Water column

About: Water column is a research topic. Over the lifetime, 13706 publications have been published within this topic receiving 496626 citations.

Hypoxia in the Baltic Sea: Biogeochemical Cycles, Benthic Fauna, and Management

Abstract: Hypoxia has occurred intermittently over the Holocene in the Baltic Sea, but the recent expansion from less than 10 000 km 2 before 1950 to (60 000 km 2 since 2000 is mainly caused by enhanced nutrient inputs from land and atmosphere. With worsening hypoxia, the role of sediments changes from nitrogen removal to nitrogen release as ammonium. At present, denitrification in the water column and sediments is equally important. Phos- phorus is currently buried in sediments mainly in organic form, with an additional contribution of reduced Fe-phos- phate minerals in the deep anoxic basins. Upon the tran- sition to oxic conditions, a significant proportion of the organic phosphorus will be remineralized, with the phos- phorus then being bound to iron oxides. This iron-oxide bound phosphorus is readily released to the water column upon the onset of hypoxia again. Important ecosystems services carried out by the benthic fauna, including bio- geochemical feedback-loops and biomass production, are also lost with hypoxia. The results provide quantitative knowledge of nutrient release and recycling processes under various environmental conditions in support of decision support tools underlying the Baltic Sea Action Plan.

Attachment of Fecal Indicator Bacteria to Particles in the Neuse River Estuary, N.C.

Abstract: Observations of microbial contamination and particle suspensions represent valuable inputs to water quality models that form the basis of regulatory decisions regarding the use of surface waters. The Neuse River Estuary in eastern North Carolina is experiencing a decline in water quality due to increasing anthropogenic inputs. Potentially serious consequences of these inputs are the introduction and persistence of bacterial pathogenic organisms from human and animal waste. A critical factor in determining human health risk is the partitioning of these organisms between particle-attached and free-living cells in the water column. Particle-associated bacteria are generally less mobile in the environment, settle faster, and may have different rates of mortality than their free phase counterparts. Surface and bottom water samples were collected during both dry weather and storm events throughout the summer of 2004 to gage changes in particle concentration, particulate organic carbon and nitrogen, and the part...

Transitions between Auhcoseira and Anabaena dominance in a turbid river weir pool

Abstract: The transitions between the diatoms Aulacoseira spp. (Melosira) and the cyanobacteria Anabaena spp. as dominant phytoplankton species in a turbid-river weir pool are shown to depend directly on the establishment or destruction of persistent thermal stratification. A transition from high to low flow through the pool resulted in the establishment of persistent thermal stratification, causing Aulacoseira to sink out of the euphotic zone at a speed of 0.95 m d-l. Concurrently, the slightly buoyant Anabaena grew within the euphotic zone with a specific growth rate of 0.37 d-l, climaxing after approximately 14 d at a population of 20,000-30,000 cells ml I, at which point its biomass may have been limited by the availability of phosphorus. The stratification thus caused the phytoplankton population to separate into two distinct layers, with Anabaena occupying the illuminated surface layer and Aulacoseiru found only in the lower layer below the euphotic depth. Under stratified conditions, the ratio of the surface layer depth to euphotic depth, z,, : z,,, was approximately 1, whereas for a mixed water column that ratio was >3. Access to light appeared to be the main factor determining the dominant phytoplankton species.

The role of biominerals in the sinking flux and preservation of amino acids in the Southern Ocean along 170°W

Abstract: In a study of the transport and transformation of particulate amino acids in the Southern Ocean, we found that silicate and calcium carbonate biominerals play an important role in the preservation of amino acids throughout the water column and surface sediments. Plankton, sinking particle and sediment samples were collected during the USJGOFS AESOPS transect across the Antarctic Polar Front (APF) along 170°W. Total hydrolyzable amino acids (THAA) made up of 17–27% of total organic carbon (Corg) in sinking particles and 6–23% of Corg in surface sediments. In addition to THAA, we measured amino acids bound in silicate (SiTHAA) and calcium carbonate (CaTHAA) biominerals. Although the fraction of biomineral bound to total amino acids in plankton was small, Amino acid composition has been used to develop a Degradation Index (sensu Dauwe and Middelburg, 1998). The unusual amino acid composition of Southern Ocean plankton, i.e., dominated by diatom cell walls, resulted in an apparent mismatch between the absolute value of the Degradation Index and the presumed extent of degradation. However, changes in amino acid composition that accompanied degradation were similar to those found in previous studies. Principal components analysis suggests that the greatest change in THAA composition occurred between the sediment surface floc layer and deeper sediments where particles had the longest residence time. Compositional changes observed in the water column suggested that degradation processes resulted in complete removal of amino acids, whereas changes in sediments were consistent both with selective degradation of plankton amino acids with depth and with the conversion of primarily phytoplankton biomass to that of bacterial biomass.

Relating estimates of CaCO3 production, export, and dissolution in the water column to measurements of CaCO3 rain into sediment traps and dissolution on the sea floor: A revised global carbonate budget

Abstract: [1] The global CaCO3 budget is constrained by new estimates of standing stocks, fluxes through the water column, and dissolution in the water column and on the sea floor. Previous estimates of carbonate production and export are indistinguishable within a large range of values, 0.4–1.8 Gt PIC yr−1. Globally, excess alkalinity (TA*) and water mass tracers indicate dissolution of 1.0 Gt PIC yr−1 between 200 and 1500 m, suggesting production and export must at least equal this amount. Most water column dissolution occurs at high latitudes, and alkalinity fluxes from outer shelf and upper slope sediments (100–1500 m) only support 5–10% of the TA* inventory. Below 2000 m, the sinking flux of PIC (0.6 Gt PIC yr−1) is consistent with the rate of sea floor dissolution (0.4 Gt PIC yr−1) plus burial (0.1 Gt PIC yr−1). This rain rate constrains the export value to >1.6 Gt PIC yr−1. Satellite-based estimates of standing stocks of CaCO3 indicate a decrease equatorward, which is opposite in trend to sediment trap fluxes. This observation may be explained by an equatorward decrease in sinking particle dissolution, systematic changes in PIC residence time with latitude, or satellite retrieval problems. Globally averaged euphotic zone standing stock (5.4 mmol m−2) and export estimates indicate PIC residence times of 5–18 days.