Groundwater contribution to the nutrient budget of Tomales Bay, California

Abstract

Abstract. Tomales Bay, a graben structure along the San Andreas Fault, was selected for modeling ecosystem nutrient dynamics because of its linear, one-dimensional morphology and relatively pristine state. Groundwater is a potentially important term in the nutrient budget. The geologic complexities created by the San Anreas Fault, however, complicate the hydrogeology and require the area to be subdivided into three regions: granite to the west, Franciscan Formation to the east, and alluvial fill in the trough. Nutrient concentrations in the groundwater were determined through extensive well sampling; groundwater discharge was estimated using both Darcy's Law calculations and a soil moisture budget. Results indicate that groundwater discharge is of the same order of magnitude as summer streamflow into the Bay, while being significantly less than other freshwater inputs in winter. Dissolved nutrient (phosphate, nitrate + nitrite, ammonium, silica and DIC) concentrations in groundwater were consistently higher (by as much as an order of magnitude) than in surface water discharges. During the summer months, groundwater flow contributes about as much nutrient load to the bay as does streamflow. During the winter, the groundwater contribution to nutrient loading is about 20% of the streamflow contribution. Our findings indicate that groundwater is a significant component of terrestrial nutrient and freshwater loading to Tomales Bay, particularly so during the summer months. However, neither groundwater nor streamflow nutrient fluxes are large in comparison to the mixing flux at the bay mouth or the flux of N 2 gas across the air-water interface.

Spatial and temporal variation in C:N:P ratios, delta15N, and delta13C of eelgrass Zostera marina as indicators of ecosystem processes, Tomales Bay, California, USA

“…Unfortunately, we have no data on the isotopic con~position of the inorganic N loading from the watershed, but the importance of terrestrially derived DIN in the N pool of Tomales Bay is not great. A small percentage of the total N loading to Tomales Bay comes from stream flow (Smith et al 1987(Smith et al , 1991(Smith et al , 1996, and groundwater inputs of N are only 20 % as large as stream flow (Oberdorfer et al 1990). If the pattern in seagrass 6I5N is a result of a gradient in 615N of the N pool, then extremely heavy N entering Tomales Bay in stream flow from Lagunitas Creek near the head of the bay could generate such a pattern.…”

Estimating the groundwater contribution into Florida Bay via natural tracers, 222Rn and CH4

“…Groundwater input into surface waters has also been shown to be a contributor of nutrients in several estuaries (D'Elia et al 1981;Capone and Bautista 1985;Capone and Slater 1990;Oberdorfer et al 1990;Valiela et al 1990). Corbett et al (1999) suggested that groundwater in the eastern part of Florida Bay may provide as much nitrogen and phosphate as surface freshwater sources from the Everglades.…”

Descarga de água subterrânea para as lagoas costeiras do litoral norte do RS, Brasil

“…Ainda que o percentual seja menor que as demais fontes de água, as águas de origem subterrânea têm uma característica marcante que engrandece sua participação, que é a sua composição química. A quantidade de nutrientes é muitas ordens de magnitude maior se comparadas às águas de fontes superficiais ou provenientes de chuvas (Lee, 1977;Valiela et al, 1978;Zimmermann et al, 1985;Valiela & D'Elia, 1990;Oberdorfer et al, 1999). Andrade (2010), inclusive, evidenciou a significativa contribuição de nutrientes associada à DAS na Lagoa Mangueira, no sul do Brasil, sendo que estes nutrientes são reciclados inúmeras vezes sustentando a produção primária de forma contínua, assim como também são importantes quando inseridos na plataforma continental (Corbett et al, 1999;Niencheski et al, 2007;Attisano et al, 2008;Santos et al, 2008b;Andrade et al, 2011).…”