THE GEOCHEMISTRY OF SMALL MOUNTAINOUS RIVERS IN SOUTHERN ITALY

Small mountains rivers (SMRs), taken collectively, can be an important source of suspended and dissolved solids to the world ocean (Milliman and Farnsworth, 2011). Over the past 15 years, our group has collected samples from SMRs globally in order to fill in data gaps of river chemistry. We have recently analyzed samples collected during base flow at the mouths of six SMRs in Italy, rivers draining the southern Apennine Range and flowing into the Adriatic Sea and the Gulf of Taranto. The watersheds of these rivers are underlain by Mesozoic and Cenozoic marine sedimentary and metamorphic rocks. Surface runoff ranges 20–50 cm annually. The cation composition of these rivers is Ca>Na>Mg>K while the anion composition is HCO₃>Cl≥SO₄. H₄SiO₄ concentrations range 59–248 mmol L^-1. The Ca:Sr and Mg:Sr ratios of these rivers suggest that the weathering of aluminosilicate minerals is probably the dominant process controlling dissolved chemistry. Two of the rivers, the Ofanto and the Bradano, have very high nitrate concentrations and their soluble reactive P and N:P ratios suggest anthropogenic input of these nutrient elements. This is not surprising as the lower elevations of these watersheds are dominated by agricultural landuse. Four of the rivers also have high precipitation-corrected sulfate concentrations, greater than 1 mmol L^-1, also suggesting a possible pollution source, or perhaps the weathering of sulfide minerals. The riverine chemical weathering yields ranged from 70 to 340 tons km^-2 year^-1 and represent 8–58% of the total landscape denudation. These data provide new information to be added to our overall understanding of the geochemical dynamics of small mountainous river systems.