Nutrient Enrichment and Food Web Composition Affect Ecosystem Metabolism in an Experimental Seagrass Habitat

Food web composition and resource levels can influence ecosystem properties such as productivity and elemental cycles. In particular, herbivores occupy a central place in food webs as the species richness and composition of this trophic level may simultaneously influence the transmission of resource and predator effects to higher and lower trophic levels, respectively. Yet, these interactions are poorly understood.Using an experimental seagrass mesocosm system, we factorially manipulated water column nutrient concentrations, food chain length, and diversity of crustacean grazers to address two questions: (1) Does food web composition modulate the effects of nutrient enrichment on plant and grazer biomasses and stoichiometry? (2) Do ecosystem fluxes of dissolved oxygen and nutrients more closely reflect above-ground biomass and community structure or sediment processes? Nutrient enrichment and grazer presence generally had strong effects on biomass accumulation, stoichiometry, and ecosystem fluxes, whereas predator effects were weaker or absent. Nutrient enrichment had little effect on producer biomass or net ecosystem production but strongly increased seagrass nutrient content, ecosystem flux rates, and grazer secondary production, suggesting that enhanced production was efficiently transferred from producers to herbivores. Gross ecosystem production (oxygen evolution) correlated positively with above-ground plant biomass, whereas inorganic nutrient fluxes were unrelated to plant or grazer biomasses, suggesting dominance by sediment microbial processes. Finally, grazer richness significantly stabilized ecosystem processes, as predators decreased ecosystem production and respiration only in the zero- and one- species grazer treatments.Overall, our results indicate that consumer presence and species composition strongly influence ecosystem responses to nutrient enrichment, and that increasing herbivore diversity can stabilize ecosystem flux rates in the face of perturbations

Distribution Patterns of Particulate Trace Metals in the Water Column and Nepheloid Layer of the Gulf of Riga

The dynamics (fate) of trace metals in suspended particulate matter within the Gulf of Riga has not yet been adequately addressed in the scientific literature. Therefore, during a two year period (2001–2002) samples of suspended particulate matter and surface sediments for trace metal analysis were collected in the Gulf of Riga and the Daugava river, and these data were combined with background information from the national marine monitoring program in Latvia. This paper presents a descriptive study of solid phase trace metals (aluminium, iron, cadmium, chromium, copper, anganese, nickel, lead and zinc) dynamics and their spatial distribution within the Gulf of Riga based on Principal Component Analysis and Cluster analysis. Fluvial particulate matter and particulate Al, Fe, Cr and Ni were brought into the Gulf of Riga mainly during spring flood and thereafter quickly diluted by the water masses of the Gulf of Riga. Finegrained suspended material and particulate Al and Fe were well mixed and evenly distributed through all deepwater basins of the Gulf of Riga. The increase of particulate Mn below the thermocline in August and a strong negative correlation with dissolved oxygen concentrations suggested that particulate Mn in the water column and the sediments were regulated mainly by changing oxic–anoxic conditions in the sediments of the Gulf of Riga. The observed correlation between Al and Fe in the water column is in contrast to that observed in the nepheloid layer where Fe correlated with Mn, obviously due to fast diagenetic processes on sediment surface. The observed negative correlation of Cd and Zn with total carbon and total nitrogen in the nepheloid layer might indicate different sedimentation mechanisms of these elements, however, this assumption is still inconclusive. 2005 Elsevier Ltd. All rights reserved.JRC.H.5-Rural, water and ecosystem resource

Discovery and Characterization of the Potent and Selective P2X4 InhibitorN [4 3 Chlorophenoxy 3 sulfamoylphenyl] 2 phenylacetamide BAY 1797 and Structure Guided Amelioration of Its CYP3A4 Induction Profile

The P2X4 receptor is a ligand gated ion channel that is expressed on a variety of cell types, especially those involved in inflammatory and immune processes. High throughput screening led to a new class of P2X4 inhibitors with substantial CYP 3A4 induction in human hepatocytes. A structure guided optimization with respect to decreased pregnane X receptor PXR binding was started. It was found that the introduction of larger and more polar substituents on the ether linker led to less PXR binding while maintaining the P2X4 inhibitory potency. This translated into significantly reduced CYP 3A4 induction for compounds 71 and 73. Unfortunately, the in vivo pharmacokinetic PK profiles of these compounds were insufficient for the desired profile in humans. However, BAY 1797 10 was identified and characterized as a potent and selective P2X4 antagonist. This compound is suitable for in vivo studies in rodents, and the anti inflammatory and anti nociceptive effects of BAY 1797 were demonstrated in a mouse complete Freund s adjuvant CFA inflammatory pain mode