Outwelling

Transcription

Thanks for that and thanks for the introduction now, and I was glad you stopped before you got too far, and I guess the other think is that again I'd like to thank the IAH, QUT, and the National Centre for Groundwater Research Training for providing this opportunity. What I want to do over the next 40 or so minutes is take you on a bit of a whirlwind tour of concepts in river ecology, but particularly to tie those concepts in river ecology to groundwater-surface water linkages, and finish by talking about some of the management implications of those groundwater-surface water linkages and how they tie in into the way river ecologists look at rivers in nowadays. I think many of you will be fairly familiar with this sort of diagram you see in a lot of textbooks, that give you this whole perception of how water is linked in a planetary sense, but what of the sorts of water sources that we get particularly interested in, and we exploit, are rivers and groundwaters and in many cases these systems are linked or connected. So this photograph in the lower right-hand corner is of a river in the Flinder's Ranges, and the farmer is basically accessing groundwater that is also river water. So for much of the time the river flows underground and the farmer wisely is able to access that water for his stock. But the main thing is that very often these waters are connected, and in being connected both the rivers and the groundwaters are providing what we'd consider as being crucial ecosystem services. Now that might be an unfamiliar term to some of you, but it's really a term that expresses the fact that, not only are ecosystems functioning in many diverse ways but many of these functions provide goods and services that are valuable to humans. The most obvious example of a service that is valuable is the provisions service. So we use groundwater for drinking, for stock, for the industry. Another form of service is the supporting service, in this case the nutrient-cycling transformations bioremediation, supporting linked ecosystems, GDE, standing for Groundwater Dependant Ecosystems, and even in a literal sense, the supporting service of preventing land subsidence. Another type of service is the regulating service, and that is one where flooding and drying and eroding can be mitigated by the presence of groundwater, in storing run-off waters, and many rivers are fed by base-flow, which is effectively groundwater coming through and supporting river flow for much of the time. And finally there is the cultural ecosystem service in many places, not only in Australia, but overseas. Groundwaters play a very important role for traditional indigenous owners in terms of spiritual values, and indeed surviving in places. There's scientific values, and I think also aesthetic pleasure. Anyone who has ever not gazed into the eyes of an ibis before, can't help but really appreciate how beautiful these animals are, but I think there is a real aesthetic pleasure looking at these wonderful animals and wondering what they're doing there. So I guess the two things that I want to make, and that is the point that many of these services rely on intact, hydrological and ecological linkages. And just because you've got an intact hydrological linkage, that's not necessarily the same as an ecological linkage. I just want to make the distinction between the two. And also it raises the question then. What do we know about rivers and how they work? And by work, how the ecosystems function, and the relevance of the intact hydrological and ecological linkages, and the conditions of these groundwater ecosystems services. And now I am going to use the term "concept" quite commonly and so I just wanted to define it. I'm using it in a vague, broad sense, as being an idea for example, about how something works. And when we've got those sorts of concepts we can start to make predictions. And so a concept, how something works, and we can ask how it will respond to a particular activity, and then we can go back, test these predictions, and modify the concepts. So it sounds like a fairly simple idea, but it's quite important to keep this in mind when you're thinking about rivers. If I was to ask any of you to describe a river, because of your concept, you would have a different view of what rivers are than the person sitting next to you. So concepts influence our perception of form and function. They influence the way we think these systems will respond to different sorts of pressures. And concepts evolve. You often hear people talking about the best available science. Often we think that the best available science is more accurate technical measurement, but it can also be the way a concept is changed and how we think about systems differently as concepts. And this is part of the reason why I find it interesting to talk about the history of a concept, because I think one of the terms that I sometimes hear used is "institutional inertia", and that refers to when you last heard of a concept, and then where you've gone since that concept has evolved, and how that's affected your perception of the way rivers work. So what I want to do is take you on a kind of historical tour over the last hundred years, of how our concepts about how rivers work have evolved. In the good old days, most early river ecologists were very sensible people indeed. That's not to say they're not sensible now, but they were fisheries biologists and fisheries ecologists, and they knew that if you wanted to go out and catch things, like trout for example, you'd head to the upper reaches, or upper zone, of a river. Lower reaches would have different species of fish. And so for many years there was this notion that rivers were zoned in particular regions, and that as you travelled from the headwaters down to the lower reaches, so you could catch different suites of fish from different kind of zones. So mysteriously these fish were smart enough to know when the zone ended and they had to stop swimming, incredible. In 1980, there was quite a dramatic change in the way river ecologists thought about rivers. So, this paper by Vannote now, called "The River Continuum Concept". It is one of the most heavily sited papers in river ecology. The "et. al." hides what is really a "who's who" of stream ecologists in the U.S. at about that time. And what was important about the River Continuum Concept was that these guys said, "ok, rivers change longitudinally as you head from the headwaters down to the lower reaches". People have known this for quite a long time, but what was more important was that there were predictions about how rivers worked, as you changed, longitudinally from say, the headwaters, where the major input for example might be from leaf litter, from well-shaded forest at the headwaters, down to the lower reaches where algal productivity, open, unshaded areas might be changing the food-web base, and the River Continuum Concept predicted a longitudinal change in the sorts of invertebrate and faunal communities you might find in the swamps that change your organic matter inputs, and this spawned a whole lot of tests and ideas, and really changed the way that people thought about rivers. It didn't take long before other workers, working out on river systems, like the Amazon here. This was work by Wolfgang Junk and others in 1989, said "well not only longitudinally, but lateral exchanges were also very important for rivers, and here in massive flood-plane river systems like the Amazon, it's very clear that this has a huge effect on the river ecology". And quick as a try, someone said, "well look, if you can go longitudinally, and you can go laterally, we can go up and down as well". James Ward had been doing a fair bit of work on critters of the underground below river systems, and he talked about vertical dimensions, and then he also added the fourth dimension of time, talked about "the four-dimensional perspective". And what I'll do is just stop here and just get a show of hands as to how many people have heard of at least one of these concepts that I've just talked about. Ok..., so many of these ideas will be quite familiar to a lot of you in the room, and a lot of these have actually pervaded textbooks. Many people hold these thoughts about how rivers work. I want to talk briefly about the vertical dimension before I hop back to the concepts, because that's the sort of stuff that I find sort of, very interesting, over the last few years. And this is the idea, that as water travels down a river system, in this case, in response to changes in topography in the river, and in the ferocity of the sediments, it can downwell into the sediments, travel for a certain distance below the river, below the riffle, and upwell at the lower end of the riffle, or where the sediments are porous enough to allow that water to come out. And in this area where surface water downwells into the sediments, and then upwells, people will call this area the "hyporheic zone". Hypo means "under", like a hypodermic needle under the skin. Rheos is a gorgeous word for flow, so the underflowing area refers to where groundwater and river water exchange below the river, and laterally below the banks. And these sorts of longitudinal linkages, of downwelling, upwelling, downwelling, upwelling, can be repeated down river systems, and of course you can also add longer flow-paths, where it might downwell on an area a fair way upstream, and then travel under several riffles, and then upwell into the surface water. Of course these exchanges are also occurring laterally, and so, this is a shot of the McClay River in Northern New South Wales. The river's flowing at you out of the wall. Look out. And basically the water is travelling through that gravel bar, as well as travelling in the main river, and outwelling in that outer area of the gravel bar. And so in a lot of rivers with "groundwater and sand beds" stream beds, you'll find these multiple, accumulative groundwater-surface water linkages, constantly exchanging. Upwelling and downwelling in three dimensions. It's a lot more complicated than you'd expect just by looking at the surface. And those sorts of ideas I think have really excited and tantalised me in thinking about how rivers and groundwaters interact. And it raises the question then, well ok, this is all fascinating stuff, but what does it mean in terms of the ecological significance of the hyporheic zones into the stream systems? In 1990, French authors Janine Gibert and Philip Vervier published some interesting or pair of interesting papers, discussing the hyporheic zone as a dynamic filter, called an "ecotone", between river water and groundwater. The first of these filters out is physical filters. So quite obviously filtering out light. You wouldn't believe it but it's dark down there. Buffering and reducing fast flows, and then in a lot of cases, also buffering the water temperature. So this system, it's called Rocky River, but it's actually full of sand, because of coal mining and various land uses. In Rocky River we did a study where we sampled along, over several days. The X-axis there is time, the vertical axis is temperature and we buried sensors. Some in the surface water, the heavy dark line, and others at various depths within the sediments. And you'll see in that one, that the surface water fluctuated between about 37 degrees Celsius down to about 20 degrees Celsius, whereas at only 30 centimetres down in the water, down in the sediments rather, below the downwelling zone, the hyporheic water, only fluctuated by several degrees around 25 degrees Celsius. And so where upwelling patches, or where upwelling water comes up at the base of the riffle, you end up with cooler areas of water. Now this is valuable, and this is very practical knowledge to have when you're out in the field, and you might have drinks or samples to keep cool. You've got a stream nearby, you forgot the ice, it was someone else's fault. Where would you put your beers or your samples? In the upwelling zones at the base of riffles, so this stuff's really practically useful to know. But there's more. The other thing that's kinda neat about this whole filter idea, is that as you go from downwelling to upwelling zones, you also have this longitudinal gradient of chemical conditions along the flow path. And a lot of this is related to microbial activity taking place along this flow path. But some of the work that's been done by Jeremy Jones and others, working in Michigan, Arazona, and other parts within the states, if you plot distances along the hyporheic flow-paths, so left is downwelling, right is upwelling, at various concentrations of particular chemicals, oxygen, which would be highly oxygenated in the surface water, will decline with distance along the flow-path, as the oxygen is taken up by various microbial activities, while for example nitrate concentrations could rise, and then begin to drop off. Don't be too perturbed by all the names of the various processes taking place, and this is just the tip of the geochemical iceberg in the graph, but processes like nitrification, denitrification, and methanogenesis are all occurring at various stages along the flow-path. The main message that I want you to take away from this is that, where the water upwells into the surface stream, so you get not only cooler, or transformed water in terms of temperature, but also a different cocktail of chemicals coming up, based on time in the subsurface pathway, and the transformations that are taking place. More than that, for example, and this is a hypothetical case, if that flow-path was as long as that little yellow blob there, you can imagine that upwelling water would be relatively rich in nitrate, for example. If the flow-path was slightly longer, you might find now that all the nitrate's gone, and so the take-home message out of that is that different lengths of flow-paths produce different chemical cocktails of water come up into the surface stream. I'll come back to this theme again and again and again, and it's the idea that the length of the flow-path can have a massive effect upon the upwelling zones, and the kinds of things that might happen in the recipient ecosystems. Ok, so to give you an example of this, this is one of the, one of my kind of favourite parts of the world. The Flinders Ranges. Lots of beautiful intermittent streams through there. And in places where you find gouged-out areas, often behind this river red gum, you'll have areas of upwelling water, so waters flowing below the sediments, all year round, and where your groundwater is seeping in, you should be able to make it out, but you can see there's this sort of hideous lurid green colour taking place there. And a lot of what's going on in that hideous, hard-to-read text there is that transformed nutrients are creating these hotspots of biological productivity. We've done various experiments to demonstrate that the algae is actually, has its growth limited by the concentrations of nitrate, and where nitrate is being supplied by the groundwater, you get these bright green traffic lights, if you like, of algal productivity in these upwelling zones. And so as you, if you expand this out now to start looking at a whole river network, you'll have areas of hot spot of productivity all the way down the river network. Not necessarily always in the upwelling zones. Why not? Because it depends on the length of the upwelling zone. But you can often find, and I think I've often chatted with people about this, and they say, "Oh yeah, we've seen the base of a gravel bar, or the end of a flow-path, these bright green patches". And this is likely to be where there is a direct ecological consequence, of upwelling groundwater into the stream. And these hotspots, if you like, are produced by these zones of upwelling groundwater. The other key thing to think about the hyporheic zone, in terms of its significance for the surface stream, and that is the high level hydrological connectivity. So as I said, the hyporheic zone overlaps with the stream water above, and with what I'll call the deep groundwater below. But it also exchanges laterally with the alluvial aquifers, and also with the riparian zone. And I think, one of the insights we've had with some of the work that we've done in the Hunter Region for example in northen New South Wales, is that some of the growth of plants in the riparian zone can be linked to the chemical transformations taking place in the hyporheic zone, where it overlaps via the alluvial aquifers. And finally I guess this was the stuff that got me first interested in this. These zones often contain quite specialised fauna of surface and groundwater animals and invertebrates. So in this hypothetical stream bed where you've got the stream above, and the groundwater down below, in down-welling zones, or areas where the sediments are wide enough apart to allow their input, you'll get small mayflies, midge larvae and all the rest of it, burrowing down into the sediments, and in areas where you get upwelling zones, coming up from below, so are these animals with very marked adaptations to a groundwater existence are coming up from below into the surface sediments. So you get this kind of mixture, if you like, of surface and groundwater invertebrates, which is very strongly influenced by the direction of surface and groundwater exchange. Occasionally some of my friends will collect these groundwater invertebrates in surface water samples, and you feel slightly sorry for this animal thrown out into a completely foreign environment. But those would be places where they collected samples in upwelling zones and the animals are being, probably a bit against their will, sent into the surface ecosystem. A lot of these animals are specialised for a interstitial existence. So many of them are quite small-bodied, a lot of them are elongated and flexible. Many of them are unpigmented, eyeless and with long antennae. And it's sometimes said in the same way that people often end up looking like their dogs. The sort of people who work on stygofauna end up a bit eyeless and a bit, you know, develop a few sensory antennae, and (inaudible comment). The other thing that's kinda cool with a lot of these groundwater and hyporheic invertebrates is that they're sometimes surprisingly diverse. Some of the work that I was involved in New South Wales in this river, with the very unlikely name of a "Never Never River" that flows through an area called "the Promised Land", lovely town trapped in the 70s. There's this beautiful sort of gravel, and let me tell you that when you're choosing study sites good bakeries are important, and Bellingen has a stunning bakery as well. I digress again. This had a lovely gravel bar, a gravel set of riffles through it, and using extraordinary technical equipment, basically a bilge-pump attached to a tin drum that we sit on. A little tube leads down into the sandpit well. You, pump away on the bilge-pump. It looks a bit odd from behind. From the wrong direction, it looks like a couple of idiots. What are they up to, ay? You've actually got an area where you can collect quite a lot of groundwater animals, which are only, sort of, 30-50 centimetres deep. And one of the things we found was that, in just a relatively short sampling campaign over a couple of sampling trips, Jodie Foster and I, and some later sampling colleagues. We ended up with about 21 new species of water mite, just by searching the hyperic zone in this area alone. Now to give you a rough idea, you'd probably expect in a bit stream sampling to come across 5 or 10 new species, if you felt cheerful, but 21 was quite extraordinary. One of the things that this particular animal is one of my favourites. We called him the "party animal" because we couldn't say its scientific name. But, I used to live-sort the samples, so what was gorgeous about watching these critters. They don't get that big, they're only about a milimetre long, but what was great about watching these animals under a microscope is that they lumber along with these two long front legs poking out with little nippers on the end. No idea what they're for, but just the fascinating diversity of forms and shapes you get really sort of raises the whole idea of, well, what's all this diversity doing down there? What kind of things do these guys play? And so we started growing interested, not only in the diversity, but what were the actual activities? How were they acting as a component of a stream ecosystem? And in a lot of cases many of these animals were grazing on the hyporheic biofilms of microbes, and all the rest of it, on the particles. A lot of them were breaking down buried leaf litter that's been buried amongst the sand and gravel particles. Many of them are predators, many of them are prey for each other and for surface invertebrates, and even in their movement they can change the whole sediment filtration processes. So in very fine sediments, as these animals travel through, they can crap out little fettle pellets, and in doing so change the whole filtration processes taking place down there. But we started promoting this idea that many of these animals and their activities were potentially promoting groundwater ecosystems services, such as water filtration and nutrient-cycling. So this the kind of a halfway mark. I'll just disappear for a drink... So, the main messages so far is the role of these groundwater exchange zones has been dynamic filters that are highly connected. The whole idea that down-welling water effects groundwater processes. And in turn, the groundwater then upwells, affects surface processes. That as water moves along sub-surface flow paths, so its water quality is changed by the physical and environmental conditions along the radius in that flow-path. And then these groundwater-surface water exchange areas, in the network, can be producing these accumulative patches of surface and sub-surface biological activity. And then of course this idea that some of the sub-surface water may be promoting groundwater ecosystem services. So back to these concepts. I've left you dangling with these sorts of three "linear corridor" sort of concepts, and a final one to add came out a bit later, by Jack Stanford and James Ward, and this was the hyporeic corridor concept. Now they're working in the study area of Montana, the Nyack floodplain. And these guys proposed that, as you go through a river ecosystem, you have an alternating sequence of constrained reaches, of alluvial floodplains. And they use this very evocative metaphor of beads along a string to describe how the river systems worked. And that as you go from the headwaters, you have a little bit of water exchange in with the groundwater. You're going to the middle reaches, where the sediments are quite course. You start having quite a large amount of surface water and groundwater exchange. And then you get down to the lower reaches, where the sediments are much finer, there's a lot more horizontal movement of water, a little bit less taking place vertically. But there's been a lot of problems with these linear and corridor concepts. And these problems started off first when people started trying to contest them and realised that there is very little data to support any of, or any or all of these particular ideas. That not a lot of these concepts included the role of human activities. A few modified the concept to do so, but not very successfully. Many of them were quite static and ignored the big changes that takes place over time, and an awful lot of them underestimated the role of disturbances. So they didn't really factor in the sort of the droughts or flood that typify so many river systems, at different scales. And I think all of these together mean that by, about the mid 90s, people were saying "look, we need a bit of change in perspective and we need it to become more realistic". And about that time in the terrestrial ecology field, there was a much greater awareness of what was being called "Landscape ecology". In essence this very big field is one that recognises the landscape as a whole mosaic of different kinds of patches. And I think anyone whose flown over in an aircraft, or looked out the window, you're immediately struck by this whole patchiness of the landscape. But landscape ecology goes further than that and asked just the questions, " well how are the sizes of the patches, the way that they are arranged, the things that take place at the edge of those patches, how do those influence ecosystem processes?". How do disturbances create patches, and so when a tree falls in the forest and no-one hears it, what's actually happening is that patches are being created in that sort of process, and in the same way floods do something similar in river systems. And finally how can patches be hierarchically scaled? In other words, if we know what's going on in a whole lot of smaller patches, can we add those together to predict what's happening in larger patches? And so what happened was, and this is slightly overwhelming, what happened was, in the last 25 years ago, in the last 25 years. This is really just the tip of the iceberg. There was a whole kind of cavalcade of concepts, as people grabbed ideas from landscape ecology and took them into the river. There were a lot of multiple applications, and I've shown some of these as braids on this river system, where maybe people weren't reading each other's literature or coming up with independent ideas . There were a lot of new acronyms and ideas, something called the "Riverine ecosystem synthesis". We thought it was all going to be solved with a bit of a catchy title like that, but alas no. And there was also a much better integration across a range of scales of hydrology and goemorphologies, at some of these sorts of ideas. And I think that raises the whole question; well, after 25 years of landscape ecology, come on, tell us, how do river ecologists view rivers today? And also, how does this view of river ecology and river systems today, relate to surface-groundwater linkages and ecosystem services? Well the sad news is that there's a lack of consensus still, so if you came here for the big answer, I'm afraid I don't have it, and leave now I guess, but let me first explain why there's lack of consensus and then let me give you a little consolatory prize. Firstly, all river ecologists come into these things from different perspectives. They come in with different goals and different backgrounds, but I think on the bright side of it there does seem to be a way in which we can relate river ecology and groundwater-surface water linkages, in this patch dynamics approach, and I want to run you through this for the last part of this talk. Remember the landscape ecology, you had this concept of patch dynamics, hierarchical scaling and disturbance, and if we take the riverscape, the surface issues on one side, and the stygoscape, the kind of, the landscape below your feet if you like, on the other, and we look at how this relates to river ecology, you've got a bunch of classical fields down one side, ranging from river and fluvial geomorphology down to hydrogeology and aquifer geology. You've got a whole slue of different forms of ecology, from groundwater ecology, up through biogeochem and terrestrial (catchment) ecology, and then most important is this idea of social-ecological systems. So I think it's unrealistic about, to talk of, concepts about how rivers work without building humans and human activities into the equation. And as a result there's been quite a break-through I think, with these ideas, touted initially by Colin Townsend and then later by Jeff Poole, where he talks about this whole idea of, as you go from rivers from their headwaters to their lower reaches, the linkages with groundwater creates a patchy discontinuum. So instead of the river continuum concept, you've got the discontinuum concept, based on patchiness. But these patches, all along the river system, lie within a hierarchy, at least governed by unidirectional flow. One of the good points I guess is that water will flow from uphill to downhill, usually, and that if we look at the way these patches might be arranged hierarchically, you can go from a stream system, down to a segment, reaches within a segment, pools and riffles within a reach, and patches, micro habitats within those sorts of pool/riffle systems. But I think the main thing is that even though the spatial and temporal scales of those you might disagree with, the key thing is that there are ways of hierarchically arranging, at least in a spacial sense, these patches nested within each other in a flow system. Importantly, and I think this has been another big break-through from a work by Lee Benda, and that is that these are hierarchies arranged in a river network where the patches are influenced by the confluences with tributaries. I'll give you a little but of background. When the river continuum concepts came out, everyone had trouble explaining these pesky tributaries and the effect they had. Benda embraces them and says "no, these are actually really, super important". And the reason they are is that, and it's no surprise to any of us, that where tributaries join the main channel, you have these abrupt changes in sediment delivery, sediment particle size, the flows and all the rest of it, and then a lot of these patterns will differ according to the arrangement of the network, so where you've got lots of braiding, you'll get different kinds of patches and right now depending upon whether you've got individual tributaries joining the main stream. Further to that, let's add a few disturbances, so fire might come through and change the shifting of sediments through the system. We see the flood down the main channel, that's obviously going to change the patchiness. We add a few trees in there, and we have a little bit of tree fall, and that now the model is sweating blood because. You're thinking "well, it looks realistic but it's going to be a struggle to model". And then of course we've got the interaction of all those feeding back on each other, so this isn't fixed in time. We've also got these movements feeding back over time. This patchiness has also been reflected by the size of the basin, its shape, its geology, and its land-use. As I said earlier, by network pattern and structure. And by the disturbance regime, and the way that might change in the short and long-term. And so the take-home out of that is that you end up within river systems, over time, from river to river, with this virtually infinite system-specific variation, and we've got the audacity to come up with, and try to conceptualise, in the short sharp sort of way. What's been kind of neat is then to say, well that's great in 2 dimensions, but luckily we've had a few drinks now, and you can start thinking in 3 or even more dimensions, perhaps, about this whole idea that this is all taking place as well, below your feet. So think about the network in 2 dimensions, and now crank it up to think of a 3 dimensional lattice of patches, that are taking place below river systems as well. So, taking you back to the Nyack floodplain, some of the work that was done by Jeff Poole and others, particularly in the late or the mid 2000s. He started publishing these ideas about ways of arranging patches and modelling them, and I went to a talk that Jeff gave. It was a lot more sophisticated than this. But in brief, Jeff said, "well look, if you take a series of surface water patches". Now I've drawn these as friendly-looking ellipses but they can be very different shapes, very different sizes, and you can define them according to water quality, speed of the water, any factor you liked. They're going to be linked to each other, laterally and longitudinally in the direction of flow , and below them will be a bunch of patches of associated hyporheic zone. Now those patches will also be linked longitudinally and laterally, and of course they will also be linked vertically, and I've drawn double-headed arrows. Why? Because you can get both down-welling and up-welling zones. And so you can imagine in this simple model that you might have some water that begins at the surface, and then travels along one, drops down one, travels along, and then up, and it gets worse. The flow paths can be different lengths and different distances. Remember that's important. And then just when you reckon that is looking bad, you can now add the groundwater component as well. Now, this visually looks like a relatively simple sort of model, but when Jeff was presenting it, he was talking a lot about the way in which water was being transferred in both these different zones and these different loads, during high-flow and low-flow, and he was talking only about the quantity of water. And I was in the audience and I was just twitching and excited, and eventually he caught eye-contact with me, and he called the bouncers to take me away. But what I was lit up about was the whole idea that if you took this hyrdrogeological model, and now started asking questions about the fact that you got these flow-paths of different lengths and residence times. What about all the ecological implications for these things? So the models are not just about the quantity of water moving from place to place, but also the effects that these things have on the quality of water of the recipient nodes, whether they're in the surface, or in the groundwater. And I think that's been sort of one of the things we've really grown excited about. Matching up the models, in the hydrogeolical sense with the sorts of concepts and ideas that ecologists have now. We can use these 3 dimensional lattices now to start testing predictions about the effects of a whole lot of problems, which will be very common-place to many of you. The first is the whole idea of the patch attributes, and what kind of effects they might have on water chemistry and microbial activity, both within patches, and at the edges of patches, where patches of different types meet. We can start thinking about the changes in subsurface water residence time. The stuff that Jeff Poole was doing. He was looking at surface water, base-flow versus low-flow, but if you start changing groundwater pressure or start adding fine sediments, you're going to change the rate at which this water's moving, from place to place. Any disturbance that alters the patch attributers, attributes, and their arrangement at different scales, are going to affect the outcome of the waters along these flow-paths. And of course the accumulative contribution to these as you go down the river network also start to come into play. And following these lovely ideas, we look at a braided system above and we think of convergences and divergences, but lone paleo channels, in response to different size sediments, you also have the same kind of divergence and convergences. So next time you look at a braded river, and you sort of marvel at the surface braiding, think that that's happening below your feet as well. In my extract I sort of raised a few kind of management issues that could be answered by some of these sorts of things, and I had a very sweeping statement, like well, a sweeping question, how would human activities in a catchment or a channel affect these surface-water or groundwater linkages? Of course the answer is deceptively simple. You knew it would be. All we need to do, any activity we do that alters patch attributes, hydrological linkages, and all of the ecological conditions within and between those patches, are going to have an affect upon the surface water and groundwater systems. And so for example we might look at a system here where massive erosion has lead to a lot of sand entering into the stream system. We often look at these for surface perspective, and sort of think, "aww that looks pretty tragic from the surface", but of course that homogenisation of the sediments is now having dramatic effects on upwelling and down-welling zones and the interactions and the heterogeneity of patches in that respect. We often alter flow-paths within and between patches, either by groundwater extraction or by change in surface-water flows, and again, although we think about what's happening on the surface, we're also changing groundwater-surface water interactions and the water quality of recipient water. Anything that alters river or groundwater quality that connect to the system, and is bound to have an affect on the water that then travels into a flow-path, and how it might be changed as it travels along that flow-path, and anything that impairs the biological activity within a particular patch will ultimately have an effect upon its biological filtration process. And so all of these sorts of things, in the end, come to have an outcome for whatever the recipient water is going to be, via the groundwater or the surface-water. Another question I guess is what happens when you start looking at the whole catchment? In other words, how do these groundwater-surface water linkages accumulatively build up as you go down the river network, and again the answer relates back to the whole notion of the patch dynamics, the flow-rates through those patches, and the ecological processes. And, to just get a very simple, single example, before I wind up, the water that comes in at the surface end of, or the upstream end, of a reach. If you have a whole series of these, they might be gravel bars, or evenly spaced meanders down the river, imagine water coming in at the leading end of 18 degrees, the water coming up at the end of the flow-path might be 15 degrees, and contrast that with another system where you might have a whole lot of gravel bars close to each other, or some tight meanders around a long straight stretch, and some more tight meanders. These different arrangements, will provide a very different longitudinal profile in water temperature. It's quite a simple example, but it makes you realise that the arrangements of hyporheic zones, and upwelling-downwelling zones, have this accumulative effect to down river systems. So what are the deeper meanings of this? I guess my concluding points really are, that firstly, there's been an evolution in terms of the way ecological concepts about how rivers work, evolve from a linear corridor continua ideas to the hierarchical network of patches. That the patchiness arises from disturbances of multiple scales along the network, and these are mediated, not only by hydrological and geomorphological processes, but ecological ones as well. That the surface-water-groundwater linkages, which cover multiple scales, vary within and between patches, and I think next time you look at a river, keep thinking about this whole hierarchical, kind of 3 dimensional lattice, rather than just the surface systems that we're used to. And then the water source, the residence time, and the processes that take place along those flow-paths , all affect what happens to the up-welling cocktail of water, that comes from either the ground into the surface, or from the surface down into the recipient ground waters. And finally that any human activity that affects these sorts of flow-paths, or the residence time and the water within them, is bound to have an affect upon the provision of the ecosystem services by these sorts of systems. I'll leave with a bunch, or finish with a bunch of acknowledgements. I won't read them all out, but I just want to again thank, QUT, IAH, and the national centre, for this opportunity to chat with you this evening. Thank you. (applause)