Diel cycles in calcite production and dissolution in a eutrophic basin

Area of Science:

• Environmental Chemistry
• Limnology
• Geochemistry

Background:

• Calcite production is typically viewed as a long-term process influencing eutrophication.
• Eutrophic basins are susceptible to nutrient loading and biogeochemical cycling.

Purpose of the Study:

• To investigate rapid, diel cycles of calcite production and dissolution in a shallow eutrophic basin.
• To determine if these calcite dynamics influence the cycling of metals sorbed to calcite particles.

Main Methods:

• Intensive 7-day in situ water quality monitoring.
• Analysis of a 7-year historical water quality dataset.
• Sediment characterization and laboratory experiments with calcite and cadmium (Cd).

Main Results:

• Significant day-night cycles in calcite production and dissolution were observed, driven by dissolved CO2 fluctuations.
• Calcite production occurred during daylight and dissolution at night, linked to diel shifts in pCa, pH, and PO2.
• Laboratory experiments showed rapid Cd interaction with calcite (<6 hours) under changing CO2 conditions, indicating diel Cd cycling.

Conclusions:

• Diel calcite dynamics in eutrophic basins can create secondary diel cycles in metal availability, such as cadmium.
• Other metals like zinc, strontium, nickel, and barium may exhibit similar diel cycling behavior.
• Understanding these rapid calcite-mediated metal cycles is crucial for assessing water quality in eutrophic systems.