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. Each of these regions is characterized by a different hydrodynamic regime and different hydrobiologic and con tamination properties. 20. \. ··2:: .. ··. ·· ...... \ L.. ···· :r:: M 0 A y K -·· ·········· -< ····... 20 ····· 0 ~ 0 ------r~\0-- -l ,.- ... ---r-_I ...... ------s ----, .. .:_,------tTl n ~~\0 :r:: ----.,_-~ . a:--- __ - ---~- ____ -·~: ~.::? ______-- s --- ,__,J-~------• z...... rn---...---;; .,_~~ - ~ Q ' I ··L· \ ,-1 .. -- ' ·- 1;· •~ ·"· ~1i• ·> ~·~'....a..l · ~ ;)\ ..;: :;-:_,~----·~ -;~' .\ :'/'\?'-'~;/?:-.;::~.,_~-::-Bfr, -.,_.. •• . 0 '. , ...... , · , '·r" 1 \ \ Kuin1c~o : · ,' /I •,'·0, . " ~ •'I '" ~ 1 -. ... "" J I \1 \ ' ' \ I \ . \ ' .,. 0 - -"- _ , ' · , _ - ' I - , , , Jonoo o 1 1 ' ' · I - L. • ' '- · • W •, ' o V · -~ I - ~ - - ' .---,I~- - 1 ' 1' --- ', '. s' 2 ' .\ 'r •~ )\'"--,-,_; tTl • - __,__- .. :\ •, ', I \1 ( ',o z -- --:~ ~:;,~--·~- ~ i '\ < ' , " •, 1I Ii a;; I\' :;a ...... _: ~ J \ i:\ 0 "'I' I 0 \ : - -Coast nourished In 1989 - 1992 z P U ( K A 1 I A T 0 K A ,...... ' c::. \. \ 3:: i ,, .. " --. \ ~ ', ';~ . 00 (J) 86 R. Dubrawski _____ Degrada_!i_on changes are accompanied by development of new, biocenotic levels and structures, remaining in unstable equilibrium. This equilibrium can be easily disturbed by the introduction of new factors of antropogenic nature. As such may be now considered the increasing inflow of waste water from sewage treatment plants, the use of Plutnica nad Gizdepka rivers as sewers for waste from stock and poultry farms, and also the borrow pits. The row of artificial hollows, formed in the coastal zone of the inner Puck Bay, may cause negative biocenotic changes in the basin. Espe cially, the high loading of waters and sediments of the pits with organic matter may strengthen reduction processes endangering life in this part of the Bay. The characteristic of hollows in the Puck Bay bottom (Tab.1) very strongly points to the unnaturalness of the borrow pits. The area/depth ratio is for the pits within 0.07 and 1.58 ha/m, whereas for natural hollows it is between 16 and 58 ha/m. This ratio shows that sedimen tation traps have been formed, in which collect organic matter and contaminating substances. Pit length to width ratio also confirms the nonnatural character of the pits (5.8) as compared with natural hollows (abt. 1.1). The shape of the pits makes removal of accumulated matter by natural forces difficult. Therefore they become a sort of "bioreactor" in which are generated strongly toxic products, endangering the biocenosis of the basin. The ratio of pit volume to the volume of the smaller of the two natural hollows, i.e. the Chalupy Hollow, suggests that dredging sand from the pits Chalupy and Kuznica I should be stopped. This ratio also defines the limits of future dredging works within the Bay's area. It results that borrowing sand should be performed layer by layer, from Tab.1 Differentiation of natural and artificial hollows of the Puck Bay bottom (state at the end of 1992) ::r: -< Area Max. depth Volume Indicators of differentiation 0 ;.:I Subbasin of Puck Bay [ha] [m] [thous. cu .m] area/depth 0 length/width pit vol./ pit area/ -l Ch.Hol.vol. Ch .Hol.area [11 (') 1. Inner ::r: ...... z Wladyslawowo pit 0 .5 6.7 10 0.07 2.0 0.01 0.007 Q Chalupy pit 19.4 12.3 1222 1.58 4.4 1.38 0.28 Chalupy Hollow 68.0 4.1 885 16.58 ~ 1 . 3 . . ~ Kuznica Hollow 553.0 9.4 16553 58 .21 ~1 . 0 . 0 Kuznica II pit 15.2 14.0 842 1.08 6.6 0.95 0.22 [11 z 2. Intermediate < Kuznica I pit 20.0 13.0 1084 1.54 6.3 1.22 0.29 :;3 0z 3. Outer s;:: Jastarnia pit 7.3 10.7 457 0.68 5.8 0.51 0.11 [11z Total/average -l Borrow pits 62.4 (11 .3) 3614 0.99 5.8 (1) 1.0 (1) 0.22(1) '"0 ;.:I Hollows 621 .0 (8 .75) 13115 53.62 1.1 . 0 ------l [11 n (1) • excluding Wladyslawowo pit -l 0 z 00 -...... ) 88 R . Dubrawski large surfaces of (azoic) bottom. The area of the pits is, on average, five times smaller than the Chalupy Hollow surface (tab. 2), while their volume is about the same (1.0); this limits water exchange in the pits and supports the develop ment of anaerobic decomposition of matter and the development of organic origin harmful substances. Diffusion in conditions of stagnation is the main process by which concentrations are equalized in water in the borrow pits. Currents and waves propagate surface waters from pit area - containing a high percentage of harmful substances- to other regions of the bay. Also a sudden outflow of polluted water from the pits is possible in result of inflow of higher density sea water. In effect the polluted water could be propagated towards and along the southern banks of the bay. The residence time for the Puck Bay waters is about three weeks (Staskiewicz 1991). However, this does not concern the natural and artificial hollows in the bay's bottom. The rate of exchange of water in the Kuznica Hollow is, on average, two times slower and in Chalupy 1 Hollow - eight times slower than in the Puck Bay. Appearance of anaerobic processes in the borrow pits confirms stagnation and a very small rate of water exchange, and resulting high accumulation of harmful substances in them. 2.2 CHANGES IN CHEMISM OF WATER AND SEDIMENTS IN THE BORROW PITS The redox potential and organic matter, hydrocarbon and trace metal content in sediments, and content of phosphorus and nitrogen in water, were measured in the Chalupy borrow pit during the period HYDROTECHNICS AND ENVIRONMENT PROTECTION 89 June - September. Mechanical or natural resuspension of surface sediments, and with them of deposited chemical compounds (mostly trace metals), is in this part of the bay very harmful to water organisms, and reduces primary production. If the secondary pollutants pass to the water layer during dredging works, then they are propagated and dispersed by surface currents acting at the given moment. Secondary pollutants influence the outer Puck Bay environment to a much smal ler degree than when a similar situation occurs in the inner Puck Bay. The content of most of the investigated chemical components grows with borrow pit depth. This suggests that in the pits accumulates material migrating over the bay bottom (table 2). Organic matter accumulation proceeds especially swiftly in the bottom zone, therefore in that zone collect all polluting components. Their concentration in sediments of the pit is even higher than in the sediments of the accumulative west part of the Puck Bay, and decidedly higher than in sediments of its eastern part (Dubrawski 1989-1992, Ciszewski 1992). Special concern is roused by the fact that the trace metal content in sediments of the pit bottom was found to be four times higher than in other areas of the Puck Bay. Alarming are also the results for phosphorus and nitrogen content in the Chalupy pit. Such situation is not observed in other areas of the inner Puck Bay. Phosphate and nitrate concentrations indicate very low oxygenation of nearbottom water layers in the borrow pit. In these conditions, the difficultly dissolvable ferric phosphate, deposited in the sediments, passes into water as dissolvable ferric phosphate. This increases phosphorus concentration in the whole water layer, resulting in eutrophication of the whole basin. 3 3 If oxygen content falls below 0.5 cm /dm , the denitrification pro cess starts, leading to the disappearance of nitric salts - and this has \0 Tab.2 Hydrochemical characteristic of borrow pit Chatupy and neighbouring areas 0 Chalupy borrow pit Investigated component West basin East basin Evaluation of processes at pit bottom surface botto~ coeff. of accum. Bottom sediments Organic matter [% dm] 5.6 1.7 8.5 5.0 2.1 accumulation Hydrocarbons total 4 .5 3.2 31.4 9.8 1.3 accumulation of resistant hydrocarbons [mg/ kg dm] Metals [pg/g dm] Pb 24.3 9.5 38.6 4.0 4.7 accumulation of metals and organic matter ~ Zn 38.6 16.3 68.0 4.2 5.4 0 Cu 7.8 5.2 26.3 5.0 2.4 c I ..,0' Cd 0.8 0.5 2.1 4.2 0.3 ~ Hg 0.3 0.2 0.6 3.0 0.005 C/J ~ Eh (redox pot.) +246 +25 -215 - +146 strong reduction conditions and presence of H2S Water 3 Total N [,umol!dm ] 6.8 4.3 2.4 0.5 3.1 denitrification 3 Total P [,umol/dm ] 6.5 1.2 8.2 4.3 0.6 mobilisation of phosphorus in anaerobic conditions Ratio N : P 1.1 : 1 3.5 : 1 0.3 : 1 5.1 : 1 non proportional HYDROTECHNICS AND ENVIRONMENT PROTECTION 91 been observed in water of the pit. This process is accompanied by an increase of ammonia concentration. In all borrow pits hydrogen sul fide was found in periods of maximum supply (end of August) of autochtonic origin organic matter. An important indicator for environmental evaluations is the level of the redox potential of bottom sediments, which defines the state of oxygen conversions in the surface layer of the bottom. In shallow bottom areas the redox potential is positive, which shows that sedi ments at 1-2 m water depth are well oxygenated. However, at slope edges the potential starts falling and becomes strongly negative at pit bottom. This suggests that at pit bottom are developing anaerobic processes which limit or even make impossible population of the pits by bottom vegetation and organisms. 2.3 HYDROBIOLOGIC INDICATORS I Accumulation of large amounts of contaminants in the borrow pits endangers bottom organisms (zoobenthos) and inhibits recolonisation of the pit and neighbouring areas. On uncovered slopes of the pits, quick recolonisation by macrobenthos and a decrease of biomass and quantity of taxons with pit depth were observed (table 3). This con firms that the process of water intoxication is proceeding. In the upper part of the pit, the bottom was recolonised by a weak (7 taxons) zoobenthos set. However, its biomass is high when com pared with neighbouring east and west basins of the bay. R. Dubrawski Table 3. Biological characteristic of borrow pit Chatupy and neighbouring areas (1991-1992) Biological component West basin Borrow pit East basin surface bottom Zoo benthos Number of taxons 9 7 0 (-8m) 21 Average biomass 90.0 275.0 0 (-8m) 68.0 2 Quantity [thous/m ] 21 17 Dominants snails, Oligochaeta, snails, Oligochaeta molluscs molluscs Phytobenthos Average biomass 7.2 10.5 0 13.4 2 [gdm/m ] Dominants Pilayella, Pota- Potamog eton, Zostera mari- mogeton Pilayella na, Pilayella 3 Chlorophyll a [mg/ m ] 10.7 1.3 0 (-5m) 4.1 Around the edges of the Chalupy borrow pit (depth 1.0- 1.5 rn), only residual vegetation (Potarnogeton) was found -in contradistinc tion to the rich phytobenthos system around the edges of the borrow pit at Kuznica. Attention should be also drawn to the marked decrease of chlorophyll content in surface waters of the pit in comparison to chlorophyll level in waters of the west and east parts of the Puck Bay coastal zone. It seems that this is one of the more significant indicators of water intoxication by harmful substances propagated from the borrow pit. The presented investigations show that results of disturbing the bottom surface in areas of sand extraction are very harmful to the HYDROTECHNICS AND ENVIRONMENT PROTECTION 93 environment, and practically make impossible biological reconstruc tion of these areas. Using, by analogy, results obtained for the Chalupy borrow pit to characterize the effects of dredging in other borrow areas, it should be stated that sand extraction at all the other sites shall result in similar negative effects. Up to this time (1992) abt. 62 ha of the bottom has been exploited. Therefore about 6,500 kg of dry mass of sea-grass and about 20,000 kg of air-dry snail and mollusc mass have been lost. In comparison with the resources of the whole inner Puck Bay these losses are quite small, but neverthaless they count in the overall balance of resources and biological production of the basin's coastal zone. 3. GENERAL EFFECT OF SAND EXTRACTION AND ENVIRONMENTAL PROCESSES IN THE BORROW PITS ON THE PUCK BAY ECOSYSTEM Basing on the analysis of obtained results and principles of marine ecosystems' functioning, a preliminary evaluation of environmental effects of sand extraction and of processes proceeding in the borrow pits, located in the coastal zone of the Puck Bay may be presented (Dubrawski, Ciszewski 1992, 1993). 3.1 DIRECT EFFECTS In result of sand extraction, the following has occured or is proceeding: - breaking of continuity of the system of coastal zone bottom stratoce nosJs, 94 R . Dubrawski - disturbance of bottom surface and change of natural bottom relief, - extermination of plant and animal organisms over the disturbed bottom area, also loss of biomass and decrease of total production of the area, - formation of unnatural hollows in the bottom (down to-14m below M.S.L.), with poor water exchange favouring stagnation of the wa ters, - formation of artificial settling tanks for migrating mud and organic matter (of plant and sewage origin), - accumulation of organic matter and of connected with it harmful and toxic substances in the borrow pits, - formation of conditions favouring anaerobic processes and produc tion of hydrogen sulfide, ammonia, nitrogen, methane and other volatile substances, - development of decay processes in borrow pits, in that denitrifica tion, - change of water chemism and change of bacterial composition of the water and sediments in the borrow pits, - intoxication of surface water, strongly lowering primary production in the area adjacent to the borrow pits, - accumulation of contaminants resistant to opera_tion of environmen tal cleaning agents, - freeing of phosphorus from organic sediments collected in the bor row pits, which process increases eutrophication, - negative change of the redox potential of sediments on pit slopes, resulting in marked limiting of recolonisation by plants, - disturbance of bottom by the permanent and floating parts of the pipelines, - danger to people engaged in various forms of water sports ( swimm- HYDROTECHNICS AND ENVIRONMENT PROTECTION 95 ing, rowing, surfing, diving), - accumulation of pathogenic bacteria and possibility of their epidemic influence on water organisms and people. In the period 1989-1992 about 0.7% of Puck Bay bottom has been damaged directly (or 2.5% of inner Puck Bay coastal zone). Connected with that negative transformation of ecosystems in the borrow pits and over areas adjacent to the pits has already been observed. Further investigation of environmental changes in areas adjacent to the bor row pits will allow to evaluate the longterm influence of, proceeding in these artificial hollows, physical, chemical and biological processes on the ecosystem of the inner Puck Bay coastal zone. 3.2 INDIRECT EFFECTS Basing on results of investigations carried out in the Chalupy borrow pit, it is expected that many negative longterm changes of Puck Bay environment will take place due to dredging works and to processes proceeding in the borrow pits. The main predicted directions of negative environmental transfor mations are as follows: -permanent change of chemism of waters adjacent to the borrow pits, in that periodical intoxication, limiting or even eliminating organisms in the water, - possibility of generation of harmful aerosol (chemical and bacteri al), lowering therapeutical and recreational value of the area, - generation of specific bacterial and pollutant "bioreactors"; tbi ~ may cause that these areas will become closed to recreation (e.g. ban on water sports), 96 R. Dubrawski - possibility of periodical flushing of "bioreactors" resulting in danger to the environment of neighbouring areas of the Puck Bay (in certain wave and current conditions), - transport of nitrogen out of borrow pits, resulting in increased overfertilisation of the basin, and in worse biogen ratio (N:P), - expansion of anaerobic processes over the Puck Bay bottom, - development of specific heterotrophic flora (bacteria, fungus, as- pergillaceae ), - activation of plant and animal weed development, - various scale reconstruction of biocenotic structures in the basin, leading to final degradation of the system. Lowering of the biocenotic potential of Puck Bay coastal zone by about 2.5% (in a nonreversible way) seems a quite insignificant loss in conditions of degraded biocenosis. However, it may be of decisive importance to the future life of the basin, and in case of a threshold stimulus, such change may be decisive for the occurence of a devasta tion shifting of the whole biocepotic structure of the basin. The natural Puck Bay biocenotic system became degraded and finally broke down at the end of the seventies in effect of massive inflow of sewage, gradual disappearance of phytobenthos and overfertilisation of water. The resultant biocenotic system of com pens a tory character (revers ible degradation), may, under influence of a new antropogenic factor, undergo further degradation or even devastation, leading to breaking of trophic relations and disappearance of the basin's dominants. Di rect negative action of borrow pits on the Puck Bay biocenotic system may be accompanied by a longterm modifying influence of the "con t ~m-~ of trre: p-irs (H2S, nanoplankton, phosphorus, heavy metals, highly resistant substances, weeds, fungus and aspergillaceae - in that pa thogenic substances). HYDROTECHNICS AND ENVIRONMENT PROTECTION 97 Compensation biocenoses have only weak adaptation mechanisms. Therefore, a breakdown of the present biocenotic system rather than its adaptive modification should be expected. It is evaluated that a single inflow of poisoned water from all borrow pits of several million cu.m., containing large amounts of toxic substan ces (e.g. heavy metals) can kill most water organisms within range. At present each new antropogenic factor (of physical, chemical or biol ogical nature) may result in an increased degree of degradation of Puck Bay biocenoses because of the instability and narrow adapta tion/compensation ability of these biocenoses. Action of factors generally considered as negative, such as persisting concentrated eutrophication, overproduction of autochtonic organic matter, mobilsation of phosphorus and nitrogen from bottom stores, development of plant and animal weeds, macrospatial changes of bottom properties, resuspension of sediments and sedimentation with oxygen deficit, and exploitation of bottom sediments for needs of protection or for widfining the He! Peninsula, could cause devastation of the present biocenotic structure of the bay. The Puck Bay ecosystem could be saved by means of paralelly realised investigation and technical works, which should lead to mi nimization of sewage inflow, cleaning of the bottom, introduction of multiannual bottom vegetation, decrease of saturation of the bioce nosis by brown algae and sticklebacks, borrow pit recultivation- espe cially in Chalupy area, and fish stocking of the basin. This comprehensive program of reconstructing natural properties of the Puck Bay requires time (11- 15 years) and financing in amounts which are at present difficult to evaluate. Since, in spite of degradation, the richest marine biocenosis of the inner Puck Bay is in its coastal zone, keeping it for the future is a first 98 R. Dubrawski priority task within the program of Baltic Sea environment protection. LITERATURE Ciszewski P. et al, 1992: Evaluation of natural value of areas planned for reclamation and of sand borrow sites and approach channels. I.O.S, Gdynia. (In Polish). Dubrawski R., 1989-1992: Investigations of the state of contamination of material for artificial nourishment of the Hel Peninsula seaward coast. WW-IM 4454, 4603, 4690, 4760, Gdansk. (In Polish). Dubrawski R. and Ciszeski P. 1992: Determination of the influence of sand extrac tion for reclamation works from borrow pit Jastarnia in the Puck Bay - state of environment.I.M.- I.O.S., Gdansk. (In Polish). Dubrawski R. and Ciszewski P. 1993: Degradation changes of the inner Puck Bay and direction of research aiming at ecoreconstruction of the basin.Inz. Morsk. i Geotechn. (in print), Gdansk. (In Polish) Musielak S., 1983: Bottom sediments of the Puck Bay. Zesz. Nauk. U.G., Oceano grafia 10. (In Polish). Staskiewicz A. et al., 19t91 : Numerical model of water flow for the Puck Bay. 1.0.-P.A.N., Sopot. (In Polish). Trokowicz D. and Domaszewicz J., 1987: Distribution of bottom sediments and evaluation of their contamination by trace metals. P.I.G.- I.O.S. (In Polish).