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Water quality of the tidal Arroyo Colorado of Texas along a salinity gradient.

Sat, March 3, 10:00am to 12:00pm, Marie Hall Building, Corridor B

Abstract

The tidal section of the Arroyo Colorado (AC) is a mesohaline stormwater, agricultural and municipal drain that empties into the Laguna Madre. The AC, it is one of the most polluted bodies of water in the state of Texas. Inorganic nutrients and fecal bacteria exceed environmental thresholds. This can lead to algal blooms, diminished light levels, oxygen deficiency and increased rates of respiration. Salinity can diminish some pollution effects. We investigated a possible relationship between salinity and water column inorganic nutrients (nitrate, ammonium, and phosphate), underwater light, dissolved oxygen and partial CO2 (pCO2)2 at four sites along a salinity gradient. Nitrate concentrations were undetectable farthest upstream but decreased at sites closet to the mouth of the AC. Ammonium and phosphate at the site farthest upstream were substantially higher than all other downstream sites. Underwater light was highly variable and the percentage of underwater light decreased from upstream to downstream in the AC, with greatest percent irradiance at the mouth of the AC. There was a clear decreasing trend in DO from upstream to downstream. We used pCO2 concentrations as a proxy for respiration. pCO2 at the sites farthest upstream where nearly identical and dropped significantly before the mouth of the AC and significantly rose again at the mouth. The pCO2 concentrations at the AC Mouth were almost the same as upstream AC values. AC water was strongly colored and suggests bloom conditions. If photosynthetic rates were high, they could have been overwhelmed by substantially greater respiration rates.

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