Changes In Hydrological Characteristics Research Articles

Root studies on grass species in a semi-arid South Africa along a degradation gradient

Understanding changes in hydrological characteristics of rangeland ecosystems with degradation is essential when making rangeland management decisions in arid and semi-arid areas to ensure sustainable animal production. The impact of rangeland degradation on root production, root/shoot ratio and water-use efficiency was therefore determined for a semi-arid rangeland, over a 7-year period (1999/00 to 2005/06 growing seasons). Water-use efficiency (WUE) is defined as the quantity of above- and/or belowground phytomass produced over a certain period of time per unit of water evapotranspired. Sampling was from rangeland artificially maintained in three different rangeland conditions, viz. good, moderate and poor. As much as 86, 89 and 94% of the roots for rangelands in good, moderate and poor conditions, respectively, occurred at a depth of less than 300 mm. Root mass was strongly seasonal with the most active growth taking place during March and April. Root mass appears to be greater than aboveground phytomass for this semi-arid area, with an increase in roots in relation to aboveground phytomass production with rangeland degradation. The mean monthly root/shoot ratios for rangelands in good, moderate and poor conditions were 1.16, 1.11 and 1.37, respectively. Rangeland degradation significantly lowered above- and belowground phytomass production as well as the water-use efficiency. The mean WUE (root production included) were 4.79, 3.54 and 2.47 kg ha −1 mm −1 for rangelands in good, moderate and poor conditions, respectively. These water-use efficiency observations are among the few also including root production in its calculation. As a proportion of annual phytomass, litter fall of 7.17, 4.64 and 3.41% was obtained for rangelands in good, moderate and poor conditions, respectively. Increasing rangeland degradation increased the replacement of total root system by about 10 months and decomposition time of litter by 6 months. The importance of a well-established root system for sustainable production in the semi-arid rangelands cannot be overemphasized.

Hydrologic Impacts of Disturbed Lands Treated with Dust Suppressants

This study presents research on changes in hydrologic characteristics of disturbed land surfaces that have been treated with dust suppressants. Disturbed land surfaces, such as construction sites and unpaved roads, are sources of fine particulate matter. The application of dust suppressants affects the runoff characteristics as well as the water quality of the runoff. The changes in runoff characteristics were investigated in the field using a rainfall simulator on plots treated with 11 different dust suppressants. The rainfall simulation system was able to provide a uniform distribution of rainfall over a 2.4×2.4 m (approximately) plot at relatively low rainfall intensities (21 mm/h). Results of the study indicate changes in runoff rates and volume, and the timing of runoff initiation. The majority of the plots had higher runoff volumes and an earlier time of runoff initiation as compared to the control plot. The total suspended solids in the runoff were reduced for the majority of the plots. Extrapolati...

COMPACTIBILITY OF CULTIVATED SPHAGNUM PEAT MATERIAL AND ITS INFLUENCE ON HYDROLOGIC CHARACTERISTICS

Deformation-stress-moisture relationships of cultivated sphagnum peat materials were studied in the laboratory using the Ottawa Texture Measuring System, an apparatus developed by Agriculture Canada. Impact of compaction on hydrologic characteristics was also investigated to determine the maximum stress which may be applied in the field during seed-bed preparation without limiting aeration for crop production. The study revealed that the compactibility of peat is relatively unaffected by moisture content at compactive pressure ≤13 kPa. However, under higher compactive pressure, the peat reaction was very similar to that of mineral soils, in which the compactibility increases with increasing moisture content until it reaches a maximum bulk density at saturation. The deformation-stress-moisture content relationships may be expressed by a simple third order polynomial equation. In response to compaction, the saturated hydraulic conductivity of the peat material reduced more than three orders of magnitude as bulk density increased from 0.1 to 0.25 g/cm3. A major increase in moisture retentivity was found in the compacted peat. Changes in hydrologic characteristics are primarily attributed to the reduction in large pores. Based on this information, it is concluded that compactive pressure exceeding 50 kPa may cause adverse effects on soil aeration.