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George Zalidis1, Thomas L. Crisman2, Vasileios Takavakoglou1, Thomas
Alexandridis1 and Nicolaos Tsotsolis3
Laboratory of Applied Soil Science, School of Agriculture, Aristotle University of
Thessaloniki, Greece
Howard T. Odum Center for Wetlands & Department of Environmental Engineering
Sciences, University of Florida, USA
Region of Central Macedonia, Water Directorate, 54655, Thessaloniki, Greece.
Lake Koronia is a Ramsar site in northern Greece that has experienced pronounced
ecosystem degradation over the past 30 years associated with water level reduction and
nutrient loading from agricultural and industrial activities. By the late 1990’s, the lake
had almost disappeared and experienced extreme cyanobacterial blooms and loss of
wildlife. The current management plan seeks to restore ecosystem structure and function
by combining watershed Best Management Practices (BMPs) with in-lake rehabilitation
of fringing wetlands and creation of deep water refugia in accordance with fully
integrated vertical and horizontal management approaches. The plan was developed in
line with the restoration principles of Ramsar and in respect to the environmental
constrains of the area, availability of natural resources, socio-economic characteristics
and other peculiarities of the catchment.
Lake Koronia (40’41’’ N., 23’09’’ E.) is one of ten national Ramsar sites. It is the
uppermost of two lakes comprising the Mygdonia Basin. The Koronia watershed is
approximately 350 km2 and drains into Lake Volvi via a modified stream channel, then to
the sea. Koronia currently had a surface area of 3,439 ha in Spring 2004. The watershed
population is approximately 45,000. Total cultivated area since 1968 has remained about
30,420 ha, and there have been significant fertilizer application and groundwater
extraction for irrigation since the mid 1970’s. Irrigated area increased progressively from
2,730 ha (9.6% of total cultivated area) in 1968 to 6,106 ha (20% of the total) in 1991 [1].
Most irrigated areas are adjacent to the lake. Nearshore industrial operations (fabric
making/dying, food products, and clothing manufacturing) expanded steadily in the early
1990’s and affect Lake Koronia via waste water discharge and groundwater pumping.
Water level in Lake Koronia declined progressively from > 4 m during the mid 1980’s to
0.8 m by 2001, resulting in a lake volume about 10% of that when water depth was > 4
m. The progressive drop in lake level from at least 1986 to 2001 can not be ascribed
principally to climatic factors. Groundwater levels of the shallow aquifer (0-50 m) in the
western part of the watershed dropped progressively during 1969-1981 as irrigated
agriculture expanded during the period [2]. Although industries, including fabric-dying
operations, also extract large volumes of groundwater from this area, the European
Commission [3] estimated that groundwater pumping by agriculture in the basin (40 x
106 m3) is over three times greater than that of industry.
Lake Koronia was eutrophic since at least the middle of the 20th century with low Secchi
transparency (0.55-0.65 m) and frequent cyanobacteria blooms [4]. The lake became
hypertrophic during the 1990’s associated with a two order of magnitude increase in
phosphorus and a five fold increase in specific conductivity, Secchi transparency has
consistently been <1.0 m, and chlorophyll a >36 μg L –1. The rapid increase of
conductivity in Lake Koronia is clearly associated with agricultural and especially
industrial activities. Papakonstantinou et al. [5] noted that specific conductivity of
channels draining the industrial area was 5-6 times greater than groundwater. Industrial
operations are significant point sources of cations/anions in Lake Koronia, and
agriculture serves mainly as a non-point source of nutrients.
As water level declined from 4 to < 3.5 meters, oxygen saturation in the water column of
Lake Koronia increased steadily from approximately 50 % in 1983 to > 100% at the end
of 1987 as the lake shifted trophic state from eutrophic to hypertrophic. Continued water
level reduction to < 1 meter by at least August 1995 was accompanied by a progressive,
rapid decline in oxygen saturation from > 100% to reach hypoxia and anoxia by the end
of 1997, and resulted in a massive fish kill, waterfowl deaths and eventual fish extirpation
from the lake [6]. The overall metabolism of Lake Koronia became increasingly
autotrophic initially associated with decreasing lake levels and increased nutrient cycling
from sediments, then water level reached at inflection point at approximately 2.5 m
below which the lake became an increasingly heterotrophic system eventually reaching
hypoxic/anoxic conditions with associated fish extirpation [2].
The restoration plan for Lake Koronia was based on current socioeconomic and
ecological status of the area recognizing that landscapes and ecosystems are continually
evolving in response to human populations, land use and increasingly climate change [7].
It is important to determine how the ecosystem can fit into the local social and economic
matrix. The lake must be viewed as an economic asset if any restoration or rehabilitation
plan is to be accepted by the local community and eventually to reach long term, selfsustainability.
Two specific objectives were addressed by the restoration plan: 1) development of a
sustainable restoration scenario for the functional and structural rehabilitation of the lake
based on availability of natural resources (mainly the water budget of the watershed) and
2) identification of the appropriate measures, at both wetland and watershed scale, both to
restore the lake and address sources of degradation. Habitat heterogeneity was stressed to
maximize biotic diversity, and a totally integrated functional and structural approach to
lake restoration was stressed. In highly modified landscapes with diminishing water
resources, it is far easier to restore ecosystem function than to return to a specific biotic
community and habitat condition [7]. Restoration must be viewed from a cost-benefit
perspective to gain the maximum benefit for the affected system and associated human
community. Attempts to return an ecosystem to a specific structure from a past period
ignores both the fact that landscapes naturally evolve and that the sediment memory of
the aquatic ecosystem has changed to reflect the intervening period of environmental
alteration and abuse. Restoration of ecosystem structure assumes a constancy of both
watershed and lake conditions, and this is contrary to reality.
The holistic restoration for the lake was developed with the context of its contributing
watershed and consisted of five steps: 1) identifying restoration constraints, 2)
performing a watershed assessment, 3) establishing a restoration ideotype for the lake, 4)
developing and evaluating possible restoration scenarios, and 5) selecting the most
appropriate measures to ensure successful restoration and sustained condition.
Restoration plans fail unless political, economic and landscape constraints are considered
from the beginning. The current plan addressed both EU and Greek legislative
constraints, especially site specific constraints of 92/43 EU Directive and Ramsar for
conservation of existing habitat types and species. Watershed assessment employed GIS
applications and modeling to identify point and non-point sources of water, sediments,
nutrients and contaminant loading to the lake. A three step approach for water treatment
is being taken through appropriate actions within the watershed, at the watershed-lake
interaction zone (ecotonal wetland) and within the lake basin. Such an integrated
watershed approach is a cascade of treatment options from the top to the bottom of the
watershed and ensures redundancy in treating potential contaminants potentially
discharged downstream to Lake Volvi and the sea.
As landscapes are constantly changing and the lake sediment record provides an
interactive memory of past ecosystem abuse, it is appropriate to talk of lake rehabilitation
to meet specific conservation and societal goals and expectations for the ecosystem. An
ideotype was developed for Lake Koronia within the following context: 1) lake depth at
least 4 m in order to create deep water habitats to serve as fish refugia during drought
periods, 2) improved water quality to sustain and improve biotic diversity. This includes
reducing salinity, nutrients and toxic chemicals and increasing dissolved oxygen in the
water column, and 3) lake area equal to or larger than now.
The vertical heterogeneity of the lake bottom has decreased significantly since 1970
associated with phytoplankton dominance by cyanobacteria and a shift to hypertrophy.
Flocculent sediments produced by the extremely eutrophic condition have filled former
deep water habitats resulting in loss of bottom relief. Fish kills resulted from the absence
of deep water refugia during drought periods. Likewise, the trophic state of the lake must
be reduced to facilitate the fish community, both for species conservation and a local
fishing economy. Finally, enhancement of lake size will maximize conservation value of
the system. Restoration scenarios were subsequently developed within a realistic water
budget for the lake and measures are being implemented to link watershed and lake for
sustainable management. Throughout, this plan took a vertical approach to lake
management that was integrated with horizontal responses to recognize their changing
importance relative to fluctuating water level [8]. The question that was not how to get
back to a previous high water level, but the more realistic one of how little water do you
need for a functioning lake and when do you need it?
Four restoration scenarios were considered for Lake Koronia. Each was evaluated against
nine criteria to maximize lake management and conservation within the reality of water
availability: 1) developed relative to a realistic water budget, 2) maximizes habitat
heterogeneity to encourage increased biotic diversity, 3) increases vertical habitat
heterogeneity to create deep water refugia, 4) reduces trophic state, 5) improves water
quality, 6) reduces and treats watershed inputs of nutrients and contaminants, 7)
integrates vertical and horizontal management approaches, 8) connectivity with upstream
and downstream ecosystems, and 9) applies practices of ecological engineering broadly.
A lake dredging scenario was rejected both because of land disposal of dredged materials
and potential contamination from nutrients and heavy metals. Two scenarios requiring
lake level expansion were rejected because of the need to obtain additional water inputs.
The scenario that was selected (lake dredging plus water level rise and wetland creation)
will raise water level by approximately 0.5 meter to 72.0 m, and incorporate a
rehabilitated wetland (376 ha) along the western shore of the lake between bottom
contours 71.5 and 73.5 m (Figure 1). A dike will be constructed on its lakeward margin
from spoil from dredging the deepest portion of the lake approximately 0.5 meters, and it
will be sealed to eliminate chemical recycling from the sediments. The open water
portion of the lake will increase approximately 86 ha from current conditions to 3525.7
ha for an increase in lake volume of 13.8 Mm3 to reach 83.8 Mm3. Water level increase
plus dredging of 117 ha will produce a maximum water depth of four meters.
This restoration scenario fully integrates vertical and horizontal management approaches
[8] and places the lake within a proper watershed context both upstream and downstream.
Not only did it utilize a realistic water budget to address the minimum amount of water
needed for ecosystem structure and function, but it stressed the importance of a
rehabilitated ecotonal wetland for enhanced biodiversity and treatment of watershed
inputs of sediments, nutrients and chemical contaminants. Such ecotonal wetlands not
only interact with the land to transform and store sediment, nutrient and contaminant
inputs, but they also interact with the open water of the lake by providing habitat for fish
reproduction and transporting organic matter and nutrients to drive productivity of the
lake proper [9]. Incorporation of such functional aspects of wetlands is crucial to proper
lake management and long term sustainability of the ecosystem.
Figure 1. Restoration plan for Lake Koronia.
The restoration plan considers the lake within the broader context of the watershed, both
upstream and downstream. It integrates both vertical and horizontal concepts of lake and
wetland management and recognized the importance of habitat diversity for maximizing
biological diversity within the rehabilitated Lake Koronia. Most importantly, it proposes
a restoration framework that will lead to sustainable lake management because it is based
on the reality of both the regional water budget and the need to incorporate social and
economic components of the local community into any management plan.
5.1 Watershed Exports
The lake is the midpoint of the greater watershed, thus it serves as an integrator of
upstream processes and exports through nutrient and sediment transformation and
storage. The control of non-point source pollution is based on the application of Best
Management Practices (BMPs) and precision agriculture throughout the watershed to
reduce erosion and movement of nutrients and contaminants into streams for ultimate
discharge into the lake. Capture, treatment and storage of stormwater for later utilization
are being considered. In addition, existing wastewater treatment facilities will be
upgraded and new facilities will be established throughout the watershed in order to
weather the point source pollution from both domestic and industrial sources.
5.2 Rehabilitation of the Groundwater Aquifer and water balance improvement
Currently, there are over 2,000 wells within the Koronia watershed, most near the lake
(Figure 2). The wells and the dry climate during the last decades resulted in an enormous
pressure on the water resources of the area and the gradual drop of the groundwater level.
The rehabilitation of the groundwater aquifer is the most critical component of the
restoration plan for Lake Koronia. Without water conservation, both agriculture and
nature conservation will soon become unsustainable. In the vicinity of the Bogdanas
Creek which is the main recharge area, the wells will be removed and a collective
irrigation network will be established. The former in addition with the implementation of
sustainable agricultural practices should lead to a savings of 20 Mm3 to the current water
budget. Such water conservation coupled with in lake and ecotonal rehabilitation
measures should lead to a sustainable water budget for Lake Koronia.
Figure 2. Location of irrigated area and wells near Lake Koronia
5.3 Ecotonal rehabilitation and creation of deepwater habitats
Creation of wetland and deep-water habitats will promote suitable conditions and shelter
for reproduction and growth of fish to support fish-feeding bird populations. Creation of
deep-water habitats and removal of organic matter excess will be accomplished through
dredging of selected areas within the lake. The dredged material, using a confined
disposal technique, will be used for the modification of the hydroperiod in the western
part of the lake aiming in the reestablishing of a wetland area and the ecotonal
rehabilitation. The wetland will provide additional wildlife habitats, and serve as a buffer
zone for the waters entering the lake. Furthermore, phytoremediation techniques will be
applied in parts of the wetland to restore areas degraded from industrial operations in the
surrounding area. Habitat diversity of Lake Koronia will be increased through marsh
rehabilitation, incorporation of open water areas within the marsh proper and creation of
deep water refugia in the lake through sediment dredging. Finally, plans are being
developed to stabilize flocculent sediments in the lake to reduce phosphorus recycling
and to provide suitable substrate for establishment of macrophytes.
5.4 Ecosystem connectivity and exports from Koronia Lake
Lake Koronia is part of a greater watershed draining into Lake Volvi and the sea. Thus
it can not be considered in isolation from processes downstream. Exports from Koronia,
including water and nutrients, can be important driving factors for the structure and
function of Lake Volvi. Gottgens and Crisman [10] demonstrated that flushing lake
volume is essential to reduce nutrient levels and stabilize sediments in algal dominated
lakes such as Koronia with flocculent sediments. The ditch connecting lakes Koronia and
Volvi will be rehabilitated to a functioning stream ecosystem, and the riparian forest will
be managed both to increase nutrient uptake and transformation and to serve as a wildlife
corridor between the two lakes. Whenever feasible hydrologically, Lake Koronia must
flush downstream and not remain a permanently closed basin. In addition, the restoration
plan in order to prevent the impacts on down stream ecosystems sets specific guidelines
as far as water quality concerns (based on Water Framework Directive) to regulate the
exports from Koronia to Volvi Lake.
Lake Koronia may serve as an example for the restoration of Meditterranean lakes where
the ever increasing demands on a finite water resource, it is critical to determine the
minimum water volume and level and the required timing and duration needed for lakes
and wetlands for maintenance of ecosystem structure and function. In most cases there is
insufficient water amount to return regional lakes to pre-impact conditions. Furthermore,
Lake Koronia demonstrates that there are cases were basing lake management more on
manipulating the balance of ecosystem autotrophy to heterotrophy, rather than on radical
alteration of autotrophic stable states or overall productivity, may be more effective and
sustainable in terms of restoration since it recognizes the reality of limited water
availability for ecosystem management and can be tailored to meet specific management
In the 8th meeting of the Conference of the Contracting Parties to the Ramsar Convention
(COP8) the Greek government stated its intention (Resolution VIII.10) to take
appropriate action, in line with Resolution VIII.16 on Principles and guidelines for
wetland restoration, for the restoration of Lake Koronia (part of Lakes Volvi and Koronia
Ramsar Site). In 2005, a restoration plan was developed by the Prefecture of Thessaloniki
and Aristotle University of Thessaloniki. The plan was developed in line with the
restoration principles of Ramsar and in respect to the environmental constrains of the
area, availability of natural resources, socio-economic characteristics and other
peculiarities of the catchment. In 2006, a multilevel effort has begun for the realization of
the project. The Greek government, through the ministries of Environment, Economics,
Development, and Agriculture and in cooperation with the Region of Central Macedonia,
the Prefecture of Thessaloniki, relative municipalities, and the Management Authority of
Koronia-Volvi made the first step for the implementation of the restoration plan through
a joint memorandum of understanding. Furthermore the Cohesion Fund of EU approved
the financial assistance of the project and today the restoration project is under way. The
project strives to rehabilitate the watershed to reduce nutrient, sediment and contaminate
loadings to the lake and to restructure the aquatic ecosystem to gain the maximum benefit
with the least amount of water required within the next decade.
1. Mitraki , C. (2003) ‘Effects of cultural eutrophication and hydrological
alterations in Lake Koronia, Greece’, Master of Science Project, Department of
Environmental Engineering Sciences, University of Florida. 42 pp.
2. Mitraki, C., T.L. Crisman and G. Zalidis (2004) ‘Lake Koronia, Greece: Shift
from autotrophy to heterotrophy with cultural eutrophication and progressive
water level reduction’, Limnologica, Vol. 34, pp.110-116.
3. European Commission, Directorate General XVI, Regional Policy and Cohesion
(1998) ‘Final Report: Environmental rehabilitation of Lake Koronia,
4. Ananiadis, C. (1977) ‘A preliminary survey of the Haghios Vassilios Lake’,
Annuals of the Hellenic Hydrobiology Institute, Vol. 2, pp. 57-71.
5. Papakonstantinou, A., A. Chatzikyrkou and E. Kalousi (1996) ‘Study of surface
and groundwater quality in the Prefecture of Thessaloniki’, Greek Geological
Institute (IGME), Thessaloniki, Greece.
6. Grammatikopoulou, N., D. Kechagias and G. Economidis (1996)
‘Environmental study: Rescuing plan for Lake Koronia’, Hellenic Ministry of
Environment, Physical Planning and Public Works. Prefecture of Thessaloniki,
Thessaloniki, Greece.
7. Crisman, T.L. (1999) ‘Constraints to successful rehabilitation of subtropical and
tropical wetlands’, pp. 319-326. In: ‘An International Perspective on Wetland
Rehabilitation’, W.J. Streever (ed.), Kluwer Academic Pub., Dordrecht,
8. Crisman, T.L., C. Mitraki and G. Zalidis (2005) ‘Integrating vertical and
horizontal approaches for management of shallow lakes and wetlands’,
Ecological Engineering, Vol. 24, pp. 379-389.
9. Crisman, T.L., L.J. Chapman and C.A. Chapman (2003) ‘Incorporating wetland
ecotones in the management and conservation of freshwater ecosystems of
Africa’, pp. 210-228. In: ‘Conservation, Ecology and Management of African
Freshwater Ecosystems’, T.L. Crisman, L.J. Chapman, C.A. Chapman, and L.
Kaufman (eds.), University Press of Florida. 514 pp.
10. Gottgens, J.F. and T.L. Crisman (1993) ‘Quantitative impacts of lake level
stabilization on material transfer between water and sediment in Newnans Lake,
Florida’, Canadian Journal of Fisheries and Aquatic Sciences, Vol. 50, pp.
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