Abstract:

Discharge was sampled daily at two stations in the Guadalupe and Tres Palacios Rivers to estimate freshwater inflow to estuaries. The Guadalupe Estuary’s average monthly freshwater inflow rate was 92% higher than the Lavaca-Colorado Estuary, so a larger flow volume increase is necessary to affect estuarine health in the Guadalupe Estuary. This analysis indicated that an increased small volume, as low as 10% of freshwater inflow volume, can have positive benefits to estuarine conditions and health. Thus, hydrological protection or restoration projects based on small volumes can improve estuaries degraded by freshwater diversions. An accompanying study conducted simultaneously contains nutrient, chlorophyll, and benthic community data (HI.x962.000:0018, https://doi.org/10.7266/6ptst906).

Suggested Citation:

Montagna, Paul A. and Cheyanne M. Olson. 2025. Effects of small freshwater inflow volumes on water and sediment quality based on USGS gaged flows from 2015-09-30 to 2016-09-15. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/0y56trjr

Purpose:

The aim of this study was to evaluate the potential environmental benefits of hydrological conservation or restoration projects by quantifying the effects of small changes of inflow volumes on estuary ecosystem health. Discharge at the two gage stations was compared to water quality (indicated by nutrients and chlorophyll) and sediment quality (indicated by benthic communities) sampled monthly at five stations in the upper reaches of the Guadalupe and Lavaca-Colorado Estuaries. Distinct oligohaline and mesohaline benthic communities were present in both estuaries. A positive correlation between multivariate water quality and benthic metrics indicates a positive relationship between small flow changes and estuarine health.

Data Parameters and Units:

Gage Discharge (cubic feet per second, cfs), Gage Discharge (acre-feet per day, ac-ft/d), Gage Discharge (million cubic meters per day, m³/d), Cumulative Discharge (million cubic meters per sample period, m³), Salinity (practical salinity units, psu).

Methods:

Hydrological flow rate data from 2015-09-30 to 2016-09-15 was obtained from the United States Geological Survey (USGS: http://nwis.waterdata.usgs.gov). Two USGS stream gaging stations were located near the sampling locations and recorded daily inflow amounts. USGS Station 08188810 (28.478052 latitude, -96.861812 longitude) is located on Guadalupe River. USGS Station 08162600 (28.927778 °N latitude, -96.170832 °W longitude) in Tres Palacios River. Because there is no gage on creeks entering Carancahua Bay, inflow was substituted using USGS flow data for the USGS Station 08162600. The National Climatic Data Center (NCDC) station at the Palacios Municipal Airport was located between Carancahua Bay and Tres Palacios Bay (28.72472 °N latitude, -96.25361 °W longitude) and recorded daily precipitation and wind data.

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