人类活动对密西西比河三角洲最近演变的影响

MAN'S IMPACT ON THE COASTAL ZONE OF THE MISSISSIPPI RIVER DELTA

密西西比河三角洲平原最近陆地消失达100km^2/a以上，且逐年增加。其原因主要是各种人类活动所造成的：（1）密西西比河上中游节节筑坝，并进行水土保持，使该河年悬移质输沙量从1953—1970年约4亿吨，减为1970—1978年的2.17亿吨，现在由密西西比河直接输入海中的泥沙仅有1.6亿吨；（2）在河口西南水道修筑了长导堤，使密西西比河入海泥沙进入较深海区；（3）沿河筑堤，阻止了泛溢、分汊等自然的河流作用，因而使沼泽地的河流泥沙供给来源断绝；（4）油气工业开挖的许多运河使海水入浸增加，导致半咸水沼泽衰亡。

: The severe and accelerating land loss in the Mississippi River deltaic plain is chiefly re- sulted from man's activity. (1) Owing to damming and canalization of the Mississippi River and soil conservation in its drainage basin, annual suspended discharge of the river has reduced from about 4×108 tons in 1953-1970 to 2.17×108 tons in 1970-1978 and that of the present Mississippi river to the sea is only 1.6× 108 tons. (2) the construction of jetty in the mouth of the Southwest Pass funnels the river sediment to the deeper sea. (3) The construction of ar- tificial levees stops the natural fluvial process of overflooding, crevassing etc. and cuts off flu- vial sediment supply from the wetland. (4) The construction of oil canals increases salt water intrusion and causes deterioration of brackish-water marsh, This is the most important factor in triggering land loss in the Mississippi River Delta.