Μain threats to the values of the system

Dr Giorgos Catsadorakis

Dr Giorgos Catsadorakis

Society for the Protection of Prespa

Starting with very basic info on the status of the precious endemic forms of the benthos, and based on all available data, there have been no worrying indications about the status of any of the endemic fish in the lakes. In contrast, the consistently small populations of some herons and the cessation of glossy ibis nesting were strong indications that the declining surfaces of shallow open water areas might well be a main limiting factor. At the same time, the water quality of the two lakes has clearly been deteriorating over the last 40 years, something which has become increasingly obvious over time.

Below are briefly described the three current major threats to the lacustrine ecosystem that we have been able to identify through a combination of literature searches and targeted research. 

A.      A. Over-expansion of Phragmites australis reedbeds

In the past the common reeds growing naturally at the edges of the lakes were managed by the local people, by cutting reed for use as a construction material and cattle fodder, burning reedbeds to remove dead above-ground old stems to facilitate local fishing methods, and direct in situ grazing and trampling by cattle. All these interventions had direct economic implications in the past.  Technological advances, together with socio-cultural and economic developments, changed livelihoods and primary sector choices, and led to the gradual abandonment of traditional uses, leaving the littoral shallow zone of the lake without any other management interventions, except for sporadic uncontrolled fires. As a result, the reedbed gradually started to encroach on the shallow areas around the edges of the lake, which are seasonally flooded in spring and are important habitats, in the absence of reed. The shallow open areas, i.e. those not covered by standing old, reed stems, are key feeding areas for the precious large, rare waterbirds and the main spawning grounds of all phytophilous fish. In addition to the expansion of reeds, climate change is causing smaller water-level fluctuations, and thus the flooded areas outside the reedbeds are reduced in area in years with low spring water levels. As a result, the shrinkage of these habitats has dramatic repercussions on the feeding efficiency of birds and the spawning success of fish, including carp, which has the highest commercial value for the local fisheries. The dynamic expansion of the common reed is favoured by increasing nutrient content in the waters (mainly originating from agricultural run-off) and higher average water temperatures. At the same time climatic conditions, such as prolonged droughts, render the expansion of wildfires over large areas of reedbed an additional threat.

B.      B. Ongoing Eutrophication

The increasing trophic status of Lesser Prespa Lake (as well as Great Prespa Lake to a lesser degree) is principally owed to the increased amounts of nutrients flowing into the lake, mainly from agriculture. The process may be amplified by lower precipitation, declining water volumes, and slower water renewal rates, etc., mostly due to climate change and water management decisions. Direct threats to organisms can be multifaceted: toxins from blue-green algae accumulate in or directly kill fish, amphibians, invertebrates, vertebrates; fish become unsuitable for consumption; the water becomes unsuitable for the irrigation of food plants; over-growth of plankton and aquatic vegetation takes place; increasingly anoxic conditions at the lake bottom lead to the impoverishment of biodiversity there; the water becomes unsuitable for recreation. Beyond a certain unknown threshold the lacustrine ecosystem may collapse. There are direct implications for the human economy through the decline of fisheries and tourism, spectacular changes to landscapes, and chain reactions and changes to biotic communities of any kind, many of which are difficult, if not impossible, to foresee. Reedbeds – and littoral vegetation in general – have been described as potential sinks for pollutants, as well as a source adding pollutants to the water column; reedbeds may retain nutrients from agricultural run-off in the littoral zone, but also provide nutrients to the water upon decomposition, with their intricate role as sinks or sources of nutrients depending on a variety of factors, such as retention time, loading rate, seasonality, and plant decomposition rate, amongst others.

C.      C. Shrinkage of lake water volumes and surfaces, narrowing of water level fluctuation breadth.

These are owed to both the natural decline of precipitation (rain and snowmelt) entering the lakes and higher evaporation attributed to climate change, but also connected to the kinds of management applied by humans through specific hydrological interventions with structures built to control the water level. The purpose of the construction and management of these structures has been: a. to maintain Lesser Prespa Lake as a lake with no dramatic shrinkage of its surface area; b. to avert the flooding of nearby cultivated fields (assigned to private owners some decades ago upon the construction of an extended irrigation system); and c. to ensure adequate water for irrigation. All these factors have led to a kind of annual and inter-annual variation of the water level,  which deviates significantly from the natural fluctuation patterns to which habitats, plants and animals of the lake have been adapted for millennia. This relatively new artificial regime includes some conservation objectives, manifested in agreements for the annual maximum spring and summer water levels, but is still far from covering the needs of all organisms and the natural ecosystem, existing in a challenging tandem with social and economic needs and priorities.

A, B and C are the main threats and pressures to the main values and the integrity of the Prespa ecosystem. They are also highly inter-connected.

For Factor A we need to find new ways of stopping the expansion of reedbeds over open shallow water areas. At the same time, acknowledging that reedbeds also play a beneficial role for wildlife (e.g. providing nesting substrate for the nests of many waterbirds and their breeding colonies), the aim is to create the ideal mosaic of undisturbed reedbeds, which will serve some needs of wildlife, and to clear them in other places, in order to serve different needs (such as feeding and spawning). However, in order to be able to sustainably carry out this management in perpetuity, the challenge is to connect it with the economic activities of local people, so that the management of reedbeds will be covered by economic benefits for the local community.

Working against the increasing trophic status of the lakes (Factor B) we must find ways to minimise, and eventually stop, more nutrients from entering the lake. In order to achieve that we must work with farmers and the state agencies, with legislation and institutions, and at the same time work on a scheme for the effective removal of nutrients that are retained within the littoral vegetation, particularly reeds. 

For Factor C we can do very little locally to stop and reverse climate change implications. However, we can do quite a few things to help the lacustrine ecosystem adapt in the best possible way to the ongoing changes, which will serve both the needs of wildlife and the needs of people in the best possible combination.