Ecosystems are biological systems that are formed by all organisms that live in a community and by all abiotic or non-biological factors (climate, relief, luminosity …) with which they interact. On our planet there is a great variability of ecosystems that are classified in aquatic, terrestrial and mixed or transitional ecosystems. For example, aquatic ecosystems encompass many environments and we can distinguish between marine and inland water ecosystems, which develop on the surface of the continents, whether fresh or salt water.
What are the freshwater aquatic ecosystems?
The aquatic ecosystems freshwater systems are very important to provide very different services: they are a source of food and water, regulate climate, maintain biodiversity and soil, stores and eliminate contaminants and participate in the process of recycling nutrients.
The inland water ecosystems can be classified into:
- Lotic systems (rivers)
- Lentic systems (lagoons and lakes, ponds, ponds, marshes, swamps …)
Examples of Freshwater ecosystems:
1. Lotic systems or rivers
Rivers are streams of water that persist over time and that flow continuously in only one direction. The characteristics of the river basin together with the climate (temperature and rainfall) will determine the vegetation of the riverbank. The main primary producers of biomass in rivers are algae ( phytoplankton if they live in suspension in the water column, and peripheral or biofilm if they live on sediments), mosses, lichens and vascular plants .
The rivers change along its route. The upper, middle and lower reaches of the rivers have different characteristics and, therefore, will present different communities of species and processes.
- High section of the river: near its birth the rivers have a great slope, shallow depth, width and flow, thick substrates and a turbulent flow (water particles move chaotically). In many high sections light is scarce due to riverbank vegetation, which makes primary production difficult.
- Middle and lower sections of the river: as we descend in its course the river will gain in depth, will have more width and more flow, the substrates will become thinner and the flow will become laminar (all water particles move in the same direction ). In these sections the temperature of the river increases, since the waters have received more solar radiation as their channel widens, so that the lighting conditions for primary production improve. However, in lower sections there is too much depth and conditions get worse again, because the river also carries a lot of sediment, with no light reaching the bottom of the basin.
An important feature of the rivers, since it will determine the communities that will be found in their environment, is the hydrological regime; which encompasses all the temporal variability of the amount of water in the river ecosystem , that is the frequency of floods, droughts, their magnitude and duration, their predictability, etc.
It should also be noted that the state of these rivers has a direct and indirect impact on the ecosystem. An example of this is groundwater , of great importance, since its waters can also be used, but they are not independent of the state of conservation of the rivers.
2. Lentic systems
Lentic systems such as lakes, ponds, ponds, ponds, marshes, swamps, etc. , are closed bodies of water with no flow or currents that persist over time. In them we can differentiate three zones: epilimnion (more superficial layer of the water column), metalimnion (intermediate layer, with very changing physical and chemical characteristics) and hypolimnion (deeper layer).
The environments present in freshwater aquatic ecosystems that are called lentic systems can be classified into three zones:
- Coastal zone: near the edge, there is vegetation present and the light reaches the bottom of the lake.
- Pelagic zone : open water zone where phytoplankton survival is possible.
- Deep zone: the survival of plant species such as phytoplankton, macrophytes (plants that we see with the naked eye) or peripheron is not possible because the light does not reach the bottom of the lake.
In these systems volume and depth are two very important factors. Increasing both decreases the volume of water in contact with the atmosphere (main source of oxygen) and sediments (the entry of nutrients to the water column is difficult), and increases the water renewal time (time that must pass so that all the water in the system is replaced).
These freshwater ecosystems can be temporary if there is no water outflow through rivers and usually house poor communities, although some organisms reach large abundances due to the drought-flood cycle and the shortage of predators.
In deep lakes , thermal stratification occurs, a phenomenon by which the layers of the water column are differentiated by changes in their density, causing the most superficial layer to float over the deepest without mixing with them, making it difficult for nutrients to rise from the bottom.
Wetlands are mixed or transitional ecosystems between inland water ecosystems and terrestrial ecosystems. They have characteristics similar to lentic ecosystems and terrestrial ecosystems , since they occur in places where at least once a year, the soil is saturated with water. When this happens, the soil is devoid of oxygen and an intermediate ecosystem is generated. Therefore, the communities in these environments are neither purely terrestrial nor purely aquatic; The fauna is usually endemic and differentiated from the surrounding areas, such as large families of birds and reptiles.
According to the RAMSAR agreement (the Convention Relating to Wetlands of International Importance especially as Waterfowl Habitat), wetlands are vital for humans as one of the most productive environments on the planet, being sources of water and places of great biological diversity and primary productivity Thus, they depend on wetlands to survive countless species, both animal and vegetable. However, the surface and quality of these environments continue to decrease, among other causes, due to their transformation for the exploitation of agriculture or aquaculture.