Limnology and Oceanography
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Contribution of ferric iron to light absorption by chromophoric dissolved organic matter This study experimentally determined the contribution of ferric iron (Fe(III)) associated with humic substances (HS) to light absorption by chromophoric dissolved organic matter (CDOM). The associations between Fe(III) and HS (HS‐Fe) were generated by mixing HS standards with Fe(III) in acidic conditions and adjusting pH to 8. HS‐associated Fe was separated from total Fe by filtering (0.7 µm and 0.2 µm filters) and by removing the free Fe ions by cation exchange chromatography. The maximum Fe‐binding capacities (at pH 8) of Suwannee River humic acid, Suwannee River fulvic acid, and Pony Lake (Antarctica) fulvic acid were 13.0, 13.5, and 7.64 µmol Fe [mg C]−1 , respectively, indicating that wetland‐derived HS had a higher Fe‐binding capacity than plankton‐derived HS. HS‐associated Fe increased the absorption coefficient of CDOM by up to several fold in the visible range of the spectrum and reduced the spectral slope coefficient of CDOM. The Fe‐induced increase in light absorption was spectrally similar among different HS examined. The Fe‐specific absorption coefficient spectrum for HS‐associated Fe (aλ, Fe *) was calculated from the Fe‐induced increase in light absorption by normalizing it with the concentration of Fe in the HS pool. The aλ, Fe * was adopted in estimation of the contribution of HS‐associated Fe to light absorption by CDOM in 13 circum‐neutral natural waters collected from a spring, 10 major rivers, a lake, and a coastal area. HS‐associated Fe was calculated to be responsible for from 0.6% (Mississippi River) to 56.4% (Löytynlähde spring) of light absorption by CDOM at a wavelength of 410 nm. This study shows that HS‐associated Fe can be an important component in light absorption by CDOM and also influence the spectral slope coefficient of CDOM.
Limnology and Oceanography - Tập 58 Số 2 - Trang 653-662 - 2013
Patterns and regulation of dissolved organic carbon: An analysis of 7,500 widely distributed lakes Dissolved organic carbon (DOC) is a key parameter in lakes that can affect numerous features, including microbial metabolism, light climate, acidity, and primary production. In an attempt to understand the factors that regulate DOC in lakes, we assembled a large database (7,514 lakes from 6 continents) of DOC concentrations and other parameters that characterize the conditions in the lakes, the catchment, the soil, and the climate. DOC concentrations were in the range 0.1–332 mg L−1 , and the median was 5.71 mg L−1 . A partial least squares regression explained 48% of the variability in lake DOC and showed that altitude, mean annual runoff, and precipitation were negatively correlated with lake DOC, while conductivity, soil carbon density, and soil C:N ratio were positively related with lake DOC. A multiple linear regression using altitude, mean annual runoff, and soil carbon density as predictors explained 40% of the variability in lake DOC. While lake area and drainage ratio (catchment : lake area) were not correlated to lake DOC in the global data set, these two factors explained significant variation of the residuals of the multiple linear regression model in several regional subsets of data. These results suggest a hierarchical regulation of DOC in lakes, where climatic and topographic characteristics set the possible range of DOC concentrations of a certain region, and catchment and lake properties then regulate the DOC concentration in each individual lake.
Limnology and Oceanography - Tập 52 Số 3 - Trang 1208-1219 - 2007
Nonlinear response of dissolved organic carbon concentrations in boreal lakes to increasing temperatures Recent increases in concentrations of dissolved organic carbon (DOC) in lakes and rivers over large regions have been related to both changes in the climate and in atmospheric deposition chemistry. Using a data set of 1041 boreal lakes along a 13° latitudinal gradient, sampled in 1995, 2000, and 2005, and an additional data set of 90 lakes along a 1000‐m altitudinal gradient at 68°N, we show that DOC concentrations increase in a nonlinear way along a latitudinal and altitudinal temperature gradient. The nonlinear relation of DOC to increasing temperatures was consistent over space and time. Out of 14 meteorological, catchment, morphometric, and atmospheric deposition variables tested, the variable best explaining this kind of nonlinear pattern was the number of days when air temperatures exceeded 0°C, i.e., the duration of the main growing and runoff season (DT>0 ). Using DT>0 as an input variable, we were able to predict the nonlinear temperature response of DOC concentrations, both spatially (R 2 = 0.90, p < 0.0001) and temporally (R 2 = 0.90, p < 0.0001). DT>0 has an advantage over other variables because it includes the time factor, which is decisive for the duration that biogeochemical processes can take place. We suggest that DOC concentrations in lakes are influenced by climate change and that present temperature increases over Sweden result in an accelerated DOC increase toward warmer geographical regions.
Limnology and Oceanography - Tập 54 Số 6part2 - Trang 2513-2519 - 2009
EXCRETION OF PHOSPHATE AND SOLUBLE ORGANIC PHOSPHORUS COMPOUNDS BY ZOOPLANKTON1 Net plankton excretes daily an amount of phosphorus nearly equal to its total phosphorus content. Slightly more than half of the excreted phosphorus is phosphate and the remainder is in soluble organic compounds. Phosphorus excreted by zooplankton may constitute a significant fraction of that required for photosynthesis by the phytoplankton.
Limnology and Oceanography - Tập 8 Số 1 - Trang 50-55 - 1963
THE CYCLE OF PHOSPHORUS IN A PLANKTON BLOOM IN THE GULF OF MAINE1 The cycle of phosphorus was studied in detail during the spring bloom of phytoplankton in the Gulf of Maine in April 1964. A parachute drogue was placed at a depth of 10 m so that the movement of the surface water could be Followed. Five stations were occupied (luring an interval of 24 hr on 8–9 April when the drogue was launched and another five stations at the location of the drogue were occupied 10 days later on 17–18 April. During this interval, the drogue had drifted to the southward about 63 km. Because the isopycnal surfaces below 50 m sloped upwards from the first to the final set of stations, the distribution of properties is compared on surfaces of equal density. Particulate, dissolved organic, and inorganic phosphorus were determined on all samples. There was a considerable decrease in inorganic and an increase of both particulate and dissolved organic phosphorus in the surface waters during this time. Much of the particulate phosphorus formed had sunk below the 50‐m cuphotic zone to the deeper waters. The data permit estimates of the exerction of organic phosphorus in the euphotic zone and of the decomposition of this fraction in the deeper water. Below about 136 m, there was no net change in any of the fractions of phosphorus and the change in total phosphorus for the entire water column was essentially zero. Measurements were made of the distribution of oxygen and of chlorophyll at these two times, which permit the computation of the primary production from the changes in phosphorus, oxygen, and chlorophyll. The average rate for the 10‐day period was slightly more than 2 g C m‐2 day‐1 . The rate of exchange of oxygen across the sea surface has been computed from these data and gives an exchange coefficient somewhat smaller than had been previously observed. The relationship between the changes of phosphorus, oxygen, and chlorophyll in primary production in the euphotic zone and in the decomposition processes in the deeper water are discussed. Both the chlorophyll and the particulate phosphorus data give indications of the sinking of particulate matter during the bloom. The sinking particles contain an unusually high proportion of chlorophyll compared to phosphorus.
Limnology and Oceanography - Tập 10 Số suppl - 1965
FURTHER MEASUREMENTS OF PRIMARY PRODUCTION USING A LARGE‐VOLUME PLASTIC SPHERE The experiment described by McAllister, et al. (1961), in which a phytoplankton bloom was induced to occur in a free‐floating 20‐ft diameter thin transparent plastic sphere has been repeated. Daily measurements were made of nutrients, particulate matter, and photosynthetic rates with less frequent assays for vitamins and dissolved organic matter. In situ light was recorded by a bolometer. The experiment was prolonged to 100 days to study phytoplankton decay, most of this period being in the dark. The phytoplankton consisted mainly of 6 species of diatom and one large dinoflagellate. The mean composition of this crop at various stages of its development is reported by ratios involving chlorophyll a and particulate organic carbon. A detailed discussion is given of the findings of the experiment which, in general, confirmed those of the earlier work and yielded, in addition, valuable new information. The plant cells excreted 35–40% of their organic matter during growth. The C14 method of measuring photosynthesis gave results agreeing well with the production of particulate carbon. The growth kinetics of the bloom were dominated by the constancy of the mean cell division rates which were relatively independent of temperature and light. The rate of photosynthesis per unit chlorophyll was also remarkably constant and not proportional to light intensity, cells developing a highly efficient photosynthetic mechanism with respect to available radiant energy. The mean chemical composition of a cell changed after depletion of nutrients from the surrounding water. The carbon, protein, chlorophyll a and phosphorus decreased. The silicon and lipid contents remained nearly constant and the carbohydrate increased. During the decay period over half the particulate phosphorus was remineralized in 2 weeks. Silicon returned to solution more slowly but at a constant rate. There was no significant nitrification even after 75 days. The consumption of oxygen occurred mainly from the oxidation of “dissolved” organic matter and not from the interaction of oxygen with particulate material. The latter may have been important as a surface for bacteria. The evolution rate of carbon dioxide was constant with time but proceeded with a variable RQ, which was around 0.5 immediately after the bloom but increased to nearly 2 in the “old” water present at the beginning and end of the experiment.
Limnology and Oceanography - Tập 8 Số 2 - Trang 166-183 - 1963
ALKALINE PHOSPHATASES AND PHOSPHORUS AVAILABILITY IN LAKE KINNERET1,2 Alkaline phosphatase activities were determined in water samples taken from three depths at a central point in Lake Kinneret (Lake Tiberias). Seasonal fluctuations were shown, and also indications of induction‐repression or activation and inhibition mechanisms, or both, with respect to total phosphorus, and, during stratification, the existence of a metalimnetic layer of intense activity. Phosphatase activities with “natural” substrates and estimates of phosphorus availabilities were derived by measuring release of soluble inorganic orthophosphate from samples saturated with chloroform. Phosphorus, which appeared to be adequate during the main bloom season, may have become limiting from the end of summer until overturn. In epilimnetic waters 30–66% of total phosphorus was hydrolyzed with a turnover time of 3–6 days.
Limnology and Oceanography - Tập 15 Số 5 - Trang 663-674 - 1970
Phosphate utilization by an oceanic diatom in phosphorus‐limited chemostat culture and in the oligotrophic waters of the central North Pacific1 Thalassiosira pseudonana from the oligotrophic waters of the central North Pacific Ocean was grown in phosphorus‐limited chemostat culture. When the chemical composition of the cells, expressed as ratios, was compared with that of nitrogen‐limited cultures, several of these ratios varied in excess of a factor of five between the two systems. Among these, which emerged as diagnostic indicators of phosphorus‐starvation vs. nitrogen‐deficiency, were the C : P, N : P. P : Chl a and Chl a : ATP ratios.The physiological responses of a population were determined by its preconditioning history. The minimum cellular phosphorus content, q o , varied with the degree of phosphorus starvation. The rate of phosphate uptake at a saturating concentration of phosphate by phosphorus‐limited cultures of T. pseudonana exceeded the rates of uptake by nonphosphorus‐limited cultures by an order of magnitude; the Ks for phosphate uptake was not a function of phosphorus deficiency. Phytoplankton in phosphorus‐starved chemostat cultures on medium made with central North Pacific Ocean water did not use naturally occurring dissolved organic phosphorus despite the presence of cell‐surface alkaline phosphatase. Phosphate uptake by natural phytoplankton assemblages in the central North Pacific was measured with 33 P. Uptake rates in the field were not significantly affected by light intensity. No circadian periodicity in uptake rates was detected in natural phytoplankton or algae cultured on a light/dark cycle.
Limnology and Oceanography - Tập 21 Số 1 - Trang 88-107 - 1976
Effect of coagulation on nutrient and light limitation of an algal bloom Coagulation is the formation of large particles from multiple collisions of smaller ones. Because larger particles fall faster than smaller ones, coagulation can be important in accelerating the export of organic matter from the ocean’s surface to the deep sea and has the potential to limit phytoplankton populations. We have developed a model of an algal bloom that includes nutrient and light limitation of algal growth rate and coagulation of single algal cells. The results show two effects of coagulation on the growth model. Loss of dividing cells to coagulating particles can occur when algal cells are growing at a fairly constant rate, placing a cap on the concentrations that algae can achieve. The second effect is enhancement of vertical particle flux from the surface mixed layer in aggregates. This enhanced transport moves algal biomass from the surface mixed layer over shorter periods at rates far greater than those associated with settling of single cells. For example, half the material associated with a bloom of 2‐µ m‐radius algae, which would take 350 d to settle out as isolated cells, took 42 d as aggregates. Aggregation was not limited to the large algae, although the rate was slower for the smaller ones. Coagulation was enhanced by higher initial nutrient concentrations, deeper mixed layers, and higher shear rates. Vertical transport associated with aggregation has the potential to be an important mechanism for removing biological material from eutrophic regions.
Limnology and Oceanography - Tập 37 Số 1 - Trang 77-89 - 1992
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