Environ Monit Assess (2008) 146:423–432 DOI 10.1007/s10661-007-0088-2
Spatio-temporal variations of organic carbon and chlorophyll degradation products in the surficial sediments of Izmir Bay (Aegean Sea/Turkey) Ugur Sunlu & Mehmet Aksu & Baha Buyukisik & Fatma Sanem Sunlu
Received: 15 June 2007 / Accepted: 12 November 2007 / Published online: 28 December 2007 # Springer Science + Business Media B.V. 2007
Abstract The aim of this research is to determine the effects of Izmir Big Channel Waste Water Treatment Project on the sediment quality of Izmir Bay. Wastewater treatment improves the water quality. However, sediment does not respond to this treatment as fast as water column. Monitoring of bottom water and sediment quality is necessary for identification of the recovery of the whole ecosystem. For this purpose, bottom water and sediment samples were collected from three stations which are located in the middle and inner parts of the Izmir Bay on a monthly basis between January 2003 and December 2003. Values measured at stations ranged between; 0.54– 12.82 µg/L for chlorophyll-a, 0.09–9.32 µg/L for phaeopigment, 0.05–1.91 mg/L for particulate organic carbon in bottom waters, 11.88–100.29 µg/g for chlorophyll degradation products and 1.12–5.39% for organic carbon in sediment samples. In conclusion, it was found that grazing activity explained carbon variations in sediment at station 2, but at station 1 and station 3 carbon variations in sediment were not related to autochthonous biological processes.
U. Sunlu (*) : M. Aksu : B. Buyukisik : F. S. Sunlu Faculty of Fisheries, Department of Hydrobiology, Ege University, 35100 Bornova-İzmir, Turkey e-mail:
[email protected]
Keywords Bottom water quality . Chlorophyll degradation products . Izmir Bay . Organic carbon . Sediment quality
Introduction Economic and social consequences of damage to the marine environment are becoming increasingly evident. Unless seas and oceans are carefully protected, their economic potential can not be sustainable. The marine environment is one of humanity’s most precious assets. Oceans and seas cover 71% of the earth’s surface and are the greatest sources of biodiversity, containing 90% of the biosphere. Marine ecosystems play a key role in climate and weather patterns. They also contribute to economic prosperity, social well-being and quality of life and are literally a source of survival for coastal communities. However, this environment is under intense pressure. The pace of degradation of biodiversity and habitats; the level of contamination by dangerous substances and the emerging consequences of climate change are some of the most visible warning signals (Environment for Europeans 2005). Only recently marine eutrophication is being regarded as pollution, particularly in near shore environments where more often low water transparency,
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Fig. 1 The Map showing the sampling stations
oxygen depletion and algal blooms occur. Nutrient concentrations in sea water and sediment increase remarkably going from offshore to inshore, due to the proximity of terrestrial and domestic inputs and to the increase of biotic and abiotic processes strictly related to the progressive decrease of water depth. The Bay of Izmir is in a state of pollution centre in Turkish Aegean coast region in respect of aesthetic and welfare where pollution increased in the course of time from what it used to be in 1960s. The most important factors of this current status are; domestic wastes of more than 3 million people; industrial wastes from 1,500 factories; wastewater discharge during maritime transportation and shipyard services filling materials arisen from the recreation of seaside alluvions carried with rivers and valleys. Izmir Bay is surrounded by major agricultural plateau. Menemen plateau in the North–North West of Izmir is one of the most important production fields where agricultural irrigation is utilized. The Bay is also influenced by the pollution caused by the agricultural activities in the Gediz River water shed and erosion of a large area by Gediz River.
Because of limited water exchange with the Outer Bay and Aegean Sea, pollution of the Inner Bay had reached unacceptable levels. Eutrophication of the Inner and the Middle Bay had started and spread progressively to the outer part of the Bay. Red-tide occurrence was reported to have increase in frequency in last decade (Sunlu et al. 2007). For this reason Izmir Municipality decided to construct Izmir Big Channel Waste Water Project in 1969. However, wastewater treatment plant construction completed in 2002. At the end of the plant construction, the pollutant levels of the Inner Bay water decreased slowly and recovery period has begun (Kaymakci et al. 2000). This is why, the pollutant levels of the Inner Bay water decreased slowly. The aim of this research is to determine the effects of “Izmir Big Channel Wastewater Treatment Project” to the sediment quality depending on some bottom water parameters of Izmir Bay. For this purpose, bottom water and sediment samples were collected from three stations which are located in the middle and inner parts of the Izmir Bay. The samples were collected at monthly intervals during 2003.
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Materials and methods The Bay of Izmir is located in the Western part of Turkey and surrounded by a densely populated community. The Bay is divided into an Inner, Middle and Outer Bay from the standpoint of topographical and hydrographical characteristics. Inner Bay is small in area (57 km2) and shallow in depth (max. 15 m). It received the majority of domestic and industrial wastewaters. At present this part of the bay still receives some inflow of several creeks which are mostly have poor water quality. Three stations were chosen for sampling, two in the inner and one in the middle part of the Izmir Bay (Fig. 1). Station 1 is near to Izmir Harbour (Inner Bay) 38°27’17’’N–27°09’ 37’’E. Station 2 is offshore of the Karsiyaka Yacht Club (Middle Bay) 38° 26’86’’N–27°06’56’’E and station 3 is offshore of the Wastewater Treatment Plant (Cigli, Middle Bay) 38°25’47’’N–27°00’05’’E. The coordinates of the stations were measured by ICON Marine PlotterSounder Model FP561. Bottom waters and sediment samples were collected from these three stations on a monthly basis between January and 2003 December 2003. Water samples were collected by using Nansen Sampling Bottle. Sediment samples were collected using Van-Veen Grap. Chlorophyll-a, and phaeopigments were analyzed according to Strickland and Parsons 1972; Parsons et al. 1984. Particulate organic carbon (POC) analyses were carried out using wet oxidation method and spectrophotometry (Strickland and Parsons 1972; Parsons et al. 1984). Chlorophyll Degradation Products (CDP) were analyzed through acetone extraction and spectrophotometry (Lorenzen 1971). Organic
Fig. 2 Temporal changes in Chlorophyll a concentration in the bottom water at Station 1
Fig. 3 Temporal changes in Chlorophyll a concentration in the bottom water at Station 2
carbon values were determined according to Modified Wakley-Black Titration Method (Gaudette et al. 1974).
Results and discussion Chlorophyll-a Bottom water chlorophyll-a values at station 1 ranged from 1.26 to 12.82 µg/L and average value was 5 µg/L (Fig. 2). A steady decrease in chlorophyll-a levels was observed from May to August. This is due to overall decrease in terrestrial nutrient input and increased biological activity as a consequence of elevated water temperature. There was a steady decrease from October to December. The increase in chlorophyll-a values during September might be explained by nutrient input (with rain out-falls) and there was a steady decrease from October to December by decrease in biological activity as a result of lower water temperature and vertical mixing. This trend lasted during January and February. Maximum value measured at station 1 and 2 in March might be explained first of all by nutrient
Fig. 4 Temporal changes in Chlorophyll a concentration in the bottom water at Station 3
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(especially silicate) accumulation from terrestrial inputs, then diatom increase on February. In this period, Thalassiosira sp. increased from 0 to 20 mgC/m2 and Rhizoslenia setigera increased from 0 to 5 mgC/m2 (Sunlu et al. 2007). Decrease in other months was due to decreased nutrient levels and nutrient stratification, and the reason for that no complete exhaustion occurred is input from the sediment. It was found that chlorophyll level was minimum in April due to decreased nutrients. When chlorophyll-a values reached highest concentrations on March, POC values were also high. While minimum chlorophyll-a concentration recorded on April sampling, minimum POC value was measured this month (Fig. 5). Chlorophyll-a level measured at station 2 was lower compared with those measured at station 1. The highest level was in March (8.38 µg/L) and the lowest one in December (1.85 µg/L). Annual mean value of chlorophyll-a was 4.29 µg/L (Fig. 3). Trend of change in chlorophyll-a level was similar to that at station 1 whereas the minimal level was measured in December, the coldest month of entire year. Chlorophyll-a concentrations ranged from 0.54 to 4.44 µg/L. Average value was 1.96 µg/L (Fig. 4). Increase in spring season was observed in May in this station. This difference was due to longer inoculation times (>10 days) into Cigli Region of phytoplankton species grown in 1 and 2 stations because of circulation of water entering the Bay from Yenikale passage in counter clockwise direction from south and growth of algae. Additionally, growth of algae and precipitation of nutrients in Melez and Cigli and transfer of them into the sediment reduces export production in Cigli station. Although dispersion of effluent from wastewater treatment plant depends on wind systems, the
Fig. 5 Temporal changes in POC concentration in the bottom water at Station 1
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Fig. 6 Temporal changes in POC concentration in the bottom water at Station 2
hypothesis that wastewater from treatment plant moving in counter clockwise direction would be toward outer bay and wouldn’t have overall influence on Cigli station. Lower chlorophyll-a levels at Cigli station than other stations supports this hypothesis. Similarity to other station from the beginning of summer might be attributed to nutrient regeneration (nutrients become homogenous in water column due to strong winds and mixing). POC POC values at station 1 were lower than 0.5 mg/L whereas these values increased to more than 1 mg/L in March. Subsequently, POC values reach to the lowest levels in April (0.21 mg/L). A similar trend was observed in chlorophyll-a content in bottom water. Annual mean value was found 0.75 mg/L (Fig. 5). An increase in POC parallel to Chlorophyll-a increase was observed from May. Whereas a steady increase was seen in POC concentrations during summer season, a steady decrease in Chlorophyll-a levels was remarkable. A decrease was seen in POC levels from autumn and the levels exhibited small fluctuations of around 0.5 mg/L.
Fig. 7 Temporal changes in POC concentration in the bottom water at Station 3
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Fig. 8 Temporal changes in phaeopigment concentration in the bottom water at Station 1
Maximum level measured in entire year was 1.91 mg/L and this was found in August. Chlorophyll-a level in the same period was 2 μg/L. This corresponded to very high POC/Chlorophyll-a ratios, indicating that heterotrophic activity was higher and autotrophic activity was lower (Eppley 1972). Minimum POC level measured at station 1 was 0.2 mg/L in April. Similar trends in chlorophyll-a and POC in winter and spring seasons demonstrate that the efficacy of autotrophic activity in bottom water. POC concentration of bottom water from station 2 decreased during winter season and reached to lowest value in February (0.13 mg/L). With phytoplankton growth at the beginning of spring, increase in POC concentration and relatively lower values until summer were observed. Increase in chlorophyll-a values in May didn’t reflect in POC values in bottom water. Increase in POC values was remarkable during summer and reached to a maximal level of 1.23 mg/ L. Average concentration was 0.61 mg/L (Fig. 6). POC concentrations were relatively lower during autumn and variations in these concentrations were lower at station 2. The trend exhibited by POC during entire year was similar to that at station 1 (Fig. 5).
Fig. 9 Temporal changes in phaeopigment concentration in the bottom water at Station 2
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POC variations in winter and at the beginning of autumn at station 3 didn’t vary remarkable by months. In contrast to other two stations, a significant increase was observed in April in this station. Subsequently, values decreased to 0.05 mg/L in May and then reached to 0.95 mg/L in August. Average POC value was 0.41 mg/L (Fig. 7). POC concentrations falling in autumn season showed a minor increase with small fluctuations. Trend in this station during winter and spring was consistent with those in other two stations albeit being 1 month later than them. It shows similarity with other two stations in summer and autumn. The fact that POC concentration reduced significantly compared to other two stations suggests that POC and chlorophyll-a content of bottom water is transported from station 1 to outer part of the bay in winter and spring seasons. Phaeopigment At station 1, concentrations decreasing from the winter months reached to a minimal level of 0.09 μg/L in February. Values increasing at the beginning of spring decreased in April but reached to 5.00 μg/L until the beginning of summer. A decrease was observed during summer and maximal level was measured in autumn (5.81 μg/L). Average concentration was 2.81 µg/L (Fig. 8). For the other periods of year, a trend of decreasing was observed in this station. Minimal value observed in February was consistent with values of POC and chlorophyll-a. Maximal value observed in September was not consistent with chlorophyll-a and was presumably originated from rapidly precipitating particle material in the form of fecal pellets due to grazing occurring in surface water.
Fig. 10 Temporal changes in phaeopigment concentration in the bottom water at Station 3
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Fig. 13 Temporal changes in organic carbon concentration in the surface sediment at Station 3 Fig. 11 Temporal changes in organic carbon concentration in the surface sediment at Station 1
Annual trend of change of phaeopigment in the second station was similar to that at station 1. For these two stations, the minimal and maximal values were found in the same sampling months. Minimum phaeopigment concentration at station 2 was 0.26 μg/L. Maximum and average values were 9.32 and 3.81 µg/L respectively (Fig. 9). Phaeopigment values at station 3 ranged from 0.21 to 4.31 µg/L. Annual mean was 1.74 µg/L. A delay of 1 month was remarkable in overall trend of change in this station until July (Fig. 10). One to one similarity was seen with changes in other two stations after midsummer until the end of the year. Organic carbon in sediment Organic carbon values at station 1 ranged from 2.63 to 3.39%. Average concentration was 3.03% (Fig. 11). Minimum, maximum and average organic carbon values at station 2 were 1.73, 5.39 and 4.33% respectively (Fig. 12).
Fig. 12 Temporal changes in organic carbon concentration in the surface sediment at Station 2
Organic carbon values at station 3 ranged from 1.12 to 2.41%. Average concentration was 1.58% (Fig. 13). Chlorophyll degradation products in sediment (CDP) Chlorophyll degradation products in sediment at station 1 ranged from 50.79 to 90.66 µg/g and average value was found 62.62 µg/g (Fig. 14). At station 2 average CDP value was 81.39 µg/g. Minimum and maximum values were measured as 41.58–100.29 µg/g respectively (Fig. 15). CDP concentrations at station 3 ranged from 11.88 to 52.12 µg/g. Annual mean was 34.44 µg/g (Fig. 16). When each three region was discussed separately, at the Station 2, algal sedimentation and/or mesozooplankton grazing explain variations of carbon in the sediment samples (r=0.7879 p=0.0023) (Fig. 17). When Csed/CDP plots are discussed for each region, variations of CDP in sediment seems independent from carbon in sediment variations for station 1 and station 3 in sequence (r=0.339, r=0.206). For the first station this situation can be explained by carbon
Fig. 14 Temporal changes in CDP concentration in the surface sediment at Station 1
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Fig. 15 Temporal changes in CDP concentration in the surface sediment at Station 2
inputs from outer sources that mask carbon contribution of algal biomass to sediment. Melez, Manda and Arap Rivers discharge their waters rich in organic mater around station 1 (Turkman 1981). At station 3, during the year CDP concentrations were at the lowest value and it can be explained by background carbon levels that mask carbon variations which is caused by algae (< %2). Besides, the output of the wastewater treatment plant is close to the station 3 and it constitutes crucial silicate source. Diatoms consist of skeleton with silica are known as having five times lower carbon content than Dinoflagellates (Hitchcock 1982 in Smayda 1997). That situation can explain that during the year phytoplankton community has lower carbon content. Even if export production to sediment increases relatively low productivity and low carbon content in water column can cause a similar situation in diatom dominated marine environments. Carbon contents resistant to biologic degradation is 1.16% (refractory carbon). That is understood by linear regression intercept (Fig. 17). By using overall data in Inner and Middle Izmir Bay, chlorophyll degradation products in sediment versus carbon values were plotted (Fig. 18). A good linear relationship between CDP and carbon was obtained (r2 =0.771, p=0.000). A general equation was found for predicting the Izmir Inner Bay’s CDP and organic carbon values in sediment. It was found that there are no significant differences in sediment carbon values depending on time but spatial variations related to sampling stations are more evident (Fig. 18). When spatial scale is widened, CDP variations explained 77% of carbon variations in the sediment for overall data. Approximately 23% of these variations were originated from allocthonous sources.
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At station 3, it is possible that grazing on diatoms and/or mixotrophy in dinoflagellates are dominant on certain months of the year. Consequently, it is not possible to explain variations of the carbon in sediment with the pigment contents of sediment. Station 2 has highest carbon and CDP values and also has a relationship between CDP and organic carbon content. This situation can be explained by the fact that station 2 is relatively away from external sources and has high biological activity (Sunlu et al. 2007). At station 1, however, relation is weak despite higher carbon and CDP values than at station 3. Contribution of external carbon sources as rivers may play important role on this weak correlation.
Conclusions General sediment texture of Izmir Bay was studied by Duman et al. (2004). Average sediment particle size was reported to be 4–8 ф and sediment texture to be sandy-silt. In Izmir Bay sorting coefficient indicates very poorly sorted deposits (SD=2–3). Prevailing wind direction in inner part of Izmir Bay was noted as Western and it has been reported that deep flow was toward to East and surface flow toward to West. Most of organic material remains in the silt near the pollution source and the correlation between grain size fractions and organic carbon was found to be highest in silt (Duman et al. 2004). One sediment component, vermiculite was found in the inner part of Izmir Bay at a rate of 3–11% and its main source was from Melez River (near station 1). Caolinit was found at a rate of 8–12% with neogen sediments coming from the rocks around the Bay (Aksu et al. 1998).
Fig. 16 Temporal changes in CDP concentration in the surface sediment at Station 3
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Fig. 17 Relationship between CDP and carbon concentrations of surficial sediment samples at station 2
Percentage of organic carbon was reported to be between 0.40 and 5.39 by Duman et al., from Izmir Bay (Duman et al. 2004). Range for these values was found to be between 1.12 and 5.39% in our study. These values were higher than previous report (Duman et al. 2004). The reason for this was that 2–
Fig. 18 Relationship between sediment CDP concentrations and sediment carbon concentrations in three stations
10 years elapsed between the two studies and the treatment facility begun to work in full capacity in 2002. On the other hand; carbon contents in the sediment samples of our study are considerably lower compared with the values obtained in a large scale
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Table 1 Previous carbon contents in the sediments samples from the different regions of Aegean Sea References
Locality
Carbon in Sediment (%)
Yaramaz et al. 1992 Yaramaz et al. 1991 Anonymous 1992 Anonymous 1997 Egemen et al. 1999 Atılgan 1997 Sunlu et al. 1999 Varnavas and Ferentionos 1982 Scoullos and Dassenakis 1982 Angelidis et al. 1980 Aydın and Sunlu 2005 Sunlu et al. 2005 In this study
Middle part of Izmar Bay Inner part of Izmir Bay Izmir Bay Izmir Bay Gulluk Bay (Southern Aegean Sea) Gulluk Bay (Southern Aegean Sea) Urla (Middle Part of Izmir Bay) Pariakos Bay (Greece) Evoikos Bay (Greece) Evoikos Bay (Greece) Southern Turkish Agean Sea Northern Turkish Agean Sea Inner and Middle parts Izmir
0.87–1.60 0.57–3.42 11.4 2.0–7.0 0.1–4.5 1.07–2.13 1.25–2.1 0.15–11.01 1.2 0.66–2.4 1.3–13.1 0.35–15.63 1.12–5.39
previous research carried out by different regions around Aegean Sea (Table 1). It can be said that high carbon levels observed in inner part of Izmir Bay were from raw sewage and industrial outfalls carried by Melez River at station 1. But at station 2 and 3 high carbon levels were due to organic material formed by secondary pollution. The biggest contribution to the sediment is provided by export production which was especially effective at station 2. A general equation was found for predicting the Izmir Inner Bay’s CDP and organic carbon values in sediment. There are no significant differences in sediment carbon values depending on time but spatial variations (related to sampling stations) are more evident (Fig. 18). In conclusion, it was found that carbon variations in sediment at station 2 (Karşıyaka, Offshore of the Yatch Club) can be explained by grazing activity, but at station 1 (Melez, Izmir Harbour) and station 3 (Cigli, Offshore of the Wastewater Treatment Plant) carbon variations in sediment could be related not only with autochthonous biological processes but also with physical processes (e.g. sweeping out of plant material by advection from the Bay). Especially wastewater treatment improves the water quality, but sediment does not respond to this treatment as fast as water column. Improvement in the quality of bottom water and sediment is the evidence of the recovery of the whole ecosystem of the Izmir Bay.
Acknowledgments The authors would like to thank TUBITAK (Turkish Scientific and Technical Research Council), Izmir Municipality Gulf Control Staff and Science and Technology Research Centre of Ege University (EBILTEM) for their efforts to join of this project and their scientific and financial supports.
Nomenclature
Symbol Meaning Chlw POC CDP Csed
Bottom water chlorophyll-a Bottom water particulate organic carbon Bottom water phaeopigment Chlorophyll degradation products in sediment Organic carbon concentration in sediment Sediment particle size
Unit µg/L mg/L µg/L µg/g % Ф
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