Sediment Phosphorus Release at Beaver Reservoir, Northwest Arkansas, USA, 2002–2003: A Preliminary Investigation

Phosphorus (P) release from bottom sediments can be a significant source to the overlying water column, potentially maintaining and enhancing algal growth and eutrophic conditions in lakes and reservoirs. Thus, the objectives of this study were to: (1) measure P flux under aerobic and anaerobic conditions from intact sediment cores collected at Beaver Reservoir, northwest Arkansas, (2) evaluate the spatial variability in measured sediment P flux under aerobic and anaerobic conditions along the reservoir, and (3) compare external and internal P loads to Beaver Reservoir. Six intact sediment cores were collected at three sites representing the lacustrine, transitional, and riverine zones during June 2003, September 2003 and February 2004 and incubated for 21 days in the dark at ～22°C. Three cores from each site were incubated under aerobic conditions and anaerobic conditions. Water samples were collected from the overlying water column in each core daily for the first five days and every other day thereafter and analyzed for soluble reactive phosphorus (SRP). Water removed from the core was replaced with filtered lake water, maintaining a constant overlying water volume of 1 l. Sediment P flux under anaerobic conditions (<0.01–1.77 mg m^?2 day^?1) was generally greater than that measured under aerobic conditions (<0.01–0.89 mg m^?2 day^?1). Some spatial variability existed in sediment P flux where P flux was generally greatest at the sites in the riverine and transitional zones. Maximum sediment P flux was observed under anaerobic conditions in cores collected from the transitional zone during September 2003. Average sediment P flux under aerobic conditions (0.09 mg m^?2 day^?1) and anaerobic conditions (0.31 mg m^?2 day^?1) was greater than the external P flux (0.05 mg m^?2 day^?1) estimated from the Beaver Reservoir tributaries. Results showed that the annual internal P load (7 Mg year^?1) from bottom sediments in Beaver Reservoir was less than 10% of the annual external P load (～81 Mg P year^?1). The internal P load was significant, but it would not currently be cost effective to manage this P source given the large surface area of Beaver Reservoir.     

Phosphorus Release and Equilibrium Dynamics of Canal Sediments within the Everglades Agricultural Area, Florida

High phosphorus (P) in surface drainage water from agricultural and urban runoff is the main cause of eutrophication within aquatic systems in South Florida, including the Everglades. While primary sources of P in drainage canals in the Everglades Agricultural Area (EAA) are from land use application of agricultural chemicals and oxidation of the organic soils, internal sources from canal sediments can also affect overall P status in the water column. In this paper, we evaluate P release and equilibrium dynamics from three conveyance canals within the EAA. Incubation and flux experiments were conducted on intact sediment cores collected from four locations within the Miami, West Palm Beach (WPB), and Ocean canal. After three continuous exchanges, Miami canal sediments reported the highest P release (66?±?37 mg m^?2) compared to WPB (13?±?10 mg m^?2) and Ocean (17?±?11 mg m^?2) canal over 84 days. Overall, the P flux from all three canal sediments was highest during the first exchange. Miami canal sediments showed the highest P flux (2.4?±?1.3 mg m^?2 day^?1) compared to WPB (0.83?±?0.39 mg m^?2?d^?1) and Ocean canal sediments (0.98?±?0.38 mg m^?2 day^?1). Low P release from WPB canal sediments despite having high TP content could be due to carbonate layers distributed throughout the sediment column inhibiting P release. Equilibrium P concentrations estimated from the sediment core experiment corresponded to 0.12?±?0.04 mg L^?1, 0.06?±?0.03 mg L^?1, and 0.08?±?0.03 mg L^?1 for Miami, WPB, and Ocean canal sediments, respectively, indicating Miami canal sediments behave as a source of P, while Ocean and WPB canal sediments are in equilibrium with the water column. Overall, the sediments showed a significant positive correlation between P release and total P (r?=?0.42), Fe_ox (r?=?0.65), and Al_ox (r?=?0.64) content of sediments. The contribution of P from the three main canals sediments within the EAA boundary corresponded to a very small portion of the total P load exiting the EAA. These estimates, however, only take into consideration diffusive fluxes from sediments and no other factors such as canal flow, bioturbation, resuspension, and anaerobic conditions.     

A Synoptic Survey of Nitrogen and Phosphorus in Tributary Streams and Great Rivers of the Upper Mississippi, Missouri, and Ohio River Basins

We combined stream chemistry and hydrology data from surveys of 436 tributary stream sites and 447 great river sites in the Upper Mississippi, Missouri and Ohio River basins to provide a regional snapshot of baseflow total nitrogen (TN) and total phosphorus (TP) concentrations, and to investigate the relationships between land use and stream chemistry. Catchments in the Upper Mississippi River basin had more land in agricultural uses (51%) than the Missouri or Ohio River basin catchments (25% and 29%, respectively). The difference in agriculture is reflected in the TN concentrations in tributary streams and the great rivers: 5,431 and 2,112 ??g L^?1 for the Upper Mississippi, 1,751 and 978 ??g L^?1 for the Missouri, and 1,074 and 1,152 ??g L^?1 for the Ohio River basins. This agricultural effect was not as evident for tributary stream or great river TP concentrations: 165 and 181 ??g L^?1 in the Upper Mississippi, 177 and 171 ??g L^?1 in the Missouri, and 67 and 53 ??g L^?1 in the Ohio River basins. We set reference thresholds based on the 75th percentile TN and TP concentrations at our least disturbed sites. The TN threshold was exceeded for 50?C63% of the tributary stream and 16?C55% of great river lengths, with the greatest proportion in the Upper Mississippi River basin. The TP threshold was exceeded in 32?C48% of tributary stream and 12?C41% of great river lengths. Tributary stream N/P ranged from 67:1 (Ohio) to 210:1 (Upper Mississippi); river N/P ranged from 20:1 (Missouri) to 60:1 (Ohio). N/P indicated that potential N-limitation occurred in 10?C21% of total tributary stream length and in 0?C46% of great river length; potential P-limitation ranged from 60?C83% of cumulative tributary stream length and from 21?C98% of cumulative great river length. Total N flux (concentration × discharge) was highest in the Upper Mississippi River basin; TP flux was lowest in the Ohio River basin. River TN yields and TP yields for both tributary streams and great rivers, was not significantly different between the sub-basins. Our study empirically links catchment land use and stream chemistry, and demonstrates using monitoring data for estimating nutrient yields at a large regional scale.     

Microfauna Community as an Indicator of Effluent Quality and Operational Parameters in an Activated Sludge System for Treating Piggery Wastewater

In order to study the potential use of microfauna as an indicator of effluent quality and operational parameters in an activated sludge system for treating piggery wastewater, an experimental sequencing batch reactor was set up and evaluated by biological and physical–chemical analyses for 12 months. Results show that microfauna (and specifically ciliate protozoa) are a good parameter for assessing effluent quality in terms of both chemical oxygen demand (COD) and ammonia and for assessing the organic and nitrogen load of the system. Specifically, the abundance of ciliates decreases from 20,000 individuals·mL^?1 to ca. 2,500 individuals·mL^?1 and from ca. 10,000 individuals mL^?1 to ca. 200 individuals mL^?1 when effluent concentration is between 550 and 750 mg L^?1 and above 100 mg L^?1 to the COD and ammonia concentrations, respectively. Furthermore, microfauna abundance is reduced from ca. 18,000 individuals mL^?1 (organic load between 0.1 and 0.2 mg COD mg total suspended solids (TSS)^?1 day^?1) to ca. 500 individuals mL^?1 (organic load between 0.3 and 04 mg COD mg TSS^?1 day^?1). Microfauna abundance also decreases as nitrogen loading increases. Nitrogen loading in the range of 5–60 mg NH₄–N g TSS^?1 day^?1 does not have any significant effect on microfauna abundance. However, ammonia loading from 60 to 120 mg NH₄–N g TSS^?1 day^?1 reduces microfauna abundance ca. 6-fold. Ciliate protozoa were the largest microfauna group during the whole period of study, representing ca. 75% of the total microfauna abundance. The largest group in the ciliate community was that of the free-swimming ciliates. This was followed by the group of attached and crawling ciliates. Specifically, the dominant ciliate species during the whole study period were Uronema nigricans, Vorticella microstoma-complex, Epistylis coronata, and Acineria uncinata.     

Fluid Catalytic Cracking Unit Emissions and Their Impact

A constructed wetland composed of a pond- and a marsh-type wetland was employed to remove nitrogen (N) and phosphorus (P) from effluent of a secondary wastewater treatment plant in Korea. Nutrient concentrations in inflow water and outflow water were monitored around 50 times over a 1-year period. To simulate N and P dynamics in a pond- and a marsh-type wetland, mesocosm experiments were conducted. In the field monitoring, ammonium (NH ₄ ⁺ ) decreased from 4.6 to 1.7 mg L^?1, nitrate (NO ₃ ^? ) decreased from 6.8 to 5.3 mg L^?1, total N (TN) decreased from 14.6 to 10.1 mg L^?1, and total P (TP) decreased from 1.6 to 1.1 mg L^?1. Average removal efficiencies (loading basis) for NO ₃ ^? , NH ₄ ⁺ , TN, and TP were over 70%. Of the environmental variables we considered, water temperature exhibited significant positive correlations with removal rates for the nutrients except for NH ₄ ⁺ . Results from mesocosm experiments indicated that NH ₄ ⁺ was removed similarly in both pond- and marsh-type mesocosms within 1 day, but that NO ₃ ^? was removed more efficiently in marsh-type mesocosms, which required a longer retention time (2?C4 days). Phosphorus was significantly removed similarly in both pond- and marsh-type mesocosms within 1 day. Based on the results, we infer that wetland system composed of a pond- and a marsh-type wetland consecutively can enhance nutrient removal efficiency compared with mono-type wetland. The reason is that removal of NH ₄ ⁺ and P can be maximized in the pond while NO ₃ ^? requiring longer retention time can be removed through both pond and marsh. Overall results of this study suggest that a constructed wetland composed of a pond- and a marsh-type wetland is highly effective for the removal of N and P from effluents of a secondary wastewater treatment plant.     

Evaluation of Vertical-Flow Constructed Wetlands for Swine Wastewater Treatment

In this study, the role of Cyperus sp. was evaluated for removal of pollutants from swine wastewater. Vertical-flow pilot scale constructed wetlands (CWs) operating with a hydraulic retention time (HRT) of 72 h were monitored in a greenhouse, located in Viçosa, Brazil. Significant differences were observed for the following parameters: Kjeldahl nitrogen, total phosphorus, alkalinity and electric conductivity, with averages removals of 37.5 and 28.5%, 55.9 and 44.4%, 30.2 and 25.6 and 26.1% and 22.9% (for planted and unplanted CWs, respectively). The rate of dry matter yield from Cyperus sp. was 7.5 g?m^?2 day^?1, and the nutrient uptake capacities were 21.8, 2.1, 14.0 and 0.9 g?m^?2 of N, P, K and Na, respectively. Evapotranspiration (2.7 mm day^?1) was statistically higher in the planted CWs. Plants in the CWs are important for achieving high nutrient removal.     

Metal fluxes at the sediment–water interface in rivers in the Turvo/Grande drainage basin, S?o Paulo State, Brazil

Purpose

The Turvo/Grande drainage basin (TGDB), located in the northwestern region of S?o Paulo state, covers an area of 15,983?km². The region is typically regarded as agricultural by the S?o Paulo State Environmental Agency, but the industrial area is expanding, and some studies have shown that metal concentrations in water can be higher than the values regulated by Brazilian law. Therefore, the aim of this study was to assess the role of sediments as a source or a sink of metals for drainage basin management.

Materials and methods

Interstitial water from different sediment depths (0?C42?cm) and the sediment?Cwater interface and sediment core samples were collected in February and July 2010 from the Preto, Turvo, and Grande rivers. Quantification of Cr, Cu, Fe, Mn, Ni, and Pb in these samples was performed by graphite furnace or flame atomic absorption spectrometry. Metal diffusive flux estimation from sediment into the overlying water was calculated by Fick??s First Law of Diffusion.

Results and discussion

The fluxes of all metals for the three rivers were positive, indicating diffusion into the overlying water. Ni and Pb showed the lowest diffusive fluxes, which ranged from 2.4 to 3,978???g?m^?2?day^?1 for Ni and from ?0.1 to 1,597???g?m^?2?day^?1 for Pb. In turn, Cu and Cr were subject to the largest transfer to water, especially in the dry season (Cr, 4.5?C7,673???g?m^?2?day^?1; Cu, 1.3?C14,145???g?m^?2?day^?1). The Preto River (urban area) showed smaller fluxes than the Grande River (agricultural area), and the values of the latter were higher than those found in other impacted areas of the world.

Conclusions

The diffusive fluxes indicate that sediments from the TGDB act as a source of metals for the water column, with increased export of metals, particularly Cr and Ni, from the sediment into the overlying water during the dry season.     

Heterotrophic nitrification is the predominant NO3 − production pathway in acid coniferous forest soil in subtropical China

To date, occurrence and stimulation of different nitrification pathways in acidic soils remains unclear. Laboratory incubation experiments, using the acetylene inhibition and ¹⁵N tracing methods, were conducted to study the relative importance of heterotrophic and autotrophic nitrification in two acid soils (arable (AR) and coniferous forest) in subtropical China, and to verify the reliability of the ¹⁵N tracing model. The gross rate of autotrophic nitrification was 2.28 mg?kg^?1?day^?1, while that of the heterotrophic nitrification (0.01 mg?kg^?1?day^?1) was negligible in the AR soil. On the contrary, the gross rate of autotrophic nitrification was very low (0.05 mg?kg^?1?day^?1) and the heterotrophic nitrification (0.98 mg?kg^?1?day^?1) was the predominant NO₃ ^? production pathway accounting for more than 95 % of the total nitrification in the coniferous forest soil. Our results showed that the ¹⁵N tracing model was reliable when used to study soil N transformation in acid subtropical soils.     

Behavior of Pilot-Scale Constructed Wetlands in Removing Nutrients and Sediments Under Varying Environmental Conditions

Water resources are threatened globally and declining water quality is primarily due to stormwater, agricultural, urban, and mining runoffs. Steamboat Creek in Nevada is the largest non point source (NPS) of pollution to the Truckee River. Treatment wetlands are a cost-effective and reliable technique to control NPS pollution, therefore, a large-scale wetland along Steamboat Creek has been proposed as a component of a regional watershed restoration plan. This study used ten parallel pilot-scale wetland mesocosms, and tested the effects of drying and rewetting, hydraulic retention time (HRT), and high nitrogen loading on the efficiency of nutrient and total suspended solids (TSS) removal. Drying and rewetting produced noticeable effects on nutrient retention, but the effect was short-lived. During longer HRT period nutrient removal in manipulated mesocosms with an 8 h HRT were higher than controls with a 4 h HRT. Reducing the HRT from 4 h to 30 min further decreased nutrient interception. During increased influent nitrogen loading (9.5?±?2.4 mg l^?1), manipulated mesocosms functioned as sinks for total nitrogen (TN) with removal efficiency increasing from 45?±?13% to 87?±?9%. The average change in TN concentration was 9.1?±?2.2 mg l^?1. Drying/rewetting and varying HRT influenced total phosphorus (TP) and TSS similarly, and TP removal was associated with TSS removal. Results can help make decisions regarding wetland construction, management, and operation more effective in order to reduce nutrient loads to the Truckee River.     

Evaluation of a Quasi-steady-state Respiration Test in a Full-scale Biopile

A quasi steady state respiration test based on Fick’s law with a correction term for advective flux, for estimating petroleum hydrocarbon degradation rates, was evaluated in a full-scale (3,000 m³) biopile study. A contaminated clayey sand soil with an average TPH content of 1,421?±?260 mg kg^?1 soil was treated in a biopile with a fixed venting and heating system. Temperature in the biopile ranged from 12.1 to 36.6°C and soil water content from 15.2 to 35.8 m³ H₂O m^?3 soil. Oxygen concentrations in the biopile showed a rapid decrease with depth, before venting and reached constant atmospheric concentration during venting. Measured oxygen consumption in the biopile ranged from ?0.04 to ?0.68 mol O₂ m^?3 soil day^?1. Average oxygen consumption rates calculated with the quasi-steady-state method were significantly (P?<?0.05) lower then the oxygen consumption rates calculated with the transient method. It was suggested that the oxygen diffusion was underestimated by the diffusivity models used and that further research is needed to determine relative effective diffusion coefficients in biopiles. Although both respiration testing and petroleum hydrocarbon concentration showed a decrease of oxygen consumption in time, the estimated degradation rate was low compared to the actual decrease in petroleum hydrocarbon concentration. Additional work will have to be done to acquire a more precise knowledge of the relationship between respirometrically determined degradation rates and the actual change in petroleum hydrocarbon concentration in the soil.     

Fertilizer micro-dosing increases crop yield in the Sahelian low-input cropping system: A success with a shadow

Over the years, a scarcity of information on nutrient gains or losses has led to overemphasis being placed on crop yields and economic income as the direct benefits from fertilizer micro-dosing technology. There is increasing concern about the sustainability of this technology in smallholder Sahelian cropping systems. This study was designed in the 2013 and 2014 cropping seasons to establish nutrient balances under fertilizer micro-dosing technology and their implications on soil nutrient stocks. Two fertilizer micro-dosing treatments [2 g hill^?1 of diammonium phosphate (DAP) and 6 g hill^?1 of compound fertilizer Nitrogen-Phosphorus-Potassium (NPK) (15-15-15)] and three rates of manure (100 g hill^?1, 200 g hill^?1 and 300 g hill^?1) and the relevant control treatments were arranged in a factorial experiment organized in a randomized complete block design with three replications. On average, millet (Pennisetum glaucum (L.) R.Br.) grain yield increased by 39 and 72% for the plots that received the fertilizer micro-dosing of 6 g NPK hill^?1 and 2 g DAP hill^?1, respectively, in comparison with the unfertilized control plots. The average partial nutrients balances for the two cropping seasons were ?37 kg N ha^?1yr^?1, ?1 kg P ha^?1yr^?1 and ?34 kg K ha^?1yr^?1 in plots that received the application of 2 g DAP hill^?1, and ?31 kg N ha^?1yr^?1, ?1 kg P ha^?1yr^?1 and ?27 kg K ha^?1yr^?1 for 6 g NPK hill^?1. The transfer of straw yields accounted for 66% N, 55% P and 89% K for removal. The average full nutrient balances for the two cropping seasons in fertilizer micro-dosing treatments were ?47.8 kg N ha^?1 yr^?1, ?6.8 kg P ha^?1 yr^?1 and ?21.3 kg K ha^?1 yr^?1 which represent 7.8, 24.1 and 9.4% of N, P and K stocks, respectively. The nutrient stock to balance ratio (NSB) for N decreased from 13 to 11 and from 15 to 12 for the plots that received the application of 2 g DAP hill^?1 and 6 g NPK hill^?1, respectively. The average NSB for P did not exceed 5 for the same plots. It was concluded that fertilizer micro-dosing increases the risk of soil nutrient depletion in the Sahelian low-input cropping system. These results have important implications for developing an agro-ecological approach to addressing sustainable food production in the Sahelian smallholder cropping system.     

Occurrence and Distribution of Perfluorooctane Sulfonate and Perfluorooctanoic Acid in the Rivers of Tokyo

Comprehensive survey of major rivers in the Tokyo metropolitan area was conducted for clarifying the emission sources of perfluorooctane sulfonate (PFOS) in Tokyo. PFOS was found at all sampling sites at concentrations ranging from 0.5 to 58 ng L^?1; in addition to this, it was also indicated that unknown PFOS emission sources are present in the midstream of the Tama River basin. The relationship between PFOS and perfluorooctanoic acid (PFOA) was constant at a ratio of 10:3 (PFOS/PFOA) throughout the Tama River basin. The sum of daily load amounts of PFOS from Tokyo’s major rivers to Tokyo Bay reached 215 g day^?1. This value corresponds to 12.8 μg day^?1 per person using the sum of wastewater treatment district populations. In contrast, an estimation of PFOS contribution of domestic wastewater was also attempted, and the contribution was 1.6 μg day^?1 per person. We took samples up trunk sewers in the Tama River and finally found at the highest PFOS concentration (58,000 ng L^?1) from one of the wastewater of the electronic parts manufacturing facilities.     

Phosphorus Dynamics in a Small Eutrophic Italian Lake

Phosphorous dynamics within Lake Sirio (NW Italy) were investigated, considering both water and sediments. The total phosphorus (TP) concentration in the water is about 79 μg l^?1 after the winter mixing, that is in homogeneous conditions; then TP content increases up to an average of 360 μg l^?1 in late autumn in the deep hypolimnium (30–45 m). This deep lake portion accounts for only 1/12 of the water volume. Close to the water-sediment interface, TP concentrations up to 530 μg l^?1 are observed. Sediment sampled at depths of 20 and 33 m contains less than 2,000 mg kg^?1 of TP, whereas cores from the deepest sediments (46 m) display TP values of 2,000–4,000 mg kg^?1 at the water-sediment interface, increasing with depth to 16,000 mg kg^?1 at about 60–100 cm. In these deep sediments the main chemical form is the Al–Fe–Mn bound P (about 90% in the high TP cores) and Fe and Mn are also highly enriched (3 and 9 times more than in the shallow sediments respectively). The P–Fe association is confirmed by SEM-EDS and XRD analyses. The vertical distribution of the P content in the water column is consistent with its release from sediments, but in this hypothesis an unrealistic P release rate from 8.1 to 3.0 g m^?2y^?1 was estimated. A more complex model is therefore proposed, involving a process of P concentration in the sediments of the central (deepest) part of the lake, and a short term sediment-water exchange. The TP vertical variability and speciation in the cores suggests a change in the sediment retention capacity, connected to the lake shift to more eutrophic conditions.     

GIS-Based Emission Inventory, Dispersion Modeling, and Assessment for Source Contributions of Particulate Matter in an Urban Environment

The Industrial Source Complex Short Term (ISCST3) model was used to discern the sources responsible for high PM₁₀ levels in Kanpur City, a typical urban area in the Ganga basin, India. A systematic geographic information system-based emission inventory was developed for PM₁₀ in each of 85 grids of 2?×?2 km. The total emission of PM₁₀ was estimated at 11 t day^?1 with an overall breakup as follows: (a) industrial point sources, 2.9 t day^?1 (26%); (b) vehicles, 2.3 t day^?1 (21%); (c) domestic fuel burning, 2.1 t day^?1 (19%); (d) paved and unpaved road dust, 1.6 t day^?1 (15%); and the rest as other sources. To validate the ISCST3 model and to assess air-quality status, sampling was done in summer and winter at seven sampling sites for over 85 days; PM₁₀ levels were very high (89?C632 ??g m^?3). The results show that the model-predicted concentrations are in good agreement with observed values, and the model performance was found satisfactory. The validated model was run for each source on each day of sampling. The overall source contribution to ambient air pollution was as follows: vehicular traffic (16%), domestic fuel uses (16%), paved and unpaved road dust (14%), and industries (7%). Interestingly, the largest point source (coal-based power plant) did not contribute significantly to ambient air pollution. The reason might be due to release of pollutant at high stack height. The ISCST3 model was shown to produce source apportionment results like receptor modeling that could generate source apportionment results at any desired time and space resolution.     

Full-Scale Experiment on Domestic Wastewater Treatment by Combining Artificial Aeration Vertical- and Horizontal-Flow Constructed Wetlands System

To improve domestic wastewater treatment for total nitrogen (TN) removal, a full-scale constructed wetlands combining an artificially aerated vertical- (AVCW) and a horizontal-flow constructed wetland (HCW) was completed in July 2007. The system covered a total area of 7,610?m². From 2 July 2007 to 7 August 2008, the treatment capacity was 2,076?m³?day^?1 with an aeration quantity of 7,400?m³?day^?1. The system effectively reduced the average annual output of BOD₅ (52.0?%), NH₄?CN (58.41?%), and TP (41.61?%), although the percentage reductions of other pollutants, including chemical oxygen demand (34.1?%), suspended solid (38.9?%), and TN (31.05?%) were lower. The purpose of the HCW was for denitrification of the effluent from the AVCW, and annual average of 34.27?% of NO₃?CN was removed compared with the reading at the AVCW outlet. With hydraulic loading increased to 4,152?m³?day^?1 from 9 September to 23 November 2007, the removal rate for NO₃?CN from the HCW decreased substantially from 48.80 to 18.86?%. The total removal rates of NH₄?CN showed significant positive correlation with DO content in the AVCW and with total TN removal rates for the combined system (P?<?0.05). The study indicated that, even with limited artificial aeration, nitrification was very effective for NH₄?CN removal.     

Phosphorus Entrainment Due to Resuspension in a Lowland River, Spree, NE Germany – A Laboratory Microcosm Study

Resuspension of benthic phosphorus (P) often constitutes a high percentage of the annual P flux in lowland rivers. To study P entrainment at controlled shear velocity (u*) sediment from lowland River Spree of slower flowing (0.1–0.3 m s^?1) stretch Kossenblatt (KOB) and of faster flowing (0.5–0.7 m s^?1) stretch Freienbrink (FRB) was incubated in a microcosm at incrementally enhanced u* (0.34–1.9 cm s^?1). Particle and P entrainment rates as well as the number of particle-associated bacteria of fine-grained mud-like KOB sediment were much higher (16.7 g m^?2 h^?1, 104.9 mg P m^?2 h^?1, 15.47 10⁶ cells ml^?1) than those (4.3 g m^?2 h^?1, 2.1 mg P m^?2 h^?1, 3.06 10⁶ cells ml^?1) of coarser sandy FRB sediment. The microcosm used so far in marine research is suited to compare riverine resuspension suggesting the lower u* the more particles are deposited and the more P can be retained (KOB ? FRB). Conversely, correspondingly more and easier particulate P and bacteria can again be remobilised (KOB ? FRB) if u* increases. The general relationship found for u* and the entrainment of particulate P and bacteria as well as their decelerated and selective deposition where bacteria may stay longer in the water implies a temporarily enhanced P bioavailability, turnover and subsequent P transformations.     

Nitrogen Removal, N2O Emission, and NH3 Volatilization Under Different Water Levels in a Vertical Flow Treatment System

Two series of laboratory-scale vertical flow systems (flooded and nonflooded columns) were designed to compare nitrogen removal performance, nitrous oxide emission, and ammonia volatilization under different water levels upon treating diluted digested livestock liquid. In these systems, influent was supplied at three hydraulic loading rates (HLRs of 1.25, 2.5, and 5 cm day^?1) during stage 1 and the rates were doubled during stage 2 when the water levels of nonflooded columns were elevated from zero to half the height of the soil column. After hydraulic loading rates doubled, the average removal rates of total nitrogen in flooded columns varied from 1.27 to 2.94 g^?2 day^?1 and those in nonflooded columns ranged from 1.23 to 3.88 g^?2 day^?1. The T-N removal at an HLR of 10 cm day^?1 in the nonflooded column with an elevated water table level had higher efficiency than that in the flooded column, suggesting T-N removal is enhanced in the nonflooded column probably due to the improved coupled nitrification–denitrification process under the elevated water table level condition. On the other hand, there was a significant correlation (r ² = 0.532, p < 0.001) between the N₂O flux and redox potential that mainly corresponded to water levels and HLRs, suggesting anoxic or aerobic conditions stimulate N₂O emission by enhancing the nitrification (nitrification–denitrification) process. In contrast, NH₃ volatilization had a high flux in the anaerobic condition mainly because of flooding. Based on the experimental results, it is hypothesized a nonflooded condition with higher water table level (Eh range of ?160 to +260 mV) would be suitable to reduce N₂O emission and NH₃ volatilization peak value by at least half while maintaining relatively efficient nitrogen removal performance.     

Variations in concentrations of N and P forms in leachates from dried soils rewetted at different rates

The rate at which dried soils are rewetted can affect the quantities and forms of nutrients in leachates. Both dried and moist replicated (n?=?3) samples of two contrasting grassland soil types (clayey vs brown earth) were irrigated during laboratory experiments with identical total amounts of water, but at different rates, ranging from 0 h, increasing by 30-min increments up to 4 h, and additionally a 24-h rewetting rate. Total P concentrations in leachates from dried samples of both soils generally decreased as rewetting rate increased, ranging from 2,923?±?589 μg P L^?1 (0.5 h rewetting rate) to 731?±?46.0 μg P L^?1 (24 h, clayey soil) and 1,588?±?45.1 μg P L^?1 (0.5 h) to 439?±?25.5 μg P L^?1 (24 h brown earth). Similar patterns in concentrations occurred for molybdate reactive P (MRP), although concentrations were generally an order of magnitude lower, indicating that the majority of the leached P was probably organic. The moist brown earth leached relatively high concentrations of MRP (maximum 232?±?10.6 μg P L^?1, 0.5 h), unlike the moist clayey soil (maximum 20.4?±?10.0 μg P L^?1, 0 h). The total oxidised N concentrations in leachates were less affected by rewetting rate, although longer rewetting rates resulted in decreased concentrations in leachates from the dried samples of both soils. The difference in responses to rewetting rates of the two soils is probably due to differences in the fate of the microbial biomass and adsorption properties in the soils. Results show that soil moisture could be an important factor in regulating nutrient losses and availability, especially under changing patterns of rainfall predicted by future climate change scenarios.     

Sufficiency ranges for lemon balm and nutrient removals in aboveground phytomass

A set of fertilizer experiments were conducted during three growing seasons with the aim of establishing sufficiency ranges and crop nutrient removals for Melissa officinalis L. Critical nutrient concentrations were determined by the Cate–Nelson method or by removing 10% of extreme high and low values, respectively if a positive response to a given nutrient was recorded or not. Sufficiency ranges for macro, micronutrients, and SPAD-readings were set as: 27.0–40.0 g N kg^?1; 0.8–2.7 g P kg^?1 (May–August); 1.5–3.8 g P kg^?1 (September–November); 10.0–25.0 g K kg^?1 (May–August); 18.0–32.0 g K kg^?1 (September–November); 5.0–25.0 g Ca kg^?1; 3.5–8.5 g Mg kg^?1; 18–125 mg B kg^?1; 5–25 mg Cu kg^?1; 75–500 mg Fe kg^?1; 20–300 mg Zn kg^?1; 30–250 g Mn kg^?1; 30–45 SPAD-units. These results will allow laboratories to use plant analysis as an important tool in improving the fertilizer recommendations for this species.     

Nutrient uptake and use efficiency of onion seed yield as influenced by nitrogen and phosphorus fertilization

Abstract

The experiment was conducted at Kulumsa, South East Ethiopia, using four levels of nitrogen (N) (0, 50,100 and 150?kg N ha^?1) and four levels of phosphorus (P) (0, 35, 70 and 105?kg P₂O₅ ha^?1) fertilizers arranged in 4?×?4 factorial arrangements in randomized complete block design with three replications. The available P was increased after harvest due to the application of N and P fertilizer at the rates of 100 or 150?kg N ha^?1 and 70 or 105?kg P₂O₅ ha^?1. More specifically, nutrients concentration and nutrient uptake were significantly (p?<?.01) varied among treatment combinations and nutrient use efficiency was declined by increasing N and P after optimum rates. The higher physiological efficiency of N (53.47?kg kg^?1) and P (580.41?kg kg^?1) and the highest apparent recovery of N (19.62%) and P (2.47%) was recorded from application of 50?kg N ha^?1 and P at 70?kg P₂O₅ ha^?1 and the highest agronomic efficiency of N (10.78?kg kg^?1) and P (15.25?kg kg^?1) was recorded from N at the rate of 50?kg N ha^?1 and P at 35?kg P₂O₅ ha^?1, respectively. The combination of N at 100?kg N ha^?1 and P at 70?kg P₂O₅ ha^?1 was promising combination that generated highest net benefit 488,878.5 ETB (Ethiopian birr) ha^?1 with the highest marginal rate of return (36638%) and gave the highest seed yield (1858.82?kg ha^?1) with yield increment of about 57.72% over the control.