scholarly journals Evapotranspiration from a riparian fen wetland

2005 ◽  
Vol 36 (2) ◽  
pp. 121-135 ◽  
Author(s):  
H.E. Andersen ◽  
S. Hansen ◽  
H. E. Jensen
Keyword(s):  
Driving Forces ◽  
Radiant Energy ◽  
Vapour Pressure Deficit ◽  
Open Water ◽  
Absolute Magnitude ◽  
Growing Season ◽  
Agricultural Landscapes ◽  
Water Evaporation ◽  
Evaporative Demand ◽  
Fine Grained

Evapotranspiration rates were measured in a riparian fen wetland dominated by vascular vegetation and surrounded by open agricultural areas and forests. The wetland is situated on a floodplain in central Denmark. Measurements were taken throughout the growing season (April–September) of 1999. Evapotranspiration rates were higher than those published for most other wetland types, with an average of 3.6 mm d−1 during the growing season and a peak rate of 5.6 mm d−1. Daily average evapotranspiration was 110% of Penman's potential open water evaporation. Evapotranspiration was the dominant sink in the energy balance of the wetland studied. During the day, evapotranspiration accounted for 82% of the available radiant energy, Rn. Due to the presence of deposited fine-grained sediments, soil-water availability was kept high at all times which resulted in moderate canopy resistances, rc (overall mean =32 s m−1). Evapotranspiration was controlled by a combination of driving forces: Rn, saturation vapour pressure deficit, D, and rc. It is hypothesized that the results presented in this study are conditioned by the proximity of the wetland to drier upland areas. During periods with high evaporative demand and low precipitation, warm, dry air is formed over the upland areas and wetland evapotranspiration rates are enhanced by local advection. Indicative evidence for the hypothesis is presented. Although the absolute magnitude of the results reported is only directly relevant to similar sites in Denmark, the processes and controls described are considered to be representative of riparian wetlands subjected to frequent flooding and/or with a high groundwater table, with vascular vegetation, and which are narrow corridors in open agricultural landscapes.

Potential Evaporation – A Matter of Definition

1993 ◽  
Vol 24 (5) ◽  
pp. 359-364 ◽  
Author(s):  
Anders Lindroth
Keyword(s):  
Evaporation Rate ◽  
Vapour Pressure Deficit ◽  
Open Water ◽  
Dry Forest ◽  
Water Evaporation ◽  
Good Representation ◽  
Large Scatter ◽  
Potential Evaporation ◽  
The Difference ◽  
Forest Conditions

The aim of this paper is to discuss the concept of potential evaporation and its use in runoff models. The potential evaporation for forest is defined on basis of estimated minimum canopy resistances for a well-watered spruce forest. The difference between the Penman open water evaporation, commonly used as “potential” evaporation, and a more realistic estimate of the potential evaporation from a dry forest showed a large scatter and a systematic seasonal deviation. Part of the differences were explained by differences in vapour pressure deficit. It was also shown that the evaporation rate of a completely wet forest was typically four times higher than the rate predicted by the Penman equation. The conclusion was that Penman open water evaporation did not give a good representation of forest conditions.

scholarly journals The contribution of PIP2-type aquaporins to photosynthetic response to increased vapour pressure deficit

2021 ◽  
Author(s):  
D Israel ◽  
S Khan ◽  
C R Warren ◽  
J J Zwiazek ◽  
T M Robson
Keyword(s):  
Vapour Pressure Deficit ◽  
Air Humidity ◽  
Wild Type ◽  
Knockout Mutant ◽  
Evaporative Demand ◽  
Co2 Transport ◽  
Whole Plant ◽  
Knockout Mutants ◽  
Leaf Level ◽  
Low Humidity

Abstract The roles of different plasma membrane aquaporins (PIPs) in leaf-level gas exchange of Arabidopsis thaliana were examined using knockout mutants. Since multiple Arabidopsis PIPs are implicated in CO2 transport across cell membranes, we focused on identifying the effects of the knockout mutations on photosynthesis, and whether they are mediated through the control of stomatal conductance of water vapour (gs), mesophyll conductance of CO2 (gm) or both. We grew Arabidopsis plants in low and high humidity environments and found that the contribution of PIPs to gs was larger under low air humidity when the evaporative demand was high, whereas any effect of lacking PIP function was minimal under higher humidity. The pip2;4 knockout mutant had 44% higher gs than the wild type plants under low humidity, which in turn resulted in an increased net photosynthetic rate (Anet). We also observed a 23% increase in whole-plant transpiration (E) for this knockout mutant. The lack of functional AtPIP2;5 did not affect gs or E, but resulted in homeostasis of gm despite changes of humidity, indicating a possible role in regulating CO2 membrane permeability. CO2 transport measurements in yeast expressing AtPIP2;5 confirmed that this aquaporin is indeed permeable to CO2.

scholarly journals Eddy covariance flux measurements confirm extreme CH<sub>4</sub> emissions from a Swiss hydropower reservoir and resolve their short-term variability

2011 ◽  
Vol 8 (9) ◽  
pp. 2815-2831 ◽  
Author(s):  
W. Eugster ◽  
T. DelSontro ◽  
S. Sobek
Keyword(s):  
Greenhouse Gas ◽  
Eddy Covariance ◽  
Land Surface ◽  
Lake Level ◽  
Driving Forces ◽  
Open Water ◽  
Short Term ◽  
Flux Measurements ◽  
Floating Chamber ◽  
Hydropower Reservoir

Abstract. Greenhouse gas budgets quantified via land-surface eddy covariance (EC) flux sites differ significantly from those obtained via inverse modeling. A possible reason for the discrepancy between methods may be our gap in quantitative knowledge of methane (CH4) fluxes. In this study we carried out EC flux measurements during two intensive campaigns in summer 2008 to quantify methane flux from a hydropower reservoir and link its temporal variability to environmental driving forces: water temperature and pressure changes (atmospheric and due to changes in lake level). Methane fluxes were extremely high and highly variable, but consistently showed gas efflux from the lake when the wind was approaching the EC sensors across the open water, as confirmed by floating chamber flux measurements. The average flux was 3.8 ± 0.4 μg C m−2 s−1 (mean ± SE) with a median of 1.4 μg C m−2 s−1, which is quite high even compared to tropical reservoirs. Floating chamber fluxes from four selected days confirmed such high fluxes with 7.4 ± 1.3 μg C m−2 s−1. Fluxes increased exponentially with increasing temperatures, but were decreasing exponentially with increasing atmospheric and/or lake level pressure. A multiple regression using lake surface temperatures (0.1 m depth), temperature at depth (10 m deep in front of the dam), atmospheric pressure, and lake level was able to explain 35.4% of the overall variance. This best fit included each variable averaged over a 9-h moving window, plus the respective short-term residuals thereof. We estimate that an annual average of 3% of the particulate organic matter (POM) input via the river is sufficient to sustain these large CH4 fluxes. To compensate the global warming potential associated with the CH4 effluxes from this hydropower reservoir a 1.3 to 3.7 times larger terrestrial area with net carbon dioxide uptake is needed if a European-scale compilation of grasslands, croplands and forests is taken as reference. This indicates the potential relevance of temperate reservoirs and lakes in local and regional greenhouse gas budgets.

scholarly journals Leaf area controls on energy partitioning of a temperate mountain grassland

2008 ◽  
Vol 5 (2) ◽  
pp. 421-431 ◽  
Author(s):  
A. Hammerle ◽  
A. Haslwanter ◽  
U. Tappeiner ◽  
A. Cernusca ◽  
G. Wohlfahrt
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Driving Forces ◽  
Vegetation Period ◽  
Soil Heat Flux ◽  
Energy Partitioning ◽  
Summer Drought ◽  
Evaporative Demand ◽  
Data Set ◽  
Mountain Grassland

Abstract. Using a six year data set of eddy covariance flux measurements of sensible and latent heat, soil heat flux, net radiation, above-ground phytomass and meteorological driving forces energy partitioning was investigated at a temperate mountain grassland managed as a hay meadow in the Stubai Valley (Austria). The main findings of the study were: (i) Energy partitioning was dominated by latent heat, followed by sensible heat and the soil heat flux; (ii) When compared to standard environmental forcings, the amount of green plant matter, which due to three cuts varied considerably during the vegetation period, explained similar, and partially larger, fractions of the variability in energy partitioning; (iii) There were little, if any, indications of water stress effects on energy partitioning, despite reductions in soil water availability in combination with high evaporative demand, e.g. during the summer drought of 2003.

scholarly journals Estimation of flooded area in the Bahr El-Jebel basin using remote sensing techniques

2006 ◽  
Vol 3 (4) ◽  
pp. 1851-1877 ◽  
Author(s):  
M. A. H. Shamseddin ◽  
T. Hata ◽  
A. Tada ◽  
M. A. Bashir ◽  
T. Tanakamaru
Keyword(s):  
Remote Sensing ◽  
Water Balance ◽  
Lake Victoria ◽  
Open Water ◽  
Unsupervised Classification ◽  
Water Balance Model ◽  
Balance Model ◽  
Water Evaporation ◽  
Flooded Area ◽  
Remote Sensing Techniques

Abstract. In spite of the importance of Sudd (swamp) area estimation for any hydrological project in the southern Sudan, yet, no abroad agreement on its size, due to the inaccessibility and civil war. In this study, remote sensing techniques are used to estimate the Bahr El-Jebel flooded area. MODIS-Terra (Moderate Resolution Imaging Spectroradiometer) level 1B satellite images are analyzed on basis of the unsupervised classification method. The annual mean of Bahr El-Jebel flooded area has been estimated at 20 400 km2, which is 96% of Sutcliffe and Park (1999) estimation on basis of water balance model prediction. And only, 53% of SEBAL (Surface Energy Balance Algorithm for Land) model estimation. The accuracy of the classification is 71%. The study also found the swelling and shrinkage pattern of Sudd area throughout the year is following the trends of Lake Victoria outflow patterns. The study has used two evaporation methods (open water evaporation and SEBAL model) to estimate the annual storage volume of Bahr El-Jebel River by using a water balance model. Also the storage changes due time is generated throughout the study years.

scholarly journals Regulation of Vegetation and Evapotranspiration by Water Level Fluctuation in Shallow Lakes

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2651
Author(s):  
Qiang Liu ◽  
Liqiao Liang ◽  
Xiaomin Yuan ◽  
Sirui Yan ◽  
Miao Li ◽  
...  
Keyword(s):  
Water Level ◽  
Open Water ◽  
Water Area ◽  
Water Level Fluctuation ◽  
Water Levels ◽  
Water Level Fluctuations ◽  
Water Evaporation ◽  
Level Fluctuation ◽  
Open Water Area ◽  
Annual Scale

Water level fluctuations play a critical role in regulating vegetation distribution, composition, cover and richness, which ultimately affect evapotranspiration. In this study, we first explore water level fluctuations and associated impacts on vegetation, after which we assess evapotranspiration (ET) under different water levels. The normalized difference vegetation index (NDVI) was used to estimate the fractional vegetation cover (Fv), while topography- and vegetation-based surface-energy partitioning algorithms (TVET model) and potential evaporation (Ev) were used to calculate ET and water evaporation (Ep). Results show that: (1) water levels were dramatically affected by the combined effect of ecological water transfer and climate change and exhibited significant decreasing trends with a slope of −0.011 m a−2; and (2) as predicted, there was a correlation between water level fluctuation at an annual scale with Phragmites australis (P. australis) cover and open-water area. Water levels also had a controlling effect on Fv values, an increase in annual water levels first increasing and then decreasing Fv. However, a negative correlation was found between Fv values and water levels during initial plant growth stages. (iii) ET, which varied under different water levels at an annual scale, showed different partition into transpiration from P. australis and evaporation from open-water area and soil with alterations between vegetation and open water. All findings indicated that water level fluctuations controlled biological and ecological processes, and their structural and functional characteristics. This study consequently recommends that specifically-focused ecological water regulations (e.g., duration, timing, frequency) should be enacted to maintain the integrity of wetland ecosystems for wetland restoration.

scholarly journals Flow patterns of shallow Palic Lake induced by the dominant winds

2012 ◽  
Vol 10 (1) ◽  
pp. 55-67
Author(s):  
Ljubomir Budinski ◽  
Djula Fabian
Keyword(s):  
Numerical Model ◽  
Flow Pattern ◽  
Coriolis Force ◽  
Wind Direction ◽  
Driving Forces ◽  
Open Water ◽  
Flow Patterns ◽  
Two Dimensional ◽  
Lake Model ◽  
Double Gyre

Studies of lake currents have highlighted that in case of stagnant waters winds are the dominant driving forces. This study is dealing with the influence of dominant winds on the flow pattern of Palic Lake. Action of steady winds of different directions has been tested on the lake by means of a two dimensional numerical model, while in addition to winds all other permanent factors like actual bathymetry, inflow and outflow as well the Coriolis force have been accounted for. The experiments have revealed that winds of different directions created corresponding characteristic flow patterns (in base plot), which were similar in cases of winds having opposite directions. However, in such cases the direction of flow was opposite. Moreover, the Palic Lake model produced the well known double-gyre flow pattern: in the coastal strip the direction of the current corresponded to the wind direction, while it was opposite in the domain of open water.

Anisohydric water use behavior links growing season evaporative demand to ring-width increment in conifers from summer-dry environments

Trees ◽  
2018 ◽  
Vol 32 (3) ◽  
pp. 735-749 ◽  
Author(s):  
Steve L. Voelker ◽  
R. Justin DeRose ◽  
Matthew F. Bekker ◽  
Chalita Sriladda ◽  
Nisa Leksungnoen ◽  
...  
Keyword(s):  
Water Use ◽  
Ring Width ◽  
Growing Season ◽  
Evaporative Demand ◽  
Use Behavior

scholarly journals Hydrological functioning of cattle ranching impoundments in the Dry Chaco rangelands of Argentina

2019 ◽  
Vol 50 (6) ◽  
pp. 1596-1608 ◽  
Author(s):  
Patricio N. Magliano ◽  
David Mindham ◽  
Wlodek Tych ◽  
Francisco Murray ◽  
Marcelo D. Nosetto ◽  
...  
Keyword(s):  
Overland Flow ◽  
Rainwater Harvesting ◽  
Open Water ◽  
Water Evaporation ◽  
Cattle Ranching ◽  
Systems Modelling ◽  
Controlling Variables ◽  
Infiltration Excess ◽  
And Control ◽  
Hydrological Functioning

Abstract Rainwater harvesting and associated storage is essential for cattle ranching in the drylands of Argentina and elsewhere. This is the first study to attempt to quantify the hydrological inflows and losses from rainwater harvesting impoundments. To address the direct effect of cattle within impoundments, a typical cattle-affected impoundment was instrumented and compared with that of a similar impoundment but without cattle access. Analysis of the storage dynamics with reference to the controlling variables demonstrated the highly episodic nature of the generation of infiltration-excess overland flow that recharged the impoundments. The impoundments experienced 43 and 35% of storage loss to open-water-evaporation for the cattle-affected and control impoundments, respectively. Critically, the cattle-effected impoundment lost only 15% of storage to leakage (after cattle consumption was taken into account), while the control lost 65% of its water to basal leakage. Indeed systems modelling of the rainfall-storage dynamics showed that the cattle-affected impoundment, despite consumption by 300 cows, maintained water in the impoundment (per a unit input of rainfall) for longer than the control (a 65- versus 25-day residence time). These results highlight the unintended beneficial effect of cattle trampling on the floor of the impoundment reducing leakage losses.

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