Physical Water Quality Research Articles

The Effect of Road Culverts on the Benthic Macroinvertebrate Community in Wadeable Lotic Ecosystems

Roads and lotic ecosystems intersect as their paths unfold across the landscape. At their intersections lotic ecosystems are often routed underneath a road through a culvert. Road culverts allow the transportation system and lotic ecosystem to coexist, but their presence can introduce physical stress on the local ecology. The purpose of this study was to investigate the effects of road culverts on the benthic macroinvertebrate community. I collected physical habitat, water quality, and benthic macroinvertebrate data from three sample units near the culverted sections of two lotic ecosystems. Sample units were positioned in a longitudinal configuration with a reference sample unit located above the road culvert, a study sample unit below the outlet, and a recovery sample unit further downstream. Non-metric Multi- Dimensional Scaling and Bray-Curtis distance showed an alteration of the benthic macroinvertebrate community at the study sample units when compared to reference conditions. In the study sample units, the benthic macroinvertebrate community was composed of a greater proportion of stressor-tolerant taxa, as assessed by the presence of Ephemeroptera, Plecoptera, and Trichoptera taxa. There was also an alteration of dominant feeding groups in the study sample units. This study shows a fundamental shift of the local lotic ecology below road culverts. Faculty Mentor: Yangdong Pan

The application and testing of diatom-based indices in the Vaal and Wilge Rivers, South Africa

Chemical monitoring of water resources is time-consuming and comparatively expensive and may not always provide a composite reflection of actual water quality. Biotic indices using faunal elements, such as macroinvertebrates and fish, are already in place in South Africa as part of the National Biomonitoring Programme for Aquatic Ecosystems (NBPAE). As yet periphyton communities are not included in this programme due to perceived difficulties in the application of these methods. Diatom samples were collected from 10 sites in the Vaal and Wilge Rivers for a period of one year. Diatom cells from these communities were enumerated and diatom-based indices were calculated using OMNIDIA v.3. Diatom index scores were correlated to physical and chemical water quality variables over different time periods and at different concentrations. It was found that the tested diatom indices in general have the best correlation with average chemical data for a one-month period, starting six weeks prior to biological sampling. The Biological Diatom Index showed the strongest relationship to general water quality, while the Eutrophication and Pollution Index showed the strongest relationship to dissolved inorganic phosphorus. Results of correlation analyses obtained in South Africa were comparable to those obtained in several European studies. Hence, it is concluded that diatom-based indices, if implemented in South Africa, will provide a valuable addition to South Africa's suite of tools for the biological monitoring of water quality.

Application of a fish health assessment index and associated parasite index to Clarias gariepinus (Teleostei: Clariidae) in the Vaal River system, South Africa

The aim of this study was to determine if the fish health assessment index (HAI) developed in the USA and associated parasite index (PI), when applied to Clarias gariepinus at two localities in the upper and middle Vaal River system, could distinguish between localities on the grounds of water quality. Elevated HAI values, correlating with poorer chemical and physical water quality, were recorded from the Vaal River Barrage site. Parasite data were congruent with the main PI premise that prevalence and intensity of endoparasite infection would be higher at the more polluted locality, with the converse being recorded for ectoparasites. It was therefore possible to distinguish between localities with different water quality, based on parasites present on the hosts.

Evaluation of quantitative real-time PCR to characterise spatial and temporal variations in cyanobacteria, Cylindrospermopsis raciborskii (Woloszynska) Seenaya et Subba Raju and cylindrospermopsin concentrations in three subtropical Australian reservoirs

Three drinking water storage reservoirs in subtropical southeast Queensland, Australia have regular blooms of the toxic cyanobacterium Cylindrospermopsis raciborskii that can produce cylindrospermopsins. We tested water samples from 16 sites in 3 reservoirs on 2 sampling occasions during a bloom of C. raciborskii in the austral summer and autumn of 2007. Using a range of parameters including quantitative real-time PCR, microscope cell counts and HPLC–MS/MS we correlated the 16S ribosomal RNA gene with total cyanobacteria, the rpoC1 gene with C. raciborskii cell concentrations, and the cyrC gene with cylindrospermopsin concentrations to assess spatial and temporal variability within and between reservoirs. While the correlation between cyrC and cylindrospermopsin cell quotas was good (mean r 2 = 0.61 for February samples and 0.75 for March samples), the correlation between total cyanobacteria and the 16S ribosomal RNA gene, and between C. raciborskii and the rpoC1 gene were poor indicating that further work is needed to develop these novel molecular methods. Spatial and temporal analysis of the distribution of rpoC1, cylindrospermopsin cell quotas, and a range of physical and chemical water quality parameters showed the greatest variation occurred between reservoirs, and within the largest and most spatially diverse reservoir. This suggests that populations of C. raciborskii strains with inherently different cylindrospermopsin cell quotas may be an important driver of toxicity in these reservoirs. An outcome of this study was the observation that deoxycylindrospermopsin always exceeded the cylindrospermopsin cell quota by up to 5-fold, and that a peak cell quota of 60 fg (cylindrospermopsin + deoxycylindrospermopsin) cell −1 was measured.

Local and ecoregion effects on fish assemblage structure in tributaries of the Rio Paraíba do Sul, Brazil

Summary1. We examined the effects of physical and chemical habitat variables and ecoregions on species occurrence and fish assemblage structure in streams of the Paraíba do Sul basin, in southeast Brazil.2. Fish and environmental data were collected from 42 sites on 26 first to fourth order streams (1 : 50 000 map scale) in three ecoregions. The sites occurred in one valley and two plateau ecoregions at altitudes of 40–1080 m and distances of 0.1–188 km from the main channel of the Rio Paraíba do Sul. Physical habitat (substratum, riparian cover, habitat types) and water quality (dissolved oxygen, pH, temperature and conductivity) variables were measured at each sampling site.3. A total of 2684 individuals in 16 families and 59 species were recorded.4. Ecoregion was a better predictor of the fish assemblage than the other environmental variables, according to the differences between the mean within‐class and mean between‐class similarities in assemblage data.5. Differing landscape characteristics were associated with differing local variables and thereby with differing fish assemblage structures. Riffles, shrub, grass, dissolved oxygen, conductivity and temperature were closely related to fish assemblage structure.6. Fish assemblages in sites far from the main river and at higher altitudes also differed from those near the Paraíba do Sul main channel, presumably as a result of differences in connectivity, covarying environmental factors and anthropogenic influence.7. These results reinforce the importance of understanding how stream communities are influenced by processes and patterns operating at local and regional scales, which will aid water resource managers to target those factors in their management and rehabilitation efforts.

Identifying sources of surface water pollution: A toolbox approach

This article examines a “toolbox” approach for identifying pollution sources, especially fecal sources, within a watershed. Distinguishing human and animal sources is important in assessing human health risks. Traditional water quality measurements cannot conclusively differentiate fecal sources, thus microbial source tracking (MST) is necessary to identify contributions from different sources. In this study, a toolbox approach that includes both traditional indicators and multiple MST targets was used to demonstrate what measures are needed in a toolbox and how to best use these measures to obtain useful data. The authors found that several physical and chemical water quality measures were redundant and could be eliminated from a sampling plan. Their toolbox approach integrates monitoring techniques that can be tailored to meet the needs of individual watershed management agencies, even those with limited resources. The MST targets in the toolbox can incorporate with bacteriological facilities already available to most watershed management agencies.

Comparison of several methods to calculate reaeration in streams, and their effects on estimation of metabolism

Metabolism is an integrative measurement of stream and river ecosystem functioning, and thus, could be used to assess impairment. Stream metabolism is measured by different methods which often yield contrasting results. Furthermore, open-channel measurements of metabolism, which offer the best potential for continuous monitoring of stream functioning, rely on calculations of gas exchange with the atmosphere, for which a plethora of methods exists. Therefore, to incorporate metabolism in stream monitoring programs, it is necessary to determine which methods yield comparable results under a given set of environmental conditions. We studied 21 streams in the Basque Country (northern Spain), ranging widely in physical characteristics and water quality. We calculated reaeration during summer baseflows using three different approaches: the night-time drop in oxygen, the lag between noon and peak oxygen concentration, and ten empirical equations relating depth and velocity with reaeration coefficients obtained from the literature. Differences among methods were very large, especially at the shallower sites. The results obtained with most empirical equations were highly correlated, but showed little agreement with the night-time and peak lag methods. We then analyzed the response of reaeration rate to river stage: reaeration calculated by the night-time method during 1 year of continuous monitoring was regressed against discharge at each site, and the resulting model was compared to the results of empirical equations, using software HecRas 2.2 to model hydraulic conditions at different river stages. The shape of reaeration-discharge plots differed greatly and in a site-dependent manner, and there was little agreement between methods. Finally, we investigated the effects of reaeration rate on estimates of metabolism. The choice of method greatly affected the estimates of both primary production and respiration. The empirical equations, except E7 and E10, yielded the most unrealistic estimations of stream metabolism. Overall, the night-time method, especially when regressed against discharge, seems to be the most robust and reliable among those tested, with the energy dissipation method (E10) appearing to be a viable alternative when the night-time method does not work.

Relationships of nitrous oxide fluxes with water quality parameters in free water surface constructed wetlands

The effects of chemical oxygen demand (COD) concentration in the influent on nitrous oxide (N2O) emissions, together with the relationships between N2O and water quality parameters in free water surface constructed wetlands, were investigated with laboratoryscale systems. N2O emission and purification performance of wastewater were very strongly dependent on COD concentration in the influent, and the total N2O emission in the system with middle COD influent concentration was the least. The relationships between N2O and the chemical and physical water quality variables were studied by using principal component scores in multiple linear regression analysis to predict N2O flux. The multiple linear regression model against principal components indicated that different water parameters affected N2O flux with different COD concentrations in the influent, but nitrate nitrogen affected N2O flux in all systems.

Survey of pathogenic free-living amoebae and Legionella spp. in mud spring recreation area

Acanthamoeba, Hartmannella, and Naegleria are free-living amoebae, ubiquitous in aquatic environments. Several species within these genera are recognized as potential human pathogens. These free-living amoebae may facilitate the proliferation of their parasitical bacteria, such as Legionella. In this study, we identified Acanthamoeba, Hartmannella, Naegleria, and Legionella using various analytical procedures and investigated their occurrence at a mud spring recreation area in Taiwan. We investigated factors potentially associated with the prevalence of the pathogens, including various water types, and physical and microbiological water quality parameters. Spring water was collected from 34 sites and Acanthamoeba, Hartmannella, Naegleria, and Legionella were detected in 8.8%, 35.3%, 14.7%, and 47.1%, respectively. The identified species of Acanthamoeba included Acanthamoeba castellanii and Acanthamoeba polyphaga. Nearly all the Hartmannella isolates are identified as Hartmannella vermiformis. The Naegleria species included Naegleria australiensis and its sister groups, and two other isolates referred to a new clade of Naegleria genotypes. The Legionella species identified included unnamed Legionella genotypes, Legionella pneumophila serotype 6, uncultured Legionella spp., Legionella lytica, Legionella drancourtii, and Legionella waltersii. Significant differences (Mann–Whitney U test, P < 0.05) were observed between the presence/absence of Hartmannella and total coliforms, between the presence/absence of Naegleria and heterotrophic plate counts, and between the presence/absence of Legionella and heterotrophic plate counts. This survey confirms that pathogenic free-living amoebae and Legionella are prevalent in this Taiwanese mud spring recreation area. The presence of pathogens should be considered a potential health threat when associated with human activities in spring water.

Trout density and health in a stream with variable water temperatures and trace element concentrations: Does a cold‐water source attract trout to increased metal exposure?

A history of hard-rock mining has resulted in elevated concentrations of heavy metals in Prickly Pear Creek (MT, USA). Remediation has improved water quality; however, dissolved zinc and cadmium concentrations still exceed U.S. Environmental Protection Agency water-quality criteria. Physical habitat, salmonid density, fish health, and water quality were assessed, and metal concentrations in fish tissues, biofilm, and macroinvertebrates were determined to evaluate the existing condition in the watershed. Cadmium, zinc, and lead concentrations in fish tissues, biofilm, and invertebrates were significantly greater than those at the upstream reference site and an experimental site farther downstream of the confluence. Fish densities were greatest, and habitat quality for trout was better, downstream of the confluence, where water temperatures were relatively cool (16 degrees C). Measures of fish health (tissue metal residues, histology, metallothionein concentrations, and necropsies), however, indicate that the health of trout at this site was negatively affected. Trout were in colder but more contaminated water and were subjected to increased trace element exposures and associated health effects. Maximum water temperatures in Prickly Pear Creek were significantly lower directly below Spring Creek (16 degrees C) compared to those at an experimental site 10 km downstream (26 degrees C). Trout will avoid dissolved metals at concentrations below those measured in Prickly Pear Creek; however, our results suggest that the preference of trout to use cool water temperatures may supersede behaviors to avoid heavy metals.

Continuous dense‐phase CO2 processing of a coconut water beverage

SummaryEffects of dense‐phase CO2 (DPCD) on microbial, physical, chemical and sensorial quality of coconut water (CW) beverage were evaluated. Pressure during DPCD treatment was not significant in microbial reduction whereas temperature and % CO2 levels were significant. DPCD‐treated (34.5 MPa, 25 °C, 13% CO2, 6 min), heat‐pasteurised (74 °C, 15 s) and untreated CW beverages were evaluated during 9 weeks of refrigerated storage (4 °C). Total aerobic bacteria of DPCD and heat‐treated samples decreased whereas that of untreated samples increased to &gt;105 CFU mL−1 after 9 weeks. DPCD increased titratable acidity but did not change pH (4.20) and °Brix (6.0). Likeability of DPCD‐treated CW was similar to untreated. Heat‐treated samples were less liked (α = 0.05) at the beginning of storage. Off flavour and taste‐difference‐from‐control scores of heated samples were higher than DPCD during the first two weeks. DPCD extended shelf life of acidified, sweetened and carbonated CW over 9 weeks at 4 °C.

Spatial and seasonal variations in phytoplankton community structure in alkaline–saline Lake Nakuru, Kenya

AbstractSpatial and seasonal variations of phytoplankton, expressed in terms of species composition, cell density, biovolumes and biomass, collected at 10 sampling sites in alkaline–saline Lake Nakuru, Kenya, were investigated monthly from March 2004 to February 2005, in relation to selected physical and chemical water quality parameters. A total of eight species, belonging to five genera and three classes, were recorded. The Cyanophyceae comprised the bulk of the phytoplankton, followed by Euglenophyceae, while Bacillariophyceae were the least abundant. Arthrospira fusiformis was the most dominant species, in terms of density, among the Cyanophyceae, while Euglena spp. and Navicula elkabs dominated the Euglenophyceae and Bacillariophyceae density, respectively. Seasonal variations in phytoplankton species composition, density and biomass were significant (P &lt; 0.05) with minimum cell density and biomass occurring during the dry season, and being maximum following the end of the two rainy seasons from May to November 2004, suggesting the possible influence of various environmental factors on the lake. Sampling sites located close to the inlets of inflowing rivers exhibited significantly (P &lt; 0.05) higher phytoplankton cell density and biomass than those by the inshore sites. Soluble reactive phosphorus, ammonia‐nitrogen, conductivity and total alkalinity accounted for most of the variations in the cell densities of phytoplankton species.

Identification of 18S ribosomal DNA genotype of Acanthamoeba from hot spring recreation areas in the central range, Taiwan

Acanthamoeba is a free-living amoebae ubiquitous to aquatic environments. Within the genus a few species are recognized as opportunistic potential human pathogens, which cause granulomatous amoebic encephalitis (GAE) and keratitis. Infections of keratitis are frequently reported through wearing lens while swimming in the non-disinfected aquatic environment. Contaminations in hot tubs, spas and public baths are also possible. As a result, in this study, we identified Acanthamoeba based on the PCR amplification with a genus-specific primer pair and investigated the distribution of Acanthamoeba at five hot spring recreation areas in central range, Taiwan. We gathered data on factors potentially associated with the pathogen's distribution, including various sampling sites, aquatic environment, physical and microbiological water quality parameters. Spring water was collected from 55 sites and Acanthamoeba was detected in 9 (16.4%). The most frequently detected was Acanthamoeba griffini, followed by Acanthamoeba jacobsi Legionella were detected in 18 (32.7%) of the sites sampled in this study. The species of Legionella identified included Legionella pneumophila serotype 6, serotype 1, and Legionella erythra. Overall, 9.1% of the samples contained both Acanthamoeba and Legionella. The prevalence of Acanthamoeba was contrary to the levels of microbiological indicators recommended by Taiwan CDC, and no significant differences (Mann-Whitney U test, P<0.05) were observed between the presence/absence of Acanthamoeba and water quality parameters. Results of this survey confirm the existence of Acanthamoeba in Taiwan spring recreation areas. Acanthamoeba, the organism responsible for the majority of Acanthamoeba keratitis and can serve as vehicles for facultative pathogens, should be considered a potential threat for health associated with human activities in spring recreation areas of Taiwan.

Natural and drinking water quality in Erbil, Kurdistan

This review evaluates and summarizes results of short term or long term projects monitoring published papers concerning water quality in Erbil governorate. Number of studies was conducted on monitoring the physical, chemical and biological quality of natural and drinking water in Erbil. The quality of water samples were generally fluctuated from safe to unsafe for drinking due to the variation of the studied properties with time and sample sites. The results indicated that investigated waters were fresh well aerated with dissolved oxygen, rich in sodium, sulphate and calcium in some sites. While other sites showed an evident case of pollution. Bacteriological examinations showed that greater zab river water was not safe for drinking due to the presence of bacterial indicators. The representative data of nutrient status suggested eutrophic conditions of lake water with alkaliphilous and hard water characteristics.

USO DE MACROINVERTEBRADOS EM PROCEDIMENTOS DE BIOMONITORAMENTO EM ECOSSISTEMAS AQUÁTICOS

Normal 0 21 false false false MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabela normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} The usual chemical procedures to analyse water samples yield information only concerning the water state on the moment of collection, thus short term contamination generally are left undetected. Moreover, this mode of analysis is not sensitive to physical alterations to habitats in aquatic ecosystems, since habitat evaluations do not depend on the simple chemical quality of local waters. This way, the integrity of the targeted ecosystem cannot be guessed from chemical and physical water quality. A more comprehensive evaluation of the health state of a given aquatic ecosystem can be obtained from the characterization of organisms that living therein. Currently, benthic macroinvertebrates (usually aquatic insects) are widely used in evaluations of ecological water quality in association with biological monitoring tools. In the present revision, we presented some traits of macroinvertebrates and how macroinvertebrate communities are used as bioindicators in association with biological monitoring tools. We focused on four methodologies, being three of which widely used in many countries in national, regional or local biological monitoring programs: Biotic Index, Predictive Models, Multimetrics Index, and a fourth methodology still under construction with great potential of application named Biological and Ecological Traits.

Physical Factors Control Phytoplankton Production and Nitrogen Fixation in Eight Texas Reservoirs

We compared regression tree analyses and multiple linear regression models to explore the relative importance of physical factors, land use, and water quality in predicting phytoplankton production and N2 fixation potentials at 85 locations along riverine to lacustrine gradients within eight southern reservoirs. The regression tree model (r2 = 0.73) revealed that differences in phytoplankton production were primarily a function of water depth. The highest rates of production (mg C m−3 h−1) occurred at shallow sites (<0.9 m), where rates were also related to total phosphorus (TP) levels. At deeper sites, production rates were higher at sites with relative drainage area (RDA, ratio of drainage area to water surface area) below 45, potentially due to longer hydraulic residence times. In contrast, multiple linear regression selected TP, RDA, dissolved phosphorus, and percent developed land as significant model variables (r2 = 0.63). The regression tree model (r2 = 0.67) revealed that N2 fixation potentials (mg N m−3 h−1) were substantially higher at sites with relatively smaller drainage areas (RDA < 45). Within this subgroup, fixation rates were additionally related to TP values (threshold = 41 μg l−1). The multiple linear regression model (r2 = 0.67) also selected RDA as the primary predictor of N2 fixation. Regression tree models suggest that nutrient controls (phosphorus) were subordinate to physical factors such as depth and RDA. We concluded that regression tree analysis was well suited to revealing nonlinear trends in data (for example, depth), but yielded large uncertainty estimates when applied to linear data (for example, phosphorus).

A fish kill related to an acid-metal spill (Little Sackville River, Nova Scotia, Canada)

This paper documents the aqueous transport of acidic drainage in the Little and Main Sackville Rivers in Nova Scotia, and contributes to a better general understanding of the movement and duration of impact in such an event. Acidic drainage has been often noted as a major environmental hazard in mainland Nova Scotia. In addition to the details of the distribution and dispersal of metal concentrations in the Sackville Rivers ecosystem, some of the effects upon the aquatic organisms in the area are presented. Both an automated and hand-held devices were used to obtain physical water quality both prior to and after the event. The environmental impacts of the contaminant are discussed in terms of their immediate effects. The immediate effects in the mixing zone, where toxicity occurred, were at the entrance of the acid-bearing outflow, where there was a presence of mixing with the higher pH waters in the main channel. More than 4000 dead fish were counted (including approximately 300 American eels (Anguilla rostrata), 1000 one-year-old salmon (Salmo salar), 150 two-year-old salmon, 24 small-mouth bass (Micropterus dolmieui) and 24 suckers (Catostomus commersonii), in addition to minnows (specific species unidentified), small gaspereau (Alosa pseudoharengus), brook trout (Salvelinus fontinalis), freshwater mussels (specific species unidentified), and a snapping turtle (Chelydra serpentina). It is most likely that the fish kill resulted from rapid suffocation due to metal flocculants clogging the gills. It was in this zone where dissolved metals precipitated (Al, Fe, Cu).

Hyperspectral remote sensing of cyanobacteria in turbid productive water using optically active pigments, chlorophyll a and phycocyanin

Nuisance blue-green algal blooms contribute to aesthetic degradation of water resources by means of accelerated eutrophication, taste and odor problems, and the production of toxins that can have serious adverse human health effects. Current field-based methods for detecting blooms are costly and time consuming, delaying management decisions. Methods have been developed for estimating phycocyanin concentration, the accessory pigment unique to freshwater blue-green algae, in productive inland water. By employing the known optical properties of phycocyanin, researchers have evaluated the utility of field-collected spectral response patterns for determining concentrations of phycocyanin pigments and ultimately blue-green algal abundance. The purpose of this research was to evaluate field spectroscopy as a rapid cyanobacteria bloom assessment method. In-situ field reflectance spectra were collected at 54 sampling sites on two turbid reservoirs on September 6th and 7th in Indianapolis, Indiana using ASD Fieldspec (UV/VNIR) spectroradiometers. Surface water samples were analyzed for in-vitro pigment concentrations and other physical and chemical water quality parameters. Semi-empirical algorithms by Simis et al. [Simis, S., Peters, S., Gons, H. (2005). Remote sensing of the cyanobacterial pigment phycocyanin in turbid inland water. American Society of Limnology and Oceanography 50(11): 237–245] were applied to the field spectra to predict chlorophyll a and phycocyanin absorption at 665 nm and 620 nm, respectively. For estimation of phycocyanin concentration, a specific absorption coefficient of 0.0070 m 2 mg PC -1 for phycocyanin at 620 nm, a PC ⁎(620), was employed, yielding an r 2 value of 0.85 ( n = 48, p < 0.0001), mean relative residual value of 0.51 ( σ = 1.41) and root mean square error (RMSE) of 19.54 ppb. Results suggest this algorithm could be a robust model for estimating phycocyanin. Error is highest in water with phycocyanin concentrations of less than 10 ppb and where phycocyanin abundance is low relative to chlorophyll a. A strong correlation between measured phycocyanin concentrations and biovolume measurements of cyanobacteria was also observed ( r = 0.89), while a weaker relationship ( r = 0.66) resulted between chlorophyll a concentration and cyanobacterial biovolume.

Land Use Effects on Runoff and Water Quality on an Eastern Arkansas Soil Under Simulated Rainfall

ABSTRACT Over the past century, a significant proportion of the native grasslands that once occupied much of the middle third of the United States have been converted to cultivated agriculture, causing short- and long-term variations in soil physical and hydraulic properties that influence runoff-infiltration partitioning and runoff water quality. Eastern Arkansas is highly agriculturally productive when irrigated. However, the long history of irrigated agriculture and more recent shifts in rainfall patterns during the growing season have resulted in regional groundwater aquifer depletion with minimal regional recharge. The objective of this study was to evaluate the effects of land use on soil physical properties, runoff-infiltration partitioning, and runoff water quality on a typical agricultural soil in the Mississippi River Delta region of eastern Arkansas. Small-plot rainfall simulations were conducted on an Immanuel silt loam, (fine-silty, mixed, active, thermic, Oxyaquic Glossudalf) in plots (1.5 × 2 m) under native tallgrass prairie (PR) and two cultivated agroecosystems, ridge-tillage (RT), and conventional-tillage (CN). Residue cover was greatest in the PR and lowest in the CN system and differed significantly (p < 0.05) among all three land uses. However, runoff from the two agroecosystems did not differ, averaging 87% of the total amount of water applied, but both were significantly greater (p < 0.05) than that from the PR system, which averaged 62% of the total amount of water applied. Runoff turbidity and suspended solid concentration and load were greater (p < 0.05) from the CN than from the RT or PR systems. The CN system also had the greatest (p < 0.05) total P concentration and load, but the RT system produced runoff with the greatest (p < 0.05) soluble reactive P concentration and load of the three systems. Results indicate that land use and the degree of soil disturbance significantly affects runoff-infiltration partitioning and runoff water quality on this typical eastern Arkansas agricultural soil. Should results prove consistent on other regional soils, further depletion of local aquifers and degradation of surface water quality will likely continue if more sustainable agricultural practices are not increased.

Estimation of nonlinear trends in water quality: An improved approach using generalized additive models

This paper advocates the use of Generalized Additive Models (GAMs) for the estimation of nonlinear trends in water quality in the presence of serially correlated errors. The GAM methodology is applicable to a range of physical, chemical and biological water quality variates. Comparison with the estimate based on Seasonal Kendall's Slope and robust regression is discussed. An example is given concerning log‐transformed stream electrical conductivity, which is adjusted for flow. The monthly data have first order autocorrelation exceeding 0.5 and the trend is markedly nonlinear. Seasonal effects are shown to have been changing over time.