Upon completion of thorough studies concerning physical and chemical parameters that compose bottom sediments of Lake Ladoga at fish breeding sites, the scientists of St. Petersburg Federal Research Center of the Russian Academy of Sciences (SPC RAS) arrived to a conclusion that specific sediment layers enriched with organic matter are formed directly below the trout tanks. The problem affects only those lake bays where fishery enterprises are located, and their influence does not spread to the rest of the reservoir. Scientists deem that potential future changes in the properties of bottom sediments can cause emissions of gases or toxic elements. The repercussions may produce certain effect both on the fishery farms and aquatic organisms living in trout breeding areas at Lake Ladoga. The scientists' work is published in the journal Aquaculture and Fisheries.
Lake Ladoga (Ladoga) is the largest freshwater body in Europe; it is an important recreational resource, and is also used in various industries, including aquaculture. Currently over 20 fish farms, mainly breeding trout, operate in the northern part of Lake Ladoga. And the greater the demand for fish and the matching profit, the worse is the harm they bring to the lake and the ecosystem.
Limnologists from St. Petersburg and the Murmansk Region made some investigations concerning current bottom sediments in the Yakkimvaara Bay area in the north of Lake Ladoga. Samples formed as cores (photo) were isolated by scientists in February, June, August and October 2021. The cores were cut into layers from 3 to 5 cm, differences in consistency, color and odor were recorded, and the physical and chemical parameters (pH, Eh) of the samples were measured. Due to the above, scientists were able to identify recent changes in the bottom sediments caused by the fisheries’ influence on the reservoir. Moreover, specialists installed special traps under the tanks to assess the quality of particles settling to the bottom during the trout life time.
The received results revealed that undigested fish food and excrement are the main constituents of the material deposited under the tanks in the waters of the bay where trout are bred. In the upper layers of bottom sediments, this material forms soft flake-like layers with a smell of decomposition and bubbles, and it contains more organic matter than the lower layers. The thickness of the layers varies from 2 to 20 cm: less in winter and early summer, more in late summer and mid–autumn because of the seasonal difference in fish feeding.
The content of dispersed organic matter in the newly formed layers of bottom sediments in August and October reaches 80%, whereas in the typical gray silt of the lake this value does not exceed 10-15%. At that, scientists have ascertained that the organic material thrown out by fish farms settles only over a small area and does not spread to the entire Ladoga basin. However, because of the accumulation of organic material and the low rate of water exchange within the Yakkimvaara Bay, conditions arise in the sediments, that stipulate toxic gases formation in the water, and the accumulated nutrients and heavy metals can get from the sediments to the water. This can make harm to the living organisms of Lake Ladoga, as well as to the here grown tank fishes.
"In Russia there exists no system for monitoring the impact of fisheries on the environment. In the given study, bottom sediments are represented as an integral indicator of the long-term impact of tank farms on the coastal water area. Based on the acquired data, recommendations can possibly be developed for a wide range of environmental structures, as well as for specialists in fish farming in order to prognosticate and reduce environmental detriment caused to water bodies. Scientifically backed recommendations will also help to increase the economic efficiency of enterprises and develop a basis in forming a balanced socio-economic approach to water resources’ management. In the future, we plan to extend the research region and prepare a model for improving the work of fish farms and prognosing their impact on reservoirs," - says Artem Lapenkov, a research participant and Head of the Field Research Team, Junior Researcher of the Institute of Limnology of the Russian Academy of Sciences (a separate structural division of SPC RAS).
The authors of the scientific article are grateful to O.V. Khlunov, Director of the Farm, A.S. Legky, the Chief Fish Breeder, and A.N. Parshukov, Ichthyopathologist, for the provided opportunity to collect the material.
Source: Indicator.ru