Downstream effects of restored freshwater inflow to Rincon Bayou, Nueces Delta, Texas, USA |
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| Authors: | Terry A Palmer Paul A Montagna Richard D Kalke |
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| Institution: | 1. University of Texas Marine Science Institute, 750 Channel View Drive, 78373, Port Aransas, Texas
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| Abstract: | Construction of two dams in 1958 and 1982 decreased freshwater inflow to the Nueces River and Nueces Delta marsh, which has become a reverse estuary where salinity increases upstream rather than downstream as would occur in a normal estuary. In 1995, an overflow channel was dug to breach the banks of the Nueces River to restore inundation of the marsh via Rincon Bayou, which is the main stem channel of the delta. Previous studies demonstrated a restoration of a normal salinity gradient and positive affects on benthos in the upper reaches of Rincon Bayou. The present study was performed to determine how far downstream the overflow channel had beneficial effects. A transect of eight stations was established and sampled quarterly between October 1998 and October 1999. Benthic characteristics were measured to assess ecological change. There were 12 precipitation and freshwater inflow events between the month preceding and ending sampling. The largest were in fall and restored normal salinity patterns. The macrobenthic community was different in three zones. The upper four stations (<6.4 km from the overflow channel) were highly variable in water inundation and salinity. The broad salinity range caused the lowest diversity and allowed short-lived pioneer speciesStreblospio benedicti, Laeonereis culveri, and Chirominid larvae to dominate. Biomass blooms occurred during fall inflow events in the upper reaches. The central stations (11.4 to 14.3 km from the overflow channel) were brackish, had more narrow salinity ranges, and were more diverse.Mulinia lateralis, Mediomastus ambiseta, Cerapus tubularis, andAmpelisca abdita were dominant species. The third zone, the lower portion of Nueces Bay (27 km from the overflow channel), was distinct from other stations in the transect, because it had the greatest marine influence. It is in a later successional stage, with a more diverse community of larger organisms, e.g.,Polydora caulleryi, Tharyx setigera, andMysella planulata, which were dominant species and contributed to the larger biomass there. Overall, the overflow channel restored normal salinity patterns in the upper reaches (<14 km) of Rincon Bayou and freshwater pulses (>106 m3) in fall increased benthic productivity indicating ecological functions were restored as well. This restoration however, only occurs intermittently for short time periods because the freshwater events are isolated and inflow volumes during the current study were too small to affect the lower Rincon Bayou or Nueces Bay. |
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