The identification of sediment sources in a small urban watershed in southern Brazil: An application of sediment fingerprinting

Abstract

Soil particles eroded from the land surface and transported into rivers by runoff are considered one of the main components of non-point source pollution in urban watersheds. These particles also serve as a vector for a wide variety of both organic and inorganic constituents. As a result, the identification of sediment sources in an urban watershed is necessary not only to understand erosion dynamics, but also to help implement more effective measures to control and/or remediate non-point source pollution. The present study employs sediment 'fingerprinting' to determine the main sediment sources in a small residential urban watershed (0.83 km2) on the outskirts of Porto Alegre in southern Brazil. Based on an evaluation spanning 12 rainfall events, the results show that paved and unpaved roads and the stream channel itself contribute, on average, 46%, 23%, and 31%, respectively, to the suspended sediment flux in the watershed. Furthermore, the source contributions varied both between events and over the course of a single event. This appears to imply that source contributions, at least to some extent, depend on local precipitation patterns. The results from this study indicate that the level of uncertainty in source ascription tends to decline with increasing numbers of tracers; hence, successful sediment fingerprinting and source ascription in complex hydrologic environments, such as urban watersheds, may require the use of a large number of chemical and/or physical tracers.

Alterações morfológicas em um canal fluvial urbano no contexto antrópico, social e ambiental: um estudo de caso

“…Essas áreas devem ser consideradas de alta fragilidade ambiental, pois são as mais suscetíveis à ocorrência dos processos erosivos, tornando-se fonte potencial de produção de sedimentos na bacia. Em especial, as ruas não-pavimentadas, que representam 6,13% da área da bacia, podem ser consideradas como uma das maiores produtoras de sedimentos e de transferência de sedimentos da bacia vertente para a calha fluvial (POLETO et al, 2009 Por essas condições, pôde-se perceber que, nas amostras coletadas no início dos eventos de chuva, principalmente em períodos de longa estiagem, ocorrem picos de concentração de matéria orgânica nos sedimentos fluviais em suspensão coletados no exutório da bacia em estudo, mas que dependendo da intensidade da precipitação, estas concentrações decresciam rapidamente. Isso ocorre principalmente pelo efeito de lavagem da calha fluvial e das ruas pavimentadas, conhecido como first-flush.…”

“…A caracterização do uso e a ocupação do solo da área da sub-bacia hidrográfica em estudo também contou com o auxílio de levantamentos de campo, com um GPS de navegação e com uma máquina fotográfica digital. Verificou-se, assim, que as condições da calha fluvial que drena a área contribuinte, a infraestrutura urbana existente como: a condição das ruas, moradias, sistemas de drenagem pluvial e de esgotos são as principais possíveis fontes de produção de sedimentos da área em estudo, conforme apresentado em Poleto e Merten (2007) e Poleto et al (2009).…”

Spatial variation of metals and phosphorus in sediments of a river influenced by urbanization

“…Chemical elements (metals and semi-metals) such as As, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn have been considered as a fingerprint to trace pollution in urban areas (GOMES et al, 2009;MINELLA, 2009;RIVARO et al, 2011;MCKEE;GILBREATH, 2015). Despite the discussion about iron, some authors also include this metal as tracer of pollution (POLETO; MERTEN; MINELLA, 2009;MCKEE;GILBREATH, 2015;SILVA;SIQUEIRA;LEANDRO, 2015), even been one of the most abundant on Earth as well Al, Ca, K, Mg, Si and Ti.…”

“…Despite the discussion about iron, some authors also include this metal as tracer of pollution (POLETO; MERTEN; MINELLA, 2009;MCKEE;GILBREATH, 2015;SILVA;SIQUEIRA;LEANDRO, 2015), even been one of the most abundant on Earth as well Al, Ca, K, Mg, Si and Ti.…”

Principle of maximum entropy in the estimation of suspended sediment concentration

“…It is known that the amount of water is not changed on the planet, but its distribution and quality make it impossible to use. Poleto et al (2009) state that most of water contamination is due to sediments, especially the fine sediments that are transported to distant areas. In urban areas this effect is greater due to large diffuse pollution.…”