Exploring the effects of land management change on productivity, carbon and nutrient balance: Application of an Ensemble Modelling Approach to the upper River Taw observatory, UK.

Agriculture is challenged to produce healthy food and to contribute to cleaner energy whilst mitigating climate change and protecting ecosystems. To achieve this, policy-driven scenarios need to be evaluated with available data and models to explore trade-offs with robust accounting for the uncertainty in predictions. We developed a novel model ensemble using four complementary state-of-the-art agroecosystems models to explore the impacts of land management change. The ensemble was used to simulate key agricultural and environmental outputs under various scenarios for the upper River Taw observatory, UK. Scenarios assumed (i) reducing livestock production whilst simultaneously increasing the area of arable where it is feasible to cultivate (PG2A), (ii) reducing livestock production whilst simultaneously increasing bioenergy production in areas of the catchment that are amenable to growing bioenergy crops (PG2BE) and (iii) increasing both arable and bioenergy production (PG2A + BE). Our ensemble approach combined model uncertainty using the tower property of expectation and the law of total variance. Results show considerable uncertainty for predicted nutrient losses with different models partitioning the uncertainty into different pathways. Bioenergy crops were predicted to produce greatest yields from Miscanthus in lowland and from SRC-willow (cv. Endurance) in uplands. Each choice of management is associated with trade-offs; e.g. PG2A results in a significant increase of edible calories (6736 Mcal ha-1) but reduced soil C (-4.32 t C ha-1). Model ensembles in the agroecosystem context are difficult to implement due to challenges of model availability and input and output alignment. Despite these challenges, we show that ensemble modelling is a powerful approach for applications such as ours, offering benefits such as capturing structural as well as data uncertainty and allowing greater combinations of variables to be explored. Furthermore, the ensemble provides a robust means for combining uncertainty at different scales and enables us to identify weaknesses in system understanding.

Measuring nerve growth factor in saliva by immunoassay: A cautionary note.

Nerve growth factor (NGF), a neurotrophin, modulates a diverse set of physiologic processes in the nervous, immune, and endocrine systems. Studies suggest that NGF can be measured in saliva (sNGF). Historically, the method for measuring sNGF involves the off-label use of an enzyme immunoassay designed for use with cell-culture supernatants/tissue extracts (Nam et al., 2007; Ruhl et al., 2004). In a series of experiments we reveal this measurement strategy is subject to non-specific interference by constituents present in oral fluids. We conclude that the measurement of sNGF by this assay is not optimal for use with oral fluid specimens.

Using artificial fluorescent particles as tracers of livestock wastes within an agricultural catchment.

Evidence for the movement of agricultural slurry and associated pollutants into surface waters is often anecdotal, particularly with relation to its 'particulate' components which receive less attention than 'bio-available' soluble phases. To assess the extent of movement of slurry particles artificial fluorescent particles were mixed with slurry and applied to a field sub-catchment within a headwater catchment. Particles were 2-60 µm in diameter and two different densities, 2.7 and 1.2 g cm(-3) representing 'inorganic' and 'organic' material. Water samples from the field and catchment outlet were collected during two storm events following slurry application and analysed for particle and suspended sediment concentrations (SSC). SSC from the field and catchment outlet always formed clockwise hysteresis loops indicating sediment exhaustion and particles of the two densities were always found to be positively correlated. Particles from the field formed clockwise hysteresis loops during the first discharge event after slurry application, but anti-clockwise hysteresis loops during the second monitored event which indicated a depletion of readily mobilisable particles. Particles from the catchment outlet always formed anticlockwise hysteresis loops. Particle size became finer spatially, between field and catchment outlet, and temporally, between successive storm events. The results indicate that slurry particles may be readily transported within catchments but that different areas may contribute to pollutant loads long after the main peak in SSC has passed. The density of the particles did not appear to have any effect on particle transport however the size of the particles may play a more important role in the 2-60 µm range.

Assessment of natural fluorescence as a tracer of diffuse agricultural pollution from slurry spreading on intensely-farmed grasslands.

The value of natural fluorescence in tracing diffuse pollution, in liquid phase, following slurry application to land was assessed by field experiment using twelve one hectare lysimeters on a heavy clay soil in Devon, UK, during autumn 2007. A strong linear relationship was found between natural fluorescence intensity and slurry concentration. The ratio of indices of tryptophan-like and fulvic/humic-like fluorescence (TI:FI) varied between 2 and 5 for a range of slurries sampled from Devon farms and allowed slurry to be distinguished from uncontaminated drainage waters (TI:FI<1). Incidental losses of slurry, indicated by significantly enhanced TI:FI ratios, high TI and high ammonium levels, occurred via the drain flow pathway of the drained lysimeters during the first small event following slurry-spreading. The maximum estimated loss from a single lysimeter was 2-8kg or 0.004-0.016% of the applied slurry. In the second larger storm event, some five weeks later, significantly enhanced TI:FI ratios in the drain flows were not associated with high TI but with high nitrate levels and, compared to the earlier storm, an increase in the humification index. This implies the loss of slurry decomposition products during this event but further work is needed to validate this. There was no significant enhancement of TI:FI in the surface/throughflow pathways of the drained or undrained lysimeters in either of the events. The observed change over a period of weeks in the strength and nature of the fluorescence signal from spread slurry restricts quantification of slurry losses to those immediately after slurry spreading. Nonetheless, this study demonstrates the utility of fluorescence as an indicator of slurry in drainage waters and the importance of field drains in diffuse agricultural pollution.