The Inner Puck Bay Is of Special Interest Because at the Brake of The
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Bulletin of the Maritime Institute Gdansk, 1993, 20, 1 Rajmund Dubrawski, Asst. Prof. Dr. Pharm. Department of Maritime Hydrotechnics The Maritime Institute in Gdansk EVALUATION OF THE INFLUENCE OF ENVIRONMENTAL PROCESSES IN BORROW PITS ON THE STATE OF INNER PUCK BAY Abstract The inner Puck Bay is of special interest because at the brake of the seventies a very deep environmental and biocenotic transformation occured in this basin in result of cumulated influence of antropogenic factors. At present, in order to protect the seacoast of the Hel Peninsu la, sand is dredged from the Puck Bay. In effect, in the bottom of the I bay's coastal zone five borrow pits have been formed. It was expected that in these pits may develop processes which could negatively in fluence the existing ecosystem of the bay, and become an additional cause of Puck Bay devastation. Results of investigations carried out in the years 1991-1992 proved that such processes do occur and that they might negatively influence the Puck Bay environment. 1. INTRODUCTION Since 1989 the seaward coast of the Hel Peninsula is protected by artificial nourishment with sandy material dredged from the coastal 80 R. Dubrawski zone of the inner Puck Bay. As a side-effect of the works, in the Puck Bay appeared a row of pits, separated by natural hollows. The borrow pits have decidedly different sedimentation, metabolic, hydrochemical and biologic properties from areas of neighbouring bottom and natural hollows (Chalupy Hollow and Kuznica Hollow). The area of the inner Puck Bay is the most strongly accumulative part of the Gulf of Gdansk, and the area in which the pits have been formed - Wladyslawowo and Chalupy- is the most strongly accumulative part of the inner Puck Bay. In the post-war period, increasing amounts of biogenes, organic matter and contaminants were discharged into the inner Puck Bay with waters of the Red a, Gizdepka and Plutnica rivers, with sewage waters of Wladyslawowo and Puck, and through atmos phere with dry and wet precipitation. Since thirty years a strong contaminating influence is exerted by sewage waters from the D~tbo g6rze sewage treatment plant, and since four years- from the Swarze wo sewage treatment plant. Excessive loading of the shallow and characterized by limited water exchange basin by biogenes and organic matter resulted in a breakdown of the autochtonic phytal system, in place of which a slum set of vegetation has developed, with its main representative- brown algae- Pilayella litoralis (period 1978- 1984 ). The process of cumulation of the constantly inflowing nutrient and toxic substances still goes on in the inner Puck Bay. At periodic massive supply, organic matter from dead brown algae is also collected in the bottom sediments. In conditions of good oxygenation of near bottom water layers, the organic matter is decomposed at bottom surface. However, when it collects in hollows (even small ones), min eralization slows down. Nonmineralized organic matter, after bonding with fine nonorganic material (silty sand, clay), is accumulated, for ming a basis for the development of anaerobic processes and for the HYDROTECHNICS AND ENVIRONMENT PROTECTION 81 modification of the maternal bottom's properties. Aerobic and an aerobic decomposition of matter in the surface layer of sediments causes emission of toxic and neutral gasses (H2S, NH3, CH4, Hz, and Nz) and freeing of soluble in lipides harmful organic substances, and of many substances (metabolites) soluble in water. These substances can lower the red-ox potential and acidify or poison bottom surface sediments, thereby limiting the enrooting or gripping ability of plants. All this, together with harmful or toxic systematic action of accumu lating substances, has strengthened processes degrading the original phytal system. The degree of intoxication and intensity of other nega tive changes occuring on the bottom surface in the Bay is proven by the reduction of areas covered in the past by resident vegetation, and by the development of species of plants not contacting with bottom sediments - mainly brown algae (Pilayella litoralis ). Organic matter (of allachtonic and autochtonic origin) undergoes various mineralization processes in the transition layer at the water/sediment phase boundary. Intense deoxygenation of water and sediments, reduction and originating from them decay processes take place here. These processes occur over the whole bottom of the Puck Bay, in spite of good oxygenation of its waters. In the transition layer, at contact of phases, propagate highly harm ful gasses (H2S, NH3), metabolites- products of organic matter decay and harmful or toxic substances of antropogenic origin. During min eralization of organic matter on the bottom, the water microlayer adjacent to sediments may for some time contain high concentrations of harmful gas and dissolved substances. Their action may lead to negative transformation of bacterial flora, resulting in reduction of the rate of organic matter decomposition and in accumulation of organic matter in most of the hollows in the bottom. 82 R. Dubrawski Accumulation of organic matter began in the Puck Bay within the natural hollows - Chalupy Hollow and Kuznica Hollow, Rzucewo BALTIC SEA GDANSK GULF . '-~i. 1·, :. ' ··: . ~ -· .. -~ ... ~ -- ~ ' ~-0.5 - I .S Y.dm =::J - -< O.S % dm. , .. ,. Fig. 1. Accumulation of organic matter in the inner Puck Bay HYDROTECHNICS AND ENVIRONMENT PROTECTION 83 Trough, and also in the adjacent to Wtadystawowo corner of the Puck Bay and in the Rewa Bay (Fig.1). Organic matter accumulation, an aerobic run of processes of mineralization and presence of highly harmful or toxic substances at the water/sediment contact resulted in a change of properties of the bottom. These changes became the cause of destroyal of plants in variuos stages of development and of very quick decrease of bottom area inhabitated by macrophytes. At first this process took place over the central part of the Puck Bay and the natural hollows. Next it moved coastwards, increasingly limiting the area covered by plants. Finally, species with low resistance were elimi nated. At present settled (rooted) plants exist mainly on the slopes of protuberances of the bottom, from which currents and waves move the nonmineralized organic matter to accumulative areas. The magnitude of organic matter accumulation on Puck Bay bottom is the basic indicator of its excessive inflow and of exceedance of decomposition ability in conditions of the Bay. It is the main factor of the basin's bottom degradation. The west and central1part of Puck Bay bottom is covered by silty sand, organic and highly organic mud (M usielak J 983, Trokowicz 1987). During the years 1975 - 1990, the percentage of organic matter in sediments increased, reaching an average of 5% dm for silty sand, while on a bottom with accumulation in the same kind of sand concentration of organic matter only rarely exceeds 2% dm. With growing fineness of sediments and content of organic matter, grows concentration of heavy metals, aliphatic, aromatic, polycyclic and chlorinated hydrocarbons and of humus and other substances resulting from mineralization of plant material. Analysis of history of the breakdown of the Puck Bay phytal system points to the existence of a longlasting cumulative incentive, the essence and strength of which has not changed or weakened to this day since 1978. The inner 84 R. Dubrawski Puck Bay basin is still under strong influence of contaminating and eutrophic agents, and the structure and organisation of the biocenosis undergoes further negative transformation, the final result of which may be nonreversible devastation. The presented above set of metabolic and contamination processes, transferred to artificial hollows - the borrow pits - may have a decisive influence on the course and biocenotic dynamics of the basin. 2. ENVIRONMENTAL PROCESSES IN THE AREA OF BORROW PITS (CHALUPY) 2.1 CHARACTERISTIC OF BORROW PITS In the years 1991 and 1992 were carried out investigations of the course of environmental processes in the area of the borrow pit at Chalupy. This pit faiils into a system of natural and artificial hollows in the Puck Bay coastal zone. Botrow pits are located in three subba sins of the Puck Bay (Fig.2): a) inner Puck Bay- borrow pits Wladyslawowo, Chalupy and Kuznica II, separated by natural hollows of Chalupy Hollow and Kuznica Hollow, b) transient zone - borrow pit Kuznica I, c) outer Puck Bay- borrow pit Jastarnia (I and II). Borrow pits Kuznica I and II are divided by a dredged channel leading to the port at Kuznica. 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