Long-Term Response of Benthic Organisms to Freshwater Inflow in Texas Coastal Bend Estuaries




Montagna, Paul A.


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The main difference between the Guadalupe and Lavaca-Colorado Estuaries relate to both size and Gulf exchange. Freshwater inflow has a larger impact on the smaller-restricted Guadalupe Estuary than in the Lavaca-Colorado. Both the smaller size and restricted inflow have synergistic effects, thus the Guadalupe is generally fresher and has higher carbon content than the Lavaca-Colorado. These conditions lead to higher benthic productivity in the Guadalupe Estuary. On the other hand, higher salinities and invasion of marine species is responsible for a more diverse community in Lavaca-Colorado Estuary. There is long-term, year-to-year variability in inflow. Higher inflow introduces higher values of dissolved inorganic nitrogen, which in turn stimulates primary production. The higher primary production, which is ephemeral and changes on very short time scales (days to weeks) drives benthic production, which changes over longer times scales (three to six months). Typically, nitrogen (which is derived from inflow and processed by estuarine organisms) is lost within the top 20 cm of sediment. Inflow also drives benthic community succession, due to different salinity tolerances of fresh, brackish, estuarine, and marine species. Due to the species changes and time scales of effects, the signal of inflow effects is easiest to measure and monitor using benthos as indicators. It is also apparent that long-term changes may be related to global climate cycles, e.g., El Niño events in the western Pacific Ocean. This study has benefitted by a statistical quirk (or trend) in climate data. There have been 11 El Niños in this century, three occurred in the first half and 8 have occurred in the second half. This short study (only 12 years) has captured three events. Because the long-term global cycles can vary from three to 20 years in length, long-term monitoring data will be required to develop reliable quantitative estimates of productivity versus inflow. Because the last few decades have been unusually wet, estimates based on the current study are likely to be over-estimates of the long-term average.






Montagna, P. A. 2007. Long-Term Response of Benthic Organisms to Freshwater Inflow in Texas Coastal Bend Estuaries. Interim Performance Report to Texas Parks and Wildlife Department. Contract #172621. Harte Research Institute, Texas A&M University-Corpus Christi, Corpus Christi, Texas, USA, 18 p.