Visualizing land‐use and management complexity within biogeochemical cycles of an agricultural landscape

Crop fields are cultivated across continuities of soil, topography, and local climate that drive biological processes and nutrient cycling at the landscape scale; yet land management and agricultural research are often performed at the field scale, potentially neglecting the context of the surrounding landscape. Adding to this complexity is the overlap of ecosystems and their biogeochemical legacies, as a patchwork of crops fields, natural grasslands, and forests develops across the landscape. Furthermore, as new technologies and policies are introduced, management practices change, including fertilization strategies, which further alter biological productivity and nutrient cycling. All of these environmental, biological, and historical legacies are potentially recorded in the isotopic signal of plant, soil, and sediment organic matter across the landscape. We mapped over 1500 plant, soil, and sediment isotopic values and generated an isotopic landscape (isoscape) over a 40-km² agricultural site in NE Germany. We observed distinct patterns in the isotopic composition of organic matter sampled from the landscape that clearly reflect the landscape complexity. C₃ crop intrinsic water-use efficiency reflected a precipitation gradient, while native forest and grassland plant species did not, suggesting that native plants are more adapted to predominant climatic conditions. δ¹³Csoil patterns reflected both the long-term input of plant organic matter, which was affected by the local climate conditions, and the repeated cultivation of corn. Soil organic matter ¹⁵N isotopic values also revealed spatial differences in fertilization regimes. Forest fragments, in which the nitrogen cycle was relatively open, were more water-use efficient. Sediments from small water bodies received substantial inputs from surrounding field vegetation but were also affected by seasonal drying. These isotopic maps can be used to visualize large spatial heterogeneity and complexity, and they are a powerful means to interpret past and current trends in agricultural landscapes

Anthropogenic Impact on Tropical Perennial River in South India: Snapshot of Carbon Dynamics and Bacterial Community Composition

Riverine systems play an important role in the global carbon cycle, and they are considered hotspots for bacterial activities such as organic matter decomposition. However, our knowledge about these processes in tropical or subtropical regions is limited. The aim of this study was to investigate anthropogenically induced changes of water quality, the distribution of selected pharmaceuticals, and the effects of pollution on greenhouse gas concentrations and bacterial community composition along the 800 km long Cauvery river, the main river serving as a potable and irrigation water supply in Southern India. We found that in situ measured pCO₂ and pCH₄ concentrations were supersaturated relative to the atmosphere and ranged from 7.9 to 168.7 µmol L⁻¹ , and from 0.01 to 2.76 µmol L⁻¹ , respectively. Pharmaceuticals like triclosan, carbamazepine, ibuprofen, naproxen, propylparaben, and diclofenac exceeded warning limits along the Cauvery. Proteobacteria was the major phylum in all samples, ranging between 26.1% and 82.2% relative abundance, and it coincided with the accumulation of nutrients in the flowing water. Results emphasized the impact of industrialization and increased population density on changes in water quality, riverine carbon fluxes, and bacterial community structure

Untersuchungen zur raum-zeitlichen Attraktion nekrophager Tiefseeamphipoden auf große Nahrungspartikel

The aim of the present study is to elucidate the feeding ecology of Eurythenes gryllus (Crustacea: Amphipoda) in the Arctic deep sea. Literature data show that this species occurs frequently and in high numbers at food falls, so it was likely to obtain data on its food finding strategies and, its aggregation dynamics at food falls, which could be combined with information on its metabolism under controlled conditions in aquaria experiments. Six large food fall experiments were carried out during expeditions with the RV Polarstern in the Arctic summer seasons 2000 and 2001 between 1400 and 2600 m water depth. For in situ investigations a tripod lander was used equipped with a baited time-lapse camera, a scanning sonar system (SSS), an acoustic doppler current profiler and baited traps.Scanning sonar data demonstrate that the amphipods swim upstream along a narrow path towards the bait. Thus, in combination with current measurements and time-lapse photography this study shows that chemoreception serves for food fall localization in the scavenging amphipod Eurythenes gryllus over relatively large distances. The findings of the investigations in situ were supported by results of respiration rate measurements in E. gryllus indicating an increase in oxygen consumption after exposure to food odour in laboratory experiments. Based on total lipids (6.1 % of wet weight) and metabolic rates, sustenance times have been calculated. The results of this study are encourage future use of these acoustic and optical combined instruments. Eurythenes gryllus must be regarded as an important component of the deep-sea food web due to their feeding efficiency, their large number attracted and their role in the consumption. To get a more detailed idea of the deep-sea community it could be useful to apply this methodological approach also in other latitudes

Aggregations of Arctic deep-sea scavenging amphipods at large food falls

The aim of the present study is to elucidate the feeding ecology of Eurythenes gryllus (Crustacea: Amphipoda) in the Arctic deep sea. Literature data show that this species occurs frequently and in high numbers at food falls, so it was likely to obtain data on its food finding strategies and, its aggregation dynamics at food falls, which could be combined with information on its metabolism under controlled conditions in aquaria experiments. Six large food fall experiments were carried out during expeditions with the RV Polarstern in the Arctic summer seasons 2000 and 2001 between 1400 and 2600 m water depth. For in situ investigations a tripod lander was used equipped with a baited time-lapse camera, a scanning sonar system (SSS), an acoustic doppler current profiler and baited traps.Scanning sonar data demonstrate that the amphipods swim upstream along a narrow path towards the bait. Thus, in combination with current measurements and time-lapse photography this study shows that chemoreception serves for food fall localization in the scavenging amphipod Eurythenes gryllus over relatively large distances. The findings of the investigations in situ were supported by results of respiration rate measurements in E. gryllus indicating an increase in oxygen consumption after exposure to food odour in laboratory experiments. Based on total lipids (6.1 % of wet weight) and metabolic rates, sustenance times have been calculated. The results of this study are encourage future use of these acoustic and optical combined instruments. Eurythenes gryllus must be regarded as an important component of the deep-sea food web due to their feeding efficiency, their large number attracted and their role in the consumption. To get a more detailed idea of the deep-sea community it could be useful to apply this methodological approach also in other latitudes

Effect of Sediment Gas Voids and Ebullition on Benthic Solute Exchange

The presence of free gas in sediments and ebullition events can enhance the pore water transport and solute exchange across the sediment–water interface. However, we experimentally and theoretically document that the presence of free gas in sediments can counteract this enhancement effect. The apparent diffusivities (Da) of Rhodamine WT and bromide in sediments containing 8–18% gas (Da,YE) were suppressed by 7–39% compared to the control (no gas) sediments (Da,C). The measured ratios of Da,YE:Da,C were well within the range of ratios predicted by a theoretical soil model for gas-bearing soils. Whereas gas voids in sediments reduce the Da for soluble species, they represent a shortcut for low-soluble species such as methane and oxygen. Therefore, the presence of even minor amounts of gas can increase the fluxes of low-soluble species (i.e., gases) by several factors, while simultaneously suppressing fluxes of dissolved species

Organic matter quality structures benthic fatty acid patterns and the abundance of fungi and bacteria in temperate lakes

Benthic microbial communities (BMCs) play important roles in the carbon cycle of lakes, and benthic littoral zones in particular have been previously highlighted as biogeochemical hotspots. Dissolved organic matter (DOM) presents the major carbon pool in lakes, and although the effect of DOM composition on the pelagic microbial community composition is widely accepted, little is known about its effect on BMCs, particularly aquatic fungi. Therefore, we investigated the composition of benthic littoral microbial communities in twenty highly diverse lakes in northeast Germany. DOM quality was analyzed via size exclusion chromatography (SEC), fluorescence parallel factor analyses (PRAFACs) and UV–Vis spectroscopy. We determined the BMC composition and biomass using phospholipid-derived fatty acids (PLFA) and extended the interpretation to the analysis of fungi by applying a Bayesian mixed model. We present evidence that the quality of DOM structures the BMCs, which are dominated by heterotrophic bacteria and show low fungal biomass. The fungal biomass increases when the DOM pool is processed by microorganisms of allochthonous origin, whereas the opposite is true for bacteria

Visualizing land-use and management complexity within biogeochemical cycles of an agricultural landscape

Crop fields are cultivated across continuities of soil, topography, and local climate that drive biological processes and nutrient cycling at the landscape scale; yet land management and agricultural research are often performed at the field scale, potentially neglecting the context of the surrounding landscape. Adding to this complexity is the overlap of ecosystems and their biogeochemical legacies, as a patchwork of crops fields, natural grasslands, and forests develops across the landscape. Furthermore, as new technologies and policies are introduced, management practices change, including fertilization strategies, which further alter biological productivity and nutrient cycling. All of these environmental, biological, and historical legacies are potentially recorded in the isotopic signal of plant, soil, and sediment organic matter across the landscape. We mapped over 1500 plant, soil, and sediment isotopic values and generated an isotopic landscape (isoscape) over a 40-km2 agricultural site in NE Germany. We observed distinct patterns in the isotopic composition of organic matter sampled from the landscape that clearly reflect the landscape complexity. C3 crop intrinsic water-use efficiency reflected a precipitation gradient, while native forest and grassland plant species did not, suggesting that native plants are more adapted to predominant climatic conditions. δ13Csoil patterns reflected both the long-term input of plant organic matter, which was affected by the local climate conditions, and the repeated cultivation of corn. Soil organic matter 15N isotopic values also revealed spatial differences in fertilization regimes. Forest fragments, in which the nitrogen cycle was relatively open, were more water-use efficient. Sediments from small water bodies received substantial inputs from surrounding field vegetation but were also affected by seasonal drying. These isotopic maps can be used to visualize large spatial heterogeneity and complexity, and they are a powerful means to interpret past and current trends in agricultural landscapes