TEMPORAL CHANGES IN THE YADKIN RIVER FLOW VERSUS SUSPENDED SEDIMENT CONCENTRATION RELATIONSHIP1

ABSTRACT: Dynamic linear models (DLM) and seasonal trend decomposition (STL) using local regression, or LOESS, were used to analyze the 50‐year time series of suspended sediment concentrations for the Yadkin River, measured at the U.S. Geological Survey station at Yadkin College, North Carolina. A DLM with constant trend, seasonality, and a log₁₀ streamflow regressor provided the best model to predict monthly mean log₁₀ suspended sediment concentrations, based on the forecast log likelihood. Using DLM, there was evidence (odds approximately 69:1) that the log₁₀ streamflow versus log₁₀ suspended sediment concentration relationship has changed, with an approximate 20 percent increase in the log₁₀ streamflow coefficient over the period 1981 to 1996. However, sediment concentrations in the Yadkin River have decreased during the decade of the 1990s, which has been accompanied by a concomitant increase in streamflow variability. Although STL has been shown to be a versatile trend analysis technique, DLM is shown to be more suitable for discovery and inference of structural changes (trends) in the model coefficient describing the relationship between flow and sediment concentration.     

THE INFLUENCE OF CLIMATE VARIATION ON THE ESTIMATION OF LOW FLOWS USED TO PROTECT WATER QUALITY: A NATIONWIDE ASSESSMENT1

ABSTRACT: Historical flow records are used to estimate the regulatory low flows that serve a key function in setting discharge permit limits through the National Pollutant Discharge Elimination System, which provides a nationwide mechanism for protecting water quality. Use of historical records creates an implicit connection between water quality protection and climate variability. The longer the record, the more likely the low flow estimate will be based on a broad set of climate conditions, and thus provides adequate water quality protection in the future. Unfortunately, a long record often is not available at a specific location. This analysis examines the connection between climate variability and the variability of biologically based and hydrologically based low flow estimates at 176 sites from the Hydro‐Climatic Data Network, a collection of stream gages identified by the USGS as relatively free of anthropogenic influences. Results show that a record of 10 to 20 years is necessary for satisfactory estimates of regulatory low flows. Although it is possible to estimate a biologically based low flow from a record of less than 10 years, these estimates are highly uncertain and incorporate a bias that undermines water quality protection.     

ENHANCING FECAL COLIFORM TOTAL MAXIMUM DAILY LOAD MODELS THROUGH BACTERIAL SOURCE TRACKING1

ABSTRACT: Surface water impairment by fecal coliform bacteria is a water quality issue of national scope and importance. In Virginia, more than 400 stream and river segments are on the Commonwealth's 2002 303(d) list because of fecal coliform impairment. Total maximum daily loads (TMDLs) will be developed for most of these listed streams and rivers. Information regarding the major fecal coliform sources that impair surface water quality would enhance the development of effective watershed models and improve TMDLs. Bacterial source tracking (BST) is a recently developed technology for identifying the sources of fecal coliform bacteria and it may be helpful in generating improved TMDLs. Bacterial source tracking was performed, watershed models were developed, and TMDLs were prepared for three streams (Accotink Creek, Christians Creek, and Blacks Run) on Virginia's 303(d) list of impaired waters. Quality assurance of the BST work suggests that these data adequately describe the bacteria sources that are impairing these streams. Initial comparison of simulated bacterial sources with the observed BST data indicated that the fecal coliform sources were represented inaccurately in the initial model simulation. Revised model simulations (based on BST data) appeared to provide a better representation of the sources of fecal coliform bacteria in these three streams. The coupled approach of incorporating BST data into the fecal coliform transport model appears to reduce model uncertainty and should result in an improved TMDL.     

AN EVALUATION OF THE AVAILABLE TECHNIQUES FOR ESTIMATING MISSING FECAL COLIFORM DATA1

ABSTRACT: This paper presents the findings of a study aimed at evaluating the available techniques for estimating missing fecal coliform (FC) data on a temporal basis. The techniques investigated include: linear and nonlinear regression analysis and interpolation functions, and the use of artificial neural networks (ANNs). In all, seven interpolation, two regression, and one ANN model structures were investigated. This paper also investigates the validity of a hypothesis that estimating missing FC data by developing different models using different data corresponding to different dynamics associated with different trends in the FC data may result in a better model performance. The FC data (counts/100 ml) derived from the North Fork of the Kentucky River in Kentucky were employed to calibrate and validate various models. The performance of various models was evaluated using a wide variety of standard statistical measures. The results obtained in this study are able to demonstrate that the ANNs can be preferred over the conventional techniques in estimating missing FC data in a watershed. The regression technique was not found suitable in estimating missing FC data on a temporal basis. Further, it has been found that it is possible to achieve a better model performance by first decomposing the whole data set into different categories corresponding to different dynamics and then developing separate models for separate categories rather than developing a single model for the composite data set.     

REGION,LANDSCAPE, AND SCALE EFFECTS ON LAKE SUPERIOR TRIBUTARY WATER QUALITY1

ABSTRACT: In 1998 and 1999, third‐order watersheds in high mature forest (HMF) and low mature forest (LMF) classes were selected along gradients of watershed storage within each of two hydrogeomorphic regions in the Lake Superior Basin to evaluate threshold effects of storage on hydrologic regimes and watershed exports. Differences were detected between regions (North and South Shore) for particulates, nutrients, and pH, with all but silica values higher for South Shore streams (p < 0.05). Mature forest effects were detected for turbidity, nutrients, color, and alkalinity, with higher values in the LMF watersheds, that is, watersheds with less that 50 percent mature forest cover. Dissolved N, ammonium, N:P, organic carbon, and color increased, while suspended solids, turbidity, and dissolved P decreased as a function of storage. Few two‐way interactions were detected between region and mature forest or watershed storage, thus threshold based classification schemes could be used to extrapolate effects across regions. Both regional differences in water quality and those associated with watershed attributes were more common for third‐order streams in the western Lake Superior drainage basin as compared with second‐order streams examined in an earlier study. Use of ecoregions alone as a basis for setting regional water quality criteria would have led to misinterpretation of reference condition and assessment of impacts in the Northern Lakes and Forest Ecoregion.     

Rapid amino acid cycling in arctic and antarctic soils

Amino acids constitute one of the largest inputs of organic nitrogen (N) to most polar soils and have been hypothesized to be important in regulating vegetational succession and productivity in Arctic ecosystems. Our understanding of amino acid cycling in these soils, however, is poor. The aim of this study was to investigate the size and rate of turnover of the amino acid pool in a range of Arctic and Antarctic soils. Our results indicate that in polar soils with either high or low ornithogenic inputs the amino acid pool is small in comparison to the inorganic N pool (NO^? ₃ and NH⁺ ₄). The free amino acid pool constituted only a small proportion of the total dissolved organic nitrogen (DON) pool in these soils. Here we show that these low concentrations may be due to rapid use by the soil microbial community in both Arctic and Antarctic soils. The turnover of the amino acid pool in soil was extremely rapid, with a half-life ranging from 2 to 24 h, indicating that this N pool can be turned over many hundred times each summer when polar soils are frequently unfrozen. The implications of amino acids in N cycling and plant and microbial nutrition are discussed.     

Correlating the spatial distribution of atmospheric ammonia with δ15n values at an ammonia release site

A field ammonia (NH₃) release experiment and open top chambers containing moorland monoliths continuously fumigated with NH₃ or sprayed with NH₄Cl were used to assess the potential for using δ¹⁵N values in determining the area of influence around a point NH₃ emission source. δ¹⁵N values are being increasingly used as environmental tracers and we tested the hypothesis that the δ¹⁵N signal from an NH₃ emission source is observable in nearby vegetation. Using modified monitoring devices, atmospheric NH₃ concentrations were found to decrease with distance from source, with δ¹⁵N values also reflecting this trend, producing a signal shift with changing concentration. Open top chamber studies of δ¹⁵N values of Calluna vulgaris (L.) Hull indicated a correlation with deposition treatments in current year shoots. Analysis of Calluna shoots from the NH₃ release showed a similar trend of δ¹⁵N enrichment. Significant linear correlations between δ¹⁵N and percent N in plant material were found, both in the controlled conditions of the open top chambers and at the NH₃ release site, illustrating the possible use of this technique in N deposition biomonitoring.     

Linking field experiments to long-term simulation of impacts of nitrogen deposition on heathlands and moorlands

The results from three long-term field manipulation studies of the impacts of increased nitrogen deposition (0–120 kg N ha^?1 yr^?1) on lowland and upland heathlands in the UK were compared, to test if common responses are observed. Consistent increases in Calluna foliar N content and decreases in litter C:N ratios were found across all sites, while increases in N leaching were not observed at any site over the range 0–80 kg ha^?1 yr^?1. However, the response of Calluna biomass did vary between sites, possibly reflecting site differences in nutrient status and management histories. Five versions of a simulation model of heathland responses to N were developed, each reflecting different assumptions about the fate and turnover of soil N. Model outputs supported the deduction from mass balance calculations at two of the field sites that N additions have resulted in an increase in immobilisation; the latter was needed to prevent the model overestimating measured N leaching. However, this version of the model significantly underestimated Calluna biomass. Model versions, which included uptake of organic N by Callunaand re-mobilisation of N from the soil organic store provided some improvement in the fit between modelled and field biomass data, but re-mobilisation also led to an overestimation of N leaching. Quantification of these processes and their response to increased N deposition are therefore critical to interpreting experimental data and predicting the long-term impacts of atmospheric deposition on heathlands and moorlands.     

A cross-country comparison of short- and long-term effects of an ergonomic intervention on musculoskeletal discomfort, eyestrain and psychosocial stress in VDT operators: selected aspects of the international project.

Three groups of data entry female visual display terminal (VDT) workers from Norway (n = 30), Poland (n = 33) and the USA (n = 29) were compared. Before intervention, the Norwegian group reported more neck pain compared with the Polish group. The Polish group reported less shoulder pain than both the U.S. and the Norwegian groups. The clinical examination documented fewer symptoms and signs of musculoskeletal illness among the Polish participants compared with the Norwegian and the U.S. groups. After intervention, the Norwegian group reported a reduction in neck pain while the U.S. group reported a reduction in shoulder pain. The Polish group reported an increase in neck, shoulder and forearm pain at follow-up compared to after intervention. The Polish group recorded higher flexion of the upper arm at follow-up parallel with an increase of pain in the upper part of the body. Visual discomfort showed variable results in the 3 countries.