Is it a lab model or field scale unit?

In a lab model, inflow and outflow is measured at the inlet and the outlet of the model along with concentration to determine the removal rate as a performance of the unit.

If it is a filed scale unit, inflow is measured. With the effective volume of the unit, Hydraulic retention time(HRT) is determined. Nutrient uptake by plants or removal by the unit is related with the HRT.

Hi Susara, what is the type of the wetland (riverine, floodplain)? And what kind of water flow do you plan to measure? What is the water source of the wetland (groundwater, rainwater, interflow)? Did you observe any "flow"? Which type? And at which scale are your working? Cheers, Beate

Firstly thank you very much for the feedback M.I.M. and Beate. I haven't decided whether it would be a field test or a lab experiment yet. Problem with removing the sediment from the wetland would be that the pore sizes may change due to the removal process and or transportation, or even the fact that I have now removed it from the water source. I am not interested in actually testing the uptake of N and P as a result of the flow, I just need to find out whether my sites have high or low flow rates in the soil which could indicate increased uptake of P as higher flow (from literature) seems to assist in P uptake in limiting situations.

Beate, my wetlands vary from floating fens and bogs to riverbeds, river floodplains, lakesides and even stagnant pools. Therefore there is some flow in certain areas and none, except perhaps horizontal in the stagnant pools, although those soils tend to consist more of clay and silt. As with the variety in types of wetlands, they also vary in water sources. And then there is the added bonus that spring runoff's also should be taken into consideration as my wetlands are all situated in Northern Ontario and most of them are flooded during the spring. I'm liking the hydraulic retention time to determine field capacity, thank you M.I.M. I didn't think o that one! Beate I am hoping to measure the flow of water around the root systems so basically through a core sample if it ends up being a lab experiment.

Looking forward to any helpful responses. Thank you so much in advance.

Like Mowjood and Beate say, more details on wetland type would help design weirs or some other methods of capturing and measuring flow. Is it surface or subsurface flow that you are interested in ? Also, for quantifying N and P uptake, you would need to analyze foliar N and P, apart from the N and P concentration in soil water. Are you looking to relate flow with uptake, or just need flow for the N and P flux ?

Sorry Beate I didn't answer your last question. Not sure by what you mean by scale, but I have 30 sites that I would like to measure.

one way to detect and estimate subsurface flow in a wetland would be to install two wells spaced some distance apart, and monitor water levels, and use the difference in levels as the head for D'arcy's law. Locating the wells is key to detecting any hydraulic head, and one can get clues from any excisting surface seeps, or even from the way wetland plants are distributed. I do not think there can be that great a range of flow in the subsurface environment, to categorize as high or low flow, given the high resistance posed by the soil (you mention clay and loam). P also gets immobilized very quickly onto the soil surface, and usually its mycorrhizae and fine roots that play a big role in P uptake. It would still be interesting to compare flow (both surface and subsurface) with N/P in soil and leaf tissue.

There are different ways to measure water flow in saturated wetland soils depending on wetland types. It would be nice to know what type of wetland soil you are talking about. Some of the methods are by tracking oxygen isotopes of water (difference between O16 and O18 gives water flow. Increase in flow generally means high O16. Another technique is by using tracer. Hope this is helpful.

Amartya, I still have to do the N & P quantification in the plant organs, I will be comparing these ratios in the roots, storage organs, shoots, leaves and inflorescence. Unfortunately I have a very limited budget so I couldn't use isotopes, we are looking at whether the nutrients are reallocated or released back into the environment. I haven't looked at soil water nutrient content, but have looked at soil nutrient content. I am hoping to see a difference between two strategies ... unfortunately I can't go into too much detail on the species ... As I mentioned before I am looking at wetlands where there are no surface flow or very little, to areas where the plants are immersed in water either at the edge of a river or lake. I'm interested in the subsurface flow as I am studying the root systems of the plants in particular and differences between the two systems. Bhanu, I am looking at soils with extremely high organic content to extremely low. Including the clay and loam, I also have organic soils and sandy soils. I am will also be comparing the organic matter content of the different sites. My question is pretty big, and I expect I probably won't answer it completely, but am hoping that my study will lead to further studies that will eventually answer my overall question. The wetlands also display a wide range of oxic to anoxic conditions. As my supervisor and committee keeps saying, its an M.Sc. not a PH.D. but I would love to do more...

I have a kettle lake that is almost completely covered with sphagnum, as well as a large stream system that has been almost completely covered by sphagnum. I'm not completely sure what the water source for my third sphagnum site is. My fourth is definitely a ombrotrophic bog. I do not have fens, as all of these sites are acidic. When I did a phyto-assay measuring growth rates of micro-algal communities (greens) these sites had very low RGR's.

It sounds like an alluvial system (or periglacially derived) that is likely to have a complex of laminated and channelized porous sediment layers threading through less permeable layers rich in fines. Therefore subsurface flow could be very complex and determined by the vertical intersection of each wetland with buried porous laminates that carry various sources of hyporheic flow. Short of tracers and a high-resolution well grid, I don't know that you can do much more than a rough categorical characterization of throughflow.

But at your latitude, you should consider temperature as a marker, in combination with seasonal variation in stage (water level). Both are inexpensive to measure, but require some time in the field. In the floodplain wetlands I've worked in, temperature variance within the pool is a rough indicator of inflow. As a rough approximation, and after accounting for depth and area, etc., wetlands with very limited throughflow tend to lose stage and go dry in summer, those with smallish throughflow tend to maintain more consistent stage, but get uniformly warm in summer; those with intermediate throughflow tend to maintain stage and show evidence of thermal stratification, with cold pockets at inflow sources; and those with very high throughflow maintain stage and tend to maintain more complete thermal mixing and to remain cooler overall through the summer. I learned and verified this in the field, but there's probably some relevant published literature describing it as a general case, perhaps from one of the European research groups--e.g., search some of the pubs of Claude Amoros and colleagues (http://umr5023.univ-lyon1.fr/index.php?pid=244&)

Thank you Christopher, that is actually promising because we had data-loggers planted at 10cm and 30cm depths in all the wetlands and the temperature was continuously monitored over a 12 month period. I can use your logic to ascertain whether my systems are at least high or low flow. We also measured water level throughout the spring and summer and I will take another look at that data with your comments in mind. I can also take a look at rainfall for the season and use that in combination with the water levels to make sure that rainfall is the sole source of inflow for some of the wetlands.

In one of our study we used to measure temperature as an indicator for water flow using thermoprofiler. Our data logger was close to the channel bottom, along with that we had 10 cm, 20 cm, and 30 cm below the surface. These four logger were attached to one long pvc pipe. That was not that expensive and was useful in measuring surface and subsurface flow (by taking temperature change as an indicator). Hence, it might be a handy one.

Thank you Bhanu. Did you use the difference between the four data loggers per site or the difference at each depth over time? I'm thinking that if the temperature is different at different depths, i.e. colder then the flow would increase at depth? I am considering a percolation experiment to measure vertical flow in addition to horizontal flow for the sites that depend mainly on rainwater for saturation. Did you perhaps publish a paper that I could review?

We deployed four different data loggers (at the fore mentioned depth) per site. We got pretty good information about water flow. You can run percolation experiment side by side as supporting data. No we have not published.

Hi Susara, when I was talking about scale, I meant the size/scale of your study design, such as catchment scale, plot scale, or - as it seems for your case - scale of rhizosphere. The scale of your study is critical for designing any flow experiment. A catchment approach (including weirs, or wells) does not make much sense in case you intend to investigate water flow around your roots (microscale). I am just thinking whether a kind of tracer experiment, (where you measure time of diluation of a tracer around your roots), might help to solve your question.

Hi Beate, yes I am looking at the scale of the rhizosphere, I was thinking of designing a horizontal through-flow system with the soil in containers an pumping the water through the soil at a given velocity, I realize that it would not give me the actual flow that would be found at the natural sites, but it would give me the potential flow for the soil with respect to the material that it is composed of. I could use my datalogger information, as mentioned by Bhanu, to see how accurate the set up is. In-situ would be very hard with lack of funding so I might have to make do with approximation.

I would also have to take into account the fact that if I remove soil from the sites then I am also modifying the structure. I need to register for a PH.D. I think. ;-)

Hi Susara,

I like the idea of a container. It might even be possible to do this kind of experiment in the field. In case it is sufficient for you to get relative data, i.e. where you compare the flow-through between several sites, you might install such a kind of porous container as close as possible to your experimental site, apply a defined amount of tracer within the container and measure the time of the dilution of your tracer (i.e. through salinity measurements). This is just an idea, I have never done such experiment before, but you might think about it. Using a container in the lab with a predefined pumping rate will hardly give any information on the flow in the field,. you only get information on the hydraulic conductivity of your soil type. Yeah, your research project is comprehensive enough for a PhD :-)

Thank you Beate, I'll take that to my supervisor. We also have to consider the fact that the roots are changing the soil as it grows every season. I'm learning that ecology is a very variable science ;-).

you are welcome! Good luck with your research!