Abstract:

This dataset contains data showing the effect of freshwater inflow on macrobenthos in minor bays and river-dominated estuaries collected from 2000-10-04 to 2005-08-06 along the Texas coast. This study compared the impact of different freshwater inflow volumes on benthic communities and water column dynamics in different estuary classes. Benthic and water column spatial dynamics were contrasted in lagoons (with no direct inflow sources), tidal rivers that empty directly into the Gulf of Mexico, and bar-built estuary systems (with direct inflow sources and connections to the sea) along the Texas (USA) coast to determine the role of inflow in regulating ecosystem structure and function. Chlorophyll-a and nutrient concentrations were inversely correlated with salinity and were thus highest in the river systems, but lowest in lagoons. All Texas estuary types studied have conservative mixing for silicate and are sinks for nitrite plus nitrate and phosphate. In contrast, ammonium is produced in lagoons and lost in bays. Macrobenthic production (abundance and biomass) was lowest in rivers and highest in lagoons. Diversity was low in estuaries with salinities between 1 and 17, but increased with salinities of up to 30, before decreasing in hypersaline conditions. Macrofaunal community structure divided the estuaries into two groups. The first group represented polyhaline communities and contained lagoons (East Matagorda, Matagorda, Christmas and South Bays). The second group represented oligo-mesohaline community characteristics and contained the secondary bays (Lavaca Bay and Cedar Lakes) and rivers (San Bernard River, Brazos River, and the Rio Grande River). The implications of these results for managing freshwater flows are that altered hydrology can change the character of estuarine systems regardless of their classification as bays, lagoons, or tidal rivers.

Suggested Citation:

Montagna, Paul A. and Rick Kalke. 2023. Effect of freshwater inflow on macrobenthos in minor bays and river-dominated estuaries collected from 2000-10-04 to 2005-08-06, Texas. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/btehjm5n

Purpose:

From the early 1970s to 2000, Texas Water Development Board (TWDB) freshwater inflow studies focused on the major bay systems of the Texas coast. In contrast, attention here is focused on minimum inflows required by minor bays and river-dominated estuaries. Freshwater inflow into minor bays is generally dominated by non-point source runoff or an indirect source via circulation from adjacent systems. Minor bays are small lagoon-like bays with no direct freshwater inflow source, instead receiving most water from indirect sources, e.g., runoff. Thus, salinity is used as an indicator of inflow because flow is not measured directly. River estuaries encompass the section of a river influenced by tidal exchange with the Gulf of Mexico. Thus, the overall goal is to determine the importance of freshwater inflow on benthic community composition in minor bays and river-dominated estuaries along the Texas coast.

Data Parameters and Units:

Date Daily Flow (m³/s) Average Flow 30 day (m³/s) 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:

Benthos are excellent indicators of environmental effects of a variety of stressors because they are abundant, diverse, sessile, and long-lived relative to plankton. Therefore, benthos integrate temporal changes in ecosystem factors over long time scales and large spatial scales. Benthic abundance, biomass, and diversity were measured to assess inflow effects on ecosystem productivity. In addition, relevant water quality and sediment variables (i.e., salinity, temperature, dissolved oxygen, nutrients, chlorophyll, grain size, carbon and nitrogen content) were measured during each sampling period to assess inflow effects on the overlying water column and sediments that make up benthic habitat. Sampling occurred in three river estuaries (Rio Grande, San Bernard River, and Brazos River), four minor bays (Christmas Bay, Cedar Lakes, East Matagorda Bay and South Bay Coastal Preserve), and a major bay system (Lavaca-Colorado Estuary including Lavaca Bay and Matagorda Bay) between October 2000 and August 2005. Hydrographic measurements (salinity, conductivity, temperature, pH, percent dissolved oxygen, and dissolved oxygen) were measured at each station during each sampling trip using a multiprobe water quality sonde and meter. Water sample were collected for nutrients and chlorophyll. Sediment was collected for content and composition. Benthic organisms were collected with a 6.7-cm diameter sediment core, extracted on a 0.5 mm sieve, and identified to species (or lowest) level if possible; then grouped by major taxa, dried at 55 degrees Celsius for 24 hours, and weighed.

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