Environ Earth Sci DOI 10.1007/s12665-012-2152-7
ORIGINAL ARTICLE
Assessment of pressures and impacts on surface water bodies of the Mediterranean. Case study: Pamvotis Lake, Greece D. Alexakis • I. Kagalou • G. Tsakiris
Received: 8 July 2012 / Accepted: 26 November 2012 Ó Springer-Verlag Berlin Heidelberg 2012
Abstract The aim of the study presented in this article is to assess the ecological status of a surface water body in the Mediterranean using the methodological approach of Driver-Pressure-State-Impact-Response. Based on this approach for the case study analyzed (Pamvotis Lake, Greece), it is concluded that the main drivers, which lead to pressures in the study area are: intensive agricultural activities, alteration of hydrological regime, contamination from point sources and changes in the land-use and fish stocking. The ecological status is assessed by analysing data series of physical, chemical and biological elements that are available from early ’80s. Findings suggest elevated nutrient concentrations sufficient for maintaining eutrophic conditions while their seasonal variability is mostly driven by factors as water level fluctuation, catchment runoff and in-lake biological processes. Subsequently, concerning biotic factors, the poor biodiversity mainly represented by the dominance of the most tolerant species, confirm the previous profile. Since, reference conditions have only recently been established in Greece, the ECOFRAME scheme and the guidelines proposed by D. Alexakis (&) G. Tsakiris Centre for the Assessment of Natural Hazards and Proactive Planning, Laboratory of Reclamation Works and Water Resources Management, School of Rural and Surveying Engineering, National Technical University of Athens, 9 Iroon Polytechniou Street, 15773 Athens, Greece e-mail:
[email protected] G. Tsakiris e-mail:
[email protected] I. Kagalou Department of Ichthyology and Aquatic Environment, School of Agricultural Sciences, University of Thessaly, Fytoko str., GR 38445 Volos, Greece e-mail:
[email protected]
the ‘‘Intercalibration Group for Mediterranean Lakes’’ were applied. In terms of the above elements; the water quality status could be characterized as ‘‘High’’, ‘‘High to Good’’ and ‘‘High to Bad’’, respectively, whereas the overall ecological status tends to shift in poor conditions. Finally, the major response actions needed should be in the direction of reduced application of fertilizers and chemicals in the cultivated land of the catchment, removal of the pointcontamination sources from the catchment, appropriate land-use management and biomanipulation. Keywords DPSIR approach Chemical status Ecological status ECOFRAME Pamvotis Lake
Introduction It is well documented that conservation and management of freshwater resources are directly related to the sustainable living, i.e. to socio-economic and environmental aspects. A better understanding of the processes that influence public perception can contribute to improvements in water management (Korsgaard and Schou 2010; Moss et al. 2003). Moreover, increased mean water temperatures and changes in extremes due to the anticipated climate change will affect water quality and exacerbate many forms of water contamination with possible negative effects on ecosystems (Quevauviller 2011a, b). The state and evolution of freshwater ecosystems are affected by a variety of biotic and abiotic factors, as well as by natural and human-induced processes that may differ both in duration and intensity. Lake ecosystems tend to maintain a state of equilibrium but their chemical resilience depends on certain site-specific factors and processes (Carpenter et al. 1999).
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The characterization of the ecological status of lakes has become a legal imperative after the endorsement of the Water Framework Directive (WFD) by the European member states (EC 2000). The aim of the WFD is to ensure sustainable management of groundwater, freshwater and marine water in the European Union, such that a minimum ‘‘good ecological status’’ will be obtained by 2015. WFD also establishes an integrated and coordinated framework for the sustainable management of water. Its purposes include preventing deterioration of the quality of water bodies, promoting sustainable water use, and ensuring enhanced protection and improvement of the aquatic environment. Currently, many surface freshwater bodies are suffering intense environmental degradation all over the world while it is claimed that many lakes in the EU territory will face difficulties in meeting the WFD criteria by 2015 if restoration and management approach does not take place (Egemose et al. 2010). The Mediterranean region encompasses the very critical water resource problems. Water resources are threatened by contamination of excess nutrients and leaching of pesticides, which cause adverse environmental degradation and eutrophication phenomena in fresh water ecosystems, as well as by seawater intrusion in aquifer systems causing degradation of the water quality of the springs and groundwater (Ahmed et al. 2012; Alexakis and Tsakiris 2010; Cruz et al. 2010; Elewa et al. 2012; Gamvroula et al. 2012; Kharroubi et al. 2012; Loukas et al. 2007; Stamatis et al. 2011; Tsakiris et al. 2009). Alvarez-Cobelas et al. (2005) and Beklioglu et al. (2007) gave an overview of the contrast between the Mediterranean and other temperate limnosystems, taking into account climatic variability and pinpointing the distinctiveness of the Mediterranean climate (Cherbi et al. 2008; Ozen et al. 2010; Quintana et al. 1998). Furthermore, many researches in major and trace elements show water quality deterioration in many lakes worldwide due to various natural and anthropogenic sources (Prasanna et al. 2012; Najar and Khan 2012). The European Water Policy and, in particular the WFD introduced the necessity to evaluate new methodological approaches for the development of strategies contributing to the sustainable water resources management. The Driver-Pressure-State-Impact-Response (DPSIR) approach was established as a possible analytical framework for determining pressures and impacts under the WFD (Borja et al. 2006; Kagalou et al. 2012). According to the DPSIR, there is a chain of causal links starting with ‘‘drivers’’ (causes) through ‘‘pressures’’ (e.g. pollutants) to ‘‘states’’ (physical, chemical, biological) and ‘‘impacts’’ on ecosystems (structure and function) and eventually leading to ‘‘responses’’ (policy) (EC 2003; Kagalou et al. 2012; Benedini and Tsakiris 2013; Tsakiris and Alexakis 2012). This methodological framework that deals with
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environmental problems was originally developed as a Stress–Response model and then was adopted by the Organization for Economic and Cooperation Development (OECD) as Pressures-State-Response (PSR) (OECD 1993). The final DPSIR framework has been adopted by the European Environmental Agency acting as a helpful instrument for the sustainable management through the presentation of indicators offering also the feedback needed by policy makers on environmental issues (EEA 1999). The surface water body under study has a long eutrophication history due to various anthropogenic pressures (Kagalou et al. 2008a). Although some traditional restoration efforts have been made such as the elimination of external nutrients loading, the lake remains a degraded ecosystem whereas at the same time several activities (irrigation, fisheries, tourism, recreation) are still taking place (Kagalou and Leonardos 2009). Whether the present activities associated with Pamvotis Lake will sustain or constrain a recovery process, is a matter which is open to discussion. The objective of this article is the application of the DPSIR scheme to a surface freshwater body under the framework of WFD: analyzing concurrently each of its components and thus offering the baseline for the abovementioned discussion. To illustrate the methodology, the case of Pamvotis Lake is studied in detail. Therefore, environmental pressures and long-term water quality data based on past monitoring efforts were addressed, and the impacts along with the policy responses were discussed.
Materials and methods The study area and data collection Pamvotis Lake is situated in NW Greece (Fig. 1). The lake occupies an area of about 22.8 km2 and is located in the broader are of the city of Ioannina (150,000 inhabitants), where about 40 % of the catchment area is used for agriculture. It is a shallow Mediterranean lake with mean depth of about 4.3 m and maximum depth of 7.5 m. The catchment has no natural surface outflows and is recharged by karstic springs. Drainage from the catchment occurs through a system of sinkholes that drain it to the rivers Arachthos, Louros and Kalamas. Under the view of Habitats Directive 92/43EEC (EC 1992) on the conservation of natural habitats and of wild fauna and flora, Pamvotis Lake is listed in the network of Natura 2000 Special Conservation areas, while the characterization of the ecological status of lakes has become a legal imperative after the approval of the WFD (EC 2000). The lake has a long eutrophication history due to the heavy point and non-point loading of nutrients, with cyanophyte blooms occurring
Environ Earth Sci
Fig. 1 Locality map of the studied surface water body showing the site of the monitoring station
since 1978 (Kagalou et al. 2008a) Traditional restoration methods, as the reduction of external P-loading, resulted in a major decline in lake nutrients concentrations, but it is still high enough to maintain eutrophic conditions (Kagalou et al. 2008a). A database was developed using all the available information, through data collection derived from relevant
databases and literature sources (Ganiatsas 1970; Anagnostidis and Economou 1989; Economidis 1989; YPECHODE 1998; Sarika-Hatzinikolaou 1999; Arapis Th and Pappas 2004; Stefanidis 2005; Kagalou et al. 2006; Stefanidis and Papastergiadou 2007; Kagalou and Leonardos 2009; HMRDF 2010; Alexakis et al. 2011). Data deal with abiotic and biotic variables of the lake have
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Environ Earth Sci Table 1 Minimum and maximum of yearly mean values of the studied water quality parameters (data was provided by HMRDF 2010)
Minimum
T (oC)
pH
Conductivity (ls cm-1)
DO (mg L-1)
TN (mg L-1)
8.33
7.04
283
5.08
0.13
29
380
9.65
0.79
389
18
17
Maximum
20.89
8.55
Number of yearly mean values
22
25
26
TP (lg L-1)
17
been examined in terms of homogeneity (i.e. methodological approach, sampling strategies) to ensure comparability. Systematically collected data series of physico-chemical parameters are available for the period 1980–2009 with monthly time-step. Chemical and physical parameters, as nutrients (nitrogen compounds-TN and total phosphorousTP), dissolved oxygen (DO), pH, Conductivity (CND); were included in the database reflecting the water chemistry of the lake (Table 1; Fig. 2). Obviously several gaps in the
data series of the chemical and physical parameters were observed. The only available monitoring station is located in the centre of the Pamvotis Lake (Fig. 1). Previous studies (Kagalou et al. 2008a; Kagalou and Leonardos 2009) revealed that Pamvotis Lake is a polymictic lake, because of its shallowness without significant differences in the spatial distribution of abiotic parameters. During the last decades, most ecological water quality assessment techniques have been using biological indicators, which are based on species known to exist in a specific ecosystem and therefore reflect its water quality, or use species diversity to estimate changes in the environmental integrity of an ecosystem (Metcalfe 1989). Sampling and identification of species-indicators that belong to different biotic groups (algae, macrophytes, invertebrates in inland water and fish) provide the means to evaluate the long-term quality changes of the water and the ecosystem (Guinda et al. 2008). In Greece, the lack of environmental data and the limited monitoring efforts, particularly concerning the biological elements suggested by the WFD, pose significant difficulties to characterize ecological conditions of water bodies (Kagalou 2010).
Fig. 2 Time series of selected water quality parameters (temperature, pH, CND, DO, TN and TP) of the Pamvotis Lake water during the monitoring period 1981–2009 (data was provided by HMRDF 2010)
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Thus, the selection of ecological indicators for the classification of the lake was based on: (a) WFD requirements; (b) their relation to the eutrophication process; and (c) data availability. Despite of the fact that quantitative and qualitative phytoplankton data was only available for the period 1998–1999, more recent data concerning cyanophytes, a quite important phytoplankton group in terms of both WFD implementation and eutrophication, was also available for the year 2005 (Kagalou et al. 2008b). Water Framework Directive suggests also the monitoring of benthic macroinvertebrates, macrophytes and fish community in order to assess the ecological status. The DPSIR approach The links within the DPSIR chain are described by indicators, which have two main functions: (1) reducing the number of parameters and (2) simplifying the communication process by which information and results are provided to the user (La Jeunesse et al. 2003). Thus, the application of the DPSIR model requires an appropriate list of indicators specification in order to describe the complex ecological and socio-economic processes in the studied area. Reviewing the literature, a number of several indicators are available representing the anthropogenic stressors and the quality of lake ecosystems. As a first step, a list of appropriate indicators was selected, mainly focused on water quality, in order to fulfill each category of the DPSIR model have been taken into consideration. The environmental conditions throughout the whole catchment area and also the ecological linkages between environmental factors and biota.
Results and discussion Characterization of a surface water body According to the WFD, the water quality and furthermore the ecological status of a lake should be defined relative to its deviation from the reference conditions, which should be varied for different lake types (i.e. shallow, deep, cold, warm, small, large, high and low altitude lakes). In Greece, the typological characteristics and the reference conditions have been recently established (Moustaka and Katsiapi 2010). In this article, the classification of the Pamvotis Lake, the typology criteria given by the WFD, as well as the ECOFRAME system (Moss et al. 2003) were applied taking into consideration the relative literature (Kagalou et al. 2008a, b; Romero et al. 2002) (Table 2). According to the ECOFRAME system, Pamvotis Lake was classified as ‘‘warm’’ lake since the ice cover period is less than 2 months per year and the mean temperature of the warmest month is more than 25 °C (Kagalou et al. 2006; Stefanidis 2005; HMRDF 2010). The typology scheme was based on the typology criteria according the Annex II of the WFD including size, altitude, geology, and depth (System A) as well as according to the selected criteria of System B and the other additional criteria (EC 2000). Annex II of the WFD suggests two choices to define lake typology. The first choice is System A, based upon ecoregions (Annex XI) and the obligatory factors such as geology, size, altitude, depth. System B is the second choice, which includes also a wide range of optional factors (Annex II) (EC 2000).
Table 2 Classification of Pamvotis Lake based on the WFD, ECOFRAME scheme and relative literature Ecoregion
According to Annex XI of the WFD, Pamvotis Lake belongs to the ‘‘Hellenic Western Balkan’’ ecoregion
Altitude
According to System A of Annex II of the WFD, three altitude classes are indicated: lowland (\200 m a.s.l), midaltitude (200–800 m a.s.l) and high-altitude ([800 m a.s.l). Pamvotis Lake is classified as mid-altitude category since it is situated at 470.25 m a.s.l.
Maximum and mean depth
System A of Annex II of the WFD, suggests three mean depth classes as follows: very shallow (\3 m), shallow (3–15 m) and deep lakes ([15 m). Pamvotis Lake has a max depth (Zmax) of 8.0 m and a mean depth (Zmean) of 4.3 falling to the shallow lakes category; while the ratio of Zmean/Zmax is equal to 0.56
Surface area-size
The lake occupies an area of 22.8 km2 and it belongs to the ‘‘large class size’’ according the Annex II while the catchment area is about 330 km2
Geology
The catchment area of Pamvotis Lake displays extensive limestone erosion resulting in the calcareous origin of the lake. Moreover, according to Romero et al. (2002) the sediments of Pamvotis Lake include mud, sand, gravels, clays and sandy materials. According to System A of Annex II of the WFD, three types of geology are indicated (calcareous, siliceous and organic), the Pamvotis Lake falls into calcareous category
Mixing regime
Pamvotis Lake is a polymictic lake appearing a slight thermal stratification during a brief period in mid-summer (Kagalou et al. 2008a)
Structure of lake shore
Across the southern part of the lake (i.e. the urban part), there is no natural lake shore. Roads, settlements and touristic infrastructures have destroyed the natural lake shore. The rest of the shoreline, affected by depositional materials, is characterized by the disappearance of wet meadows and the extension of reed beds
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Taking into consideration, the typological characteristics which are presented in Table 2, as well as the Lake Mediterranean GIG Intercalibration Report, Pamvotis Lake is classified as a Mediterranean lake, of Type B which includes natural large, shallow lakes of mid altitude, with polymictic regime and human controlled outlet (Moustaka and Katsiapi 2010). Identification and estimation of drivers and pressures Agriculture, livestock and domestic sewage Agriculture in the catchment area is dominated by vegetable crops, fruit trees and vineyards. Farming practices are highly intensive with wide spread use of fertilizers and pesticides. In Table 3, the quantities of several fertilizer types and pesticides per cultivated species applied in the area are presented (Arapis Th and Pappas 2004). Nutrients (nitrogen and phosphorus) release is associated with the farming practices and they are among the major pressures exerting from this sector. It has been estimated that the nitrogen and phosphorous loads because of the agricultural activities are 0.6 and 0.21 kg/ha/year correspondingly (YPEKA 2012). Livestock activity is carried out intensively in the entire area and represents the most important sector in the local economy. It is mainly based in sheep/ goats farming while poultry farms are also a very important sector of activities in the area accounting for the 18.3 % of the national poultry production. Specifically in the catchment area of Pamvotis Lake the pig farming is also common (1,018 tons/year); while the annual production of honey is about 40 tons/year. The main pollutants related to the animal breeding are organic load, nitrogen and phosphorus. According to the data extracted from the Ministry of Environment, the exerted pressures from the livestock are presented in Table 4 (YPEKA 2012). A wastewater treatment plant (WWTP) with a secondary treatment stage, which was set in full operation during the year 1994, is diverting the treated wastewater of the city of Ioannina to Pamvotis Lake; while during the last 5 years a tertiary treatment stage has been set up. The treated effluents are discharged directly to the Kalamas river—by flowing through Pamvotis Lake—unless a part of them which is attributed to the incomplete wastewater network is Table 3 Quantities of various types of fertilizers and pesticides used in the contributing area of Pamvotis Lake
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Table 4 Factors concerning production rates for animal farming waste (kg/tn of animal weight/d) Farm animal
Organic load kg/ha/year
TN kg/ha/year
TP kg/ha/year
Sheep/goats
6
3.8
0.2
Poultry
19
4.0
0.3
Cattle Pigs
3 1.5
1.0 0.2
0.05 0.05
discharged directly into the lake It is estimated that the diffuse pollution load originated from the urban and semi urban settlements corresponds to BOD5: 6,6510 kg/year TN: 19,003 kg/year, TP: 790 kg/year (YPEKA 2012). Irrigation Irrigation is intensively practiced in the Pamvotis catchment, covering the 70 % of the total requirements for irrigation use. The total irrigated area is about 2,850 ha (average value corresponding to the last 10 years), while the average annual water volume for irrigation purposes is about 12 9 106 m3 (Romero et al. 2002). This results in high intra-annual water level fluctuations influencing also the concentration of nutrients. Irrigation networks are also quite old whereas the pricing policy, set by the official local organization of reclamation (GOEV), underestimates the economic cost of the water potential. Land-use changes and urbanization A significant part of the lake shoreline, across the lake perimeter, has been used mainly for urban development of the city of Ioannina. The problem in fact continues even today and this particular area is still under development to accommodate recreational (e.g. new hotels, fun parks, entertainment infrastructure, etc.) and minor agricultural activities. The alteration of land use of the area during the period 1945–1970 is significant, since the extent of many wetland habitats has been decreased by 57.8 %, particularly of the littoral zone of the lake. Additionally, from 1970 till today, the urban areas increased by 216.4 % with the consequent construction of roads that resulted in diminishing the area occupied by the riparian zone (scrubs 38.7 %), and
Fertilizers kg ha-1 yr-1
Insecticides
Corn
500
5–10 kg
Tobacco
800–1000
100–150 kg
Vegetables
2000
0.3–0.5 L
0.3 L
200–300
116.8
Vineyards
500
0.5 L
1L
250–300
118.5
Grain
500
–
0.1 L
–
150
Crop
Acaricides
Fungicides (g)
Mixed (type11-15-15)
600 g
–
441.2
–
200–250
-
Environ Earth Sci
the reeds expanded (17.2 %) mainly as a result of the increased nutrients inflow to the lake and water level decline (Papastergiadou et al. 2010). Moreover, ephemeral wetlands drainage, which was caused by both land-use change and alterations in the hydrological regime had also negative effects on wetlands biota of Pamvotis Lake. Construction of dikes and spring diversion A major perturbation to Pamvotis Lake occurred in 1974 with the construction of dikes in the N-NW part of the lake. Two primary effects resulted from the construction of the dikes: (a) the dikes caused an alteration in the hydraulic connection between the karst aquifer of the adjacent mountain (Mitsikeli) and the lake; and (b) after the construction of the dikes the springs, previously inflowing into the lake, have since given quite low discharge acting rather as sink holes. Then, the springs discharged directly into the outflow channel rather than replenishing the lake from its northern part. Tourism and recreation Tourism and recreation in the broader area is continuously increasing, illustrating a promising development trend. Although touristic activity focused on the lake and on the small historic islet in the lake, it is now mostly characterized by the absence of planning, arbitrary buildings and roads construction without prior impact assessment of potential threats especially in protected habitats along the lake shoreline.
planktivorous species (Hypophthalmichthus molitrix, Aristichthys nobilis) in order to control the excessive vegetation and to support fishery (personal communication, data deriving from Greek Ministry of Agriculture, Prefecture of Ioannina, Dept. of Fisheries and Aquaculture). Common carp species (Cyprinus carpio) are systematically introduced annually at annual basis. Both the common carp and the introduced Asian carps, which were very abundant in the ’90s, are known to destroy the submerged aquatic vegetation directly by damaging macrophyte beds thus limiting the nursery habitats. Moreover, high abundances of these species diminish light availability by re-suspending the sediment and increase nutrient loading. Specifically during the period 1986–2005, 9.3 9 106 larvae of common carp and 4 9 106 larvae of Asian carps were introduced into the lake. The fish community of the lake is currently dominated by planktivorous (Rutilus ylikiensis) and some benthivorous species (Leonardos et al. 2008). Based on the above information, the Table 5 was composed presenting the dataset of DPSIR indicators. As can be seen from Table 5, agriculture, livestock and domestic sewage are the most significant drivers for exert pressures to the lake. Quite significant are also irrigation and landuse changes and urbanization. Assessment of the state and impacts analysis The different pressures on ecosystems caused by both human intervention and physical factors rarely act separately. Moreover ecosystems, respond to a ‘‘contextdependent’’ way to anthropogenic stressors, rendering it difficult to predict accurately the effect of a given pressure.
Demand for protection of the ecosystem Physico-chemical criteria Hydromorphological alterations as the constructed outlet (Lapsista channel), roads and the embankments along the lake perimeter caused a fragmentation in the ecosystem of the lake, thus reducing its catchment scale connectivity and creating also barriers for living organism’s dispersion and migration. Water level fluctuations can seriously affect habitats and thus community structure. It is also anticipated that the climate change will create new pressures to the lake ecosystem. Additionally the expansion of cultivations and urban areas have eliminated the wetland habitats (e.g. wet meadows, fens, pastures) mainly in the northern and southern parts of the lake and also decreased the riparian zone, with negative effects to the entire ecosystem and especially to avifauna. Fish stocking Since 1986, the lake has been stocked with the exotic herbivorous Asian species (Ctenopharygodon idella) and
Two classification schemes proposed for the evaluation of Mediterranean lakes have been used in combination with the Pamvotis Lake water quality data, namely the Mediterranean GIG (Poikane 2009) and ECOFRAME (Moss et al. 2003). The worst-case scenario has been selected for the assessment of the chemical status. The Pamvotis Lake water dataset was categorized into two sub-datasets: (a) wet period and (d) dry period. Based on the Mediterranean climate type, the hydrological year consists of a wet and a dry period; the wet period lasts from October to March and the dry period from April to September. For each period, the mean values were calculated from monthly observations (Fig. 2). In the case of temperature mean values, the highest water mean temperature (24.6 °C) was observed during the dry period of 1994; while the lowest water mean temperature (8.1 °C) was recorded during the wet period of 1993 (Fig. 2). The pH mean values vary between 6.83 (during dry period of 1987
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Environ Earth Sci Table 5 Dataset of DPSIR indicators Driver
Pressure
State
Impact
Response
Agriculture, livestock and domestic sewage
Fertilizer use, pesticide use, land use change, irrigation, livestock, domestic waste, sewage untreated effluents
Nutrients concentration, chlorophyll-a concentration, habitat destruction
Deterioration of water quality, eutrophication, conservation status
Agricultural policies, management plans for diffuse pollution loads and point pollution, completion of wastewater network, connection of the semi-urban settlements with WWTP
Irrigation
Irrigation demands
High intra-annual water level fluctuations
Low dilution capacity
Agricultural policies, management plans
Land use changes and urbanization
Loss of self-purification, habitat loss, growth of urban and semi urban areas, demand for sewage treatment
Nutrients ‘‘sink-hole’’, conservation status, dissolved oxygen, nutrients concentration
Deterioration of water quality, habitat loss, species extinction, eutrophication, increase of oxygen demand, habitat loss
Implementation of WFD, evaluation of WWTPs, designation of settlement zones
Construction of dikes and spring diversion
Alteration of hydraulic balance
Increase of water retention time
Low dilution capacity
Restoration of hydrological regime
Tourism and recreation
Recreation demands
Waste disposal, touristic infrastructure/ facilities
Water quality degradation, habitat alterations
Holistic management approach
Demand for protection of the ecosystem
Demands for conservation, species conservation, climate change (floods/droughts)
Area demand for nature, populations decline, invasive species
Conservation status, effects on biodiversity
Measures for species and habitats conservation, evaluation of goods and services, community participation
Fish stocking
Degradation of the trophic web
Low biodiversity, loss of macrophytes, turbidity
Increase of eutrophication, persistence of turbid phase, cyanobacteria
Bio-manipulation
and 1998) and 8.61 (during dry period of 2008) (Fig. 2). The variability of pH mean values is high during both wet and dry periods of the examined years. With regard to conductivity values, highest mean value (389.8 lS cm-1) was recorded during the dry period of 2004 and the lowest mean value (274.4 lS cm-1) was observed in the dry period of 1988; while there is no apparent change of CND mean values during the wet and dry periods of the examined years (Fig. 2). The highest DO mean concentration (10.02 mg L-1) was recorded during the wet period of 1984; while the lowest mean concentration (4.42 mg L-1) was observed during the dry period of 1991 (Fig. 2). All the mean DO concentrations recorded during the dry period are lower than the mean DO concentrations observed during the wet period. This is attributed to the high temperature of water during the dry period (up 24.6 °C), which mainly controls the DO concentration. The DO concentration is a very important parameter for the aquatic life such as for the fish fauna of the Pamvotis Lake, since according to Novotny (2002) and Chang (2005), where most fish fauna cannot survive when DO concentration is less than 3 mg L-1.
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The lowest TN mean concentration (0.064 mg L-1) in the water of Pamvotis Lake was recorded during the dry period of 1981; while the lowest TP mean concentration (13 lg L-1) was observed during the dry period of 2004. Moreover, the highest TN mean concentration (0.99 mg L-1) was recorded during the dry period of 1989 and the highest TP mean concentration (452 lg L-1) was observed during the wet period of 1981. The low water levels which were recorded during dry periods to all Mediterranean shallow lakes, including Pamvotis Lake, in combination with the presence of high TN and TP loadings which were mainly derived by agricultural activities and the high water temperature leads to a higher production of plant biomass increasing the rates of the denitrification process (Beklioglu et al. 2007). In Pamvotis Lake water, the TP mean values appeared to increase significantly during the dry period (Fig. 2). Furthermore, Moss et al. (2003) have reported that an increase in the TP concentrations in shallow lake water during summer may be an added result of release of the phosphate from sediments. Regarding Pamvotis Lake, this is also discussed by Kagalou et al. (2008a). These seasonal
Environ Earth Sci
variation patterns may be attributed to the dilution process of TN and TP concentrations during the wet period. The deterioration of water quality of Pamvotis Lake during the dry period may be explained by the decreased recharge and consequently the reduced dilution effects, which impact the TN and TP concentrations. Lower TN and TP mean values of both wet and dry periods were recorded in the Pamvotis Lake water after the 8 years of the diversion of sewage in 1994. The chemical status of Pamvotis Lake according to the classification system of ECOFRAME can be classified as ‘‘High’’ in terms of pH, and also ‘‘High’’ in terms of TN while it is characterized as ‘‘Good’’ for the years 1986, 1989 and 1991 (Table 6). In terms of TP, the status of the lake varies between ‘‘Moderate’’ and ‘‘Bad’’ classes. The MED-GIG (Poikane 2009) classification system provided slight different quality rankings classified the lake mostly as ‘‘Bad’’ and ‘‘Poor’’ (Table 6). Biological elements Regarding to the phytoplankton diversity and its abundance, the following diversity of species was recorded (YPECHODE 1998): 67 diatoms, 68 chlorophytes and 83 cyanophytes. The most common species were the following: Cyclotella sp., Melosira granulate, Selanastrum gracile, Scenedesmus sp., Pediastrum sp., Dinobryon divergens, Ceratium Hirundinella, Euglena viridis, Aphanocapsa elachista, Microcystis aeruginosa, Microcystis sp., Aphanothece sp. Aphanizomenon flos-aquae. The monthly average biovolume for the three taxonomic groups was, 450 9 106, 200 9 106 and 350 9 106, respectively. The only available data for comparison is reported by Kagalou et al. (2008a, b), indicating that on the period March–October 2005, a tenfold increase of cyanophyte species (i.e. Microcystis sp. 12 9 103, Anabaena sp. 90 9 103) has been recorded. According WFD guidelines (EC 2000), the proportion of cyanophytes would be a valuable measure since their occurrence is synonymous to a heavily polluted and eutrophicated water body. For the Mediterranean lake typology, the index of the percentage contribution of cyanobacteria in the total phytoplankton biovolume has been suggested. The contribution of cyanobacteria to the total biovolume of phytoplankton is considered as a reliable, meaningful and easy-to-use indicator, bearing in mind the following reasons (EEA 1999; EC 2003): (a) most of cyanobacteria species show a strong preference for eutrophic conditions; and (b) cyanobacterial blooms are highly visible, widespread indicators of eutrophication. Foul odors and tastes, oxygen depletion, fish kills and drinking/recreational impairment are symptoms of bloominfested waters. The boundary value for Good/Moderate
Table 6 Mean values of water quality parameters of the studied surface water body and chemical status classification according to ECOFRAME and MED-GIG system (data was provided by HMRDF 2010, aCriteria given by Moss et al. 2003, bCriteria given by Poikane 2009) YEAR pH
TNa (mg L-1)
TPa (µg L-1)
TPb (µg L-1)
1981
7.95
0.14
192
192
1982
8.00
0.55
390
390
1983
7.46
0.29
94
94
1984
7.37
0.56
102
102
1985
7.61
0.38
129
129
1986
7.34
0.64
102
102
1987
7.15
0.29
64
64
1988
7.15
0.45
161
161
1989
7.43
0.73
213
213
1990
7.58
No data
No data
No data
1991
7.29
0.79
101
101
1992
7.28
0.22
81
81
1993
7.04
No data
No data
No data
1994
7.69
No data
No data
No data
1995
7.63
No data
No data
No data
1996
7.79
No data
No data
No data
1997
7.57
No data
No data
No data
1998
7.57
No data
No data
No data
1999
7.78
No data
No data
No data
2000
7.62
No data
No data
No data
2001
7.60
No data
No data
No data
2002
8.18
0.35
117
117
2003
8.23
0.46
90
90
2004
8.04
0.32
29
29
2005
No data No data
No data
No data
2006
No data 0.13
148
148
2007
No data No data
No data
No data
2008
8.55
0.21
33
33
2009
8.42
0.15
45
45
High
Good
Moderate Poor Bad
conditions is proposed to be 28.5 % (Poikane 2009), whereas the reference conditions suggest a percentage contribution of cyanobacteria of 10 % in the total biovolume (YPEKA 2012). Pamvotis Lake is classified into ‘‘Poor to Bad’’ conditions with a monthly contribution of cyanobacteria of 30 % while during the sensitive dry period this percentage increases to 40–50 %. Furthermore, taking also into consideration the dominance of toxigenic cyanobacteria species, Microcystis sp. and Anabaena flosaquae; the deterioration of water quality is obvious (Kagalou et al. 2008a).
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The benthic fauna of Pamvotis Lake was found to be very limited with a total of ten species belonging to five taxonomic groups. The oligochaete community constitute the 80 % of the total benthic fauna with Potamothrix bavaricus and Potamothrix hammoniensis, being the dominant benthic species representing more than 61 % of the total benthic fauna of Chironomus plumosus is the most abundant chironomid species contributing with about 6 % of the total benthic fauna, and Chaoborus flavicans with 19 % is the important dipteran (Kagalou et al. 2006). According to Moss et al. (2003) the proposed index for evaluating the ecological conditions in terms of macroinvertebrates is the ratio of Oligochaetes to Chironomides abundance. This ratio for Pamvotis Lake is about 4. The boundaries for the ‘‘moderate’’ conditions are between 0.5 and 1 while when the ratio is [1 the recorded conditions are characterized as ‘‘Poor’’. The plant community, especially the submerged vegetation, is among the key variables for the function of a lake ecosystem. Emerged macrophytes are also very important concerning the littoral habitats. In the framework of ECOFRAME three measures are suggested for the lake ecology assessment: namely the plant community composition, the plant diversity and the plant abundance. Concerning the plant community in Pamvotis Lake, Stefanidis (2005) showed that there is a dominance of emergent species and also a serious decline of submerged vegetation which is an indication of eutrophication. Plant community is mainly composed of extensive communities of nymphaeids and canopy forming poorly rooted plants (Ceratophyllum sp., Lemna sp., Nuphar sp.) suggesting poor ecological conditions. Concerning the submerged plant abundance, it can be described by ‘‘absence of some plants visible but sparse,’’ which also suggest ‘‘Poor to Bad’’ conditions. Water Framework Directive specifically asks for the fish community information since it is considered as a key biological monitoring component. Trends in one or more fish communities can be used to monitor the ecological functioning and ‘‘health’’ of a particular ecosystem (Coates et al. 2007). The first metric is the faunal composition and according to recent fish data (Leonardos et al. 2008), Pamvotis Lake accommodates only 4 native fish species, which are under serious threat, and 20 translocated fish species, thus suggesting ‘‘a very impacted site’’. The ratio of planktivorous to piscivorous fish biomass is extremely valuable, as a metric, reflecting the ecological conditions (Moss et al. 2003; Jeppesen et al. 1997). The proposed boundary for the moderate state is between 0.2 and 0.5, while for the ‘‘Poor’’ to ‘‘Bad’’ conditions is smaller than 0.2. In Pamvotis Lake, the 93 % of the total fish fauna are planktivorous species; while the 4.5 % of the fish fauna are Piscivorous species. The founded ratio is approximately 0.05, very far even from the boundary of the ‘‘Bad’’ conditions.
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Proposed responses The assessment of the DPSIR approach provides a quite clear identification of pressures and the subsequent impacts of the quality status of the Pamvotis Lake. The next step is to set up future projects concerning restoration and sustainable management practices. It is obvious that Pamvotis Lake has a long eutrophication history due to the heavy point and non-point loading of nutrients, with frequent cyanophyte blooms. Lake restoration efforts were traditionally focused on reducing the external phosphorus loading, originated from the point-pollution sources (i.e. sewages), but they are still sufficiently high to maintain eutrophic conditions. Besides the further reduction in external P-loading, the removal of some P-rich sediment may allow a more effective response and recovery. Diffused pollution load by intensive agricultural activities (livestock impacts included) constitute also a major source of nutrient’s release. Reducing diffuse P-loading has become a major issue since it is related to the achievement of good ecological status by 2015, according to WFD. Although agro-environmental measures were introduced in Greece through the application of the Council Regulation EEC/No2078/92 (EEC 1992), only a limited number of measures (especially organic farming), were introduced so far. A possible suggestion could be the application of good agricultural practices along with the establishment of strictly protected zones in the catchment area, where at least, the land cultivation should be practiced based on ecological criteria. A remedial strategy should also include the increase of spring water recharge in order to improve the flushing rate and its water quality. Concerning biomanipulation measures, it seems that a substantial management of fish community could act as a ‘‘reverse switch’’ for the recovery of Pamvotis Lake and the re-establishment of the submerged vegetation. Planktivorous fish removal may lead in a consequence of changes in the nutrient levels, as it has happened in many other cases, and thus leading to the improving of the water clarity. It is understood that the increased urbanization and, generally, land-use changes have led to the deterioration of the habitats, the extinction of some fish species and the degradation of spawning and nursery areas. Among the most important steps towards the lake conservation is its designation as a ‘‘Natura 2000 site’’ through the implementation of Habitats Directive 92/43/ EEC (EC 1992).
Conclusions The article demonstrated the application of the DPSIR methodology for assessing the ecological status of a
Environ Earth Sci
surface water body in the Mediterranean. As a case study for this demonstration, Pamvotis Lake (Greece) was studied. The analysis of existing data series of physical, chemical and biological elements proved that high nutrient concentrations maintain the eutrophic conditions of the lake. Biotic factors also support this finding. For the categorization of the quality of the lake the ECOFRAME scheme and the guidelines of the Intercalibration Group for Mediterranean Lakes were applied. Based on biological and chemical elements the ecological status of the lake is assessed as ‘‘Poor to Bad’’ moving soon to ‘‘Bad’’ if no reclamation measures are not taken. Among the remedial measures proposed the spring water recharge seems to be the most tangible and effective for immediate action. All the measures considered could be rationally accessed if a continuous monitoring system is in operation. Acknowledgments The authors gratefully acknowledge the assistance and advice of Prof. Hossam Elewa and the four anonymous reviewers whose valuable comments helped the authors improving the quality of this manuscript.
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