Nutrient retention and transformation in relation to hydraulic flushing rate in a small impoundment

SUMMARY. The fluxes of water, chloride, silicale and various forms of nitrogen and phosphorus into and out of a 3925 ha impoundment (Lake Taiquin) in north Florida were examined over a 3 year period. Annual hydraulic flushing rates for the lake varied by a factor of more than 2 during the study period and provided an opportunity to examine the effect of flushing rate on nutrient cycling within the lake. The results support the hypothesis that nutrient retention and transformation in lakes and impoundments with high flushing rates (> 1 year^-1) are appreciably influenced by annual variations in flushing rates. Higher fractions of input silicate and total phosphorus were retained by Lake Taiquin during the years with average flushing rates (8 year^-1) than during a year with abnormally high flushing rate (16 year^-1). Nitrogen was not appreciably retained during any of the three study years, and thus N: P ratios in the lake outflow were higher than in the inflow.
Phytoplankton productivity was appreciably higher (70%) during the year with the higher flushing rate, apparently in response to higher reactive phosphorus concentrations in the lake and perhaps to a higher standing crop of phytoplankton during that year. Reactive phosphorus and dissolved inorganic nitrogen inputs could account for only about 30% and 25%, respectively, of the phosphorus and nitrogen required to support observed photosynthetic rates in all three study years. Recycling of nutrients apparently accounted for most of the remainder, although nitrogen fixation could not be ruled out as a factor in the nitrogen budget.     

LA ENPRENO DE STRONTIO EN KOKOLITOFOROJ

Pure cultures of the coccolithophorid Syracosphaera carleraewere grown in a synthetic saline medium containing 3.4mM Ca++and 2.0, 1.0, 0.5 or 0.0 mM Sr⁺⁺. The coccoliths were separatedby differential centrifugation, washed, dried, and examinedby flame photometry and by X-ray diffraction. In the absenceof Sr, they consisted of pure calcite. In media containing Sr,the concentration factor or incorporation factor (Sr/Ca in coccolithsSr/Ca in medium) was approx. 0.02 in each case, indicating ahigh degree of discrimination against Sr. ¹ Nuna adreso: Scripps Instituto por Oceanografio, La Jolla,California, U. S. A. (Received March 4, 1961; )     

Crustecdysone Mediated Changes in Crayfish

Molting in crayfish, essential for growth is preceded by a decreasein total organic content during premolt. Mineral, as calcium,is conserved in gastroliths after mobilization from the exoskeleton.Crustecdysone treatment results in gastrolith formation by intactcrayfish in intermolt, state C, but does not influence the rateof gastrolith formation in eyestalkless animals. Moreover, therate of gastrolith formation is not increased at higher hormonedoses; conversely, less dense, abnormal gastrohths result, whileapolysis is evident by 48 to 60 hours after treatment. It appearsthat crustecdysone promotes reabsorption of the organic matrixsince treatment with this hormone does not lead to a measureabledecrease in calcium content of shell based on dry weight. Premolt crayfish normally have a higher amino acid pool in alltissues than do those in intermolt, and eyestalk removal fromintermolt crayfish results in an increase in the free-aminoacid level of all tissues by 24 hours; crustecdysone treatmentresults in a significant increase in muscle amino acids by 12hours after a hormone dose of 5 µg/g body weight. In thecontext of integumentary growth and protein synthesis low dosesof crustecdysone (1 µg/g) increase the in vivo incorporationof amino acid into hypodermis, but not hepatopancreas, by 24hours, and the increase is significant by 36 hours; a higherdose (5 µg) does not change this rate of incorporation.Selective increase in hypodermis protein is not evident in acidphosphatase levels from 12 to 48 hours, but respiration of thistissue is significantly elevated within two hours after hormoneinjection.     

Phylogeny of Australasian agamid lizards based on nuclear and mitochondrial genes: implications for morphological evolution and biogeography

Recent mtDNA phylogenies of Australasian agamid lizards are highly incongruent with existing morphological views. To resolve this discrepancy we sequenced two nuclear gene regions, c- mos and brain-derived neurotrophic factor (BDNF). These were highly concordant with each other and the mtDNA phylogeny, but not the morphology. A combined molecular analysis reveals substantial hidden support (additional phylogenetic signal that emerges only when the data sets interact in a combined analysis). Bayesian posteriors, and a partitioned bootstrap procedure introduced here, indicate strong support for most nodes. The resultant tree implies extensive morphological homoplasy, with many genera emerging as non-monophyletic ( Amphibolurus , Rankinia , Ctenophorus , Physignathus , Diporiphora ). The water and forest dragons ( Physignathus and Hypsilurus ) form a paraphyletic basal assemblage to the more derived Australian forms such as Amphibolurus and Ctenophorus , which include almost all the xeric taxa. However, the thorny devil Moloch horridus is a basal lineage and not closely related to the other arid forms. Tree topology, inferred divergence dates, palaeogeographical and palaeoclimatic data are all consistent with Miocene immigration into Australia from the north by mesic forest ecomorphs, followed by initial diversification in mesic habitats before radiation into xeric habitats facilitated by increasing aridity.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 343–358.