USGS Publications Warehouse

Concentrations and loads of nutrients in the tributaries of the Lake Okeechobee watershed, south-central Florida, water years 2004-2008

Mon, 14 May 2012 00:00 -0600

Lake Okeechobee in south-central Florida is the second largest freshwater lake in the contiguous United States. Excessive phosphorus loading, harmful high and low water levels, and rapid expansion of non-native vegetation have threatened the health of the lake in recent decades. A study was conducted to monitor discharge and nutrient concentrations from selected tributaries into Lake Okeechobee and to evaluate nutrient loads. The data analysis was performed at 16 monitoring stations from December 2003 to September 2008. Annual and seasonal discharge measured at monitoring stations is affected by rainfall. Hurricanes affected three wet years (2004, 2005, and the latter part of 2008) and resulted in substantially greater discharge than the drought years of 2006, 2007, and the early part of 2008. Rainfall supplies about 50 percent of the water to Lake Okeechobee, discharge from the Kissimmee River supplies about 25 percent, and discharge from tributaries and groundwater seepage along the lake perimeter collectively provide the remaining 25 percent. Annually, tributary discharge from basins located on the west side of the Kissimmee River is about 5 to 6 times greater than that from basins located on the east side. For the purposes of this study, the basins on the east side of the Kissimmee River are called "priority basins" because of elevated phosphorus concentrations, while those on the west side are called "nonpriority" basins. Total annual discharge in the non-priority basins ranged from 245,000 acre-feet (acre-ft) in 2007 to 1,322,000 acre-ft in 2005, while annual discharge from the priority basins ranged from 41,000 acre-ft in 2007 to 219,000 acre-ft in 2005. Mean total phosphorus concentrations ranged from 0.10 to 0.54 milligrams per liter (mg/L) at the 16 tributaries during 2004–2008. Mean concentrations were significantly higher at priority basin sites than at non-priority basin sites, particularly at Arbuckle Creek and C 41A Canal. Concentrations of organic nitrogen plus ammonia ranged from 1.27 to 2.96 mg/L at the 16 tributaries during 2004–2008. Mean concentrations were highest at Fisheating Creek at Lake Placid (a non-priority site), and lowest at Wolff Creek, Taylor Creek near Grassy Island, and Otter Creek (three priority basin sites), and at Arbuckle Creek (a non-priority basin site). Mean concentrations of nitrite plus nitrate ranged from 0.01 to 0.55 mg/L at the 16 tributaries during 2004–2008. Mean concentrations measured in priority basins were significantly higher than those measured in non-priority basins. Nutrient concentrations were substantially lower in the non-priority basins; however, total loads were substantially higher due to discharge that was 5 to 6 times greater than from the priority basins. Total phosphorus, organic nitrogen plus ammonia, and nitrite plus nitrate loads from the non-priority basins were 1.5, 4.5, and 3.5 times greater, respectively, than were loads from the priority basins. In the non-priority basins, total phosphorus loads ranged from 35 metric tons (MT) in 2007 to 247 MT in 2005. In the priority basins, the loads ranged from 18 MT in 2007 to 136 MT in 2005. In the non-priority basins, organic nitrogen plus ammonia loads ranged from 337 MT in 2007 to 2,817 MT in 2005. In the priority basins, organic nitrogen plus ammonia loads ranged from 85 MT in 2007 to 503 MT in 2005. In the non-priority basins, nitrite plus nitrate loads ranged from 34 MT in 2007 to 143 MT in 2005. In the priority basins, nitrite plus nitrate loads ranged from 4 MT in 2007 to 27 MT in 2005.

Limitations and potential of satellite imagery to monitor environmental response to coastal flooding

Mon, 14 May 2012 00:00 -0600

Storm-surge flooding and marsh response throughout the coastal wetlands of Louisiana were mapped using several types of remote sensing data collected before and after Hurricanes Gustav and Ike in 2008. These included synthetic aperture radar (SAR) data obtained from the (1) C-band advance SAR (ASAR) aboard the Environmental Satellite, (2) phased-array type L-band SAR (PALSAR) aboard the Advanced Land Observing Satellite, and (3) optical data obtained from Thematic Mapper (TM) sensor aboard the Land Satellite (Landsat). In estuarine marshes, L-band SAR and C-band ASAR provided accurate flood extent information when depths averaged at least 80 cm, but only L-band SAR provided consistent subcanopy detection when depths averaged 50 cm or less. Low performance of inundation mapping based on C-band ASAR was attributed to an apparent inundation detection limit (>30 cm deep) in tall Spartina alterniflora marshes, a possible canopy collapse of shoreline fresh marsh exposed to repeated storm-surge inundations, wind-roughened water surfaces where water levels reached marsh canopy heights, and relatively high backscatter in the near-range portion of the SAR imagery. A TM-based vegetation index of live biomass indicated that the severity of marsh dieback was linked to differences in dominant species. The severest impacts were not necessarily caused by longer inundation but rather could be caused by repeated exposure of the palustrine marsh to elevated salinity floodwaters. Differential impacts occurred in estuarine marshes. The more brackish marshes on average suffered higher impacts than the more saline marshes, particularly the nearshore coastal marshes occupied by S. alterniflora.

The structure of Mediterranean rocky reef ecosystems across environmental and human gradients, and conservation implications

Fri, 18 May 2012 00:00 -0600

Historical exploitation of the Mediterranean Sea and the absence of rigorous baselines makes it difficult to evaluate the current health of the marine ecosystems and the efficacy of conservation actions at the ecosystem level. Here we establish the first current baseline and gradient of ecosystem structure of nearshore rocky reefs at the Mediterranean scale. We conducted underwater surveys in 14 marine protected areas and 18 open access sites across the Mediterranean, and across a 31-fold range of fish biomass (from 3.8 to 118 g m-2). Our data showed remarkable variation in the structure of rocky reef ecosystems. Multivariate analysis showed three alternative community states: (1) large fish biomass and reefs dominated by non-canopy algae, (2) lower fish biomass but abundant native algal canopies and suspension feeders, and (3) low fish biomass and extensive barrens, with areas covered by turf algae. Our results suggest that the healthiest shallow rocky reef ecosystems in the Mediterranean have both large fish and algal biomass. Protection level and primary production were the only variables significantly correlated to community biomass structure. Fish biomass was significantly larger in well-enforced no-take marine reserves, but there were no significant differences between multi-use marine protected areas (which allow some fishing) and open access areas at the regional scale. The gradients reported here represent a trajectory of degradation that can be used to assess the health of any similar habitat in the Mediterranean, and to evaluate the efficacy of marine protected areas.

National wildlife refuge visitor survey 2010/2011: Individual refuge results

Wed, 16 May 2012 00:00 -0600

The National Wildlife Refuge System (Refuge System), established in 1903 and managed by the U.S. Fish and Wildlife Service (Service), is the leading network of protected lands and waters in the world dedicated to the conservation of fish, wildlife and their habitats. There are 556 national wildlife refuges and 38 wetland management districts nationwide, encompassing more than 150 million acres. The Refuge System attracts more than 45 million visitors annually, including 25 million people per year to observe and photograph wildlife, over 9 million to hunt and fish, and more than 10 million to participate in educational and interpretation programs. Understanding visitors and characterizing their experiences on national wildlife refuges are critical elements of managing these lands and meeting the goals of the Refuge System. The Service collaborated with the U.S. Geological Survey to conduct a national survey of visitors regarding their experiences on national wildlife refuges. The survey was conducted to better understand visitor needs and experiences and to design programs and facilities that respond to those needs. The survey results will inform Service performance planning, budget, and communications goals. Results will also inform Comprehensive Conservation Plan (CCPs), Visitor Services, and Transportation Planning processes. This data series consists of 53 separate data files. Each file describes the results of the survey for an individual refuge and contains the following information: * Introduction: An overview of the Refuge System and the goals of the national surveying effort. * Methods: The procedures for the national surveying effort, including selecting refuges, developing the survey instrument, contacting visitors, and guidance for interpreting the results. * Refuge Description: A brief description of the refuge location, acreage, purpose, recreational activities, and visitation statistics, including a map (where available) and refuge website link. * Sampling at This Refuge: The sampling periods, locations, and response rate for the refuge. * Selected Survey Results: Key findings for the refuge, including: - Visitor and Trip Characteristics - Visitor Spending in the Local Communities - Visitors Opinions about This Refuge - Visitor Opinions about National Wildlife Refuge System Topics * Conclusion * References * Survey Frequencies (Appendix A): The survey instrument with the frequency results for this refuge. * Visitor Comments (Appendix B): The verbatim responses to the open-ended survey questions for this refuge. Combined results for the 53 participating refuges are available at http://pubs.usgs.gov/ds/685/ as part of USGS Data Series 685.

Archive of digital boomer seismic reflection data collected offshore east-central Florida during USGS cruises 96FGS01 and 97FGS01 in November of 1996 and May of 1997

Mon, 14 May 2012 00:00 -0600

This Digital Versatile Disc (DVD) publication was prepared by an agency of the United States Government. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, nor shall the act of distribution imply any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and (or) contained herein. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.

Archive of digital boomer seismic reflection data collected offshore northeast Florida during USGS cruise 02FGS01, October 2002

Mon, 14 May 2012 00:00 -0600

National wildlife refuge visitor survey results: 2010/2011

Tue, 15 May 2012 00:00 -0600

The U.S. Fish and Wildlife Service (Service) collaborated with the U.S. Geological Survey to conduct a national survey of visitors regarding their experiences on national wildlife refuges. The survey was conducted to better understand visitor needs and experiences and to design programs and facilities that respond to those needs. The survey results will inform Service performance planning, budget, and communications goals. Results will also inform Comprehensive Conservation Plan (CCPs), Visitor Services, and Transportation Planning processes. The survey was conducted on 53 refuges across the National Wildlife Refuge System (Refuge System) to better understand visitor needs and experiences and to design programs and facilities that respond to those needs. A total of 14,832 visitors agreed to participate in the survey between July 2010 and November 2011. In all, 10,233 visitors completed the survey for a 71% response rate. This report provides a summary of visitor and trip characteristics; visitor opinions about refuges and their offerings; and visitor opinions about alternative transportation and climate change, two Refuge System topics of interest. The Refuge System, established in 1903 and managed by the Service, is the leading network of protected lands and waters in the world dedicated to the conservation of fish, wildlife and their habitats. There are 556 National Wildlife Refuges and 38 wetland management districts nationwide, encompassing more than 150 million acres. The Refuge System attracts more than 45 million visitors annually, including 25 million people per year to observe and photograph wildlife, over 9 million to hunt and fish, and more than 10 million to participate in educational and interpretation programs. Understanding visitors and characterizing their experiences on national wildlife refuges are critical elements of managing these lands and meeting the goals of the Refuge System. These combined results are based on surveying at 53 participating refuges during 2010/2011 and contain the following information: * Synopsis: Brief summary of the survey results. * Introduction: An overview of the Refuge System and the goals of the national surveying effort. * Methods: The procedures for the national surveying effort, including selecting refuges, developing the survey instrument, contacting visitors, and guidance for interpreting the results. * Survey Results: Key findings from the survey, including: - Visitor and trip characteristics - Visitors opinions about refuges - Visitor opinions about alternative transportation - Visitor opinions about climate change * Conclusion * References Individual results for each of the 53 participating refuges are available at http://pubs.usgs.gov/ds/643/ as part of USGS Data Series 643.

Beryllium--important for national defense

Thu, 17 May 2012 00:00 -0600

Beryllium is one of the lightest and stiffest metals, but there was little industrial demand for it until the 1930s and 1940s when the aerospace, defense, and nuclear sectors began using beryllium and its compounds. Beryllium is now classified by the U.S. Department of Defense as a strategic and critical material because it is used in products that are vital to national security. The oxide form of beryllium was identified in 1797, and scientists first isolated metallic beryllium in 1828. The United States is the world's leading source of beryllium. A single mine at Spor Mountain, Utah, produced more than 85 percent of the beryllium mined worldwide in 2010. China produced most of the remainder, and less than 2 percent came from Mozambique and other countries. National stockpiles also provide significant amounts of beryllium for processing. To help predict where future beryllium supplies might be located, U.S.Geological Survey (USGS) scientists study how and where beryllium resources are concentrated in Earth's crust and use that knowledge to assess the likelihood that undiscovered beryllium resources may exist. Techniques to assess mineral resources have been developed by the USGS to support the stewardship of Federal lands and to better evaluate mineral resource availability in a global context. The USGS also compiles statistics and information on the worldwide supply of, demand for, and flow of beryllium. These data are used to inform U.S. national policymaking.

Logs and data from trenches across and near the Green Valley Fault at the Mason Road site, Fairfield, Solano County, California, 2006-2009

Tue, 15 May 2012 20:35 -0600

The primary purpose of this report is to provide drafted field logs of exploratory trenches excavated across the Green Valley Fault in 2007 and 2009 that show evidence for four surface rupturing earthquakes in the past one thousand years. The site location and site detail are shown on sheet 1. The trench logs are shown on sheets 1, 2, and 3. We also provide radiocarbon laboratory dates used for chronological modeling of the earthquake history. Sheets 4 and 5 show additional data obtained in 2006–2009 to document data obtained in our studies of the long-term geologic slip rate on the Green Valley Fault. However, that effort ultimately did not prove feasible and no slip rate estimate resulted.

Geochemical data from groundwater at the proposed Dewey Burdock uranium in-situ recovery mine, Edgemont, South Dakota

Wed, 16 May 2012 09:50 -0600

This report releases groundwater geochemistry data from samples that were collected in June 2011 at the Dewey Burdock proposed uranium in-situ recovery site near Edgemont, South Dakota. The sampling and analytical methods are summarized, and all of the data, including quality assurance/quality control information are provided in data tables.

National assessment of hurricane-induced coastal erosion hazards--Gulf of Mexico

Mon, 14 May 2012 00:00 -0600

Sandy beaches provide a natural barrier between the ocean and inland communities, ecosystems, and resources. However, these dynamic environments move and change in response to winds, waves, and currents. During a hurricane, these changes can be large and sometimes catastrophic. High waves and storm surge act together to erode beaches and inundate low-lying lands, putting inland communities at risk. A decade of USGS research on storm-driven coastal change hazards has provided the data and modeling capabilities to identify areas of our coastline that are likely to experience extreme and potentially hazardous erosion during a hurricane. This report defines hurricane-induced coastal erosion hazards for sandy beaches along the U.S. Gulf of Mexico coastline. The analysis is based on a storm-impact scaling model that uses observations of beach morphology combined with sophisticated hydrodynamic models to predict how the coast will respond to the direct landfall of category 1-5 hurricanes. Hurricane-induced water levels, due to both surge and waves, are compared to beach and dune elevations to determine the probabilities of three types of coastal change: collision (dune erosion), overwash, and inundation. As new beach morphology observations and storm predictions become available, this analysis will be updated to describe how coastal vulnerability to storms will vary in the future.

Evaluation of geophysical techniques for the detection of paleochannels in the Oakland area of eastern Nebraska as part of the Eastern Nebraska Water Resource Assessment

Mon, 14 May 2012 15:35 -0600

Over the winter and spring of 2009, the U.S. Geological Survey conducted a general assessment of the capabilities of several geophysical tools to delineate buried paleochannel aquifers in the glacial terrain of eastern Nebraska. Mapping these paleochannels is an important objective for the Eastern Nebraska Water Resources Assessment group. Previous attempts at mapping these channels included a helicopter electromagnetic survey flown over an area near the town of Oakland, Nebraska, in March 2007. This survey had limited success in imaging the paleochannels due to the restricted depth of investigation of the system in the clay-rich till overburden. The purpose of this study was to investigate whether other airborne electromagnetic or surface geophysical techniques, including audio-magnetotelluric, time-domain electromagnetic, gravity, and magnetic methods, could be used to image the paleochannels in the clay-rich tills of eastern Nebraska. This report releases the results of testing the ability of selected geophysical techniques to map aquifers in glacial deposits near the town of Oakland, Nebraska.

Surface audio-magnetotelluric and time-domain electromagnetic methods achieved sufficient depth of penetration and indicated that the paleochannel was much more complex than the original geological model. Simulated and observed gravity anomalies indicate that imaging sand and gravel aquifers near Oakland, Nebraska, would be difficult due to the complex basement density contrasts. Interpretation of the magnetic data indicates no magnetic sources from geologic units above the bedrock surface. Based upon the analysis and interpretation of the four methods evaluated, we suggest a large-scale survey using a high-powered time-domain airborne system. This is the most efficient and cost-effective path forward for the Eastern Nebraska Water Assessment group to map paleochannels that lie beneath thick clay-rich glacial tills.

Water-quality assessment of the Cambrian-Ordovician aquifer system in the northern Midwest, United States

Mon, 14 May 2012 00:00 -0600

This report provides a regional assessment of groundwater quality of the Cambrian-Ordovician aquifer system, based primarily on raw water samples collected by the NAWQA Program during 1995 through 2007. The NAWQA Program has published findings in local study-unit reports encompassing parts of the Cambrian-Ordovician aquifer system. Data collected from the aquifer system were used in national synthesis reports on selected topics such as specific water-quality constituent classes, well type, or aquifer material; however, a synthesis of groundwater quality at the principal aquifer scale has not been completed and is therefore the major purpose of this report. Water samples collected by the NAWQA Program were analyzed for various classes of characteristics including physical properties, major ions, trace elements, nutrients and dissolved organic carbon, radionuclides (tritium, radon, and radium), pesticides, and volatile organic compounds. Subsequent sections of this report provide discussions on these classes of characteristics. The assessment objectives of this report are to (1) summarize constituent concentrations and compare them to human-health benchmarks and non-health guidelines; (2) determine the geographic distribution of constituent concentrations and relate them to various factors such as confining conditions, well type, land use, and groundwater age; and (3) evaluate near-decadal-scale changes in nitrate concentrations and pesticide detections. The most recent sample collected from each well by the NAWQA Program was used for most analyses. Near-decadal-scale changes in nitrate concentrations and pesticide detections were evaluated for selected well networks by using the most recent sample from each well and comparing it to the results from a sample collected 7 or 11 years earlier. Because some of the NAWQA well networks provide a limited areal coverage of the aquifer system, data for raw water samples from other USGS sources and state agencies were included to expand the data coverage into areas between the NAWQA well networks and into northeastern Missouri. Many of the maps in this report that show concentrations of selected constituents include data from other sources to expand on the geographic area covered by the NAWQA data.

Transient effects on groundwater chemical compositions from pumping of supply wells at the Nevada National Security Site, 1951-2008

Fri, 18 May 2012 00:00 -0600

Nuclear testing and support activities at the Nevada National Security Site have required large amounts of water for construction, public consumption, drilling, fire protection, hydraulic and nuclear testing, and dust control. To supply this demand, approximately 20,000 million gallons of water have been pumped from 23 wells completed in 19 boreholes located across the Nevada National Security Site starting as early as the 1950s. As a consequence of more or less continuous pumping from many of these wells for periods as long as 58 years, transient groundwater flow conditions have been created in the aquifers that supplied the water. To evaluate whether long-term pumping caused changes in water compositions over time, available chemical analyses of water samples from these 19 boreholes were compiled, screened, and evaluated for variability including statistically significant temporal trends that can be compared to records of groundwater pumping. Data used in this report have been extracted from a large database (Geochem08, revision 3.0, released in September 2008) containing geochemical and isotopic information created and maintained by primary contractors to the U.S. Department of Energy, National Nuclear Security Administration, Nevada Site Office. Data extracted from this source were compiled for the entire period of record, converted to uniform reporting units, and screened to eliminate analyses of poor or unknown quality, as well as clearly spurious values. The resulting data are included in accompanying spreadsheets that give values for (1) pH and specific conductance, (2) major ion concentrations, (3) trace element concentrations and environmental isotope ratios, and (4) mean, median, and variance estimates for major ion concentrations. The resulting data vary widely in quality and time-series density. An effort has been made to establish reasonable ranges of analytical uncertainty expected for each analyte and eliminate analyses that are obvious outliers. Analysis of chemical trends in this report primarily rely on specific conductance measurements and major ion concentrations, data considered to be the most accurate and reliable over the entire time span of investigation. The analysis uses parametric and non-parametric evaluations to provide a statistical basis for trend identification. Trace element and isotope data are examined for consistency, but typically are too inaccurate or infrequent to provide a reliable long term basis for trend evaluation. Groundwater withdrawal records compiled in a companion report are included graphically in this report to allow qualitative comparisons between water quality and pumping history. Data for each supply well include (1) a borehole description and summary of pumping history, (2) a description of water-quality parameters, (3) an evaluation of temporal variations of specific conductance and major ion concentrations, and (4) an examination of supporting information from trace element and isotope data. A range of responses are observed for individual supply wells that likely include the effects of both aquifer dynamics and changing borehole conditions. Data from most wells show little or no evidence for temporal variation in water-quality parameters indicating that aquifers at the Nevada National Security Site are capable of producing large volumes of compositionally uniform water over many years of pumping. A smaller number of wells show evidence of transient changes. Wells that have ceased pumping commonly show compositions that shift toward lower concentrations in subsequent bailed samples, which indicates that more dilute water entered the well over time due to either leakage of meteoric water into the well casing or more wide-spread recharge into the shallow phreatic zone. Wells that show systematic changes in water compositions during episodes of pumping commonly have multiple open intervals whose contributions to water in the well may change over time due to hydraulic conditions or well dynamics.

Microbial mineralization of cis-dichloroethene and vinyl chlorided as a component of natural attenuation of chloroethene contaminants under conditions identified in the field as anoxic

Mon, 14 May 2012 00:00 -0600

Chlororespiration is a key component of remediation at many chloroethene-contaminated sites. In some instances, limited accumulation of reductive dechlorination daughter products may suggest that natural attenuation is not adequate for site remediation. This conclusion is justified when evidence for parent compound (tetrachloroethene, PCE, or trichloroethene, TCE) degradation is lacking. For many chloroethene-contaminated shallow aquifer systems, however, non-conservative losses of the parent compounds are clear but the mass balance between parent compound attenuation and accumulation of reductive dechlorination daughter products is incomplete. Incomplete mass balance indicates a failure to account for important contaminant attenuation mechanisms, and is consistent with contaminant degradation to non-diagnostic mineralization products. An ongoing technical debate over the potential for mineralization of dichloroethene (DCE) and vinyl chloride (VC) to CO₂ in the complete absence of diatomic oxygen has largely obscured the importance of microbial DCE/VC mineralization at dissolved oxygen (DO) concentrations below the current field standard (DO < 0.1-0.5 milligrams per liter) for nominally anoxic conditions. This study demonstrates that oxygen-based microbial mineralization of DCE and VC can be substantial under field conditions that are frequently characterized as "anoxic." Because mischaracterization of operant contaminant biodegradation processes can lead to expensive and ineffective remedial actions, a modified framework for assessing the potential importance of oxygen during chloroethene biodegradation was developed.

The systematic geologic mapping program and a quadrangle-by-quadrangle analysis of time-stratigraphic relations within oil shale-bearing rocks of the Piceance Basin, western Colorado

Wed, 16 May 2012 09:33 -0600

During the 1960s, 1970s, and 1980s, the U.S. Geological Survey mapped the entire area underlain by oil shale of the Eocene Green River Formation in the Piceance Basin of western Colorado. The Piceance Basin contains the largest known oil shale deposit in the world, with an estimated 1.53 trillion barrels of oil in place and as much as 400,000 barrels of oil per acre. This report places the sixty-nine 7½-minute geologic quadrangle maps and one 15-minute quadrangle map published during this period into a comprehensive time-stratigraphic framework based on the alternating rich and lean oil shale zones. The quadrangles are placed in their respective regional positions on one large stratigraphic chart so that tracking the various stratigraphic unit names that have been applied can be followed between adjacent quadrangles. Members of the Green River Formation were defined prior to the detailed mapping, and many inconsistencies and correlation problems had to be addressed as mapping progressed. As a result, some of the geologic units that were defined prior to mapping were modified or discarded. The extensive body of geologic data provided by the detailed quadrangle maps contributes to a better understanding of the distribution and characteristics of the oil shale-bearing rocks across the Piceance Basin.

Use of real-time monitoring to predict concentrations of select constituents in the Menomonee River drainage basin, Southeast Wisconsin, 2008-9

Tue, 15 May 2012 20:09 -0600

The Menomonee River drainage basin in southeast Wisconsin is undergoing changes that may affect water quality. Several rehabilitation and flood-management projects are underway, including removal of concrete channels and the construction of floodwater retention basins. The city of Waukesha may begin discharging treated wastewater into Underwood Creek, thus approximately doubling the current base-flow discharge. In addition, the headwater basins, historically dominated by agriculture and natural areas, are becoming increasingly urbanized.

In an effort to monitor these and future changes to the basin, the U.S. Geological Survey and the Milwaukee Metropolitan Sewerage District initiated a study in 2008 to develop regression models to estimate real-time concentrations and loads of selected water-quality constituents. Water-quality sensors and automated samplers were installed at five sites in the Menomonee River drainage basin. The sensors continuously measured four explanatory variables: water temperature, specific conductance, dissolved oxygen, and turbidity. Discrete water-quality samples were collected and analyzed for five response variables: chloride, total suspended solids, total phosphorus, Escherichia coli bacteria, and fecal coliform bacteria. Regression models were developed to continuously estimate the response variables on the basis of the explanatory variables.

The models to estimate chloride concentrations all used specific conductance as the explanatory variable, except for the model for the Little Menomonee River near Freistadt, which used both specific conductance and turbidity as explanatory variables. Adjusted R² values for the chloride models ranged from 0.74 to 0.97. Models to estimate total suspended solids and total phosphorus used turbidity as the only explanatory variable. Adjusted R² values ranged from 0.77 to 0.94 for the total suspended solids models and from 0.55 to 0.75 for the total phosphorus models. Models to estimate indicator bacteria used water temperature and turbidity as the explanatory variables, with adjusted R² values from 0.54 to 0.69 for Escherichia coli bacteria models and from 0.54 to 0.74 for fecal coliform bacteria models. Dissolved oxygen was not used in any of the final models. These models may help managers measure the effects of land-use changes and improvement projects, establish total maximum daily loads, estimate important water-quality indicators such as bacteria concentrations, and enable informed decision making in the future.

Well network installation and hydrogeologic data collection, Assateague Island National Seashore, Worcester County, Maryland, 2010

Thu, 17 May 2012 00:00 -0600

The U.S. Geological Survey, as part of its Climate and Land Use Change Research and Development Program, is conducting a multi-year investigation to assess potential impacts on the natural resources of Assateague Island National Seashore, Maryland that may result from changes in the hydrologic system in response to projected sea-level rise. As part of this effort, 26 monitoring wells were installed in pairs along five east-west trending transects. Each of the five transects has between two and four pairs of wells, consisting of a shallow well and a deeper well. The shallow well typically was installed several feet below the water table—usually in freshwater about 10 feet below land surface (ft bls)—to measure water-level changes in the shallow groundwater system. The deeper well was installed below the anticipated depth to the freshwater-saltwater interface—usually in saltwater about 45 to 55 ft bls—for the purpose of borehole geophysical logging to characterize local differences in lithology and salinity and to monitor tidal influences on groundwater. Four of the 13 shallow wells and 5 of the 13 deeper wells were instrumented with water-level recorders that collected water-level data at 15-minute intervals from August 12 through September 28, 2010. Data collected from these instrumented wells were compared with tide data collected north of Assateague Island at the Ocean City Inlet tide gage, and precipitation data collected by National Park Service staff on Assateague Island. These data indicate that precipitation events coupled with changes in ambient sea level had the largest effect on groundwater levels in all monitoring wells near the Atlantic Ocean and Chincoteague and Sinepuxent Bays, whereas precipitation events alone had the greatest impact on shallow groundwater levels near the center of the island. Daily and bi-monthly tidal cycles appeared to have minimal influence on groundwater levels throughout the island and the water-level changes that were observed appeared to vary among well sites, indicating that changes in lithology and salinity also may affect the response of water levels in the shallow and deeper groundwater systems throughout the island. Borehole geophysical logs were collected at each of the 13 deeper wells along the 5 transects. Electromagnetic induction logs were collected to identify changes in lithology; determine the approximate location of the freshwater-saltwater interface; and characterize the distribution of fresh and brackish water in the shallow aquifer, and the geometry of the fresh groundwater lens beneath the island. Natural gamma logs were collected to provide information on the geologic framework of the island including the presence and thickness of finer-grained deposits found in the subsurface throughout the island during previous investigations. Results of this investigation show the need for collection of continuous water-level data in both the shallow and deeper parts of the flow system and electromagnetic induction and natural gamma geophysical logging data to better understand the response of this groundwater system to changes in precipitation and tidal forcing. Hydrologic data collected as part of this investigation will serve as the foundation for the development of numerical flow models to assess the potential effects of climate change on the coastal groundwater system of Assateague Island.