Modelling the effects of land-use change on runoff and sediment yield for a meso-scale catchment in the Southern Pyrenees

The Southern Pre-Pyrenees experienced a substantial land-use change over the second half of the 20th century owing to the reduction of agricultural activities towards the formation of a more natural forest landscape. The land-use change over the last 50 years with subsequent effects on water and sediment export was modelled with the process-based, spatially semi-distributed WASA-SED model for the meso-scale Canalda catchment in Catalonia, Spain. It was forwarded that the model yielded plausible results for runoff and sediment yield dynamics without the need of calibration, although the model failed to reproduce the shape of the hydrograph and the total discharge of several individual rainstorm events, hence the simulation capabilities are not yet considered sufficient for decision-making purposes for land management. As there are only a very limited amount of measured data available on sediment budgets with altered land-use and climate change settings, the WASA-SED model was used to obtain qualitative estimates on the effects of past and future change scenarios to derive a baseline for hypothesis building and future discussion on the evolution of sediment budgets in such a dryland setting. Simulating the effects of the past land-use change, the model scenarios resulted in a decrease of up to 75% of the annual sediment yield, whereas modelled runoff remained almost constant over the last 50 years. The relative importance of environmental change was evaluated by comparing the impact on sediment export of land-use change, that are driven by socio-economic factors, with climate change projections for changes in the rainfall regime. The modelling results suggest that a 20% decrease in annual rainfall results in a decrease in runoff and sediment yield, thus an ecosystem stabilisation in regard to sediment export, which can only be achieved by a substantial land-use change equivalent to a complete afforestation. At the same time, a 20% increase in rainfall causes a large export of water and sediment resources out of the catchment, equivalent to an intensive agricultural use of 100% of the catchment area. For wet years, the effects of agricultural intensification are more pronounced, so that in this case the intensive land-use change has a significantly larger impact on sediment generation than climate change. The WASA-SED model proved capable in quantifying the impacts of actual and potential environmental change, but the reliability of the simulation results is still circumscribed by considerable parameterisation and model uncertainties.     

Re-Evaluation of Soil Nitrogen Sampling Strategy Effects on Statistical Power

Soil sampling may be used as a decision-making tool for late-vegetative stage nitrogen (N) fertilizer applications in corn (Zea mays L.). Recommended sampling strategies following banded fertilizer applications commonly suggest taking cores from both on the fertilizer band (B) and off the band (O-B), however we hypothesized that soil nitrate concentrations (NO₃^?ppm) in the O-B were not influenced by N application rate. Analyzing samples from six experiments, we found there was a strong relationship between NO₃^?ppm and applied N rate in the B, but not the O-B position. Power analysis revealed that finding significant differences in applied N rates was only likely when sampling on the B and the difference in N rate was greater than 110 kg N ha^?1. This demonstrates that soil N sampling is not sensitive to small differences in applied N, and that O-B soil cores may only dilute the ability to detect these differences.

Abbreviations: B, on N fertilizer band; O-B, halfway between the corn row and the N fertilizer band; NO₃^?ppm, log-transformed nitrate-N concentration (ppm); NH₄⁺ppm; ammonium-N concentration (ppm); D1, 0–30 cm depth; D2, 30–60 cm depth; C-220, contrast of N rates differing by 220 kg N ha^?1; C-110, contrast of N rates differing by 110 kg N ha^?1; C-55H, contrast of N rates differing by 55 kg N ha^?1 at high N rates; C-55L, contrast of N rates differing by 55 kg N ha^?1 at low N rates; A:N, ratio of non-transformed ammonium-N to nitrate-N concentrations; 0N, unfertilized treatment; CV, coefficient of variation; SE, standard error.     

Influence of metam sodium on the dissipation and residual biological activity of the herbicides EPTC and pebulate in surface soil under black plastic mulch

Metam sodium is a potential replacement for methyl bromide, which is used to control soil pests. Metam sodium rapidly breaks down in the soil to form methylisothiocyanate (MITC). Dissipation of the herbicides EPTC and pebulate in a silt loam soil under plastic mulch in the absence and presence of metam sodium was examined in field experiments in 1998 and 1999 at Knoxville, Tennessee. EPTC half-life (DT(50)) was 9 d, but when applied in conjunction with metam sodium DT(50) increased to 22 d. Similarly, average pebulate DT(50) was 8 d and increased to 23 d when applied in conjunction with metam sodium. This increase in herbicide DT(50) with the addition of metam sodium is thought to be due to a reduction in soil microorganisms that degrade EPTC and pebulate. EPTC applied with metam sodium injured tomato plants and reduced total crop yield more than EPTC, pebulate, or pebulate with metam sodium. The increased tomato injury may have been related to the greater and prolonged activity of EPTC and slower EPTC dissipation in the presence of metam sodium or MITC.     

Assessment of tree species richness as a surrogate for macrofungal species richness

Attempts to understand and conserve biodiversity are hampered by a lack of information about many taxonomic groups, particularly those groups that are the most species rich. Although fungi are ubiquitous and play an important role in decomposition, nutrient cycling and nutrient uptake, little is known about fungal diversity, as fungi are usually cryptic and ephemeral. Based on a meta-analysis of macrofungal diversity studies, we show that tree diversity is a promising surrogate for macrofungal diversity at large spatial scales. We present evidence that trees species richness can be used to predict macrofungal species richness and that on the global scale, the distribution of individual tree and macrofungal species notably differs. Additionally our findings provide support for the use of “ratio estimates” to estimate fungal species richness.     

Evolutionary history of the symbiosis between fungus-growing ants and their fungi

The evolutionary history of the symbiosis between fungus-growing ants (Attini) and their fungi was elucidated by comparing phylogenies of both symbionts. The fungal phylogeny based on cladistic analyses of nuclear 28S ribosomal DNA indicates that, in contrast with the monophyly of the ants, the attine fungi are polyphyletic. Most cultivated fungi belong to the basidiomycete family Lepiotaceae; however, one ant genus, Apterostigma, has acquired a distantly related basidiomycete lineage. Phylogenetic patterns suggest that some primitive attines may have repeatedly acquired lepiotaceous symbionts. In contrast, the most derived attines have clonally propagated the same fungal lineage for at least 23 million years.     

Solar photovoltaic power systems: will they reduce utility peaking requirements?

From an analysis of the long-run electric generating requirements of several representative utilities, it is concluded that the energy supplied by solar photovoltaic power devices will displace primarily base-load, and to a lesser extent intermediate, generating plants, even at relatively modest penetrations corresponding to several percent of the utility peak load. Attaching photovoltaic devices to the utility grid will not yield significant fuel oil savings over the long run, in which utilities approach the economic optimum generating mix, and will increase peak plant requirements. Utility capacity and fuel savings of photovoltaic devices are reported both for the case without storage and for the case in which the utility has access to load-leveling storage.     

Solar Availability for Winter Space Heating: An Analysis of SOLMET Data, 1953 to 1975

Solar availability for space heating on coldest-weather days has been determined from an analysis of SOLMET data tapes. The tapes contain hourly readings of insolation and ambient temperature over the period from 1953 through 1975. Scatter diagrams of insolation versus heating degree-days, compiled on a daily basis, indicate a wide variation in the insolation level, even during coldest-weather periods. For all but one of the eight sites studied, the peak-day backup energy requirement of the solar system was in excess of 85 percent of the peak-day energy requirement of the conventional (nonsolar) heating system.     

Ocular hazard from picosecond pulses of Nd: YAG laser radiation

Seven rhesus monkeys (14 eyes) were exposed to 1064-nanometer radiation in single pulses of 25 to 35 picoseconds fromn a mode-locked Nd: YA G laser. Threshold injury resulted from single pulses with a mnean energy of 13 +/- 3 mnicrojoules. Electron microscopy of the retina revealed that damnage was highly localized in the photoreceptor and pigmented epithelial cells at the oluter retina. Membrane disruption, distorted outer segmtzents, and abnormnal melanin granules resembling fetal premelanosomnies were observed.