Mesotrophic State Research Articles

Assessments of trophic state in lakes and reservoirs of Wuhan using Sentinel-2 satellite data

ABSTRACT With the rapid development of economy, many lakes in Wuhan have been polluted to different degrees and suffer from eutrophication. The main objective of this study was to conduct the monthly trophic state assessments of waters in Wuhan from March 2019 to June 2020 using 111 Sentinel-2 images. The Forel-Ule index (FUI) and empirical Gaussian process regression (GPR) were, respectively, applied to obtain monthly area percentage (AP) of waters with each trophic state. Both FUI-derived and empirical GPR-retrieved results showed that majority of water bodies (>90%) in Wuhan were in mesotrophic and eutrophic states. The GPR-retrieved results based on FUI-derived water types were more reliable than the retrieval without classification, which reduced RMSE of trophic-level index (TLI) from 9.2 to 5.8, and MAPE from 14% to 9% (N = 213). Severe eutrophication occurred in the summer and early autumn (June–October). Stepwise multiple linear regression analysis indicated that temperature and wind speed were the two most important meteorological factors influencing eutrophication variability: the temperature accounted for 63% and 55% dynamic eutrophication from FUI-derived and GPR-retrieved results, respectively; the wind speed explained 44% and 52% variability of FUI-derived and GPR-retrieved results.

Spatiotemporal variations of water quality in Lake Baihua, Guiyang City in the past decade (2009-2018)

百花湖是贵阳市重要的城市饮用水源地，并且近年来经常发生水质异常现象.本文利用2009-2018年百花湖长时间序列的监测数据，采用综合营养状态指数法和Pearson相关性分析，研究了百花湖10年间的水质变化特征和影响因素.结果表明：1）库区叶绿素a（Chl.a）、总磷（TP）、总氮（TN）、高锰酸盐指数（COD_Mn）和透明度（SD）的浓度范围分别是3.43~39.72 mg/m³、0.034~0.115 mg/L、1.200~2.759 mg/L、1.41~5.51 mg/L和0.75~2.07 m，且高氮磷比（12~63）表明百花湖是磷限制型.2）在空间上，TP、TN、氨氮、COD_Mn和Chl.a浓度沿水体流向逐渐降低，SD呈相反变化趋势.3）10年来，百花湖水质由Ⅳ类转变为Ⅲ类，综合营养状态由轻度富营养化状态转变为中营养状态，水质整体向好.4）入库支流是影响百花湖库区水质的主要因素，长期以来，东门桥河、南门河水质TP和TN等超标严重，给库区水质稳定达标带来威胁.5）百花湖Chl.a浓度与气温、水位、风速和TP等指标显著相关，是受水文、气象及营养盐因素的综合控制.未来在百花湖水环境保护治理过程中，应加大对东门桥河、南门河等重点支流的污染治理，加强对水动力学、气候变化等水文气象因素影响库区水质（藻类水华）的机制研究.;Lake Baihua is an important source of urban drinking water in Guiyang City, and water quality anomalies often occur for many years. The long-term water quality monitoring data (from 2009 to 2018), together with the comprehensive trophic level index(TLI) method and Pearson correlation analysis, are used to study the water quality change characteristics and influencing factors of Lake Baihua over the past ten years. The results show that:1) The concentrations of chlorophyll-a(Chl.a), total phosphorus(TP), total nitrogen(TN), permanganate(COD_Mn) and transparency(SD) ranged from 3.43 to 39.72 mg/m³, from 0.034 to 0.115 mg/L, from 1.200 to 2.759 mg/L, from 1.41 to 5.51 mg/L and from 0.75 to 2.07 m, respectively. The high N/P ratio (12-63) indicates that Lake Baihua is a phosphorus limited type. 2) In space, the concentrations of TP, TN, ammonia nitrogen, COD_Mn and Chl.a decreased gradually along the flow direction of the water body, and SD showed the opposite trend. 3) The water quality of Lake Baihua has gradually improved from class Ⅳ to class Ⅲ from 2009 to 2018, and TLI has changed from light-eutrophic state to mesotrophic state. 4) The inflow tributaries are the main factors affecting the water quality in the reservoir area. The water TP and TN in Dongmenqiao and Nanmen Rivers were seriously over standard, which threatens the stability of water quality in the reservoir area. 5) The concentration of Chl.a was significantly related to temperature, water level, wind speed, and total phosphorus, which is considered to be controlled by the combination of hydrological, meteorological and nutrient factors. In the future, the pollution control of Dongmenqiao, Nanmen Rivers needs to be strengthened. Meanwhile, the mechanism of water quality (algal bloom) influenced by hydrodynamics, climate change and other hydrometeorological factors also needs to be further studied.

Trophic status index and natural fisheries potential of some Iranian reservoirs.

The Iran Water Resources Management Company constructs many dams to control surface water that provide a new potential for aquaculture activities. Trophic status index and natural potential for fish production were investigated in nine small dam reservoirs from northwest of Iran. Prediction of fish productivity was calculated based on phytoplankton biomass (using chlorophyll a concentration in water; p Chl-a) and benthic macro invertebrate biomass (p BMI). Average p Chl-a and p BMI of reservoirs were estimated as 233.9±479.4 kg ha-1yr-1 and 14.76±19.18 kg ha-1yr-1 respectively. Concentrations of total phosphorus and total nitrogen varied between 0.023-0.345 and 0.42-3.58 mgl-1, respectively. According to Carlson's transformed model (TSIPN) the mesotrophic status was dominant in reservoirs in which TSIPN varied between 38.7 and 51.2. The eutrophication trend seems to be very fast in these reservoirs because of high nutrient input by aquacultures activities. The usage of fertilizers and amounts of food for aquaculture proposes and expansions of exotic species decline the natural fisheries potential of these reservoirs. Maintenance of water quality and investigation of native species should be planned to preserve sustainable fisheries activities in these reservoirs.

The monitoring of the phytoplankton condition in the Luga Bay of the Gulf of Finland under natural and anthropogenic impacts

The technogenic transformation of the ecosystem of the southeast part of Luga Bay water area (the second bay of the Baltic Sea) where Ust-Luga commercial seaport situated was determined by longstanding dredging, dumping and other types of anthropogenic impact. The development of phytoplankton as the main primary production former and the base of food reserve for aquatic biological resources was investigated during the monitoring of aquatic biological resources of the Luga Bay which was held due to the seaport construction. The investigation of phytoplankton content and development took part in the main seasons of the ice-free period of 2005–2018 in the water areas of dredging, damping, and adjacent areas. The maximum values of the phytoplankton abundance and biomass were detected in spring. The main part of biomass was formed by diatoms and dinoflagellates. The summer biomass mainly was lower than in spring and the proportion of cyanoprokaryotes (in some years also cryptophytes and green) increased. In autumn the biomass decreasing was continued, cyanoprokaryotes and cryptomonads dominated. The quantitative indicators of phytoplankton development were varied from year to year in all seasons of 2005–2018 but they kept in frames of values which previously observed for the water area of the Luga Bay. The influence of the Gulf of Finland water warming on phytoplankton development was not traced. The certain differences between the quantitative development and composition of the dominant phytoplankton complex on the water areas of dredging, damping, and adjacent areas weren’t observed. The average phytoplankton biomass for the ice-free period in the most part of years corresponds to the mesotrophic state of the Luga Bay water area. There was not a significant impact of dredging and dumping on the phytoplankton of the Luga Bay which indicates the stable state of its ecosystem primary producer and the preservation of the productional resource of the fish food base.

Trophic state index linked to partial pressure of aquatic carbon dioxide in a typical karst plateau lake

Trophic state index (TSI) can assess lake trophic status and trace in-situ metabolism, exhibiting a high potential in explaining autochthonous carbon dioxide (CO2) in aquatic environments. However, there remains a knowledge gap in how TSI links to the partial pressure of CO2 (pCO2) generated and consumed in lakes. Here we explored the temporal variations of lake pCO2 and TSI, as well as their linkages in a karst plateau lake. Lake pCO2 ranged from 90.1 to 7169.3 μatm and was significantly high in the post-wet period (2534.3 ± 1637.9 μatm). Over 58% of samples were found to be supersaturated in CO2 with respect to the atmospheric equilibrium (410 μatm). Biological and hydrological processes regulated lake trophic status, resulting in mesotrophic state (30 < TSI < 50) in the post-wet period and eutrophic state (TSI > 50) in the drought and initial-wet periods. Coupled carbonate dissolution and photosynthesis consumed the pCO2, whereas groundwater and respiration contributed the pCO2 in the karst lake. Our results highlighted that lake TSI could decipher trophic status and further partially explain the pCO2 dynamics and sources.

Phytoplankton Biomass Dynamics in Tropical Coastal Waters of Jakarta Bay, Indonesia in the Period between 2001 and 2019

A study of nutrients, underwater light dynamics, and their correlation with phytoplankton biomass was conducted in the tropical estuary of Jakarta Bay, Indonesia, in the dry season during the period from 2001 to 2019. This study analyzed the spatial and temporal dynamics of phytoplankton biomass and its correlation with phytoplankton biomass. There was significant increase in nutrient concentration in Jakarta Bay, with annual means of 27.97 µM dissolved inorganic nitrogen (DIN) and 11.31 µM phosphates in 2001, increasing to 88.99 µM DIN and 25.92 µM phosphates in 2019. Increased mean nutrient concentrations were accompanied by increased mean phytoplankton biomass, from 15.81 µg Chl-a L−1 in 2001 to 21.31 µg Chl-a L−1 in 2019. The eutrophication status of Jakarta Bay waters was calculated using the Tropical Index for Marine Systems eutrophication index, which showed increased areas of hyper-eutrophic and eutrophic zones, while the mesotrophic area decreased. The hyper-eutrophic zone dominated the areas around river mouths and the inner part of the bay, while eutrophic status was observed in the middle part of the bay and mesotrophic status was found in the outer part of the bay. The area of hyper-eutrophic water increased 1.5-fold, from 75.1 km2 in 2001 to 114.0 km2 in 2019. Increasing eutrophication of the bay has had negative ecological consequences including algal blooms, hypoxic conditions, and mass mortality of marine biota, and it urgently requires remediation.

Physico-chemical parameters of Ikere-Gorge, Iseyin, Oyo State, Nigeria

Water quality determines the distribution of aquatic organisms within aquatic ecosystem. Deterioration of water quality is of a great concern in freshwater ecosystem because of its adverse effects on freshwater organisms. Therefore, the physico-chemical parameters of Ikere-gorge were examined in this study to determine its suitability for fish production. Air and water temperature, transparency, electrical conductivity and totaldissolved solids were determined in-situ. Dissolved oxygen, alkalinity, hardness, phosphate and nitrate were determined with standard analytical methods. The selected parameters examined in this study were determined monthly between January 2017 and December 2018. The mean monthly values of physico-chemical parameters of Ikere-gorge obtained are as follows: air temperature (27.46±1.82 ºC), water temperature (28.14±1.57 ºC), pH (6.50±0.63), water transparency (1.34±0.12 m), dissolved oxygen (5.93±0.29 mg/L), electrical conductivity (130.59±7.59 μS/cm), total dissolved solids (67.67±4.37 mg/L), total hardness (56.70±15.76 mg/L), total alkalinity (58.97±9.53 mg/L), total phosphate (2.22±0.67 μg/L) and nitrate (2.90±1.23 μg/L). Likewise, it was observed that surface water temperature had negative significant relationship with dissolved oxygen at P &lt; 0.05.Transparency has negative significant relationship with phytoplankton abundance at 0.05 (P ˂ 0.05) and with phosphate and nitrate at 0.01 significant level. The annual mean of Trophic Status Index based on total phosphate is 15.04±1.63. This classified Ikere-gorge trophic status as mesotrophic at stage 2. The result of this study reveals the mesotrophic status of Ikere-gorge and water quality are within the ranges recommended for fish production and should be adequately managed for sustainable fish production.&#x0D; Keywords: Aquatic organisms, Ecosystem, Freshwater, Trophic state, Abundance

Diversity and ecological characteristic of algae and cyanobacteria of thermokarst lakes in Yakutia (northeastern Russia)

AbstractA total of 437 species (453 with infraspecific taxa) of algae and Cyanobacteria were identified in 2034 samples collected during the first research on nine thermokarst lakes in Yakutia carried out in 1986–1994 and 2001–2015. The richest algal flora was determined in Lake Aalah, represented by 241 taxa. Bacillariophyta species dominated in four lakes, whereas Chlorophyta and Cyanobacteria dominated in the others. The algal bioindication demonstrated preferences for benthic and plankticbenthic life, temperate temperature, low alkalinity, waters with moderate oxygenation, low to medium enrichment with chloride, low organic pollution, and mesotrophic state. Comparative floristic, CANOCO and JASP statistical methods divided the species and environmental variables into groups of lakes related to landscape terraces. Local landscape positions and high summer water temperatures may play a major role in the formation of algal flora. The index of algae taxa per area stabilized at about 70 species per km2. The highest polymorphism of algae floras, defined by the Subspecies/Species Index, was determined for the lakes of the Tungulunskaya terrace: Lake Ynakh, Lake Nal Tungulu and Lake Tungulu (1.041–1.058), and the average total flora was 1.036. Our results can help in monitoring and protecting the ecosystems of thermokarst lakes in Yakutia in the harsh climate environment of Northeastern Eurasia.

Evaluation of the trophic state predicted from lab and Landsat data of western coastal water of Suez Bay, Egypt

This study aimed to compare the trophic status assessments of the western coastal waters of Suez Bay, Gulf of Suez, Egypt. The Trophic Index (TRIX) that depends on the lab-based water quality measurements of nutrients, chlorophyll-a (Chl-a) and dissolved oxygen, was compared with the Carlson trophic state index that integrates lab-based data such as NH4 or PO4 concentration with Landsat data and geographic information system (GIS) techniques. The physicochemical properties were determined, which indicated that Suez Bay was in an eutrophication state limited by both N and Si. It was suggested that the most influential activities be the industrial and domestic drains that raised the TRIX value to 5.59 with a mesotrophic state on average. Likewise, phosphorus trophic status mapping applying Carlson trophic state index showed high activity nearby drain outlets, especially at the Cabanon drain. The regression statistical model indicated a relationship between lab data of nutrients and band values extracted from Landsat images. Accordingly, the integration of remote sensing and GIS techniques with laboratory data is useful for predicting the state of water quality in the coastal areas with a single lab-based water quality parameter.

Palaeoecological and palaeoclimatic conditions on the Karelian Isthmus (northwestern Russia) during the Holocene

AbstractThe Holocene evolution of climate in easternmost Fennoscandia and adjoining regions is poorly known, compared with regions to the west. To address this, a 224-cm-long sediment core from Lake Medvedevskoe, situated on the Central Upland of the Karelian Isthmus, northwestern Russia, was examined to investigate variations in the Holocene climate. Analyses indicate that the dry and cold late Pleistocene climate was replaced by the warmer and more humid early Holocene climate after ca. 10.5 cal ka BP. During the early Holocene, the lake transitioned from an oligotrophic to a mesotrophic state, characterized by a “Corynocera ambigua/Microtendipes pedellus-type” phase, which has been found in other lakes across Fennoscandia. Taxonomic shifts in the chironomid and cladoceran communities associated with climatic amelioration were identified at ca. 10.6 and 9.17 cal ka BP using breakpoint analysis. Reconstructed July temperatures indicate climatic patterns comparable to those seen in eastern Fennoscandia. The warm period between ca. 9.5 and 5.5 cal ka BP (T July 14.5–15°C) was interrupted by a slight cooling between ca. 8.5 and 8.1 cal ka BP, possibly relating to the 8.2 event, with peak temperature reached at ca. 7.8 cal ka BP. Neoglacial cooling started after ca. 5.5 cal ka BP, the median reconstructed July temperature dropped to 2–3°C cooler than present (mean T July 13.5°C) before recovering in recent time.

Sustainable development and environmental restoration in Lake Erhai, China

Eutrophication of lakes is an environmental issue that has attracted increasing attention all over the world. This study analyses the monitoring data of the Lake Erhai, Yunnan Province in China with Carlson’s TSI, Improving Carlson’s TSI (TSIM) and TLI. The results reveal that the eutrophication index for this lake is in the Mesotrophic status. The mechanism of the eutrophication in Lake Erhai is also investigated. The mechanism shows that rate of nutrient transformation is the core issue and the process of eutrophic evolution involves natural, social, and economic factors. The restrictions on sustainable development in Lake Erhai are discussed. To maintain sustainable development, green watershed construction (GWC) and its corresponding effective measures are proposed. Moreover, lessons learned from Lake Erhai watershed management are presented, to provide valuable experiences for alleviating water pollution caused by insufficient environmental management during rapid economic development. Perspective future research works are proposed, including establishment of the early warning system with remote sensing (RS) and geographic information system (GIS) as well as the artificial intelligence (AI) technology.

Pattern of the state of eutrophication in the floodplain wetlands of eastern India in context of climate change: a comparative evaluation of 27 wetlands.

The floodplain wetlands in different regional settings vary with time and space in terms of function and geomorphological diversity. In recent decades, these eco-sensitive waterbodies have been exposed to a wide range of anthropogenic threats and climatic changes. Therefore, assessment of these ecological and environmental threats is prerequisite to understand the state of ecosystem and to develop a sustainable management strategy for conservation of wetland biodiversity and fisheries enhancement. This paper discusses the region-specific pattern of trophic state index (TSI) of the 27 floodplain wetlands in West Bengal, India. Carlson TSI and Lamparelli TSI methods were used to determine a better approach based on historical and continuous dataset and to delineate the interrelationship among historical climatic variability for sustainable management of the resources. The study revealed that agro-climatic divisions do not unveil any significant impact on the TSI calculated using Carlson TSI as well as Lamparelli TSI method. The TSI scores for the two methods were significantly different (p < 0.01) for different zones based on wetland habitat types. The TSI scores revealed most of the wetlands to be in mesotrophic state. Principal component analysis (PCA) indicated that TSI scores were having similar pattern of variation with rainfall and water temperature. The present study also conveys fundamental information on ecological status based on the trophic state, which will aid to develop region-specific strategies for sustainable fisheries enhancement.

Современное состояние и динамика флоры некоторых малых озер Ярославской области

The phytoplankton and vascular aquatic plants have been studied in small lakes Vashutinskoe, Chashnitskoe, Ryumniki, and Zaozer’e, located in the southern part of the Yaroslavl Region, Russia. The taxonomic composition of phytoplankton comprised 137 species of algae belonging to 8 divisions, 18 orders, and 76 genera. The studied water bodies were characterized by high biomass of cyanobacteria. Aphanizomenon flos-aquae (L.) Ralfs ex Born et Flah. and the species of the genus Anabaena had a significant contribution to the phytoplankton biomass in the lakes Zaozer’e, Chashnitskoe, and Ryumniki, Limnothrix planctonica (Wołosz.) Meff. and Microcystis aeruginosa (Kütz.) Kütz, in the Lake Vashutinskoe. In terms of phytoplankton biomass, the pelagial and shallow areas of the Lake Vashutinskoe belonged to eutrophic reservoirs, of the Lake Ryumniki, to oligotrophic. The phytoplankton biomass in the pelagial zone of the lakes Chashnitskoe and Zaozer’e indicated the mesotrophic status of these water bodies, in the littoral zone, eutrophic. The study of the phytoplankton of the lakes was carried episodically and was often performed at different periods of the growing season. Therefore, the obtained data did not allow one to assess the direction of the successional changes in the algal flora. The flora of vascular plants of lakes was represented by 118 species belonging to 4 divisions, 5 classes, 22 orders, and 37 families. Thirty-four species were common to all studied water bodies. The differences in the The differences in the flora of vascular aquatic plantsof the studied lakes were associated with differences in their trophic status, the presence of various biotopes, the nature of anthropogenic load, and the degree of eutrophication. During a hundred years of observations, some species have disappeared, but some have appeared, including adventive species (such as Elodea canadensis Michx., Bidens frondosa L., Epilobium adenocaulon Hausskn, Zizania latifolia Griseb., and Juncus tenuis Willd.). The study of the current state of rare and protected species of vascular plants made it possible to reveal the eventual causes and period of disappearance of some species from the lakes. The taxonomic and ecological structure of phytoplankton and vascular plants of lakes was quite diverse and usual for the water bodies of the European part of Russia.

Spatio-temporal changes in surface water quality and sediment phosphorus content of a large reservoir in Turkey

The Keban Dam Reservoir, located on the Euphrates River, is the second largest reservoir of Turkey. Water quality of this reservoir is of great importance because it is widely used for recreation, aquaculture production, fishing, and irrigation. In this study, discriminant analysis, principal component analysis (PCA), factor analysis (FA) and cluster analysis (CA) were conducted to evaluate the seasonal and spatial variations in surface water quality of the reservoir. Also, total phosphorus (TP) content in sediments, water type and trophic status of the reservoir were determined. For this, 19 water quality variables and TP in sediments were monitored seasonally at 11 sampling stations on the reservoir during one year. Hierarchical CA classified 11 stations into three groups, i.e., upstream (moderate polluted), midstream (low polluted) and downstream (clean) regions. PCA/FA allowed to group the variables responsible for variations in water quality, which are mainly related to mineral dissolution (natural), organic matter and nutrients (anthropogenic), and physical parameters (natural). Discriminant analysis (DA) gave better results for both data reduction and spatio-temporal analysis. Stepwise temporal DA identified eight variables: water temperature (WT), chemical oxygen demand (COD), nitrate nitrogen (NO3–N), soluble reactive phosphorus (SRP), chlorophyll-a (Chl-a), potassium (K+), magnesium (Mg2+), and calcium (Ca2+), which are the most significant variables responsible for temporal variations in water quality of the reservoir, while stepwise spatial DA identified three variables: K+, chloride (Cl−), and sulphate (SO4−2), which are the most significant variables responsible for spatial variations. According to Ontario sediment-quality guidelines, sediments of the reservoir can be considered as unpolluted in terms of mean TP content. The water type of the reservoir was calcium-bicarbonate. According to trophic state index values based on TP and Chl-a, upstream region (moderate polluted) of the reservoir was in the eutrophic status, whereas other regions were in the mesotrophic status.

Modeling sediment oxygen demand in a highly productive lake under various trophic scenarios.

Hypolimnetic oxygen depletion in lakes is a widespread problem and is mainly controlled by the sediment oxygen uptake (SOU) and flux of reduced substances out of the sediments (Fred). Especially in eutrophic lakes, Fred may constitute a major fraction of the areal hypolimnetic mineralization rate, but its size and source is often poorly understood. Using a diagenetic reaction-transport model supported by a large data set of sediment porewater concentrations, bulk sediment core data and lake monitoring data, the behavior of Fred was simulated in eutrophic Lake Baldegg. Transient boundary conditions for the gross sedimentation of total organic carbon and for hypolimnetic O2 concentrations were applied to simulate the eutrophication and re-oligotrophication history of the lake. According to the model, Fred is dominated by methanogenesis, where up to70% to the total CH4 is produced from sediments older than 20 years deposited during the time of permanent anoxia between 1890 and 1982. An implementation of simplified seasonal variations of the upper boundary conditions showed that their consideration is not necessary for the assessment of annual average fluxes in long-term simulations. Four lake management scenarios were then implemented to investigate the future development of Fred and SOU until 2050 under different boundary conditions. A comparison of three trophic scenarios showed that further reduction of the lake productivity to at least a mesotrophic state is required to significantly decrease Fred and SOU from the present state. Conversely, a termination of artificial aeration at the present trophic state would result in high rates of organic matter deposition and a long-term increase of Fred from the sediments of Lake Baldegg.

Characterization of CDOM in reservoirs and its linkage to trophic status assessment across China using spectroscopic analysis

Chromophoric dissolved organic matter (CDOM) represents the optically active component of the DOM pool, and originates from both allochthonous and autochthonous sources. The fluorescent characteristics of dissolved organic matter (FDOM) has been widely used to trace CDOM sources and infer its composition. However, little is known about the optical and fluorescent properties of CDOM in drinking water reservoirs, and the variability of CDOM properties along trophic gradients in these aquatic systems. A total of 536 water samples were collected between 2015 and 2017 from 131 reservoirs across China to characterize CDOM and FDOM properties using both light absorption and fluorescence spectroscopies, and examine relationships with water-quality condition as expressed by the modified trophic state index (TSIM) of the reservoirs (range: 12 < TSIM < 78). With increased reservoir trophic status, CDOM absorption coefficients at 254 nm (aCDOM(254)) and total fluorescence of FRI-EEMs (excitation-emission matrix coupled with fluorescence regional integration) increased significantly (p < 0.01). Our results indicated that the nutrients in aquatic systems and the social economy factors (including wastewater, sewage, cultivated land, GDP, population) and altitude affect the CDOM absorption and fluorescence significantly (p < 0.05). Most importantly, we proposed a new classification standard associated with eutrophic status via CDOM humification index (HIX) due to the significant correlation between each other (p < 0.01). HIX less than 4 was corresponding to TSIM less than 30 as oligotrophic states; 4 < HIX ≤ 12 was corresponding to TSIM less than 50 as mesotrophic states; 12 < HIX ≤ 18 was corresponding to TSIM less than 70 as eutrophic states; HIX more than 18 is defined as hypereutrophic status with TSIM > 70. This method highlights the importance of CDOM fluorescence for aquatic DOM input and strengthens the linkage between the trophic status index and CDOM characteristics, it also contributes to establish a new rapid assessing model with quick experimental measurements to monitor the trophic status of water reservoirs.

From Saprotrophic to Clear Water Status: the Restoration Path of a Degraded Urban Lake

The study was conducted on Długie Lake in Olsztyn, which for 20 years since the mid-1950s served as a domestic and storm wastewater receiver, which led to its complete degradation. The discontinuation of wastewater inflow in 1976 caused a change in the trophic state from saprotrophic to hypertrophic. Evident improvement of water quality was possible only after the implementation of proper restoration techniques. Długie Lake was subjected to artificial aeration with thermal destratification (1987–2000). After all opportunities to improve water quality in the lake by artificial aeration (low phosphorus sorption capacity of sediment) had been exhausted, it was decided that a phosphorus inactivation method using the coagulant PAX 18 be used (2001–2003). Before restoration, the nutrient concentration in the near-bottom water layer of Długie Lake was very high at 22.9 mg TN L−1 and 3.50 mg TP L−1. The average amount of chlorophyll a was ca. 200 μg L−1, and the Secchi disc visibility did not exceed 1 m. In 2017, 14 years after termination of the lake restoration process, the total phosphorus concentration at the bottom was 0.21 mg P L−1 on average, and the total nitrogen was 1.5 mg N L−1. The mean transparency of the water oscillated around approximately 5 m, and the amount of chlorophyll a was 1.86 μg L−1. Studies have shown that the most important step in reclamation is to prevent pollutants from entering the lake to the maximum extent possible and to use a combination of several reclamation methods as a matter of good practice. Stable environmental conditions have developed in the lake, and the values of chlorophyll a and the Secchi disk visibility indicate that the lake has reached a mesotrophic state.

Potential of Shrubs, Shore Vegetation and Macrophytes of a Lake to Function as a Phytogeochemical Barrier against Biogenic Substances of Various Origin

The objective of this study was to perform a comprehensive botanical analysis of shore and littoral vegetation of a model mesotrophic lake and investigate their effectiveness as a phytogeochemical barrier against biogens of various origin. A lake catchment was characterised by natural (forests) as well as anthropogenic land use (extensive agriculture and stationary and unorganised recreation), generating a determined variability in the load of biogenic substances to lake waters. High potential effectiveness of the phytogeochemical barriers of the analysed phytocoenoses in the assimilation of biogenic substances was found to be particularly related to: species richness, diversity of life forms, presence of specific groups and species of plants and width of the buffer zone. This situation results from the natural properties of the habitat and the modifying effect of anthropogenic transformations in the catchment, affecting the biocoenotic composition of the shore and littoral vegetation of the lake, and therefore shaping the structure of its buffer zones. The morphometric parameters and hydrological conditions of the catchment, combined with variable human pressure and modified by the effectiveness of ecotone biogeochemical barriers, contribute to the mesotrophic limnological status of the lake.

Age, Growth, and Mortality Rates of the Giant Cichlid in Guatemala

AbstractAge, growth, and mortality were assessed in Giant Cichlids Petenia splendida from lakes in northern Guatemala by using cross‐sectioned sagittal otoliths. Marginal increment and edge analyses of Giant Cichlid otoliths indicated that one annulus formed per 12‐month period in Lakes Yaxhá and Petén Itza. Opaque zone formation was associated with the peak of the rainy season from May to September. Ages ranged from 0 to 8 years for Giant Cichlids in Lake Yaxhá and from 0 to 5 years in Lake Petén Itza. Within both lakes, males were larger than females, although the difference was slight in Lake Petén Itza. Lake Yaxhá Giant Cichlids had faster growth rates than those from Lake Petén Itza, and fish over 2 years old from Lake Yaxhá were larger at age than fish from Lake Petén Itza. This is counter‐intuitive because Lake Petén Itza is heavily exploited, whereas Lake Yaxhá is unfished. However, long‐term exploitation in Lake Petén Itza may have resulted in selection for fish with reduced growth rates. Alternatively, the mesotrophic state of Lake Yaxhá may explain the differences in growth, although areas of Lake Petén Itza are changing from oligotrophic to meso‐eutrophic due to rapid cultural eutrophication. Total mortality (Z) estimates for Giant Cichlids were 0.81 for Lake Yaxhá, with most of the age structured on 2–4‐year‐old fish, and 1.05 for Lake Petén Itzá, where the age structure was dominated by 0–2‐year‐old fish; these results were consistent with expectations based on the low fishing pressure in Lake Yaxhá.

Ecological health assessment of a coastal ecosystem: Case study of the largest brackish water lagoon of Asia

This study focuses on the ecological health assessment of Chilika, a shallow lagoon present in east coast of India, through nutrient stoichiometry and trophic state index (TSI). Multivariate statistical analysis such as ANOVA, Pearson's correlation, Principal Component Analysis (PCA), and Discriminant Analysis (DA) were employed for data interpretation. Nutrient stoichiometry revealed that the Chilika Lagoon experiences phosphorus limitation with regard to nitrogen and silicate (N:P:Si = 16:1:16) throughout the study period. As per the computed TSI values, the southern sector (SS), central sector (CS), and outer channel (OC) were assigned with a mesotrophic status, whereas the northern sector (NS) was assigned with the eutrophic status. From PCA, total nitrogen was found to be negatively correlated with salinity and positively correlated with silicate, thus indicating that the major source of nitrogen in the lagoon was freshwater ingress by rivers with high silicate content. DA indicated that it was successful in discriminating the groups as predicted.