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USGS1984

Phosphorus loading to McGrath and Ellis ponds, Kennebec County, Maine

McGrath and Ellis Ponds in south-central Maine have been identified as having nuisance algae blooms. In 1978, a cooperative study between the U.S. Geological Survey and the Maine Department Environmental Protection was begun to evaluate areas in which restoration effort would best improve water quality of the ponds. Streamflow and phosphorus data were collected from 28 tributaries to the ponds, April 1 through September 30, 1978 and 1979. Phosphorus yields from each tributary watershed were compared to determine their relative importance to the phosphorus budgets of the ponds. Three tributaries to the ponds were estimated to contribute 44 percent of the phosphorus load, yet drain only 22 percent of the watershed. Phosphorus input to the ponds likely would be most easily reduced by instituting phosphorus control practices in parts of the basin drained by the three tributaries. (USGS)

Water-Resources Investigations Report↗

USGS1986

Results of a preimpoundment water-quality study of Swatara Creek, Pennsylvania

The water quality of Swatara Creek prior to impoundment by the proposed Swatara Creek Reservoir in south-central Pennsylvania was studied from July 1981 through October 1982. The report, done in cooperation with the Pennsylvania Department of Environmental Resources (PaDER), Bureau of State Parks, presents information on existing water-quality conditions. A discussion of possible water-quality conditions in and downstream from the planned impoundment is also included. Precipitation measured near the study area at Lebanon, Pennsylvania from October 1981 through September 1982 was 8 percent below normal. Streamflow for the same period at Swatara Creek at Harper Tavern just downstream from the study area was 15 percent below the average annual flow. Swatara Creek above Highway 895 has been degraded by acid mine drainage. The main inflow to the planned impoundment has 2.1 times the discharge of Lower Little Swatara Creek--a forested and agricultural basin that is also tributary to the proposed impoundment. During the 1982 water year, 17,400 tons of suspended sediment were transported from the study area. About 46 percent of the annual load was transported during 3 days of high flow. Inflows to the planned impoundment from both Lower Little Swatara Creek and Swatara Creek above Highway 895 were poorly buffered. Measured concentrations of alkalinity and acidity were usually less than 10 mg/L (milligrams per liter) and 5 mg/L as CaCO3, respectively. The inflows contain high concentrations of nutrients and metals that would probably stratify in a reservoir. Maximum concentrations of dissolved nitrate and total phosphorus were 2.6 mg/L and 0.31 mg/L, respectively. At Lower Little Swatara Creek; these concentrations are well above those needed for growth of algae. Maximum observed concentrations for total recoverable iron, aluminum, and manganese at Swatara Creek above Highway 895 at Pine Grove were 100,000 ug/L (micrograms per liter), 66,000 ug/L, and 2,300 ug/L, respectively. Large increases in metal concentrations along with simultaneous decreases in pH and increases in acidity confirm that mine drainage continues to degrade the water quality of Swatara Creek and may have a large impact on water quality of the planned impoundment. Iron, lead, copper, and zinc concentrations periodically exceeded the U.S. Environmental Protection Agency (U.S. EPA) criteria for freshwater aquatic life. Concentrations of manganese and lead also exceeded the U.S. EPA criteria for domestic water supplies and human health, respectively. The water quality of the Swatara Creek Reservoir will depend on characteristics such as (1) the detention time of water in the lake, (2) the timing and extent of thermal and chemical stratification, (3) sedimentation, and (4) the chemical loading and concentrations in the lake. Each of these characteristics may depend in part, on streamflow. The impoundment will act as a sediment trap and thus reduce the concentrations of total phosphorus, iron, aluminum, lead, copper, and zinc immediately downstream from the impoundment. Large storm discharges and releases from the hypolimnion of the reservoir to attain the winter-pool level may contain low oxygen concentrations and elevated concentrations of iron, aluminum, lead, copper, and zinc. Unless conservation releases from the multi-level release gates are carefully controlled, low dissolved-oxygen levels and high metal concentrations may degrade the downstream water quality and be detrimental to the aquatic community.

Pennsylvania↗

USGS1985

Water-quality of Lake Conroe on the West Fork San Jacinto River, southeastern Texas

Thermal stratification in Lake Conroe, Texas usually begins to develop in March and persists until October. Thermal stratification has resulted in significant seasonal and areal variations in the concentrations of dissolved oxygen, dissolved iron, dissolved manganese, total inorganic nitrogen, and total phosphorus. Volume-weighted-average concentration of dissolved solids generally was < 120 mg/L, that of dissolved chloride generally was < 22 mg/L, and that of dissolved sulfate was < 10 mg/L in Lake Conroe during the 1973-82 water years. The concentrations of each of these constituents usually were largest during the summer. The water was moderately hard (hardness > 60 but < 120 mg/L as calcium carbonate). The average concentrations of dissolved oxygen at most sites in the downstream one-half of the lake averaged 3.2 mg/L during summer stratification and > 9 mg/L during winter circulation. The concentrations at most sites in the headwaters of the lake averaged < 4.3 mg/L during the summer and < 7.9 mg/L during the winter. Water below depths of 25 to 35 ft usually contained < 1 mg/L dissolved oxygen during the summer. The concentrations of dissolved iron and dissolved manganese in water throughout the reservoir during winter circulation and in water near the reservoir surface during summer stratification were < 100 micrograms/L. The greatest concentration occurred during summer stagnation near the reservoir bottom at a deep site near Lake Conroe Dam. The concentrations of total inorganic nitrogen and total phosphorus were greatest during summer stratification in water near the reservoir bottom at deep sites. No accumulation of these constituents within the reservoir was detected during the study. The densities and composition of algal populations varied seasonally. Algal densities were greatest during the summer with blue-green algae being the predominant phylum.

Texas↗

USGS1990

Summary of biological investigations relating to surface-water quality in the Kentucky River basin, Kentucky

The Kentucky River basin, an area of approximately 7,000 sq mi, is divided into five hydrologic units that drain parts of three physiographic regions. Data on aquatic biological resources were collected and reviewed to assess conditions in the major streams for which data were available. The North, Middle, and South Forks of the Kentucky River are in the Eastern Coal Field physiographic region. Streams in this region are affected by drainage from coal mines and oil and gas operations, and many support only tolerant biotic stream forms. The Kentucky River from the confluence of the three forks to the Red River, is in the Knobs physiographic region. Oil and gas production operations and point discharges from municipalities have affected many streams in this region. The Red River, a Kentucky Wild River, supported a unique flora and fauna but accelerated sedimentation has eliminated many species of mussels. The Millers Creek drainage is affected by brines discharged from oil and gas operations, and some reaches support only halophilic algae and a few fish. The Kentucky River from the Red River to the Ohio River is in the Bluegrass physiographic region. Heavy sediment loads and sewage effluent from urban centers have limited the aquatic biota in this region. Silver Creek and South Elkhorn Creek have been particularly affected and aquatic communities in these streams are dominated by organisms tolerant of low dissolved oxygen concentrations. Biological data for other streams indicate that habitat and water quality conditions are favorable for most commonly occurring aquatic organisms. (USGS)

Water-Resources Investigations Report↗

USGS1993

Hydrology and water quality of Wind Lake in southeastern Wisconsin

The hydrology and water quality of Wind Lake-a recreational lake in a densely populated area of southeastern Wisconsin was studied from October 1, 1987 through September 30,1989. A drought in 1988 affected the hydrologic budget of Wind Lake in water years 1988-89. Precipitation was 5.9 inches less than normal in water year 1988 but was 2.3 inches greater than normal in water year 1989. Streamflows were near normal in water year 1988 and 25 percent less than normal in water year 1989 as indicated by data from a nearby streamflow-gaging station. Surface runoff was the dominant source of water to the lake in water year 1988 and 75 percent of the inflow was from Big Muskego Lake. The water level in Big Muskego Lake was 1.1 feet below the dam crest at the start of the 1989 water year because of the 1988 drought. About 2,510 acre-feet of water had to fill Big Muskego Lake before water could discharge to Wind Lake. In water year 1989, surface runoff was still the dominant source of water to the lake, but Big Muskego Lake only contributed 52 percent of the water inflow. Streamflow dominated the outflow budget for both years. In water year 1988, 88 percent of the outflow budget left by way of Wind Lake outlet and 12 percent evaporated from the lake surface. In water year 1989, 81 percent of the outflow budget left by way of Wind Lake outlet and 19 percent evaporated from the lake surface. On the basis of outflow from Wind Lake for water year 1988, the hydraulic residence time was 0.46 year; in water year 1989 it was 1.05 years. The total phosphorus input to Wind Lake from external sources was the same for both years, 3,160 pounds. The largest percentage of the phosphorus load came from Big Muskego Lake-- 70 percent in water year 1988 and 65 percent in water year 1989. Analysis of data by use of Vollenweider's model indicates that the phosphorus loadings for each year would cause eutrophic conditions. Data from a nearby gaging station indicate that phosphorus loading to Wind Lake was less than normal. Phosphorus retention in the lake is small and averages 14 percent of the incoming load for both years. Oxygen depletion occurs in the bottom waters during winter and summer months. A maximum anoxic zone was reached on July 18, 1988, when depths greater than 15 feet (about 21 percent of the lake bottom area) were anoxic. Total phosphorus concentrations at the lake surface for both years ranged from 11 to 78 micrograms per liter. Mean total phosphorus concentrations in June, July, and August that had averaged 49 micrograms per liter in 1985 through 1987 declined to 20 micrograms per liter in water year 1988 and 22 micrograms per liter in water year 1989. This reduction was related to the drought and reduced phosphorus loadings. Phosphorus concentrations 1.5 feet above the lake bottom increase during summer anoxic periods. The phosphorus concentration increased at a rate of 5.2 and 4.8 micrograms per liter per day for total and dissolved orthophosphate phosphorus. A maximum concentration of 760 micrograms per liter of total phosphorus and 650 micrograms per liter of dissolved orthophosphate phosphorus occurred on September 21, 1988, just before autumn turnover. Internal loading of phosphorus for the period October 15, 1987 through October 14, 1988, was estimated to be 2,890 pounds. This represents 48 percent of the combined internal and external total-phosphorus input of 5,960 pounds. Algal populations in water year 1988 ranged from 28,200 to 1,610,000 cells per milliliter. A total of 143 species were identified. Blue-green algae dominated the algal population and ranged from 56 percent (February 16, 1988) to 99 percent (five other sampling dates). Aphanocapsa delicatissima caused the largest algal bloom, which reached a maximum concentration of 934,000 cells per milliliter (September 7, 1988). Zooplankton populations in water year 1988 ranged from 52.5 to 686 organisms per liter. Eighteen species were identified. The cladoceran, Daphnia, dominated 12 of the 18 samples.

Wisconsin↗

USGS1994

Calibration, verification, and use of a water-quality model to simulate effects of discharging treated wastewater to the Red River of the North at Fargo, North Dakota

A 30.8-mile reach of the Red River of the North receives treated wastewater from plants at Fargo, North Dakota, and Moorhead, Minnesota, and streamflows from the Sheyenne River. A one-dimensional, steady-state, stream water-quality model, the Enhanced Stream Water Quality Model (QUAL2E), was calibrated and verified for summer streamflow conditions to simulate some of the biochemical processes that result from discharging treated wastewater into this reach of the river. Data obtained to define the river's transport conditions are measurements of channel geometry, streamflow, traveltime, specific conductance, and temperature. Data obtained to define the river's water-quality conditions are measurements of concentrations of selected water-quality constituents and estimates of various reaction coefficients. Most of the water-quality data used to calibrate and verify the model were obtained during two synoptic samplings in August 1989 and August 1990. The water-quality model simulates specific conductance, water temperature, dissolved oxygen, ultimate carbonaceous biochemical oxygen demand, total nitrite plus nitrate as nitrogen, total ammonia as nitrogen, total organic nitrogen as nitrogen, total phosphorus as phosphorus, and algal biomass as chlorophyll a. Of the nine properties and constituents that the calibrated model simulates, all except algae were verified. When increases in dissolved-oxygen concentration are considered, model sensitivity analyses indicate that dissolved-oxygen concentration is most sensitive to maximum specific algal growth rate. When decreases in dissolved-oxygen concentration are considered, model sensitivity analyses indicate that dissolved-oxygen concentration is most sensitive to point-source ammonia. Model simulations indicate nitrification and sediment oxygen demand consume most of the dissolved oxygen in the study reach. The Red River at Fargo Water-Quality Model and the verification data set, including associated reaction-coefficient values as input, were used to simulate total ammonia as nitrogen, total nitrite plus nitrate as nitrogen, 5-day carbonaceous biochemical oxygen demand, and dissolved oxygen for water-quality conditions that result from three hypothetical boundary conditions. The model was applied to various combinations of three hypothetical waste loads when the headwater streamflow was either 50 or 75 cubic feet per second, when Fargo's wastewater-treatment plant outflow was either 15 or 37.8 cubic feet per second, and when total ammonia as nitrogen concentration of the outflow was either 5,9, or 15 milligrams per liter. For each hypothetical waste load, at least one water-quality standard for either total ammonia as nitrogen, total nitrite plus nitrate as nitrogen, or dissolved oxygen was contravened, and, for one scenario, all three standards were contravened.

Water-Resources Investigations Report↗

USGS1994

Land use in, and water quality of, the Pea Hill Arm of Lake Gaston, Virginia and North Carolina, 1988-90

The City of Virginia Beach currently (1994) supplies water to about 400,000 people in southeastern Virginia. The city plans to withdraw water from the Pea Hill Arm of Lake Gaston to meet projected water needs of the population to the year 2030. The purpose of this report is to (1) describe the temporal and spatial distribution of selected water-quality constituents, (2) document current (1989) land use and land cover in the Pea Hill Arm drainage basin, and (3) discuss relations, if any, between the quality of water in the inlets within the Pea Hill Arm and land uses. The report focuses on water-quality problems in the basin, including changes in concentrations of major ions, nutrients, and algae associated with urban development adjacent to water bodies. The Pea Hill Arm was classified as mesotrophic on the basis of the range of concentrations of total phosphorus (0.001 to 0.61 milligrams per liter); the range of concentrations of total organic-plus-ammonia nitrogen (0.2 to 1.4 milligrams per liter); and the range of concentrations of chlorophyll a (1.4 to 56 micrograms per liter). These water-quality data were collected at 3 feet below the water surface during water years 1989-90. Thermal stratification in Pea Hill Arm generally began in April and ended in September. Water below a depth of about 25 feet generally became anoxic by June. Destratification generally began in late September and was completed by November. Lake Gaston followed the same general stratification and destratification pattern as Pea Hill Arm, except Lake Gaston was partially destratified during the summer when large amounts of water were released from John H. Kerr Reservoir and Lake Gaston Dams. During water year 1988, streamflows were 33 percent below the long-term mean-annual streamflows at one of the major streams to Lake Gaston. Low streamflows contributed to elevated specific conductances and concentrations of sodium, calcium, magnesium, and alkalinity from October 1988 to February 1989 at sampling stations in the Pea Hill Arm and Lake Gaston. About 75 percent of the land use in the Pea Hill Arm is forest land. The remaining 25 percent of the Pea Hill Arm drainage basin is 8 percent pasture/open land, 8 percent open water, 6 percent residential land, and 3 percent cropland. No statistical relations are present between water-quality constituents measured and developed land uses within 11 basins in the Pea Hill Arm Basin, except during periods of stormwater runoff. During a stormwater-runoff event, there was a relation between total nitrite plus nitrate and land use (Kendall's tau correlation coefficient of 0.69). The relation between the developed land use and total nitrite plus nitrate can also be related to the increased ground-water inputs during high base-flow periods. Spatial differences in water-quality constituents as determined by Wilcoxon (matched-pairs) signed-rank tests and cluster analyses were longitudinal and primarily grouped into riverine, transition, and lacustrine zones. These zones were grouped on the basis of flow characteristics and nutrient concentrations.

North Carolina, Virginia↗

USGS1995

Aquatic communities and contaminants in fish from streams of the Red River of the North basin, Minnesota and North Dakota

Available data on the ecology of aquatic organisms in the Red River of the North Basin, a study unit of the U.S. Geological Survey's National Water-Quality Assessment program, were collated from numerous sources. Lack of information for invertebrates and algae precluded a general summary of distribution and ecology throughout the basin. Data on fish species distributions in the major streams of the Red River of the North Basin were analyzed based on the drainage area of the stream and the number of ecoregions the stream flowed through. Species richness increased with both drainage area (log drainage area in square kilometers, R 2 =0.41, p=0.0055) and the number of ecoregions a river flowed through. However, theses two factors are autocorrelated because the larger the drainage, the more likely that the river will flow through more than one ecoregion. A cluster analysis identified five river groups based on similarity of species within the fish community. Analysis of trophic and taxonomic composition provided justification for the cluster groups. There were significant differences (p=0.05) in the trophic composition of the river cluster groups with respect to the number of predator species, omnivore species, benthic insectivore species, and general insectivore species. Although there were no significant differences in the number of species in the bass and sunfish family or the sucker family, the number of species in the minnow family and the darter subfamily were different (p=0.05) among the groups identified by cluster analysis. Data on contaminant concentrations in fish from the Red River of the North indicated that most trace elements and organochlorine compounds present in tissues were not at levels toxic to fish or humans. Minnesota and North Dakota have issued a fish consumption advisory based on levels of mercury and (or) PCBs found in some species.

Minnesota, North Dakota, South Dakota↗

USGS1996

Water quality and processes affecting dissolved oxygen concentrations in the Blackwater River, Canaan Valley, West Virginia

The water quality and environmental processes affecting dissolved oxygen were determined for the Blackwater River in Canaan Valley, West Virginia. Canaan Valley is oval-shaped (14 miles by 5 miles) and is located in the Allegheny Mountains at an average elevation of 3,200 feet above sea level. Tourism, population, and real estate development have increased in the past two decades. Most streams in Canaan Valley are a dilute calcium magnesium bicarbonate-type water. Streamwater typicaly was soft and low in alkalinity and dissolved solids. Maximum values for specific conductance, hardness, alkalinity, and dissolved solids occurred during low-flow periods when streamflow was at or near baseflow. Dissolved oxygen concentrations are most sensitive to processes affecting the rate of reaeration. The reaeration is affected by solubility (atmospheric pressure, water temperature, humidity, and cloud cover) and processes that determine stream turbulence (stream depth, width, velocity, and roughness). In the headwaters, photosynthetic dissolved oxygen production by benthic algae can result in supersaturated dissolved oxygen concentrations. In beaver pools, dissolved oxygen consumption from sediment oxygen demand and carbonaceous biochemical oxygen demand can result in dissolved oxygen deficits.

Water-Resources Investigations Report↗

USGS1996

Detailed study of water quality, bottom sediment, and biota associated with irrigation drainage in the Klamath Basin, California and Oregon, 1990-92

The effect of irrigation drainage on the water quality and wildlife of the Klamath Basin in California and Oregon was evaluated during 1990-92 as part of the National Irrigation Water Quality Program of the U.S. Department of the Interior. The study focused on land serviced by the Bureau of Reclamation Klamath Project, which supplies irrigation water to agricultural land in the Klamath Basin and the Lost River Basin. The Tule Lake and Lower Klamath National Wildlife Refuges, managed by the U.S. Fish and Wildlife Service, are in the study area. These refuges provide critical resting and breeding habitat for waterfowl on the Pacific flyway and are dependent on irrigation drainwater from upstream agriculture for most of their water supply. Water-quality characteristics throughout the study area were typical of highly eutrophic systems during the summer months of 1991 and 1992. Dissolved-oxygen concentrations and pH tended to fluctuate each day in response to diurnal patterns of photosynthesis, and frequently exceeded criteria for protection of aquatic organisms. Nitrogen and phosphorus concentrations were generally at or above threshold levels characteristic of eutrophic lakes and streams. At most sites the bulk of dissolved nitrogen was organically bound. Elevated ammonia concentrations were common in the study area, especially downstream of drain inputs. High pH of water increased the toxicity of ammonia, and concentrations exceeded criteria at sites upstream and downstream of irrigated land. Concentrations of ammonia in samples from small drains on the Tule Lake refuge leaseland were higher than those measured in the larger, integrating drains at primary monitoring sites. The mean ammonia concentration in leaseland drains [1.21 milligrams per liter (mg/L)] was significantly higher than the mean concentration in canals delivering water to the leaseland fields (0.065 mg/L) and higher than concentrations reported to be lethal to Daphnia magna (median lethal concentration of 0.66 mg/L). Dissolved-oxygen concentrations also were lower, and Daphnia survivability measured during in situ bioassays was correspondingly lower in the leaseland drains than in water delivery canals. In static laboratory bioassays, water samples collected at the primary monitoring sites caused toxicity in up to 78 percent of Lemna minor tests, in up to 49 percent of Xenopus laevis tests, in 17 percent and 8 percent of Hyalella azteca and Pimephales promelas tests, respectively, and 0 percent in Daphnia magna tests. In situ exposure at the sites caused mortality in more than 83 percent of Pimephales tests and in more than 41 percent of Daphnia and Hyalella tests. Much of the observed toxicity appears to have been caused by low dissolved oxygen, high pH, and ammonia. Although water in the study area was toxic to a variety of organisms, no statistically significant differences in the degree of toxicity between sites were observed above or below irrigated agricultural land in any of the bioassays. Pesticides were frequently detected in water samples collected at the monitoring sites during the 1991 and 1992 irrigation seasons. Among the most frequently detected compounds were the herbicides simazine, metribuzin, EPTC, and metolachlor and the insecticide terbufos. All the insecticides detected were at concentrations substantially below acute toxicity values reported for aquatic organisms. The herbicide acrolein has been used extensively in the basin to manage aquatic plant growth in irrigation canals and drains. The concentration of acrolein was monitored in a canal near Tule Lake after an application in order to evaluate the potential for the pesticide to be transported to refuge waters. Although acrolein concentrations were toxic to fish in the channels adjacent to Tule Lake, very little of the canal water entered the refuge during the monitoring period. Organochlorine pesticide concentrations in 25 surficial sediment samples collected in 1990 were below baseline levels commonly found in soils and sediment. Seventeen sediment samples were analyzed for chlorophenoxy acid herbicides and two samples were analyzed for organophosphorus and carbamate insecticides in 1992. No pesticides were detected in any of these samples. Residues of the trace elements selenium, mercury, and arsenic in algae, invertebrates, fish, and avian eggs revealed no bioaccumulation problems. Concentrations of organochlorine compounds, especially of p,p' DDE, were associated with a mean 11-percent eggshell thinning in white-faced ibis. However, ibis populations appear to be increasing, and some eggs of ibis were relatively low in DDE concentration. DDE concentrations in eggs of western grebes were not as high as in the eggs of ibis. Concentrations and types of organochlorine compounds detected in grebe and ibis eggs were highly variable, indicating that the birds were exposed to these compounds outside the basin. Fish and invertebrates inhabiting drainwater were representative of pollution-tolerant species assemblages. The aquatic communities retained little of their historic ecological structure. Extensive hydrologic modifications and hypereutrophic conditions in Klamath Basin waterways have degraded the quality of aquatic habitat and altered aquatic communities.

California, Oregon↗

USGS1996

Habitat characteristics of benchmark streams in agricultural areas of eastern Wisconsin

Stream habitat characteristics were measured at twenty sites in agricultural areas of eastern Wisconsin by the U.S. Geological Survey in May and June, 1993 as part of the National Water-Quality Assessment Program Western Lake Michigan Drainages study unit. These "benchmark" stream sites were selected for study to represent standards of reference for comparison to other streams in similar physical settings that appear to be more detrimentally affected by agriculture. The agricultural benchmark streams were selected from four physical settings, or relatively homogeneous units (RHU's), that differ in bedrock type and texture of surficial deposits. Habitat characteristics at streams in these four physical settings are described and compared to each other, and a habitat classification scheme was used to rank the quality of habitat in these streams. Additional aquatic information was collected along with the habitat data: water-quality data and population surveys of fish, invertebrates, and algae. Habitat data were collected at three levels: drainage basin, stream segment between major tributaries (length from 1 to 14 km), and stream reach (approximately 150m). Results of statistical analyses show that, in general, most correlations are among basin-level habitat characteristics. Few correlations were observed among reach- and basin-level characteristics. Principal components analysis (PCA) on basin-level data resulted in principal components that reflect RHU, land use or latitude, and basin size. Groupings of habitat characteristics at the reach level are less clearly attributed to some outside environmental factor. Streams that have undergone habitat restoration for fisheries group closely together on PCA ordination plots. Less than half of the habitat characteristics were found to be significantly different between one RHU and the other three. Characteristics that differed between RHU's were mainly at the basin level but also included some reach-level characteristics. Stream-habitat characteristics were classified according to the Michigan Department of Environmental Quality, Great Lakes Environmental Assessment Section (GLEAS) Procedure 51. No relation was found between GLEAS scores and RHU or the percentage of agricultural land in the drainage basins above the benchmark-stream sites. GLEAS scores were varied in each RHU. Streams with high GLEAS scores (rated good or excellent) can be considered benchmark or reference streams as far as habitat is concerned. Of the 20 streams sampled, 16 met this criterion.

Wisconsin↗

USGS1997

Fish communities of benchmark streams in agricultural areas of eastern Wisconsin

Fish communities were surveyed at 20 stream sites in agricultural areas in eastern Wisconsin in 1993 and 1995 as part of the National Water-Quality Assessment (NAWQA) Program. These streams, designated "benchmark streams," were selected for study because of their potential use as regional references for healthy streams in agricultural areas, based on aquatic communities, habitat, and water chemistry. The agricultural benchmark streams were selected from four physical settings, or relatively homogeneous units (RHU's), that differ in bedrock type, texture of surficial deposits, and land use. Additional data were collected along with the fish-community data, including measures of habitat, water chemistry, and population surveys of algae and benthic invertebrates. Of the 20 sites, 19 are classified as trout (salmonid) streams. Fish species that require cold or cool water were the most commonly collected. At least one species of trout was collected at 18 sites, and trout were the most abundant species at 13 sites. The species with the greatest collective abundance, and collected at 18 of the 20 sites, were mottled sculpin (Cottus bairdi), a coldwater species. The next most abundant species were brown trout (Salmo trutta), followed by brook trout (Salvelinusfontinalis), creek chub (Semotilus atromaculatus), and longnose dace (Rhinichthys cataractae). In all, 31 species of fish were collected. The number of species per stream ranged from 2 to 14, and the number of individuals collected ranged from 19 to 264. According to Index of Biotic Integrity (IBI) scores, 5 sites were rated excellent, 10 sites rated good, 4 rated fair, and 1 rated poor. The ratings of the five sites in the fair to poor range were low for various reasons. Two sites appeared to have more warmwater species than was ideal for a high-quality coldwater stream. One was sampled during high flow and the results may not be valid for periods of normal flow; the other may have been populated by migrating warmwater species. Two sites had insufficient deep-water habitat to support large numbers offish, especially top carnivores. Finally, one stream may be too cool to support enough warmwater species and too warm to support trout. In general, two methods of evaluating site habitat indicate that habitat is not a limiting factor for fish communities. However, two sites were rated as fair according to both habitat evaluation methods due to low base flow. Two sites rated below good according to one habitat evaluation method but rated good or excellent according to the other. Detrended correspondence analysis (DCA) of data for 17 sites showed three station groupings. These groupings fell along RHU divisions and each group was associated with one of three trout species. A species-richness gradient was evident on the station-ordination diagram. Intolerant species were associated with each grouping, a reflection of the generally high water quality at the sites. However, no significant differences were found between IBI scores or habitat indices among the site groupings. The DCA axis 1 and 2 scores correlated with average velocity and percent pool as well as RHU factors percent sandy surficial deposits, percent wetland, percent agriculture, and bedrock. Average velocity was highest at three sites which also had among the highest measured flow and largest drainage areas. Percent pool was generally lower at sites with smaller percentages of sandy surficial deposits, with one exception. The usefulness of ordination methods in conjunction with more traditional methods of defining biotic integrity (IB I) has been noted in previous studies. In this study, however, perhaps because of the relative homogeneity of the benchmark streams, the IBI did not correlate with the same kinds of factors as the DCA axis scores did.

Wisconsin↗

USGS1996

Relation between selected water-quality variables and lake level in Upper Klamath and Agency Lakes, Oregon

Upper Klamath Lake is a large (140 square-mile), shallow (mean depth about 8 ft) lake in south-central Oregon that the historical record indicates has been eutrophic since its discovery by non-Native Americans. In recent decades, however, the lake has had annual occurrences of near- monoculture blooms of the blue-green alga Aphanizomenon flos-aquae. In 1988 two sucker species endemic to the lake, the Lost River sucker (Deltistes luxatus) and the shortnose sucker (Chasmistes brevirostris), were listed as endangered by the U.S. Fish and Wildlife Service, and it has been proposed that the poor water quality conditions associated with extremely long and productive blooms are contributing to the decline of those species. It has also been proposed that the low lake levels made possible by the construction of a dam at the outlet from the lake in 1921 have contributed to worsening water quality through a variety of possible mechanisms (Jacob Kann, Klamath Tribes, written commun., 1995). One such mechanism would be an increase in internal phosphorus loading from resuspended sediments (Jacoby and others, 1982), resulting from an increase in bottom shear stresses at lower lake levels (Laenen and LeTourneau, 1996), leading in turn to more intense algal blooms. Another possible mechanism is an earlier triggering of algal blooms. When early spring lake levels are low, greater light intensity at the sediment surface might speed recruitment of algal cells from the sediments. Sediment recruitment has been shown to be an important contributor to water column biomass increases in A. flos aquae (Barbiero and Kann, 1994) and Gloeotrichia echinulata (Barbiero, 1993). An earlier bloom could result in poor water quality conditions occurring earlier in the year, when young-of-the-year fish may be more susceptible to those conditions. Lake level can also influence water quality directly. An increased frequency of sediment resuspension at lower lake levels could increase chemical and biological oxygen demand, resulting in decreased dissolved oxygen concentrations. Sediment oxygen demand also may be enhanced at lower lake levels because it is concentrated over a smaller volume of water. Some compensation for increased oxygen demand at lower lake levels might be provided by increased reaeration, if the water column mixes from top to bottom more frequently. Based on the analysis of data that they have been collecting for several years, the Klamath Tribes recently recommended that the Bureau of Reclamation (Reclamation) modify the operating plan for the dam to make the minimum lake levels for the June-August period more closely resemble pre-dam conditions (Jacob Kann, written commun., 1995). The U.S. Geological Survey (USGS) was asked to analyze the available data for the lake and to assess whether the evidence exists to conclude that year-to-year differences in certain lake water-quality variables are related to year-to-year differences in lake level. The results of the analysis will be used as scientific input in the process of developing an operating plan for the Link River Dam.

Oregon↗

USGS1996

Nutrient sources and analysis of nutrient water-quality data, Apalachicola-Chattahoochee-Flint River basin, Georgia, Alabama, and Florida, 1972-90

In 1991, the U.S. Geological Survey began full-scale implementation of the National Water-Quality Assessment (NAWQA) program. One of the initial tasks of the NAWQA program is to compile and evaluate existing data from individual study units. Available nutrient data from 1972 through 1990 water years were used to estimate nutrient sources to the Apalachicola–Chattahoochee–Flint (ACF) River basin and describe the presence, distribution, and transport of nutrients in surface and ground waters. In 1990, about 2,500 tons of nitrogen and 1,100 tons of phosphorus were discharged as point-source loads by 127 municipal wastewater-treatment facilities (WWTF). Nonpoint-source inputs, an unknown percentage of which entered the hydrologic system, included about 120,000 tons of nitrogen and 28,000 tons of phosphorus from animal manure; 82,000 tons of nitrogen and 20,000 tons of phosphorus applied as fertilizer; and 24,000 tons of nitrogen from atmospheric deposition. Estimates of nutrient input to the ACF River basin were not made for natural sources and for the following anthropogenic sources: industrial-wastewater effluent; storm drains; sanitary and combined sewer outflows; and runoff from agricultural, urban, and suburban areas. Nutrient outflow from the Apalachicola River into Apalachicola Bay, Fla., was about 13 percent of estimated nitrogen sources and about 3 percent of estimated total-phosphorus sources in the ACF River basin. For 1972–90, nutrient concentrations in surface water were high enough to warrant concerns about accelerated eutrophication based on total-phosphorus concentrations and to warrant concerns intermittently about toxicity to fish based on dissolved-ammonia concentrations downstream of wastewater-treatment outfalls from Metropolitan Atlanta and LaGrange, Ga. Many improvements to the water quality of the Chattahoochee and Flint Rivers in the 1980’s and early 1990’s can be directly attributed to improvements in WWTF, legislation directed at decreasing point-source loads of phosphorus, and changes in locations of wastewater-treatment outfalls. However, limited data indicate that nonpoint-source inputs increased upstream of Atlanta and in the Chipola River watershed. Significant increases in nutrient concentrations, loads, and yields occurred from upstream to downstream of the metropolitan areas of Atlanta, Ga.; Columbus, Ga., and Phenix City, Ala.; and Albany, Ga. The highest mean-annual yields estimated in the ACF River basin for total nitrogen (2.9 tons per square mile (tons/mi 2 )), total-inorganic nitrogen (2.0 tons/mi 2 ), dissolved ammonia (1.1 tons/mi 2 ), and total phosphorus (0.75 tons/mi 2 ) were downstream of Atlanta. Most significant trends in nutrient-concentration data from 1980–90 in the Chattahoochee River and the Middle and Lower Flint River basins were increasing, except dissolved ammonia which decreased at several sampling sites in reaches downstream of Atlanta, Columbus and Phenix City, and Albany. At sampling sites on the Chattahoochee and Flint Rivers downstream of Atlanta and Albany, decreasing trends in dissolved-ammonia concentration and increasing trends in dissolved-nitrate concentration were the result of improved wastewater treatment at WWTF. Dissolved-ammonia concentrations decreased and dissolved-nitrate concentrations increased along river reaches downstream of wastewater-treatment facility outfalls for Atlanta and Albany because of nitrification of ammonia to nitrate. Increasing trends in total-phosphorus concentrations are an accurate representation of data for the period 1980–90. However, legislated restrictions on the use of phosphate detergents and improvements to WWTF in the late 1980’s and early 1990’s, resulted in substantial reductions of phosphorus concentrations in wastewater effluent and in rivers at many locations in the 1990’s. Reservoirs affect nutrient transport because of uptake by phytoplankton and aquatic plants, denitrification,and accumulation of phosphorus associated with sediment in reservoirs. Yields of total-inorganic nitrogen, dissolved ammonia, dissolved nitrate, and total phosphorus decreased between sampling sites upstream and downstream of four reservoirs on the Chattahoochee River. The only exception was the yield of dissolved ammonia increased slightly from upstream to downstream of Lake Sidney Lanier. Much of the nutrient load in the Chattahoochee River downstream of Atlanta is utilized by algae or settles out primarily in West Point Lake, and to a lesser extent, in Lake Harding and Walter F. George Reservoir. In general, the Flint River arm of Lake Seminole had significantly higher concentrations of nutrients than the Chattahoochee River arm of Lake Seminole, which may be the result of the large percentage of the Middle and Lower Chattahoochee River in backwater from reservoirs, the absence of reservoirs on the Flint River downstream of Albany until Lake Seminole, and nonpoint-source inputs of nutrients from intensively farmed areas in the Lower Flint River basin. Decreases in dissolved-ammonia, dissolved-nitrate, and total-phosphorus concentrations in reservoirs and backwater along the Chattahoochee River from West Point Lake to Lake Seminole during summer months are related to the seasonality of phytoplankton production. The Chipola River had the highest yields of dissolved nitrate (1.2 tons/mi 2 ) estimated in the ACF River basin. Estimated loads of dissolved nitrate increased fairly steadily from 500 to 1,500 tons per year from 1972–90. These factors strongly suggest an agricultural nonpoint source of elevated dissolved-nitrate concentrations from increased irrigated agriculture and fertilizer applications in the Chipola River watershed. Analyses of nutrients in ground water within the ACF River basin for 1972–90 water years were restricted because of limited available data. The distribution of nitrate concentrations in the ACF River basin for 1972–90 water years included 10 percent of wells and 6 percent of springs with concentrations that probably have elevated nitrate concentrations (3.1 to 10 milligrams per liter (mg/L)), and 1 percent of wells with median nitrate concentrations exceeding the maximum contaminant level of 10 mg/L. Dissolved-nitrate concentrations were significantly lower in the Providence aquifer than in the Floridan aquifer system and the crystalline-rock aquifers. Dissolved-nitrate concentrations in wells used for public supply were significantly lower than in wells used for domestic use or unused wells.

Alabama, Florida, Georgia↗

USGS1997

Nitrogen and phosphorus loading from drained wetlands adjacent to Upper Klamath and Agency lakes, Oregon

Upper Klamath Lake and the connecting Agency Lake constitute a large, shallow lake in south-central Oregon that the historical record indicates has likely been eutrophic since its discovery by non-Native Americans. In recent decades, however, the lake has had annual occurrences of near-monoculture blooms of the blue-green alga Aphanizomenon flos-aquae that are thought to be a result of accelerated eutrophication. In 1988, two sucker species endemic to the lake, the Lost River sucker ( Deltistes luxatus ) and the shortnose sucker ( Chasmistes brevirostris ), were listed as endangered by the U.S. Fish and Wildlife Service, and it has been proposed that their decline is due to the poor water quality associated with extremely long and productive algal blooms. It has also been proposed that the effluent drained from wetlands has contributed to accelerated eutrophication. Since the turn of century, most of the wetlands adjacent to Upper Klamath Lake have been drained for agriculture--cultivation of crops and grazing of cattle. Wetland areas were reclaimed from the lake by building dikes to isolate them from the lake, constructing a series of drainage ditches, and installing pumps to drain the water and maintain a lowered water table. A consequence of lowering the water table is the increased ability of air and oxygenated water to move through the subsurface and facilitate the rapid aerobic decomposition of the peat soils. Nutrients, nitrogen and phosphorus, are then liberated, leach into adjacent ditches, and are subsequently pumped to the lake or its tributaries. The rate of peat decomposition may be related to the time since drainage and the type of agricultural land use. On lands cultivated for crops, farming practices, such as disking and furrowing, could enhance the movement of air and oxygenated water, resulting in a rapid rate of decomposition. In contrast, on grazed lands, the compaction of soils by cattle probably inhibits the movement of air and oxygenated water and results in a slower rate of decomposition relative to drained wetlands used for the cultivation of crops. This report presents the results of a cooperative study between the U.S. Geological Survey and the Bureau of Reclamation whose overall objective was to determine the nutrient loading to Upper Klamath Lake from adjacent drained wetlands. Nutrient loading from drained wetlands was estimated using two independent techniques. The first method involved the measurement of the quantity and quality of water discharged by pumps draining the wetlands. The second method was used to estimate the initial (before drainage) and present-day nutrient mass of the organic soils within the drained wetlands and to calculate the change (or loss) in nutrient mass. In an effort to estimate the nutrient contributions from the water pumped off selected drained wetlands adjacent to Upper Klamath Lake, annual loads and yields of total nitrogen and total phosphorus were estimated from concentration data and the volume of water pumped during the water year. In general, there was little variation among sites or among years in the annual total nitrogen (median load of about 18 tons per year and median yield of about 8 pounds per acre per year) or the annual total phosphorus (median load of about 3 tons per year and median yield of about 2 pounds per acre per year) contributions. The sum of the annual loads of nitrogen and phosphorus calculated for each of the pumping stations in 1995 was 80 tons per year and 15 tons per year, respectively. In 1995, soil-coring activities were undertaken to ascertain the nature and extent of the organic soils in the drained and undrained wetlands. The present-day nutrient mass was calculated for each drained wetland using the nutrient content (concentration) and the present-day peat mass. The initial nutrient mass prior to drainage was estimated for each drained wetland by using the initial nutrient content (assumed to be equal to the nutrient content of the undrained wetlands) and the initial peat mass as determined using the amount of accumulated decomposition residue. The cumulative loss of nutrient mass since drainage was calculated as the change between initial and present-day nutrient mass for each drained area. The cumulative yield of total nitrogen and total phosphorus loss from the organic soils of individual wetlands since drainage ranged from 3,000 to 70,000 pounds per acre and from 0 to 1,300 pounds per acre, respectively. For all the drained wetlands sampled, the cumulative nitrogen and phosphorus loss since drainage totaled 250,000 tons and 4,300 tons, respectively. This represents about 30 percent and 22 percent of the mass of nitrogen and phosphorus, respectively, that initially existed in the organic soils. The loss of nutrients from the drained wetlands is considered to be a maximum estimate of the possible contribution of nutrients to Upper Klamath Lake from the peat soils of the drained wetlands sampled. However, not all the nutrients released by the soils are discharged to the lake. Nutrients lost from the peat soils of the drained wetlands may have been taken up by crops and harvested or consumed by grazing cattle. In addition, nitrogen can be lost to the atmosphere by denitrification and the volatilization of ammonia; phosphorus may be bound to adjacent soil layers by adsorption. The annual nutrient loss for the period 1994–95 was calculated using a first-order rate law to describe nutrient loss since drainage began. For individual drained wetlands, the yield of nitrogen and phosphorus lost from the organic soils for the period 1994–95 ranged from 27 to 540 pounds per acre per year and from 0 to 15 pounds per acre per year, respectively. The total mass of nitrogen and phosphorus loss during this period was 3,000 tons per year and 60 tons per year, respectively, for all drained wetlands that were sampled. The yield and mass of nutrient loss determined in this fashion reflect what might be expected on the basis of time-averaged or longterm contributions of nutrients to the lake and do not reflect the specific conditions existing during the period 1994–95. The results of this study could be useful in helping to prioritize which drained wetlands may provide the greatest benefits with regard to reducing nutrient loads to the lake if restoration or land-use modifications are instituted. Recent acquisition and planned restoration of drained wetland areas at the Wood River and Williamson River North properties may produce significant reduction in the quantity of nutrients released by the decomposition of peat soils of these areas. If the water table rises to predrainage levels, the peats soils may become inundated most of the year, resulting in the continued long-term storage of nutrients within the peat soils by reducing aerobic decomposition. The maximum benefit, in terms of decreasing potential nutrient loss due to peat decomposition, could be the reduction of total nitrogen and total phosphorus loss to about one-half that of the 1994–95 annual loss estimated for all the drained wetlands sampled for this study.

Oregon↗

USGS1997

Eutrophication potential of Payette Lake, Idaho

Payette Lake was studied during water years 1995-96 to determine the 20.5-square-kilometer lake's assimilative capacity for nutrients and, thus, its eutrophication potential. The study included quantification of hydrologic and nutrient budgets, characterization of water quality in the limnetic and littoral zones, development of an empirical nutrient load/lake response model, and estimation of the limnological effects of a large-scale forest fire in the lake's 373-square-kilometer watershed during the autumn of 1994. Streamflow from the North Fork Payette River, the lake's primary tributary, delivered about 73 percent of the lake's inflow over the 2 years. Outflow from the lake, measured since 1908, was 128 and 148 percent of the long-term average in 1995 and 1996, respectively. The larger volumes of outflow reduced the long-term average water- residence time of 2.35 years to 1.84 and 1.42 years for 1995 and 1996, respectively. The lake retained 54 percent of its 1995-96 influent load of nitrogen and 79 percent of its influent load of phosphorus. The North Fork Payette River contributed an average of 69.4 percent of the lake's nitrogen load and 28.2 percent of its phosphorus load. The 1994 forest fires substantially increased the loads of nitrogen and phosphorus delivered to the lake; however, only nitrogen concentrations were noticeably increased in the lake. Payette Lake was classified as oligotrophic on the basis of annual geometric mean concentrations, in micrograms per liter, of total phosphorus (4.7), total nitrogen (225), and chlorophyll- a (1.3) during 1995-96. Secchi-disc transparencies ranged from 2.3 to 8.0 meters, indicative of mesotrophic conditions. Median ratios of dissolved inorganic nitrogen to dissolved orthophosphorus ranged from 38 to 254, thereby indicating phosphorus limitation of phytoplankton growth. Phytoplankton populations were taxonomically dominated by diatoms; blue-green algae were rare. One diatom, Tabellaria fenestrata , contributed 52 percent of the biovolume. Within the littoral zone, median periphyton production, normalized to photosynthetically active radiation input, ranged from 0.0007 to 0.02 milligrams of chlorophyll- a per square meter per Einstein, a difference of 28.6 times. Multiple linear regression analysis failed to detect any significant relation between periphyton production and various indices of nearshore development. Nine genera of aquatic macrophytes were identified, including Eurasian milfoil ( Myriophyllum spicatum var. spicatum ), which is considered a nuisance aquatic plant. Despite its oligotrophy, Payette Lake had substantial dissolved-oxygen deficits in 1995-96, which led to 4-month periods of anoxia in the near-bottom waters of its southwest basin. The hypolimnetic dissolved-oxygen deficit was much larger than that predicted by the nutrient load/lake response model. The southwest basin's propensity for developing anoxia was related to the lengthy water-residence time and incomplete water-column circulation and reaeration during the spring and autumn, coupled with a long-term accumulation of oxygen- demanding organic matter produced within the lake or delivered by its watershed.

Idaho↗

USGS1997

Nitrate in ground water and stream base flow in the lower Susquehanna River Basin, Pennsylvania and Maryland

High concentrations of nitrate in both ground and surface water have been identified as a significant water-quality issue in the Lower Susquehanna River Basin. This report uses data collected by the National Water Quality Assessment (NAWQA) Program in the basin and compares nitrate concentrations found in ground water and surface water on both a spatial and temporal basis and relates nitrate concentrations to land use. Nitrate concentrations in the Lower Susquehanna River Basin in Pennsylvania and Maryland were higher in ground water than in surface water in agricultural areas underlain by carbonate bedrock and agricultural areas underlain by crystalline bedrock. Nitrate concentrations were higher in surface water than in ground water in urban areas underlain by carbonate bedrock. Nitrate concentrations also were higher in surface water than ground water in both agricultural and forested areas underlain by sandstone and shale. Nitrate concentrations in ground water vary in areas with different land use and bedrock type. Ground-water nitrate concentrations were highest in agricultural areas underlain by carbonate bedrock, where 45 percent of the samples exceeded the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Level (MCL) of 10 mg/L (milligrams per liter as N). Waters from 36 percent of the wells in agricultural areas underlain by crystalline bedrock also had nitrate concentrations greater than 10 mg/L. Nitrate concentrations in water from wells in urban areas underlain by carbonate bedrock and in forested and agricultural areas underlain by sandstone and shale seldom exceeded the MCL. Nitrate concentrations were generally higher in surface water in areas underlain by carbonate bedrock than in areas underlain by noncarbonate bedrock; however, when an agricultural area underlain by carbonate bedrock and an agricultural area underlain by sandstone and shale with similar manure application rates were compared, nitrate concentrations in surface water were not significantly different. A comparison of three agricultural areas underlain by carbonate bedrock shows that the manure application rate is strongly correlated with nitrate concentration. Nitrate concentrations in stream base flow at seven sites where samples were collected throughout the year were commonly higher in the winter months than in the summer months. A statistically significant correlation between streamflow and nitrate concentration existed for six of the seven sites, indicating that seasonal variability in precipitation may be the cause of some of the seasonal variation in concentration. Other possible explanations for this variation include the seasonal cycle in plant uptake of nitrogen and seasonal fluctuations in uptake of nitrate by algae in streams. Because no information was available about the traveltime for ground water, interpretation of this temporal variation was not conclusive. Estimates of base-flow loads and yields of nitrate showed that agricultural areas underlain by carbonate bedrock provide the highest yield of nitrate when compared with the other areas studied. Agricultural areas underlain by sandstone and shale and crystalline bedrock also provide large amounts of nitrate to the river. The large amount of nitrate in the water from these areas cause a significant increase in nitrate loads transported by the Susquehanna River to the Chesapeake Bay. Urban areas underlain by carbonate bedrock had a high yield of nitrate but comprise such a small part of the basin that the nitrate load from these areas was small. In contrast, forested areas underlain by sandstone and shale bedrock had low base-flow nitrate yields, but these areas comprise a large percentage of the basin, making the overall nitrate load from these areas high.

Maryland, Pennsylvania↗

USGS1998

Relation of algal biomass to characteristics of selected streams in the Lower Susquehanna River basin

Seven small tributary streams with drainage areas ranging from 12.6 to 71.9 square miles, representative of both limestone and freestone settings, in the Lower Susquehanna River Basin were sampled for algae, nutrients, water quality, habitat, land use, hydrology, fish, and invertebrates. Nutrients, site characteristics, and selected characteristics of the invertebrate and fish communities known to influence algal growth were compared to chlorophyll a concentrations. Nitrogen was not found limiting in these streams; however, phosphorus may have been limiting in five of the seven streams. Concentrations of chlorophyll a in riffles increased with the degree of open canopy and as bottom substrate reached the gravel/cobble size fraction. These increased chlorophyll a concentrations and the substrate size in turn raised the levels of dissolved oxygen in the streams. Freestone streams had increased chlorophyll a concentrations associated with increases in percentage of omnivorous fish and in pH and decreases in percentage of collector/gatherer invertebrates. Concentrations of chlorophyll a in limestone riffles decreased as the percentage of omnivorous fish increased. Depositional chlorophyll a concentrations increased as the Bank Stability Index decreased and as the riffle velocity increased. Depositional chlorophyll a concentrations increased in limestone streams as collector/gatherer invertebrates increased and as phosphorus concentrations decreased. No relations were seen between chlorophyll a concentrations and land-use characteristics of the basin. In this study, there were too few sampling sites to establish statistically based relations between algal biomass and nutrient concentrations. Further study is needed to generate data suitable for statistical interpretation.

Water-Resources Investigations Report↗