The role of freshwater inflow in lagoons, rivers, and bays

Abstract

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.

Impacts of droughts and low flows on estuarine water quality and benthic fauna

“…Consequently, decreased nutrient concentrations coincided with decreased primary production (chlorophylla concentrations) in the water column. The inverse relationship that droughts (low-inflow/high salinity periods) have with water nutrients and water column primary production is expected (Caffrey et al, 2007;Pollack et al, 2009;Palmer et al, 2011). In the Patos Lagoon, Brazil, drought periods led to low phytoplankton biomass due to lower nutrients (mainly silicate; Abreu et al, 2010).…”

“…Chironomid larvae are most common in oligohaline (low salinity) conditions around the world (e.g., Grenon, 1982;Schlacher & Wooldridge, 1996) including Texas (e.g., Pollack et al, 2009;Palmer et al, 2011) and are a good indicator of wet conditions. Chironomid larvae were rarely found in the three primary bays or Nueces Bay in this current study.…”

Linkage between Freshwater Inflow and Primary Productivity in Texas Estuaries: Downscaling Effects of Climate Variability

“…The major source of nitrogen is fertilizer applied in agriculture, and the demise of phytoplankton that utilizes anthropogenic nutrients is sedimented and eventually causes harmful effects on benthic ecosystems because of hypoxic conditions (Justic et al, 1993;Rabalais et al, 1996;Turner and Rabalais 1994). Land cover/land use changes by human activities are linked to varying nutrient loadings and subsequent ecosystem responses in Texas coastal waters (Arismendez et al, 2009;Palmer et al, 2011;Pollack et al, 2009). Land cover/land use changes by human activities are linked to varying nutrient loadings and subsequent ecosystem responses in Texas coastal waters (Arismendez et al, 2009;Palmer et al, 2011;Pollack et al, 2009).…”

Understanding the Potential Impacts of Global Climate Change on Marsh Birds in the Gulf of Mexico Region

“…For example, anthropogenic development in coastal watersheds can contribute significant levels of nutrients to estuaries (Boesch et al 2001;Boesch 2002;Scavia and Bricker 2006). When coupled with hydrologic conditions, nutrient enrichment can also lead to changes in estuarine community composition, a situation especially true for organisms at lower trophic levels (Bilkovic et al 2006;Beseres Pollack et al 2011;Palmer et al 2011). Subsequently, most estuarine marsh birds, who occupy higher trophic positions, may be vulnerable to these disturbances via bottom-up controls (DeLuca et al 2008;Cardoni et al 2011).…”