The definition of many freshwater areas is often rather arbitrary, for example the terms ‘stream’ and ‘river’ often constitute the same thing. However, as a rule, streams consist of clear water which flow over gravel or rock, and often contain pools, whilst rivers are generally deeper, muddier and usually lack pools. The definition for wetlands, on the other hand have, set boundaries, but even these have exceptions. The Ramsar Convention (1971) defines a wetland as;

“Areas of marsh, fen, peatland or water that is static or flowing, fresh, brackish, or salt, including areas of marine water, the depth of which, at low tide, does not exceed six meters.”

However the second article in the convention adds to this and says;

“Riparian and coastal zones adjacent to the wetlands, and islands or bodies of marine water deeper than six meters at low tide lying within the wetlands.”

Freshwater ecosystems are dynamic ecosystems; they are constantly changing. The rivers, streams, lakes and wetlands that make up this constantly changing physical environment are very closely linked to their surrounding catchment areas. They should, therefore, never be considered or looked at just by themselves. They may vary greatly in their appearance, influence, impacts and species diversity along their entirety. For example there is often far greater anthropogenic pressures near their mouth than there is at its highland source.

These areas are ecologically important, not only do they support valuable flora and fauna, wetlands, especially, can protect the surrounding areas. For example wetlands and slow flowing rivers recharge underground aquifers. These aquifers will hydrate an area during drought periods. Wetlands also collect a lot of sediment that is being both washed down the river and flowing up the river with the tide. Along with this silt trapping they may also trap toxins which would otherwise reduce the water quality of the area.

Despite the fact that humans can benefit from having freshwater ecosystems near them ignorance in the past has lead to a large quantity being destroyed. In the Mediterranean region, especially Greece, freshwater ecosystems are vitally important and come complete with their own associated flora and fauna. The destruction of these habitats will lead to the reduction of these rare and specialised organisms.
 

The flora and fauna that is found within the freshwater systems and their surrounding areas of Greece is diverse and ecologically important. All of the organisms found in these systems have adapted themselves to survive in a changing ecosystem with a constant unidirectional water flow. The number and type of species found reflect the quality of both the water and the overall wetland habitat. Below are four species that are very typical to Greek island freshwater habitats.

Rana ridibunda – Marsh Frog
Rana ridibunda (Marsh Frog) This is the largest frog species to be found native to Europe and may grow up to 15 cm in length. It is a fairly robust species and can be found in a variety of freshwater ecosystems including the systems within the Aegean island of Ikaria. Generally the Marsh Frog is a diurnal species; however it can be seen during the night. It is a very vocal species and it is likely to be heard before it is seen. Asides from this it is a highly social species and can be found in large groups along river banks. As the moment, due to its large population numbers and widespread distribution, the IUCN only has it classified as Least Concern. Luckily it is quite a tolerant species, to both polluted and saline conditions; therefore it should be a resident in freshwater systems for a long time to come.

Nerium oleander – Oleander
Nerium oleander is the only species found within its genus. It is a common, evergreen, shrub found along river banks and streams at low elevations. Due to this N. oleander can often be used as an indicator of the presence of freshwater. It ranges between one meter high and five meters and its long branches stand erect. It has long narrow fruits that, at maturity, split open lengthwise to release the seeds. The flowers, whilst normally pink, can range anywhere between white and red. They flower during a long summer period. Again the IUCN has only classified this species as Least Concern because it is very widespread. However without this species many freshwater ecosystems would not have the same ecological or aesthetic value.

Calopteryx virgo – Beautiful Demoiselle
Calopteryx virgo, like all damselflies, are closely associated with freshwater habitats. As damselflies go they are a fairly large and robust species measuring up to 49 mm in length. Male C. virgo are a metallic blue in colour and their wings are a dark purplish blue. The females, on the other hand, are a metallic green or brown and their wings have a white spot at the tips. They are more likely to be found upstream in closely shaded habitats than the more open lower sections of river. In these more open habitats C. virgo will give way to a similar species; C. splendens (Banded Demoiselle). It has not been recorded on the IUCN Red List of Threatened Species, however in many areas it is locally abundant and it is a common sight on many streams.

Alnus glutinosa – Black Alder
Alnus glutinosa is a deciduous tree that within the Greek islands can grow up to 20 m in height, yet in ideal conditions can grow up to 35 m. It has a straight trunk with spreading branches. At maturity its bark begins to split creating great fissures down the length of the trunk. Male flowers group together in catkins, whilst the female flowers also form catkins they are green and egg shaped. It likes wet and damp habitats so it is most likely to be found growing alongside rivers, streams and down ravines. It is perfectly capable of growing in areas of marsh or wetland where its roots are completely submerged. Despite this it is most often found in more semi-montane areas. The IUCN classifies this species as Least Concern due to its numbers; however it does fall under the Habitats Directive (92/43/EEC Directive) Annex I as ‘Alluvial forests with Alnus glutinosa and Fraxinus excelsior’.
 

Many freshwater and wetland ecosystems have been lost or irreversibly damaged. For example in the last two generations Greece has lost two thirds of its wetland habitats. There are many different factors that are currently threatening freshwater ecosystems. Some of these are listed below.

Aquifer Salinization
Aquifers that are found in low lying areas are often linked to wetland ecosystems. If these underground aquifers are pumped too often for water they may become salinized via seawater intrusion. This alone is an anthropogenic problem, however when the aquifer rehydrates the wetland ecosystem this saline water may cause problems for the local flora and fauna.

Expansion of Farmland
The expansion of farmland in modern times has led to rivers and freshwater systems coming under greater pressure. Freshwater is needed for the irrigation of crops; very few crop species can tolerate a saline water quality. This is especially the case in areas, such as small Greek islands, where freshwater may be at a premium. Many of the rivers on the island of Ikaria are suffering from the illegal pumping of water for irrigation purposes.

River Modification
Many rivers have been modified – to some degree – by man, for example the construction of reservoirs or dams and the straightening of river channels. This alteration changes the way in which the water flows and puts pressure on the surrounding catchment area. Localised flora and fauna are likely to suffer, especially if concrete, or artificial, base layers are added to rivers. For example a dam may block the natural migration route of species. Ultimately modification of any freshwater system leads to changes in the way in which the system and its associate organisms function.

Introduction of Invasive Species
The introduction of exotic or non-native species to a freshwater ecosystem can seriously damage it. The introduced species may out-compete the native species and there is likely to be competition for resources. Often these introductions are accidental, some however are not. For example the introduction of goldfish into Myrsonas River was done to make the river more aesthetically pleasing for tourists.

Tourism
Within the island of Ikaria one of the largest threats to freshwater ecosystems is the influx of tourists during the summer months. Tourists who are not respectful of the environment, predominantly due to ignorance, often utilise the river in ways they should not. For example the use of detergents to wash clothes releases toxins into the water system that are potentially lethal to flora and fauna. In general the amount of litter left behind is damaging to the environment both aesthetically and physically.

There are, of course, natural threats to the freshwater system, such as erosion, flooding and drought, yet theses are often seen as out of our control. Therefore anthropogenic impacts are the ones that are most focused on.
 

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