Reactions of nitrite with goethite and surface Fe(II)-goethite complexes.

Chemodenitrification-the abiotic (chemical) reduction of nitrite (NO2-) by iron (II)-plays an important role in nitrogen cycling due in part to this process serving as a source of nitrous oxide (N2O). Questions remain about the fate of NO2- in the presence of mineral surfaces formed during chemodenitrification, such as iron(III) (hydr) oxides, particularly relative to dissolved iron(II). In this study, stirred-batch kinetic experiments were conducted under anoxic conditions (to mimic iron(III)-reducing conditions) from pH 5.5-8 to investigate NO2- reactivity with goethite (FeOOH(s)) and Fe(II)-treated goethite using wet chemical and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Nitrite removal from solution by goethite was more rapid at pH 5.5 than at pH 7 and 8. Spectral changes upon nitrite adsorption imply an inner-sphere surface interaction (monodentate and bidentate) at pH 5.5 based on ATR-FTIR spectra of the nitrite-goethite interface over time. In iron(II)-amended experiments at pH 5.5 with high aqueous Fe(II) in equilibrium with goethite, nitrous oxide was generated, indicating that nitrite removal involved a combination of sorption and reduction processes. The presence of a surface complex resembling protonated nitrite (HONO) with an IR peak near ~1258 cm-1 was observed in goethite-only and iron(II)-goethite experiments, with a greater abundance of this species observed in the latter treatment. These results might help explain gaseous losses of nitrogen where nitrite and iron(II)/goethite coexist, with implications for nutrient cycling and release of atmospheric air pollutants.

Potential nitrification in alum-treated soil slurries amended with poultry manure.

Alum is used to reduce environmental pollutants in poultry production. Alum decreases NH3 volatilization and increases total N and NH4+-N compared to untreated poultry manure. Nitrification in poultry wastes could therefore be stimulated due to higher NH4+ concentrations or could be inhibited because the soil environment is acidified. A 10-day laboratory study was conducted to study potential nitrification rates in soil slurries (20 g soil in 150 ml water) amended with 2.0 g alum-treated poultry manure. Fecal bacteria, NH4+, NO2-, NO3-, orthophosphate, pH, and NH3 were measured at 2-day intervals. Alum significantly reduced fecal bacteria concentrations through day 6. Water-soluble P was reduced 82% by day 10. Alum-treated manure had significantly increased NH4+ concentrations by day 8 and 10, and significantly decreased NO2- and NO3- concentrations by days 6-10. Alum's effect on potential nitrification was inhibitory in the soil environment. Slurries with alum-treated poultry manure had reduced nitrification rates, fecal bacteria, and soluble P. Therefore, in addition to reducing P loss, alum could temporarily reduce the risk for environmental pollution from land-applied manures in terms of both NO3- and fecal bacteria loss.

Estimating soil phosphorus requirements and limits from oxalate extract data.

Excessive fertilizer and manure phosphorus (P) inputs to soils elevates P in soil solution and surface runoff, which can lead to freshwater eutrophication. Runoff P can be related to soil test P and P sorption saturation, but these approaches are restricted to a limited range of soil types or are difficult to determine on a routine basis. The purpose of this study was to determine whether easily measurable soil characteristics were related to the soil phosphorus requirements (P(req), the amount of P sorbed at a particular solution P level). The P(req) was determined for 18 chemically diverse soils from sorption isotherm data (corrected for native sorbed P) and was found to be highly correlated to the sum of oxalate-extractable Al and Fe (R2 > 0.90). Native sorbed P, also determined from oxalate extraction, was subtracted from the P(req) to determine soil phosphorus limits (PL, the amount of P that can be added to soil to reach P(req)). Using this approach, the PL to reach 0.2 mg P L(-1) in solution ranged between -92 and 253 mg P kg(-1). Negative values identified soils with surplus P, while positive values showed soils with P deficiency. The results showed that P, Al, and Fe in oxalate extracts of soils held promise for determining PL to reach up to 10 mg P L(-1) in solution (leading to potential runoff from many soils). The soil oxalate extraction test could be integrated into existing best management practices for improving soil fertility and protecting water quality.

Diagenesis of Organic Matter in a Wetland Receiving Hypereutrophic Lake Water: II. Role of Inorganic Electron Acceptors in Nutrient Release.

Constructed marshes are currently being used as a low-cost alternative for treatment of nutrient-enriched waters. These marshes may function as net sinks for nutrients, especially for particulate organic forms of N and P. However, decomposition of organic matter and nutrient release may influence the ability of the marsh to function for this purpose. One of the main factors affecting decomposition is the availability of inorganic electron acceptors (e.g., O2 , NO- 3 , and SO2- 4 ). The role of electron acceptor consumption on N and P regeneration and release was investigated using batch incubation experiments with recently deposited organic matter (floc sediment) and peat soils collected from the constructed marsh. In electron acceptor-amended soil cores, electron acceptor consumption proceeded rapidly in the order O2 > NO- 3 > SO2- 4 . Mean oxygen reduction rate (OR) was 1.6 g O2 m-2 d-1 (2025 g O2 m-3 d-1 ), with corresponding values for NO- 3 and SO2- 4 of 0.23 g N m-2 d-1 (60 g N m-3 d-1 ) and 0.086 g S m-2 d-1 (5.4 g S m-3 d-1 ), respectively. If electron acceptor consumption was coupled to decomposition of organic matter in floc sediment with a C/N/P ratio of 190:14:1, aerobic catabolism accounted for 92% of NH+ 4 , and soluble P regenerated in the soil, with anaerobic activity (NO- 3 - and SO2- 4 -reduction) accounting for the remaining 8%. In the constructed marsh receiving allochthonous inputs of labile organic matter, however, anaerobic decomposition was expected to be the dominant mechanism for nutrient regeneration. Under SO2- 4 -reducing conditions, net rates of organic N and P mineralization were 3.3 to 14 mg N L-1 sediment d-1 and 0.5 to 0.6 mg P L-1 , respectively, and were highly correlated to production of dissolved inorganic C plus CH4 -C. Once released to the soil porewater, nutrients were available for transport to the water column by diffusion and advection (e.g., gas ebullition), thus impacting water quality.

Diagenesis of Organic Matter in a Wetland Receiving Hypereutrophic Lake Water: I. Distribution of Dissolved Nutrients in the Soil and Water Column.

A recently constructed marsh from previously drained agricultural land currently receives nutrient-laden water from adjacent hypereutrophic Lake Apopka, located in central Florida. Lake water is allowed to cycle through the marsh, allowing settlement of participate organic matter, which forms a floc sediment layer on the native peat soil surface. The water leaving the marsh is returned to the lake after a retention time of 3 to 12 d. This study determined changes in temporal and spatial distribution of selected nutrients in the soil-water column of the marsh during the first 13 mo of operation. In situ distribution of selected chemical species (H+ , NH+ 4 , soluble P, SO2- 4 , dissolved organic C, dissolved inorganic C, CH4 , Ca, Mg, Fe, Mn, Al) were measured using soil pore water equilibrators at 3, 8, and 13 mo after marsh creation. Initial flooding of the agricultural soils resulted in high concentrations of NH+ 4 (11 mg N L-1 ) and soluble P (31 mg P L-1 ) as a result of solubilization and anaerobic decomposition. Initially rapid soluble P flux (mean = 2.4 mg P m-2 d-1 ) occurred from soil to the water column, although lower flux (mean = 0.8 mg P m-2 d-1 ) occurred after 10 additional months of operation. In contrast, initial flux of NH+ 4 into the water column was generally lower (mean = 3.4 mg N m-2 d-1 ) than observed after 10 additional months (mean = 8.2 mg N m-1 d-1 ). Microbial degradation and nutrient regeneration from settled labile organic matter appeared to support nutrient flux to the water column. After 13 mo of flooding, 75% of the variability of NH+ 4 -N and 65% of the variability of soluble P contained in the water and floc sediment was explained by (DIC + CH4 )-C mineralized from settled organic matter. Anaerobic conditions in both the floc sediment and peat soil layers (indicated by increased amounts of dissolved CH4 and Fe, and by SO2- 4 reduction) had significant effects on nutrient retention and release in the soil-water column.