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Methane measurements at lander_2 in a coastal peatland at the German Baltic Sea in 2021

Rewetting peatlands is an important measure to reduce greenhouse gas (GHG) emissions. However, after rewetting, the areas are highly heterogeneous in terms of GHG exchange, which depends on water level and source, vegetation, previous use, and duration of rewetting. These challenging conditions require new technologies that go beyond discrete sampling. Here we present data from two autonomous lander platforms deployed at the sediment-water interface (bottom lander) of a shallow coastal peatland (approx. 1 m water depth) that was rewetted by brackish water from the Baltic Sea, thus becoming part of the coastal water through a permanent connection. These landers were equipped with six commercially available state-of-the-art sensors, and temporal high-resolution measurements of physico-chemical variables, including partial pressures of carbon dioxide (CO2) and methane (CH4), were made. The resolution of the field data ranged from 10 seconds to 120 minutes and was obtained for partial pressure of CO2 (Contros HydroC-CO2) and CH4 (Contros HydroC-CH4), temperature, salinity, pressure (water depth), oxygen (O2) (CTD-O2 with SBE-37SMP-ODO), the concentrations of phosphate (SBE HydroCycle PO4), nitrate (SBE SUNA V2), chlorophyll a and the turbidity (both with SBE-FLNTUSB ECO) as stationary measurements at two different locations in close proximity. The CTD and oxygen measurements provide exact water depth data for the respective lander locations. In the other data sets (e.g., CO2 measurements) rounded data are inserted instead of the exact depth data, which is 0.6 m for lander_1 and 0.9 m for lander_2. SUNA raw data are provided for completeness. However, we found them of insufficient quality to estimate nitrate concentrations due to interferences and biofouling. The deployment and recovery of the landers, and thus the measurements, took place between 02 June 2021 and 09 August 2021, and the sensors were operated under permanent wired power supply and a centralized timestamp. The sensors were maintained and cleaned bi-weekly. Results show considerable temporal fluctuations expressed as multi-day, diurnal, and event-based variability, with spatial differences caused by biologically-dominated variables.

Bottom water data of sediment incubation experiments under anoxic conditions

Enhanced mineral dissolution in the benthic environment is currently discussed as a potential technique for ocean alkalinity enhancement (OAE) to reduce atmospheric carbon dioxide (CO2) levels. This study explores how biogeochemical processes affect the dissolution of alkaline minerals in surface sediments during laboratory incubation experiments. These involved introducing dunite and calcite to organic-rich sediments from the Baltic Sea under controlled conditions in an anoxic to hypoxic environment. The sediment cores were incubated with Baltic Sea bottom water. Eight sediment cores were positioned vertically in a rack. Since the sediment surface was slightly oxidized by the bottom water (∼125 μmol l−1 upon recovery), the cores were left plugged on the top for 13 days to settle after recovery until the sediment surface was anoxic. To achieve chemical conditions that are expected in the natural system, 500l of retrieved sea water were degassed via bubbling with pure dinitrogen gas in batches of 100 l. Afterwards, between 50 and 60 l were transferred into an evacuated gas tight bag. After the transfer, pH and total alkalinity (TA) were measured to determine the dissolved inorganic carbon (DIC) of the water. Afterwards the DIC was increased via adding pure CO2 until a CO2 partial pressure (pCO2 ) of ∼2,300–∼3,300 μatm was established mimicking conditions prevailing in Boknis Eck during summer. Stirring heads were installed on the cores. To prevent the development of oxic conditions, it was ensured that as little gas phase as possible was left in the cores. Elimination of pelagic autotrophs, heterotrophs, and suspended particles was achieved by flushing the cores with modified bottom water for 2 days with a flow rate of 1.5 mml min−1. Afterwards, a continuous throughflow of 700 μl min−1 from the reservoir of modified bottom water was applied, leading to a residence time of ∼2.1 days inside the cores. For the experimental incubations, six cores received additions of alkaline materials, three with calcite (Cal1 - Cal3) and three cores with dunite (Dun1 - Dun3), leading to three replicates per treatment. Two control cores remained untreated (C1, C2). The amount of added substrate was based on the rain rate of particulate organic carbon observed in Boknis Eck (0.5 mmol cm−2 a−). The incubation lasted for 25 days. The volume of water in each core was determined at the end of the experiment via measuring the height of the water column after removing the stirring heads. Bottom water samples were taken from the outflow of each core over a time period of several hours. Thus, samples represent the average outflow over the respective time period. Sampling intervals increased from daily during the first two weeks to every three to four days and weekly towards the end of the experiment. All samples were filtered through a 0.2 µm cellulose membrane filter and refrigerated in 25 ml ZinsserTM scintillation vials. Samples for TA were analyzed directly after sampling by titration of 1 ml of bottom water with 0.02N HCl. Titration was ended when a stable purple color appeared. During titration, the sample was degassed by continuous bubbling with nitrogen to remove any generated CO2 and H2S. The acid was standardized using an IAPSO seawater standard. Acidified sub-samples (30 μl suprapure HNO3- + 3 ml sample) were prepared for analyses of major and trace elements (Si, Na, K, Li, B, Mg, Ca, Sr, Mn, Ni and Fe) by inductively coupled plasma optical emission spectroscopy (ICP-OES, Varian 720-ES).

Methane measurements at lander_1 in a coastal peatland at the German Baltic Sea in 2021

Rewetting peatlands is an important measure to reduce greenhouse gas (GHG) emissions. However, after rewetting, the areas are highly heterogeneous in terms of GHG exchange, which depends on water level and source, vegetation, previous use, and duration of rewetting. These challenging conditions require new technologies that go beyond discrete sampling. Here we present data from two autonomous lander platforms deployed at the sediment-water interface (bottom lander) of a shallow coastal peatland (approx. 1 m water depth) that was rewetted by brackish water from the Baltic Sea, thus becoming part of the coastal water through a permanent connection. These landers were equipped with six commercially available state-of-the-art sensors, and temporal high-resolution measurements of physico-chemical variables, including partial pressures of carbon dioxide (CO2) and methane (CH4), were made. The resolution of the field data ranged from 10 seconds to 120 minutes and was obtained for partial pressure of CO2 (Contros HydroC-CO2) and CH4 (Contros HydroC-CH4), temperature, salinity, pressure (water depth), oxygen (O2) (CTD-O2 with SBE-37SMP-ODO), the concentrations of phosphate (SBE HydroCycle PO4), nitrate (SBE SUNA V2), chlorophyll a and the turbidity (both with SBE-FLNTUSB ECO) as stationary measurements at two different locations in close proximity. The CTD and oxygen measurements provide exact water depth data for the respective lander locations. In the other data sets (e.g., CO2 measurements) rounded data are inserted instead of the exact depth data, which is 0.6 m for lander_1 and 0.9 m for lander_2. SUNA raw data are provided for completeness. However, we found them of insufficient quality to estimate nitrate concentrations due to interferences and biofouling. The deployment and recovery of the landers, and thus the measurements, took place between 02 June 2021 and 09 August 2021, and the sensors were operated under permanent wired power supply and a centralized timestamp. The sensors were maintained and cleaned bi-weekly. Results show considerable temporal fluctuations expressed as multi-day, diurnal, and event-based variability, with spatial differences caused by biologically-dominated variables.

Water and sediment analysis from column experiments

This data set contains data from water analyses from column experiments. The water analyses included cations (sodium, potassium, calcium, magnesium, iron and manganese), anions (nitrate, chloride, sulphate, bromide and phosphate) and selected trace elements (arsenic, cobalt, nickel, vanadium and zinc). The column experiments were conducted with two different types of unconsolidated sandy sediments from aquifers in Denmark (Quaternary) and Germany (Cretaceous). In both sediments, the nitrate degradation capacity was almost exhausted. To induce denitrification, 5 mmol ethanol was added to the column experiments. This also caused a decrease in the concentration of trace elements in the water. A sequential extraction procedure was performed to determine the trace element sinks. The data set therefore also contains contents of selected elements (equal to water analyses) from the sequential extraction procedure of the sediment before and after the column tests. The results observed in the laboratory were additionally modeled with Phreeqc. The Phreeqc input data complete the data set.

Organic parameters obtained from Röttingen core

The total carbon (TC), total organic carbon (TOC), and total sulfur (TS) were determined using a LECO CS-230 system (Laboratory Equipment Corporation). Samples were heated up to 2000 °C under an oxygen atmosphere and an infrared detector subsequently measured the amount of produced CO₂ and SO₂. TOC was measured the same way after removing inorganic carbonates using 10 % HCl solution at 80 °C. Rock-Eval Pyrolyses were performed on a Rock-Eval-6 analyser (Vinci Technologies) using up to 180 mg initial sample material and a standard program (Espitalié et al., 1977; Lafargue et al., 1998), starting isothermal with 300°C for 3 min, succeeded by a heating rate of 25°C/min up to 650°C. Standard deviations for hydrogen indices (HI) and Tmax values are ± 5 % and ± 2°C, respectively.

Organic parameters obtained from Metzingen core

The total carbon (TC), total organic carbon (TOC), and total sulfur (TS) were determined using a LECO CS-230 system (Laboratory Equipment Corporation). Samples were heated up to 2000 °C under an oxygen atmosphere and an infrared detector subsequently measured the amount of produced CO₂ and SO₂. TOC was measured the same way after removing inorganic carbonates using 10 % HCl solution at 80 °C. Rock-Eval Pyrolyses were performed on a Rock-Eval-6 analyser (Vinci Technologies) using up to 180 mg initial sample material and a standard program (Espitalié et al., 1977; Lafargue et al., 1998), starting isothermal with 300°C for 3 min, succeeded by a heating rate of 25°C/min up to 650°C. Standard deviations for hydrogen indices (HI) and Tmax values are ± 5 % and ± 2°C, respectively.

Carbonate chemistry speciation of the 2023 KOSMOS Helgoland experiment on the effects of ocean alkalinity enhancement on pelagic foodwebs

This dataset contains carbonate chemistry speciation data of the 2023 KOSMOS mesocosm study on Helgoland, Germany. This study tested the effects of ocean alkalinity enhancement simulating lime additions on pelagic ecosystem functioning during a spring bloom. Carbonate chemistry speciation (fCO2, pHT, calcium carbonate saturation state) was generally calculated from measurements of total alkalinity (TA) and dissolved inorganic carbon (DIC) in depth-integrated water samples. There were 12 mesocosms in total and in 6 of them an alkalinity gradient of up to +1250 umol/kg was established in steps of 250 umol/kg. In the remaining 6 the same amount of alkalinity was added only to the upper portion of the mesocosms, resulting in twice the alkalinity increase there, before being mixed in after 48 hours. The two treatments simulated the immediate dilution of TA after ship deployment as well as a delayed one from a point source.

Historical water chemistry monitoring records from multiple stations between 1959 and 2017

Long-term water-chemistry measurements from multiple Elbe River monitoring stations establish a baseline for carbonate-system variability and were used to assess the alkalinity transport potential. The dataset from 1959 to 1977 was digitized from handwritten notes provided by Dr. Mewius (Kempe 1982). The water chemistry data from 1984 to 2017 (e.g., pH, water temperature, and major ions) was obtained from the Fachinformationssystem (FIS) der FGG Elbe (data source: www.fgg-elbe.de, accessed on 2021-02-26).To generate a single river chemistry time series, data from (Zollenspieker (Strom-km 598,7), Geesthacht (Strom-km 585,9), Schnackenburg (Strom-km 474,5), Boizenburg (Strom-km 559,0), Doemitz (Strom-km 505,0), and Hamburg Waterworks (Strom-km ~623,1) were used. Saturation state of calcite and aragonite were calculated using phreeqpython, a Python wrapper of the PhreeqC engine (Vitens 2021) with pH, water temperature, total alkalinity, and major ions as major input, and phreeqc.dat as database for the thermodynamic data (Parkhurst and Appelo 2013).

Carbonate chemistry from laboratory incubation experiments using water samples from the Elbe conducted in 2023

This dataset comprises key carbonate chemistry parameters measured and calculated in incubation experiments under different experimental conditions. pH, water temperature, and salinity were measured with a WTW multimeter (MultiLine® Multi 3630 IDS). Total alkalinity was determined by open-cell titration with an 888 Titrando (Metrohm). Saturation state of calcite and aragonite were calculated using phreeqpython, a Python wrapper of the PhreeqC engine (Vitens 2021) with pH, water temperature, total alkalinity, and major ions as major input, and phreeqc.dat as database for the thermodynamic data (Parkhurst and Appelo 2013). As the original Elbe water was supersaturated with carbon dioxide (CO2) with respect to the atmosphere, its partial pressure of CO2 (pCO2) level decreased during the incubation period with open flasks, which caused an adjustment of calcite saturation state (ΩC) for ambient air conditions. To adapt for the impact of pCO2 variations during the experiment, saturation state of calcite and aragonite was calculated assuming an equilibrium with an atmospheric pCO2 of 415 ppm (normalized ΩC and normalized aragonite sautration state ΩA). Since ion concentrations were measured for only a small number of samples, the ion concentrations of the remaining samples were reconstructed using stoichiometry based on the initial solution composition and total alkalinity. The concentrations of conservative ions (Na+, K+, Cl-, SO42-) were assumed remain constant, while ions related to carbonate precipitation (Ca2+, Mg2+) were calculated based on changes in measured alkalinity (see Figure 5 of the associated paper). Detailed analysis and calculation procedures are described in the Method section of the associated paper.

Langjährige Entwicklung der Luftqualität - Berliner Luftgütemessnetz - Standorte und Messdaten (Umweltatlas)

Darstellung aller Stationen und Messwerte der BLUME-, RUBIS- und Passivsammler-Messnetze seit 1975 sowie ausgewählter langjährig betriebener Berliner Klimastationen

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