Forest influences the dynamics of water, sediment, and materials both globally and locally since the forest canopy intercepts precipitation and changes water volume and quality reaching soil surface. The author has measured raindrops and throughfall drops to estimate erosivity in the forest, however, it is found that drop data is useful tool for physical clarification of precipitation partitioning process by trees. The method was developed to partition whole throughfall into free throughfall, splash throughfall, and canopy drip using raindrop data both open and throughfall. Foliage height to generate canopy drips can be estimated by their fall velocities. The theory on the interface between solid (a plant surface) and liquid (a water drop) could explain the difference of canopy drip generation processes among different canopy species and between leafy and woody surfaces, as well as throughfall generation process in different canopy layer structures. This paper illustrates not only the fun, but the usefulness, importance, and future prospects on the raindrop studies.
Chemical countermeasures against hazardous metal contamination in paddy fields were introduced, which include the use of soil washing methods for cadmium and the use of iron materials for reducing arsenic in brown rice by combining with waterflooding cultivation. Iron (III) chloride was selected as the most suitable detergent from various chemicals. The extraction mechanism of soil cadmium by iron (III) chloride is a function of iron ion hydrolysis reaction, which causes pH decrease. The formation of complexes between chlorine ions and cadmium also contribute to the cadmium extraction. After the washing, a wastewater treatment system installed on site was used to treat the wastewater. Soil cadmium and brown rice cadmium were reduced by 60∼80 % and 70∼90 %, respectively. For arsenic, steel slag, iron hydroxide and zero-valent iron were applied to the paddy field to reduce arsenic in brown rice. The results showed application of zero-valent iron reduced arsenic in soil solution and brown rice. This may be due to the formation of hardly soluble arsenic sulfides on the strongly reducing iron zero-valent surface.
Mine soil contains high concentrations of heavy metals and shows acidity; these environmental factors would generally inhibit plant growth. Recently, several researches have clarified that functional microbes, such as root endophytes, could enhance heavy-metal tolerance in plants naturally growing at mine sites. For example, heavy-metal tolerance in Clethra barbinervis growing at mine site, could be enhanced by root endophytes; without root endophytes, C. barbinervis might not survive at mine soil, showing terrestrial and root growth inhibitions. Aluminium in acidic soil is known to show toxicity to plants and Al tolerance in Miscanthus sinensis might be enhanced by root endophytes, which could detoxify Al in the plant. From the above, native species at mine site, such as C. barbinervis and M. sinensis, seem to develop symbiotic interaction with root endophytes, which could enhance metal tolerance in both plants, and these plants could adapt to severe mine environment, due to microbial support.