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- Assessing the quality of wetlands as refuelling areas for migrating waterbirds based on resource distribution patterns is challenging. Resources in wetlands can vary both horizontally and vertically and may be differentially available to different bird species at different times of the year. Therefore, the extent to which wetland quality can be generalised across seasons and for a diversity of birds remains unresolved.
- Spatiotemporal variation in abundance and quality of macrobenthos as food for migrating waders was studied in a set of wetland areas near a Mediterranean migration bottleneck in the Balkan peninsula, during both spring and autumn migration. Samples were subdivided into different depth layers to differentiate between parts of the sediment that are accessible to different groups of wader species. To quantify food availability and the resulting refuelling capacity in different wetland habitat types, abundance, wet weight, and lipid and protein content of invertebrate taxa were determined for each sample.
- Invertebrate food availability and quality were markedly higher in spring than in autumn. Given the higher abundance and protein and lipid content of prey in spring, the total energy that could be harvested in spring (3.81 ± 0.79 kJ/m2) was about 7 times higher than in autumn (0.56 ± 0.12 kJ/m2). Most prey were found in the top layer of the sediment (0–22 mm depth), but about a third of the total energy was present in the deepest soil layer that only longer-billed species could reach (55–200 mm depth). Higher quality prey items such as larger-bodied and heavier polychaetes and bivalves were found in the deeper sediment layers.
- For other taxa, there was no evident vertical pattern of increasing individual body size. Prey abundance differed between certain habitat types but, overall, food availability could not be linked to distinct habitats. In spring, redox potential tended to be higher, while pH, vegetation cover, conductivity, and temperature were lower than in autumn.
- Different wetland habitat classes used in a conservation framework may provide similar food resources for waders. As a result, linking food availability to habitat classifications is not straightforward. Furthermore, seasonal variation in wetland quality requires a re-evaluation of the importance of wetland areas during spring and autumn migration. Finally, nutritional analyses are essential for determining the capacity of wetlands to support refuelling by migratory waterbirds.
The low phosphorus (P) fertilizer use efficiency in weathered, P deficient soils calls for better fertilizer formulations. We previously formulated nanoparticles containing P (NP-P) that were a successful fertilizer in nutrient solution. This study was set up to test the fate and the bioavailability of nanofertilizer-P and of that of native (colloid) P naturally present in soil.
MethodsThe NP-P consisted of nano-ferrihydrite (~ 10 nm) loaded with phosphate (P-nFh) and stabilized with either natural organic matter (NOM) or hexametaphosphate (HMP). Natural colloid concentrations were increased with KOH addition, as deflocculating agent, to soil; all tests used samples from P deficient, highly weathered soils.
ResultsPot trials with rice seedlings did not reveal larger P uptake in the NP-P amended soils compared to equal doses of soluble PO4 or soluble HMP. Total Fe concentrations in soil solutions were unaffected by NP-P addition, whereas natural colloidal Fe and P markedly increased by KOH addition. The bioavailability of native colloidal P, mobilized by KOH addition, could not be assessed due to lack of growth, likely related to collapse of the soil structure.
ConclusionsThis study showed that P-loaded iron oxyhydroxide NPs insufficiently enhanced soluble P in soil to offer benefits over soluble fertilizers, likely because of a combined effect of lower diffusivity of NPs compared to Pi and lower bioavailability of NP-P than Pi. Smaller particles or small labile organic colloids might offer an improvement in both aspects.
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