Changes in Physical and Chemical Properties of Fen Soils Induced by Long-term Drainage, Followed by Recent Rewetting

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1 Thi paper wa peer-reviewed for cientific content. Page In: D.E. Stott, R.H. Mohtar and G.C. Steinhardt (ed) Sutaining the Global Farm. Selected paper from the 10th International Soil Conervation Organization Meeting held May 24-29, 1999 at Purdue Univerity and the USDA-ARS National Soil Eroion Reearch Laboratory. Change in Phyical and Chemical Propertie of Fen Soil Induced by Long-term Drainage, Followed by Recent Rewetting ABSTRACT Intenive agricultural ue of fen oil in eatern Germany elicit oil formation procee that may lead to oil degradation. The oil propertie of fen oil are decribed according to ubtratum-horizon group. The ecological effect and propoal of an alternative fen ue are dicued. Since 19, a highly degraded fen area (10 ha) ha been rewetted by damming up drainage canal and urface irrigation for retoration and cultivation of reed a an indutrial raw material. Beneath ecological and economical invetigation, the project i joined by hydrological and oil cientific reearch. With the rewetting of the area, there have been remarkable change in redox potential joined by a decreae of diolved element in oil olution. INTRODUCTION Fen oil have been ued intenively for agriculture during the pat 30 year in eatern Germany. The management of fen oil, following the former German Democratic Republic objective of economic independence and high productivity, led to a dratic decreae in oil fertility. The main caue wa the lowering of the groundwater level to permit intenive utilization. Thi drainage made the ite acceible at all time even for heavy machine with a high-preure index. Degradation and drying out of the fen were increaed by intenive gra cultivation with regular cutting three to four time a year. Soil degradation wa increaed by the high calcium carbonate content of the glacial till around the fenland and by the relatively dry climate in eatern Germany. Thi intenive agricultural ue modified the oil parameter to uch an extent that the peat underwent oil formation with the development of everal diagnotic oil horizon. If intenive agriculture reduce the fertility of fen oil below a certain value, it i aid to be degraded. In fen oil, degradation mean development of an earthy tructure in the topoil and of a highly egregated tructure in the uboil. More than 40% of fen oil in eatern Germany are degraded. The original function of fen in the landcape have been largely lot, particularly with regard to the water regime and nutrient cycle. Eventually, agriculture became unprofitable due to oil degradation and the damage to the environment wa not any longer acceptable. New way of utilizing fen oil had to be found which were not only economically and ocially Jutta Zeitz* and Andrea Genior acceptable, but alo ecologically compatible in the ene of utainable development. Le intenive cultivation alone cannot top the degradation. Retoration of a fenland i only poible by rewetting. An interdiciplinary reearch project entitled Retoration of a degraded fen by cultivation of reed a indutrial plant uing purified wate water wa therefore promoted by the Federal German Foundation for the Environment (DBU). In thi project, a 10 ha area of degraded fen oil in the Randow-Wele landcape (100 km NNE of Berlin) wa elected a a trial retoration ite. After planting typical fen vegetation (e.g. reed and edge), the degraded fen flooded again uing water from a ditch nearby. From the viewpoint of oil conervation, one of the mot important aim of the project i to reactivate the natural function of a fen uch a being an element ink and water reervoir in the landcape. A pecial experimental area (6250 m 2 ) at the trial ite wa et up to invetigate element fluxe and to make out a balance heet for carbon. Thi paper decribe the change that have taken place in oil propertie in fen in the eatern part of Germany within the lat 30 year: firtly, due to oil degradation becaue of drainage and intenive agricultural ue, and econdly, due incipient recovery becaue of rewetting. METHODS Change in elected parameter of fen oil were invetigated by analying water-retention curve and meauring the hydraulic conductivity of unaturated oil (Vetterlein, 18). Sample of topoil were taken from the paludification mire "Upper Rhinluch" (fen landcape 70 km north-wet of Berlin; about 8000 ha) and typical oil parameter meaured. The unit water content a a pecial parameter (UWC, no dimenion; German Democratic Republic tandard TGL 24300/04), which i the water content of a peat ample after conolidation at a preure of 100 kpa, wa alo determined. On the trail retoration ite at four different depth, the compoition of oil olution (monthly 24 parameter) and the redox potential were meaured. In addition, the element depoition and the fluxe in the catchment were meaured (Genior et al., 19, Genior et al., 1999). RESULTS Univeral pedogenic procee The pedogenic procee reult in the formation of typical organic oil horizon with ditinctive oil propertie. *Jutta Zeitz and Andrea Genior, Humboldt-Univerität zu Berlin, Faculty of Agriculture and Horticulture, Deviion of Ecology of Reource Utilization, Berlin, Invalidentr. 42, Germany. *Correponding author: jutta.zeitz@rz.hu-berlin.de. Sponoring organization: German Federal Foundation of the Environment; PO box 17 05, Onabrück, Germany.

2 Table 1: Definition and ymbol of organic oil horizon (Bodenkundliche Kartieranleitung, 1994). Horizon Decription H Horizon with more than 30 %wt. organic matter (peat), originating from the reidue of peat-forming plant at the oil urface (peat) (univeral decription of all peat horizon) Hm H-horizon on the oil urface of intenive drained and tilled peatland, trongly humified ( earthified ), highly decompoed; duty tructure and highly water repellent when dry Hv H-horizon on the oil urface of drained peatland, poorly to moderately humified ( earthified ) by aerobic mineralization and humification, crumb or fine ub angular tructure Ha Suboil horizon of thoroughly drained peat land, aggregate horizon ; coare to fine, angular, blocky tructure caued by hrinking and welling and the formation of vertical and horizontal hrinkage crack Ht Suboil horizon, hrinkage horizon, vertical crack and coare primatic tructure caued chiefly by hrinkage Hw H-horizon, affected by a fluctuating groundwater table or perched groundwater table, partially oxidized Hr H-horizon, permanently below the groundwater table and preerved in a reduced tate Table 2: Soil parameter for ubtratum-horizon group compried of mixed edge-and-reed peat. Subtratum-horizon group PV CPI UFC MPI CPII Horizon Subtratum; claification parameter nhv x<30; hare of dry ma: vol.% n: nhm x<30; hare of dry ma: vol.% n: nha to 40 cm b. Hnp; Hnr/Hnp; hare of dry ma: vol.% n: nht >40 cm b.. Hnr/Hnp; hare of dry ma: vol.% n: nhr Hnr/Hnp with x<20; hare of dry ma: vol.%; n: nhv, nhm, nha, nht and nhr ee table 1; nh = fen (in German "Niedermoor") horizon; Hnp = reed peat; Hnr = edge peat; CPI = coare pore >50 µm (vol.%); Hnr/Hnp = mixed edge-and-reed peat; PV = pore volume (vol.%); CPII = coare pore µm (vol.%); x = ah (w/w); MPI = medium pore 3 10 µm (vol.%); UFC = ueful field capacity (vol.%); b.. below urface; n = number of ample; = tandard deviation; = mean. Table 3: Selected ecological parameter of topoil (0 30 cm) in fen oil of the Upper Rhinluch (Brandenburg). Parameter nhv nhm n mean tandard deviation n mean tandard deviation Share of dry ma (vol.%) * * 2.01 Ah (w/w) * * 4.84 Bulk denity (g/cm 3 ) * * 3.64 Unit water content (without dimenion) * * 0.19 * level of ignificance α=0.05, n = number of ample For the firt time in Germany, the 4 th edition of Bodenkundliche Kartieranleitung (1994), the official German guideline for oil mapping, how everal horizon derived from an organic ubtratum in a claification that diverge from the FAO-claification. Thi new claification of organic oil replace the much impler one in previou edition of the guideline, which claified peat oil mainly on the bai of geogenic and anthropogenic parameter. There were two main reaon for a more detailed claification of peat oil: 1) The pedogenic procee initiated by drainage and agriculture are given more conideration, and 2) Unambiguou ymbol mut be aigned to the variou horizon a a prerequiite for more efficient computer ue (Benne et al., 1992). Conequently, even horizon with different pedogenic parameter can be decribed right in the field (Table 1). From the viewpoint of oil conervation, the Hm- and Ha-horizon are conidered to be degraded. The change that have occurred in the propertie of the peat due to pedogenic procee are highly ignificant when future peat land utilization, conervation, and regeneration are being planned. Change in oil parameter due to oil degradation Analyi of water retention curve from fen oil ha hown that, owing to drainage and aeration, the oil propertie differ mainly between the variou horizon; however, within ome horizon they can be hown to differ a a function of the kind of peat. In fen oil trongly anthropogenic influence, the pedogenic difference mak the botanical difference. Altogether 14 ubtratum-horizon group were identified from the data under review (Zeitz, 1992). The mixed edge-and-reed peat, which i quite common in fenland, i ued a an example to illutrate that

3 the proportion of the variou pore clae change in the coure of oil development and horizon formation (Table 2). Auming that all ubtratum-horizon group (Table 2) have an identical initial ubtratum, thee group could be conidered to exhibit, from bottom to top, tage of increaing oil development and, hence, of increaing amount of welling and hrinkage. The pore volume decreaed lightly, from 91.1 % in the nhr-horizon to 87.8 % in the nha-horizon, while the proportion of coare pore and, conequently, the air capacity increaed from 14.2 to 16.4 %. The change in oil propertie permitted increaed aeration. Shrinkage went hand in hand with a decreae in the volume of coare and medium pore, which drain lowly. Compared with the initial ubtrate, the nhr-horizon, which wa permanently below the groundwater table, the CP-II and MP-II (< µm) fraction in the trongly egregated nha horizon decreaed by 62 % and 46 %, repectively. Thi had a direct impact on the hydraulic conductivity and on capillary rie from the groundwater. The more the peat wa decompoed, the lower the hydraulic conductivity became. Calculation of the capillary rie of given quantitie of water (e.g., flux 0.3 cm d -1 ) uing van Genuchten' (10) method and a one-layer model gave water tranport value of le than 10 cm in the highly egregated horizon nhv and nhm (Zeitz, 1992). From the oil protection and agronomic point of view, it i very important to ae the oil propertie in the top cm of fen oil, a thi i the main rhizophere of mot graland plant. During development of oil from the nhvhorizon to the nhm-horizon, the ueful field capacity a one of the major ecological oil parameter decreaed from about 38 to a little a 27 % volume. Auming topoil with an average rooting depth of 30 cm, only about 80 mm of oil water wa till available to the plant. Under the climatic condition in Brandenburg, thi increaed the danger of oil deiccation and wind eroion. Determination of the unit water content howed that oil degradation lead to a coniderable decreae in waterretention capacity. Invetigation of the Upper Rhinluch paludification mire, which ha been under intenive agricultural ue for more than 200 year, revealed obviou ymptom of degradation (Table 3). The unit water content (UWC) i a rough meaure of how much the tructure of the original peat ha been retained. The lower the UWC, the lower the water-retention capacity and the more advanced the oil development. In peat oil that had reached an advanced tage of oil development, the tructure wa imilar to the ingle-grain tructure of mineral oil. The UWC allowed four degree of peat decompoition (from lightly earthy peat with UWC > 2.2 to trongly decompoed peat with UWC < 1.5) to be ditinguihed. Due to oil degradation, the unit water content of the nhm-horizon were 20 % lower than thoe of the nhv-horizon (Table 3). The topoil wa denely packed and the phyical parameter value of the trongly decompoed nhm-horizon differed ignificantly from thoe of lightly earthy peat. All reult howed that drainage and agricultural ue of organic oil gave rie to pedogenic procee, which lead to the development of ditinct oil horizon. Thee horizon howed a high degree of oil degradation. Such fen oil did not fulfil their original function in the landcape. Since decreaing the intenity of land ue did not arret oil degradation ufficiently, it wa neceary to etablih alternative type of land ue for fen oil. Change in oil propertie becaue of rewetting CO 2 -C - efflux Due to the rewetting, meaured the CO 2 - efflux from the fen oil decreaed coniderably (Fig. 1). The method of rewetting the fen influenced the CO 2 - efflux too. The efflux from exce flooded part of the invetigation ite ha been maller than from irrigated. The calculation of yearly CO 2 -C loe baed on thee reult were invetigated by the method of Lundegardh (1927), which when neglecting factor could influence the CO 2 dynamic coniderably. The CO 2 -C efflux from a drained and rewetted fen oil (rewetted by damming up (flooded) and irrigation) (mean and [range] in CO 2 -C g (m 2 *a) -1, etimated by releae intalment) wa the following: drained = 560 [344]; rewetted = 205 [124]; flooded = 143 [50] and irrigated = 267 [199]. Neverthele, the value howed the ame order for the drained variant, which were imilar to thoe reported by other author for imilar location (Mundel, 16). Value for a completely rewetted fen are not known. Although the quantitative evaluation of thee reult required a careful interpretation, the reult pointed out that organic ubtance were le decompoed and the gaeou CO 2 -C effluxe from the fen oil decreaed becaue of the rewetting. The development of the Eh - value were elucidated at the beginning of flooding between February and March 19 by ignificant peak at all depth. Thee peak mainly were due to the upply of freh water, which wa till rich on oxygen. The oxygen would be ued up within a few hour. While the rewetting caued dramatic change in the redox potential in the upper horizon after a hort time, the Eh - value for the deeper horizon were only changed lightly, becaue they were influenced by groundwater before flooding (Fig. 2). On average, the retoration meaure have led to continuouly anaerobic, trongly reductive condition in the whole fen oil. The ignificant hort time peak in all horizon howed that partially oxidative condition could occur at any time and anywhere in the oil after rewetting the fen oil completely. Reaon for thee abrupt change in redox potential were light variation of water level, in the cae of irrigation oxygen rich freh a water upply, oxygen tranferred by the reed rhizome into the oil, air added to water and differing hydraulic conductivitie due to preferential flow. A working drainage ytem influenced the redox condition in the fen oil, coniderably. Additional invetigation, which were carried out at the 45 and 75 cm depth in the acidic part of the ite reulted in poitive redox potential (E h = mv). In the area around the drainage tube, aturated water conductivity increaed, with more water paing through oil in time. Therefore, oxygen rich water wa upplied and drawn off permanently, and cauing a partial to fully oxidative condition.

4 CO2-C in g/m rewetting variant drained rewetted reflooded irrigated Figure 1: Sum of gaeou CO 2 -C-loe (mean, minimum and maximum in g m -2 ) during 151 day from a drained and rewetted fen oil cm 45 cm 75 cm 125 cm 0 Eh in mv Aug Sep Oct Nov Dec Jan Feb Mar Apr Mai Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr Mai Jun Jul Figure 2: Mean E h -value (mv) in four depth of degraded fen. Aug Sep Oct Nov Dec The ph value of the oil olution changed lightly due to flooding. While in the 45 cm and 75 cm depth there were no change in the ph, the ph decreaed lightly at the 20 and 125 cm depth. While the temporary variability wa very mall in all horizon, the patial heterogeneity at the 45 and 75 cm depth wa prominent. The low ph value at 45 and 75 cm wa caued by the formation of ulfuric acid from the oxidation of ulfide. The reaon for thee procee occurred wa caued by the change in the oil aeration due to the drainage ytem. Becaue of the drainage ytem, the production of acid wa very high in the fen oil after rewetting. Subequently the tranfer within the fen i dominant and lead to irreverible acidification (the decreaing ph in 125 cm reulted from thee procee). The element concentration in the oil olution were very high in all horizon before flooding (Fig. 3A). The compoition of the oil olution wa dominated by calcium (61-79 %) and ulfate (62-82 %) in all horizon. Concerning the anion, chloride (8-11%) and bicarbonate (7-27%) howed appreciable concentration. Due to the ph, the bicarbonate concentration in the partially acid horizon (45 cm, 75 cm) were much lower than in the depth of 20 cm and 125 cm. In all horizon, organic anion (< 0.5%) and nitrate appeared only in trace amount. Phophate wa not detectable in oil olution. Of the cation, Mg 2+ (9-12 %) and Na + (12-15 %) howed appreciable concentration, wherea K + (< 0.3 %) wa found only in trace amount. NH + 4-, H + -, Al 3+ - and the heavy metal, epecially Fe 2+ (13 % in the depth of 75 cm), were detected in ignificant amount only in the acid horizon (Fig. 3A). Fourteen month after flooding, the element concentration at the 20 and 45 cm depth decreaed ignificantly (Fig. 3B). The concentration at 125 cm increaed, wherea at 75 cm no change were found. At 125 cm depth the concentration of mot element meaured increaed due to rewetting, the change in the upper horizon were more ignificant. Beide the dramatically decreaed concentration of Ca and SO 4 (alo Mg 2+, Na +, Cl -, Al 3+ concentration decreaed), the

5 concentration of ome element like K +, P, and heavy metal (epecially Fe and Mn) increaed, particularly in the top horizon, with time after rewetting. The abence of nitrate concentration after flooding indicate denitrification occurred. Beide diplacement, the increae of ome element concentration wa mainly caued by the olution of iron oxide and hydroxide. Due to the decreaed redox potential in the upper horizon, thi proce tarted three month after rewetting meaure and led to a ditinct increae of Fe in oil olution, particularly in the top horizon. In addition, element, which were aociated with the iron oxide, like P, Mn, and a were releaed and gradually increaed concentration could be detected. Thi fact i alarming becaue the content of iron i very high in the fen oil (about 100 g kg -1 ) and % of thi iron exit in form of amorphou, crytalline oxide or hydroxide (Genior et al., 1999). Additionally the A content are extremely high ( 200 mg kg -1 ). The reult of the element fluxe in the fen oil ytem and a balance heet for the firt year after rewetting howed three group of element in the fen oil ytem, namely element with a: Poitive balance - heet: diolved organic C, K +, NH 4 +, NO 3 - and H + Conitent balance - heet: Si 4+, Al 3+ and HCO 3 - Negative balance - heet: Ca 2+, Mg 2+, Na +, Fe, Mn, Cl - and SO 4 2- The reult howed that the fen oil ha primarily functioned a an element ource due to the rewetting (Table 4). While the output of Ca and ulfate ha been extremely large, even element like Fe and Mn increaed due to the rewetting and reached alarming concentration for trace metal. Generally, the output by leaching ha been very large. The element fluxe were large in the part of the experiment ite, which were influenced by the drainage ytem. For example, the ytem output of SO S (125 cm) 6.3 t ha 1 in the rewetted area in contrat with 4.2 t ha 1 in the untreated area. In addition, the difference in ulfur fluxe between 75 cm and 125 cm depth elucidate the influence of the drainage ytem. While in the acidic area of the ite the difference in SO S fluxe between the two Kationen mmol c/l Anionen cm 45 cm 75 cm 125 cm Ca2+ Mg2+ K+ Na+ Si4+ Al3+ Fe2+ Mn2+ HM NH4+ H+ SO42- NO3- Cl- PO43- F- HCO3- org. Anion Kationen mmolc/l Anionen cm 45 cm 75 cm 125 cm Ca2+ Mg2+ K+ Na+ Si4+ Al3+ Fe2+ Mn2+ HM NH4+ H+ SO42- NO3- Cl- PO43- F- HCO3- org. Anion Figure 3: Mean compoition of oil olution in 20 cm, 45 cm, 75 cm and 125 cm depth of the degraded fen oil at the beginning (A: before reflooding) and the end (B: after reflooding) of the invetigation (mmol c l -1 ; HM=Zn 2+ +A 3+ +Pb 2+ +Cu 2+ +Cd 2+ +Hg 2+ )

6 Table 4: Annual element fluxe in the fen oil of the invetigation ite (um of monthly mean from April to March (Balance = precipitation + irrigation 125 cm). kg ha -1 g ha -1 DOC Ca Mg K Na Si Al Fe + Mn NH 4 - NO 3 Cl - 2- SO 4 - HCO 3 H Precipitation Irrigation cm cm cm cm Balance horizon amount to 2.8 t ha -1 (flux in 75 cm = 9 t ha -1 ), there wa almot no difference in the flux in the undrained area. The coniderable difference between the element fluxe in 75 and 125 cm depth were caued by leaching procee due to the drainage ytem (the dominant proce), and the element were removed from the oil olution by chemical procee like adorption (due to the rewetting the content of organic C increaed between 85 and 100 cm, ubequently increaing the caution exchange capacity) and precipitation (ulfide). The decreaed flux of proton caued buffering (carbonate buffering, exchange buffering) and reduction. SUMMARY AND PROSPECTS The hitherto exiting invetigation have hown that the rewetting meaure ha led to a trong decreae in Eh in the top oil, conequently leading to permanent anaerobic and trongly reductive condition in the whole fen oil. Therefore, the decompoition and humification of organic ubtance decreaed and the CO 2 efflux wa reduced. Whether or not the change in CO 2 efflux are relevant with regard to climate depend mainly on the crocheck with the increaed CH 4 efflux. Becaue of thee change and the poitive C and N balance of the fen ecoytem (gaeou CO 2 loe were compenated by the reed bioma), by the retoration action providing condition for renewed peat growth were managed and therefore the requirement for the reactivation of the natural function of the fen in the landcape ecology. The high water level in the experimental plot (compared with the urrounding area) and the effective drainage ytem elevated the potential gradient and lead to a large water conumption, and to partially oxidative and oxidative condition, repectively in the fen oil. Thee condition were the reaon for the formation of acid, the ubequent acidification of the fen oil, and the mobilization, tranlocation, and leaching of nutrient and pollutant. Thee were leached very fat in appreciable amount into the groundwater via the main ditch under thee condition. In addition, procee, which could lead to torage of mobilized nutrient and pollutant (e.g. the formation of ulfide) or to an elevation of ph, were reduced or totally prevented. Due to of the totally changed condition in the fen oil, the ytem wa detabilized by rewetting. To tabilize the ytem, procee began that decreae of the element concentration in the oil olution due to the formation of ulfide, adorption, procee of tranlocation and leaching, increaed olubilization of iron oxide and hydroxide, the releae of aociated element, and increaed leaching of nutrient and pollutant (ditinctly influenced by the working drainage ytem). Due to rewetting, the fen ha been in a tranitional ince at the end of the invetigation period. How long the lited procee will be active, to what extent they will increae, decreae, or be replaced by other and if and when they will lead to the tabilization of the ytem can only be hypotheized. Reult of thi invetigation make it poible to draw concluion for the management of imilar project: Procee of rewetting hould be carried out on larger area in future time becaue the effect in the border area of the experiment would be marginal. The conequence would be decreaed amount of water needed for rewetting. The latter i important with regard to the irrigation of watewater. Any effective working drainage ytem mut be cloed. The conequence would be a ditinctly decreae in redox potential and ubequent immobilization of nutrient and pollutant by reduction procee and by increaing ph. Furthermore, the amount of leached element would be reduced, a would the conumption of water. The rewetting hould not be undone. The conequence would be a ditinct increae of redox potential and ubequent mobilization of tored nutrient and pollutant (epecially heavy metal and acid). REFERENCES Benne, I., Benzler, J. & A. Capelle (1992): Vorchlag zur Bodentypologichen Profilanprache und Klaifikation der Böden in Niederachen.-Techn.Ber.NIBIS, 3-55, Hannover Bodenkundliche Kartieranleitung (1994) Aufl., 392 S., Hannover. Genior, A. et al. (19): Fen retoration and reed cultivation:firt reult of an interdiciplinary project an northeatern Germany.-Proc. IPS Duluth, ; Duluth. Genior, A. & J. Zeitz (1999): Einflu einer Wiedervernäungmaßnahme auf die Dynamik chemicher und phyikalicher Bodeneigenchaften eine degradierten Niedermoore. Archiv für Naturchutz und Landchaftforchung, , Berlin Lundgarth, H. (1927): Carbon dioxide evolution of oil and crop growth.-soil Sci. 23;

7 Mundel, G. (16): Unteruchungen zur Torfmineraliation in Niedermooren. Arch. Acker u. Pflanzenbau u. Bodenkunde, 20, , Berlin TGL 24300/04 (15): Aufnahme landwirtchaftlich genutzter Standorte - Moortandorte. -DDR - Fachbereichtandard, Berlin. van Genuchten, M. Th. (10): A cloed-form equation for predicting the hydraulic conductivity of unaturated oil.-soil Sci. Of Americ. 11, Vetterlein, E. (18): Zur Anwendung der Doppel- Membran- und Doppel-Platten-Methode für Meungen der kapillaren Leitfähigkeit von Bodenproben.-Albrecht- Thear-Archiv 12, 3-991, Berlin. Zeitz, J. (1992): Bodenphyikaliche Eigenchaften von Subtrat-Horizont-Gruppen in landwirtchaftlich genutzten Niedermooren.-Z.f.Kulturtechnik und Landentw. 33, , Berlin.