Graduate Student Profile Joshua Cain

Joshua Cain, M.S. StudentJoshua Cain

Natural Resources: Soil and Water Resource Management

Advisor: Dr. Wil Wollheim

Research Topic: Dissolved oxygen dynamics and metabolism in fluvial wetlands along a shallow-sloped stream continuum

This research aims to understand the impact of fluvial wetlands, including beaver ponds, on dissolved oxygen (D.O.) and metabolism throughout the headwaters of the Ipswich and Parker River Watersheds, MA, USA, which drain to the Plum Island Estuary. In several fluvial wetland dominated systems, we measured diel D.O. and metabolism in the upstream inflow, the surface water transient storage zones of fluvial wetland sidepools, and at the outflow to understand how the wetlands modify dissolved oxygen. D.O. was also measured longitudinally along entire surface water flow paths (x-y km long) to determine how low levels of D.O. propagate downstream.  Nutrient samples were also collected to understand how their behavior was related to D.O. behavior. In order to calculate reaeration coefficients and metabolism in these wetlands, we used the BASE model presented in Grace et al. 2015 and modified it to incorporate hydrologic exchange between the main channel and storage zone of the wetland. Results show that D.O. in fluvial wetlands has large swings with periods of very low D.O. at night.  D.O. swings were also seen in downstream outflow, though lagged and somewhat attenuated.  Flow conditions affect the level of inundation and the subsequent effects of fluvial wetlands on main channel D.O.. Metabolic rates (GPP and R/day) are higher within the wetland and at the outflow than at the inflow to the wetland, with respiration being greater than primary production during each deployment. Understanding the D.O. behavior throughout river systems has important implications for the ability of river systems to remove anthropogenic nitrogen and reduce loading to coastal zones.