Wastewater influences nitrogen dynamics in a coastal catchment during a prolonged drought

Abstract

Ecosystem function measurements can enhance our understanding of nitrogen (N) delivery in coastal catchments across river and estuary ecosystems. Here, we contrast patterns of N cycling and export in two rivers, one heavily influenced by wastewater treatment plants (WWTP), in a coastal catchment of south Texas. We measured N export from both rivers to the estuary over 2 yr that encompass a severe drought, along with detailed mechanisms of N cycling in river, tidal river, and two estuary sites during prolonged drought. WWTP nutrient inputs stimulated uptake of N, but denitrification resulting in permanent N removal accounted for only a small proportion of total uptake. During drought periods, WWTP N was the primary source of exported N to the estuary, minimizing the influence of episodic storm‐derived nutrients from the WWTP‐influenced river to the estuary. In the site without WWTP influence, the river exported very little N during drought, so storm‐derived nutrient pulses were important for delivering N loads to the estuary. Overall, N is processed from river to estuary, but sustained WWTP‐N loads and periodic floods alter the timing of N delivery and N processing. Research that incorporates empirical measurements of N fluxes from river to estuary can inform management needs in the face of multiple anthropogenic stressors such as demand for freshwater and eutrophication.

Wastewater treatment plant effluent inputs induce large biogeochemical changes during low flows in an intermittent stream but small changes in day-night patterns

“…This result suggest that denitrification played a limited role in the N cycle, challenging the idea that in-stream denitrification in urban streams is high in summer (Lofton et al, 2007;Ribot et al, 2012). On the contrary, this finding supports previous research showing that other factors such as carbon availability can limit denitrification in WWTP-impacted streams (Bruesewitz et al, 2017). In this line of though, experimental additions of labile carbon in mesocosms and flumes have shown abrupt increases in denitrification rates in WWTP effluent waters (Ribot et al, 2017;.…”

“…These results highlight that receiving streams are less vulnerable to contaminant sources when their dilution capacity is high (> 40%), while they become more sensitive to point-source inputs as discharge decreases. Similar conclusions have been draw in other streams experiencing severe drought periods such as the Bush River in South Carolina (Andersen et al, 2004) and the Aransas river in Texas (Bruesewitz et al, 2017).…”

“…standard error], and was mostly driven by the input from the WWTP effluent. This humaninduced shift in the hydrological regime is typical of intermittent streams receiving point sources, and disrupts the temporal patterns of water and solute fluxes (Bruesewitz et al, 2017). Stream Q at the downstream reach was usually lower than discharge at the WWTP effluent (ca.…”

Transporte e retenção de nutrientes em corpos da água tropicais receptores de efluentes de Estações de Tratamento de Esgoto

“…Com exceção do Rio Quilombo, no qual o efluente foi rapidamente diluído pela vazão do corpo receptor, os lançamentos das demais ETEs tiveram um efeito significativo sobre a vazão nos corpos receptores estudados (Tabela 7) bem como também relatado por outros estudos (Martí et al 2004;Ekka et al 2006;Figueroa-Nieves et al 2014). O lançamento de efluentes, no entanto, não dominou a vazão total dos corpos receptores estudados para nenhum caso, conforme observado principalmente em ambientes intermitentes (Bruesewitz et al 2017;Romero et al 2019;Bernal et al 2020). Uma razão para isso é que os corpos receptores selecionados eram ambientes perenes com vazões substanciais a montante das ETEs, caracterizando ambientes típicos do bioma Cerrado, onde os níveis de pluviosidades ao longo do ano e os reservatórios de água subterrânea são capazes de sustentar o fluxo de base durante as estações úmida e seca, respectivamente (Cabral et al 2015).…”

“…Apesar de alguns autores associarem elevadas taxas de desnitrificação em corpos receptores à disponibilidade do DOC lábil e do NO3-N em estudos in situ (Gücker et al 2006;Huang et al 2019) e em mesocosmos (Ribot et al, 2017), outros atribuíram mínimas parcelas da remoção total do NID (e.g., 2-15%) a este mecanismo (Lofton et al 2007;Bruesewitz et al 2017). Essa reduzida desnitrificação em corpos receptores foi associada principalmente às elevadas cargas de NO3-N lançadas continuamente na coluna da água dos corpos receptores, e à menor qualidade do DOC disponível (formas mais refratárias, menos biodisponíveis) (Lofton et al 2007).…”