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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 73 records · Page 4Linked to original sources
USGS2006

Step wise, multiple objective calibration of a hydrologic model for a snowmelt dominated basin

The ability to apply a hydrologic model to large numbers of basins for forecasting purposes requires a quick and effective calibration strategy. This paper presents a step wise, multiple objective, automated procedure for hydrologic model calibration. This procedure includes the sequential calibration of a model's simulation of solar radiation (SR), potential evapotranspiration (PET), water balance, and daily runoff. The procedure uses the Shuffled Complex Evolution global search algorithm to calibrate the U.S. Geological Survey's Precipitation Runoff Modeling System in the Yampa River basin of Colorado. This process assures that intermediate states of the model (SR and PET on a monthly mean basis), as well as the water balance and components of the daily hydrograph are simulated, consistently with measured values.

Journal of the American Water Resources Associatio↗
USGS1989

Bias in groundwater samples caused by wellbore flow

Design of physical installations and sampling procedures for ground-water monitoring networks, particularly for detection and analysis of possible contaminants, is a topic of great scientific and practical interest at the present time. Recent practice in the design of monitoring networks associated with known contaminant sources sometimes includes an array of monitoring wells with long well screens (up to 50 feet or more). Numerical experiments with a detailed three-dimensional ground-water flow model indicate that significant wellbore flow can occur in contaminant monitoring wells with long well screens that are embedded in homogeneous aquifers with very small vertical head differences in the aquifer. This ``short circuiting'' of flow through boreholes should exist at some level on all scales. Consideration of the general flow pattern within the borehole, the flow pattern in the aquifer adjacent to the borehole, and the process of obtaining water samples from the borehole suggests that in many situations the practice of installing long well screens in contaminant monitoring wells should be abandoned.

Journal of Hydraulic Engineering↗
USGS1988

Water resources publications of the U.S. Geological Survey for Tennessee, 1906-1987

A bibliography was compiled of the water-resources investigations published by the U.S. Geological Survey, Water Resources Division, in Tennessee. The bibliography includes an alphabetical listing by author, as well as listings by general and specific areas in Tennessee. The publications are classified also by discipline and type of report: open- file reports, water-supply papers, water-resources investigations, professional papers, circulars, hydrologic investigations atlases, miscellaneous investigations maps, journal and symposium articles, water-resources bulletin articles, and water-resources data reports.

Tennessee↗
USGS1983

Groundwater observation network design for the Kansas groundwater management districts, U.S.A.

Concerns about the efficiency and economic soundness of the Kansas groundwater monitoring program led to a systematic redesign of this network, a tentative phase of which is presented in this study. The objectives of this paper include monitoring of major aquifers within each groundwater management district at a spatially more uniform level of accuracy, elimination of redundant measurements and optimization of the information gained from each observation well. The theory of regionalized variables is employed to estimate the amount of spatial variability of the water table, on which the network design is based. This study shows that it is not practical to attempt to reduce the already existing level of uncertainty uniformly throughout the various districts; to do so would tremendously increase the cost of well monitoring, which is already very high. Assuming that the currently existing network is satisfactory for the State's objectives, a reduced network consisting of one well every 6.4 km is equally satisfactory. The reduced network yields district-wide maps that do not differ significantly from those produced using the present network and at the same time it reduces the already-existing network by 18–47%. Therefore, adoption of a rearranged square well network is recommended, which is reduced to a 6.4-km spacing to achieve both a uniform level of information about the water table and a minimum required accuracy.

Kansas↗
USGS1996

Bibliography of selected water-resources publications on Nevada by the U.S. Geological Survey, 1885 through 1995

References to 898 water-resources publications are listed alphabetically by senior author and indexed by hydrographic-area name or other geographic features. Most of the publications were written between 1960 and 1995 by U.S. Geological Survey scientists and engineers of the Water Resources Division, Nevada District. Also included are references to publications by other Water Resources Division authors that deal with Nevada hydrology. References to publications written before 1960 are included to provide a historical perspective. The references include several types of Geological Survey book and map publications, as well as State-series reports, journal articles, conference and symposium papers, abstracts, and graduate- degree theses. Information on publication availability is provided also.

Open-File Report↗
USGS2023

Incorporating temperature into seepage loss estimates for a large unlined irrigation canal

Quantifying seepage losses from unlined irrigation canals is necessary to improve water use and conservation. The use of heat as a tracer is widely used in quantifying seepage rates across the sediment–water interface. In this study, field observations and two-dimensional numerical models were used to simulate seepage losses during the 2018 and 2019 irrigation season in the Truckee Canal system. Nineteen transects were instrumented with temperature probes and stage recording devices for inverse modeling to derive seepage flux and volumetric losses over the 39 km length of canal. The numerical models for each transect were calibrated and validated using the two-year dataset. Soil zones and observation data were used in each numerical model to help guide calibration of vertical and lateral heat and fluid fluxes. Model simulations were used to derive multivariable regression equations that consider stage, temperature, and hydraulic gradient. The results demonstrate the value of long-term datasets that illustrate the seasonality of groundwater levels, siltation, stage, and temperature on seepage rates. Seepage rates estimated by the numerical models range from 0.16 to 4.6 m 3 /d m −1 . Total annual volumetric losses estimated for 2018 and 2019 were 1.6 × 10 -2 to 1.2 × 10 -2 km 3 , respectively. The seepage losses estimated by this study account for 32 % to 41 % of the inflow volumes. Regression models were able to reproduce seepage time-series simulated by the numerical models reasonably well. In arid environments, water diverted into irrigation canals may be influenced by seasonal variations in temperature sufficient to influence the water accounting of conveyed surface flows.

Nevada↗
USGS2001

Processes regulating watershed chemical export during snowmelt, fraser experimental forest, Colorado

In the Central Rocky Mountains, snowfall dominates precipitation. Airborne contaminants retained in the snowpack can affect high elevation surface water chemistry during snowmelt. At the Fraser Experimental Forest (FEF), located west of the Continental Divide in Central Colorado, snowmelt dominates the annual hydrograph, and accounts for >95% of annual stream water discharge. During the winters of 1989-1993, we measured precipitation inputs, snowpack water equivalent (SWE) and ion content, and stream water chemistry every 7-10 days along a 3150-3500 m elevation gradient in the subalpine and alpine Lexen Creek watershed. The study objectives were to (1) quantify the distribution of SWE and snowpack chemical content with elevation and aspect, (2) quantify snowmelt rates, temperature of soil, snowpack, and air with elevation and aspect, and (3) use change in upstream-downstream water chemistry during snowmelt to better define alpine and subalpine flowpaths. The SWE increased with elevation (P < 0.001) and was greater on NE aspects (P < 0.05). Subalpine soils were unfrozen. Snowmelt occurred throughout winter at low elevation (3150 m), SE aspect stations. By snowpack peak water equivalent (PWE), the snowpack lost about a third (0.24 m) of its moisture. The subalpine snowpack had warm (> - 3??C) temperatures throughout winter which resulted in significant snowpack ion loss. By snowpack PWE in mid May, the snowpack had lost almost half the cumulative precipitation H+, NH4+, and SO42- inputs and a third of the NO3- input. Windborne soil particulate inputs late in winter increased snowpack base cation content. Variation in subalpine SWE and snowpack ion content with elevation and aspect, and wind redistribution of snowfall in the alpine resulted in large year-to-year differences in the timing and magnitude of SWE, PWE, and snowpack ion content. The alpine stream water ion concentrations changed little during snowmelt indicating meltwater passed quickly through surface porous soils and was well mixed before entering the stream. Conversely, subalpine stream water chemistry was diluted during snowmelt suggesting much melt water moved to the stream as shallow subsurface lateral flow. Published by Elsevier Science B.V.

Journal of Hydrology↗
USGS1998

Persistent water level changes in a well near Parkfield, California, due to local and distant earthquakes

Coseismic water level rises in the 30-m deep Bourdieu Valley (BV) well near Parkfield, California, have occurred in response to three local and five distant earthquakes. Coseismic changes in static strain cannot explain these water level rises because (1) the well is insensitive to strain at tidal periods; (2) for the distant earthquakes, the expected coseismic static strain is extremely small; and (3) the water level response is of the incorrect sign for the local earthquakes. These water level changes must therefore be caused by seismic waves, but unlike seismic water level oscillations, they are monotonic, persist for days or weeks, and seem to be caused by waves with periods of several seconds rather than long-period surface waves. Other investigators have reported a similar phenomenon in Japan. Certain wells consistently exhibit this type of coseismic water level change, which is always in the same direction, regardless of the earthquake's azimuth or focal mechanism, and approximately proportional to the inverse square of hypocentral distance. To date, the coseismic water level rises in the B V well have never exceeded the seasonal water level maximum, although their sizes are relatively well correlated with earthquake magnitude and distance. The frequency independence of the well's response to barometric pressure in the frequency band 0.1 to 0.7 cpd implies that the aquifer is fairly well confined. High aquifer compressibility, probably due to a gas phase in the pore space, is the most likely reason why the well does not respond to Earth tides. The phase and amplitude relationships between the seasonal water level and precipitation cycles constrain the horizontal hydraulic diffusivity to within a factor of 4.5, bounding hypothetical earthquake-induced changes in aquifer hydraulic properties. Moreover, changes of hydraulic conductivity and/or diffusivity throughout the aquifer would not be expected to change the water level in the same direction at every time of the year. The first 2.5 days of a typical coseismic water level rise could be caused by a small coseismic discharge decrease at a point several tens of meters from the well. Alternatively, the entire coseismic water level signal could represent diffusion of an abrupt coseismic pore pressure increase within several meters of the well, produced by a mechanism akin to that of liquefaction. The coseismic water level changes in the BV well resemble, and may share a mechanism with, coseismic water level, stream discharge, and groundwater temperature changes at other locations where preearthquake changes have also been reported. No preearthquake changes have been observed at the BV well site, however.

Journal of Geophysical Research B: Solid Earth↗
USGS2021

Months-long spike in aqueous Arsenic following domestic well installation and disinfection: Short- and long-term drinking water quality implications

Exposure to high concentration geogenic arsenic via groundwater is a worldwide health concern. Well installation introduces oxic drilling fluids and hypochlorite (a strong oxidant) for disinfection, thus inducing geochemical disequilibrium. Well installation causes changes in geochemistry lasting 12 + months, as illustrated in a recent study of 250 new domestic wells in Minnesota, north-central United States. One study well had extremely high initial arsenic (1550 µg/L) that substantially decreased after 15 months (5.2 µg/L). The drilling and development of the study well were typical and ordinary; nothing observable indicated the very high initial arsenic concentration. We hypothesized that oxidation of arsenic-containing sulfides (which lowers pH) combined with low pH dissolution of arsenic-bearing Fe (oxyhydr)oxides caused the very high arsenic concentration. Geochemical equilibrium considerations and modeling supported our hypothesis. Groundwater equilibrium redox conditions are poised at the Fe(III) (s) /Fe(II) (aq) stability boundary, indicating arsenic-bearing Fe (oxyhydr)oxide mineral sensitivity to pH and redox changes. Changing groundwater geochemistry can have negative implications for home water treatment (e.g., reduced arsenic removal efficiency, iron fouling), which can lead to ongoing but unrecognized hazard of arsenic exposure from domestic well water. Our results may inform arsenic mobilization processes and geochemical sensitivity in similarly complex aquifers in Southeast Asia and elsewhere.

Minnesota↗
USGS2000

Modeling regional salinization of the Ogallala aquifer, Southern High Plains, TX, USA

Two extensive plumes (combined area > 1000 km2) have been delineated within the Ogallala aquifer in the Southern High Plains, TX, USA. Salinity varies within the plumes spatially and increases with depth; Cl ranges from 50 to >500 mg 1-1. Variable-density flow modeling using SUTRA has identified three broad regions of upward cross-formational flow from the underlying evaporite units. The upward discharge within the modeled plume area is in the range of 10-4-10-5 m3 day-1, and the TDS concentrations are typically >3000 mg 1-1. Regions of increased salinity, identified within the Whitehorse Group (evaporite unit) underlying the Ogallala aquifer, are controlled by the structure and thickness variations relative to the recharge areas. Distinct flow paths, on the order of tens of km to >100 km in length, and varying flow velocities indicate that the salinization of the Ogallala aquifer has been a slow, ongoing process and may represent circulation of waters recharged during Pleistocene or earlier times. On-going pumping has had negligible impact on the salinity distribution in the Ogallala aquifer, although simulations indicate that the velocity distribution in the underlying units may have been affected to depths of 150 m after 30 years of pumping. Because the distribution of saline ground water in this region of the Ogallala aquifer is heterogeneous, careful areal and vertical characterization is warranted prior to any well-field development. (C) 2000 Elsevier Science B.V.Two extensive plumes (combined area >1000 km2) have been delineated within the Ogallala aquifer in the Southern High Plains, TX, USA. Salinity varies within the plumes spatially and increases with depth; Cl ranges from 50 to >500 mg l-1. Variable-density flow modeling using SUTRA has identified three broad regions of upward cross-formational flow from the underlying evaporite units. The upward discharge within the modeled plume area is in the range of 10-4-10-5 m3 day-1, and the TDS concentrations are typically >3000 mg l-1. Regions of increased salinity, identified within the Whitehorse Group (evaporite unit) underlying the Ogallala aquifer, are controlled by the structure and thickness variations relative to the recharge areas. Distinct flow paths, on the order of tens of km to >100 km in length, and varying flow velocities indicate that the salinization of the Ogallala aquifer has been a slow, ongoing process and may represent circulation of waters recharged during Pleistocene or earlier times. On-going pumping has had negligible impact on the salinity distribution in the Ogallala aquifer, although simulations indicate that the velocity distribution in the underlying units may have been affected to depths of 150 m after 30 years of pumping. Because the distribution of saline ground water in this region of the Ogallala aquifer is heterogeneous, careful areal and vertical characterization is warranted prior to any well-field development.

Journal of Hydrology↗
USGS1998

Vulnerability of desert biological soil crusts to wind erosion: The influences of crust development, soil texture, and disturbance

Biological soil crusts, consisting of cyanobacteria, green algae, lichens, and mosses, are important in stabilizing soils in semi-arid and arid lands. Integrity of these crusts is compromised by compressional disturbances such as foot, vehicle, or livestock traffic. Using a portable wind tunnel, we found threshold friction velocities (TFVs) of undisturbed crusts well above wind forces experienced at these sites; consequently, these soils are not vulnerable to wind erosion. However, recently disturbed soils or soils with less well-developed crusts frequently experience wind speeds that exceed the stability thresholds of the crusts. Crustal biomass is concentrated in the top 3 mm of soils. Sandblasting by wind can quickly remove this material, thereby reducing N and C inputs from these organisms. This loss can result in reduced site productivity, as well as exposure of unprotected subsurface sediments to wind and water erosion. Actions to reduce impacts to these crusts can include adjustments in type, intensity, and timing of use.

Journal of Arid Environments↗
USGS1991

Importance of closely spaced vertical sampling in delineating chemical and microbiological gradients in groundwater studies

Vertical gradients of selected chemical constituents, bacterial populations, bacterial activity and electron acceptors were investigated for an unconfined aquifer contaminated with nitrate and organic compounds on Cape Cod, Massachusetts, U.S.A. Fifteen-port multilevel sampling devices (MLS's) were installed within the contaminant plume at the source of the contamination, and at 250 and 2100 m downgradient from the source. Depth profiles of specific conductance and dissolved oxygen at the downgradient sites exhibited vertical gradients that were both steep and inversely related. Narrow zones (2-4 m thick) of high N2O and NH4+ concentrations were also detected within the contaminant plume. A 27-fold change in bacterial abundance; a 35-fold change in frequency of dividing cells (FDC), an indicator of bacterial growth; a 23-fold change in 3H-glucose uptake, a measure of heterotrophic activity; and substantial changes in overall cell morphology were evident within a 9-m vertical interval at 250 m downgradient. The existence of these gradients argues for the need for closely spaced vertical sampling in groundwater studies because small differences in the vertical placement of a well screen can lead to incorrect conclusions about the chemical and microbiological processes within an aquifer.Vertical gradients of selected chemical constituents, bacterial populations, bacterial activity and electron acceptors were investigated for an unconfined aquifer contaminated with nitrate and organic compounds on Cape Cod, Massachusetts, USA. Fifteen-port multilevel sampling devices (MLS's) were installed within the contaminant plume at the source of the contamination, and at 250 and 2100 m downgradient from the source. Depth profiles of specific conductance and dissolved oxygen at the downgradient sites exhibited vertical gradients that were both steep and inversely related. Narrow zones (2-4 m thick) of high N2O and NH4+ concentrations were also detected within the contaminant plume. A 27-fold change in bacterial abundance; a 35-fold change in frequency of dividing cells (FDC), an indicator of bacterial growth; a 23-fold change in 3H-glucose uptake, a measure of heterotrophic activity; and substantial changes in overall cell morphology were evident within a 9-m vertical interval at 250 m downgradient. The existence of these gradients argues for the need for closely spaced vertical sampling in ground-water studies because small differences in the vertical placement of a well screen can lead to incorrect conclusions about the chemical and microbiological processes within an aquifer.

Journal of Contaminant Hydrology↗
USGS2004

Infection experiments with Aphanomyces invadans in four species of estuarine fish

Along the eastern seaboard of the US, Atlantic menhaden, Brevoortia tyrannus, develop characteristic ulcerative lesions, a condition termed ulcerative mycosis. These lesions are identical to those seen across Asia in fish affected by epizootic ulcerative syndrome, a condition caused by the fungus-like oomycete Aphanomyces Invadans. Young-of-the-year menhaden inhabiting estuarine environments are the primary species affected in the USA and little is known about the factors involved in the initiation of the lesions, or why menhaden are predominantly infected. Atlantic menhaden, hogchoker, Trinectus maculatus, striped killifish, Fundulus majalis, and mummichog, Fundulus heteroclitus, were inoculated with A. invadans (80 zoospores per fish) to explore species differences in infection and lesion development. All four species developed lesions. Killifish developed frank lesions similar to those observed in menhaden but the gross lesions occurred later, approximately 5-10 days after those on menhaden. Hogchoker and mummichog did not develop gross skin ulcers; rather, their lesions appeared as reddened areas under the epidermis. Mummichogs also showed evidence of significant healing with a well-developed granuloma and significant myocyte regeneration. These experiments show that species barriers as well as ecological barriers can explain some of the factors involved in the development of lesions in, and specificity of the water mould for, menhaden.

Journal of Fish Diseases↗
USGS2009

Effects of temperature on disease progression and swimming stamina in Ichthyophonus‐infected rainbow trout, Oncorhynchus mykiss (Walbaum)

Rainbow trout, Oncorhynchus mykiss , were infected with Ichthyophonus sp. and held at 10°C, 15°C and 20°C for 28 days to monitor mortality and disease progression. Infected fish demonstrated more rapid onset of disease, higher parasite load, more severe host tissue reaction and reduced mean‐day‐to‐death at higher temperature. In a second experiment, Ichthyophonus ‐infected fish were reared at 15°C for 16 weeks then subjected to forced swimming at 10°C, 15°C and 20°C. Stamina improved significantly with increased temperature in uninfected fish; however, this was not observed for infected fish. The difference in performance between infected and uninfected fish became significant at 15°C ( P =0.02) and highly significant at 20°C ( P = 0.005). These results have implications for changes in the ecology of fish diseases in the face of global warming and demonstrate the effects of higher temperature on the progression and severity of ichthyophoniasis as well as on swimming stamina, a critical fitness trait of salmonids. This study helps explain field observations showing the recent emergence of clinical ichthyophoniasis in Yukon River Chinook salmon later in their spawning migration when water temperatures were high, as well as the apparent failure of a substantial percentage of infected fish to successfully reach their natal spawning areas.

Journal of Fish Diseases↗
USGS1993

Pesticides in shallow groundwater in the Delmarva Peninsula

A regional study of the areal and depth distribution of pesticides in shallow groundwater in the Delmarva Peninsula of Delaware, Maryland, and Virginia was done to (i) relate the pesticides detected to landscape and shallow subsurface features, and (ii) evaluate aquifer vulnerability and the potential contamination of drinking-water supplies. Water samples collected at 100 wells from 1988 to 1990 were analyzed for concentrations of 36 pesticides, four metabolites, and other constituents. The most commonly detected residues were atrazine, cyanazine, simazine, alachlor, metolachlor, and dicamba. Concentrations were low; few exceeded 3 µg L −1 . Most detections correlate with the intensive use of these herbicides in three widely distributed and commonly rotated crops—corn ( Zea mays L.), soybean [ Glycine max (L.) Merr.], and small grain—particularly if grown in well-drained soils. Most detections occurred in samples collected from shallow wells screened within 10 m of the overlying water table. The shallow depth distribution of most residues is consistent with their suspected history of use (ca. 20 yr), and patterns in shallow groundwater flow in the surficial aquifer in the study area. The areal and depth distributions of detectable residues in groundwater did not correlate with a vulnerability index, nor any of the component scores developed to estimate that index using the DRASTIC method. The shallow depth of most detections also indicates why few samples from water-supply wells in this study had measurable concentrations of pesticides; most supply wells are deeper than 10 m below the water table. The low number of contaminated samples from supply wells implies that deep groundwater currently (1992) used for drinking generally does not contain detectable pesticide residues.

Journal of Environmental Quality↗
USGS1986

Limnological characteristics of selected lakes in the Nebraska sandhills, U.S.A., and their relation to chemical characteristics of adjacent ground water

Limnological characteristics of Crane, Hackberry, Island and Roundup Lakes, and chemical characteristics of shallow ground water, within the Crescent Lake National Wildlife Refuge, western Nebraska, were determined during a preliminary investigation of the interaction between lakes and ground water in this study area between 1980 and 1984. When ice cover was absent, the lakes were well-mixed vertically, regardless of season. Depth to which 1% of surface illumination penetrated was commonly less than 1m. Variability in light penetration, as measured by Secchidisk transparency, appeared to be unrelated to changes in algal biomass, even though algal biomass, measured as chlorophyll a, varied seasonally within a two-order-of-magnitude range. Blue-green algae were the most abundant phytoplankton; this condition occurred most often when the ratio of total nitrogen to total phosphorus in the lakes' water was less than 29. Although rotifers and copepod naupli commonly were the most abundant zooplankton in the lakes, cladocerans were dominant occasionally. Either sodium or calcium was the most abundant cation, and bicarbonate was the most abundant anion, in water from water-table wells and lakes sampled during the study. The second most abundant cation in the ground water was related to the location of the sampled well within the ground-water system. The lakes were a source of dissolved organic carbon seeping to ground water. Chemical and hydrologic data indicate there is interaction between lakes and ground water in the study area.

Nebraska↗
USGS2007

Effects of dietary selenium on tissue concentrations,pathology, oxidative stress, and immune function in common eiders (Somateria mollissima)

Common eiders ( Somateria mollissima ) were fed added Se (as L-selenomethionine) in concentrations increasing from 10 to 80 ppm in a pilot study (Study 1) or 20 (low exposure) and up to 60 (high exposure) ppm Se in Study 2. Body weights of Study 1 ducks and high-exposure ducks in Study 2 declined rapidly. Mean concentrations of Se in blood reached 32.4 ppm wet weight in Study 1 and 17.5 ppm wet weight in high-exposure birds in Study 2. Mean Se concentrations in liver ranged from 351 (low exposure, Study 2) to 1252 ppm dry weight (Study 1). Oxidative stress was evidenced by Se-associated effects on glutathione metabolism. As Se concentrations in liver increased, Se-dependent glutathione peroxidase activity, glutathione reductase activity, oxidized glutathione levels, and the ratio of hepatic oxidized to reduced glutathione increased. In Study 2, the T-cell-mediated immune response was adversely affected in high-exposure eiders, but ducks in the low-exposure group exhibited evidence of an enhanced antibody-mediated immune response. Gross lesions in high-exposure ducks included emaciation, absence of thymus, and loss of nails from digits. Histologic lesions included severe depletion of lymphoid organs, hepatopathy, and necrosis of feather pulp and feather epithelium. Field studies showed that apparently healthy sea ducks generally have higher levels of Se in liver than healthy fresh-water birds, but lower than concentrations found in our study. Data indicate that common eiders and probably other sea ducks possess a higher threshold, or adverse effect level, for Se in tissues than fresh-water species. However, common eiders developed signs of Se toxicity similar to those seen in fresh-water birds.

Journal of Toxicology and Environmental Health, Pa↗
USGS1994

Loma sp. salmonids from the Eastern United States: Associated lesions rainbow trout

A microsporidian of the genus Loma was noted in the gills of rainbow trout Oncorhynchus mykiss from a state hatchery (Buford Trout Hatchery) in Georgia. Mortalities of varying severity occur at this hatchery every fall, and the microsporidian was noted during an experiment from August 1991 to January 1992 to determine the effects of water source on disease. Infections first appeared to be systemic in the October sample; xenomas were observed in heart, spleen, and peripheral vessel walls. The presence of unidentified intracellular material preceded the appearance of xenomas in all tissues, but whether this material was associated with inflammation or represented immature stages of the parasite has yet to be determined. These structures were also noted in the intestine and liver, although xenomas were not noted in these organs. Mature xenomas did not elicit an inflammatory response but appeared to be short-lived. When the xenoma wall ruptured and released spores, an inflammatory response was again observed. The prevalence and severity of the infection were determined in fish maintained in troughs with well water, Chattahoochee River water, or hatchery (treated river) water. The infection tended to be more prevalent and more severe in fish maintained in the hatchery or river water than in those maintained in the well water. Stress induced by poor water quality may increase mortality from this parasite. This report extends the range of Loma sp. into the eastern United States.

Journal of Aquatic Animal Health↗