Chemistry of stream water from the Luquillo Mountains, Puerto Rico
July 12, 2022
Susanne Grossman-Clarke and Miguel C. Leon
McDowell, W. 2021. Chemistry of stream water from the Luquillo Mountains ver 4923058. Environmental Data Initiative. https://doi.org/10.6073/pasta/0a09f5aa2e6f11451553c92b102279a6.
This data package represents one of the long-term, continuous data sets in the EDI data repository and contains weekly water quality data from several streams in the Luquillo Experimental Forest (LEF). To our knowledge this is the longest such record of tropical stream chemistry on Earth (McDowell et al. 2021). LEF, a protected area of tropical rainforest in the Luquillo Mountains in Puerto Rico's El Yunque National Forest, was designated as a UNESCO Biosphere Reserve in 1976.
In 1988 the Luquillo Long-term Ecological Research Project (LUQ) was established to study the long-term effects of natural and human disturbances on tropical forests and streams in LEF. It is one of 26 sites of the National Science Foundation funded Long Term Ecological Research Network. The Luquillo Critical Zone Observatory was established in 2009 to study how Critical Zone processes and water balances differ in landscapes with contrasting bedrock but similar climatic and environmental histories.
Since the founding of the first research station in the Luquillo Mountains in 1940, hundreds of research studies have been carried out. The studies encompass a large variety of topics, including how a changing climate and disturbance regimes (e.g. hurricanes, landslides, alterations in agricultural practice) alter hydrological and biogeochemical processes as well as the resilience of the ecosystem.
Stream water sampling in LEF began in 1983. Weekly water chemistry sampling started in 1988 at 13 sites along the El Verde, Bisley and other streams. All water samples are measured for pH, conductivity, ammonium and nitrate content. A continuous record of stream stage (height) is recorded by a datalogger at all some ongoing stream sampling sites and recorded manually during sampling at others, while 15 minute and average daily streamflows are available from USGS at other locations in LEF. Such long-term data are extremely important for the analysis of ecosystem changes over time as well as synthesis research. More information about the sampling regime can be found on the Story Map Stream Water Chemistry Sampling Sites in the Luquillo LTER.
Studies using the featured data
Below, we summarize several catchment science publications that used the stream data from the LEF featured here.
A paper by McDowell et al. (2021) on the "Luquillo Experimental Forest: Catchment science in the montane tropics" highlights the importance of several LEF data sets that provide some of the longest available records of biogeochemical fluxes in tropical forests. The data were used to document and understand montane tropical watersheds in the context of disturbance and global environmental change, specifically the effects of major hurricanes including Hugo (1989), Georges (1998) and Maria (2017) on LEF vegetation, biota and catchment biogeochemistry. Interception rates decline following hurricane defoliation and canopy damage; rates return to background levels once canopy cover has been re-established after 2–3 years of regrowth (Heartsill-Scalley et al., 2007). The LEF receives significant atmospheric North African dust inputs annual fluxes of K+ in throughfall are twice as high as litterfall K+ fluxes (McDowell, 1998) periodic North African dust transport can also suppress precipitation (Mote et al., 2017). Vegetation is not limited to any significant extent by nitrogen availability. A long-term N fertilization experiment resulted in no change in biomass increment or litterfall, and only modest increases in N content of leaf litter (Cusack et al., 2011). Stream chemistry in the Luquillo Mountains is typically circumneutral, has relatively high concentrations of sea salts due to large inputs of marine aerosols, and high concentrations of weathering products (e.g., SiO2 and bicarbonate) due to the warm and wet environment that promotes rapid weathering in both primary volcaniclastic and granitoid lithologies in the LEF (McDowell & Asbury, 1994; Murphy & Stallard, 2012; Shanley et al., 2011).
A recent study by Mariani-Ríos et al. (2022) investigated the natural history of Odonate species assemblages (dragonflies and damselflies) in headwater montane streams following major hurricane impacts in Puerto Rico. Odonates are important freshwater macroinvertebrate predators that play an important role in maintaining stream food webs and serve as indicators of stream health. The authors studied relations between species abundance and stream discharge, canopy cover, water temperature, and rainfall. Findings show a lack of strong temporal seasonality in the natural history of Odonata in relation to the environmental variables assessed, which coincides with the aseasonal environment of montane streams in the LEF.
Chapela et al. (2017) are concerned with the influence of critical zone processes on Magnesium concentrations and isotopic signatures of tropical streams in the well constrained, highly weathered andesitic volcaniclastic Quebrada Bisley 1 catchment in the Luquillo Critical Zone Observatory. The study highlights the importance of atmospheric input of nutrients to the vegetation in tropical areas covered by thick, highly leached regolith, whereas the Magnesium flux and Magnesium isotopic signature of watershed exports are dominated by bedrock dissolution delivered to the stream through deeper, usually un-sampled critical zone pathways. Moore et al. (2019) studied incipient chemical weathering at bedrock fracture interfaces, a process that is not yet well understood but might affect long-term, global carbon dioxide concentrations by producing substantial fluxes of silicate weathering products. The study was carried out on thin sections of rock obtained from the Bisley bedrock, a part of LEF's critical zone system. Mineralogy, elemental chemistry, porosity and weathering of the rock were analyzed using a number of methods such as Scanning Electron Microscopy with energy dispersive spectrometry, electron probe microanalysis, and others. The weathering advance rate calculated at a watershed scale (from stream chemistry data) represents a contemporary weathering advance rate which compares well with that calculated for the weathering rind, suggesting that the Bisley watershed has been weathering at steady-state for the last ∼4000 years.
This dataset was established in collaboration with the USDA Forest Service International Institute of Tropical Forestry (IITF), in support of the LUQ LTER program at the Luquillo Experimental Forest.
Chapela Lara M, Buss LH, Pogge von Strandmann PAE, Schuessler JA, Moore OW (2017) The influence of critical zone processes on the Mg isotope budget in a tropical, highly weathered andesitic catchment. Geochimica et Cosmochimica Acta, 202, 77– 100, https://doi.org/10.1016/j.gca.2016.12.032.
Cusack DF, Silver WL, Torn MS et al. (2011) Effects of nitrogen additions on above- and belowground carbon dynamics in two tropical forests. Biogeochemistry 104, 203–225. https://doi.org/10.1007/s10533-010-9496-4.
Heartsill-Scalley T, Scatena FN, Estrada C, McDowell WH, Lugo AE (2007) Disturbance and long-term patterns of rainfall and throughfall nutrient fluxes in a subtropical wet forest in Puerto Rico. Journal of Hydrology, 333(2–4), 472–485,https://doi.org/10.1016/j.jhydrol.2006.09.019.
Mariani-Ríos A, Maldonado-Benítez N, Ramírez A (2022) Natural history of Odonata assemblages in tropical streams in Puerto Rico, Neotropical Biodiversity, 8:1, 112-123, https://doi.org/10.1080/23766808.2022.2043699.
McDowell, WH (1998) Internal nutrient fluxes in a tropical rain forest. Journal of Tropical Ecology, 14, 521–536, https://doi.org/10.1017/S0266467498000376.
McDowell WH, Asbury CE (1994) Export of carbon, nitrogen, and major ions from three tropical montane watersheds. Limnology and Oceanography, 39, 111–125, https://doi.org/10.4319/lo.1994.39.1.0111.
McDowell WH, Leon MC, Shattuck MD, Potter JD, Heartsill‐Scalley T, González G, Shanley JB, Wymore AS (2021) Luquillo Experimental Forest: Catchment science in the montane tropics. Hydrological Processes. 35, e14146, https://doi.org/10.1002/hyp.14146.
Moore OW, Buss HL, Dosseto A (2019) Incipient chemical weathering at bedrock fracture interfaces in a tropical critical zone system, Puerto Rico, Geochimica et Cosmochimica Acta, 252, 61-87, https://doi.org/10.1016/j.gca.2019.02.028.
Mote TL, Ramseyer CA, Miller PW (2017) The Saharan air layer as an early rainfall season suppressant in the eastern Caribbean: The 2015 Puerto Rico drought. Journal of Geophysical Research-Atmospheres, 122(20), 10–966, https://doi.org/10.1002/2017JD026911.
Murphy SF, Stallard RF (2012, 1789). Water quality and landscape processes of four watersheds in eastern Puerto Rico. U.S. Geological Survey Professional Paper: U.S. Geological Survey Professional Paper 1789, 292 p.https://pubs.usgs.gov/pp/1789/PP1789.pdf.
Shanley JB, McDowell WH, Stallard, RF (2011) Long-term patterns and short-term dynamics of stream solutes and suspended sediment in a rapidly weathering tropical watershed. Water Resources Research, 47(7), W07515, https://doi.org/10.1029/2010WR009788.