Water Level Fluctuations in Rich Fens: an Assessment of Ecological Benefits and Drawbacks

UvA-DARE (Digital Academic Repository) Water level fluctuations in rich fens: an assessment of ecological benefits and drawbacks Mettrop, I.S. Publication date 2015 Document Version Final published version Link to publication Citation for published version (APA): Mettrop, I. S. (2015). Water level fluctuations in rich fens: an assessment of ecological benefits and drawbacks. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:25 Sep 2021 The relative importance of calcium and iron Chapter 6 The relative importance of calcium and iron for nutrient availability, productivity and species composition in brown moss-dominated rich fens Ivan S. Mettrop, Tessa Neijmeijer, Casper Cusell, Leon P.M. Lamers, Lars Hedenäs, Annemieke M. Kooijman Abstract Rich fens are characterized by minerotrophic conditions, in which calcium (Ca) and iron (Fe) concentrations show large variations. The relative importance of Ca and Fe, particularly in relation to the availability of phosphorus (P) for rich fen vegetation, is however largely unknown. To elucidate this, we examined the relation between vegetation characteristics and peat chemistry in 24 stands of rich fen vegetation: 12 in the Netherlands (strong anthropogenic forcing) and 12 in central Sweden (weak anthropogenic forcing). In addition, specific habitat preferences of three typi- cal brown moss spp. were assessed. Ca and Fe turned out to be important drivers of species composition in rich fens through their differential effects on plant P-availability. Fens dominated by Scorpidium scorpioides or S. cossonii were characterized by high porewater Ca-concentrations and total soil Ca-contents, but low P-availability. In these Ca-rich, but Fe-poor fens, foliar N:P ratios of vascular vegetation were above 20 g g-1, indicating P-limitation due to Ca-P precipitation. In contrast, fens dominated by Hamatocaulis vernicosus were characterized by high porewater Fe-concentrations and total soil Fe-contents, but also relatively high P-availability. Total soil Fe-content showed a positive correlation with total soil P- content and P-concentration in plant tissue, and a negative correlation with foliar N:P ratios. N:P ratios in these fens were even below 13.5 g g-1, indicating potential nitrogen (N)-limitation. The remarkable positive correlation between soil Fe-content and P-availability contrasts the idea that high Fe-contents automatically lead to low values of plant-available P. We instead propose that high groundwater Fe discharge leads to the accumulation of P that is still available to plants due to the relatively weak binding of P within abundant Fe-OM (Organic Matter) complexes. Furthermore, total biomass production was regulated by plant P-availability in Sweden. In the Netherlands, however, where above-ground biomass was 2.5 times higher, only the vegetation composition was regulated by plant P-availability. Finally, Dutch rich fens were more acidic than Swedish, which is probably related to the much higher atmospheric N-deposition. 115 Chapter 6 We conclude that the relative roles of Ca and Fe strongly differ with respect to nutrient limitation and vegetation development in rich fens, and should therefore be included in studies relating vegetation development to geohydrological conditions. 6.1 Introduction Mesotrophic and minerotrophic, species-rich fens are considered ecologically valu- able because of their high floristic diversity including many red list species (Wassen et al., 2005; van Diggelen et al., 2006). These so-called ‘rich fens’ have become very rare in densely populated and heavily exploited landscapes, and are therefore protected as EU priority habitat H7140 – Transition mires and quaking bogs. Gener- ally, the most important habitat characteristics explaining floristic diversity in fens are considered to be differences in water level, acid neutralizing capacity (ANC), nutrient-availability, and toxicity (e.g. Wheeler and Proctor, 2000; Hájek et al., 2006; Lamers et al., 2015). Autogenic succession in fens, and/or anthropogenic intervention in areas with intensive agriculture, have resulted in hydrological isolation from base-rich groundwater and surface water, and hence reduced ANC (van Wirdum, 1991; Van Diggelen et al., 1996). Presumably, increased atmospheric deposition of nitrogen (N) has exacerbated the acidification of fens in industrialized countries (Gorham et al., 1987). In addition to sufficient ANC, phosphorus (P) limitation has been shown to be important to enable high biodiversity and the occurrence of rare and endangered bryophytes and plant species in rich fens (Boeye et al., 1997; Wassen et al., 2005; Cusell et al., 2014). In rather calcareous rich fens, Ca-related precipitation (co-precipitation with CaCO3 and precipitation as Ca phosphates) reduces the bio-availability of P (Boyer and Wheeler, 1989; Wassen et al., 1990). In addition, the bio-availability of P has been reported to be reduced by Fe-related P-precipitation (to Fe oxides and hydroxides, and as organic Fe phosphates) in mires (e.g. Roden and Edmonds, 1997; Zak et al., 2004). For rich fens, however, the general assumption that Fe-rich conditions automatically imply a lower P-availability is called into question (Aggenbach et al., 2013; Pawlikowski et al., 2013; Cusell et al., 2014). Therefore, and because it is important for the mechanistic understanding of the functioning and biodiversity of fens, the objective of this study was to reconsider the relative biogeochemical importance of Ca and Fe, particularly in relation to plant-available P in rich fens in regions with either high (the Netherlands) or low (central Sweden) anthropogenic pressure. In addition to soil porewater analyses, we therefore included additional soil extractions to assess different fractions of P in fen 116 The relative importance of calcium and iron Table 6.1 The different sampling locations in the Netherlands and central Sweden. Species The Netherlands Coordinates Central Sweden Coordinates Scorpidium scorpioides Binnenpolder Tienhoven 52 10’31 N; 05 59’01 E Gulåstjärnen 63 29’17 N; 14 53’48 E Stobbenribben 52 47’09 N; 05 59’03 E Gulåstjärnen lakesite 63 29’17 N; 14 53’48 E Kikkerlanden 52 39’45 N; 06 02’27 E Storflon 63 13’32 N; 16 00’45 E De Haeck 52 08’59 N; 04 50’36 E Stormyran 63 13’15 N; 16 09’22 E Scorpidium cossonii Geleenbeekdal 50 55’34 N; 05 54’03 E Flärkarna 63 04’01 N; 16 10’43 E Bennekomse Meent 52 00’22 N; 05 35’37 E Gulåstjärnen 63 29’17 N; 14 53’48 E Veerslootlanden 52 37’09 N; 06 08’15 E Gulåstjärnen lakesite 63 29’17 N; 14 53’48 E Veldweg 52 41’29 N; 06 06’45 E Stormyran 63 13’15 N; 16 09’22 E Hamatocaulis vernicosus Blauwe Hel 52 00’48 N; 05 34’16 E Flärkarna 63 04’01 N; 16 10’43 E Meppelerdieplanden 52 40’05 N; 06 07’37 E Storflon 63 13’33 N; 16 00’45 E Kiersche Wiede 52 41’48 N; 06 07’57 E Källmyren 63 24’10 N; 14 34’07 E Meppeler Diep 52 41’00 N; 06 08’51 E Stormyran 63 13’15 N; 16 9’22 E soils. Our main hypothesis was that the relative abundances of Ca and Fe are important drivers of rich fen functioning, diversity and species composition, through their differential effects on plant P-availability. 6.2. Materials and methods Sampling Samples were collected from 12 rich fens in the Netherlands and 12 rich fens in central Sweden (Table 6.1). Dutch samples were collected in August 2011, and Swedish samples from the province Jämtland in August/September 2012. We selected the sampling sites based on dominance of either Scorpidium scorpioides (Hedw.) Limpr., Scorpidium cossonii (Schimp.) Hedenäs, or Hamatocaulis vernicosus (Mitt.) Hedenäs. For each site, species composition and cover percentages of vascular plants and bryophytes were recorded in a 10 m2 plot. In each plot, three subplots of 25 cm2 with dominant coverage by one of the three bryophytes were randomly selected. At each subplot the height of the water level relative to the soil surface just beneath the living moss layer was measured, and above-ground biomass of the vascular vegetation was clipped at soil surface and harvested for further analysis. At each subplot, also porewater samples from the upper 10 cm of the soil were collected with Rhizon SMS soil moisture samplers (Rhizon SMS-10 cm; Eijkelkamp Agrisearch Equip- ment, Giesbeek, the Netherlands), connected to vacuumed syringes of 50 mL. In addition, peat soil samples were collected from the upper 10 cm of the peat soil, just below the living moss layer. Furthermore, samples for bulk density were collected 117 Chapter 6 using a steel corer with an exact volume of 100 mL. All samples were collected in airtight plastic bags to avoid oxygen exposure, and stored at 4˚C until further analysis. Analytical techniques Porewater pH-values were measured with a standard Ag/AgCl electrode and al- kalinity was determined by titration down to pH 4.2 by using 0.01 mol L-1 HCl.

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