The role of freshwater inflow in lagoons, rivers, and bays
The aim of this study was to compare 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 bay systems (with direct inflow sources) 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 ammonium but are sinks for nitrite plus nitrate and phosphate. 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). The implications of these results for managing freshwater flows is that altered hydrology can change the character of estuarine systems regardless of their classification as bays, lagoons, or tidal rivers.
KeywordsBenthos Macrofauna Meta-analysis Nutrients Salinity Texas
The field work for this study was supported by the Texas Water Development Board, Research and Planning Fund, Research Grants, authorized under the Texas Water Code, Chapter 15, and as provided in §16.058 and §11.1491. This support was administered by the Board under interagency cooperative contracts 2001-483-362, 2002-483-414, 2003-483-471, 2004-483-012, 2005-483-541, and 2006-483-026. Much of the analytical work was supported by grant number NA09NMF4720179 from the National Oceanic and Atmospheric Administration under the Comparative Assessment of Marine Ecosystem (CAMEO) program. The study also benefitted by partial support from the University of Texas at Austin, Marine Science Institute, and Texas A&M University—Corpus Christi. Larry Hyde, Christopher Kalke, Jeff Baguley, Marc Russell, Julie Kinsey, and others aided in field collections. Tracy Villareal and Lynn Tinnin performed nutrient analyses and measurements. Carrol Simanek also provided significant help in data management. Anne Evans and Laura Ryckman provided help with the initial development of this manuscript. Review and advice on earlier drafts was provided by the Bay and Estuaries Division of the Texas Water Development Board. This manuscript was improved with the assistance of two anonymous reviewers.
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