Algae: The group of algae is polyphyletic, meaning it is not composed of organisms from one single taxonomic ancestor, but is rather a taxonomically diverse group. In general, they are single-celled or colony-forming photosynthetic organisms, so-called primary producers, which produce organic compounds from inorganic materials, usually using solar energy, thus building up their very own biomass. They form the first level of food webs. Several groups of algae can be distinguished, e.g. - green algae, dinoflagellates, diatoms, red algae, blue algae, also known as cyanobacteria.
Algae blooms,: algae bloom is the term used when algae in a water body start to multiply very rapidly and their mass grows significantly. This typically occurs when there is a sudden increase in the availability of nutrients in the algal habitat. Algae blooms usually occurs in the warm summer months, but it is not uncommon for this to happen in early spring or even under the ice cover of frozen lakes. Lake Balaton is characterised by two algae growth peaks, a small spring peak, mainly caused by diatoms, and a larger summer-autumn peak, most often caused by blue-green algae.
Floodplain forest: Forest strips along rivers, which used to be flooded in the past, and still present partial flooding nowadays. The forests closer to the river, which can tolerate prolonged flooding, are softwood (willow-shrub) floodplain forests, with a varied herbaceous and shrub cover (sparse where flooding is frequent), and are characterised by climbing plants (e.g. hops, grove vines). Due to reduced depth and frequency of flooding resulting from river regulation practices and climate change, introduced alien plants (e.g. wild cucumber, false indigo) are now common in floodplains, spreading in masses. In more remote areas, which were less frequently flooded before river regulation, oak, ash and elm are typical species, with rich undergrowth. This forest type nowadays only has access to groundwater along rivers and is drying out due to reduced availability of water. The remaining floodplain forests in Hungary are Natura 2000 protected habitats.
Biodiversity crisis: The extinction of certain groups of organisms is well known from prehistoric times (dinosaurs) or from historic times (the dodo). Compared to total extinction, local extinction is a more common occurrence today: an organism, a group of organisms or even a plant communitygrows extinct in parts of its former habitat range and is replaced by another, often poorer community or an organism or group with reduced ecological functions. The current human-induced process is called the biodiversity crisis, or the sixth extinction wave (the first five occurred in different eras of the Earth's history, independently of human activity). On Earth, living organisms maintain soil formation, pollinate plants, maintain the self-cleaning of water and the atmosphere, and regulate local and global climate, therefore the extinction wave is causing direct economic and immaterial damage. Localised extinctions weaken these vital processes, which also entail serious social, economic and health risks for humans. Primarily agriculture and forestry, i.e. food production, is directly impacted, but since we all share the same air, water and planet, everyone is affected sooner or later. The biodiversity crisis can be counteracted by conscious land use, protecting natural habitats and reducing pollution and consumption.
Almond willow: Many willow species tolerate periodic or prolonged periods of waterlogged ground and grow in littoral areas, e.g. in reed beds. Within almond willow habitats (Salix triandra) willow typically occurs in isolated patches or shrubs, and may harbour seeded sedge, pond sedge, reed beds or waterlogged marshes.
Disturbance: (Oborny and Pásztor 2007) An external impact that damages or possibly destroys at least one of the species of the community. Some degree of disturbance occurs in all natural habitats and is therefore not isolated from the functioning of ecosystems.
Alder: Alder (Alnus glutinosa) is a tree found mainly around small rivers, streams and sometimes near lakes, on well-watered but not permanently waterlogged soils, and may be part of the natural riparian vegetation zone. Alders are considered a rare and highly valuable habitat, protected under Natura2000.
Balance: a system is in balance if its state is constant over time.
Habitat (alliance, biotope, habitat type): a community of species that typically occur co-existing, preferring or maintaining similar inanimate environments.
Habitat (habitat patch): Area covered by a particular alliance or habitat type.
Habitat patch network: adjacent habitat patches may be connected to each other (in a 'stepping stone' role), enabling individuals of a given species to move between patches at any stage of their development (ecological connectivity). In the case of sessile organisms (e.g. plants), passage is considered to occur if reproductive elements (e.g. seeds) can move from one patch to another and germinate and grow to mature plants there.
Living system - ecosystem: (Pásztor and Oborny 2007) a system of interconnected species and their abiotic environment. The whole earth is an ecosystem, but to answer many questions the system can and should be reduced to a smaller unit, even to one habitat (used synonymously with ecosystem). For example, we can consider Lake Balaton or the Balaton region as an ecosystem.
Eutrophication: (Padisák 2005) refers to the enrichment of water with plant nutrients, mainly phosphorus and nitrogen, which causes increased algae or seaweed growth (algal blooms). The water turns green from floating algae or the sediment surface is densely covered with pondweed. The decomposition and nocturnal respiration of the resulting plant material consumes oxygen, which can lead to the production of toxic substances or even fish kills due to oxygen deficiency alone. In Hungary, the vast majority of surface standing waters are affected by eutrophication due to nutrient run-off from agricultural land and leachate reaching the water.
Ceratium: Until the 1960s, the Balaton dinoflagellate algae (Ceratium hirundinella) was one of the most widespread, particularly large, algae in Lake Balaton. In the past decades, cyanobacteria were the most common algae in the summer algal blooms of the lake, but since 2010, the number of Ceratium has increased again, indicating improving water quality. The record algal peak in 2019, which covered the western half of Lake Balaton, was formed by another invasive but similar species, Ceratium furcoides, together with a species of syanobacteria. Ceratium algae belong to the armoured dinoflagellates family and are considered giants among algae, growing up to 0.1 mm in size. They get their name from the fact that they grow a distinctive cellulose armour with long flagella resembling swallow tails.
Groundwater: two-thirds of the earth's freshwater is found in the form of ice and about 30% underground. Thus, groundwater reserves are about ten times greater than the available surface water stored in rivers, lakes and marshes. Some of the groundwater is moving in a similar way to surface water, but the movement is much slower. Part of the supply (typically near the surface) is linked to the surface water cycle (recharged from precipitation and discharged into watercourses), while another part exists as residual water bodies, more or less isolated (fossil waters). Sustainable use of groundwater is possible if extraction does not exceed recharge.
Land cover: natural or artificial cover present on the ground surface. Land cover is of crucial importance for microclimate and water balance (evaporation/run-off/infiltration). Areas with dense vegetation have a balanced water flow, while artificially covered surfaces drain and dry out more quickly. On vegetated surfaces, part of the rainwater is deposited on the leaves and part of it evaporates immediately. The water reaching the soil surface typically infiltrates and increases groundwater supplies. Water runoff from the vegetation-free surface often carries the topsoil with it (erosion). Water from impermeable pavements does not infiltrate into the soil, but runs off the surface of the pavement.
Phosphorus cycle: (based on Istvánovics 1998) Phosphorus is a key nutrient for plants and animals. Its cycle in the abiotic environment is very slow, through the formation, surfacing, erosion, run-off and redeposition rocks composed of minerals with high phosphorus content (mainly apatite). Phosphorus is essential to living organisms for the most basic cellular functions. In living organisms, phosphorus is usually present in concentrations hundreds to thousands of times higher than in the environment, and the uptake of relatively scarce phosphorus from soil and water is a major challenge for unicellular organisms and plants. The phosphorus cycle involving living organisms is much faster than in the case of abiotic processes: an important part of it is the work of decomposing organisms and the decomposition of dead organic matter in soils and waters, which makes phosphorus reabsorbable from their remains - while some of the phosphorus that ends up in soil or water is converted back into a form that is more difficult to reabsorb. Much of the phosphorus that reaches water is accumulated in the sediments of lakes and rivers, and whether, when and how much of it finds its way back to the water is key to nutrient cycling. As succession occurs, increasingly species-rich, spatially complex living systems become more closed in their own phosphorus cycles, storing more phosphorus as living matter and losing less phosphorus through erosion and runoff. Humans have significantly increased the amount of phosphorus available to biota through targeted mining of phosphorus-rich rocks for use in agricultural fertilizers. It therefore accumulates in soils and is dissolved in water or bound to leaching soil particles and released into water bodies. A relatively small portion of phosphorus is used as a softener in detergents and is also released into living water through sewage - but the majority of phosphorus in wastewater is due to human food consumption. Typically, half of the phosphorus entering living water comes from run-off from agricultural land and half from domestic sewage.
In contrast to traditional agriculture, intensive, industrialised agriculture and the sanitation systems required by urbanisation have made human phosphorus use much more wasteful, as the phosphorus that does reach water is no longer usable by humans. However, the Earth's underground phosphorus reserves are finite and very unevenly distributed (e.g. none at all in Europe) and should be exploited sparingly to conserve them (Elser & Bennett 2011). In temperate freshwaters, dissolved phosphate is usually the factor that mostly limits the growth of algae and aquatic plants, therefore excess phosphorus in the water can cause serious problems: it initially increases the growth of aquatic plants and, with higher amounts, of algae (eutrophication) and fundamentally changes the food network (resilience).
Cattail stand: a zone of riparian vegetation dominated by narrow-leaved or broad-leaved bulrush/cattail (Typha angustifolia, T. latifolia). It usually develops on soft, oxygen-depleted sediments rich in organic matter, in places sheltered from waves. In the interior of some reed beds of Lake Balaton, in areas away from the open water and the shore, the cattail spreads at the expense of the reed.
Pondweed: sediment-rooted plants whose stems and leaves are typically in the water column rather than floating on the water surface. They play an important role in binding sediment and its nutrients, thus limiting algal growth. They supply oxygen to the water, reduce wave action, provide a stable substrate for other, smaller organisms (e.g. Gammarus roeseli, molluscs), providing a hiding and spawning place for many species of fish and thus maintaining species-rich habitats. Typical species in Lake Balaton include the sago pondweed (Stuckenia pectinata), the clasping-leaved pondweed (Potamogeton perfoliatus) and the spiked water-milfoil (Myriophyllum spicatum).
Thermal stratification: the density of water depends on its temperature and the concentration of the substances dissolved in it. The specific mass of warmer water is lower than that of colder water, although there is only a slight difference. It is common in deeper lakes, and a periodic ocurrence in Lake Balaton, that the lake water is cold at the bottom and significantly warmer at the surface (this is easily detectable when swimming in shallow lakes in calm weather). At such times, the difference in density makes it difficult for these two layers of water to mix, limiting the exchange of water between them. Until the wind picks up, the processes in these separated water layers are partially isolated and oxygen deficits can occur in the deeper parts.
Karst water: water collected in water-carved crevices, channels and caves of sedimentary rock (Padisák 2005)
Blue-green algae (cyanobacteria): a strain of bacteria that, like algae, can photosynthesise with the release of oxygen, (this is a unique feature among bacteria). They are unicellular or multicellular. Some species are able to absorb and metabolise nitrogen molecules dissolved in water from the air when needed. The growth of these species is not limited by the amount of nitrogen in the water in molecular formats available to other algal species, but only by the amount of available phosphorus compounds. Therefore they can cause algal blooms when nitrogen is low but phosphorus is abundant, often becoming visible to the naked eye at the surface. When the cells die, the nitrogen they have fixed becomes available to other algae. Some species/strains can produce toxins that are dangerous to other organisms or even humans. These can cause allergic reactions, skin rashes, diarrhea and are particularly dangerous for children (and pets).
Climate change: (IPCC, Climate Strategy of Zala County) Climate summarises the weather conditions (temperature, wind, precipitation, humidity, cloud cover, etc. and their distribution over time) in a given area. Different climates are found in different parts of the world. The main features of the climate have been constantly changing throughout the Earth's history, but the rate of climate change over the last 70 years is much faster than any known climate change - including the warming after the "Little Ice Age" of the 16th and 19th centuries. A typical and easily interpreted process of change is the rise in average temperature: the Earth's average temperature has now risen by 1.1°C compared to the period before the industrial revolution. There is a broad scientific consensus that 95% of warming is caused by human activity. The main cause for it is the increased emissions of greenhouse gases (mainly carbon dioxide and methane) from the combustion of fossil fuels (coal, petroleum derivatives, natural gas). Experience shows that this change is not only causing general warming, but also more extreme weather and quite a few sudden changes in the functioning of all ecosystems which are difficult to predict. In the Lake Balaton area, the most important changes are an increase in the frequency, duration and severity of summer heat waves, droughts and flash floods. These are also changing the expanse and timing of nutrient loads to water bodies. Lake Balaton's biota is also significantly affected by the reduction or absence of winter ice cover. If the average surface temperature increase reaches +2°C, irreversible changes can be expected. The later we succeed in reducing greenhouse gas emissions, the more practically irreversible changes in ecosystems (resilience) can take place. This change must be adapted to (e.g. urban heat island; water level regulation) and mitigated by drastic reductions in consumption and emissions and a shift in technologies in the transportation, agriculture and energy sectors.
Diatoms: usually brownish algae, which can be a common component of plankton floating in the water, but are also often found as a coating on sediment or submerged surfaces (rocks, reed stems, even turtle shells). The individual cells develop a silica cell wall with symmetrical patterns, which can be observed by microscope as a beautiful "glass box". They can be found in all waters (but also in soil or on wet walls), and in winter, diatoms tend to remain active the longest. Subsequently, the brownish sediment coating visible through the water of a stagnant lake is also formed by diatoms.
Decomposer organisms: organisms that feed on other organisms that have died, returning the organic matter bound in their bodies back into the nutrient cycle for reabsorption by plants and algae. Most decomposers are bacteria and fungi, but there are also more complex ones. In Lake Balaton, important decomposers are the larvae of certain species of mosquitoes and crustaceans.
Limnology: literally meaning 'lake science', whose subject of study are continental waters, especially lakes and rivers. Limnology is an nterdisciplinary science, including hydrobiology, hydrology, physical limnology, geophysics, geo(bio)chemistry
Pond sedge/tufted sedge stands: zone of riparian vegetation dominated by tall-growing sedge (Carex) species. Typically occurs at water depths of 10-50 cm and grows to 1-1.5 m above the water surface in areas with intermittent water level variation. The characteristic feature of the tufted sedge (Carex elata) is the small island of dry leaves and soil at the base of the plants, the tussock, which rises above the water surface. Tufted sedge stands are rare, species-rich habitats.
Macroinvertebrates: A community of invertebrates, such as worms, aquatic beetles, insect larvae, but also including sessile molluscs and slow-moving snails, that are larger than zooplankton, visible to the naked eye and even capable of more vigorous movements. Their diet is very varied, including eating remains of organic matter (e.g. pondweed) that enters the water, filter feeding or "grazing" on algal coating deposited on the surface of plants and other objects, but some are predators such as dragonfly larvae. Because of their mass, the most common species to be seen at Lake Balaton are the non-biting midge larvae, whose shed pupae often give the impression of "polluted" water by floating on the surface and forming foam. Adults can be seen in large swarms above reeds and around street lamps in summer. They are an important part of the food network due to their decomposing activity, but also constitute food for fish, amphibians, waterfowl, etc.
Micropollutants: anthropogenic pollutants that are typically present in very small amounts in natural systems (water, sediment, biophytes, biota) but are still able to affect a group of organisms at the individual, tissue, cellular or molecular level. In the case of Lake Balaton, the physiological and environmental toxicological effects of anthropogenic micropollutants (e.g. pharmaceutical residues, pesticides, microplastics) are being investigated.
Monitoring: collecting information on the state of a system through regular, accurate, standardised (therefore comparable) measurements, with the aim of obtaining knowledge on possible changes in a system and, if necessary, of intervening to achieve or maintain a certain state. It is not to be confused with research (which is usually aimed at answering a question or confirming a hypothesis), although it does provide useful data for research purposes.
Reedbeds (riparian vegetation): The word "reed" is most commonly used in connection with Balaton to refer to tall, herbaceous vegetation along the water's edge. This plant community extends from the water, which is about one and a half metres deep, to the edge of the coast on dry land where the soil is still water-logged. It has a distinctive structure (zonation) depending on water depth, with each zone constituting a specific habitat. In addition to common reed (Phragmites australis), other tall monocot plants may dominate the zones (mainly cattail (Typha latifolia) and sedge species (Carex sp.)), also willow scrub patches and open water lagoons may occur. Of all the habitats in the lake, the reedbed presents the highest biomass production, CO2 sequestration by biomass and species richness. Many terrestrial and pelagic animals feed or breed in reedbeds.
Reed die-back: the apparent unusual, irreversible, waterward loss of area and fragmentation of mature stands of common reed on a decade-scale period(van der Putten 1997, Aquatic Botany). It is a phenomenon experienced throughout Europe, sometimes linked to nutrient enrichment (eutrophication) or to successive years of high water levels. The stabilization of banks with built shorewalls inhibits the regeneration of reed beds, thus inhibiting the natural self-cleansing process that is essential for maintaining the good ecological state of lakes.
Nitrogen cycle: nitrogen is essential for living organisms, in particular for building cellular proteins. Nitrogen can occur in a wide variety of compounds and these can be converted into each other during both the living and non-living cycles. The most common form of nitrogen is nitrogen gas, which makes up two-thirds of the atmosphere and is less reactive. It is mostly converted by bacteria into nitrite and nitrate, which can be absorbed by living organisms from their aqueous solution. Blue-green algae are bacteria which can also fix atmospheric nitrogen gas in this way. Nitrogen-fixing crops used in agriculture, such as alfalfa, peas and soya (all legumes) actually do this in tiny root tubers using their own bacterial cultures. Decomposition of living organisms usually produces ammonia from organic nitrogen, followed by nitrite and nitrate, which moves in aqueous solution with groundwater and living water. In oxygen-deficient environments, some bacteria can produce nitrogen gas from ammonia. Humans have significantly increased the amount of nitrogen available to biota by industrially converting atmospheric nitrogen and spreading it as fertilisers. Nitrogen entering living waters can contribute to the development of algal blooms, while nitrogen compounds leaching into land habitats or even deposited from the air can transform their flora and lead to the spread of more nutrient-demanding (nitrate-hungry) weeds.
Ecology: the science of the distribution, occurrence and relationships of species with each other and their environment
Ecological connectivity: two patches of habitat are interconnected in an ecological sense if organisms can move between them. The greater the number of species that can move between the two patches, the stronger the connectivity between them. Interconnectivity can be examined at several levels; we can examine it at the level of a species or community, or on different spatial scales. For animals, it is usually a continuous chain of hiding places and feeding sites that provide interconnectivity, while for plants, a patch is interconnected if its seeds can germinate densely enough to allow the plant population to spread between the two patches.
Riparian zone: the transition zone between land and water where plants have ample access to water, nutrients and light. The riparian zone is separated from land by a strip along the shore where plants do not have sufficient water anymore for part of the year (the soil is not continuously saturated with water or the groundwater flow is deep) and from open water by a zone where the sediment surface is already too low in light for photosynthesis. The plants of the riparian zone show a characteristic zonation, e.g. from areas of continuous water cover with pondweed to areas dominated by reed or wet grasslands with only temporary water cover.
Shoreline protection: human activity (typically construction) aimed at maintaining the location and topography of the shoreline. (Szabó, Krámer, Zlinszky 2017 Ecology of Lake Balaton)
Population: a group of organisms of a species that occur in the same geographical area and are can potentially reproduce with each other.
Softwood riparian woodland: composed mainly of willow and aspen, occurring in wet or previously intermittently wet zones – or where some places have changed water flow and may have dried out. While swamp woodland vegetation is very species-rich, softwood woodland is composed of more disturbance-tolerant, less demanding plant species. On the shores of Lake Balaton, especially on the south shore, the old trees of some campsites and parks are probably remnants of former waterfront forests. These remnant patches (habitat patch network) are of high value for wildlife due to their ecological connectivity and their positive environmental effects (urban heat island; land cover).
artesian aquifer: groundwater body between two impermeable layers (Padisák 2005).
Resilience: The ability of (ecological) systems to return to the original equilibrium state after a strong perturbation (displacement from the balance state). Several balance states can and do exist in a system, such as the pondweed and algae dominated states in shallow water bodies. The transition between equilibrium states may be linked to certain thresholds: sudden changes in the functioning of the system may occur, which are often difficult to reverse as the threshold for a change in one direction is different from the threshold for a change in the other direction.
Imagine a pencil balanced standing on its end on a table. The pencil is in a state of equilibrium, but if the tip is pushed sideways a bit, it tilts, falls and ends up on the table in a different state of equilibrium. If you now push the tip of the pencil in the other direction, as hard as before, it will not return to the previous equilibrium state, set on its end: the transition between the two states is more difficult in one direction than the other.
Shore squeeze: for the marine coast, this is the term used to describe the phenomenon where rising sea levels would cause the vegetation of the coastal zone to shift towards higher ground, but it is prevented from doing so by the building of structures. On Lake Balaton, a similar phenomenon is caused by artificially high water levels, to which the coastal vegetation zones would adapt by shifting higher, but this is prevented by the presence of roads, railways and waterfront buildings. The riparian zone can adapt to the raised water level only where the reedbed is bordered by grassland or woodland on the uphill side - everywhere else, the rise in water level causes a reduction in reedbed area.
Succession: the natural process whereby generations of many species over time in a given place form increasingly complex habitats and communities - for example, as fast-growing herbaceous (pioneer and weed) plants colonise a bare soil surface, then woody, fast-growing, undemanding species (e.g. birch, poplar) colonise and, after a longer period of uninterrupted growth, slower-growing woody species become the main component of the community. In the case of a lake (especially a small lake), succession means the natural silting up of the lake, turning it into a wetland and then a meadow. While this succession in the traditional sense can last for extremely long periods (up to centuries), rapidly reproducing microscopic organisms are capable of similar phenomena. Because of their generation time (frequency of division) of about 3 days, algae can progress from a major disturbance event (e.g. a big storm) to the emergence of more stable, complex communities in a matter of weeks.
Groundwater: water that completely fills the gaps between soil particles between the impermeable upper rock layers and the soil surface.
Nutrients: In the case of plants and algae, nutrients are considered to be those substances that are soluble in water and are incorporated into their cells during growth. Plant nutrients can be inorganic (H2O, CO2, nitrate, phosphate, potassium) or organic. We usually consider those elements as nutrients whose sufficiency may be critical for plants (nutrient limitation), the most important nutrient for aquatic plants and algae being phosphorus (phosphorus cycle) and nitrogen (nitrogen cycle).
Nutrient limitation: living organisms can only use nutrients in proportions specific to them. For this reason, with some simplification it can be stated that typically, growth is limited by the amount of the relatively most difficult nutrient to access. In Lake Balaton, this is typically phosphorus for algae. Even if there is plenty of carbon, oxygen or nitrogen, algae can only grow slowly when access to phosphorus is limited. Nutrient limitation is similar to when you want to make pancakes but only have one egg at home. You can have any amount of flour or milk, the amount of pancakes will be determined by the most limited ingredient available.
Nutrient load: the amount of nutrients entering a habitat from outside. In the case of waters, nutrient loading is generally understood as nitrogen and phosphorus input, usually carried by runoff into watercourses or washed off from surrounding areas (the watershed) by precipitation, depending on the land cover and land use (e.g. intensive fertilizer agriculture or natural forests).
Nutrient cycle: the amount of a given element (e.g. nitrogen, phosphorus) in a closed system is constant due to the principle of mass conservation, but nutreints can move between different components of the system. In an ecosystem, nutrients can be transferred primarily from water or soil (or even from the air, e.g. nitrogen fixation) to primary producers (algae), then passed through various elements of the food web and returned to water, soil or air by decomposers. In the case of some nutrients, this cycle can also be driven by abiotic processes (e.g. phosphorus compounds released during rock weathering). Nutrients can take the form of different compounds and that can change into each other in some cases. The closed system here is the Earth's ecosystem, where nutrient fluxes are not evenly distributed, so a pond can experience an increase (even a very large increase) in the amount of a nutrients, for instance, due to fertilisation.
Food web: a food web is a model that shows which groups of organisms feed on which other groups of organisms. A food network can be modelled at the level of species or functional groups ( these are species that feed in a similar way/share similar characteristics). An organism may even feed in completely different ways at different stages of its life cycle. The members of the food web can be classified into different levels (e.g. producers, consumers, and decomposers). The separation of each group is not complete. Some species of algae may be heterotrophic for periods of time if sufficient organic nutrients are available, and some predatory species may be scavengers for periods of time.
Lake : 'standing water is a body of stagnant water in the depressions of land, closed on all sides and not in direct communication with the sea. A lake is a standing body of water in which the open water surface is dominant, with vegetation confined to a narrow coastal area." (Padisák 2005) In wetlands, the entire area may be covered with reed or other riparian vegetation. In geological, or geodetic terms, a pond is a body of water with a horizontal surface, without flowing water induced by gravity.
Turbidity: floating (undissolved) substances in water reduce the transparency of clear water. The degree of this process is called turbidity. In the case of Lake Balaton, turbidity may be increased by sediment stirred up by waves or by small lime crystals precipitated as carbon dioxide is absorbed from the water during photosynthesis of algae. Turbidity alone does not necessarily mean poor water quality, but it can also be caused by algal mass production, as the amount of algae also increases turbidity.
Floatingisland vegetation: a reed bed where water goes to a greater depth beneath the sediment (soil) bound by floating roots near the water surface. The rhizomes and the organic matter bound to them float on top of the water, following changes in water level.
Floating-leaved aquatic plants: plants whose leaves float on top of the water but whose stems do not rise above the surface. They may be rooted in the sediment (e.g. Alba water lily (Nymphea alba), yellow water lily (Nuphar lutea)) or directly in the water - frogweed (Lemna spp.), water caltrop (Trapa natans), water pineapple (Stratiotes aloides)) - the latter occurring in more nutrient-rich waters. They typically occur in sheltered, gently undulating areas.
Urban heat island: densely built-up areas are warmer than green areas in winter and summer. Plants cool their surroundings by evaporation and shading, while paved surfaces heat up, reflecting and storing the sun's heat. In summer, in hot sunshine, paved/concrete areas can be up to ten degrees warmer than nearby vegetation. As part of climate change adaptation, the use of uniform, easily heated paved surfaces should be reduced as much as possible (e.g. by creating green spaces, shade arbours, tree plantations in cities, or even by installing solar panels over parking lots).
Water level: the elevation of the water surface above sea level. The water level of a lake or river can be measured using a water gauge. A water gauge is a stationary vertical measuring device (a bar or column graduated in centimetres) whose height is known in relation to the national elevation network. The 0 point of the water gauges is marked and levelled based on the knowledge of common water level conditions, but the water level does not characterise the average depth of the water body. The water level is the current elevation of the water surface relative to the water gauge. The water level can be negative if the water surface elevation falls below the 0 point of the gauge (which is 103.41 m above the average level of the Baltic Sea for Lake Balaton). The water level of Lake Balaton is usually expressed in centimetres relative to the 0 point of the water level gauge at Siofok. Typically, the water level is around 100 cm, at which point the average depth of the lake is 3.3 m, while at 0 cm the average depth is 2.3 m. Important measures of water level are the annual minimum, maximum and average water levels, as well as the daily, monthly and annual fluctuations, as well as the difference between the minimum and maximum of a given period.
Wet meadow: grassland with species composition and growth determined by good water availability or even occasionally flooding. Wet meadows are the most species-rich habitats around Lake Balaton. They generally develop on relatively nutrient-poor soils - nutrient-rich soils are more likely to have tall-stalk vegetation.
Water level regulation: the water level of many lakes is controlled by the amount of water entering and leaving the lake, usually by the use of sluices. In the case of Lake Balaton, only the amount of water flowing out is controlled by sluice gates. Regulation is usually done by setting a maximum permissible level. If the water level is higher than the maximum allowed level, the sluice is opened to lower the water level. If the level is lower, the sluice is closed. Water levels are naturally influenced (water balance) by the weather, therefore different water level regimesshould be expected as the climate changes. On Lake Balaton, the frequency of years with negative natural water balance will increase, that is, the water level of the lake will decrease more often from one year to the next even without draining. The current water level regulation regime of Lake Balaton is described in the Fejér County Emergency Management Directorate's Authority Department’s decision No: 35700/9132-14/2018 as follows:
The water level of Lake Balaton shall be controlled by the water level control device system in such a way that the daily average water level of Lake Balaton does not exceed the upper control line values specified in the table below, taking into account the application of the linear interpolation rule.
The water level specified in the table is the upper regulatory water level on the first day of the month. The water level data between two specified values, and thus the continuous upper control line, shall be formed by linear interpolation.
Regulation levels of Lake Balaton raised by 10 cm from the start of the trial period
Wetland habitat: an area of intermittent water cover, with vegetation that may consist of reedbeds, grass (sedge), grassland (water-covered grassland) or woody (alder, shrubs, grove forest/gallery forest) species. They are ecologically very valuable habitats in many respects (rich in species, purifying, regulating water), but are difficult to delineate and map because of their variable extent and character.
Catchment area: the surface catchment area of a water body (lake, river) is the area from which water enters the water body directly or via other rivers, i.e. the area from which the water body can be accessed by moving continuously downstream. The catchment areas are separated by drainage divides (usually ridges or hills).
Water balance: the amount of water in a water body (lake, river) is determined by the balance of water entering the body through inflows, leaving through outflows (if any), falling on the water surface through precipitation, leaving through evaporation, exchanging with groundwater, and withdrawals for human use. If more water enters the lake than leaves it, the water balance is positive, and if more water is currently leaving the lake than entering, the water balance is negative. A positive water balance increases the amount of water in the body and thus the water level, a negative water balance decreases the water level.
Dredged material disposal site: an area used to deposit sediment removed by dredging. On Lake Balaton, since the 1980s, attempts have been made to remove the most phosphorus-rich upper layer of sediment by dredging (scraping off only the top 20 centimetres approximately) and by digging sediment traps, i.e. pits dug into the bed to collect the top layer of sediment through natural movement by water currents.The high water content made it difficult to transport the excavated sludge, so it had to be deposited as close to the lake as possible. For this purpose, undeveloped waterfront sites (typically reedbeds, shore woodland, marshes) were designated, where a low dike was built to isolate an area where the sludge was pumped into. This led to the loss of local habitats. The creation of these disposal sites has caused the most significant loss of area to the natural riparian vegetation of Lake Balaton in the last 50 years. The abandoned dredged material sites are slowly being reclaimed by vegetation, but this vegetation is less rich in species than the original, in some cases forest, in other cases reedbeds or invasive plant stands. These semi-natural areas can be important elements of the habitat network.
Zoobenthos: animals living on the sediment surface, feeding on plankton or organic debris, with limited ability to move independently. Typically molluscs, insect larvae, worms.
Zooplankton: a collection of small animals (a few millimetres or less) floating in the water with limited ability to swim. Their movements cannot counteract the drifting effect of currents, but they do occasionally perform a characteristic diurnal vertical migration in the water. Filter feeder zooplankton typically collect on algae, bacteria or suspended organic matter in the water. Some species are predatory and can move surprisingly fast. Zooplankton are an important food source for the offspring of many fish species, but many fish also consume them as mature individuals. Typical representatives are microscopic crustaceans (freshwater crustaceans, e.g. Eudiaptomus spp., Daphnia spp.), rotifers (Rotatoria) and some mollusc larvae.