Concentrations Of Water Quality Variables Research Articles

Anthropogenic Drivers of Spatial Trends in Groundwater Quality in the Upper Athi River Basin of Kenya, East Africa

Rapid urbanization and population growth in the upper Athi River basin in Kenya have increased the strain on the sub catchments water supply and sanitation situation. Due to increasing demand, inadequate supply of drinking water and lack of sanitation facilities, people in the sub-catchment are increasingly reliant on groundwater as a primary or supplementary water source. However, the use of on-site wastewater systems and agricultural pollution, mainly from runoff containing fertilizers, pesticides, herbicides, and faeces, pose a threat to groundwater in the sub catchment. Subsequently, the current study was conducted in the Thiririka sub catchment, Kiambu County, Kenya, to determine the safety of groundwater sources and to examine the factors influencing groundwater quality in the catchment area. This study assessed the influence of anthropogenic activities on the physical, chemical, and bacteriological quality of groundwater in the Upper Athi River basin of Kenya between April and June 2022. Twenty variables were analyzed and compared with water quality standards to determine hydro chemical characteristics, evidence of contamination, and suitability of groundwater. Shallow wells (SW) had higher concentrations of major ions and key parameters than boreholes (BH), such as alkalinity (7%), turbidity (96%), nitrates (92%), sulfates (48%), phosphates (93%), chlorides (77%), potassium (84%), sodium (30%) and fecal coliforms (99%) significant at p < 0.01. Concentrations of eleven water quality variables however were comparable in both systems. Farming, animal husbandry, and pit latrines were negatively but significantly correlated with the water quality of SW explaining substantial amounts of variation (≤ 45%) in concentrations of water quality variables. Ionic and coliform levels increased with decreasing distance and vice versa. IDW interpolation maps were generated in ArcGIS software to determine the spatial variability of groundwater quality in the basin. Anthropogenic activities such as pit latrines and animal husbandry impaired the quality of groundwater which in most cases was not potable.

TROPICAL REHABILITATION FOREST CONTROL ON WATER CHEMISTRY PATTERN IN BINTULU SARAWAK MALAYSIA

With rapid development in South East Asian countries, there is a risk of serious degradation of stream water quality in areas adjacent to developing city areas, where basic information on toxic heavy metals and acidic compounds (NO3- and SO42-) concentrations and spatiotemporal variation is still unknown in these areas. The concentrations of water quality parameters, major ions, and heavy metals were examined from selected stream in a rehabilitation forest near a developing city having petroleum refinery facility in Bintulu, Sarawak, Malaysia. The concentrations of water quality parameters, major ions, and heavy metals were examined from twelve stream locations in a rehabilitation forest near a developing city with a petroleum refinery facility. Analyses suggested that there is no clear tendency that is detected in heavy metals and basic water properties (EC, DO, BOD, COD, alkalinity and pH) except for turbidity, total suspended solids, and major ion which were high during rainy seasons. Annual means of SO42-, NO3- and NH₄⁺ concentrations were 6.34, 1.05 and 0.24 mg/L. The concentration in K+, Mg2+, Na+ and Ca2+ were 0.61, 1.21, 2.82 and 1.12 mg/L during hot and rainy season. The mean concentration in almost all heavy metals (Mn, Fe, Cu, Zn) were less than 0.01 mg/L. The concentrations of water quality variables in all samples collected across the seasons except for turbidity found within the permissible limit by the WHO and NWQS for Malaysia. Rehabilitation forest might give a positive impact in preserving water quality especially for COD and major ions except SO42-.

Phosphorus and thermotolerant coliforms’ loads in Brazilian watersheds with limited data: considerations on the integrated analysis of water quality and quantity

ABSTRACT Integrated analyses of the qualitative and quantitative aspects of aquatic ecosystems play an important role in decision making, which is linked to water resources management and promotion of ecosystem services. However, the possible advantages of such integration are still hampered by basic aspects, such as high uncertainties due to the partial and non-synchronized monitoring of discharges and observed concentrations of water quality variables. The lack of data has been limiting the adequate representation of a more accurate hydrological regime, which is in turn possibly affected by the potential effects of land use and size of drainage areas. The aim of this research was to discuss the advantages of the integrated analysis of qualitative and quantitative data from water bodies. Under different specific discharge regimes (L.s -1.km-2), we assessed the total phosphorus (TP, t.day-1 .km-2) and thermotolerant coliforms’ (TC, CFU.day-1.km -2) specific loads in rivers with different drainage areas (27-26,500 km 2) and land uses. We compared such loads with the admissible specific loads for these variables, which were estimated based on long-term average discharges and water quality guidelines (i.e., Brazilian environmental standards). Based on data from 2001-2013, we sought to contribute to the qualitative and quantitative analysis of surface waters, focusing on the discussion of the results on critical thresholds of duration and critical loads and discharges. The results showed the existence of significant time intervals with conflicts between the specific admissible and observed loads. This non-compliance varied between 10 and 100% of the duration of the regime for TP, and between 25 and 100% for TC, with a more critical situation observed in rivers with smaller drainage areas. The critical loads ranged from 1 10-4 to 8 10-3 t.day-1.km-2 (TP) and 1 10-2 to 1 10-1 CFU.day-1.km-2 (TC). Although a relatively limited dataset was considered (total N=1,402), the significant variations in discharges and critical loads highlighted the need for considering how these dynamics would affect the traditional methodology for estimating ecological flows, whose current approach is almost exclusively quantitative.

Effects of Liming on Quality of Water Discharged from the Supply Reservoir at a Fisheries Research Station

AbstractAnnual treatment of a water supply reservoir with agricultural limestone at the E. W. Shell Fisheries Center at Auburn University has roughly doubled conductivity and concentrations of total alkalinity, total hardness, and calcium hardness in the discharge water. It also has prevented pH values below 6.7. Concentrations of water quality variables decreased following some large rainfall events and during periods of prolonged rainfall. Calcium hardness concentrations were sometimes lower than recommended for hatchery water supplies intended for Channel Catfish Ictalurus punctatus. Nevertheless, liming has improved the quality of the reservoir discharge for use in both the hatchery and research ponds at the station.

Prediction of taxon occurrence: a test on taxon‐specific change point values of stream benthic invertebrates

Summary Ecological thresholds represent abrupt species responses to minor changes in the environment. However, as aquatic organisms are frequently exposed to multiple stressors, prediction of taxon occurrence is challenging and often associated with much uncertainty. In this study, we analysed the response of stream benthic invertebrates to selected environmental gradients and determined the frequency and predictability of threshold responses. Re‐analysis of taxon‐specific change point values for 213 riverine benthic invertebrate taxa and nine water quality variables showed that the predictive performance was acceptable for 30.4% and excellent for 9.6% of the total number of validated change points (n = 978). In total, 48.3% of the taxa that were predicted to occur (taxon presence predicted) and 67% of the taxa predicted not to occur (taxon absence predicted) were correct but with high variability across taxa and chemical variables. Predictive performance was the highest for stenoecious taxa and for certain chemical variables, such as ammonium nitrogen and the daytime dissolved oxygen concentration. Responses to peak level concentrations of water quality variables were less threshold‐like compared with relationships with mean values. However, model predictions were equal for both of the approaches. Successful prediction of taxon absence at stress levels beyond the change point values showed that the latter can well represent the upper limit of the taxon‐specific range of occurrence. Thus, change points are valuable for establishing and evaluating new water management tools, such as water quality criteria. By contrast, prediction of taxon presence at low levels of stress was associated with relatively high uncertainty, reflecting the limitation of taxon occurrence by stressors other than those investigated.

Identification of optimal water transfer schemes for restoration of a eutrophic lake: An integrated simulation-optimization method

This research developed an integrated simulation-optimization method (ISOM). This model incorporated eutrophication modeling, water resource allocation and trophic status assessment within a general modeling framework. In ISOM, the simulation effort [i.e. environmental fluid dynamics code (EFDC)] was used to forecast the concentration of water quality variables to evaluate the lake trophic status under various conditions, while the optimization studies were used to identify the optimal water transfer strategies from a number of alternatives. To solve the model, a surrogate-based genetic algorithm (GA) was proposed in which the support vector regression (SVR) was used to create a set of easy-to-use and rapid-response surrogates for identifying the functional relationships between water transfer and lake trophic status. By replacing the EFDC and the corresponding trophic state index (TSI) equations with the surrogates, the computation efficiency could be improved. The developed ISOM was applied to the inter-basin water transfer management of the Niulanjiang-Dianchi Water Transfer Project (NDWTP) to support the eutrophication restoration of Lake Dianchi. Optimal water transfer schemes for three different remediation durations were generated from the model. The results demonstrated that NDWTP could exert a positive influence on the ecology and environment of Lake Dianchi, and that the trophic level for the Lake Dianchi could be effectively mitigated through the adoption of optimal water transfer schemes.

Influence of a Bacterial Amendment on Water Quality in Small Research Ponds for Channel Catfish, Ictalurus punctatus, Production

AbstractThere has been considerable interest worldwide in applying bacterial inocula to channel catfish ponds for improving water quality, especially for acceleration of ammonia nitrogen oxidation through bacterial nitrification. The effects of a selected bacterial amendment on water quality in small research ponds for channel catfish production were evaluated at the E. W. Shell Fisheries Center, Auburn University, Auburn, Alabama. Three ponds were treated with the bacterial amendment Waste & Sludge Reducer™ (Keeton Industries, Wellington, CO, USA) at three times the dose recommended by the manufacturer every 2 wk, and three ponds served as controls. There were nonconsistent minor differences in water quality between ponds treated with a commercial bacterial amendment and control ponds on several sampling dates. However, the average concentrations of water quality variables did not differ (P > 0.05) between the treatments and control. Channel catfish yield was not improved by applying the bacterial amendment. This study demonstrates that the bacterial amendment was of no benefit in improving water quality in well‐managed catfish ponds where stocking rates, feeding rates, and amount of aeration are balanced.

Equilibrium Concentrations of Major Cations and Total Alkalinity in Laboratory Soil-Water Systems

Three soils and four waters were used to prepare laboratory soil-water mesocosms. Soil-water mesocosms contained 5-cm-deep layers of soil and 21 L of water from each of the four sources: artificial rainwater, stream water, saline well water, and seawater. Water pH, conductivity, major cations, and total alkalinity were measured at intervals for 200 days. In some instances, equilibrium was not attained during the trial. Soils from the Coastal Plain and Blackland Prairie regions of Alabama caused greater increases in intensities of variables in rain and stream water than did Piedmont Plateau soil, while conductivity, calcium, sodium, and total alkalinity in rain and stream water increased most in mesocosms with Blackland Prairie soil; magnesium increased most in mesocosms with Coastal Plain soil. In mesocosms with saline well water and Blackland Prairie soil, there were changes in all measured variables other than pH and conductivity. In mesocosms with seawater and Blackland Prairie soil, only calcium, magnesium, and potassium in the water were different from the original source water. Shaker experiment revealed that equilibrium concentrations of water quality variables increased as the ratio of soil to water increased.

Mesohabitat-specific macroinvertebrate assemblage responses to water quality variation in mid-continent (North America) great rivers

Abstract We compared the responsiveness of macroinvertebrate assemblages to variation in water quality (ions, nutrients, dissolved metals, and suspended sediment) in two mesohabitats within the main channel of three North American great rivers, the Upper Mississippi, Missouri, and Ohio. Based on about 400 paired samples, we examined the responsiveness of benthic assemblages sampled in the littoral zone and assemblages sampled from the surface of woody snags in the main channel. The assemblages in the two mesohabitats were different in all rivers. Taxa richness was much higher in the benthos than on snags. Macroinvertebrate assemblage response to water quality variation was weak on the Mississippi River, but the reasons for this are unknown. Based on analysis of the similarity between the composition of assemblages from groups of sites with high and low concentrations of water quality variables, benthic assemblages were only slightly more sensitive to water chemistry variation than were snag assemblages. Results of two-sample comparisons between groups of sites with high and low concentrations of water quality variables were consistent with rank correlations of assemblage metrics with water quality. In general, there was little difference between habitats in response to variation in water quality on any river. Our simple method of snag sampling in great rivers is usually much easier than littoral benthic sampling because it does not require wading. Snag sampling in large rivers has some limitations (e.g., natural snags are sometimes absent, samples are semi-quantitative), but lack of sensitivity to water quality gradients compared to the benthos is not among them.

Design of River Water Quality Monitoring Networks: A Case Study

Karoon River, from Gotvand Dam to Persian Gulf with more than 450 km in length and an annual discharge of 11,891 million cubic meters, is the largest river in Iran. Increasing water withdrawal from and wastewater discharge to the river has endangered the aquatic life of this important ecosystem. Furthermore, the drinking and in-stream water quality standards have been violated in many instances. In this paper, a river water quality monitoring network is designed, including determination of sampling frequencies as well as location of water quality monitoring stations. In this regard, two models are developed. The first model is a Genetic Algorithm-based optimization model and the second one is a combination of Kriging method and Analytical Hierarchy Process. The temporal variation of the concentration of water quality variables along Karoon and Dez Rivers are evaluated and the main water quality indicators are selected. Then, thirty five stations are selected and the application of Entropy Theory in calculating the sampling frequency is demonstrated. The results show the significant value of the proposed methodology in the design of monitoring network.

Design of on-line river water quality monitoring systems using the entropy theory: a case study

The design of a water quality monitoring network is considered as the main component of water quality management including selection of the water quality variables, location of sampling stations and determination of sampling frequencies. In this study, an entropy-based approach is presented for design of an on-line water quality monitoring network for the Karoon River, which is the largest and the most important river in Iran. In the proposed algorithm of design, the number and location of sampling sites and sampling frequencies are determined by minimizing the redundant information, which is quantified using the entropy theory. A water quality simulation model is also used to generate the time series of the concentration of water quality variables at some potential sites along the river. As several water quality variables are usually considered in the design of water quality monitoring networks, the pair-wise comparison is used to combine the spatial and temporal frequencies calculated for each water quality variable. After selecting the sampling frequencies, different components of a comprehensive monitoring system such as data acquisition, transmission and processing are designed for the study area, and technical characteristics of the on-line and off-line monitoring equipment are presented. Finally, the assessment for the human resources needs, as well as training and quality assurance programs are presented considering the existing resources in the study area. The results show that the proposed approach can be effectively used for the optimal design of the river monitoring systems.

Stream restoration in urban catchments through redesigning stormwater systems: looking to the catchment to save the stream

Restoration of streams degraded by urbanization has usually been attempted by enhancement of instream habitat or riparian zones. Such restoration approaches are unlikely to substantially improve instream ecological condition because they do not match the scale of the degrading process. Recent studies of urban impacts on streams in Melbourne, Australia, on water chemistry, algal biomass and assemblage composition of diatoms and invertebrates, suggested that the primary degrading process to streams in many urban areas is effective imperviousness (EI), the proportion of a catchment covered by impervious surfaces directly connected to the stream by stormwater drainage pipes. The direct connection of impervious surfaces to streams means that even small rainfall events can produce sufficient surface runoff to cause frequent disturbance through regular delivery of water and pollutants; where impervious surfaces are not directly connected to streams, small rainfall events are intercepted and infiltrated. We, therefore, identified use of alternative drainage methods, which maintain a near-natural frequency of surface runoff from the catchment, as the best approach to stream restoration in urban catchments and then used models of relationships between 14 ecological indicators and EI to determine restoration objectives. Ecological condition, as indicated by concentrations of water-quality variables, algal biomass, and several measures of diatom and macroinvertebrate assemblage composition, declined with increasing EI until a threshold was reached (EI = 0.01–0.14), beyond which no further degradation was observed. We showed, in a sample catchment, that it is possible to redesign the drainage system to reduce EI to a level at which the models predict detectable improvement in most ecological indicators. Distributed, low-impact design measures are required that intercept rainfall from small events and then facilitate its infiltration, evaporation, transpiration, or storage for later in-house use.

Stream restoration in urban catchments through redesigning stormwater systems: looking to the catchment to save the stream

Restoration of streams degraded by urbanization has usually been attempted by enhancement of instream habitat or riparian zones. Such restoration approaches are unlikely to substantially improve instream ecological condition because they do not match the scale of the degrading process. Recent studies of urban impacts on streams in Melbourne, Australia, on water chemistry, algal biomass and assemblage composition of diatoms and invertebrates, suggested that the primary degrading process to streams in many urban areas is effective imperviousness (EI), the proportion of a catchment covered by impervious surfaces directly connected to the stream by stormwater drainage pipes. The direct connection of impervious surfaces to streams means that even small rainfall events can produce sufficient surface runoff to cause frequent disturbance through regular delivery of water and pollutants; where impervious surfaces are not directly connected to streams, small rainfall events are intercepted and infiltrated. We, therefore, identified use of alternative drainage methods, which maintain a near-natural frequency of surface runoff from the catchment, as the best approach to stream restoration in urban catchments and then used models of relationships between 14 ecological indicators and EI to determine restoration objectives. Ecological condition, as indicated by concentrations of water-quality variables, algal biomass, and several measures of diatom and macroinvertebrate assemblage composition, declined with increasing EI until a threshold was reached (EI = 0.01–0.14), beyond which no further degradation was observed. We showed, in a sample catchment, that it is possible to redesign the drainage system to reduce EI to a level at which the models predict detectable improvement in most ecological indicators. Distributed, low-impact design measures are required that intercept rainfall from small events and then facilitate its infiltration, evaporation, transpiration, or storage for later in-house use.

Community composition and distribution of macroinvertebrates in the Umzimvubu River, South Africa: a pre-impoundment study

This paper presents baseline biological data on aquatic macroinvertebrates and water quality in the Umzimvubu River and selected tributaries, Eastern Cape Province, South Africa, prior to the construction of proposed large-scale water resource developments. Sampling was conducted seasonally at 14 sites between 1996 and 1998. The macroinvertebrate community composition was strikingly similar (±70%) across sites. Faunal diversity was low (104 taxa in total), but many taxa found were sensitive to water quality change (ASPT 5.0 to 9.6), indicating good water quality, which is attributed to the currently undeveloped nature of the catchment. Concentrations of water quality variables fell within a narrow range, except for total suspended solids, which at times was very high (up to 8 532mg l–1). The highly variable concentration of the total suspended solids and its potential effects on biodiversity need to be investigated further. It is likely that bilharzia will spread and that pest blackflies may become a problem to livestock if the water resources become developed as is proposed. We suggest that more flow gauging weirs are needed to measure flows better for future management and also that the implications of the proposed developments on the estuary need to be investigated.

Bayesian hot spot detection in the presence of a spatial trend: application to total nitrogen concentration in Chesapeake Bay

AbstractExtreme concentrations of water quality variables can cause serious adverse effects in an ecosystem, making their detection an important environmental issue. In Chesapeake Bay, a decreasing gradient of total nitrogen concentration extends from the highest values in the north at the mouth of the Susquehanna river to the lowest values in the south near the Atlantic ocean. We propose a general definition of ‘hot spot’ that includes previous definitions and is appealing for processes with a spatial trend. We model these data using the Bayesian Transformed Gaussian (BTG) random field model proposed by De Oliveira et al. (1997), which combines the Box–Cox family of power transformations and a spatial trend. The median function is used as the measure of spatial trend, which offers some advantages over the customarily used mean function. The BTG model is fitted by an enhanced Monte Carlo algorithm, and the methodology is applied to the nitrogen concentration data. Copyright © 2002 John Wiley & Sons, Ltd.

Effects of ammonia on juvenile silver perch ( Bidyanus bidyanus)

Continued development of commercial pond culture of silver perch ( Bidyanus bidyanus) depends on determining concentrations of water quality variables that limit production. The effect of ammonia on the short-term growth of juvenile silver perch was evaluated in a 39-day experiment. Survival was not significantly affected by exposures up to 0.36 mg l −1 un-ionised ammonia–nitrogen (UAN), the highest concentration tested in this study. Growth was reduced at 0.36 mg l −1 UAN. The EC 5 (the concentration at which growth is reduced by 5%) was estimated to be 0.06 mg l −1 UAN. Some changes in gill histopathology were observed in fish exposed to ammonia.

Effects of a Bacterial Inoculum in Channel Catfish Ponds

Abstract.A commercial bacterial Inoculum cultured on site called Biostart was applied to three channel catfish Ictalurus punctatus ponds at Auburn, Alabama, USA, three times per week from May until October 1996. There were few significant differences (P × 0.1) in concentrations of water quality variables between ponds treated with bacteria and control ponds. In addition, bottom soil carbon and nitrogen did not differ between treated and control ponds. However, survival and net production of fish was significantly (P × 0.1) greater in ponds that received the bacterial inoculum than in controls. The mechanism by which the bacterial treatment influenced fish survival cannot be explained from data collected in this study. Further studies of probiotics are needed to define the potential benefits of these treatments to aquacultural production and to determine their mechanisms of action in pond ecosystems.

Evidence for Control of Water Quality in Channel Catfish Ictalurus punctatus Ponds by Phytoplankton Biomass and Sediment Oxygenation

AbstractA data set describing annual variation of water quality in ten commercial channel catfish Ictalurus punctatus ponds was subjected to exploratory statistical analysis to infer ecological processes affecting pond water quality. Two factors explained 67% of the variation in concentrations of water quality variables. The first factor (Factor 1) explained 49% of the variance and was associated with a large negative loading by total ammonia‐nitrogen and large positive loadings by total nitrogen, total phosphorus, chemical oxygen demand, and chlorophyll a. Factor 1 was interpreted with respect to factor loadings to represent the effect of phytoplankton biomass. The second factor (Factor 2) explained an additional 18% of the variance and was associated with a large negative loading by soluble reactive phosphorus and large positive loadings by nitrite‐nitrogen and, to a lesser extent, nitrate‐nitrogen. Factor 2 was interpreted to be related to variation in pond sediment oxygenation. Although factor analysis indicated the overwhelming effect of phytoplankton biomass on water quality, opportunities for management of phytoplankton communities in large commercial aqua‐culture ponds are limited. However, maintenance of an oxidized sediment‐water interface may improve water quality by limiting the diffusion of reductant‐soluble phosphorus from sediment to water and increasing sediment nitrification rates.

Chemical Budgets for Organically Fertilized Fish Ponds in the Dry Tropics

AbstractChemical budgets were determined for nitrogen, phosphorns, dissolved oxygen and chemical oxygen demand for three 0.1‐ha earthen ponds stocked with Onwchrornis nilotieus at the El Carao National Fish Culture Research Center, Comayagna, Honduras, for two 150‐d culture periods, corresponding to the rainy and dry seasons. Layer chicken litter was added to ponds weekly at 500 kg dry matter/ha. Concentrations of nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) in pond water increased during each season. No significant seasonal differencea in concentrations of water quality variables were observed. Chicken litter added to ponds represented 92–94% of N input, 93–95% of P input, and 43–52% of COD input. Photosynthesis by phytoplnnkton provided 47–56% of COD and 98% of dissolved oxygen (DO) added to ponds. Net inward diffnsion of oxygen added 1.2–1.5% of total DO. Regulated inflow was a minor source of nutrients, and contributed 3–4% of input N, 3–4% of input P, 1% of COD input, and 1% of DO input. Nutrient inputs from rain were ≤1% of total for each nutrient. Fish harvest accounted for 18–21% of total N, 16–18% of total P and 2% of COD added to ponds. Community respiration accounted for 48–57% of COD and 99.5% of DO added to ponds. Nutrient losses in pond effluent at draining were: 7–9% of total N, 29–37% of total P and 2–3% of COD. While measured gains exceeded measrued losses, significpntly greater N, P and organic matter concentrations in pre‐drain samples indicated pond mud was a major sink for added nutrients, accumulation in mud represented 70% of total N, 35–40% of total P, and 38–46% of COD.

Channel Catfish Pond Effluents

Abstract Water samples were collected four times a year for 2 years from the surface and bottom of 25 ponds used for commercial culture of channel catfish (Ictalurus punctatus) in central and west-central Alabama. Samples were analyzed for 5-d biochemical oxygen demand (BOD5), nitrite-nitrogen, nitrate-nitrogen, total ammonia nitrogen, total Kjeldahl nitrogen, total phosphorus, soluble reactive phosphorus, suspended solids, volatile solids, settleable solids, pH, and dissolved oxygen. Ranges for variables were as follows: BOD5, 1.9–35.54 mg/L; settleable solids, 0–1.8 mL/L; suspended solids, 5.2–336.7 mg/L; volatile solids, 0.02–221.0 mg/L; total phosphorus, 0–1.85 mg/L; soluble reactive phosphorus, 0–0.074 mg/L; total Kjeldahl nitrogen, 0.58–14.04 mg/L; total ammonia nitrogen, 0.008–8.071 mg/L; nitrite-nitrogen, 0.001–1.410 mg/L; nitrate-nitrogen, 0–6.661 mg/L; dissolved oxygen, 0.8–16.8 mg/L; and pH, 4.9–9.5. Concentrations of water quality variables were skewed towards the lower ends of these ranges. O...