Variability of dissolved organic carbon in precipitation during storms at the Shale Hills Critical Zone Observatory

Abstract

Organic compounds are removed from the atmosphere and deposited to the Earth's surface via precipitation. In this study, we quantified variations of dissolved organic carbon (DOC) in precipitation during storm events at the Shale Hills Critical Zone Observatory, a forested watershed in central Pennsylvania (USA). Precipitation samples were collected consecutively throughout the storm during 13 events, which spanned a range of seasons and synoptic meteorological conditions, including a hurricane. Further, we explored factors that affect the temporal variability by considering relationships of DOC in precipitation with atmospheric and storm characteristics. Concentrations and chemical composition of DOC changed considerably during storms, with the magnitude of change within individual events being comparable or higher than the range of variation in average event composition among events. Although some previous studies observed that concentrations of other elements in precipitation typically decrease over the course of individual storm events, results of this study show that DOC concentrations in precipitation are highly variable. During most storm events, concentrations decreased over time, possibly as a result of washing out of the below‐cloud atmosphere. However, increasing concentrations that were observed in the later stages of some storm events highlight that DOC removal with precipitation is not merely a dilution response. Increases in DOC during events could result from advection of air masses, local emissions during breaks in precipitation, or chemical transformations in the atmosphere that enhance solubility of organic carbon compounds. This work advances understanding of processes occurring during storms that are relevant to studies of atmospheric chemistry, carbon cycling, and ecosystem responses.

Spatial and Temporal Patterns in Atmospheric Deposition of Dissolved Organic Carbon

“…Changes in solute concentrations during precipitation events have been observed, but the causes can be difficult to pinpoint because the dissolved constituents can be incorporated by within‐cloud or below‐cloud scavenging or advection (Beverland & Crowther, 1992). There is not a consistent pattern of DOC concentration over time in storm events, but the middle of the storm tends to have the lowest concentrations (Iavorivska et al., 2017). The DOC concentration can reflect multiple possible source areas containing gases and aerosols that can be incorporated in precipitation as well as changes in the rate of precipitation over time.…”

Dinâmica de Carbono Orgânico Dissolvido em Ecossistemas Florestais: Uma Revisão Sobre a Lixiviação pela Chuva (Dissolved Organic Carbon Dynamics in Forest Ecosystems Through Rainfall Mediated Leaching: A Review )

“…Considerando-se que o COD de origem atmosférica foi liberado/emitido de outros lugares, áreas que se localizem próximas a grandes centros urbanos ou parques industriais podem receber uma entrada de COD via precipitação maior do que áreas mais distantes destes centros, embora a força da circulação atmosférica possa transportar tais moléculas até longas distâncias (Zhang et al, 2017;Iavorivska et al, 2017). A tabela 1 apresenta valores de concentração de COD na precipitação inicial observados por diferentes pesquisadores em variados ambientes.…”

“…Um estudo detalhado sobre as variações de concentração de COD na precipitação ao longo dos eventos de chuva foi conduzido por Iavorivska et al (2017). Estes autores indicaram a tendência de redução das concentrações com o progresso dos eventos.…”

Dissolved organic matter in surface runoff in the Loess Plateau of China: The role of rainfall events and land‐use

“…Apparently, stream DOM can be significantly influenced by allochthonous loading and autochthonous products from riparian zones and uplands(Williams et al, 2010;Wilson & Xenopoulos, 2009). The observed flow paths, including surface runoff, interflows, fracture flows, groundwater and even precipitation, have a significant influence on DOM quantity and quality in hydrological processes; variations in the preferential flows of stream would change DOM sources under different hydrological conditions(Iavorivska et al, 2017;Xian et al, 2018). However, due to the very thick layer of loess covering the study area, the groundwater table was measured at approximately 60-80 m and was found to supply little discharge for stream flows (Groundwater Research Group of the Loess Plateau Comprehensive Scientific Expedition Team, Chinese Academy ofSciences, 1990).…”