Lake Balaton and its human use - a system of connections

All lakes are living systems with their own food web, habitat patch network, nutrient transportation links, and connections with the surrounding catchment areas.

Humans tend to influence the function of most lake systems with their own activities. Here we attempt to outline the connections of the main components within the Lake Balaton system. This illustration aims to serve decision support and scientific outreach, and is based on limnological literature and specific scientific studies of the lake. It is obviously a radical simplification of a very complex system. The wildlife of Lake Balaton was represented by the main functional groups and their usual habitat.

“Algae” represent the microorganisms floating in the water, typically single-cell systems using photosynthesis, regardless of taxonomy. “Seaweed” and “reeds'' are used for the macroscopic plants found in rooting in the shoreline, including their habitat - differentiation is from whether they float in the water column (“seaweed”) or reach above water (“reeds”). In both cases the habitat includes the single- or multicellular organisms living on the surface of these plants or around them, both photosynthesizing and or helping with decomposition (“living coating”, phytobentos).

“Zooplankton” is used in a loose term for the drifting multicellular, heterotrophic (non-photosynthesizing) beings, mostly worms, larvae and arthropods, their main food source being algae. “Zoobentos” is used for heterotrophic creatures living on solid surfaces, mostly made up of mollusks (shells and snails). “The group “fishes” are obviously for the phyto- and zooplankton-consuming and carnivore fishes, including their offsprings. “Other vertebrates” compiles amphibians, reptiles, birds and mammals. The last two groups represent the lake’s more charismatic fauna, that is the animals, who are better known in the general public and more people know of the significance of their preservation.

We categorized human influences mainly in activities: below “water level” means the changes in the water level, which can be caused indirectly (through climate change and land use) or directly (the opening and closing of the sluice-gate at Sió). “Nutrient overload” covers the introduction of organic nutrients from the shoreline and catchment areas, prominently with the overload of nitrogen and phosphorus. “Bathing, fishing” represent the recreational activities practiced in and around the water; “boating” has been separated, referring to scheduled passenger traffic, recreational sailing and motor boating. Finally “coast guarding” stands for the maintenance of a shoreline, with a constructed solution.

The diagram shows the positive and negative effects, correlations (green and red arrows): in this sense we can look positively upon instances, where the growth, elevated frequency of one function causes a similar growth for another (for example, the overload of nutrients causes the elevated reproduction of algae), negative is where the growth of one part can cause a decrease in the other (like the feeding system). From this, some self-regulatory process (negative reinforcement) or self-amplifying (positive reinforcements) can be derived. Blue arrows stand for cases, where we know there’s a connection but we don’t know the nature of it. It’s important to emphasize that where two points are not connected by an arrow, doesn’t automatically mean they have no correlation, simply that we don’t know if there’s one!

The network diagram that comes out of these points wants to direct attention to the complexity of Lake Balaton, as a landscape and as a living system. Despite the fact that Balaton is one of the most researched lakes in the world, there’s a lack of information about its interconnections. The intricacy of this network shows that the consequences of an intervention in the living system can multiply and are not always predictable.

Illustration: Zlinszky A. and partners in prep. /szabadonbalaton, 2019