Simulated terrestrial runoff shifts the metabolic balance of a coastal Mediterranean plankton community towards heterotrophy
<p>Climate change is projected to increase the frequency and intensity of extreme rainfall events in the Mediterranean region, increasing runoffs of terrestrial matter into coastal waters. To evaluate the consequences of terrestrial runoff for plankton key processes, an in situ mesocosm experi...
| Prif Awduron: | , , , , , , , , |
|---|---|
| Fformat: | Erthygl |
| Iaith: | English |
| Cyhoeddwyd: |
Copernicus Publications
2024-04-01
|
| Cyfres: | Biogeosciences |
| Mynediad Ar-lein: | https://bg.copernicus.org/articles/21/1887/2024/bg-21-1887-2024.pdf |
| Crynodeb: | <p>Climate change is projected to increase the frequency and intensity of extreme rainfall events in the Mediterranean region, increasing runoffs of terrestrial matter into coastal waters. To evaluate the consequences of terrestrial runoff for plankton key processes, an in situ mesocosm experiment was conducted for 18 d in the spring of 2021 in the coastal Mediterranean Thau Lagoon. Terrestrial runoff was simulated in replicate mesocosms by adding soil from an adjacent oak forest that had matured in water from the main tributary river of the lagoon. Automated high-frequency monitoring of dissolved oxygen, chlorophyll <span class="inline-formula"><i>a</i></span> fluorescence, salinity, light, and temperature was combined with manual sampling of organic and inorganic nutrient pools, pH, carbonate chemistry, and maximum quantum yield (<span class="inline-formula"><i>F</i><sub><i>v</i></sub>:<i>F</i><sub><i>m</i></sub></span>) of photosystem II (PSII). High-frequency data were used to estimate the gross primary production (GPP) of oxygen, community respiration (CR), and phytoplankton growth (<span class="inline-formula"><i>μ</i></span>) and loss (<span class="inline-formula"><i>L</i></span>) rates. During the first half of the experiment (d2–d11), the simulated runoff reduced light availability (<span class="inline-formula">−</span>52 %), chlorophyll <span class="inline-formula"><i>a</i></span> concentrations (<span class="inline-formula">−</span>70 %), and phytoplankton growth rates (<span class="inline-formula">−</span>53 %). However, phytoplankton maintained a certain level of primary production by increasing its photosynthetic efficiency. Meanwhile, the runoff enhanced CR (<span class="inline-formula">+</span>53 %), shifting the metabolic status (GPP : CR) of the system toward heterotrophy and increasing the partial pressure of carbon dioxide (<span class="inline-formula"><i>p</i></span>CO<span class="inline-formula"><sub>2</sub></span>), potentially switching the direction of the air–sea CO<span class="inline-formula"><sub>2</sub></span> exchange. However, during the second part of the experiment (d11–d17), remineralized nutrients boosted phytoplankton growth (<span class="inline-formula">+</span>299 %) in the terrestrial runoff treatment but not its loss rates, leading to phytoplankton biomass accumulation and suggesting a mismatch between phytoplankton and its predators. Our study showed that a simulated terrestrial runoff significantly affected key plankton processes, suggesting that climate-change-related increases in runoff frequency and intensity can shift the metabolic balance of Mediterranean coastal lagoons towards heterotrophy.</p> |
|---|---|
| ISSN: | 1726-4170 1726-4189 |