Acrotelm Survey of Clara Bog I I Part One
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I IRISII - DlITCH RAISED BOG STUDY ~4u~D I GEOHYDROLOGY ECOLOGY :-Jer'C"-~:r.en~ Er:y~ru~i::-em~1 ~:c:~,:,~io=: cn~ 8' Ne'io:loJ Fo:-k, C:~~ \tv"iicli'iie SC':--.·i:~ o of r':oru:e (o:uervo1icn.. I 01 the ·:>Hice o! PLl~;it Works, ;-l..biin 'v,lildliie M!:""u2e.,~e,r,. TIM; Hogue ~ N oli,;,n~J ~ores: SeTvj~e, Drie!:l(!T'<!cn I I A.CROTELlvI SIJRVEY OF CLARo\. BOG I .1 J.R.G. van der Cruiisen _A. r'urent. .. I R. van VVolfswin.4.el I I Agricaltural University, Dept, of Water Resources Nieu...ve Kanaalll, NL-6709PA Wageningen, I The Netherlands I I .... I • Q ( il .---------~---------- I I I I Acrotelm survey of Clara Bog I I Part one: I J.H.G. van der Cruijsen A. Grent I R. van Wolfswinkel I Part two: I R. van Wolfswinkel I Appendices: I J.H.G. van der Cruijsen A. Grent I R. van Wolfswinkel I August, 1993 I I I~ I Wageningen Agricultural University Department of Water Resources "I" Nieuwe Kanaal 11, 6709 PA Wageningen, The Netherlands I l ' ~,----".----"-'----- ~ -------------------- 'I I I I I Erratum I The map scaleson appendices V.1, V.2, VI.1 and VI.2 show 2.5em to 1 km. I This should be 2.5 cm to 200 m I' I I I I I I .-I I I I I I ------------------•••• 2 ;? ? 'I_ ', _. ~-r- ,- -,,"=¥,",:, ,.'" -' ,- -- - .. I I I I· I I I PART ONE I I I- I I I I I I I I II lJ___.. ------'(N),.J -~-~-~-------------- I I PREFACE I This report is the result of a close cooperation between the authors. But we never could have done this without some very good help and assistance. Therefore we would like to thank everyone who has given us a helping hand. Especially we would I like to thank Sake van der Schaaf, our supervisor, for giving us directions and keeping us in touch with the Netherlands, Mr. F. Dolezal for the supply of the evaporation I figures and last but not least our Irish colleagues: Ray, lara and Mary. For this research we spent five months in Ireland. Although we were staying in Clara I during one of the wettest winters in years, we enjoyed almost every minute of it. The sport- and publife was a welcome diversion after working on a cold and wet bog all day. We thank the people of Clara for their hospitality and friendship which we I enjoyed during our stay. I Wageningen, April 1993. I I I I I I I I I I I I ..-..-_----------------~(~ -------------------- I I INDEX I PREFACE I INDEX INDEX OF TABLES AND FIGURES I SUMMARY I page 1 INTRODUCTION 1 1.1 The project 1 I 1.2 The report 2 2 RECONSTRUCTION AND GENERAL DESCRIPTION 3 I 2.1 Reconstruction of the development of raised bogs 3 2.2 Clara Bog 5 I 2.3 The main discharge systems on Clara-West 8 3 ACROTELM 11 3.1 The diplotelmic bog 11 I 3.2 Acrotelm mapping 13 3.2.1 The acrotelm map 13 3.2.1.1 Introduction 13 I 3.2.1.2 Methods ' 13 3.2.1.3 Results 14 3.2.2 The augerholes and hummock/hollow map 15 I 3.2.2.1 Introduction 15 3.2.2.2 Methods 15 I 3.2.2.3 Results 16 . 3.3 Relation acrotelm thickness and vegetation 17 3.3.1 Introduction ················ 17 I 3.3.2 Methods 1:- 3.3.3 Results ············ 18 3.3.4 Conclusions 22 I 3.4 Relation acrotelm thickness and slope 23 3.4.1 Introduction ············ 23 3.4.2 Methods 23 I 3.4.3 Results ········ 24 3.4.3.1 Clara-West 24 3.4.3.2 Clara-East 24 I 3.4.4 Conclusions 25 3.5 Relation acrotelm thickness and the fluctuation of the phreatic level 26 I 3.5.1 Introduction ············· 26 3.5.2 Methods 26 I I ( vi) I 3.5.2.1 Clara-West 26 I 3.5.2.1 Clara-East 27 3.5.3 Results ········ 27 3.5.3.1 Clara-West 27 'I 3.5.3.2 Clara-East 28 3.5.4 Conclusions 28 3.6 The methods for measuring the transmissivity .: 29 I 3.6.1 Introduction ········· 29 3.6.2 The two methods 29 3.6.2.1 The Guinness method 29 I 3.6.2.2 The Pitbailing method 30 3.6.3 The conditions for the two methods and the accuracy of the measurements 31 I 3.6.4 The accuracy of the measured transmissivities in general 36 3.7 Transmissivity 36 I 3.7.1 Introduction ·· .. ·.·· 36 3.7.2 Humification degree 37 3.7.3 Depth of the phreatic level 38 I 3.7.4 Transmissivity related to acrotelm thickness 39 3.7.5 Transmissivity related to vegetation cover 41 3.8 A and m as indicators of the condition of the bog 47 I 4 EVAPOTRANSPIRATION 49 ,I 4.1 Introduction 49 4.2 The different methods 49 4.2.1 The Penman and the Thorn & Oliver equations 49 I 4.2.2 lysimeters 50 4.3 Results 52 4.3.1 The Penman and the Thorn & Oliver equations 52 I 4.3.2 lysimeters 53 5 SYNTHESIS 57 I 5.1 Introduction 57 5.2 Synthesis 57 I 6 CONCLUSIONS AND RECOMMENDATIONS 59 6.1 Introduction 59 6.2 Conclusions 59 I 6.3 Recommendations 61 I REFERENCES I I I I ~-\~ . I I INDEX OF TABLES AND FIGURES I Tables page 2.1 Time table for the blo-geological periods after the Weichsel-Pleniglacial 5 I 2.2 Preference of Sphagna for range of pH and the bog water level 8 2.3 The discharge of the Rossum, Thomson and Tunnel drains and their mutual I ratio's, measured with a bucket and a stop-watch .- 9 3.1 . Characteristic differences between the properties of acrotelm and catotelm . 12 3.2 Augerhole classification 16 I 3.3 Relation complex type and acrotelm thickness 19 3.4 Vegetation and presence of acrotelm 23 3.5 The chosen cross sections 24 I 3.6 The acrotelm thickness at the different tubes 26 3.7 Transmissivities calculated by using different methods .. " 33 3.8 Transmissivity calculated according the Guinness method, using different. I imaginary J1 and t values 34 3.9 Transmissivity depending on drawdown, pumping time and discharge, measured at location 03 at a water level of 2.8 em. below surface, using the I Guinness method 36 3.10 Average values for the A and m factors and the standard deviations per acrotelm thickness 40 I 3.11 The m- and A-values for areas with different acrotelm thicknesses within the Sphagnum magellanicum zone : ..•.... 41 I 3.12 Acrotelm holes, vegetation zone, acrotelm thickness, m- and A-values .... 45 4.1 Evapotranspiration in mmlday according to the Penman and Thorn & Oliver equation ..........................................•~ ..... 52 I 4.2 Daily average evapotranspiration in mmlday measured with Iysimeters ..•. 53 I 4.3 Monthly evapotranspiration 54 I I I I I I I • (riit) I Figures page I 1.1 location of Clara and Raheenmore bogs 1 I 2.1 Stages in the development of a raised bog 4 2.2 Raised bog confined in a deep basin 6 I 3.1 Relation storage coefficient and humification degree 34 3.2 The effect upon the transmissivity when u, t and Sw differ 35 3.3 Humification-permeability correlation in top layer 37 I 3.4 Relation kD and depth for a degree of humification of: 38 a 4 b 5 I c 6 d 7 3.5 The relation transmissivity-depth of the water table for different acrotelm I thicknesses within the Sphagnum magellanicum zone 42 3.6 Variation with depth z of the mean estimate of hydraulic conductivity, LIII: Sphagnum capil/ifolium, lIV Sphagnum magellanicum 43 I 4.1 Evapotranspiration Thorn & Oliver versus Iysimeters 54 I 4.2 Monthly evapotranspiration calculated with the two equations and measured with the lysimeters 55 I I I I I I I I I. I I ~i)._ I I SUMMARY I In the north-western part of Europe raised bogs have become rare, The Irish government tries to preserve the raised bog remnants now as good as possible. Sound hydrological management is therefore needed. The Irish-Dutch bog project is set up to I find solutions concerning this management. The project is a cooperation between the Irish Wildlife Service and the Dutch National Forest Service. I This report consists mainly of an inventory of the health of Clara Bog, especially of the toplayer, the acrotelm. To understand the importance of the acrotelm first a I reconstruction and a general description of Clara Bog is given. The acrotelm is the toplayer of the bog. It is defined here as the top layer that consists of fresh to almost unhumified plant remains with a humification degree of 1 or 2. It is I important for the bog because of its hydrological characteristics, like its relatively high permeability and its periodically fluctuating phreatic level.. The main discharge of excess rainwater is through this layer. A thick acrotelm normally means that the bog I is healthy. To gain information about the spatial variabi lity of the acrotelm layer, an acrotelm I thickness map was made for both Clara-East and Clara-West. This was done with the "foot-spade" method. Also some augerings were made to give some information about the state of health the bog is in.