7%1, cgivEs FISHERIES RESEARCH BOARD OF CANADA Translation Series No. 1248 Formation of ecological conditions in the shoals of reservoirs in spring. I I By G.L. Mel l nikova Original title: Formirovanie ekologicheskoi obstanovki na melkovod l yakh vodokhranilishch v vesennii From: Biologiya Vnutrennikh yod, Informatsionnyi , Byullete .Akadèmiya Nauk SSSR. (2): 18-21, 1968. • Translated by the Translation Bureau(GM) Foreign Languages Division Department of the Secretary of State of Canada Fisheries Research Board of Canada • Freshwatér Institute. Winnipeg, Man., . 1969 9 pages typescript SECRÉTARIA T D'ÉTAT DEPARTMENT OF THE SECRETARY OF STATE TRANSLATION BUREAU BUREAU DES TRADUCTIONS FOREIGN LANGUAGES DIVISION DIVISION DES LANGUES ÉTRANGÈRES CANADA DI VI S ION/RANC H CITY YOUR NO. DEPARTMENT VILLE VOTRE N ° MINISTRE DIVISION/DIRECTION • Freshwater InstitutelWinnipeg # Manitoba F.R.B. i • TRANSLATOR (INITIALS) DATE OUR NO. LANGUAGE f TRADUCTEUR (INITIALES) NOTRE N ° LANGUE i ' S u 1 April 16, 1969. Formirovanie ekologicheskoi_obstanovki ma melkovodlyakh vodokhranilisheh v vesennii period, published in.Biologiya vnutrennikh vod, Informatsionny ByUlletent, The Formation of Ecological Conditions on the Shoals of Reservoirs in_Spring by G.L. Melvnikov mom.grommmairoil Within the confines of large reservoirs an . 1 flatland rivers the shoals with depths of up to 2 metres often account for more than i of the area of the water body, and by our calculations this means 21% of the Rybinsk 1To obtain comparative data on the scale of large regions or an entire country it seems most sensible to us to adopt the.following constant criterion: "the interactio n between the waves and the bcttom within stable boundaries from the normal water level (XWL) to a depth of 2 metres". Howeyer, such a limitation Li t° some degree arbitrary since, when the level is lowered, parts Of the deepwater zone may also p become, Shoals, whereas areas with depths of Up to 2 metres avem the NWL never become deePs (Vendrov, 1966).. UNEDITED DRAFT TRANSLATION Only for inrorma',ion TRADUCTION MON REVISEE SOI-200— 10-3 1 Inf.rmation s..-etliernent reservoir, 27,6% of the Uglich reservoir, 3.04% of the Dneprodzerzhinsk reservoir, 32% Of the Kiev reservoir, 37% of the Plyavinsk reservoir, and 41.7% of the Dmprovsk reservoir. The shoals occur in different . areas and vary greatly in type.' On the strength of a.study made of the reservoirs of the Volga river basin we suggested a scheme for classifying shoals, which would distinguish three basic types; A - inlet shoals, strongly affected by the topography of the drainage system, B - island shoals, forming at the base of the waters of the reservoir itself or of its affluents, and O - open water shoals, the natural conditions of which are strongly influenced by the processes taking place in the open reservolx and slightly influencedi by the surrounding )dk thy of the shore (Meltnikov, 1967). The small volumes of water accumulated by shoals have little thermal inertia, and all the processes are strongly seasonal. The regime of the levels in many re- spects determines the distinctive features of shoals as 2 _Page nuniber in the original. 3. habitats for organisns. Early in spring, before the floods, the water sinks to its lowest level. Inmost reservoirs the.shoals are already showing above the surface by.this time, and the conditions of existence of the aquatic organism (particularly the benthos) are governed by the depth to which the ground is frozen. Protected shoals (island and inlet shoals), Which are ebove water during the warm part of the year, are dry by the time winter arrives. They are relatively usually covered by land plants capable of forming turf protecting the soil from deep freezing. The example of the island shoal near Bork on the Volga reach of the Rybinsk reservoir shows that such areas are not frozen . below a depth of 7.5-8 cm (Luferov, 1985). When the drying up of the bottom coincides with the advent of. sezero temperatures, the depth of freezing may exceed 10 cm. When the level is reduced in winter the shoals of the reaèhes are covered by settling ice, which melts in situ. Deep freezing does not occur below the ioe'layer, and often only the soil against theumderside of the ièe is frozen. This soil is later swept away with the remaining ice by the flood waters. Although ice erosion in the early springtime is not a crucial factor in living conditions on the shoals, the removal of the soil may have a detrimental effect on the subsequent fate of the benthos, since the major part wlnters in the upper 2-3 cm of the soi]. (Greze, 1960). The disintegration and removal of the upper layers of shoals is also fostered by weathering, which is particularly intense in spring, when the rock is thoroughly wetted by melt-water flowing off the slope and abrupt diurnal fluctuations of the air temperature occur. These phenomena are most frequently observed on clay soils, but on sandy shoala eolian processes play a prominent part (Ikonnikov, 1963). In inlets which have'heen formed on affluents, flooding occurs earlier than in the main basin, and the ihoals are filled with waters which may differ markedly in their composition from the waters of the reaches. Thus, in the Gorkovik reservoir theTspring mineralization of the water of the Nemda and the Unzha 13 equal to 30.5045.3 mg/1„ whiCh is 3-4 times less than for the Volga - 144.1 mg/1 (Zenin, 1965). The earlier inundation of the shoals of the affluents makes for'better heating of the water. .In the more deeply indented inlets, where wind and wave mixing is minimal, the temperature conditions provide a favourable environment for the development of aquatic organisms. In lobulate inlets the calmness of the water also leads to rapid and intense heating, the temperature of the water matching the temperature of the air. Our observations of the Rybinsk reservoir in May 1966 revealed that the differenees in the water temperatures of the open part of the reservoir (the Mol- oga reach) and the protected shoals (on the river Teresha and the river Udrisa) during stormy weather (air temperature o 19 C) amounted to 3 °C (14-17A). The spring heating causes thermal stratification throughout the entire depth of water with a ringe of up to 13.5°C (Butorin and Kurdina, 1965). However, in the open stretches the thermal stratification is generally unstable and disturbed by wind mixing, which leads to homothermia. On the other hand, on the shoals, Where the water is calm, the temperature differences between the surface and bottom layera of water are preservèd for a long time, and even in May, when the depth is 160-170 cm, the difference may be as much as 1.5-2°C. The good heatability of the water and its clarification due to the settling of suspended Oolid materials in areas out off from the main reach ensure an early beginning to macrophyte vegetation. In the Rybinsk reservoir, in the shallow inlets of its upper reaches, we observed spring deYelopment of aquatic plants, with pondweed and Polygonum amnhibium L. most prominent among them. The huge leaves of Caltha sp. rose above the water of the inundated flood plains frOm a depth of 60-70 cm. The May floods of 1966 slightly exceeded the NWL, and this provided us with an opportunity to study not only the areas inundated every year but also freshly flooded areas which are covered with water only in exceptional circumstances. In the freshly flooded areas Pomatogeton lucens L. stood out among flowering willows and green pines. The surface layer consisted of meadow soil with a covering of moss. It is probable that these turfs harbour eMbryos of aquatic plants , umtil the floods, with the eMbryos only vegetating at the highest water levels. In concluding that the spring floods are one of the key factors in the formation of the ecological conditions of a shoal we should stress that time in relation to the water temperature and the temperature of the flooded area is very important. If the flood waters inundate unfrozen or slightly frozen ground, i.e. if the water temperature is greater than or equal to the temperature of the ground, then, as was mentioned above, when the protected shoal is rapidly heated the conditions created stimulaie the development of aquatic organisms. Such a situation ebtainm when the floods occur in April or the beginning of May. If the flooding occurs later, say at the end of May or in June (in reservoirs situated on the laver steps of a cascade or whore the level rises slowly), i.e. if the water temperature is lower than the temperature of the ground, the shoal becomes very dry and this hinders settlement by aquatic organisms. As examples we can cite the shallows of the Volgograd reservoir and part of the Kulbyshev reservoir (Ekzertsev, 1963), or the shoals off the bank of Sylvinsk inlet of the Kama reservoir, which are inundated by the waters of the Sylva only during the early part of June (Ovesnov and Aristova, 1962). Most embryos of aquatic plants cannot withstand prolonged execcation and lose their ability to vegetate, particularly in cases where flood water of low temperature inundates well-heated soils. Thus, early floods promote the development of animals and plant organisms on shoals and, Ience, hoip to increase their productivity. On the other hand, later 8. flooding coupled with a marked disparity in the temperatures of the water and ground'has an adverse •ffect on the lives of aquatic organisms, and this is one of the-reasons for the poverty of such bodids of water.