. Trophic dynamics and resource use are part of the coexistence mechanisms of both decapod species. Implications This may have important consequences in the aquatic trophic webs in which these organisms participate, because when segregating the use of resources, they intervene in different energetic pathways.

A review of wind-driven hydrodynamics in large shallow lakes: Importance, process-based modeling and perspectives

Abstract In many large shallow lakes across the globe, the surface wind field drives the hydrodynamic process directly through the momentum and energy exchange at the air–water interface. Numerous field measurements, experiments and modeling show that wind-driven hydrodynamic disturbances have profound impacts on the structure and function of lake ecosystems. In this article, we review the response of the shallow lake to the wind-driven wave and flow field, which may accelerate the sediment resuspension and nutrient cycling and, in turn, affect the concentrations of nutrients and dissolved oxygen. Furthermore, the life activities of bacterioplankton, plankton and fish in the aquatic ecosystem are closely related to these water-quality factors. Although we have a developed understanding of the physical processes and biogeochemical cycles of lakes by process-based modeling, the most basic wind-driven hydrodynamic process in some lake models is imprecise. Comprehensive results of physical parameterization, including the wind stress and wind drag coefficient, with their mathematical expressions for depicting the wind-driven force in the hydrodynamic model of lakes are synthesized. Some of these expressions are empirically determined without considering the dynamic environment, and expressions based on physical mechanisms have been widely recognized. Additionally, the adaptation standard of wind-driven force parameterizations to inland lake models under light winds is provided. This article highlights the importance of heterogeneous wind field variability and suggests future studies on the wind fields in extreme climates, which could also cause damage to deep lake ecosystems and the biodiversity effects of wind wave turbulence.

Three-dimensional observations of particulate organic carbon in shallow eutrophic lakes from space

Particulate organic carbon (POC) storage play an essential role in determining carbon sinks and water quality in shallow eutrophic lakes. Although satellite data have been adopted to observe surface POC content, the previous remote sensing results cannot indicate water column-integrated POC storage in shallow eutrophic lakes with vertically nonuniform POC profiles. Based on 272 in-situ POC profiles collected from 19 shallow eutrophic lakes in China's Yangtze-Huai Plain (YHP), this study developed a novel process-oriented method to derive water column-integrated POC storage from OLCI/Sentinel-3A satellite data. The method included three critical steps: remotely estimating surface POC contents, identifying POC profile types (uniform, exponential decay, or power decay) through a binary decision tree, and parameterizing POC profiles using surface POC concentrations. The developed algorithms showed a bias of -25.79% for in-situ match-ups from 15 lakes (N = 88). The POC in the eutrophic lakes was mainly produced by phytoplankton (R2 = 0.87). As a result, the surface POC content presented a unimodal peak in summer. However, in addition to air temperature regulations (0.52 – 68.53%), the water level also showed apparent effects on increasing POC storage, with relative contributions of 29.29 – 95.51% for the six largest lakes. Therefore, multisource satellite data are needed to derive POC storage in global eutrophic lakes remotely. This study is the first attempt to three-dimensionally observe lake POC contents from space and is important for understanding the carbon cycle in shallow eutrophic lakes.

New insights into the carbon cycle and depositional models of the Eocene saline lake, Jianghan basin, China

Geochemical characteristics and sedimentary processes of sediments, especially mixed sediments, have long been hot topics of research in basin systems, which can be used to infer runoff, evaporation, productivity, precipitation patterns of the paleoenvironment, as well as records of a diverse range of climate-related signs. However, compared with shallow marine mixed siliciclastic-carbonate sediments, the study of lacustrine mixed sedimentary systems in combination with geochemical information is relatively limited. Also, model-based study on the reconstruction of the lacustrine carbon biogeochemical cycle is defective, especially in saline lacustrine environments. In this work, a total of 26 mixed siliciclastic–carbonate sediment core samples from Well BX-7 in the Qianjiang Depression were sequentially selected for scanning electron microscope observation, major and minor element test, and isotope measurements (e.g., δ13Ccarb, δ18Ocarb, and δ34SCAS). Two types of mixed sediments were generated in the overall inflow/outflow balance of water within the saline basin during the Eocene: siliciclastic-dominated mixed sediment (SDMS) and carbonate-dominated mixed sediment (CDMS). The δ13Ccarb values of SDMS and CDMS samples range from −7.13‰ to −4.52‰ (average −5.82‰) and −9.00‰ to −6.11‰ (average −7.48‰), respectively. The δ18Ocarb values of SDMS and CDMS samples range from −10.26‰ to −1.40‰ (average −4.73‰) and −3.80‰ to −0.96‰ (average −1.55‰), respectively. In addition, combining the geochemical parameters of sedimentation rate, Mn2+ content in carbonate lattice ([Mncarb]), carbonate mass fraction, and [Mg2+]/[Ca2+] ratio, we established a lacustrine δ13C variation model at the sediment-water interface (SWI) with the aim of accurately reflecting δ13Ccarb changes during carbonate formation. Based on the sedimentary processes and geochemical characteristics, we established two depositional models for these two types of mixed sediments in a saline lacustrine basin in the overall inflow/outflow balance of water. Model I illustrates SDMS sedimentary processes with a relative low salinity, low FluxDIC-O, high water inflow, and the organic carbon oxidation is dominated by Fe (III) reduction. Model II demonstrates CDMS sedimentary processes with a high salinity, high FluxDIC-O, high water outflow, and the organic carbon oxidation is dominated by sulfate reduction.

Fine-scale dynamics of calcite precipitation in a large hardwater lake

In hardwater lakes, calcite precipitation is an important yet poorly understood process in the lacustrine carbon cycle, in which catchment-derived alkalinity (Alk) is both transformed and translocated. While the physico-chemical conditions supporting the supersaturation of water with respect to calcite are theoretically well described, the magnitude and conditions underlying calcite precipitation at fine temporal and spatial scales are poorly constrained. In this study, we used high frequency, depth-resolved (0–30 m) data collected over 18 months (June 2019 – November 2020) in the deeper basin of Lake Geneva to describe the dynamics of calcite precipitation fluxes at a fine temporal resolution (day to season) and to scale them to carbon fixation by primary production. Calcite precipitation occurred during the warm stratified periods when surface water CO2 concentrations were below atmospheric equilibrium. Seasonally, the extent of Alk loss due to calcite precipitation (i.e., [30–42] g C m−2) depended upon the level of Alk in surface waters. Moreover, interannual variability in seasonal calcite precipitation depended on the duration of stratification, which determined the volume of the water layer susceptible to calcite precipitation. At finer timescales, calcite precipitation was characterized by marked daily variability with dynamics strongly related to that of planktonic autotrophic metabolism. Increasing daily calcite precipitation rates (i.e., maximum values 9 mmol C m−3 d−1) coincided with increasing net ecosystem production (NEP) during periods of enhanced water column stability. In these conditions, calcite precipitation could remove as much inorganic carbon from the productive layers as NEP. This study provides mechanistic insights into the conditions driving pelagic calcite precipitation, and quantifies its essential contribution to the coupling of organic and inorganic carbon cycling in lakes.

Species evenness affects algae driven co-metabolism with aquatic plant residues

Understanding the mixed decomposition processes of aquatic plant residues is crucial for evaluating the carbon cycle of lakes. However, the complex effect of species evenness, and especially the algae driving co-metabolism effect in eutrophic lakes are still far from clear. In this study, three dominant aquatic plants (Phragmites australis, Nymphoides peltatum, and Potamogeton malaianus) and algae from the typical eutrophic and shallow Lake Taihu, China, were selected to simulate their mixed decomposition process. The addition of algae accelerated the mass loss of cellulose, hemicellulose, and lignin of aquatic plant residues and increased the total mass loss by 2.29~6.32% in mixed decomposition. The positive co-metabolism effect, with the intensity ranging from 10% to 17%, occurred during the mixed decomposition process. In addition, the positive co-metabolism effect was also found among plant residues during mixed decomposition and the co-metabolism intensity of species evenness mixed decomposition was more than twice as high as that of non-evenness mixed decomposition. The addition of algae during the decomposition of aquatic plant residues altered the stoichiometry of available nutrients and affected the microbial decomposition activity. The abundance of decomposition bacteria, especially Bacteroidetes, was increased and the community structure also changed, as evidenced by a 71% increase in the number of bacteria phylum. As a result, these biogeochemistry processes accelerated the decomposition rates of aquatic plant residues and thus produced the positive co-metabolism effect. Therefore, the co-metabolism effects of mixed decomposition described in this study are prevalent in eutrophication lakes and have important effects on the lake carbon cycle, which need to be considered in future lake management.Graphical

Influence of salinity on the diversity and composition of carbohydrate metabolism, nitrogen and sulfur cycling genes in lake surface sediments.

Exploring functional gene composition is essential for understanding the biogeochemical functions of lakes. However, little is known about the diversity and composition of biogeochemical cycling genes and their influencing factors in saline lakes. In this study, metagenomic analysis was employed to characterize the diversity and composition of microbial functions predicted from genes involved in carbohydrate metabolisms, nitrogen, and sulfur cycles in 17 surface sediments of Qinghai-Tibetan lakes with salinity ranging from 0.7 to 31.5 g L-1. The results showed that relative abundances of carbohydrate-active enzyme (CAZy), nitrogen, and sulfur cycling genes were 92.7-116.5, 15.1-18.7, 50.8-63.9 per 1,000 amino acid coding reads, respectively. The Shannon diversity indices of CAZy and sulfur cycling genes decreased with increasing salinity, whereas nitrogen cycling gene diversity showed an opposite trend. Relative abundances of many CAZy (i.e., carbohydrate-binding module and carbohydrate esterase), nitrogen (i.e., anammox and organic degradation and synthesis) and sulfur (i.e., dissimilatory sulfur reduction and oxidation, link between inorganic and organic sulfur transformation, sulfur disproportionation and reduction) cycling gene categories decreased with increasing salinity, whereas some CAZy (i.e., auxiliary activity), nitrogen (i.e., denitrification) and sulfur (i.e., assimilatory sulfate reduction and sulfur oxidation) gene categories showed an increasing trend. The compositions of CAZy, nitrogen, and sulfur cycling genes in the studied lake sediments were significantly (p < 0.05) affected by environmental factors such as salinity, total organic carbon, total nitrogen, and total phosphorus, with salinity having the greatest influence. Together, our results suggest that salinity may regulate the biogeochemical functions of carbohydrate metabolisms, nitrogen, and sulfur cycles in lakes through changing the diversity and composition of microbial functional genes. This finding has great implications for understanding the impact of environmental change on microbial functions in lacustrine ecosystems.

The dissolved oxygen budget of a small Canadian Shield lake during winter

AbstractDeep‐water hypoxia is an environmental concern in temperate lakes. Seasonal turnover events provide a mechanism for deep‐water oxygenation; however, the lake oxygen budget and mixing dynamics during turnovers are poorly understood. In the present study, the oxygen cycle in a small dimictic lake was investigated from long‐term field measurements supplemented with output from a three‐dimensional numerical model. Photosynthetic production and atmospheric exchange were modeled to predominate during spring and fall turnovers, respectively, contributing 92% (surprisingly) and 8% of the net dissolved oxygen (DO) input to the lake. Of the DO production, 41% occurred under‐ice, with a potential to supply 17% ± 11% of the hypolimnetic DO saturation deficit at spring turnover. The corresponding DO sinks were sediment oxygen demand (− 54%), mineralization (− 33%), and nitrification (− 13%). The watercolumn circulation and stratification during pre‐winter and spring turnover controlled the inter‐annual variability in hypoxia during the following summer. Warm winters (~ 4°C watercolumn leading to rapid summer stratification) and severely cold winters (strong winter stratification with shallow convective mixing in spring) were followed by incomplete spring turnover, whereas, following cold winters (moderate winter stratification and extended convection) turnover was complete. This underscores the connection between winter hydrodynamics and summer water quality in dimictic lakes.

Sediment organic matter compositional changes in a tropical rift lake as a function of water depth and distance from shore

Little is known of modern carbon cycling in East African rift lakes. These large tropical systems with anoxic bottom waters can act as test cases for carbon cycling under future climate change scenarios as well as key sediment repositories for paleolimnology studies and fossil fuel generation. This study is the first to combine stable and radiocarbon isotopic information on bulk sediment and biomarkers (n-alcohols) in an African rift lake by investigating surface sediments collected on a nearshore to offshore transect in northern Lake Malawi. This study is also the first to report radiocarbon content in water column particulate organic, dissolved organic and inorganic carbon from an African rift lake. General surface-sediment trends with increasing water depth were an increase in %TOC, and decreases in grain size, δ13C and C/N. Carbon radioisotope analyses showed that bulk sedimentary organic matter was modern across the transect. Biomarker data indicated a primarily aquatic origin for sedimentary organic matter at offshore sites; terrestrial material dominated the n-alcohol signature closest to the shore. Protokerogen stable isotope signatures were similar, and radiocarbon was somewhat depleted relative to bulk sediment organic matter. As compared to bulk organic matter, lipids were 13C-depleted throughout the sampling transect and 14C-depleted at the most nearshore location. This indicates an aged lipid carbon source and likely significant diagenetic alteration of modern sources prior to deposition in nearshore sediments, perhaps a combination of soil erosion, in-river processing, sediment resuspension and mobilization, and preferential degradation of younger organic matter in the oxic nearshore region.

Variation in Sediment Available-Phosphorus in Dianchi Lake and Its Impacts on Algal Growth.

Sediment phosphorus (P) is an active component of the P cycle in lakes and its availability and movement could play an important role in eutrophication. Sediments from different depths in five representative sites of Dianchi Lake China, i.e., Haigeng, Dounan, Luojiacun, Xinjie, and Kunyang, were studied from January to December to evaluate the spatial and temporal dynamics in available-P and soluble-P and their impacts on algal growth. The results showed that the average sediment available-P and soluble-P were 41.2 mg kg-1 and 0.27 mg kg-1, respectively. Sediment available-P and soluble-P concentrations varied significantly among seasons, sites, and layers, with the following order: surface (0-5 cm) &gt; middle (5-10 cm) &gt; bottom (10-20 cm). The release and transformation characteristics of available-P and soluble-P at the sediment-water interface varied among sites. The Haigeng site, with the most severe algae blooms, had significantly higher average available-P and soluble-P in sediment than other sites. This indicated that phosphorus release and availability were associated with algal growth, and that the sediment surface (0-5 cm) is an important internal source that supports algal growth in Dianchi Lake.

Amino acids as indicators of seasonal variations in organic matter degradation in surface sediments from a shallow lake

Degradation of organic matter (OM) in sediments is a key link in nutrient cycling and sedimentation processes in lakes. The aim of this study was to explore the degradation of OM in surface sediments of a shallow lake (Baiyangdian Lake, China) under seasonal temperature variations. For this, we used the amino acid-based degradation index (DI) and the spatiotemporal distribution characteristics and sources of OM. Sediment OM in the lake mainly originated from freshwater aquatic plants and terrestrial C4 plants. The sediment at some sampling sites was affected by surrounding crops. The organic carbon and total nitrogen contents, and the total hydrolyzed amino acid concentrations in the sediments were highest in summer and lowest in winter. The lowest DI occurred in spring, which indicated that the OM in the surface sediment at this time was highly degraded and relatively stable, and the highest DI occurred in winter, which showed that the sediment was fresh. The water temperature was positively correlated with the organic carbon content (p < 0.01) and total hydrolyzed amino acids concentration (p < 0.05). Seasonal variations in the overlying water temperature had a large effect on OM degradation in the lake sediments. Our results will facilitate the management and restoration of lake sediments that suffer from endogenous release of OM in a warming climate.

Communities of culturable freshwater fungi present in Antarctic lakes and detection of their low-temperature-active enzymes.

We evaluated the diversity and enzymatic activities of culturable fungi recovered from cotton baits submerged for 2years in Hennequin Lake, King George Island, and from benthic biofilms in Kroner Lake, Deception Island, South Shetland Islands, maritime Antarctica. A total of 154 fungal isolates were obtained, representing in rank abundance the phyla Ascomycota, Basidiomycota and Mortierellomycota. Thelebolus globosus, Goffeauzyma sp., Pseudogymnoascus verrucosus and Metschnikowia australis were the most abundant taxa. The fungal community obtained from the biofilm was more diverse and richer than that recovered from the cotton baits. However, diversity indices suggested that the lakes may harbour further fungal diversity. The capabilities of all cultured fungi to produce the extracellular enzymes cellulase, protease, lipase, agarase, carrageenase, invertase, amylase, esterase, pectinase, inulinase and gelatinase at low temperature were evaluated. All enzymes were detected, but the most widely produced were protease and pectinase. The best enzymatic indices were obtained from Holtermanniella wattica (for invertase, esterase), Goffeauzyma sp. (amylase), Metschnikowia australis (protease), Mrakia blollopis (cellulase, pectinase), Pseudogymnoascus verrucosus (agarase, carrageenase) and Leucosporidium fragarium (inulinase). The detection of multiple enzymes reinforces the ecological role of fungi in nutrient cycling in Antarctic lakes, making nutrients available to the complex aquatic food web. Furthermore, such low-temperature-active enzymes may find application in different biotechnological processes, such as in the textile, pharmaceutical, food, detergent and paper industries, as well as environmental application in pollutant bioremediation processes.

Dynamics, distribution, and transformations of mercury species from pyrenean high-altitude lakes

While mercury (Hg) is a major concern in all aquatic environments because of its methylation and biomagnification pathways, very few studies consider Hg cycling in remote alpine lakes which are sensitive ecosystems. Nineteen high-altitude pristine lakes from Western/Central Pyrenees were investigated on both northern (France) and southern (Spain) slopes (1620–2600 m asl.). Subsurface water samples were collected in June 2017/2018/2019 and October 2017/2018 for Hg speciation analysis of inorganic mercury (iHg(II)), monomethylmercury (MMHg), and dissolved gaseous mercury (DGM) to investigate spatial and seasonal variations. In June 2018/2019 and October 2018, more comprehensive studies were performed in four lakes by taking water column depth profiles. Besides, in-situ incubation experiments using isotopically enriched Hg species (199iHg(II), 201MMHg) were conducted to investigate Hg transformation mechanisms in the water column. While iHg(II) (0.08–1.10 ng L−1 in filtered samples; 0.11–1.19 ng L−1 in unfiltered samples) did not show significant seasonal variations in the subsurface water samples, MMHg (<0.03–0.035 ng L−1 in filtered samples; <0.03–0.062 ng L−1 in unfiltered samples) was significantly higher in October 2018, mainly because of in-situ methylation. DGM (0.02–0.68 ng L−1) varies strongly and can exhibit higher levels in comparison with other pristine areas. Depth profiles and incubation experiments highlighted the importance of in-situ biotic methylation triggered by anoxic conditions in bottom waters. In-situ incubations confirm that significant methylation, demethylation and photoreduction extents are taking place in the water columns. Overall, drastic environmental changes occurring daily and seasonally in alpine lakes are providing conditions that can both promote Hg methylation (stratified anoxic waters) and MMHg photodemethylation (intense UV light). In addition, light induced photoreduction is a major pathway controlling significant gaseous Hg evasion. Global warming and potential eutrophication may thus have direct implications on Hg turnover and MMHg burden in those remote ecosystems.

Exploring methane cycling in an arctic lake in Kangerlussuaq Greenland using stable isotopes and 16S rRNA gene sequencing

Lakes are currently responsible for a significant amount of total natural methane emission. Microbial oxidation of methane plays a central role in Arctic carbon cycling, potentially reducing methane emissions from lakes, though little is known about methane cycling in the water column of Arctic lakes. We previously detected surprisingly large enrichments of heavy carbon and hydrogen isotopes of methane in three small lakes in Greenland suggesting unusually efficient methanotrophic communities in these Arctic lakes. Using stable isotope and 16S rRNA gene sequencing we determined carbon and hydrogen isotopes and microbial community composition down the water column of Teardrop lake, under open-water conditions. We found that isotopic values of methane in Teardrop lake were again highly enriched 13C and 2H at 4 m depth with −13.2‰ and −27.1‰ values for carbon and hydrogen isotopes, respectively. Methane concentrations slightly increased at the depth interval with isotope enrichment, not typical of classic methanotrophy. Consistent with isotopic enrichment of the heavy isotopes we detected the highest relative abundance of putative methanotrophs, in particular Methylovulum at 4 m. The highest relative abundance of putative methanogens was detected at 3 m as well as at 5 m. At the same depth interval, temperature and oxidation reduction potential also increase, supporting increased microbial activity within the water column. Based on geochemical and microbial observations, we suggest that the methane cycling in Teardrop lake is decoupled from a traditional depth dependent model where the dominant source of methane is in the anoxic sediments. Instead, methane in the water column is likely from a combination of anoxic sediment, littoral transport and oxic methanogenesis in the mid-water column, and recycling of carbon within the water column is leading to extreme isotope enrichments. Thus, understanding linkages between depth-dependent microbial dynamics and methane biogeochemistry are necessary to constrain the sensitivity of the methane cycle to future climate change.

Eutrophication has a greater influence on floodplain lake carbon cycling than dam installation across the middle Yangtze region

Carbon cycling in shallow floodplain lakes is complex due to variability in delivery of flood-derived allochthonous organic matter (OM). Human activities have potential to significantly modify the carbon balance of lakes by damming which restricts external OM inputs and via eutrophication which can increase the in-lake production of algae and/or aquatic plants. In order to understand how these human activities influence carbon cycling in shallow floodplain lakes over decadal-centennial timescales, we analysed C/N ratios and δ13C from terrestrial plants, catchment soils, aquatic plants and dated sediment cores from six heavily modified lakes in the middle Yangtze floodplain. Submerged macrophytes (−21.4 ± 4.6 ‰) had higher δ13C than C3 plants from the catchment (−26.6 ± 0.6 ‰) and emergent and floating plants (−26.6 ± 4.0 ‰). Increases in sedimentary chlorophyll a (from primary producers) were associated with a decline in sedimentary δ13C in the severely eutrophic Dongting, Luhu, Wanghu and Poyang Lakes after the 1980s. In contrast, sedimentary δ13C increased in Honghu and Futou Lakes which have abundant submerged macrophytes. The timing and scale of sedimentary δ13C changes indicated stronger responses to eutrophication than damming, with eutrophication responses ranging from a macrophyte proliferation to the dominance of phytoplankton.

Concentrations of dissolved organic matter and methane in lakes in Southwest China: Different roles of external factors and in-lake biota

Many factors have been reported to affect material cycling in lakes, but the combined and cascading impacts of external environmental factors and in-lake biota on lake carbon cycling are poorly understood. We elucidated the influencing pathways of geoclimatic factors, lake morphometry, land-use type, chemical and physical factors, and biological taxa (phytoplankton and macroinvertebrates) on the concentrations of two important components of carbon cycling, i.e., dissolved organic matter (DOM) and methane (CH4) based on datasets from 64 plateau lakes in Southwest China. Partial least squares path modelling (PLS-PM) indicated that (1) geoclimatic factors influenced DOM and CH4 by affecting land use and lake physical factors (e.g., water temperature), (2) lake morphometry (water depth and lake area) had a direct and great negative effect on the CH4 concentration related to the production and oxidation of CH4 and affected phytoplankton and macroinvertebrates by influencing chemical and physical factors, (3) land-use type affected DOM and CH4 concentrations in both direct and indirect ways, (4) terrestrial humic-like DOM was mainly discharged from forestland and also affected by macroinvertebrates, while the impacts of agricultural and construction land on autochthonous DOM and CH4 concentrations mainly occurred by changing nutrients and then the aquatic biota. Moreover, changes in aquatic biota, primarily affected by water quality, influenced DOM spectral properties, and the two biotas affected DOM and CH4 concentrations differently. Phytoplankton, especially cyanobacteria contributed to (protein-like and humic-like) DOM in both direct and indirect ways related to eutrophication, whereas macroinvertebrates influenced DOM possibly by utilization, bioturbation, and microbial decomposition of feces according to their different relationships with DOM spectral indices. Additionally, CH4 production can be enhanced by DOM accumulation, and the significant positive correlations of CH4 concentrations with protein-like DOM and biological index indicate that autochthonous DOM may play an important role for the CH4 production. Our findings contribute to the understanding of lake carbon cycling under natural conditions and anthropogenic disturbances.

Late Miocene reorganization of lake hydrological systems on the northern Tibetan Plateau linked to topographic growth

The hydrological cycles of lakes on the Tibetan Plateau (TP) have had profound impacts on the climatic and environmental evolution of the Asian interior and hence they are crucial for the well-being of the large human population of this region. The late Miocene is regarded as the most recent interval when the TP was extensively occupied by large paleolakes. However, it is unclear when and how these mega paleolakes shrank and the environment evolved into its present domination by desert and semi-desert. To address these issues, we conducted detailed analyses of diffuse reflectance spectroscopy, sedimentology, paleomagnetic-based tectonic rotation, and biogeochemistry of a Middle to Late Miocene sedimentary sequence in the Xining Basin in the North-eastern (NE) TP, supplemented by a spatiotemporal comparison of our results with equivalent records from adjacent regions. The results reveal a clear transition of the lacustrine system in the Xining Basin at ∼ 11 Ma, characterized by decreased water level and an increase in the oxidation state of the depositional environment. Combined with a summary of sedimentary evidence from seven different basins in the NE TP, we propose that a fundamental reorganization of lake hydrological systems occurred in the NE TP at ∼ 11 Ma. This reorganization was synchronous with tectonic deformation and topographic growth in the NE TP, as revealed by our new tectonomagnetic and other available tectonic evidence. Therefore, tectonic activity—rather than changes in climate or solar insolation, as previously proposed—was the principal factor responsible. This hydrological reorganization was of profound significance for the regional hydrological cycle and the climatic and ecological environment of Asia, because the elevated topography prevented the NE TP from regaining its Middle Miocene paleohydrological configuration.

Modelling the transport of sloughed cladophora in the nearshore zone of Lake Michigan

The invasion of dreissenid mussels has profoundly altered benthic physical environments and whole-lake nutrient cycling in the Great Lakes over the past several decades. The resurgence of the filamentous green alga Cladophora appears to be one of the consequences of this invasion. Sloughed Cladophora deteriorates water quality, fouls recreational beaches, and may contribute to outbreaks of avian botulism, which have been especially severe in the Sleeping Bear Dunes National Lakeshore (SLBE) region of Lake Michigan. To help determine the fate of sloughed Cladophora, a Lagrangian particle trajectory model was developed to track the transport of Cladophora fragments in the nearshore zone based upon a physical transport-mixing model. The model results demonstrate that the primary deposition sites of sloughed Cladophora within the SLBE region are mid-depth sites not far away from their initial growth area. Because of high algae production in the nearshore waters and limited exchange between the inner and outer bay, the shoreline beach of Platte Bay appears to be particularly vulnerable to fouling, with overall three times as many accumulated particles as those along the Sleeping Bear Bay and Good Harbor Bay. The results of this model may be used to guide regional environmental management initiatives and provide insights into the mechanisms responsible for avian botulism outbreaks. This model may also inform the development of whole-lake ecosystem models that account for nearshore-offshore interactions.

Inland lake temperature initialization via coupled cycling with atmospheric data assimilation

Abstract. Application of lake models coupled within earth-system prediction models, especially for predictions from days to weeks, requires accurate initialization of lake temperatures. Commonly used methods to initialize lake temperatures include interpolation of global sea-surface temperature (SST) analyses to inland lakes, daily satellite-based observations, or model-based reanalyses. However, each of these methods have limitations in capturing the temporal characteristics of lake temperatures (e.g., effects of anomalously warm or cold weather) for all lakes within a geographic region and/or during extended cloudy periods. An alternative lake-initialization method was developed which uses two-way-coupled cycling of a small-lake model within an hourly data assimilation system of a weather prediction model. The lake model simulated lake temperatures were compared with other estimates from satellite and in situ observations and interpolated-SST data for a multi-month period in 2021. The lake cycling initialization, now applied to two operational US NOAA weather models, was found to decrease errors in lake surface temperature from as much as 5–10 K vs. interpolated-SST data to about 1–2 K compared to available in situ and satellite observations.