Michael E. Q. Pilson

Spectrophotometric determination of arsenite, arsenate and phosphate in natural waters

Summary A spectrophotometric method is presented for the determination of arsenite, arsenate, and phosphate in fresh and salt waters. By the use of an oxidizing and a reducing reagent, these species may be determined in a mixture of all three. Appro priate conditions for the use of these reagents are described. The method is applicable to solutions where the total phosphorus and arsenic molar concentration is less than about 3 · 10 −6 . The precision is of the order of ±0.015 μM.

On the residence time of water in Narragansett Bay

For Narragansett Bay, Rhode Island, newly calculated and archival data for the area, mean depth, total volume, mean salinity and fresh water input are presented. Estimates of the residence time of the water, derived from 22 sets of monthly mean values, were related to estimates of the fresh water input according to the empirical relationship T=41.8 e−0.00435(FW), where T is the flushing time in days, and FW is the fresh water input in m3 per s; the r2 value is 0.841. Adding estimates of the mean wind speed into a multiple regression increased the correlation coefficient only to 0.864. At the long-term mean rate of fresh water input (105 m3 per s) the flushing time is 26 days. At the lowest mean monthly input rate observed the flushing time was nearly 40 days, while at the highest mean monthly input rate in the data set (325 m3 per s) the flushing time was about 10 days. Known sources of random error appear sufficient to account for most of the deviations from the relationship. The evidence suggests that variation in the flushing time is largely determined by variation in the fresh water input.

Carbon isotope fractionation by marine phytoplankton in culture: The effects of CO2 concentration, pH, temperature, and species

Closed cultures of marine phytoplankton were established under variable conditions of CO2 concentration, temperature, growth rate (by light limitation), and pH (but with nearly identical [CO2aq]) in order to assess the relative influence of these variables on the extent of carbon isotope fractionation relative to dissolved inorganic carbon sources. Culture biomass was not allowed to increase beyond levels that would significantly affect the dissolved carbon system in the closed cultures. In experiments with Skeletonema costatum and Emiliania huxleyi, increasing CO2 concentrations led to increased carbon isotope discrimination (resulting in organic matter progressively depleted in δ13C, i.e., a greater, more negative ϵp). ϵp values for E. huxleyi were 8–10‰ less than for S. costatum under identical conditions. For the S. costatum cultures, there was nearly a 20 ‰ range in [CO2aq]-dependent ϵp. The effect was nonlinear with a leveling off at high [CO2aq]. Over a pH range of 7.5–8.3 but at a constant [CO2aq] there was a variation in carbon isotope fractionation by S. costatum of about 9 ‰ with a minimum at pH 7.8–7.9. There was a temperature effect of ∼8‰ on fractionation even after equilibrium temperature dependency of δ13C of CO2aq was taken into account. No growth rate effect was found for S. costatum over a modest range of growth rates. Culture experiments used to determine the carbon isotope fractionation by phytoplankton species must be conducted under well-defined conditions of temperature, pH, and CO2 concentrations. Hindcasts of ancient atmospheric pCO2 from measurements of δ13C of organic carbon in marine sediments will require careful calibration because of the variety of possible factors that influence δ13Corg.

Denitrification and N2O production in near-shore marine sediments

Abstract Methods were developed for determining rates of denitrification in coastal marine sediments by measuring the production of N2 from undisturbed cores incubated in gas-tight chambers. Denitrification rates at summer temperatures (23°C) in sediment cores from Narragansett Bay, Rhode Island, were about 50μmol N2m−2 hr−1. This nitrogen flux is equal to approximately one-half of the NH+4flux from the sediments at this temperature and is of the magnitude necessary to account for the anomalously low N/P and anomalously high O/N ratios often reported for benthic nutrient fluxes. The loss of fixed nitrogen as N2 during the benthic remineralization of organic matter, coupled with the importance of benthic remineralization processes in shallow coastal waters may help to explain why the availability of fixed nitrogen is a major factor limiting primary production in these areas. Narragansett Bay sediments are also a source of N2O, but the amount of nitrogen involved was only about 0.2 μmol m−2 hr−1 at 23°C.

Interstitial Silica and pH in Marine Sediments: Some Effects of Sampling Procedures

The temperature at which the interstitial water was squeezed from a marine sediment had a profound effect on the measured interstitial silica concentrations which showed an average increase of 51 percent after the sediment was exposed to a temperature 20�C higher than the in situ temperature. Similar effects were not found for interstitial phosphate or alkalinity, but the pH was slightly higher in the water squeezed at the higher temperature. These tempreature-induced changes were completed in a few hours. The use of filter paper can significantly lower the pH of expressed pore waters. Until some important questions about temperature effects are answered, all future data on the pH and silica concentration of pore waters of marine sediments should be obtained from samples extracted at in situ temperatures.

GAMETOGENESIS AND EARLY DEVELOPMENT OF THE TEMPERATE CORAL ASTRANGIA DANAE (ANTHOZOA : SCLERACTINIA)

1. The coral Astrangia danae is dioecious, with an early age of first reproduction.2. In Narragansett Bay, this species exhibits an annual reproductive cycle with gametogenesis starting in March-April. Spawning occurs during August, and vestigial gametes are absorbed during the winter months.3. Gametes originate from interstitial cells which differentiate in the mesenterial mesoglea.4. Ova are 100-130-µm in diameter and sperm are 2-3-µm in length, excluding the tails. Egg production was estimated at up to 6000 eggs per polyp.5. Fertilization and development are external; no fertilization membrane was seen even though a layer of cortical vesicles was present before fertilization.6. Embryonic cell divisions are around 30 min apart and the larval planual stage is reached within 12-15 hr after fertilization. Larval settlement was not observed.7. Ova from colonies containing zooxanthellae did not contain zooxanthellae when spawned.

Accumulation of sediments, trace metals (Pb, Cu) and total hydrocarbons in Narragansett Bay, Rhode Island

Abstract The accumulation of sediments, trace metals and hydrocarbons has been estimated from the analysis of the sediment from six coring sites in Narragansett Bay. Radionuclides ( 234 Th xs , 210 Pb xs , 239,240 Pu) with known input functions and trace metals (Cu, Pb) were used. We estimate that 6·9 × 10 4 tons of sediments, 51–90 tons of Pb, 72–100 tons of Cu and 400–1000 tons of total hydrocarbons accumulate annually under present conditions in the bay. This represents 64–117% (Pb), 89–123% (Cu) and 23–58% (hydrocarbons), respectively, of present day inputs to the bay. Furthermore, close to 100% of the particle-reactive radionuclides 210 Pb and 239,240 Pu accumulate in the bay. Present day inputs to the bay were calculated independently as 77–80 tons Pb and 81 tons of Cu. Sewage effluents were the dominant source of Cu, whereas atmospheric deposition and urban runoff were most important for Pb. Dredging activities by the U.S. Army Corps of Engineers between 1946 and 1971 removed more sediments from the bay than would have accumulated during the same time in the undredged areas of the bay. Copper smelting and coal mining on the shores of the upper bay during 1866–1880 left an imprint in the sediments which is still evident. Model derived accumulation rates of Pb, Cu and coal during that time were 3–4 times present-day inputs.

Surface-water acidification and extinction at the Cretaceous-Tertiary boundary

If published estimates of SO2 volatilization and NOx generation by the Cretaceous-Tertiary (K-T) impact were atmospherically converted to sulfuric and nitric acid, globally dispersed, and rapidly rained out, the resulting acid concentrations would bracket a critical threshold in surface-ocean chemistry. Rapid and globally uniform deposition of masses corresponding to the lowest estimates would have had no major effect on sea-surface chemistry. However, similar deposition of masses corresponding to the highest estimates would have provided enough acid to destroy the carbonate-buffering capacity of the upper 100 m of the world ocean and catastrophically reduce surface-ocean pH. Despite the possible effect of the highest estimated acid yields, scenarios that rely on acid rain as the primary explanation of global K-T extinctions are not readily compatible with K-T records of terrestrial and marine survival or culturing studies of modern marine plankton. The possibility that acid rain was a primary cause of K-T extinctions can be tested further by analysis of geographic variation in extinction intensity, because such variation was a likely consequence if the impact resulted in global dispersal and rapid globally uniform deposition of more than ∼6 x 1016 mol of H2SO4 or 1.2 x 1017 mol of HNO3.

The effects of feeding frequency and symbiosis with zooxanthellae on the biochemical composition of Astrangia Danae Milne Edwards & Haime 1849

The coral Astrangia danae Milne Edwards & Haime 1849 occurs naturally with and without symbiotic algae and thus may have two sources of nourishment: (1) particles captured by the coral polyps, and (2) photosynthetic products translocated from their zooxanthellae. Symbiotic colonies may have both sources, and nonsymbiotic ones certainly have only the former. The relative importance of these two food sources was studied in the laboratory by examining the tissues of corals fed with frozen brine shrimp. Stock corals were fed once per week. Two to three weeks prior to each experiment, selected corals were placed on one of three feeding schedules: starved (S), fed once per week (1/wk), and fed three times per week (3/wk). The coral tissues were analyzed for protein, lipid, carbohydrate, and zooxanthellae content. Increased feeding frequency (1/wk → 3/wk) resulted in an increased tissue biomass and lipid to protein (L/P) ratio; starvation (1/wk → S) caused a decrease in these parameters. Symbiosis with zooxanthellae had an effect similar to increased feeding frequency in that the S and 1/wk symbiotic corals had a higher L/P ratio than comparable nonsymbiotic ones. There were no significant differences in L/P ratios between the 3/wk symbiotic and nonsymbiotic corals. Freshly collected colonies had a tissue composition most similar to the laboratory animals fed 3/wk. This result is consistent with the hypothesis that ingestion of solid food is the major nutritional source for A. danae in Narragansett Bay, Rhode Island, but our experiments suggest that the algae can have an important effect on tissue L/P ratios during times of food scarcity.

A comparative study of the effects of sedimentation on symbiotic and asymbiotic colonies of the coral Astrangiadanae Milne Edwards and Haime 1849

Abstract The effect of heavy sedimentation on corals was examined in the laboratory using both symbiotic and asymbiotic colonies of Astrangia danae Milne Edwards and Haime. Colonies receiving applications of clean fine sand at a rate of 200mg·cm −2 once per day for 4 wk were not different from controls with respect to symbiotic index, colony weights, growth rates, or net oxygen exchange rates. Slight adverse effects relative to controls were noted after increasing the sand applications to three times per day, which became more evident during a 2-wk period of starvation combined with the sand applications. Starved symbiotic colonies were more susceptible than starved asymbiotic colonies to the sediment loading. After the starvation period, sediment-exposed colonies processed for histopathological examination revealed loss of mucous secretory cells in the epidermis, compared to starved controls, along with an increase in mucoid material accumulations in the gastrodermis and calicoblastic epithelium. These results are consistent with previous field observations that sediment loading is harmful to stony corals. However, damage may be minimal as long as adequate nutrients, from either internal (zooxanthellae) or external (Zooplankton, particulates) sources, are available to the coral animal to meet the additional energy expenditures required to rid themselves of sediment.