Syed I. Ahmed

Pesticide Transport with Surface Runoff and Subsurface Drainage through a Vegetative Filter Strip

Vegetative filter strips (VFS) have become an established best management practice during the last 25 years. This study examined the effectiveness of VFS of brome grass in central Iowa for reducing the mass transport of sediment and pesticides (atrazine, acetochlor, and chlorpyrifos) with surface runoff under natural rainfall conditions. Measurements of pesticide concentrations in water from a single subsurface drain under the plots were also made. Overall results showed that many factors affect pesticide transport, such as rainfall timing and intensity, hydrology, source–to–VFS area ratios, and the adsorption properties of pesticides in VFS inflow. Two primary mechanisms (inflow water infiltration and sediment deposition) had a significant effect on pesticide passage through VFS. Sediment deposition increased with decreased flow volume and velocity, and was considerably higher for the 15:1 area–ratio plots than for the 45:1 plots; this in turn aided in the reduction of transport of pesticides adsorbed to sediment. Reductions in atrazine and acetochlor transport were primarily controlled by the infiltration efficiency of the VFS, as they are moderately adsorbed, and the major portion of these pesticides moved in solution in the surface runoff water phase. Chlorpyrifos was highly adsorbed to the sediment, making sediment deposition in the VFS equally, if not more, important than infiltration for mass removal. The herbicides (atrazine and acetochlor) had low to moderate adsorption characteristics and moved primarily in the runoff water phase. Data collected for the subsurface drainage from the tile line showed that there were measurable concentrations of the moderately adsorbed herbicides in the tile flow at the time surface runoff was taking place; however, concentrations of the more strongly adsorbed chlorpyrifos were below detection. The statistical difference was most prominent in the event with the smallest runoff volume. This showed that at lower flow rates, VFS can effectively reduce runoff, sediment, and pesticide transport from cropland.

Livestock grazing and vegetative filter strip buffer effects on runoff sediment, nitrate, and phosphorus losses

Livestock grazing in the Midwestern United States can result in significant levels of runoff sediment and nutrient losses to surface water resources. Some of these contaminants can increase stream eutrophication and are suspected of contributing to hypoxic conditions in the Gulf of Mexico. This research quantified effects of livestock grazing management practices and vegetative filter strip buffers on runoff depth and mass losses of total solids, nitrate-nitrogen (NO3-N), and ortho-phosphorus (PO4-P) under natural hydrologic conditions. Runoff data were collected from 12 rainfall events during 2001 to 2003 at an Iowa State University research farm in central Iowa, United States. Three vegetative buffers (paddock area:vegetative buffer area ratios of 1:0.2, 1:0.1, and 1:0 no buffer [control]) and three grazing management practices (continuous, rotational, and no grazing [control]) comprised nine treatment combinations (vegetative buffer ratio/grazing management practice) replicated in three 1.35 ha (3.34 ac) plot areas. The total 4.05 ha (10.02 ac) study area also included nine 0.4 ha (1.0 ac) paddocks and 27 vegetative buffer runoff collection units distributed in a randomized complete block design. The study site was established on uneven terrain with a maximum of 15% slopes and consisted of approximately 100% cool-season smooth bromegrass. Average paddock and vegetative buffer plant tiller densities estimated during the 2003 project season were approximately 62 million and 93 million tillers ha−1 (153 million and 230 million tillers ac−1), respectively. Runoff sample collection pipe leakage discovered and corrected during 2001 possibly reduced runoff depth and affected runoff contaminant mass losses data values. Consequently, 2001 runoff analysis results were limited to treatment comparisons within the 2001 season and were not compared with 2002 and 2003 data. Analysis results from 2001 showed no significant differences in average losses of runoff, total solids, NO3-N, and PO4-P among the nine vegetative buffer/grazing practice treatment combinations. Results from 2002 indicated significantly higher losses of runoff and total solids from 1:0 no buffer/rotational grazing and 1:0 no buffer/continuous grazing treatment combination plots, respectively, compared among other 2002 season treatment combinations. The 2003 results showed significantly higher runoff and total solids losses from 1:0 no buffer/no grazing treatment combination plots compared among all 2003 treatment combinations and from 1:0.1 vegetative buffer/no grazing treatment combination plots compared among all 2003 treatment combinations and with respective 2002 treatment combinations. However, the 2003 results indicated effective vegetative buffer performance with significantly lower runoff, total solids, and NO3-N losses from the larger 1:0.2 buffer area compared among the smaller 1:0.1 buffer area and 1:0 no buffer treatment combinations. The 2003 results also indicated a highly significant increase in losses of NO3-N from 1:0.1 buffer/no grazing treatment combination plots compared among other 2003 season treatment combinations and with respective 2002 treatment combinations. Overall results from this study suggest a shift from significantly higher 2002 season plot losses of continuous and rotational grazing treatment combinations to significantly higher 2003 season losses of no grazing treatment combinations. We speculate this shift to significantly higher runoff and contaminant losses from no grazing treatment combination plots during 2003 reflects the variability inherent to a complex and dynamic soil-water environment of livestock grazing areas. However, we also hypothesize the environmental conditions that largely consisted of a dense perennial cool-season grass type, high-relief landscape, and relatively high total rainfall depth may not necessarily include livestock grazing activities.

Comparing the Performance of SWAT and AnnAGNPS Model in a Watershed in Ontario

Safe distribution of water from source to tap is a major concern in Ontario after the Walkerton tragedy. The Nutrient Management Act and Source Water Protection Act in Ontario are being planned to protect the quality of water resources by controlling pollutant transport from upland contributing areas. To achieve the objective of providing safe, clean, and affordable water supply and aquatic ecosystem, it is essential to assess the contribution of pollution from different sources to the stream. While source water protection is a major issue in Ontario, a number of watershed models are being used by different agencies to mitigate the water quality and quantity problems. The Guelph Watershed Research Group at the University of Guelph is also assessing the performance of different watershed models to best apply in Ontario conditions. This study has investigated the hydrology and sediment output from two widely used watershed models (SWAT and AnnAGNPS). The models are daily time step, watershed scale, pollutant-loading model developed to simulate long-term runoff, sediment, and chemical transport from agricultural watersheds. The models were run for a period of ten years (1991-2000) and the output data for the first five years (1991-1995) were used to calibration and that for the last five years data (1996-2000) for validation. The results of the study indicate that the models performed fairly well in simulating the runoff and sediment yield for Ontario conditions. For annual water balance, the model underpredicted the evapotranspiration, but the average difference was under acceptable range (3.1% for AnnAGNPS and 11.2% of SWAT). For surface runoff, the average difference between the observed and simulated annual runoff for the calibration period was 2.1% for AnnAGNPS, and 4.5% for SWAT model. The deviations for validation period were 1.8% for AnnAGNPS and 18.8% for the SWAT model. The Nash-Sutcliffe coefficients for monthly outputs were 0.79 for AnnAGNPS and 0.7 for AnnAGNPS in the calibration phase and 0.69 for AnnAGNPS and 0.57 for SWAT model for the validation phase. A significant challenge in calibrating and validating the sediment portion of the model was a shortage of observed sediment data, which might have lead to the over prediction of sediment yield by both the models during validation period. A detailed evaluation of SWAT model on the watershed is still in progress and the output for SWAT might be improved once the work is completed.

Within-Storm Rainfall Distribution Effect on Soil Erosion Rate

This study investigates the effect of rainfall temporal distribution pattern within a storm event on soil erosion rate and the possibility of using rain power type model for rainfall erosivity. Various rainfall distribution patterns, simulated by rainfall simulator, were used on 1.0 m2 plot of silica sand and loam soil with a minimum of three replications. The results show that the soil erosion rates spiked following every sharp increase in rainfall intensity followed by a gradual decline to a steady erosion rate. Transient effects resulted in the soil erosion rates for an oscillatory rainfall distribution to be more than two fold higher than those obtained for a steady-state rainfall intensity event with same duration and same average rainfall intensity. The 3-parameter and 4-parameter rain power models were developed for a process-based measure of rainfall erosivity. The 4 parameter model yielded better match with the observed data and predicted soil erosion rates more accurately for silica sand under all rainfall distributions, and good results for loam soil under low intensity rainfall. More research is necessary to improve the accuracy of soil erosion prediction models for a wider range of rainfall distributions.

Conservation management practices: Success story of the Hog Creek and Sturgeon River watersheds, Ontario, Canada

The soil erosion from agricultural watersheds can be reduced by implementation of conservation management practices. In this study, the effectiveness of most popular agricultural best management practices (BMPs) for reducing sediment loads within Hog Creek and Sturgeon River watersheds in Ontario was investigated using measurement of the shift in the sediment rating curves from pre-BMP (1989 to 1993) to post-BMP (2004 to 2008) implementation periods. The data from the water quality monitoring program for the Hog Creek and the Sturgeon River watersheds over this decade of extensive conservation management program implementation showed significant reductions in the sediment loads of 49% for Hog Creek and 41% for the Sturgeon River. The results showed that the most widely adopted BMPs that greatly influenced the overall removal in sediment loads were stream bank fencing, no-till farming, and vegetative buffer strips. Overall, the outcome of the study recommends these promising practices to protect and improve receiving water quality. The practical novel technique presented in this study for quantification of the overall long-term water quality benefits of conservation management practices can be an integral part of an adaptive strategy for a watershed-scale BMP implementation program.

Evaluation of Nutrient Component of AnnAGNPS Model in a Watershed in Ontario

Abstract: The water impairment with nutrient losses from non-point source pollution (NPS) is a major concern in different watersheds in Ontario where agricultural and live stock production are the major activities. The Annualized Agricultural Non-Point Source (AnnAGNPS) model has been applied in a watershed situated in the Southern Ontario to investigate model simulated N (N) and P (P) output. The model was run from 1991 to 1995 and the transport of dissolved and attached part of both the nutrients with runoff and clay particles was investigated. Since very limited observed nutrient data was available in the studied watershed and thus it was difficult to obtain a reasonable comparison between the simulated and observed values. The study results show that the dissolved and attached N has followed the similar trend of transport with the runoff and clay particles respectively. The model underpredicetd the total N and overpredicted the total P. The R2 and correlation coefficient was 0.75 and 0.19 for N and 0.82 and 0.23 for P respectively. The uncertainty of the input parameters and excessive use of manure were assumed to be the main reason behind the discrepancy. However, it was also obvious from the study that the model performance may be improved with proper calibration and further investigation on the fate and transport of the nutrient components.

Impact of contributing area on the performance of Vegetative Filter Strips

The sediment and dissolved pollutants carried by surface runoff enter into the stream network. The vegetative filter strip (VFS) within buffer zone of stream can effectively reduce the pollutants by trapping the sediment within vegetative strip. The main objective of this study was to use AGNPS_VFS (Agricultural Nonpoint Source Pollution_Vegetative Filter Strip) tool kit to determine the impact of contributing area of each flow path on VFS performance for Canagagigue Creek watershed, Ontario, Canada. The 10m, 20m, and 30m wide VFS were simulated for nine storm scenarios (5-yr, 10-yr and 25-yr return period, and storm duration of 6-hr, 12-hr and 24-hr).The simulated results showed that some flow paths carried either very small sediment load or no load. The linear regression trends for sediment load and sediment removal efficiency (SRE) revealed that SRE decreased as contributing area increased. The maximum SRE was 90%, 94%, and 95% for 5yr-6hr duration, and the minimum SRE were observed as 9%, 40%, and 55% for 25yr-24hr for 10m, 20m, and 30m VFS. The sediment loads enter the system increased as flow regime changed from 5-yr to 25-yr return period and 6 hr to 24 hr duration. The area of flow path in watershed reduced 68% for 5yr-6hr scenario and 37% for 25yr-24hr scenario. This indicates that amount of storm considerably affects the contributing area of flow path. The analysis would help in identifying the flow path where VFS would produce the efficient results.