Water courses

Watercourses are one of the 7 environments identified in the Provincial Nature Reserves.

They include bodies of water with very different characteristics in terms of water flow, slope and substrate type, and bank vegetation, all of which share the presence of running water:

• tumultuous torrents bursting from the glacial front
• high altitude springs
• mountain valley bottom streams
• placid streams flow ing through the main valleys

One type of running water environment that escapes longitudinal classification is the piedmont resurgence. Its very special characteristics - the brevity of its course, its origin from low-lying springs - prevent it from being included in the spring-river-river scheme. The springing of the water after long underground journeys gives it certain characteristics that also strongly influence its biological community. The water, which generally gushes out at the base of large rock walls at the intersection with the plain or the valley floor, in riverbeds often regularised by man (these are the so-called ditches), has a temperature and chemical characteristics that tend to be constant throughout the year. Dissolved salts are very low due to the very short journey to the surface. The very high transparency and constant flow rate allow for the development of a flourishing and varied underwater vegetation, which is also the main food source for many bottom invertebrate organisms. These, in turn, are the essential food source for the resurgence's particular fish population.

Generally speaking, along its course a watercourse undergoes a progressive enrichment of its biological community, both in terms of fauna and flora.

When the torrents reach the mountain valley floors and those of the main valleys, the impetus of the water diminishes considerably, and so does its capacity to re-mould the debris and rejuvenate the riverbed: diverse and fairly stable plant communities can thus be established on the bed. Even if the riverbanks are largely dry during the summer, the plants that grow there can make use of the water present among the alluvial materials, as the water table is always close to the surface. These phytocoenoses are usually characterised by the presence of narrow-leaved willows, mainly Salix purpurea, S. eleagnos, S. viminalis and S. triandra, all species that usually assume a shrub or low tree habit. Various pioneer plants grow among the willows, such as Glyceria plicata, Agrostis tolonifera, Phalarisarundinacea, Calamagrostis epigejos, Petasites hybridus and Tussilago farfara. In the water, watercress(Nasturtium officinale) is frequent in sections with a weak current. The riparian willow grove(Salix eleagnos) can be considered a precursor stage of the white alder woodland, however, the phytocoenosis of the river beds rarely evolves into tree formations, since floods periodically reshape the riverbed, wiping out or nearly wiping out the vegetation. The forests of white willow(Salix alba) used to represent the typical riparian vegetation of rivers, but they have been almost totally destroyed by capillary works of embankment and water channelling, which have not even spared the secondary courses, profoundly distorting the characteristics of their precious flora.

Watercourses, especially those with the greatest flow, are certainly among the most important environments for avifauna. The presence of water in fact represents a guarantee in terms of feeding possibilities, which depending on the species can be oriented towards invertebrates, fish, the plant component or other. If the watercourse is endowed with a strip of riparian vegetation, this can be an excellent site for nesting.

In mountain torrents, which have rather nutrient-poor waters and show extreme conditions of current velocity and turbulence, only the brown trout is widely present, mostly staying in the small holes between waterfalls and rapids, sometimes flanked by a few other species. Valley bottom streams, on the other hand, in which rapids are alternated with frequent large holes, present a somewhat greater fish diversity and a much higher productivity. Here, the absence of turbulence and somewhat higher summer temperatures allow the stable settlement of a greater number of fish species than in streams. In fact, many cyprinids, although they also tolerate cold water, can only successfully reproduce at temperatures above 15°C. Thus, in addition to the still dominant presence of salmonids, such as the marble trout and grayling, there are also many cyprinids, known as rheophiles (=river lovers), such as the common barbel and the pigo, as well as tench, pike and other marginal species. In foothill resurgences, there are not many species permanently present. Being mostly in direct communication with the river, however, and by virtue of their characteristics, the resurgences are ascended by various species during the breeding season. This is the case, for example, for the Pike, which spends its trophic phase inside the river, but takes itself to these vegetation-rich peripheral environments to spawn.

The watercourses teem with a hidden life made up of an astonishing array of small invertebrates, most of which live firmly anchored to the stones on the bottom. There are countless species, which also possess the very important function of contributing, by consuming organic substances, to the natural purification of the watercourse.

The mammal species that frequent aquatic environments are numerous, but such frequentation is almost always occasional, linked to the search for food or to the role of 'wildlife corridors' possessed by watercourses. On the other hand, a real link with watercourses is shown by the water shrew, a little-known 'micro-mammal' but characterised by an extraordinarily interesting way of life.

Reptiles are vertebrates normally bound to warm, sunny environments and for this reason are not frequent visitors to watercourses. The only exception is the taxidermy snake, a snake that finds its preferred habitat in rivers and low-lying streams.

Watercourses are unsuitable environments for the presence of Amphibians, which generally occupy stagnant water habitats. In fact, running water is not used for laying eggs, as these risk being carried far away. The only Amphibian closely related to this type of environment is the spotted salamander, which uses streams to lay its larvae.