hrvatski

Tomina jama kod Krvavca u dolini rijeke Neretve

Tomina jama cave was explored and preliminary research conducted from 2015 to 2019. Tomina jama is currently the only known anchialine cave in the Neretva River area. At this time, the cave has been explored up to 58 m with the last 23 to 25 m submerged. Tomina jama is a typical anchialine cave system with a freshwater lens at the surface and seawater layer at the bottom. Salinity in the cave increased from 0 at the surface to 33 at a depth of 22 m, whereas dissolved oxygen concentrations decreased from 9.1 mg/L to anoxic conditions at depth. The hypoxic/anoxic zone extended for more than 10 m. Water temperature ranged from 14.8°C at the surface to 17.2°C at the bottom while pH decreased with depth from 7.74 to 6.86. Redox sensitive trace metals (i.e. Mo and U) deviated from salinity driven conservative mixing behavior. The upper freshwater layer was characterized by low Mo and U concentrations, 6.5 and 2.1 nmol/L, respectively. As salinity increased with depth, Mo and U concentration also increased (65.0 and 8.1 nmol/L, respectively). Of interest however, as depth continued to increase to the bottom salt layer (salinity 33) the Mo and U concentrations were significantly lower than for open ocean (~115 and ~13.5 nmol/L, respectively) implying removal process of Mo and U within the anoxic bottom waters. Further investigation of possible Mo and U enrichment within the cave sediment and porewaters is needed in order to establish possible linkages between the water and porewater chemistry (i.e. especially sulphide concentration, a trigger for Mo water column exhaustion) and the removal processes of Mo and U within the water column. Within the anoxic bottom waters, increased concentrations of Fe and Mn were observed indicating the formation of reduced Fe and Mn minerals within. Several stygobionts were discovered in the freshwater layer including serpulids Marifugia sp. and crustaceans of the genera Monolistra, Troglocaris and Niphargus. Most notable is the finding of the endemic serpulids, which is the first record of this animals for an anchialine cave. Prior to this discovery, Marifugia has only been found in freshwater caves from Dinaric karst region. Preliminary DNA results indicate that this specimen might not belong to Marifugia cavatica species and may be a new species. Below the halocline, the cave walls and bottom were covered with a significant bacterial mat. Samples were collected for future microbiome analyses.

Tomina jama ; speleologija ; anhialina jama ; Neretva ; Metković

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