R. Christian Jones

Effect of temperature on photosynthesis-light response and growth of four phytoplankton species isolated from a tidal freshwater river

Three cyanobacteria (Microcystis aeruginosa Kütz. emend. Elenkin, Merismopedia tenuissima Lemmermann, and Oscillatoria sp.) and one diatom (Aulacoseira granulata var. angustissima O. Mull. emend. Simonsen) were isolated from the tidal freshwater Potomac River and maintained at 23° C and 40 μmol photons·m−2·s−1 on a 16:8 L:D cycle in unialgal culture. Photosynthetic parameters were determined in nutrient‐replete cultures growing exponentially at 15, 20, 25, and 30° C by incubation with 14C at six light levels. P  Bmax was strongly correlated with temperature over the entire range for the cyanobacteria and from 15 to 25° C for Aulacoseira, with Q10 ranging from 1.79 to 2.67. The α values demonstrated a less consistent temperature pattern. Photosynthetic parameters indicated an advantage for cyanobacteria at warmer temperatures and in light‐limited water columns. P  Bmax and Ik values were generally lower than comparable literature and field values, whereas α was generally higher, consistent with a somewhat shade acclimated status of our cultures. Specific growth rate (μ), as measured by chlorophyll change, was strongly influenced by temperature in all species. Oscillatoria had the highest μ at all temperatures, joined at lower temperatures by Aulacoseira and at higher temperatures by Microcystis. Values of μ for Aulacoseira were near the low end of the literature range for diatoms consistent with the light‐limited status of the cultures. The cyanobacteria exhibited growth rates similar to those reported in other studies. Q10 for growth ranged from 1.71 for Aulacoseira to 4.16 for Microcystis. Growth rate was highly correlated with P  Bmax for each species and the regression slope coefficients were very similar for three of the species.

Phytoplankton as a factor in the decline of the submersed macrophyte Myriophyllum spicatum L. in Lake Wingra, Wisconsin, U.S.A.

A dramatic decline in biomass and areal coverage of the submersed macrophyte Myriophyllum spicatum in Lake Wingra, Wisconsin, USA during the mid-1970s is documented using aerial photography, vegetation surveys, and quadrat biomass sampling. Over the same period, light penetration as measured by Secchi disc transparency and extinction coefficient decreased substantially. During this period, extinction coefficient was closely correlated with chlorophyll a levels implicating phytoplankton as the major source of decreased light penetration. A growth model for M. spicatum predicts a substantial decline in macrophyte biomass when extinction coefficient is increased to the levels reported since 1977. Available data do not show whether the phytoplankton increase preceeded or followed the macrophyte decline. Nonetheless it is clear that phytoplankton growth can account for a substantial portion of the decline and that macrophyte recovery will be difficult given the phytoplankton-induced decrease in water clarity.

A comparison of water-column macroinvertebrate communities in beds of differing submersed aquatic vegetation in the tidal freshwater Potomac River.

Macroinvertebrates are a major food source for fish species and macrophyte beds are hypothesized to harbor a rich community of these organisms. Macroinvertebrates inhabiting the water column in two macrophyte beds and an adjacent open area were sampled in a small embayment of the tidal freshwater Potomac River. One macrophyte bed consisted of an almost complete monoculture ofHydrilla verticillata, while the second community was a more diverse mixture of plant species. In samples with substantial amounts of submersed aquatic vegetation (SAV), macroinvertebrate density was two orders of magnitude higher than and substantially more taxa were found than at the open water site. Total macroinvertebrate abundance was significantly greater at theH. verticillata site than at the mixed site in July, but no significant difference was observed in August. Taxa richness did not vary between the two vegetated sites in July but was higher in the mixed bed in August. While the two vegetated sites shared similar taxa, they differed in their abundance. TheH. verticillata site harbored more hydrobiid snails, and the mixed site was characterized by more chironomids and hydroptilid caddisflies. Differences between July and August collections were even greater than between sites. Numbers of hydroptilid caddisflies, baetid mayflies, and coenagrionid damselflies were substantially higher in August, while oligochaetes, hydrobiids, and chironomids were reduced. Results support the hypothesis that water-column macroinvertebrates are greatly enhanced in the presence of macrophytes. The ecological significance of the less substantial differences in macroinvertebrates between macrophyte beds requires further study.

The Effect of Submersed Aquatic Vegetation on Phytoplankton and Water Quality in the Tidal Freshwater Potomac River

ABSTRACT Phytoplankton biomass and water quality were determined at two sites in the tidal freshwater Potomac River. At each site three plant treatments were sampled twice each during the summer and the fall. Phytoplankton biomass, as measured by chlorophyll a, was negatively related to macrophyte density. High density Hydrilla beds harbored the least phytoplankton chlorophyll, while low density mixed beds were most similar to the open water areas. This effect was more pronounced in summer than in fall. Variation in dissolved oxygen and pH reflected the standing crop of both phytoplankton and macrophytes. Phytoplankton were the dominant influence in the open water; macrophytes were more important in the dense weedbeds. Greatest variation in temperature was observed in the dense weedbeds.

Productivity of algal epiphytes in a Georgia salt marsh: effect of inundation frequency and implications for total marsh productivity

Primary production by algal epiphytes of dead Spartina alterniflora shoots in a Georgia salt marsh was measured using the 14C technique. A 23 factorial design was used to quantify the effects of light intensity and inundation frequency (stem height) on carbon fixation at two sites along a salt marsh creek. Algae inundated daily fixed carbon more rapidly than those which had dried for several days, but this may have been the results of greater biomass on more frequently immersed stems. This result corroborates studies showing desiccation is not always a severe stress for intertidal algae. Similarity of epiphyte algal productivity to that of salt marsh benthic diatoms suggests that, given adequate substrate, the epiphytes may be an important source of primary production during some seasons of the year.Primary production by algal epiphytes of dead Spartina alterniflora shoots in a Georgia salt marsh was measured using the 14C technique. A 23 factorial design was used to quantify the effects of light intensity and inundation frequency (stem height) on carbon fixation at two sites along a salt marsh creek. Algae inundated daily fixed carbon more rapidly than those which had dried for several days, but this may have been the results of greater biomass on more frequently immersed stems. This result corroborates studies showing desiccation is not always a severe stress for intertidal algae. Similarity of epiphyte algal productivity to that of salt marsh benthic diatoms suggests that, given adequate substrate, the epiphytes may be an important source of primary production during some seasons of the year.

Seasonal variations in photosynthetic response of algae epiphytic on Myriophyllum spicatum L.

Abstract The photosynthetic response to light of epiphytic algae from Lake Wingra, Wisconsin was determined monthly during the 1978 and 1979 growing seasons. A 14 C technique was developed for measurement of photosynthesis of the intact epiphyte community which was then removed by shaking. The photosynthetic rate at low light, α, varied from 5.56 to 18.26 μg C (mg Chl a ) −1 h −1 (μE m −2 s −1 ) −1 while P max B , the photosynthetic rate at light saturation, ranged from 1.0 to 2.6 mg C (mg Chl a ) −1 h −1 . During 1979, variations in α and P max B followed the sun—shade model for photosynthetic adaptation: P max B was highest in summer and lowest in spring and fall, while α followed the opposite pattern. Patterns in α and P max B for 1978 were less apparent. During 1979, P max B was significantly correlated with both temperature and long-term average irradiance. When data from both years were combined, P max B was significantly correlated only with temperature, but the derived parameter I K (= P max B / α ) correlated significantly with both temperature and long-term average irradiance. Epiphytic algae growing at different depths could not be shown to have different photosynthetic responses to light. This is perhaps due to the large variation in response between replicate samples which could not be reduced due to logistical limitations.

Spatial and seasonal patterns in water quality in an embayment-mainstem reach of the tidal freshwater Potomac River, USA: a multiyear study

Spatial and temporal patterns in water quality were studied for seven years within an embayment-river mainstem area of the tidal freshwater Potomac River. The purpose of this paper is to determine the important components of spatial and temporal variation in water quality in this study area to facilitate an understanding of management impacts and allow the most effective use of future monitoring resources. The study area received treated sewage effluent and freshwater inflow from direct tributary inputs into the shallow embayment as well as upriver sources in the mainstem. Depth variations were determined to be detectable, but minimal due mainly to the influence of tidal mixing. Results of principal component analysis of two independent water quality datasets revealed clear spatial and seasonal patterns. Interannual variation was generally minimal despite substantial variations in tributary and mainstem discharge among years. Since both spatial and seasonal components were important, data were segmented by season to best determine the spatial pattern. A clear difference was found between a set of stations located within one embayment (Gunston Cove) and a second set in the nearby Potomac mainstem. Parameters most highly correlated with differences were those typically associated with higher densities of phytoplankton: chlorophyll a, photosynthetic rate, pH, dissolved oxygen, BOD, total phosphorus and Secchi depth. These differences and their consistency indicated two distinct water masses: one in the cove harboring higher algal density and activity and a second in the river with lower phytoplankton activity. A second embayment not receiving sewage effluent generally had an intermediate position. While this was the most consistent spatial pattern, there were two others of a secondary nature. Stations closer to the effluent inputs in the embayment sometimes grouped separately due to elevated ammonia and chloride. Stations closer to tributary inflows into the embayment sometimes grouped separately due to dilution with freshwater runoff. Segmenting the datasets by spatial region resulted in a clarification of seasonal patterns with similar factors relating to algal activity being the major correlates of the seasonal pattern. A basic seasonal pattern of lower scores in the spring increasing steadily to a peak in July and August followed by a steady decline through the fall was observed in the cove. In the river, the pattern of increases tended to be delayed slightly in the spring. Results indicate that the study area can be effectively monitored with fewer study sites provided that at least one is located in each of the spatial regions.

Spatial, temporal, and storm runoff-related variations in phytoplankton community structure in a small, suburban reservoir

Phytoplankton abundance and community structure were determined routinely over an annual period and intensively during two storm-runoff events in a small suburban reservoir in northern Virginia, U.S.A. Traditional graphical techniques and a multivariate approach (Principal Components Analysis) were used to demonstrate a seasonal pattern of phytoplankton succession with greens and blue-greens dominant in summer, diatoms and chrysophytes in spring and fall, and cryptophytes in winter. Spatial variations were minor over horizontal and vertical dimensions during spring mixis, but depth variations were substantial during summer stratification. Storm runoff had little effect on phytoplankton composition during the stable summer period, but was associated with a substantial perturbation in community structure during the spring to summer transition.

Algal biomass dynamics during colonization of artificial islands: experimental results and a model

Algal biomass during colonization of polyurethane foam islands (5.1 cm × 7.6 cm × 7.6 cm) was approximated by measuring chlorophyll a levels on islands after exposure periods of 1, 2, 3, 4, and 6 weeks at six locations in a small lake in central Tennessee, USA. Chlorophyll, ash-free dry weight, and concurrent environmental data were collected for two colonization periods: one in late winter and spring (Set 1), a second in summer (Set 2).During Set 1 algal biomass levels, as indicated by chlorophyll a, showed a sharp rise initially, but Set 2 islands exhibited a lag period of 7 to 12 days before a rapid increase in algal biomass was noted. Equilibrium chlorophyll a values were similar for both sets. High levels of phaeopigments were found at Stations 2, 3, and 4 during Set 2 resulting in large corrections in chlorophyll a readings. Ash-free dry weight values increased steadily through each colonization period.A model of biomass accumulation during colonization was constructed postulating three major processes — photosynthesis, respiration, and passive accumulation — which were modulated by three environmental factors — light, temperature, and plankton chlorophyll a levels. For simulations parameter values were taken from the literature where possible. Additional parameter values were set and literature values adjusted when the model was ‘tuned’ to Set 2 data. A simulation with the tuned model using Set 1 environmental input resulted in a good prediction of equilibrium values, but a misinterpretation of initial values. The discrepancy between model predictions and data was alleviated when the passive accumulation rate was increased demonstrating the dependence of biomass values early in colonization on passive accumulation from the plankton.

Long-term trends in summer phytoplankton chlorophyll a in the tidal freshwater Potomac River, USA: relationship to climatic and management factors

The management of freshwater systems has been prefaced on the belief that nutrient reduction from point sources is an effective way to control eutrophication. This paradigm is based on results from a number of studies relating dramatic reductions in algal standing crops which have occurred when loading of nutrients, notably phosphorus, has been substantially reduced. However, in any given situation the response to point source nutrient control may be influenced by a number of other factors, such as flushing, turbidity, or temperature, which may limit algal growth for at least part of the year. Furthermore, the system may also be influenced by noncontrolled sources such as runoff and sediment release. Since these factors may vary in importance from year-to-year, interannual trends and relationships to nutrient loading changes may be difficult to decipher. These factors may be especially important in tidal freshwater.