Tropical river suspended sediment and solute dynamics in storms during an extreme drought

Abstract

Droughts, which can strongly affect both hydrologic and biogeochemical systems, are projected to become more prevalent in the tropics in the future. We assessed the effects of an extreme drought during 2015 on stream water composition in the Luquillo Mountains of Puerto Rico. We demonstrated that drought base flow in the months leading up to the study was sourced from trade‐wind orographic rainfall, suggesting a resistance to the effects of an otherwise extreme drought. In two catchments (Mameyes and Icacos), we sampled a series of four rewetting events that partially alleviated the drought. We collected and analyzed dissolved constituents (major cations and anions, organic carbon, and nitrogen) and suspended sediment (inorganic and organic matter (particulate organic carbon and particulate nitrogen)). The rivers appeared to be resistant to extreme drought, recovering quickly upon rewetting, as (1) the concentration‐discharge (C‐Q) relationships deviated little from the long‐term patterns; (2) “new water” dominated streamflow during the latter events; (3) suspended sediment sources had accumulated in the channel during the drought flushed out during the initial events; and (4) the severity of the drought, as measured by the US drought monitor, was reduced dramatically after the rewetting events. Through this interdisciplinary study, we were able to investigate the impact of extreme drought through rewetting events on the river biogeochemistry.

Long-Term Suspended Sediment Concentrations and Loads from a Relatively Undisturbed Agroforested Catchment in the Northwest of the Iberian Peninsula

“…The results highlight the predominant contribution of a few large events to the annual SS load in this catchment, as already reported by several authors worldwide [7,[13][14][15]19,47]. Within the 12-year period (2004/2005-2016/2017), 15 events (<1% of time) produced about 40% of total recorded SS, suggesting a moderate irregularity in SS transport in the study area.…”

Hysteretic Response of Solutes and Turbidity at the Event Scale Across Forested Tropical Montane Watersheds

“…The lack of differentiation between concentrations on the rising and falling limbs of the storms indicates reservoirs of sediment both proximal and distal to the stream channel. This conclusion contrasts with many reports (Smith and Dragovich, 2009;Aich et al, 2014;Rose et al, 2018) including from the Luquillo Mountains and RI (Gellis, 2013;Clark et al, 2017). In an assessment of sensor-collected turbidity data during rewetting events following a major drought in RI, Clark et al (2017) reported a clockwise C-Q response for turbidity (Figure 6).…”

Concentration‐Discharge Relations in the Critical Zone: Implications for Resolving Critical Zone Structure, Function, and Evolution

“…For example, correlation of in situ electrical conductivity (EC) measurements with discharge enabled Singley et al () to identify hydrologic mechanisms governing hysteretic behavior across the hydrograph in the McMurdo Dry Valleys of Antarctica. Using in‐stream sensors (combined with stable isotopes) for hydrograph separation enabled Clark et al () to show that new water, transmitted laterally downslope in the near subsurface, dominated storm hydrographs in events following extreme drought in the Rio Icacos watershed of the Luquillo CZO.…”