Research

My research explores biogeochemical connections between land and water at landscape to macrosystem scales.  I use a combination of field/lab methods, satellite remote sensing, and GIS analyses to examine ecosystem processes of estuaries, rivers, and lakes. My CV is available here. If you have questions about my research, please don't hesitate to contact me!

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Biogeochemistry of big Arctic rivers 

While small streams are responsible for much of the biogeochemical cycling in the Arctic, major rivers systems represent a conduit of organic matter, nutrients, and sediments to the coastal Arctic ocean. In a rapidly changing climate, these fluxes of terrestrially-derived material are sensitive to shifts in temperature, hydrology, permafrost thaw, and other watershed processes. I use a combination of field, lab, and satellite remote sensing to understand how big river systems in the Arctic respond to climate, and what the fate of riverine material might be in the Arctic Ocean.

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REMOTE SENSING OF WATER QUALITY IN TEMPERATE LAKES

The Upper Midwest (MN, MI, WI) is dotted with tens of thousands of lakes of different colors, trophic states, sizes, and watershed features.  Remote sensing allows us to map colored dissolved organic matter (CDOM) across the region, and use that data to explore watershed controls on lake chemistry; trends in lakes DOM through time; and model lake DOM storage.

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Coupled Built-Natural Systems in the Arctic

Not only is the Arctic responding rapidly to climate change, but development and human activities are changing and expanding. Planning for the New Arctic will require an integrated understanding of natural and built systems, from the human to landscape scales.

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STORM-DRIVEN NITROGEN EXPORT TO TEXAN ESTUARIES

Nitrogen from agricultural run-off and wastewater drives estuarine eutrophication. In coastal Texas, alternating wet-dry years results in large variations in nitrogen delivery from rivers.

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Carbon and Nitrogen cycling in permafrost polygons

Tundra landscapes feature geometric, polygonal patterns, created by the development and degradation of ice wedges. The mechanisms of carbon and nitrogen cycling by water, plants, and soils in these changing landscapes remains poorly understood.

 
 
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Organic matter in Arctic Rivers

Remote SEnsing of DOM

Colored dissolved organic matter (CDOM) is a useful proxy for dissolved organic carbon in Arctic rivers, an important part of the carbon cycle and source of energy and nutrients to aquatic and estuarine microbes. I built remote sensing models for six large Arctic rivers to estimate CDOM (Griffin et al., 2018a), then applied those models to historical imagery from 1985 - 2017 (Griffin, 2016).  Time series analyses showed increased discharge-normalized CDOM in the Ob' River, where warming likely led to DOM mobilization from extensive peatlands. The adjacent Yenisey River, in contrast, decreased in discharge-normalized CDOM. The Yenisey lacks the deep, extensive peatlands on the Ob', and as permafrost thawed, hydrological flowpaths deepened and flowed through more mineral soils.

River export of OM

I have been lucky to be involved with the Arctic Great Rivers Observatory, which provided the data used for my remote sensing methods. Methodologically-consistent, seasonally explicit sampling of large river mouths allows researchers to quantify how much terrestrial material enters the Arctic Ocean, and use biogeochemical signals as indicators of widespread change throughout a watershed. Through Arctic-GRO, I have contributed to work on fluxes of particulate organic matter (POM), addressing the variability in export driven by both seasonal and annual hydrology (McClelland et al., 2016). Organic matter in Arctic rivers generally increases in age by the end of the ice-free season. Radiocarbon dating of lignins demonstrated that such ancient pools of carbon are far more prevalent in the Kolyma River than the Mackenzie River (Feng et al., 2017).

 

 
 
 
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CDOM in Midwestern Lakes

Watershed controls on Lake chemistry

Our group on Remote Sensing of Water Resources at University of Minnesota is working to produce maps of remotely sensed CDOM, chlorophyll-a, and suspended sediment in 10,000+ lakes across MN and parts of WI and MI. With such a rich dataset, I am exploring what watershed characteristics control the wide variety of lake types within this geographic region. Wetlands and land cover, lake connectivity, and lake morphology all influence CDOM, and can limit the reliability of CDOM as proxy for DOC (Griffin et al., 2018b).

Time Series analysis of CDOM

Using Google Earth Engine, our remote sensing algorithms developed recently can be applied to historical Landsat imagery dating to the 1980s. Other boreal and north temperate regions, particularly the Northeast USA and Scandinavia, have shown increases in DOC and CDOM over the past thirty years, but this has not been well constrained for the Upper Midwest. Preliminary time series analyses show little unidirectional change in CDOM in our study area, however, possibly owing to differences in acid rain impacts and climatic change compared to the NE and Scandinavia.

 
 
 
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Natural and Built Landscapes in the Arctic

Sensor networks from human to landscape scales

I joined the Arctic CoLab at the University of Virginia in 2019, a team that links environmental science, architecture, engineering, and landscape design. We are developing a project to install sensor networks in Utqiagvik, Alaska that would span the watershed to human scales. We plan to explore how human activities impact the surrounding landscape, while the environment itself constrains development and behavior, all in a climate change context. I am particularly interested in how nearby lagoons - the drinking water source, and the sewage treatment facilities - will be impacted by coastal erosion, human development, and permafrost thaw.

Convergence and Co-Production of Knowledge

Our work in Utqiagvik centers on input from the local community and North Slope stakeholders. We are seeking the perspectives and cooperation of organizations like the North Slope Borough, the Cold Climate Housing Research Center, Ukpeagvik Inupiat Corporation Science, and others to help us determine target areas of research. Our ultimate goal is for the knowledge we produce to enhance both our fundamental understanding of Arctic processes, and be a tool for local stakeholders to use in planning for a more sustainable future.

 
 
 
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Nitrogen in Texas Rivers

Storm Driven Nitrogen Export

Water quantity in Texas rivers is dominated by two factors: reservoirs and storms. While the Texas legislature has mandated episodic releases of water from reservoirs to help maintain salinity regimes in estuaries, the difference in nutrient export from these releases and more "natural" storm events are poorly understood. We studied six rivers across a climatic and land use gradient in coastal Texas to examine these two types of hydrological events. Storm events, especially in small rivers, dominated both water and nitrogen export (Griffin and McClelland, in prep) except in the Nueces River, which has a reservoir very low in the watershed.

climate, land use, and estuarine production

The data collected along these six rivers was part of a larger project linking climate, land use change, river routing (Tavakoly et al., 2016), and nitrogen export as drivers of estuarine productivity. The holistic approach of this project aimed to integrate  climate, hydrological, and productivity models from land to sea.

 
 
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Permafrost Polygons

Aquatic organic matter

As part of my postdoc with Howie Epstein at UVA, I’m joining a project that aims to understand how the physical degradation and stabilization of permafrost polygons interacts with carbon and nitrogen cycling. In summer 2019, I will be collecting data on the composition, quantity, and lability of aquatic organic matter, from ice wedges, pore water, and surface waters in northern Alaska. This will complement ongoing efforts to understand carbon and nitrogen dynamics in soils and vegetation.

Stable isotopes

As ice wedges thaw, land subsides low-centered permafrost polygons with ponds shift to high-centered ponds, surrounded by troughs of water. I am analyzing stable isotope data of terrestrial vegetation and soils (particularly the active layer), to understand how this process might impact processes like water use efficiency, plant functional types, and microbial activity.