The trio of papers from the UMN work on the MPCA sulfate standard

The trio of papers from the UMN work on the MPCA sulfate standard
LRC Amy Myrbo, Ph.D. LacCore/CSDCO and Department of Earth Sciences University of Minnesota Freshwater Society, October 4, 2017 The views expressed here do not reflect those of the University of Minnesota

Field paper: sulfide harms wild rice Equation (SEM) paper: we can predict how much sulfide will be present Mesocosm paper: sulfate can have other important ecosystem effects

Sulfate: SO4 Sulfide: H2S
oxygen Nitrogen: N Phosphorus: P Alkalinity: alk Dissolved organic carbon: DOC Mercury: Hg water mud SO4 + organic matter ~10 cm Methylmercury: MeHg All you need to understand is this figure Sulfate: SO4 Sulfide: H2S +Fe  FeS(solid) no oxygen

oxygen Nitrogen: N Phosphorus: P Alkalinity: alk Dissolved organic carbon: DOC Mercury: Hg water Field paper mud SO4 + organic matter ~10 cm Methylmercury: MeHg Illustrating the different parts of the system that the three papers talk about Field paper looks at all the variables we measured and shows that sulfide is the most likely cause of wild rice scarcity and absence Sulfate: SO4 Sulfide: H2S +Fe  FeS(solid) no oxygen

oxygen Nitrogen: N Phosphorus: P Alkalinity: alk Dissolved organic carbon: DOC Mercury: Hg water Equation (SEM) paper mud SO4 + organic matter ~10 cm Methylmercury: MeHg Equation (SEM) paper, again, looks at all the field data and determines that only three things determine how much sulfide is in the sediment: sulfate, organic matter, and iron Sulfate: SO4 Sulfide: H2S +Fe  FeS(solid) no oxygen

oxygen Nitrogen: N Phosphorus: P Alkalinity: alk Dissolved organic carbon: DOC Mercury: Hg water Mesocosm paper mud SO4 + organic matter ~10 cm Methylmercury: MeHg And the mesocosm paper looks at how the process of changing sulfate to sulfide changes other ecosystem properties Sulfate: SO4 Sulfide: H2S +Fe  FeS(solid) no oxygen

oxygen water mud ~10 cm Field paper is the easiest to explain. Sulfide is poison to nearly all organisms. If it’s in the rooting zone – in the porewater – it has deleterious effects on wild rice. John Pastor showed this in mesocosms and hydroponic experiments We showed it in the field One interesting thing is that all three methods converged on the same number for a sulfide concentration harmful to wild rice Sulfate: SO4 Sulfide: H2S no oxygen

oxygen water mud ~10 cm Sulfate: SO4 Sulfide: H2S no oxygen

oxygen water mud SO4 ~10 cm So how does the sulfide get there? Sulfate in the surface water diffuses into the porewater And there are microbes there waiting Sulfate: SO4 Sulfide: H2S no oxygen

oxygen water mud SO4 + organic matter ~10 cm And using organic matter And because there is no oxygen They convert sulfate to sulfide Don’t worry about it being H2S – S-, S Poison Builds up and builds up, because microbes are hungry Sulfate: SO4 Sulfide: H2S no oxygen

oxygen water mud SO4 + organic matter ~10 cm BUT if there is dissolved iron in the sediments, it grabs onto the sulfide – very favorable reaction – “detoxifies” the sulfide by bonding to it (Although there are still questions about the effects of the precipitate on plant roots at certain times of the year – ongoing Pastor group research) Sulfate: SO4 Sulfide: H2S +Fe  FeS(solid) no oxygen

oxygen water mud SO4 + organic matter ~10 cm So you can already see the basis of the equation that the MPCA is proposing. More sulfate  bigger source of sulfate to reduce More organic matter  more sulfate can be reduced More iron  more sulfide can be trapped So that’s the SEM/equation paper Makes a huge amount of sense geochemically The equation makes me happy Sulfate: SO4 Sulfide: H2S +Fe  FeS(solid) no oxygen

oxygen water mud SO4 + organic matter ~10 cm So we know where the S is going from the sulfate But what happens to this organic matter? That’s what the mesocosm paper is all about OK, what is organic matter made of? Sulfate: SO4 Sulfide: H2S no oxygen

oxygen water mud SO4 + Carbon ~10 cm Carbon is what the microbes are using (Hiding the sulfide because it’s a small part of the mesocosm paper) Sulfate: SO4 Sulfide: H2S no oxygen

oxygen water mud SO4 + Carbon Nitrogen Phosphorus Oxygen, Hydrogen ~10 cm But organic matter also contains other elements Including nutrients! N, P Sulfate: SO4 Sulfide: H2S no oxygen

oxygen Nitrogen: N Phosphorus: P Alkalinity: alk Dissolved organic carbon: DOC Mercury: Hg water mud SO4 + organic matter ~10 cm So when you decompose organic matter You release these nutrients And carbon in other forms To the water column Sulfate: SO4 Sulfide: H2S no oxygen

2(CH2O)x(NH3)y(H3PO4)z + xSO42-
Organic matter Sulfate 2(CH2O)x(NH3)y(H3PO4)z + xSO42- → 2xHCO3- + xH2S + 2yNH3 + 2zH3PO4 Doesn’t matter how much iron there is! This still matters Ignore the stuff in gray – just bookkeeping Alkalinity Sulfide Nutrients

So let’s pause a moment Decomposition happens naturally But it usually takes oxygen So when oxygen is used up No more decomposition happens And that organic matter (and the nutrients in it) Are sequestered, buried, and don’t get back out into the environment BUT these microbes “breathe” sulfate instead of oxygen So when you dump a bunch of sulfate into the system You increase the amount of decomposition that can happen And can increase the nutrients in the system

oxygen Nitrogen: N Phosphorus: P Alkalinity: alk Dissolved organic carbon: DOC Mercury: Hg water mud SO4 + organic matter ~10 cm The carbon forms, alkalinity and DOC, can cause ecosystem changes as well Alkalinity increases buffering capacity DOC changes water clarity Sulfate: SO4 Sulfide: H2S no oxygen

oxygen Nitrogen: N Phosphorus: P Alkalinity: alk Dissolved organic carbon: DOC Mercury: Hg water mud SO4 + organic matter ~10 cm And the kicker here is our finding that total mercury increased as well Mercury is deposited from the atmosphere Gets incorporated into organic matter And ideally gets buried But when OM gets decomposed That releases the mercury back into the environment. Makes it available to be methylated and get into the food web Sulfate: SO4 Sulfide: H2S no oxygen

oxygen Nitrogen: N Phosphorus: P Alkalinity: alk Dissolved organic carbon: DOC Mercury: Hg water mud SO4 + organic matter ~10 cm Methylmercury: MeHg AND those little microbes that are turning sulfate into sulfide ALSO methylate mercury So it’s a double whammy for the food web Sulfate: SO4 Sulfide: H2S no oxygen

Miigwech! Pidamayaye! Gracias! Thank you! Three linked manuscripts accepted, JGR-Biogeosciences

It’s also water temperature and depth
Why

oxygen Nitrogen: N Phosphorus: P Alkalinity: alk Dissolved organic carbon: DOC Mercury: Hg water mud SO4 + organic matter ~10 cm Methylmercury: MeHg Sulfate: SO4 Sulfide: H2S +Fe  FeS(solid) no oxygen

Experimental Mesocosms
Different sulfate treatments

Wild rice sulfate standard field survey
And to figure this out, MPCA funded a three-pronged research project: Field survey of over 100 sites, lots of characterization

A standard standard is not better!
Ex.: Lakes and rivers are different PW sulfide is not linearly dependent on SW sulfate – that is, there’s something else going on Duluth News Tribune statement about scientists supporting 10 is wrong

Why the equation makes me happy
Nuanced Targeted Smart Based on ALL the data

Considerations about the equation
$ to characterize sites – people, analyses Sampling strategy – where, how many, how often? How protective, i.e., how much wiggle room around the 120mg sulfide benchmark?

Wild rice lakes/rivers
sulfate Here is the distribution High Low

> 10 ppm < 10 ppm Wild rice lakes/rivers sulfate GEOLOGY + CLIMATE This pattern of low-high NE to SW Partly geology partly climate Geology in blue has sulfur locked up in rocks Geology in rest of the state, sulfur dissolves out very easily Also drier in WSW Concentrates any sulfur by evaporation High Low

Glacial Lake Agassiz Mafic Calcareous

> 10 ppm < 10 ppm Wild rice lakes/rivers sulfate But what about this area of >10 completely surrounded by <5? Natural? Geology? Doesn’t fit with the rest of the pattern We can zoom in on this High Low

The trio of papers from the UMN work on the MPCA sulfate standard

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The trio of papers from the UMN work on the MPCA sulfate standard

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