Temperature is determinant for all the biological processes. The global warming is originating an alteration in the living beings biological cycles, which for the aquatic ecosystems would mean a displacement upriver of the fluvial species, a biological cycle overtaking to earlier stages, and even the species extinction due to the leak of their development optimal characteristics. The atmospheric temperature predetermines many other processes such as the snow cover duration, the water retention at the basins, the circulating flows and even the living beings growth and development.
The water temperature is linked to the atmospheric temperature, but other factors also influence it, such as the altitude, the snow cover width and length, the thaw etc. It is a fundamental variable in the vegetative period, as well as for the oxygen concentration dissolved in the water, the emergency of insects’ aquatic larval stages etc.
The Sierra de Guadarrama National Park maintains a continuous measurement tracking of the water temperature, both for the rivers and streams and the lakes. In the case of the water courses the network is scattered at different altitudes along the Alto Lozoya, although at the Peñalara Lagoon the temperature is registered at different depth levels. The temperature measurements started in 1998 at the Peñalara Lake and in 2006 at the Lozoya River.
The data gathering is made with waterproof temperature sensors fed with a small battery. The data are registered with ten minutes intervals measurements, getting this way a very high accuracy of the daily, monthly and yearly averages. The devices resolution and error is +/- 0,02% ºC (at 25ºC). The temperature series are periodically gathered in situ, then validated and registered in a database.
The Lozoya River temperatures
As higher is the altitude station location, as lower is the water temperature. That way it is established a thermal gradient with an average yearly value of 0,65ºC every 100 meters ( although it oscillates for the different years between 0,59-0.73ºC/100 m above sea level). The high water temperature oscillation between night and day is remarkable, very related to the atmosphere temperature. Through this network it is possible for example to calculate the common trout eggs hatching time, in accordance with the temperature accumulation in degrees/day, linking it with the double spawn at the mountain rivers.
The maximum water temperatures in the mid summer oscillate between 15ºC and 19ºC, for the altitudes interval of 1.090m-1.452m above sea level. By the contrary, in winter we always observe freezing spells at the highest stations.
Peñalara Lake temperatures
The water density changes with the temperature. That is why occasionally the lakes water column is organized in layers at different depth levels according to their temperature. This process is known as stratification and it is essential to determine the wetlands ecologic behavior. The water temperature continuous measurements tracking at different depth levels allows the process characterization and the identification of other ones such as the ice cover formation, the massive entrance of thaw water or even sporadic summer storms.
The Peñalara Lagoon water temperature rarely exceeds 20ºC at the summer peak, although in winter it remains (under the ice cover) between 0ºC and 4ºC.
The placement of several autonomous measurements systems of diverse environment variables is being consolidated as an excellent tool to support management and to study the Global Change. It will become as much valuable as longer will the available series be.