Abstract:

This study contains data showing effects of small freshwater inflow volumes on water and sediment quality obtained from bays in Texas, specifically Lavaca-Colorado and Guadalupe estuaries, from to 2015-09-30 to 2016-09-15. The aim of this study was to quantify the effects of small changes of inflow volumes on ecosystem health to evaluate the potential environmental benefits of hydrological conservation or restoration projects. Discharge, water quality (indicated by nutrients and chlorophyll), and sediment quality (indicated by benthic communities) were 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. Flow discharge, water quality, and benthic metrics were correlated. The positive correlation between multivariate water quality parameters, and benthic metrics indicates a positive relationship between small flow changes and estuarine health. The Guadalupe estuary had a 92% higher mean monthly freshwater inflow rate than the Lavaca-Colorado estuary, thus a larger flow volume increase was necessary to affect estuarine health in the Guadalupe estuary. This analysis indicated that a 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.

Suggested Citation:

Montagna, Paul A., Hannah Ehrmann, Cheyanne M. Olson, and Evan L. Turner. 2023. Effects of small freshwater inflow volumes on water and sediment quality obtained from bays in Texas from 2015-09-30 to 2016-09-15. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/6ptst906

Purpose:

The study design tests the hypotheses above by examining abiotic (i.e., water quality) and biotic (i.e., sediment quality) responses to freshwater inflow volumes over space and time. Locations closer to the river mouth, which is the source of fresh water, should respond differently than stations further downstream because of the dilution of the freshwater. Over time, the change in inflow is caused by variability in rainfall, and thus the ecosystem should respond to either wetter or dryer conditions.

Data Parameters and Units:

Date (dd-mmm-yyyy), Time (hh:mm), Depth (m), Temperature (°C), Salinity (psu), Dissolved Oxygen (mg/L), Dissolved Oxygen Saturation (%), pH, Chl a (ug/L), Ammonium (μmol/L), Nitrite+Nitrate (μmol/L), Orthophosphate (μmol/L), Silicate SIO4 (μmol/L), Secchi disk depth (m), Turbidity (NTU), Total Suspended Solids (mg/L), Ash-Free Dry Weight (mg/L), Particulate Organic Matter (mg/L), Rubble (%), Sand (%), Silt (%), Clay (%), Porewater (%), Biomass (g/m²), Abundance (ind./m²), Richness (S/sample), Diversity (N1/sample), Diversity (H'/sample), Evenness (J'/sample). Blank cells indicate no data collected.

Methods:

Hydrographic water condition data was collected using multiple YSI Sondes at the surface (directly below the water line) and bottom (approx. 15 cm from the benthos) depths. Water samples were also taken monthly at each station to measure total suspended solids (TSS), nutrients, and chlorophyll-a from surface, bottom and mid depths using a 1-L Van Dorn bottle, and the methods are described in detail in Paudel et al. (2015, http://doi.org/10.1016/j.ecss.2015.02.011; 2017, https://doi.org/10.1071/MF16260) and Montagna et al. (2018, https://doi.org/10.1002/lno.10953). Benthic communities were collected using a 6.7-cm diameter core tube, each core sample was cut into 0-3 cm and 3-10 cm vertical sections, preserved in formalin, and stained with Rose Bengal to facilitate sorting; organisms were extracted using a 500 µm mesh, stored in 70% ethanol, counted and identified to lowest taxonomic level practical, and dried at 50 °C for 24 hours and weighed (mollusk shells are removed using an acidic vaporization technique so that biomass includes tissue only), benthic methods described in Montagna and Kalke (1992, https://doi.org/10.2307/1352779).

Instruments:

YSI Sonde

Provenance and Historical References:

Bhanu Paudel, Paul A. Montagna, and Leslie Adams. 2015. Variations in the release of silicate and orthophosphate along a salinity gradient: Do sediment composition and physical forcing have roles? Estuarine, Coastal and Shelf Science, 157:42-50. http://doi.org/10.1016/j.ecss.2015.02.011 Montagna, P.A., Hu, X., Palmer, T.A. and Wetz, M. 2018. Effect of hydrological variability on the biogeochemistry of estuaries across a regional climatic gradient. Limnol. Oceanogr., 63: 2465-2478. https://doi.org/10.1002/lno.10953 Montagna, P.A., and R.D. Kalke. 1992. The effect of freshwater inflow on meiofaunal and macrofaunal populations in the Guadalupe and Nueces Estuaries, Texas. Estuaries 15, 307–326. https://doi.org/10.2307/1352779 Paudel, Bhanu, Paul A. Montagna, Mark Besonen, and Leslie Adams. 2017. Inorganic nitrogen release from sediment slurry of riverine and estuarine ecosystems located at different river regimes. Marine and Freshwater Research 68, 1282-1291. https://doi.org/10.1071/MF16260

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