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Increasing global CO₂ and local land-use changes coupled with increased nutrient pollution are altering the geochemistry of estuaries worldwide. Ocean acidification-driven changes in estuaries, which support shellfish communities, have direct impacts due to decreasing pH negatively influencing shell production, growth and hardness, and development of immature shellfish. Rates of increasing acidification are commonly documented in pelagic waters and in a limited number of estuaries. Within estuaries, the most common study sites include the confluence between two water sources (e.g., pelagic waters and mouths of estuaries, river-discharge points within estuaries, and groundwater discharge along estuary shorelines). The same changes at the regional scale have not been previously investigated. Florida provides a unique opportunity to evaluate changes in ocean acidification as related to geochemistry within estuaries at a regional scale, which includes two climatic zones: sub-tropical and tropical.

A new study published in Estuaries and Coasts compares pH, dissolved-oxygen, temperature, and salinity data from 10 Florida estuaries that support commercial shellfish harvesting and hundreds of shellfish bed stations within those estuaries. Historical data from a 28-year period (1980–2008) provided approximately 80,000 independent measurements collected from estuaries on the Atlantic Ocean and Gulf of Mexico coasts of Florida.

Collectively, eight out of the 10 estuaries exhibited a decrease in pH over this time period, with an average rate of decrease of 7.3 × 10⁻⁴ pH units per year for estuaries on the Gulf of Mexico and 5.0 × 10⁻⁴ pH units per year for estuaries on the Atlantic Ocean coast. Those rates of change in pH are approximately 2–3.4 times slower than observed in pelagic waters of the Atlantic and Pacific Oceans. Other significant trends in geochemistry over this same period of time and within these estuaries include: decreasing dissolved oxygen (nine estuaries), increasing salinity (six estuaries), and increasing temperature (three estuaries).

The data provide a synoptic regional assessment of geochemical trends in Florida estuaries that reflect the complexities of changing climate and coastal ocean acidification. These data provide a historical context from which resource managers can interpret past historical water-quality data and predict changes in the geochemistry in estuary waters that promote the health and production of shellfish and other organisms of commercial and ecological significance along the coasts of Florida.

The full citation for the article is:

Robbins, L.L., and Lisle, J.T. 2017, Regional acidification trends in Florida shellfish estuaries—a 20+ year look at pH, oxygen, temperature, and salinity: Estuaries and Coasts, https://doi.org/10.1007/s12237-017-0353-8.