Ein Vergleich Zwischen Küstenlagunen Der Südlichen Ostsee
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Stoffflüsse in Makrophytensystemen: Ein Vergleich zwischen Küstenlagunen der südlichen Ostsee Inauguraldissertation zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) der Mathematisch-Naturwissenschaftlichen Fakultät der Ernst-Moritz-Arndt-Universität Greifswald vorgelegt von Jutta Meyer geboren am 03.05.1982 in Berlin Rostock, 8. Februar 2017 Dekan: Prof. Dr. Werner Weitschies 1. Gutachter: PD. Dr. habil. Irmgard Blindow 2. Gutachter: Prof. Dr. rer. nat. habil. Brigitte Nixdorf Tag der Promotion: 16.06.2017 Abstract In the past decades, Eutrophication led to an unsatisfying ecological state of several coastal lagoons around the Baltic Sea, resulting e. g. in extensive harmfull algae blooms. To regain a good ecological state of coastal waters was therefore a central aim of the EU-Water Framework Directive. For restoration of freshwater ecosystem submerged macrophytes, such as charophytes and angiosperms, are already used to improve water quality (Gulati et al., 2008; Hilt et al., 2006). Macrophytes directly reduce water turbidity as they promote sedimentation of suspended matter and limit resuspension of sediment. They also provide zooplankton a refuge against predators. As zooplankton graze on phytoplankton, macro- phytes indirectly promote reduction of phytoplankton biomass and therefore, reduce water turbidity. Additionally, they can successfully compete with phytoplankton for nutrients. It was stated by Jeppesen et al., (1994) that these feedback mechanisms are less effective in brackish waters, as e. g. zooplankton grazing on phytoplankton is less efficient due to a different species composition and a higher mortality of zooplankton caused by fishes and invertebrates within macrophyte stands. In the present thesis, interactions between submerged macrophytes and their biotic and abiotic environment were determined in two shallow brackish coastal lagoons of the southern Baltic Sea. The macrophyte-dominated mesotrophic (LUNG, 2008) Vitter Bodden experiences no river run-off and probably has a larger water exchange with the Baltic adjacent Baltic Sea than the phytoplankton-dominated, eutrophic to heavily eutrophic (LUNG, 2008) Darss-Zingster-Bodden chain (DZBC). The effects of submerged vegetation on the ecological status of the two studied brackish lagoons were discussed, and possible implications on management of the DZBC are highlighted. To analyse the interactions and limiting factors for macrophyte depth distributions and phytoplankton biomass, the following abiotic and abiotic parameter were determined, from June to September 2013 (Vitter Bodden) and from March to November 2014 (DZBC): Light attenuation, concentrations of total suspended matter (TSM), detritus (only Vitter Bodden), chlorophyll a (Chl a), total phosphorus (TP) and total nitrogen (TN, only Vitter Bodden), and the ratios of TP to TN (only Vitter Bodden) and of Chl a to TP. Grazing pressure of zooplankton on phytoplankton were calculated, by determining zooplankton abundance, biomass and grazing rate, both at day and at night. Macrophyte composition, coverage and biomass, as well as percentage of the water column infested by macrophytes (PVI) were estimated at water depths below 1 m in the Vitter Bodden. Macrophyte biomass was measured down to 1.9 m in the DZBC. Macrophytes’ depth distribution was not limited by light availability in the Vitter Bodden but in the DZBC. Macrophytes grew down to 2.9 m in the Vitter Bodden (Bühler, 2016), whereas the major portion of macrophytes biomass was found in water depth not deeper then1 m in the DZBC. Phytoplankton had a substantial contribution to water turbidity and therefore, probably limited light availability for macrophytes and for itself as well. TN to TP ratios (gained by monitoring data, provided by the LUNG) indicated P-limitation of the phytoplankton in the DZBC, and own data indicated P-limitation with co-limitations by nitrogen in the Vitter Bodden. Zooplankton grazing had probably a limiting effect on phytoplankton biomass in the Vitter Bodden but not in the DZBC. The range of mean grazing pressure were 2.1-77.9 % and 0.9-22.2 % of phytoplankton biomass per day in the Vitter Bodden in the DZBC, respectively. Charophytes (Chara aspera, C. baltica, C. canescens), Potamogeton pectinatus, Ruppia spp., Zannichellia spp. and Myriophyllum spicatum were found in both lagoon systems, while extensive mats of drifting Fucus vesiculosus f. balticus were only found in the Vitter Bodden. An overall small growth form of the macrophytes limited the vertical expansion of macrophytes into the water column, especially in the Vitter Bodden, leading to low PVI values despite high coverages. In conclusion, the considerable water exchange with the Baltic Sea and missing river- runoff probably sustained a high light availability in the Vitter Bodden. Possible influences of macrophytes, on water turbidity, phytoplankton nourishment and zooplankton protection against predation, were probably masked by the water exchange with the Baltic Sea at the studied shallow parts of the Vitter Bodden. There are no or negligible effects of macro- phytes on nutrients in the water column, on phytoplankton biomass and on zooplankton abundance and biomass in the DZBC, as the macrophytes are restricted to the lagoons’ margins. Phytoplankton biomass was high despite nutrient limitation in the DZBC, because it consisted mainly of cyanobacteria, which are well adapted to low nutrient availability (Schumann & Karsten, 2006). Additionally, single cells and colonies of many cyanobacte- ria species were surrounded by high, self-produced mucoid masses, which may have protect them from grazing (Schumann et al., 2001; Schumann & Karsten, 2006). There- fore, it might be difficult to restore the DZBC by biomanipulation, e. g. by reducing predation on zooplankton or by reducing nutrient input in the DZBC. As sedimentation and resuspension play a major role for water turbidity in shallow waters, the aim of the second part of this study was to determine an influence of wind-induced waves on sedimentation rates by resuspending instantaneous settled matter. For this purpose, sedimentation rates of suspended matter were determined at one location in the DZBC between 0.9-1.6 m water depths. Two different types of sedimentation traps were used, cylindrical traps (CT) and plate traps (PT). PT allowed already settled matter to resuspend, whereas CT did not. For the first time the PT were used at a wave exposed location. Wave exposure was calculated by dividing half wave length (λ/2) by the water column above the traps (dT). High wave exposure was defined as (λ/2) / dT >1. The sedimentation rates in both trap types was influenced by wave exposure, however, in two contrary ways. At high wave exposure, PT trapped less percentage of TSM per hour than at low wave exposure, whereas the CT trapped more percentage of TSM per hour. Sedimentation rates in both trap types accurately followed natural short-term sedimentation rates at low wave exposure, whereas cylindrical traps overestimated sedimentation rates at high wave exposure. In conclusion, the used plate traps are a promising tool to estimate sedimentation rates at shallow, wave exposed locations, as they reflected the instantaneous influences of wave motions on sedimentation of suspended matter more realistically than the, up to now, more commonly used cylindrical traps. Inhaltsverzeichnis Abkürzungsverzeichnis …………………………………………………….…….… I Abbildungsverzeichnis ………………………………………………………..….… III Tabellenverzeichnis ……………………………………………………………….... VI 1.1 Einleitung ……………………………………………………………………... 1 1.2 Beschreibung der Untersuchungsgewässer Vitter Bodden und Darß-Zingster- Boddengewässer …………………………………………………………….... 8 2 Verhältnisse zwischen submersen Makrophyten und ihrer biotischen und abiotischen Umgebung im Vitter Bodden ……………………………………. 13 Ziele & Hypothesen ……………………………………………………… 13 Methoden ………………………………………………………………... 14 Ergebnisse ……………………………………………………………….. 19 Beantwortung der Hypothesen …………………………………………... 35 3 Makrophyten in der DZBK ………………………………………………….... 36 3.1 Interaktionen zwischen Makrophyten und ihrer biotischen und abioti- schen Umgebung ……………………………………….…………….. 36 Ziele & Hypothese ……………………………………………….. 36 Methoden ……………………………………………………….... 38 Ergebnisse ……………………………………………………….. 42 Beantwortung der Hypothesen …………………………………... 61 3.2 Ermittlung der aktuellen, potentiellen Gesamt-Makrophytenbiomasse in der DZBK …………………………………………….……………. 62 Ziele ……………………………………………………………… 62 Methoden & Ergebnisse ………………………………………..... 62 4 Diskussion der Interaktionen zwischen Makrophyten und ihrer abiotischen und biotischen Umgebung in Makrophyten bzw. Phytoplankton dominierten Küstengewässern ……………………………………………………………... 68 Lichtlimitation von Makrophyten und Phytoplankton und Interaktion zwischen beiden Primärproduzenten …………………………………….. 68 Limitationen durch verfügbare Nährstoffe und Interaktion zwischen Nährstoffen und Primärproduzenten …………………………………….. 73 Limitierende Interaktionen zwischen Phytoplankton und Zooplankton .. 77 5 Sedimentation in einer flachen, inneren Küstenlagune, beeinflusst durch Wind induzierte Wellen ……………………………………………………............... 81 Hintergrund …………………………………………………………….... 81 Ziele & Hypothesen ……………………………………………………… 82 Methoden ………………………………………………………………... 84 Ergebnisse ……………………………………………………………….. 87 Beantwortung der Hypothesen …………………………………………... 96 Diskussion ……………………………………………………………….. 97 6 Schlussfolgerungen und Wissenschaftlicher Ausblick ……………………….. 100 7 Literaturverzeichnis