Designing a Sensor Network to Investigate how Redox Regimes Control Iron and Phosphorus Biogeochemistry

Title: Designing a Sensor Network to Investigate how Redox Regimes Control Iron and Phosphorus Biogeochemistry

Investigators: Dr. Lauren Kinsman-Costello (College of Arts and Sciences)

Collaborator: Dr. Elizabeth Herndon (Oak Ridge National Laboratory)

This proposal will support a multidisciplinary pilot project in the area of water resources, hydrology, and biogeochemistry by co-Investigators Herndon (Geology) and Kinsman-Costello (Biological Sciences). We will investigate how geochemical and biological processes compete for nutrient phosphorus in soils with contrasting redox regimes, broadly defined by the availability of dissolved oxygen within the system. We first aim to develop a quantitative framework for defining redox regimes in vernal ponds at Jennings Woods. As part of this objective, we will generate time-resolved redox maps that visually communicate our science. We will then couple high-resolution redox data with field experiments on iron-phosphorus interactions. This information will provide critical information regarding 1) how redox potential responds to hydrologic change in soils and wetlands; 2) how biogeochemical processes operate in different redox regimes. The ultimate goal of this local pilot project is to refine methods that will be implemented in an arctic system (Arctic LTER at Toolik Lake, http://arc-lter.ecosystems.mbl.edu/) where redox regimes and biogeochemical cycles are poorly understood and particularly vulnerable to climate change. This proposal describes both the local pilot project to be completed this summer and the long-term project in the arctic tundra for which we will seek external funding.

This proposal is based on initial findings from NSF-funded research into iron-phosphorus associations in high-latitude peat soils. PIs Herndon and Kinsman-Costello previously obtained peat soils from across hydrological gradients (dry to wet) within four long-term experimental sites that span boreal and tundra ecosystems. 

It remains unclear what factors regulate competition between organisms and minerals for phosphate, or over what timescales oxide-associated phosphate is removed from biological cycling. Climate change is likely to strengthen geochemical controls over phosphate availability as more phosphate and mineral binding sites become available due to both gradual permafrost thaw and abrupt exposure of mineral soils during permafrost collapse associated with thermokarst events.

The overarching goal of this project is to investigate how geochemical and biological controls over phosphorus cycling vary under different hydrologic/redox regimes. We will explore redox regimes in a hydrologically dynamic system using data obtained from a network of redox probes. Then, we will conduct field incubation experiments in different redox regimes to assess differences in iron-phosphorus interactions. This pilot project will be refined locally in vernal ponds with the intent to expand to an arctic field site (Toolik Field Station) in the subsequent year. Three redox probes will also be installed by a collaborator in western Alaska in year one in order to test their suitability for arctic environments.
 
The project team (Herndon, Kinsman-Costello, Barczok, Smith) visited Jennings Woods on an unseasonably warm day in January to survey potential field sites. Numerous vernal ponds were identified along a hillslope. Previous chemical measurements indicate that vernal ponds on the upper hillslope are derived from rainwater, while vernal ponds located on the footslope receive groundwater inputs. We identified a candidate pond on the upper hillslope characterized by low conductivity and moderately acidic water that is similar to sites examined in the arctic. The pond is surrounded by elevated ground (“uplands”) that will serve as a relatively well-drained control site.
 
This project will provide preliminary data for a proposal to be submitted to the Arctic Natural Sciences program at the National Science Foundation. Additional products will include time- resolved redox maps used for publications and outreach, and presentations at the American Geophysical Union meeting in December 2018, where the investigators will organize a session on arctic biogeochemistry and current students will present on their pilot project. This project will also allow the PIs to establish a collaboration with Dr. Michael Weintraub at the University of Toledo. The pilot project outlined here is also anticipated to generate two peer-reviewed publications which will be led by graduate students in Geology and Biological Sciences.