A trophic state index for Laguna lake in the Philippines

A multivariate approach was used to develop a trophic state index. The index TSI(AVE), based on the four trophic state variables (transparency, phytoplankton, nitrate and temperature) was applied to Laguna Lake in the Philippines. The results indicated a hypereutrophic state of the lake. A Carlson‐type index was also used for the lake, but it was found that the index was not applicable to Laguna Lake.     

Spatio‐temporal variations in the trophic status of Lake Naivasha,Kenya

The spatio‐temporal dynamics of the trophic state of a lake are crucial in defining its water quality, as well as biodiversity. Accordingly, this study focused on the spatio‐temporal variations of the trophic state, and the possible causes of the heterogeneous turbidity in Lake Naivasha, Kenya. The trophic state of the lake oscillated between a eutrophic and hypereutrophic condition, being found to be more eutrophic than reported in previous studies, indicating a progressive deterioration of its water quality. Inferences from the graphical representation of the deviations of total phosphorus and Secchi depth from the chlorophyll‐a trophic state indices revealed that the lake is predominantly phosphorus limited. Furthermore, the turbidity in the northern part of the lake is dominated by suspended sediment and dissolved coloured material. Discriminant analysis resulted in identification of three distinct trophic state regions in Lake Naivasha, namely the northern region, the mid and southern part and the more or less isolated Crescent Lake. The results of this study provide a good basis for further investigation of the current loading magnitude of both nutrients and sediments, in order to facilitate sustainable management to ensure community integrity and ecosystem functions of the lake.     

Lakes of Malaysia: Water quality,eutrophication and management

The present study was undertaken to evaluate and verify the water quality status and trophic state of 15 major lakes and reservoirs in Malaysia. The lake water quality assessments were based on the National Water Quality Index (NWQI), while the trophic state assessments were based on Carlson's Trophic State Index (TSI). The findings of this water quality assessment, based on data collected between September and October 2012, indicated that a majority of the lakes were classified as Class II (Clean) waters suitable for recreational use. The results of the trophic state assessments, however, indicated that all of the lakes were eutrophic, meaning they were nutrient‐rich, they could experience algae blooms or macrophyte problems, and they were likely to exhibit poor water quality. Sustainable management measures and strategies are suggested to address the eutrophication problems of Malaysian lakes and reservoirs, with the national responses on lake and reservoir management also being discussed.     

Warming and eutrophication effects on the phytoplankton communities of two tropical water systems of different trophic states: An experimental approach

Both global warming and eutrophication are predicted to promote cyanobacterial blooms. At the same time, how tropical phytoplankton communities exhibiting different trophic state systems will respond to temperature variations is less clear. To investigate the effects of temperature changes and nutrient additions on phytoplankton communities, and gain insights regarding possible resistance to these effects, the present study focused on testing the hypothesis that temperature variations and nutrient additions will have a stronger effect on cyanobacteria dominance in eutrophic water system than in oligo‐mesotrophic water systems. Experiments were conducted with phytoplankton communities from two aquatic ecosystems exhibiting different trophic states. To this end, water samples from a eutrophic and oligo‐mesotrophic system were collected and incubated at 25 and 30ºC. Samples receiving additional surplus nitrogen (N) and phosphorus (P) inputs were included to serve as eutrophication treatments. The study results indicated that temperature variations alone did not promote cyanobacteria in water from either the oligo‐mesotrophic or eutrophic water system. However, nutrient enrichment of the water from the eutrophic system significantly boosted the cyanobacteria, with the biomass increasing by factor of 10 for both the 25°C and 30°C treatments. In contrast, eutrophication of the water from the oligo‐mesotrophic system did not change the relative contribution of phytoplankton groups, with the response ratios being much lower than those for the water from the eutrophic system. Although based on a simple experimental design, the results of the present study suggest that cyanobacteria dominance is favoured by further nutrient additions for eutrophic water systems, independently of any direct temperature effects, and that more pristine environments possess some resistance against eutrophication effects. Since global warming is assumed to indirectly intensify eutrophication symptoms, the results of the present study underscore the importance of nutrient control.     

Zooplankton as an indicator of trophic conditions in two large reservoirs in Brazil

The physical and chemical variables of the water, and the composition and structure of the zooplankton communities, in Três Marias and Furnas Reservoirs in Minas Gerais, Brazil, were compared to characterize these environments in relation to their trophic state. Higher values of electrical conductivity and chlorophyll‐a, total solids, suspended organic matter and total nitrogen concentrations were recorded in Três Marias Reservoir. Higher water transparency and nitrite and nitrate concentrations were observed in Furnas (P < 0.000). Higher zooplankton densities were always obtained in Três Marias Reservoir and, during the rainy period (P < 0.000), with mean values in the dry and rainy periods of 23 721 and 90 872 org m^?3, respectively, in Três Marias Reservoir and 9022 and 40 434 org m^?3, respectively, in Furnas Reservoir. Copepoda was the dominant group in both reservoirs, mainly the younger stages (nauplii and copepodids). Based on the absolute and relative values, the contribution of rotifers was higher in Três Marias Reservoir than in Furnas Reservoir. Although the Trophic State Index, based on water transparency and chlorophyll‐a and total phosphorus concentrations, indicated an oligotrophic state for both reservoirs, the higher densities of the zooplankton community in Três Marias Reservoir, as well as the predominance of cyclopoids and smaller‐sized species such as bosminids, characterized this environment as mesotrophic. Larger‐sized species such as calanoids, daphniids and sidids in Furnas Reservoir characterized the better water quality of this reservoir.     

Influence of hydrology on water quality and trophic state of irrigation reservoirs in Sri Lanka

Many reservoirs provide multiple benefits to people around the world, in addition to primary uses such as irrigation. Thus, reservoir management should address their multiple uses. The water quality of ten irrigation reservoirs in Sri Lanka was examined in the present study with the objective of better understanding the effects of hydrological regimes on reservoir water quality and trophic state. Basic limnological parameters pertinent to the nutrient loads to, and trophic state of, the reservoirs were collected from June 2013 to February 2016. The sampling period was arbitrarily divided into two periods of approximately similar duration (period 1 = June 2013–September 2014; period 2 = October 2014–February 2016) to investigate whether or not there was a seasonal variation in the water quality parameters. Although temporal and spatial variations were observed, most water quality parameters were within the levels acceptable for drinking water standards. The 10 reservoirs were also ordinated by principal component analysis (PCA) on the basis of the water quality parameters of the two sampling periods in a two‐dimensional score plot. Reservoirs in the first principal component (PC1) axis were represented by negative scores attributable to the dissolved oxygen concentration and pH and, to a lesser extent, by electrical conductivity and chlorophyll‐a concentration. Positive scores in PC1 were represented by reservoirs with a score loading attributable to alkalinity, nitrate concentration, Secchi depth, temperature and seston weight and, to a lesser extent, from the total phosphorus concentration. There was a significant negative correlation of PC1 scores with relative reservoir water‐level fluctuation (RRLF; the ratio of mean reservoir water‐level amplitude to mean reservoir depth). Furthermore, Carlson's trophic index also were influenced by RRLF, although not by hydraulic retention time (HRT), indicating allochthonous nutrient inputs into the irrigation reservoirs were mainly governed by RRLF, but not by HRT. Thus, the results of the present study provide useful insights into achieving desirable reservoir water quality through the manipulation of the hydrological regime.     

鹤地水库富营养化状况分析与防治对策

利用鹤地水库2002—2007年的水质监测资料,通过卡尔森指数方法对水库富营养化现状进行评价,同时分析其变化趋势及成因,最后提出一些防治对策。     

Chemical, physical and biological characteristics of Saladito Reservoir, Cienfuegos Province, Cuba

Saladito Reservoir, located in Cienfuegos Province in Cuba, lies in an intermediate position between tropical and subtropical climatic conditions. Although Cuba only had 13 reservoirs before 1959, the government has constructed 229 reservoirs since that time, with a total storage capacity of 8.81 km³, administered by the National Hydraulic Resources Institute. In 1995, it was proposed to use waste water from the Swinish Farm to fertilize small reservoirs, providing nitrogen and phosphorus to increase primary production in the reservoirs as a means of facilitating high fish production levels. Saladito Reservoir, with a hydrographic basin of 34.5 km², a mean depth of 3.4 m and a water retention time of 2 years, was constructed as the final part of the wastewater treatment system for Swinish Farm in the Palmyra Municipality. The main objective of this study is to determine the level of eutrophication in the reservoir after it had received waste water from the Farm for 17 months, based on relevant biological (phytoplankton), chemical and physical indicators sampled at five stations on 22 and 23 May 1995. Based on the measured parameters, the concentration of dissolved salts was generally high, with calcium and bicarbonate being the dominant ions. The nitrite‐nitrogen and nitrate‐nitrogen concentrations were relatively low at the surface, increasing with depth, while the ammonium‐nitrogen concentrations were extremely high, likely related to the high organic content of the reservoir. The total phosphorus concentration also exhibited high values, indicating the possible existence of soluble phosphorus in a complex with iron, which would allow algae to assimilate it like phosphate. The water transparency, measured as Secchi disk, was 0.2 m at all sampling stations. The chlorophyll‐a concentration ranged from 111 µg L⁻¹ in the surface water to 50 µg L⁻¹ at the bottom depth. The phytoplankton cell counts identified 27 algal species contained in five classes. The dominant group was Cyanophyceae, with Oscillatoria sp. being the largest contribution to the reservoir biomass. Twenty‐seven taxa were present in the reservoir in concentrations of at least 1 mg m⁻³. The results of this study indicate that Saladito Reservoir is hyper‐eutrophic, based on its measured biomass (cell counts), and chlorophyll‐α, inorganic nitrogen and total phosphorus concentrations. The possible production of algal toxins from blue‐green algal growths also could be affecting the productivity of Saladito Reservoir.     

Nutrient reference concentrations and trophic state boundaries in subtropical reservoirs

Nutrient criteria as reference concentrations and trophic state boundaries are necessary for water management worldwide because anthropogenic eutrophication is a threat to the water uses. We compiled data on total phosphorus (TP), nitrogen (TN) and chlorophyll a (Chl a) from 17 subtropical reservoirs monitored from 2005-2009 in the S?o Paulo State (Brazil) to calculate reference concentrations through the trisection method (United States Environmental Protection Agency). By dividing our dataset into thirds we presented trophic state boundaries and frequency curves for the nutrient levels in water bodies with different enrichment conditions. TP and TN baseline concentrations (0.010 mg/L and 0.350 mg/L, respectively) were bracketed by ranges for temperate reservoirs available in the literature. We propose trophic state boundaries (upper limits for the oligotrophic category: 0.010 mg TP/L, 0.460 mg TN/L and 1.7 μg Chl a/L; for the mesotrophic: 0.030 mg TP/L, 0.820 mg TN/L and 9.0 μg Chl a/L). Through an example with a different dataset (from the Itupararanga Reservoir, Brazil), we encouraged the use of frequency curves to compare data from individual monitoring efforts with the expected concentrations in oligotrophic, mesotrophic and eutrophic regional systems. Such analysis might help designing recovery programs to reach targeted concentrations and mitigate the undesirable eutrophication symptoms in subtropical freshwaters.     

Understanding and management of cyanobacterial blooms in sub-tropical reservoirs of Queensland,Australia

A three year study of two sub-tropical water supply (potable and irrigation) reservoirs - Baroon Pocket and Leslie - aimed to develop an improved understanding and effective management strategy for the control of low level toxic cyanobacterial ‘blooms’. The two reservoirs appear to be typical of those elsewhere in tropical and sub-tropical Australia, being strongly stratified and monomictic if deep, or polymictic to monomictic (depending on inter-annual climatic variation) if shallow. In both reservoirs, thermal stratification appeared to be the key factor influencing the onset and demise of cyanobactenal blooms. Hypolimnetic deoxygenation was rapid during periods of stratification, and high rates of nitrogen and phosphorus release from bottom sediments occurred during anoxia. External nutrient inputs were dominated by episodic storm in-flows following the passing of (sub)tropical depressions, carrying massive sediment and nutrient loads into the reservoirs. As a consequence of this, and coupled with the high degree of internal nutrient recycling and the low national targets for cyanobacterial control in Australia, we believe that reduction of external nutrient inputs alone, through improved catchment management, may not be sufficient to prevent cyanobacterial blooms. Therefore, more emphasis should be given to ‘in-lake’ control strategies such as destratification, biomanipulation and in situ sediment treatment.     

Environmental variables and diversity index as a tool for management in tropical man‐made lakes

Fish and water samples were collected from various randomly situated sampling sites in two tropical man‐made lakes, Peechi and Pothundi reservoirs, in South India. The fish samples collected during 2014 to 2015 were taxonomically identified and the fish diversity indices of these reservoirs evaluated. The water samples collected were analysed for such environmental variables as pH, electrical conductivity, dissolved oxygen concentration, alkalinity, hardness, chlorophyll and nutrient concentrations. T‐tests indicated significant difference in both the fish diversity and environmental variables between these two reservoirs. The Pearson correlation test identified electrical conductivity as a highly correlated environmental variable to the ichthyodiversity index in Peechi and Pothundi reservoirs, with coefficients of 0.939 and 0.7012, respectively. Principal co‐ordinate analysis also was conducted on the variables to identify the best combination of variables subjective to the particular sampling site influencing the fish diversity. The analyses explained 72.8% of the total variations for Peechi reservoir, which was represented with eigenvalues of 7.53 and 3.393, respectively, for the first two dimensions. A similar analysis of Pothundi reservoir produced eigenvalues 7.05 and 3.01, respectively, for the first two dimensions, explaining 67.1% of the total inertia. The individual factor maps (IFM‐I and IFM‐II) for Peechi and Pothundi reservoirs identified a high diversity at sampling site 3 in Peechi reservoir, and a similar finding for sites 3 and 7 in Pothundi reservoir, being related to the interactions with other environmental variables, which were greatly influenced by the predominance of macrophytes. The latter is a characteristic of rainfed tropical reservoirs, with special reference to the native fish diversity and environmental variables. The findings of this study suggest management decisions for any aquatic system may be considered after prior assessment of environmental variables and the ichthyodiversity index of the indicated waterbody.     

长江流域水体富营养化演化驱动机制及防控对策

富营养化已成为长江流域河流、湖泊与水库面临的共性问题,基于近10 a来长江流域水质状况、营养物质含量、水文泥沙过程、富营养化评价指数等数据及相关历史文献,分析了长江流域水体富营养化现状及演化趋势,以典型河流、水库与湖泊为例,剖析了长江流域水体富营养化驱动机制。结果表明:①长江流域水体富营养化程度为河流水库湖泊,上游四川盆地与中游江汉平原是长江流域富营养化湖泊与水库的主要聚集区。②近10 a来,中度富营养化湖泊比例从2009年的31.3%增加至2018年的42.7%,水库营养水平正从中营养向轻度富营养快速发展。③长江流域水体营养充足,受闸坝建设运行影响,流速减缓、流量偏枯,水体交换慢与河湖连通性差是河流、水库与湖泊富营养化的重要驱动力。为防控水体富营养化,建议监测重要控制断面氮磷浓度与通量,加强农田灌溉退水与水产养殖废水排放管理,开展流域水、沙、营养物质耦合输送调控。     

Determining the spatial variation of phosphorus in a lake system using remote sensing techniques

Lakes are versatile ecosystems, with eutrophication being a serious problem affecting their condition and trophic status. Eutrophication can lead to an over‐abundance of macrophytes in lakes, producing favourable conditions for mosquito larvae. Increased eutrophication is attributed in most to excessive phosphorus concentrations in lake water. Satellite imagery analysis now plays a prominent role for quickly assessing water quality over a large area. The present study is an attempt to illustrate the variation of phosphate and total phosphorus concentrations in Akkulam–Veli Lake, Kerala, India, using Indian Remote Sensing satellite (IRS P6‐ LISS III) imagery. A multiple regression equation derived using radiance in the red and MIR bands in the imagery was found to yield superior results for predicting the phosphate concentration, whereas a simple regression equation using radiance in red band was found to yield good results for the total phosphorus concentration in lake water. Accordingly, the trophic status of the lake system can be determined easily from satellite imagery in this manner.     

Relationships between environmental factors,periphyton biomass and nutrient content in Garças Reservoir,a hypereutrophic tropical reservoir in southeastern Brazil

This study focused on evaluating the factors related to seasonal variations of periphyton biomass and nutrient content (N, P) in Garças Reservoir, a tropical, shallow hypereutrophic tropical reservoir in southeastern Brazil that exhibits a permanent cyanobacteria bloom. Artificial substrata were placed in the subsurface water (20 cm) of the lake on a monthly basis (incubation time of 28 days) over a 1‐year period. Two limnological periods were characterized, including: (i) a period of decreased water clarity, higher levels of soluble reactive phosphorus and higher phytoplankton biomass; and (ii) a period of relatively higher water clarity (as measured by Secchi depth), higher nitrate concentration and lower phytoplankton biomass. The periphyton chlorophyll‐a levels were lower during the first period, being negatively correlated with phytoplankton biomass. The results of this study suggest that during the period of decreased water clarity, periphyton was primarily light‐limited. In contrast, the periphyton biomass was higher during the second period, regardless of P limitation of periphyton growth. Rehabilitation of this highly degraded tropical reservoir must consider the light regime, which is controlled by phytoplankton abundance. Thus, a reduction in the P loading to the lake should be considered to suppress its cyanobacterial blooms, thereby improving conditions for submerged macrophytes and the re‐establishment of periphyton.     

Combined effects of organic pollution and eutrophication in the South para reservoirs,South Australia

Preliminary results of a comparative limnological study of three Mediterranean reservoirs in South Australia from August 1995 until March 1996 am presented. The reservoirs are characterised by meso- to eutrophic and dystrophic conditions. Dynamics and interactions between DOC, SRP and phytoplankton biomass were investigated regarding differences in mixing conditions, water levels and catchment links of the reservoirs. A scenario analysis was conducted to predict effects of artificial aeration and DOC removal in the Barossa reservoir. Results indicate positive and negative feedbacks between organic pollution and eutrophication such as nutrient limitation by organic complexation of phosphorus, light limitation of phytoplankton growth by water colour and DOC release after phytoplankton breakdowns. Orientation of further research and management options are discussed.     

长湖水质演变特征及水环境现状评价

利用湖北省长湖2001-2011年的水质监测资料,分析了长湖年际及月际的水质演变规律。结果表明,2005年长湖水质达到最差,然后呈逐渐好转趋势,至2011年,长湖水质已有明显改善。在1个水文年内,长湖的水质优劣顺序依次是：丰水期,平水期,枯水期。利用模糊综合评价方法对2011年长湖水质状况进行评价,结果表明,该年3个水期长湖水质状况的最大隶属等级为Ⅰ类,水质较好。利用卡尔森指数法对长湖2011年丰水期进行富营养化评价,结果表明,除习家口水域外,全湖水体基本上处于中度富营养化水平。对长湖水环境压力进行分析,结果表明,长湖的生态系统正面临衰退困境,而主要污染物的年入湖量已大大超出长湖的纳污能力。     

Characterization of water quality in a small hydropower plant reservoir in southern Brazil

The construction of large reservoirs can cause profound environmental changes. Reduced water flow, increased water residence time, thermal stratification, increased sedimentation rates and decreased dissolved oxygen concentrations are examples of such changes. These changes can affect water quality and the biota in the environments adapted to the natural conditions of a river. Small reservoirs developed in conjunction with hydropower plants, however, could reduce the degraded water quality. This study focuses on characterizing water quality in a small hydroelectric reservoir. The study reservoir has an area of 1.4 km² and a short water retention time. The Monte Claro Hydroelectric Power Plant is part of a complex consisting of three plants on the Antas River in the north‐west of Rio Grande do Sul state, Brazil. The reservoirs associated with these plants are operated as run‐of‐the‐river facilities. Monitoring results obtained by CERAN, the Energetic Company of Antas River (Companhia Energética Rio das Antas), were used to evaluate the reservoir water quality. Three samples were collected seasonally (spring, summer, autumn and winter) in the area of influence of this plant following the filling of the reservoir (2005–2008). The examined water quality parameters were electrical conductivity, colour, turbidity, alkalinity, pH, biological oxygen demand (BOD), chemical oxygen demand (COD), total phosphorus, dissolved oxygen, sulphate, nitrate, nitrite, ammonia, suspended and dissolved solids, chlorophyll‐a, total and faecal coliforms, water temperature and Secchi depth transparency. The results were interpreted using an index of water quality, Trophic State Index, reservoir water quality and CONAMA Regulation 357/05 (Brazilian legislation). Based on these analyses, no significant changes were exhibited in the water quality of the reservoir from the hydroelectric plant operation.     

Bacteriological eutrophication indicators in four Colombian water bodies (South America)

For the first time in Colombia the relative abundance of Pseudomonas spp., Vibrio spp., Plesiomonas shigelloides , the Aeromonas hydrophila group, and the faecal and total coliforms were studied in three dams and a natural lagoon with a different trophic state. Coliforms were low in all the water bodies, but their number was greater in the dams with a greater anthropic activity. Vibrio spp. was not detected. The density of P. shigelloides was irregular. Pseudomonas spp. was always present and showed relatively high abundance. The bacteria of the A. hydrophila group were constant and their numbers increased with the trophic state, for which they could be indicators of the eutrophication phenomena. Significant correlation ( P < 0.05) was established between total and faecal coliforms and pH, transparency, nitrites, nitrates, and orthophosphates. P. shigelloides was correlated with faecal coliforms and Aeromonas hydrophila with total coliforms and transparency.     

Bacteriological eutrophication indicators in four Colombian water bodies (South America)

For the first time in Colombia the relative abundance of Pseudomonas spp., Vibrio spp., Plesiomonas shigelloides , the Aeromonas hydrophila group, and the faecal and total coliforms were studied in three dams and a natural lagoon with a different trophic state. Coliforms were low in all the water bodies, but their number was greater in the dams with a greater anthropic activity. Vibrio spp. was not detected. The density of P. shigelloides was irregular. Pseudomonas spp. was always present and showed relatively high abundance. The bacteria of the A. hydrophila group were constant and their numbers increased with the trophic state, for which they could be indicators of the eutrophication phenomena. Significant correlation ( P < 0.05) was established between total and faecal coliforms and pH, transparency, nitrites, nitrates, and orthophosphates. P. shigelloides was correlated with faecal coliforms and Aeromonas hydrophila with total coliforms and transparency.     

Basis for the protection and management of tropical lakes

Management of lakes for the protection of water quality, aquatic life and other uses must be approached somewhat differently in the tropics from how it is approached at temperate latitudes. More than half of all tropical lakes are accounted for by natural river lakes or reservoirs. Therefore, degradation of water quality in rivers will have direct negative effects on the majority of lakes in the tropics. Also, regulation of rivers, which is one result of river impoundment, is a potential cause of damage to river lakes. Tropical lakes are more sensitive than temperate lakes to increases in nutrient supply and show higher proportionate changes in water quality and biotic communities in response to eutrophication. Tropical lakes are especially prone to loss of deep‐water oxygen, and in order to maintain ecological stasis therefore require more stringent regulation of organic and nutrient loading than temperate lakes. Nutrient containment must be more strongly oriented toward nitrogen, the most probable limiting nutrient in tropical lakes, than has been the case at temperate latitudes. However, phosphorus control is also important. Nitrogen management may be more feasible in the tropics because of high temperature, which is one of the critical conditions for efficient denitrification. Planktonic and benthic communities of the tropics bear a close resemblance, both in composition and diversity, to those of temperate latitudes; there is no parallel to the latitudinal gradient in biodiversity that is characteristic of terrestrial ecosystems. Foci of biodiversity, which require special attention, include the endemic species of ancient lakes and the diverse fish communities of very large rivers. The latter are an especially valuable untapped economic resource, but face severe impairment due to hydrological regulation and pollution of rivers. Effective management programs for tropical lakes will focus on interception of nutrients, protection of aquatic habitats from invasive species, and minimization of hydrological changes in rivers to which lakes are connected. In the absence of protective management, tropical lakes will decline greatly in their utility for water supply, production of commercially useful species, and recreation.