Μain threats to the values of the system
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.