Macronutrients, Soil Organic Matter (SOM), Atmospheric Inputs and Landuse 

 Previous work on the Luquillo surface soils has shown that: (1) pools of plant available macronutrients (Ca, Mg, K, and P) are much larger in the upper horizons (< 60 cm) than they are at depth (Zarin & Johnson 1995a); (2) soil nutrient pools are strongly dependent on SOM (Zarin & Johnson 1995b); (3) atmospheric inputs of macronutrients are substantial and nutritionally important to forest re-growth (Zarin 1995b, Frizano etal. 2002); and (4) macronutrient pools differ by landscape position, vegetation, season and land use (Silver etal.1994, Scatena etal. 1995, Cox etal. 2002). The gross stocks of SOM have also been quantified in forests and landslides (Silver etal. 1994, Scatena etal. 1995, Zarin etal 1995ab, McGroddy etal 2000). Unfortunately, most of these studies were focused on shallow surface soils in the VC. The physical and chemical quality of SOM has not been fully assessed in areas underlain by either lithology and SOM and nutrient stocks at depths greater than 0.5 m are virtually unknown. Nevertheless, studies elsewhere suggest that bedrock lithology can significantly modify SOM stabilization and storage, including studies on Hawaiian basalts and Sierra Nevadan granites, basalts and andesites (Torn etal. 1997, Rasmussen etal. 2005; 2006). Soil architecture, mineralogy, and chemistry also influence SOM incorporation into the subsurface (Mayer, 1994, Baldock and Skjemstad, 2000, Mikutta etal. 2006) such that we hypothesize that SOM incorporation in the GD soils will be dominated by physical occlusion while SOM stabilization in VC soils will be dominated by sorption on reactive mineral surfaces. These differences are expected to influence the depth of weathering (H2), riparian processes (H5) and the fate of atmospheric inputs (H7). To address these basic questions the LCZO is quantifying soil nutrients and stream exports by lithology, hillslope position, and forest type. Process based experiments are also underway to quantify the role of microbial communities and soil oxygen on nutrient availability. Available infrastructure include monitored watersheds, long-term vegetation plots, and legacy information on vegetation nutrient use.

For additional information regarding ongoing Biogeochemical research please see LCZO data website.