Water Quality Determinants Research Articles

The spatial impact of rural economic change on river water quality

This paper, using Ireland as a case study, examines the relationship between rural economic activities and river water quality. The stipulation from the EU water framework directive (WFD) that all surface waters in the EU must be of ‘good ecological status’ necessitates a quantitative understanding of the major determinants of water quality. Within this context, this paper combines a number of spatial datasets relating to agricultural, land use, residential and industrial activities, to examine the major economic influences on the ecological quality of water resources. It is hoped that providing a comprehensive understanding of the effect of a variety of economic activities that influence the ecological quality of water will be an important tool in the management of risk and will allow for more appropriate land use planning aimed at restoring and maintaining water quality as required by the WFD. Results indicate that the level of forestry, industrial activity, the intensity and type of agricultural activity and the type of wastewater treatment in an area are all critical factors affecting the quality of water resources. The model finds that relationship between agriculture and water quality improved over time during a period where there was substantial legislative measures and financial support to facilitate improved water quality.

Antifungal agents, yeast abundance and diversity in surface water: Potential risks to water users

South African surface waters are subject to various forms of pollution. Recent findings in aquatic systems suggest an association exists between yeast diversity, chemical pollutants and land coverage, which are important water quality determinants. Yeast abundance and diversity, as well as antifungal agents in two river systems in South Africa, were investigated and related to the existing land coverage. Yeast abundance and diversity were determined from environmental DNA by quantitative polymerase chain reaction and next-generation sequencing, respectively, of the 26S ribosomal ribonucleic acid (rRNA) gene. Antifungal agents were qualitatively and/or quantitatively detected by ultra-high-pressure liquid chromatography-mass spectrometry. Analyses of 2 031 714 high-quality 26S rRNA sequences yielded 5554 amplicon sequence variants (ASVs)/species. ASV richness and Shannon-Wiener index of diversity reflected the southward flow of the river with higher values observed downstream compared to the upstream. Fluconazole concentrations were quantifiable in only two samples; 178 and 271 ng L−1. Taxonomically, at least 20 yeast species were detected, including the dominant Candida tropicalis, Cryptococcus spp. as well as the lesser dominant Bensingtonia bomiensis, Fereydounia khargensis, Hericium erinaceus, Kondoa changbaiensi, Pseudozyma spp. and Sphacelotheca pamparum. The two dominant species are known opportunistic pathogens which had antifungal resistant traits in previous studies from the same rivers and therefore is a public health threat. The present study provides further evidence that yeasts should be included as part of water quality parameters, especially in developing countries where much of the population are economically disadvantaged, and also immunocompromised due to age and disease.

Water Quality Modelling for River Activities Management: Example from a Low- and Middle-Income Country.

Background.Rivers are susceptible to pollution and water pollution is a growing problem in low- and middle-income countries (LMIC) with rapid development and minimal environmental protections. There are universal pollutant threshold values, but they are not directly linked to river activities such as sand mining and aquaculture. Water quality modelling can support assessments of river pollution and provide information on this important environmental issue.Objectives.The objective of the present study was to demonstrate water quality modelling methodology in reviewing existing policies for Malaysian river catchments based on an example case study.Methods.The MIKE 11 software developed by the Danish Hydraulic Institute was used to model the main pollutant point sources within the study area - sand mining and aquaculture. Water quality data were obtained for six river stations from 2000 to 2015. All sand mining and aquaculture locations and approximate production capacities were quantified by ground survey. Modelling of the sand washing effluents was undertaken with the advection-dispersion module due to the nature of the fine sediment. Modelling of the fates of aquaculture deposits required both advection-dispersion and Danish Hydraulic Institute ECO Lab modules to simulate the detailed interactions between water quality determinants.Results.According to the Malaysian standard, biochemical oxygen command (BOD) and ammonium (NH4) parameters fell under Class IV at most of the river reaches, while the dissolved oxygen (DO) parameter varied between Classes II to IV. Total suspended solids (TSS) fell within Classes IV to V along the mid river reaches of the catchment.Discussion.Comparison between corresponding constituents and locations showed that the water quality model reproduced the long-term duration exceedance for the main body of the curves. However, the water quality model underestimated the infrequent high concentration observations. A standard effluent disposal was proposed for the development of legislation and regulations by authorities in the district that could be replicated for other similar catchments.Conclusions.Modelling pollutants enables observation of trends over the years and the percentage of time a certain class is exceeded for each individual pollutant. The catchment did not meet Class II requirements and may not be able to reach Class I without extensive improvements in the quality and reducing the quantity of both point and non-point effluent sources within the catchment.Competing Interests.The authors declare no competing financial interests.

Impacts of gold mine effluent on water quality in a pristine sub-Arctic river

Impacts of mining on water quality are a great concern in the Arctic region. This study evaluated the impact of pre-treated mine effluent on river water quality. The study was conducted along the Seurujoki River in sub-Arctic Finland, which is impacted by Kittilä gold mine. The study analyzed water quality and hydrological data upstream and downstream of the mining area over an eight-year period, including a tailing dam leakage event in 2015. The analysis focused on water quality determinants such as electrical conductivity (EC), sulfate, antimony, manganese, and total nitrogen (Ntotal). Descriptive statistics on river water at four stations along the river corridor showed negative impacts of mining activities on the recipient water body. In order to find an indicator for water quality, correlation analysis between the water quality determinants was carried out. It identified EC as a good indicator for continuous water quality monitoring, especially to detect mining accidents such as partial failure of a tailings dam. The results showed increasing contaminant concentrations due to mining as more mine effluent was generated over time. A linear mixed model was developed to predict the coefficient of different elements affecting EC at river water monitoring stations impacted by mining effluents. The results provide new information on how to assess mining water impacts and plan future water quality monitoring.

Qualitative Analysis of Groundwater Quality Indicators Based on Schuler and Wilcox Diagrams: IDW and Kriging Models

Introduction: It is generally accepted that groundwater is one of the most vital sources of water for drinking use in cities and rural areas. The water drawn from these sources should be sanitary, have low soluble substances, and be free of any pathogens and microorganisms. Materials and Methods: In this study, 90 wells were sampled with proper dispersion over the study area to achieve suitable estimation accuracy. Results: The assessments made based on 10-year averages of water quality in the studied plain showed that according to the Schuler and Wilcox criteria of water quality for drinking and agricultural use, the northern and southern parts of the plain have unsuitable water quality compared to central parts. Interpolation RMSE value of the Inverse Distance Weighting (IDW) model for SO4-, TDS, TH, Mg2+, Cl-, Ca2+ and HCO3- were 8.46, 2615, 246, 6.8, 38.9, 8.3 1.16 also 8.4, 2628, 750.9, 7.0, 39.8, 8.1, 8.1 (mg L-1) for Kriging, respectively. Conclusion: The cause of low groundwater quality in northern regions is the high rate of SO4-, TH, Cl-, and TDS, which are of the most important determinants of water quality for drinking. The examination of samples in the assessment of water quality for agricultural use clearly showed a higher value of EC compared to SAR.

EFFECTS OF CONTROLLED DRAINAGE ON SOIL WATER REGIME AND QUALITY IN LITHUANIA

Lithuania remains one of the most extensively drained of the Baltic and Nordiccountries. The overall drained area (ditches plus tile drains) totalled 87% of theagricultural land area. Many nutrients from soil are leached through drainageresulting in polluting streams (drain flow receivers) water. Drain flow is treated asa major determinant of water quality. Therefore, the reduction of nutrients enteringthe drains is very important. Controlled drainage conception, when the outflowheight is increased at the mouth, helps reduce drainage runoff and partially purifywater. The aim of the research was to establish controlled drainage influence on thesoil moisture regime, nitrogen and phosphorus leaching. Investigations werecarried out in sandy loam and loam soils in the Middle Lithuanian Lowland. Basedon studies, several tendencies were observed: when drainage outflow began, theamount of soil moisture in subsoil (50-80 cm layer of the soil) of controlleddrainage plot was higher than in the conventional drainage plot, and highermoisture supplies stayed for a longer period of time. Controlled drainage had nodirect impact on phosphorus and nitrogen concentrations but they were influencedby the leaching quantities of plant usable nutrients. The reason that in many caseslower nitrate nitrogen (54% of all measurements) and phosphorus concentrations(77% of all measurements) were found in the conventional system rather than inthe controlled drainage might be connected to the fact that the latter area containedpredominantly lighter textured soils (sandy loam) making it easier to wash awaythe nutrients unused by plant.

Effects of land use, topography, climate and socio-economic factors on geographical variation pattern of inland surface water quality in China.

The deterioration of water quality has become a primary environmental concern worldwide. Understanding the status of water quality and identifying the influencing factors are important for water resources management. However, reported analyses have mostly been conducted in small and focused areas. It is still unclear if factors driving spatial variation in water quality would be different in extended spatial scales. In this paper, we analyzed spatial pattern of inland surface water quality in China using a dataset with four water quality parameters (i.e., pH, DO, NH4+-N and CODMn) and the water quality level. We tested the effects of anthropogenic (i.e., land use and socio-economic) and natural (i.e., climatic and topographic) factors on spatial variation in water quality. The study concluded that the overall inland surface water quality in China was at level III (fair). Water quality level was strongly correlated with CODMn and NH4+-N concentration. In contrast to reported studies that suggested land use patterns were the determinants of inland surface water quality, this study revealed that both anthropogenic and natural factors played important roles in explaining spatial variation of inland surface water quality in China. Among the tested explanatory variables, mean elevation within watershed appeared as the best predictor for pH, while annual precipitation and mean air temperature were the most important explanatory variables for CODMn and DO, respectively. NH4+-N concentration and water quality level were most strongly correlated with the percent of forest cover in watershed. Compared to studies at smaller spatial scales, this study found different influencing factors of surface water quality, suggesting that factors may play different roles at different spatial scales of consideration. Therefore management policies and measures in water quality control must be established and implemented accordingly. Since currently adopted parameters for monitoring of inland surface water quality in China are largely influenced by natural variables, additional physicochemical and biological indicators are needed for a robust assessment of human impacts on water quality.

A comparison between weighted arithmetic and Canadian methods for a drinking water quality index at selected locations in shatt al-kufa

Shatt Al-Kufa (Kufa River) is the major supply of surface waters in Najaf; the length and width of the river are 73 km and about 100 m respectively. In the various seasons of the year, the water level at the river is unstable, and population increases and higher living standards are likely to cause increased demand for the river water; thus, river water quality is a key concern, especially for drinking purposes.Water Quality Index (WQI) is defined as a rating reflecting the compound effects of various water quality determinants on the total quality of water. WQI is a mathematical tool used to convert large amounts of water quality data into a single number, providing a simple and explicable tool for managers and decision-makers to use to examine the quality and potential uses of a given body of water.This study is concerned with assessing an appropriate WQI for drinking use at several locations on Shatt Al-Kufa. The twelve water quality parameters of pH, Turbidity (Turb.), Electrical Conductivity (EC), Alkalinity (Alk.), Total Dissolved Solid (TDS), Total Hardness (T.H), Calcium (Ca+2), Magnesium (Mg+2), Sodium (Na+), Potassium (K+), Chlorides (Cl-1) and Sulphate (SO4) were studied over a period of ten months (January to October 2014) for nine selected locations, including Zerkh, Kufa, Manathira, Hira, Mashkhab and Qadisiya on Shatt Al-Kufa. Two methods (Weighted Arithmetic and Canadian) were applied to classify the WQI of the treated river water for drinking use, and then a comparison of the two methods was made to ascertain the difference between them.The Results of the overall and seasonal WQI according to both the Weighted Arithmetic Method and the Canadian method were classified as good (50.1 to 100 and 80 to 94, respectively) in all selected locations with the exception of certain locations in the winter season that applied to both methods.The results indicate that the difference between the two methods is very small; the high values of EC and high concentrations of SO4 were the main reasons lowering the water quality index in all locations according to both methods.

Microbial water quality and the detection of multidrug resistant E. coli and antibiotic resistance genes in aquaculture sites of Singapore

Poor microbial water quality jeopardizes the health and safety of food produced by aquaculture farms. Three fish farms and transect sites in Singapore were assessed for microbial water quality and antimicrobial resistance determinants. Of the 33 multidrug resistant E. coli isolated from surface waters of the Johor Straits, 81.8% were ESBL producers. The relative abundance of sul1, qnrA and intI1 genes were higher in sediments than surface waters. Among the surface water samples, higher concentrations (10−1−101) of beta-lactamases (blaSHV, blaOXA, blaCTX-M) were detected in the transect sites. This study highlights a potential antimicrobial resistance transmission chain from environmental waters, to animal carriers and humans.

Opportunities and Limits of Using Meteorological Reanalysis Data for Simulating Seasonal to Sub-Daily Water Temperature Dynamics in a Large Shallow Lake

In lakes and reservoirs, physical processes control temperature dynamics and stratification, which are important determinants of water quality. In large lakes, even extensive monitoring programs leave some of the patterns undiscovered and unresolved. Lake models can complement measurements in higher spatial and temporal resolution. These models require a set of driving data, particularly meteorological input data, which are compulsory to the models but at many locations not available at the desired scale or quality. It remains an open question whether these meteorological input data can be acquired in a sufficient quality by employing atmospheric models. In this study, we used the European Centre for Medium-Range Weather Forecasts’ (ECMWF) ERA-Interim atmospheric reanalysis data as meteorological forcing for the three-dimensional hydrodynamic General Estuarine Transport Model (GETM). With this combination, we modelled the spatio-temporal variation in water temperature in the large, shallow Lake Chaohu, China. The model succeeded in reproducing the seasonal patterns of cooling and warming. While the model did predict diurnal patterns, these patterns were not precise enough to correctly estimate the extent of short stratification events. Nevertheless, applying reanalysis data proved useful for simulating general patterns of stratification dynamics and seasonal thermodynamics in a large shallow lake over the year. Utilising reanalysis data together with hydrodynamic models can, therefore, inform about water temperature dynamics in the respective water bodies and, by that, complement local measurements.

Environmental Determinants of Surface Water Quality Based on Environmetric Methods

A multivariate statistical technique, exploratory factor analysis-FA, has been used to assess the natural and anthropogenic impacts on surface water quality in two river basins in Western part of Turkey (Buyuk Menderes and Kucuk Menderes River Basins). The method attempted to explain the correlations between the observations in terms of the underlying factors, which were not directly observable and to reduce a great number of the water quality variables to a smaller number of attributes, grouped in common factors. Furthermore, by using the Confirmatory Factor Analysis-CFA method, the reliability of separated factors and the dimensionality have been determined. Then the path diagram was designed to investigate the structural model. Results revealed that ionic composition and water oxygenation of waters were factors controlling overall water quality in the region. Since components of first factors were observed in higher levels in Buyuk Menderes Basin, it can be concluded that this region was affected from anthropogenic activities severely, compared to the Kucuk Menderes Basin. Overall results revealed that FA confirmed by CFA can be used to identify probable pollution sources of surface waters.

English

Metal contamination in water is a major determinant of water quality. People who consume this water suffer from water borne diseases. There are various natural and anthropological activities at the sample collection site leading to increase in concentration of trace elements in drinking water. Activities like corrosion of metal coated pipes, herbicides, insecticides, ceramic wastes, taking gravel from near water source, etc. may lead to pollution of drinking water by heavy metals like chromium. The objective of this study was to detect metal concentration in spring and tap water from selected residential areas in the Gurage Zone. Tap water samples were collected from seven different locations during the rainy season. Samples were analyzed using atomic absorption spectrometry to determine the concentration of dissolved metal. Metal analysis was done to detect chromium, copper, zinc, lead, cadmium, magnesium and calcium. The results obtained were compared with guidelines for drinking water quality such as the World Health Organization (WHO) guidelines. Key words: Cadmium, copper, lead metal concentration, chromium, Gurage Zone.

Water quality in a mining and water-stressed region

The aim of this study was to evaluate trends in water quality and mineral footprint along the catchment of a dam located in a coal mining area and water-stressed region. The study was conducted along the upper Olifants River, which is the catchment of Witbank Dam, in the jurisdiction of Emalahleni Local Municipality in South Africa. The study analysed water quality data over an eight-year period, obtained from the water authorities, and two-year data from the municipality. The analysis focused on water quality determinants such as pH, turbidity, total dissolved solids, sulphates and manganese. The analysis was conducted in line with South African National Standard 241:2015 on drinking water. By using allowable mineral concentration limits and thresholds, a statistical process capability index was calculated to determine the efficiency of controls on the potential of water being contaminated by land use and mining activities. It was found that the coal mining region was associated with adverse effects on the raw water quality. The paper presents a generic method in terms of a concentration-independent process capability index for monitoring deterioration of water across many water quality determinants. The results provide a warning signal to stakeholders. There is a time-critical and growing deterioration of water quality, which may pose health risks to consumers if there is no reduction in contamination sources or improved efficacy of water purification systems.

Identifying (subsurface) anthropogenic heat sources that influence temperature in the drinking water distribution system

Abstract. The water temperature in the drinking water distribution system and at customers' taps approaches the surrounding soil temperature at a depth of 1 m. Water temperature is an important determinant of water quality. In the Netherlands drinking water is distributed without additional residual disinfectant and the temperature of drinking water at customers' taps is not allowed to exceed 25 °C. In recent decades, the urban (sub)surface has been getting more occupied by various types of infrastructures, and some of these can be heat sources. Only recently have the anthropogenic sources and their influence on the underground been studied on coarse spatial scales. Little is known about the urban shallow underground heat profile on small spatial scales, of the order of 10 m × 10 m. Routine water quality samples at the tap in urban areas have shown up locations – so-called hotspots – in the city, with relatively high soil temperatures – up to 7 °C warmer – compared to the soil temperatures in the surrounding rural areas. Yet the sources and the locations of these hotspots have not been identified. It is expected that with climate change during a warm summer the soil temperature in the hotspots can be above 25 °C. The objective of this paper is to find a method to identify heat sources and urban characteristics that locally influence the soil temperature. The proposed method combines mapping of urban anthropogenic heat sources, retrospective modelling of the soil temperature, analysis of water temperature measurements at the tap, and extensive soil temperature measurements. This approach provided insight into the typical range of the variation of the urban soil temperature, and it is a first step to identifying areas with potential underground heat stress towards thermal underground management in cities.

Assessing landscape and contaminant point-sources as spatial determinants of water quality in the Vermilion River System, Ontario, Canada.

The Vermilion River and major tributaries (VRMT) are located in the Vermilion watershed (4272km2) in north-central Ontario, Canada. This watershed not only is dominated by natural land-cover but also has a legacy of mining and other development activities. The VRMT receive various point (e.g., sewage effluent) and non-point (e.g., mining activity runoff) inputs, in addition to flow regulation features. Further development in the Vermilion watershed has been proposed, raising concerns about cumulative impacts to ecosystem health in the VRMT. Due to the lack of historical assessments on riverine-health in the VRMT, a comprehensive suite of water quality parameters was collected monthly at 28 sites during the ice-free period of 2013 and 2014. Canadian water quality guidelines and objectives were not met by an assortment of water quality parameters, including nutrients and metals. This demonstrates that the VRMT is an impacted system with several pollution hotspots, particularly downstream of wastewater treatment facilities. Water quality throughout the river system appeared to be influenced by three distinct land-cover categories: forest, barren, and agriculture. Three spatial pathway models (geographical, topographical, and river network) were employed to assess the complex interactions between spatial pathways, stressors, and water quality condition. Topographical landscape analyses were performed at five different scales, where the strongest relationships between water quality and land-use occurred at the catchment scale. Sites on the main stem of Junction Creek, a tributary impacted by industrial and urban development, had above average concentrations for the majority of water quality parameters measured, including metals and nitrogen. The river network pathway (i.e., asymmetric eigenvector map (AEM)) and topographical feature (i.e., catchment land-use) models explained most of the variation in water quality (62.2%), indicating that they may be useful tools in assessing the spatial determinants of water quality decline.

Coupling fine particle and bedload transport in gravel-bedded streams

Fine particles in the silt- and clay-size range are important determinants of surface water quality. Since fine particle loading rates are not unique functions of stream discharge this limits the utility of the available models for water quality assessment. Data from 38 minimally developed watersheds within the United States Geological Survey stream gauging network in California, USA reveal three lines of evidence that fine particle release is coupled with bedload transport. First, there is a transition in fine particle loading rate as a function of discharge for gravel-bedded sediments that does not appear when the sediment bed is composed of sand, cobbles, boulders, or bedrock. Second, the discharge at the transition in the loading rate is correlated with the initiation of gravel mobilization. Third, high frequency particle concentration and discharge data are dominated by clockwise hysteresis where rising limb discharges generally have higher concentrations than falling limb discharges. These three observations across multiple watersheds lead to a conceptual model that fine particles accumulate within the sediment bed at discharges less than the transition and then the gravel bed fluidizes with fine particle release at discharges above the transition discharge. While these observations were individually recognized in the literature, this analysis provides a consistent conceptual model based on the coupling of fine particle dynamics with filtration at low discharges and gravel bed fluidization at higher discharges.

Trihalomethane concentrations in tap water as determinant of bottled water use in the city of Barcelona

Bottled water consumption is increasing worldwide, despite its huge economic and environmental cost. We aim to describe personal and tap water quality determinants of bottled water use in the city of Barcelona. This cross-sectional study used data from the Health Survey of Barcelona in 2006 (N=5417 adults). The use of bottled water to drink and to cook was evaluated in relation to age, gender, educational level, district and levels of trihalomethanes (THMs), free chlorine, conductivity, chloride, sodium, pH, nitrate and aluminium in municipal tap water using Robust Poisson Regression. The prevalence of bottled water use to drink and cook was 53.9% and 6.7%, respectively. Chemical parameters in water had a large variability (interquartile range of THMs concentrations: 83.2–200.8μg/L) and were correlated between them, except aluminium. Drinking bottled water increased with educational level, while cooking with bottled water was higher among men than among women and decreased with age. After adjusting by these personal determinants, a dose–response relationship was found between concentrations of all chemicals except aluminium in tap water and bottled water use. The highest association was found for THMs, with a Prevalence Ratio of 2.00 (95%CI=1.86, 2.15) for drinking bottled water and 2.80 (95%CI=1.72, 4.58) for cooking with bottled water, among those with >150μg/L vs. <100μg/L THMs in tap water. Conclusion: More than half of Barcelona residents regularly drank bottled water, and the main determinant was the chemical composition of tap water, particularly THM level.

THM and HAA formation from NOM in raw and treated surface waters

The disinfection by-product (DBP) formation potential (FP) of natural organic matter (NOM) in surface water sources has been studied with reference to the key water quality determinants (WQDs) of UV absorption (UV254), colour, and dissolved organic carbon (DOC) concentration. The data set used encompassed raw and treated water sampled over a 30-month period from 30 water treatment works (WTWs) across Scotland, all employing conventional clarification. Both trihalomethane (THM) and haloacetic acid (HAA) FPs were considered. In addition to the standard bulk WQDs, the DOC content was fractionated and analysed for the hydrophobic (HPO) and hydrophilic (HPI) fractions. Results were quantified in terms of the yield (dDBPFP/dWQD) and the linear regression coefficient R2 of the yield trend.The NOM in the raw waters was found to comprise 30–84% (average 66%) of the more reactive HPO material, with this proportion falling to 18–63% (average 50%) in the treated water. Results suggested UV254 to be as good an indicator of DBPFP as DOC or HPO for the raw waters, with R2 values ranging from 0.79 to 0.82 for THMs and from 0.71 to 0.73 for HAAs for these three determinants. For treated waters the corresponding values were significantly lower at 0.52–0.67 and 0.46–0.47 respectively, reflecting the lower HPO concentration and thus UV254 absorption and commensurately reduced precision due to the limit of detection of the analytical instrument.It is concluded that fractionation offers little benefit in attempting to discern or predict chlorinated carbonaceous DBP yield for the waters across the geographical region studied. UV254 offered an adequate estimate of DBPFP based on a mean yield of ∼2600 and ∼2800 μg per cm−1 absorbance for THMFP for the raw and treated waters respectively and ∼3800 and2900 μg cm−1 for HAAFP, albeit with reduced precision for the treated waters.

Evaluation of groundwater quality in parts of the Southern Gangetic Plain using water quality indices

In India, persistent dependence on groundwater for intensively irrigated agriculture, industrial use and domestic activities imposes substantial threat to the quality and quantity of groundwater. This study assesses the suitability of groundwater for drinking purposes in parts of the Southern Gangetic Plain based on samples collected from 33 dug wells. In this scope, two robust indices are utilized, namely Groundwater Quality Index (GQI) and the Canadian Council of Ministers of the Environment (CCME) Water Quality Index (CCME_WQI), to assess the overall quality of groundwater by integrating observed water quality determinants like pH, TDS and major ion concentration. The concentration of major anions and cations is observed to be in the order of HCO3 − > Cl− > SO4 2− > NO3 − and Na+ > Ca2+ > Mg2+ > K+, respectively. The pH values of the analyzed samples vary between 6.2 and 7.37 during the post-monsoon (POM) period and between 6.6 and 7.9 during the pre-monsoon (PRM) period. Similarly, TDS concentrations are observed to vary between 6.7 and 1535 mg/l (POM) and 1.43 and 1327 mg/l (PRM). The values of GQI in the study area range between 10.41–108.56 and 16.03–130.06 for the PRM and POM periods, respectively. Among the groundwater samples collected during the PRM period, about 21, 73 and 6% are found to be excellent, good and poor quality, respectively. While the percentage of poor quality water for POM period is exactly the same as that of PRM, about 42 (52%) of the samples are found to be of excellent (good) quality for drinking purposes. The analysis of CCME_WQI for groundwater samples reveals that 3 (21%), 42 (36%), 33 (18%), 21 (24%) of the samples collected during PRM (POM) are classified to be of excellent, good, fair and marginal category, respectively. The spatial distribution of GQI and CCME_WQI illustrates that excellent quality water occurs primarily in the northeast part of the study area during the POM period. However, some localized patches with excellent quality are also observed in both the seasons. Results from this study will be crucial for proper utilization and management of already depleted groundwater resources of the study area.

Remote sensing of nutrients in a subtropical African reservoir: testing utility of Landsat 8

Remote sensing is useful for water quality assessments but current remote sensing applications favour parameters that are easy to detect such as chlorophyll-a. An assessment of the utility of Landsat 8 for detecting nutrients was conducted in Mazvikadei reservoir in Zimbabwe. The main objective was to determine whether nutrients often overlooked by remote sensing and yet are the main determinants of water quality can be remotely sensed. Sampling targeted ammonia, nitrates and reactive phosphorus from May to October 2015. In situ nutrient concentrations were regressed against reflectance derived from Landsat 8 imagery. Strong negative relationships were found between ammonia and the near-infrared band in July (R2 = 0.80, p < 0.05) as well as between nitrates and the blue band (R2 = 0.67, p < 0.05) in June. Overall, the results suggest that the cool dry season is the optimum time to use Landsat 8 for monitoring nutrients in tropical lakes.