Posted on December 6, 2024 in ASRC News, Environmental Sciences Initiative, Uncategorized
Nicolas Maxfield is a graduate student in the lab of Professor Charles Vörösmarty, director of the Environmental Sciences Initiative at the CUNY ASRC, whose doctoral work focuses on modeling various factors that affect the movement of nitrogen across land and water. Maxfield and Vörösmarty’s work has been supported by two major grants in the last few years: one from the National Sciene Foundation (NSF) and a recent grant from NASA. We caught up with Maxfield to learn all about these exciting projects.
What is your NSF funded project about?
Maxfield: Up until the beginning of this, year my work has focused on an NSF-funded model framework called Climate-induced Extremes on the Food, Energy, Water Nexus (C-FEWS). The goal of this project is to test nitrogen systemic responses to management practices, technology, and policy strategies. These systemic responses include issues of water quality, energy supply, and agriculture, hence the food-energy-water nexus in the name. We then look at all of this within the context of climate change and climate extremes.
The project brings several modelers together to try to integrate their simulations across different factors, like water quality and carbon sequestration, into one clear model. Our solution was to create a single delta factor that can be used to compare different models.
How does the model work?
Maxfield: Our baseline model works off data from 1980 to 2019, from which you can derive a yearly output of total nitrogen in rivers and streams. Then we can ask, ‘what if we turn off X or Y management factor?’ For example, if we turn off tile drainage, do we suddenly get a change in movement of contaminants from the fields to the rivers? By changing the parameters, we can compare the impacts of management, technology, policy, and climate on nitrogen across several systems. Our models are also calibrated to various meteorological inputs that can be also tested. We can subject the system to sequences of droughts or heat waves or extreme precipitation and see what happens. Climate change will cause massive fluctuations in temperature and in precipitation that will vary geographically, in terms of duration and intensity. Those are all things we wanted to test within the parameters of our various models.
ISo using C-FEWS you can change different factors in the past to see how the data changes, and compare it to the real data? Can you use this to predict how these changes will impact the future?
Maxfield: The temptation to project into the future is really big, and although we did do a little in our modeling, its complicated because it requires depth and breadth of knowledge that are often beyond what any one specific scientist or group of scientists might be able to provide; Especially if you want to figure out the impact of different mandates, because it may not be realistic to say something like ‘we’re going to mandate that we reduce nitrogen fertilizer application by 50%’. It seems like a made-up number at that point. But if we instead ask what people were doing 40 years ago and is the nitrogen deposition better or worse than what we’re doing today, then we can get a picture of what is not only impactful but feasible.
What did you find most interesting in your modeling?
Maxfield: There are interesting interactions that the model picked up between the occurrence of drought and heat waves, as well as wet periods and cold waves. In a way, it strengthens what we already knew about the relationship between temperature and nitrogen flux. But these statistical relationships suggest more nuanced processes are happening at the biochemical level, during the nitrogen cycle, that are changing the availability of stored nitrogen in the soil. When you apply nitrogen to the soil in the form of fertilizer, a certain amount gets taken up by the plants, and the rest gets leached among the soil, atmosphere, groundwater, and nearby rivers. We found that the amount entering the rivers was increasing following droughts, which was interesting, because one would assume the opposite based on what we see in dynamic short-term models. What we think is happening is in these times of extreme drought, there’s an increase in plant mortality which increases the amount of detritus. Because of the lack of moisture in the soil, due to dry conditions, you’re less likely to have bacterial microbial processing of nitrogen which turn it into a gas, meaning more nitrogen is available for flux into the rivers whenever the next rainfall occurs.
Can you tell me about the NASA project, and how it relates to C-FEWS?
Maxfield: You can think of the NSF model as inputs and outputs, changing what’s going in, thereby, changing what’s coming out. A lot of that is linear, like if you lower the amount of nitrogen applied, it’s going to just reduce the amount of nitrogen coming out. But we noticed some responses were nonlinear and seemed to be happening at a nitrogen cycle level. The NASA project uses a framework called Climate-event Framework for Analysis of Macro-Environmental Systems (C-FRAMES) to look dynamically at nitrogen over several different domains, including terrestrial loading, gas emissions, nitrogen in the rivers, and coastal nutrient blooms. The focus of the NASA project is on what’s happening chemically within the nitrogen cycle as nitrogen transitions between these domains of land, water, and air, with a particular focus on the Mississippi River/Gulf of Mexico. We’re working not only with modelers for this project, but also in situ and remote sensing analysts that can measure the changes in mass of nitrogen over short timescales. With this we can try to parse out how the flow of nitrogen is contributing to the duration and extent of coastal hypoxia in the Gulf waters.
Any findings from the NASA project to share?
Maxfield: The grant is new, so we’re still in the tinkering phase, but we’re starting work on some really interesting stuff.
What’s your role for these different projects?
Maxfield: I’m a modeler, but I am also what I call a ‘cat herder’. I get everyone together at meetings to present their findings and coordinate our work, so we don’t go off in different directions. I bring together the modelers, the analysts and researchers, as well as stakeholders, which help us develop research questions that meet their practical goals.
What are you interested in studying as your work continues?
Maxfield: One of the things I’m very interested in is the concept of nature-based infrastructure, and how it compares to traditionally engineered infrastructure. Specifically, what nature with its natural filtration is capable of assimilating versus what we would have to actively remove through machines. One example is how denitrification is higher in slower moving rivers, due to less dissolved oxygen. So long, slow moving rivers perform a cleaning function in that regard. Compare that to treatment facilities which remove nitrogen pollution from downstream. They only work on point source nitrogen, and don’t do anything for fertilizer or manure pollution. You probably can’t rely on nature-based infrastructure around big population centers, but in areas like the Midwest, where there is a lot of non-point source nitrogen pollution and longer rivers are already present, this could be something to explore to help with denitrification.