Finland is called the land of a thousand lakes. How many lakes are there in Estonia?
According to the Estonian Encyclopedia Estonica 4.7% of Estonia’s territory is occupied by lakes and reservoirs. The area of the lakes is 1 hectare (imagine a square with a side of 100 meters) about 1200. By the way, swamps are also called lakes.
Estonia’s largest inland lake – Vyrtsjärv (269.19 km²). And the fifth largest in Europe is Lake Peipsi (2613 km²), which Estonia shares with Russia. The lake is about 96 km long and up to 50 km wide. Interestingly, Lake Peipsi is only 73% of the lake complex, which also includes Teploe (7%) and Pihkvajärv (20%), the total area of which, together with Lake Peipus, is 3555 km². The area of lakes fluctuates depending on the season and changes in water levels. The average depth of Lake Peipsi is 7.5 meters, the largest is 16.6 meters. The name of the deepest lake in Estonia is Rõuge -Suurjärv – its depth is 38 meters and its size is only 585 m × 300 m. 42 The area of Estonian Lake is over 1000 per 1000 m and only a few dozen of them are deeper than 20 meters.
The deepest Narva River (Narova) runs along the Estonian-Russian border. It originates from Lake Peipsi and has a speed of 390-410 m 3 / s takes its waters to the Gulf of Finland. The Emajõgi River flows from south to north and connects the two largest lakes in Estonia – Lake Peipsi and Lake Võrtsjärv. The average water consumption at its mouth is about 70.1 m³ / s. Estonia’s longest river – Võhandu (162 km) – flows into Lake Warm, which connects with Lake Peipsi.
There are also man-made reservoirs. They were once created for agricultural needs and watermills, and not just in rural areas. On the map of the Reval dacha area from 1865 (Reval I Vorstadt quarter) you can see a large number of ponds, which, as the old days say, disappeared from the urban landscape only in the twentieth century. Die Stadt is the part of Tallinn that we call the “Old Town”. To his left is the North Tallinn district. As there were many wooden buildings in this district, the ponds could also be used for firefighting.
The artificial reservoirs of the Pirita, Jagala and Sodla rivers are still used for Tallinn’s water supply.
At first it was lacustrine oceanography, then it was expanded to limnology
It turns out that there is science that studies the physical, chemical, biological aspects of lakes, including reservoirs, and this is called limnology. The name “limnology” comes from the Greek words translated as “lake” and “learning”, in other words – lake science. Limnology was founded by a Swiss scientist François Gigolo Trout (1841-1912). He studied biology, chemistry, the water cycle, the sediments of Lake Geneva and their interrelationships, calling his profession “the oceanography of the lake.” He proposed a method for determining the color of reservoirs and the Forel-Ule scale for its determination. Limnology studies water pigmentation, the biodiversity of species living there, and changes in chemical composition.
Relationship between limnology and other sciences
As is often the case in science, the division of research areas is conditional and interrelated. For example, hydrobiologists study aquatic organisms, ie organisms that have adapted to living in the aquatic environment and for most of their life cycle in water, including: fish, plankton, algae, crustaceans, as well as most amphibians and even mosquitoes and wedges. Ichthyologists study fish and the factors that affect their reproduction. The presence of food is one such factor, so all links in the food chain are always taken into account, and the food chain starts with plankton, small organisms that drift freely in the water column. In turn, one of the most important factors in the development of plankton is the overall salinity and pH of the water. Studying the composition of water is very similar to the problem of a chemistry lesson, isn’t it? The issue of water composition can be linked to human economic activity and already points to environmental problems. The growth and vital activity of phytoplankton (algae, cyanobacteria) are influenced by the amount of sunlight entering the reservoir, which can also be measured as the temperature distribution with depth, and is already a link between biology and physics.
Is it possible to study limnology at school?
PASCO’s scientific digital laboratories can be used by the university’s research team at the lake, as well as by a teacher and students at the school. Lessons outside the school walls were strongly encouraged before the transition to distance learning. Research can take place both in the classroom based on previously collected samples and at the sampling site if we organize a class expedition to the nearest reservoir.
Answering the question, is it possible to study limnology at school? – Yes of course. What substances? And in physics and biology, and in science, geography and chemistry, there is an opportunity to draw a parallel with research.
We measure the tank temperature
Let’s get back to the task of studying temperature changes with depth – you can use a water temperature sensor to measure it PS-2151 … The sensor can be used not only in fresh water but also in sea water. There are corresponding switching modes, taking into account the density of the water. The maximum reading depth of the sensor is limited by the wire length of 10.5 meters. Bluetooth adapter Airlink The PS-2151 water temperature sensor can be connected to Android, iOS and Chromebook smartphones.
In most Estonian lakes, the water is completely mixed twice a year. Spring mixing usually takes place in April-May and autumn in October-November, when the temperature of the whole water column is 4 ° C. In deeper lakes (for example Lake Verevi in Elva, where the maximum depth is 11 meters), water does not mix during spring floods, but only in autumn and it does not happen every year. In summer, the temperature of the water column can vary greatly between layers. In large shallow lakes exposed to winds (eg Chudskoye, Vyrtsjärve, Vagule, Ermus) the water temperature is relatively uniform. In shallow small lakes with dark water, the temperature difference is especially noticeable during the summer months. The temperature of the surface layer can be 20-25 ° C, but at a depth of 3-4 m it starts to drop to 10 degrees per meter.
Improvement of sampling points
In order to compare the measurements in different seasons, it is necessary to determine the geographical coordinates and the time of the measurements. There are several ways to do this by storing the data in a single file as part of a complex measurement of different sensors. This is feasible with software SPARKvue … Up to 5 wireless sensors can be connected at a time via Bluetooth.
SPARKvue Is a data collection and analysis application. You can install and use it for free from the Google Play Store, APP Store, and Chrome Store, respectively. No sensor is required to start it. Install and try!
Method 1: You can connect a portable GPS station to confirm the coordinates PS-3209 , which also allows you to record wind direction and speed, air temperature and water surface lighting. You can upload data to the map from SPARKvue. The map shows the coordinates and route of the sampling points.
SPARKvue wireless weather sensor
The second method is more suitable for boat explorers. For example, the water temperature sensor PS-2151 has a low speed overboard. The GPS tracker can be used to record the coordinates and speed of the boat. PS-2175 also connected via a Bluetooth adapter Airlink to your tablet using SPARKvue.
Method 3: If your smart device has built-in GPS, allow SPARKvue to use it and select from the GPS sensors available in the program.
The analysis of the total flow rate helps to understand the processes of water circulation in the reservoir. If you need to measure a flow rate of 0 to 3.5 meters per second at a depth of 1.8 meters on the surface layer, you can use PS-2130 and if the flow velocity is faster than 3.5 m / s, it can be measured with a sensor up to 9.98 m / s PS-2222 with Pitot tube … Data from this and other sensors in the PASPORT series can be collected via an adapter Airlink up to 10 meters from the sensor itself.
Determination of dissolved oxygen concentration in water
As you know, fish breathe dissolved oxygen in the water, releasing it through the gills. Lack of oxygen causes fish to die. The sensor can be used to determine the concentration of dissolved oxygen in the water. PS-3224 … In shallow lakes, the risk of oxygen deprivation is high due to the uneven distribution of oxygen. The lower layers are oxygen deficient and the surface layers are supersaturated. As a result of microbiological processes, the lower layers of some water bodies may contain sulfur and ammonia, making them unsuitable for the life of multicellular organisms.
Color and transparency sensor
The water layer in which phytoplankton produces oxygen can vary greatly depending on the clarity of the water. It is now possible to use a digital sensor instead of the Trout-Ole scale to determine the color of the water and its transparency / turbidity. PS-3215 … The lighting conditions in Estonia’s small lakes are quite variable throughout the year. In summer, the water transparency in half of the lakes is less than 1.5 m. The lowest water transparency (6 cm) was registered in 1977. in heavily polluted Lake Pappjärve. Lake Äntu Sinijärv (visibility up to 13.5 m) is considered to be the most transparent. The color of the water in Estonian lakes is mainly yellowish green or greenish yellow with a brownish tinge. There are lakes with reddish-brown and dark brown water.
Hydrochemical properties
As mentioned above, phytoplankton is affected by pH or, as it is also called, by size acidity aqueous solutions. The pH of lake water is between 3.5 and 10. In bulk, the pH in lakes is between 6.5 and 8.5 (close to neutral to slightly basic). Interestingly, the darker the color of the water, the lower the pH level. The sensor is useful for measuring pH PS-3204 – This sensor is quite versatile. When changing the probe, the pH sensor may change to examine the calcium ion concentration in seconds PS-3518 , potassium ions PS-3520 , nitrate ion concentration PS-3521 , chloride ions PS-3519 or ammonium ions NH4 + PS-3516 …
Potassium ions are capable of conducting electricity. They have a positive charge. The conductivity of the solution can be measured using PS-3210 … Brown-colored bog lakes have the highest number of sulphate ions. Sulphates and chlorides are found in saline and heavily polluted lakes. Concentrations of calcium cations also increase strongly in salt lakes. The amount of nitrogen varies greatly during the growth of plants and phytoplankton. Phosphorus content is not high, but its absence or deficiency strongly affects the growth of phytoplankton and plants.
PH, in turn, is related to the concentration of carbon dioxide, which can be measured with a CO sensor. 2 PS-3208 and apply a waterproof membrane PS-3545 …
Everyone loves to play
By looking at water research, you can show students again how measurements relate to observing and understanding natural phenomena. It is not necessary to drive far on the expedition to the largest or deepest lake. To get started, you can test tap water samples from different parts of the city that students can take from home. Organize a “forensic” game: have everyone take 50 ml of water with them, show the post office index of your place of residence on the sample and compare, if available, the chemical composition and acidity of the water. Let one sample be unsigned. The task for the lesson is to determine from which part of the city an unknown sample.
PS
The time coincides with World Water Day, which is celebrated every year on the 22nd. March.