News & Events

Grad student talk - Erosion, soil development and nitrogen in a topographically dissected landscape

Thursday, November 21, 2013, 4:30PM - 5:30PM

Speaker

Samantha Weintraub

Location:

RL-1 room 269

Full title

Erosion, soil development and nitrogen cycling in a topographically dissected landscape, Osa Peninsula, Costa Rica

Abstract

Lowland tropical forests are thought to cycle nitrogen in relative excess because old, highly weathered soils are broadly viewed as poor in rock-derived nutrients, such as phosphorus. However, exposure to diverse geomorphologic and hydrologic processes can give rise to differential weathering and erosion across topographically dissected landscapes, especially those in a transient state. Topographic variation has been shown to influence the availability of rock-derived nutrients, such as phosphorus, through effects on soil erosion and residence times, though analogous effects remain unexplored for nitrogen.

In this talk I will demonstrate that spatial patterns in soil N availability are closely associated with landscape position in a highly dissected, wet (~ 3,500 mm annual rainfall) tropical lowland forest on the Osa Peninsula, Costa Rica. I will discuss how correlations between soil biogeochemical data with soil development and weathering indices suggest a strong geomorphic control on the N cycle. Measurements of overland erosional N transport from this forest suggest that slopewash fluxes (~ 64 mg N m-2 yr-1) are relatively small. However, if slopewash is only ~ 7 % of annual erosion rates (which we think it is), then when all erosion is considered the N flux (954 mg N m-2 yr-1) may be high enough to constrain the accumulation of N within the ecosystem, potentially contributing to N limitation in eroding zones. Overall, these results demonstrate how topography and erosion drive within-watershed gradients in soil N availability, which may be relevant to biogeochemical dynamics in watersheds worldwide.