Attempts to determine the effects of forest cover on stream flow by direct hydrological measurements in Los Negros,Bolivia

Underlying many payments for watershed services (PWS) schemes in tropical montane forest contexts is the assumption of a direct positive relationship between forest cover and dry season stream flow. We developed a low cost research program to assess the forest cover-stream flow relationship in the Los Negros watershed in eastern Bolivia. We asked three questions: (1) can watersheds that are similar enough to undertake paired catchment studies be identified using only simple parameters such as size, aspect and geographic proximity; (2) can a functioning locally based hydrological monitoring system be set up for less than $10 000 by training local farmers to collect hydrological data, and (3) can such data be used to improve the functioning of a PWS initiative? A land use map of the upper Los Negros valley was created from a 2005 Landsat image and a digital elevation model used to calculate physical and hydrological properties of 10 sub-watersheds. Farmers measured stream flow rates in these sub-watersheds from 2005 to 2008 and maintained 10 automatic rain gauges. We found no relationship between forest cover and stream flow. This may indicate that no such relationship exists, but could also reflect the short period of the study, the low quality of the data, and the fact that the sub-watersheds had relatively similar forest coverage (54–76%). We conclude that (1) watersheds can be identified as “similar-enough-for-analysis” using the criteria of size, aspect and proximity without undertaking further research, (2) a useful hydrological monitoring system can be developed for <$10,000 and (3) although our local farmers did not collect sufficiently high quality data to fully explore the forest/water relationship in Los Negros, with improvements in methodologies, low cost, locally based monitoring has the potential to be an important component of future PWS initiatives. We recommend that stream discharge should be calculated directly; only the most locally relevant hydrological criteria, rather than scientifically complete criteria, should be monitored; locally based monitoring must be institutionalized to reduce staff turnover and hydrological monitoring must be embedded within a context that makes it socially acceptable.     

Crack propagation in mixed mode in wood: a new specimen

Summary For studies on wood structures it is important to have a reliable specimen for mixed mode loading (I+II) of a crack. A new type of specimen derived from the compact tension shear (CTS) specimen proposed by Richard for isotropic materials has been studied. A finite element modelization for pine (Pinus pinaster) gives calibrations in the RL, TL and TR directions. Fracture experiments show a fair agreement between stress intensity factors obtained by calibrations and by the compliance method.     

Spatial and temporal assessment of linear erosion in catchments under sloping lands of northern Laos

Linear erosion (LE), including rilling and gullying, has been identified as the major problem for sustainable agriculture in steepland areas. It causes severe environmental, economic, and social impacts. This issue is even more crucial in those areas undergoing rapid changes in land use, as for example northern Laos, and may dramatically affect soil conservation. Despite an increasing interest in the sloping lands of tropical areas, field evaluations of LE are still infrequent. Furthermore, the controlling environmental factors of topography, land use, climate and soils at the catchment level are seldom analysed. Our main objective was to quantify the spatial and temporal variations of LE at the catchment level and at a yearly basis. The study was conducted in a 0.62 km² watershed of Laos (Luang Prabang province) representative of the slash and burn systems of sloping lands. Linear erosion was monitored from 2001 to 2003 within 9 sub-catchments of differing surface areas, topographic characteristics and land use. The length, depth and width of the linear erosion features were recorded every 5-m from their headcuts to their outlets in order to estimate the total catchment LE. 52 linear features, mainly rills, were formed or developed within the study area with a mean erosion rate of 1.3 Mg ha^{− 1} y^{− 1}. LE rates ranged between 0.1 Mg ha^{− 1} y^{− 1} in 2003 to 2.4 Mg ha^{− 1} y^{− 1} in 2001. LE features mostly occurred within croplands where erosion rates reached 18 Mg ha^{− 1} y^{− 1}. In 2001 and 2002 there was a significant correlation between LE and the proportion of the catchment area under crops (r = 0.88 and r = 0.69, respectively). However this was not the case in 2003 when few rills developed. In 2002 only, LE correlated well with the catchment surface area, the mean slope gradient and the sub-catchment perimeter confirming the non-constancy of LE landscape relation under varying rainstorm conditions. A linear regression model for LE prediction at the catchment level, generated from 2001 data, was able to explain 78% of LE variance for the 9 sub-catchments. However, this model was unable to predict accurately LE for 2002 and 2003 (ME > 5 Mg ha^{− 1} y^{− 1}). This method for quantifying the linear erosion at the catchment level and some of its controlling factors can also be used for prediction over larger areas since topography and land use data, closely correlated with LE, are easily accessible.     

Dynamic modelling for linear erosion initiation and development under climate and land-use changes in northern Laos

Linear erosion (LE) induced either by piping or overland flow is one of the most active factors in the evolution of soils. During single storm events LE may remove enormous amounts of soil material from the uplands to the bottomlands and has thus become a broad challenge for food supply, food security, and human health. Recent and rapid changes in land-use and climate patterns in the sloping lands of tropical areas may dramatically increase LE. Our main objective was to investigate to what extent one could use direct flow velocity estimations from dynamic models for predicting LE initiation and development at the event level. The second objective was to estimate the impact of expected land-use and climate changes on LE. The study was conducted in the 0.62 km² watershed of northern Laos presented inChaplot et al. (2005). Field observations of the formation and the development of LE features throughout 2001 were compared to flow velocity estimations from an existing surface water routing algorithm developed at Utrecht University ([De Roo, A.P.J., Wesseling, C.G. and Ritsema, C.J. 1996. LISEM: a single event physically based hydrologic and soil erosion model for drainage basins. I: theory, input and output. hydrological processes 10 (8): 1107–1117.]). In 2001, two main rainfall events were responsible for the formation or development of 14 linear features with a total length of 972 m and an erosion rate of 3.5 Mg ha^{− 1}. The water routing algorithm was calibrated using the water and the sediment hydrographs observed at the watershed outlet during the first rainfall event. Assuming realistic estimations of flow velocity in hillslopes, a threshold of 0.062 m s^{− 1} for linear erosion estimated over 10-m cells was defined. This threshold, validated using the remaining rainfall event, accurately predicted the length (mean error of estimate of less than 15%) and location of LE features. Using this simulation tool, an increase of the percentage of land under cultivation from 9% to 100% resulted in 600% increase in linear erosion. The tested scenarios of climate changes had less impact on linear erosion.     

Temperature effects on xylem sap osmolarity in walnut trees: evidence for a vitalistic model of winter embolism repair

We studied the effect of temperature on the carbohydrate status of parenchyma cells during winter in relation to the efflux and influx of sugars between parenchyma cells and xylem vessels in 1-year-old twigs of walnut (Juglans regia L.). The mechanism of sugar transfer between contact cells and vessels was also investigated. We obtained new insights into the possible osmotic role of sugars, particularly sucrose, in stem pressure formation and winter embolism repair. Accumulation of sucrose in the xylem sap during winter was mainly influenced by: (1) abundant conversion of starch to sucrose in the symplast at low temperatures; (2) sucrose efflux into the apoplast at low temperatures (1 degrees C); and (3) inefficient sugar uptake at low temperatures, although efficient sugar uptake occurred at 15 degrees C. We hypothesize that a diethyl pyrocarbonate (DEPC)-sensitive protein mediates facilitated diffusion of sucrose from parenchyma cells to xylem vessels (efflux) in walnut. We discuss the possible occurrence of active H+-sucrose symports and the coexistence of both influx and efflux processes in walnut in winter and the modulation of the relative importance of these flows by temperature.     

A natural product that lowers cholesterol as an antagonist ligand for FXR

Extracts of the resin of the guggul tree (Commiphora mukul) lower LDL (low-density lipoprotein) cholesterol levels in humans. The plant sterol guggulsterone [4,17(20)-pregnadiene-3,16-dione] is the active agent in this extract. We show that guggulsterone is a highly efficacious antagonist of the farnesoid X receptor (FXR), a nuclear hormone receptor that is activated by bile acids. Guggulsterone treatment decreases hepatic cholesterol in wild-type mice fed a high-cholesterol diet but is not effective in FXR-null mice. Thus, we propose that inhibition of FXR activation is the basis for the cholesterol-lowering activity of guggulsterone. Other natural products with specific biologic effects may modulate the activity of FXR or other relatively promiscuous nuclear hormone receptors.     

Quantitative and qualitative characterisation of humic products with spectral parameters

Purpose

The application of different humic products for the treatment of soils and plants has increased in recent years. The characteristics of humic products, such as the content and composition of organic carbon and the maturity, provide valuable information which is essential for an adequate application. Such information is crucial for manufacturers, business consultants and users involved in the production, distribution and implementation of humic products. This article presents the correlation between the quantitative indicators of commercial humic products and their spectral characteristics via measurements in the ultraviolet spectrum at 300 nm, in the visible area at 445 and 665 nm and in the near-infrared spectrum at 850 nm.

Materials and methods

We evaluated humic products (liquid and solid) of different origins. Via wet combustion, the content of total organic carbon in humic products can be determined. The precipitation of humic acids from the starting solution determines the composition of the humic products in terms of humic acids (HAs) and fulvic acids (FAs). The dissolution of HAs determines their concentration by titration, while the specific extinction can be assessed via spectrophotometry via measuring the absorption of HAs spectra at the following wavelengths: 300, 465, 665 and 850 nm. The degree of aromaticity and condensation of humic products determines the optical density of the HAs via the E₄/E₆ ratio.

Results and discussion

The content of total organic carbon varied widely from 0.55 to 37.5% across all groups. The content of carbon in HAs, as a percentage of the total carbon in fulvic-type humic products, ranged from 1.29 to 16.00%, while in humic-type products, it ranged from 51.43 to 91.92%. The minimum value of the E₄/E₆ ratio was 2.97, while the maximum value was 6.35. We observed a direct relationship between the dominant type of acids in humic products and the E₄/E₆ ratio.

Conclusions

The optical density of HAs indicates their quality characteristics. The presented optical characteristics for humic products show that there is a direct relationship, especially between HAs/FAs and E₄/E₆ ratios. Measurement at 300 nm (E₃₀₀) in the near-ultraviolet area and at 850 nm (E₈₅₀) in the near-infrared area can increase the range of the spectral study.

     

The role of soil chemical properties,land use and plant diversity for microbial phosphorus in forest and grassland soils

Management intensity modifies soil properties, e.g., organic carbon (C_org) concentrations and soil pH with potential feedbacks on plant diversity. These changes might influence microbial P concentrations (P_mic) in soil representing an important component of the P cycle. Our objectives were to elucidate whether abiotic and biotic variables controlling P_mic concentrations in soil are the same for forests and grasslands, and to assess the effect of region and management on P_mic concentrations in forest and grassland soils as mediated by the controlling variables. In three regions of Germany, Schwäbische Alb, Hanich‐Dün, and Schorfheide‐Chorin, we studied forest and grassland plots (each n = 150) differing in plant diversity and land‐use intensity. In contrast to controls of microbial biomass carbon (C_mic), P_mic was strongly influenced by soil pH, which in turn affected phosphorus (P) availability and thus microbial P uptake in forest and grassland soils. Furthermore, P_mic concentrations in forest and grassland soils increased with increasing plant diversity. Using structural equation models, we could show that soil C_org is the profound driver of plant diversity effects on P_mic in grasslands. For both forest and grassland, we found regional differences in P_mic attributable to differing environmental conditions (pH, soil moisture). Forest management and tree species showed no effect on P_mic due to a lack of effects on controlling variables (e.g., C_org). We also did not find management effects in grassland soils which might be caused by either compensation of differently directed effects across sites or by legacy effects of former fertilization constraining the relevance of actual practices. We conclude that variables controlling P_mic or C_mic in soil differ in part and that regional differences in controlling variables are more important for P_mic in soil than those induced by management.     

Susceptibility of Waxy Starch Granules to Mechanical Damage

Starch samples isolated from wheat flour that represented four possible waxy states (0, 1, 2, and 3‐gene waxy) were subjected to crushing loads under both dry and wet conditions. Calibrated loads of 0.5–20 kg were applied to the starch samples and the percentage of damaged granules was visually determined. Under dry crushing conditions, starches containing amylose (0, 1, and 2‐gene waxy) had between 1% (5‐kg load) to 3% (15‐ and 20‐kg load) damaged granules, whereas waxy starch (3‐ gene waxy; <1% amylose) began rupturing at 0.5‐kg load (3.5% damaged granules) and had 13% damaged granules when ≥10‐kg load was applied. Under wet crushing conditions, normal and partial waxy starch (0, 1, and 2‐gene waxy) showed little difference in percentage of damaged granules when compared to the results of dry crushing. Waxy starch (3‐gene waxy), however, showed substantially increased numbers of damaged granules: 12% damaged granules at 0.5‐kg load, rising to 55% damaged granules at 15‐kg load. The results indicate that waxy starch granules are less resistant to mechanical damage than normal starch granules. Furthermore, blends of normal and waxy wheats or wheat flours intended to have a particular amylose‐amylopectin ratio will be a complex system with unique processing and formulation considerations and opportunities.