Upwelling and Lagoonal Ecosystems of the Dry Pacific Coast of Baja California
323
ta, Laurencia pacifica, Pterocladia capillaceae, Eisenia arborea, Sargassum
sinicola, Caulerpa sertularioides, Colpomenia tuberculata) become abundant.
21.4.1 Bahia San Quintin
21.4.1.1 Environmental Setting
Bahia San Quintin (30°27'N, l16°00'W) has an area of 42km 2 and an average depth of-2m. An important part of the watershed (-2,000 km 2 ) consists of agricultural lands. Despite a high ratio of watershed: bay area, the
only significant surface flow into the bay occurs during extreme rainfall
events though groundwater from the San Simon basin may contribute
about 1 x 10 3 m 3 day- 1 in the winter. Since total evaporation in summer
(164 x 10 3 m 3 day- 1 ) and winter (91 x 10 3 m 3 day- 1 ) exceeds total rainfall
(4 x 10 3 m 3 d- 1 and 67 x 10 3 m 3 day- 1 , respectively), Bahia San Quintin is a
net evaporative system. The bay can be considered a negative estuary with
summer and winter salinities in the interior (34.7-33.8) always higher than
in the adjacent ocean (33.8-33.6; Milhin-Nufiez et al.1982).
The lack of continuous freshwater input to Bahia San Quintin emphasizes
the exchange of dissolved and particulate materials with the adjacent ocean.
The horizontal advection of upwelled waters, which surface immediately off
the mouth, into the bay occurs mostly by tide-induced currents. The distribution of salinity, temperature and dissolved inorganic nutrients in Bahia
San Quintin therefore depends, apart from water residence time and internal biogeochemical processes, upon the alternation of upwelling events
(mostly in spring and summer) and spring-neap tidal cycles (mostly in
autumn and winter) . An "erratic" behavior of nutrient concentrations may
be related to turbulence and irregular mixing, owing to bathymetry, winds
and solar radiation input (Millan-N ufiez et al. 1982 ). Salinity and phosphate
concentrations usually increase from the mouth to the inner bay (Fig. 21.2).
The spatial distribution of dissolved inorganic nitrogen (DIN) follows no
clear overall trend, owing partially to complex biogeochemical cycling and
because nitrogen acts as a limiting nutrient throughout the year (Fig. 21.2).
The N JP ratios at the mouth of the bay ( -16 in winter) decrease to extremely low values ( <0.5 in summer) at the innermost part of the bay, probably as
a result of prolonged water residence and high N requirement by sea grasses, which are dominant primary producers (Fig.21.2) .An inverse relationship between silicate and salinity in different years (Fig. 21.2) may reflect
consumption by diatoms vs. regeneration processes.
323
ta, Laurencia pacifica, Pterocladia capillaceae, Eisenia arborea, Sargassum
sinicola, Caulerpa sertularioides, Colpomenia tuberculata) become abundant.
21.4.1 Bahia San Quintin
21.4.1.1 Environmental Setting
Bahia San Quintin (30°27'N, l16°00'W) has an area of 42km 2 and an average depth of-2m. An important part of the watershed (-2,000 km 2 ) consists of agricultural lands. Despite a high ratio of watershed: bay area, the
only significant surface flow into the bay occurs during extreme rainfall
events though groundwater from the San Simon basin may contribute
about 1 x 10 3 m 3 day- 1 in the winter. Since total evaporation in summer
(164 x 10 3 m 3 day- 1 ) and winter (91 x 10 3 m 3 day- 1 ) exceeds total rainfall
(4 x 10 3 m 3 d- 1 and 67 x 10 3 m 3 day- 1 , respectively), Bahia San Quintin is a
net evaporative system. The bay can be considered a negative estuary with
summer and winter salinities in the interior (34.7-33.8) always higher than
in the adjacent ocean (33.8-33.6; Milhin-Nufiez et al.1982).
The lack of continuous freshwater input to Bahia San Quintin emphasizes
the exchange of dissolved and particulate materials with the adjacent ocean.
The horizontal advection of upwelled waters, which surface immediately off
the mouth, into the bay occurs mostly by tide-induced currents. The distribution of salinity, temperature and dissolved inorganic nutrients in Bahia
San Quintin therefore depends, apart from water residence time and internal biogeochemical processes, upon the alternation of upwelling events
(mostly in spring and summer) and spring-neap tidal cycles (mostly in
autumn and winter) . An "erratic" behavior of nutrient concentrations may
be related to turbulence and irregular mixing, owing to bathymetry, winds
and solar radiation input (Millan-N ufiez et al. 1982 ). Salinity and phosphate
concentrations usually increase from the mouth to the inner bay (Fig. 21.2).
The spatial distribution of dissolved inorganic nitrogen (DIN) follows no
clear overall trend, owing partially to complex biogeochemical cycling and
because nitrogen acts as a limiting nutrient throughout the year (Fig. 21.2).
The N JP ratios at the mouth of the bay ( -16 in winter) decrease to extremely low values ( <0.5 in summer) at the innermost part of the bay, probably as
a result of prolonged water residence and high N requirement by sea grasses, which are dominant primary producers (Fig.21.2) .An inverse relationship between silicate and salinity in different years (Fig. 21.2) may reflect
consumption by diatoms vs. regeneration processes.