Abstract:
The current climate change in the tropical Andean rain forests in south Ecuador alters the distribution of rain events with increasing dry and wet phases. The present research focuses on the concentration response of some elements to signi cant changes on rainfall distribution. It seeks to determine whether changes in the concentrations of elements in an ecosystem of a rainforest are an eect of dilution by precipitation or other factors that may be aecting these variations, such as microbiological activities. The study examines chloride, ammonium, nitrate, phosphate, total organic carbon (TOC), dissolved organic nitrogen (DON), and dissolved organic phosphorus (DOP) in soil solution as well as the ratio of organic nitrogen to organic carbon (C : N) in soil solution samples taken in a tropical rain forest of Ecuador. Soil samples were taken weekly from 1998 to 2007, both below the organic layer and 15 and 30 cm into the mineral layer. Concentrations were measured with a chloride electrode , Continuous Flow Analyzer (CFA for ammonium, nitrate, DON, and DOP) and Total Organic Carbon Analyzer. The results were analyzed with statistical
software packages R and SPSS using statistical methods of descriptive statistics and ANOVA. The average weekly precipitation was 38.73 mm and weekly precipitation varied between 0 and 155.2 mm. The variation of chloride concentrations served as reference to detect dilution/concentration effects of the other elements because it is assumed that chloride concentrations behave inversely proportional to the volume of water in soil. Thus, the higher the precipitation the lower is the concentration of chloride in soil solutions. I found that the mineral elements presented similar concentration variations as chloride indicating the strong if not exclusive eect of dilution. The phosphate concentrations were an exception showing irregular variation. Measurement problems due to the low P concentrations, often below the detection limit of the instrument may be the explanation for such irregularities. The variation in chloride-normalized organic components diered from that of chloride. The concentrations of TOC, DON and C : N ratio showed a fairly steep increase with increasing precipitation, especially observable at 15 cm depth in the mineral soil and in some cases also at 30 cm depth. A small TOC consumption by the microbial community during rewetting, a strong microbial TOC production or increased leaching of TOC to the mineral soil are possible explanations for this result. My results demonstrate that the response of inorganic N and P species is mainly driven by concentration/dilution eects while for organic compounds microbial activity in relation to soil moisture was an additional factor controlling the concentrations.
