Elkhorn Slough (ELK) NERR Nutrient Metadata (January- December 2003) Latest Update: June 9, 2005

Nutrient monitoring is conducted at 26 National Estuarine Research Reserves (NERR) from
four locations within or adjacent to the reserve on a monthly basis of the following parameters:
orthophosphate, ammonium, nitrite, nitrate, and chlorophyll a. Note: Reserves may collect
additional parameters which are available by searching the Yearly Files directory. Research
objectives Elkhorn Slough (ESNERR) is a unique estuary along the central Californian coast.
There are fresh water inputs during the wet season (October through May) causing a brackish
environment, while during the dry season (June through September) there is very little
freshwater input resulting in a much more saline environment. The surrounding area is mostly
farmlands, which causes concern as they may be a source of significant amounts of nutrients
entering the slough. With the base monitoring program we are able to quantify the variability of
these nutrients in different areas of the slough. a) Monthly Grab Sampling Program Monthly grab
samples are collected to quantify the spatial variability of important nutrients in the water
column at sites representing the estuarine endpoints of the Elkhorn Slough estuary. b) Diel
Sampling Program Once per month, samples are collected every hour through a 24-hour tidal cycle
to quantify the temporal variability of important nutrients in the water column as a function of
tidal forcing.

SUPPLEMENTAL INFORMATION:
Associated researchers and projects: Ken Johnson et al.
are looking at nutrient budgets in the slough with real time nitrate loggers in the main channel
of the slough. , Adina Paytan, Scott Wankle et al are looking at nitrogen isotopes to assess the
contributions of nitrogen through ground water. Nicholas Welshmier et al are looking at
nutrients and phytoplankton populations in the main channel of the slough on a weekly basis.
Marc Los Huertos et al are investigating nutrient budgets in the Elkhorn Slough watershed and
identifying "hot spots" of nutrients in the slough and working with local farmers to attempt to
decrease high nutrient loads. Other Remarks Rainfall was less than 5mm 72 hours prior to
sampling for each sampling period with the exception of December, where 6mm fell on 12/5/03 and
7.6 mm fell 12/6/03 and the sampling occurred 12/8-12/9/03.

CURRENTNESS REFERENCE:
Observed

SPATIAL DATA ORGANIZATION INFORMATION:
Indirect Spatial Reference: Site location and character a) Monthly Grab Sampling Program Monthly grab samples were taken at the
four principle ESNERR data sonde stations (Azevedo Pond, North Marsh, South Marsh and Vierra
Mouth) within the Elkhorn Slough estuary. All grab samples were taken on the same day between +3
hrs before slack low-water and low-water. No distinction was made between neap and spring tide
conditions. Efforts were made to allow for an antecedent dry period of 72 hours prior to
sampling. Replicate (N=2) samples were collected by hand at an approximate depth of 10 cm. All
samples were collected in amber, narrow-mouth, nalgene sample bottles that were previously acid
washed (10%), rinsed (3x) with distilled-deionized water, dried, and followed by rinsing (3x)
with ambient water prior to collection of the sample. Samples were immediately placed on ice in
the dark and returned to the laboratory. Once in the laboratory, samples were shaken and
processed for nutrient and Chl-a analysis. At the time of sample collection, water temperature,
salinity, and dissolved oxygen was measured with a YSI Model 650 meter. This data is not
included in this dataset but will be available upon request by calling the reserve. b) Diel
Sampling Program On the first Monday of every month, within the same 24-hour period of grab
sample collection, we deploy an ISCO water sampler approximately 30 cm above the bottom from the
bank of the marsh at South Marsh. This device automatically samples 500 ml of water every 1 hrs
2min. All samples are pumped into polyethylene sample bottles that were previously acid washed
(10% HCL), rinsed (3x) with distilled-deionized water and dried. Samples are kept cold with ice
until the end of the 24 hr period; the 24 samples are kept in the dark and returned to the
laboratory for immediate processing. Site location and character Elkhorn Slough is located on
the West Coast of the United States in Central California. It connects with the Pacific Ocean in
central Monterey Bay near Moss Landing, California. There are four sampling sites. Azevedo Pond
(AP) (36(50 44.64 N, 121(45 13.24 W) receives fertilizer
and pesticide runoff from a strawberry field in year-round production. The YSI is located about
10m from a culvert connecting the pond to the slough. Tide ranges from 0 to 1.3 meters while
salinity ranges from 8.8 during heavy runoff to 41 ppt during strong evaporation. The sonde is
located approximately 10 cm off the bottom, which is composed of silty mud. Depth for this site
is approximately 1 meter. North Marsh (NM) (36(50 04.75 N,
121(44 18. 33 W) is located in between South Marsh and Azevedo Pond. This
site is impacted by both agricultural and urban runoff. With a mean depth of 1 meter, the tidal
range is approximately 0.4 meters while salinity ranges between 20 and 40 parts per thousand.
There is freshwater runoff from upland and agricultural sites. The sonde is approximately 10 cm
off the bottom, which is composed of silty mud. South Marsh (SM)
(36(49 05.00 N, 121(44 21.83 W), located about 3 km
south of NM, is in a side channel of the slough and is relatively free from impact by
anthropogenic influences as it is surrounded by mostly reserve land. The YSI is located on the
side of a bank in one of the secondary slough channels. This site receives runoff mostly from
uplands and some from cattle ranches, receiving the least amount of pollution. Tidal ranges from
0 to 3 meters while the salinity range is from 22 to 36 parts per thousand. The sonde is
approximately 30 cm off the bottom, which is composed of compacted silty mud. Depth for this
site is approximately 2 meters. The fourth site Vierra Mouth (VM)
(36(48 39.95 N, 121(44 45.40 W) is located at the mouth
of the slough and is used to identify oceanic influence. With a mean depth of 2.5 meters, the
tidal range is from 0 to 3.2 meters while salinity ranges from 26 to 34 parts per thousand. The
sonde is located approximately 30 cm off the bottom which is composed of compacted mud and sand
due to strong tidal currents. This site receives drainage from the entire watershed due to its
location at the mouth. There are several auto wreaking yards located approximately 2 km east of
this site.