Journal Article

Submarine groundwater discharge as a major source of nutrients to the Mediterranean Sea

Garcia-Orellana, Jordi, Weinstein, Yishai, Rodellas, Valentí, Feldman, Mor, Masqué, Pere

2015

Overview

The Mediterranean Sea (MS) is a semienclosed basin that is considered one of the most oligotrophic seas in the world. In such an environment, inputs of allochthonous nutrients and micronutrients play an important role in sustaining primary productivity. Atmospheric deposition and riverine runoff have been traditionally considered the main external sources of nutrients to the MS, whereas the role of submarine groundwater discharge (SGD) has been largely ignored. However, given the large Mediterranean shore length relative to its surface area, SGD may be a major conveyor of dissolved compounds to the MS. Here, we used a ²²⁸Ra mass balance to demonstrate that the total SGD contributes up to (0.3–4.8)⋅10 ¹² m ³⋅y ⁻¹ to the MS, which appears to be equal or larger by a factor of 16 to the riverine discharge. SGD is also a major source of dissolved inorganic nutrients to the MS, with median annual fluxes of 190⋅10 ⁹, 0.7⋅10 ⁹, and 110⋅10 ⁹ mol for nitrogen, phosphorous, and silica, respectively, which are comparable to riverine and atmospheric inputs. This corroborates the profound implications that SGD may have for the biogeochemical cycles of the MS. Inputs of other dissolved compounds (e.g., iron, carbon) via SGD could also be significant and should be investigated. Significance The Mediterranean Sea (MS) is one of the most oligotrophic seas in the world, and external inputs of nutrients are especially relevant to sustaining primary productivity in this basin. Here we evaluate the role of submarine groundwater discharge (SGD) as a source of nutrients to the entire MS, a pathway that has been largely overlooked. This study demonstrates that SGD is a volumetrically important process in the MS, is of a larger magnitude than riverine discharge, and also represents a major source of dissolved inorganic nitrogen, phosphorous, and silica to the MS.

• Publisher: National Academy of Sciences,CCSD
• Subject: Atmosphere / Basins / Biogeochemical cycles / Discharge / dissolved inorganic nitrogen / Environmental Monitoring - methods / Environmental Sciences / Groundwater / Groundwater - chemistry / Groundwater discharge / Mediterranean Sea / Micronutrients / Nitrogen - chemistry / Nutrients / Phosphorus - chemistry / Physical Sciences / primary productivity / Radioisotopes - chemistry / Radium - chemistry / River discharge / Rivers / Runoff / Seawater - chemistry / Silica / Silicon Dioxide - chemistry / Spectrometry, Gamma / Water Movements