Shree K. Giri

Evaluation of Two Langmuir Models for Phosphorus Sorption of Phosphorus-Enriched Soils in New York for Environmental Applications

The phosphorus (P) sorption isotherm experiment is a widely used tool in environmental applications for assessing soils vulnerability to P loss to runoff or drainage. The sorbed legacy P (S0) (i.e., the P retained in soils from previous P applications) participates in sorption processes but cannot readily be determined in a sorption experiment. Thus, it is important to accurately estimate S0 for P-enriched soils (e.g., the soils that heavily receive fertilizer, manure, farm wastewater, or sewage sludge). Two curve-fitting procedures (i.e., one-step method and two-step method) with Langmuir models have been used to estimate S0 and other sorption parameters, including the P sorption maxima (Smax), the bonding energy constant (k), and the zero-sorption equilibrium concentration (EPC0). This study evaluated these two methods on 16 samples of Langford, Volusia, and Mardin channery silt loam soils at surface (0-8 cm) and subsurface (61-91 cm) in New York. The results indicate that the two methods agreed well in estimating P sorption maxima, and the estimates of k were close. The S0 estimates by the two methods had a good agreement for surface soils but a poor agreement for subsurface soils, which may be of little concern because of small S0 of subsurface soils. Although the one-step method yielded greater EPC0 estimates, the EPC0 estimates by the two methods had an excellent linear correlation for P-enriched surface soils, suggesting that both methods could work equally if only the relative magnitudes of EPC0 among soils are needed. Overall, both methods are acceptable to fit the Langmuir isotherms.

Selenium promotes sulfur accumulation and plant growth in wheat (Triticum aestivum)

Selenium (Se) is an essential micronutrient for animals and humans and a target for biofortification in crops. Sulfur (S) is a crucial nutrient for plant growth. To gain better understanding of Se and S nutrition and interaction in plants, the effects of Se dosages and forms on plant growth as well as on S level in seven wheat lines were examined. Low dosages of both selenate and selenite supplements were found to enhance wheat shoot biomass and show no inhibitory effect on grain production. The stimulation on plant growth was correlated with increased APX antioxidant enzyme activity. Se forms were found to exert different effects on S metabolism in wheat plants. Selenate treatment promoted S accumulation, which was not observed with selenite supplement. An over threefold increase of S levels following selenate treatment at low dosages was observed in shoots of all wheat lines. Analysis of the sulfate transporter gene expression revealed an increased transcription of SULTR1;1, SULTR1;3 and SULTR4;1 in roots following 10 μM Na2 SeO4 treatment. Mass spectrometry-based targeted protein quantification confirmed the gene expression results and showed enhanced protein levels. The results suggest that Se treatment mimics S deficiency to activate specific sulfate transporter expression to stimulate S uptake, resulting in the selenate-induced S accumulation. This study supports that plant growth and nutrition benefit from low dosages of Se fertilization and provides information on the basis underlying Se-induced S accumulation in plants.

Can pore-clogging by ash explain post-fire runoff?

Ash plays an important role in controlling runoff and erosion processes after wildfire and has frequently been hypothesised to clog soil pores and reduce infiltration. Yet evidence for clogging is incomplete, as research has focussed on identifying the presence of ash in soil; the actual flow processes remain unknown. We conducted laboratory infiltration experiments coupled with microscope observations in pure sands, saturated hydraulic conductivity analysis, and interaction energy calculations, to test whether ash can clog pores (i.e. block pores such that infiltration is hampered and ponding occurs). Although results confirmed previous observations of ash washing into pores, clogging was not observed in the pure sands tested, nor were conditions found for which this does occur. Clogging by means of strong attachment of ash to sand was deemed unlikely given the negative surface charge of the two materials. Ponding due to washing in of ash was also considered improbable given the high saturated conductivity of pure ash and ash–sand mixtures. This first mechanistic step towards analysing ash transport and attachment processes in field soils therefore suggests that pore clogging by ash is unlikely to occur in sands. Discussion is provided on other mechanisms by which ash can affect post-fire hydrology.

Field Performance of Denitrifying Bioreactors in the Northeastern United States

Abstract. Denitrifying bioreactors are increasingly being used for treating nitrate-rich agricultural drainage water. Filled with carbon substrates, often woodchips, denitrifying bioreactors provide a favorable environment for denitrification under anaerobic conditions. Despite several installations across the Midwestern United States, there have not been any field studies demonstrating and investigating the efficiency of denitrifying bioreactors in the northeastern United States which has cold winters and numerous relatively shallow sloping soils over glacial till. Thus, this study investigates the seasonal efficiency of denitrifying bioreactors in different landscapes throughout two years of application. Paired bioreactors (one filled with woodchips only and one filled with woodchips amended with biochar) were installed at three sites in upstate New York. Flow rate, temperature, nitrate (NO 3 –N), and dissolved organic carbon (DOC) were measured in the inflow and outflow water of the bioreactors. Results show the average reduction in NO 3 –N concentrations in the bioreactors ranged from 38 to 68%, with average removal rates ranging from 4 to 15 g N m -3 d -1 . The removal efficiency improved with increasing temperature, however, sporadic high flow events temporarily lowered NO 3 –N removal for a period afterwards. Bioreactors in the northeastern United States have potential to remove NO 3 –N from agricultural drains when soil temperatures are above 5°C. Below this temperature, DOC release and NO 3 –N removal are not optimal.