Driving variables for eutrophication in lakes of Hanoi by data‐driven technique

To investigate eutrophication in 31 freshwater lakes in Hanoi, Vietnam, water quality and Chlorophyll‐a content were monitored to calculate trophic indices. Twelve of the 15 urban lakes investigated were eutrophic, of which five were hypertrophic, while only seven of the 16 suburban lakes were eutrophic. The Trophic Index (TRIX) was the best predictive index to identify the eutrophication level of the lakes. Classification trees (CTs) were applied to study the trophic status of lakes and identify the driving variables. The results demonstrated that eutrophication in the lakes of Hanoi was driven by nutrients and organic enrichment, as well as by inappropriate management such as unplanned embankment and water uses. DIN, BOD, lake size and embankment were the key parameters controlling eutrophication in the lakes of Hanoi.     

Multiplatform optical monitoring of eutrophication in temporally and spatially variable lakes

Representative spatial patterns of eutrophication variables cannot be produced using traditional in situ sampling techniques. Spatial heterogeneity complicates the study of seasonal and long-term trends and the evaluation of water management policies. Remote sensing, however, with its broad view has the potential to deliver the relevant information. This paper will address the added value of synoptic eutrophication maps to the standard monitoring program of two large, spatially and temporally variable lakes in the Netherlands, Lakes IJssel and Marken. Remote sensing images were obtained from SeaWiFS; and combined with hyperspectral reflectance data from the airborne EPS-a sensor and the shipboard PR-650 spectroradiometer. The PR-650 data were used in selecting the most appropriate algorithms for SeaWiFS and EPS-a. A special algorithm for case II waters with high chlorophyll content was applied to SeaWiFS data to obtain chlorophyll concentrations. Synoptic maps of suspended matter were retrieved using inversion of a model for irradiance reflectance. For the airborne sensor inversion of reflectance was used for both suspended matter and chlorophyll. Satellite and airborne sensors clearly are complementary to each other. Comparison of satellite data with the airborne data and the (scarcely available) in situ data reveal underlying problems with: (i) validation of remote sensing images; and (ii) comparing data at different spatial and temporal scales. In our study, we found a reasonable agreement between different data sources at seasonal time scales, but at shorter time scales the differences can be (much) larger. In situ data suffer from poor reproducibility, related to the natural variability at small spatial scales (patchiness), combined with a significant temporal variability. The standard in situ monitoring program in Lakes IJssel and Marken lacks both the necessary spatial coverage as well as an appropriate sampling frequency. This indicates that for reliable monitoring, a synoptic data set, sampled at a high frequency is required. Remote sensing can partially fulfil this demand but still lacks the demanded frequency, mainly due to regular cloud cover. The answer may be in a multiplatform monitoring approach, as used in our study (combining in situ data with shipboard, airborne and satellite optical data) and in combining monitoring data with models. Satellite remote sensing is most powerful in determining properties that are inherent to the whole lake system, like the overall mean chlorophyll-a concentration. Computational models may meet the demand for a sufficiently high sampling frequency by deterministic interpolation of the data in time.     

Detection of water quality using simulated satellite data and semi-empirical algorithms in Finland

The aim of the study was to test the feasibility of the band combination of the TERRA MODIS and ENVISAT MERIS instruments for operational monitoring of lakes and coastal waters in Finland. Also simulated LANDSAT TM data were tested. Satellite bands were simulated using airborne measurements with AISA imaging spectrometer. Semi-empirical algorithms with simulated satellite data were tested against field observations using regression analysis. Interpretation of chlorophyll a, suspended matter, turbidity and secchi-disk depth was included in the analyses. The data for this study were gathered in campaigns carried out in May and August 1997 and August 1998 both for lakes in southern Finland and coastal waters of the Baltic Sea. The data set included 85 in situ observations for lakes and 107 for coastal waters. Our results show that the band combination to be included in the ENVISAT MERIS instrument enables the interpretation of water quality, including chlorophyll a concentration using semi-empirical algorithms both for lakes and coastal waters. MERIS band 9 centred at 705 nm is proven to be of vital importance for the detection of chlorophyll a in local surface waters.     

The N:P ratio and tests with Selenastrum to predict eutrophication in lakes

During the spring overturn, at the time of maximum potential phytoplankton growth, 26 Italian lakes were sampled to carry out enrichment experiments in which single and mixed treatments of nitrate and phosphate were applied to laboratory cultures of Selenastrum capricornutum. The method, in conjunction with chemical analysis, can be used to classify the lakes and to evaluate the limiting values of each nutrient. It was possible to correlate the phosphorus concentration to the maximal primary production and obtain threshold levels for phosphorus in predicting eutrophication trends in lakes.     

Responses of the three test algae of the algal assay procedure: Bottle test

The Algal Assay Procedure (AAP): Bottle Test utilizes three test organisms which, under standardized culture conditions, give a range of responses to the physical and nutritional states of test waters. The test algae of the AAP are Selenastrum capricornutum, Microcystis aeruginosa and Anabaena flos-aquae. The responses of these organisms to light intensities and to micro- and macronutrients are described. Phosphate spikes as low as 1–2 μg P l⁻¹ are shown to give a measurable bioassay response in highly oligotrophic waters.The AAP test algae are used to assess the effects of nutrient enrichment with sewage in waters from a cross-section of U.S. lakes. Enrichment of oligotrophic waters with primary or secondary sewage effluent results in significant growth of the three algae, while sewage additions to eutrophic waters cause little or no significant increase in algal growth rate or maximum standing crop. The response of the AAP algae also indicate that nutrient removal by tertiary treatment greatly reduces the stimulatory properties of sewage. In the presence of tertiary sewage, growth rate and maximum standing crop of the three test organisms are near those of lake water controls.The AAP test protocol is shown to be useful in the determination of limiting nutrients and in the comparison of the algal growth potential of natural waters to that of defined media.     

A tiered risk-based approach for predicting diffuse and point source phosphorus losses in agricultural areas

Implementation of the European Union Water Framework Directive requires an assessment of the pressures from human activity, which, combined with information on the sensitivity of the receiving waterbody to the pressures, will identify those water bodies at risk of failing to meet the Directive's environmental objectives. Part of the process of undertaking the risk assessment for lakes is an assessment of diffuse agricultural phosphorus (P) pressures. Three approaches of increasing sophistication were developed for this purpose: a basic 'risk screening' approach (tier 1) applicable to all lakes in Great Britain (GB) and based on export coefficients for different land cover classes and animal types; the Pressure Delivery Risk Screening Matrix approach (tier 2) that differentiated between pressures in surface water and groundwater river basins; and the Phosphorus Indicators Tool (PIT), a simple model of locational risk and P delivery potential (tier 3). Application of the three approaches to a range of lake catchments in England demonstrated that a tiered risk assessment approach was appropriate which was tailored to the quality of the available data. A step-wise procedure was developed whereby if the tier 1 and 2 approaches showed a catchment to be at high risk of failing to meet the Directive's environmental objectives with regard to P, it was justifiable to undertake a more detailed assessment using the tier 3 approach. The tier 1 approach was applied to all lakes in GB greater than 1 ha in size on the assumption that the boundary between the good/moderate status classes under the Water Framework Directive guidelines represented a doubling of the total P (TP) reference conditions. The initial outputs suggested that 51% of lakes in GB are predicted to not meet the TP targets identified for high or good status and must, therefore, be considered at risk. There were regional differences in numbers of lakes at risk. Scotland appeared to have the fewest sites at risk (18%); England the most (88%), with Wales having an intermediate percentage (56%). A comparison of P pressures on freshwaters using the tier 2 approach with other pressures on waterbodies (e.g. nitrate, sediment) in GB is shown as risk maps on the Environment Agency website at: . The tier 3 approach was applied to data-rich catchments and identified at the 1 km(2) areas of relatively high risk of P delivery to water.     

Evaluation of water column and sediment toxicity from an abandoned uranium mine using a battery of bioassays

Uranium mining activities in Cunha Baixa, Mangualde (Portugal), were extensive between 1967 and 1993, with high production of poor ore. Ore exploitation left millions of tons of tailings in the surrounding area, close to human houses. Contamination of the area (water and soil compartment) presently represents a serious hazard to humans and wildlife. The aim of this work was to evaluate the acute toxicity of water and sediments from a pond that floods a uranium mine pit, in two periods (spring and autumn). High contents of metals were found in water samples (chiefly Mn, Fe, Al, U, Sr). A battery of assays was applied to screen the acute toxicity of the different compartments using algae, crustaceans and dipterans. Results showed that the sediments were non-toxic, unlike the superficial water. Water toxicity was higher in the autumn, when the effluent was more acidic, compared to spring. In the water toxicity assays, the relative sensitivity of the test species used was Daphnia longispina>Pseudokirchneriella subcapitata>Daphnia magna. The present study is part of the chemical and ecotoxicological characterisation of the aquatic compartment performed in the Tier 1 of the Ecological Risk Assessment of the Cunha Baixa mining area.     

Cyanobacterial blooms: statistical models describing risk factors for national-scale lake assessment and lake management

Cyanobacterial toxins constitute one of the most high risk categories of waterborne toxic biological substances. For this reason there is a clear need to know which freshwater environments are most susceptible to the development of large populations of cyanobacteria. Phytoplankton data from 134 UK lakes were used to develop a series of Generalised Additive Models and Generalised Additive Mixed Models to describe which kinds of lakes may be susceptible to cyanobacterial blooms using widely available explanatory variables. Models were developed for log cyanobacterial biovolume. Water colour and alkalinity are significant explanatory variables and retention time and TP borderline significant (R²-adj = 21.9%). Surprisingly, the models developed reveal that nutrient concentrations are not the primary explanatory variable; water colour and alkalinity were more important. However, given suitable environments (low colour, neutral-alkaline waters), cyanobacteria do increase with both increasing retention time and increasing TP concentrations, supporting the observations that cyanobacteria are one of the most visible symptoms of eutrophication, particularly in warm, dry summers. The models can contribute to the assessment of risks to public health, at a regional- to national level, helping target lake monitoring and management more cost-effectively at those lakes at the highest risk of breaching World Health Organisation guideline levels for cyanobacteria in recreational waters. The models also inform restoration options available for reducing cyanobacterial blooms, indicating that, in the highest risk lakes (alkaline, low colour lakes), risks can generally be lessened through management aimed at reducing nutrient loads and increasing flushing during summer.     

Serum PCB profiles in Native Americans from Wisconsin based on region, diet, age, and gender: Implications for epidemiology studies

BACKGROUND: Different PCB congeners and different mixtures of congeners have been demonstrated to have different biological actions. More complete characterization of congener profiles in exposure sources may assist in predicting health outcomes. METHODS: Thirty-six (36) polychlorinated biphenyl (PCB) congeners were measured by gas chromatography isotope-dilution mass spectrometry (IDMS) in 314 serum samples from Native Americans in Wisconsin, Michigan and Minnesota. Five dietary groups were established based on the quantity and species of fish consumed and the waters from which the fish were caught. Multivariate statistical methods were able to resolve gender and dietary differences in PCB homologue and PCB congener patterns. RESULTS: Females had higher proportions of lower chlorinated homologues, including a consistently higher proportion of pentaCB 118. The relative presence of the very labile and volatile PCB 18, above 1% of the total PCB in females from the minimal fish consumption and "other" groups, suggests possible exposure to PCBs in the atmosphere. The dietary group consuming predatory fishes from Lakes Michigan and Superior had the highest serum concentrations of total PCB (mean of 3.1 ng/ml) and the most distinct congener profile. The two dietary groups least dependent on fishing or fishing mostly from inland lakes (non-Great Lakes) had the lowest total PCB concentrations, both with means of 1.4 ng/ml. CONCLUSIONS: These serum PCB concentrations were less than those found in earlier studies of fish consumers in the Great Lakes region and may reflect the decrease in PCBs in these lakes.     

Modified risk assessment tool for embankment dams: case study of three dams in Turkey

Dam failures are catastrophic accidents resulting in property damage and loss of life. Risk prioritisation systems should be used in accordance with dam safety regulations to prevent these disasters. The purpose of this paper is to develop a risk assessment software which can be used by the decision makers for ranking of dams. Risk assessment was conducted on three embankment dams from Turkey to obtain information about the dam performance based on piping, earthquake, normal stability and flood failure modes. Parameters are incorporated into the programme to develop a new model that could predict variables such as breach width, dam failure time, side slope and peak breach discharge. The proposed tool gives flexibility to choose dam elements for describing the primary features of the evaluated dam; so users can make hazard categorisation of dams according to their risk level which is based on unique project conditions.     

The use of epiphyton and epilithon data as a base for calculating ecological indices in monitoring of eutrophication in lakes in central Sweden

Eutrophication was monitored with the aid of one similarity and seven diversity indices in the lakes of different trophic levels (eutrophic, mesotrophic and oligotrophic) in central Sweden. The ecological indices were applied separately to epiphyton and epilithon communities. Epiphyton turned out to be inappropriate for assessing eutrophication in the lakes studied. On the other hand, Hurlbert's, Simpson's and the similarity indices turned out to be promising environmental tools when applied to the data of epilithon.     

Long-term lake water quality predictors

Daily water temperature and dissolved oxygen profiles in 3002 Minnesota lakes have been simulated by deterministic process-based water quality models with daily meteorological conditions from 1955 to 1979 as input. From the simulated results, indicators of lake water quality and fish habitat characteristics have been extracted and correlated selectively with normal air temperature, lake mean depth, wind-related densimetric Froude number and Lake number. A seasonal maximum Lake number was found to be a good predictor for volume averaged water temperatures, maximum water temperatures near lake bottom, seasonal stratification characteristics, volume averaged dissolved oxygen concentrations, anoxia characteristics and fish good-growth habitat. Lakes with a maximum daily Lake number bigger than 1.0, are seasonally stratified, have low hypolimnetic dissolved oxygen concentration, and only a fraction of lake depth available for good-growth of fish. Lakes with maximum daily Lake number less than 1.0 are polymictic, with high dissolved oxygen concentration, and with maximum depth available for good fish growth. Empirical formulas for lake water quality and stratification indicators derived from the simulation results give good predictions of temperature and dissolved oxygen characteristics estimated from measurements in seven Minnesota lakes.     

Determining reference conditions for nutrients,chlorophyll a and Secchi depth in Yungui Plateau ecoregion lakes,China

Establishing nutrient reference condition (baseline environmental condition) of lakes in ecoregion is a critical consideration in the development of scientifically defensible aquatic nutrient criteria. Three methods were applied to determine reference conditions in Yungui Plateau ecoregion lakes with respect to total phosphorus, total nitrogen, planktonic chlorophyll a (chl a) and Secchi depth. First, minimally developed lake/catchment units were identified based on existing geographical database and visual basin survey. Lakes in these catchments were considered minimally disturbed ‘reference lakes’. Second, the frequency distribution of all of the lake data presently available by each variable was plotted, and the lower 25th percentile was selected as the reference condition for each value. Third, median nutrient, chl a and Secchi depth values were determined for the best one‐third of lakes and applied as indicators of reference condition. The result of model prediction and data from historical record were used to test three techniques for determining reference condition. Reference conditions, as determined by these three methods, broadly agreed for all parameters. Overall, the data suggest that multiple methods can be used to determine reference condition, and that in Yungui lakes, reference condition corresponds to oligotrophic–mesotrophic status.     

Trends of phosphorus,nitrogen and chlorophyll a concentrations in Finnish rivers and lakes in 1975-2000

During recent decades the amounts of nutrients discharged to Finnish surface waters have markedly decreased. This has been achieved by considerable investments in water protection, which were made mainly to improve municipal and industrial wastewater purification. We investigated whether these water protection measures have decreased phosphorus and nitrogen concentrations in Finnish rivers and lakes. In addition, possible trends in chlorophyll a concentrations in lakes were studied. The data consisted of a total of over 68000 monitoring results of 22 rivers and 173 lakes (or sub-basins of lakes) with different types of catchment areas. The study period covered the years 1975-2000 and the non-parametric Kendall Tau b and Seasonal Kendall tests were applied for detecting trends. Decreasing nutrient concentration trends were typical in many lakes and rivers earlier polluted by municipal and industrial wastewaters. Increasing nutrient concentration trends were common in smaller rivers and lakes receiving diffuse loading from agriculture. The results show that the investments directed towards wastewater purification have effectively improved the quality of Finnish inland waters. However, no clear effects of decreasing non-point loading were found. Thus, more effective measures should be directed towards decreasing non-point source loading.     

基于物元可拓法的水库富营养化评价

以沈阳市中型水库富营养化评价为例,探讨了物元可拓法评价水体富营养化的可行性。通过建立水库富营养化评价标准以及选取评价因子,并利用关联度来确定水体富营养化等级。对沈阳市中型水库评价结果表明,丰水期40％的水库为中度富营养化,60％为重度富营养化;枯水期60％为中度富营养化,40％为重度富营养化。采用物元可拓法可以较精确地评价水体富营养化程度,还可以反映水体富营养化的趋势,该方法较其他方法更适用于水体富营养化评价。     

Eutrophication: Assessment, Research and Management with Special Reference to Scotland's Freshwaters

In response to the extraordinarily high profile currently maintained by algae, this paper discusses aspects of pure and applied research on eutrophication. In addition to restating a number of issues which were raised decades ago when the importance of this environmental problem was first recognized, the following aspects are explored using data collected mainly over the last 20 years and referring primarily to Scottish studies: (i) algal-nutrient relations and the contrasting manner in which nitrogen and phosphorus enter freshwaters and are sequestered by planktonic organisms; (ii) estimates of the loadings of phosphorus to freshwaters from various sources; (iii) the effects on our perception of algal problems and the use to which the waters are intended; (iv) the extent and limitations of existing scientific knowledge about eutrophication, and its application to the formulation and execution of eutrophication control strategies; and (v) the arguments for maintaining in-depth limnological surveillance programmes.     

Seasonal changes of arsenic speciation in lake waters in relation to eutrophication

In this study, the influence of eutrophication on arsenic speciation in lake waters was investigated. Surface water samples (n = 1-10) were collected from 18 lakes in Japan during July 2007 and February 2008. The lakes were classified into mesotrophic (7 lakes) and eutrophic (11 lakes) based on the total phosphate (T-P) and chlorophyll-a (Chl-a) concentrations in water column. Inorganic, methylated and ultraviolet-labile fractions of arsenic species were determined by combining hydride generation atomic absorption spectrometry with ultraviolet irradiation. Organoarsenicals (mainly methylated and ultraviolet-labile fractions) comprised 30-60% of the total arsenic in most lakes during summer. On the other hand, inorganic arsenic species (As(III + V)) dominates (about 60-85%) during winter. The occurrence of ultraviolet-labile fractions of arsenic was higher in eutrophic lakes than those in mesotrophic lakes in both seasons. The concentration of dimethyl arsenic (DMAA) was high in eutrophic lakes during winter; and in mesotrophic lakes during summer. The results suggest that the conversion of As(III + V) to more complicated organoarsenicals occurred frequently in eutrophic lakes compared to that in mesotrophic lakes, which is thought to be the influence of biological activity in the water column. The distribution of arsenic species were well correlated with phosphate concentrations than those of Chl-a. This might be due to the competitive uptake of As(V) and phosphate by phytoplankton. The organoarsenicals (OrgAs)/As(V) ratio was higher at low phosphate concentration indicating that conversion of As(V) to OrgAs species was more active in phosphate-exhausted lakes with high phytoplankton density.     

Is the Negro River Basin (Amazon) impacted by naturally occurring mercury?

In order to investigate the major sources and cycling of mercury in the Negro River Basin (Amazon), total metal measurements were carried out in soils, in river and lake waters, in the atmosphere, and in bulk precipitation during the period 1995 throughout 1998. Median values of 1.3 ng m(-3) in the atmosphere, 172 microg kg(-1) in soils, 4.6-7.5 ng l(-1) in three different lakes, 4.5 ng l(-1) in 17 different Negro River tributaries and 20.3 microg m(-2) year(-1) in bulk precipitation were found. Mercury concentrations in rivers and lakes waters, as well as in soils and bulk precipitation were high, considering the scarcity of anthropogenic point sources in the region. Mercury leaching from soil, the largest regional reservoir of this metal, was considered to be the major pathway to mercury enrichment in the region.     

Long-term phosphorus budgets and an examination of a steady-state mass balance model for central Ontario lakes

The objective of this study was to evaluate, modify if necessary, and calibrate a mass balance steady-state total phosphorus (TP) model for use in the Precambrian Shield area of Ontario. Hydrologic data, TP mass balances and lake concentrations data were collected between June 1978 and May 1992 from seven oligotrophic and oligomesotrophic lakes located on the Precambrian Shield in central Ontario. Two of the lakes (Dickie and Harp) had substantial shoreline development; four lakes had alkalinities <25 μ eql⁻¹. The gross settling or loss coefficient, v, was underestimated when internal load was ignored. Long-term mean v ranged about three-fold, from 4.7 m yr⁻¹ in Plastic Lake to 13.7 m yr⁻¹ in Dickie Lake with an average for six lakes of 7.9 m yr⁻¹. The exception was Harp Lake where v was 23.2 m yr⁻¹. The difference in v between heavily developed Dickie and Harp Lakes may have been due to the unusually thick glacial tills in the Harp catchment and their likely ability to retain at least some of the TP from septic effluent. The current inability to predict septic TP retention rates by soils/tills, the highly variable nature of soils/tills, and the decades required to reach equilibrium after installation leave environmental managers with little choice but to apply the “precautionary principle” to ensure adequate protection of inland recreational waters and assume that soils do not retain septic TP. There was no evidence that enhanced sedimentation of TP (“oligotrophication”) occurred in any of the three most acidic lakes. In fact, losses via sedimentation were lowest in these lakes. Average retention, R ((input-output)/input) of TP during the ice-free months of May to November was much higher than average R in winter (December–April) in all lakes. Lack of wind-induced mixing, low biological activity and thermal stratification caused by ice cover make it more likely that stream loads are discharged directly from lakes during winter. Seasonal variation in retention suggests that R and v should be higher in warmer climatic zones. There may be no globally valid v, although the data presented here suggest that a regionally applicable estimate of v may be appropriate. The model should only be calibrated with a long-term data set and should be only used to predict long-term, average responses to changes in average TP loading.     

How green is my river? A new paradigm of eutrophication in rivers

Although the process of eutrophication is reasonably well understood in lakes, there is currently no conceptual understanding of how eutrophication develops in rivers. This issue is addressed here. A review of the main processes controlling the development of eutrophication in lakes has been carried out as a precursor to considering the effect in rivers. The importance of hydraulic flushing in controlling algal growth suggests that short-retention-time rivers will show different effects compared to long retention-time, impounded rivers. The latter are likely to operate like lakes, moving from macrophyte domination to phytoplankton domination whereas the former move to benthic and filamentous algal domination. Subsequently, a conceptual model of the development of eutrophic conditions in short-retention-time rivers is developed. Although there is general agreement in the literature that an increase in nutrients, particularly phosphorus, is a pre-requisite for the eutrophic conditions to develop, there is little evidence in short-retention-time rivers that the plant (macro and micro) biomass is limited by nutrients and a good case can be made that the interaction of hydraulic drag with light limitation is the main controlling factor. The light limitation is brought about by the development of epiphytic algal films on the macrophyte leaves. The implications of this conceptual model are discussed and a series of observable effects are predicted, which should result if the model is correct.