During the last few decades the methods have developed rapidly. Today we can apply a wide range of physical, chemical and biological analytical methods and analyses for monitoring purposes, and in principle almost all chemical compounds and microbes can be identified. This is in theory but in water quality monitoring the reality may be different; our methods and analytical tools may often be insufficient to meet the targets. In general, our knowledge of ecosystems and their function is often limited and typically only a small set of analyses and measurements can be carried out due to a shortage of funding. The costs have increased more rapidly than the funding available for monitoring, and this is one reason why automated sensors have become more common in monitoring. Another reason is that high-frequency measurements and analyses can provide much more data than monitoring based on traditional manual sampling, and also with high accuracy and better coverage both spatially and temporally in the area in focus. At present we are facing a new challenge: how can we take advantage of the vast amount of data the sensors provide us?
The “Vanajavesi-portal” collects data from a number of sensors located in the watercourse of the Vanajanselkä catchment, which in turn belongs to the upper reaches of Kokemäenjoki River basin, in southern Finland. The portal provides high-frequency water quality data for both ordinary people and scientists who are interested in the area. We hope the data can be used for teaching and research purposes, but also for learning how our lakes and rivers are functioning and responding, for example, to different stressors such as episodic weather patterns with high floods and/or droughts.
The drainage basin upstream from the Sääksmäki bridge (2774 km2) comprises 10% of the whole Kokemäenjoki drainage basin (27010 km2), which is the 4th largest drainage basin in Finland. Lake Vanajanselkä is the largest lake (103 km2) with a maximum depth of 23 m. The largest inflow to Vanajanselkä is called Lepaanvirta, and its discharge is on average 18 m3 s-1, which corresponds to 90% of the total inflow to the lake. The lake basin is wide and vulnerable to wind mixing, although there is almost 100 small and larger islands and rocky islets. During the last four decades the ecological status of the lake has improved as a result of better wastewater treatment of industry and municipalities. Today a major proportion of nitrogen and phosphorus comes from agriculture, and only a small fraction originates from wastewaters. However, the main water systems is still suffering the consequences of eutrophication although many smaller lakes and upstream rivers have better water quality than the downstream systems.
The ”second lake” within the Vanajavesi watercourse is called Kernaalanjärvi in Janakkala. It receives water from Pääjärvi, the upstream lake in the eastern part of the drainage basin, through the rivers Teuro ja Puujoki, and from the western part of the drainage basin from Loppijärvi lake through river Tervajoki (25.7 km2, from Renkajärvi lake through Hyvikkälänjoki (16.5 km2) and from Takajärvi lake through Räikälänjoki (53.6 km2). From Kernaalanjärvi lake, water drains via Hiidenjoki through the city of Hämeenlinna to Lepaanvirta and further to Vanajanselkä.
