Session 10: Non-conservative Processes in Estuaries/ Groundwater/Hydrothermal

The following content is provided under a Creative Common License. Your support will help MIT Open Courseware continue to offer high-quality educational resources for free. To make a donation or view additional materials from hundreds of MIT courses, visit MIT Open Courseware at ocw. mmit. edu. — Today, we're going to finish up talking about um some of the inputs from rivers and hydrothermal uh vents. So what we're going to talk about today, we discussed the generation of vent fluid and the generation of rivers. So today we're going to talk about what happens when these enter the oceans. So when rivers enter the and this is in terms of estuaries. So I'm going to spend the first third of the class on that. Then I'm going to talk some about groundwater and how groundwater input can also affect estimates of uh fluxes from the continents into the oceans. And then finally, we're going to look at uh vent fluid entering the oceans. And this includes both depos the formation of deposits as well as of plumes. And while the deposits are left on the ocean floor and are sort of a near source issue, the plumes actually can rise 200 to 300 meters above the seafloor. and you're at about 2500 m depth in the oceans and you actually create a lot of mixing in a part of the ocean where you wouldn't normally suppose that you were going to have a large driver of mixing. So it has um implic a lot of implications for physical oceanography and for chemical processes that are at a depth that we didn't really consider that important 30 years ago. Okay. Um all right. So before I start or the first thing I want to talk about is that when rivers enter oceans and when vent fluid enters oceans you have contrasts and you're going to have different contrasts for different ones of the fluids. For rivers your dominant contrast versus the oceans is the change in salinity. So that's the key one for rivers. And vent fluids or there's two really. It's temperature which actually creates a large buoyancy and I'll get to that. So it's temperature and pH are your key differences. So going back I want to remind you of what the rivers were like or how rivers were generated. We started with rainwater and rock. You have weathering. You have congruent dissolution, disongruent dissolution. Um, and the key thing is you create a fluid that's carrying both dissolved um dissolved ions, but also you have particles. And on those particles you have absorbed metals and you also have clays, iron oxyhides and humic matter. Put that up there. And those all have negative charges. And so those have um ions associated with them as well. And we'll get into that. And we went briefly through at the very end of the river lecture, we went briefly through uh trace metal release when you have pH changes. So you can have subtle changes. The pH of river water is going to vary from about five to about seven. Is that right? Probably maybe a little more. And depending on what its pH is, that can have some effect, but those aren't the dominant ones. It really is this change in salinity. And then the last thing for the rivers was on top of all of this you have the cyclic salt cycle the cyclic salts. Okay. So that's just sort of a review. I need to show that. Okay. Um hopefully you have your notes today. If not, you'll have to remember them because it's much easier to show

these pictures as we go through the different types of estuaries. So, essentially what you're doing is a river is coming down to the oceans and it's going to enter. And any of you who've been near a river mouth, there's multiple different types of estuaries. And the key things that are going to affect the type of mixing in that estuary have to do with the discharge rate. If you've got a very high rate of discharge, you're going to have one style of mixing. And it also has to do with the depth that the estuary is at. And so we're going to discuss four different types of estuaries briefly. And in this in these figures, and my apologies for the quality, they were xeroxed initially, I think about 15 years ago, and have been written on and xeroxed again. So, um, the first type is type A. And here you have, and it's where you have a shallow estuary with a small river. So, you have a small discharge coming into a small estuary. Um, you have a lot of these around here. And what on this figure what we have, you have four stations, one, two, three, and four. And then this just shows the mixing. So you have a station, I mean the surface. What is that? I don't even know what that's supposed Oh, this is station one, two, three, four. But this is the surface. This is the bottom of the estuary. And this is simply showing the type of mixing that's going on. So when you have low discharge into a small estuary, you have a well-mixed a well vertically mixed um processes going on. So you're basically bringing fresh water out and then you're going to have some tidal slloshing back and forth. But you end up what you want to do is take a look at if you look at what the salinity profile is at each of these stations, you go over to the next side of your figure and pretty much the salinity is not stratified at all. Okay, so these estuaries are they're dominated by tidal mixing. They're vertically well mixed. And this is all in your notes, probably not as bulleted as this, but um they're vertically well mixed. There's a net outward flow at all depths, and there's a seawward increase in salinity that's similar at all depths. Okay. Now, you can also have the same thing going on, but you can end up with um also in a shallow estuary, but you can end up with a two-layer system. And for this two-layer system, we have the same thing going on. First, let's look at what's happening with the flow. The low salinity river water is flowing out on the upper part. Sea water is flowing in on the lower part. And this is dominantly density driven. But then you still have fairly you do have some mixing, some vertical mixing. And you end up if you take a look at the profiles across each of these stations, you end up with a slightly stratified salinity gradient. — And what happens [snorts] if penaries type A or type B? What would cause the inflow of seawater? [clears throat] — I think it has to do with the discharge. A lot of discharge rate. If you have a correct me if I'm wrong if anybody I mean if you have a high enough discharge it's simply a mass you know you're pushing flow out. You're going to draw fluid back in. Um it's more of a physic you'd have to look at the physics of the system. — Also if you have a really shallow estuary it gives you more turbulent mixing and so you better vertical mixing too. — Right. But these were both for small for shallow. So, — both of these have fairly good vertical mixing, but you do have the — um but you can also, and this is the other thing, you can also have the same estuary have the different types at different times of the year. Um, in fact, so now I'm going to jump to the there's a type D, which I really think should be type C. Um, because it's one, it's sort of a variation on type B. And this is when you have a large river entering a shallow estuary. So again this has to do with discharge rate and here you end up with a salt wedge and as in the case before the surface waters have uh low salinity seawater intrudes underneath as a wedge. And again here's what the flow looks like. You have a higher rate of discharge. So the flow is coming out here and this draws in seawater is coming in here. And it's a mass balance of what's going to happen as the fluid flows. But here instead of having a very well stratified the one of the key differences is you end up with this wedge. So out at station 4 the salinity increases at a much shallower depth whereas at station one it's fairly fresh down towards the bottom.

And there's an example in your notes about the Ches Chesapeake Bay where at times of high discharge you have a salt wedge and at times of lower discharge you have a stratified a vertically stratified. Now you also have the situation where you have a very deep estuary and the example we're using here is that of a fjord and you have a sill located here and again this shows the flow the fresh water is flowing out at the upper levels. You have return of seawater at lower levels but not at the deepest levels because you have the sill blocking those deep levels. But then what happens is this the you end up with higher salinity fluid basically pooling underneath behind the sill and it's not mixing up as often and so you end up with a very highly stratified salinity gradient. And the reason we're talking about these salinity gradients is it's that is that the major change the key uh property that is affecting whether or not what the whether or not you have non-conservative processes is this change of salinity. So it's important to know where the major change in salinity is occurring within the estuary. Okay. And so again, this just shows a picture of the different types. And you'll have a lot of mixing, but you're mixing up in the shallower region because you have a sill which is preventing entrainment down here. Okay. Right. So now we get into what are the processes that are going to occur the non-conservative processes that occur in estuaries and we went over this last week. I'm going to show you a lot of diagrams and most of these are going to be salinity diagrams where you have the seawater salinity here [clears throat] and freshwater salinity here. And if it's and you have some element here and so if this is seawater solenity and this is freshwater salinity, if it's conservative mixing, you're simply going to have a straight line. And of course, if you have removal, you're going to be coming on this side of the straight line. So that's removal here. And this is addition here. Okay. So you have a number of different things going on. A key one you have going on. We talked about what's in the water. And one of the main things that's going on is you have particles in the water. So you have col river colloids. And again these are dominantly iron and humic substances. And what happens is the sea salt well for all of these we talked about them having a negative charge on the outside. And this is described well in your notes. Basically the colloids are electrically charged submicron particles. Okay. there's going to be clay the clays the organic material um and some of the humic uh iron oxy hydroxides. So they're too small. They're very small. They're not going to undergo gravitational settling and this negative charge on the outside there these um electrostatic interactions which keep them in solution and help to keep them in solution. What happens is when you bring in a higher salinity fluid and you bring in salts this neutralizes the electrostatic charges the electric charges. So when the electric charges are neutralized, the colloids clump together. They aggregate and then they're large enough to gravitate to settle by gravity. Okay. So basically you are neutralizing salts. If I could write today — salts neutralize the electric charges which allows aggregation and then settling. — You'll sometimes hear it described as fauculate, — right? which actually drives me crazy because fauculation to me is all fluffy and it stays in the water and it does for a little while but then it gradually settles.

So I'll put that as fauculation. There's two C's, right? As opposed to flagagillate fauculation. Okay. The second one. So that's sort of the first key. The second one that's very important is desorption. And this is what I talked about. We talked some about this going on within rivers where the pH changes because when the pH gets uh lower, you can disorb some of that um when it gets higher, some of the um trace metals from particle surf surfaces. But the disorption in the river um you sometimes and Scott talked about this on an earlier lecture and I talked about it as well. You can have calcium released from clay surfaces and replaced by sodium. You can also have radium can do the same thing. The third one, the first two are the key ones that are going on right in the water. If you just took a batch of um seawater and took a bang on or disorption going on in terms of non-conservative processes, but there's a third one when you can't explain it by these two. The other thing you can have happening is um our interactions with marine with estuary sediments. So basically you have um there's poor water gradients and so you can if you actually stir up sediment on the bottom you release pore fluids that are in the sediment. You also uh bring up sediments that have ions absorbed on the outside. So you can release those. So really the process is one of resuspension an interaction with the resuspended material and the other one is release of poor waters. It's not just release. It can be release and exchange. I know. Okay. All on one page. [snorts] What do you guys think the poor waters in an estuary look like? You guys been to any of the little estuaries around here, the salt marshes? There's lots of wet in an estuary, lots of organic matter. So, if you dig down into the mud, it's a good field trip for you guys this weekend. Go over that [snorts] area. Dig down into the mud, you very quickly get to an oxic — and you'll be able to tell because it'll start to smell really, really bad. — Um, and so that's one of the things when poor waters from eststerase is you're now releasing anoxic pore waters, which are going to have very different metal composition. So in some ways there is some analogy between the pH and right — eh changes that we're going to talk about at the end. — Yeah. And in fact at the very end when I'm talking about the vents I'm going to talk about the microbial activity but I'm not going to talk about it for the estuaries. But um — we we'll talk about microbes more than you guys after the midterm. — Oh is that right? — Okay. All right. And then speaking of bugs, this is the last one which is you can have uptake. Did you like read the notes this morning so that you could interject that properly when I needed it? Uptake by estuary. — I have this one burned in the library. I think I have this class burned in. — You have uptake by estuary and by biota and they can remove elements or this can remove elements presumably. It can also release elements but um I think it's more the up word or not uptake but the regurgitation no the I guess it's kind of confusing as to what the definition of conservative mixing is. — Oh we'll get there. You're about to see more graphs than you ever wanted to see. Basically each of these processes either adds or removes material. If you mixed seawater and you mixed fresh water and you didn't do any of these things, then you'd see a perfect straight line like this.

Okay? [snorts] But we don't always and for some elements we do and I'm going to go through those. And for some of them, we clearly don't. And so you have to explain why you're seeing their removal or the addition. And the a key reason why you need to know that is because if you just take the iron value that's in rivers and say that all of that iron makes it all the way out into the ocean, you're wrong. because a lot of it is left in the estuaries and you have to try and figure out and try to quantify how much of that iron is fauculates and is settles within the estuary. So, right now we're going to show you a bunch of plots. question that line it doesn't I mean it that to me looks like you have something that's not in fresh water — and then you increase it as you go in salt water — whereas if it was — right sorry — I'm thinking in you're right this could be the if it's high and you're right most of them are higher in fresh water and drop that way — it can go either way — but but let me just it's easier to look at real data. The old confusing them by trying to be simple. — But if it's conservative, would it just be a horizontal? — Well, let's just show you. I'll show you the first one. — Then the concentration would be the same in the — boron. Okay. Most of these things in order to look at mixing. First of all, you have to figure out what to plot it against. And you have to be plotting it against something that you're pretty confident is conservative. And in general, the salinity is relatively conservative. You are not dumping large amounts of halite or large amounts of any sea salt into estuaries and we know that. Therefore, you can say either chloride or salinity tends to be conservative and so an element that is conservative should plot on a straight line relative to that property. — And on the axis — the axes again this is one of these um this is I believe it's micro it's a concentration. It doesn't matter what it is. It's a concentration unit. And this is salinity. Okay. And if you take a look at this, you can see that within error, this boron is falling pretty much along a straight line. And so unless you know whether or not there's something actually going on here or actually going on here, um you'd have to put the error bars on your analyses and really try and figure that out. And we're going to get to issues with that in a little bit. But this is one where you clearly have conservative processes. You obviously can't be dumping a whole bunch of boron out unless you're dumping it with the salt. But we know that you're not dumping salt out. Okay. In contrast, here's iron. And again, it's simply concentration versus salinity. [snorts] And so, as you'll see, as Kristen pointed out, it can be either direction. Here, there's more boron in seawater than there is in fresh water. And here, there's more iron in the rivers than there is in the salt water. — That straight line is what it would be without, — right? And the if there wasn't. And these little dots which are much smaller than the big fat pen line are the actual measurements. And one of the things that they've noted is in general iron and humic substances tend to follow this type of curve pretty well. And that's dominantly from fauculation of material and dumping in estuaries and precipitation in estuaries. That's in contrast to some other things which I'll show you which are much more complicated. Um here you have barium and again all of these are real profiles instead of trying to show you these idealistic profiles. Um these have all been taken directly out of the literature and it's real data which is why they're not all beautiful profiles. Um this is for barium and there's a fair amount of barryium in both the fresh water and in the salt water but they're subtly different but then you see this very large increase in barium and that is likely from disorption. Okay. And then they show some really nice fun ones where you have copper. And again, this is the kind of thing where you go out and a lot of this work was being done in the 70s. Um, and they were really trying to figure out um both Ed Bole and Ed Shakovitz um in our program did a lot of this work trying to make sense of the data they were collecting and trying to quantify what's going on in the estuary so we can better quantify uh river fluxes into the oceans. And here you can see that copper

it looks like it's being added at very low salinity but then as the salinity increases some it looks like some is being removed and then at higher salinities it looks like some is being added again. So copper is one that is more complicated and you'll find that a lot of these that are more complicated are ones that have multiple different veance states and so there's a lot of redux processes that are going on at the same time that affect what's going on. And then manganese is another um and here you show there there's a in this profile. There's a large removal at low salinity and a large addition at higher salinity — on the iron. Sorry. — Is there a question up there? — Um, it might be the same one. I'm not sure. Uh, — can you just describe again why the barium has the shape that it does? — Oh, does. Well, I'd have to go back to the paper to be sure why it is, but my suspicion is it's from disorption. So that you have barium um on various particles that are coming into the estuaries and then when it mixes with the salt um the barium is being there's exchange going on and some other ion is replacing the barium and the barium is being released sort of like calcium and sodium exchange. — Could you explain what was happen — in the iron profile — on these plots are you seeing just the free concentration or are you seeing also that's in solution but bound to some particle. — What you are measuring here when you do this and we'll get to it when we do the in laboratory ones is you're taking the fluid and you're taking the filtered portion the less than 045 micron portion of the fluid you're analyzing that and coming up with a total iron. So this is looking at total iron in the 045 micron and less fraction I believe. Yeah, that's what they usually do. You'd have to read each paper carefully to find out exactly what they're doing, but in general, that's what they do. So, no, you're not looking at the iron that's on the large particles that are left on the 045 micron filter paper, but anything that can pass through that filter is included in this. — So, that would be truly dissolved free ions. It would be things that are complex in solution. So, it includes — and colloids, right? So, if we go back to this figure where we were looking at what was in the river water, once you get down below this 045 micron, it would include some of these clays as well. Um, Caitlyn, did you have another question? — Well, I was just wondering, um, it looks like in the iron profile that it's below the conservative level and rejoins it. — Perfect. Perfect question. Okay. Now, one of the things is it one simple process going on and these are all assuming that you only have two end members. You either you have a uh seawater end member and you have a freshwater don't have any other N members. and they're trying to simplify these things and come up with fairly straightforward um processes that they can extrapolate globally so they can come up with good a good idea of what global fluxes are. However, because of the type of thing you just talked about, Caitlyn, there's also concern about whether or not there might be a third component. And so there are some examples and this shows one here. This was work done by Ed Bole. He went and looked back at this is a dissolved silica profile and what could be it could be interpreted a lot of people would just interpret that as simple from either coloids or dis or uh disorption. No not disorption absorption or something else. But what he attributed it to instead was a third component, a third mixing, I mean a third end member. Um, and the reason for that is silica tends to be conservative when you mix and it was very uh it was somewhat confusing why you would see this decrease because what would be the removal mechanism? Nobody had a removal mechanism. So his hypothesis is that there's a third source here of fluid that has a lower silica composition and that you actually have conservative mixing between this and the seawater source and between this source and the river source. — Can you point out what in the iron that

you're talking about? — Oh, you know, we're going to get there. to that's messy data. Again, none of these have error bars on them. Um, you also, all you have to do is have one aggregate get into your bottle or have one colloid stick to the side of your container. I mean, there's a lot there are a lot of things that can create noise in these data sets. Okay? But the key thing of this is for you to understand how to look at a profile and determine whether there's been removal or addition and to have some idea of what is likely causing that removal or the addition. And again here what confused the reason Ed Bole went back to look at this was in general he was finding in other profiles that silica was conservative. So an alternative interpretation of this is that you have a third source fluid source. — So an example of that would be like two different ocean — mixing with a river — or having — two rivers and the coastal water something like that, — right? Either two rivers and a coastal water or in this case it was actually um a shelf source and we're going to get into groundwater flow as well. You can end up with a groundwater flow source. Okay. He ba. Yes, he had ended up with a for this one in particular, he had a river source, an open ocean source, and then an intermediate shelf source. I'm not sure what the source of the shelf source was, but it didn't go into that. But there was basically you could go out so you could you then go out and sample that body of water, do some CTD tests, and see if you can actually find that fluid out there. Okay. All right. Now, because of these complexities and some of the um questions that Caitlyn was raising, you do have a concern and a problem when you have messy data. I talked about some of the issues and here is a profile that shows copper and a mixing line. And the real question is, is this actually conservative mixing or do you have some addition going on here and a little bit of addition going on there? You know, what's really going on and the data are very, very noisy. So Ed Shovitz was one of the key people who helped develop this. You can also do your own mixing diagrams. This is all field data. So you can just take one option is to go out to the open ocean. So go to this station, collect a bunch of this water, go to the river source, collect a bunch of that water, the fresh source, and then do the mixing in the lab after you've and you can either do this mixing depending on if you want to look at particle processes or colloid processes. Um you either filter or un or do it unfiltered. This is an example of an unfiltered river water. Um it was says unfiltered river waters 04 mill micron filters which implies that it's filtered seawater but um anyway you have to know what you would report in the paper exactly what you did with those fluids but when they did that mixing experiment this was the data they got from the mixing experiment and it really — I'm still confused as the definition of conservative mixing versus nonservative mixing because I mean is it lab mixing or is it field mixing because some of the processes that we went over wouldn't happen in the lab — and if they're not happening in the lab but they're happening in the field what you call it and you know — you call it non-conservative mixing no matter what's going on but you have to identify the process that's going on. So you're right. This type of mixing experiment is only going to look at disorption, you know, chemical processes between those two bodies of water. It's not going to be considering any of this resuspension of sediment — or bod — or biota, right? Unless there's in well except for microbial activity that's actually taking place in the water column in the two fluid samples that you've taken, — but it's certainly not going to um but for this is what they were looking at. They were trying to figure out is copper being disorbed? Is there addition or is there removal or is it being absorbed? Okay. Um and then this was, you know, some other examples are in your notes. Um this is a much messier one. Take a look at that nice nickel profile. And I'm sure that scatter in large part has to do with uh um errors on the analyses. And then when they did it in the lab, they got a much cleaner data set. And similarly uh and then for calcium I mean for cadmium the data

were again ambiguous. For instance, is there actually a third source sitting or is this simple disorption? And when they did the mixing calculation or the mixing experiments in the lab, they saw that you get this non uniform, you know, you get more disorption occurring at low salinity than at high salinity. And that but the entire profile can be explained by disorption. Okay. And again, all of these details, I mean, there isn't you cannot just look at a data set and identify exactly what's going on. It's c it's simply um an interpretation of field data. And as shown by Ed Bole going back and reinterpreting one, the interpretations that are out there for all of these profiles are not necessarily 100% true. I mean, this is their hypothesis as to what's going on right now. [snorts] — Now, there's a again in your notes there's sort of a generalization. This table sort of gives you an idea of in general what happens with various ions. And in general, silica, can you actually see that? Probably not. But silica, uranium, nickel, selenium, arsenic, a lot of these things in most um river and estuaries are conservative except for manganesees. Actually, it can differ. It can be any. So this basically talks about whether or not there's input, namely addition, whether there's removal or whether there tends to be conservative mixing. And it generalizes and you'll see that copper, manganesees, and a couple of other elements can have any one of the three going on depending on what estuary they're in. — Okay. Um what's the uh the sign for the universal behavior that got cut off the bottom? Is that like the underlined or the circle? — I believe it's the underlined. You're right. That's sorry. That's universal behavior. And so you'll see that barium is almost always so barium, radium, cadmium are almost always added whereas iron and burillium and aluminum are almost and rare earth elements are almost always removed and humix. — Is that what they use? — The humic acids. Okay. But you'll notice that it's not very many of these that have this universal behavior. — The following content is provided under a creative common license. Your support will help MIT Open Courseware continue to offer highquality educational resources for free. To make a donation or view additional materials from hundreds of MIT courses, visit MIT Open Courseware at ocw. mit. edu. Today we're going to finish up talking about um some of the inputs from rivers and hydrothermal uh vents. So what we're going to talk about today, we discussed the generation of vent fluid and the generation of rivers. So today we're going to talk about what happens when these enter the oceans. So when rivers enter the and this is in terms of estuaries. So I'm going to spend the first third of the class on that. Then I'm going to talk some about groundwater and how groundwater input can also affect estimates of uh fluxes from the continents into the oceans. And then finally we're going to look at uh vent fluid entering the oceans. And this includes both depos the formation of deposits as well as of plumes. And while the deposits are left on the ocean floor and are sort of a near source issue, the plumes actually can rise 200 to 300 meters above the seafloor. and you're at about 2500 m depth in the oceans and you actually create a lot of mixing in a part of the ocean where you wouldn't normally suppose that you were going to have a large driver of mixing. So it has um implic a lot of implications for physical oceanography and for chemical processes that are at a depth that we didn't really consider that important 30 years ago. Okay. Um all right. So before I start or the first thing I want to talk about is that when rivers enter oceans and when vent

fluid enters oceans you have contrasts and you're going to have different contrasts for different ones of the fluids. For rivers your dominant contrast versus the oceans is the change in salinity. So that's the key one for rivers. And vent fluids or there's two really. It's temperature which actually creates a large buoyancy and I'll get to that. So it's temperature and pH are your key differences. So going back I want to remind you of what the rivers were like or how rivers were generated. We started with rainwater and rock. You have weathering. You have congruent dissolution, disongrent dissolution. Um, and the key thing is you create a fluid that's carrying both dissolved um, dissolved ions, but also you have particles. And on those particles you have absorbed metals and you also have clays, iron oxyhydroxides and humic matter that there. And those all have negative charges and so those have um ions associated with them as well. And we'll get into that. And we went briefly through at the very end of the river lecture, we went briefly through uh trace metal release when you have pH changes. So you can have subtle changes. The pH of river water is going to vary from about five to about seven. Is that right? Probably. Maybe a little more. And depending on what its pH is, that can have some effect, but those aren't the dominant ones. It really is this change in salinity. And then the last thing for the rivers was on top of all of this, you have the cyclic salt cycle, the cyclic salts. Okay, so that's just sort of a review. Need to show that. Okay. Um hopefully you have your notes today. If not, you'll have to remember them because it's much easier to show these pictures as we go through the different types of estuaries. So essentially what you're doing is a river is coming down to the oceans and it's going to enter and any of you who've been near a river mouth. There's multiple different types of estuaries. And the key things that are going to affect the type of mixing in that estuary have to do with the discharge rate. If you've got a very high rate of discharge, you're going to have one style of mixing. And it also has to do with the depth that the estuary is at. And so we're going to discuss four different types of estuaries briefly. And in this in these figures, and my apologies for the quality, they were xeroxed initially, I think about 15 years ago, and have been written on and xeroxed again. So um the first type is type A. And here you have, and it's where you have a shallow estuary with a small river. So you have a small discharge coming into a small estuary. Um you have a lot of these around here. And what on this figure what we have you have four stations one two three and four. And then this just shows the mixing. So you have a station I mean the surface. What is that? I don't even know what that's supposed Oh this is station 1 2 3 4. But this is the surface. This is the bottom of the estuary. And this is simply showing the type of mixing that's going on. So when you have low discharge into a small estuary, you have a well mixed a well vertically mixed um processes going on. So you're basically bringing fresh water out and then you're going to have some tidal slloshing back and forth. But you end up what you want to do is take a look at if you look at what the salinity profile is at each of these stations, you go over to the next side of your figure and pretty much the salinity is not stratified at all. Okay, so these estuaries are they're dominated by tidal mixing. They're vertically well mixed. And this is all in your notes. probably not as bulleted as this, but um they're vertically well mixed. There's a net outward flow at all depths, and there's a seawward increase in

salinity that's similar at all depths. Okay? Now, you can also have the same thing going on, but you can end up with um also in a shallow estuary, but you can end up with a two-layer system. And for this two-layer system, we have the same thing going on. First, let's look at what's happening with the flow. The low salinity river water is flowing out on the upper part. Seawater is flowing in on the lower part. And this is dominantly density driven. But then you still have fairly you do have some mixing, some vertical mixing. And you end up, if you take a look at the profiles across each of these stations, you end up with a slightly stratified salinity gradient. And what happens if pedestri type A or type B? What would cause the pink flow of sea water? [clears throat] — I think it has to do with the discharge. A lot of discharge rate. If you have a correct me if I'm wrong if anybody I mean if you have a high enough discharge it's simply a mass you know you're pushing flow out. You're going to draw fluid back in. Um it's more of a physic you'd have to look at the physics of the system. Also, if you have a really shallow estuary, it gives you more turbulent mixing and so you have better vertical mixing too, — right? But these were both for small for shallow. So, — both of these have fairly good vertical mixing, but you do have the — um but you can also, and this is the other thing, you can also have the same estuary have the different types at different times of the year. Um, in fact, so now I'm going to jump to the there's a type D, which I really think should be type C. Um, because it's one it's sort of a variation on type B. And this is when you have a large river entering a shallow estuary. So again, this has to do with discharge rate. And here you end up with a salt wedge. And as in the case before, the surface waters have uh low salinity. seawater intrudes underneath as a wedge. And again, here's what the flow looks like. You have a higher rate of discharge. So the flow is coming out here and this draws in seawater is coming in here. And it's a mass balance of what's going to happen as the fluid flows. But here instead of having a very well stratified, one of the key differences is you end up with this wedge. So out at station 4, the salinity increases at a much shallower depth, whereas at station one, it's fairly fresh down towards the bottom. And there's an example in your notes about the Ches Chesapeake Bay where at times of high discharge you have a salt wedge and at times of lower discharge you have a stratified a vertically stratified. Now you also have the situation where you have a very deep estuary and the example we're using here is that of a fjord and you have a sill located here and again this shows the flow the fresh water is flowing out at the upper levels. You have return of seawater at lower levels but not at the deepest levels because you have the sill blocking those deep levels. But then what happens is this the you end up with higher salinity fluid basically pooling underneath behind the sill and it's not mixing up as often and so you end up with a very highly stratified salinity gradient. And the reason we're talking about these salinity gradients is it's that is that the major change the key uh property that is affecting whether or not what the whether or not you have non-conservative processes is this change of salinity. So it's important to know where the major change in salinity is occurring within the estuary. Okay. And so again, this just shows a picture of the different types. And you'll have a lot of mixing, but you're mixing up in the shallower region because you have a sill which is preventing entrainment down here. Okay. Right. So now we get into what are the processes that are going to occur the non-conservative processes that occur in estuaries and we went over this last week. I'm going to show you a lot of diagrams and most of these are going to be salinity diagrams where you have the seawater and freshwater salinity here. And if it's and you have some element

here and so if this is seawater solenity and this is freshwater solinity if it's conservative mixing you're simply going to have a straight line. And of course, if you have removal, you're going to be coming on this side of the straight line. So that's removal here. And this is addition here. Okay. So you have a number of different things going on. A key one you have going on. We talked about what's in the water. And one of the main things that's going on is you have particles in the water. So you have col river colloids. And again these are dominantly iron and humic substances. And what happens is the sea salt well for all of these we talked about them having a negative charge on the outside. And this is described well in your notes. Basically the colloids are electrically charged submicron particles. Okay. there's going to be clay the clays the organic material um and some of the humic uh iron oxy hydroxides. So they're too small. They're very small. They're not going to undergo gravitational settling and this negative charge on the outside there these um electrostatic interactions which keep them in solution and help to keep them in solution. What happens is when you bring in a higher salinity fluid and you bring in salts this neutralizes the electrostatic charges the electric charges. So when the electric charges are neutralized, the colloids clump together. They aggregate and then they're large enough to gravitate to settle by gravity. Okay. So basically you are neutralizing salts. If I could write today — salts neutralize the electric charges which allows aggregation and then settling. — You'll sometimes hear it described as fauculate, — right? which actually drives me crazy because fauculation to me is all fluffy and it stays in the water and it does for a little while but then it gradually settles. So I'll put that as fauculation. There's two C's, right? As opposed to flagagillate fauculation. Okay. The second one. So that's sort of the first key. The second one that's very important is disorption. And this is what I talked about. We talked some about this going on within rivers with the pH changes because when the pH gets uh lower, you can disorb some of that um when it gets higher, some of the um trace metals disorb from particle surf surfaces. But the disorption in the river um you sometimes and Scott talked about this on an earlier lecture and I talked about it as well. You can have calcium released from clay surfaces and replaced by sodium. You can also have radium can do the same thing. The third one, the first two are the key ones that are going on right in the water. If you just took a batch of um seawater and took a bang on or desorption going on in terms of non-conservative processes, but there's a third one when you can't explain it by these two. The other thing you can have happening is um our interactions with marine with estuary sediments. So basically you have um there's poor water gradients and so you can if you actually stir up sediment on the bottom you release pore fluids that are in the sediment. You also uh bring up sediments that have ions absorbed on the outside. So you can release those. So really the process is one of resuspension

an interaction with the resuspended material and the other one is release of poor waters. It's not just release. It can be release and exchange. I know. Okay. All on one page. [snorts] What do you guys think the poor waters in an estuary like? You guys been to any of the little estuaries around here? The salt marshes? There's lots of wet in an estuary, lots of organic matter. So, if you dig down into the mud, it's a good field trip for you guys this weekend. Go over [snorts] that area. Dig down into the mud, you very quickly get to anoxic mud, — and you'll be able to tell because it'll start to smell really, really bad. — Um, and so that's one of the things when poor waters from eststerase is you're now releasing anoxic pore waters, which are going to have very different metal composition. So in some ways there is some analogy between the pH and [snorts] right — eh changes that we're going to talk about at the end. — Yeah. And in fact at the very end when I'm talking about the vents I'm going to talk about the microbial activity but I'm not going to talk about it for the estuaries. But um — we we'll talk about microbes more than you guys after the midterm. — Oh is that right? — Okay. All right. And then speaking of bugs, this is the last one which is you can have uptake. Did you like read the notes this morning so that you could interject that properly when I needed it? Uptake by estuary. — I have this one burned in my I think I have this class burned in. — You have uptake by estuary and by biota — and they can remove elements or this can remove elements presumably. It can also release elements but um I think it's more the up word or not uptake but the regurgitation no the I guess it's kind of confusing as to what the definition of conservative mixing is. — Oh we'll get there. You're about to see more graphs than you ever wanted to see. Basically each of these processes either adds or removes material. If you mixed seawater and you mixed fresh water and you didn't do any of these things, then you'd see a perfect straight line like this. Okay? But we don't always and for some elements we do and I'm going to go through those. And for some of them, we clearly don't. And so you have to explain why you're seeing their removal or the addition. And the a key reason why you need to know that is because if you just take the iron value that's in rivers and say that all of that iron makes it all the way out into the ocean, you're wrong. because a lot of it is left in the estuaries and you have to try and figure out and try to quantify how much of that iron is fauculates and is settles within the estuary. So, right now we're going to show you a bunch of plots. question that line it doesn't I mean it that to me looks like you have something that's not in fresh water — and then you increase it as you go into salt water — whereas if it was — right sorry — well — I'm thinking in you're right this could be the if it's high and you're right most of them are higher in fresh water and drop that way — it can go either way — but but let me just it's easier to look at real data. The old confusing them by trying to be simple. — But if it's conservative, it would just be a horizontal. — Well, let's just show you. I'll show you the first one. — Then the concentration would be the same in the — boron. Okay. Most of these things in order to look at mixing. First of all, you have to figure out what to plot it against. And you have to be plotting it against something that you're pretty confident is conservative. And in general, the salinity is relatively conservative. You are not dumping large amounts of halite or large amounts of any sea salt into estuaries and we know that. Therefore, you can say either chloride or salinity tends to be conservative and so an element that is conservative should plot on a straight line relative to the to that property. — On the axis, — the axes again this is one of these um this is I believe it's micro it's a concentration. It doesn't matter what it is. It's a concentration unit. And this is salinity.

Okay. And if you take a look at this, you can see that within error, this boron is falling pretty much along a straight line. And so unless you know whether or not there's something actually going on here or actually going on here, um you'd have to put the error bars on your analyses and really try and figure that out. And we're going to get to issues with that in a little bit. But this is one where you clearly have conservative processes. You obviously can't be dumping a whole bunch of boron out unless you're dumping it with the salt. But we know that you're not dumping salt out. Okay. In contrast, here's iron. And again, it's simply concentration versus salinity. And so, as you'll see, as Kristen pointed out, it can be either direction. Here, there's more boron in seawater than there is in fresh water. And here, there's more iron in the rivers than there is in the salt water. — That straight line is what it would be without, — right? And the if there wasn't. And these little dots which are much smaller than the [snorts] big fat pen line are the actual measurements. And one of the things that they've noted is in general iron and humic substances tend to follow this type of curve pretty well. And that's dominantly from fauculation of material and dumping in estuaries and precipitation in estuaries. That's in contrast to some other things which I'll show you which are much more complicated. Um here you have barium and again all of these are real profiles instead of trying to show you these idealistic profiles. Um these have all been taken directly out of the literature and it's real data which is why they're not all beautiful profiles. Um this is for barium and there's a fair amount of barium in both the fresh water and in the salt water but they're subtly different but then you see this very large increase in barium and that is likely from disorption. Okay. And then they show some really nice fun ones where you have copper. And again, this is the kind of thing where you go out and a lot of this work was being done in the 70s. Um, and they were really trying to figure out um both Ed Bole and Ed Shakovitz um in our program did a lot of this work trying to make sense of the data they were collecting and trying to quantify what's going on in the estuary so we can better quantify uh river fluxes into the oceans. And here you can see that copper it looks like it's being added at very low salinity but then as the salinity increases some it looks like some is being removed and then at higher salinities it looks like some is being added again. So copper is one that is more complicated and you'll find that a lot of these that are more complicated are ones that have multiple different veilance states and so there's a lot of redux processes that are going on at the same time that affect what's going on. And then manganese is another um and here you show there there's a in this profile. There's a large removal at low salinity and a large addition at higher salinity — on the iron. Sorry. — Is there a question up there? — Um, it might be the same one. I'm not sure. Uh, — can you just describe again why the barium has the shape that it does? — Oh, does. Well, I'd have to go back to the paper to be sure why it is, but my suspicion is it's from disorption. So that you have barium um on various particles that are coming into the estuaries and then when it mixes with the salt um the barium is being there's exchange going on and some other ion is replacing the barium and the barium is being released sort of like calcium and sodium exchange. — Could you explain what was happen — in the iron profile — on these plots are you seeing just the free concentration or are you seeing also that's in solution but bound to some particle. — What you are measuring here when you do this and we'll get to it when we do the in laboratory ones is you're taking the fluid and you're taking the filtered portion the less than 045 micron portion of the fluid you're analyzing that and coming up with the total iron. So this is looking at total iron in the 045 micron and less fraction I believe.

Yeah, that's what they usually do. You'd have to read each paper carefully to find out exactly what they're doing, but in general, that's what they do. So, no, you're not looking at the iron that's on the large particles that are left on the 045 micron filter paper, but anything that can pass through that filter is included in this. — So, that would be truly dissolved free ions. It would be things that are complex in solution, right? So, it includes and colloids, — right? So, if we go back to this figure where we were looking at what was in the river water, once you get down below this 045 micron, it would include some of these clays as well. Um, Caitlyn, did you have another question? — Well, I was just wondering, um, it looks like in the iron profile that is below the conservative rejoins it. — Okay, perfect. Perfect question. Okay. Now, one of the things is it one simple process going on and these are all assuming that you only have two end members. You either you have a uh seawater end member and you have a freshwater don't have any other end members. and they're trying to simplify these things and come up with fairly straightforward um processes that they can extrapolate globally so they can come up with good a good idea of what global fluxes are. However, because of the type of thing you just talked about, Caitlyn, there's also concern about whether or not there might be a third component. And so there are some examples and this shows one here. This was work done by Ed Bole. He went and looked back at this is a dissolved silica profile. And what could be it could be interpreted a lot of people would just interpret that as simple from either coloids or dis or uh disorption. No, not disorption, absorption or something else. But what he attributed it to instead was a third component that a third mixing I mean a third end member. Um and the reason for that is silica tends to be conservative when you mix and it was very uh it was somewhat confusing why you would see this decrease because what would be the removal mechanism? Nobody had a removal mechanism. So his hypothesis is that there's a third source here of fluid that has a lower silica composition and that you actually have conservative mixing between this and the seawater source and between this source and the river source. — Can you point out what in the iron that you're talking about? — Oh, you know, we're going to get there. to that's messy data. Again, none of these have error bars on them. Um, you also, all you have to do is have one aggregate get into your bottle or have one colloid stick to the side of your container. I mean, there's a lot there are a lot of things that can create noise in these data sets. Okay? But the key thing of this is for you to understand how to look at a profile and determine whether there's been removal or addition and to have some idea of what is likely causing that removal or the addition. And again here what confused the reason Ed Bole went back to look at this was in general he was finding in other profiles that silica was conservative. So an alternative interpretation of this is that you have a third source fluid source. So an example of that would be like two different ocean — mixing with a river — or having — two rivers and the coastal water something like that, — right? Either two rivers and a coastal water or in this case it was actually um a shelf source and we're going to get into groundwater flow as well. You can end up with a groundwater flow source. Okay. He ba. Yes. He ended up with a for this one in particular, he had a river source, an open ocean source, and then an intermediate shelf source. I'm not sure what the source of the shelf source was, but it didn't go into that. But there was basically you could go out. So you could you then go out and sample that body of water, do some CTD tests, and see if you can actually find that fluid out there. Okay. All right. Now, because of these complexities and some of the um questions that Caitlyn was raising, you do have a concern and a problem when you have messy data. I talked about some of the issues. And here is a profile that shows copper and a mixing line.

And the real question is, is this actually conservative mixing or do you have some addition going on here and a little bit of addition going on there? You know, what's really going on and the data are very, very noisy. So Ed Shovitz was one of the key people who helped develop this. You can also do your own mixing diagrams. This is all field data. So you can just take one option is to go out to the open ocean. So go to this station, collect a bunch of this water, go to the river source, collect a bunch of that water, the fresh source, and then do the mixing in the lab after you've and you can either do this mixing depending on if you want to look at particle processes or colloid processes. Um you either filter or un or do it unfiltered. This is an example of an unfiltered river water. Um it was says unfiltered river waters 04 mill micron filters which implies that it's filtered seawater but um anyway you have to know what you would report in the paper exactly what you did with those fluids but when they did that mixing experiment this was the data they got from the mixing experiment and it really — I'm still confused as the definition of conservative mixing versus nonservative mixing because I mean is it lab mixing or is it field mixing because some of the processes that we went over wouldn't happen in the lab — and they're not happening in the lab but they're happening in the field what you call it and you know — you call it non-conservative mixing no matter what's going on but you have to identify the process that's going on. So you're right. This type of mixing experiment is only going to look at disorption, you know, chemical processes between those two bodies of water. It's not going to be considering any of this resuspension of sediment — or bod — or biota, right? Unless there's in well except for microbial activity that's actually taking place in the water column in the two fluid samples that you've taken, — but it's certainly not going to um but for this, this is what they were looking at. They were trying to figure out is copper being disorbed? Is there addition or is there removal or is it being absorbed? Okay. Um and then this was, you know, some other examples are in your notes. Um this is a much messier one. Take a look at that nice nickel profile. And I'm sure that scatter in large part has to do with uh um errors on the analyses. And then when they did it in the lab, they got a much cleaner data set. And similarly uh and then for calcium I mean for cadmium the data were again ambiguous. For instance, is there actually a third source sitting or is this simple disorption? And when they did the mixing calculation or the mixing experiments in the lab, they saw that you get this non uniform, you know, you get more disorption occurring at low salinity than at high salinity. And that but the entire profile can be explained by disorption. Okay. And again, all of these details, I mean, there isn't you cannot just look at a data set and identify exactly what's going on. It's c it's simply um an interpretation of field data. And as shown by Ed Bole going back and reinterpreting one, the interpretations that are out there for all of these profiles are not necessarily 100% true. I mean, this is their hypothesis as to what's going on right now. [snorts] Now, there's a again in your notes there's sort of a generalization. This table sort of gives you an idea of in general what happens with various ions. And in general, silica, can you actually see that? Probably not. But silica, uranium, nickel, selenium, arsenic, a lot of these things in most um river and estuaries are conservative except for manganesees. Actually, it can differ. It can be any. So this basically talks about whether or not there's input, namely addition, whether there's removal or whether there tends to be conservative mixing. And it generalizes and you'll see that copper, manganesees, and a couple of other elements can have any one of the three going on depending on what estuary they're in. — Okay. Um what's the uh the sign for the universal behavior that got cut off the bottom? Is that like the underlined or the circle around? — I believe it's the underlined. You're right. That's sorry. That's universal behavior.

And so you'll see that barium is almost always so barium, radium, cadmium are almost always added whereas iron and burillium and aluminum are almost and rare earth elements are almost always removed and humix — is that what they — the humic acids. Okay. But you'll notice that it's not very many of these that have this universal behavior. I'm surprised silica is removed sometimes. Okay. Um, you can also have some other interesting things happen. There's an example of uranium, a nice nasty one. And this I'm sorry, this plot is truly hideous. Um, it's best to read the notes and read the figure caption, but all this is really showing is that in some places you tend to have conservative mixing of uranium. In others, um, you have a removal of uranium and in others you have addition. And supposedly on this diagram you see addition of uranium, but I can't see it myself. Um, and one of the hypotheses for what's going on is that the uranium is bound in the iron oxyhydroxides. These colloids, and this is in your notes, these colloids fauculate. They settle on the bottom. Then these iron oxyhydroxide coatings dissolve releasing the uranium back up into the water column. So with time, you end up with an addition of uranium in the estuary. — Well, the iron oxyhydroxides dissolve in the opposite sediment, right? Is that the key step? — I would think because — except you can also have exchange. I mean uranium and is we don't need to go into all the details. The the point is as I said before I don't want you to memorize exactly what's happening to every element. I want you to understand that the processes that can go on and another additional another process that can leads to addition is interaction is dissolution of material that has settled on the bottom as the conditions change. Um and if there's any dissolution or any ion exchange going on things can get desorbed later things that take a longer time than they take. So it it's just you just have to think about what processes could possibly be going on. Okay, now we're going to get into radium isotopes, which is going to segue us into groundwater. Um, but in general, radium isotopes can help unravel some of these very complex processes that are going on. I have to make sure that I have to speed up otherwise I won't get to my favorite part. So, um the vents will get shafted again. Okay. So, radium isotopes. Um Bill talked about radium isotopes. I'm not going to go into all the details, but you know that there are multiple different isotopes of radium. Radium behaves similarly to calcium and barium. And you can have radium absorbed on exchange sites um such as negatively charged on the exchange sites of negatively charged um clay particles in river water. And then it um it is rapidly disorbed in estuaries by ion exchange. The ion exchange occurs as salinity increases. However, if the radium was only occurring because of this mixing, you would expect to see the exact same ratios. So you'd expect if you see um the isotope ratios, you ask yourself the question, are isotope ratios the same on the particles on the river particles as they are in the estuary water? And the answer is no. Okay. Basically, there's a lot more radium 224 than um the radium 224 is too high in the estuary.

And when they looked at that, they then took a look at what other processes might be happening. And that was when they decid they um they account for this excess radium 224 by resuspension of sediments and that results in extra release of radium 224 which can grow into the sediments because it grows in rapidly whereas radium 226 and radium 228 take a lot longer to grow in. Okay. So 224 radium grows in to set particles more rapidly. Okay. And that allows you to use radium isotopes as um tracers of processes. And there are a couple graphs in your notes. I'm not going to go through them because you can look at them, but they show excesses. they show addition of radium. Um, and when you do these calculations, well, I'll just show you one. Take a look at the radium 224, 226, and 228. And you see that there's much greater inrowth of I mean much greater abundancies in addition of radium 224. — Wonderful figures. — I just you can't see the symbol so you don't really know the transmission. — Well, you can in your notes. You can. Okay. — Yeah. One of the things we're trying to do is figure out the time to reddraft every single one of these figures, but we also have to go back and find exactly what paper they all came out of. So, okay. — All right. — How not to obey copyright law. — Right. Exactly. That's the next problem. Okay. So, well, for it's fine for as long as your lecture — mean these since we don't have the paper. — That's right. Yeah. Okay. All right. [snorts] So groundwater — question. — Yeah. — I'm a little confused by this term that you said growth in that radium 224 has a — do you remember Bill Martin had the whole lecture on thorium radium and thorium isotopes. — Are you saying that it's how fast it is derived from its parent isotopes? Is that what you mean by growth? — Yes. So radium 224 you're basically producing much radium 224 is being produced much more rapidly than radium 226. It's growing in it's called growing in. — Another way of saying that is because radium 224 has a shorter halflife. Right? — When you have a perturbation it will reach secular equilibrium with its parent more rapidly than a longer lived radium isotope. And we went through that a little bit. the how long something takes after perturbation to get back to secular equilibrium and that depends upon the halflife of the daughter isotope. Okay. And again it's described in fairly well in the lecture notes but then you'd also want to go back to the lecture notes or actually do a problem where you're using radioisotopes so that you really understand how it works. It's tough to understand it the first time you go through a lecture. — And how do you distinguish from a radioactive process versus kinetic fractionation of different isotopes? Like if you're — the but what's the mass difference between radar? — Well, sure it's relatively small, but I mean — very small, — but you could presumably measure very small. — Well, okay. But that the signals you're seeing are much larger than what you can expect by mass fraction. — And I'm going to just be right in context of what you see. — And I'm going to be talking about radios a little more in the groundwater. So let's answer those questions once we've gone through all of this. — I won't talk about it. — Oh, you will? Okay, good. Because otherwise I won't get to vent fluids. Okay. Groundwater. Groundwater [clears throat] is fairly well, it's um it was overlooked for many years. Basically, you have a continent, you have just as you know, you have uh the oceans here, you have a continental system, and you've got some kind of