Prenart tension lysimeters at HJ Andrews (WS 10)

For my master’s work at Oregon State University I examined nutrient flux in watersheds at small and large scales. My research interests revolved around hydrologic processes that control nutrient export.

It is understood that most of the organic matter in small streams comes from terrestrial sources, how these organic constituents reach the stream channel and what controls are exerted over these export processes is not clearly understood. My work characterized dissolved organic matter (DOM) to clarify sources of organic matter to streams at my research site in the HJ Andrews Experimental Forest (HJA).

The gauged hillslope trench at watershed 1

DOM in streams plays a strong role in controlling stream chemistry and nutrient supply – critical for the floral and faunal inhabitants of the stream. DOM can also influences the transport of heavy metals (i.e. Mercury). Also, high organic matter concentrations in drinking water facilities can contribute to the creation of secondary chemicals as a part of the chlorination process. DOM is not a homogenous entity and the variable quality and quantity of DOM has wide-reaching impacts.

In the temperate rainforests of the Pacific Northwest, where my research site is located, rain dominates the calendar from

Sampling lysimeters

October through May. During the summer months, little precipitation falls and moisture becomes depleted

from the soil profile. Organic matter, which is produced and decomposed during the highly productive summer months, is largely restricted to the soil profile and remains upslope from the stream channel. The onset of the rainy season in the fall produces a strong flushing effect, wherein the stored organic matter is quickly released to the streams.

Hydrologic studies in the watersheds of the HJA indicate that a significant portion of the stream water during the winter come from groundwater sources. If groundwater dominates the winter hydrograph, why is there such a strong flushing effect? During the winter hydrograph, the proportion of water in the stream from groundwater fluctuates, with multiple flow processes contributing to the stream. How do the changing flowpaths affect the quantity and quality of DOM exported to the stream? Where in the watershed does stream DOM emanate and does this source change throughout the year or even during individual storms? My work addresses these questions.