Kis-Balaton Wetland Research Articles

Carbon dioxide emission and its impacting factor from goldenrod (Solidago canadensis) and bulrush (Typha angustifolia) decomposition during the winter period

Leaf litter decomposition in solution is an important part of the carbon cycle. When leaf litter is deposited in water, the decomposition process takes place, releasing carbon dioxide into the atmosphere. In Hungary, the goldenrod and bulrush are spreading over increasing areas along lakes and rivers, including the shores of Lake Balaton. The primary role of the Kis-Balaton wetland is to retain inorganic nutrients, thereby improving the water quality of Lake Balaton. As the water movement in this area is not very intensive and the water retention time is long, carbon dioxide emissions of parts of decomposing plants can be higher in this area. We set up a microcosm experiment in a climate chamber to determine the carbon dioxide emissions from the decomposition of goldenrod and bulrush leaves and stems in winter when information about the process is limited. Due to short investigation time, the difference in the impact of temperatures on decomposition of the studied plants was restricted to leaves only. In the study, significant difference was obtained for the plant species and the plant parts. The carbon dioxide increments ranged from 46.7 (p<0.001) to 54.5% (p<0.001) in every plant treatment related to control one. Changes in water temperature are reflected in carbon dioxide release with a minor time delay. The results showed that the decomposition of plant parts in water during winter contributes to the increase of carbon dioxide emissions from shallow water bodies, such as the Kis-Balaton wetland.

Impacts of wintertime meteorological variables on decomposition of Phragmites australis and Solidago canadensis in the Balaton System

A field experiment was carried out in plant litter decomposition at three sites of the Balaton System (Balaton — Kis Balaton wetland — Zala Mouth) differing in their environment type during winter 2019/2020. The largest freshwater shallow lake in Central Europe (Carpathian Basin) is the Balaton, with a surface area of about 600 km2 and an average depth of 3.25 m. Right around the lake, a nutrient filtering system, the Kis-Balaton wetland, is functioning to avoid water deterioration and eutrophication. The aim of the study was to investigate crop-weather relations in two sample species, the widely distributed native P. australis and the allied S. canadensis incubated beneath the water using leaf-bag technique to characterise plant organ decomposition. Based on our results, the most consistent meteorological variable regarding decomposition process was global radiation (r = − 0.62* to − 0.91**; r: correlation coefficient; * and ** mean that correlations are significant at the 0.05 and 0.01 levels), in each treatment. In modelling the decomposition process, out of eight meteorological variables, only the daily mean air temperatures and humidity were excluded from regression equations. On dominatingly windy days, with the increase in water temperature of the Zala Mouth, the sensitivity of the decomposition of S. canadensis litter tended to decrease as compared to P. australis. The remaining litter masses were in a Kis-Balaton > Balaton > Zala order, contrasting the water temperature gradient that decreased from the Zala to the Kis-Balaton wetland under wind-dominated conditions. Considering all sampling places in three aquatic ecosystems, there was a 2.2 and a 2.7% daily mean detritus mass loss in P. australis and S. canadensis, respectively. We concluded that the invasive S. canadensis litter decomposed more quickly than those of native P. australis, irrespective to sampling site. Increase in winter water temperature significantly promoted the litter decomposition of both plant species. The originality of the study is that it quantifies the litter decomposition for an Eastern European wetland, during wintertime.

Evapotranspiration estimation at the Kis-Balaton wetland

Evapotranspiration rate, ETaand vegetation composition strongly influence the water budget of wetland impacting available water and water resource management. One of the goals of this study was to estimate the areal ETa of the Kis-Balaton wetland, KBW (natural ecosystem) between 1997 and 2012. This time period was free of any human intervention. ETa was accounted for different vegetation classes through the multiplication of the reference evapotranspiration, ET0 by previously determined crop coefficients in each vegetation/open water classes. Besides common reed and cattail, five other groups were separated, including open water as an independent class. The evapotranspiration sums were strongly impacted by annual mean air temperature, Ta. One degree increment in annual average Ta will increase the yearly ETa sums in about 100 mm. The yearly areal ETaof KBW ranged from 737.08 mm to 896.63 mm with an average of 802.07 mm during the 16-year study.

Lessons Learnt from the Long-Term Management of a Large (Re)constructed Wetland, the Kis-Balaton Protection System (Hungary)

Environmental management decisions should be made based on solid scientific evidence that relies on monitoring and modeling. In practice, changing economic, societal, and political boundary conditions often interfere with management during large, long, and complex projects. The result may be a sub-optimal development path that may finally diverge from the original intentions and be economically or technically ineffective. Nevertheless, unforeseen benefits may be created in the end. The Kis-Balaton wetland system is a typical illustration of such a case. Despite tremendous investments and huge efforts put in monitoring and modeling, the sequence of decisions during implementation can hardly be considered optimal. We use a catchment model and a basic water quality model to coherently review the impacts of management decisions during the 30-year history. Due to the complexity of the system, science mostly excelled in finding explanations for observed changes after the event instead of predicting the impacts of management measures a priori. In parallel, the political setting and sectoral authorities experienced rearrangements during system implementation. Despite being expensive as a water quality management investment originally targeting nutrient removal, the Kis-Balaton wetland system created a huge ecological asset, and thereby became worth the price.

Investigation of the decomposition and leaching dynamics of Salix, Populus and mixed leaves in the area of Lake Balaton and Kis-Balaton Wetland

In lakes and wetlands, leaf litter input from the coastal vegetation represents a major nutrient load and plays a basic structural and functional role in several ecosystems. In Hungary, at the banks of lakes and wetlands, Salix and Populus trees are the most common species. In an experiment in Lake Balaton and Kis-Balaton Wetland between 16 November 2017 to and 3 June 2018, the decomposition rates and leaching dynamics of Salix, Populus and mixed leaves (50% Salix and 50% Populus) were investigated. Total nitrogen and phosphorus content of biomass samples were measured at the beginning and end of the experiment for the leaching dynamics experiment. We found that litter mass losses (Salix, Populus and mixed leaves) were not significantly different between the two mesh size litterbags and between Lake Balaton and Kis-Balaton Wetland. Different amounts of the total nitrogen and phosphorus leaching from Salix, Populus and mixed leaves were detected. The total nitrogen contents of the plant samples were around 8-18% at the end of the investigated period. Slightly higher values were measured compared to phosphorous (27-29%).

Investigation of Salix alba and Populus tremula leaf litter decomposition in the area of Lake Balaton and Kis-Balaton Wetland

Plant litter decomposition in inland waters contributes significantly to nutrient load, particularly in still waters, such as shallow lakes and wetlands. The decomposition rates of Salix alba and Populus tremula leaf litter was examined in Lake Balaton and Kis-Balaton Wetland, using litter bag technique. Leaf litter was incubated in small (ᴓ=3 mm) and large (ᴓ=900 μm) mesh size bags for the assessment of the relative contribution of macroinvertebrates to leaf litter decomposition. Dry mass, exponential decay coefficient and chemical parameters of water (pH, conductivity, NH4 +, NO3 -, SO4 2-, PO4 3-, Cl-) were determined. Leaf mass loss showed negative exponential pattern during the 168 days of the decomposition period. Leaf litter mass loss generally did not differ between the small and large mesh sizes, suggesting that macroinvertebrates generally have a negligible role in leaf decomposition in the winter period.

Spatio-seasonal variability of chromophoric dissolved organic matter absorption and responses to photobleaching in a large shallow temperate lake

Abstract. The development and validation of remote-sensing-based approaches for the retrieval of chromophoric dissolved organic matter (CDOM) concentrations requires a comprehensive understanding of the sources and magnitude of variability in the optical properties of dissolved material within lakes. In this study, spatial and seasonal variability in concentration and composition of CDOM and the origin of its variation was studied in Lake Balaton (Hungary), a large temperate shallow lake in central Europe. In addition, we investigated the effect of photobleaching on the optical properties of CDOM through in-lake incubation experiments. There was marked variability throughout the year in CDOM absorption in Lake Balaton (aCDOM(440) = 0. 06–9.01 m−1). The highest values were consistently observed at the mouth of the main inflow (Zala River), which drains humic-rich material from the adjoining Kis-Balaton wetland, but CDOM absorption decreased rapidly towards the east where it was consistently lower and less variable than in the westernmost lake basins. The spectral slope parameter for the interval of 350–500 nm (SCDOM(350–500)) was more variable with increasing distance from the inflow (observed range 0.0161–0.0181 nm−1 for the mouth of the main inflow and 0.0158–0.0300 nm−1 for waters closer to the outflow). However, spatial variation in SCDOM was more constant exhibiting a negative correlation with aCDOM(440). Dissolved organic carbon (DOC) was strongly positively correlated with aCDOM(440) and followed a similar seasonal trend but it demonstrated more variability than either aCDOM or SCDOM with distance through the system. Photobleaching resulting from a 7-day exposure to natural solar UV radiation resulted in a marked decrease in allochthonous CDOM absorption (7.04 to 3.36 m−1, 42 % decrease). Photodegradation also resulted in an increase in the spectral slope coefficient of dissolved material.

Practical use of Phragmites australis to study evapotranspiration in a wetland zone of Lake Balaton (southwest Hungary)

In the present study, evapotranspiration (ET) data from a common reed-dominated wetland and its meteorological controls was analysed using measured ET (ET m) in compensation evapotranspirometers. Six seasons in the time period between 2003 and 2012 were assessed with the objective of converting theoretical observations into long-term practical use. They reveal the effects of annual fluctuations and allow for a more exact understanding of the results of ET losses, which remain an elusive and substantial part of the hydrologic budget particularly in wetland habitats. Daily measured ET rates were strongly influenced by weather variables causing considerable variation of ET characteristics between the two distinguished season types. The results of multiple stepwise regression analysis showed that the major meteorological elements impacting the sum of seasonal ET was much higher in the warm growing seasons (857 mm), due to increased available energy for ET, than in the cool season (385 mm). The sum of average ET totalled 778.6 mm over measurements. A simplified water budget analysis confirmed that adequate water volume, caused by precipitation, entered the Kis-Balaton wetland (KBW) area during the cool season. Conversely, in warm seasons, only 21.5 % of total ET resulted from rainfall, accentuating its seasonality in wetland. This information about annual variability of long-term ET values would assist in finding an ideal solution for determining the proper water level needed. The current balance of habitat types in wetland should be permanently assessed by selection of the suitable water level in order to sustain the most appropriate wetland ecological conditions.

A rule-based approach for mapping macrophyte communities using multi-temporal aquatic vegetation indices

Abstract Macrophytes are important components of freshwater ecosystems, playing a relevant role in carbon and nutrient cycles. Notwithstanding their widespread diffusion in temperate to subtropical shallow lakes, little effort has been performed so far in extensively mapping macrophyte communities at regional to continental scale. A rule-based classification scheme was implemented for mapping four macrophyte community types (helophyte, emergent rhizophyte, floating, and submerged-floating association). Input features were selected among multi-spectral reflectance and multi-temporal vegetation indices, based on Landsat data acquired over four test sites: Lake Taihu (China), Kis-Balaton wetland (Hungary), Lake Trasimeno and Mantua Lakes system (Italy). The best performing features were derived from Water Adjusted Vegetation Index (WAVI) computed at: early spring, maximum growth, and late autumn conditions. Overall accuracy (OA) and Kappa coefficient (k) of macrophyte maps produced with our approach over the ensemble of four sites were 90.1% and 0.865, respectively, with best performance in European temperate areas (OA = 93.6–94.2%, k = 0.887–0.916), and lower scores for subtropical Lake Taihu (OA = 82.8%, k = 0.762). Per-class accuracies were higher than 80% for all target classes, except for the submerged-floating association, with misclassifications concentrated in Taihu site. The robustness of the approach was tested over two independent validation cases: a different site (i.e. Lake Varese, Italy), and a different input dataset (i.e. AVNIR-2 data, for Mantua Lakes system). Consistent accuracy results were achieved: OA = 94.3% (k = 0.922) and OA = 85.6% (k = 0.766), with some misclassification due to spatial resolution of AVNIR-2 data.

Regional evapotranspiration from a wetland in Central Europe, in a 16-year period without human intervention

Regional evapotranspiration (ET) for Fenéki “Pond” (FP, Kis-Balaton wetland, Hungary) was estimated using weighted canopy areas of five macrophyte classes and open water over an uninterrupted period without any human intervention between 1997 and 2012. In addition to the dominant common reed (Phragmites australis), the cover ratio of the other four plant groups and open water was monitored. The different cover categories of the wetland were separated using images with surface interpretation using the maximum likelihood classification method. Although the annual cover ratio for any class only changed slightly by 1–2%, this wetland was not considered to be in equilibrium, since species turnover (sedge-grass) was observed during this study. Reference ET was calculated by the widely accepted Penman–Monteith (FAO-56) formula from the data of a nearby climate station. Of the five macrophyte classes studied, crop coefficients (as the ratio of measured and reference ET) of three groups were measured locally with a lysimeter. To process the 16-year long ET time series, the means of six-season long Kc values were applied. As the open water of FP was frequently covered by seaweed (Ceratophyllumdemersum), a special evaporation (E) was defined using seaweed settled “A” pans. Compared to evaporation of standard “A” pan, the seasonal average evaporation was 7% higher in “A” pans containing seaweed (C.demersum). Annual and seasonal mean ET totals fluctuated depending on environmental conditions (air temperature) and the type of macrophyte. The range of macrophytes’ 16-year annual mean ET varied from 876.8±54.58mm year−1 (dominant common reed) to 662.8±41.57mm year−1 (woody deciduous, Salix fragilis, Alnus glutinosa, Populus tremula) with a weighting average of 802.1±50.4mm year−1 for the regional ET of FP. The average winter ET sum was 17.1±1.19% with a range of 15.7±1.09–20.7±1.43% for common reed and woody deciduous, respectively. The annual mean ET totals were highly correlated with mean daily ET rates of different macrophyte classes. Seasonal daily average ET rates of different macrophyte classes varied between 4.0±0.26mm day−1 and 2.9±0.19mm day−1 in common reed and woody deciduous, respectively. The long-term weighted daily mean ET rate for FP was 3.6±0.24mm day−1. The highest ET/E ratio of 1.09 was for common reed, in an agreement with previous observations, but was lowest in woody deciduous (0.81). In addition to classic statistical approaches, monthly ET data were also used for modeling purposes (ARIMA models). The projected monthly regional ET values supported earlier observed seasonal patterns likely due to peculiarities in wetland water supply. Instead of exclusively using dominant species to estimate regional ET, more accurate results were possible by extending the ET approach to include several macrophyte species. Neglecting the smaller-scale differences in macrophyte, ET could cause more than a 10% overestimation in the regional ET sum. The SARIMA(1,0,0)(0,1,1)12 model contributed positively to the existing information about the ET of the study site. The projected monthly regional ET values retained the earlier observed seasonal pattern until 2020.

Analysis of long-term water quality changes in the Kis-Balaton Water Protection System with time series-, cluster analysis and Wilks’ lambda distribution

Lake Balaton is the largest shallow freshwater lake in Central Europe. Its water quality is mainly affected by the supplying rivers and other water sources. The primary source is the Zala River. Its water used to be filtered by the Kis-Balaton Wetland (KBW) before entering Lake Balaton. During the nineteenth century, as a result of artificial water level modifications, the KBW disappeared and the Zala River's waters became partially unfiltered. It is for this reason that the Kis-Balaton Water Protection System (KBWPS) had to be constructed as a mitigation wetland. The aim of the study is to examine the available physical, chemical and biological parameters to get a more comprehensive picture of the processes evolving in the functioning of the KBWPS, and to make suggestions concerning the management and preservation of the system's wetland habitat. The central concept of the present study was to group the sampling points of the KBWPS and to determine which parameters had the greatest effect on the groups, and where. Multivariate data analysis was applied to the data concerning 25 chemical, biological and physical parameters for the time period 1984–2008 from 13 monitoring stations. The sampling locations were clustered then grouped. The groups were formed annually. The change of alignment of similar sampling points shows how the border between the determining groups (covering the eutrophic pond and wetland habitats) changed over the years. This change followed the transition from macrophyte vegetation to an open water area which took place as a result of the water level being kept artificially constant, and which did not therefore follow the weather conditions (rain, drought, etc.). Using Wilks’ λ distribution it was possible to determine that the parameters responsible for eutrophication were primarily responsible for forming the groups of the sampling points. The next most important factors determining the groups were the variables in close relation with the parameters characteristic of eutrophication. The inorganic chemical components affected the conformation of the groups the least. Finally, by examining the phosphorous forms and chlorophyll-a we tried to show the milestones in the history of the mitigation wetland, the KBWPS. The result of this research was that it points out changes in the KBWPS over a long time period, which had not been done previously. This research could hopefully help scientists to gain a broader perspective on processes evolving in the KBWPS. When it comes to finishing the second phase of the reservoir system, more knowledge will be available on what can be expected regarding the quality of the water entering Lake Balaton, and the conservation of the nature preserve wetland area.

Morlet wavelet and autocorrelation analysis of long-term data series of the Kis-Balaton water protection system (KBWPS)

Lake Balaton is the largest shallow freshwater lake in Central Europe. Its water quality is mainly affected by the supplying rivers and other water sources. The primary source is the Zala River. The water of this river used to be filtered by the Kis-Balaton wetland (KBW) before entering Lake Balaton at Keszthely Bay. In the course of the nineteenth century, water level modifications at KBW shrank and it lost its full capacity to function as a filter for the Zala's waters, so the nutrient load of Lake Balaton greatly increased, and its water quality started to deteriorate. This is the reason an artificial extended wetland called the Kis-Balaton water protection system (KBWPS) had to be constructed–to retain the inorganic nutrients at the mouth of the Zala River and stop the further degradation of Balaton's water quality. In this study, Morlet wavelet spectrum (periodicity) analysis and autocorrelation (memory) analysis were used with weekly chemical, biological and physical data for the KBWPS for the period 1993–2007. We compared the periodicity and the memory of the parameters in the two different habitats of the KBWPS and the Zala River. We also analyzed the tracking capability of the periodical seasons of the two phases (the complete Phase I, and the incomplete Phase II) and the river. The results showed that the incomplete Phase II is unable to conserve the periodicity and sustain long memory because of the shading provided by the macrophyte cover and the extra inflows. In conclusion, we were able to point out the dependence of the system's processes on temperature and climate conditions with methods that have not yet been used for this kind of purpose.

Transition from shallow lake to a wetland: a multi-proxy case study in Zalavári Pond, Lake Balaton, Hungary

Lake Balaton, the largest shallow lake in Central Europe, has no natural outlet, therefore, underwent water level changes during its 15,000–17,000 years of history. The lake is very sensitive to both climate changes and human impacts. Surroundings have been inhabited since the Stone Age; however, heavy human impact can be recognized during the past 6000 years. In this study, we established three different stages for and reconstructed water level changes of Lake Balaton by geochemical data, subfossil Cladocera and diatom remains in the sediments of the Zalavari Pond, a part of the Kis-Balaton wetland. In 9900–8600 cal. year BP, climate was dry, water level was low, and there was a wetland in this area. Although organic matter content was low in the sediment, the ratio of Fe/Mn was high. Between 5600 and 5000 cal. year BP, water level increased, Fe/Mn ratio shows that oxygen conditions of sediments was improved in agreement with the relatively low number of diatom remains and dense chydorid remains. About 5000 cal. year BP, water level of Lake Balaton decreased as indicated by high organic content with low carbonate and high Fe/Mn ratio in the sediments (oxygen depletion). At the bottom of this section, high Fe and S concentrations showed accumulation of pyrite (FeS2) that is common in wetlands with very low redox potential. Low abundance of Cladocera remains together with rich and diverse diatom flora confirm the low water level hypothesis. Our data support that the water level of Lake Balaton was higher between 8600 and 5000 cal. year BP than it is at present.

Low levels of reserve carbohydrates in reed ( Phragmites australis) stands of Kis-Balaton, Hungary

Seasonal dynamics of concentrations of reserve carbohydrates (starch, sucrose, glucose, fructose and their sum denoted as total non-structural carbohydrates, TNC) were followed in five reed stands of Kis-Balaton wetland area in Hungary. The stands included three stands of tall and robust reed, situated in the Ingói area, and two stands of short and subtle reed situated in the downstream part. While both the seasonal pattern and the proportions of single carbohydrate species corresponded to findings for other sites, the absolute concentrations were markedly lower as compared to other European reed stands except lake Fertö in Hungary. The seasonal minimum values ranged from 54 to 87 mg g −1 dry weight. During the seasonal minimum, glucose reached the lowest concentrations (down to 0.01 mg g −1 dry weight) of all carbohydrates measured. The seasonal maximum concentrations of TNC reached 160–270 mg g −1 dry weight. Maximum TNC standing stock ranged from 240 to 520 g m −2, and was depleted by 60–80% during the period of spring shoot growth. It is proposed that the remaining TNC pool may not suffice to support complete recovery after a subsequent catastrophic event.