Phosphorus regeneration and burial in near-shore marine sediments (the Gulf of Trieste, N Adriatic)

N. OgrincJ. Stefan Institute, Dept. of Environ. Sci., Ljubljana, Slovenia

J. FaganeliMarine Biological Station, Piran, Slovenia

Aime . . . Investigation of the biogeochemical cycling of phosphorous to elucidate the present and future naturally and anthropogenically induced changes in this coastal ecosystem using

Pore water chemistry

Sediment analysis to reconstruct sedimentary phosphorus budget

Examination of historical changes of sedimentary P - (long core GT3)

Benthic flux experiment (oxic and anoxic conditions)

Some characteristics ILocation:N Adriatic seaarea: approx. 500 km2max. depth: 25m

Inflow:river Isonzo in the N

Water characteristicstemperature at the bottom: 8-22oCsalinity: 33-38.5overlying water oxic, in late summer hypoxia (occasionally anoxia)

length: 130 cmwater depth: 25 mAA1GT3 coreFSampling locations - the Gulf of Trieste

Some characteristics II

Composition of the sediment:

clay and silt-sized material carbonates: mostly low-Mg calcite: biogenic, up to 70%no carbonate fraction: quartz, illite, chlorite and mixed illite/montmorilloniteorganic content: 0.3 0.7 wt.% bioturbated: 10-15 cm

AnalysesWater samples: O2, nutrients, sulphide, sulphate, Fe, Mn

Sediment samples:Organic C, Total N, Total P, Inorganic P, Total S, Reducible S, Total Fe, Total Mn

Previous results in the Gulf of TriesteRedfield: N:P = 16

Suspended particulate matter: N:P = 9

Sedimenting organic matter: N:P = 11

Surficial Sediment: N:P = 7

Pore water I

Pore water II

EXAFS - Goethite the predominant crystalline structure

Reduction of Fe oxide 8% of the P flux

Precipitation and nucleation - fluoroapatiteP - remobilization

Incubation experiment I

Incubation experiment II

Sedimentary P - budgetPinput = Pefflux + Pburial

Pburial = w TP (1- )w sedimentation rate density ... porosity

E = Pefflux/Pinput ~ 50%

Mass balance of particulate phosphorus

Conclusions IPore water and incubation experiment:

Degradation of organic matter is a principal mechanism of phosphate regeneration

The high C:N:P ratio of degradable sedimentary organic matter suggests precipitation of phosphates - fluoroapatite

Conclusions IISediment

The results of the tentative mass balance estimation indicate the preservation of TP in the form of fluoroapatite (about 50%)

Palaeoenvironmental reconstruction - the increase of TP, OP, TN and OC in the sediment core probably indicate the use of inorganic fertilizers and detergents after 1950

10th International Symposium on the Interactions Between Sediments and WaterBled, SloveniaAugust 28th September 2nd, 2005Organized by:National Institute of BiologyJ. Stefan Institutewww.icjt.org/iasws2005E-mail: iasws@ijs.si