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Miscanthus is a productive perennial grass that is suitable as a bioenergy crop in "marginal" lands (e.g., eroded soils) with low water holding capacity. However, little is known about the impact of miscanthus residues on vapor transport and soil water budgets. Laboratory experiments were conducted to measure the vapor conductance through miscanthus residues and its effect on soil water evaporation. The ranges for the length, width, and thickness of residue elements were 0.5–9.0, 0.1–0.5, and 0.1–0.5 cm, respectively. Average residue areal, bulk, and skeletal densities were 0.88 kg m−2, 24 kg m−3, and 1006 kg m−3, respectively, giving a porosity of 0.98 m3 m−3. A power function described the decrease in conductance with increasing residue load. The corresponding conductance for a residue load of 0.88 kg m−2 was 1.6 mm s−1. During the first days of a 60‐day drying experiment, cumulative evaporation showed logarithmic decay with increasing residue load. Conversely, cumulative evaporation during the last days of the study showed little difference between treatments. Measurements indicated that there is a "critical" residue load (∼1.0 kg m−2) beyond which evaporation no longer decreases appreciably when the soil is under the stage 1 evaporation regime. Results suggest that soil water conservation in marginal lands may be accomplished by maintaining moderate amounts of bioenergy grass residue covering the soil. Determining "critical" loads for different residue types is a knowledge gap that merits further research. Core Ideas: Residues had skeletal density of 1006 kg m−3 and porosity of 0.98 m3 m−3.Residue conductance to water vapor decreased with increased areal density.Evaporation decreased with increased residue load during the first 15 days of drying.After 60 days of drying, treatments showed little difference in cumulative evaporation. [ABSTRACT FROM AUTHOR]

The most common method for in situ measurement of saturated hydraulic conductivity (Ksat) of the vadose zone is the constant head well permeameter method. Our general objective is to provide an empirical method for determining volume of water required for measuring Ksat using this procedure. For one-dimensional infiltration, steady state reaches as time (t) → ∞. For three-dimensional water flow from a cylindrical hole under a constant depth of water, however, steady state reaches rather quickly when a saturated bulb forms around the hole. To reach a quasi-steady state for measuring Ksat, we assume an adequate volume of water is needed to form the saturated bulb around the hole and increase the water content outside of the saturated bulb within a bulb-shaped volume of soil, hereafter, referred to as wetted soil volume. We determined the dimensions of the saturated bulb using the Glover model that is used for calculating Ksat. We then used the values to determine the volume of the saturated and wetted bulbs around the hole. The volume of water needed to reach a quasi-steady state depends on the difference between the soil saturated and antecedent water content (Δθ). Based on our analysis, between 2 and 5 L of water is needed to measure Ksat when Δθ varies between 0.1 and 0.4 m3 m−3, respectively. [ABSTRACT FROM AUTHOR]

There has been widespread interest in using compost to improve the hydrologic functions of degraded soils at construction sites for reducing runoff and increasing infiltration. The objective of this study was to determine the effects of compost amendment rate on saturated hydraulic conductivity (Ks) and water retention in order to identify target compost rates for enhancing soil hydrologic functions. Samples were prepared with three soil textures (sandy loam, silt loam, and sandy clay loam), amended with compost at 0%, 10%, 20%, 30%, 40%, and 50%. All soils were tested at a porosity of 0.5 m3/m3, and the sandy loam was further tested at high (0.55 m3/m3) and low (0.4 m3/m3) porosities. The Ks and water retention data were then used to model infiltration with HYDRUS‐1D. With increasing compost amendment rate, Ks and water retention of the mixtures generally increased at the medium porosity level, with more compost needed in heavier soils. As porosity decreased in the sandy loam soil, the amount of compost needed to improve Ks rose from 20% to 50%. Water distribution in pore fractions (gravitational, plant‐available, and unavailable water) depended on texture, with only the highest compost rates increasing plant‐available water in one soil. Results suggest soil texture should be taken into consideration when choosing a compost rate in order to achieve soil improvement goals. Hydrologic benefits may be limited even at a high rate of compost amendment if soil is compacted. [ABSTRACT FROM AUTHOR]

A challenging aspect of educating secondary students is integrating complex scientific concepts related to modern research topics into lesson plans that students can relate to and understand at a basic level. One method of encouraging the achievement of learning outcomes is to use real-world applications and current research to fuel student interest and excitement. This approach can be reinforced by use of demonstrations, which spur in-class discussions and can be integrated into out-of-class assignments. To attempt to develop improved curricular materials, a workshop was organized that combined the teaching expertise of a number of secondary school teachers with the research experience of a number of scientific experts to produce lesson plans centered around trace metal cycling and toxicity. These areas are important current research topics but are often neglected in pre-college education. A significant portion of the material presented at the workshop involved the use of visual and hands-on demonstrations of chemical principles that relate to geochemical processes that impact the environment. Materials provided to the instructors included suggestions for hands-on, interactive activities for use in the classroom, as well as teacher-administered demonstrations that would explore the physical and chemical bases of the principles being discussed. The participants all expressed positive feedback in terms of their confidence to administer student-centered lesson plans on the topic of biogeochemistry and their personal understanding of the subject matter, and a number of lesson plans were developed for use by the teachers to integrate the scientific principles discussed in the body of their courses. (Contains 2 tables and 4 figures.)

Turfgrass managers have suspected that runoff-independent movement of herbicides and fertilizers is partially responsible for uneven turfgrass quality in sloped areas. We hypothesized that subsurface lateral solute transport might explain this phenomenon especially in areas with abrupt textural changes between surface and subsurface horizons. A study was conducted to track solute transport using bromide (Br−), a conservative tracer, as a proxy of turfgrass soil inputs. Field data confirmed the subsurface lateral movement of Br− following the soil slope direction, which advanced along the boundary between soil horizons over time. A model based on field data indicated that subsurface lateral movement is a mechanism that can transport fertilizers and herbicides away from the application area after they have been incorporated within the soil, and those solutes could accumulate and resurface downslope. Our results demonstrate that subsurface lateral transport of solutes, commonly ignored in risk assessment, can be an important process for off-target movement of fertilizers and pesticides within soils and turfgrass systems in sloped urban and recreational landscapes. [ABSTRACT FROM AUTHOR]

Soil particle density (ρs) is often assumed as 2.65 g cm−3 (density of quartz). The objectives of this study were to compare the use of different gases for determining ρs in a gas pycnometer and relate measured ρs to soil particle size distributions. The ρs of 36 natural soil samples representing 12 USDA textural classes, fine glass beads, crushed granite rock, kaolinite, and bentonite were measured by a commercial gas pycnometer using He, N2, and dry air. The ρs of 30 of the soil samples, glass beads, and crushed rock were also determined with a water pycnometer. The ρs of 36 soil samples determined by He and 30 samples determined by water had narrow ranges with averages of 2.65 and 2.59 g cm−3, respectively. The ρs determined by air and N2 had much wider ranges with averages of 2.93 and 2.97 g cm−3, respectively. There was a near 1:1 relationship between ρs of all samples determined by air and N2 with a highly significant (p <.001) correlation coefficient (r =.99). The average ratio of ρs determined by He and water was 1.03, but the correlation coefficient for their relationship was only.416. Although the relationship between ρs determined by He and either air or N2 was relatively strong (r <.61), the regression coefficient was <.17. There was a strong relationship between soil clay content and ρs determined by N2 or air but a weaker, yet statistically significant (p <.05) relationship when using He. Core Ideas: Average particle density of soils belonging to 12 textural classes determined by helium was 2.65 g cm−3.Average particle density measured by air and nitrogen were 2.93 and 2.97 g cm‐3, respectively.Helium, nitrogen, or air can be used to measure particle density of coarse‐textured soils.Only helium should be used to measure particle density of medium‐ and fine‐textured soils. [ABSTRACT FROM AUTHOR]

Infiltration rate measurements are used to assess soil health and develop land management practices to address runoff from precipitation and irrigation. Differences in observed infiltration rates determined by available methods can be attributed to both the technique and soil property differences. The primary objective of this study was to compare two methods for measuring steady infiltration rate: the Cornell sprinkle infiltrometer (single‐ring) method (CSI), and the double‐ring infiltrometer method (DRI). Measurements were made at four sites using four replications of 13 sets of conditions (52 total paired measurements). The relationship between CSI and DRI measurements was significant (p <.001) and strong (R2 =.71). For 8 of 13 conditions, there was no difference between CSI and DRI steady infiltration rates. Variability in measurements was high (CVs ranged from 0.04 to 1.18) but similar for both methods. Both CSI and DRI results were strongly related to saturated hydraulic conductivity of the surface soil layer determined using a laboratory constant head method on intact soil cores. Overall, results suggest that estimates of steady infiltration rate determined by the CSI and standard DRI methods are comparable. Core Ideas: Cornell sprinkle and double‐ring infiltrometer measurements were compared.Results for the methods were strongly related and similar over a range of conditions.Both methods had large variability in replicate infiltration measurements.Infiltration rates were strongly related to surface saturated hydraulic conductivity. [ABSTRACT FROM AUTHOR]

Featured Application: Results of this study can be used by health authorities to set limits on the thickness of saprolite material needed below on-site septic system drainfields in order to remove E. coli from home sewage. Results will also be of interest to field personnel evaluating sites for on-site wastewater disposal. Saprolite, weathered bedrock, is being used to dispose of domestic sewage through septic system drainfields, but the thickness of saprolite needed to remove biological contaminants is unknown for most saprolites. This study developed and tested a simple method for estimating the thickness of saprolite needed below septic drainlines to filter E. coli from wastewater using estimates of the volume of pores that are smaller than the length of the coliform (≤10 μm). Particle size distribution (texture) and water retention data were obtained for 12 different saprolites from the Piedmont and Mountain regions of North Carolina (N.C.). Saprolite textures ranged from clay loam to coarse sand. The volume of pores with diameters ≤10 μm were determined by water retention measurements for each saprolite. The data were used in an equation to estimate the saprolite thickness needed to filter E. coli. The estimated saprolite thicknesses ranged from 36 cm in the clay loam to 113 cm for the coarse sand. The average thickness across all samples was 58 cm. Saprolite thickness estimates increased as silt percentage decreased and as sand percentage and in situ saturated hydraulic conductivity increased. Silt percentage may be most useful for estimating appropriate saprolite thicknesses in the field. [ABSTRACT FROM AUTHOR]

Soil texture is known to affect soil organic C (SOC) concentration and microbial activity, but these relationships are not always straightforward. We characterized total, mineral-associated and mineralizable C fractions along a gradient of soil texture within a flood plain field in the Coastal Plain region of North Carolina. Soil was collected from 0- to 5-, 5-to 15- and 15- to 30-cm depth intervals at 204 locations within a 7-ha area. Samples were analyzed for soil particle size distribution, specific surface area (SSA), oxalate-extractable Al and Fe to estimate short-range-ordered (i.e., poorly crystalline) oxyhydroxides and soil C fractions. Overall, relationships among soil C fractions, textural classes and depths were complex. Both SOC (0.4-13.9 g kg-1 soil) and mineral-associated organic C (0-12 g kg-1 soil) increased as soil clay concentration increased (73-430 g kg-1 soil), but having two distinct slopes in each relationship with an inflection point of ∼150 g clay kg-1 soil at 0 to 5 and 5 to 15 cm and an inflection point of ∼250 g clay kg-1 soil at 15 to 30 cm. As clay concentration increased, SSA (12-76 m2 g-1 soil) and oxalateextractable Fe (0.45-5.9 g kg-1 soil) also increased. A weaker relationship was observed between oxalate-extractable Al (0.38-1.5 g kg-1 soil) and either SSA or mineral-associated organic C. Mineralizable C increased with increasing clay concentration up until 143 ± 3, 152 ± 5, and 161 ± 11 g kg-1 (0-5, 5-15 and 15 -30 cm, respectively), but decreased (0-5 and 5-15 cm) or stayed constant (15-30 cm) at higher clay concentrations. On the basis of untested observations, we surmise that binding of C to oxalate-extractable Fe contributed to the accumulation of SOC and suppression of mineralizable C as the clay concentration increased. These results suggest that complex soil texture- physicochemical interactions underlie the inherent fertility of floodplain soils. [ABSTRACT FROM AUTHOR]

Polyacrylamide (PAM) has been demonstrated to reduce erosion under many conditions, but less is known about the effects of its application method on erosion and concentrations in the runoff water. A rainfall simulation study was conducted to evaluate the performance of an excelsior erosion control blanket (cover) and two PAM application methods. The treatments were (i) no cover + no PAM (control), (ii) cover + no PAM, (iii) cover + granular PAM (GPAM), and (iv) cover + dissolved PAM (DPAM) applied to soil packed in wooden runoff boxes. The GPAM or DPAM (500 mg L-1) was surface-applied at a rate of 30 kg ha-1 1 d before rainfall simulation. Rainfall was applied at 83 mm h-1 for 50 min and then repeated for another 20 min after a 30-min rest period. Runoff samples were analyzed for volume, turbidity in nephelometric turbidity units (NTU), total suspended solids (TSS), sediment particle size distribution, and PAM concentration. The cover alone reduced turbidity and TSS in runoff by >60% compared with the control (2315 NTU, 2777 mg TSS L-1). The PAM further reduced turbidity and TSS by >30% regardless of the application method. The median particle diameter of eroded sediments for PAM treatments was seven to nine times that of the control (12.4 µm). Loss of applied PAM in the runoff water (not sediment) was 19% for the GPAM treatment but only 2% for the DPAM treatment. Both GPAM and DPAM were effective at improving groundcover performance, but DPAM resulted in much less PAM loss. [ABSTRACT FROM AUTHOR]

A dry surface layer (DSL) forms when wet soil is exposed to the sun; development of a DSL coincides with a shift between surface and subsurface evaporation. There remains debate as to when this shift from surface to sub-surface evaporation occurs relative to the timing of the shift between potential and falling-rate evaporation. We performed a field experiment to investigate the onset of subsurface evaporation, development of the DSL, and the extent of the evaporation zone. Our objective was to determine the timing of the onset of subsurface evaporation with respect to decline in evaporation rates. We estimated total (surface plus subsurface) and subsurface soil evaporation rates using microlysimeter (water mass balance) and sensible heat balance (SHB) approaches, respectively, for a bare loamy sand soil under natural wetting and drying cycles. Results showed that the onset of subsurface evaporation coincided with the beginning of falling-rate evaporation. The evaporation zone extended into the subsurface when evaporation rates fell below the potential rate but were still as high as 50% of potential evaporation. Over a 5-d drying event, estimated evaporation zones were as deep as 4 to 9 mm, and the estimated DSL had a maximum depth of approximately 6 mm. A low soil water content-dependent albedo was observed when evaporation occurred at potential rates, but albedo increased as evaporation rates declined. Data from the intensive observation period suggest that this increase in albedo corresponded to formation of a DSL and onset of subsurface evaporation. Overall, surface drying and formation of a DSL appeared to be a dominant process for this coarse-texture soil exposed to ambient boundary conditions, even as evaporation rates remained relatively high (0.3 mm h-1). [ABSTRACT FROM AUTHOR]

Concerns over runoff water quality from agricultural lands and construction sites have led to the development of improved erosion control practices, including application of polyacrylamide (PAM). We developed a quick and reliable method for quantifying PAM in soil extracts at low carbon content by using a turbidimetric reagent, Hyamine 1622. Three high-molecular weight anionic PAMs differing in charge density (7, 20, and 50 mol%) and five water matrices, deionized (DI) water and extracts from four different soils, were used to construct PAM calibration curves by reacting PAM solutions with hyamine and measuring turbidity development from the PAM-hyamine complex. he PAM calibration curve with DI water showed a strong linear relationship (r² = 0.99), and the sensitivity (slope) of calibration curves increased with increasing PAM charge density with a detection limit of 0.4 to 0.9 mg L-1. Identical tests with soil extracts showed the sensitivity of the hyamine method was dependent on the properties of the soil extract, primarily organic carbon concentration. Although the method was effective in mineral soils, the highest charge density PAM yielded a more reliable linear relationship (r² > 0.97) and lowest detection limit (0.3 to 1.2 mg L-1), compared with those of the lower charge density PAMs (0.7 to 23 mg L-1). Our results suggest that the hyamine test could be an efficient method for quantifying PAM in environmental soil water samples as long as the organic carbon in the sample is low, such as in subsurface soil material often exposed at construction sites. [ABSTRACT FROM AUTHOR]

[i] Accurate quantification of energy and mass transfer during soil water evaporation is critical for improving understanding of the hydrologie cycle and for many environmental, agricultural, and engineering applications. Drying of soil under radiation boundary conditions results in formation of a dry surface layer (DSL), which is accompanied by a shift in the position of the latent heat sink from the surface to the subsurface. Detailed investigation of evaporative dynamics within this active near-surface zone has mostly been limited to modeling, with few measurements available to test models. Soil column studies were conducted to quantify nonisothermal subsurface evaporation profiles using a sensible heat balance (SHB) approach. Eleven-needle heat pulse probes were used to measure soil temperature and thermal property distributions at the millimeter scale in the near-surface soil. Depth-integrated SHB evaporation rates were compared with mass balance evaporation estimates under controlled laboratory conditions. The results show that the SHB method effectively measured total subsurface evaporation rates with only 0.01-0.03 mm h_l difference from mass balance estimates. The SHB approach also quantified millimeter-scale nonisothermal subsurface evaporation profiles over a drying event, which has not been previously possible. Thickness of the DSL was also examined using measured soil thermal conductivity distributions near the drying surface. Estimates of the DSL thickness were consistent with observed evaporation profile distributions from SHB. Estimated thickness of the DSL was further used to compute diffusive vapor flux. The diffusive vapor flux also closely matched both mass balance evaporation rates and subsurface evaporation rates estimated from SHB. [ABSTRACT FROM AUTHOR]

It is often assumed that soils are homogeneous when designing septic systems or modeling wastewater flow from their trenches. The main objective of this study was to assess water infiltration and movement from the trenches similar to the ones commonly used for on-site wastewater dispersal by septic systems. Four separate experiments, each using a small drainfield with four parallel trenches, were conducted at three sites with different soils. In two experiments the trenches were in the coarse-textured soil above a clayey Bt horizon. In the other two experiments the trenches were in the Bt horizon. For each experiment, 50 L of a solution containing potassium bromide and brilliant blue FCF (as a tracer dye) were applied once a day to each trench for 14 or 15 days. A sampling pit was dug perpendicular to the trenches after the tracer solution application, and the distribution of the tracer dye and Br- around the trenches on the two walls of the pit were assessed. Tracer solution infiltration from the trenches was not uniform in any of the experiments. Water flow in the Bt horizon was mainly through macropores. Further, water containing Br- and dye moved a substantial distance from the trenches through macropores when trenches were installed in the Bt horizon. When trenches were installed in the coarse-textured soil above the Bt horizon, most of the tracer solution moved away laterally from the drainfield through the zone above the Bt horizon. Overall, the results indicate that soil morphological properties and soil horizonations, as well as the nature of water movement from trenches must be considered when modeling water flow from septic system trenches or when designing septic system drainfields. [ABSTRACT FROM AUTHOR]

Mobile colloids in soils and their underlying strata may play an important role in the translocation of some contaminants from surface sources to groundwater. This study was conducted to evaluate the role of adsorbed natural organic matter (NOM) in the transport of submicron soil colloids through a commonly occurring type of saprolite in North Carolina. Intact saprolite columns from 4 m below the soil surface were used to study the movement of a conservative tracer (3H2O) and of soil colloids with and without adsorbed NOM. For natural (i.e., untreated) soil colloids having high colloidal stability due to adsorbed NOM, the filier efficiency of the saprolite decreased rapidly to zero as increasing amounts of colloids were deposited on the pore walls in the saprolite (blocking effect). Colloid breakthrough curves exhibited little tailing, indicating that colloid deposition was largely irreversible. The colloids were excluded from about 33% of the water-filled pore space, resulting in faster transport of colloids as compared to 3H2O. When the colloids were treated with NaOCl to remove adsorbed NOM, colloidal stability and mobility were strongly decreased. For these suspensions the filter efficiency of the columns increased as increasing amounts of colloids were deposited in the saprolite (filter ripening). After addition of small amounts of humic acid (1 mg L−1) to the NaOCl-treated colloids, they exhibited very similar transport behavior as the untreated soil colloids. Stabilization of colloids by NOM and the possible occurrence of the blocking effect or filter ripening must be considered in future models of subsurface colloid transport. [ABSTRACT FROM AUTHOR]

Lateral transport of waterborne contaminants is generally assumed to occur below the water table (WT), but recent laboratory studies have suggested that subsurface lateral solute transport could occur above the WT through the capillary fringe (CF). The objective of this study was to evaluate the horizontal transport of solutes in the CF and shallow groundwater (SGW). Two consecutive field experiments were conducted in a Leon sand (Aeric Alaquod) at a site with a shallow WT. In both experiments, a bromide (Br-) solution was applied to the bottom of an auger hole dug to within 10 cm above the projected CF. Movement of Br- in the subsurface was monitored by collecting CF and SGW samples using nests of tension samplers installed at radial distances of 60, 120, 220, and 320 cm from the application spot. Each nest of samplers contained a tension sampler at 45, 60, 75, 90, and 105 cm depth. Bromide transport was monitored for 58 d in the first experiment while the more detailed second experiment was conducted for 84 d. Peak Br- concentration generally occurred in the upper 60 cm of the soil where the CF was located for most of the experiment. The Br- plume that entered the CF moved horizontally in it until Br- was partially moved into the SGW by the fluctuating WT. In the second experiment, approximately 48% of the Br- detected in the CF at a distance of 320 cm from the application spot was still in the CF after 15 cm of rain through 59 d. [ABSTRACT FROM AUTHOR]

• DRAINMOD model was modified to simulate macropore flow using an empirical approach. • Modeling macropore flow improved daily drainage prediction for a drained field with cracking soil. • Predicted macropore flow contributed about 15% of annual subsurface drainage. • Modeling macropore flow is key for modeling phosphorus dynamics in drained cropland. Macropores are critical pathways through which water and pollutants can bypass the soil matrix and be rapidly transported to subsurface drains and freshwater bodies. We modified the DRAINMOD model to simulate macropore flow using a simple approach as part of developing the DRAINMOD-P model to simulate phosphorus dynamics in artificially drained agricultural lands. The Hagen-Poiseuille's law was used to estimate the flow capacity of macropores. When ponding depths on the soil surface are greater than Kirkham's depth, water is assumed to flow through macropores directly to tile drains without interaction with the soil matrix. In the modified model, macropore size is adjusted based on wet or dry conditions while connectivity is altered by tillage. The model was tested using a 4-year data set from a subsurface drained field in northwest Ohio. The soils at the field are classified as very poorly drained and are prone to desiccation cracking. The modified model predicted the daily and monthly subsurface drainage with average Nash-Sutcliffe efficiency (NSE) values of 0.48 and 0.59, respectively. The cumulative drainage over the 4-year simulation period was under-predicted by 8%. The new macropore component was able to capture about 75% of 60 peak drainage flow events. However, surface runoff was over-predicted for the entire study period. Annual water budgets using measured data (precipitation, subsurface drainage, and surface runoff) and model predictions (evapotranspiration, vertical seepage, and change in storage) were not balanced with an average annual imbalance of 6.4 cm. The lack of closure in the water balance suggests that errors may have occurred in field measurements, particularly, surface runoff. Overall, incorporating macropore flow into DRAINMOD improved predictions of daily drainage peaks and enabled the model to predict subsurface drainage flux contributed by macropore flow, which is critical for expanding DRAINMOD to simulate phosphorus transport in subsurface drained agricultural land. [ABSTRACT FROM AUTHOR]

Polyacrylamide (PAM) has been demonstrated to reduce erosion under many conditions, but less is known about the effects of its application method on erosion and concentrations in the runoff water. A rainfall simulation study was conducted to evaluate the performance of an excelsior erosion control blanket (cover) and two PAM application methods. The treatments were (i) no cover + no PAM (control), (ii) cover + no PAM, (iii) cover + granular PAM (GPAM), and (iv) cover + dissolved PAM (DPAM) applied to soil packed in wooden runoff boxes. The GPAM or DPAM (500 mg L) was surface-applied at a rate of 30 kg ha 1 d before rainfall simulation. Rainfall was applied at 83 mm h for 50 min and then repeated for another 20 min after a 30-min rest period. Runoff samples were analyzed for volume, turbidity in nephelometric turbidity units (NTU), total suspended solids (TSS), sediment particle size distribution, and PAM concentration. The cover alone reduced turbidity and TSS in runoff by >60% compared with the control (2315 NTU, 2777 mg TSS L). The PAM further reduced turbidity and TSS by >30% regardless of the application method. The median particle diameter of eroded sediments for PAM treatments was seven to nine times that of the control (12.4 μm). Loss of applied PAM in the runoff water (not sediment) was 19% for the GPAM treatment but only 2% for the DPAM treatment. Both GPAM and DPAM were effective at improving groundcover performance, but DPAM resulted in much less PAM loss., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Concerns over runoff water quality from agricultural lands and construction sites have led to the development of improved erosion control practices, including application of polyacrylamide (PAM). We developed a quick and reliable method for quantifying PAM in soil extracts at low carbon content by using a turbidimetric reagent, Hyamine 1622. Three high-molecular weight anionic PAMs differing in charge density (7, 20, and 50 mol%) and five water matrices, deionized (DI) water and extracts from four different soils, were used to construct PAM calibration curves by reacting PAM solutions with hyamine and measuring turbidity development from the PAM-hyamine complex. The PAM calibration curve with DI water showed a strong linear relationship ( = 0.99), and the sensitivity (slope) of calibration curves increased with increasing PAM charge density with a detection limit of 0.4 to 0.9 mg L. Identical tests with soil extracts showed the sensitivity of the hyamine method was dependent on the properties of the soil extract, primarily organic carbon concentration. Although the method was effective in mineral soils, the highest charge density PAM yielded a more reliable linear relationship ( > 0.97) and lowest detection limit (0.3 to 1.2 mg L), compared with those of the lower charge density PAMs (0.7 to 23 mg L). Our results suggest that the hyamine test could be an efficient method for quantifying PAM in environmental soil water samples as long as the organic carbon in the sample is low, such as in subsurface soil material often exposed at construction sites., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)