Effect of hydrological variability on the biogeochemistry of estuaries across a regional climatic gradient

Abstract

Given projected changes in river flow to coastal regions worldwide due to climate change and increasing human freshwater demands, it is necessary to determine the role hydrology plays in regulating the biogeochemistry of estuaries. A climatic gradient exists along the Texas coast where freshwater inflow balance ranges from hydrologically positive to negative (where evaporation exceeds inflow) within a narrow latitudinal band, providing a natural experiment for examining inflow effects. Four Texas estuaries ranging from mesosaline to hypersaline were studied for 3 yr to determine how hydrological changes alter the biogeochemistry within and among the estuaries. Trends in dissolved inorganic nutrients, chlorophyll, dissolved organic matter, and carbonate chemistry indicated that these estuaries had drastically different biogeochemical signatures. Nutrients and chlorophyll patterns illustrated an emerging paradigm where phytoplankton biomass in positive estuaries is supported by “new” nitrogen from riverine input, while high concentrations of reduced nitrogen (organic, ammonium) allowed for high chlorophyll in the negative estuary. For carbonate chemistry, a positive estuary receiving river input from a limestone‐dominated watershed was well‐buffered under moderate to high freshwater inflow conditions. When weathering products were diluted during high‐flow conditions, there is carbonate undersaturation (for aragonite) and decreases in pH. However, “acidification” was not observed in the negative estuary because evaporation concentrated the dissolved species and increased buffering capacity. Hydrological changes over spatial gradients are analogous to climatic changes over time, meaning climate change forecasts of higher temperatures and decreased precipitation can make the biogeochemistry of fresher estuaries change to the patterns of saltier estuaries.

Hydrologic controls on CO2 chemistry and flux in subtropical lagoonal estuaries of the northwestern Gulf of Mexico

“…However, during the wet period, intense flooding strongly diluted riverine DIC and TA (Table ; Fig. b,f), this type of strong dilution effect was also observed in other studies in this region (Mooney and McClelland ; Montagna et al ). This dilution effect varied significantly across the entire region, from the strongest in MAE (both TA and DIC were diluted more than half, ∼ 2800 μ mol·kg −1 ), to the weakest in NE (diluted by 200 μ mol·kg −1 ).…”

Timescales and Magnitude of Water Quality Change in Three Texas Estuaries Induced by Passage of Hurricane Harvey

“…These systems are shallow (< 5 m), well mixed by winds, have minimal tidal influence (~15 cm, Zetler and Hansen 1970), and are separated from the Gulf of Mexico by a series of barrier islands. Despite similar geomorphology, hydrology varies between the three systems and influences biogeochemical processes (Montagna et al 2018). There is a natural precipitation gradient along the Texas coast, with decreasing precipitation and increasing salinity from the northeast to southwest (Montagna et al 2013).…”

“…There is a natural precipitation gradient along the Texas coast, with decreasing precipitation and increasing salinity from the northeast to southwest (Montagna et al 2013). As a result of this precipitation gradient, LC and GE are considered positive estuaries because freshwater inputs exceed evaporation on average, while NC is considered a neutral estuary where freshwater inputs are roughly balanced by evaporation (Montagna et al 2018). Hurricane Harvey made landfall near Port Aransas, TX, on 26 August 2017, accompanied by category 4 winds and heavy rainfall totaling over 152 cm in areas.…”

Does physiological tolerance to acute hypoxia and salinity change explain ecological niche in two intertidal crab species?

“…Over the course of a tidal cycle, an aquatic organism living in an intertidal setting may experience changes in water availability, variable water salinity, temperature oscillations and fluctuations in dissolved oxygen (DO). For example, tidal pool DO has been shown to range from 10 to 955 μmol l −1 (~0.8–87 kPa) over the course of 6 h (Legrand et al., 2018), whilst salinity in estuaries can range from near zero to hypersaline depending on the magnitude of freshwater influx (Montagna et al., 2018). This instability of environmental physicochemical factors challenges organism homeostasis.…”