Lake States Research Articles

A significant loop of lake sedimentation state links catchment eco‐surroundings and lake biogenic regime shifts

AbstractAs an important destination for upstream materials and element accumulation, lake sediments hold a multitude of contextual information about climatic changes and anthropogenic disturbances. However, understanding the lake sedimentation state to link catchment pressures and biogenic regime shifts remains challenging. To address this, research was conducted on the lake sedimentation state, including the dynamics, catchment drivers, effects on biogenic regimes, and responses to typical historical events using nine sediment cores from Dongting Lake, China, a typical global priority ecoregion. Three transitions of lake sedimentation state were distinguished over the century (1937, 1968, and 1993), whereby hydrologic dynamics and land‐use changes in the watershed were the direct drivers with relative contributions of 16.30% and 14.56%, respectively. Lake sedimentation state and organic matter inputs not only preceded sediment biogenic elements at the shift time but also exhibited nonlinear trigger effects on biogenic element contents (R2 = 0.47, p < 0.01), which promoted an increase in sediment biogenic element burial rates. Rate of change analysis indicated that intensive human activities altered the relationship between the sedimentation state and biogenic regime shift, thus revealing the response to anthropogenic events in the catchment. Pathways quantified by the partial least squares path model established the link between watershed attributes and lake biogenic properties via the lake sedimentation state. Our findings revealed a cascading linkage among catchment eco‐surroundings, lake sedimentation states, and biogenic regime shifts. The research further provided insights into driver‐response relationships in lake‐catchment systems.

Shell morphometric variation of the freshwater snail, Melanoides tuberculata (Müller, 1774) across the seven lakes of San Pablo City, Laguna, Philippines

The seven maar lakes of San Pablo City in Laguna Province constantly face natural and anthropogenic disturbances that affect the water quality and habitat condition of various aquatic species, including freshwater gastropods. Freshwater gastropods exposed to multiple biotic and abiotic stressors are known to alter their shells as a form of ecomorphological adaptation. However, there are no studies yet regarding shell variations across these lakes as subjected to perturbations in water quality. The shell morphometrics of the common native freshwater snail, Melanoides tuberculata, distributed across the seven lakes was examined to address this research gap. Various water parameters were measured prior to collection of snails along the littoral zones. One hundred ninety-seven M. tuberculata shells were subjected to linear and geometric morphometrics. The biggest shells were sampled in Lake Sampaloc while the smallest was in Lake Bunot. Centroid size also contributed significantly to the shell shape variation. Generalized linear mixed modeling results suggest water temperature had the most significant effect on shell shape change. Shells exposed to colder waters exhibited wider and shorter whorls with constricted apertures, whereas those collected in warmer waters have slender and slightly taller whorls with expanded apertures. The present study demonstrated the possible plasticity of M. tuberculata shells which could serve as important information in understanding the habitat conditions of the maar lakes of San Pablo City.

Towards Tree Species Preservation: Protecting Ash Amidst the Emerald Ash Borer Invasion in the Northeast

Abstract The introduced emerald ash borer (EAB) represents the costliest invasive forest insect in US history, causing significant mortality of ash species across much of eastern North America as well as in Colorado and Oregon. Few surviving overstory ash trees exist in areas first invaded by EAB, such as the Lake States region; however, forests with healthy, mature ash remain in recently invaded regions, such as the northeastern United States. Given the importance of ash to cultural lifeways of Indigenous peoples and the ecology and economies of working forest lands, there is growing interest in applying protection measures to maintain ash in forested settings. We further develop our call for species preservation by presenting Indigenous and Western science case studies of ongoing efforts to mitigate the impacts of EAB, illustrating specific applications of these strategies for meeting different preservation goals in lowland and northern hardwood forests in northeastern North America. Study Implications: The introduced emerald ash borer (EAB) threatens to functionally eliminate ash species from large portions of the United States. Although the impacts of EAB are now widespread in many areas, portions of the United States, such as the Northeast, still contain forests with healthy, mature ash. This presents a unique opportunity to apply the integrated pest management strategies and knowledge gained from other invaded regions to preserve the cultural and ecological values provided by ash in the forest. Multistakeholder partnerships built around preserving the cultural and ecological values of ash have provided a powerful approach for sustaining ash into the future.

Plankton community composition in mountain lakes and consequences for ecosystem services

Mountain lakes provide a variety of ecosystem services (ES) such as water, habitat, recreation and aesthetic values. However, global change pressures increasingly affect lake ecosystems, necessitating suitable indicators to monitor changes in ES so that targeted protection measures can be developed. Limnological data in ES assessments are mostly limited to transparency for evaluating recreational and aesthetic values, but to date, limnological parameters related to plankton community composition have rarely been associated with ES. This study therefore aims to link limnological parameters to potential ES provision using widely applied standard parameters as well as metabarcoding based on 16S/18S rDNA high-throughput sequencing (HTS) to obtain information on phytoplankton communities. We collected 10 limnological parameters of 26 mountain lakes in the European Alps (1,489 to 2,922 m a.s.L.) and related them to six ES identified by local stakeholders. Our results generally indicate low to moderate concentrations of total phosphorus and chlorophyll a and high Secchi depths. Therefore, the trophic state of the majority of lakes was classified as ultra- (n = 6) or oligotrophic (n = 18), while two lakes were assigned to oligo-mesotrophic conditions. The phytoplankton functional groups were generally in agreement with the trophic state, i.e., we observed a decreasing relative abundance of mixotrophic vs. phototrophic phytoplankton with increasing trophic state. With regard to the ES, our results indicate that most lakes had high potential in providing multiple ES. Only six of the 26 lakes were inhabited by larger cladocerans, indicating reduced food availability for newts and thus less potential for the maintenance of populations and habitats. The high transparency of most lakes indicated a high potential for aesthetic and recreational values, whereas a few lakes with a greater proportion (>30%) of phototrophic phytoplankton manifested reduced water clarity, probably due to eutrophication. Our findings suggest that a deterioration of ecological conditions in mountain lakes may negatively affect future ES provision. Therefore, it will become increasingly important to protect pristine lakes, with data on plankton community composition potentially providing useful guidance for deciding which lakes should receive priority for protection measures.

Green algae outcompete cyanobacteria in a shallow lake, Longhu Lake

Abstract Green algae are natural competitors of cyanobacteria, but we still do not know why green algae have a competitive advantage in shallow lakes. In this study, we used qPCR to quantify and monitor green algae and cyanobacteria in Longhu Lake. Our results showed that green algae were dominant in Longhu Lake, accounting for 71.80–80.31%. The temporal and spatial dynamics of green algal blooms were consistent with that of total organic nitrogen (TON), indicating that organic nitrogen may be the key trigger of green algal blooms. Nitrogen and phosphorus were excessive, and the peak of ammonia nitrogen occurred during the blooms, implying that ammonia nitrogen may be one of the important factors stimulating green algal blooms. Spearman correlation analysis and RDA analysis showed that green algae and cyanobacteria were positively correlated with water temperature, TON, and ammonia nitrogen, indicating that they have similar favorable growth conditions in Longhu Lake. Our results indicated that the combined effects of elevated water temperature, excessive nitrogen and phosphorus, non-stratification, and short water retention time could favor the competitive dominance of green algae in Longhu Lake. The findings here improve our understanding of the competition between green algae and cyanobacteria in shallow lakes.

Таксономический состав и экологические особенности фитопланктона озера Островито (Псковская область)

Lake Ostrovito is located in the Pskov region and belongs to the basin of the Belyavitsa River, a tributary of the Velikaya River. The lake covers an area of 1.1 km2, with a maximum depth of 16.0 m and presents an important recreational and fishery facility in the Pskov region, constantly experiencing anthropogenic impact due to the close proximity of villages and recreation centers. Monitoring works have been conducted to assess the ecological state of this lake. The aim of the work was to study the species richness, quantitative characteristics and ecological features of phytoplankton of Lake Ostrovito in the autumn period of 2020. The study identified 65 species and intraspecific phytoplankton taxa from 7 phylums. The basis of the floral complex was made up of representatives of the departments Chlorophyta, Bacillariophyta and Cyanobacteria. The analysis of the floral similarity of phytoplankton communities of the studied lake stations using the Sierensen-Chekanovsky index showed their average degree of similarity (from 43.3 to 58.1%). The values of the abundance of autumn phytoplankton varied from 127 thousand cells/l to 488 thousand cells/l (the average number is about 290 thousand cells/l). Phytoplankton biomass ranged from 68.7-110 micrograms/l (average biomass – 96.1 micrograms/l). The average value of the Milius trophic index was 21.1, which indicates an oligotrophic type of reservoir. According to ecological and geographical analysis, freshwater widespread planktonic forms of microalgae predominated in Lake Ostrovito, preferring slightly alkaline waters and indicating moderate pollution of the reservoir.

Post-Little Ice Age glacial lake evolution in Svalbard: inventory of lake changes and lake types

AbstractThe rapid formation of glacial lakes is one of the most conspicuous landscape changes caused by atmospheric warming in glacierised regions. However, relatively little is known about the history and current state of glacial lakes in the High Arctic. This study aims to address this issue by providing the first inventory of glacial lakes in Svalbard, focusing in particular on the post-Little Ice Age evolution of glacial lakes and their typology. To do so, we used aerial photographs and satellite imagery together with archival topographic data from 1936 to 2020. The inventory comprises the development of 566 glacial lakes (146 km2) that were still in direct contact with glaciers during the period 2008–2012. The results show a consistent increase in the total area of glacial lakes from the 1930s to 2020 and suggest an apparent link between climatic and geological factors, and the formation of specific lake dam types: moraine, ice, or bedrock. We also detected 134 glacial lake drainage events that have occurred since the 1930s. This study shows that Svalbard has one of the highest rates of glacial lake development in the world, which is an indicator of the overall dynamics of landscape change in the archipelago in response to climate change.

Theoretical efficiency of the pulverising aerator – A case study based on Lake Swarzędzkie

Lakes can be restored by the aeration method with the use of wind driven pulverising aerators. The method allows for moderate oxygenation of hypolimnion waters and it may be part of an integrated surface waters restoration system. The paper attempts to use the author’s method of maximum wind speeds to assess the volumetric flow of water through the aerator pulverisation mechanism. The study was conducted in 2018 in windy conditions of Lake Swarzędzkie. The introduction to the paper includes the characteristic of the lake and discusses the construction and operation of the wind driven pulverising aerator. Based on the maximum wind speed model, the theoretical capacity of the machine was calculated, which in the conditions of Lake Swarzędzkie was less than 111,500 m3 per year. Based on maximum wind speeds, the method of assessing the efficiency of the wind driven pulverising aerator is suitable for determining the volumetric flow rate of the pulverisation unit. This can significantly facilitate the planning of water reservoir restoration.

Seawater sulphate heritage governed early Late Miocene methane consumption in the long-lived Lake Pannon

Sulphate deficiency makes lake environments a key source of atmospheric methane because sulphate-driven anaerobic oxidation of methane (SD-AOM) is hindered. Miocene to Pliocene Lake Pannon was the largest European lake, although the extent of its methane production remains unclear. When sulphate is available, SD-AOM occurs commonly in anoxic sediments and is recorded by authigenic iron sulphides. Here we identify abundant tubular pyrite and greigite aggregates from Lake Pannon sediments, which record brackish early lake conditions at ~11.3 Ma. The iron sulphides are morphologically similar to those reported elsewhere from methane seep and gas hydrate environments. Microscale sulphur isotope analysis and multiple sulphur isotope patterns of iron sulphides, and elevated sedimentary Ba/Al and Mo/Al ratios, are consistent with their derivation from SD-AOM under marine conditions. These results indicate substantial methane consumption in early Lake Pannon, and that sulphate was the dominant oxidant for AOM, which reduced the release of sedimentary methane to the atmosphere. SD-AOM signals archived by iron sulphides are valuable for evaluating methane consumption in lacustrine sediments.

Evaluation of survival and cost to harvestable age of stocked fall fingerling walleye (Sander vitreus) in Northern Wisconsin Lakes

Walleye Sander vitreus are culturally and recreationally important in Wisconsin, USA and have experienced population declines in some lakes due to reduced natural recruitment. In 2013, the Wisconsin legislature implemented the Wisconsin Walleye Stocking Initiative, a statewide rehabilitation effort to help declining walleye populations through increased stockings of fall fingerling walleye (150–250 mm). Our objectives were to: (1) test for differences in natural mortality (M) of stocked walleye among stocking densities (12.4, 24.7, 37.1 fish/ha), lake recruitment status (some natural recruitment or no natural recruitment), and lake conductivity (surrogate for lake productivity); (2) estimate cost to harvestable age (i.e., age-4); and (3) compare predicted adult walleye abundance among lakes across various stocking densities in relation to Wisconsin walleye adult abundance standards (i.e., naturally reproducing population ≥7.4 adults/ha, “fishable” population ≥ 3.7 adults/ha). Fall fingerling stocked walleye M was lowest in lakes with some natural recruitment, with medium-low and high conductivities, and stocked at 24.7 and 37.1 fish/ha, respectively. Using a mixed-effects model, fall fingerling M was negatively related to stocking density but not lake recruitment status or conductivity. No conditions resulted in the naturally reproducing population density standard to be met after multiple stockings. Two to four stocking events were required to achieve the “fishable” population standard, depending on lake conditions. When estimating cost to harvestable age, lakes stocked at 24.7 fish/ha generally had the best survival resulting in the lowest cost to age-4 ($17.70 - $35.41/fish). Lakes stocked at 12.4 fish/ha had the highest cost to age-4 ($91.17 - $182.34/fish). Juvenile walleye survival from age-0 to age-1 was dependent on lake conductivity and recruitment status, with lakes stocked at 24.7 fish/ha providing the lowest cost to age-4. Our results may inform science-based decision making and best-case scenario stocking rates to increase the probability of reestablishing walleye natural recruitment.

Do submerged macrophyte species influence crustacean zooplankton functional group richness and their resource use efficiency in the low-light environment?

During the high grazing of epiphytic zooplankton in submerged macrophyte beds, the changes in crustacean zooplankton functional groups are crucial for stabilizing a clear water state in shallow lakes. However, submerged macrophytes often experience low-light stress due to many ecological processes. It is unclear whether submerged macrophytes alter the zooplankton functional group and their resource use efficiency in the low-light environment. We conducted two mesocosm experiments involving the treatments of low-light and submerged macrophyte species (Vallisneria natans and Potamogeton maackianus). The results show that abiotic factors (e.g., light) were the most important variables in explaining the change in the zooplankton community. Specifically, zooplankton functional group (i.e., pelagic species, plant-associated species, and substrate scrapers) richness and zooplankton species diversity decreased with the decreasing light intensity, especially for low substrate scraper abundance. In addition, structural equation models showed that low-light stress reduced zooplankton resource use efficiency by reducing zooplankton functional group richness and species diversity. Compared to species diversity, zooplankton functional group richness had a greater influence on their resource use efficiency (Zp/Chl-a) in the low-light environment. Our results suggest that the low-light stress reduced zooplankton resource use efficiency by changing their functional group richness. Moreover, the abundance of substrate scrapers shaken from V. natans was higher than that from P. maackianus. Therefore, submerged macrophyte species influence crustacean zooplankton functional group richness and their resource use efficiency in the low-light environment. Selecting appropriate aquatic plant species to assure the high diversity of zooplankton should be considered when conducting lake restoration using submerged macrophytes.

Uncertainty in projections of future lake thermal dynamics is differentially driven by lake and global climate models.

Freshwater ecosystems provide vital services, yet are facing increasing risks from global change. In particular, lake thermal dynamics have been altered around the world as a result of climate change, necessitating a predictive understanding of how climate will continue to alter lakes in the future as well as the associated uncertainty in these predictions. Numerous sources of uncertainty affect projections of future lake conditions but few are quantified, limiting the use of lake modeling projections as management tools. To quantify and evaluate the effects of two potentially important sources of uncertainty, lake model selection uncertainty and climate model selection uncertainty, we developed ensemble projections of lake thermal dynamics for a dimictic lake in New Hampshire, USA (Lake Sunapee). Our ensemble projections used four different climate models as inputs to five vertical one-dimensional (1-D) hydrodynamic lake models under three different climate change scenarios to simulate thermal metrics from 2006 to 2099. We found that almost all the lake thermal metrics modeled (surface water temperature, bottom water temperature, Schmidt stability, stratification duration, and ice cover, but not thermocline depth) are projected to change over the next century. Importantly, we found that the dominant source of uncertainty varied among the thermal metrics, as thermal metrics associated with the surface waters (surface water temperature, total ice duration) were driven primarily by climate model selection uncertainty, while metrics associated with deeper depths (bottom water temperature, stratification duration) were dominated by lake model selection uncertainty. Consequently, our results indicate that researchers generating projections of lake bottom water metrics should prioritize including multiple lake models for best capturing projection uncertainty, while those focusing on lake surface metrics should prioritize including multiple climate models. Overall, our ensemble modeling study reveals important information on how climate change will affect lake thermal properties, and also provides some of the first analyses on how climate model selection uncertainty and lake model selection uncertainty interact to affect projections of future lake dynamics.

Development of macroinvertebrate based multimetric index for ecological health monitoring in Lake Hawassa, Ethiopia

Little information is available on the use and applicability of biotic indices in aquatic resource conservation and management in Eastern Africa, especially in lentic ecosystems. The aim of this study was to develop a macroinvertebrate multimetric index (MMIH) to assess the ecological condition of Lake Hawassa. Sampling sites were clustered based on percentage disturbance score (PDS) and categorized into minimally (three sites), moderately (three sites) and highly disturbed (three sites). Physicochemical and invertebrate sampling was done at these clustered sites along the lakeshore area from February to November 2015 and 2016. Out of a total of 35 macroinvertebrate candidate metrics, ten core metrics were selected based on redundancy analysis, metrics response to environmental parameters, percent discriminatory efficiency (%DE) and box and whisker plots, and incorporated in the development of MMIH. The developed MMIH index performed well and showed a clear demarcation between the reference and non-reference sites and between the three-disturbance levels. The validation of the MMIH index performed well in discriminating the independent data sets taken from Lake Hawassa and L. Ziway. Besides, it also showed a strong but inverse relation with PDS (R2 = 0.91, P = 0.0003). Hence, in a lentic ecosystem, this index should be considered as a starting point in terms of lake bio-assessment in Ethiopia, but additional data in all ecoregions of the country are necessary to determine the long-term reliability and usefulness of the MMIH. In the short-term, this index will provide resource managers and aquatic environmentalists with a tool to assess the ecological condition of freshwater lakes.

Water Quality and Microbiological Assessment of Burullus Lake and Its Surrounding Drains

Burullus Lake, which is the second-largest coastal lagoon in Egypt, is deteriorating due to nutrient enrichment and pollutant loading. The study aims to assess the lake’s water quality using water quality indices and microbiological assessment. Surface water samples were collected from Burullus Lake in winter and summer, as well as samples from drains that discharge waste into the lake. Most lake stations are classified in the marginal category based on the water quality index (WQI). Dissolved oxygen, ammonia, copper, and cadmium have the greatest impact on WQI, reflecting pollution loads. Based on the contamination index, heavy metal classification results ranged from “lowly polluted” to “highly polluted.” According to the Nemerow Index, human activity has significantly impaired the ecology of the lake and surrounding drains through copper and cadmium pollution. The fecal coliform/fecal streptococci ratio was less than 0.6 in lake water samples, suggesting fecal contamination from domesticated animal wastes. Drain water contaminated with fecal streptococci indicated frequent contamination. Several drains allow a significant amount of effluent, including high amounts of pesticides and fertilizers, to enter the lake, causing serious metal and microbiological pollution Dredging and deepening the inlet link between the lake and Mediterranean Sea have had a positive impact on water quality. However, there are still other options for improving the lake’s health. Therefore, it is recommended to routinely check Burullus Lake’s water quality and its surrounding drains to keep track of its condition and assess any improvement efforts’ effectiveness.

Seasonal Dynamics of Phytoplankton Population of Ramadugu Lake in Nizamabad District Telangana, India

Phytoplanktons are one of the smallest and the most plentiful organisms ranging from unicellular to multicellular forms. These organisms play a vital role in aquatic ecosystems. Algae being photoautotrophs take part in photosynthesis process, they form the food base for other organisms living in lakes, reservoirs, ponds, streams and oceans. Lakes are very important water resources which are used in daily life for several purposes. Majority of fresh water lakes showed distinct seasonal variation in phytoplankton abundance. The primary objective of this paper is to highlight the current status and to provide a quantitative record of the seasonal changes of phytoplankton and to examine their distribution and diversity in relation to environmental gradients of the Ramadugu lake which is located in Ramadugu village of Nizamabad district, Telangana. The present work was carried out to identify the fresh water algal flora and its diversity for a period of one year from January 2018 to December 2019 in different seasons. Water samples were collected seasonally over three seasons – March to June(summer), July to october(Monsoon) and November to February(winter) from selected four sampling stations of lake. The algal forms were identified by using various keys. Mainly four major algal groups were identified in Ramadugu lake throughout the study period. They are Chlorophyceae, Bacillariophyceae, Cyanophyceae and Euglenophyceae. Seasonal variations were observed in the presence and density of various algae. The density of diatoms are high in winter season indicates that lake water is unpolluted and good to support life. The lake water is used for irrigation and pisciculture but not suitable for drinking purpose.

Paleohydrologic history of pluvial lake San Agustin, New Mexico: Tracking changing effective moisture in southwest North America through the last glacial transition

Paleoclimate records across the Intermountain West region of North America show significant regional variation in timing and magnitude of wet conditions that accompanied the last glacial-interglacial transition. To understand the climate controls on paleohydrologic change, well-dated records are needed across the region. The Plains of San Agustin (New Mexico, USA) is a closed-basin watershed of the American Southwest influenced by both winter westerly and summer North American Monsoon precipitation. The flat valley floors of the Plains contain lake and groundwater discharge deposits that record multiple periods of past wet climate. We present a record of hydroclimate for the past 26,000 years based on radiocarbon, U–Th series, and OSL dating of these deposits and stratigraphic correlation across the three sub-basins of the lake system. We find that two major lake oscillations occurred, coincident with the global Last Glacial Maximum (∼23–18 ka) and with Heinrich Stadial 1 (∼17–14 ka). The LGM lake cycle created a deep lake in the lowermost sub-basin, fed by marsh/lake overflow in the upper sub-basins. The Heinrich Stadial 1 wet interval attained the highest recorded lake level between ∼17.0 and 15.3 ka, merging the lower two sub-basins into one lake. Both lake cycles agree well in timing and magnitude with other lake-based records from the southwestern U.S., supporting previous interpretations that a south-shifted cool season storm track brought a dipole-like pattern of enhanced moisture to the southwest at the expense of drier conditions in the northwest during the LGM and deglaciation. A transition from lake to groundwater discharge conditions followed during the Bølling-Allerød (14.7–12.9 ka) across the study area. Wet meadows prevailed in the lower sub-basin during the Younger Dryas (12.9–11.7 ka), with marsh and open lake conditions in the upper and middle sub-basins, respectively. During the early Holocene, discrete wet intervals are recorded by ages for wet meadow deposits in all sub-basins with centennial-millennial frequency at 9.9, 8.8, 8.2 ka. These events agree well with other Intermountain West records showing wetter-than-present conditions prior to 8 ka. Two additional wet periods, centered at 6.8 and 5.4 ka, occurred during the driest known interval of the middle Holocene, and likely were partly supported in the Plains of San Agustin by summer moisture associated with the peak strength of the North American Monsoon. Our record highlights that both winter and summer moisture support water resources in New Mexico watersheds.

Ecological assessment of pit lakes in Raniganj, India: Application of different indices and multivariate statistics

ABSTRACT Coal mine generated open pit lakes are well distributed in Raniganj coal field area, West Bengal, India. This paper screened out ecological state macrophyte index (ESMI), water quality index (WQI) and multivariate statistical methods to assess the ecological status of four pit lakes, Nagrakonda, Joyalbhanga, Dalurbandh, and Kumardihi. Seven water quality parameters (pH, total dissolved solids, dissolved oxygen, Secchi depth nitrate, chloride, and phosphate) and six sediment quality parameters (pH, organic carbon, bulk density, particle density, available nitrogen and phosphorus) were analyzed for one year on a monthly basis from four pit lakes. The abundance and diversity of aquatic macrophytes were also analyzed. In the studied pit lakes, water and sediment quality variables showed significant spatial variation. WQI showed that the water quality in all pit lakes was good and according to ESMI these lakes were categorized into good ecological status. The results of this study indicated the values of water quality and macrophyte based indices highlighted the ecological condition of the pit lakes of the study sites thus should be considered it as reliable tool for assessing of the ecological status of any wetlands.

Fecal bacteria in coastal lakes: An anthropogenic contamination or natural element of microbial diversity?

The effects of multiple stressors (salinity, temperature, nutrient and light availability or human activities) on the abundance of FIB (Escherichia coli and Enterobacteriaceae) were studied in nine lakes on the southern Baltic coast. Monitoring also included physicochemical factors and land use in the catchment. The results showed that FIB is a natural component of microbial community in coastal lakes, with its abundance varying temporally and spatially. The key factors predicting the abundance of E. coli and Enterobacteriaceae are the availability of ammonia nitrogen and water temperature. Regardless of the degree of connection with the sea, the sanitary condition of coastal lakes deteriorates during the summer months. Although agricultural use and residential development do not significantly affect fecal bacteria counts (PLS-R model), human pressure on the sanitary condition of lakes increases seasonally and is limited to the vicinity of tourist sites. The degree of contact with seawater regulates the size of the microbial community, but is not a factor that directly affects the presence of E. coli in the microbial community in coastal lakes. Monitoring the sanitary conditions of these ecosystems using sensitive, rapid survey methods based on hydrochemical and microbiological inventories, supported by GIS, is important for public health.

Evaluation and comparison of the benthic and microbial indices of biotic integrity for urban lakes based on environmental DNA and its management implications

With the intensification of human disturbance in urban lakes, the loss of eukaryotic biodiversity (macroinvertebrates, etc.) reduces the accuracy of the index of biotic integrity (IBI) assessment. Therefore, how to accurately evaluate the ecological status of urban lakes based on IBI has become an important issue. In this study, 17 sampling sites from four lakes in Wuhan City, China were selected to analyze the composition and diversity characteristics of benthic and microbial communities and their relationship with environmental factors based on eDNA high-throughput sequencing, and compare the application effects of the benthic index of biotic integrity (B-IBI) and the microbial index of biotic integrity (M-IBI). Canonical correspondence analysis showed that the key environmental factors affecting benthic family/genus composition were temperature, conductivity, total phosphorus (TP), and total nitrogen (TN). Redundancy analysis showed that pH, TP, conductivity, and ammonia nitrogen had the greatest impact on microbial phyla/genera. After screening, four and six core metrics were determined from candidate parameters to establish B-IBI and M-IBI. The B-IBI evaluation results showed that healthy, sub-heathy, and poor accounted for 58.8%, 35.3%, and 5.9%, respectively, in the sites. The results of the M-IBI evaluation showed that 29.4% of the sites were healthy, 47.1% were sub-healthy, and 23.5% were common. M-IBI was positively correlated with water quality (r = 0.74, P < 0.001), whereas B-IBI was not. Further results showed that M-IBI was negatively correlated with the relative abundance of bloom-forming cyanobacteria Planktothrix (r = -0.54, P < 0.05). Therefore, M-IBI is more sensitive than B-IBI and can better reflect the actual water pollution status. This study can provide a new perspective for ecological assessment and management of urban lakes strongly disturbed by human activities.

Buffering capacity of submerged macrophytes against nutrient pulses increase with its coverage in shallow lakes

Submerged macrophytes can improve water quality and buffer the effects of external nutrient loading, which helps to maintain a clear-water state in shallow lakes. We constructed 12 large enclosures with contrasting coverages (treatments) of submerged macrophytes (SMC) to elucidate their buffering capacity and resilience to nutrient pulses. We found that aquatic ecosystems with high SMC had higher buffering capacity and resilience, vice versa, i. e, the enclosures with high SMC quickly buffered the nutrient pulse and rebounded to clear-water state after a short stay in turbid-water state dominated by algae, while the treatments with low SMC could not fully buffer the pulse and rebound to clear-water state, and they slowly entered the transitional state after staying in turbid-water state. This means that the enclosures with high SMC had a better water quality than those with low SMC, i.e., the levels of nutrients and Chl-a were lower in the treatments with high plant coverage. In addition, plant coverage had a significantly positive buffering effect against nitrogen and phosphorus pulses, i.e., the nutrient concentrations in the treatments with high SMC took shorter time to return to the pre-pulse level. Overall, our results evidenced that the higher that the SMCs is, the better is the water quality and buffering capacity against nutrient pulses, i.e. the more stable is the clear-water state. However, low SMC may not be able to resist the impact of such strong nutrient pulse. Our results provide reference and guidance for water pollution control and water ecological restoration.