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Algal Productivity (algal + productivity)
Selected AbstractsAssessing the sources and magnitude of diurnal nitrate variability in the San Joaquin River (California) with an in situ optical nitrate sensor and dual nitrate isotopesFRESHWATER BIOLOGY, Issue 2 2009BRIAN A. PELLERIN Summary 1.,We investigated diurnal nitrate (NO3,) concentration variability in the San Joaquin River using an in situ optical NO3, sensor and discrete sampling during a 5-day summer period characterized by high algal productivity. Dual NO3, isotopes (,15NNO3 and ,18ONO3) and dissolved oxygen isotopes (,18ODO) were measured over 2 days to assess NO3, sources and biogeochemical controls over diurnal time-scales. 2.,Concerted temporal patterns of dissolved oxygen (DO) concentrations and ,18ODO were consistent with photosynthesis, respiration and atmospheric O2 exchange, providing evidence of diurnal biological processes independent of river discharge. 3.,Surface water NO3, concentrations varied by up to 22% over a single diurnal cycle and up to 31% over the 5-day study, but did not reveal concerted diurnal patterns at a frequency comparable to DO concentrations. The decoupling of ,15NNO3 and ,18ONO3 isotopes suggests that algal assimilation and denitrification are not major processes controlling diurnal NO3, variability in the San Joaquin River during the study. The lack of a clear explanation for NO3, variability likely reflects a combination of riverine biological processes and time-varying physical transport of NO3, from upstream agricultural drains to the mainstem San Joaquin River. 4.,The application of an in situ optical NO3, sensor along with discrete samples provides a view into the fine temporal structure of hydrochemical data and may allow for greater accuracy in pollution assessment. [source] VARIABILITY IN THE ECOPHYSIOLOGY OF HALIMEDA SPP. (CHLOROPHYTA, BRYOPSIDALES) ON CONCH REEF, FLORIDA KEYS, USA,JOURNAL OF PHYCOLOGY, Issue 4 2003Kevin Beach The photosynthetic performance, pigmentation, and growth of a Halimeda community were studied over a depth gradient on Conch Reef, Florida Keys, USA during summer,fall periods of 5 consecutive years. The physiology and growth of H. tuna (Ellis & Solander) Lamouroux and H. opuntia (L.) Lamouroux on this algal dominated reef were highly variable. Maximum rate of net photosynthesis (Pmax), respiration rate, and quantum efficiency (,) did not differ between populations of either species at 7 versus 21 m, even though the 21-m site received a 66% lower photon flux density (PFD). Physiological parameters, as well as levels of photosynthetic pigments, varied temporally. Pmax, saturation irradiance, compensation irradiance, and growth were greatest in summer months, whereas ,, chl a, chl b, and carotenoid concentrations were elevated each fall. Halimeda tuna growth rates were higher at 7 m compared with 21 m for only two of five growth trials. This may have arisen from variability in light and nutrient availability. Individuals growing at 7 m received a 29% greater PFD in August 2001 than in 1999. In August 1999 and 2001 seawater temperatures were uniform over the 14-m gradient, whereas in August 2000 cold water regularly intruded upon the 21-m but not the 7-m site. These results illustrate the potentially dynamic relationship between nutrients, irradiance, and algal productivity. This suggests the necessity of long-term monitoring over spatial and temporal gradients to accurately characterize factors that impact productivity. [source] Flood disturbance, algal productivity, and interannual variation in food chain lengthOIKOS, Issue 1 2000Jane C. Marks The length of a river food chain changed from year to year, shifting with the hydrologic regime. During drought years, grazers suppressed algae across a nutrient gradient, while predators were functionally unimportant. Following flood disturbance, predators suppressed grazers, releasing algae. These results suggest that hydrologic regime, rather than productivity, determines the functional length of this river food chain. Within years, algae and grazer biomass responded to an experimental productivity gradient in patterns predicted by simple trophic models that assume efficient energy transfer. Understanding differences among species within trophic levels, however, was crucial in delineating the controlling interactions. [source] Composition and activity of external carbonic anhydrase of microalgae from karst lakes in ChinaPHYCOLOGICAL RESEARCH, Issue 2 2008Yanyou Wu SUMMARY The species composition, the net photosynthetic O2 evolution rate and the activity of external carbonic anhydrase (CA) of microalgae from three reservoirs were studied. Carbonic anhydrase activity had a significant positive correlation with the density of Cyanobacteria in Lake Aha. Microalgae's carbonic anhydrase activity in Lakes Baihua and Hongfeng was related to the density of Chlorophyceae. The species abundances of microalgae in Lake Aha, Lake Baihua, and Lake Hongfeng were different. A relationship between carbonic anhydrase activity and net photosynthetic O2 evolution rate had also been established. Algae with external CA influenced the algal productivity. These results demonstrate the role of external CA in facilitating the availability of CO2 that limits the photosynthesis of microalgae in karst lakes in China. [source] | |||||||||||||||||||