Temporal Variations Of Water Quality Research Articles

Spatial and Temporal Variation of Water Quality in the Bertam Catchment, Cameron Highlands, Malaysia.

The spatio-temporal variability of water quality associated with anthropogenic activities was studied for the Bertam River and its main tributaries within the Bertam Catchment, Cameron Highlands, Malaysia. A number of physico-chemical parameters of collected samples were analyzed to evaluate their spatio-temporal variability. Nonparametric statistical analysis showed significant temporal and spatial differences (p < 0.05) in most of the parameters across the catchment. Parameters except dissolved oxygen and chemical oxygen demand displayed higher values in rainy season. The higher concentration of total suspended solids was caused by massive soil erosion and sedimentation. Seasonal variations in contaminant concentrations are largely affected by precipitation and anthropogenic influences. Untreated domestic wastewater discharge as well as agricultural runoff significantly influenced the water quality. Poor agricultural practices and development activities at slope areas also affected the water quality within the catchment. The analytical results provided a basis for protection of river environments and ecological restoration in mountainous Bertam Catchment.

Spatial and Temporal Variations of Water Quality and Trophic Status in Xili Reservoir: a Subtropics Drinking Water Reservoir of Southeast China

Controlling of water quality pollution and eutrophication of reservoirs has become a very important research topic in urban drinking water field. Xili reservoir is an important water source of drinking water in Shenzhen. And its water quality has played an important role to the city’s drinking water security. A fifteen-month’s field observation was conducted from April 2013 to June 2014 in Xili reservoir, in order to analyze the temporal and spatial distribution of water quality factors and seasonal variation of trophic states. Xili reservoir was seriously polluted by nitrogen. Judged by TN most of the samples were no better than grade VI. Other water quality factor including WT, SD, pH, DO, COD, TOC, TP, Fe, silicate, turbidity, chlorophyll-a were pretty good. One-way ANOVA showed that significant difference was found in water quality factors on month (p<0.005). The spatial heterogeneity of water quality was obvious (p<0.05). The successions of water quality factors y were similar and the mainly pattern was Pre-rainy period > Latter rainy period > High temperature and rain free period > Temperature jump period > Winter drought period. Two-way ANOVA showed that months rather than locations were the key influencing factors of water quality factors succession.TLI (Σ) were about 35~52, suggesting Xili reservoir was in mycotrophic trophic states. As a result of runoff pollution, water quality at sampling sites 1 and 10 was poor. In the rainy season, near sampling sites 1 and 10, water appeared to be Light-eutrophic. The phytoplankton biomass of Xili reservoir was low. Water temperature was the main driving factor of phytoplankton succession.The 14 water quality factors were divided into five groups by factor analysis. The total interpretation rate was about 70.82%. F1 represents the climatic change represented by water temperature and organic pollution. F2 represents the concentration of nitrogen. F3 represents the phytoplankton biomass. F4 represents the sensory indexes of water body, such as turbidity, transparency.

English

Awash River has important socio-economic and ecological values in Ethiopia. On the contrary, it is prone to serious water pollution. This study aims to assess the spatial and temporal variation of water quality of the river. Means of the 9 years’ (2005-2013) water quality dataset of 19 parameters from 10 stations in the basin were considered. After validating, normalizing and checking the sampling adequacy and internal consistency of the data, principal component analysis was computed and four principal components were generated. Factor loadings, correlations between variables and the principal factors as well as between sites and the principal factors were tabulated. Agglomerative hierarchical clustering done on the dataset resulted in four clusters based on similarity of water quality characteristics. The Mann-Kendall’s two tailed trend test detected temporal trends for total hardness in February over all sites and for most parameters in the basin in the 9 years period. Spatial analysis of the 14 sampling sites of the basin showed that as one moves from upper to lower parts of the basin, electrical conductivity, total hardness and chloride decrease in the dry season. However, total hardness slightly increases and total dissolved solids, chloride, and sulfate decrease in the rainy season. Key words: Agglomerative hierarchical clustering, Ethiopia, Mann Kendall trend, principal component analysis, water pollution.

A generic framework to analyse the spatiotemporal variations of water quality data on a catchment scale

Most spatiotemporal studies treat spatial and temporal analysis separately. However, spatial and temporal changes occur simultaneously and are correlated. In this study, we propose a generic framework to simultaneously analyse the spatial and temporal variations of water quality on a catchment scale. Specifically, we analyse the heterogeneity of temporal evolution of water quality data among different sampling sites, and the heterogeneity of spatial distribution of water quality data over different sampling times, respectively, by integrating the techniques of normalized mutual information, dynamic time wrapping and cluster analysis. To bring deep insight into the spatiotemporal variations, inter-change and intra-change are further defined and distinguished, respectively. Taking the Fuxi River catchment as a case study, results indicate that the proposed framework is intuitive and efficient. Beyond this, the generic framework can be expanded for other catchments and various environmental data.

Combined statistical techniques for the water quality analysis of a natural wetland and evaluation of the potential implementation of a FWS for the area restoration: the Torre Flavia case study, Italy

The paper focussed on the analysis of the environmental status of a natural wetland and the assessment of potential solutions to preserve the area, the related ecosystem services and natural equilibria. Data on water quality parameters and on climatic conditions were derived from a yearly monitoring campaign and web sources respectively. Chemometric techniques and a water quality index (WQI) were applied in order to assemble the obtained information and define an exhaustive overview of the wetland status. Data processing allowed to estimate the system water balance and to evaluate spatial and temporal variations of water quality. A water deficit as well as a major wetland sensitivity respect to pollution loads was verified during the warmer season (June-September). Local criticalities and environmental pressure were assessed and possible solutions to properly manage and restore the natural system were evaluated. The use of the wetland as a free water system (FWS) receiving treated wastewater from a local UWWTP was considered in the view of using local resources and restoring the water balance, avoiding environmental impacts and excessive management costs. Wetland auto-depurative capacity was assessed through common empirical plug flow models which revealed the ammonia nitrogen loads during the winter season as the limiting conditions. By deriving the maximum capacity of the system to receive pollutants, the study showed how water balance restorations as well as environmental and economic savings are achievable. Additional benefits have to be associated to ecosystem services and the possibility for recreational, cultural and educational activities.

Riparian restoration for protecting water quality in tropical agricultural watersheds

Land use change in riparian zones is one of the most significant threats to water quality in watershed ecosystems. Riparian forests play a major role in protecting water quality, and there is a need to assess the role of riparian restoration in reducing nutrients and sediment loading. This study uses watershed simulation modeling to evaluate impacts of riparian forest restoration on water quality in a tropical agricultural watershed. Soil Water Assessment Tool (SWAT) is used to simulate streamflow, suspended sediment and nutrients of the Sarapuí River watershed, located in southeast Brazil. We observe a spatial and temporal variation in water quality impacts of changes in land use/land cover (LULC) and rainfall patterns. Watersheds with agricultural and some residential areas had a higher sediment and nutrients loads than forest and with pasture land uses, especially during the wet season. Forested watersheds in general had a better water quality than other LULC types. Riparian restoration in the study watershed can reduce suspended sediment (9.26%), total nitrogen (22.6%), and total phosphorus (7.83%). Protecting riparian zone and site-conservation practices is critical to improve water quality. We observe that the simulation model provides a satisfactory baseline of the watershed system to evaluate impacts of land use changes.

Spatial and Temporal Variations of Water Quality in Songhua River from 2006 to 2015: Implication for Regional Ecological Health and Food Safety

The Songhua River is the largest river in northeastern China; the river’s water quality is one of the most important factors that influence regional ecological health and food safety in northeastern China and even the downstream of the Heilong River in Russia. In recent years, the Chinese government implemented several water resource protection policies to improve the river’s water quality. In order to evaluate the influence of the new policies on the water quality in the Songhua River, water quality data from 2006 to 2015 were collected monthly from the nine sites along the mainstream of the Songhua River. Results show that the water quality in the Songhua River could be divided into two groups during the last 10 years. Before 2010, water quality in the Songhua River was primarily influenced by regional human activities. Industries were the major pollutant sources in the upstream of the Songhua River. After several new policies were implemented by the local government in 2010, water quality in the Songhua River improved. As a result, the biodiversity of fish and ecological health in the Songhua River improved.

Groundwater Quality: Analysis of Its Temporal and Spatial Variability in a Karst Aquifer.

This study develops an approach based on hierarchical cluster analysis for investigating the spatial and temporal variation of water quality governing processes. The water quality data used in this study were collected in the karst aquifer of Yucatan, Mexico, the only source of drinking water for a population of nearly two million people. Hierarchical cluster analysis was applied to the quality data of all the sampling periods lumped together. This was motivated by the observation that, if water quality does not vary significantly in time, two samples from the same sampling site will belong to the same cluster. The resulting distribution maps of clusters and box-plots of the major chemical components reveal the spatial and temporal variability of groundwater quality. Principal component analysis was used to verify the results of cluster analysis and to derive the variables that explained most of the variation of the groundwater quality data. Results of this work increase the knowledge about how precipitation and human contamination impact groundwater quality in Yucatan. Spatial variability of groundwater quality in the study area is caused by: a) seawater intrusion and groundwater rich in sulfates at the west and in the coast, b) water rock interactions and the average annual precipitation at the middle and east zones respectively, and c) human contamination present in two localized zones. Changes in the amount and distribution of precipitation cause temporal variation by diluting groundwater in the aquifer. This approach allows to analyze the variation of groundwater quality controlling processes efficiently and simultaneously.

Spatial and temporal variation of water quality of a segment of Marikina River using multivariate statistical methods.

Payatas landfill in Quezon City, Philippines, releases leachate to the Marikina River through a creek. Multivariate statistical techniques were applied to study temporal and spatial variations in water quality of a segment of the Marikina River. The data set included 12 physico-chemical parameters for five monitoring stations over a year. Cluster analysis grouped the monitoring stations into four clusters and identified January-May as dry season and June-September as wet season. Principal components analysis showed that three latent factors are responsible for the data set explaining 83% of its total variance. The chemical oxygen demand, biochemical oxygen demand, total dissolved solids, Cl- and PO43- are influenced by anthropogenic impact/eutrophication pollution from point sources. Total suspended solids, turbidity and SO42- are influenced by rain and soil erosion. The highest state of pollution is at the Payatas creek outfall from March to May, whereas at downstream stations it is in May. The current study indicates that the river monitoring requires only four stations, nine water quality parameters and testing over three specific months of the year. The findings of this study imply that Payatas landfill requires a proper leachate collection and treatment system to reduce its impact on the Marikina River.

Temporal variations in water quality in a brackish tidal pond: Implications for governing processes and management strategies

Brackish tidal ponds have been constructed along coastal areas in many parts of the world for aquaculture, including some Ramsar Sites. Such ponds are considered a sustainable, wise use of wetlands if managed properly, but they can also pose serious environmental problems if mismanaged. To understand the governing processes and to promote sustainable management strategies, this study examines the different temporal variations in water quality parameters in a brackish tidal pond located within the wetland complex of the Mai Po Ramsar Site in Hong Kong, China. The variations are compared with those of the receiving bay, and the water channel that connects the pond and the bay. Equations are then developed to link the dissolved oxygen (DO) concentrations in the pond with the governing processes, and to analyze their relative contributions to DO levels. Field data show seasonal patterns in water temperature and salinity in response to the seasonal variations in solar radiation and rainfall. For the pond and the channel, DO, chlorophyll and pH exhibit fortnightly variations due to the bi-weekly water exchange between the pond and the bay. There were also diurnal variations in water temperature and DO in response to changes in solar radiation for both locations, and the tidal flushing for the water channel. Analysis of the findings indicates that water exchange influences the DO concentration more strongly than solar radiation. The DO equation links pond water quality with the time of day, and the time in a water exchange cycle, and thus provides some guidance for determining water exchange and water sampling schedules. The study sheds light on the governing processes and management strategies related to the sustainable management of a brackish tidal pond. The results are thus beneficial in elucidating and promoting the sustainable management and wise use of wetlands in other locations.

Using fuzzy theory and variable weights for water quality evaluation in Poyang Lake, China

Achieving water purity in Poyang Lake has become a major concern in recent years, thus appropriate evaluation of spatial and temporal water quality variations has become essential. Variations in 11 water quality parameters from 15 sampling sites in Poyang Lake were investigated from 2009 to 2012. An integrative fuzzy variable evaluation (IFVE) model based on fuzzy theory and variable weights was developed to measure variations in water quality. Results showed that: 1) only chlorophyll-a concentration and Secchi depth differed significantly among the 15 sampling sites (P < 0.01), whereas the 11 water quality parameters under investigation differed significantly throughout the seasons (P < 0.01). The annual variations of all water quality variables except for temperature, electrical conductivity, suspended solids and total phosphorus were considerable (P < 0.05). 2) The IFVE model was reasonable and flexible in evaluating water quality status and any possible ′bucket effect′. The model fully considered the influences of extremely poor indices on overall water quality. 3) A spatial analysis indicated that anthropogenic activities (particularly industrial sewage and dredging) and lake bed topography might directly affect water quality in Poyang Lake. Meanwhile, hydrological status and sewage discharged into the lake might be responsible for seasonal water quality variations.

Water-quality variability in dryland riverine waterholes: a challenge for ecosystem assessment

Waterholes in intermittent dryland rivers are important biotic refugia, but detailed water-quality descriptions of these habitats are rare. Their possible variability in water quality, due to variable flow regimes, may impede development of appropriate water-quality guidelines. We investigated this issue by describing spatial and temporal variation in water quality in waterholes in a tropical Australian dryland system. Water quality varied considerably among three rivers, between sites within rivers and within sites, reflecting lithology, hydrology, bathymetry, local catchment influences, stratification and within-site patchiness. Seasonal variation was due to differences in insolation, temperature, flow and depth. Diel variation was high for pH and dissolved oxygen (DO) at some sites. Variation among locations within waterholes was low for DO, temperature and pH, but higher for chlorophyll and nutrients, due to shade-related patchy photosynthesis. Neither the rivers nor the waterholes within them could indicate water-quality reference conditions because of their different characteristics. Our results highlight the need for strategic timing and location of sampling to capture spatial and temporal variation in key water-quality variables and to identify critical ecological conditions in dryland riverine waterholes.

Assessment of Seasonal Variation in Water Quality in River Rwizi Using Multivariate Statistical Techniques, Mbarara Municipality, Uganda

Assessment of seasonal variations in surface water quality characteristics is an essential aspect for evaluating water pollution due to both natural and anthropogenic influences on water resources. In this study, temporal variations of water quality in river Rwizi section within Mbarara municipality, Uganda, were assessed using multivariate statistical methods. This river section is a major source of water for the inhabitants of Mbarara municipality. Water samples from five sites were analyzed for physicochemical parameters such as pH, EC, turbidity, temperature, TSS, TDS, alkalinity, salinity, colour, NH3-N, , total hardness, BOD, COD, DO, Ca, Mg, Fe, and Mn. About 50% of sites recorded colour above 800 Pt Co, 60% of sites recorded turbidity above maximum permissible limit of 100 mg/l, attributable to erosion and mineral matter. pH for dry season ranged between 6.5 and 8.5 whereas for rainy season was below 6.0. All study sites recorded total Fe above 0.3 mg/l and Mn below 0.5 mg/l, attributable to chemical weathering of host rock materials as well as from industrial effluent. About 60% of sites recorded COD above 100 mg/l, 40% and 80% of study sites showed BOD above 50 mg/l in dry and rainy seasons respectively. Hardness ranged between 50 and 100 mg/l indicating that the water is moderately soft. Colour, turbidity, alkalinity, TSS, TDS, salinity, pH, hardness, Fe, Mn, NH3-N, BOD, COD, and DO were higher in rainy season, as a result of erosion, discharge of domestic and industrial waste. Mg, Ca, and were higher during dry season due to high evaporation of water from the river. PCA/FA determined that 81.2% of the total variance was explained by the first factor for the dry season and 69.2% for rain season. These results revealed that water pollution resulted primarily from domestic waste water, agricultural runoff and industrial effluents.

Description of Chemical Changes in a Large Karstic System: Montebello, Mexico

Lake complex “Lagunas de Montebello” is a karstic system composed by sixty lakes, all apparently connected. This system is localized at south of Chiapas state, SE Mexico. It is considered one of most beauties landscapes of the country. Main importance is due to climatic and hydrological regulation of this region. However anthropic activities as deforestation and waste water spills begin to produce risky conditions to water quality. This work presents spatial and temporal variability of water quality considering the study of ten lagoons through three sampling periods. Two of these periods of field work, (april and september 2013) consider sampling of only one point at surface in each lagoon. A very extensive sampling was developed in august 2014 in ten lagoons. Results show that this karstic system can be divided in two groups of water quality. First group of lakes contains calcic-magnesic-bicarbonated-sulfated waters and second group contains calcic-magnesic-bicarbonated waters. At first group, is possible to identify impacts related to inlet of waters high in sulfates and chlorides, these solutes dilutes along two first lagoons. An independent flow system rich in sulfates, probably of groundwater that circulates deeply was identified.

Assessment of spatial and seasonal water quality variation of Oum Er Rbia River (Morocco) using multivariate statistical techniques

The aim of this study is to assess the spatial and temporal water quality variation and to determine the main contamination sources in the Oum Er Rbia River and its main tributary, El Abid River. The water quality data were collected during 2000–2012 from fourteen sampling stations distributed along the river. The water quality indicators used were TEMP, pH, EC, turbidity, TSS, DO, NH4+, NH3–, TP, BOD5, COD and F. coli. The water quality data was analyzed using multivariate statistical methods including Pearson's correlation, PCA, and CA. The results showed that in some stations the water quality parameters were over Moroccan water standards. PCA applied to compare the compositional patterns among the analyzed water samples, identified and four factors accounting for almost 63% of the total variation in the data. This suggests that the variations in water compounds’ concentration are mainly related to point source contamination (domestic and industrial wastewater), non-point source contamination (agriculture activities), as well as natural processes (weathering of soil and rock). CA showed relatively spatial and seasonal changes in surface water quality, which are usually indicators of contamination with rainfalls or other sources. Overall, this study showed that the water was potentially hazardous to health of the consumers and highlighted the need to treat industrial and municipal wastewater and to encourage sustainable agricultural practices to prevent adverse health effects. We therefore suggest wise management of anthropogenic activities in the catchment of Oum Er Bia River and their tributaries.

Determination of Shelf Life of Selected Sachet Water in Ogbomoso, Oyo State Nigeria

Water is life and every living thing depends on it for existence. Sachet water has gradually become the most widely consumed liquid in Nigeria with varying qualities. This study investigates the temporal variation in water quality of Sachet water produced in Ogbomoso, Oyo State. Ten (10) brands of sachet water from Ogbomoso South and North Local government area were collected within 24 hours of production and stored at standard room temperature and conditions. Sub-samples were drawn from the stock samples on daily basis for physico-chemical measurements on the water samples Temperature, pH, colour, turbidity, Hardness, Total Alkalinity, Dissolve Oxygen (DO), Biological Oxygen Demand (BOD), Electrical Conductivity (EC) and Nitrate values were determined in accordance with World Health Organization (W.H.O) analytical methods. Temperature, pH and Colour values ranged from (28.3 - 30.5) ̊C, (7.96 - 8.80) and (20-70) Hazen, respectively. The Total hardness EC and DO and BOD values varied from (45-105)mg/l, (11 - 184)µs, (2.83 - 12.24)mg/L and (18.2 - 28.4)mg/l, respectively. Shelf life for the selected sachet water in Ogbomoso is 12 weeks from the date of production under laboratory condition with partial exposure to sunlight.

Application of water quality index to evaluate groundwater quality (temporal and spatial variation) of an intensively exploited aquifer (Puebla valley, Mexico).

The spatial and temporal variation of water quality in the urban area of the Puebla Valley aquifer was evaluated using historical and present data obtained during this investigation. The current study assessed water quality based on the Water Quality Index developed by the Canadian Council of Ministers of the Environment (CCME-WQI), which provides a mathematical framework to evaluate the quality of water in combination with a set of conditions representing quality criteria, or limits. This index is flexible regarding the type and number of variables used by the evaluation given that the variables of interest are selected according to the characteristics and objectives of development, conservation and compliance with regulations. The CCME-WQI was calculated using several variables that assess the main use of the wells in the urban area that is public supply, according to criteria for human use and consumption established by Mexican law and international standards proposed by the World Health Organization. The assessment of the index shows a gradual deterioration in the quality of the aquifer over time, as the amount of wells with excellent quality have decreased and those with lower index values (poor quality) have increased throughout the urban area of the Puebla Valley aquifer. The parameters affecting groundwater quality are: total dissolved solids, sulfate, calcium, magnesium and total hardness.

Relação entre padrões de uso e ocupação do solo e qualidade da água em uma bacia hidrográfica urbana

RESUMO O uso e a ocupação do solo alteram sensivelmente os processos físico-químicos e biológicos dos sistemas naturais. Dessa forma, os mananciais de superfície são integradores dos fenômenos ocorrentes sobre a área da bacia hidrográfica. Assim, os objetivos do trabalho foram explorar a variabilidade temporal e espacial da qualidade da água e avaliar as possíveis relações entre os padrões de uso e ocupação do solo da bacia hidrográfica do Ribeirão Vermelho. Foram coletadas amostras de água em dois períodos (verão e inverno) e em 15 seções ao longo do curso d'água. Verificou-se forte influência temporal e espacial na qualidade das águas, e foram apresentadas no período de inverno as maiores concentrações de nutrientes (Cl-, P, NO3 -), condutividade elétrica e matéria orgânica. Esses valores interferem nos valores do Índice de Qualidade da Água, que varia entre 84 e 9 no período do verão e 66 e 6 no inverno. Quanto à trofia dos mananciais, foram encontrados valores médios de Índice de Estado Trófico de 30 no período chuvoso e de 93 no inverno. No tocante aos padrões de uso do solo, observaram-se fortes relações na qualidade da água nos dois períodos avaliados; a principal fonte de contaminação são as áreas urbanas. O Ribeirão Vermelho e seus afluentes apresentam forte influência das formas de uso e ocupação do solo confirmada pela entrada de matéria orgânica e de nutrientes nos sistemas hídricos por meio do lançamento de esgoto doméstico sem tratamento e pela agropecuária na rede de drenagem da bacia.

Assessment of Water Quality of Tung Dhab Drain—An International Water Channel—Using Multivariate Statistical Techniques

Different multivariate statistical techniques were applied to interpret the temporal variations in water quality of Tung Dhab drain, Amritsar, India and further to identify water pollution sources. Data was collected seasonally for a period of two years (2012-2013) using 34 water quality parameters. The recorded values for variables like turbidity, total suspended solids, biochemical oxygen demand, chemical oxygen demand, oil & grease, nitrate as N, lead, chromium, nickel and zinc were much higher than the recommended permissible discharge limits into inland waters. Significant correlations were found in between different physicochemical parameters ( p ≤ 0.05; p ≤ 0.01). Cluster Analysis (CA) grouped four sampling seasons into two clusters. CA confirmed that the water quality of rainy season was different from other three seasons in terms of similarity and distance indices. Principal Component Analysis/Factor Analysis (PCA/FA) explained minerals, organic, agricultural and industrial pollutants responsible for deterioration of drain water quality. The present study will help environmental agencies to make and enforce decisions regarding improvement of water quality of Tung Dhab drain.

Water quality of Nilwala River, Sri Lanka in relation to land use practices

The Nilwala River is the third largest in the southern province of Sri Lanka which runs through 72 km along its cause. Conversion of forest lands to agricultural lands, expansion of urban areas and clearing of land for construction purposes in the catchment are major issues affecting water quality in Nilwala River. The water quality of the Nilwala River lower basin at 16 locations was estimated for 4 months from September2010 to December 2010 in two-week intervals. Water quality parameters pH, Electrical conductivity(EC), Dissolved oxygen (DO), Biochemical Oxygen demand (BOD5), turbidity, colour, Total Dissolved Solids (TDS), total hardness, alkalinity, Nitrite-N (NO2--N), Nitrate -N (NO3--N), Phosphate (PO43- -P), Sulphate (SO43-), Total Fe, Ca2+, F- and Cl- were evaluated in the sampling locations. The spatial and temporal variation of water quality associated with different land use categories were analyzed using Two-way ANOVA. Principal Component Analysis (PCA) and Cluster Analysis (CA) were also conducted to determine the association between water quality variation and land use impacts of the catchment. A significant (p &lt;0.05) spatial variation of water quality parameters, except the hardness, Fluoride and Ca+2among sites were observed to be associated with different land use categories. No significant (p &gt;0.05) temporal variability in water quality parameters except Nitrite and hardness was detected. PCA and CA also indicated a strong association between the water quality variables and the land use types of the river basin. Urban impacts, land clearance in the catchment and sand mining activities of the river bed were found to be the most significant impacts to the water quality of the river and areas with forest cover having positive impact to the water quality. These findings emphasize the need of better catchment management approaches and remediation of urban impacts on river water quality.