Lotic Intersite Nitrogen eXperiment II (LINX2): Stream nitrogen (N) dynamics in streams on the eastern side of Puerto Rico

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Stream nitrogen (N) dynamics were studied in streams on the eastern side of Puerto Rico. Rates of nitrate uptake and denitrification were measured in nine tropical low-order streams with contrasting land use as part of the Lotic Intersite Nitrogen eXperiment II (LINX II) in Puerto Rico using short term (24-hour) additions of K15NO3 and NaBr. Background nitrate concentrations ranged from 105 to 997 µg N L-1 and stream nitrate uptake lengths were long, varying from 315 to 8480 m (median of 1200 m). Other indices of nitrate uptake (Vf,, cm s-1 and U, g N m-2 s-1) were low in comparison to other regions and were related to chemical, biological, and physical parameters. Denitrification rates were highly variable (0 to 133 g N m-2 min-1; median = 15), were dominated by the end product N2 (rather than N2O), and were best predicted by whole-stream respiration rates and stream NO3 concentration. Denitrification accounted for 1 to 97% of nitrate uptake with 5 of 9 streams having 35% or more of nitrate uptake via denitrification, showing that denitrification is a substantial sink for nitrate in tropical streams. Whole-stream nitrate uptake and denitrification in our study streams closely followed 1st order uptake kinetics, indicating that NO3 uptake is limited by delivery of substrate (NO3) to the organisms involved in uptake or denitrification.

Date Range: 
2004-02-04 00:00:00 to 2006-02-23 00:00:00



Additional Project roles: 

Name: Eda Melendez-Colom Role: Data Manager
Name: Jody Potter Role: Associated Researcher
Name: Jeffrey Merriam Role: Associated Researcher
Name: Bruce J. Peterson Role: Associated Researcher
Name: Wilfred M Wollheim Role: Associated Researcher
Name: Alonso RamIrez Role: Associated Researcher
Name: Jorge R. Ortiz-Zayas Role: Associated Researcher
Name: Frederick Scatena (In Memorium) Role: Associated Researcher


Nine streams of contrasting land use were selected based on size (1st to 2nd order). Background chemistry, biology, geomorphology, and hydrology was measured at each of the nine sites. Reaches for the experiment were chosen based on the lack of significant surface water inputs from tributaries. An addition of K15NO3 and NaBr was done at each stream over a span of 24 hours. The NaBr was used as a conservative tracer to determine discharge and dilution along the reach. The rates of uptake and denitrification were determined from the loss of 15N in water, uptake of 15N in biomass compartments, ans the increase in 15N in streamwater gases (N2 and N2O). Isotopic samples were collected before the addition and 12 hours, 24 hours, 72 hours after the addition. Whole stream metabolism was measured concurrently with the 15N addition using the 2 station dissolved oxygen approach. Gas exchange was determined by the addition of propane or SF6 & monitoring its loss downstream. Organic matter standing stocks were sampled using a random, stratified sampling design.


Dionex ion chromatograph

Shimadzu total organic carbon analyzer

Smartchem automated colorimetric discreet analyzer

YSI chemical dissolved oxygen probe

Agilent Gas Chromatograph

Mass Spectrophotometer


Maintenance is done by WQAL staff and the lab manager. Routine maintenance is done by schedule, periodic maintenance is also done on a needed basis.

Quality Assurance: 

Data calculated and summarized by Jody Potter and then data was sent to UNH Water Quality Analysis Lab manager for QA/QC. Data that passes the QC procedure is entered into the WQAL database and then exported upon request by J. Potter.



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