Annual Load Estimates Research Articles

Annual nutrients export modelling by analysis of landuse and topographic information: case of a small Mediterranean catchment

The preservation of water bodies from eutrophication implies accurate estimation of phosphorus and nitrogen loads and the control of nutrient production on a catchment scale. In this paper, a simple tool for the modelling of annual nutrient loads is presented. It is implemented in ARC/INFO GIS using Arc Macro Language (AML). The use of a GIS is justified as the spatial characteristics of the catchment area (land use, industrial wastewater location) dictate water quality. The annual nutrient loads are worked out on the catchment scale, using existing GIS routines together with specific routines developed in AML for hydrological and water quality modelling purposes. The catchment area is divided into hydrological subcatchments with relatively homogeneous spatial characteristics. Each subcatchment is linked to a specific nutrient export potential. These nutrient loads, calculated on a subcatchment-by-subcatchment basis, are conveyed to the outlet of the catchment and allow annual nutrient load estimation. A comparison with a water monitoring study is conducted to verify the adequation of modelling results for phosphorus and nitrogen loads.

Influence of various water quality sampling strategies on load estimates for small streams

Extensive streamflow and water quality data from eight small streams were systematically subsampled to represent various water‐quality sampling strategies. The subsampled data were then used to determine the accuracy and precision of annual load estimates generated by means of a regression approach (typically used for big rivers) and to determine the most effective sampling strategy for small streams. Estimation of annual loads by regression was imprecise regardless of the sampling strategy used; for the most effective strategy, median absolute errors were ∼30% based on the load estimated with an integration method and all available data, if a regression approach is used with daily average streamflow. The most effective sampling strategy depends on the length of the study. For 1‐year studies, fixed‐period monthly sampling supplemented by storm chasing was the most effective strategy. For studies of 2 or more years, fixed‐period semimonthly sampling resulted in not only the least biased but also the most precise loads. Additional high‐flow samples, typically collected to help define the relation between high streamflow and high loads, result in imprecise, overestimated annual loads if these samples are consistently collected early in high‐flow events.

Use of Ambient Water Quality Data to Refine Emission Estimates in the Danube Basin

In the frame of an EU/Phare project nutrient balances of the Danube countries were studied. As an element of the procedure, N and P emissions to surface waters were estimated on various scales. The “immission” loads computed from water quality and flow data were used to refine these estimates. The evaluation indicated the significant role of uncertainties related to scarce observations typical for many countries in the Danube Basin. To obtain the error of annual nutrient load estimates statistical analyses of a number of Hungarian rivers (in the 2 m3/s - 2000 m3/s mean flow range) were performed. Both, analytical expressions of sampling theory and Monte Carlo simulations were used. The ratio estimate and an analysis of the relation of errors of the annual mean flow and the load, resp. were used to take advantage of the additional information of flow data in comparison to water quality. An empirical error function for the range of rivers considered was derived. The effort led to useful results in relation to the selection of the estimation method, the role of sampling frequency and size of the catchment. Conclusions were also drawn on estimation errors of loads of first order tributaries of the Danube and their use in the frame of a nutrient balance study.

Estimating the suspended sediment loads of rivers in the LOIS study area using infrequent samples

A central objective of the LOIS Community Research Programme is to provide estimates of the land–ocean flux of suspended sediment from the LOIS study area. While high frequency (15-minute interval) suspended sediment concentration data are recorded within the programme at six tidal limit sites, infrequent (weekly–monthly) sampling undertaken by the Harmonized Monitoring (HM) Programme provides additional concentration data for 23 tidal limit sites in the LOIS study area. In order that these infrequent data can be used to generate sediment flux estimates, the accuracy and precision of 22 load estimation procedures are assessed in the context of sampling frequency (weekly, fortnightly and monthly) and basin scales representative of the LOIS study area. Sampling frequency is demonstrated to exert a significant influence on the precision of the individual procedures, with precision being inversely related to sampling frequency. Accuracy is less clearly influenced by sampling frequency, although different procedures were identified as being the most accurate at the three sampling frequencies. Basin scale is shown to exert a significant influence upon accuracy and precision, with the performance of the load estimation procedures being inversely related to basin scale. For one interpolation procedure, an error correction procedure is developed, based on the strong relationship identified in this study between the error associated with individual flux estimates and the ratio of mean sampled discharge to the mean discharge obtained from the high frequency record. This relatively high resolution error correction method is applied to HM data from eight tidal limit sites in the LOIS area, and corrects the initial annual load estimates to provide values that are considered to be more representative of rivers from the LOIS study area. Copyright © 1999 John Wiley & Sons, Ltd.

Use of ambient water quality data to refine emission estimates in the Danube Basin

In the frame of an EU/Phare project nutrient balances of the Danube countries were studied. As an element of the procedure, N and P emissions to surface waters were estimated on various scales. The “immission” loads computed from water quality and flow data were used to refine these estimates. The evaluation indicated the significant role of uncertainties related to scarce observations typical for many countries in the Danube Basin. To obtain the error of annual nutrient load estimates statistical analyses of a number of Hungarian rivers (in the 2 m3/s - 2000 m3/s mean flow range) were performed. Both, analytical expressions of sampling theory and Monte Carlo simulations were used. The ratio estimate and an analysis of the relation of errors of the annual mean flow and the load, resp. were used to take advantage of the additional information of flow data in comparison to water quality. An empirical error function for the range of rivers considered was derived. The effort led to useful results in relation to the selection of the estimation method, the role of sampling frequency and size of the catchment. Conclusions were also drawn on estimation errors of loads of first order tributaries of the Danube and their use in the frame of a nutrient balance study.

Annual Loading Estimates of Selected Metals and PAHs in CSOs, using a Continuous PCSWMM Approach

Hamilton Harbour, Ontario, is an industrial port principally for the steel manufacturing industry, but also is a waterbody that increasingly supports recreatio…

Nutrient management at the catchment scale using a decision support system

To effectively manage the nutrient status of waterbodies, an ability to predict the likely external nutrient loadings from both point and diffuse sources under present and future conditions is important. The processes of nutrient export and transport are very complex, and detailed data and knowledge of these processes are seldom available without lengthy and expensive investigations. As an alternative, estimates of average annual catchment nutrient loads can provide an initial basis for strategic decision making, and indicate where more detailed investigations would be most beneficial. The Catchment Management Support System (CMSS) is a PC-based programme that was developed to calculate average annual nutrient loads and to allow the effects of land-use changes and land management changes to be investigated with ease. In addition, the CMSS approach stresses the importance of wide community involvement in the decision-making process for catchment management. The CMSS package is described, including the nutrient load prediction model used and its data requirements and the features of the user interface. A discussion of the role of CMSS in the decision-making process is made with reference to the imminent development of Nutrient Management Plans for many Australian catchments.

Estimated Annual Loads of Selected Organic Contaminants to Chesapeake Bay via a Major Tributary

The aim of the Chesapeake Bay Fall Line Toxics Monitoring Program has been to determine the annual loads for selected organonitrogen, organophosphorus, and organochlorine pesticides, polychlorinated biphenyls, and polynuclear aromatic hydrocarbons to Chesapeake Bay derived from above the fall line of the Susquehanna River, the bay's largest tributary. Load results are presented in this report for 15 samples collected from March 1992 through February 1993. Annual load estimates were obtained using 14 methods, grouped according to whether they are of averaging, ratio, or regression type to ensure convergence to an approximate mean load value for each contaminant. The results indicated a high degree of uniformity across the methods with most yielding relative deviations 1.5 or less when normalized to the mean load derived from all 14 load estimation methods.

Nutrient management at the catchment scale using a decision support system

To effectively manage the nutrient status of waterbodies, an ability to predict the likely external nutrient loadings from both point and diffuse sources under present and future conditions is important. The processes of nutrient export and transport are very complex, and detailed data and knowledge of these processes are seldom available without lengthy and expensive investigations. As an alternative, estimates of average annual catchment nutrient loads can provide an initial basis for strategic decision making, and indicate where more detailed investigations would be most beneficial. The Catchment Management Support System (CMSS) is a PC-based programme that was developed to calculate average annual nutrient loads and to allow the effects of land-use changes and land management changes to be investigated with ease. In addition, the CMSS approach stresses the importance of wide community involvement in the decision-making process for catchment management. The CMSS package is described, including the nutrient load prediction model used and its data requirements and the features of the user interface. A discussion of the role of CMSS in the decision-making process is made with reference to the imminent development of Nutrient Management Plans for many Australian catchments.

手賀沼流入河川における汚濁負荷量の流出特性および年間負荷量の把握

The Ohhori and Ohtsu Rivers are the two major rivers flowing into Lake Teganuma. To gain an understanding of SS, BOD, COD, nitrogen and phosphorus loads flowing into the lake, pollutant loadings were observed at downstream points of the two rivers. According to the runoff characteristics of the observed pollutant loadings, pollutant load could be separated into “dry weather load” and “wet weather load”. The wet weather load is caused by direct runoff of rainfall and could be represented by a regression equation using depth of runoff, antecedent precipitation factor and peak rainfall intensity as independent variables. As a result of annual pollutant load estimation, the ratio of annual wet weather load to annual total (dry+wet) was about 70 percent for SS, about 30 percent for BOD and COD, and 10-20 percent for T-N and T-P. Moreover, the ratios between dissolved and particulate constituents in dry and wet weather loads for COD, T-N and T-P were clarified. Furthermore, the runoff characteristics of constituents of T-N, i.e., nitrite, nitrate and so on, were investigated.

Metered end-use consumption and load shapes from the ELCAP residential sample of existing homes in the Pacific Northwest

Hourly end-use data have been collected from 454 residences and 140 commercial buildings in the Pacific Northwest. The data presented here provide an overview of electricity consumption patterns for 288 homes in the End-Use Load and Consumer Assessment Program (ELCAP) Residential Base Study. The Base Study is a sample of 454 regional single-family, owner-occupied, electrically space-heated houses. Metered residential electrical end-use loads collected as part of the ELCAP are summarized. The ELCAP was conducted by Pacific Northwest Laboratory for the Bonneville Power Administration. This paper addresses a number of load research questions: • What are the mean annual loads for specific end uses? • How much do end-use loads vary across residences? • Are load shares less variable across residences than end-use loads? • How do end-use loads vary with respect to common demographic variables, such as income level or number of occupants? • To what degree do end-use loads vary by time of year? • What are average hourly end-use load shapes? • What are the estimates of average annual end-use loads and load shares for the residential sector after applying assumed appliance and fuel saturation rates to the metered loads? Descriptions are presented of the metered hourly end-use loads aggregated across time and across time and across the sample of homes. Observations are made regarding common assertions about energy consumption patterns, but models or detailed statistical analyses of these loads are not included because they are the subject of other current and pending analyses.

Evaluation of the accuracy and precision of annual phosphorus load estimates from two agricultural basins in Finland

The accuracy and precision of phosphorus load estimates from two agricultural drainage basins in western Finland were evaluated, based on continuous flow measurements and frequent flow-proportional sampling of total phosphorus concentration during a 2 year period. The objective was to compare different load calculation methods and to evaluate alternative sampling strategies. An hourly data set of concentrations was constructed by linear interpolation, and these data were used in Monte Carlo runs for producing replicate data sets for calculating the accuracy and precision of load estimates. All estimates were compared with reference values computed from the complete hourly data sets. The load calculation methods based on summing the products of regularly sampled flows and concentrations produced the best precision, whereas the best accuracy was achieved using methods based on multiplying annual flow by flow-weighted annual mean concentration. When comparing different sampling strategies, concentrating sampling in high runoff periods (spring and autumn) was found to give better accuracy and precision than strategies based on regular interval sampling throughout the year. However, the best result was obtained by taking samples flow-proportionally within the highest peak flows plus additional regular interval (e.g. biweekly) samples outside these flow peaks. Using this strategy, which calls for automatic sampling equipment, accuracies better than 5% and precisions better than 10% can be achieved with only 30–50 samples year −1.

Great Lakes Total Phosphorus Model: Post Audit and Regionalized Sensitivity Analysis

The multisegment mass balance model of Great Lakes total phosphorus presented by Chapra and Sonzogni (1979) was used with annual phosphorus loading estimates to simulate phosphorus concentrations in 11 Great Lakes basins for the period 1974 to 1987. Comparison of the model results with field data collected since 1980 shows fairly good agreement, in spite of some overprediction of concentration in Lakes Superior and Ontario. A Monte Carlo technique known as regionalized sensitivity analysis was used both to identify those model parameters (including initial conditions) that were most important for producing an acceptable simulation and to examine new values for some model parameters. The model results were most sensitive to the parameters representing within-lake removal processes. Despite its simplicity, the Great Lakes total phosphorus model performed well and could be useful for establishing data quality objectives for phosphorus load estimates and surveillance programs.

Estimation of Storm Water Quality Characteristics and Overflow Loads from Treatment Plant Influent Data

A simple model, based on tanks in series, for the estimation of mean annual loads and frequency distributions of loads from combined sewer systems is presented. The input data, dry weather flow, dry weather quality, and storm water quality are estimated from treatment plant influent data. Two similar methods for the estimation of flow-average storm water quality were tested by using treatment plant influent data generated by the model in comparison with the model input. Both methods are based on daily mass balances, but differ slightly with respect to the averaging procedures used. The performance of both methods is about the same. They show a small bias, but the variability introduced is small when compared with the variation occurring in real storm water quality data. Application of one of the methods on field data revealed no distinct relationships between the flow-averaged storm water quality concentration and the dry weather period or the total daily rain depth. By combination of continuous and Monte Carlo simulation techniques the model can be used to estimate mean annual loads and frequency distribution of loads from combined sewer overflows. For the extreme events a large 90 % confidence interval was found due to the large variations in storm water quality.

Evaluation of phosphorus loads from Ontario municipal wastewater treatment plants

Results are presented from an evaluation of the nature and accuracy of phosphorus loads discharged by Ontario municipal wastewater treatment plants into the Great Lakes. Data were examined for the 96 plants treating flows in excess of 4546 m(3)d(-1) for the period 1981 to 1985. For the Lake Erie, Lake Ontario/St. Lawrence River and Upper Great Lakes basins, total basin phosphorus loads were classified according to type of wastewater treatment system, the type of chemical added for phosphorus removal, plant capacity, and sampling frequency. Load estimation techniques were compared using the 1985 daily data from three representative treatment plants. Annual phosphorus loads were compared using the complete data records for the plants and using Monte Carlo techniques to simulate an incomplete data record typical of once per week effluent phosphorus sampling. Potential sources of bias were identified in annual phosphorus load estimates from municipal treatment plants.

THE AUXILIARY HEATING REQUIREMENTS OF SIX HOUSE TYPES IN SYDNEY OR “OF WHAT SHOULD I BUILD MY HOUSE?” ASKED THE THREE LITTLE PIGS

SUMMARY The results of winter space heating of the living areas of six houses in the Bonnyrigg Solar Village (three controls and three passive solar/low energy houses) are used in a linear regression model to relate indoor temperature elevation to auxiliary heating and solar gains. Methods of comparing results where different thermostat set-points were used are discussed and a method for presenting annual heating load estimates is explained. Some relationships between construction and heating load are presented.

Groundwater seepage as a nutrient source to a drainage lake; Lake Mendota, Wisconsin

The flux of groundwater through shallow-water sediments into Lake Mendota was calculated from hydrologic studies and was measured directly with seepage meters at 106 sites around the lake. Groundwater accounted for a substantial amount (around 30%) of the water budget. Pore water in seepage zones was collected for chemical analysis by two methods: (1) dialysis samplers; and (2) direct gentle suction. This pore water, which was assumed to represent seepage inflow, was considerably lower in nitrogen and phosphorus than surface inflow but was higher in phosphorus and lower in nitrogen than well water, indicating that well chemistry does not provide a good indication of the composition of groundwater entering lakes. Calculations indicated that seepage accounted for 12% of the total phosphorus loading to Lake Mendota and 2% of the total nitrogen budget. These results are interpreted in terms of the annual nutrient loading estimates that have been done on Lake Mendota involving only surface water measurements.