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M. A. Ayers

Publications and source records attributed to M. A. Ayers.

12 recordsLinked to original sources
USGS2012

Use of weather types to disaggregate general circulation model predictions

General circulation models (GCMs) simulate climatic conditions with a grid cell resolution on the order of 100,000 km 2 . This resolution is inadequate to assess the effects of climatic change on water resources at a regional scale. A method has been developed that uses weather-type analysis as a tool to spatially disaggregate GCM predictions to make them useful for water resource studies. The method has been applied to the Delaware River basin to predict the effects of doubling atmospheric carbon dioxide on precipitation patterns in the region. An application of the technique to the Delaware River basin indicates that future climatic conditions will show minimal changes in weather-type frequency, implying that air circulation patterns will remain unchanged. Results of this study indicate that changes in regional precipitation patterns under a doubling of atmospheric carbon dioxide will be a result of within-type changes in weather characteristics.

Journal of Geophysical Research↗
USGS2008

Use of an integrated flow model to estimate ecologically relevant hydrologic characteristics at stream biomonitoring sites

We developed an integrated hydroecological model to provide a comprehensive set of hydrologic variables representing five major components of the flow regime at 856 aquatic-invertebrate monitoring sites in New Jersey. The hydroecological model simulates streamflow by routing water that moves overland and through the subsurface from atmospheric delivery to the watershed outlet. Snow accumulation and melt, evapotranspiration, precipitation, withdrawals, discharges, pervious- and impervious-area runoff, and lake storage were accounted for in the water balance. We generated more than 78 flow variables, which describe the frequency, magnitude, duration, rate of change, and timing of flow events. Highly correlated variables were filtered by principal component analysis to obtain a non-redundant subset of variables that explain the majority of the variation in the complete set. This subset of variables was used to evaluate the effect of changes in the flow regime on aquatic-invertebrate assemblage structure at 856 biomonitoring sites. We used non-metric multidimensional scaling (NMS) to evaluate variation in aquatic-invertebrate assemblage structure across a disturbance gradient. We employed multiple linear regression (MLR) analysis to build a series of MLR models that identify the most important environmental and hydrologic variables driving the differences in the aquatic-invertebrate assemblages across the disturbance gradient. The first axis of NMS ordination was significantly related to many hydrologic, habitat, and land-use/land-cover variables, including the average number of annual storms producing runoff, ratio of 25-75% exceedance flow (flashiness), diversity of natural stream substrate, and the percentage of forested land near the stream channel (forest buffer). Modifications in the hydrologic regime as the result of changes in watershed land use appear to promote the retention of highly tolerant aquatic species; in contrast, species that are sensitive to hydrologic instability and other anthropogenic disturbance become much less prevalent. We also found strong relations between an index of invertebrate-assemblage impairment, its component metrics, and the primary disturbance gradient. The process-oriented watershed modeling approach used in this study provides a means to evaluate how natural landscape features interact with anthropogenic factors and assess their effects on flow characteristics and stream ecology. By combining watershed modeling and indirect ordination techniques, we were able to identify components of the hydrologic regime that have a considerable effect on aquatic-assemblage structure and help in developing short- and long-term management measures that mitigate the effects of anthropogenic disturbance in stream systems.

New Jersey↗
USGS2007

USGS goals for the coming decade

The U.S. Geological Survey (USGS) proposes six strategic directions for managing ecosystems along with modernization of observation networks of land, water, and biological resources.

Science↗
USGS2000

Comparison of nitrate, pesticides, and volatile organic compounds in samples from monitoring and public-supply wells, Kirkwood-Cohansey aquifer system, southern New Jersey

The number and total concentration of volatile organic compounds (VOCs) per sample were significantly greater in water from public-supply wells than in water from shallow and moderate-depth monitoring wells in the surficial Kirkwood-Cohansey aquifer system in the Glassboro area of southern New Jersey. In contrast, concentrations of nitrate (as nitrogen) and the number and total concentration of pesticides per sample were statistically similar in samples from shallow and moderate-depth monitoring wells and those from public-supply wells. VOCs in ground water typically are derived from point sources, which commonly exist in urban areas and which result in spatially variable contaminant concentrations near the water table. Because larger volumes of water are withdrawn from public-supply wells than from monitoring wells, their contributing areas are larger and, therefore, they are more likely to intercept water flowing from VOC point sources. Additionally, public-supply wells intercept flow paths that span a large temporal interval. Public-supply wells in the Glassboro study area withdraw water flowing along short paths, which contains VOCs that recently entered the aquifer system, and water flowing along relatively long paths, which contains VOCs that originated from the degradation of parent compounds or that are associated with past land uses. Because the volume of water withdrawn from monitoring wells is small and because shallow monitoring wells are screened near the water table, they generally intercept only relatively short flow paths. Therefore, samples from these wells represent relatively recent, discrete time intervals and contain both fewer VOCs and a lower total VOC concentration than samples from public-supply wells. Nitrate and pesticides in ground water typically are derived from nonpoint sources, which commonly are found in both agricultural and urban areas and typically result in lowlevel, relatively uniform concentrations near the water table. Because nonpoint sources are diffuse and because processes such as degradation or sorption/dispersion do not occur at rates sufficient to prevent detection of these constituents in parts of the aquifer used for domestic and public supply in the study area, concentrations of nitrate and pesticides and numbers of pesticide compounds are likely to be similar in samples from shallow monitoring wells and samples from public-supply wells. Results of a comparison of (1) the general characteristics of, and water-quality data from, public-supply wells in the Glassboro study area to available data from public-supply wells screened in the Kirkwood-Cohansey aquifer system outside the study area, and (2) land-use settings, soil characteristics, and aquifer properties in and outside the study area indicate that the findings of this study likely are applicable to the entire extent of the Kirkwood- Cohansey aquifer system in southern New Jersey.

New Jersey↗
USGS1989

Assessment of the potential effects of climate change on water resources of the Delaware River basin; work plan for 1988-90

The current consensus is that some global atmospheric warming will occur as a result of increasing ' greenhouse ' gases. Water resources scientists, planners, and managers are concerned about the uncertainty associated with climatic-change effects on water supplies and what planning might be necessary to mitigate the effects. Collaborative studies between climatologists, hydrologists, biologists, and others are needed to gain this understanding. The Delaware River basin study is an interdisciplinary effort on the part of the U.S. Geological Survey that was initiated to improve understanding of the sensitivity of the basin 's water resources to the potential effects of climate change. The Delaware River basin is 12,765 sq mi in area, crosses five physiographic provinces, and supplies water for an estimated 20 million people within and outside the basin. Climate change presumably will result in changes in precipitation and temperature and could have significant effects on evapotranspiration, streamflow, and groundwater recharge. A rise in sea level is likely to accompany global warming and, depending on changes in freshwater inflows, could alter the salinity of the Estuary and increase saline-water intrusion into adjacent aquifer systems. Because the potential effects are not well understood, this report discusses how the effects of climate change on the basin 's water resources might be defined and evaluated. The study objective is to investigate the basin 's hydrologic response, under existing water management policy and infrastructure, to various scenarios of climate change. Specific objectives include defining the temporal and spatial variability of basin hydrology under existing climate conditions , developing climate-change scenarios, and evaluating the potential effects and sensitivities of basin water availability to these scenarios. The objectives will be accomplished through intensive modeling analysis of the basin 's climate, watershed, estuary, and aquifer systems. (USGS)

Open-File Report↗
USGS1985

Runoff and chemical loading in small watersheds in the Twin Cities Metropolitan Area, Minnesota

Flow, rainfall, and water-quality data were collected during 1980 for 15 to 30 rainfall and snowmelt events on 6 rural and 11 urban watersheds in the Twin Cities Metropolitan Area. Event or daily flow and load models (for seven constituents) were developed and used with runoff and rainfall data for 1963-80 to compute 2-year frequency annual and seasonal flows and loads for each watershed. In models of storm-sewered watersheds, total storm rainfall proved to be the most significant factor controlling runoff and loads. Depending on the watershed type, antecedent soil-moisture indices and rainfall intensity also were important factors in estimating runoff. Annual runoff from storm-sewered watersheds averaged about 27 percent of annual precipitation, ranging from 13 to 57 percent. Runoff in urban main-stem streams ranged from 13 to 20 percent and was related to the percent of urbanization in the watershed. Annual runoff in rural watersheds ranged from 6 to 20 percent of annual precipitation. Runoff responses were highest in the snowmelt season for all watersheds and declined through the rest of the year. Rural watersheds showed a considerable decrease in runoff response during late summer and fall. Urban-watershed response from season to season was more consistent than rural watersheds because of the impervious area and storm sewers in urban watersheds. (USGS)

Minneosta↗
USGS1981

Water quality of Alimagnet, Farquar, and Long Lakes in Apple Valley, Minnesota

Alimagnet, Farquar, and Long Lakes, in Apple Valley, Minnesota, were sampled from 1973-79 to determine their physical and chemical characteristics. A storm-sewer inlet to Alimagnet Lake was also sampled during two storms in 1978. The 1976-77 drought caused a more noticeable effect on the quality of the lakes than any other factor. Chloride concentrations were 10 to 15 milligrams per liter before the drought, but increased 2 to 4 times during the drought. Dissolved solids reacted similarly. Dissolved oxygen and pH were governed mainly by biological activity. In February 1977, dissolved-oxygen concentration was less than 0.5 milligrams per liter in the three lakes. Ratios between mean total nitrogen and mean total phosphorus ranged from 22:1 to 26:1. Trophic-state indices indicate that the lakes are eutrophic. Blue-green algae dominated the phytoplankton populations. Storms sampled at a storm-sewer inlet to Alimagnet Lake showed higher concentrations of chromium, copper, nickel, and zinc than of lead, arsenic, cadmium, and mercury. Total phosphorus for the September 1978 storm had a concentration of 1.7 milligrams per liter, which means that approximately 29 pounds entered the lake during the 5.5-hour sampling period.

Minnesota↗
USGS1980

Effects of urbanization on the water quality of lakes in Eagan, Minnesota

Water-quality characteristics of 17 lakes and ponds in the city of Eagan were described from data collected from 1972 through 1978. The data showed that differences in water quality between lakes were related to differences in the percentage of urbanization. However, water-quality variations within each lake were affected more by climatic variations than by land-use changes during that period. Dissolved solids, alkalinity, and chloride concentrations varied most in lakes with urbanized watersheds, in lakes with outlets, and in lakes less than 6 feet deep. Certain lakes without outlets showed an increase in chloride during the study, caused in part by urbanization but intensified by drought conditions of 1976-77. Fifteen of the lakes studied are less than 10 feet deep and frequently mix during open water. These lakes are highly eutrophic, primarily because of high nutrient loading and recycling of nutrients. Holland and Fish Lakes, with depths of 52 and 30 feet, respectively, were the least eutrophic. These lakes limit continuous recycling of nutrients from bottom materials to water surface by thermal stratification and entrapment of nutrients in the hypolimnion. Three phosphorus-prediction models developed during the study are applicable to shallow (less than about 12 feet), nonstratifying lakes and ponds. The data base was not sufficient to select an appropriate model to predict the effects of future loading from continuing urbanization on the deeper lakes.

Minnesota↗