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COURSE TITLE: Livestock grazing affects microbial activity at different soil depths via the groundwater level with potential implications for carbon sequestration

INSTRUCTORS Stefanie Nolte,, PhD
Amr Keshta, PhD

COURSE DESCRIPTION Saltmarshes, as many other wetlands, provide various ecosystem functions and services including shoreline protection and carbon (C) sequestration. The salt marshes of the Wadden Sea (Germany), have been strongly altered by anthropogenic influences such as livestock grazing, which has been practiced for centuries. It is, however, unclear how grazing affects some ecosystem functions and services. Carbon sequestration, for example, might be affected by livestock grazing both positively and negatively. On the one hand, grazing will reduce aboveground biomass, but was also previously found to increase belowground biomass, which is likely contributing more to soil organic C. On the other hand, livestock grazing can alter soil properties by soil compaction leading to lower pore space. This could lead to a reduced water drainage and thus a reduced Oxygen availability, which in turn hampers the breakdown of organic material by microorganisms. Therefore, the aim of this study was to assess the effect of grazing on soil structure and its influence on hydrology in salt marshes of the Wadden Sea. Additionally, we aim to quantify microbial activity as a proxy for the decomposition of organic matter at different soil depths. Our hypotheses were that soil at the grazed saltmarshes would have higher soil bulk density, lower C content, and lower water drainage rate.

Two saltmarshes were selected at the coast of the Wadden Sea: Dieksanderkoog marsh (DSK) and S�nke-Nissen-Koog marsh (SNK). Both DSK and SNK are part of the Schleswig-Holstein Wadden Sea National Park, Germany. With the establishment of National Parks in the 1990s, livestock grazing was abandoned in large areas. To study the effect of this grazing reduction on vegetation, two experiments were established at DSK and SNK in 1992 including a grazing treatment with sheep and an ungrazed control treatment at both sites. To assess the impact of grazing on soil properties in this experiment, a total number of 8 undisturbed soil cores (20 X 50 cm) were collected by inserting sharp-edged PVC pipes in October 2017. The soil cores were scanned in collaboration with Dr. J�rgen Titschack (MARUM Bremen) using a Computer Tomograph (CT) at the hospital Klinikum Bremen-Mitte, Germany, with an x-ray source voltage of 120 kV and a current of 600 mA. Following the soil CT scan and side-opening the cores, soil sub-samples were taken; where soil bulk density (g cm-3) and total C content (%) were estimated by core method and CHN analyses, respectively. Water level for both sites was recorded every 5 minutes for the last two years using slotted PVC wells and pressure sensors.

Data analyses of the cores indicated that ungrazed salt marshes have higher porosity (i.e. the percentage of pore spaces relative to sediment material) and connectivity (i.e. the ratio of number of disconnected pores relative to the total pore volume per slice) compared with grazed sites. Additionally, sediment density was higher at the grazed sites and increased with soil depth. Furthermore, the soil sub-samples results indicated that grazing had an impact on soil properties with higher soil bulk density and lower C content, most noticeable in the upper 5-10 cm. In line with this result, monitoring of water level indicated faster drainage rates for the ungrazed marshes as a result of higher porosity and less compaction. Furthermore, we expect that the longer retaining of the water between soil particles as a result of soil compaction by trampling might also impact the soil microbial activity. This parameter will therefore be assessed in soil cores from the same site in spring 2018.

Dr. Nolte earned her PhD at the University of Gronigen, Netherlands, in 2014, studying the effects of different grazing treatments on vegetation and sedimentation in salt marshes. She is currently a Junior research group leader in Coastal Ecology at the University of Hamburg, Germany; and her research interests include studies into the effects of global change and land use change on biodiversity, ecosystem functions, and ecosystem services of tidal marshes. Her aim is to understand the processes at work within these systems in order to promote their conservation, management, and restoration in times of global change.

Amr Keshta earned his PhD in 2017, at the University of Maryland, College Park, Maryland, USA. The topic of his Dissertation: Hydrology, Soil Redox, and Pore-water Iron Regulate Carbon Cycling in Natural and Restored Tidal Freshwater Wetlands in The Chesapeake Bay, Maryland, USA. His current research interests include environmental health, sea level rise, remote sensing, carbon sequestration, soil carbon stocks, hydrology, hydrodynamics, carbon and nitrogen cycling, greenhouse gas emissions, climate change, forest and wetlands ecosystems, urban ecosystems, ArcGIS, and processing of large data sets.

Credit Points: 0.06

SYLLABUS/TOPICAL OUTLINE Saltmarshes, as many other wetlands, provide various ecosystem functions and services including shoreline protection and carbon (C) sequestration. The salt marshes of the Wadden Sea (Germany), have been strongly altered by anthropogenic influences such as livestock grazing, which has been practiced for centuries. It is, however, unclear how grazing affects some ecosystem functions and services. Carbon sequestration, for example, might be affected by livestock grazing both positively and negatively. On the one hand, grazing will reduce aboveground biomass, but was also previously found to increase belowground biomass, which is likely contributing more to soil organic C. On the other hand, livestock grazing can alter soil properties by soil compaction leading to lower pore space. This could lead to a reduced water drainage and thus a reduced Oxygen availability, which in turn hampers the breakdown of organic material by microorganisms. Therefore, the aim of this study was to assess the effect of grazing on soil structure and its influence on hydrology in salt marshes of the Wadden Sea. Additionally, we aim to quantify microbial activity as a proxy for the decomposition of organic matter at different soil depths. Our hypotheses were that soil at the grazed saltmarshes would have higher soil bulk density, lower C content, and lower water drainage rate. Two saltmarshes were selected at the coast of the Wadden Sea: Dieksanderkoog marsh (DSK) and S�nke-Nissen-Koog marsh (SNK). Both DSK and SNK are part of the Schleswig-Holstein Wadden Sea National Park, Germany. With the establishment of National Parks in the 1990s, livestock grazing was abandoned in large areas. To study the effect of this grazing reduction on vegetation, two experiments were established at DSK and SNK in 1992 including a grazing treatment with sheep and an ungrazed control treatment at both sites. To assess the impact of grazing on soil properties in this experiment, a total number of 8 undisturbed soil cores (20 X 50 cm) were collected by inserting sharp-edged PVC pipes in October 2017. The soil cores were scanned in collaboration with Dr. J�rgen Titschack (MARUM Bremen) using a Computer Tomograph (CT) at the hospital Klinikum Bremen-Mitte, Germany, with an x-ray source voltage of 120 kV and a current of 600 mA. Following the soil CT scan and side-opening the cores, soil sub-samples were taken; where soil bulk density (g cm-3) and total C content (%) were estimated by core method and CHN analyses, respectively. Water level for both sites was recorded every 5 minutes for the last two years using slotted PVC wells and pressure sensors. Data analyses of the cores indicated that ungrazed salt marshes have higher porosity (i.e. the percentage of pore spaces relative to sediment material) and connectivity (i.e. the ratio of number of disconnected pores relative to the total pore volume per slice) compared with grazed sites. Additionally, sediment density was higher at the grazed sites and increased with soil depth. Furthermore, the soil sub-samples results indicated that grazing had an impact on soil properties with higher soil bulk density and lower C content, most noticeable in the upper 5-10 cm. In line with this result, monitoring of water level indicated faster drainage rates for the ungrazed marshes as a result of higher porosity and less compaction. Furthermore, we expect that the longer retaining of the water between soil particles as a result of soil compaction by trampling might also impact the soil microbial activity. This parameter will therefore be assessed in soil cores from the same site in spring 2018.

COURSE CONTACT

Louis Mantini
9225 CR 49, Live Oak, FL 32060
lfm@srwmd.org
P: 386.647.3144
F:

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