Quasi-estuary processes and consequences for human activity, south Baltic

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Abstract

On the coasts of inland half-open seas, such as the Baltic, there is observed a phenomenon of periodic intrusions of sea waters into land waters. They are caused by a current meteorological and hydrological situation and not by tides. However, due to the similarity of the processes of water exchange and the results brought about by them in the geographical environment, they are described as quasi-estuary processes. The course, scope and results of the phenomenon depend on the hydrography of the coast. In order to illustrate this dependency there were chosen four characteristic hydrographic situations which occur on the coast of the southern Baltic. These are: a deltaic system, a cut off distributary arm of a big European river, a system in which the mouth section of a river connects a large coastal lake with an open sea, and marshes. The consequence of the occurrence of the phenomenon of quasi-estuary is such problems which must be taken into consideration in the use of the geographical environment of the southern Baltic coast. This necessity becomes especially vital with the prospect of a rising of sea levels related to global climatic changes.

Introduction

On the coasts of inland half-open seas, such as the Baltic, there are no tides. Yet, also on such coasts in specific anemobaric and hydrological situations, there are observed intrusions of sea waters into inland waters. They influence the hydrological regime of hydrographic objects situated in the immediate neighbourhood of the sea shore and cause changes in the chemical and physical composition of their waters. This is an effect of the mixing of sea and land waters (Drwal, 1984, Drwal and Cieśliński, 1998, Drwal and Cieśliński, 2002, Cieśliński, 2000). Consequently, there arise several problems which have to be taken into consideration when various strategies for the use of the geographical environment are undertaken (Drwal, 2001). This is important as this influence may decide on the manner of use of individual areas. It is becoming especially urgent to signal them in the light of the forecast rising of sea levels related to global climatic changes (Tobolski, 1989, Drwal, 1995, Rotnicki, 1995, Zeidler, 1995).

The area of the present coast of the southern Baltic was in the Pleistocene within the scope of accumulation operation of Scandinavian glaciers. The richness of postglacial forms characteristic of areas of such an origin is favourable for hydrographic diversification (Fig. 1). Hence, there occur heavily waterlogged bottoms of ice marginal streamways (D), mouths of near-shore rivers (C), deltas of large European rivers (B), lagoons (A), lakes cut off from the open sea by a sandbar.

The southern Baltic coast has been under the influence of human pressure lasting for many centuries up to even 800 years, so they are being heavily transformed by man. These transformations often lead to threats. However, on the other hand, they sometimes condition further existence of these areas (those situated in depression). One of the consequences of this interference of man, indirectly related to the problems discussed here, is the penetration of saline waters into polder areas.

Section snippets

Quasi-estuary processes

Many authors, including Majewski, 1972, Jasińska, 1991, believe that on the Polish coast of the southern Baltic there occur more or less typical estuaries. They adopted the definition suggested by Pritchard (1952) who believed that an estuary is a half-closed near-shore water body with a free connection with the open sea and containing measurable quantities of sea salt. Whereas, according to the definition of an estuary used by Davidson et al. (1991), it is a water body occurring on the

Elbląg Bay–river Elbląg–lake Druzno

The system is situated in the eastern part of the Vistula delta (Fig. 1A). Individual objects – the water body, lagoons, canal, deltaic lake form one inseparable hydrographic system. Lake Druzno is a recipient of waters flowing from a land catchment of 1084 km2 of area. The outflow from the lake is through a canal – the river Elbląg. This is also the way through which there are periodically inflows between 22 and 33% of slightly salty water (Mikulski and Bojanowicz, 1967) from the Elbląska Bay,

Consequences of intrusions

The coast of the southern Baltic is a transitional area where there overlaps the influence of the sea and land background and where various forms of man's activity and interests clash. Natural processes, including the presented quasi-estuary processes for example infiltration of salty waters to ground and superficial waters, the floods, the abrasion of seacoast may hamper this activity, and even prevent some of its aspects.

The phenomenon of intrusions of sea waters into coastal land waters,

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