Different Dissolved Organic Carbon Research Articles

Atrazine uptake, elimination, and bioconcentration by periphyton communities and Daphnia magna: effects of dissolved organic carbon.

The bioconcentration and toxicokinetics of atrazine in three different periphyton communities and in laboratory reared Daphnia magna were studied in natural and artificial waters with different dissolved organic carbon (DOC) concentrations and qualities. The exposure concentrations were similar to those short-lived peak concentrations found in contaminated waters. Atrazine uptake and elimination were very fast, and the bioconcentration was low both in periphyton and D. magna. The bioconcentration factors in D. magna were approx. 16% of those in periphyton. The uptake and elimination rates were also higher in periphyton than in Daphnia. The periphyton properties affected the bioconcentration of atrazine more than the DOC concentration and water quality. A steady state was reached within a few hours of uptake by the periphyton and within 24 h by D. magna. A residue of atrazine was left in the periphyton and D. magna after an 8-h biphasic depuration with clearly distinct fast and slow phases. In D. magna, atrazine may be eliminated during the normal life span of the organism. These results suggest that DOC has a minor influence on the toxicokinetics of atrazine.

DISSOLVED ORGANIC CARBON IN TWO BRAZILIAN COASTAL LAGOONS: SOURCES AND UTILIZATION FOR HETEROTROPHIC BACTERIA

We evaluated the bacterial utilization of dissolved organic matter (DOM) of a leachate from emergent macrophytc, Typha domiingensis Pers, dominant in two coastal lagoons of different dissolved organic carbon (DOC) concentrations, in the north of Rio de Janeiro State, Brazil. The leachate was added to microcosms with pelagic water Iron the two lagoons and inoculated with natural bacteria. Control experiments were performed using only pelagic fi1tered water added to inocculum. Bacterial production, density and biomass were measured every 24 hours, during five days. Bacterial production and biomass were significantly higher in experiments with leachate addition, in both lagoons, in comparison to the controls. Those results indicate that DOM from the macrophyte has a positive ini1ucncc on bacterial growth. Normalized results also indicate it is not a matter of quantity, but the quality of DOM is better utilized than the DOM Iron pelagic region.

Ciliate community structure in two South Andean lakes: the effect of lake water on Ophrydium naumanni distribution

Planktonic ciliates were examined during a spring-summer period (November 1998 to April 1999) in 2 South Andean lakes in Argentina, with different dissolved organic carbon (DOC) and nutrient concentrations. Lake Moreno Oeste is a deep warm monomictic lake (Zmax= 90 m), while Lake Morenito is shallower (Zmax = 12 m) and polymictic. Sampling was performed in a mid-lake station, where vertical profiles of temperature, light, and chlorophyll a concentration were measured in situ. In addition, DOC and phosphorus concentrations were determined, and samples for bacteria, phyto- plankton and ciliate enumeration were taken along the water columns. Lake Morenito presented DOC and phosphorus concentrations 3-fold higher than those of Lake Moreno Oeste. Two different ciliate assemblages were present. Lake Moreno Oeste was dominated by the large mixotrophic ciliate Ophry- dium naumanni, which was absent in Lake Morenito. In order to test 0. naumanni water dependence, a series of laboratory experiments were performed during the sampling season. The experiments con- sisted of the incubation of the ciliate in filtered water from both lakes and the subsequent analysis of growth rates in each treatment. In addition, experiments with Moreno Oeste lake water with a 4-fold increased phosphorus concentration (addition of MBL culture medium) were conducted. The incuba- tion of 0. naumanni in Lake Morenito water led to highly negative growth rates of the ciliate. Results showed that the addition of nutrients did not cause significant differences in the growth rates.

Ultraviolet Radiation Effects on a Microscopic Green Alga and the Protective Effects of Natural Dissolved Organic Matter

Abstract— The population and photosynthetic responses of a microscopic green alga (Selenastrum capricornutum) to realistic levels of UV radiation (UVA and UVB) were assessed in natural lake waters of different dissolved organic carbon (DOC) concentration. Specific growth rates and photosynthetic competence (as reflected by Fv/Fm [measure of maximal quantum efficiency of photosystem II] and t1/2 [estimate of electrons transported to the plastoquinone pool] measured by in vivo variable chlorophyll a fluorescence) were compared between two exposure levels of UVR and two concentrations of DOC (2.5 mg C L−1 7.7 mg C L−1). Exposure periods of 6–9 days (five to nine generations) were used. Exposure to UVA primarily affected the efficiency of photosystem II, as evidenced by significant decreases of Fv/Fm but not growth rates or t1/2 Exposure to UVB, in the presence of UVA, did not cause significant additional decreases of Fv/Fm but did diminish growth rates. In the low DOC water, t1/2 was also diminished, suggesting different proximate sites of action from those for UVA. The high DOC water decreased the effective exposure to both UVA and UVB and diminished the negative impact of UV radiation on the cells, but the apparent protection was not explicable solely by the shading action of the DOC. Control values for Fv/Fm, growth rates and t1/2 were all lower in the high DOC water, suggesting a negative side effect to the apparent protective action of the DOC against UVB.

Ultraviolet Radiation Effects on a Microscopic Green Alga and the Protective Effects of Natural Dissolved Organic Matter

Abstract— The population and photosynthetic responses of a microscopic green alga (Selenastrum capricornutum) to realistic levels of UV radiation (UVA and UVB) were assessed in natural lake waters of different dissolved organic carbon (DOC) concentration. Specific growth rates and photosynthetic competence (as reflected by Fv/Fm [measure of maximal quantum efficiency of photosystem II] and t1/2 [estimate of electrons transported to the plastoquinone pool] measured by in vivo variable chlorophyll a fluorescence) were compared between two exposure levels of UVR and two concentrations of DOC (2.5 mg C L−1 7.7 mg C L−1). Exposure periods of 6–9 days (five to nine generations) were used. Exposure to UVA primarily affected the efficiency of photosystem II, as evidenced by significant decreases of Fv/Fm but not growth rates or t1/2 Exposure to UVB, in the presence of UVA, did not cause significant additional decreases of Fv/Fm but did diminish growth rates. In the low DOC water, t1/2 was also diminished, suggesting different proximate sites of action from those for UVA. The high DOC water decreased the effective exposure to both UVA and UVB and diminished the negative impact of UV radiation on the cells, but the apparent protection was not explicable solely by the shading action of the DOC. Control values for Fv/Fm, growth rates and t1/2 were all lower in the high DOC water, suggesting a negative side effect to the apparent protective action of the DOC against UVB.