Long-Term Relationships Between Ocean Variability and Water Resources in Northeastern Utah1

Tingstad, Abbie H. and Glen M. MacDonald, 2010. Long-Term Relationships Between Ocean Variability and Water Resources in Northeastern Utah. Journal of the American Water Resources Association (JAWRA) 46(5):987-1002. DOI: 10.1111/j.1752-1688.2010.00471.x Abstract: The Uinta Mountains in the northwestern Colorado River Basin are an important source of water for Utah and the western United States. This article examines 20th Century hydrology in the Uinta Mountains region in the context of the previous four to eight centuries as well as possible relationships with Pacific and Atlantic Ocean variability using new tree-ring based reconstructions for streamflow and snowpack. The 20th Century appears to have been unusually wet compared with previous centuries. Relationships between hydrology in the region and the El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) are largely insignificant in instrumental datasets but may have been stronger, although inconsistent, over the longer time spans represented by the paleoclimate records. Impacts of individual modes of sea surface temperature variability may sometimes be enhanced by periods when climate forcing by ENSO, PDO, and/or AMO coincide. Such episodes are associated with deviations from mean hydrology as high as +14% and as low as −18%. The 20th Century could be a misleading benchmark to base water resource estimates upon and flexible water management strategies are necessary to take into account the large range of natural variability observed in the longer-term hydroclimatology as well as the challenges to predictability due to the apparently complex and inconsistent influence of ocean-driven variability.     

Increased Frequency of Low‐Magnitude Floods in New England1

Armstrong, William H., Mathias J. Collins, and Noah P. Snyder, 2012. Increased Frequency of Low‐Magnitude Floods in New England. Journal of the American Water Resources Association (JAWRA) 48(2): 306‐320. DOI: 10.1111/j.1752‐1688.2011.00613.x Abstract: Recent studies document increasing precipitation and streamflow in the northeastern United States throughout the 20th and early 21st Centuries. Annual peak discharges have increased over this period on many New England rivers with dominantly natural streamflow – especially for smaller, more frequent floods. To better investigate high‐frequency floods (<5‐year recurrence interval), we analyze the partial duration flood series for 23 New England rivers selected for minimal human impact. The study rivers have continuous records through 2006 and an average period of record of 71 years. Twenty‐two of the 23 rivers show increasing trends in peaks over threshold per water year (POT/WY) – a direct measure of flood frequency – using the Mann‐Kendall trend test. Ten of these trends had p < 0.1. Seventeen rivers show positive trends in flood magnitude, six of which had p < 0.1. We also investigate a potential hydroclimatic shift in the region around 1970. Twenty‐two of the 23 rivers show increased POT/WY in the post‐1970 period when comparing pre‐ and post‐1970 records using the Wilcoxon rank‐sum test. More than half of these increases have p < 0.1, indicating a shift in flow regime toward more frequent flooding. Region wide, we found a median increase of one flood per year for the post‐1970 period. Because frequent floods are important channel‐forming flows, these results have implications for channel and floodplain morphology, aquatic habitat, and restoration.     

A PRELIMINARY STUDY OF THE EFFECTS OF DRAINAGE AND HARVESTING ON WATER QUALITY IN OMBROTROPHIC BOGS NEAR SEPT-ILES,QUEBEC1

ABSTRACT: Runoff and ground-water samples were collected from four ombrotrophic bogs, representing undisturbed and drained/harvested conditions, at two-week intervals during the summer of 1984. Analyses of samples for water quality parameters revealed significant (P < 0.05 level) increases in specific conductance, NH4⁺-N, total dissolved P, Mg, K, and Na and a decrease in the E₄:E₆ ratio (suggesting increased proportions of humic acid) associated with drainage. There were no significant changes in dissolved organic carbon, Ca concentrations, or pH. Comparison of samples collected before, during, and after ditching showed increases in the dissolved organic carbon, NH₄⁺-N, total dissolved P, K, and Na and a decrease in the E₄:E₆ ratio, but these changes were short lived; water quality returned to preditching values after about a week. The observed changes in water quality are small, probably because the peat is very acid (pH 3.0 to 4.5).     

NONPOINT SOURCE POLLUTION POTENTIAL IN AN AGRICULTURAL WATERSHED IN NORTHWESTERN PENNSYLVANIA1

ABSTRACT: A 155,947 ha portion of the Shenango River watershed in western Pennsylvania was evaluated as to the potential impact of agriculture drainage on water quality. Approximately a third of the area is being used as either cropland or pasture with approximately an equal percentage in forest lands. Eleven subwatersheds were evaluated as to their potential for nonpoint source pollution according to the criteria established by the Pennsylvania Department of Environmental Resources for the Chesapeake Bay Pollution Abatement Program. The individual components and overall rating for each subwatershed were then evaluated as to their correlation with four water quality variables based on 104 samples collected at 26 sampling stations throughout the watershed. There was a significant correlation between the overall rating factor for each subwatershed and each of the four water quality variables. In general, the watershed delivery factor, animal nutrient factor, and management factors were correlated with fecal coliform and phosphorus in the receiving streams, whereas the ground water delivery factor appeared to be more important in determining nitrate concentrations in these streams. These results indicate that manure and nutrient management, along with the exclusion of livestock from streams and the enhancement and/or replacement of riparian wetlands, are important approaches in reducing agricultural impacts in fresh water ecosystems.     

REGIONAL SCALE TREND MONITORING OF INDICATORS OF TROPHIC CONDITION OF LAKES1

ABSTRACT: The U.S. Environmental Protection Agency has proposed a sample survey design to answer questions about the ecological condition and trends in condition of U.S. ecological resources. To meet the objectives, the design relies on a probability sample of the resource population of interest (e.g., a random sample of lakes) each year on which measurements are made during an index period. Natural spatial and temporal variability and variability in the sampling process all affect the ability to describe the status of a population and the sensitivity for trend detection. We describe the important components of variance and estimate their magnitude for indicators of trophic condition of lakes to illustrate the process. We also describe models for trend detection and use them to demonstrate the sensitivity of the proposed design to detect trends. If the variance structure that develops during the probability surveys is like that synthesized from available databases and the literature, then the trends in common indicators of trophic condition of the specified magnitude should be detectable within about a decade for Secchi disk transparency (0.5–1 percentiyear) and total phosphorus (2–3 percent/year), but not for chlorophyll-a (> 3–4 percent/year), which will take longer.     

A WATERSHED-LEVEL ECOLOGICAL RISK ASSESSMENT METHODOLOGY1

ABSTRACT: We present an ecological risk assessment methodology at the watershed level for freshwater ecosystems. The major component is a pollutant transport and fate model (a modified EUTROMOD) with an integrated uncertainty analysis utilizing a two-phase Monte Carlo procedure. The uncertainty analysis methodology distinguishes between knowledge uncertainty and stochastic variability. The model assesses the ecological risk of lentic (lake) ecosystems in response to the stress of excess phosphorus resulting in eutrophication. The methodology and model were tested on the Wister Lake watershed in Oklahoma with the lake and its trophic state as the endpoint for ecological risk assessment. A geographic information system was used to store, manage, and manipulate spatially referenced data for model input.