Data Set (knb-lter-sbc.87.1)

SBC LTER: Pore water constituents and residence times (Radon activity) from Santa Barbara beaches, 2012-2013

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These methods, instrumentation and/or protocols apply to all data in this dataset:

Protocols and/or Procedures
Description:

Pore Water and Nearshore Seawater Sample Collection and Analysis

Pore water samples were collected during ebb tides for ammonium, nitrite + nitrate (hereafter nitrate), total dissolved nitrogen (TDN), dissolved organic carbon (DOC), particulate organic carbon and nitrogen (POC and PON, respectively), and salinity using hollow-core stainless steel piezometers (0.6 cm diameter, 2 cm screen length) and a hand-held peristaltic pump. Ammonium, nitrate, TDN, and DOC samples were filtered with 0.7 micron GF/F filters (Whatman), POC and PON samples were collected on 25 mm 0.7 micron GF/F filters (Whatman), and salinity samples were unfiltered. Nearshore seawater samples were collected for the same analytes as pore water samples on the ebb to flood tide transition by wading in ∼1 m water depth. Pore water samples were collected at multiple locations (distance between sample locations was 6.3 +/- 4.6 m; mean +/- 1 std. dev.) and at multiple depths (0.7 +/- 0.4 m; mean +/- 1 std. dev.; range of 0.1 to 1.6 m), where feasible, along shore-normal transects running from the base of the bluff on the back beach to the wave run-up line.

Ammonium and nitrate concentrations were determined on a Lachat Flow Injection Autoanalyzer (Hach Company). The detection limit for ammonium and nitrate was 0.5 micromolar, precision was +/-0.4 micromolar for ammonium and +/-0.1 micromolar for nitrate, and accuracy was +/-6% for ammonium and nitrate. DOC and TDN were measured by high temperature combustion (HTC) using a Shimadzu (Shimadzu) TOCVCSH system coupled with a Shimadzu Total Nitrogen analyzer. The precision for DOC and TDN was +/-1 to 2 micromolar. Dissolved organic nitrogen (DON) was calculated as the difference between TDN and the sum of ammonium and nitrate. POC and PON were preacidified with HCl and measured by high-temperature combustion using a CE440 CHN elemental analyzer (Exeter Analytical). Specific electrical conductance values were measured using a YSI 3100 conductivity instrument (YSI) and were converted to salinity using a simplified general equation.

Pore Water and Nearshore Seawater Radon Activity Sample Collection and Analysis

Pore water and nearshore seawater radon activity samples (Rnpw and Rnsw, respectively) were collected in 615 mL glass bottles (radon bottles) with custom gastight sampling caps. Rnpw was collected by driving piezometers to target sampling depths and filling with approximately 250 mL pore water (260 +/- 22 mL). Rnsw were collected during the ebb to flood tide transition in ∼1 m water depth by filling with approximately 500 mL of surf zone seawater (452 +/- 65 mL). Rnpw and Rnsw were determined on a RAD7 Radon-in-Air instrument (Durridge Company) using a closed-loop, continuous circulation with 15 min count intervals and total count durations of 1.25−3 h. The manufacturer quoted detection limit was 0.2 Bq L−1 (Durridge Company).

Equilibrium Pore Water Radon Activity Incubations

Equilibrium radon activity samples (Rneq) were collected at distance intervals of 5.0 +/- 1.8 m along the shore-normal transects at two depths where permissible, the top of the pore water table and at a depth equal to half the distance between the pore water table and sand surface. If sand at the sampling location was saturated, as occurred on the seepage face, then sand from only the top of the pore water table was sampled (i.e., at the surface). Approximately 50 mL of sand was collected and mixed in an approximate 1:4 to 1:5 volume ratio with unfiltered nearshore seawater in radon bottles. The sand-seawater mixture was initially purged for 20 min with ambient laboratory air to remove initial radon and incubated undisturbed (i.e., no shaking or agitation) in the laboratory for 2 weeks (16.6 +/- 3.3 days) to allow ingrowth of radon. No temperature controls were implemented since fluctuations in water temperature were small; 21.5 _/- 0.3 degrees C (mean +/- 1 std. dev.). At the end of the incubation period, equilibrium radon activities were determined using a closed-loop, continuous circulation on the RAD7 as described above. Equilibrium radon activity was calculated as Goodridge, B. M. and J. M. Melack. 2014. Temporal evolution and variability of dissolved inorganic nitrogen in beach pore water revealed using radon residence times. Environmental Science and Technology, 48: 14211-14218. DOI:10.1021/es504017j