Settling flux and sinking velocity of Seston in Lago di Mergozzo (Northern Italy) and influence of microbial activity on the decomposition of entrapped organic material

Abstract

Settling flux and velocity of seston, Particulate Organic Carbon (POC) and chlorophyll a were measured at three depths during 8 seven-day exposure periods in Lago di Mergozzo (Northern Italy). Sedimentation rates of seston varied from 250 to 1200 mg me2 d-' with a prevalence of the inorganic fraction (130-900mgm-2d-1) over the organic (160-320mgm-2d-'). The percentage of organic fraction inside the traps was always lower than outside. The comparison of preserved and unpreserved traps showed no significant difference in both organic matter content and bacterial numbers. We inferred from this result that bacterial activity in the traps did not cause a measurable POC loss during the seven day exposures. Therefore, the higher settling velocity of the inorganic particles was responsible for the higher percentage of this fraction in the traps. The settling velocity of sestonic particles increased, during the stratification period, with increasing depth and reached a maximum value of 2.5 m d-I.

Phosphorus Fractions and Fluxes in the Water Column and Sediments of a Tropical Reservoir (Lobo-Broa - SP)

“…pers.). The mean sedimentation rate of chlorophyll a (5.8 mg m -2 day -1 ) was in the same order of magnitude as that reported by CALLIERI et al (1991). The sedimentation rates of metals are presented in Tab.…”

Changes in Deposition of Phytoplankton Constituents in a Ca2+Polluted Lake

“…The organic C fluxes in the post-closure interval exceed most values reported for other eutrophic lakes, including Rotsee (49), Frains Lake (50), Third Sister (50), Lake Lugano (66), Lake Hallwil (67), Lake Zug (2), and Lake Sempack (12). The only two exceptions (68,69) (2,7,70). The high settling velocity for Onondaga Lake is consistent with the unusually high Ca 2+ concentrations that continue to prevail (Figure 1b) and the coagulation mechanism for enhanced deposition.…”

Seston fluxes in the dam of a Colombian tropical reservoir

“…The question now is why after thermocline establishment, particles flux decreases, if several authors have found that stratification processes accelerating sedimentation and total fluxes of sestonic material? (Karl et al, 1988;Galvez et al, 1989;Callieri et al, 1991;Alvarez-Cobelas et al, 1993;Maricato, 1994;Wetzel, 2001). As has been raised previously, the sestonic material collected in traps is mainly allochthonous, and this depends on the loads entering the reservoir by the three tributaries and of the period of greatest stratification.…”

“…In the water from each tube it was measured TS, TSF, TVS, TDS, TSS, TVS and TSF by gravimeter (APHA, 1995); and electrical conductivity, turbidity, pH, dissolved inorganic carbon (DIC) (Mackereth et al, 1972). The sedimentation rate (flux) g m -2 d -1 was established only for the TS, TSS, TVS and TSF and was calculated according to the Equation 1 in Callieri et al (1991):…”