Time series analyses reveal transient relationships between abundance of larval anchovy and environmental variables in the coastal waters southwest of Taiwan

We investigated environmental effects on larval anchovy fluctuations (based on CPUE from 1980 to 2000) in the waters off southwestern Taiwan using advanced time series analyses, including the state-space approach to remove seasonality, wavelet analysis to investigate transient relationships, and stationary bootstrap to test correlation between time series. For large-scale environmental effects, we used the Southern Oscillation Index (SOI) to represent the El Niño Southern Oscillation (ENSO); for local hydrographic conditions, we used sea surface temperature (SST), river runoff, and mixing conditions. Whereas the anchovy catch consisted of a northern species ( Engraulis japonicus ) and two southern species ( Encrasicholina heteroloba and Encrasicholina punctifer ), the magnitude of the anchovy catch appeared to be mainly determined by the strength of Eng. japonicus (Japanese anchovy). The main factor that caused the interannual variation of anchovy CPUE might change through time. The CPUE showed a negative correlation with combination of water temperature and river runoff before 1987 and a positive correlation with river runoff after 1988. Whereas a significant negative correlation between CPUE and ENSOs existed, this correlation was driven completely by the low-frequency ENSO events and explained only 10% of the variance. Several previous studies on this population emphasized that the fluctuations of larval anchovy abundance were determined by local SST. Our analyses indicated that such a correlation was transient and simply reflected ENSO signals. Recent advances in physical oceanography around Taiwan showed that the ENSOs reduced the strength of the Asian monsoon and thus weakened the China Coastal Current toward Taiwan. The decline of larval anchovy during ENSO may be due to reduced China Coastal Current, which is important in facilitating the spawning migration of the Japanese anchovy.     

红壤区土壤中镁肥肥效的研究

虽然早在一个世纪以前,就已经知道镁是植物正常生长所必需的养分之一,但道到本世纪三十年代才开始施用镁肥.最近,对镁的作用和镁肥施用间题.给予了较大的注意^p[1,2].这是由于镁在植物营养上的重要作用日益为人们所了解;以往认为是由病害所引起的一些症状,查明了往往是由镁素缺乏而引起;随着氮、磷、钾等化学肥料的大量施用,农作物产量增加,但由于没有相应地施用镁肥,加剧了土壤中镁素的缺乏.在某些国家,过去随钾肥可带入一些镁素,但后来由于肥料的精制提纯,这种无意的施用也停业了,因而作物缺镁症状增多.     

层状土中毛管水上升的实验研究

土壤盐渍化的重要机制是地下水中可溶盐在蒸发作用下不断向表土聚集;次生盐渍土的形成则可能是由于人为抬高地下水位,土壤毛管水重新分配土中盐分所致.不管怎样,防止土壤盐渍化的积极而彻底的方法是消除地下水位抬高的因素.但是,全面而根本的措施,往往限于客观条件不易做到,因此大多数都采取治标措施.例如,利用耕耘增加毛管水上升的困难,以及洪淤压碱等等.