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Evaluation of the impact from the Black Sea on the pollution of the Marmara Sea
e:>
Pergamon PII:S0273-1223(96)00064-9
Wat. Sci. Tech. Vol. 32, No.7. 1'1'.191-198.1995. CopynShl «) 19961AwQ Prinled in Greal Britain. All riShll merved. 0273-1223195 $9'50 + lHlO
EVALVAnON OF THE IMPACT FROM THE BLACK SEA ON THE POLLUTION OF THE MARMARA SEA Derin Orhon Istanbul Technical University, Environmental Engineering Department, I.T.V. Insaat Faki4ltes~ 80626 Maslak,Istanbul. Turkey
ABSTRACT The Mannara Sea is now the recipient of a large number of wastewater discharges from land-based sources. At the same time, it is in direct exchange both with The Black Sea and The Mediterranean. A correct and efficient wastewater management programme with nutrient removal may be acceptable if it can effectively reduce the pollution in The Mannara Sea. This can only be evaluated by means of a comparative evaluation of the relevant pollutant loads originating from the land-based sources in the coastal zone and from the adjacent seas. This paper evaluates significant quality parameters related to the Black: Sea - The Bospborus • The Mannara Sea system, quantifies the pollution exchange between The Mannara Sea and The Black Sea and provides a critical appraisal of the effect of The Black Sea on the pollution in The Mannara in comparison with land-based sources.
KEYWORDS Land-based pollution; marine water quality; Istanbul; The Black Sea; The Marmara Sea; eutrophication; nutrients. INTRODUCTION The Marmara Sea is now a critically polluted water body, subject to a multitude of wastewater discharges from major land-based sources located along the coastal line. including the Istanbul metropolitan area. The water quality measurements indicate severe signs of present and future eutrophication problems. Consequently, effective wastewater management including nutrient control may be required for an effective pollution prevention programme in the region. The Marmara Sea is in active exchange with The Black Sea and The Mediterranean. The Bosphorus, a strongly stratifted natural channel between The Marmara Sea and The Black Sea, with significant mixing at the entrance to The Marmara Sea is also a major polluter for the Marmara basin, since it carries the highly polluted waters of the Black Sea. Consequently, relative impact of the Black Sea through The Bosphorus as compared to the local wastewater discharges should be given serious consideration for the right choice of the wastewater management programme, the priorities and the levels of treatment to be implemented for land• based sources.
191
192
O.ORHON
The paper intends to review major factors contributing to the pollution in The Marmara Sea and provides numerical evaluation on the exchange of pollutants between The Black Sea and The Marmara Sea. (~SOOOmJ
........ 1.,0 .JIO • • •10.
..., - '''10 ....
(a)
i1ro en Oi Iribution
.........
00'1
I
a
'·00"
1006 •
.....
.......
(\I) Ph
0.00'
phor
0Il1O •
DI II ibul ion
...... I.n 0., • • •
In
01»-0'00
....
(c) Prim if)' Produetivil Oi lribUlion Figure J. Distribution of nilrogen. phosphorus and primary productivity in The Marmara Sea
••ts
Pollution exchange between The Black Sea and The Marmara Sea
193
WATER QUALITY IN THE MARMARA SEA The Mannara Sea is an internal water body with close interactions with The Black Sea and The Mediterranean. Its total volume is estimated as 3.378 x 10 12 m 3. It is permanently and strongly stratified with totally different characteristics between the euphotic layer in the upper 30m and the lower layer showing the typical properties of The Mediterranean. Extensive scientific surveys carried out during the last 10 years provide a good basis for the magnitude of critical pollutant concentrations. The average P04-P concentration in the upper layer is calculated as 61lg I-I, with a temporal and spatial variation in the range of 0.0-12 J.lg I-I. Corresponding values in the lower layer are 4 to 5 times higher. Similarly, the NO x concentration characterizing the upper layer varies between 0.0 and 40 Ilg I-I depending upon time and location, with an average value of 15-20 J.lg 1. 1. The same parameter is measured as 120-140 Ilg I-I in the deeper waters. As previously mentioned both nutrient levels appear to be strongly affected by seasonal changes, a sign of severe future eutrophication potential. An evaluation of the spatial distribution of nutrient concentrations under spring conditions is presented in Fig. 1. as part of a modelling and simulation effort recently carried out by DHI (1994). The primary productivity in the upper layer can also be considered as a significant index of pollution in The Mannara Sea. Relatively few measurements have so far been made on this parameter compared to other pollutants. The existing data show that the upper layer can be characterized with a primary productivity level of 150-200 g C m·2 year -I. This is confirmed by the simulation model of DHI (1994) predicting an average annual production of around 200 g C m·2 year -I for the open parts of The Mannara Sea, 220-270 g C m·2 year l for the coastal areas and 300-330 g C m·2 year l for The Izmit Bay. This parameter is also strongly affected by seasonal changes. Fig. 1 also gives simulated primary production prof1le in The Mannara Sea under spring conditions. These values are in the same order of magnitude with 79-261 g C m·2 year-I associated with the North Sea and 290 g C m·2 year l generally defining inner Danish waters. both evaluated as eutrophic water bodies. DISCHARGE OF POLLUTANfS FROM LAND-BASED SOURCES The Mannara Sea receives pollutant discharges from a number of land-based sources. The Metropolitan Area of Istanbul, located on the northern shore of The Mannara Sea and on both sides of The Bosphorus is the major polluting source in the area. A number of engineering studies have provided estimations for the magnitude of wastewater flow and pollutant loads from the city. In this context, the total wastewater flow originating from 14 different discharge points within the metropolitan area has been calculated as 1,332,000 m3 day'I. An extensive survey of wastewater characterization in Istanbul ( Orhon et aL. 1994a) indicated that unit emission rates of 40 g BODs capita·I d· I , 45 g S5 capita· I d-I, 6.7 g total N capita· I d· 1 and 1.3 g total P capita· I d-I may be selected as suitable values together with a unit flow rate of 160 I capita· I d· 1 for the calculation of wastewater flows and pollution loads. The calculated values are outlined in Table 1. As shown in the Table, a management plan for the present situation should involve a total wastewater discharge of 15.4 m- 3 s·1 with a potential pollution load of 335 tons of BODs. 54.1 tons of nitrogen and 9.1 tons of phosphorus per day. These values have been basically adopted with slight modifications for the water quality and eutrophication of The Mannara Sea as indicated in Fig. 2 (Bach et al.• 1995). Aside from Istanbul, The Izmit Bay Area, The Gemlik Bay Area, The Susurluk River and the adjacent residential areas, and The Tekirdag area contribute to different degrees to the pollution of The Mannara Sea (Fig. 2). Pollutant discharges from these land-based sources, as adopted in the modelling studies (DHI, 1994) are summarized in Table 2. From this table. it is noted that The Mannara Sea receives a daily load of 477 tons of BODS or 157 tons of TOC. 100 tons of unoxidized nitrogen and 21 tons of total phosphorus. The impact of non-point sources such as drainage and agriculture is assumed to be relatively small compared to anthropogenic point-sources, namely 1.7% (8 tons d· l ) for 'BODS. 7.4% (7.36 tons d· l ) for nitrogen and 1.3% (0.27 tons d· l ) for phosphorus; practically insignificant aside from nitrogen. The reliability of these values is however questionable.
D.ORHON
194
Table I. 1990 wastewater flows and pollution loads for Istanbul Wastewater flow
Region
mJ day"
I. KadikOy 2. Yenikapi 3. Baltalimani 4. AlakOy 5. Tuzla 6. Kll~ilk~ekmece 7. Bilyilk~ekm_ B. Tanneries 9.0sklldar 10. Kll~llksu 11. TarBbya 12. Princes Islands
13.
Pasab.h~
14. B. Cekmece Beyond
319400 313000 198700 105200 92500 66500 49000 36000 42300 30700 20220 12958 12700 32830 I 332008
TOTAL
m1s- 1
3-69 3-63 2·31 1·20 1·07 0·77 0·568 0·416 0·49 0·355 0·234 0·15 0,147 0·38 15·41
Suspended solids Total Kjheldal (SS) nitrogen (TKN) tons day" % tons day" %
BOD,
%
tons day"
24
ns IS
8 7 5 4 3 3 2 1·5 I 1 2
100
60·1 63·93
45·5
25·14 19·5 13·5 10·5
65
9·3 6·17 3·73 2·8 3·16
6·5
334·83
%
71-6 73-91 52·2 29·2 24·1 16·5
18 19 \3·6 7·5 5·8 4
H
12·5 72
19·4 2·8 1·8 1·1 0·8 0·9 1·19
10·7
6·58
4·25
HS
3-71 7·3 387·7
100
18·5 19 13·5 7·5 6·2 4·3 3·2 18·5 2·8 1·7 I 0.8 0·95 1·9 100
9·36 10·33 7-44 4·03 3·2 2·2 1·7 10·6 1·53 1·075 0·61 0·47 0·5 1·09 S4·135
Total phosphorus (f·P)
17-3 19 13-7 7·4 5·9 4 3 19·8
2-8
2 1·2 0·9 0·9 2 100
Ions day" 1-93 2·04 1,46 0·8 1·12 0·44 0·33
21 22·2 16 9 12 5 3·0
0·296 0·2 0·12 0·09 0·1 0·207
3·2 2·1 1·3 1 I 2·4
9·133
Table 2. Land-based pollutant loads to The Mannara Sea Pollutanl Loads (Ion d' l ) Region
BOD,
TOC
TKN
Tolal P
335
54.1 16.0 8.6 21.9 8.7
9.1 2.0 0.1 9.7 0.37
109.3
21.3
Istanbul Metropolilan Area Izmit Bay Area Gemlik Bay Area Susurluk River Tekirdag Area
7.4 74.0 40.9
110 19.8 2.5 24.5 13.7
TOTAL
517.3
170.5
60
BlackSe.
s•• of
Manna
Figure 2. Nutrient loads to The Marmara Sea from IBnd-based sources (OHI. 1994).
%
100
Pollutioo exchange between The Black Sea and The Marmara Sea
19S
HYDRODYNAMIC PROPERTIES OF TIlE BOSPHORUS The waters of The Bosphorus are strongly stratified, with the upper layer comprising low salinity outflow from The Black Sea and the bottom denser layer generated by the northerly, highly saline flow from The Mediterranean. Mixing between the two layers along The Bosphorus and the Bosphorus/Marmara junction, (BMJ), is strongly affected by the main features related to the physical oceanography of the area, namely the respective Salinity of the approaching currents, the topography of the strait and the prevailing meteorological conditions. Extensive measurements have indicated that the flow from The Marmara Sea in the bottom layer may be characterized by an average salinity of 37.3 ppt: the salinity of this layer remains unaffected through the BMI and drops to 35.54 ppt at the outlet to The Black Sea with a net loss of 1.76 ppt along the Bosphorus. An average salinity of 17.86 ppt is associated with the upper flow to The Bosphorus from The Black Sea; this flow leaves The Bosphorus with a salt content of 20.17 ppt. corresponding to an increase of 2.31 ppt The vertical mixing in the BMJ imparts an additional salinity of 3.03 ppt to the upper flow which enters The Marmara Sea with a salinity of 23.2 ppt.
14OW) ,...,.- • PI'!
QIO .',.
~a 4__•
noD -. I'''''
-t---t----+--..--~t-_4-----+-
"100
.a,.
8OSPHOAUS
MOD ""II
..--
eOSPHOAUS
I ~"""II'" I 1no",'"
.....
'--
THE BLACK SEA
Figure 3. Milling and trlIIISport between The Black Sea and The Marmara Sea.
On the basis of the experimental data presented above and other systematic observations carried out between 1986-1989, Orhon ~t al. (l994b) suggest that the lower layer may be characterized by an average flow rate of 14,450 m 3 s·1 in front of the mixing zone at the BMJ. In this zone it is calculated to loose 29.4% of its flow to the upper layer and it enters The Bosphorus with a flow rate of 10,270 m 3 s·l; the mixing along The Bosphorus takes away 1900 m 3 s·1 or 13% of this flow while imparting 13230 m 3 s·l. In this way, only 9600
196
D.ORHON
m 3 s-1 enters The Black Sea as a yearly average figure. containing 8370 m 3 s·1 of the original Mediterranean water and 1230 m 3 s-I of The Black Sea water recirculated from the upper layer. Conversely. the upper layer from The Black Sea, with an average flow rate of 19.100 m 3 s·1 is similarly affected by the mixing and discharges to the Marmara sea with a flow rate of 24.050 m 3 s·l. representing a 26.0% increase with respect to the value entering The Bosphorus. as schematically shown in Fig. 3. These estimations are in very good agreement with values presented as a result of a numerical modelling study performed by DHI (1994). using the same set of experimental observations. The significant feature of the hydrodynamics of the Bosphorus is the intense mixing of the deeper Marmara waters into the upper layer at the BMJ. While the significance of this mixing is now unanimously accepted. its magnitude is still debatable. WATER QUALITY AROUNDTHEBOSPHORUS Extensive observations carried out for three years between 1987-1989 at three stations for the upper layer at the Bosphorus-Black Sea opening section and at four stations for the lower layer at the BMJ opening section have been evaluated to reflect average concentrations of P0 4-P (DIP). oxidized nitrogen (NO x) organic carbon. considered as significant pollutant parameters (Orhon et al., 1994b). They are outlined in Table 3 together with the data provided by Polat and Tugrul (1995) who interpreted the same observations and provided additional information concerning other forms of phosphorus and nitrogen. It should be noted that date related to phosphorus and nitrogen fractions other than P04-P and NO x are erratic and not suitable to draw general conclusions at this stage. For example. the dissolved organic nitrogen concentrations (DON) of the upper and lower layers around The Bosphorus. constituting the major fraction of the total nitrogen content. have been suggested with practically no current measurement support. The Table also includes results of a few spot measurements made during the last year in another survey (IMC. 1995). Therefore. only P04-P and NOx fractions have been taken into consideration in evaluating pollution exchange between The Black Sea and The Marmara Sea as outlined below. Table 3. Average pollutant concentrations in the upper and lower layers
..
Orhon et al.,(1994b)
Polat and Tugrul (1995)
IMC (1995)
Cu'
CL '
Cu
CL
Cu
~
DIP (P04-P) PP (Particulate P) DOP (Dissol.org.P) TP (Total P)
0.17
1.04
0.18 0.17 0.15 0.50
1.01 0.05 0.05 1.11
0.13
0.89
0.45
1.8
NOx NH3-N PON (Partic.org.N) DON (Dissol.org.N) TN (Total N)
1.46
9.26
1.6 0.5 2.4 18.0 22.5
95 0.2 0.4 3.0 13.1
0.82 0.3
9.62 0.4
TOC (mgl-I )
2.61
0.62
5.57
1.82
Parameters
all units in pmol I-I except for TOC from the Black Sea (upper layer) ~ outflow from the Marmara Sea (lower layer)
Cu =outflow
=
The analysis of the data presented in Table 3 indicates that the average upper layer DIP (P04'"P) concentration outside the Bosphorus-Black Sea opening section is 0.17 \lmol pn or 0.0053 mgn, whereas the lower layer of the Marmara Sea beyond the BMJ-Marmara Sea opening section is noted to have accumulated a much I!reater concentration of 1.04 umol pn or 0.0322 m~. The dailv discharl!e of
Pollution exchange between The Black Sea and The Marmara Sea
197
phosphorus from Istanbul wastewaters is 9.13 tons, corresponding to an average load of 3,333 tons per year. Consequently, the natural DIP input via the upper stream may be calculated as 3,178 tons/year, a level which is 95% of the anthropogenic phosphorus introduced to the system. As illustrated in Table 3, this is around 30% of the total P load entering The Bosphorus via The Black Sea. However the Marmara Sea appears to receive 9,259 tons/year or 2.78 times more than the total Istanbul phosphorus discharge, 6,287 tons/year being recirculated from the lower layer due to mixing in the transition zone. As the result of the complex interactions and mass transfer mechanism between the two layers, the Marmara Sea discharges 5,539 tons of P04-P per year to the Black Sea via the lower layer, 50% more than what it receives annually from the Istanbul Metropolitan Area.
...I
1 12511 147118
Ion~'
6287
Ion>/teat
-..y•. , _
38173
82711
..
1~-lOt\Ilfye-..;....,--_l..J-----.-.,;.....
- + - - -I t - - - 1 - - - · - 4 - - - - 1
-.1\''''
l
3171
..",..,..,
..",..,..,
IIOSPHQRUS
l
111710
1IlnUt-
J
_
THE M.tIRMARA SEA
-
138.'0'
WIa/yea' 1424.'0'
!~---~--_r---.!.!-------.,.-.tye.,.. 1)13.010·-......
c THE MAflIMAA SF'"
Figure 4. Exchange of pollutants between The Black Sea and The Marmara Sea.
D.ORHON
198
The general balance of nitrogen between The Marmara Sea and The Black Sea has quite a similar character. The NOx concentrations in The Black Sea upper layer and The Marmara Sea lower layer are 0.02 mg/l and 0.137 mg/l respectively exhibiting an almost 7-fold accumulation in the latter. The Black Sea input is 12,235 tons per year, amounting only to 62% of the anthropogenic nitrogen load, but it is increased to 38,173 tons per year at The Marmara Sea entrance incorporating 26,645 tons/year from the bottom layer in the transition zone. The mass balance is established with a net annual discharge of 24,545 tons of NO x from The Marmara Sea to The Black Sea, 25% more than the amount it receives from Istanbul sewage discharges. The NIP ratio in these discharges is assessed as 5.8. In the lower layer of The Marmara Sea beyond the transition zone, observations yield a lower value of 4.28 for the same ratio which is slightly increased to 4.43 when it is evaluated in terms of respective annual net discharges of the system to The Black Sea. The third parameter included in the monitoring and evaluation is the organic carbon which shows a picture totally opposite of what has been observed for nitrogen and phosphorus. In the lower layer of The Marmara Sea, the average TOC concentration is calculated as 0.62 mg/l, nearly 25% of 2.31 mg/l which is associated with the upper stream entering Bosphorus from The Black Sea. This stream introduces to the system an annual TOC load of 1.39 x 106 tons, 15.7 times the amount contained in the wastewater discharges in Istanbul. The latter is only 88.9 x 103 tons/year and calculated on the basis of a BODsfI'OC ratio of 1.375. Unlike the nitrogen and phosphorus balance, there is a net TOC input of 1.14 x 106 tons/year to The Marmara Sea, excluding the anthropogenic load totalling only 8% of this figure. The schematic evaluation of the nitrogen, phosphorus and TOC balances is illustrated in Fig. 4. CONCLUSIONS The Marmara Sea receives via the natural exchange from The Black Sea roughly 15 times more organic matter than what is contained in the sewage discharges from Istanbul; on the other hand, aside from coastal areas, the main pollution problem in The Marmara Sea is the nutrient accumulation which cannot be remedied, as it is illustrated in the paper, by conventional biological treatment Therefore, the magnitude of pollutant discharges from land-based sources and the pollution state of The Marmara Sea calls for effective nutrient control. The experimental evidence on the basis of extensive observations also indicates that the nutrient input from The Black Sea to The Marmara Sea is much more significant than coastal wastewater discharges. Therefore, nutrient removal from wastewater should not be regarded as the required corrective action without effective measures to reduce pollution in The Black Sea. REFERENCES Bacb, H. K., Orbon, D., Jensen, O. K. and Hansen, I. S. (1995). Environmenla1 model studies for !be Istanbul Master Plan Pan n: Water quality and eutropbication, War. Sci. Tech.. 32(2),149·158. Danisb Hydraulic Institute (1994). 3D Numerical Modelling of tbe Environmenla1 Conditions of tbe Seas Around Istanbul, Final Report. IMC Istanbul Masterplan Consortium (1995) Istanbul water supply and drainage, sewage lreabIlent and disposal master plan study, vol. 7, draft report. Orbon, D., Silzen, S. and Ubay, E. (1994a). Assessment of nitrification-<1enitrification potential of Istanbul domestic wastewaters, War. Sci. Tech.. 30(6), 21·30. Orbon, D., Uslu, 0., Meri~, S., Saliboglu, I. and Filibeli, A. (l994b) "Wastewater Management for Istanbul: Basis for TreabIlent and Disposal", Envirofl. Pollut., 84(1), 167·178. Polal, <;. S. and Tugru\, S., (1995). Nutrient and organic carbon exchanges between The Black and Marmara Seas through The Bosphorus sltail, Cont. ShelfRes., (in press).
Pergamon PII:S0273-1223(96)00064-9
Wat. Sci. Tech. Vol. 32, No.7. 1'1'.191-198.1995. CopynShl «) 19961AwQ Prinled in Greal Britain. All riShll merved. 0273-1223195 $9'50 + lHlO
EVALVAnON OF THE IMPACT FROM THE BLACK SEA ON THE POLLUTION OF THE MARMARA SEA Derin Orhon Istanbul Technical University, Environmental Engineering Department, I.T.V. Insaat Faki4ltes~ 80626 Maslak,Istanbul. Turkey
ABSTRACT The Mannara Sea is now the recipient of a large number of wastewater discharges from land-based sources. At the same time, it is in direct exchange both with The Black Sea and The Mediterranean. A correct and efficient wastewater management programme with nutrient removal may be acceptable if it can effectively reduce the pollution in The Mannara Sea. This can only be evaluated by means of a comparative evaluation of the relevant pollutant loads originating from the land-based sources in the coastal zone and from the adjacent seas. This paper evaluates significant quality parameters related to the Black: Sea - The Bospborus • The Mannara Sea system, quantifies the pollution exchange between The Mannara Sea and The Black Sea and provides a critical appraisal of the effect of The Black Sea on the pollution in The Mannara in comparison with land-based sources.
KEYWORDS Land-based pollution; marine water quality; Istanbul; The Black Sea; The Marmara Sea; eutrophication; nutrients. INTRODUCTION The Marmara Sea is now a critically polluted water body, subject to a multitude of wastewater discharges from major land-based sources located along the coastal line. including the Istanbul metropolitan area. The water quality measurements indicate severe signs of present and future eutrophication problems. Consequently, effective wastewater management including nutrient control may be required for an effective pollution prevention programme in the region. The Marmara Sea is in active exchange with The Black Sea and The Mediterranean. The Bosphorus, a strongly stratifted natural channel between The Marmara Sea and The Black Sea, with significant mixing at the entrance to The Marmara Sea is also a major polluter for the Marmara basin, since it carries the highly polluted waters of the Black Sea. Consequently, relative impact of the Black Sea through The Bosphorus as compared to the local wastewater discharges should be given serious consideration for the right choice of the wastewater management programme, the priorities and the levels of treatment to be implemented for land• based sources.
191
192
O.ORHON
The paper intends to review major factors contributing to the pollution in The Marmara Sea and provides numerical evaluation on the exchange of pollutants between The Black Sea and The Marmara Sea. (~SOOOmJ
........ 1.,0 .JIO • • •10.
..., - '''10 ....
(a)
i1ro en Oi Iribution
.........
00'1
I
a
'·00"
1006 •
.....
.......
(\I) Ph
0.00'
phor
0Il1O •
DI II ibul ion
...... I.n 0., • • •
In
01»-0'00
....
(c) Prim if)' Produetivil Oi lribUlion Figure J. Distribution of nilrogen. phosphorus and primary productivity in The Marmara Sea
••ts
Pollution exchange between The Black Sea and The Marmara Sea
193
WATER QUALITY IN THE MARMARA SEA The Mannara Sea is an internal water body with close interactions with The Black Sea and The Mediterranean. Its total volume is estimated as 3.378 x 10 12 m 3. It is permanently and strongly stratified with totally different characteristics between the euphotic layer in the upper 30m and the lower layer showing the typical properties of The Mediterranean. Extensive scientific surveys carried out during the last 10 years provide a good basis for the magnitude of critical pollutant concentrations. The average P04-P concentration in the upper layer is calculated as 61lg I-I, with a temporal and spatial variation in the range of 0.0-12 J.lg I-I. Corresponding values in the lower layer are 4 to 5 times higher. Similarly, the NO x concentration characterizing the upper layer varies between 0.0 and 40 Ilg I-I depending upon time and location, with an average value of 15-20 J.lg 1. 1. The same parameter is measured as 120-140 Ilg I-I in the deeper waters. As previously mentioned both nutrient levels appear to be strongly affected by seasonal changes, a sign of severe future eutrophication potential. An evaluation of the spatial distribution of nutrient concentrations under spring conditions is presented in Fig. 1. as part of a modelling and simulation effort recently carried out by DHI (1994). The primary productivity in the upper layer can also be considered as a significant index of pollution in The Mannara Sea. Relatively few measurements have so far been made on this parameter compared to other pollutants. The existing data show that the upper layer can be characterized with a primary productivity level of 150-200 g C m·2 year -I. This is confirmed by the simulation model of DHI (1994) predicting an average annual production of around 200 g C m·2 year -I for the open parts of The Mannara Sea, 220-270 g C m·2 year l for the coastal areas and 300-330 g C m·2 year l for The Izmit Bay. This parameter is also strongly affected by seasonal changes. Fig. 1 also gives simulated primary production prof1le in The Mannara Sea under spring conditions. These values are in the same order of magnitude with 79-261 g C m·2 year-I associated with the North Sea and 290 g C m·2 year l generally defining inner Danish waters. both evaluated as eutrophic water bodies. DISCHARGE OF POLLUTANfS FROM LAND-BASED SOURCES The Mannara Sea receives pollutant discharges from a number of land-based sources. The Metropolitan Area of Istanbul, located on the northern shore of The Mannara Sea and on both sides of The Bosphorus is the major polluting source in the area. A number of engineering studies have provided estimations for the magnitude of wastewater flow and pollutant loads from the city. In this context, the total wastewater flow originating from 14 different discharge points within the metropolitan area has been calculated as 1,332,000 m3 day'I. An extensive survey of wastewater characterization in Istanbul ( Orhon et aL. 1994a) indicated that unit emission rates of 40 g BODs capita·I d· I , 45 g S5 capita· I d-I, 6.7 g total N capita· I d· 1 and 1.3 g total P capita· I d-I may be selected as suitable values together with a unit flow rate of 160 I capita· I d· 1 for the calculation of wastewater flows and pollution loads. The calculated values are outlined in Table 1. As shown in the Table, a management plan for the present situation should involve a total wastewater discharge of 15.4 m- 3 s·1 with a potential pollution load of 335 tons of BODs. 54.1 tons of nitrogen and 9.1 tons of phosphorus per day. These values have been basically adopted with slight modifications for the water quality and eutrophication of The Mannara Sea as indicated in Fig. 2 (Bach et al.• 1995). Aside from Istanbul, The Izmit Bay Area, The Gemlik Bay Area, The Susurluk River and the adjacent residential areas, and The Tekirdag area contribute to different degrees to the pollution of The Mannara Sea (Fig. 2). Pollutant discharges from these land-based sources, as adopted in the modelling studies (DHI, 1994) are summarized in Table 2. From this table. it is noted that The Mannara Sea receives a daily load of 477 tons of BODS or 157 tons of TOC. 100 tons of unoxidized nitrogen and 21 tons of total phosphorus. The impact of non-point sources such as drainage and agriculture is assumed to be relatively small compared to anthropogenic point-sources, namely 1.7% (8 tons d· l ) for 'BODS. 7.4% (7.36 tons d· l ) for nitrogen and 1.3% (0.27 tons d· l ) for phosphorus; practically insignificant aside from nitrogen. The reliability of these values is however questionable.
D.ORHON
194
Table I. 1990 wastewater flows and pollution loads for Istanbul Wastewater flow
Region
mJ day"
I. KadikOy 2. Yenikapi 3. Baltalimani 4. AlakOy 5. Tuzla 6. Kll~ilk~ekmece 7. Bilyilk~ekm_ B. Tanneries 9.0sklldar 10. Kll~llksu 11. TarBbya 12. Princes Islands
13.
Pasab.h~
14. B. Cekmece Beyond
319400 313000 198700 105200 92500 66500 49000 36000 42300 30700 20220 12958 12700 32830 I 332008
TOTAL
m1s- 1
3-69 3-63 2·31 1·20 1·07 0·77 0·568 0·416 0·49 0·355 0·234 0·15 0,147 0·38 15·41
Suspended solids Total Kjheldal (SS) nitrogen (TKN) tons day" % tons day" %
BOD,
%
tons day"
24
ns IS
8 7 5 4 3 3 2 1·5 I 1 2
100
60·1 63·93
45·5
25·14 19·5 13·5 10·5
65
9·3 6·17 3·73 2·8 3·16
6·5
334·83
%
71-6 73-91 52·2 29·2 24·1 16·5
18 19 \3·6 7·5 5·8 4
H
12·5 72
19·4 2·8 1·8 1·1 0·8 0·9 1·19
10·7
6·58
4·25
HS
3-71 7·3 387·7
100
18·5 19 13·5 7·5 6·2 4·3 3·2 18·5 2·8 1·7 I 0.8 0·95 1·9 100
9·36 10·33 7-44 4·03 3·2 2·2 1·7 10·6 1·53 1·075 0·61 0·47 0·5 1·09 S4·135
Total phosphorus (f·P)
17-3 19 13-7 7·4 5·9 4 3 19·8
2-8
2 1·2 0·9 0·9 2 100
Ions day" 1-93 2·04 1,46 0·8 1·12 0·44 0·33
21 22·2 16 9 12 5 3·0
0·296 0·2 0·12 0·09 0·1 0·207
3·2 2·1 1·3 1 I 2·4
9·133
Table 2. Land-based pollutant loads to The Mannara Sea Pollutanl Loads (Ion d' l ) Region
BOD,
TOC
TKN
Tolal P
335
54.1 16.0 8.6 21.9 8.7
9.1 2.0 0.1 9.7 0.37
109.3
21.3
Istanbul Metropolilan Area Izmit Bay Area Gemlik Bay Area Susurluk River Tekirdag Area
7.4 74.0 40.9
110 19.8 2.5 24.5 13.7
TOTAL
517.3
170.5
60
BlackSe.
s•• of
Manna
Figure 2. Nutrient loads to The Marmara Sea from IBnd-based sources (OHI. 1994).
%
100
Pollutioo exchange between The Black Sea and The Marmara Sea
19S
HYDRODYNAMIC PROPERTIES OF TIlE BOSPHORUS The waters of The Bosphorus are strongly stratified, with the upper layer comprising low salinity outflow from The Black Sea and the bottom denser layer generated by the northerly, highly saline flow from The Mediterranean. Mixing between the two layers along The Bosphorus and the Bosphorus/Marmara junction, (BMJ), is strongly affected by the main features related to the physical oceanography of the area, namely the respective Salinity of the approaching currents, the topography of the strait and the prevailing meteorological conditions. Extensive measurements have indicated that the flow from The Marmara Sea in the bottom layer may be characterized by an average salinity of 37.3 ppt: the salinity of this layer remains unaffected through the BMI and drops to 35.54 ppt at the outlet to The Black Sea with a net loss of 1.76 ppt along the Bosphorus. An average salinity of 17.86 ppt is associated with the upper flow to The Bosphorus from The Black Sea; this flow leaves The Bosphorus with a salt content of 20.17 ppt. corresponding to an increase of 2.31 ppt The vertical mixing in the BMJ imparts an additional salinity of 3.03 ppt to the upper flow which enters The Marmara Sea with a salinity of 23.2 ppt.
14OW) ,...,.- • PI'!
QIO .',.
~a 4__•
noD -. I'''''
-t---t----+--..--~t-_4-----+-
"100
.a,.
8OSPHOAUS
MOD ""II
..--
eOSPHOAUS
I ~"""II'" I 1no",'"
.....
'--
THE BLACK SEA
Figure 3. Milling and trlIIISport between The Black Sea and The Marmara Sea.
On the basis of the experimental data presented above and other systematic observations carried out between 1986-1989, Orhon ~t al. (l994b) suggest that the lower layer may be characterized by an average flow rate of 14,450 m 3 s·1 in front of the mixing zone at the BMJ. In this zone it is calculated to loose 29.4% of its flow to the upper layer and it enters The Bosphorus with a flow rate of 10,270 m 3 s·l; the mixing along The Bosphorus takes away 1900 m 3 s·1 or 13% of this flow while imparting 13230 m 3 s·l. In this way, only 9600
196
D.ORHON
m 3 s-1 enters The Black Sea as a yearly average figure. containing 8370 m 3 s·1 of the original Mediterranean water and 1230 m 3 s-I of The Black Sea water recirculated from the upper layer. Conversely. the upper layer from The Black Sea, with an average flow rate of 19.100 m 3 s·1 is similarly affected by the mixing and discharges to the Marmara sea with a flow rate of 24.050 m 3 s·l. representing a 26.0% increase with respect to the value entering The Bosphorus. as schematically shown in Fig. 3. These estimations are in very good agreement with values presented as a result of a numerical modelling study performed by DHI (1994). using the same set of experimental observations. The significant feature of the hydrodynamics of the Bosphorus is the intense mixing of the deeper Marmara waters into the upper layer at the BMJ. While the significance of this mixing is now unanimously accepted. its magnitude is still debatable. WATER QUALITY AROUNDTHEBOSPHORUS Extensive observations carried out for three years between 1987-1989 at three stations for the upper layer at the Bosphorus-Black Sea opening section and at four stations for the lower layer at the BMJ opening section have been evaluated to reflect average concentrations of P0 4-P (DIP). oxidized nitrogen (NO x) organic carbon. considered as significant pollutant parameters (Orhon et al., 1994b). They are outlined in Table 3 together with the data provided by Polat and Tugrul (1995) who interpreted the same observations and provided additional information concerning other forms of phosphorus and nitrogen. It should be noted that date related to phosphorus and nitrogen fractions other than P04-P and NO x are erratic and not suitable to draw general conclusions at this stage. For example. the dissolved organic nitrogen concentrations (DON) of the upper and lower layers around The Bosphorus. constituting the major fraction of the total nitrogen content. have been suggested with practically no current measurement support. The Table also includes results of a few spot measurements made during the last year in another survey (IMC. 1995). Therefore. only P04-P and NOx fractions have been taken into consideration in evaluating pollution exchange between The Black Sea and The Marmara Sea as outlined below. Table 3. Average pollutant concentrations in the upper and lower layers
..
Orhon et al.,(1994b)
Polat and Tugrul (1995)
IMC (1995)
Cu'
CL '
Cu
CL
Cu
~
DIP (P04-P) PP (Particulate P) DOP (Dissol.org.P) TP (Total P)
0.17
1.04
0.18 0.17 0.15 0.50
1.01 0.05 0.05 1.11
0.13
0.89
0.45
1.8
NOx NH3-N PON (Partic.org.N) DON (Dissol.org.N) TN (Total N)
1.46
9.26
1.6 0.5 2.4 18.0 22.5
95 0.2 0.4 3.0 13.1
0.82 0.3
9.62 0.4
TOC (mgl-I )
2.61
0.62
5.57
1.82
Parameters
all units in pmol I-I except for TOC from the Black Sea (upper layer) ~ outflow from the Marmara Sea (lower layer)
Cu =outflow
=
The analysis of the data presented in Table 3 indicates that the average upper layer DIP (P04'"P) concentration outside the Bosphorus-Black Sea opening section is 0.17 \lmol pn or 0.0053 mgn, whereas the lower layer of the Marmara Sea beyond the BMJ-Marmara Sea opening section is noted to have accumulated a much I!reater concentration of 1.04 umol pn or 0.0322 m~. The dailv discharl!e of
Pollution exchange between The Black Sea and The Marmara Sea
197
phosphorus from Istanbul wastewaters is 9.13 tons, corresponding to an average load of 3,333 tons per year. Consequently, the natural DIP input via the upper stream may be calculated as 3,178 tons/year, a level which is 95% of the anthropogenic phosphorus introduced to the system. As illustrated in Table 3, this is around 30% of the total P load entering The Bosphorus via The Black Sea. However the Marmara Sea appears to receive 9,259 tons/year or 2.78 times more than the total Istanbul phosphorus discharge, 6,287 tons/year being recirculated from the lower layer due to mixing in the transition zone. As the result of the complex interactions and mass transfer mechanism between the two layers, the Marmara Sea discharges 5,539 tons of P04-P per year to the Black Sea via the lower layer, 50% more than what it receives annually from the Istanbul Metropolitan Area.
...I
1 12511 147118
Ion~'
6287
Ion>/teat
-..y•. , _
38173
82711
..
1~-lOt\Ilfye-..;....,--_l..J-----.-.,;.....
- + - - -I t - - - 1 - - - · - 4 - - - - 1
-.1\''''
l
3171
..",..,..,
..",..,..,
IIOSPHQRUS
l
111710
1IlnUt-
J
_
THE M.tIRMARA SEA
-
138.'0'
WIa/yea' 1424.'0'
!~---~--_r---.!.!-------.,.-.tye.,.. 1)13.010·-......
c THE MAflIMAA SF'"
Figure 4. Exchange of pollutants between The Black Sea and The Marmara Sea.
D.ORHON
198
The general balance of nitrogen between The Marmara Sea and The Black Sea has quite a similar character. The NOx concentrations in The Black Sea upper layer and The Marmara Sea lower layer are 0.02 mg/l and 0.137 mg/l respectively exhibiting an almost 7-fold accumulation in the latter. The Black Sea input is 12,235 tons per year, amounting only to 62% of the anthropogenic nitrogen load, but it is increased to 38,173 tons per year at The Marmara Sea entrance incorporating 26,645 tons/year from the bottom layer in the transition zone. The mass balance is established with a net annual discharge of 24,545 tons of NO x from The Marmara Sea to The Black Sea, 25% more than the amount it receives from Istanbul sewage discharges. The NIP ratio in these discharges is assessed as 5.8. In the lower layer of The Marmara Sea beyond the transition zone, observations yield a lower value of 4.28 for the same ratio which is slightly increased to 4.43 when it is evaluated in terms of respective annual net discharges of the system to The Black Sea. The third parameter included in the monitoring and evaluation is the organic carbon which shows a picture totally opposite of what has been observed for nitrogen and phosphorus. In the lower layer of The Marmara Sea, the average TOC concentration is calculated as 0.62 mg/l, nearly 25% of 2.31 mg/l which is associated with the upper stream entering Bosphorus from The Black Sea. This stream introduces to the system an annual TOC load of 1.39 x 106 tons, 15.7 times the amount contained in the wastewater discharges in Istanbul. The latter is only 88.9 x 103 tons/year and calculated on the basis of a BODsfI'OC ratio of 1.375. Unlike the nitrogen and phosphorus balance, there is a net TOC input of 1.14 x 106 tons/year to The Marmara Sea, excluding the anthropogenic load totalling only 8% of this figure. The schematic evaluation of the nitrogen, phosphorus and TOC balances is illustrated in Fig. 4. CONCLUSIONS The Marmara Sea receives via the natural exchange from The Black Sea roughly 15 times more organic matter than what is contained in the sewage discharges from Istanbul; on the other hand, aside from coastal areas, the main pollution problem in The Marmara Sea is the nutrient accumulation which cannot be remedied, as it is illustrated in the paper, by conventional biological treatment Therefore, the magnitude of pollutant discharges from land-based sources and the pollution state of The Marmara Sea calls for effective nutrient control. The experimental evidence on the basis of extensive observations also indicates that the nutrient input from The Black Sea to The Marmara Sea is much more significant than coastal wastewater discharges. Therefore, nutrient removal from wastewater should not be regarded as the required corrective action without effective measures to reduce pollution in The Black Sea. REFERENCES Bacb, H. K., Orbon, D., Jensen, O. K. and Hansen, I. S. (1995). Environmenla1 model studies for !be Istanbul Master Plan Pan n: Water quality and eutropbication, War. Sci. Tech.. 32(2),149·158. Danisb Hydraulic Institute (1994). 3D Numerical Modelling of tbe Environmenla1 Conditions of tbe Seas Around Istanbul, Final Report. IMC Istanbul Masterplan Consortium (1995) Istanbul water supply and drainage, sewage lreabIlent and disposal master plan study, vol. 7, draft report. Orbon, D., Silzen, S. and Ubay, E. (1994a). Assessment of nitrification-<1enitrification potential of Istanbul domestic wastewaters, War. Sci. Tech.. 30(6), 21·30. Orbon, D., Uslu, 0., Meri~, S., Saliboglu, I. and Filibeli, A. (l994b) "Wastewater Management for Istanbul: Basis for TreabIlent and Disposal", Envirofl. Pollut., 84(1), 167·178. Polal, <;. S. and Tugru\, S., (1995). Nutrient and organic carbon exchanges between The Black and Marmara Seas through The Bosphorus sltail, Cont. ShelfRes., (in press).