Quantifying the effects of alternative surface inlet protection strategies on water quality

Subsurface drainage systems with surface inlets are widely used to divert water in crop producing areas, but pose problems because they can allow unfiltered, sediment-laden water to travel quickly to other waterways. The project tested several modest, uncomplicated inlet protection practices with potential to keep nutrient and sediment flows in check

Experimental Watersheds at Coshocton, Ohio, USA: Experiences and Establishing New Experimental Watersheds

The North Appalachian Experimental Watershed (NAEW) in Ohio was established in 1935 to improve economical and physical sustainability in agriculture. The objectives were to test management practices on small watersheds, investigate scaling of runoff and erosion to larger areas, and research ways to extrapolate the results to ungauged areas. The facility was equipped with a permanent infrastructure consisting of runoff stations and rain gauges for watersheds ranging in size from 0.26 to 1854 ha, and 11 large (0.008 ha) monolith lysimeters to investigate small-scale water balances, all in an area greater than 2000 ha. After about 1970, the NAEW was reduced in size to 425 ha consisting of mostly small watersheds (“test beds”) ranging in size from 0.26 to 3.07 ha. The NAEW was in operation for approximately 81 years generating a long record of runoff and other data for various watersheds, and closed in 2015. A wide variety of experiments were conducted on the NAEW with many high-impact accomplishments and addressing emerging issues that founders never envisioned. Nearly, 500 publications came from investigations during the history of the facility, and insights for establishing new experimental watersheds are presented covering site selection, funding, site specificity, extrapolation of results, generation of runoff in different physiographic regions, collaboration, off-site investigations, and instrumentation. The research on water quality was added to the research objectives in the 1970s, including nutrients (nitrogen and phosphorus) and pesticides in surface runoff and subsurface flow

All Washed Out? Foliar Nutrient Resorption and Leaching in Senescing Switchgrass

Ideal bioenergy feedstocks are low in nutrients that act as anti-quality factors during conversion processes. Research has shown that delaying harvest of temperate perennial grasses until late winter reduces nutrient content, primarily due to end-season resorption, but also indicates a role for foliar nutrient leaching. While end-season resorption has been estimated, foliar nutrient leaching has not, and is a factor that could refine harvest recommendations. Additionally, establishing a baseline of mineral loss during switchgrass senescence will improve our understanding of leaf-level nutrient resorption. Therefore, we applied simulated rainfall to replicated (n = 5) plots within a previously established switchgrass stand to determine if heavy precipitation can induce nutrient leaching in senescing, unharvested foliage. Hour-long simulated rainfalls of ∼120 mm were applied every 2 weeks from early September to a killing frost in 2014 and 2015. Leaf samples were taken from the upper and lower canopy before and after simulated rainfalls and from no-rain controls and analyzed for elemental N, P, K, S, Mg, and Ca. Nutrient resorption estimates ranged from 33 to 82% in control plots. Comparison of rainfall plots to controls indicated that lower canopy leaves, upon reaching ≥50% senescence, were slightly susceptible to foliar nutrient leaching, with losses ranging from 0.3 to 2.8 g kg−1dry matter for K, P, and Mg. Nitrogen, Ca, and S were not susceptible to foliar leaching. Although statistically significant (P ≤ 0.05), these values suggested that foliar leaching was not a strong driver of nutrient loss during senescence

Rational Polynomial Functions for Modeling E. coli and Bromide Breakthrough

Fecal bacteria peak concentrations and breakthrough times as affected by preferential flow to subsurface (tile) drainage systems following irrigation or rainfall are important when assessing the risk of contamination. Process-based, convective-dispersive modeling of microbial transport through preferential flow has been conducted. Likewise, regression modeling has been used to study solute transport (e.g., nitrate) under agricultural systems and can have advantages over process-based modeling, such as fewer or easier to determine parameters and easier determination of confidence intervals. However, empirical models (e.g., regression) have only rarely been used to investigate microbial transport. In addition, the selection of time response curves to empirically model simple, right skewed, single breakthrough events from field or laboratory data is generally an arbitrary choice and often considers only conventional distribution-shaped response curves, such as lognormal distributions. In this study, we evaluate four rational polynomial functions for modeling bromide and E. coli data from a single breakthrough event from a tile-drained field near Nashua, Iowa. Bromide and liquid swine manure were applied to the plot immediately prior to 42 mm of overhead sprinkler irrigation. E. coli and bromide concentrations were determined in subsurface drainage water samples collected for the next 24 h. Nonlinear iteratively re-weighted least squares regression procedures were used to model the breakthrough data. The maximum event value, time of occurrence, and event total were estimated from the parameters for each model. Selection of the best model was based on multiple performance criteria. A simple rational polynomial with a linear factor in the numerator and quadratic form in the denominator was the overall best choice for E. coli (R² = 0.92). A related fractional order form also known as the Gunary model was the best choice for bromide (R² = 0.93). In comparison, the more commonly assumed lognormal distribution described only 78% of the variation in E. coli and 68% of the variation in bromide, with a weighted mean square error 3.0 to 4.6 times larger than each selected rational polynomial model. In this experiment, the chosen models clearly tracked E. coli and bromide distribution better than the lognormal model

Dew-worms in white nights: High-latitude light constrains earthworm (Lumbricus terrestris) behaviour at the soil surface

Soil is an effective barrier to light penetration that limits the direct influence of light on belowground organisms. Variation in aboveground light conditions, however, is important to soil-dwelling animals that are periodically active on the soil surface. A prime example is the earthworm Lumbricus terrestris L. (the dew-worm), an ecosystem engineer that emerges nocturnally on the soil surface. In the summer, the northernmost populations of L. terrestris are exposed to a time interval with no daily dark period. During a two-week period preceding the summer solstice, we studied the constraints that boreal night illumination imposes on L. terrestris surface activity by comparing their behaviour under ambient light with artificially-induced darkness. Looking for evidence of geographical divergence in light response, we compared the behaviour of native L. terrestris (Jokioinen, S–W Finland; 60°48′N) with two markedly more southern populations, from Preston (Lancashire, UK; 53°47′N) and Coshocton (Ohio, USA; 40°22′N) where the nights have a period of darkness throughout the year (total latitudinal range ca. 2300 km). Under ambient light conditions, L. terrestris emergence on the soil surface was diminished by half compared with the darkened treatment and it peaked at the darkest period of the night. Also mating rate decreased considerably under ambient light. The native dew-worms were generally the most active under ambient light. They emerged earlier in the evening and ceased their activity later in the morning than dew-worms from the two more southerly populations. The differences in behaviour were, however, significant mainly between native and UK dew-worms. In the darkened treatment, the behaviour of the three earthworm origins did not differ. Under the experimental conditions light condition was the dominant environmental factor controlling surface activity, but elevated night-time air temperature and humidity also encouraged dew-worm emergence without discernible differences among geographical origins. Our results show, that in boreal summer, the high level of night illumination strongly limits soil-surface activity of dew-worms. Considering the important regulatory role of L. terrestris in many ecosystem processes, this can have significant corollaries in dew-worm impacts on the environment. Although evidence for geographical differentiation in behaviour was obtained, the results point to phenotypic flexibility in L. terrestris light response

Corn stover harvest increases herbicide movement to subsurface drains – Root Zone Water QualityModel simulations

BACKGROUND: Crop residue removal for bioenergy production can alter soil hydrologic properties and the movement of agrochemicals to subsurface drains. The Root Zone Water Quality Model (RZWQM), previously calibrated using measured flow and atrazine concentrations in drainage from a 0.4 ha chisel-tilled plot, was used to investigate effects of 50 and 100% corn (Zea mays L.) stover harvest and the accompanying reductions in soil crust hydraulic conductivity and total macroporosity on transport of atrazine, metolachlor andmetolachlor oxanilic acid (OXA). RESULTS: The model accurately simulated field-measured metolachlor transport in drainage. A 3 year simulation indicated that 50% residue removal reduced subsurface drainage by 31% and increased atrazine and metolachlor transport in drainage 4–5-fold when surface crust conductivity and macroporosity were reduced by 25%. Based on itsmeasured sorption coefficient, approximately twofold reductions in OXA losses were simulated with residue removal. CONCLUSION: The RZWQM indicated that, if corn stover harvest reduces crust conductivity and soil macroporosity, losses of atrazine andmetolachlor in subsurface drainagewill increase owing to reduced sorption related tomorewatermoving through fewermacropores. Losses of the metolachlor degradation product OXA will decrease as a result of themore rapid movement of the parent compound into the soil