DIATOM PALEOLIMNOLOGY OF TWO FLUVIAL LAKES IN THE ST. LAWRENCE RIVER: A RECONSTRUCTION OF ENVIRONMENTAL CHANGES DURING THE LAST CENTURY

Water quality degradation is a serious concern for the St. Lawrence River. While some environmental data are available for the St. Lawrence ecosystem, long-term monitoring data are generally lacking. To infer past environmental changes, we undertook a paleolimnological assessment of diatom assemblages preserved in four ²¹⁰Pb- and ¹³⁷Cs-dated sediment cores from two fluvial lakes in the river, and used diatom transfer functions to infer past shoreline habitat characteristics. At sites in Lake Saint-François, a fluvial lake downstream from Cornwall, water quality decreased this century in response to human impacts (e.g. macrophyte density and nutrient levels increased). These trends were apparent from an increase in epiphytic diatom taxa, followed by an increase in eutrophic planktonic taxa. Water quality, however, appears to have improved somewhat in response to rehabilitation measures during the last two decades. From a sediment core near Montréal (Lake Saint-Louis), we also noted a large proportion of eutrophic and epiphytic taxa, but less evidence was recorded of a recent improvement in water quality. The diatom-based inference model for habitat characteristics appeared to reconstruct environmental conditions in the St. Lawrence River during the last century. The most notable shift has been an increase in diatom taxa commonly associated with macrophyte substrates. Trends in some of the planktonic diatoms were similar to those recorded in paleolimnological investigations from Lake Ontario, but cores from the river also may be reflecting local environments. This study shows that diatom-based paleolimnological studies are possible in large river systems, if coring sites (e.g. fluvial lakes) are carefully selected.     

Distribution and speciation of phosphorus along a salinity gradient in intertidal marsh sediments

We examined forms of solid phosphorus fractions in intertidal marsh sediments along a salinity (0–22%.) gradient in a river-dominated estuary and in a marine-dominated salt marsh with insignificant freshwater input. Freshwater marsh sediments had the highest ratio of organic N:P of between 28:1 and 47:1 mol:mol, compared to 211 to 311 molmol in the saltmarshes, which is consistent with a trend toward P-limitation of primary production in freshwater and N-limitation in salt marshes. However, total P concentration, 24.7±11.1mol P g dw^–1 (±1 SD) averaged over the upper meter of sediment, was greatest in the freshwater marsh where bioavailablity of P is apparently limited. In the freshwater marsh the greatest fraction of total P (24–51%.) was associated with humic acids, while the importance of humic-P decreased with increasing salinity to 1–23%. in the salt marshes. Inorganic P contributed considerably less to total sediment P in the freshwater marsh (15–40%.) than in the salt marshes (33–85%.). In reduced sediments at all sites, phosphate bound to aluminum oxides and clays was an important inorganic P pool irrespective of salinity. Inorganic P associated with ferric iron [Fe(III)] phases was most abundant in surface sediments of freshwater and brackish marshes, while Ca-bound P dominated inorganic P pools in the salt marshes. Thus, our results showed that particle-bound P in marsh sediments exhibited changes in chemical association along the salinity gradient of an estuarine system, which is a likely consequence of changes in ionic strength and the availability of iron and calcium.     

Release rates and biological availability of phosphorus released from sediments receiving aquaculture wastes

Aquaculture is an increasingly significant user of freshwater resources in Scotland. In 1989, the total fish biomass produced in Scottish freshwater amounted to 7000 t. 50% of this total was reared in floating cage systems situated in lochs (lakes). Both solid (mainly in the form of uneaten feeds and faecal matter) and dissolved byproducts of the production cycle enter the limnetic environment untreated. Much solid waste material accumulates directly on the sediments beneath the cage systems. This leads to a localised enrichment in nutrient elements of the sedimentary environment. The experiments served to quantify rates of total phosphorus (TP) and dissolved reactive phosphorus (DRP) release from undercage and control sites, and to relate such releases to the biological availability of the released P. Results indicate significantly higher levels of NH₄Cl-extractable P in sediments affected by waste deposition from fish cages. TP and DRP release, and greater growth of Chla are obtained from undercage cores compared with control sites. No link between extractable-P content of sediments, or release rate and Chla production was established.     

Diatoms in surface sediments of the Gotland Basin in the Baltic Sea

A sediment core, 55 cm long, from station F81 in the Gotland Basin of the Baltic Sea was analysed for diatoms and ebridians. Chrysophyte stomatocysts found in the core were also counted but not identified. The aim was to trace environmental changes, e.g. eutrophication and salinity variations. There is evidence that eutrophication has been increasing in the Baltic Sea in recent decades.Brackish-marine plankton diatoms dominate the entire core and reflect the local planktonic taxa rather well. The dominant taxon is the polyhalobous Actinocyclus octonarius. The main biostratigraphical change within the core analysed takes place at a depth of about 22 cm, where the abundance of diatoms, and especially of Chaetoceros spp., Thalassiosira hyberborea var. pelagica and T. baltica start to increase. This may reflect eutrophication which can be estimated to have started c. 200 years ago.     

Transformations between organic and inorganic sediment phosphorus in Lake Balaton

In order to estimate microbial P content and biological P uptake in sediments, the tungstate precipitation method of Orrett & Karl (1987) was used in sediment extracts. This method allows a simple and rapid separation of organic and inorganic ³²P radioactivity. Either inorganic ³²P (as carrierfree H₃ ³²PO₄) or organic ³²P (as ³²P-labelled algal material) was added to surface sediment suspensions of shallow Lake Balaton. Inorganic ³²P was rapidly transformed into organic ³²P, and this process was completely inhibited by formaline. P content of living benthic microorganisms was estimated from steady state distribution of the radioactivity. Transformation of algal organic P into inorganic P could also be detected.In extremely P limited Lake Balaton benthic microorganisms were shown to supplement their high P requirements by inorganic P uptake. The velocity of the inorganic into organic P transformation, i.e. the rate of microbial P uptake, was comparable to P uptake in the water column. Microbial P uptake contributed significantly to total P fixation by sediments, particularly at low ( 100 µg P l^–1) phosphate additions.     

Microbial reductive dechlorination of PCBs

Reductive dechlorination is an advantageous process to microorganisms under anaerobic conditions because it is an electron sink, thereby allowing reoxidation of metabolic intermediates. In some organisms this has been demonstrated to support growth. Many chlorinated compounds have now been shown to be reductively dechlorinated under anaerobic conditions, including many of the congeners in commercial PCB mixtures. Anaerobic microbial communities in sediments dechlorinate Aroclor at rates of 3 µg Cl/g sediment × week. PCB dechlorination occurs at 12° C, a temperature relevant for remediation at temperate sites, and at concentrations of 100 to 1000 ppm. The positions dechlorinated are usually meta > para > ortho. The biphenyl rings, and the mono-ortho- and diorthochlorobiphenyls were not degraded after a one year incubation. Hence subsequent aerobic treatment may be necessary to meet regulatory standards. Reductive dechlorination of Arochlors does reduce their dioxin-like toxicity as measured by bioassay and by analysis of the co-planar congeners. The most important limitation to using PCB dechlorination as a remediation technology is the slower than desired dechlorination rates and no means yet discovered to substantially enhance these rates. Long term enrichments using PCBs as the only electron acceptor resulted in an initial enhancement in dechlorination rate. This rate was sustained but did not increase in serial transfers. Bioremediation of soil contaminated with Aroclor 1254 from a transformer spill was dechlorinated by greater than 50% following mixing of the soil with dechlorinating organisms and river sediment. It is now reasonable to field test reductive dechlorination of PCBs in cases where the PCB concentration is in the range where regulatory standards may be directly achieved by dechlorination, where a subsequent aerobic treatment is feasible, where any co-contaminants do not pose an inhibitory problem, and where anaerobic conditions can be established.This paper was presented at the Pacific Basin Conference on Hazardous Waste, April, 1992, Bangkok, Thailand. Published by permission of the Pacific Basin Consortium for Hazardous Waste Research, East-West Center, Honolulu, HI     

Comparison of anaerobic and aerobic biodegradation of mineralized skeletal structures in marine and estuarine conditions

The knowledge of the biodegradation rates is essential to studies of the biogeochemistry and ecology of aquatic systems. It helps us to quantify the production and uptake rates of chemical components and their recycling, and to understand the mechanisms and rates of organic matter accumulation in sediments. Experimental studies of biodegradation processes in six types of mineralized skeletons were performed in shallow-marine waters of Calvi Bay, Corsica and in estuarine waters of Roscoff, Brittany. Three types of mollusk shells, sea urchin skeletal plates, crab cuticle and fish vertebrae were exposed to oxic and anoxic conditions over periods of 15 days to 30 months. After recovery of the substrates, protein assays, bacterial counts and organic carbon analyses were performed.Quantitative protein assays and bacterial counts indicate that biodegradation of mineralized skeletal structures occurs at a slower rate in anoxic conditions than in oxic conditions. Bacterial analysis showed that in anoxic environment, less than 0.5% of the consumed organic matter is converted into bacterial biomass. The aerobic biodegradation rate was positively correlated with the organic content of the skeletons.Anoxic biodegradation of skeletons occurred at much slower rates in estuarine sediments than in shallow marine sediments. Preservation of skeletal structures in estuarine conditions appears to be correlated with the abundance of dissolved organic matter rather than with high sedimentation rates.     

The effects of sediment slurrying on microbial processes,and the role of amino acids as substrates for sulfate reduction in anoxic marine sediments

In sediment slurry experiments with anoxic marine sediments collected in Cape Lookout Bight, NC, and a site in mid-Chesapeake Bay, the rates of sulfate reduction and ammonium production decrease with increasing dilution of sediment with oxygen-free sea-water. The effect of sediment dilution on the rates of these processes can be described by a simple mathematical relationship, and when these rates are corrected for sediment dilution they yield values which agree well with direct measurements of these processes.In sediment slurry studies of amino acid utilization in Cape Lookout Bight sediments, the fermentative decarboxylation of glutamic acid (to -aminobutyric acid) or aspartic acid (to alanine or -alanine) did not occur when either of these amino acids were added to Cape Lookout Bight slurries. The addition of glutamic acid did however lead to a small (1) transient build-up of -aminoglutaric acid. Measured rates of glutamic acid uptake in these slurries also decreased with increasing sediment dilution.Molybdate inhibition experiments demonstrated that dissolved free amino acids represent 1–3% of the carbon sources/electron donors used for sulfate reduction in Cape Lookout Bight sediments. The direct oxidation of amino acids by sulfate reducing bacteria also accounts for 13–20% of the total ammonium produced. Glutamic acid, alanine, -aminoglutaric acid, aspartic acid and asparagine are the major amino acids oxidized by sulfate reducing bacteria in Cape Lookout Bight sediments.     

Clostridium halophilium sp. nov. and C. litorale sp. nov., an obligate halophilic and a marine species degrading betaine in the Stickland reaction

Two new mesophilic, sporeforming, gram-positive, strictly anaerobic, rod-shaped bacteria were isolated which utilized betaine in the Stickland reaction. Strain M1 was obtained from pasteurized hypersaline sediments. Cells were motile rods and formed spherical terminal spores. Betaine was used with hydrogen and several amino acids as electron donors. In addition, several carbohydrates served as substrates. Growth required 1.5% NaCl with an optimum at 6.0% NaCl. The guanine plus cytosine content of the DNA was 26.9%. This strain is described as a new species, Clostridium halophilum.Strain W6 was isolated from marine sediments. Cells were motile rods and formed ovoid, subterminal spores. Betaine was used with hydrogen and several amino acids as electron donors. Carbohydrates were not fermented. Growth optimum was at 1.0% NaCl. The guanine plus cytosine content of the DNA was 26.1%. This strain is described as a new species, Clostridium litorale.Non standard abbreviations DMG N,N-dimethylglycine - TMA trimethylamine - PY peptone-yeast extract - PYG peptone-yeast extract-glucose     

Ceramic processing of polluted dredged mud

About 45 million m³ of bottom sediment, with an estimated dry matter content of 30%, have to be dredged annually in the Netherlands, of which several million m³ are strongly contaminated with heavy metals and toxic organic substances. Contaminated dredged muds are dumped in special locations on land.The problems of severely polluted muds are likely to remain from many decades to come, and the present disposal reserve may not be adequate. In a densely populated country, large-scale disposal on land is not a satisfactory long-term solution, and a method of cleaning these muds has to be developed. This paper presents some of the results of an investigation into the feasibility of ceramically processing severely polluted dredged muds. Ceramic processing not only destroys the organic micro-pollutants; the leaching of heavy metals is reduced by ceramic bonding and the end-product is a hard, lightweight gravel-size particulate, useful as a building material. Extensive tests have been carried out on the leaching behaviour of the ceramic products and the results showed little or no differences in comparison with other commonly used building materials; the results are better than those of aggregates made from pulverized fuel ashes.