Floristic and taxonomic notes on Najas (Hydrocharitaceae) in Argentina

Urban lakes represent the most extensive water bodies in cities and provide blue ecosystem services, by retaining pollutants, offering cultural services, and mitigating climate change. Human activities threaten to decrease the supply of ecosystem services associated with urban lakes. Exorheic lakes play an essential role in reducing and changing the characteristics of pollutants and organic matter along the environmental continuum. This study aims to gain further understanding on the distribution and fate of organochlorine pesticides (OCPs) in relation to fluorescent dissolved organic matter (DOM) within an exorheic lake system, located along Colentina river, Bucharest. Results indicated a historical usage of HCHs, which were present in lake water and sediment samples, in concentrations exceeding the regulatory limits, with potential eco-toxicity on aquatic biota. Decades of intense applications along the river, before OCPs ban, led to their accumulation in sediments and their re-mobilization, each year, after the lakes were drained, dredged, and refilled. Fluorescence measurements revealed that DOM accumulated in certain lakes due to wastewater discharges, and surface runoff, but decreased towards the end of the exorheic lakes through dilution, sedimentation, and biodegradation. The results also showed that fluorescent DOM may have a substantial impact on OCPs cycle in urban lakes and may help to determine the conditions and effectiveness of removing OCPs from water and sediments. These issues contribute to the decrease of ecosystem services supply associated with urban lakes, having multiple hidden consequences on the urban environment.

Chlorophyll-nutrient relationship changes with lake type, season and small-bodied zooplankton in a set of subtropical shallow lakes

Effects of nitrogen and phosphorus on phytoplankton composition and biomass in 15 subtropical, urban shallow lakes in Wuhan, China

Lake restoration in developing economies, particularly in the tropics, is a major challenge given the severe levels of pollution from untreated wastewater and the warm climate conducive to microbial and algal growth. Restoration goals are often ill-defined or unachievable. Here we describe the successes that can be achieved through a control, compared with intervention case study of the two urban lakes in Bengaluru, India, one of the world's largest and fastest growing mega-cities. The unrestored control, Bellandur Lake, was severely polluted by 231 million litres per day (MLD) of untreated wastewater. The restoration site, Jakkur Lake, receives 10 MLD of treated wastewater and also receives some tertiary treatment by circulating the effluent through a constructed wetland before it enters the lake. The water quality of Bellandur Lake can only be described as extremely bad. Organic pollution levels in the main inflow were high (BOD5 of 199mg/l, faecal coliforms 6.9 Log MPN/100ml, total suspended solids (TSS) of 285mg/l) leading to the complete deoxygenation of lake even at the surface. The levels exceeded use-base standards for bathing water and fisheries. The high levels of organic pollution and low oxygen conditions also led to extreme levels of methane emissions that occasionally led to the lake surface catching fire. Total nitrogen (TN) and total phosphorus (TP) concentrations in the lake were extremely high (47mg/l and 6.3mg/l) respectively with low Secchi depth (SD). Despite the high nutrient levels, very little phytoplankton growth occurred (chlorophyll-a of 0mg/l), most likely due to the high TSS loads which restricted light availability. In comparison, the wastewater treatment and wetland at Jakkur Lake markedly reduced organic pollution of the main inflow (BOD5 of 32mg/l, faecal coliforms 4.1 Log MPN/100ml, TSS of 48mg/l). Levels of coliforms in the lake were above the standards for bathing waters. Total nitrogen (TN) and total phosphorus (TP) concentrations in the lake reduced (10.5mg/l, 2.4mg/l) but still classify the lake as extremely hypereutrophic. The lower TSS levels did, however, enable dense phytoplankton blooms to develop (max chlorophyll-a of 600 µg/l) which are in part responsible for the higher levels of dissolved oxygen in the lake water, albeit and as expected with large diurnal fluctuations. The comparison highlights the benefits that standard wastewater treatment provides to restore urban tropical lakes in context of rapidly urbanising catchments, and even though Jakkur Lake is by no means fully restored, it sustains water quality that allow propagation of fisheries and shore-based recreation. It also greatly contributes to greenhouse gas emission reductions. Further restoration measures are likely needed for urban tropical lakes, particularly to tackle pollutant loads in monsoon periods, but restoring community pride in the uses of a lake is an important milestone of the restoration efforts.

The impact of the acidic polysaccharides pool on CO2 concentrations and fluxes: A case study on urban waters of China

Environmental processes in cities and suburbs are significantly impacted by climate change. The development of reliable ecological models may successfully direct agricultural activities. Numerous models have been put forth as of late; however, because to the complexity of environmental microorganisms, their use in complex systems is still restricted. For a better understanding of the ecological restoration of an urban lake system that had been disturbed by rainfall, an improved ecological dynamic model that took into account inundation plants, phytoplankton and microorganisms was proposed based on the field survey. Observed data from a shallow urban lake with a surface area of approximately 66 600 m2 in the heart of Shunde district, Foshan, in South China, was used to validate the model. In this model, five hypotheses—phytoplankton, microorganisms, NH3‐N, COD and TP in water—were selected as experimental variables. To assess the model's correctness and dependability, the correlation coefficients (R) and root mean square error‐observations standard deviation ratio (RSR) were computed. The results from the establish model (0.446 < R < 0.985, RSR < 0.7) are very similar to those of actual observations. In addition, four microbe species (Aquabacium, Bradyrhizobium japonicum, Curvibacter and Cyanobacteria) multiplied when pollutant concentration dropped. Our model provides a useful tool for managing urban shallow water lakes by properly simulating the dynamic changes of aquatic species and microbes in urban shallow water lakes.

This study describes the morphology of Rhabdias elegans Gutierrez, 1945, isolated from the lungs of the toad Rhinella arenarum (Hensel, 1867) from Lomas de Tafi Tucumán, Argentina. This is the first record of R. elegans in R. arenarum from northwestern Argentina as previously described Rhabdias truncata is a species inquirendae. The distribution of R. elegans is extended since it was previously recorded in Buenos Aires, Chaco and Corrientes Provinces, Argentina. Our light microscopical study of morphological details of R. elegans revealed a few previously unreported structures in the apical region including position of the excretory pore and lateral sessile papillae in the tail. In addition, morphometric variability was observed on comparing present specimens and those described in previous studies. Our study made it possible to validate the occurrence of three Rhabdias species occurring in Argentina: R. elegans, R. füelleborni and R. cf. sphaerocephala. The information presented in this study represents an important contribution to the parasitological knowledge of R. arenarum from northwestern Argentina.

The influence of road salt on seasonal mixing, redox stratification and methane concentrations in urban kettle lakes

Thirty-four water samples and twenty-three sediment samples from the urban rivers, ten water samples and five sediment samples from urban lakes were collected in Beijing. Ten PPCPs (acetaminophen, lincomycin, caffeine, trimethoprim, azithromycin, sulfamethoxazole, diltiazem, tylosin, carbamazepine, fluoxetine) were extracted from water samples by solid-phase extraction (SPE) and from sediment samples by ultrasonic extraction, and then analyzed by high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). The ranges of geometric mean values were 0-655 ng·L-1 and 0-252 ng·L-1 in water samples from urban rivers and lakes,respectively. The range of detection ratio was 0-100% for 10 PPCPs in river water samples, caffeine was the dominant pollutant in water samples and the detection ratio was 100%, whereas sulfamethoxazole, diltiazem and tylosin were not detected in river samples. The range of detection ratio was 0-100% for 10 PPCPs in lake water samples. The detection ratios of acetaminophen, lincomycin, caffeine and azithromycin were 100%, whereas sulfamethoxazole, diltiazem, tylosin, carbamazepine were not detected in lake water samples. The ranges of geometric mean values were N.D.-1709 ng·g-1and N.D.-35.9 ng·g-1in sediment samples from urban rivers and lakes, respectively. The ranges of detection ratio were 4%-96% and 0-100% for 10 PPCPs in river and lake sediment samples, respectively. The detection ratio of trimethoprim was 96% and that of tylosin was 4% in river sediment, the detection ratio of diltiazem was 100% and caffeine, tylosin,carbamazepine were not detected. The concentrations of PPCPs in water and sediment samples from Yongyin River, Liangshui River, Tonghui River, Bahe River were higher than those in other rivers. The concentrations of PPCPs in water and sediment samples from Yongding River,Kunyu River were lower than those in other rivers. Further risk assessment results showed that the overall risk was not high in water of rivers and lakes and the RQ values were below 0.1, which showed low risk to microorganisms. But the condition was not the same in sediment from rivers and lakes. The RQ values of acetaminophen were between 0.1 and 1 in sediments from Yongyin River, Tonghui River, Bahe River. The RQ values of lincomycin were between 0.1 and 1 in sediments from Yongyin River, Wenyu River,Tonghui River, Hucheng River, Bahe River, Liangshui River, Houhai Lake. The RQ values of trimethoprim were between 0.1 and 1 in sediments from Yongyin River, Qinghe River, Wenyu River, Tonghui River Hucheng River, Bahe River, Liangma River, Liangshui River and Houhai Lake. The RQ values of azithromycin were between 0.1 and 1 in sediments from Liangma River, Liangshui River, which all showed medium risk to microorganisms in sediments. The RQ values of azithromycin exceeded 1 from Yongyin River, Qinghe River, Wenyu River, Tonghui River, Bahe River and Houhai Lake, which showed high risk to microorganisms in sediments.

Knowing the hydrological response of subtropical urban shallow lakes subjected to drought or flood events is essential to guide sustainable urban space management policies. The province of Corrientes (Argentina) presents a landscape characterized by numerous subtropical shallow lakes in which urban structures are built on its edges. In this context, the study of rainfall variability and its effects on these water bodies is crucial to generate an early warning system to reduce the risk of flood. In this sense, this study aims to analyse the rainfall variability of Corrientes as well as the morphometric changes in the shallow lakes and ponds during normal rainfall events and extreme events such as floods and droughts. Meteorological data from the period 1962-2018 were analysed applying normal, quintiles methods and a standardized precipitation index. Dry and wet events were identified and subsequently, satellite images were studied to measure the building area. Results demonstrate that the peri-urban shallow lakes have a relationship with the pluviometrical events and they vary immediately in line with local climate conditions, exposing the areas of these lakes to be replaced by urban buildings. These water bodies change their size and even dry out, although there are extreme events of flooding.

What drives the changing characteristics of phytoplankton in urban lakes: Climate, hydrology, or human disturbance?

Organic matter in the soil is a key factor in determining soil fertility. Addition of soil conditioner is the best way to provide organic matter in the soil. The aim of this study is to analyze the effect of aquatic plants as source of soil conditioner on organic contain of sandy and clay soil. This study analyze as much as 17 species of aquatic plants either from fresh water, brackish water and marine plants. Results indicated that addition of soil conditioner from aquatic plants significantly increased organic contain either in sandy or clay soil (p<0,05). In sandy soil, the highest organic contain (917%) was provided by brackish water plants, Najas marina , whereas in Clay soil was provided by marine plant, Gracilaria verrucosa (220%) Keywords : Soil conditioner, aquatic plant, sandy, clay soil

Eutrophication is prevalent in urban lakes; however, a knowledge gap exists regarding eutrophication influences on carbon dynamics in these ecosystems. In the present study, we investigated the carbon dioxide (CO2) and methane (CH4) concentration and diffusion fluxes in Lake Tangxun (the largest shallow Chinese urban lake) in the autumn and winter of 2022 and spring and summer of 2023. We found that Lake Tangxun served as a source of GHGs, with average emission rates of 5.52 ± 12.16 mmol CO2 m−2 d−1 and 0.83 ± 2.81 mmol CH4 m−2 d−1, respectively. The partial pressure of dissolved CO2 (pCO2) (averaging 1321.39 ± 1614.63 μatm) and dissolved CH4 (dCH4) (averaging 4.29 ± 13.71 μmol L−1) exceeded saturation levels. Seasonal variability was observed in the pCO2 and dCH4 as well as CH4 fluxes, while the CO2 flux remained constant. The mean pCO2 and dCH4, as well as carbon emissions, were generally higher in summer and spring. pCO2 and dCH4 levels were significantly related to total nitrogen (TN), total phosphorus (TP), and ammonium-nitrogen (N-NH4+), and N-NH4+ was a main influencing factor of pCO2 and dCH4 in urban eutrophic lakes. The positive relationships of pCO2, dCH4 and trophic state index highlighted that eutrophication could elevate CO2 and CH4 emissions from the lake. This study highlights the fact that eutrophication can significantly increase carbon emissions in shallow urban lakes and that urban lakes are substantial contributors to the global carbon budget.

Insights into priming effects of dissolved organic matter degradation in urban lakes with different trophic states

The study of bacterial community diversity and metabolic function in lake water is of great significance to the healthy development of the urban landscape lake water environment. In this study, Hancheng Lake, Nanhu Lake, Xingqing Lake, and Taohuatan Lake were selected as the study area. Illumina Nova high-throughput sequencing technology was used to study the composition and structure of bacterial communities in four different types of lakes. The correlation between bacterial communities and environmental factors was analyzed using the RDA method. Tax4Fun was used to predict the metabolic function of bacterial communities. The results showed that the diversity of bacterial communities was different in different lakes. The α diversity of Taohuatan Lake was the highest, and that of Xingqing Lake was the lowest. The bacterial community structure of the same lake had a trend of aggregation. The dominant phyla of bacteria in the four lakes were similar, mainly Proteobacteria, Bacteroidetes, and Actinobacteria. The difference was only in the proportion of bacteria. Additionally, the distribution of bacterial communities at the genus level in the four lakes was quite different. The physical and chemical properties of lakes were significantly correlated with bacterial community, and the most critical factor was nitrogen and phosphorus nutrients(P<0.05). Tax4Fun function prediction showed that the metabolic function of bacterial communities in the four lakes was similar, and the relative abundance of amino acid metabolism and carbohydrate metabolism was the highest. In addition, the potential drug-resistant bacterial pollution and the possibility of human infectious diseases were higher. These results are helpful for understanding the current situation of bacteria in urban lakes in Xi'an and providing a theoretical basis for the management and sustainable development of urban lakes.