Abstract:

Long-term sampling to identify freshwater inflow effects on benthos began in 1984 and continued through 2019. Five estuaries were sampled. Benthic organisms are ideal bioindicators of freshwater inflow effects in bays and estuaries because they are fixed in space and integrate ephemeral processes in the over-lying water column over long periods of time. Freshwater inflow regulates water quality, which drives benthic abundance, productivity, diversity, and community structure. Texas estuaries have different long-term characteristic fauna that reflect the long-term average salinity and sediment conditions in each bay system. Within estuary systems, the secondary bays have distinct communities compared to the primary bays because secondary bays are closer to freshwater inflow sources and are more oligohaline and/or brackish in nature than primary bays that are more marine influenced. Similar responses occur over time when conditions change with droughts and floods. Because of the relationship between salinity and community structure, benthos community conditions can indicate a “sound ecological environment” as required by 2007 Texas Senate Bill 3.

Suggested Citation:

Montagna, Paul A.. 2023. Long-term monitoring of water and sediment quality to identify freshwater inflow effects from 1984-01-01 to 2019-10-01. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/aa36pm7h

Purpose:

Long-term monitoring of freshwater inflow effects on Texas estuaries.

Data Parameters and Units:

Depth (m), Temperature (°C), Salinity (psu), Dissolved Oxygen (mg/L), pH Chl a (ug/L), Ammonium (μmol/L), Nitrite+Nitrate (μmol/L), Orthophosphate (μmol/L), Silicate SIO4 (μmol/L), Rubble (%), Sand (%), Silt (%), Clay (%), Porewater (%), δ 15Nitrogen (ppt), Nitrogen content (%), Total Carbon δ 13C (ppt), Total Carbon content (%), TOC δ 13C (ppt), TOC content (%), Biomass (g/m²), Abundance (ind./m²), Richness (S/sample), Diversity (N1/sample), Diversity (H'/sample), Evenness (J'/sample).

Methods:

Water quality condition data was collected using multiparameter sondes at surface (directly below the water line) and bottom (approx. 15 cm from the bottom) 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/10.10MPMP02/lno.10953). Sediment grain size analysis performed on sediment core samples sectioned at 0 - 3 cm and 3 - 10 cm depth intervals. Analysis followed standard geologic procedures (Folk, 1964, Petrology of sedimentary rocks; ). A 20 cc sediment sample was mixed with 50 ml of hydrogen peroxide and 75 ml of deionized water to digest organic material in the sample. The sample was wet sieved through a 62 μm mesh stainless steel screen using a vacuum pump and a Millipore Hydrosol SST filter holder to separate rubble and sand from silt and clay. After drying, the rubble and sand were separated on a 125 μm screen. The silt and clay fractions were measured using pipette analysis. Percent contribution by weight was measured for four components: rubble (e.g. shell hash), sand, silt, and clay. Carbon and nitrogen percent content measured. Total Organic Carbon measured on acidified samples. The proportion of organic and inorganic carbon and nitrogen content in the sediment was also measured. In addition to this, carbon and nitrogen isotopes δ13C and δ15N were measured. More details of sediment analyses provided in Palmer et al. 2011, https://doi.org/10.1007/s10750-011-0637-0 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:

Multiparameter sondes

Provenance and Historical References:

Bhanu P., P.A. Montagna, and L. 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. Montagna, P.A., 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/10.2307/135277 Montagna, P.A., X. Hu, T.A. Palmer, and M. Wetz. 2018. Effect of hydrological variability on the biogeochemistry of estuaries across a regional climatic gradient. Limnol. Oceanogr., 63: 2465-2478. Effect of hydrological variability on the biogeochemistry of estuaries across a regional climatic gradient Palmer, T.A., P.A. Montagna, J.B. Pollack, et al. 2011. The role of freshwater inflow in lagoons, rivers, and bays. Hydrobiologia 667, 49–67. https://doi.org/10.1007/s10750-011-0637-0 Paudel Bhanu, Paul A., Montagna Mark Besonen, 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.

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