E.A. Pappas’s research while affiliated with United States Environmental Protection Agency and other places

The prognostic capabilities of a lumped hydrologic modeling approach may be complicated by routing and connectivity among infiltrative and impervious surfaces. We used artificial rainfall to generate runoff from impervious and bare soil boxes arranged in series to simulate different extents and connectivity of impervious surfaces under different moisture conditions for pervious areas. Curve numbers were calculated from observed rainfall and runoff data, compared with published values, and used in the curve number infiltration algorithm in the U.S. EPA Storm Water Management Model 5 (USEPA SWMM5) to generate runoff hydrographs. Experimental curve numbers were higher than tabular USDA values, ranging from 91 to 96. Simulations of infiltration and runoff response with experimental curve numbers showed overall good agreement with observed data, although SWMM5 was unable to re-create early term infiltration patterns, and simulated runoff lagged observed, which is attributed to implicit accounting for soil moisture and other assumptions of the SWMM5 curve number application. Our results highlight some prospects for the use of curve numbers in modeling infiltration and runoff.DOI:10.1061/(ASCE)IR.1943-4774.0000301. (C) 2011 American Society of Civil Engineers.

As a watershed is urbanized, characteristics of runoff from new upslope impervious surfaces may differ from runoff generated on the predevelopment soil surface in quantity, time of concentration, and sediment load. This may cause changes to the erosion regime on downslope soil surfaces. We simulated rainfall at three rates (20, 30, 40 mm/h) to generate runoff from 0: 6 m(2) boxes. Boxes were either treated with an impervious surface or filled with soil 0.2 m deep and were connected together in series of four boxes along the 4-m slope to produce different arrangements of impervious and pervious soil surfaces (0, 25, 50% impervious) and under different antecedent soil moisture conditions. Results indicate that previously established numerical models predicting runoff characteristics as a function of run-on characteristics generate good correlations at 0% imperviousness, but these correlations become insignificant as imperviousness increases. Imperviousness significantly influenced sediment regime, suggesting that some previously established equations relating soil erosion to run-on characteristics cannot be simply applied to areas where runoff production occurs on surfaces having an impervious component. DOI: 10.1061/(ASCE)HE.1943-5584.0000325. (C) 2011 American Society of Civil Engineers.

To help minimize the negative hydrologic impacts of urbanization, such as increased flooding and decreased time of concentration, urban best management practices (BMPs) are continually being developed. Several BMPs have been developed to allow infiltration on certain transportation surfaces. Among others, these include substituting traditional pavement with pervious pavers. Gaps between paver blocks typically represent about 3-30% perviousness by area. In addition, some paver blocks are themselves permeable through open pore spaces, in theory increasing the overall permeability of the system. This comes however at a cost in terms of durability, especially under freezing or heavier traffic conditions. Surface sealing by fine particles deposited by water, wind, trees, or vehicles may result in reduction or elimination of infiltration in between and / or within paver blocks. To test the extent to which this phenomenon can influence runoff and infiltration dynamics, a series of laboratory rainfall simulations was performed on pairs of soil boxes (1.0 x 0.6 x 0.2 m each). One box was equipped with a pervious paver system (with either permeable or impermeable blocks) and located down slope from a second soil box representing an erodible soil surface area. Rainfall representing a 5-yr return period storm was simulated and timed runoff and infiltration samples were collected to determine discharge rates of water and sediment from each 1-m long section. Surface runoff and deep percolation were collected from pervious block (PB) and impervious block (IB) paver systems, and average steady state infiltration rates are given in Figure 1. Eleven consecutive rainfall simulation events were performed, 24-72 hours apart.

When natural or agricultural land is converted for (sub)urban or commercial use, the addition of impervious surfaces becomes a dominating factor in the new urban hydrologic regime. To help minimize the negative hydrologic effects of this land use change, urban best management practices (BMPs) are continually being developed. Several BMPs have been developed to allow infiltration on certain transportation surfaces. Among others, these include substituting traditional pavement with pervious pavers. Small gaps between paver blocks typically represent about 10% perviousness by area. It is generally accepted that infiltration is maintained on this portion of the surface, resulting in an overall reduction in runoff discharge, versus a traditional pavement. However, surface sealing resulting from silt or clay particles deposited by water, wind, or vehicles may result in reduction or elimination of infiltration. To test the extent to which this phenomenon can influence runoff and infiltration dynamics, a series of laboratory rainfall simulations was performed on 1.0 x 0.6 x 0.2-m boxes a pervious paver surface located down slope from a soil box representing an erodible soil surface area. Rainfall representing a 5-yr return period storm was simulated and timed runoff and infiltration samples were collected to determine discharge rates of water and sediment from each 1- m long section. Results indicate that almost all of the rainfall and run-on applied to pervious paver surfaces initially infiltrated. However, infiltration rates decreased and runoff rates increased with successive rainfall events, and after 10 to 11 5-yr rainfall events, siltation and surface sealing between paver blocks prevented infiltration from taking place entirely. This indicates employment of pervious paver blocks requires ongoing maintenance to prevent surface silting and sealing for sustained effectiveness.

The National Phosphorus Research Project coordinated a tremendous amount of research at the plot scale to assess the influence of nutrient management on phosphorus (P) transport at the fields scale. The objective of this research was to determine if plot-scale rainfall simulations could be used to assess P transport from two fields that were managed using no-tillage or rotational tillage. Plots were constructed within the management zone but adjacent to monitored fields. Phosphorus transport at the field scale from throughout the growing season was compared to confidence limits established by the rainfall simulations, and a secondary analysis compared values from individual storms to the rainfall simulations. Soluble phosphorus (SP) loads from the no-tillage AS1 field (75 g ha-1 [0.066 lb ac-1]) were greater than from the rotationally tilled AS2 field (11g ha-1 [0.010 lb ac-1]) in 2004. Stratification of P in the uppermost portion of the soil profile is a known contributor to SP loading in long-term no-tillage fields. This trend was reversed in 2006 though, as SP loads were 16 g ha-1 (0.014 lb ac-1) from the AS1 field and 55 g ha-1 (0.049 lb ac-1) from the AS2 field. The greater loads from the AS2 field were due to greater discharge and a greater P application rate, compared to the AS1 field. Soluble P and total P loads were generally directionally correct, but the values obtained from plots were not necessarily similar to those observed at the field scale. Precipitation normalized loads for SP and total P were the most similar metric when comparing values from the plot to the field scale (i.e., more field scale values fell within the 95% confidence limits set by the plot data than the other metrics). Using cumulative field-scale data from each year or the mean values from storms by year did not appear to change the results of this study. This study would appear to confirm that the management decisions based on the National Phosphorus Research Project are likely to be sound and will probably lead to improved quality of runoff water from fields. Precipitation normalized loads appear to be a metric that may provide additional insight into P transport at various scales.

Herbicide losses from agriculture represent potential environmental and human health hazards, and are the target of various conservation practices. Measuring herbicides at the watershed scale can be rigorous and expensive, and sampling frequency should be based upon the monitoring purpose and expected associated uncertainties. Atrazine, simazine, alachlor, metolachlor, and glyphosate were monitored in tile-fed drainage ditches for conservation effects assessment and source water protection. A total of 20,428 water samples were collected during the 2004 to 2009 cropping seasons at eight monitoring sites located at the outlets of sub basins ranging in size from 298 to 19,341 ha. However, it may be possible to analyze fewer samples without incurring unacceptable errors. To identify other possible methods to reduce analytical cost for determination of drinking water source suitability, we further analyzed the potential errors associated with compositing every 2 daily samples into a single sample representing 2 days by electronically simulating composites, while sampling more frequently during storm flow events. Compositing samples in this matter was found to introduce infrequent and minimal error in water quality compliance for atrazine and simazine only, and represent an average reduction in analytical cost of 21%. Since herbicide transport is closely associated with the first few rainfall events following application, targeting sampling when levels are temporally most variable may be another efficient way to assess conservation efforts and ensure adequate water filtration methods are employed at the right time. The abilities of truncated the sampling seasons (105, 122, and 226 days) to predict water quality compliance on an annual basis were evaluated. Results indicate that the ideal sampling season of atrazine and simazine is April 1 – November 15, while sampling of other measured herbicides can be truncated by August 15 with infrequent and minimal errors.

Natural resource systems involve highly complex interactions of soil-plant-atmosphere-management components that are extremely difficult to quantitatively describe. Computer simulations for prediction and management of watersheds, water supply areas, and agricultural fields and farms have become increasingly complex in an effort to more accurately describe natural resource processes. However, often times the development and application of natural system models do not include careful testing against high quality field measured data and variables. This study reports on the assimilation of state-of-the-art monitored hydrologic states and fluxes into a vadose zone model. The specific study objectives were: 1) to calibrate and validate the Root Zone Water Quality Model (RZWQM) for water and chemical transfer in two, 2.5 ha tile-drained agricultural fields in the Upper Cedar Creek Watershed of northeastern Indiana, USA; 2) to assess the space-time evolution of soil hydraulic functions in response to no-till (NT) and rotational tillage (RT) practices in each field; and 3) to evaluate model performance in simulating chemical transfer to surface and subsurface flows. Model parameterization and performance were tested in each field based on data collected from state-of-the-art water quality samplers, weather stations, and soil moisture/temperature sensors, as well as detailed field and laboratory measurements of soil physical and hydraulic properties. Model performance was assessed using the Nash-Sutcliffe Efficiency coefficient (NSE), coefficient of determination (R2), Root Mean Square Error (RMSE), and percent bias (PBIAS). The results show that the RZWQM was able to simulate water and chemical transport in runoff and subsurface flow with sufficient quality. In addition, the use of pedotransfer functions in RZWQM were adequate in characterizing effective field-scale soil hydraulic behavior. Thus, the model should serve as a suitable tool in quantifying the impact of different management practices on water quantity and quality at the field or small watershed scale.

The widespread use and potential human health effects of the herbicides atrazine and glyphosate have generated interest in establishing how no-tillage impacts loading of these herbicides to runoff water in comparison to other tillage practices. In this study, potentially confounding factos such as time in tillage practice and type and distribution of residue cover, are weighed against inherent tillage impacts to soil structure in terms of relative effects on herbicide transport with runoff water. In this study, two small watersheds (one in no-till (NT) and one rotational till (RT)) were monitored during the first three years since conversion of the RT watershed from NT. In addition, rainfall simulation was applied to plots within each watershed during the first, third, and fifth years since the conversion. Runoff atrazine and glyphosate losses from RT areas were compared to losses from NT areas as a ratio of RT:NT. Results indicate a trend of increasing RT:NT value with time in tillage. Watershed monitoring indicated greater herbicide loading to runoff water from the NT watershed than the RT watershed during the first year since RT conversion, but this relationship reversed by the third year since conversion to RT. In addition, rainfall simulations were performed on small boxes of NT or RT soil having varying types and levels of residue cover in an attempt to isolate residue cover effects from true tillage effects.

To protect human health, atrazine concentrations in finished municipal drinking water must not exceed a maximum contaminant level (MCL) of 3 microg/L, as determined by a specific monitoring regime mandated by the United States Environmental Protection Agency. Atrazine levels were monitored along tile-fed drainage ditches draining to a major drinking water source and used to predict MCL exceedance frequencies of intake and finished drinking water. Water samples were collected daily at eight monitoring sites located at the outlets of subbasins draining 298-19 341 ha (736-47 794 ac). Flow-weighted average (FWA) atrazine concentrations ranged from 0.9 to 9.8 microg/L, and were above 3 microg/L for the majority of sites, including the largest site, which represents water quality at the intake of the local municipal water treatment plant. However, a relatively low percentage of samples near the water utility intake exceeding 3 microg/L atrazine (10.4%) made this problem difficult to detect. In order to have a 95% probability of detecting any intake sample exceeding 3 microg/L atrazine in a drainage system exceeding 3 microg/L atrazine on a FWA basis, sampling frequency would need to be every 7 days or more often during the second quarter when the potentials for field atrazine losses and temporal variability of atrazine concentrations are highest.