Surface Runoff Water Quality Research Articles

Water quality effects of cover crop, grazing and tillage implementation in a long-term no-till wheat system

Agricultural anthropogenic nitrogen (N) and phosphorus (P) continue to be major surface and subsurface water pollutants in developed countries. Integrated crop-livestock systems in the semi-arid Texas Rolling Plains are characterized by continuously cultivated monoculture combined with grazing. Improperly managed grazing can increase soil compaction, and subsequently, decrease infiltration, which leaves the soil exposed to erosion. Grazing is therefore of paramount importance to water quality. Cover crop (CC) use improves soil ecosystem services and functions. The objective of the current study was to characterize soil water quality following CC under continuous wheat (Triticum aestivum), grazing, tillage, and no-till practices under a typic Haplustepts, Rotan clay loam soil type. Treatments evaluated include 1) conventional tillage without a CC (CT); 2) no-till without a CC (NT); 3) no-till with a CC (NTC); and 4) no-till with a grazed CC (NTCG). Portable rainfall simulators were used to assess surface runoff water quantity and quality after CC implementation in a long-term no-till continuous wheat system. Cover crop treatments, both grazed and un-grazed, reduced the amount of runoff by 4–6 times compared to no CC treatments (NT and CT). Converting 12-year-old NT to CT reduced infiltration by at least 43 % and increased runoff by 58 % compared to long-term NT. Consequently, total solids load and concentration for CT were 4–14 times greater than all NT treatments (NT, NTC, NTCG). Conventional tillage (CT) also increased total P loads and concentrations by 2–11-fold compared to all NT treatments (p < 0.05). Rainfall events occurring within three weeks after CC termination resulted in about 6 times greater soluble reactive P (SRP) (except NTCG) and about 2–3 times greater dissolved organic C (DOC) concentrations from CC treatments than non-CC treatments, although this was not observed for subsequent runoff events. Tilling the soil had more deleterious effects compared to flash grazing CC. Adopting NT, either alone, or long-term in combination with CC (either flash grazed or un-grazed) are potentially sustainable viable practices in semiarid regions that can reduce environmental contamination.

Impact of Flue Gas Desulfurization Gypsum Applications to Corn-Soybean Plots on Surface Runoff Water Quality

Impact of Flue Gas Desulfurization Gypsum Applications to Corn-Soybean Plots on Surface Runoff Water Quality

Field scale discharge and water quality response, to drainage water management

Subsurface (tile) drainage, while necessary for viable agricultural crop production in the humid, poorly drained regions of the world, has been linked to offsite nutrient transport, culminating in harmful algal blooms and hypoxia in downstream waterbodies. Drainage water management (DWM), also known as controlled drainage, has been promoted as a method to reduce nitrogen (N) and phosphorus (P) loss from field scale tile drainage; however, subsequent changes in surface runoff and associated water quality have not been explored. Four years of surface and subsurface discharge, N, and P loss from two sets of paired field sites in northwest Ohio, USA were evaluated using a before-after control-impact (BACI) design to quantify the impact of DWM. Mean event surface runoff was greater (significant at one site) under DWM while tile drainage discharge was less at both sites but not significant. There was no significant difference in surface nitrate-N (NO3--N) loss; however, significant reductions in tile NO3--N loss under DWM were measured at both sites. Similar to discharge, dissolved reactive P (DRP) loss measured in surface runoff was greater under DWM (significant at one site), while no significant differences were noted in mean event tile drainage DRP loss. Total P (TP) surface runoff losses were significantly greater under DWM at the site with significantly greater surface runoff, while DWM reduced tile drainage TP loss at only one site. These findings suggest that DWM reduced tile NO3--N loss, while also highlighting that any benefit from DWM with respect to tile DRP or TP loss could be negated in part by increased surface losses. Furthermore, these findings emphasize the need to understand the natural resource concern to which the practice is targeted and also call for additional research on DWM implementation that includes surface runoff across a range of soil textures, cropping management, and climates.

The Effect of Urban Land-Use Change on Runoff Water Quality: A Case Study in Hangzhou City.

The main functions of this research are to guide the proportion of urban land that is used and the layout of the facilities on it, help understand the changes to surface runoff that are caused by land being used in urban development, and thus solve surface runoff pollution. Hangzhou City, China has been selected for the experiment, and the way in which its land is utilized as well as the grading of urban construction projects in the demonstration area are specifically analyzed. This study systematically distinguishes the definitions of impervious area based on the Sutherland equation and analyzes the impact of different impervious area subtypes on surface runoff water quality. Then, we compare the impact of impervious area subtypes with the impact of other land-use patterns on surface runoff water quality. This study shows the relationship between different land-use types and runoff water bodies: Land-use index can affect runoff water quality; Greening activities, impervious surface, and the water quality index are negatively correlated; the effective impervious area rate is positively correlated with the water quality index. The paper suggests that increasing the proportion of green spaces and permeable roads in build-up land reduces the effective impervious area (EIA) and thus controls land runoff pollution and improves runoff water quality.

Evaluation of Water Circulation by Modeling: An Example of Nonpoint Source Management in the Yeongsan River Watershed

Owing to urbanization, impervious areas within watersheds have continuously increased, distorting healthy water circulation systems by reducing soil infiltration and base flow; moreover, increases in surface runoff deteriorate water quality by increasing the inflow of nonpoint sources. In this study, we constructed a Hydrological Simulation Program—Fortran (HSPF) watershed model that applies the impervious area and can set medium- and long-term water circulation management goals for watershed sub-areas. The model was tested using a case study from the Yeongsan River watershed, Korea. The results show that impervious land-cover accounts for 18.47% of the upstream reach in which Gwangju City is located; approximately twice the average for the whole watershed. Depending on the impervious area reduction scenario, direct runoff and nonpoint source load could be reduced by up to 56% and 35%, respectively; the water circulation rate could be improved by up to 16%. Selecting management goals requires the consideration of both policy objectives and budget. For urban areas with large impervious cover, the designation of nonpoint source management areas is required. For new cities, it is necessary to introduce water circulation systems (e.g., low impact development techniques) to improve rainwater penetration and recharge and activate preemptive water circulation.

Investigation of heavy metals pollution in Piyungan Landfill underground and surface water

Assessing the potential hazard to the groundwater resource and surface runoff from solid waste disposal activities is considered necessary. This study focused on the effect of the leachate produced from the Piyungan landfill to both groundwater resources and surface runoff water quality. Groundwater samples were taken from point W1 (control) and W26, leachate samples were taken from LP1 (before treatment) and LP5 (after treatment), and drain samples were taken from L6 and L14, respectively. Heavy metals in these samples were analyzed using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). The results showed that leachate and drain samples had higher heavy metals content compared to groundwater samples. Leachate migration might happen in W26 since it located in the lower elevation of the landfill. For the leachate sample, the concentrations of Cr, Mn, Ni, As, and Se exceeded the allowable limit for raw water and leachate effluent. Deposition of heavy metals (Cr, Mn, Ni, As and Se) were also detected in W1 and W26 but still within the permissible limit. Continuous monitoring for heavy metals migration and the addition of leachate treatment processes in the landfill are suggested to avoid the occurrence of risky pollution to the surrounding area.

Winter Rye Cover Crop Impacts on Runoff Water Quality in a Northern New York (USA) Tile-Drained Maize Agroecosystem

Nonpoint source phosphorus (P) and nitrogen (N) pollution from agriculture is a global concern. Planting a cover crop after harvesting annual crops such as maize may help mitigate nutrient transport risk to surface and groundwater. Few studies have focused on the impact of a winter rye cover crop on both surface runoff (SR) and tile drainage (TD) water quality. Here, we measured N and P losses in SR and TD from maize plots grown with and without a winter rye cover crop. Four plots (46 × 23 m) in northern New York, USA, equipped with automated SR and TD flow monitoring were planted with winter rye (Secale cereal) in 2016 and 2017 after maize silage harvest. Plots were managed as typical silage fields for dairy farms in the region and received fertilizer and manure applications. Dissolved reactive P (DRP), total P (TP), nitrate-N, total N (TN), and total suspended solids (TSS) loads were monitored from 4/7/16 to 6/29/17. Cumulative SR (volumetric depth equivalent) was 1.8-fold lower for rye compared to control plots. Although runoff and loading were variable, cumulative TSS, TP, and DRP losses were approximately 3-fold lower for rye plots compared to control. Cumulative TN and nitrate-N loads for TD were similar; however, cumulative TN loss for SR was lower for rye plots. Surface runoff was the main pathway of P loss (> 90% of DRP and TP loss) with > 90% of cumulative P exported from 2017 snowmelt events. Results suggest winter rye mitigated N and P transport risk in SR compared to the common practice of leaving maize silage fields bare after harvest.

Physics-Informed Data-Driven Models to Predict Surface Runoff Water Quantity and Quality in Agricultural Fields

Contaminants can be rapidly transported at the soil surface by runoff to surface water bodies. Physically-based models (PBMs), which are based on the mathematical description of main hydrological processes, are key tools for predicting surface water impairment. Along with PBMs, data-driven models are becoming increasingly popular for describing the behavior of hydrological and water resources systems since these models can be used to complement or even replace physically based-models. Here we propose a new data-driven model as an alternative to a physically-based overland flow and transport model. First, we have developed a physically-based numerical model to simulate overland flow and contaminant transport. A large number of numerical simulations was then carried out to develop a database containing information about the impact of various relevant factors on surface runoff quantity and quality, such as different weather patterns, surface topography, vegetation, soil conditions, contaminants, and best management practices. Finally, the resulting database was used to train data-driven models. Several Machine Learning techniques were explored to find input-output functional relations. The results indicate that the Neural Network model with two hidden layers performed the best among selected data-driven models, accurately predicting runoff water quantity and quality over a wide range of parameters.

Surface and Subsurface Phosphorus Discharge from a Clay Soil in a Nine-Year Study Comparing No-Till and Plowing.

No-till as a water protection measure is highly efficient in controlling erosion and particulate P (PP) loss but tends to increase dissolved reactive P (DRP) concentrations in runoff water. In a 9-yr field study on a clay soil in Southwest Finland, the effects of no-till and autumn plowing on surface runoff and subsurface drainage water quality were compared. The site had a 2% slope and was under spring cereal cropping, with approximately replacement fertilizer P rates. Vertical stratification of soil-test P that had developed during a preceding 6-yr grass ley was undone by plowing but continued to develop under no-till. During the 9-yr study period, no-till soil had 27% lower cumulative total P losses than plowed soil (10.0 vs. 13.7 kg total P ha). Concentrations and losses of PP were clearly lower under no-till than under plowing (5.6 vs. 12.3 kg PP ha), but DRP loss showed the opposite trend (4.3 vs. 1.4 kg DRP ha). There was an increasing trend in subsurface drainflow DRP concentration under no-till, possibly because of development of a conductive pore structure from soil surface to drain depth. The potential benefit of no-till in water protection depends on how much of the PP transported to water is transformed into a bioavailable form and used by aquatic organisms. The beneficial effect of no-till in controlling P-induced eutrophication at the study site would only be realized if the bioavailable share of PP exceeds 43%. Otherwise, no-till would not be an efficient eutrophication control measure at this site.

Response of Winter Manure Application on Surface Runoff Water Quantity and Quality from Small Watersheds in South Dakota

Manure application on frozen soil, which is a common practice in the upper Midwest of USA, results in degraded soil and water quality. During snowmelt or precipitation events, water runoff carries nutrients into nearby streams and impairs the water quality. There is a need, therefore, to identify improved management of manure application in the soils. This study was conducted to assess water quality impacts associated following manure application during winter months when soil is completely covered with snow. The study site included three watersheds, named south (SW), east (CW), and north (NW) managed with a corn (Zea mays L.)-soybean (Glycine max L.) rotation located in South Dakota. The SW and NW were used as treatment, and CW as the control watershed. The treatments included manure application on the upper half of the SW and lower half of the NW, and CW received no manure application. This study showed that manure improved soil properties including infiltration rate and organic matter. Nitrogen and phosphorus losses in the surface runoff were higher from NW compared to that of SW. The CW had similar nutrient losses compared to the NW with slight differences. It can be concluded that maintaining a setback distance can help in improving the environmental quality as well as managing the agricultural wastes during the winter months.

A quantitative microbial risk assessment model for total coliforms and E. coli in surface runoff following application of biosolids to grassland

In Ireland, the land application of biosolids is the preferred option of disposing of municipal sewage waste. Biosolids provide nutrients in the form of nitrogen, phosphorus, potassium and increases organic matter. It is also an economic way for a country to dispose of its municipal waste. However, biosolids may potentially contain a wide range of pathogens, and following rainfall events, may be transported in surface runoff and pose a potential risk to human health. Thus, a quantitative risk assessment model was developed to estimate potential pathogens in surface water and the environmental fate of the pathogens following dilution, residence time in a stream, die-off rate, drinking water treatment and human exposure. Surface runoff water quality data was provided by project partners. Three types of biosolids, anaerobically digested (AD), lime stabilised (LS), and thermally dried (TD)) were applied on micro plots. Rainfall was simulated at three time intervals (24, 48 and 360 h) following land application. It was assumed that this water entered a nearby stream and was directly abstracted for drinking water. Consumption data for drinking water and body weight was obtained from an Irish study and assigned distributions. Two dose response models for probability of illness were considered for total and faecal coliform exposure incorporating two different exposure scenarios (healthy populations and immuno-compromised populations). The simulated annual risk of illness for healthy populations was below the US EPA and World Health Organisation tolerable level of risk (10−4 and 10−6, respectively). However, immuno-compromised populations may still be at risk as levels were greater than the tolerable level of risk for that subpopulation. The sensitivity analysis highlighted the importance of residence time in a stream on the bacterial die-off rate.

A quantitative risk assessment for metals in surface water following the application of biosolids to grassland

During episodic rainfall events, land application of treated municipal sludge (‘biosolids’) may give rise to surface runoff of metals, which may be potentially harmful to human health if not fully treated in a water treatment plant (WTP). This study used surface runoff water quality data generated from a field-scale study in which three types of biosolids (anaerobically digested (AD), lime stabilised (LS), and thermally dried (TD)) were spread on micro-plots of land and subjected to three rainfall events at time intervals of 24, 48 and 360h following application. Making the assumption that this water directly entered abstraction waters for a WTP without any grassed buffer zone being present, accounting for stream dilution, and modelling various performance scenarios within the WTP, the aim of this research was to conduct a human health risk assessment of metals (Cu, Ni, Pb, Zn, Cd and Cr), which may still be present in drinking water after the WTP. Different dose-response relationships were characterised for the different metals with reference to the lifetime average daily dose (LADD) and the Hazard Quotient (HQ). The results for the LADD show that child exposure concentrations were highest for Cu when the measured surface runoff concentrations from the LS biosolids treatment were used as input into the model. The results for the HQ showed that of all the scenarios considered, Cu had the highest HQ for children. However, values were below the threshold value of risk (HQ<0.01 - no existing risk). Under the conditions monitored, metal concentrations in the biosolids applied to grassland were not considered to result in a risk to human health in surface water systems.

Temporal Variation of Sedimentation from Surface Runoff from Agricultural Land Uses in Sondu-Miriu Basin, Kenya

The study was conducted at two sites in Sondu-Miriu basin between November 2010 and May 2011, using runoff plots to determine the temporal variation of sediments, organic matter, solids and surface runoff from agricultural land uses. At Kabianga, lower sediment and surface runoff values were observed in natural vegetation while runoff was generally higher in April-May 2011 wet season. While there were significantly lower sediment concentrations and higher runoff volumes, organic content was significantly lower in April-May 2011. Principal Components Analysis correlated surface runoff and erosion to seasonal land use activities particularly during wet seasons depicting the influence of hydrology on surface runoff pollution. In Sondu, sediment concentrations were lower in natural vegetation. Surface runoff was higher in January-March 2011 in natural vegetation but lowest in cropped systems during April-May, 2011. Solids and organic matter were significantly higher in November-December 2011 (p<0.05). PCA linked surface runoff quality to changes in hydrological periods which influenced the nature, quality and quantity of material transported via surface runoff. PCA for River Sondu-Miriu at Kabianga suggested ionic pollution by dissolved substances (r = 0.77-0.99, p<0.01) and sediment load introduced via surface runoff during wet seasons. In Sondu, PCA associated ionic pollutants and sediment loads to hydrological changes relating to seasonality (r = -0.75-0.99, p<0.01). Temporal variations in surface runoff volumes, water quality and sediment load correlated significantly to hydroperiods in Sondu-Miriu basin. Hydrological changes impacted highly in agricultural land uses with reduced land cover which increased surface runoff accompanied by higher sediment loads.

Update on the Effects of a Sierran Wildfire on Surface Runoff Water Quality

Wildfire has been shown to increase the short-term (1-3 yr) mobilization of mineral N and P in forest ecosystems of the Sierra Nevada Mountains and Lake Tahoe Basin. The ensuing effects on tributary and lake water quality are uncertain. The purpose of this investigation was to assess the impacts on runoff water quality over an intermediate time frame of 5 yr (2002-2007) after a wildfire event. Our design included fixed plots randomly placed within burned and unburned areas. Because each plot was sampled repeatedly during the study, we treated plots as repeated random effects in the analysis. We used a mixed model approach to analyze nutrient runoff concentrations and load for NH-N, NON and P in phosphate form (designated as ortho P or PO-P) where treatment (unburned vs. burned), time (pre-wildfire, post-wildfire year 1, year 2, etc.), and their interaction were fixed effects. Concentrations and loads of mineral N and P were higher in runoff from the burned areas immediately after wildfire. Because high water years may also contribute to higher runoff nutrient concentrations and loading, a wildfire followed by a high water year within the first season after a wildfire would likely have a much greater impact on runoff (and hence tributary) water quality than a wildfire followed by a low runoff water year.

Impact of mixed land-use practices on the microbial water quality in a subtropical coastal watershed

Surface runoff water is an important non-point source of fecal pollution to downstream water; however, there is a lack of systematic studies on the microbial quality of surface runoff water from watersheds with mixed land uses. In this study water samples from 12 surface runoff holding water bodies (SRW), which collected runoff from various patterns of land use within the St. Lucie watershed along the southeastern coastline of Florida, were collected monthly for 22months. The concentration of fecal indicator bacteria (FIB) and frequency of detection of Salmonella and host specific markers (HF183, CF128, CF193, and HS-esp) were determined, and their associations with land use, rainfall, and water physico-chemical parameters were investigated. Higher FIB concentrations were observed from urban land and cattle ranch sites. Within the same primary land use pattern, different sub-patterns did not have the same level of FIB: golf communities contributed less to fecal pollution than residential areas, and plant nursery sites contained relative higher FIB concentrations than other agricultural sites. Salmonella, CF128, and CF193 markers were more frequently detected from the cattle ranch sites. In contrast the frequency of detecting human specific markers (HF183 and HS-esp) was much higher in residential sites. Rainfall positively affected the concentration of FIB and occurrence of Salmonella, possibly by providing more inputs or mobilizing the sources from sediments. Water temperature, dissolved organic carbon (DOC), and nutrient levels were positively correlated with FIB concentrations and occurrence in SRW, possibly by promoting their growth and survival. This study indicated the need for site specific mitigation strategies to improve SRW and downstream water quality.

Roadway Runoff Water Quality from Milled and Unaltered Surfaces during Convective Storms

Time series of total suspended solids, and total and dissolved copper, zinc, and lead concentrations were compared between milled hot-mix asphalt (HMA) roadway sections (n=6) and unaltered HMA roadway sections (n=6). Milled and unaltered road surface runoff water quality parameter values were within the ranges reported previously for unaltered rural and urban roadways. Event mean concentrations of suspended solids and lead were greater for milled roadway surfaces than for unaltered surfaces. No differences in copper and zinc concentrations were observed between road treatments. Contaminant mobilization was flow-driven, with incomplete wash-off of roadway constituents during the short-duration convective storm events. Storm precipitation intensity was not an indicator of storm-water quality. The presence of lead in runoff from milled roadway sections in this study indicated a road side soil source of the solids resulting from overland flow from adjacent land surfaces onto the roadway. Future milling operat...

Water infiltration in urban soils and its effects on the quantity and quality of runoff

Urban soil characteristics, especially soil physical properties, are subject to dramatic changes due to compaction by intensive human activities, which may cause frequent flood events during the rainy seasons. The aim of this study was to explore the water infiltration characteristics of urban soils with different degrees of compaction and to determine the effects of infiltration on environmental problems in urban areas. Ten typical land use patterns with various vegetation and age were selected in Nanjing City, China to determine the infiltration rates by the dual-ring method. Three replicated sites were done in the same combined mode. At the same time, other soil physical and chemical properties that may affect infiltration rate were also determined. In addition, urban surface runoff coefficients were estimated according to final infiltrations and rain intensities in the different degrees of soil compaction. The quality of flood water from a strong rainstorm in a main road in Nanjing was analyzed. The final infiltration rates of urban soils were highly variable (from very slow to very fast). Low soil infiltration rates are related to many factors; however, urban soil compaction is the leading one. Infiltration rates decreased with an increase in the bulk density and with a reduction in the air-filled porosity. Thus, large amounts of macropores increase the infiltration rate and reduce surface runoff. Runoff coefficients of compacted soils with low infiltration rates were high, especially for extremely compacted soil. As a result, the prevalence of flooding is high in compacted soils, and the quality of surface runoff water is reduced during flooding events. The concentrations of NO 3 − -N, total nitrogen, molybdate-reactive phosphorus, total phosphors, and suspended material in urban surface runoff were significantly higher than those observed in forested or agricultural watersheds. In urban areas, low infiltration rates caused by soil compaction have negative effects on the eco-environment of the city and result in increased instantaneous flooding and poor surface water quality. Thus, to improve the eco-environment of urban areas, the amount of greenbelt soil must be increased and soil compaction must be reduced.

Surface Run-Off Water Quality from Agricultural Lands and Residential Areas

This study was conducted to characterize surface run-off water quality from sugar cane fields, pasturelands and residential areas, and to assess the effectiveness of best management practices (BMPs) in controlling non-point source pollution. From October 2002 to September 2005, the five-day biological oxygen demand (BOD5), total suspended solids (TSS), nitrate/nitrite-N (NO3/NO2-N), soluble reactive phosphate (SRP), total phosphorus (TP), total nitrogen (TN) and pH were determined in surface run-off water from two sugar cane fields, two pasturelands and two residential areas in south-western Louisiana. Faecal coliform counts were carried out on run-off samples from the two pasturelands. The BMPs implemented in one of the sugar cane fields included drop-pipe structures, nutrient management, reduced tillage and the application of herbicides to eliminate summer cultivations, while those implemented in one of the pasturelands included drop-pipe structures, cross-fencing, water points, nutrient management, improved forage planting and managed rotational grazing. Average TSS concentration in surface run-off from the sugar cane fields was significantly higher than the average TSS concentration in the surface run-off from the pastureland and residential areas. Average BOD5 concentrations in surface run-off from the sugar cane fields and pasturelands were significantly higher than the average BOD5 concentration in surface run-off from the residential site. Average TN and NO3/NO2-N concentrations in surface run-off from the sugar cane fields were significantly higher than the average concentration for the pasturelands and residential areas surface run-off. Average TP and SRP concentrations in surface run-off from the pasturelands were significantly higher than the average TP and SRP concentrations in surface run-off from the sugar cane fields and residential areas. The BOD5 was significantly positively correlated with TSS, TN, TP, SRP and NO3/NO2-N. Surface run-off from the sugar cane field with BMPs showed relatively lower median values of TN, TP, NO3/NO2-N and SRP and a slightly higher BOD5 value than the surface run-off from the sugar cane field without BMPs. Similarly, the surface run-off from pastureland with BMPs showed lower median values for TSS, TN and NO3/NO2-N than the surface run-off from pastureland without BMPs.

Assessment of the Effects of Poultry Litter on Surface Runoff Water Quality from Agricultural Lands

The use of pelletized poultry litter (PPL) as a substitute for inorganic fertilizers is increasingly being en-couraged in states like Delaware which have a considerable surplus of poultry litter. However, we know very little about the impacts of PPL on runoff water quality and whether it is an environmentally-sound and sus-tainable alternative to inorganic fertilizer. To address these questions we compared the exports of nutrients (NH4-N, NO3-N and PO4-P) and trace elements (As, Cu, and Zn) in surface runoff from agricultural plots receiving PPL, raw poultry litter (RPL), urea and no-fertilizer (control) treatments. The study was conducted on agricultural land located in Middletown, Delaware with corn as the cover crop. The experimental plots were 5 m wide and 12 m long with reduced tillage and no-tillage management practices. Sampling was con-ducted for six natural rainfall events from April through August 2008. Nutrient (NH4-N, NO3-N and PO4-P) exports from plots receiving PPL were less than those with urea or raw litter applications. While exports of trace elements from the PPL treatment exceeded those from urea, they were much lower than the corre-sponding exports from the RPL treatments. Mass exports of nutrients and trace elements were correlated with event size (rainfall amount) but were not correlated with timing of event (days since litter application). Results from this study suggest that the use of PPL in combination with no-tillage may provide an environ-mentally safe alternative to synthetic fertilizers.

Manual composite sampling in edge-of-field surface runoff for assessing nonpoint source pollution from agricultural lands and residential areas

While there are several surface water quality sampling techniques such as flow-interval, time-interval, and composite sampling, it is still a challenging task to select the appropriate sampling technique for edge-of-field surface runoff water quality monitoring. We hypothesized that manual composite sampling gives comparable results with discrete flow-paced sampling for edge-of-field surface runoff water quality. We collected discrete flow-paced and manual composite surface runoff water samples from sugarcane (<i>Saccharum officinarum</i> L.) fields, pasture lands, and residential areas from October 2002 to October 2003 and analyzed for total suspended solids (TSS), total combustible solids (TCS), five-day Biological Oxygen Demand, nitrate/nitrite-nitrogen (NO₃/NO₂-N), soluble reactive phosphate (SRP), total phosphorus (TP), total nitrogen (TN), and pH in the Vermilion-Teche River Basin in Southwestern Louisiana. Overall, compared to the flow-paced sampling, average five-day Biological Oxygen Demand, TSS, TCS, SRP, TP, NO₃/NO₂-N, and TN concentrations using composite sampling were lower by 4.3%, 8.1%, 8.2%, 9.5%, 4.1%, 36.8%, and 8.2%, respectively. As expected, the constituent concentrations with the flow-paced sampling and the composite sampling were significantly (α = 0.05) positively correlated. Although TSS, TCS, and SRP concentrations slightly declined with flow levels and TP, NO₃/NO₂-N, and TN concentrations showed a general trend of slight increase from 15,142 L (4,000 gal) to 227,125 L (60,000 gal), correlation analysis of the pooled dataset showed no significant correlation (α = 0.05) between flow level and water quality constituents in this study. Similarly, no significant differences were found on event loads of TSS, TCS, SRP, TP, NO₃/NO₂-N, and TN calculated from flow-paced sampling and manual composite sampling strategies. Therefore, manual composite sampling is suggested over flow-paced sampling for edge-of-field water quality monitoring in agricultural lands and residential areas because, while producing comparable results, it reduces the cost of laboratory determination.