 My name is Perin Hamel. I'm a hydrologist at the Natural Capital Project and in this video I'm going to present the nutrient retention model. So the model is very similar in terms of objectives and approaches to the sediment retention model. If you're familiar with the latter, it's going to help understanding the concepts. So like most invest models, we can describe the nutrient retention model in terms of supply, service and value here at the bottom of the slide. Starting with the end, the value of the nutrient retention can be understood in terms of improvement to water quality for drinking water and freshwater ecosystems. So typically we're looking at nitrate, nitrogen or phosphorous that are going to have an effect on the water quality. Moving backwards, the service that is of interest is the water purification and this service is provided by the natural landscape. So depending on the location with regard to the stream or areas of high nutrient production, these natural landscapes are going to retain more of the nutrients. So in short, the model helps answer questions like how much nutrient, how much phosphorous or nitrogen are retained on the landscape? Where is it retained and then how does this nutrient retention benefit people? So going more into details, the model first computes the sources of nutrients and they are defined spatially. So say a user has a piece of land with a forest or agriculture and urban areas, each cell is assumed to have a characteristic nutrient load. And so the local literature will help inform these values since they are obviously dependent on the agricultural practices or stormwater management in urban areas. The model represents the transport of the nutrient and it does so with two components. First, the upslope area, which looks at the flow and the amount of energy that is available to transport nutrients from the pixel of interest to the stream and also the downslope component. So this second component looks at the potential for the areas on the downstream flow path to retain nutrients before it reaches the stream. So this depends on the distance, the slope or the retention capacity, say of a natural forest as opposed to bassoid, for example. So this very simple representation of nutrient generation and retention means that there are limitations to the model. You see the biogeochemical processes involved in the nutrient dynamics are much more complex and depend on factors like temperature, flow rate, and they are represented here in a lumped way. In-stream processes like dams or retention of nutrients along the stream also poorly represented in the model, which needs to be considered when interpreting the results. So the model is not a design tool. It represents long-term trends. Finally, calibration data is needed to gain confidence in the quantitative export predicted by the model. So this will have consequences also for the valuation step. So moving on to the inputs, what do we need to run the model? First information about topography, the digital elevation model or DEM, land use land cover and the spatial distribution, the water sheds, so these areas that drain to a single point in the landscape, and then socio-economic data to inform the valuation step. With these inputs, the model is going to produce the nutrient exported for each subcatchment and the nutrient retained, and also the value of the nutrient retained in terms of avoided treatment, for example. So as a summary, going back to the overview slide, you can see how the biophysical part of the model can be used to inform this production of service and benefits provided by different parts of the landscape. So it's really this understanding of the nutrient dynamics that can be used in combination with other ecosystem services to inform land management decisions in general.