Sedge-grass Marsh Research Articles

Addressing Effects of Environment on Eddy-Covariance Flux Estimates at a Temperate Sedge-Grass Marsh

We examined the net-ecosystem-exchange (NEE)-based annual carbon-balance estimates obtained from eddy-covariance (EC) measurements at an unmanaged sedge-grass marsh ecosystem (Třeboň, Czech Republic, 49°1′ N, 14°46′ E), seeking methods to improve the EC measurements in inhomogeneous environment. The data filtering procedure was developed using three thresholds: (a) a stationarity test; (b) a stability {u}_{*}-threshold; and (c) a high relative humidity RH-threshold. This procedure was tested in 2014, a year without significant floods and drought events led to a stable water table, reducing the effect of soil respiration on the EC measurements. Estimates of annual carbon-balance were reduced from 182 to 234 ± 12 gC m−2 year−1 for the initial data to 39–44 ± 8 gC m−2 year−1 after the RH ≤ 95% filtering and to 24–26 ± 7 gC m−2 year−1 after the further {u}_{*} ≥ 0.1 m s−1 filtering. Applying the precipitation/fog threshold reduced this balance to 10–12 ± 7 gC m−2 year−1, closer to carbon neutrality. Up to 9.5% of this identified shift occurred during apparent nocturnal downslope katabatic drainage flows or plume descent coming from the nearby town of Třeboň. High-RH conditions account for up to 27% of this shift. Moreover, both conditions together account for an additional 67% of the identified carbon-balance change. Removing these non-ecosystem-related processes brings EC measurements closer to values of an unmanaged-ecosystem productivity, providing a better NEE-based estimate for the net ecosystem production. The presented procedure is applicable to EC measurements conducted at different wetlands or terrestrial ecosystems with similar conditions.

Photosynthetic parameters of a sedge-grass marsh as a big-leaf: effect of plant species composition

The study estimates the parameters of the photosynthesis–irradiance relationship (PN/I) of a sedge-grass marsh (Czech Republic, Europe), represented as an active “green” surface—a hypothetical “big-leaf”. Photosynthetic parameters of the “big-leaf” are based on in situ measurements of the leaf PN/I curves of the dominant plant species. The non-rectangular hyperbola was selected as the best model for fitting the PN/I relationships. The plant species had different parameters of this relationship. The highest light-saturated rate of photosynthesis (Asat) was recorded for Glyceria maxima and Acorus calamus followed by Carex acuta and Phalaris arundinacea. The lowest Asat was recorded for Calamagrostis canescens. The parameters of the PN/I relationship were calculated also for different growth periods. The highest Asat was calculated for the spring period followed by the summer and autumn periods. The effect of the species composition of the local plant community on the photosynthetic parameters of the “big-leaf” was addressed by introducing both real (recorded) and hypothetical species compositions corresponding to “wet” and “dry” hydrological conditions. We can conclude that the species composition (or diversity) is essential for reaching a high Asat of the “big-leaf ”representing the sedge-grass marsh in different growth periods.

Extreme precipitation and long-term precipitation changes in a Central European sedge-grass marsh in the context of flood occurrence

ABSTRACTThis study offers a detailed analysis of the extreme precipitation and long-term precipitation changes in a sedge-grass marsh in the “Wet Meadows” area in the Czech Republic (Central Europe) in the context of flood occurrence. Namely, trends in annual maxima of daily precipitation and trends in the occurrence and amount of rainfall are investigated. The analysis is based on daily measurements of precipitation from 1977 to 2015. We found out that extreme precipitation has become significantly more frequent in recent years, and there are also other significant changes in the rainfall distribution. Possible negative effects on the wetland can be linked to a change of carbon exchange between the ecosystem and the atmosphere and a change of biodiversity. Awareness of these changes is necessary for possible positive human intervention when a desirable wetland functioning is threatened.

Entropy based statistical inference for methane emissions released from wetland

We concentrate on the paradigm question how much stochasticity and how much chaos are present in the methane emission model. In particular we analyze the residua from the process of methane emissions from wetlands in the sedge-grass marsh, in South Bohemia, Czech Republic. Relation to entropy and a specific version of Kullback–Leibler divergence will be given. A graphical tool to assess the amount of entropy in the system is developed and illustrated on real data from the sedge-grass marsh methane emission.

Microergodicity effects on ebullition of methane modelled by Mixed Poisson process with Pareto mixing variable

We model the process of exceedences of the ebullition of methane from wetlands in the sedge–grass marsh, South Bohemia, Czech Republic by a Mixed Poisson process with mixing variable that is Pareto distributed. We investigate the properties of this process and describe it as a particular case of a counting process. We define Mixed Poisson Pareto random variable, Exponential–Pareto and Erlang–Pareto distributions and investigate their properties.

Modeling methane emission via the infinite moving average process

The aim of this paper is to provide guidelines for the statistically efficient estimation of the methane emission in the sedge-grass marsh, South Bohemia, Czech Republic. Such a study is important for a better understanding of the rate and dynamics of methane emissions from wetland ecosystems, and in particular to build a model of local methane flux. We have modeled a time series of the data via an infinite moving average process with Pareto tails of the exceedances. To assure the consistency of such an estimator, we have used both Hill and t-Hill estimators. We have provided proof of the weak consistency of the t-Hill estimator in the case of dependent data. This estimator has a simple form and it provides a nice trade-off between efficiency and robustness. Finally, we have presented a discussion on its robustness.

Fluctuating water table affects gross ecosystem production and gross radiation use efficiency in a sedge-grass marsh

The eddy covariance method was used for continuous measurement of the seasonal courses of the following parameters of the carbon cycle in a sedge-grass marsh type of wetland ecosystem (49°01′29″N, 14°46′13″E, South Bohemia, Czech Republic, Central Europe): gross ecosystem production (GEP), net ecosystem production (NEP) and ecosystem respiration. During a 3-year series of measurements, we recorded marked fluctuations of the water table, which affected the overall water regime of the wetland studied. Between-year differences in the water regime strongly influenced the total annual carbon sequestration. The lowest annual GEP and NEP of 996 and 152 g m−2 of carbon, respectively, were recorded in 2006, a year with two large floods, one in the spring, the other in the summer. By contrast, in the dry year of 2007, with no flood, the highest annual GEP and NEP were recorded: 1,328 and 274 g m−2, respectively. Significant differences were found in the efficiency of solar energy use for GEP [gross radiation use efficiency, GRUE = GEP/PhAR (photosynthetically active radiation), i.e., amount of carbon gained per energy unit]. The highest GRUE was recorded immediately after the 2006 summer flood. In 2007, the GRUE decreased linearly with rising water table. A variable water regime thus markedly affects the processes of carbon accumulation and the efficiency of solar energy use for organic matter production in freshwater wetlands of the sedge-grass marsh type.

Influence of summer flood on the net ecosystem exchange of CO 2 in a temperate sedge-grass marsh

Characteristics of CO 2–C exchange were studied in a temperate herbaceous wetland in 2006 and 2007, years with contrasting hydrological regimes. The wetland Mokré Louky (the “Wet Meadows” near Třeboň), Czech Republic (49°01′30″ N, 14°46′20″ E) is a sedge-grass marsh dominated by Carex acuta L. The site is situated in the inundation area of a large human-made lake (Rožmberk fishpond, 5 km 2). The water table is near the soil surface and is fairly stable throughout the year (±0.1 m), except for flood events, when it can reach up to 2 m above the soil surface. Net ecosystem production (NEP) was calculated from the CO 2 fluxes measured by the eddy-covariance technique and was compared with the seasonal course of plant live aboveground biomass. The results show that: (1) the annual net uptake of CO 2–C was 199 and 220 g C m −1 yr −1 in 2006 and 2007, respectively. The daily net CO 2–C uptake reached 12–20 g C m −2 day −1 in sunny summer days. These values are among the highest values reported for wetlands of the northern hemisphere. (2) Although the observed wetland is adapted to floods, the summer flood substantially reduced its net CO 2–C uptake. The daily courses of net CO 2–C uptake point to reduced rates of CO 2–C fixation by the vegetation cover. (3) A recovery growth of plant biomass was associated with a second peak of NEP in September 2006. (4) Lack of knowledge on the dynamics of methane emissions presently limits deeper understanding of the effect of floods on carbon balance in wetlands.

Phenology and growth of Dermocybe uliginosa in a willow carr. I. Phenology of fruiting

The onset of fruiting by Dermocybe uliginosa was studied in a willow carr surrounded by a sedge-grass marsh. The seasonal courses of various micrometeorological factors, monitored for 10 yr, were analysed as to their importance in relation to the initiation and intensity of fruiting. The regime of soil temperature at 0·05 m depth (Ts), daily minimum temperature above the soil surface (Tmin) and water-vapour pressure (e) were found to control the initiation of fruiting. Ts must attain, at least, 12·5 °C. A fall of Tmin betw I and about 5·5° for one or two days during this time was an additional stimulus to the initiation of fruiting. A decrease or increase of e for 10–20 d immediately afterwards determined whether fruit bodies were abundant or scarce.

Patterns of temperature and humidity in wetland biotopes

Less predictable hydrological changes in the catchment area, superimposed on the general climatic seasonality, affect the distribution and stratification of temperature in central European wetlands. Long-term observations in sedge-grass marsh, willow carr and shallow water bodies in Czechoslovakia suggest an efficient role of life forms, geometry of vegetation and dead litter in the seasonal and diurnal course of temperature.

Evapotranspiration of a willow carr in summer

The daily course of evapotranspiration ( E) in a willow carr (stand of Salix cinerea L. and Salix pentandra L.) was calculated from meteorological data for 3 months (July–September 1983) by the Bowen-ratio method, and compared with evapotranspiration of the surrounding sedge-grass marsh ( Carex gracilis Curt., Calamagrostis canescens (Weber) Roth and Glyceria maxima (Hartm.) Holmberg evaluated in the previous years by the same method. A considerable difference was found only for July, which was extremely hot in 1983. The daily average E was 4.8, 3.2 and 2.4 mm day −1, in July, August and September, respectively. The enhancement or reduction of E under non-neutral air stability conditions were less than 10% of E under air stability conditions. Calculation of E for non-neutral air stratification is discussed in the paper.

Heat balance components and evapotranspiration from a sedge-grass marsh

Daily course of heat balance components (sensible heat, latent heat of evaporation and ground heat fluxes) and evapotranspiration were computed from meterological data recorded in a sedge-grass marsh in South Bohemia, Czechoslovakia. Bowen-ratio method and tank measurements were used, and several comparisons made with parallel aerodynamic measurements. Two simplified empirical formulae for calculating evapotranspiration are suggested: one based on net radiation, the other based on net radiation and on the difference between the mean relative air humidities at the upper and lower levels of the boundary layer above the stand. The seasonal courses and totals of heat-balance components and evapotranspiration obtained in three years (1977 to 1979) are compared and discussed.

Xylem water flow in a crack willow tree (Salix fragilis L.) in relation to diurnal changes of environment.

The diurnal course of the xylem water flow in a solitary Salix fragilis L. tree in a wet grassland was measured using the tissue heat-balance method. There was considerable variation due to meteorological factors. Maximum flow rate was 0.4 kg h-1 m-2 of crown projection area, or 5.9 kg h-1 kg-1 leaf dry weight. The daily total was 2.4 kg m-2 day-1 or 36 kg kg-1 day-1. Water flow decreased immediately at the tree base and at the branches after start of rain, and in a branch, after cutting it off: the time constant of the system was 600-700 s in both cases. The part of the crown oriented to the sun transpired up to ten times as much as the shaded part. Over 70% of the total cross-sectional area of the conductive xylem vessels of the trunk was used by the transpiration flow. The water content of the trunk tracked the diurnal changes of the xylem water flow rate with a short time-lag. During the day, 1% of the trunk volume was temporarily exploited as water reserve, an amount equalling 3% of daily water loss. The stereometric configuration of the crown significantly influenced its water loss. During the summer period, about 33 mature (polycormic) trees per ha may drain 100% of water consumed by the present-day sedge-grass marsh.

The Daily and Seasonal Course of Evapotranspiration from a Central European Sedge-Grass Marsh

(1) Evapotranspiration from a marshy meadow in southern Bohemia, Czechoslovakia, was determined over the period April to November 1977, by measuring water losses from a tank installed within the area and planted with the local vegetation. (2) Simultaneously, heat balance components were calculated by the Bowenratio method from climatic data recorded at hourly intervals on each day during the measurement period. (3) The daily, weekly and monthly course of the heat-balance components and their totals are given. (4) Mean daily evapotranspiration during the period of measurement was 2.6 mm, and the maximum daily value in summer was 6.5 mm.