Biogeochemical Output and Typology of Rivers Draining Patagonia’s Atlantic Seaboard

Between June 1995 and November 1998, eight Patagonian rivers were sampled for the suspended and dissolved loads delivered to the SW Atlantic. The most important rivers (Negro and Santa Cruz) jointly deliver ;90% of the total Patagonian freshwater budget (;60 km3 y21). Of the total sediment load (;1.7 1012 g y21), 2.8% was accounted for by particulate organic carbon (POC), 0.9% by inorganic particulate carbon (PC), 0.7% by particulate nitrogen (PN), and 0.7% by particulate phosphorus (PP). The mean dissolved organic carbon (DOC) yield was ;0.50 g m22y21, and POC ;0.3 g m22y21. Nitrogen is the limiting nutrient in all rivers; the mean molecular C:N:P ratio is 37:1:1. POC:PN ratios (4.4–10) indicate an autochthonous origin for the organic matter in suspended particulate matter (TSS). Many factors, such as proglacial oligotrophic lakes, coal-bearing strata, wetlands, aridity, as well as various human impacts, suggest a complex typology. The analysis (Euclidean distance cluster analysis) of biogeochemical variables [SiO2, NO3 2, PO4 32, DOC, POC, PC, PP, PN, C:N, DOC:POC, PC:POC, POC (%)] indicates that runoff, superimposed on biogeochemical variables, plays an important role in Patagonian riverine typology: a) Low runoff rivers (,100 mm y21): the Chubut, Chico, Deseado are characterized by low yields and POC:PN ratios; the Coyle River, by high DOC:POC; b) Medium discharge rivers (100–300 mm y21): the Negro River has high dissolved yields and high POC(%TSS); the Colorado is distinguished by high PP and PC specific yields, and POC:PN ratio; c) High runoff rivers (.1000 mm y21): Santa Cruz and Gallegos rivers, are both characterized by above-average specific yields; the Gallegos has high POC(%TSS), POC:PN and DOC:POC