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USGS2019

Chapter A7. Section 7.4. Algal biomass indicators

Indicators of algal biomass are used to assess water quality in both moving (lotic) and stillwater (lentic) ecosystems. Algal biomass in a water body can be estimated in three ways: (1) by quantifying chlorophyll a (CHL a ), (2) by measuring carbon biomass as ash-free dry mass (AFDM), or (3) by measuring the particulate organic carbon (POC) in a sample. The CHL a procedure measures photosynthetic pigment common to all types of algae, while AFDM and POC procedures measure the carbon in a filtered water sample. Each chapter of the National Field Manual is published separately and revised periodically. Newly published and revised chapters will be announced on the USGS Home Page on the World Wide Web under 'New Publications of the U.S. Geological Survey.'

Techniques of Water-Resources Investigations↗
USGS2008

Chapter A7. Section 7.5. Cyanobacteria in lakes and reservoirs: Toxin And taste-and-odor sampling guidelines

Cyanobacteria (also referred to as blue-green algae) cause a multitude of water-quality concerns, including the potential to produce toxins and taste-and-odor compounds. Toxins and taste-and-odor compounds may cause significant economic and public health concerns, and are of particular interest in lakes, reservoirs, and rivers that are used for drinking-water supply, recreation, or aquaculture. The purpose of NFM 7.5 is to provide guidelines for collecting, processing, and handling samples to be analyzed for cyanobacterial community composition (enumeration and identification) and total, particulate, and dissolved cyanobacterial toxins and taste-and-odor compounds in lakes and reservoirs (sections 7.5.5 through 7.5.9). Sections 7.5.1 through 7.5.4, however, are designed to provide some background information about cyanobacteria, including typical study designs and objectives related to the spatial and temporal occurrence of cyanobacteria (modified from Graham and others, 2008), in order to provide a useful context for sampling activities. The information presented here pertains to the occurrence of planktonic (free-floating) cyanobacteria in lakes and reservoirs. Each chapter of the National Field Manual is published separately and revised periodically. Newly published and revised chapters will be announced on the USGS Home Page on the World Wide Web under 'New Publications of the U.S. Geological Survey.'

Techniques of Water-Resources Investigations↗
USGS1998

Chapter A8. Bottom-material samples

The National Field Manual for the Collection of Water-Quality Data(National Field Manual) describes protocols (requirements and recommendations) and provides guidelines for U.S. Geological Survey (USGS) personnel who collect data used to assess the quality of the Nation's surface-water and ground-water resources. This release of Chapter A8 provides guidelines for the equipment and procedures needed to collect and process samples of bottom material for the evaluation of surface-water quality. Each chapter of the National Field Manual is published separately and revised periodically. Newly published and revised chapters are posted on the World Wide Web on the USGS page 'National Field Manual for the Collection of Water-Quality Data.' The URL for this page is http://pubs.water.usgs.gov/twri9A/ (accessed April 2005).

Techniques of Water-Resources Investigations↗
USGS1998

Chapter A9. Safety in Field Activities

The National Field Manual for the Collection of Water-Quality Data (National Field Manual) describes protocols (requirements and recommendations) and provides guidelines for U.S. Geological Survey (USGS) personnel who collect data used to assess the quality of the Nation's surface-water and ground-water resources. This chapter of the manual addresses topics related to personal safety to be used in the collection of water-quality data, including: policies and general regulations on field safety; transportation of people and equipment; implementation of surface-water and ground-water activities; procedures for handling chemicals; and information on potentially hazardous environmental conditions, animals, and plants. Each chapter of the National Field Manual is published separately and revised periodically. Newly published and revised chapters will be announced on the USGS Home Page on the World Wide Web under 'New Publications of the U.S. Geological Survey.' The URL for this page is http://pubs.usgs.gov/publications/ index.html.

Techniques of Water-Resources Investigations↗
USGS2016

Capsule- and disk-filter procedure

Capsule and disk filters are disposable, self-contained units composed of a pleated or woven filter medium encased in a polypropylene or other plastic housing that can be connected inline to a sample-delivery system (such as a submersible or peristaltic pump) that generates sufficient pressure (positive or negative) to force water through the filter. Filter media are available in several pore sizes, but 0.45 µm is the pore size used routinely for most studies at this time. Capsule or disk filters (table 5.2.1.A.1) are required routinely for most studies when filtering samples for trace-element analyses and are recommended when filtering samples for major-ion or other inorganic-constituent analyses.

Techniques of Water-Resources Investigations↗
USGS1977

Water resources data for North Carolina, water year 1976

Water resources data for the 1976 water year for North Carolina consist of records of stage, discharge, and water quality of streams; stage and contents of lakes and reservoirs; and ground-water levels. This report contains discharge records for 146 gaging stations; stage and contents for 24 lakes and reservoirs; water quality for 20 gaging stations; and water levels for 54 observation wells. Additional water data were collected at various sites, not involved in the systematic data-collection program, and are published as miscellaneous measurements in this report. The collection of water-resources data in North Carolina is a part of the National Water-Data System operated by the U.S. Geological Survey in cooperation with State, municipal, and Federal agencies.

North Carolina↗
USGS1990

Water resources data, North Carolina, water year 1989

Water resources data for the 1989 water year for North Carolina consists of records of stage, discharge and water quality of streams; stage and contents of lakes and reservoirs; and ground-water levels. This report contains discharge records for 178 gaging stations and stage and contents for 26 lakes and reservoirs; water quality for 26 gaging stations and 10 miscellaneous sites; continuous daily tide stage for 12 sites; and water levels for 43 observation wells. Additional water data were collected at various sites not involved in the systematic data-collection program, and are published as miscellaneous measurements in this report. The collection of water-resources data in North Carolina is a part of the National Water-Data System operated by the U.S. Geological Survey in cooperation with State, municipal, and Federal agencies.

North Carolina↗
USGS2000

Surface- and ground-water characteristics in the Upper Truckee River and Trout Creek watersheds, South Lake Tahoe, California and Nevada, July-December 1996

The Upper Truckee River and Trout Creek watersheds, South Lake Tahoe, California and Nevada, were studied from July to December 1996 to develop a better understanding of the relation between surface water and ground water. Base flows at 63 streamflow sites were measured in late September 1996 in the Upper Truckee River and Trout Creek watersheds. Most reaches of the main stem of the Upper Truckee River and Trout Creek had gaining or steady flows, with one losing reach in the mid-section of each stream. Twenty-seven of the streamflow sites measured in the Upper Truckee River watershed were on 14 tributaries to the main stem of the Upper Truckee River. Sixteen of the 40 streamflow sites measured in the Upper Truckee River watershed had no measurable flow. Streamflow in Upper Truckee River watershed ranged from 0 to 11.6 cubic feet per second (ft3/s). The discharge into Lake Tahoe from the Upper Truckee River was 11.6 ft3/s, of which, 40 percent of the flow was from ground-water discharge into the main stem, 40 percent was from tributary inflows, and the remaining 20 percent was the beginning flow. Gains from or losses to ground water along streams ranged from a 1.4 cubic feet per second per mile (ft3/s/mi) gain to a 0.5 ft3/s/mi loss along the main stem. Fourteen of the streamflow sites measured in the Trout Creek watershed were on eight tributaries to the main stem of Trout Creek. Of the 23 streamflow sites measured in the Trout Creek watershed, only one site had no flow. Flows in the Trout Creek watershed ranged from zero to 23.0 ft3/s. Discharge into Lake Tahoe from Trout Creek was 23.0 ft3/s, of which, about 5 percent of the flow was from ground-water discharge into the main stem, 75 percent was from tributary inflows, and the remaining 20 percent was the beginning flow. Ground-water seepage rates ranged from a 1.4 ft3/s/mi gain to a 0.9 ft3/s/mi loss along the main stem. Specific conductances measured during the seepage run in September 1996 increased in a downstream direction in the main stem of the Upper Truckee River and remained relatively constant in the main stem of Trout Creek. Water temperatures measured during the seepage run also increased in a downstream direction in both watersheds. Depths to ground water measured at 62 wells in the study area were used with the results of the seepage run to produce a water-level map in the Upper Truckee River and Trout Creek watersheds. Ground-water levels ranged from 1.3 to 69.8 feet below land surface. In the upper sections of the watersheds ground-water flow is generally toward the main stems of Upper Truckee River and Trout Creek, whereas in the lower sections, ground-water flow generally parallels the two streams and flows toward Lake Tahoe. The altitude of ground water between Lake Tahoe and Highway 50 was nearly the same as the lake-surface altitude from July to November 1996. This suggests ground-water discharge beneath the Upper Truckee River and Trout Creek drainages directly to Lake Tahoe was minimal and that much of the ground-water discharge was to the channels of the Upper Truckee River and Trout Creek upstream from Highway 50. Hydraulic gradients ranged from near zero to 1,400 feet per mile. Samples were collected at six surface-water-quality and eight ground-water-quality sites from July through mid-December 1996. Specific conductance of the ground-water-quality sites was higher than that of the surface-water-quality sites. Water temperature and pH median values were similar between ground-water-quality and surface-water-quality sites but ground water had greater variation in pH and surface water had greater variation in water temperature. Ground-water nutrient concentrations were generally higher than those in streams except for bioreactive iron.

Water-Resources Investigations Report↗
USGS2000

Pesticides in surface waters of the Upper Colorado River Basin, Colorado, 1996-98

Forty-four river, stream, and drain sites in the Upper Colorado River Basin in Colorado were sampled during 1996-98 to determine the occurrence and distribution of pesticides in the basin. In a fixed-station study, 57 surface-water samples were collected from October 1996 through January 1998 at four sites. Each site was sampled approximately monthly for up to a year, with more frequent sampling during the spring and summer growing season. In a synoptic study, surface-water samples were collected at 43 sites in the agricultural areas of the Grand Valley and the Uncompahgre River Valley in May 1998. Each site was sampled once. Pesticide concentrations generally were low and varied seasonally and across land uses. Thirty-five pesticides were detected at least once in the two studies, and 11 pesticides accounted for almost 82 percent of the detections. Herbicides were more commonly detected than insecticides, and only the herbicides alachlor and atrazine were detected in more than 50 percent of the samples. Carbofuran was the most commonly detected insecticide and was detected in 19 percent of the samples. Pesticide detections increased and were measured at higher concentrations in the summer months and at the agriculture sites. All pesticide concentrations were less than drinking-water standards, and most complied with human-health advisories and criteria for the protection of freshwater aquatic life. Pesticides in the Upper Colorado River Basin in Colorado were detected slightly less frequently and generally at lower concentrations than in 20 National Water-Quality Assessment Program study-unit basins that collected water-quality data from 1992 through 1996. Results from surface-water sampling conducted during 1996?98 in the Upper Colorado River Basin in Colorado indicate that beneficial uses of water were not being impaired by the presence of pesticides in surface waters in the basin.

Colorado↗
USGS2000

Water, ice, and meteorological measurements at South Cascade Glacier, Washington, 1986-1991 balance years

Mass balance and climate variables are reported for South Cascade Glacier, Washington, for the years 1986-91. These variables include air temperature, precipitation, water runoff, snow accumulation, snow and ice melt terminus position, surface level, and ice speed. Data are reduced to daily and monthly values where appropriate. The glacier-averaged values of spring snow accumulation and fall net balance given in this report differ from previous results because amore complete analysis is made. Snow accumulation values for the1986-91 period ranged from 3.54 (water equivalent) meters in 1991 to2.04 meters in 1987. Net balance values ranged from 0.07 meters in1991 to -2.06 meters in 1987. The glacier became much smaller during the 1986-91 period and retreated a cumulative 50 meters.

Water-Resources Investigations Report↗
USGS2000

Assessment of the effect of road construction and other modifications on surface-water flow at St. Vincent National Wildlife Refuge, Franklin County, Florida

St. Vincent National Wildlife Refuge is managed by the U.S. Fish and Wildlife Service (USFWS). The refuge was acquired in 1968 from a private land owner and occupies all of St. Vincent Island, a barrier island located off the southern coast of the Florida Panhandle near Apalachicola (fig. 1). The island, which covers 12,358 acres, is about 9 miles long and 4 miles across at its widest point. Eighty miles of unpaved roads that grid the island are presently used for refuge management, law enforcement, and visitor hiking trails. Prior to becoming a refuge, the natural flow of surface water on the island was altered by road and ditch construction that enabled timbering of pine. Restoring the natural flow of surface water on the island to its historical state is one of the USFWS's goals for ecosystem restoration. During past road construction activities, fill was placed in the creeks to create raised roadbeds. This activity changed the natural flow of surface water by (1) acting as an earthen dam that impounded creeks; (2) restricting flow, thus increasing the depth of water in the channels of creeks; or (3) blocking the natural movement of saltwater in the creeks in coastal areas, thus altering water salinity. Along some sections of road, grading substantially lowered land-surface elevations. Along these sections of roads, adjacent creeks commonly flowed into one another during high-water conditions, thus allowing the transfer of water from one drainage basin to another. In some areas on the island, ditches were dug to manipulate the movement of surface water.

Florida↗
USGS2000

The importance of ground water in the Great Lakes Region

Ground water is a major natural resource in the Great Lakes Region because it indirectly contributes more than 50 percent of the stream discharge to the Great Lakes. In addition, ground water is the source of drinking water for millions of people in the region, is an important source of supply for agriculture and many industries, and provides a relatively uniform supply of water in some ecologically sensitive areas to sustain plant and animal species. Therefore, to improve our understanding of water-resources issues in the Great Lakes Region, it is important to have a better understanding of the role that ground water plays in the overall hydrologic system of the lakes. The main ground-water resources issues in the Great Lakes Region are related to the amount of ground water, the interaction of ground water and surface water, changes in ground-water quality as development expands, and ecosystem health related to quantity and quality of water. Issues related to the amount of ground water Although the amount of water in the Great Lakes Region is vast, issues related to relatively small quantities of water are being raised more and more often. For example, even though the amount of ground water pumped in the region is small compared to the total amount of water present, ground water is an important source of public-water supply as well as an important source of supply for industrial, agricultural, and domestic needs. Less clearly understood, however, is the relation between the amount of streamflow discharging to the Great Lakes and the large portion of that flow that originates as ground water. The implications of this understanding for water- and land-use practices and, in turn, their effects on water quantity and quality, have not been fully incorporated into a policy framework. To help include information about the implications of the role that ground water plays in addressing regional water issues, a comprehensive analysis of indirect ground-water discharge to the Great Lakes is needed. Direct ground-water discharge to the Great Lakes is not a large factor in water-budget analyses for the Great Lakes. Locally, however, direct ground-water discharge to the Great Lakes may be important, even though the rates and places of discharge are not well known. A long-term evaluation of direct ground-water discharge to the Great Lakes would help place this hydrologic process in proper perspective. Near-shore areas with high rates of direct ground-water discharge may provide valuable habitat for aquatic organisms. Issues related to the interaction of ground water and surface water Withdrawal of ground water removes that water from the watershed when it is consumptively used or when the return flow is discharged to another drainage basin. Under these circumstances, pumping ground water constitutes a diversion of Great Lakes water. Alternatively, ground-water withdrawal could have the opposite effect of diverting ground-water flow into the watershed by altering the ground-water divides. In particular, as withdrawals associated with urban expansion increase, more accurate data on the amount and effects of ground-water use need to be collected. Data on the amounts of ground water pumped both within the watershed and outside, but near the watershed boundaries needs to be collected and evaluated for potential diversion of water to or from the Great Lakes. It is currently thought that both irrigation and ground-water withdrawals near the watershed boundaries constitute relatively small amounts of water; however, both rapidly changing farming practices and rapidly expanding urban communities could alter these amounts in a relatively short timeframe, especially during drought periods. At present, the effects of ground-water withdrawals have been quantified in detail at only a few urban locations. In addition to quantifying the amount of water pumped out of aquifers, it is also important to improve our knowledge of the amount of water that is recharging them. Ground-water recharge rates estimated in earlier studies cover only a small part of the Great Lakes Region. A comprehensive study of ground-water recharge rates for the entire watershed is needed to more completely determine the role of ground water in the hydrologic budget of the Great Lakes. Issues related to changes in ground-water quality as development expands Ground-water quality is as important as quantity for most water uses. As ground-water development proceeds, the possibility of altering the quality of ground water increases. The quality of ground water can be altered when water levels are drawn below the layer that confines the aquifer or by inducing water of lesser quality into an aquifer. Many local studies of these problems have been conducted, but few regional-scale analyses of changes in ground-water quality as a result of ground-water development have been done. Issues related to ecosystem health and quantity and quality of ground water Ground water is essential to maintain wetlands and to provide healthy habitat for other aquatic systems. Wetland hydrology is widely recognized as the primary influence on wetland ecology, development, and persistence, and information about hydrology is essential to understanding and quantifying wetland functions and processes. Studies of the role of ground water in selected wetlands in a range of physiographic settings throughout the Great Lakes watershed are needed to more fully understand the role of wetlands in the Great Lakes Region.

Lake Erie, Lake Huron, Lake Michigan, Lake Ontario↗
USGS2000

Status of water levels and selected water-quality conditions in the Sparta and Memphis aquifers in eastern and south-central Arkansas, 1999

During the spring of 1999, water levels were measured in the Sparta and Memphis aquifers in 321 wells in eastern and south-central Arkansas. Water samples were collected during the spring and summer of 1999 from wells completed in these aquifers. The specific conductance of the ground water was measured from 147 samples and dissolved chloride was measured from 98 samples. Maps of areal distribution of potentiometric surface and specific conductance generated from these data reveal spatial trends across the study area. The altitude of the potentiometric surface ranged from 214 feet below sea level in Union County to 332 feet above sea level in Grant County. The regional direction of ground-water flow in Arkansas is from the north and west to the south and east, away from the recharge zone in the outcrop and subcrop area, except near areas affected by intense ground-water withdrawals; such areas are characterized by large cones of depression centered in Columbia, Jefferson, and Union Counties. Heavy pumpage locally has altered or reversed the natural direction of flow in some areas. Flow in these areas is toward the cones of depression at the center of pumping. Comparison of potentiometric surface maps through time shows that the cones of depression in Columbia and Union Counties are coalescing at or near the Columbia and Union County line. Long-term hydrographs of 20 wells indicate trends of water-level decline over a 31-year period. During the period 1969-1999, average water-level declines generally were less than 0.7 foot per year in Craighead, Drew, Lee, Ouachita, and Phillips Counties, and between 0.7 and 1.1 feet per year in Bradley, Cleveland, Cross, Dallas, Poinsett, and Prairie Counties. Analysis of water-level data from Calhoun, Desha, Jefferson, Lonoke, Lincoln, and Union Counties indicates water levels declined between 1.1 and 2.0 feet per year since 1969. Water levels in Arkansas and Columbia Counties have declined more than 2.0 feet per year for the past 31 years. Water-level data from counties with cones of depressions indicate that water levels continued to decline in three cones of depression from 1995 to 1999; however, water levels increased in one cone of depression. Water levels declined an average of 2.5 feet per year in Union County, 1.4 feet per year in Jefferson County, and 1.7 feet per year in Cross County since 1995. One relatively new cone of depression has formed in Arkansas County. Water levels declined 4.0 feet per year in Arkansas County since 1995. However, water levels appear to be increasing in Columbia County where the same 11 wells were monitored in 1995 and 1999, and the water levels increased at a rate of 0.6 foot per year. Specific conductance measurements made on water samples collected during the study ranged from 44 microsiemens per centimeter at 25 degrees Celsius at a well in Ouachita County to 1,510 microsiemens per centimeter at 25 degrees Celsius at a well in Lee County. Dissolved chloride concentrations ranged from 1.1 milligram per liter at a well in Lincoln County to 220 milligrams per liter at a well in Union County.

Water-Resources Investigations Report↗
USGS2000

Effects of the Paradox Valley Unit on dissolved solids, sodium, and chloride in the Dolores River near Bedrock, Colorado, water years 1988-98

During 1999, a study was conducted by the U.S. Geological Survey (USGS) in cooperation with the Bureau of Reclamation to evaluate the effect of the Paradox Valley Unit on dissolved solids, sodium, and chloride in the Dolores River downstream from the Paradox Valley Unit. This report describes this evaluation and presents the results from this study. Daily mean flow and daily mean specific conductance, measured at gages upstream and downstream from the Paradox Valley Unit, and results from monthly water-quality samples are used to estimate changes in the dissolved-solids load and concentrations of sodium and chloride in the river as it crosses the valley and to correlate these changes with withdrawals of brine by the Paradox Valley Unit. The time period for this evaluation was restricted to October 1987-September 1998 (water years 1988-98) because regular collection of water-quality samples from the Dolores River in the valley began in 1987.

Colorado↗
USGS2000

Quality assurance and analysis of water levels in wells on Pahute Mesa and vicinity, Nevada Test Site, Nye County, Nevada

Periodic and continual water-level data from 1963 to 1998 were compiled and quality assured for 65 observation wells on Pahute Mesa and vicinity, Nye County, Nevada. As part of the quality assurance of all water levels, ancillary data pertinent to computing hydraulic heads in wells were compiled and analyzed. Quality-assured water levels that were not necessarily in error but which did not represent static heads in the regional aquifer system, or required some other qualification, were flagged. Water levels flagged include those recovering from recent pumping or well construction, water levels affected by nuclear tests, and measurements affected by borehole deviations. A cursory examination of about 30 wells with available water-level and down-hole temperature data indicate that water levels in most wells on Pahute Mesa would not be significantly affected by temperature if corrected to 95 degrees Fahrenheit. Wells with large corrections (greater than 10 feet) are those with long water columns (greater than 1,500 feet of water above the assumed point of inflow) in combination with mean water-column temperatures exceeding 105 degrees Fahrenheit. Water-level fluctuations in wells on Pahute Mesa are caused by several factors including infiltration of precipitation, barometric pressure, Earth tides, ground-water pumpage, and seismic events caused by tectonic activity and underground nuclear testing. No observed water-level fluctuations were attributed to a naturally occurring earthquake. The magnitude and duration of changes in water levels caused by nuclear tests are affected by the test size and the distance from a well to the test. Identifying water levels that might be affected by past nuclear tests is difficult because pre-testing water-level data are sparse. Hydrologically significant trends were found in 13 of 25 wells with multiple years of water-level record. The largest change in water levels (1,029 feet in 25 years) occurred in well U-19v PS 1D as a result of the Almendro nuclear test. Likely explanations for trends in most of the wells are either changes in precipitation patterns that affect recharge rates to the ground-water system, pumping effects from water-supply well U-20 WW, or a combination of these two factors.

Nevada↗
USGS2000

Microbiological monitoring for the U.S. Geological Survey National Water-Quality Assessment Program

Data to characterize the microbiological quality of the Nation's fresh, marine, and estuarine waters are usually collected for local purposes, most often to judge compliance with standards for protection of public health in swimmable or drinkable waters. Methods and procedures vary with the objectives and practices of the parties collecting data and are continuously being developed or modified. Therefore, it is difficult to provide a nationally consistent picture of the microbial quality of the Nation's waters. Study objectives and guidelines for a national microbiological monitoring program are outlined in this report, using the framework of the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) program. A national program is designed to provide long-term data on the presence of microbiological pathogens and indicators in ground water and surface water to support effective water policy and management. Three major groups of waterborne pathogens affect the public health acceptability of waters in the United States—bacteria, protozoa, and viruses. Microbiological monitoring in NAWQA would be designed to assess the occurrence, distribution, and trends of pathogenic organisms and indicators in surface waters and ground waters; relate the patterns discerned to factors that help explain them; and improve our understanding of the processes that control microbiological water quality.

Water-Resources Investigations Report↗
USGS2000

Water-quality trend analysis and sampling design for the Souris River, Saskatchewan, North Dakota, and Manitoba

The Souris River Basin is a 24,600-square-mile basin located in southeast Saskatchewan, north-central North Dakota, and southwest Manitoba. The Souris River Bilateral Water Quality Monitoring Group, formed in 1989 by the governments of Canada and the United States, is responsible for documenting trends in water quality in the Souris River and making recommendations for monitoring future water-quality conditions. This report presents results of a study conducted for the Bilateral Water Quality Monitoring Group by the U.S. Geological Survey, in cooperation with the North Dakota Department of Health, to analyze historic trends in water quality in the Souris River and to determine efficient sampling designs for monitoring future trends. U.S. Geological Survey and Environment Canada water-quality data collected during 1977-96 from four sites near the boundary crossings between Canada and the United States were included in the trend analysis. A parametric time-series model was developed for detecting trends in historic constituent concentration data. The model can be applied to constituents that have at least 90 percent of observations above detection limits of the analyses, which, for the Souris River, includes most major ions and nutrients and many trace elements. The model can detect complex nonmonotonic trends in concentration in the presence of complex interannual and seasonal variability in daily discharge. A key feature of the model is its ability to handle highly irregular sampling intervals. For example, the intervals between concentration measurements may be be as short as 10 days to as long as several months, and the number of samples in any given year can range from zero to 36. Results from the trend analysis for the Souris River indicated numerous trends in constituent concentration. The most significant trends at the two sites located near the upstream boundary crossing between Saskatchewan and North Dakota consisted of increases in concentrations of most major ions, dissolved boron, and dissolved arsenic during 1987-91 and decreases in concentrations of the same constituents during 1992-96. Significant trends at the two sites located near the downstream boundary crossing between North Dakota and Manitoba included increases in dissolved sodium, dissolved chloride, and total phosphorus during 1977-86, decreases in dissolved oxygen and dissolved boron and increases in total phosphorus and dissolved iron during 1987-91, and a decrease in total phosphorus during 1992-96. The time-series model also was used to determine the sensitivity of various sampling designs for monitoring future water-quality trends in the Souris River. It was determined that at least two samples per year are required in each of three seasons--March through June, July through October, and November through February--to obtain reasonable sensitivity for detecting trends in each season. In addition, substantial improvements occurred in sensitivity for detecting trends by adding a third sample for major ions and trace elements in March through June, adding a third sample for nutrients in July through October, and adding a third sample for nutrients, trace elements, and dissolved oxygen in November through February.

Water-Resources Investigations Report↗