Evaluation of nitrogen sources in the Urias lagoon system, Gulf of California, based on stable isotopes in macroalgae

Abstract

in 738 samples of macroalgae collected during one year across the Urías lagoon system (Mazatlán, Sinaloa, Mexico) were analyzed in order to study the N sources. The  15 N-macroalgae premise is that they register and integrate the variability of N and may provide time-integrated information about N pollution. To validate this premise, we applied two models to predict the isotopic variability of N available in the water column ( 15 N-DIN): one is based on a physical mixing balance of N sources (simple model), and the second includes the effects of the biogeochemical processes on the signals (coupled model, CM). Both models showed significant R 2 , but CM better explained the  15 N-DIN variability. The relation between δ 15 N-DIN CM and δ 15 N-macroalgae also showed a good fit, although lower than expected and with higher dispersion. The multiple N sources and co-occurring biogeochemical reactions, which produce a mixture of chemical species of N and of their isotopic compositions, as well as the high diversity of species (45) explained the elevated variability and lack of fit. Even so,  15 N in macroalgae is the most useful available tool to quantify the relative contributions of N to ecosystems from different sources. Based on Bayesian isotopic mixing models, the main anthropogenic sources of N to the Urías lagoonal system were domestic effluents (50%), atmospheric deposition (24%), and seafood processing plant effluents (21%), and to a lesser extent, aquaculture effluents (3%), agriculture runoff (1%), and oceanic N (1%).Key words: δ 15 N, eutrophication, biogeochemical cycle, NLOAD model, MixSIR. RESUMEN. Las concentraciones de las formas químicas de nitrógeno (N) y su composición isotópica en la columna de agua y las señales deδ 15 N en 738 muestras de macroalgas recolectadas durante un año en el sistema lagunar de Urías (Mazatlán, Sinaloa, México) fueron analizadas para estimar las fuentes de N. La premisa sobre el uso de  15 N en macroalgas es que las macroalgas asimilan 15 N en proporción a la disponibilidad y reflejan la fuente de N de una manera predecible. Para validar esta premisa, se aplicaron dos modelos para la predicción de la variabilidad isotópica del N en el agua ( 15 N-NID): el primero se basa en una mezcla física de las fuentes de N (modelo simple), y el segundo integra los efectos de procesos biogeoquímicos sobre sus señales isotópicas (modelo acoplado, MA). Ambos modelos mostraron valores de R 2 significativos, pero el MA explicó mejor la variabilidad del δ 15 N-NID. La relación entre δ 15 N-NID MA y δ 15 N-macroalgas también mostró un buen ajuste, aunque menor al esperado y con una alta dispersión. Las múltiples fuentes de N y reacciones biogeoquímicas concurrentes, que producen una mezcla compleja de especies químicas de N y de sus composiciones isotópicas, además de la alta diversidad de especies (45), explicaron la elevada variabilidad y la falta de ajuste. Aun así, la técnica de  15 N en macroalgas es la herramienta más útil que existe para cuantificar las contribuciones relativas...

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“…Most of those draining into AEP come from agricultural fields or from agriculture-related activities, while those of UR are urban wastewaters or originate from shrimp farms and fish and shrimp processing plants. In the latter case, the N and P concentrations give a mean annual N:P ratio which coincides with that calculated for the known inputs (692 to 711 Mg N, 79.2 Mg P, N:P ratio 19.3-19.9: Del Río-Chuljak, 2003; Ochoa-Izaguirre and Soto-Jiménez, 2013). Since the estimated average N:P ratio of the municipal wastewater of Mazatlán is close to 9-9.5 (Alonso- Rodríguez et al, 2000), the high mean N:P ratio of UR surface waters indicates a high P content of the industrial wastewaters and shrimp farm effluents draining into UR.…”

Selection of effective macroalgal species and tracing nitrogen sources on the different part of Yantai coast, China indicated by macroalgal δ15N values

“…Distinguishing nitrogen sources is not only necessary to understand the biogeochemical cycle in coasts and estuaries but also important to establish effective coastal environmental management policies (Rogers, 2003;Kamer et al, 2004). Nitrogen stable isotope ratio (δ 15 N) has been successfully applied to trace nitrogen sources over the last decade, depending on their specific signatures (McClelland and Valiela, 1998;Savage and Elmgren, 2004;Ochoa-Izaguirre and Soto-Jiménez, 2013;Viana and Bode, 2015). For example, sewage effluent or animal wastewaters are characterized by high values of δ 15 N, from 7‰ to 50.1‰ (Kendall, 1998;Savage and Elmgren, 2004;Dailer et al, 2010), while fertilizer derived from industrial fixation of N 2 are depleted in δ 15 N values, from − 7.5‰ to 6.6‰ (Heaton, 1986;Macko and Ostrom, 1994;Vitòria et al, 2004;Dailer et al, 2010).…”

Spatiotemporal distribution of the bacterial contamination of agricultural and domestic wastewater discharged to a drainage ditch (Sinaloa, Mexico)

“…Fecal coliforms, found in the intestine and feces of animals, are indicators of pollution and consequently of water quality, and thus warn about the possible presence of human pathogens. The presence of fecal coliforms in aquatic environments may be due to the abundant incorporation of water contaminated by sewage and other organic wastes from anthropogenic activities (Cupul-Magaña et al 2006, Bagordo et al 2012, Sidhu et al 2012, Barrera-Escorcia et al 2013, Ochoa-Izaguirre and Soto-Jiménez 2013, Valdés et al 2014, Wu et al 2014.…”

“…Hence, the main economic activities of Sinaloa depend on sufficient water resources and good water quality (CONAPESCA 2012). It is now known that contaminated agricultural drainage water adversely affects aquatic and terrestrial life in Sinaloa (Escobedo-Urías et al 1999, Haws et al 2006, Ochoa-Izaguirre and Soto-Jiménez 2013, in Mexico, and around the world (Bagordo et al 2012, Matano et al 2013, Riera et al 2013, Valdés et al 2014, Wu et al 2014). On the other hand, agricultural drains can function as artificial surface wetlands and reduce water pollution and its adverse effects, but the drainage flow must be low permitting the presence of aquatic plants (Kadlec and Wallace 2009).…”