Limnology and Oceanography

Karentz, Deneb; Lutze, Louise H.

doi: 10.4319/lo.1990.35.3.0549pmid: N/A

A biological dosimeter has been developed for use in aquatic environments. This method is based on the sensitivity of a DNA repair‐deficient strain of Escherichia coli (CSR06) to ultraviolet (UV) radiation. The dosimeter permits evaluation of the penetration of biologically active UV radiation within a water column, reflecting the potential effect of exposure over selected time intervals. With the use of various filters, the biological dosimeter can discriminate between the effects of UV‐B (280–320 nm) and UV‐A (320–400 nm) or other selected portions of the solar UV spectrum. During springtime ozone depletion over the Antarctic in 1988, a general relationship was observed between stratospheric ozone concentration and the contribution of incident solar UV‐B radiation to lethality of dosimeter cells. The use of dosimeters within the water column indicated that significant amounts of UV‐B can be transmitted to a depth of 10 m and biological effects of UV could be detected to 20 and 30 m. Biological dosimeters may provide a means of standardizing in‐water UV measurements across all types of aquatic habitats and at any geographical location.

Bricaud, Annick; Stramski, Dariusz

doi: 10.4319/lo.1990.35.3.0562pmid: N/A

Absorption coefficients of total particulate (biogenous) matter were determined in the mesotrophic waters of the Peruvian upwelling and the oligotrophic waters of the Sargasso Sea. A method based on spectral criteria was used to partition these coefficients into absorption by living algal cells and by nonalgal (mainly detrital) material. This method was tested by independently measuring absorption by nonalgal material for samples from the Sargasso Sea.

Chalup, Michael S.; Laws, Edward A.

doi: 10.4319/lo.1990.35.3.0583pmid: N/A

The marine phytoplankter Pavlova lutheri was grown in both batch and continuous culture under various conditions of light and nitrate limitation in order to examine the accuracy of certain assumptions and predictions of growth models. The N : C ratio cells was found to be uniquely related to their relative growth rate. There was no unique relationship, however, between Chl a : C ratios and relative growth rate. Optical absorption coefficients normalized to Chl a were negatively correlated with relative growth rate at a fixed irradiance and positively correlated with irradiance at a fixed relative growth rate when light intensity was varied with neutral‐density filters. Quantum yields were positively correlated with relative growth rate at a fixed irradiance and negatively correlated with irradiance at a fixed relative growth rate. Certain parameters or combinations of parameters which appear in nutrient‐saturated growth models were found to be either independent of relative growth rate at a fixed irradiance or uniquely correlated with relative growth rate. This discovery facilitates extension of nutrient‐saturated growth models to nutrient‐limited conditions.

Laws, Edward A.; Chalup, Michael S.

doi: 10.4319/lo.1990.35.3.0597pmid: N/A

Recent experimental evidence has made it clear that effects of irradiance and nutrient limitation on light absorption and photosynthetic quantum yields of microalgae and the relationship between cellular N: C ratios and nutrient‐limited growth rates are inconsistent with the assumptions and predictions of current models of algal growth. A new algal growth model was therefore developed to overcome these inconsistencies. The new model predicts a hyperbolic relationship between nutrient‐saturated growth rates and irradiance and a linear relationship between growth rate and both respiration rate and Chl a : C ratios. The correlation between growth rate and Chl a : C is positive under nutrient‐limited conditions and negative under nutrient‐saturated (light‐limited) conditions. The requirement that N: C ratios be linearly related to relative growth rates leads to the conclusion that the product of the Chl a‐specific absorption coefficient and the quantum yield coefficient be hyperbolically related to nutrient‐limited growth rates, a result consistent with experimental observations. The equations relating respiration rate and compositional ratios to absolute and relative growth rates appear to be insensitive to photoperiod.

Kremer, Patricia; Costello, John; Kremer, James; Canino, Michael

doi: 10.4319/lo.1990.35.3.0609pmid: N/A

Symbiotic dinoflagellates (zooxanthellae) associated with the medusa of Linuche unguiculata constituted 22–26% of the total C and N biomass. The maximal net production for intact medusae (Pm) averaged 4.5 mg O2 (mg Chl a)−1 h−1, equivalent to an assimilation number of 2.0 mg C (mg Chl a)−1 h−1. At the midday maximum, gross oxygen production averaged four times the respiration rate. The saturating light intensity was 200–300 µEinst m−2 s−1 (Einstein = mol quanta) and the compensation light intensity (dO2 = 0) was ∼20 µEinst mn−2 s−1. On a diel basis Pgrow : R averaged 1.7 for intact medusae at ambient near‐surface light. Diel periodicity with a midday maximum was measured for the production potential under artificial, saturating light. Both intact medusae and freshly isolated zooxanthellae demonstrated similar diel production patterns. Respiration did not show the same strong diel pattern as net production, but respiration declined steadily when medusae were held unfed in the dark. Respiration was independent of the ambient oxygen concentration over a range from 4 to 16 mg O2 liter−1. Diel periodicity was measured in egg release and division rates of zooxanthellae. Estimates of both algal and host growth ranged from 0.01 to 0.04 d−1. Calculations indicated that only 21% of the C fixed in photosynthesis was used in algal respiration and growth. If the remaining photosynthate were translocated, it could provide all the C required for host respiration and somatic growth. Egg production represented another large C flux in adult females, with a daily release equivalent to 4–8% of host body C for medusae of 0.2–1.2 ml in displacement volume.

Crosby, Michael P.; Newell, Roger I. E.; Langdon, Christopher J.

doi: 10.4319/lo.1990.35.3.0625pmid: N/A

Unattached, cellulolytic bacteria isolated from a salt marsh were cultured on [15N]ammonium sulfate and [14C]glucose and fed to the American oyster Crassostrea virginica. Oysters were able to digest and assimilate bacterial C with an assimilation efficiency of 52.5%. We estimate that free‐living bacteria may be capable of supplying up to ∼9.5% of the total C requirements of oysters in their natural habitat. Cellulolytic bacteria were also cultured on 14C‐labeled refractory Spartina alterniflora particles as the sole C source and [15N]ammonium sulfate as a source of N. These labeled bacteria, together with the S. alterniflora, were fed to the oysters. The refractory C from these detrital complexes was assimilated by the oysters with an efficiency of 10.3%. It was (P= 0.0007) greater than the assimilation efficiency of 2.7% measured in a previous study for oysters feeding on the refractory S. alterniflora substrate alone. This result provides direct experimental evidence that cellulolytic bacteria in the environment can contribute to the transfer of C from refractory detritus to an ecologically important suspension‐feeding macroinvertebrate. We calculated that C. virginica, when fed detrital complexes, assimilated bacterial N with an efficiency of 57.2% but that assimilation of total N present in the detrital complexes was only 3.4%. We speculate that this low assimilation efficiency was due to most (94%) of the N being in the form of condensation products such as humic geopolymers and extracellular polymeric substances secreted by bacteria which could not be digested and absorbed by the oysters. Calculations show that detrital complexes in the natural environment may provide a significant contribution to an oyster’s C demand. The magnitude of this contribution can increase from 1.3 to 60% as both absolute bacterial abundance and proportion of bacteria attached to detrital particles increase, raising the oysters’ efficiency of filtration for these substrates.

Christensen, Peter Bondo; Nielsen, Lars Peter; Sørensen, Jan; Revsbech, Niels Peter

doi: 10.4319/lo.1990.35.3.0640pmid: N/A

Seasonal variation of chlorophyll content, photosynthesis, O2 respiration, and denitrification was measured under light and dark conditions in the sediment of a nutrient‐rich Danish lowland stream. Exponential growth of benthic microalgae was observed in early spring (April–May) and photosynthetic capacity persisted until fall. The benthic algae were a major C source for heterotrophic activity as indicated by a close correlation between O2 respiration and Chl content in the sediment. Denitrification activity was related to Chl content, NO3− availability, and O2 conditions. Diffusion from the overlying water was always the major NO3− source for denitrification. Under lighted conditions, photosynthetic O2 production increased the oxic zone and reduced denitrification activity by up to 85% in spring. A simple diffusion‐reaction model allowed denitrification rates to be estimated from O2 respiration rates and concentrations of O2 and NO3− in the stream water. Throughout the season, estimated denitrification rates correlated well with those actually measured. The model demonstrated that denitrification activity was controlled primarily by the thickness of the oxic surface layer which served as a diffusion barrier for NO3− to the denitrification zone.

Rich, Hans Walter; Morel, François M. M.

doi: 10.4319/lo.1990.35.3.0652pmid: N/A

Three different types of iron oxo‐hydroxo colloids with well‐defined sizes and chemistries have been synthesized by hydrolysis of Fe(III) in acidic and alkaline medium as well as by oxidative hydrolysis of Fe(II), resulting in solutions of β‐FeOOH (30 nm), a hexanuclear complex (HN; 2 nm), and a polynuclear oxidation product (OP; 3 nm). These colloids were tested for their availability to the coastal diatom Thalassiosira weissflogii. Iron‐limited cells were grown in synthetic seawater containing 0–0.5 µM of total iron in colloidal form as the only iron source. We found no evidence of direct uptake of colloids by the algae. The β‐FeOOH colloids, which dissolve exceedingly slowly in the light or in the dark, did not support diatom growth. In contrast, maximal growth rates and cell yields were observed in the presence of either 50 nM OP or HN. Photoreduction accounted for the availability of HN. In the case of OP, thermal (dark) dissolution of the colloid appears sufficient to satisfy the iron requirement of the diatom.

Rudd, John W. M.; Kelly, C. A.; Schindler, D. W.; Turner, M. A.

doi: 10.4319/lo.1990.35.3.0663pmid: N/A

The acidification efficiencies of nitric and sulfuric acids were compared for 5 yr by separate experimental additions of the acids to the partitioned north and south basins of Lake 302. In the epilimnion, nitric acid was 70% as efficient as sulfuric acid in reducing alkalinity. On a whole‐lake basis, acidification by nitric acid was about half as efficient as by sulfuric acid. In‐lake processes removed 70 and 57% of the added nitric and sulfuric acids.

Monismith, Stephen G.; Koseff, Jeffrey R.; Thompson, Janet K.; O'Riordan, Catherine A.; Nepf, Heidi M.

doi: 10.4319/lo.1990.35.3.0680pmid: N/A

We carried out experiments studying the hydrodynamics of bivalve siphonal currents in a laboratory flume. Rather than use living animals, we devised a simple, model siphon pair connected to a pump. Fluorescence‐based flow visualization was used to characterize siphon‐jet flows for several geometric configurations and flow speeds. These measurements show that the boundary‐layer velocity profile, siphon height, siphon pair orientation, and size of siphon structure all affect the vertical distribution of the excurrent flow downstream of the siphon pair and the fraction of excurrent that is refiltered. The observed flows may effect both the clearance rate of an entire population of siphonate bivalves as well as the efficiency of feeding of any individual. Our results imply that field conditions are properly represented in laboratory flume studies of phytoplankton biomass losses to benthic bivalves when the shear velocity and bottom roughness are matched to values found in the field. Numerical models of feeding by a bivalve population should include an effective sink distribution which is created by the combined incurrent‐excurrent flow field. Near‐bed flows need to be accounted for to properly represent these benthic‐pelagic exchanges. We also present velocity measurements made with a laser‐Doppler anemometer (LDA) for a single configuration (siphons flush with bed, inlet downstream) that show that the siphonal currents have a significant local effect on the properties of a turbulent boundary layer.