Concentration‐Duration‐Frequency Curves for Stream Turbidity: Possibilities for Assessing Biological Impairment1

Abstract: Siltation and subsequent biological impairment is a national problem prompting state regulatory agencies to develop sediment total maximum daily loads (TMDL) for many streams. To support TMDL targets for reduced sediment yield in disturbed watersheds, a critical need exists for stream assessments to identify threshold concentrations of suspended sediment that impact aquatic biota. Because of the episodic nature of stream sediment transport, thresholds should not only be a function of sediment concentration, but also of duration and dose frequency. Water quality sondes can collect voluminous amounts of turbidity data, a surrogate for suspended sediment, at intervals that can be used to characterize concentration, duration, and frequency of elevated turbidity events. To characterize turbidity sonde data in an ecologically relevant manner, a methodology for concentration‐duration‐frequency (CDF) curves was developed using turbidity doses that relate to different levels of biological impairment. To illustrate this methodology, turbidity CDF curves were generated for two sites on Little Pigeon River in the Great Smoky Mountains National Park, Tennessee, using over 30,000 sonde data measurements per site for a one‐year period. Utilizing a Poisson arrival approach, turbidity spikes were analyzed stochastically by observing the frequency and duration of recorded events over a turbidity level that relates to a biological dose response. An exponential equation was used to fit duration and frequency of a specified turbidity level to generate concentric‐shaped CDF curves, where at specific turbidities longer durations occurred less frequently and conversely shorter durations occurred more frequently. The significance of the equation fit to the data was accomplished with a Kolmogorov‐Smirnov goodness‐of‐fit test. Our findings showed that the CDF curves derived by an exponential function performed reasonable well, with most curves significant at a 95% confidence level. These CDF curves were then used to demonstrate how they could be used to assess biological impairment, and identify future research needs for improved development of sediment TMDLs.     

A Sampler for Measuring Deposited Fine Sediments in Streams1

Turner, Andy W., Jeff J. Hillis, and Charles F. Rabeni, 2012. A Sampler for Measuring Deposited Fine Sediments in Streams. Journal of the American Water Resources Association (JAWRA) 48(2): 366‐378. DOI: 10.1111/j.1752‐1688.2011.00618.x Abstract: Improvements and standardization of methodologies to quickly and accurately quantify deposited sediment in streams will allow advances in our understanding of biological effects of sedimentation. Most methods used to evaluate streambed conditions as part of biological monitoring or assessment programs are selected for ease of use, but can be subjective, inappropriate, and often of unknown accuracy. We developed a portable, light‐weight device to quantify deposited unconsolidated sediment (particles <2 mm) in wadeable streams. This deposited sediment sampler is a hand‐held unit that circumscribes an area of the streambed and through suction creates a force that suspends unconsolidated materials into a collector. Laboratory evaluations determined the efficiency (percent of available deposited sediment recovered) of the sampler to collect different sizes and concentrations of deposited sediment under differing streambed conditions, which allowed appropriate correction factors to be applied to each of four categories of streambed particle size. Field trials comparing our sampler to other methods commonly used by many state and federal agencies showed high comparability. The sampler can be constructed in just a few hours from inexpensive, easily obtained materials.     

Estimation of Suspended‐Sediment Concentration From Total Suspended Solids and Turbidity Data for Kentucky, 1978‐19951

Williamson, Tanja N. and Charles G. Crawford, 2011. Estimation of Suspended‐Sediment Concentration From Total Suspended Solids and Turbidity Data for Kentucky, 1978‐1995. Journal of the American Water Resources Association (JAWRA) 47(4):739‐749. DOI: 10.1111/j.1752‐1688.2011.00538.x Abstract: Suspended sediment is a constituent of water quality that is monitored because of concerns about accelerated erosion, nonpoint contamination of water resources, and degradation of aquatic environments. In order to quantify the relationship among different sediment parameters for Kentucky streams, long‐term records were obtained from the National Water Information System of the U.S. Geological Survey. Suspended‐sediment concentration (SSC), the parameter traditionally measured and reported by the U.S. Geological Survey, was statistically compared to turbidity and total suspended solids (TSS), two parameters that are considered surrogate data. A linear regression of log‐transformed observations was used to estimate SSC from TSS; 72% of TSS observations were less than coincident SSC observations; however, the estimated SSC values were almost as likely to be overestimated as underestimated. The SSC‐turbidity relationship also used log‐transformed observations, but required a nonlinear, breakpoint regression that separated turbidity observations ≤6 nephelometric turbidity units. The slope for these low turbidity values was not significantly different than zero, indicating that low turbidity observations provide no real information about SSC; in the case of the Kentucky sediment record, this accounts for 30% of the turbidity observations.     

SUSPENDED SEDIMENT AND TURBIDITY FOLLOWING ROAD CONSTRUCTION AND LOGGING IN WESTERN MONTANA1

ABSTRACT: Forest management activities in a second order drainage basin increased suspended sediment yields 7.7 fold in the first year following road construction, and two-fold following logging in the second year. Sediment supply limitations resulted in poor correlations between sediment concentrations with discharge. Sediment transport was strongly hysteretic, with the highest sediment concentrations occurring on the rising limbs of snowmelt hydrographs and individual peaks. In addition to discharge, hydrograph characteristics such as limb, dQ/dt, and the product of dQ/dt and limb aided in explaining variability of observed sediment concentrations. Sediment-turbidity relationships were strongly discharge dependent, reflecting the changing composition of the suspended load with stream power and sediment supplies.     

Sediment Source Fingerprinting: Transforming From a Research Tool to a Management Tool1

Abstract: Information on the nature and relative contribution of different watershed sediment sources is recognized as a key requirement in the design and implementation of targeted management strategies for sediment control. A direct method of assessing sediment sources in a watershed that has attracted attention in recent years is sediment fingerprinting. The aim of this article is to describe the development of sediment fingerprinting as a research tool and to consider how the method might be transformed from a research tool to a management tool within a regulatory framework, with special reference to the United States total maximum daily load (TMDL) program. When compared with the current source assessment tools in developing sediment TMDLs, sediment fingerprinting offers considerable improvement as a tool for quantifying sources of sediment in terms of source type (e.g., channel vs. hillslope) as well as spatial location (subwatershed). While developing a conceptual framework for sediment TMDLs, we recognize sediment fingerprinting along with sediment budgeting and modeling as valuable tools in the TMDL process for developing justifiable sediment TMDLs. The discussions presented in this article may be considered as a first step toward streamlining the sediment fingerprinting approach for its wider application in a regulatory framework.     

“Nutrient Inputs to the Laurentian Great Lakes by Source and Watershed Estimated Using SPARROW Watershed Models” by Dale M. Robertson and David A. Saad2

Richards, R. Peter, Ibrahim Alameddine, J. David Allan, David B. Baker, Nathan S. Bosch, Remegio Confesor, Joseph V. DePinto, David M. Dolan, Jeffrey M. Reutter, and Donald Scavia, 2012. Discussion –“Nutrient Inputs to the Laurentian Great Lakes by Source and Watershed Estimated Using SPARROW Watershed Models” by Dale M. Robertson and David A. Saad. Journal of the American Water Resources Association (JAWRA) 1‐10. DOI: 10.1111/jawr.12006 Abstract: Results from the Upper Midwest Major River Basin (MRB3) SPARROW model and underlying Fluxmaster load estimates were compared with detailed data available in the Lake Erie and Ohio River watersheds. Fluxmaster and SPARROW estimates of tributary loads tend to be biased low for total phosphorus and high for total nitrogen. These and other limitations of the application led to an overestimation of the relative contribution of point sources vs. nonpoint sources of phosphorus to eutrophication conditions in Lake Erie, when compared with direct estimates for data‐rich Ohio tributaries. These limitations include the use of a decade‐old reference point (2002), lack of modeling of dissolved phosphorus, lack of inclusion of inputs from the Canadian Lake Erie watersheds and from Lake Huron, and the choice to summarize results for the entire United States Lake Erie watershed, as opposed to the key Western and Central Basin watersheds that drive Lake Erie’s eutrophication processes. Although the MRB3 SPARROW model helps to meet a critical need by modeling unmonitored watersheds and ranking rivers by their estimated relative contributions, we recommend caution in use of the MRB3 SPARRROW model for Lake Erie management, and argue that the management of agricultural nonpoint sources should continue to be the primary focus for the Western and Central Basins of Lake Erie.     

Turbidity and nitrate transfer in karstic aquifers in rural areas: the Brionne Basin case-study

The degradation of water quality in many groundwaters of Europe is a major source of concern. Rises in turbidity and nitrate concentrations represent present or potential threats for the quality of drinking water in rural areas. They are for the most part a consequence of agricultural intensification which has considerably affected land cover and land use in recent decades. In our case-study (a karstic catchment) the mechanisms which explain changes in water quality, as far as turbidity and nitrate are concerned, result from a strong continuity between surface and underground waters. The karstic system of the Brionne Basin can be considered as both the focus of rapid horizontal flows (runoff, a rapid process in which rainwater reaches the spring directly through sinkholes) and slow vertical flows (leaching, in which rainwater filters through the soil to the spring). A hierarchical approach to the water pollution problem of the basin suggests that turbidity or nitrate concentrations peak during heavy rain episodes and are short-term events. In terms of management, this implies that the solution to water pollution caused by such events is also short-term and can therefore be addressed at a local scale. The rise of nitrate concentrations during the past twenty years is the main concern. The solution can only be found at a global scale (all the catchment area must be taken in account: land plots and their spatial configuration), and by taking a long-term approach.     

Tributary Plunging in an Urban Lake (Onondaga Lake): Drivers,Signatures, and Implications1

Abstract: A combination of long‐term fixed‐frequency and robotic monitoring information for a polluted urban lake, Onondaga Lake, New York, and two of its tributaries is used to resolve the propensity for, and occurrences of, tributary plunging. Cooler temperatures (T) and higher salinity (S) are primarily responsible for the elevated density and plunging of one of these polluted streams for the summer through early fall interval. In‐lake transport of this plunging tributary, which receives inputs from combined sewer overflows (CSOs), is tracked by its high S during dry weather, its high turbidity (T_n) with associated lower S (dilution with rainwater) following runoff events, and by its characteristic ionic composition. These signatures are documented extending from the creek mouth, through a connecting navigation channel, through the inflow zone of the lake, and into metalimnetic depths of pelagic portions of the lake. The entry of this polluted tributary below the depth interval(s) of primary production and contact recreation has important implications for the ongoing major rehabilitation program for this lake. The plunging phenomenon diminishes the benefits previously expected for related features of the lake’s water quality from ongoing management efforts to abate CSO inputs and reduce nonpoint nutrient loading from the tributary. Previously this tributary tended to instead enter the upper layers of the lake during the operation of an adjoining soda ash manufacturing facility (closure in 1986), as a result of high lake S caused by the industry’s ionic waste discharge.     

NONPOINT SOURCE DISCHARGES OF NUTRIENTS FROM PIEDMONT WATERSHEDS OF CHESAPEAKE BAY1

ABSTRACT: We measured annual discharges of water, sediments, and nutrients from 10 watersheds with differing proportions of agricultural lands in the Piedmont physiographic province of the Chesapeake Bay drainage. Flow-weighted mean concentrations of total N, nitrate, and dissolved silicate in watershed discharges were correlated with the proportion of cropland in the watershed. In contrast, concentrations of P species did not correlate with cropland. Organic P and C correlated with the concentration of suspended particles, which differed among watersheds. Thus, the ratio of N:P:Si in discharges differed greatly among watersheds, potentially affecting N, P or Si limitation of phytoplankton growth in the receiving waters. Simple regression models of N discharge versus the percentage of cropland suggest that croplands discharge 29–42 kg N ha^-1 yr^-1 and other lands discharge 1.2–5.8 kg N ha^-1 yr^-1. We estimated net anthropogenic input of N to croplands and other lands using county level data on agriculture and N deposition from the atmosphere. For most of the study watersheds, N discharge amounted to less than half of the net anthropogenic N.