Characterisation of the potamal Danube River and the Delta: connectivity determines indicative macrophyte assemblages

Abstract

The complexity of water bodies in the eupotamal river corridor and the main delta channels of the Romanian Danube is exemplified by the macrophyte vegetation. Two hypotheses provided the background for our study: (a) is the macrophyte vegetation of large, permanently connected branches significantly separated from that of the main river channel; (b) is the macrophyte composition of the Danube main stem significantly altered when the river divides into the three large navigable Delta channels. Water bodies considered were two contiguous sections of the main river channel, two large branches remaining from the historical floodplain, and the three main Delta channels. We quantified macrophyte diversity and floristic variation. Our data set was prepared from the MIDCC-project data base, in which macrophyte occurrence, abundance and habitat parameters are stored for contiguous survey units of the whole Danube river corridor. Field survey method followed that of Kohler and the European Standard EN14184. Results confirmed our first hypothesis: permanently connected side branches still support significantly different macrophyte assemblages, making them important indicators of floodplain connectivity. The diversion of the Danube into its three large navigable delta channels significantly alters the macrophyte vegetation from the c. 300 km of main stem up-river, substantially supporting our second hypothesis. Our results largely enhance the knowledge on aquatic plant biodiversity in the eu-potamal Danube, forming a solid base for long-term studies. We also discuss the relevance of our results regarding the ecological, as well as the conservational, quality of rivers and their floodplains.

Changes in Vascular Flora of the Rzeszow Reservoir after 20 Years (SE Poland)

“…A similar phenomenon is observed in the study area, where floristic diversity increased remarkably, especially in the group of apophytes. This is confirmed by results of other authors [1,19,24], who showed that in relation to the diversification of habitats and land use, floristic richness also is enhanced [8].…”

“…This process is observed in many parts of Europe as a result of a remarkable increase in nutrient loads from sewage and surface runoff from arable fields [2,4,62,64]. River valleys are characterized by a high degree of complexity and patchiness of habitats, and consequently also of vegetation [3,8,24,35]. The increased number of phanerophytes in the study area is associated with the natural process of succession.…”

“…This results from the high natural diversity of sites [2,24]. River valleys play a role of ecological corridors [3,18,[25][26][27] and are refuges of biodiversity [3,8,21,28].…”

“…Sites located along rivers are also exceptionally vulnerable to alien species invasion [18,[29][30][31][32][33][34][35][36]. Artificial water bodies are similar in this respect, and various ecosystems affect them [8,24,37]. In Poland, like all over Europe, wetlands are disappearing, which causes the gradual loss of many rare and threatened species of plants and animals [8,16,28,38].…”

“…As far as the kenophytization index is concerned, urban areas are distinguished by the high contribution of newcomers [63] as well as specificity of dam reservoirs [24]. The index reaches high values also in waterside ecosystems [17,20].…”