SS3.06 Large Scale Change in Prominent Ecosystems
Date: Wednesday, June 12, 2002
Time: 4:00:00 PM
Location: Lecture Theatre
 
GardnerWS, Univ of Texas Marine Science Institute, Port Aransas, TX, USA, gardner@utmsi.utexas.edu
An, S, , Kyungnam University, , Republic Of Korea, sman@kyungnam.ac.kr
McCarthy, M, J, Univ of Texas Marine Science Institute, Port Aransas, TX, USA, markm@utmsi.utexas.edu
 
Potential changes in nitrogen dynamics caused by decreased freshwater flow to semi-arid coastal ecosystems
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Population growth in coastal areas leads to competition for freshwater resources between natural and anthropogenic interests in semi-arid coastal regions such as south Texas estuaries. Resulting impairment of freshwater inflow to estuaries causes increases in salinity and, thus, sulfide, which inhibits nitrification/denitrification (a nitrogen sink). However, sulfide enhances dissimilatory nitrate reduction to ammonium (DNRA), which keeps nitrogen in the system in a reduced form. Studies at the University of Texas Marine Science Institute indicate that potential DNRA rates are higher than denitrification rates in hypersaline regions (upper Laguna Madre and Baffin Bay, Texas). Conversely, DNRA rates were negligible in low salinity areas (Sabine Lake) and intermediate at mid-salinities (East Matagorda Bay). This effect on nitrogen biogeochemistry may be a factor in the occurrence and longevity of harmful or nuisance algal blooms, which prefer or require reduced forms of nitrogen. For example, the Texas brown tide (TBT) organism (Aureomonas lagunensis) cannot assimilate nitrate but thrives on ammonium. This effect may help explain why TBT has persisted, especially in summer, in hypersaline South Texas coastal waters since at least 1990.