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Community primary productivity patterns along a salinity gradient in the Lower Laguna Madre of Texas

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

Abstract

The Laguna Madre (LM) of Texas is an historically hypersaline lagoon along the Gulf of Mexico bordering several counties. The Arroyo Colorado (AC) is a mesohaline stormwater, agricultural and municipal drain that empties in to the LM. Both hyper- and hyposalinity can influence primary productivity. We examined the effect of salinity on primary productivity rates at four sites along a north-south transect during June 2017. There was a clear south to north geographic trend in primary productivity rates and salinity. Primary productivity was inversely related to salinity. Lowest rates were found nearest the southernmost Brazos-Santiago Pass (B-S) (salinity of 33; 0.94 µmol O2 hr-1). Highest rates were at the confluence of the Lower LM and AC (2.50 µmol O2 hr-1; salinity of 39). The mesohaline AC upstream site had the lowest mean rate (0.70 µmol O2 hr-1; salinity of 18). Respiration rates were nearly equal for all LM sites (0.20 to 0.17 µmol O2 hr-1; salinity range of 33-39), but were more than three times greater in the mesohaline AC Upstream site. Water column inorganic nitrogen (NO3- and NH4+) concentrations ranged from undectable to 1.0 ppm. Secchi depth ranged from 80 cm nearest the tidal pass (B-S) to 23 cm at the AC Upstream site. Primary productivity and respiration rates at the AC Upstream site reflect the dual influences of salinity and water clarity. The AC, as a municipal drain, may carry a substantial bacterial load with correspondingly high respiration rates.

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