Stoichiometry of hydrological C, N, and P losses across climate and geology: An environmental matrix approach across New Zealand primary forests

Hydrologic losses can play a key role in regulating ecosystem nutrient balances, particularly in regions where baseline nutrient cycles are not augmented by industrial deposition. We used first- order streams to integrate hydrologic losses at the watershed scale across unpolluted old- growth forests in New Zealand. We employed a matrix approach to resolve how stream water concentrations of dissolved organic carbon ( DOC), organic and inorganic nitrogen ( DON and DIN), and organic and inorganic phosphorus ( DOP and DIP) varied as a function of landscape differences in climate and geology. We found stream water total dissolved nitrogen ( TDN) to be dominated by organic forms ( medians for DON, 81.3%, nitrate- N, 12.6%, and ammonium- N, 3.9%). The median stream water DOC: TDN: TDP molar ratio of 1050: 21: 1 favored C slightly over N and P when compared to typical temperate forest foliage ratios. Using the full set of variables in a multiple regression approach explained approximately half of the variability in DON, DOC, and TDP concentrations. Building on this approach we combined a simplified set of variables with a simple water balance model in a regression designed to predict DON export at larger spatial scales. Incorporating the effects of climate and geologic variables on nutrient exports will greatly aid the development of integrated Earth- climate biogeochemical models which are able to take into account multiple element dynamics and complex natural landscapes.