title: Benthic bacterial response to variable estuarine water inputs.
abstract: Estuarine waters are known to enhance productivity in coastal environments, but little is known about the impact that nutrient-rich waters can have on benthic microbial processes. After intensive surface sediment sampling in a wide coastal area impacted by river plume waters, we performed on-site microcosm experiments in which we added estuarine waters, rich in both organic and inorganic N and P, to pristine offshore sediments. This experimental approach has been conducted in different coastal areas for two consecutive years, in which the river-plume waters differed in both inorganic and organic N and P content. Benthic bacterial response (total bacterial abundance and biomass, aminopeptidase, beta-d-glucosidase and bacterial C production) was investigated in treated and non-treated sediments. All structural and functional microbial variables increased significantly after plume-water supply (within 12-24 h bacterial abundance in the sediment doubled and enzymatic activities increased up to >50%). Results indicate that inorganic N supply from plume waters was sufficient to induce a significant response in benthic bacterial abundance, independently from the presence of high and/or variable N:P ratios. However, bacterial carbon production and exo-enzymatic activities increased significantly when the supply of organic P from plume waters was associated with a decrease of organic N:P ratios. We conclude that plume waters have important effects on benthic bacterial dynamics, but the extent of their biogeochemical implications is largely dependent upon their organic P availability and on stoichiometric ratios of organic nutrients supplied by plume waters.
authors.affiliation: Department of Marine Sciences, Polytechnic University of Marche, Via Brecce Bianche, Monte D'Ago, Ancona, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Manini
authors.forename: Gian Marco
authors.initials: GM
authors.lastname: Luna
authors.forename: Roberto
authors.initials: R
authors.lastname: Danovaro
mesh_terms: D001419:Bacteria / Q000254:growth & development* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D018533:Biomass; D002244:Carbon / Q000378:metabolism; D015169:Colony Count, Microbial; D004798:Enzymes / Q000378:metabolism; D005618:Fresh Water / Q000737:chemistry*; D019015:Geologic Sediments / Q000382:microbiology*; D007287:Inorganic Chemicals / Q000032:analysis; D017672:Nitrogen Compounds / Q000032:analysis; D009930:Organic Chemicals / Q000032:analysis; D010710:Phosphates / Q000032:analysis; D012623:Seawater / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins; D004798:Enzymes; D007287:Inorganic Chemicals; D017672:Nitrogen Compounds; D009930:Organic Chemicals; D010710:Phosphates; D002244:Carbon