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Modelling of man-made contribution to salinity increase into the Vistula Lagoon (Baltic Sea)
Ecological Modelling 138 (2001) 87 – 100 www.elsevier.com/locate/ecolmodel
Modelling of man-made contribution to salinity increase into the Vistula Lagoon (Baltic Sea) Irina Chubarenko *, Irina Tchepikova P.P. Shirsho6 Institute of Oceanology of Russian Academy of Sciences, Atlantic Branch Prospect Mira, 1, Kaliningrad 236000, Russia
Abstract The man-made contribution to significant increase in salinity in the Vistula Lagoon (south-eastern Baltic) during the last century is discussed in this paper: (a) diversion of the main part of the Vistula River discharge from the Vistula Lagoon directly into the Baltic Sea at the beginning of this century; (b) the intensification of water exchange with the sea because of the deepening of the Lagoon entrance and (c) significant simplification of sea water penetration into the distant parts of Lagoon aquatory through deepened ship channels. The numerical modelling results (MIKE21) for salinity field annual dynamics in the whole Lagoon under different hydrological conditions are presented: before the reduction of the Vistula River inflow in 1916, under present-day conditions, if there are different ship channels in the Lagoon aquatory. The impacts of different man-made hydrological and morphological interventions that contribute to the salinity field variations are estimated and graded in order of effect. Temporal and spatial salinity variations, and mean annual values are discussed. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Numerical model MIKE21; Estuary; Hydrodynamics
1. Introduction The Vistula Lagoon is located in the south-eastern Baltic (Fig. 1). It is intensively exploited by Poland and Russia both for fishery and recreation. Industrial and agricultural activities in the catchment area of the Lagoon contribute to the high load on its ecosystem. Today the Lagoon belongs to the category of aquatic systems with intermediate salinity (2 – 5 psu). Its ecosystem is * Corresponding author. Tel.: + 7-0112-451574; fax: + 70112-272945. E-mail address: [email protected] (I. Chubarenko).
therefore very sensitive to salinity variations. Biologists indicated the changes both in species composition and their abundance over the last decades caused by the increase in salinity (Hlopnikov, 1996, Atlantic Institute for Fishery and Resourses, oral presentation). The Vistula Lagoon is named after the Vistula River, which flows into the Lagoon from the south (Fig. 1). After man-made changes of the Vistula’s hydrological regime the Lagoon became actually the estuary of the Pregel River. The Pregel flows into the north-eastern part of the Lagoon. These changes were a part of the overflow prevention in the south regions of the
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Lagoon catchment: in 1916 the major part of the drain of the biggest Vistula branch — Nogat River — was directed from the Vistula Lagoon to the Baltic Sea through other Vistula branches (Lazarenko and Maevskiy, 1971). Such serious changes undoubtedly reflected in the hydrological regime of the Lagoon as a whole. The mean annual
salinity in the Lagoon, which was practically fresh at the beginning of the century, grew up to 3.5 psu. The significant reduction of fresh water inflow to the southern part of the Lagoon caused more intensive sea-water penetration to the south. It is also favoured by the Pregel River drain that flows into the Lagoon from the north-east.
Fig. 1. (a) A map of the south-eastern part of the Baltic Sea; (b) bathymetry and numerical grid for the Vistula Lagoon. Circles 1, 2, 3 indicate locations of navigation channels. Points A, B, C, D are chosen to visualize time variation in the salinity field.
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One other important factor that influences the salinity field dynamic in the Lagoon significantly is the deepening and enlargement of Baltiysk Strait, which connects the Lagoon to the sea (Chubarenko and Chubarenko, 1996, 1997; Chubarenko, 1998). For navigation purposes the dredging is made regulary not only in the strait, but also along the navigable channels that pass through the northern part of the Lagoon and connect the marine harbour of Kaliningrad to the Baltic sea. The aim of this article is to analyse quantitatively the man-made contribution to the changes in the Lagoon salinity mode, caused by the reduction of river run-off and intensification of the water exchange with the sea through deepened Baltiysk Strait and by the dredged Navigable Channels. Possible impacts from three projected bathymetry interventions are also estimated: deepening of shipping channels from Baltiysk Straight to the (i) central and (ii) northern parts of the Lagoon and opening of the second exit from the Lagoon to the Baltic Sea through the southern part of the Vistula Spit. In this paper natural reasons for long-term variations of salinity fields, like the variations in atmospheric precipitation and general increase in salinity of the Baltic Sea will not be considered. These factors vary only slightly (Lazarenko and Maevskiy, 1971), while the salinity of the southern part of the Lagoon increased more than twice during the last century.
2. Area description The shallow Vistula Lagoon (Fig. 1) has an average depth of 2.7 m (maximum is 5.2 m). The surface area and the volume of the Lagoon are 838 and 2.3 km3 respectively (Lazarenko and Maevskiy, 1971). The Baltiysk Strait of width equal to 400 m is the only connection between the Lagoon and the Baltic Sea; it has a ship channel in width of about 100 m and in depth of 12 m. The history provides some examples of its deepening and enlargement both of natural and of man-made origin. It is known
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that in the 17th century the strait’s depth was as low as 2.5 m. At the beginning of the 19th century the strait was still shallow — its depth only about 5 m. After the catastrophic ice throng in the Vistula River in 1840 and the subsequent overflow the strait was deepened naturally to the depth of 7.8 m. In 1923 the strait was deepened artificially, and from those times the navigation activity demands persistent dredging works. All these changes intensified the marine influence on the Lagoon, causing the increase in salinity. Now the Baltiysk Strait is rather wide and rectilinear. It is 400 m wide, about 2 km long, with an average depth of 8.8 m and a minimum cross-section area of 4300 m2. Several dozen of rivers flow into the Vistula Lagoon. More than ten of them are Vistula branches, bringing water to the south-western part of the Lagoon (Fig. 1a). The low land of the Vistula downstream-so called Vistula Zhulaves — experienced often overflows. The dams constructed to regulate river drain direct it away from the Vistula Lagoon towards the Baltic Sea. Today not the Vistula, but the Pregel is the biggest river flowing into the Lagoon: its discharge makes up 42% of the total fresh Lagoon inflow (Lazarenko and Maevskiy, 1971).
3. Method The numerical model MIKE21 fron the Danish Hydraulic Institute was used for all the simulations. The hydrodynamic part (MIKE 21 HD) is a general numerical modelling system for the simulation of water levels and flows in estuaries, bays and coastal areas. It simulates unsteady two-dimensional flows in one layer (vertically homogeneous) fluids and has been applied in a large number of studies (User guide and reference manual for MIKE21, 1994). The following equations, the conservation of mass and momentum integrated over the vertical, describe the flow and water level variations: (n (p (q + + =0 (t (x (y
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n
(p ( p 2 ( pq (n gp q 2 +p 2 + + +gh + C 2h 2 (t (x h (y h (x −
1 ( (u ( (u hE + hE zw (x (x (y (y
+
h ( (pa)=0 zw (x
−Vq −fVVx
n
(p ( p 2 ( pq (n gp q 2 +p 2 + + +gh + (t (y h (x h (y C 2h 2 −
1 ( (6 ( (6 hE + hE zw (y (y (x (x
+
h ( (pa)=0 zw (y
−Vq −fVVy
The following symbols are used: h(x, y, t) — water depth (m); (x, y, t) — surface elevation (m); p, q(x, y, t) — flux densities in x- and y-directions (m3/s per m) =(uh, 6h); (u, 6) — depth averaged velocities in x- and y-directions; C(x, y) — Chezy resistance (m0.5/s); g — acceleration due to gravity (m/s2); f(V)-wind friction factor; V, Vx, Vy (x, y, t) — wind speed and components in x- and y-directions (m/s); V(x, y) — Coriolis parameter, latitude dependent (1/s); pa (x, y, t) — atmospheric pressure (kg/m per s2); zw-density of water (kg/m3); x, y — space coordinates (m); t — time (s); E — eddy viscosity coefficient (m2/s). MIKE21 HD makes use of so-called alternating direction implicit technique to integrate these equations in the time– space domain. The equation matrices that result for each direction and each individual grid line are resolved by a double sweep algorithm. Salinity variations were simulated by MIKE 21 AD (advection– dispersion module), which solves so-called advection– dispersion equation for dissolved or suspended substances in two dimensions (this is in fact the mass-conservation equations): ( ( ( (hc)+ (uhC)+ (6hC) (t (x (y =
( ( (c (c hDx + hDy −FhC =S (x (x (y (y
Symbol list: C — compound concentration (arbitrary units); u,6 — horizontal velocity components in the x- and y-directions (m/s); h — water depth (m); Dx, Dy — dispersion coefficients in the x- and y-directions (m2/s); F — linear decay coefficient, equals to 0 for the salinity simulations (1/s); S= Qs (Cs − C); Qs — source/sink discharge (m3/s per m2); Cs — concentration of compound in the source/sink discharge. Information on u, 6 and h at each time step is provided by the hydrodynamic module. The model was initially fed by real data (bathymetry, 21 river discharges and seven point sources) and calibrated with data from the 1994 field study held during the Danish–Russian– Polish project ‘Vistula Lagoon’ (Chubarenko, 1997). It was found that MIKE21 model simulates adequately levels and fluxes in the Vistula Lagoon, and effectively represents the features of time and space variations in salinity field. Maximum deviation of simulated salinity from measured data was obtained for dynamical autumn conditions and didn’t exceed 0.6 psu for the south-western part of the Lagoon and 0.3 for the north-eastern part. The following values for calibrating coefficients were used in simulations: the wind friction factor f= 0.0017; the Chezy coefficient C =32 (m0.5/s); horizontal eddy viscosity coefficient E= 20 m2/s, horizontal dispersion coefficient D= 45 m2/s. The circulation and salinity field throughout the entire 1994 year were modelled using a grid with 1000× 1000 m meshes (see Fig. 1b). The computational time step was equal to 5 min. Real wind and level variation data measured with the time step 6 h during the whole year near the Lagoon entrance (Baltiysk station) were used (Fig. 2). The salinity at the open boundary (Baltiysk; Krynica Morska for one of simulations) was specified as 6.5 psu, initial salinity in the Lagoon — 4.5 psu, and the ice — coverage (no wind) was taken to be 56 days — as in the winter 1994/ 95. The numerical modelling results under current hydrological conditions (1994 year) are presented on the great part of the figures for comparison with simulated ones under other conditions: Fig. 3a, Fig. 4a, Fig. 5a
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Fig. 2. Forcing factors, used for MIKE21 numerical simulations: (a) open boundary condition (for Baltiysk Strait and the channel near Krynica Morska, when opened) — sea level variations, measured with the time step 6 h during 1994 near the Lagoon entrance (Baltiysk Station); (b) wind speed, measured with the time step 6 h during 1994 at the open sea (Baltiysk Station); (c) the discharges of the Vistula (trough the largest branch Nogat) and the Pregel River (two from 21 rivers used for simulations), measured with the time step of 2 weeks in 1994, and the discharge of Vistula (through Nogat) before 1916, obtained by rescaling from measurements during 1994.
— salinity fields during spring overflow, summer low water, and in autumn; Fig. 6, Fig. 7b — dotted line ‘Base solution’. The time of current and level stabilization for simulated tasks is 1– 2 days, the time of adaptation of salinity field characteristics to significant hydro-
logical changes such as those discussed in this paper is about 1– 3 months, for most distant parts — no more than 5 months. Characteristic features of Lagoon’s salinity mode were well simulated without use of a hot start or of several years simulation period.
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4. Results and discussion
4.1. The characteristics of Baltiysk Strait The Baltiysk Strait is now the only connection between the Vistula Lagoon and the Baltic Sea. Its minimal cross-section limits the water-exchange with the sea, which is the key factor for salinity mode. Numerical results show, that the change in cross-sectional strait area of 11% from present-day value, that corresponds to deepening through total width of about 1.2 m, causes the change in mean annual salinity in the Lagoon of about 1% (i.e. 0.03 psu) (Chubarenko, 1997, 1998). The relationship between the cross-sectional strait area and the salinity in the Lagoon is not likely linear, but estimations made are sufficient to conclude that the deepening of total width of the strait in meters (i.e. much significant value for the navigation) causes the increase in annual salinity of no more than a few percents. For the numerical simulations presented below, the recent morphometric characteristics of Baltiysk Strait were used.
4.2. The situation before Vistula Ri6er regulating For prevention of spring overflows in low landscape of Vistula Zhulaves the main part of Vistula River discharge was artificially transferred in 1916 from the Nogat branch, flowing into the Lagoon, directly to the Baltic Sea through other Vistula branches. We compared the simulated salinity field under present-day conditions (‘base solution’) with salinity field under hydrological conditions before Vistula regulating. Due to a lack of real data for discharges of Vistula branches before 1916, the Nogat discharge variations during the year was obtained from those for 1994 by multiplying by 8.5 to obtain the mean annual value of 72% of Pregel discharge (see Fig. 2c). The salinity field in the Lagoon during spring overflow (on April, 12), in typical calm summer conditions (on June, 11) and under intensive autumn water-exchange with the Baltic (on September, 29) are presented on Figs. 3– 5. Each of these figures have three plots: (a) for present-day hydrological conditions (‘base solution’); (b) before the
Vistula River regulation and (c) in the case where two channels connect the Vistula Lagoon and the Baltic Sea (Section 4.3.3). As for the scenario under discussion (Fig. 3b, Fig. 4b, Fig. 5b) the salinity into the south-western part of the Lagoon did not exceeded 1 psu until autumn. The mean annual salinity into the Lagoon, obtained from the daily salinity fields by averaging over time and space, is under present-day hydrological conditions 30% higher than what it was before regulating the Nogat discharge. Time variations during the whole year for four points A, B, C, D (Fig. 1b) under different hydrological conditions are shown on Fig. 6a–d, correspondingly. As was to be expected for the scenario discussed, the maximal salinity modifications experienced by the south-western and the central parts of the Lagoon (points A and B). For example, the present-day salinity in point A in July is ten times higher (increase from 0.2 to 2 psu), and in October–November 2.8 times higher (increase from 1 to 2.8 psu) greater than that before reduction of the Nogat drain. Nevertheless, temporary variations of salinity in these regions are not following the sea water inflow distinctly, i.e. both before and after Vistula regulating the Lagoon remains separate from the see itself, which ‘follows for the most part its own rules’. The last conclusion is also true for the north-eastern part of the Lagoon (point D): salinity curves for this point have mostly seasonal variations, the synoptic variations are minor. However, there is a principal difference in comparison with the southern part of the Lagoon. Salinity change in the north-eastern part is quite small (2–4%) and reversed in comparison with the southern part: salinity is decreased by 0.1– 0.2 psu after the closure of the Nogat discharge. This feature has a logical explanation: the lack of fresh water input from the Vistula run-off enhances the sea water penetration in the southern part of the Lagoon, and correspondingly decreases its influence on the northern parts, whereas under great Nogat discharge the salty marine water flowing into the Lagoon was directed mostly to the north-eastern part. The contrast in reaction of different parts of the Lagoon is evident from comparison of salinity curves in Fig. 7b. In this figure the cross-section
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of the salinity field from the south to the north across the whole Lagoon (along the line AB, Fig. 7a) is placed: present-day statement (dotted line) and the situation before 1916 (dashed line).
4.3. Na6igable channels Modelling estimations of the Lagoon salinity variations were also undertaken for three recent projects discussed in connection with trade shipping and yacht-tourism development.
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4.3.1. Shipping channel from the Baltiysk Strait to the central part of the Lagoon Under the Bilateral Intergovernmental Russian–Polish Agreement on Shipping in the Kaliningrad part of the Vistula Lagoon the Polish vessels will cruise across the Lagoon to the entrance into the Baltic Sea. In this case some deepening of fairways is necessary (Fig. 1b, Fig. 8). The length of the projected channel is 2550 m, its depth is 3 m, and the volume of soil to be dredged would be 423 000 m3. Modelling results,
Fig. 3. Salinity fields for the spring overflow (April) under following hydrological conditions: (a) present situation (‘base solution’); (b) before the reduction of the Vistula River discharge in 1916; (c) for the case of two channels between the Vistula Lagoon and the Baltic Sea.
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Fig. 4. Salinity fields for a steady calm summer situation (June) under following hydrological conditions: (a) present situation (‘base solution’) (b) before the reduction of the Vistula River discharge in 1916, (c) for the case of two channels between the Vistula Lagoon and the Baltic Sea.
taking into consideration these bathymetry changes, indicate only a small increase in salinity in the Lagoon (less than 0.1 per mile). It is only vizible during May– July when the discharge of rivers decreases significantly, and only for the central part of the Lagoon (Chubarenko, 1997).
4.3.2. Dredging works in connection with new port construction in the Russian part of Vistula Lagoon Because of the long-term plan for new port construction it is important to analyse the impact of another project — the possible deepening of the
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Kaliningrad Navigable Channel from 9 to 12 m depth for the passage of large-tonnage ships (Fig. 1b, Fig. 8). Length and width of the fairway to be dredged would be 8250 and 100 m, respectively, corresponding to a dredged volume of soil of 2475 m3. Simulations show the results to be similar to those stated above: an increase in the cross-section of the channel between the Baltic Sea and the
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Vistula Lagoon of 3% and simplification of water penetration into the Lagoon through the new channel causes an increase in salinity in the Russian part of the Lagoon of less than 0.1 per mile, and this only during the May–July period (Chubarenko, 1997). For both simulated tasks the mean annual salinity increases no more than 0.3%
Fig. 5. Salinity fields for a typical autumn situation (strong wind and intensive water exchange with the Baltic Sea) under following hydrological conditions: (a) present situation (‘base solution’); (b) before the reduction of the Vistula River discharge in 1916; (c) for the case of two channels between the Vistula Lagoon and the Baltic Sea.
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Fig. 6. Time variation of salinity in different parts of the Vistula Lagoon for present hydrological conditions (‘base solution’), before the reduction of Vistula discharge and in the case of two channels between the Lagoon and the Baltic Sea: (a) in the south-western part (point A); (b) in the central part of the Lagoon (point B); (c) near Baltiysk Strait (point C); (d) in the north-eastern part (point D).
4.3.3. Two channels between the Vistula Lagoon and the Baltic Sea The opening of a new channel, connecting the Vistula Lagoon with the Baltic Sea near Krynica Morska, Poland (Fig. 1), was discussed in connection with the yacht-tourism development. According to our simulations the hydrodynamic regime of the Lagoon as a whole will change significantly if a new 2.5-m depth channel would be built through the south part of the Vistula spit. It would effectively result in the water exchange between the Lagoon aquatory and the Baltic Sea. The cross-sectional area of this supposed channel
was chosen as equal to 17% from that of the Baltic strait, the water level variations on the new open boundary — as those in Baltiysk. The results of simulations are presented on Fig. 3c, Fig. 4c, Fig. 5c and on Figs. 6 and 7 (‘two channels’ curves). The salinity fields for the whole Lagoon during the spring overflow, typical summer and autumn situations are placed on Figs. 3– 5: (a) for present situation and (c) for two opposite channels. There are significant differences in the central and southern parts of the Lagoon. The same tendency is illustrated by Fig. 7, where the salinity variations along the Lagoon
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are shown both for ‘base’ and ‘2-channel’ solutions: for the north-eastern part differences are negligible. The mean annual salinity of the Lagoon as a whole will be increased by 40% in comparison with the present one. As for example, the new hydrodynamic situation, where the regime of water-exchange is like a strong draught, is shown on Fig. 7a. The associated intensification of the water-exchange with the Baltic through two opposite channels would cause a rapid increase of the salinity up to 5– 6 psu in the southern and central parts where nowadays it is no greater than 2.5 – 4 psu (see curves on Fig. 6a and b — comparison of salinity variations for southern and central parts of the Lagoon during the whole modelled 1994 year). The average annual salinity
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in the central part of the Lagoon increases by 40–60% (in the point B by 54%), in south-west — by 140–170% (in the point A on 125%). At the same time variations for the regions near Baltiysk channel (Fig. 6c) are not so serious. As for the north-eastern part of the Lagoon (Fig. 6d) the changes are quite small. During the spring overflow the salinity expected in the case of the two channels should be even smaller than at present. An important point is that the second channel would change principally the features of salinity curves in central and south-western parts of the Lagoon: the temporary variations in salinity in these parts of the Lagoon become similar to those
Fig. 6. (Continued)
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Fig. 7. The numerical modelling results (MIKE21) for the case of two channels between the Vistula Lagoon and the Baltic Sea: (a) current field on 2 May 1994 is an example of a new hydrodynamic regime (the strong draught) occurring from time to time due to the existence of two opposite channels; (b) salinity variations along the line AB on the 2 May 1994 (solution). The present situation, i.e. the ‘base solution’ (dotted line) and the solution for hydrodynamic conditions before regulating Vistula River (dashed line ‘Vistula’).
at the open boundary. So, the salinity regime becomes completely dependent on the inflow – outflow regime. The Vistula Lagoon would therefore loose the insularity and would become completely dependent from marine influence, except of its north-eastern part.
5. Conclusions Significant increase in the salinity of the Vistula Lagoon during the last century is due to manmade interventions that changed the morphology of the Lagoon.
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The main reasons for the increase in salinity were: (a) the diversion in flow on the part of the Vistula River drain from the Vistula Lagoon directly to the Baltic Sea; (b) intensification of water-exchange with the Baltic Sea with deepening of the Baltiysk Strait; (c) the simplification of water exchange between the different parts of the Lagoon through persistently dredged navigable channels. The greatest contribution to the salinity was made by the diversion in flow of on the part of the Vistula River drain from the Vistula Lagoon directly to the Baltic Sea. Numerical simulations demonstrate that the mean annual salinity of the Lagoon, obtained by averaging over time and space daily salinity fields, is today more than 30% higher than that before the Vistula River was regulated — directed from the Vistula Lagoon to the Baltic Sea. The deepening of the Baltiysk Strait, the only connection from the Lagoon to the Baltic Sea, causes the intensification of water exchange and, correspondingly, the increase of the salinity into the Lagoon. The deepening of the strait through total width (but not the navigable channel only) by about 1.2 m would cause the mean Lagoon annual salinity to increase by about 1%. Dredging in different parts of the Lagoon, enlargement of existing fairways and new navigable
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channels, all generate an increase in salinity by enhancing the marine water penetration to distant parts of the Lagoon. From the point of view of temporal variations in salinity, the Lagoon under present-day hydrological conditions remains the separate from the sea, with its own unique characteristics despite the increase in marine influence. If a new artificial channel at the southern part of the Vistula spit were constructed, the hydrodynamic regime of the Lagoon as a whole would change drastically. Both central and south-western parts of the Lagoon would then resemble the marine bay, and the salinity would reach values as high as 5–6 psu. The time scale of adaptation of salinity field characteristics to significant hydrological changes like those considered above in Sections 4.2 and 4.3.3 is about 1–3 months, for most distant parts — no more than a half of a year. It seems reasonable to conclude that the salinity of the Vistula Lagoon water will increase further. The main reason for this is that the dredging works are consistently carried out in Baltiysk Strait and navigable channels to maintain the navigation of ships.
Acknowledgements We thank our Danish, Polish, and Russian colleagues for their co-operation during the setting up and calibration of MIKE21 numerical model for the Vistula Lagoon under the international project ‘Prioritising Hot Spot Remediations in Vistula Lagoon Catchment: Environmental Assessment and planning for the Polish and Kaliningrad parts of the Lagoon’. We are also sincerely grateful to Boris Chubarenko for his critical remarks and important additions.
References
Fig. 8. The two projects of the deepening and enlargement of the navigation channels in the Baltiysk Strait region.
Chubarenko, B.V., Chubarenko, I.P., 1996. The transport of Baltic water along deep channel in gulf of Kaliningrad and its influence on fields of salinity and suspended solids. In: Proceedings of Baltic Marine Science Conference, October 22 – 26, 1996, Bornholm, Denmark.
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Chubarenko, B.V., Chubarenko, I.P., 1997. Regionalization of river Pregel estuary and Russian part of Vistula Lagoon on hydrological parameters. In: Proceedings of the International Conference on Regionalization in Hydrology, March 10 – 14, 1997, Braunschweig, Germany, pp. 41 –44. Chubarenko, I.P., 1997. Deepening works at Vistula Lagoon and Kaliningrad Marine channel. In: Prioritising Hot Spot Remediations in Vistula Lagoon Catchment: Environmental Assessment and Planning for the Polish and Kaliningrad Parts of the Lagoon. Water Quality Institute (DK); Danish Hydraulic Institute (DK); GEOMOR (Poland); P.P.Shirshov Institute of Oceanology, Atlantic Branch (Russia), 1993 – 1995, pp. 8 –26 Scientific Report, v. 6.
Chubarenko, I.P., 1998. Influence of deepening works in Baltiysk Channel on the water salinity in Vistula Lagoon (numerical model MIKE21). In: Monographs in System Ecology. System Research in Ecology: Linking, Watershed, Riverine and Marine Processes. Proceedings of the Second International Workshop on Interdisciplinary Approaches in Ecology, August 25 – 26, 1997. Coastal Research and Planning Institute, Klaipeda, pp. 18 – 21 V.2. Lazarenko, N., Maevskiy, A. (Eds.), 1971. Hydrometeorological regime of the Vistula Lagoon, p. 280 in Russian. User guide and reference manual for MIKE21 (1994). Danish Hydraulic Institute Release 1.2.
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Modelling of man-made contribution to salinity increase into the Vistula Lagoon (Baltic Sea) Irina Chubarenko *, Irina Tchepikova P.P. Shirsho6 Institute of Oceanology of Russian Academy of Sciences, Atlantic Branch Prospect Mira, 1, Kaliningrad 236000, Russia
Abstract The man-made contribution to significant increase in salinity in the Vistula Lagoon (south-eastern Baltic) during the last century is discussed in this paper: (a) diversion of the main part of the Vistula River discharge from the Vistula Lagoon directly into the Baltic Sea at the beginning of this century; (b) the intensification of water exchange with the sea because of the deepening of the Lagoon entrance and (c) significant simplification of sea water penetration into the distant parts of Lagoon aquatory through deepened ship channels. The numerical modelling results (MIKE21) for salinity field annual dynamics in the whole Lagoon under different hydrological conditions are presented: before the reduction of the Vistula River inflow in 1916, under present-day conditions, if there are different ship channels in the Lagoon aquatory. The impacts of different man-made hydrological and morphological interventions that contribute to the salinity field variations are estimated and graded in order of effect. Temporal and spatial salinity variations, and mean annual values are discussed. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Numerical model MIKE21; Estuary; Hydrodynamics
1. Introduction The Vistula Lagoon is located in the south-eastern Baltic (Fig. 1). It is intensively exploited by Poland and Russia both for fishery and recreation. Industrial and agricultural activities in the catchment area of the Lagoon contribute to the high load on its ecosystem. Today the Lagoon belongs to the category of aquatic systems with intermediate salinity (2 – 5 psu). Its ecosystem is * Corresponding author. Tel.: + 7-0112-451574; fax: + 70112-272945. E-mail address: [email protected] (I. Chubarenko).
therefore very sensitive to salinity variations. Biologists indicated the changes both in species composition and their abundance over the last decades caused by the increase in salinity (Hlopnikov, 1996, Atlantic Institute for Fishery and Resourses, oral presentation). The Vistula Lagoon is named after the Vistula River, which flows into the Lagoon from the south (Fig. 1). After man-made changes of the Vistula’s hydrological regime the Lagoon became actually the estuary of the Pregel River. The Pregel flows into the north-eastern part of the Lagoon. These changes were a part of the overflow prevention in the south regions of the
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Lagoon catchment: in 1916 the major part of the drain of the biggest Vistula branch — Nogat River — was directed from the Vistula Lagoon to the Baltic Sea through other Vistula branches (Lazarenko and Maevskiy, 1971). Such serious changes undoubtedly reflected in the hydrological regime of the Lagoon as a whole. The mean annual
salinity in the Lagoon, which was practically fresh at the beginning of the century, grew up to 3.5 psu. The significant reduction of fresh water inflow to the southern part of the Lagoon caused more intensive sea-water penetration to the south. It is also favoured by the Pregel River drain that flows into the Lagoon from the north-east.
Fig. 1. (a) A map of the south-eastern part of the Baltic Sea; (b) bathymetry and numerical grid for the Vistula Lagoon. Circles 1, 2, 3 indicate locations of navigation channels. Points A, B, C, D are chosen to visualize time variation in the salinity field.
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One other important factor that influences the salinity field dynamic in the Lagoon significantly is the deepening and enlargement of Baltiysk Strait, which connects the Lagoon to the sea (Chubarenko and Chubarenko, 1996, 1997; Chubarenko, 1998). For navigation purposes the dredging is made regulary not only in the strait, but also along the navigable channels that pass through the northern part of the Lagoon and connect the marine harbour of Kaliningrad to the Baltic sea. The aim of this article is to analyse quantitatively the man-made contribution to the changes in the Lagoon salinity mode, caused by the reduction of river run-off and intensification of the water exchange with the sea through deepened Baltiysk Strait and by the dredged Navigable Channels. Possible impacts from three projected bathymetry interventions are also estimated: deepening of shipping channels from Baltiysk Straight to the (i) central and (ii) northern parts of the Lagoon and opening of the second exit from the Lagoon to the Baltic Sea through the southern part of the Vistula Spit. In this paper natural reasons for long-term variations of salinity fields, like the variations in atmospheric precipitation and general increase in salinity of the Baltic Sea will not be considered. These factors vary only slightly (Lazarenko and Maevskiy, 1971), while the salinity of the southern part of the Lagoon increased more than twice during the last century.
2. Area description The shallow Vistula Lagoon (Fig. 1) has an average depth of 2.7 m (maximum is 5.2 m). The surface area and the volume of the Lagoon are 838 and 2.3 km3 respectively (Lazarenko and Maevskiy, 1971). The Baltiysk Strait of width equal to 400 m is the only connection between the Lagoon and the Baltic Sea; it has a ship channel in width of about 100 m and in depth of 12 m. The history provides some examples of its deepening and enlargement both of natural and of man-made origin. It is known
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that in the 17th century the strait’s depth was as low as 2.5 m. At the beginning of the 19th century the strait was still shallow — its depth only about 5 m. After the catastrophic ice throng in the Vistula River in 1840 and the subsequent overflow the strait was deepened naturally to the depth of 7.8 m. In 1923 the strait was deepened artificially, and from those times the navigation activity demands persistent dredging works. All these changes intensified the marine influence on the Lagoon, causing the increase in salinity. Now the Baltiysk Strait is rather wide and rectilinear. It is 400 m wide, about 2 km long, with an average depth of 8.8 m and a minimum cross-section area of 4300 m2. Several dozen of rivers flow into the Vistula Lagoon. More than ten of them are Vistula branches, bringing water to the south-western part of the Lagoon (Fig. 1a). The low land of the Vistula downstream-so called Vistula Zhulaves — experienced often overflows. The dams constructed to regulate river drain direct it away from the Vistula Lagoon towards the Baltic Sea. Today not the Vistula, but the Pregel is the biggest river flowing into the Lagoon: its discharge makes up 42% of the total fresh Lagoon inflow (Lazarenko and Maevskiy, 1971).
3. Method The numerical model MIKE21 fron the Danish Hydraulic Institute was used for all the simulations. The hydrodynamic part (MIKE 21 HD) is a general numerical modelling system for the simulation of water levels and flows in estuaries, bays and coastal areas. It simulates unsteady two-dimensional flows in one layer (vertically homogeneous) fluids and has been applied in a large number of studies (User guide and reference manual for MIKE21, 1994). The following equations, the conservation of mass and momentum integrated over the vertical, describe the flow and water level variations: (n (p (q + + =0 (t (x (y
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n
(p ( p 2 ( pq (n gp q 2 +p 2 + + +gh + C 2h 2 (t (x h (y h (x −
1 ( (u ( (u hE + hE zw (x (x (y (y
+
h ( (pa)=0 zw (x
−Vq −fVVx
n
(p ( p 2 ( pq (n gp q 2 +p 2 + + +gh + (t (y h (x h (y C 2h 2 −
1 ( (6 ( (6 hE + hE zw (y (y (x (x
+
h ( (pa)=0 zw (y
−Vq −fVVy
The following symbols are used: h(x, y, t) — water depth (m); (x, y, t) — surface elevation (m); p, q(x, y, t) — flux densities in x- and y-directions (m3/s per m) =(uh, 6h); (u, 6) — depth averaged velocities in x- and y-directions; C(x, y) — Chezy resistance (m0.5/s); g — acceleration due to gravity (m/s2); f(V)-wind friction factor; V, Vx, Vy (x, y, t) — wind speed and components in x- and y-directions (m/s); V(x, y) — Coriolis parameter, latitude dependent (1/s); pa (x, y, t) — atmospheric pressure (kg/m per s2); zw-density of water (kg/m3); x, y — space coordinates (m); t — time (s); E — eddy viscosity coefficient (m2/s). MIKE21 HD makes use of so-called alternating direction implicit technique to integrate these equations in the time– space domain. The equation matrices that result for each direction and each individual grid line are resolved by a double sweep algorithm. Salinity variations were simulated by MIKE 21 AD (advection– dispersion module), which solves so-called advection– dispersion equation for dissolved or suspended substances in two dimensions (this is in fact the mass-conservation equations): ( ( ( (hc)+ (uhC)+ (6hC) (t (x (y =
( ( (c (c hDx + hDy −FhC =S (x (x (y (y
Symbol list: C — compound concentration (arbitrary units); u,6 — horizontal velocity components in the x- and y-directions (m/s); h — water depth (m); Dx, Dy — dispersion coefficients in the x- and y-directions (m2/s); F — linear decay coefficient, equals to 0 for the salinity simulations (1/s); S= Qs (Cs − C); Qs — source/sink discharge (m3/s per m2); Cs — concentration of compound in the source/sink discharge. Information on u, 6 and h at each time step is provided by the hydrodynamic module. The model was initially fed by real data (bathymetry, 21 river discharges and seven point sources) and calibrated with data from the 1994 field study held during the Danish–Russian– Polish project ‘Vistula Lagoon’ (Chubarenko, 1997). It was found that MIKE21 model simulates adequately levels and fluxes in the Vistula Lagoon, and effectively represents the features of time and space variations in salinity field. Maximum deviation of simulated salinity from measured data was obtained for dynamical autumn conditions and didn’t exceed 0.6 psu for the south-western part of the Lagoon and 0.3 for the north-eastern part. The following values for calibrating coefficients were used in simulations: the wind friction factor f= 0.0017; the Chezy coefficient C =32 (m0.5/s); horizontal eddy viscosity coefficient E= 20 m2/s, horizontal dispersion coefficient D= 45 m2/s. The circulation and salinity field throughout the entire 1994 year were modelled using a grid with 1000× 1000 m meshes (see Fig. 1b). The computational time step was equal to 5 min. Real wind and level variation data measured with the time step 6 h during the whole year near the Lagoon entrance (Baltiysk station) were used (Fig. 2). The salinity at the open boundary (Baltiysk; Krynica Morska for one of simulations) was specified as 6.5 psu, initial salinity in the Lagoon — 4.5 psu, and the ice — coverage (no wind) was taken to be 56 days — as in the winter 1994/ 95. The numerical modelling results under current hydrological conditions (1994 year) are presented on the great part of the figures for comparison with simulated ones under other conditions: Fig. 3a, Fig. 4a, Fig. 5a
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Fig. 2. Forcing factors, used for MIKE21 numerical simulations: (a) open boundary condition (for Baltiysk Strait and the channel near Krynica Morska, when opened) — sea level variations, measured with the time step 6 h during 1994 near the Lagoon entrance (Baltiysk Station); (b) wind speed, measured with the time step 6 h during 1994 at the open sea (Baltiysk Station); (c) the discharges of the Vistula (trough the largest branch Nogat) and the Pregel River (two from 21 rivers used for simulations), measured with the time step of 2 weeks in 1994, and the discharge of Vistula (through Nogat) before 1916, obtained by rescaling from measurements during 1994.
— salinity fields during spring overflow, summer low water, and in autumn; Fig. 6, Fig. 7b — dotted line ‘Base solution’. The time of current and level stabilization for simulated tasks is 1– 2 days, the time of adaptation of salinity field characteristics to significant hydro-
logical changes such as those discussed in this paper is about 1– 3 months, for most distant parts — no more than 5 months. Characteristic features of Lagoon’s salinity mode were well simulated without use of a hot start or of several years simulation period.
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4. Results and discussion
4.1. The characteristics of Baltiysk Strait The Baltiysk Strait is now the only connection between the Vistula Lagoon and the Baltic Sea. Its minimal cross-section limits the water-exchange with the sea, which is the key factor for salinity mode. Numerical results show, that the change in cross-sectional strait area of 11% from present-day value, that corresponds to deepening through total width of about 1.2 m, causes the change in mean annual salinity in the Lagoon of about 1% (i.e. 0.03 psu) (Chubarenko, 1997, 1998). The relationship between the cross-sectional strait area and the salinity in the Lagoon is not likely linear, but estimations made are sufficient to conclude that the deepening of total width of the strait in meters (i.e. much significant value for the navigation) causes the increase in annual salinity of no more than a few percents. For the numerical simulations presented below, the recent morphometric characteristics of Baltiysk Strait were used.
4.2. The situation before Vistula Ri6er regulating For prevention of spring overflows in low landscape of Vistula Zhulaves the main part of Vistula River discharge was artificially transferred in 1916 from the Nogat branch, flowing into the Lagoon, directly to the Baltic Sea through other Vistula branches. We compared the simulated salinity field under present-day conditions (‘base solution’) with salinity field under hydrological conditions before Vistula regulating. Due to a lack of real data for discharges of Vistula branches before 1916, the Nogat discharge variations during the year was obtained from those for 1994 by multiplying by 8.5 to obtain the mean annual value of 72% of Pregel discharge (see Fig. 2c). The salinity field in the Lagoon during spring overflow (on April, 12), in typical calm summer conditions (on June, 11) and under intensive autumn water-exchange with the Baltic (on September, 29) are presented on Figs. 3– 5. Each of these figures have three plots: (a) for present-day hydrological conditions (‘base solution’); (b) before the
Vistula River regulation and (c) in the case where two channels connect the Vistula Lagoon and the Baltic Sea (Section 4.3.3). As for the scenario under discussion (Fig. 3b, Fig. 4b, Fig. 5b) the salinity into the south-western part of the Lagoon did not exceeded 1 psu until autumn. The mean annual salinity into the Lagoon, obtained from the daily salinity fields by averaging over time and space, is under present-day hydrological conditions 30% higher than what it was before regulating the Nogat discharge. Time variations during the whole year for four points A, B, C, D (Fig. 1b) under different hydrological conditions are shown on Fig. 6a–d, correspondingly. As was to be expected for the scenario discussed, the maximal salinity modifications experienced by the south-western and the central parts of the Lagoon (points A and B). For example, the present-day salinity in point A in July is ten times higher (increase from 0.2 to 2 psu), and in October–November 2.8 times higher (increase from 1 to 2.8 psu) greater than that before reduction of the Nogat drain. Nevertheless, temporary variations of salinity in these regions are not following the sea water inflow distinctly, i.e. both before and after Vistula regulating the Lagoon remains separate from the see itself, which ‘follows for the most part its own rules’. The last conclusion is also true for the north-eastern part of the Lagoon (point D): salinity curves for this point have mostly seasonal variations, the synoptic variations are minor. However, there is a principal difference in comparison with the southern part of the Lagoon. Salinity change in the north-eastern part is quite small (2–4%) and reversed in comparison with the southern part: salinity is decreased by 0.1– 0.2 psu after the closure of the Nogat discharge. This feature has a logical explanation: the lack of fresh water input from the Vistula run-off enhances the sea water penetration in the southern part of the Lagoon, and correspondingly decreases its influence on the northern parts, whereas under great Nogat discharge the salty marine water flowing into the Lagoon was directed mostly to the north-eastern part. The contrast in reaction of different parts of the Lagoon is evident from comparison of salinity curves in Fig. 7b. In this figure the cross-section
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of the salinity field from the south to the north across the whole Lagoon (along the line AB, Fig. 7a) is placed: present-day statement (dotted line) and the situation before 1916 (dashed line).
4.3. Na6igable channels Modelling estimations of the Lagoon salinity variations were also undertaken for three recent projects discussed in connection with trade shipping and yacht-tourism development.
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4.3.1. Shipping channel from the Baltiysk Strait to the central part of the Lagoon Under the Bilateral Intergovernmental Russian–Polish Agreement on Shipping in the Kaliningrad part of the Vistula Lagoon the Polish vessels will cruise across the Lagoon to the entrance into the Baltic Sea. In this case some deepening of fairways is necessary (Fig. 1b, Fig. 8). The length of the projected channel is 2550 m, its depth is 3 m, and the volume of soil to be dredged would be 423 000 m3. Modelling results,
Fig. 3. Salinity fields for the spring overflow (April) under following hydrological conditions: (a) present situation (‘base solution’); (b) before the reduction of the Vistula River discharge in 1916; (c) for the case of two channels between the Vistula Lagoon and the Baltic Sea.
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Fig. 4. Salinity fields for a steady calm summer situation (June) under following hydrological conditions: (a) present situation (‘base solution’) (b) before the reduction of the Vistula River discharge in 1916, (c) for the case of two channels between the Vistula Lagoon and the Baltic Sea.
taking into consideration these bathymetry changes, indicate only a small increase in salinity in the Lagoon (less than 0.1 per mile). It is only vizible during May– July when the discharge of rivers decreases significantly, and only for the central part of the Lagoon (Chubarenko, 1997).
4.3.2. Dredging works in connection with new port construction in the Russian part of Vistula Lagoon Because of the long-term plan for new port construction it is important to analyse the impact of another project — the possible deepening of the
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Kaliningrad Navigable Channel from 9 to 12 m depth for the passage of large-tonnage ships (Fig. 1b, Fig. 8). Length and width of the fairway to be dredged would be 8250 and 100 m, respectively, corresponding to a dredged volume of soil of 2475 m3. Simulations show the results to be similar to those stated above: an increase in the cross-section of the channel between the Baltic Sea and the
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Vistula Lagoon of 3% and simplification of water penetration into the Lagoon through the new channel causes an increase in salinity in the Russian part of the Lagoon of less than 0.1 per mile, and this only during the May–July period (Chubarenko, 1997). For both simulated tasks the mean annual salinity increases no more than 0.3%
Fig. 5. Salinity fields for a typical autumn situation (strong wind and intensive water exchange with the Baltic Sea) under following hydrological conditions: (a) present situation (‘base solution’); (b) before the reduction of the Vistula River discharge in 1916; (c) for the case of two channels between the Vistula Lagoon and the Baltic Sea.
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Fig. 6. Time variation of salinity in different parts of the Vistula Lagoon for present hydrological conditions (‘base solution’), before the reduction of Vistula discharge and in the case of two channels between the Lagoon and the Baltic Sea: (a) in the south-western part (point A); (b) in the central part of the Lagoon (point B); (c) near Baltiysk Strait (point C); (d) in the north-eastern part (point D).
4.3.3. Two channels between the Vistula Lagoon and the Baltic Sea The opening of a new channel, connecting the Vistula Lagoon with the Baltic Sea near Krynica Morska, Poland (Fig. 1), was discussed in connection with the yacht-tourism development. According to our simulations the hydrodynamic regime of the Lagoon as a whole will change significantly if a new 2.5-m depth channel would be built through the south part of the Vistula spit. It would effectively result in the water exchange between the Lagoon aquatory and the Baltic Sea. The cross-sectional area of this supposed channel
was chosen as equal to 17% from that of the Baltic strait, the water level variations on the new open boundary — as those in Baltiysk. The results of simulations are presented on Fig. 3c, Fig. 4c, Fig. 5c and on Figs. 6 and 7 (‘two channels’ curves). The salinity fields for the whole Lagoon during the spring overflow, typical summer and autumn situations are placed on Figs. 3– 5: (a) for present situation and (c) for two opposite channels. There are significant differences in the central and southern parts of the Lagoon. The same tendency is illustrated by Fig. 7, where the salinity variations along the Lagoon
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are shown both for ‘base’ and ‘2-channel’ solutions: for the north-eastern part differences are negligible. The mean annual salinity of the Lagoon as a whole will be increased by 40% in comparison with the present one. As for example, the new hydrodynamic situation, where the regime of water-exchange is like a strong draught, is shown on Fig. 7a. The associated intensification of the water-exchange with the Baltic through two opposite channels would cause a rapid increase of the salinity up to 5– 6 psu in the southern and central parts where nowadays it is no greater than 2.5 – 4 psu (see curves on Fig. 6a and b — comparison of salinity variations for southern and central parts of the Lagoon during the whole modelled 1994 year). The average annual salinity
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in the central part of the Lagoon increases by 40–60% (in the point B by 54%), in south-west — by 140–170% (in the point A on 125%). At the same time variations for the regions near Baltiysk channel (Fig. 6c) are not so serious. As for the north-eastern part of the Lagoon (Fig. 6d) the changes are quite small. During the spring overflow the salinity expected in the case of the two channels should be even smaller than at present. An important point is that the second channel would change principally the features of salinity curves in central and south-western parts of the Lagoon: the temporary variations in salinity in these parts of the Lagoon become similar to those
Fig. 6. (Continued)
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Fig. 7. The numerical modelling results (MIKE21) for the case of two channels between the Vistula Lagoon and the Baltic Sea: (a) current field on 2 May 1994 is an example of a new hydrodynamic regime (the strong draught) occurring from time to time due to the existence of two opposite channels; (b) salinity variations along the line AB on the 2 May 1994 (solution). The present situation, i.e. the ‘base solution’ (dotted line) and the solution for hydrodynamic conditions before regulating Vistula River (dashed line ‘Vistula’).
at the open boundary. So, the salinity regime becomes completely dependent on the inflow – outflow regime. The Vistula Lagoon would therefore loose the insularity and would become completely dependent from marine influence, except of its north-eastern part.
5. Conclusions Significant increase in the salinity of the Vistula Lagoon during the last century is due to manmade interventions that changed the morphology of the Lagoon.
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The main reasons for the increase in salinity were: (a) the diversion in flow on the part of the Vistula River drain from the Vistula Lagoon directly to the Baltic Sea; (b) intensification of water-exchange with the Baltic Sea with deepening of the Baltiysk Strait; (c) the simplification of water exchange between the different parts of the Lagoon through persistently dredged navigable channels. The greatest contribution to the salinity was made by the diversion in flow of on the part of the Vistula River drain from the Vistula Lagoon directly to the Baltic Sea. Numerical simulations demonstrate that the mean annual salinity of the Lagoon, obtained by averaging over time and space daily salinity fields, is today more than 30% higher than that before the Vistula River was regulated — directed from the Vistula Lagoon to the Baltic Sea. The deepening of the Baltiysk Strait, the only connection from the Lagoon to the Baltic Sea, causes the intensification of water exchange and, correspondingly, the increase of the salinity into the Lagoon. The deepening of the strait through total width (but not the navigable channel only) by about 1.2 m would cause the mean Lagoon annual salinity to increase by about 1%. Dredging in different parts of the Lagoon, enlargement of existing fairways and new navigable
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channels, all generate an increase in salinity by enhancing the marine water penetration to distant parts of the Lagoon. From the point of view of temporal variations in salinity, the Lagoon under present-day hydrological conditions remains the separate from the sea, with its own unique characteristics despite the increase in marine influence. If a new artificial channel at the southern part of the Vistula spit were constructed, the hydrodynamic regime of the Lagoon as a whole would change drastically. Both central and south-western parts of the Lagoon would then resemble the marine bay, and the salinity would reach values as high as 5–6 psu. The time scale of adaptation of salinity field characteristics to significant hydrological changes like those considered above in Sections 4.2 and 4.3.3 is about 1–3 months, for most distant parts — no more than a half of a year. It seems reasonable to conclude that the salinity of the Vistula Lagoon water will increase further. The main reason for this is that the dredging works are consistently carried out in Baltiysk Strait and navigable channels to maintain the navigation of ships.
Acknowledgements We thank our Danish, Polish, and Russian colleagues for their co-operation during the setting up and calibration of MIKE21 numerical model for the Vistula Lagoon under the international project ‘Prioritising Hot Spot Remediations in Vistula Lagoon Catchment: Environmental Assessment and planning for the Polish and Kaliningrad parts of the Lagoon’. We are also sincerely grateful to Boris Chubarenko for his critical remarks and important additions.
References
Fig. 8. The two projects of the deepening and enlargement of the navigation channels in the Baltiysk Strait region.
Chubarenko, B.V., Chubarenko, I.P., 1996. The transport of Baltic water along deep channel in gulf of Kaliningrad and its influence on fields of salinity and suspended solids. In: Proceedings of Baltic Marine Science Conference, October 22 – 26, 1996, Bornholm, Denmark.
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Chubarenko, B.V., Chubarenko, I.P., 1997. Regionalization of river Pregel estuary and Russian part of Vistula Lagoon on hydrological parameters. In: Proceedings of the International Conference on Regionalization in Hydrology, March 10 – 14, 1997, Braunschweig, Germany, pp. 41 –44. Chubarenko, I.P., 1997. Deepening works at Vistula Lagoon and Kaliningrad Marine channel. In: Prioritising Hot Spot Remediations in Vistula Lagoon Catchment: Environmental Assessment and Planning for the Polish and Kaliningrad Parts of the Lagoon. Water Quality Institute (DK); Danish Hydraulic Institute (DK); GEOMOR (Poland); P.P.Shirshov Institute of Oceanology, Atlantic Branch (Russia), 1993 – 1995, pp. 8 –26 Scientific Report, v. 6.
Chubarenko, I.P., 1998. Influence of deepening works in Baltiysk Channel on the water salinity in Vistula Lagoon (numerical model MIKE21). In: Monographs in System Ecology. System Research in Ecology: Linking, Watershed, Riverine and Marine Processes. Proceedings of the Second International Workshop on Interdisciplinary Approaches in Ecology, August 25 – 26, 1997. Coastal Research and Planning Institute, Klaipeda, pp. 18 – 21 V.2. Lazarenko, N., Maevskiy, A. (Eds.), 1971. Hydrometeorological regime of the Vistula Lagoon, p. 280 in Russian. User guide and reference manual for MIKE21 (1994). Danish Hydraulic Institute Release 1.2.
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