Vertical distribution of phosphorus species and iron in sediment at open sea stations in the middle Adriatic region

Sedimentary phosphorus species concentrations were examined in cores (0-10 cm) from 5 locations in the open middle Adriatic in June 2002. Measurements included organic phosphorus (OP) and inorganic P species: P in biogenic apatite (P-FD), P adsorbed onto iron oxy/hydroxides (P-Fe), P in authigenic apatite (P-AUT) and P in detrital apatite (P-DET). Total iron (Fe-TOT) and iron-oxyhydroxides (Fe(III)OOH) concentrations were also determined as well as granulometric composition, organic matter (OM), organic carbon (C-ORG) and carbonate content (CA). Sediment pore water measurements included redox-potential (E sub(H)) and orthophosphate concentration. All relevant data were subjected to correlation, Cluster and Principal Component Analysis (PCA). Cluster analysis indicated that granulometric composition and carbonate content are the leading factors of distinction between the stations. PCA revealed that the fine fraction of sediments has a key role in the vertical distribution of Fe-TOT and P-ORG. Linkage among P-AUT, P-DET and C-ORG results from river input influence, while association between OM, P-Fe, E sub(H) and OP arises from complex internal processes in the sedimentary P cycle.Original Abstract: U sedimentu sa 5 postaja otvorenog mora srednjeg Jadrana ispitane su koncentracije razlicitih oblika fosfora (P) u jezgrama debljine 0-10 cm. Mjerenja su ukljucivala organski fosfor (OP) i anorganske vrste P: P u biogenom apatitu, (P-FD), P adsorbiran na okside i hidrokside zeljeza (P-Fe), P u autigenom apatitu (P-AUT), i P u detritusnom apatitu (P-DET). Koncentracije ukupnog zeljeza i zeljeznih oksi-hidroksida (Fe(III)OO H) su takodjer odredjene kao i granulometrijski sastav, sadrzaj organske tvari (OM), organskog ugljika (C-OR G) i karbonata (CA ) u sedimentu. U pornoj vodi sedimenta su izmjereni redoks potencijal (E sub(H)) i koncentracija ortofosfata. Svi su podaci bili predmet korelacijske, Cluster i PC analize. Cluster analiza je ukazala na granulometrijski sastav i sadrzaj karbonata kao vodece cimbenike razlikovanja izmedju postaja. PC analiza je pokazala da sitno-zrnata frakcija sedimenta ima kljucnu ulogu u vertikalnoj raspodjeli Fe-TOT i P-ORG u sedimentu. Povezanost izmedju P-AUT, P-DET i C-OR G je rezultat utjecaja rijecnog donosa, dok veza izmedju OM, P-Fe, E sub(H) and OP proizlazi iz kompleksnih procesa ciklusa P u sedimentu.