The Role of Urea in the Coastal Nitrogen Biogeochemical Cycle As a Sign of Environmental Health

THE ROLE OF UREA IN THE COASTAL NITROGEN BIOGEOCHEMICAL CYCLE AS A SIGN OF ENVIRONMENTAL HEALTH

Elisabete de Santis Braga1, Janaína Lopes Rodrigues Torres 2

Abstract - The urea is an organic nitrogenous compound eliminated by zooplankton excretion and in other animal present in coastal environment introduced by excretion of excretions, is also originated from anoxic bacterial some terrestrial and aquatic animals, including human respiration, introduced by effluent inputs in the rivers and by being. The estuarine-lagoon complex of Cananeia-Iguape precipitation over the sea. The main ammonium whirlpool is shows anthropic differences between northern and southern the assimilation process by phytoplankton and the regions. Iguape is characterized beyond human occupation, ammonium oxidation process to nitrite and nitrate by by the presence of an artificial channel that introduce fresh nitrification [8]. water into estuary. Cananéia is naturally preserved. The In balanced conditions, the nitrate is the principal northern part showed salinity from 0.04 to 1.75 and urea inorganic form present in the sea water due to its very stable from 0.66 to 1.49 µM. In the southern part, the salinity oxidation state. Considering the N assimilation forms, the ranged from 17.97 to 31.44 and the urea values ranged from N-ammonium has preference by phytoplankton. At this 0.01 to 2.46 µM. Analyses performed in samples taken point, the N inorganic forms are preferable on the organics, during 13h, in two fix points showed the depuration capacity but that is known some preferences in urea assimilation by of the southern part with association to the tide action. The phytoplankton species as reported by Phaedacthylum more constant urea values were observed in northern part, tricronutum [2] . with similar values to the Ribeira river water. This study The organic dissolved nitrogenous pool is very low in belongs to VAGRA and INCT-TMCOcean projects. oceanic waters, but near the continental margin and in estuarine systems, this compartment has a new dimension Index Terms ⎯ urea, estuarine system, nitrogen that reveals the N biogeochemical cycle involving anthropic biogeochemical cycle input influences. The N is included in the excretion product list of some INTRODUCTION marine organisms. The N derived from the amino-acids is very common. The urea, creatine and trimethylamine are The nitrogen compounds in the marine ecosystem are excretion products eliminate in the water column. In the sea influenced by biological, physical and chemical processes water, the urea has source in the purine-urea cycle and in that contribute to the complex nitrogen biogeochemical ornitine-urea cycle [3], the last compound mentioned is also cycle (Fig. 1). The coastal cycle of nitrogen includes involved in the water mammal metabolism or in the effluent inorganic to organic passages and vice-versa, contributing to tracers. Thus, the ocean urea input occurs as arginine organic matter formation and degradation and its relation to hydrolisis by arginase, elimination by dead fishes the biological process. zooplankton excretion and other animal excretions, domestic The nitrogen (N) is an important element to constitute effluent wastes [8]. As a part of organic nitrogenous oceanic the living organic matter and the inorganic compounds pool, the urea represents important biosphere molecules [2] commonly used in the primary production are N-ammonium To assimilate the urea molecule by primary production and nitrate. it is necessary to have an available enzymatic apparatus The N biogeochemical cycle depends overall on the involving urease. If this organic nitrogenous molecule is microorganism activities that contribute to the introduced in the coastal water and its use is not by bioavailability of the inorganic N to the biological syntheses assimilation process, the degradation to N-ammonium will and organic matter regeneration into inorganic including occur in function of temperature and other environmental mineralization processes. parameters. The increasing in N-ammonium concentration The organic nitrogen sometimes represents N refractory has origin in organic matter decomposition, denitrification form due to the complexity of its molecules. On the other process and also in the urea molecules degradation. hand, the first level of the microorganism protein Some studies reveal that in estuarine systems, the urea degradation forms ammonium. This N inorganic compound assimilation rate is more important than nitrate and is similar constitute an important inorganic form of nitrogen is also

1 Elisabete de Santis Braga, PhD responsible for Nutrients, micronutrients and traces laboratory. Oceanographic Institute – São Paulo University. Praça do Oceanográfico, 191, room 165, 05508-120, São Paulo, SP, Brazil, [email protected] 2 Janaína Lopes Rodrigues Torres. Graduated in Oceanography. Nutrients, micronutrients and traces Laboratory. Oceanographic Institute. São Paulo University. Praça do Oceanográfico, 191. São Paulo/SP. 05508-120. Brazil, [email protected]. Acknowledgment for CNPq financial support Processes n. 552437/2007-7 and 573601/2008-9.

to N-ammonium. This physical and chemical dynamic seems fix points were studied in the system for 13h: Iguape to occur in environments with low concentrations of urea in (Northern part) and Cananéia (Southern part). The water was relation to the dissolved inorganic nitrogen. sampled each 2 hours. The addition of nitrogenous compounds in the coastal The temperature was obtained using a reversion environment contributes to unbalanced situations with protected thermometers (± 0.02 °C). The tide curves were eutrophication results whose the urea cycling is involved obtained in provisional tables published by [7]. linked to human activities. The salinity was determined using an inductive The nitrogenous compounds with source in human Backman salinometer®, model RS 10 (±0.02) referenced by metabolism can unbalance the coastal environment by 3vias: standard seawater. i) atmospheric deposition; ii ) marine and estuarine disposal; The urea concentration was analyzed using de procedure iii) transport by the river water. described in [1] using an automatic processing and adapted This study intends to know the urea concentration and to manual analyses by [4] Braga et al. (in prepar). distribution in two sectors of the estuarine-lagoon complex The dissolved oxygen samples were collected in of Cananéia-Iguape submitted to different environmental calibrated flasks covered with a dive stopper. The anthropogenic impacts. determinations were based on Winkler method (iodine titration) as described in [6]. The precision was ± 0.02 MATERIAL AND METHODS cm3.dm-3 for levels of 2 cm3.dm-3 and 0.04 ± cm3.dm-3 for higher levels. Study Area The pH was measured using a pHmeter Radiometer, with precision ±0.02. The estuarine-lagoon complex of Cananéia-Iguape is a The plastic flasks were manipulated using guns to avoid protected system involved by Atlantic vegetables and the contamination and preserved with water at -20°C before mangrove systems. In the Northern part of the system, an analyses. At LABNUT-laboratory, in São Paulo, the filtered artificial channel was constructed to facilitate agricultural (Whatmann GF/F) samples were analyzed using a Genesys products and nowadays, the dimension of it is enlarged, and spectrophotometer. The precision was ± 0.02 µM N-Urea. the river debit decreases the salinity to low values The N-ammonium was analyzed by colorimetric method corresponding to the fresh water (< 5‰). as described by [9] Treguer & Le Corre (1976), using a cited This region, the Ribeira valley is a natural UNESCO + spectrophotometer. The precision was ± 0.02 µM N-NH3 + inheritance [5] . The Southern part is preserved sheltering a NH +. modest human occupation and activity near Cananéia city. 4 RESULTS AND DISCUSSION

North station The summer period in this region is known as wet period with intensive rains. The meteorological conditions showed a partial cover of the sky at the two regions studied and the charge of terrestrial inputs influenced the euphotic layer depth, mainly in the Northern part due to the river inputs by the Valo Grande Channel and the erosion present in the Ribeira valley (Table I). The temperature values showed the main aspects of summer water condition, and in the two part of the system it was possible to observe high values of temperature ranged from 28.20- 30.70 °C at Cananéia in the first hour sampled, on low tide. The salinity values were from 20.58 to 31.44 South station and the lowest values were observed in low tide and the high values were observed in high tide period (~18h). The N- ammonium values varied from 0.48 to 7.70 µmol L-1, with FIGURE 1 the highest values observed in ebb-tide moment. The urea ESTUARINE-LAGOON COMPLEX OF CANANÉIA-IGUAPE. NORTH STATION data varied from 0.00 to 2.48 µmol.L-1 and the urea maxima (IGUAPE) AND SOUTH STATION (CANANÉIA). ADAPTED FROM WWW. values occurred in a movement from high tide to ebb-tide. GOOGLE EARTH.COM. The Cananéia data is presented in Table I. In Iguape region (Table II), the temperature varied from Sampling 26.30 to 27.19 °C with the highest values in the initial The water was sampling using Hydrobios® bottles on board moment of ebb-tide movement, after 13h. The salinity of the Oceanographic Ship “Albacora” from Oceanographic values were completely low, under the limit for salt water, Institute. The study was in February 2009 (summer). Two and the values corresponded to fresh water (CONAMA

TABLE I Classification), It reflects the anthropic intervention of the TEMPERATURE, SALINITY, N-AMMONIUM AND UREA IN CANANÉIA – “Valo Grande” artificial channel mentioned in the FEBRUARY introduction of this article. The N-ammonium values varied from 0.76 to 3.60 µmol L-1 corresponding to modest values in relation to those observed in Cananéia system. The highest values were observed around 7:30h in low tide moment. The urea values presented concentrations from 0.66 to 1.34 µmol L-1 values, in general, lowest than those observed in Cananéia, and the variation between them was very slightly, on the other hand, the presence of values around to 1.00 µmol L-1 was constant and the depuration process (dilution) was less important than in Cananéia region.

CONCLUSION Analyses performed in samples taken during 13h, in two fix points, one in each region showed the capacity of depuration of the Southern sector (Cananéia) strongly associated to the tide action. The more constant urea values were observed in

Northern part, with values similar to the Ribeira river water that reflects the anthropic influence in relation to the TABLE II desalinization of the system in the Northern part. There was TEMPERATURE, SALINITY, N-AMMONIUM AND UREA IN IGUAPE - an important environmental alteration in function of the FEBRUARY 2009. decrease of the tide action attributing a high degree of fragility to Northern part of the system due to the human impact. The Southern part of the system (Cananéia) although showed the highest values of urea also showed a dilution capacity. At this moment, the N-ammonium present in the complex showed high values in the Southern part of the system, but not only associated to the urea degradation but also involved in the N biogeochemical processes, with a contribution of the denitrification processes evidenced in low tide period. More studies are necessary to understand this N biogeochemical cycle considering organic and inorganic phases, but it was possible to signalize the different degrees of fragility in these two parts of the system, even when submitted to the same climate forces.

ACKNOWLEDGMENT The authors would like to thank the support from R/V Albacora and R/V Velliger II crew, the IBAMA and the Oceanographic Institute support during this study.

REFERENCES

[1] Aminot, A. & Kerouel, R.. Automatic-determination of urea in seawater – A sensible method using diacetilmonoxime. Can. J. Fish. Aquat. Sciences. 39 (1): 1982. 174-183. [2] Antia, N.J., H, P. 1. & Oliveira, L. The role of dissolved organic nitrogen in phytoplankton nutrition, cell biology and ecology. Phycologia 30, 1991. 1-89. [3] Braga, E.S. Bioquímica marinha – efeitos da poluição nos processos bioquímicos. 2ª ed. Fundespa, São Paulo. 2002. 108p

[4] Braga et al. (in prepar). Manuel determination of urea in marine estuarine system.

[5] CETESB. Relatório de Qualidade das Águas Litorâneas do Estado de São Paulo. 2003. Disponível no www.cetesb.sp.gov.br – acessado em 14/01/09 [6] Grasshoff, K.; Ehrhardt, M & Kremling, K. Methods of seawater analysis. 2nd Ed., Weinhein, Verlag Chemie. 1983. 419p. [7] Mesquita, A. R de, 2009. Tabua de marés – 2009. Disponível em www.mares.io.usp.br. Acessado em 23/05/09. [8] Mesquita, A. R . de. Tabua de marés – 2009. 2009. Disponível em www.mares.io.usp.br. Acessado em 23/05/09. [9] Tréguer, P. & Le Corre, P. Manuel d’analyses dês sels nutritifs dans l’eau de mer. 2a Ed. Université de Bretagne Occidentalle, Brest. 1975. [10] Wada, E. & Hattori, A. Nitrogen in the Sea: Forms, Abundances, and Rate Processes. CRC Press, USA, Boston. 1991. 208p.