Observations on the Geochemistry of Soluble Copper, Iron, Nickel, and Zinc in the San Francisco Bay Estuary Andrew Eaton C h e s a p e a k e Bay Institute, J o h n s Hopkins University, Baltimore, Md. 2121 8
At discharges of 300-400 m3h, surface waters of the San Francisco Bay estuary contain dissolved Cu and Ni a t levels of 1 to 4 ppb. This is approximately an order of magnitude higher than waters outside the Bay. Zn concentrations are 2-6 ppb within the estuary and generally less than 1ppb outside. Cd concentrations are 0.08 to 0.2 ppb within the estuary and 0.05 to 0.11 ppb outside. The behavior of all these elements is probably dominated by physical processes during most seasons, although Cu shows evidence for removal during summer months when river flow is low. Cu, Ni, and Zn show an excess of about 1ppb relative to conservative mixing in the more saline portion of the estuary. This excess is attributed to municipal and industrial discharges. The San Francisco Bay estuary is one of the larger estuaries on the West Coast of the United States, with a combined average yearly discharge from the Sacramento and San Joaquin Rivers of 800 m3/s. It is currently used extensively for recreation, waste disposal. and fisheries. Studies of the biological, chemical, and physical oceanography of the Bay system have been conducted by various groups since the early 1960's (1-5). In spite of this extensive study, little work has been done regarding the distributions of minor elements in the Bay waters. Recent ongoing investigations of the water chemistry in the Bay by the U.S. Geological Survey (2-4,6) have made it possible to study the distributions of minor elements in the estuary and correlate these data with other constituents measured by the Survey to provide preliminary explanations for the distributions of these metals. The San Francisco Bay estuary (Figure 1)is defined herein as the northern portion of the San Francisco Bay between the Golden Gate and Rio Vista. In this reach freshwater inflow from the Sacramento and San Joaquin Rivers mixes with high salinity water from the open ocean and the southern portion of the Bay. In contrast, the southern reach of the Bay is characterized by low freshwater discharge and fairly uniform salinities a t a given season (6).This study has been oriented entirely toward the northern or estuarine portion. The study was designed to investigate a variety of questions about trace metal distributions in the Bay waters. First, what are typical concentrations for soluble metals in the estuary? There are currently only a few data available on levels of dissolved metals in the San Francisco Bay estuary, although some work has been conducted in limited portions of the Bay in conjunction with dredged waste disposal ( 7 , 8 ) .Second, what are the factors controlling seasonal and longitudinal variations of metals within the estuary? Four explanations are commonly used to account for the distributions of metals in natural 0013-936X/79/0913-0425$01.00/0
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1979 American Chemical Society
SAN FRANCISCO BAY 122'30'
122'
,'
TLi "CSE
-
Figure 1. The San Francisco Bay system. Numbers and small dots indicate USGS water sampling stations. Triangles indicate municipal or industrial discharges with water flow of more than 10 mgd
waters: simple mixing of different end members, adsorption or solubility controls, biological uptake and/or regeneration, and more complicated mixing of multiple sources.
Experimental Methods of Collection. Samples were collected in July and September 1975 and March 1976 for analysis of dissolved trace metals. Sampling locations are shown in Figure 1. In July and September, 1975, samples were taken a t 1m by rapidly submerging a polyethylene bottle suspended in a polyethylene harness from the boom of the ship, some 6 to 10 m away from the vessel. This procedure should minimize the contribution of the surface film. Immediately after collection, samples were filtered through Nucleopore (0.6 pm in July, 0.4 pm in September and March) filters on board ship using a nitrogen drive pressure filtration system. The entire filtration system was placed inside a plexiglass box to minimize dust contamination. In March 1976, samples were pumped directly on board and through the filters using acid-cleaned polyethylene tubing and a peristaltic pump. While discrete trace metal samples were being collected, the United States Geological Survey (USGS) obtained data on other constituents including "3, Nos, NOz, PO4, SiOn, salinity, temperature, dissolved oxygen, chlorophyll a , turbidity, light transmission, pH, pCO2, and alkalinity using a Volume 13, Number 4,April 1979
425
Table 1. Sampling Information date
7128-29/75
dlscharge Into delta,
no.
m3/s
samples
Nucleopore filter used, Mm
280
14
0.6
Of
data obtained by USGS
collection method
S,T, Chl a,
stations occupied
poly bottle
3, 5-12, 14, 17, 19, off-
poly bottle
3, 6 , 9, 12, 14, 16, 17, 19
peristaltic
TL, 3, 6, 9,
turbidity
shore 9116-23/75
350
14
0.4
312-3. 16/76
39 1
11
0.4
S, T, Chl a, turbidity, nutrients, I4C pro-
ductivity S,T, Chl a, turbidity, nutrients, I4C productivity
12, 15, 17, 19, 3 offshore
Pump
Table 11. Sampling Biases and lntercalibrationResults for March 1976 statlon
NI
Zn
lrgh cu
Fe
Cd
1.6 1.2
160 1.6
0.17 0.14
1.4 1.05
0.47 0.32
8.0 0.7
0.075 0.075
0.5
0.33 0.31
4.3 3.2
12, CIT sampler (0.4 g m filter) 12, LBL sampler (0.2 pm filter)
1.55 1.60
2.4 2.4
plume, CIT sampler (0.4 p m filter) plume, LBL sampler (0.2 pm filter)
0.36 0.34
Far. surf, CIT sampler (0.4 p m filter) Far. surf, LBL sampler (0.2 pm filter)
0.26 0.35
0.5
'
0.08 0.06
intercalibrationa9, Eaton intercalibrationa9, Holm (Environmental Engineering,CIT)
2.25 2.20
0.155 0.160
intercalibration 17, Eaton intercalibration 17, Holm (Environmental Engineering,CIT)
1.45 1.44
0.16 0.13
a
lntercalibration exercise: analyses by both workers done using APDC/DDDC/MIBK extraction. For sampler comparison all analyses performed by author using
APDC/DDDC/MIBK extraction.
continuous through the hull pumping system ( 4 ) . Table I summarizes the information obtained during each cruise. Methods of Storage and Cleaning Procedures. Bottles and filters were cleaned using a modification of the procedure of Patterson and Settle (9).Conventional polyethylene bottles were cleaned by soaking in hot 8 N H N 0 3 for 3 days, hot 0.5% HNO3 for 1day, and hot 0.5% H N 0 3 again for 3 or more days. Filters were cleaned by soaking in hot 6 N HC1 for 2 days, followed by hot 0.5% HCl for 2 days, and a final soak in hot 0.5% HC1 for 2 more days. Polyethylene tubicg used in the pumping system was acid leached using the same procedures as for the bottles, except that the acid was continuously circulated using a peristaltic pump. All glassware used in analysis was cleaned using the same procedures and rinsed thoroughly with quartz-distilled water. Reagents used in analysis were either redistilled or extracted several times to purify them. Total procedural blanks were
