Assessing the Linkages Between Tree Species Composition and Stream Water Nitrate in a Reference Watershed in Central Appalachia
Abstract
Many factors govern the flow of deposited nitrogen (N) through forest ecosystems and into stream water. At the Fernow Experimental Forest in WV, stream water nitrate (NO3) discharge from a long-term reference watershed (WS 4) increased around 1980, presumably due to chronic N deposition. Around the same time, the species composition of the forest was also changing in ways that could potentially alter forest N demand and the retention of deposited N. In particular, there was an increase in the importance of Acer saccharum - a species thought to have a low affinity for NO3. Thus, we measured the relative uptake of NO3 and ammonium (NH4) by six important temperate broadleaf tree species, including A. saccharum, and estimated stand uptake of total N, NO3, and NH4. We then used long-term records of stream water NO3 and stand composition to evaluate the potential impact of a change in species composition on NO3 discharge. Surprisingly, the tree species we examined all used both mineral N forms approximately equally. Overall, the total N taken up by the stand into aboveground tissues (wood and leaves) remained relatively unchanged from 1959 through 2001 (51.3 to 51.5 kg N ha-1yr-1). Therefore, a reduction in the stand N demand did not contribute to the 5.6 kg NO3-N ha-1yr-1 increase in stream water NO3 discharge from 1975 through 1984. However, the changes in species composition may have increased the net supply of NO3 in the soil, since A. saccharum is typically associated with high soil nitrification rates. We estimate this potentially resulted in a net increase of 3.2 kg N ha-1yr-1 available for leaching from 1959 through 2001, accounting for a significant fraction ( 57%) of the elevated stream water NO3 discharge and contributing to the low inorganic N retention observed in WS 4.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B53K2208P
- Keywords:
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- 0444 Evolutionary geobiology;
- BIOGEOSCIENCESDE: 0465 Microbiology: ecology;
- physiology and genomics;
- BIOGEOSCIENCESDE: 0469 Nitrogen cycling;
- BIOGEOSCIENCESDE: 4870 Stable isotopes;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL