Characterisation of agricultural drainage ditch sediments along the phosphorus transfer continuum in two contrasting headwater catchments

Purpose

This study investigated the phosphorus (P) source, mobilisation and transport potential of ditch bed sediments as well as surrounding field and bank soils in two agricultural headwater catchments with contrasting soil drainage capacities. This information is important for discerning the potential for ditches to attenuate or augment transfers of P from upstream sources and thus for developing appropriate management strategies for these features.

Materials and methods

Phosphorus sources were characterised using the Mehlich3-P, water-soluble P and total P tests. Phosphorus mobilisation potential was characterised using the Mehlich3-AL/P, Mehlich3-Ca/P and DESPRAL P tests. Phosphorus transport potential was characterised using data collected on the presence/absence of surface water in ditches during field surveys and downstream turbidity data.

Results and discussion

Ditch sediments had similar P source contents (Mehlich3-P, water-soluble P and total P) to the surrounding field soils and higher P contents than bank soils. However, calcium contents of sediments in the poorly drained catchment reflected the deep sub-soils rather than the surrounding field and bank soils. Mehlich3-Al/P and Mehlich3-Ca/P contents of ditch sediments in the well (non-calcareous) and poorly (calcareous) drained catchments respectively indicated potential for P retention (above thresholds of 11.7 and 74, respectively). However, sediments were less aggregated than field soils and may mobilise more particulate P (PP) during rain events. Nevertheless, the majority of surveyed ditches dried out from March to September 2011; thus, their potential to mobilise PP may be less important than their capacity to attenuate soluble and PP during this time.

Conclusions

In these and similar catchments, soluble P attenuation and particulate P mobilisation should be maximised and minimised, respectively, for example, by cleaning out the sediments before they become saturated with P and encouraging vegetation growth on ditch beds. This study also highlighted the influence of deep sub-soils on soluble P retention in ditches and thus the utility of characterising soils below depths normally included in soil classifications.

     

Fruit maturity affects the response of apples to heat stress

Quality changes of apple fruit at different maturity stages in response to heat stress were investigated. ‘Jonagold’ and ‘Cortland’ apples at immature (pre-climacteric), commercial harvest maturity (CHM) and post climacteric maturity (PCM, CHM plus 4 weeks) were harvested and held at 46 °C for 0, 4, 8, or 12 h. Following treatments, fruits were stored in air at 0 °C and evaluated after 0, 1, 2, or 3 months. Quality indices including peel and flesh browning, firmness, titratable acidity, soluble solids, chlorophyll fluorescence (CF), and ethanol production were measured. Results indicated that different cultivars and maturities affected the fruit's resistance to heat stress. ‘Jonagold’ was more resistant to heat stress than ‘Cortland’. Fruit at PCM were most sensitive to heat stress, followed by fruits at CHM and immature stages. When ‘Jonagold’ apples at immature and CHM stages were held at 46 °C for 12 h and then stored for 3 months, flesh browning ratings were negligible compared with 1.4 or 2.9, respectively in ‘Cortland’. Flesh browning rating increased to 1.4 or 4.5 in PCM ‘Jonagold’ held at 46 °C for 8 or 12 h and then stored for 3 months while it was 4.9 or 5.0, respectively, in ‘Cortland’. Heat treatment-induced flesh injury was associated with a decrease in CF. After fruit were exposure to 46 °C for 12 h and then stored for 3 months, Fv/Fm was reduced by 13%, 30%, and 55% in ‘Jonagold’ at immature maturity, CHM and PCM, respectively, while it was reduced by 51%, 58% and 75%, respectively, in ‘Cortland’. Heat stress also caused a decrease in fruit titratable acidity, but had no effect on soluble solids contents. The 8 or 12 h heat treatment resulted in an increase in ethanol production, which was greatest in PCM apples.     

Heparin promotes the inactivation of antithrombin by neutrophil elastase

Heparin is an acceleratory cofactor for antithrombin, a circulating inhibitor of blood coagulation enzymes. The presence of heparin on blood vessel walls is believed to contribute to the nonthrombogenic properties of those surfaces. In apparent opposition to this function, heparin was found to greatly accelerate the in vitro inactivation of antithrombin by neutrophil elastase. Inactivation rates in solution were potentiated several hundredfold by specific heparin fractions with anticoagulant activity. Although the data suggest that a heparin-antithrombin complex is essential for the inactivation by elastase to occur, the enzyme itself interacts tightly with heparin. These results suggest a mechanism which, if operating in vivo, could lead to a localized neutralization of the anticoagulant function of heparin at the endothelial surface.     

Lehmann discontinuity as the base of an anisotropic layer beneath continents

Long-period surface-wave (R(1), G(1)), body-wave (S, SS, SSS), and ScS-reverberation data have been inverted to obtain anisotropic structures along seismic corridors that sample Australia and the western Pacific. These models support the proposal that the Lehmann discontinuity beneath stable continents represents a transition from an anisotropic lithosphere to a more isotropic material in the lower part of the continental tectosphere.     

Heterogeneous reaction probabilities, solubilities, and the physical state of cold volcanic aerosols

On 19 January 1992, heterogeneous loss of HNO(3), ClNO(3), and HCl was observed in part of the Mount Pinatubo volcanic cloud that had cooled as a result of forced ascent. Portions of the volcanic cloud froze near 191 kelvin. The reaction probability of ClNO(3) and the solubility of HNO(3) were close to laboratory measurements on liquid sulfuric acid. The magnitude of the observed loss of HCl suggests that it underwent a heterogeneous reaction. Such reactions could lead to substantial loss of HCl on background sulfuric acid particles and so be important for polar ozone loss.