Re: Sulphur Affecting MangrovesPosted by Russell Davis on January 03, 19100 at 12:40:38: In Reply to: Re: Sulphur Affecting Mangroves posted by CRMP on October 10, 1999 at 20:32:12: The following sulfur dynamic comes from an oyster context. The aging, ammendment, and cultivation strategies would apply to mangroves. From plant nutrition and toxicolgy you may want to look up aluminum toxicity and oxidative stress. If transition metals like iron are relatively impovrished in your situation elemental sulfur may rule your dymanics. You may wish to follow the link http://home.worldnet.att.net/~deep_structures_playground/saturation2.htm rather than reading the attachment since the html has links to references. Best Regards, Russell ********************************** It appears that for estuarine chemical-sorting processes to occur, and be quantitatively significant, certain process conditions must be established: Consider the sulfate reduction of organic mater in estuarine sediments: These sulfate reduction end products separate and sort primarily according to phase and secondarily according to solubility and diffusion speed within the liquid phase which in turn impacts solid-liquid phase change. The quantitative result of the second sort (according to solubility and diffusion speed) is determined by the size and degree of the super-saturation zone in the diffusion gradient extending from the source of the chemical species. The size and degree of the super-saturation zone is determined by the degree of sediment turbation and sediment pore water transport. Sediment turbation is driven by animal movement, water movement, and sediment gas escape. Sediment pore water transport is by diffusion and mass transport. Digenesis will change the character of the sediment according to the proportion of retained end products. The interaction of the local environment and the differing end product transport rates will determine the exact outcome. Four exemplarily cases are examined: These conditions were assessed visually for iron sulfide (an alternate is by 20% H2O2 digestion with a pH test or hydrochloric acid digestion with hydrogen sulfide gas liberation ) and by acetic acid digestion with CO2 gas liberation to test for calcium carbonate. 1) The proportion of transition metal sulfide retained to calcium carbonate retained will be equal on a molar basis to the sulfide in the transition metal sulfide and equal to the molar portion of the digested carbon when transition metal is adequate to complete sulfide capture and the sediment is completely captive so that no hydrogen or carbon dioxide gas may escape. 2) In conditions of high turbation and no transition metal availability such as would exist in the gravel bar at the mouth of Lynnhaven Inlet, Sulfate reduction of organic mater will occur in the presence of a organic substrate and anoxia, but no sulfate reduction end products are retained to concrete the gravel. Volatile hydrogen sulfide escapes and calcium bicarbonate is washed away. 3) In conditions of low turbation and no transition metal availability such as would exist in quartz gravel contained in a jar of salt water sulfate reduction of organic mater will occur in the presence of a organic substrate and in anoxia. The volatile hydrogen sulfide escapes and calcium bicarbonate will not be washed away. Some calcium carbonate will concrete the gravel and some carbon dioxide will escape as calcium bicarbonate precipitates as calcium carbonate. 4) In conditions of modrate turbation and high transition metal availability such as would exist in an oxidized iron rich fluid mud contained in a jar of salt water, sulfate reduction of organic mater will occur in the presence of an organic substrate and anoxia. The iron will capture the sulfide; hydrogen gas can escape the mud causing turbation and assisting the escape of calcium bicarbonate. Some calcium bicarbonate may precipitate as calcium carbonate releasing carbon dioxide, some of which can gas off and create more turbation with consequent calcium bicarbonate escape. If this mud is subsequently irrigated under oxic generated hypercapnic/suboxic conditions the precipitated calcium carbonate will dissolve leaving the sediment metal sulfide enriched and calcium carbonate impoverished. This anticipated condition was confirmed by acetic acid drench of black fluid mud - no gas bubbles resulted but it stank of rotten eggs. Consider irrigation an iterative process; possibly subject to management intervention in oyster culture to affect both the increment and content of sediment irrigated. Conditions approaching this fourth case are predicates needed to create water capable of digesting oyster shells as observed in Linkhorn Bay. When the iron sulfide sediment is resuspended under oxic conditions another set of bacterial intermediaries use the iron sulfide as an energy source producing oxidized iron and sulfuric acid. To consider this acidification's impact on oyster shells we see the resulting sulfuric acid in proportion to the CaCO3 in the estuary water. Sea water recipes that address the dry anion balance for CO2 with CaCO3 peg the CaCO3 content of sea water at around 0.123 grams per kilogram of sea water. Now dilute that seawater to 28ppt and you have 100 g per metric ton. Call it a cubic meter for visualization’s sake. CaCO3 weighs 100 grams per mole and we have 1 mole. I can easily imagine that I have eroded much more than that proportion of sediment on one pass with my motorboat. Bioturbation can be as effective even if not as dramatic. Even though the sediment is very fine I don’t imagine that all the iron sulfide I lifted from the anaerobic bottom will be oxidized before settling out; but the process is repetitive and the direction of the reaction still holds. My understanding is that the increased ionic concentration of CO2 and sulfate in the water will make the water able to dissolve nearly .25 moles of CaCO3 ( as Ca(HCO3)2 ) more than it could prior to the sulfide oxidation. The proportionate result is that the water is roughly (100-25)/(100+25) as saturated it was. Given the established existence of water column sulfate impoverishment in sulfate reducing environments it is surprising that this existence of water column sulfate enrichment is controversial. It appears that the instances of sulfate enrichment have never been measured directly but only inferred by the evidence of its passing and by the activity in the sulfide oxidation pathway. It is likely that patches of sulfate enrichment are small, transient, and vigorous in their affect. ********************************** The wave and current scouring conditions found on oyster reefs are acknowledged to enhance oyster survival. In addition to bringing food, the turbulence removes silt, feces, and pseudo-feces. The waste management aspect of reef, rack and float culture can be extended to bed culture by the management practices of washing the beds by boat wave or pressure board drag. Periodic scouring and resuspension can prevent critical accumulation and resuspensions. Marl beds for oyster bed culture can reduce the likely hood of critical accumulation and resuspension by their calcium carbonate fines diluting the accreting iron sulfide fines. A balanced resuspension of iron sulfide fines and calcium carbonate fines under oxic conditions will not produce a noxious sulfuric acid burst, but it will produce a relatively innocuous calcium sulfate burst. In addition to the acid factor, the chemical oxygen demand of those iron sulfide sediments makes large resuspendable accumulations very dangerous. Timely resuspensions can develop sediment reserves of iron bound oxygen to meet late summer demand for oxygen and hydrogen sulfide scrub. Timely resuspensions can also remove the potential problem sediment to a stable location. Iron has been implicated in the Dermo disease. 8.083 8.093 And given the potential of iron to catalyze super-oxide radicals, iron sediments on the oysters’ gills are apt to be significant contributors to the oysters' cumulative oxidative stress and telomere expiration. 10.10 The high degree of mortality experienced by oysters appears to be greater than the combination of the nominal causes such as Dermo and MSX. 8.076 An overwhelming iron sulfide resuspension offers a common cause to many of the paths to an oyster’s demise. The dilution, reduction and/or mitigation of oyster gill capture of iron may be a valuable goal in oyster cultivation. Dilution and burial of iron sediments by calcium sediments will effectively take iron sulfide out of the resuspension loop for an enduring solution to the buried portion of the problem. The practice of management by intentional resuspention may well have a contribution margin sufficient to complete an economic success for oyster culture. The practice nearly requires a whole-river approach to cultivation. Without whole-river culture to manage iron sulfide resuspension it is unlikely that we will never know the degree of economic benefit to the practice. Thanks, ********************************** Do you know of any research measuring pH and CaCO3 saturation of seawater as it varies on added sulfuric acid? The closest I find is “Influence of sulfate enrichment on the carbon dioxide and phosphate fluxes across the sedimentwater interface” by V.Clavero, M.J.Carcia-Sanchez, F.X.Niell and J.A.Fenandez “Hydrobiologica” 1997 345/1 (pp59-65). Do you know of any research that will predict the ratio of metal sulfide to calcium carbonate precipitated in a sediment on sulfate respiration of organic mater? The closest I find is “What determines sedimentary C/S ratios?” by J.W.Morse & R.A.Berner, “Geochemica Cosmochimica Acta” 59(6), 1995, pp 1073-1077 **********************************
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