Relationships between sedimentation, submergence, and deterioration, of a Mississippi River deltaic-plain coastal wetland forest were investigated. Measured sedimentation rates (0.63 ± 0.35 cm per yr) as determined by 137Cs-dating were considerably less than the rapid increase in water-level (c. 1.36 cm per yr). Transplanted seedlings of Quercus lyrata (Overcup Oak) and of Taxodium distichum (Bald Cypress) survived only on the most elevated natural ridge in this swamp-forest.

Sagittaria lancifolia L, plants were subjected to floodmg, salmity, and combined treatments. Effects of each treatment and their interaction on stomatal conductance and net photosynthesis were evaluated after 4 wk of acclimation to the imposed condtions. Effect of floohng on leaf conductance was not significant while the sahnity effect was significant. Both flooding and salinity reduced net photosynthesis significantly. However, their interaction was not significant. The stomata1 limitation of photosynthesis was relatively small ranging from 12 to 18 %. Results indicated that for plants subjected to salinity or to combined salinity and floodmg, photosynthetic capacity was reduced through stomatal limitations as well as non-stomata1 (metabohc) factors.

Three heptapeptide toxins, microcystin-RR, microcystin-RY and microcystin-LR, which can cause health problems in animals and humans were monitored in Bang Phra Reservoir, Thailand using reversed-phase high performance liquid chromatography. The concentrations of the three toxins in the reservoir varied greatly depending on location and time water samples were collected. Water quality parameters such as light intensity, temperature, pH, dissolved oxygen, suspended solid, chemical oxygen demand, dissolved organic carbon, total nitrogen, total phosphorus, ammonia, nitrate, phosphate, total dissolved nitrogen, total dissolved phosphorus and chlorophyll-a were also measured in parallel with microcystin determinations. Relationships among water quality parameters, toxins and chlorophyll-a were established. Toxin concentration increased in proportion to increases in total phosphorus, fraction of dissolved phosphorus, but was inversely correlated with water pH and total suspended solids. The other measured parameters in the study showed no correlations to toxin level in reservoir water. Significant correlations between chlorophyll-a and suspended solids, phosphate, nitrate and ammonia were observed suggesting that nitrogen and phosphorus are the two major nutrients governing growth of algae in the reservoir. This relationship suggests that algal production as well as toxin concentration are dependant on nutrient levels in the water body, since both measured light intensity and temperature level was favorable for algal growth. A small algal bloom observed in the rainy season of each year (lasting for only a couple of months) paralleled measured increases in toxin concentration, chlorophyll-a, TP and TN in the water column. Toxin level in the water column remain detectable for 3-4 months period following the initiation of algal bloom. Results indicate that major blooms are likely to occur following the raining season which usually occurs near the end of October when runoff would increase nutrient level entering the reservoir. This study also demonstrated that an ongoing field-monitoring program is needed in these lakes and reservoirs for predicting toxic level of microcystin production for use in risk assessment and for alerting the public to potential health hazards. Concentration of toxin in the reservoir can perhaps be controlled by reducing non point source nutrient input within the watershed.

Laboratory expenments were conducted to evaluate the effects of increased so11 salinity on gas exchange functlonlng and growth of the braclush-marsh grass Spartlna patens (Alt) Muhl under controlled soil redox potentials (Eh) which were malntalned at either aerobic (+489 mV) or hypoxlc (-40 mV) conditions Plants were subjected to salinities of 0 5, 15 and 25 ppt gradually over a 7 d penod and leaf tissue chlorophyll content, gas exchange and growth responses were measured Leaf hssue chlorophyll content was not affected by the treatments Gas exchange of S patens was adversely influenced by increases in salinity Leaf conductance was reduced by 36 % and net photosynthesis by 23 % of control plants under aeration plus 25 ppt salinity and water use efficiency increased to 161 % of control plants When increased salinity accompanied hypoxia leaf conductance and net photosynthesis were reduced by 60 and 44 % of control plants respectively The Interaction between sallnity and hypoxla was not significant Sahnity of 25 ppt reduced root dry weight leaf dry weight and height growth sign~f~cantly Sallnlty and hypoxla combined affected various biomass components whlle hypoxla pnmanly affected root dry weights Elevated salinity and hypoxia also adversely affected gas exchange functions and growth Results presented suggested that saltwater intrusion is a malor factor contnbuting to the rapid rate of marsh deterioration in coastal Lolusiana (USA) brackish marshes which are dormnated by S patens

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