Production economics of the emerging private fish farming industry in Bulgaria

The production economics of the emerging Bulgarian private carp and trout farming industry were assessed by surveying a representative sample of 20 private and state-controlled farms as well as visiting the National Fresh Water Fish Research Institute, the state-owned fish feed production plant and a fish processing plant.The major constraints for the development of profitable fish farming were found to be the lack of capital and the insecurity of tenure, which nonetheless, do not serve to discourage new entrants into the industry. The expected gross margin per tonne of carp produced in reservoirs or earth ponds is USD 487, while a tonne of trout farmed in concrete raceways shows a gross margin figure of USD 525. State-owned trout farms are only available for outright purchase at auctions, whereas carp farms may be rented, but only for a short term.Fish farmers could benefit from organizing themselves into producer groups in order to improve marketing and secure quality inputs. In particular, there is scope to source quality dry fish diets on both economic and environmental grounds.An extension advisory service is needed to support inexperienced new entrants and researchers should urgently evaluate what seem to be the most cost-effective methods of production.     

Assessment of SoilGrids data for soil erosion estimation at watershed scale: A case study in northern Thailand

Soil erosion has been identified as one of the most destructive forms of land degradation, posing a threat to the sustainability of global economic, social and environmental systems. This underscores the need for sustainable land management that takes erosion control and prevention into consideration. This requires the use of state-of-the-art erosion prediction models. The models often require extensive input of detailed spatial and temporal data, some of which are not readily available in many developing countries, particularly detailed soil data. The soil dataset Global Gridded Soil Information (SoilGrids) could potentially fill the data gap. Nevertheless, its value and accuracy for soil erosion modelling in the humid tropics is still unknown, necessitating the need to assess its value vis-à-vis field-based data. The major objective of this study was to conduct a comparative assessment of the value of SoilGrids and field-based soil data for estimating soil loss. Soil samples were collected from five physiographic positions (summit, shoulder, back slope, foot slope, and toe slope) using the soil catena approach. Samples were collected using a 5-cm steel sample ring (undisturbed) and a spade (disturbed). Data of the landform, predominant vegetation types, canopy cover, average plant height, land use, soil depth, shear strength, and soil color were recorded for each site. The soil samples were subjected to laboratory analysis for saturated hydraulic conductivity, bulk density, particle size distribution, and organic matter content. Pedotransfer functions were applied on the SoilGrids and field-based data to generate soil hydrological properties. The resultant field-based data were compared with the SoilGrids data for corresponding points/areas to determine the potential similarities of the two datasets. Both datasets were then used as inputs for soil erosion assessment using the revised Morgan-Morgan-Finney model. The results from both datasets were again compared to determine the degree of similarity. The results showed that with respect to point-based comparison, both datasets were significantly different. At the hillslope delineation level, the field-based data still consistently had a greater degree of variability, but the hillslope averages were not significantly different for both datasets. Similar results were recorded with the soil loss parameters generated from both datasets; point-based comparison showed that both datasets were significantly different, whereas the reverse was true for parcel/area-based comparison. SoilGrids data are certainly useful, especially where soil data are lacking; the utility of this dataset is, however, dependent on the scale of operation or the extent of detail required. When detailed, site-specific data are required, SoilGrids may not be a good alternative to soil survey data in the humid tropics. On the other hand, if the average soil properties of a region, area, or land parcel are required for the implementation of a particular project, plan, or program, SoilGrids data can be a very valuable alternative to soil survey data.     

Experiments on Water-Sediment Nutrient Partitioning Under Turbulent, Shear and Diffusive Conditions

Cultural eutrophication from excessive input of nutrients is a major problem for many water bodies around the world. Phosphorus and to a lesser degree nitrogen constitute the limiting elements for growth of plankton cells. Mobility, speciation and partition of nutrients in aquatic ecosystems depend on a number of physicochemical parameters. Experiments have been conducted for quantification of nutrient partition between ambient water and cohesive sediments. The experiments included nitrate and soluble phosphorus (superphosphate - 46% P₂O₅ fertilizer) partitioned between tap water and sediment slurries. The slurries involved kaolinite and bentonite as well as natural organic rnud from, Lake Okeechobee, Florida. The nutrient exchange was promoted by sediment resuspension. Resuspension was induced either under homogeneous turbulent conditions in an oscillating-grid tank or by shear flow in a lock-exchange flume. The effects of phosphorus or nitrogen concentration, sediment concentration, water temperature, pH and salinity on nutrient partition were quantified. The results obtained through this study appear to be in agreement with data from other similar laboratory or field studies.     

Seasonal Variation of Phenolic Antioxidant-mediated α-glucosidase Inhibition of <Emphasis Type="Italic">Ascophyllum nodosum</Emphasis>

Ascophyllum nodosum is a brown seaweed that grows abundantly in the US Northeast coastal region. This study examined the seasonal variation of A. nodosum in phenolic contents and subsequent antioxidant, α-glucosidase and α-amylase inhibitory activities. A. nodosum was harvested monthly and extracted in hot water and the resulting extracts were spray-dried. The results indicate a clear seasonal variation in terms of phenolic content, with June and July being the highest (36.4 and 37 mg/g, respectively) and May the lowest (21.8 mg/g). The antioxidant activities, in terms of 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity, correlated with the phenolic contents observed (r = 0.81), with the month of July being the highest (58%) and April the lowest (26%). Similarly in terms of Trolox equivalent, July had the highest activity (15.53 μM) and April and May the lowest (8.40 and 8.27 μM, respectively). α-glucosidase inhibitory activity exhibited a pattern similar to the phenolic contents observed with July having the highest inhibitory activity (IC₇₀ 2.23 μg) and April the lowest (IC₇₀ 26.13 μg), resulting in an inverse correlation between IC₇₀ values and total phenolic content (r = −0.89). Such seasonal variation is believed to be caused by temperature-related stress considering that A. nodosum is a cold water species.