General considerations for modeling water table dynamics in peatlands

2021 ◽  
Author(s):  
Alex Cobb ◽  
Charles Harvey
Keyword(s):  
Water Table ◽  
Time Derivative ◽  
Water Levels ◽  
Richards Equation ◽  
Specific Yield ◽  
High Temporal Resolution ◽  
Precipitation Data ◽  
Water Table Fluctuations ◽  
Peatland Hydrology ◽  
Vertical Gradients

<p>A basic and universal characteristic of peatlands is that the water table frequently rises near the surface of the soil profile. Surface peat is naturally loose and open-structured, and often has microtopographic features; the water table frequently rises above the level of local depressions. Therefore, water table fluctuations in peatlands cause rapid changes in the permeability and effective porosity of the medium through which flow occurs. We use a simple model based on Boussinesq's equation to explore the challenges that arise from these basic and universal physical aspects of peatland hydrology. We show that simulation of water table fluctuations in peatlands requires precipitation data with a high temporal resolution, and careful attention to the time derivative for accuracy of the mean water tables and correct water balance for two reasons. First, large vertical gradients in specific yield can result in large mass balance errors analogous to errors from naive discretization of the Richards equation; a change of variables from water table elevation to water storage can eliminate these errors and also speed up calculations by allowing larger time steps. Second, large vertical gradients in permeability near the peat surface cause a strongly nonlinear response to precipitation, so that time-averaged precipitation data or neglect of diurnal cycles of evapotranspiration results in erroneously high water levels, and careful time stepping is required around rain storms.  Consideration of these features of peatland hydrology results in efficient hydrologic models that can be used to predict spatial and temporal patterns in greenhouse gas uptake and emissions in peatlands.</p>

High temporal resolution measurements of CO2, CH4 and N2O in a Norwegian mire ecosystem using automated light-dark chambers

2020 ◽  
Author(s):  
Linsey Avila ◽  
Klaus Steenberg Larsen ◽  
Andreas Ibrom ◽  
Norbert Pirk ◽  
Poul Larsen
Keyword(s):  
Water Table ◽  
Natural Water ◽  
Water Levels ◽  
Organic Soils ◽  
High Temporal Resolution ◽  
Decomposition Rates ◽  
Microbial Decomposition ◽  
Enhanced Production ◽  
Nature Restoration ◽  
Ch4 And N2o

<p>Regeneration of natural hydrology in previously drained peatlands is becoming a widespread practice in nature restoration projects around the world. The drained peatlands are well known for their high emissions of CO<sub>2</sub> caused by increased microbial decomposition rates in these very organic soils when suddenly exposed to higher levels of oxygen availability. Restoring natural water levels reduces again the decomposition rates and CO<sub>2</sub> emissions. It remains uncertain, however, how rates of the much stronger greenhouse gases, CH<sub>4</sub> and N<sub>2</sub>O, respond to the restored water table and these fluxes can potentially offset the GHG balance of rewetting peatlands.</p><p> </p><p>In a new project in Norway (close to Trysil, Innlandet), we installed five ECO<sub>2</sub>flux automated chambers and one eddy flux tower in each of two areas of drained peatlands.  The automatic chambers were placed with different distances to the ditches reflecting variation in water table with greatest water level variability at the edges of the ditches. After two years, the ditches will be filled and the natural water table will be regenerated in one of the areas in order to follow the differences in the fluxes of CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O upon rewetting.</p><p> </p><p>We here present an analysis of the first year’s data from the ECO<sub>2</sub>flux chambers including the total greenhouse gas budget for the period measured. The fluxes of CO<sub>2</sub> showed only little spatial heterogeneity whereas we observed a significant spatial pattern of higher fluxes of CH<sub>4</sub> in plots where the water table was closer to the surface. The driest plots, i.e. the edges of the drain ditches, showed also the lowest emissions of CH<sub>4</sub>. The trend was similar in the two areas. This is an indicating that planned rewetting after two years of the project may lead to enhanced production and emission of CH<sub>4</sub> in the area. So far, we observed no N<sub>2</sub>O emissions above the detection limit of the system indicating that CO<sub>2</sub> and CH<sub>4</sub> are the major components of the GHG budget.</p>

scholarly journals Analyzing Trends in Water Table Elevations at the Marcell Experimental Forest, Minnesota, U.S.A.

2021 ◽  
Vol 17 (4) ◽  
pp. 19-32
Author(s):  
Anna Stockstad ◽  
Ella Gray ◽  
Stephen Sebestyen ◽  
Nina Lany ◽  
Randall Kolka ◽  
...  
Keyword(s):  
Water Table ◽  
Linear Trend ◽  
Forest Products ◽  
Water Levels ◽  
Monthly Precipitation ◽  
Significant Linear Trend ◽  
Water Table Fluctuations ◽  
Water Tables ◽  
Over Time

Water table fluctuations in peatlands are closely coupled with the local climate setting and drive critical ecosystem processes such as nutrient cycling. In Minnesota, USA, peatlands cover ten percent of the surface area, approximately 2.5 million hectares, some of which are actively managed for forest products. To explore the relationship between peatland water tables and precipitation, long-term data (1961 to 2019) were used from the Marcell Experimental Forest in northern Minnesota. Starting in 1961, water table data from seven peatlands, including two types of peatlands (bogs and fens), were measured. We used the Theil-Sen estimator to test for monotonic trends in mean monthly water table elevations for individual peatlands and monthly precipitation. Water levels in bogs were both more variable and had mean water table elevations that were closer to the surface. Individual trends of water table elevations differed among peatlands. Water table elevations increased over time in three of the bogs studied and decreased over time in two of the bogs studied. Trends within fens were notably nonlinear across time. No significant linear trend was found for mean monthly precipitation between 1961 and 2019. These results highlight differences in peatlands types, local physiography, and the importance of understanding how changes in long-term dynamics coupled with changing current conditions will influence the effects of water table fluctuations on ecosystem services. The variability of water table elevations in bogs poses potential difficulties in modeling these ecosystems or creating adaptive management plans. KEYWORDS: Peatlands; Hydrology; Water tables; Bogs; Fens; Monitoring; Minnesota; Climate Change

Estimation of specific yield using water table fluctuations and cropped area in a hardrock aquifer system of Rajasthan, India

2018 ◽  
Vol 202 ◽  
pp. 146-155 ◽  
Author(s):  
Pennan Chinnasamy ◽  
Basant Maheshwari ◽  
Peter Dillon ◽  
Ramesh Purohit ◽  
Yogita Dashora ◽  
...  
Keyword(s):  
Water Table ◽  
Specific Yield ◽  
Aquifer System ◽  
Water Table Fluctuations

scholarly journals A critical assessment of simple recharge models: application to the UK Chalk

2012 ◽  
Vol 9 (10) ◽  
pp. 12061-12102 ◽  
Author(s):  
A. M. Ireson ◽  
A. P. Butler
Keyword(s):  
Water Table ◽  
Groundwater Resources ◽  
Climatic Conditions ◽  
Water Levels ◽  
Richards Equation ◽  
Predictive Capacity ◽  
Monthly Basis ◽  
Physically Based Model ◽  
Flow Processes ◽  
Physically Based

Abstract. A framework for the rigorous quantification of the timing and magnitude of groundwater recharge is proposed. This involves developing a physically based model for the flow processes in the unsaturated and saturated zones that is consistent with the conceptualisation of the system, and with field observations. Subsequently, the essential behaviour of this model is emulated using a simpler model that can be applied within operational groundwater models. We take a UK Chalk aquifer as a case study. Flow processes are simulated convincingly using a dual permeability, equivalent continuum, Richards' equation model, applied to a 2-D hillslope transect along which four monitoring wells recorded water levels in the unconfined aquifer. A simple conventional recharge model that has been widely used was calibrated to reproduce the water table response simulated by the physically based model. The performance in reproducing the water table was surprisingly good, given the known discrepancies between the actual processes and the model representation. However, comparisons of recharge fluxes simulated by each model highlighted problems with the recharge processes in the simple model. Specifically, artificial bypass flow events during the summer were compensating for recharge that should have come from slow, continual drainage of the unsaturated zone. Such a model may still be useful for assessment of groundwater resources on a monthly basis, under non-extreme climatic conditions. However, under extreme wet or dry conditions, or under a changed climate the predictive capacity of such models is likely to be inadequate.

Estimation of natural groundwater recharge in the Aguascalientes semiarid valley, Mexico

2018 ◽  
Vol 35 (3) ◽  
pp. 268-276 ◽  
Author(s):  
Lilia Guerrero-Martínez ◽  
Martín Hernández-Marín ◽  
Thomas J. Burbey
Keyword(s):  
Groundwater Recharge ◽  
Water Table ◽  
Boussinesq Equation ◽  
Specific Yield ◽  
High Temporal Resolution ◽  
Groundwater Levels ◽  
The North ◽  
Vertical Hydraulic Conductivity ◽  
Recharge Rates ◽  
Aguascalientes Valley

Groundwater recharge (GWR) is analyzed and evaluated within the Aguascalientes Valley by means of a modified linearized Boussinesq equation and the Water Table Fluctuations (WTF) technique. These techniques use the specific yield, water table variations and the subsurface drainage of groundwater. The methodology is applied to the semiarid Aguascalientes valley, which contains a thick vadose zone. The combination of the analytical solution based on the Boussinesq equation and the WTF technique, allows the method to be applied in areas with deep groundwater levels, such as the Aguascalientes valley, without the need for high temporal resolution data. The data for the application of the method were provided by various government agencies and includes information on 145 wells positioned within the valley during the period 1985-2015. The specific yield and the transmissivity were integrated from the results of two previous investigations. Results indicate that the variation of recharge ranges from 0.86 to 525.69 mm/year in the analyzed period, with the highest recharge rates occurring in the north and center parts of the valley and is likely attributed to high specific yield and vertical hydraulic conductivity due to the presence of coarse permeable soils present in the area. Conversely, the lowest recharge rates were found to occur near the north and south borders of the valley.

scholarly journals Water table variations on different land use units in a drained tropical peatland island of Indonesia

2021 ◽  
Author(s):  
Ismail ◽  
Ali Torabi Haghighi ◽  
Hannu Marttila ◽  
Uun Kurniawan ◽  
Oka Karyanto ◽  
...  
Keyword(s):  
Water Table ◽  
Large Scale ◽  
Fire Risk ◽  
Specific Yield ◽  
Spatial And Temporal Variability ◽  
Coastal Zones ◽  
Peatland Hydrology ◽  
Drainage Networks ◽  
Site Water ◽  
Recession Rates

Abstract Restoration and water table control on peatlands to limit fire risk are national priorities in Indonesia. The present study was initiated at Padang Island, Sumatra, to increase understanding on peatland hydrology in the tropic. At the pilot site, water table and precipitation were monitored at different stations. The results show variation in water table depths (WTDs) over time and space due to spatial and temporal variability in rain intensity and drainage networks. In part of the island, large-scale drainage for plantations led to deep WTD (−1.8 m) and high WTD recession rates (up to 3.5 cm/day). Around villages, farm-scale drainages had a smaller impact with a lower recession rate (up to 1.8 cm/day) and shallow WTD, typically below −0.4 m, the threshold for sustainable peatland management in Indonesia. The recession rates levelled off at 1.0 cm/day near the drained forest/plantation and at 0.5 cm/day near the farm. Deeper layers had much lower specific yield (Sy), 0.1 at −1.5 m depth, compared with top peat soils with Sy up to 0.3. Proximity to drainages extended discharge flow to deeper layers. The results highlighted the severity of peatland drainage impact on most coastal zones of Padang Island, which have intensive drainage networks.

Using groundwater levels and Specific Yield to Estimate the Recharge, South of Erbil, Kurdistan Region, Iraq

2018 ◽  
Vol 7 (4) ◽  
pp. 191
Author(s):  
Sherwan Sh. Qurtas
Keyword(s):  
Unconfined Aquifer ◽  
Middle Part ◽  
Water Levels ◽  
Specific Yield ◽  
Aquifer System ◽  
Groundwater Levels ◽  
Monitoring Wells ◽  
Water Table Fluctuation Method ◽  
Recharge Estimation ◽  
Fluctuation Method

Recharge estimation accurately is crucial to proper groundwater resource management, for the groundwater is dynamic and replenished natural resource. Usually recharge estimation depends on the; the water balance, water levels, and precipitation. This paper is studying the south-middle part of Erbil basin, with the majority of Quaternary sediments, the unconfined aquifer system is dominant, and the unsaturated zone is ranging from 15 to 50 meters, which groundwater levels response is moderate. The purpose of this study is quantification the natural recharge from precipitation. The water table fluctuation method is applied; using groundwater levels data of selected monitoring wells, neighboring meteorological station of the wells, and the specific yield of the aquifers. This method is widely used for its simplicity, scientific, realistic, and direct measurement. The accuracy depends on the how much the determination of specific yield is accurate, accuracy of the data, and the extrapolations of recession of groundwater levels curves of no rain periods. The normal annual precipitation there is 420 mm, the average recharge is 89 mm, and the average specific yield is around 0.03. The data of one water year of 2009 and 2010 has taken for some technical and accuracy reasons.

Drawdowns at the Free Water Table During Pumping Tests in Artesian and Semiartesian Aquifers

1980 ◽  
Vol 11 (3-4) ◽  
pp. 159-168 ◽  
Author(s):  
Henrik Kærgaard
Keyword(s):  
Water Table ◽  
Free Water ◽  
Pumping Test ◽  
Water Withdrawal ◽  
Specific Yield ◽  
Minor Role ◽  
Long Term Effects ◽  
Long Term Storage ◽  
Term Storage

In an earlier paper I have shown an example of how long term drawdowns can be used for the computation of long term storage in artesian and semiartesian areas. In most cases the long term storage is more or less equivalent to the specific yield at the water table; the storage mechanisms of consolidation playing a minor role in long term situations. The specific yield in artesian areas is a very important parameter in the prediction of long term effects of ground water withdrawal. Especially the stream depletion will often mainly be governed by draw-downs in upper nonpumped aquifers near the water table, and these drawdowns depend to a great extent on the specific yield at the water table. A determination of long term storage will often necessitate long term draw-down data, however, under certain circumstances a determination can be made on the basis of a pumping test of limited duration (3-5 weeks) provided drawdown observations at the water table can be made. In this paper some formulas dealing with water table drawdowns in different geohydrologic systems are reviewed, and two cases in which these formulas have been used in practice are presented.

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