Abstract

By the beginning of the 1970s, only two large regions with natural vegetation, namely the Volga–Akhtuba floodplain and the Volga delta, had remained in the Volga River valley. The largest part of the remaining valley had been converted into a cascade of reservoirs. The conservation of meadow, marsh, and forest plant communities in the lower reaches of the Volga River located in the semi-desert and desert zones is due to regular water releases of the Volgograd hydroelectric power station downstream. These artificial water discharges into the Lower Volga valley in the spring–summer period have taken the place of natural floods. However, in the conditions of regulated water flow, the rise in the water level decreased during floods and the duration of flooding of the floodplain ecotopes shortened. The river channel deepened along a 100-km river section in the near-dam part of the Volgograd hydroelectric power station in the northern part of the floodplain. These dams hinder water flow to the Akhtuba–Volga floodplain during spring and summer floods. They surround agricultural lands with artificial irrigation systems and settlements in the floodplain. The recreational use of the Lower Volga valley has increased in the past few decades. Before the construction of the largest Volga hydroelectric complexes (the Kama, Gorky, Kuibyshev, Volgograd, and Saratov ones) in 1954–1955, five geobotanical transects were laid out in the course of the Caspian expedition of Moscow State University. Subsequently, four of the transects were surveyed in 1982 and 2008 –2013. It was established that xerophytization and ruderalization of vegetation occurred on all transects. These phenomena were not similar in different sections of the floodplain. They were most pronounced near the Volgograd Hydroelectric Power Station and in the places of narrowing of the valley. The reduction in the height and duration of floods after the regulation of the water flow, high local grazing, and recreation pressure is the main reason for xerophytization and ruderalization of vegetation. Among the invasive species, Fraxinus pennsylvanica, Conyza canadensis, Bidens frondosa, and Xanthium strumarium s.l. play the most important role in changes in the vegetative cover of the Volga–Akhtuba floodplain. Thus, not all phenomena related to the dynamics of the vegetation and flora in the Volga–Akhtuba floodplain were caused by restructuring of the Volga hydrological regime after regulation of its water flow. The invasion of alien plants, increased recreation load, and changes in the economic use of the vegetation cover in the territory have played a particular role in this process.

中文翻译：

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伏尔加-阿赫图巴泛滥平原固定断面的长期观测结果

摘要

到1970年代初，伏尔加河流域仅剩下两个拥有天然植被的大区域，即伏尔加河－阿赫图巴泛滥平原和伏尔加河三角洲。剩余山谷的最大部分已被改造成一系列的水库。位于半沙漠和沙漠地区的伏尔加河下游的草甸，沼泽和森林植物群落的保护归因于伏尔加格勒水电站下游的定期放水。在春夏季，这些人造水排入下伏尔加河谷已取代了自然洪水。但是，在水流量调节的条件下，洪水期间水位的上升下降，洪泛区生态环境的洪水持续时间缩短。在洪泛区北部伏尔加格勒水电站的近坝部分，河道沿100公里的河段加深。这些大坝在春季和夏季洪水期间阻碍了水流向阿克图巴–伏尔加河平原。它们用人工灌溉系统和洪泛区周围的居民区包围着农田。下伏尔加河谷的娱乐用途在过去几十年中有所增加。在1954年至1955年建造最大的伏尔加河水电综合体（卡马，高尔基，库比雪夫，伏尔加格勒和萨拉托夫的水电综合体）之前，在莫斯科国立大学里海考察中布置了五个地质植物样带。随后，在1982年和2008年–2013年对四个样带进行了调查。已经确定，在所有样带上都发生了植被的干旱化和去矿质化。这些现象在洪泛区的不同区域并不相似。在伏尔加格勒水电站附近和山谷狭窄的地方，它们最为明显。调节水流量，提高局部放牧和恢复压力后洪水的高度和持续时间的减少是植被进行干旱植物化和反矿化的主要原因。在入侵物种中，游憩压力是植被干旱化和粗化的主要原因。在入侵物种中，游憩压力是植被干旱化和粗化的主要原因。在入侵物种中，伏特加-阿赫图巴泛滥平原的植被覆盖变化中最重要的作用是水曲柳，加拿大Conyza canadensis，Bidens frondosa和Stranarium sl。因此，并非所有与伏尔加河-阿赫图巴泛滥平原植被和植物群落动态相关的现象都是由伏尔加河水流调节后的水文状况的重组引起的。外来植物的入侵，增加的娱乐负荷以及该地区植被的经济利用变化在这一过程中发挥了特殊作用。